CA2160117A1 - Hydraulically setting sheath and methods - Google Patents

Abstract

This invention is a marking implement (10) with a hydraulically setting sheath (12) and a marking core (14). The hydraulically setting sheath (12) has a hydraulically setting matrix formed from the reaction products of hydraulic cement and water. Additional components may be utilized in the hydraulically setting matrix such as aggregate materials, fibrous materials, and rheology modifying agents.

Description

HYDRAULICALLY SETTING SHEATH AND METHODS

BACKGROUND OF I~IE INVI~NTION

1. The Field of the Invention.
The present invention relates to novel hydraulically settable materials and their methods of m~nl-f~-re and, more particularly, to marking implements with hydraulically settable sheaths co."a~,l,.g a marking core. The marking implements with a hydraulically settable sheath and a m~rkin~ core, such as pencils, pens and the like, can be m~n~f~ct--red in a manner which is efficient, inexpensive, and environmentally neutral.

2. The Related Technolon.
A. Traditional Markin~ Implements.
Sheaths used in traditional marking implements such as disposable and nondisposable pens, mechanical and non-me~h~nical pencils, ink markers, and cosmetic pencils, etc. typically consist primarily of either plastic or wood. Plastic and wood have been regarded as the plere-~ble materials in m~n~f~ch~ring sheaths for marking implements but their use creates problems related to cost, efficiency and environmf~nt~
impact.
, Plastic is the m~t.o.ri~l used in the vast ",ajoliLy of marking implement sheaths such as plastic pencils, disposable and non~ posable pens, .necll~nical pencils, ink markers (som~.times reÇ~Ied to as "magic 1ll~1~ ll), and cosmetic pencils. The widespread use of plastic resulted from its apparel" superiority as sheaths for such marking implements.
Plastic is generally incAI~en~ e, lightweight, strong, and durable. The cost of producing marking hll~le~..el-ls with a plastic sheath is directly related to the cost of petroleum SUBSTITUTE SHEET (RULE 26) products which provide the raw materials necessary for plastic production. Although plastic is generally il~ ,ensive, as petroleum resources become more scarce, the cost of items dependent on the availability of petroleum products will increase.
In addition, to the obvious chemical hazards of plastic production, plastics used 5 in pens, and pencils are very slow to degrade. This is especially true when buried deep inside of landfills and away from the corrosive effects of light, air, and water.
The continued use of plastic, however, is due in part to economic forces such as r~ict~nce to change, habit, and the fact that large m~mlf~ctllrers set an industry standard and tend to resist the creation of a new standard, thereby risking losing their market share l 0 of the old industry.
While pencils are commonly m~nuf~ct~1red with plastic sheaths, wood continues to be the doll~inalll utilized material in disposable pencils. Manufacturing pencils with a wooden sheath has, however, become more expensive based upon the increasing cost of slats for the wooden sheath. Additionally, it is not possible to m~mlf~ctllre pencils with 15 a wooden sheath by an in~ .ell~ e contin-10uc process. Pencils with a wooden sheath are conventionally m~nllf~ch1red by a process involving considerable work, many special conditions, and individual operations.
In the standard method of making pencils with a wooden sheath, only wood that is first class and specially selected may be used. The number of suitable woods is limited, 20 and it is only cedar wood that is normally used for high grade products. The wood has to be dried under suitable climatic conditions. The resin or essçnti~l oil content should neither exceed nor fall below certain limits. The prepared wood is cut with special saws into thin boards which are subjected to the following operations: st~ining, grooving, illse~ lg the leads, gluing together, coarse s~nrling cutting into crude pencils, and further 25 s~n-ling to give the familiar hexagonal or round forms. The polishing and varnishing process also involves considerable work and a number of individual operations. Finally, erasers are inct~lled SUBSTITUTE SHEET (RULE 26) This technique for manllf~ctllring pencils with a wooden sheath is costly and time consuming; additionally, a large quantity of wood is wasted. With the increasingshortage of wood acceptable for pencils, the ~aste factor becomes less tolerable.
Additionally, the environmental impact of obtaining the wood used to produce pencils contributes to global deforestation.
Substitutes for the wooden ~h~th~, as well as for the involved m~nllf~rturing process, have long been sought. Substitute materials for traditional wooden sheaths include plastics, recycled paper products, and wood flour mixed with a nonabsorbent cellulose m~trri~l. Although pencils with sheaths made from materials other than wood slats, these substitutes have been unable to replace tra~- tional wooden pencils.
M~nllf~rtllring pencils with sheaths made from m~tçri~l~ other than wooden slatsalleviates some of the problems associated with using wooden slats, such as the costly multistep process and depending upon the increasingly c~cllsive wood. The ~ltrrn~tive m~trri~lc, however, also produce their own problems. For in~t~nre, the pollutants created from lltili7:ing recycled paper, wood pulp, and plastic in the manufacturing process.
Metals are also used as sheaths for some m~rking implements. Manufacturing sheaths from metals is c~cll~7ive and also results in environment~l degradation.

B. Traditional Cementitious Materials.
The need for an inexpensive and environmentally benign m~tçri~l in the m~mlf~qcture of m~rking implPnnrnt.~ has not lead to the use of hydraulically settable materials, such as cement or gypsum (hereinafter "hydraulically settable," "hydraulic,"
or "crmrntitious" compositions~ m~trr~ o mlli~Lulcs). Hydraulically settable m~t~.ri~
however, are inexpensive and comprise environment~lly innocuous components like rock, sand, clay and water. From an economic and ecological standpoint, hydraulically settable m~t~i~l~ are ideally suited to replace wood, plastics and metals, as the m~tçri~
of choice for such m~rking implements.

WO 95/21063 . PCT/US95/01497 216~117 Hydraulically settable materials have not been utilized for manl-f~cturing lightweight objects such as marking implements due to the recognized characteristics of hydraulically settable materials and problems associated with processing the materials.
Some of the recognized characteristics and problems associated with such materials and 5 the processing of such materials include: high fluidity, low tensile strength, low form stability after shaping the matçrial~, lengthy curing times, adhesion to the forming apparatus and bleeding of water to the surface of the formed article. As a result of the recognized characteristics and processing problems of hydraulically settable materials, their usefulness has generally been limited to large, bulky structures that are durable, 10 strong, and relatively inexpensive.
Structures co.ll~;..ing a hydraulic cement are generally formed by mixing hydraulic cement with water and usually some type of aggregate to form a cementitious mixture, which hardens into concrete. Ideally, a freshly mixed cementitious mixture is fairly nonviscous, semi-fluid, and capable of being mixed and formed by hand. Because 15 of its fluid nature, concrete is generally shaped by being poured into a mold, worked to elimin~te large air pockets, and allowed to harden. Some concrete mixtures have also been extruded into substantially flat slabs of simple shape. In the latter case, the cementitious mixture must be viscous and cohesive enough to avoid slumping (that is, ch~n~in~ from the desired shape). If the surface of the concrete structure is to be 20 exposed, such as on a concrete sidewalk, additional efforts are made to finish the surface to make it more functional and to give it the desired surface characteristics.
Due to the high level of fluidity required for typical cPrn~ntitious llliX.lUl~S to have adequate workability, the uses of conc~ and other hydraulically settable mixtures have been limited mainly to simple shapes which are generally large, heavy, and bulky, and 25 which require mP~.h~nical forces to retain their shape until sufficient hardening of the m?~t~.ri~l has occurred. The uses of cC~ ;ous m~tPri~l~ have also been limited by the strength properties of cunc,~t~, namely, the high ratio of colnples~ e strength to tensile WO 95/21063 2 1 6 0 1 17 PCT/US9~/01497 -s strength with relative low tensile strength. The ratio of compressive strength to tensile strength is typically in the order of 10:1.
Another limitation has been that traditional c~mentitious mixtures or slurries have little or no form stability and are molded into the final form by pouring the mixture into 5 a space having externally supported boundaries or walls. It is precisely because of this lack of moldability, coupled with the low tensile strength per unit weight, that cementitious m~tPri~l~ have traditionally been useful only for applications where size and weight are not limiting factors and where the forces or loads exerted on the concrete are generally limited to cwlll"es~ e forces or loads, as in, e.g., columns, foundations, roads, 10 sidewalks, and walls.
The lack oftensile strength (about 1-4 MPa) in concrete is ubiquitously illustrated by the fact that concrete readily cracks or fractures upon shrinkage or bending, unlike other m~teri~l~ such as metal, paper, plastic, or ceramic. Consequently, typical ct mPntitious m~t~ri~lc have not been suitable for making small, thin-walled, lightweight 15 objects, such as .che~th~, which must be made from m~teri~l~ with much higher tensile and flexural strengths per unit weight co.np~ed to typical cementitious materials and where a large cross-section is impractical. More recently, higher strength c~" .~ ;ous materials have been developed which might be capable of being formed into smaller, denser objects. One such m~teri~l is known as "Macro-defect Free" or "MDF" concrete, such as is disclosed in U.S. Patent No. 4,410,366 to Birchall et al. See also, S.J. Weiss, E.M. Gartner & S.W. Tresouthick, "High Tensile Cement Pastes as a Low Energy S-lbsti~te for Metals, Plastics, Ceramics, and Wood," U.S. Department of Energy CTL
Project CR7851-4330 (Final Report, November 1984). However, such high strength cementitious m~teri~ have been prohibitively ~x~ellsi-~e and would be Im.c-lit~ble for 25 making h~ ensi~e sheaths where much che~" m~t~ lc better suited for such uses (e.g, wood and plastic) are readily available. Another drawback is that MDF conc~

cannot be used to mass produce small lightweight objects due to the high amount of time 216a~l7 6 and effort involved in forming and hardening the material and the fact that it is highly water soluble. Additionally, such materials have high viscosity and high yield stress which impedes molding and achieving form stability after molding.
Anotherproblem with traditional, and even more recently developed high strength concretes has been the lengthy curing times almost universally required for mostconcretes. Typical concrete products formed from a flowable ~ lule require a hardening period of 10-24 hours before the concrete is mechanically self-supporting, and upwards of a month before the concrete reaches a substantial amount of its maximum strength. Ex~eme care has had to be used to avoid moving the cern~ntitious articles until they have obtained sufficient strength to be demolded. Movement or demolding prior to this time has usually resulted in cracks and flaws in the cementitious structural matrix.
Once self-~u~uffillg, the object could be demolded, although it has not typically attained the majority of its ultimate strength until days or even weeks later.
Economically and commercially mass producing cementitious objects has been difficult since the molds used in forming cementitious objects are generally reused in the production of concrete products and a substantial period of time is required for even minim~l curing of the concrete. The molding difficulties are m~gnified for small, lightweight articles. Although zero slump concrete has been used to "mass produce"
large, bulky object such as molded slabs, large pipes, or bricks which are imme~ tely self-supporting, such "mass production" is only useful in producing objects at a rate of thousands per day. Such compositions and methods cannot be used to mass produce small, lightweight, objects at a rate of thousands per hour. Additionally, zero slump concrete generally has high viscosity and high yield stress which impedes molding and achieving form stability after molding.
Demolding the cçm~nfitious object can create further problems. As concrete cures, it tends to bond to the forms unless cAl,en~ e releasing agents, such as release oil, are used. It is often .~ecçs~.y to wedge the forms loose to remove them. Such wedging, WO95121063 ~ 0 1 ~ 7 PCT/U$95/01497 -if not done properly and carefully each time, often results in cracking or breakage around the edges of the structure. This problem further limits the ability to make small, lightweight, cementitious articles or shapes other than flat slabs, particularly in any type of a commercial mass production.
S If the bond between the outer wall of the molded cementitious article and the mold is greater than the internal cohesive or tensile strengths of the molded article, removal of the mold will likely break the relatively weak walls or other structural features of the molded article. Hence, traditional cem~ntitious objects must be large in volurne and thickness, as well as extraordinarily simple in shape, in order to avoid breakage during demolding unless expensive releasing agents and other precautions are used.
Typical proces~ing techniques of concrete also require that it be p~ ly consolidated after it is placed in order to ensure that no voids exist between the forms or in the structural matrix. This is usually accomplished through various methods of vibration or poking. The problem with consolidating, however, is that extensive overvibration of the concrete after it has been placed can result in segregation or bleeding of the concrete.
Bleeding is the migration of water to the top surface of freshly placed concretecaused by the settling of the heavier aggregate. Excessive bleeding increases the water to cement ratio near the top surface of the conclete slab, which co~ s~ondingly weakens and reduces the durability of the surface of the slab. The o~ volking of concrete during the fini~hin~ process not only brings an excess of water to the surface, but also fine ,, m~t~ri~l, res llting in subsequent surface defects.
Additionally, the nature of traditional ce...~l.L;lious materials presents another design limitation related to the porosity of the cenn~ntitious m~t-?n~l~ and costs.
Utilization of tr~lition~l CemPntitiQus m~t~ri~lc requires either lln-le~ bly high porosity to achieve a low cost product or lower porosity at a high cost.

WO 9St21063 PCT/US9S/01497 21~117 For each of the foregoing reasons, as well as numerous others, cementitious materials have not had significant commercial application outside of the formation of large, slab-like objects, such as in buildings, foundations, walk-ways, highways, roofing materials or as mortar to adhere bricks or cured concrete blocks. It is completely 5 counte~ luilive, as well as contrary to human experience, to even im~gine (let alone actually experience) the manufacture from cementitious materials of small, lightweight objects such as sheaths for m~rking implements, which are presently m~nnf~rtllred from lightweight, yet relatively high strength to mass, materials such as wood, plastic and paper.
In short, what are needed are improved methods for manufacturing sheaths for marking implements at a cost that is competitive with or even superior to, the costs involved in manufacturing m~rking implements with sheaths made from wood, plastic, or metal materials.
Additionally, it would be a significant advancement to produce sheaths from 15 materials which have a much lesser impact on the environment; decrease the need for wood, plastic and metal m~t~ri~l~; comprise renewable m~tçri~l~; and do not result in the generation of wastes involved in the m~mlf~ch~re of sheaths from wood, plastic or metal m~tçr~
It would also be a completely novel and an important advancement if such 20 methods yielded sheaths and other objects having a chemical composition compatible with the earth into which they eventually might be discarded.

It would also be novel in the art of cement making to provide sheaths and methods for m~nllf~cturing sheaths which can be commercially formed from hydraulically settable materials, will rapidly obtain form stability and m~int~in their 25 shape without external support for subsequent h~nl11ing shortly after formation.
It would be still another advanc~m~nt in the art to provide sheaths formed from hydraulically settable mixtures and methods for mass producing such sheaths which do not adhere to the forming app;~dllls and can be removed from the forming apparatus directly after forming without degradation to the sheaths.
Finally, it is still another object of the present invention to provide sheaths and methods for removing sheaths from the forming apparatus directly after forming without 5 degradation to the sheath. Such methods are disclosed and claimed herein.

BRIEF SUMMARY OF THE INVENTION
The present invention encu" ,p~cses m~rking implements with a m~rking core and a sheath having a structural matrix formed Irvm hydraulically settable materials, such as 10 hydraulic cement, gypsum and other m~t~ri~l~ that set or harden with water, and methods for m~nllf~r,tnring such m~rking implçnn~nt~. Marking implements with a m~rking core and a sheath having a structural matrix formed from hydraulically settable materials within the scope of the present invention are particularly useful for m~rking, writing, drawing, coloring, p~inting, or applying cosmetics in the manner that pencils, pens, 15 mechanical pencils, ink markers, and cosmetic pencils and the likr~ are used.
The structural matrix of the sheaths (hereinafter "hydraulically settable sheath"
or "sheath") formed from the hydraulically settable m~tçri~lc have properties that have not previously been achieved through the use of such m~teri~l~ Utilization of these materials allows the economic mass production of sheaths without the processing 20 problems typically associated with such m~teri~l~ Additionally, additives can be optionally utilized with the binders which also results in a structural matrix having unique pGl lies.
The m~mlf~rture of sheaths through the use of hydraulically settable materials without the undesirable char~ctçri~tics and proces~ing problems associated with 25 traditional hydraulically settable m~tçri~l~ was achieved through microstructural engin-?~ring. Microstructural ~ngin~.ring is the process of building into the microstructure of hydraulically settable compositions certain desired, pre(l~t~...,;,.rd WO 95/21063 21 6 ~117 PCT/US95/01497 properties into the final product such as strength, flexibility, color and density. This microstructural engineering approach allows for the design of sheaths having a structural matrix with predetermined plol)~llies from a wide variety of commonly available materials. Utilizing this method, the desired ~lopellies are ~lesign~cl into the 5 microstructure of the structural matrix, while optimi~ing the costs and other aspects of a mass production manllf~çtllring system.
The result of the microstructural engineering approach is the ability to m~nuf~cture a wide variety of different products heretofore m~nllf~rtured from wood, plastic, and metal. Moreover, the present invention can be manufactured at a cost that 10 is usually competitive with, and in most cases even superior to, the costs involved in m~nuf~cturing m~rking implements with sheaths made from wood, plastic, or metal materials.
Because the hydraulically settable sheaths of the present invention comprise only environment~lly neutral co~ )olle~ , which also are far more renewable, the m~mlf~r,tllre 15 of such sheaths has a much lesser impact on the environment than the m~nllf~rture of m~rking implements with a sheath made from wood, plastic, or metal materials. Unlike the manufacture of wood .chP~thc, hydraulically settable sheaths require no cutting of trees to supply the raw m~teri~lc for their m~nllf~ re.
The major components within the sheaths ofthe present invention include mainly 20 inorganic m~teri~lc; such as hydraulically settable binders (such as hydraulic cement and gypsum), aggregates (such as sand, calcite, bauxite, dolomite, granite, quartz, glass, silica, perlite, vermiculite, clay, and even waste concrete products), fibers (organic and inorganic fibers), rheology-modifying agents, dispersants, and accelerators along with water nececs~ry to hydrate, or react with, the hydraulically settable binders. These 25 materials form a hydraulically settable lllixlulc.
The plcrtllcd structural matrix of the sheaths m~nllf~ctured according to the present invention is formed from the reaction products of a cem~ntitious or other -hydraulically settable ~ C. The hydraulically settable mixture will at a minimnmcontain a hydraulic binder, such as hydraulic cement or gypsum hemihydrate, and water.
The porosity of the hydraulically settdble structural matrix resulting from these mixtures can be minimi7Pd by m~int~ining a low water to hydraulic binder ratio.
In order to design the desired plopellies into the hydraulically settable mixture and/or the cured hydraulically settable structural matrix, a variety of other additives are included within the hydraulic mixture, such as one or more aggregate materials, fibers, rheology-modifying agents, di~el~alll~, accelerators, air elllldillillg agents, blowing agents or reactive metals. The identity and quantity of any additive will depend on the desired l.lop~l lies of both the hydraulically settable mixture, as well as the final hardened sheath made therefrom.
In some cases it may be preferable to include one or more aggregate materials within the mixture to create a smooth surface, to add bulk and decrease the cost of the mixture. Aggregates often impart significant strength plol,el lies and improved workability. Examples of such ag~cgdles are ordinary sand, calcite, limestone, bauxite, dolomite, granite and quartz which are completely environmentally safe, extremely inexpensive, and essenti~lly inPxh~ tible.
In other cases, lightweight ag~lcgdles can be added to yield a lighter, final cured product. Examples of lightweight aggregate are exr~n-led perlite, vermiculite, hollow glass spheres, aerogel, xerogel, and other lightweight mineral m~tPri~l~ These aggregates are likewise environmPnt~lly safe and relatively inexpensive.
Fibers are added to the hydraulically settable mixture to increase the tensile strength, flexural strength, colll~ e strength, cohesive strength and impact resistance of the ~he~th~ Fibers should preferably have high tear strengths, burst strengths, and tensile strengths. Fibers with a high aspect ratio work best in hl~lillg strength and tonghnes~ to the hydraulically settable m~tPri~l.

WO 95/21063 2 1 ~ O 1 17 PCT/US95/01497 Due to the versatility of the hydraulically settable mixtures used in the manufacture of the ~h~th~, a wide range of fibers, both organic and inorganic, can be used. Examples of preferred fibers include biodegradable plastics, glass, silica, ceramic, metals, carbon, hemp, plant leaves and stems, wood fibers (such as southern pine), flax, 5 bagasse (sugar cane fiber), cotton and hemp (high aspect ratio). Abaca is a l,re~lled fiber which is extracted from a banana-like hemp plant found naturally in the Philippines.
Additionally, continuous fibers can be utilized such as Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers.
Rheology-modifying agents can be added to increase the cohesive strength, 10 "plastic-like" behavior, and the ability of the mixture to retain its shape when molded or extruded. They act as thickeners and increase the viscosity of the mixture as well as the yield stress of the mixture, which is the amount of force nf~cç~s~ry to deform the rnixture.
This creates higher "green strength" in the molded or extruded product. Suitable rheology-modifying agents include a variety of cellulose-, starch-, and protein-based 15 materials which act by both bridging the individual cement particles together and by gelation of the water.
Di~c,~ , on the other hand, act to decrease the viscosity and yield stress of the mixture by dispersing the individual hydraulic binder particles. This allows for the use of less water while m~ g adequate levels of workability. Suitable di~. ~
20 include any material which can be adsorbed onto the surface of the hydraulic binder particles and which act to disperse the particles, usually by creating an electrical charged surface area on the particle or by placing electrical charges in the near colloid double layer.
In the case where both a rheology-modifying agent and di~f~ll are used, it will 25 usually be advantageous to add the f~ first and then the rheology-modifying agent second in order to obtain the beneficial effects of each. Otherwise, if the rheology-modifying is first adsorbed by the binder particles, it may create a protective colloid WO 95/21063 2 1 ~ ~ 1 1 7 PCT/US9S/01497 -layer, which will prevent the dispersant from being adsorbed by the particles and hllpal Lhlg its beneficial effect to the hydraulically settable mixture.
The hydraulically settable structural matrix is composed of mainly inorganic materials, although, certain embo-limPnt~ may also include organic components, such as S cellulose-based fibers and/or rheology-modifying agents. These organic components, however, lc~lcsclll only a small fraction of the overall mass of the hydraulically settable materials used to manufacture the sheaths. Additionally, some of the organic fibers utilized in this invention can be planted and harvested in an agribusiness setting, such as the abaca fibers.
Additionally, the m~rking implements with hydraulically settable sheaths utilize no petroleum-based products or derivatives as starting materials unlike the manufacture of m~rking implements with plastic ~h~th~. Thus, although some amount of fossil fuel is necessary to generate the energy used in the m~mlf~chlre of the m~rking implements with a hydraulically settable sheath, far less will be consumed.
The general method of m~nllf~tnring the m~rking implements includes: (1) mechanically mixing a powdered hydraulic cement and water in order to form a cement paste in a high shear mixer and (2) forming a sheath from the mixtu.e around a m~rking core or forming a sheath and later inserting a m~rking core into the sheath. In addition to mixing a powdered cement and water, it may be desirable to add other desired 20 materials such as aggregates, fibers, rheology-modifying agents, di~cl~ , and accelerants to create a hydraulically settable mixture having the desired rheological as - well as llltim~te streng~, weight, and low cost plop~llies. The sheaths formed from the mixture can subsequently be dried or cured. The manner of mixing and curing can also effect the final properties of the hardened hydraulically settable structural matrix.
25 Additionally, co~tings and l~min~tes can be utilized tr ~,hieve a desired finish.
The present invention can be rapidly process~.. into sheaths of a desired shape having sufficient strength to be self-~u~,~ol Lillg, form stable, and moveable shortly after WO 95t21063 PCT/US95/01497 2l6all7 --formation for subsequent curing. Furthermore, the m~rking implements with a hydraulically settable sheath and a m~rkin~ core are easily removed from their forming device.

BRIEF DESCRlPTION OF THE DRAWINGS
In order to more fully understand the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical emboriime?nt~ of the invention and are therefore not to be considered limiting of its scope, the invention in its presently understood best mode for making and using the same will be described with additional specificity and detail through the use of the accompanying drawings in which:
Figure 1 is a perspective view of a m~rking implement in accordance with the present invention, the implement being in a sharpened condition.
Figure 2 is a perspective view of a m~rking implement in accordance with the present invention.
Figure 3 is a pçr.cpective view of another m~rking implement in accordance with the present invention.
Figure 4 is a perspective view of still another m~rking implement in accordance with the present invention.
Figure 5 is a pe,~e-;Live view of another m~rking implement in accordance with the present invention.
Figure 6 is a perspective view of yet another m~rking implement in accordance with the present invention.
Figure 7 is a p.,l~c~ e view of still another m~rking implement in accordance with the present invention.

wo 95/21063 21 ~ O 1 1 7 PCT/US95/01497 Figure 8 is a perspective view of yet another m~rking implement in accordance with the present invention.

- DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to m~rkine implements with a hydraulically settable sheath and a m~rking core for use in m~rking, writing, drawing, coloring, p~intin~, or applying cosmetics, as used by traditional m~rking implements with sheaths made from wood, plastic, or metal such as mechanical and non-mechanical pencils, pens, and ink markers. Using a microstructural engineering approach it is possible to design ahydraulically settable mixture that can be readily and economically mass produced into sheaths with significantly less environmçnt~l impact - ~ conventional sheaths. More particularly, the present invention is directed to m~rking lmplements with a hydraulically settable sheath and a m~rking core in which the sheath is m~nllf~rtl-red from hydraulically settable m~t~ri~l~ that are generally lightweight and yet have a high strength to bulk density ratio, can be cost effectively produced, and are more environmentally neutral than ~ elllly used m~rking implements. The m~rking implements within thepurview of the present invention can be either a disposable or nondisposable m~rking implement.

I. General Discussion.
The sheaths result in a decreased cost in materials and production co~ d to conventional sheaths and a decreased environm~nt~l impact in obtaining the materials to manufacture the ~h~th~, proces~ing the m~t~ri~l~ into ~he~th~, and disposing of used ~h~th~ These objectives are achieved through the utilization of sheaths formed from hydraulically settable m~t~ while overcollling the undesirable characteristics and procec~ing problems associated with traditional hydraulically settable m~t~ri~l~

WO 95/21063 21~ (~ 1 17 PCT/US95/01497 The undesirable characteristics associated with traditional hydraulically settable materials has indicated until now that hydraulically settable materials could not be utilized to mass produce sheaths which are small, lightweight, and thin-walled. The characteristics and processing problems of traditional hydraulically settable materials which have precluded the mass production of these materials for sheaths includes: high porosity, low tensile strength, low form stability after shaping the materials, lengthy curing times, adhesion to the forming a~p~lus and bleeding of water to the surface of the formed article. These undesirable characteristics and processing problems are overcome by unique combinations of mixture designs and proces~ing.
To achieve the desired plo~ ies in the resultant sheaths without the undesirablecharacteristics and processing problems of traditional hydraulically settable m~tçri~lc, suitable hydraulically settable binders have been developed based on a microstructural en~in~ering approach. A detailed description of the hydraulically settable binders used to m~nuf~tllre food or beverage containers is set forth in detail in co-pending application Serial No. 08/095662 entitled "Hydraulically Settable Cont~in~rs for Storing, Dispensing, and Pack~ging Food and Beverages and Methods for their M~nllf~ctllre" filed July 21, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson. In addition, a detailed description of the cçm~ntitious m~tçri~l~ used to m~nllf~r,tnre general p~ ging and storing cont~inPrs for all kinds of goods is set forth in detail in co-pending applicationSerialNo.08/019,151,entitled"CemPntitiousM~tPri~l~ForUseinP~ in3~
Containers and Their Methods of ~ mlf~ctllre," filed February 17, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson. For purposes of disclosure, these applications are incorporated herein by specific reference. Once suitable hydraulically settable m~tto.ri~l~ were produced, the specific methods of more rapidly and inexpensively m~nuf~cturing sheaths disclosed and cl~imç~l herein were developed.
In short, the undesirable properties and proces~ing problems of traditional hydraulically settable m~t~ori~lc are overcome by the present invention, in part, by collaborative combinations of some of the following: the disclosed hydraulically settable mixture components, mixture component ratios, mixing components morphology and chemical propellies, sequence of adding the mixture components, mixing methods, ~ltili7ing microstructural tonginç~ring to plop~lly place the mixture components resulting S in uniform properties throughout the sheath, methods of forming the sheaths from the mixture, the forming equipment, curing methods, application of coatings, and l~ tes, as well as the structural dPsi~n~ This technology is disclosed in greater detail hereinafter.
The specific l~lu,u~llies or qualities desired for any product can be engin~ered by 10 proper selection of the components and m~nllf~çturing processes as taught herein.
Hence, the m~rking implements within the scope of the present invention can be made to have a variety of physical characteristics and pfop~llies based on varied types of materials and concelllldlions utilized to create the llli~Lules which are subjected to either molding, casting, or extrusion.
15 The matrix of the present invention may be designed to have a tensile strength to bulk density ratio within the range from about 1 to about 300 MPa-cm3/g. The tensile strength to bulk density ratio of the matrix will be more preferably within the range from about 2 to about 50 MPa-cm3/g and most preferably within the range from about 3 to about 20 MPa- ~n3/g A. MicrostructuralFngi~.c~ De~
As mentioned above, the implements of the present invention have been developed from the perspective of microstructural engin~ring Microstructural ~n~ ç~ g involves configuring the microstructure and lltili7ing proces~in~ steps to 25 achieve a ul~irOllll microstructure reslllting in a final product with matrix ul~irullllity.
Microstructural enginPçring permits desi~ing into the microstructure of the hydraulically settable material certain desired, precletermined prol)ellies, while at the same time rem~ining cognizant of costs and other manufacturing complications. The microstructural engineering approach, instead of the traditional trial-and-error mix and test approach, has resulted in the ability to design the hydraulically settable materials with those properties of strength, weight, cost, and environm~ntAl concerns that are necessary 5 for ~pplo~ ;ate m~rking implements.
The number of materials available to engineer a specific product is enormous estimates range between fifty thousand and eighty thousand. They can be drawn from such disparately broad classes as metals, polymers, elastomers, ceramics, glasses, composites, and cPn Pnt~ Within a given class, there is some commonality in properties, 10 proces~ing, and use-p~ttern~ Ceramics, for instance, have high modula, while polymers have low modula; metals can be shaped by casting and forging, while composites require lay-up or special molding techniques; cements have high flexural strength, while elastomers have low flexural strength.
However, this colllp~L~ .nt~li7~tion has its dangers; it can lead to specialization l S (the metallurgist who knows nothing of ceramics) and to conservative thinking ("we use steel because that is what we have always used"). It is this specialization and conservative thinking that has limited the consideration of using hydraulically settable m~ttori~lc for a variety of products, such as in connection with m~rkin~ implements.
Nevertheless, once it is realized that hydraulically settable materials have such a wide 20 utility and can be designed and microstructurally engineered, then their applicability to a variety of possible products becomes obvious.
The design ofthe compositions ofthe present invention have been developed and narrowed, first, by primary collsL~ai~ dictated by the design, and then by seeking the subset of m~teri~l.c which m~imi7~ the performance of the components. At all times 25 during the process, however, it is i~ oll~l to realize the neces~ily of designing products which can be m~nllf~ctnred by a cost-competitive process.

WO 95/21063 2 16 0 1 1~ PCT/US95101497 Primary co~ di~ in materials selection are imposed by characteristics of the design of a component which is critical to a successful product. With respect to a m~rking implement with a hydraulically settable sheath, those primary col~ aillt~
- include minim~l weight, strength, and tol~ghness requirements while keeping the costs 5 comparable to or less than wood, plastic or metal counterparts. In addition, other restraints include creating hydraulically settable m~tçri~ which are comparable to sheaths of traditional m~rking implements in weight, strength, tollghnes.s and flexibility.
As discussed above, one of the problems in the past with hydraulically settable materials such as cement has been that typical cement ~ L~I~s are poured into a form, 10 worked, and then allowed to set and cure over a long period of time, typically days or weeks. Experts generally agree that it takes at least one month for concrete products to reach a substantial degree of their oplilllulll strength, but they also admit that most concrete products do not reach their maximum strength for several dec~des. Such time periods are certainly impractical for the economic mass production of m~rking 15 implements, particularly disposable m~rking implements.
As a result, an important feature of the present invention is that when the hydraulically settable mixture is molded, it will m~int~in its shape (i.e., support its own weight subject to minor forces such as gravity and movement through the proces~ing eqnirmPnt) in the green state without external support. Further, from a m~mlf~tllring 20 perspective, in order for economical production, it is important that the formed hydraulically settable sheath rapidly (in a matter of Illill-l~es if not seconds) achieve suff1-- cient strength so that it can be handled for further procec~in~, even though the hydra-ulically settable llli~lule may still be in a green state and not fully hardened.
Another advantage of the microstructural en~ ling approach of the present 25 invention is that it is possible to develop a composition in which cross-sections of the structural matrix are more homogeneous than have been typically achieved in the prior art. Ideally, when any two given samples of about 0.5 n3 (whel~ "n" is the ~m~llest cross-section of the material) of the hydraulically settable structural matrix are taken, they will have substantially similar amounts of voids, aggregates, fibers, or any other additives and properties of the matrix. Achieving matrix uniformity is based on the proper placement of mixture components, which optimizes the plop~ ies of each mixture 5 component and permits collaboration between the components to achieve the desired properties. The net effect of this uniformity is uniform performance throughout the product. Evidence of the collaboration between the components through this method is given by a tensile strength to compressive strength ratio which is substantially greater than that of traditional hydraulically settable materials.
From the following discussion, it will be appreciated how each of the component materials within the hydraulically settable mixture conkibutes to the primary design constraints. Specific m~t~ri~l~ and compositions are set forth in the examples to demonstrate how the m~xill,i~lion of the p~,lr~ll,l~,ce of each colllpol~lll accomplishes the combination of desired ~lope, Lies.

B. Marking Implements with a Markin~ Core and a Sheath Havin~ a Hydr~nlil ~lly Settable Structural Matrix.
The term "m~rking implement(s)" as used in this specification and the appended claims is int~n-l~d to include a m~rking core and a sheath formed from hydraulically 20 settable m~t~ri~l~. Marking implements within the scope of this invention include any pencils, cosmetic pencils, ink markers, me~h~nical pencils, pens, china markers, crayons and oil pastels as used for m~rking, writing, drawing, coloring, p~inting, or applying cosmetics having a hydraulically settable sheath. The m~rking implement with a hydraulically settable sheath and a m~rking core should be capable of being utilized to 25 make a mark, write, draw, color, paint, or apply cosmetics.
The term "hydraulically settable sheath(s)" as used in this specification and the appended claims is int~n(led to include any sheath formed from hydraulically settable W O 95/21063 216 0 ~ 17 PCTAUS95/01497 m~t~ori~l~ which is shaped and used similarly to sheaths m~nl]f~chlred from conventional m~t~ri~l.c to form pencils, mechanical pencils, pens, cosmetic pencils, plastic ink markers, metal ink markers, china markers, crayons, and oil pastels.
The term "m~rking core(s)" as used in this specification and the appended claims S is intenrled to include any means for making a mark on a surface, and includes but is not limited to any ~,d~ clay leads; colored leads; a cartridge co.-t~ini.,g a m~rking fluid and having means for dispensing the m~rking fluid, such as the ball point pen configuration; absorbent fil~m~nt.c s~ dled with a m~rking fluid as used in penmarkers;
absorbent fil~m~nt~ connected to a reservoir co-,l;lini"g a m~rking fluid; a marking fluid 10 applied in any traditional manner by pens and ink markers; a predetermined amount of m~rking fluid retained within the sheath and dispensed thel~rlolll by means for dispensing the m~rkinp fluid; and solid cosmetics traditionally applied with a pencil;
china markers; crayons; oil pastels; etc. The term "m~rking fluid(s)" as used in this - specification and the appended claims is int~n~ed to include any flowable solid or liquid 15 which can be contained and dispensed to mark a surface, and includes but is not limited to liquid inks, paste inks, pi~m~nt~, and dyes.
The term "m~rking core(s)" as used in this specification and the appended claims is also int~n~ecl to include m~rking cores which are removable from the sheath and m~rking cores which are fixedly retained within the sheath. Additionally, m~rking 20 implements with a m~rking core which is fixedly retained within the sheath can be designed to form an adhesiveless bond between the sheath and the m~rking core, - although the use of adhesives is also within the scope of this invention.
Marking implem~nt~ with a hydraulically settable sheath can be utilized with any structure utilized with conventional m~rking implem~.nt~ within the scope this invention, 25 these structures can be formed from conventional m~t~ri~l.c such æ metal, plastic, rubber and wood or from hydraulically settable m~tP.ri~l~. Marking implements within the scope of this invention also include such structures as clips secured to the m~rking implement WO 95/21063 21~ 0 1 17 PCT/US95/01497 for pocket ~ çhments and protective caps or covers to protect an exposed end of the m~rking core. Also, within the scope of this invention are means for COI~t~ g erasers.
An example of a means for co~ ;nil~g erasers is the f~mili~r crimped ring utilized with conventional pencils. Additionally, an end of the hydraulically settable sheath can be configured to receive an eraser and secure the eraser without the use of such a metal ring.
Another useful means for col.~ -g erasers is provided by configurations utilized with conventional mechanical pencils.
Other structures within the scope of this invention include means for affixing the m~rking core in a secure manner within the sheath and means for moving the marking core within the sheath. An example of a means for affixing the m~rking core in a secure manner is a conical portion similar to the conical portion utilized with inexpensive ink pens to support the ink cartridge and inserted into the plastic sheath. There are numerous means for moving the m~rking core within the sheath which are widely used. An example of a means for moving the m~rking core involves the use of a spring around one end of the m~rking core, the spring being secured within the sheath, and a mech~ni ~m at the other end of the m~rkinE core for eng~ging the m~rking core so that the m~rking core extends out of the sheath or is retracted within the sheath. Another f~mili~r means for moving the m~rking core within the sheath is provided by a two piece sheath which moves the m~rking core when the sheath pieces are rotated in opposite directions. The means utilized with conventional mechanical pencils is also useful for moving the m~rking core within the sheath of m~rking implements within the scope of this invention.

II. Hvdraulically Settable Mixture Components A. Hydraulically Settable Materials.
The m~t~ri~l.c used in conjunction with the methods of the present invention develop strength through the chemical reaction of water and a hydraulic binder such as hydraulic cement, c~lcil-m sulfate (or gypsum) hemihydrate, and other substances which WO 95/21063 21~ ~ 1 17 PCT/US9S/01497 harden after being exposed to water. The term "hydraulically settable m~teri~l~" as used in this specification and the appended claims includes any material with a structural matrix and strength properties derived from the hardening or curing of a hydraulic binder.
These include cementitious m~t~ , plasters, and other hydraulically settable materials as defined herein. The hydraulically settable binders used in the present invention are to be distinguished from other cements or binders such as water insoluble polymerizable organic cements such as glues or adhesives.
The terms "hydraulically settable m~tçri~l~", "hydraulic cement materials" or "cementitious m~tPri~l~," as used herein, are inten~lecl to broadly define compositions and materials that contain both a hydraulically settable binder and water, regardless of the extent of hydration or curing that has taken place. Hence, it is intçn(1e~1 that the term "hydraulically settable materials" shall include hydraulic paste or hydraulically settable mixtures in a green (i. e., unhardened) state~ as well as hardened hydraulically settable or concrete products.
1. Hydraulically Settable Binders.
The terms "hydraulically settable binder" or "hydraulic binder" as used in this specification and the appended claims are int~n~l~cl to include any inorganic binder such as hydraulic cem~nt, gypsum hemihydrate, or calcium oxide which develop strength~,o~c.lies and hardness by chemically reacting with water and, in some cases, carbon dioxide within the air and water. The terms "hydraulic cement" or "cement" as used in this specification and the appended claims are intçnded to include clinker and crushed, ground, milled, and processed clinker in various stages of pulverization and in various particle sizes.
Examples oftypical hydraulic ceTntont~ known in the art in~.lude the broad farnily of portland c~nnpntc (including oldin~y portland cement without ~y~ ), calcium al..nnin~te cement~ (including calcium al~ e cçrn~nt~ without set regulators), WO 95/21063 21 (i 01 17 PCT/US95/01497 plasters, silicate cements (including n-dicalcium silicates, tricalcium silicates, and ix~UlCS thereof), gypsum cements$ phosphate cPnnçnt.C, high alumina cements, microfine cements, slag cements, m~gnPsium oxychloride cements, and aggregates coated with microfine cement particles. Other useful cements include: MDF cement, DSP cement, 5 Pyrament-type cement, and Densit-type cement.
The term "hydraulic cement" is also intended to include other cements known in the art, such as c~-dicalcium silicate, which can be made hydraulic under hydrating conditions within the scope of the present invention. The basic chemical components of the hydraulic cements within the scope of the present invention usually include CaO, SiO~, Al203, Fe203, MgO, SO3, in various combinations thereof. These react together in a series of complex reactions to form insoluble calcium silicate hydrates, carbonates (from CO2 in the air and added water), sulfates, and other salts or products of calcium and magnesium, together with hydrates thereof. The alllminum and iron constituents are thought to be incorporated into elaborate complexes within the above mentioned 15 insoluble salts. The cured cement product is a complex matrix of insoluble hydrates and salts which are complexed and linked together much like stone, and are similarly inert.
Hydraulically settable compositions are typically formed by mixing a hydraulic binder or combinations thereof (such as hydraulic cement) and water; the resulting nlixlulc may be referred to as a "hydraulic paste" (or "cement paste"). The hydraulic 20 binder and water are mixed either simultaneously or subsequently, with some sort of aggregate blended to form a "hydraulically settable llli~llJlC." Mortar and concrete are examples of hydraulically settable mixtures formed by mixing hydraulic cçment, water, and some sort of aggregate, such as sand or rock.
Gypsum is also a hydraulically settable binder that can be hydrated to form a 25 hardened binding agent. One hydratable form of gypsum is calcium sulfate hemihydrate, commonly known as "gypsum hemihydrate." The hydrated form of gypsum is calcium sulfate dihydrate, commonly known as "gypsum dihydrate." Calcium sulfate hemihydrate can also be mixed with calcium sulfate anhydride, cornmonly known as "gypsum anhydrite" or simply "anhydrite."
Although gypsum binders or other hydraulic binders such as calcium oxide are generally not as strong as hydraulic cement, high strength may not be as important in S some applications. In terms of cost, gypsum and calcium oxide have an advantage over hydraulic cement, because they are somewhat less expensive. Moreover, in the case where the hydraulically settable material contains a relatively high percentage of weak, lighter weight aggregates (such as perlite), the aggregates will often comprise a "weak link" within the structural matrix. At some point, adding a stronger binder may be 10 inefficient because the binder no longer contributes its higher potential strength due to a high content of weaker aggregates.
In addition, gypsum hemihydrate is known to set up or harden in a must shorter time period than traditional cements. In fact, in use with the present invention, it will harden and attain most of its nltim~te strength within about thirty minutes Hence, 15 gypsum hemihydrate can be used alone or in combination with other hydraulically settable m~tçriAl~ within the scope of the present invention.
Terms such as "hydrated" or "cured" hydraulically settable lllixlu~e, material, or matrix refers to a level of substantial water-catalyzed reaction which is sufficient to produce a hydraulically settable product having a substantial amount of its potential or 20 final ~ x;lllUlll strength. Nevertheless, hydraulically settable m~tPri~l~ may continue to hydrate long after they have ~tt~in~d significant hal~less and a substantial amount of their final m;.xi~nl~ strength.
In addition to a hydraulic binder and water, the hydraulically settable mixtures according to the present invention may include aggregates, fibers, rheology-modifying 25 agents, di~lJe~ , air c-llh~ining agents, and other additives in order to build into the structural matrix of both the cured and uncured lllixlu~e the desired strength and other pc.rc~ ance plop~,llies.

WO 95t21063 216 0 1 ~ 7 PCTtUS95/01497 Terms such as "green" or "green state" are used in conjunction with hydraulically settable mixtures which have not achieved a substantial amount of their final strength, regardless of whether such strength is derived from artificial drying, curing, or other means. Hydraulically settable mixtures are said to be "green" or in a "green state" just prior and subsequent to being molded into the desired shape. The moment when a hydraulically settable lllixlule is no longer "green" or in a "green state" is not altogether clear, since such llliXLu~s generally attain a substantial amount oftheir total strength only gradually over time. Hydraulically settable mixtures can of course show an increase in "green strength" and yet still be "green." For this reason, the discussion herein often refers to the form stability of the hydraulically settable material in the green state.
As mentioned above, preferable hydraulic binders include white cement, portland cement, microfine cement, high alumina cement, slag cement, gypsum hemihydrate, and calcium oxide, mainly because of their low cost and suitability for the manufacturing processes of the present invention. This list of cements is by no means exhaustive, nor in any way is it intended to limit the types of binders which would be useful in making the hydraulically settable sheaths within the scope of the claims appended hereto.
The present invention may include other types of cPrn~ntitious compositions suchas those discussed in co-pending patent application Serial No. 07/981,615, filedNovember 25,1992 in the names of Hamlin M. Jenning~, Ph.D., Per Just Andersen, Ph.D. and Simon K. Hodson, and entitled "Methods of M~nllf~ctllre and Use for Hydraulically Bonded Cement," which is a continll~tion-in-part of patent application Serial No. 07/856,257, filed March 25,1992 in the names of Hamlin M. Jennings, Ph.D.
and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of M~nllf~hlre and Use" (now abandoned), which was a file wrapper colllill~lion of patent application Serial No. 07/526,231 filed May 18,1990 in the names of Hamlin M. J~nnings, Ph.D and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and Use" (also abandoned).

wo 95121063 2 16 ~ 1 17 PCT/US9~/01497 In these applications, powdered hydraulic cement is placed in a near net final position and comp~ctecl prior to the addition of water for hydration.
Additional types of hydraulic cement compositions include those wherein carbon dioxide is mixed with hydraulic cement and water. Hydraulic cement compositions made 5 by this method are known for their ability to more rapidly achieve green strength. This type of hydraulic cement composition is ~liccl-~secl in copending patent application Serial No. 07/418,027 filed October 10, 1989, in the names of Hamlin M. Jennings, Ph.D. and Simon K. Hodson, and entitled "Process for Producing Improved Building Material and Products Thereof," wherein water and hydraulic cement are mixed in the presence of a 10 carbonate source selected from the group consisting of carbon dioxide, carbon monoxide, carbonate salts, and mixtures thereof.
An important advantage of using a hydraulically settable mixture is that the resulting structural matrix is generally water insoluble (at least over the period of time during which use of the product is intended), which allows it to encapsulate water soluble 15 materials or other materials added to the hydraulically settable mixture. Hence, an otherwise water soluble component can be incorporated into the greatly insoluble hydraulically settable matrix and impart its advantageous plop~lLies and characteristics to the final product.

2. HydraulicPaste.
In each embodiment of the present invention, the hydraulic paste or cement paste is the con~tit~ent which eventually gives the sheath the æ~ility to set up and develop strength plU~ .lies. The term "hydraulic paste" shall refer to a hydraulic binder which has been mixed with water. More specifically, the term "cement paste" shall refer to hydraulic cement which has been mixed with water. The terms "hydraulically settable,"
"hydraulic," or "c~ ,.l;lious" llli~ e shall refer to a hydraulic cement paste to which aggregates, fibers, rheology-modifying agents, dispersants, or other m~teri~l~ has been added, whether in the green state or after it has hardened and/or cured. The other ingredients added to the hydraulic paste serve the purpose of altering the plop~llies of the unhardened, as well as the final hardened product, including, but not limited to, strength, shrink~ge, flexibility, bulk density, in~ul~ting ability, color, porosity, surface finish, and 5 texture.
Although the hydraulic binder is understood as the component which allows the hydraulically settable mixture to set up, to harden, and to achieve much of the strength properties of the m~teri~l, certain hydraulic binders also aid in the development of better early cohesion and green strength. For example, hydraulic cement particles are known 10 to undergo early gelating reactions with water even before it becomes hard; this can contribute to the internal cohesion of the mixture.
It is believed that al-lmin~tes, such as those more prevalent in portland grey cement (in the form of tricalcium alllmin~tes) are responsible for a colloidal interaction between the cement particles during the earlier stages of hydration. This in turn causes 15 a level of flocculation/gelation to occur between the cement particles. The gelating, colloidal, and flocculating affects of such binders has been shown to increase the moldability (i.e., plasticity) of hydraulically settable lllixlwes made thelerlolll.
As set forth more fully below, additives such as fibers and rheology-modifying agents can make substantial contributions to the hydraulically settable m~t~ri~l~ in terms 20 of tensile, flexural, and colllpres~ e strengths. Nevertheless, even where high concentrations of fibers and/or rheology-modifying agents are included and contribute subst~nti~lly to the tensile and flexural strengths of the hardened m~teri~l, it has been shown that the hydraulic binder nevertheless contiml~s to add substantial amounts of colll~les~ e strength to the final hardened m~teri~l In the case of hydraulic c~ment it 25 also subst~nti~lly reduces the solubility of the hardened m~t~ri~l in water.
The pc.cc;ll~ge of hydraulic binder within the overall llli~lw~ varies depending on the plop~llies that are to be microstructurally enginPered into the hydraulically WO 95/21063 2 1 ~ O 1 17 PCT/US95/01497 settable ~hP~th.c, as well as the identities of the other ingredients. However, the hydraulic binder is preferably added in an amount ranging from between about 5% to about 90%
as a percentage by weight of the wet hydraulically settable mixture, preferably from about 8% to about 60%, and most preferably from about 10% to about 45%.
S Despite the foregoing, it will be appreciated that all concentrations and amounts are critically dependent upon the qualities and characteristics that are desired in the final product. For example, in a very thin sheath where final cured strength is needed, it may be more economical to have a very high percentage of hydraulic binder with little or no added aggregate. In such a case, it also may be desirable to include a high amount of fiber to give flexibility or to-lghnP,ss.
The other h~,uol k~ll con~tit~lPnt of hydraulic paste is water. By definition, water is an essPnti~l coll~onent of the hydraulically settable materials within the scope of the present invention. The hydration reaction between hydraulic binder and water yields reaction products which give the hydraulically settable m~tPri~l~ the ability to set up and develop strength properties.
In most applications of the present invention, it is hllpolkulL that the water to cement ratio be carefully controlled in order to obtain a hydraulically settable llliX~
which after forming is self-~u~Gl ~hlg in the green state. Nevertheless, the amount of water to be used is tlepentlPnt upon a variety of factors, including the types and amounts of hydraulic binder, aggregates, fibrous m~t~ri~l~, rheology-modifying agents, and other materials or additives within the hydraulically settable mixture, as well as the molding or forming process to be used, the specific product to be made, and its p~u~cl~ies.
The preferred amount of added water within any given application is primarily dependent on two key variables: (1) the amount of water which is required to react with and hydrate the binder; and (2) the amount of water required to give the hydraulically settable llli~Ul~ the ~-eces~-y rheological pl`ûl)elLies and workability.

W O 95/21063 2 1 6 G 1 1 7 PCTAUS9~/01497 In order for the green hydraulically settable mixture to have adequate workability, water must generally be included in quantities sufficient to wet each of the particular components and also to at least partially fill the interstices or voids between the particles (including e.g., binder particles, aggregates, and fibrous m~teri~l~). If water soluble addi-tives are included, enough water must be added to dissolve or otherwise react with the additive. In some cases, such as where a di~cl~ant is added, workability can be increased while using less water.
The amount of water must be carefully b~l~nred so that the hydraulically settable mixture is sufficiently workable, while at the same time recognizing that lowering the water content increases both the green strength and the final strength of the hardened product. Of course, if less water is initially included within the mixture, less water must be removed in order to allow the product to harden.
The appropl;ate rheology to meet these needs can be defined in terms of yield stress. The yield stress of the hydraulically settable mixture will usually be in the range from between about 5 kPa to about 5,000 kPa, with the more plc~.lcd mixtures having a yield stress within a range from about 100 kPa to about 1,000 kPa, and the most prcfe.l~ d mixtures having a yield stress in the range from about 200 kPa to about 700 kPa. The desired level of yield stress can be (and may necess~rily have to be) adjusted depending on the particular forrning process being used to form the .~hr~th~
In each of the forming processes, it may be desirable to initially include a relatively high water to cement ratio in light of the fact that the excess water can be removed by heating the products during or shortly after the forming process. One of the important features of the present invention as compared to the m~nnf~rtllre of paper composites is that the amount of water in the initial lllixlulc is much less; hence, the yield stress is greater for the hydraulically settable ",i~lu,cs. The result is that the total amount of water that must be removed from the initial llli~lU,C to obtain a self-supporting wo 95/21063 2 1 6 ~1 1 7 PCTIUS95/01497 material (i.e., a form stable material) is much less in the case of the present invention when compared to the m~nllf~ture of paper composites.
Nevertheless, one skilled in the art will understand that when more aggregates or other water absorbing additives are included, a higher water to hydraulically settable 5 binder ratio is n~cec~ry in order to provide the same level of workability and available water to hydrate the hydraulically settable binder. This is because a greater aggregate concentration provides a greater volume of interparticulate interstices or voids which must be filled by the water. Porous, lightweight aggregates can also intern~lly absorb significant amounts of water due to their high void content.
Nevertheless, one skilled in the art will understand that when more aggregates or other water absorbing additives are included, a higher water to hydraulically settable binder ratio is necessary in order to provide the same level of workability and water available to hydrate the hydraulically settable binder. This is because a greater aggregate concen-tration provides a greater volume of interparticulate interstices or voids which must be 15 filled by the water. Porous, lightweight aggregates can lead to high permeability and can also int~rn~l Iy absorb significant amounts of water due to their high void content.
Both ofthe co~ clillg goals of sufficient workability and sufficient green strength can be accommodated by initially adding a relatively large amount of water and then driving off much of the water as steam during the forming process and through the use 20 of drying tunnels. Additionally, these compclillg goals can be accommodated by reducing the hl~ lilial volume though high plCS~ulc during the forming process such that workability is sufficient and after formation the water level is low and sufficient green strength is achieved.
It is often preferable to mix the hydraulic binder, water, and other componclnts 25 together in a high shear mixer such as that disclosed and claimed in U.S. Patent No.
5,061,319 entitled "Process for Producing Cement Building Material", U.S. Patent No.

4,944,595 entitled "A~d.~lus for Producing Cement Building Material", U.S. Patent No.

4,552,463 entitled "Method and Apparatus for Producing a Colloidal Mixture" and U.S.
Patent No. 4,225,247 entitled "Mixing and Agitating Device". For purposes of underst~nrling such high shear energy mixers and their methods of use, the disclosures of the aforesaid U.S. Patent Nos. 5,061,319; 4,944,595; 4,552,463; and 4,225,247 are S incorporated herein by specific reference. High energy mixers within the scope of these patents are available from E. Khashoggi Tn-lllstries of Santa Barbara, California, the assignee of the present invention. The use of a high shear mixer results in a more homo-geneous hydraulically settable mixture, which results in a product with higher strength.
Based on the foregoing qualifications, typical hydraulically settable compositions 10 within the scope of the present invention will have a water to cement ratio within the range from about 0.2 to about 10, preferably from about 0.5 to about 5, and most preferably from about 0.75 to about 3. Additionally, the total amount of unreacted water will be less than 10% by weight with respect to the dry, hardened lllixlule. It should be understood that the hydraulic binder has an int~rn~l drying effect on the hydraulically 15 settable mixture because binder particles chemically react with water and reduce the amount of free water within the h.l~,l,a, liculate interstices. This int~rn~l drying effect can be enhanced by including faster reacting hydraulic binders such as gypsum hemihydrate along with slower reacting hydraulic cem~nt B. Fibers.
As used in the specifications and appended claims, the terms "fibers" and "fibrous m~teri~l~" include both inorganic fibers and organic fibers. Fibers may be added to the hy~r~l-lic~lly settable mixture to h~clease the cohesion, toughness, fracture energy, and tensile, and, on occasion, even col"pres~ e strengths of the resulting hydraulically settable material. Fibrous m~teri~l~ reduce the likelihood that the hydraulically settable sheath will shatter when a strong cross-sectional force is applied.

WO 95/21063 2 1 6 ~)1 17 PCT/US95/01497 Fibers which may be incorporated into the structural matrix are include naturally occurring fibers, such as fibers made from glass, silica, ceramic, metal, carbon. Glass fibers are preferably pl~Lleated to be alkali resi~t~nt Other naturally occurring fibers include extracted from hemp, plant leaves and stems, and wood fibers. Other fibers 5 which can be incorporated include plastics, polyaramite, and Kevlar. Biodegradable plastics, such as polylactic acid and Biopol, are environmentally benign fibers which provide significant reinforcement to the matrix.
Preferred fibers of choice include glass fibers, abaca, bagasse, wood fibers (both hard wood or soft wood, such as southern pine), and cotton. Recycled paper fibers can 10 be used, but they are somewhat less desirable because of the fiber disruption that occurs during the original paper m~m-f~rtllring process. Any equivalent fiber, however, which imparts strength and flexibility is also within the scope of the present invention. Abaca fibers are avail~bl~from Isarog Inc. in the Philippines. Glass fibers, such as Cemfill are available from PiL~ington Corp. in Fngl~n(l These fibers are preferably used in the present invention due to their low cost, high strength, and ready availability. Nevertheless, any equivalent fiber which imparts co~llplessi~te and tensile strength, as well as to~lghnPss and flexibility (if needed), is certainly within the scope of the present invention. The only lirniting criteria is that the fibers impart the desired plop~,l Lies without adversely reacting with ~he other con~titllPnt~
20 of the hydraulic m~teri~l and without co~ g substances stored in the sheaths cont~ining such fibers.
The fibers should preferably have a high length to width ratio (or "aspect ratio") because longer, narrower fibrous m~t~ri~le can impart more strength to the matrix without adding more bulk and mass to the llfL~Lulc;. Fibrous m~tPri~l~ should have an aspect ratio of at least about 10:1, preferably at least about 900:1, and most preferably at least about 3000: 1.

2~60117 Preferred fibers should also have a length that is many times the diameter of the hydraulic binder particles. Fibers having at least twice the average diameter of the hydraulic binder particles will work, at least 10 times being plerell~d, at least 100 times being more preferred, and at least 1000 times being most preferred.
The amount of fibrous material added to the hydraulically settable matrix will vary depending upon the desired properties of the final product, with strength, tollghness, flexibility and cost being the principal criteria for determining the amount of fiber to be added in any mix design. In most cases, fiber will be added in an amount within the range from about 0.2% and to about 50% by volume ofthe hydraulically settable mixture, more preferably within the range from about 0.5% to about 30%, and most preferably within the range from about 1% to about 15%.
It will be appreciated, however, that the strength of the fiber is a very important feature in dçtçnnining the amount of the fiber to be used. The stronger the tensile strength of the fiber, the less the amount that must be used to obtain the same tensile strength in the resulting product. Of course, while some fibers have a high tensile strength, other types of fibers with a lower tensile strength may be more elastic. Hence, a combination of two or more fibers may be desirable in order to obtain a resulting product that m~ximi7ed multiple char~ctçri~tics, such as high tensile strength and high elasticity.
It should also be understood that some fibers such as southern pine and abaca have high tear and burst strengths, while others such as cotton have lower strength but greater flexibility. In the case where both flexibility and high tear and burst strength is desired, a lllixlure of fibers having the various prol)~l lies can be added to the mixture.
Additionally, some embo~liment~ may utilize continuous fibers or fil~ment winding with such fibers as Kevlar, poly~d~ glass fibers, carbon fibers and cellulose fibers in the llliXLulc. Continuous fibers are also very useful in spiral winding, which provides significant reinforcement to the matrix. Spiral winding involves the use of WO 95/21063 21 ~ O 1 1 7 PCT/US95/01497 fibers as an overlay wrapped onto or into the sheath in a spiraling fashion. Additional overlays of spiral winding can be wrapped onto or into the sheath. A significant increase in strength results from criss-crossing the fibers by spiral winding in opposite directions.
- The continuous fibers can be co-extruded in the sheath, in a manner such that the fibers S overlap each other in a crisscrossing fashion.
The continuous fibers can also be utilized ~vith the other fibers. Utilizing continuous fibers and combination of the other fibers with the continuous fibers results in a reduction in the volume percent of the fibers in the mixtures.

C. Rheolo~y-modifyingA~ents.
The inclusion of a rheology-modifying agent acts to increase the plastic or cohesive nature of the hydraulically settable llliXlulc so that it behave more like clay.
The rheology-modifying agent tends to thicken the hydraulically settable mixture by increasing the yield stress of the llliXLulc without greatly hlclca~hlg the viscosity of the 15 mixture. Raising the yield stress in relation to the viscosity makes the material more plastic-like and formable, while greatly increasing the green strength.
A variety of natural and synthetic organic rheology-modifying agents may be use~ which have a wide range of properties, including viscosity and solubility in water.
Inasmuch as the sheaths may be expected to experience prolonged exposure to human 20 pcl~h~lion which is water-based, it may be preferable to use a rheology-modifying agent which is less soluble in water after hardening of the hydraulically settable nlix~ or to use a high content of the hydraulic binder with respect to the rheology-modifying agent.
On the other hand, it may be ~lefc.dble to use a rheology-modifying agent which is more water soluble when it is desirable for the sheath to more quickly breakdown into environ-25 mentally benign colllponelll~.
The various rheology-modifying agents colllelllplated by the present invention can be roughly olga~ cd into the following categories: poly~rrll~ ;des and derivatives thereof, proteins and derivativés thereof, and synthetic organic m~t~ Polysaccharide rheology-modifying agents can be further subdivided into cellulose based materials and derivatives thereof, starch based m~t~ and derivatives thereof, and other polysacchar-ides.
Suitable cellulose based rheology-modifying agents include, for example, methyl-hydroxyethylcellulose, hydroxymethylethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxyethylpropylcellulose, wood flour, etc. The entire range of possible p~ llllul~lions is enormous and cannot be listed here, but other cellulose materials which have the same or similar properties as these would also work well.
Suitable starch based materials include, for example, amylopectin, amylose, seagel, starch ~cet~tes, starch hydroxyethyl ethers, ionic starches, long-chain alkylstarches, dextrins, amine starches, phosphate starches, and dialdehyde starches.
Other natural polysaccharide based rheology-modifying agents include, for example, alginic acid, phycocolloids, agar, gum arabic, guar gum, locust bean gum, gum karaya, and gum tr~g~r~nth Suitable protein based rheology-modifying agents include, for example, Zein~
(a prolamine derived from corn), collagen (derivatives extracted from animal connective tissue such as gelatin and glue), and casein (the principal protein in cow's milk).
Finally, suitable synthetic organic plasticizers include, for example, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides, and ethylene oxide polymers, synthetic clay, and latex, which is a styrene-butadine copolymer.
More than one of the rheology-modify agents listed above can be utilized in a particular mi~ e to achieve the desired plup.,.lies of plasticity or rheology-modifying effect and to optimize yield stress. Additionally, combinations of the rheology-WO 95t21063 21~ 01 17 PCT/US95/01497 modifying agents optimize the rheology-modifying effect versus form stability at a minimum differential of temperature and water content.
Another potentially valuable rheology-modifying agent which does not n~cec~rily clearly fall within the various categories mentioned above is polylactic acid.
S The rheology of this polymer is significantly modified by heat and can be used alone or in combination with other of the foregoing rheology-modifying agents.
A plcfe"cd rheology-modifying agent is methylhydroxyethylcellulose, examples of which are Tylose~ FL 15002 and Tylose~) 4000, both of which are available from Hoechst Aktiengesell~cl-~ft of Frankfurt, Germany. Lower molecular weight rheology-10 modifying agents such as Tylose(~) 4000 can act to plasticize the mixture rather thanthicken it, which helps during forming procedures.
More particularly, lower molecular weight rheology-modifying agents improve the intern~l flow of the hydraulically settable mixlu,c during molding processes by lubricating the particles. This reduces the friction between the particles as well as 15 between the llli~ and the adjacent mold surfaces. Although a methylhydroxyethyl-cellulose rheology-modifying agent is plefellcd, almost any non-toxic rheology-modifying agent (including any listed above) which imparts the desired l~lup~ llies would be appropl;ate.
Another plcrcllcd rheology-modifying agent that can be used instead of, or in 20 conj ~ ;ction with, Tylose(~) is polyethylene glycol having a molecular weight of between 20,000 and 35,000. Polyethylene glycol works more as a lubricant and adds a smoother con~ nr,y to the llli~lUlC. For this reason, polyethylene glycol might be lcr~ ,lcd more precisely as a "plasticizer." In addition, it gives the molded hydraulically settable material a smoother surface. Finally, polyethylene glycol can create a coating around 25 soluble components of the llli~lulc thereby ren(1ering the hardened product less water soluble and red~lcing the permeability of the hardened product.

WO 95/21063 216 ~ 1 17 PCT/US95/01497 The rheology-modifying agent within the hydraulically settable m~tçri~l~ of the present invention will generally be included in an amount of up to about 50% by weight of the mixture.

D. Di~e. ~ants.
The term "dispersant" is used hereinafter to refer to the class of materials which can be added to reduce the viscosity and yield stress of the hydraulically settable mixture.
A more detailed description of the use of di~ ls may be found in the Master's thesis of Andersen, P.J., "Effects of Organic Superplasticizing Admixtures and their 10 Components on Zeta Potential and Related Properties of Cement Materials" (1987).
Di~."~ generally work by being adsorbed onto the surface of the hydraulic binder particles and/or into the near colloid double layer of the binder particles. This creates a negative charge around or on the surfaces of particles, causing them to repel each other. This repulsion of the particles adds "lubrication" by reducing the friction or 15 attractive forces that would otherwise cause the particles to have greater interaction.
Hence, less water can be added initially while m~ the workability of the hydraulically settable lllixlu~c.
Greatly recl~lcing the viscosity and yield stress may be desirable where clay-like plopcllies, cohesiveness, and/or form stability are less important. Adding a di~tl~anl 20 aids in keeping the hydraulically settable nlixlulc workable even when very little water is added, particularly where there is a "deficiency" of water. Hence, adding a di~l~ant allows for an even greater deficiency of water, although the molded sheath may have somewhat less form stability if too much di~e,~lL is used. Nevertheless, including less water initially will theoretically yield a stronger final cured sheath according to the Feret 25 Equation.
Whether or not there is a deficiency of water is both a function of the stoichiometric amount of water required to hydrate the binder and the amount of water WO 95/21063 PCT/US9~/01497 - 216~117 needed to occupy the interstices between the particles in the hydraulically settable mixture, including the hydraulically binder particles themselves and the particles within the aggregate m~tPri~l and/or fibrous m~t~ri~l. As stated above, particle pa~ king reduces the volume of the interstices between the hydraulic binder and aggregate particles and, hence, the amount of water necessary to fully hydrate the binder and m~int~in the workability of the hydraulically settable mixture by filling the interstitial space.
However, due to the nature of the coating meçh~ni.~m of the di~c~ , the order in which the di~cl~ll is added to the llliXl~llc iS often critical. If a flocculating/gelating agent such as Tylose~) is added, the di~el~alll must be added first and the flocculating agents second. Otherwise, the di~cl~ll will not be able to become adsorbed on the surface of the hydraulic binder particles as the flocculating agents will be irreversibly adsorbed onto forming a protective colloid, and the surface, preventing the dispc from being absorbed.
A ~lcr~llcd dis~ ~ll is sulfonated n~phth~lene-formaldehyde con~len~te, an example of which is WRDA 19, which is available from the W.R. Grace Co. in Baltimore, Maryland. Other dis~el~ which would work well include sulfonated mela-mine-formaldehyde conllen~te, lignosulfonate, and polyacrylic acid.
The amount of added dispcl~alll will generally range up to about 5% by weight of the hydraulic binder, more preferably within the range of between about 0.25% to about 4%, and most preferably within the range of between about 0.5% to about 2%.
However, it is important not to include too much dispersant as it tends to retard the hydration reactions between, e.g., hydraulic cement and water. Adding too much dispersant can, in fact, prevent hydration, thereby destroying the binding ability of the cement paste altogether.
The di~cl~lls col~f~ te~l within the present invention have sometimes been referred to in the concrete industry as "superplasticizers." In order to better distinguish WO 95/21063 216 ~ ~ 17 PCT/US95/01497 dispersants from rheology-modifying agents, which often act as plasticizers, the term superplasticizer will not be used in this application.

E. A~rf ~j",.t~
Aggregates common in the concrete industry may be used in the hydraulically settable mixtures of the present invention, except that they often must be more finely ground due to the size limitations imposed by the generally thin-walled structures of the present invention. Aggregates utilized within the hydraulically settable Ini~lures will typically have a rli~rneter within the range from about 0.01 microns to about 3 mm. More preferably, aggregates with a fli~meter within the range from about 0.1 microns to about 0.5 mm and most preferably within the range from about 0.2 microns to about 100 microns.
Aggregates may be added to increase the strength, decrease the cost by acting asa filler, decrease the weight, and/or increase the insulation ability of the resultant hydraulically settable m~t~ri~l~. Aggregates are also useful for creating a smoother surface finish, particularly platelike aggregates. Examples of useful aggregates include perlite, vermiculite, sand (any combination of quartz, calcined bauxite and dolomite), gravel, rock, limestone, sandstone, glass beads, aerogels, xerogels, seagel, mica, clay, synthetic clay, ~ tom~eous earth, alun~ina, silica, fly ash, silica fume, tabular alumina, kaolin, micro spheres, hollow glass spheres, porous ceramic spheres, gypsum dihydrate, calcium carbonate, calcium al~min~fe, cork, seeds, lightweight polymers, xonotlite (a crystalline calcium silicate gel), lightweight 5xp~n~1e~1 clays, unreacted cement particles, pumice, exfoliated rock and other geologic m~teri~
Unreacted cement particles may also be considered to be "aggregates" in the broadest sense of the term. Even discarded hydraulically settable m~eri~l~, such as discarded sheaths of the present invention can be employed as aggregate fillers and strengtheners.

WO 95/21063 21 ~ O ~ 17 PCT/US95/01497 Both clay and gypsum are particularly important aggregate materials because of their ready availability, extreme low cost, workability, ease of formation, and because they can also provide a degree of binding and strength if added in high enough amounts.
Clay is a general term used to identify all earths that form a paste with water and harden when dried. The predolllillanl clays include silica and alumina (used for making pottery, tiles, brick, and pipes) and kaolinite. The two kaolinitic clays are anauxite, which has the chemical formula Al2O3-3SiO2-2H2O, and montmorillonite, which has the chemical formula Al2O3-4SiO2-H2O. However, clays may contain a wide variety of other substances such as iron oxide, titanium oxide, calcium oxide, zirconium oxide, and 1 0 pyrite.
In addition, although clays have been used for millennia and can obtain hardnesseven without being fired, such unfired clays are vulnerable to water degradation and have not been used to form sheaths that will be exposed to moisture. Nevertheless, unfired clay and fired clay provide a good, extremely inexpensive aggregate within the cementi-tious structural matrix.
Similarly, gypsum hemihydrate is also hydratable and forms the dihydrate of calcium sulfate in the presence of water. Thus, ~,y~ ll ma~ exhibit the characteristics of both an aggregate and a binder depending on whether (and the concentration of) the hemihydrate or dihydrate form is added to a hydraulically settable m. ~ re.
Examples of ag~ es which can add a lightweight characteristic to the cementitious mixture include perlite, vermiculite, glass beads, hollow glass spheres, calcium carbonate, synthetic m~teri~l~ (e.g., porous ceramic spheres, tabular alumina, etc.), cork, lightweight exr~ntlecl clays, sand, gravel, rock, limestone, sandstone, pumice, and other geological m~t~ri~l~
In addition to conv~ntion~l aggr~g~es used in the cement industry, a wide variety of other aggregates, including fillers, strengtheners, including metals and metal alloys (such as stainless steel, c~lcil-m alllmin~te7 iron, copper, silver, and gold), balls or hollow spherical m~t~ri~l~ (such as glass, polymeric, and metals), filings, pellets, powders (such as microsilica), and fibers (such as graphlte, silica, alumina, fiberglass, polymeric, organic fibers, and such other fibers typically used to prepare various types of composites), may be combined with the hydraulic cem~nt~ within the scope ofthe present 5 invention. Even m~t~ri~l~ such as seeds, starches, gelatins, and agar-type materials can be incorporated as aggregates in the present invention.
From the foregoing, it will be understood that the amount of aparticular aggregate within a mixture will vary clepen-ling upon the desired performance criteria of a particular sheath. The amount can vary greatly from no added aggregate up to about 90% by 10 weight of the hydraulically settable mixture, more preferably within the range from between about 3% to about 60%, and most preferably from between about 20% to about 50%.
Further, it will be appreciated that for any given product, certain of these aggregates may be preferable while others may not be usable. For example, certain of 15 the aggregates may contain harmful materials that, for some uses, could leach from the hydraulically settable mixture, nevertheless, most of the l~lcfcl~d m~t~n~l~ are not only nontoxic but they are also more environm~nt~lly neutral than the components in existing disposable products.
Fibrous m~t~ri~l~ are used in the present invention prim~rily to modify the weight 20 charactçri.~tics of the cementitious ~ e, to add form stability to the mixture, and to add strength and flexibility to the resulting cementitious matrix, although certain fibers may also impart some level of insulation to the final product. Therefore, the term "ag~egatcs" will refer to all other filler m~tçri~, which are nonfibrous, and whose function is mainly to impart strength, rheological, textural, and insulative plop~.lies to 25 the m~tçr~
It is often preferable accordillg to the present invention to include a plurality of di~~ ly sized and graded ag~eg~les capable of more completely filling the interstices WO 95/21063 2 ~ 6 ~1 17 PCT/US9S/01497 between the aggregate and hydraulic binder particles. Optimi7ing the particle packing density reduces the amount of water necessary to obtain adequate workability by elimin~ting spaces which would otherwise be filled with int~r.~titi~l water, often referred to as "capillary water." In addition, using less water increases the strength of the final hardened product (according to the Feret Equation).
In order to o~)tilllize the p~c~ing density, dirrelelllly sized aggleg~les particle sizes ranging from as small as about 0.5~1m to as large as about 2 mm may be used. (Ofcourse, the desired purpose and thickness of the resulting product will dictate the al)plopl;ate particle sizes of the various aggregates to be used.) It is within the skill of one in the art to know generally the identity and sizes of the aggregates to be used in order to achieve the desired characteristics in the final hydraulically settable sheath.
In certain preferred embo-1im~nt.~ of the present invention, it may be desirable to m~imi7~ the amount of the aggregates within the hydraulically settable llliXlw~ in order to maximize the plopcllies and characteristics of the aggregates (such as qualities of strength, low density, or high insulation). The use of particle p~c~ing techniques may be employed within the hydraulically settable material in order to m~-~imi7P the amount of the aggregates.
A detailed disc~ ~.sion of particle p~r~ing can be found in the following article co-authored by one ofthe inventors ofthe present invention: Johansen, V. & ~n-ler~en, P.J, "Particle Packing and Concrete Properties," Materials Science of Concrete II at 111-147, The ~m~.ri~n Ceramic Society (1991). Further il~lll~lion is available in the Doctoral Dissertation of Anderson, P.J., "Control and Monitoring of Concrete Production -- A
Study of Particle Packing and Rheology," The Danish Academy of Technical Sciences.
The advantages of such packing of the aggregates can be further understood by reference to the examples which follow in which hollow glass spheres of varying sizes are mixed in order to m~illli~ the amount of the glass balls in the hydraulically settable llli~lw~ .

216~117 The preferred lightweight aggregates, which are also in~ ting, include expanded or exfoliated vermiculite, perlite, calcined diatomaceous earth, and hollow glass spheres -- all of which tend to contain large amounts of incol~uul~l~d hllc,~liLial space. However, this list is in no way intçn~led to be exh~llctive, these aggregates being chosen because 5 of their low cost and ready availability.
Aggregates can also be added to the mixture to impart a predetermined color or texture. The color or design can also be altered by adding metal fillings or conventional dyes. Additionally, magnetized metal could be added to magnetize the m~rking implement.

F. Air Voids.
It is generally desirable to minimi7.~ air voids in order to m~ximi7P strength.
~i";",i~ g air voids is especially desirable in m~rking implements where the m~rking core bonds directly to the hydraulically settable sheath to increase the strength of the 1 5 bond.
Air voids within the cement matrix will be Illillillli,rd in the m~mlf~ctllre of most m~rking implements but air voids can be intentionally incorporated into the structure of a sheath when a very light weight sheath is desired. The incorporation of air voids into the hydraulically settable mixture can be carefully calculated to impart the requisite 20 density to the sheath, without ~egr~-ling its strength to the point of nomltility. Air voids can be utilized in addition to, or in place of, lightweight aggregates in order to decrease the density of the sht ~th.~. Generally, however, if the density or insulation ability is not an hllpolL~ll feature of a particular product, it is desirable to minimi7e any air voids i n order to maximize strength and i",l,~,l",eability while minimi7ing volume. A
25 matrix having air voids can be utilized in conjunction with a coating or a l~min~te to increase the strength of the sheath. The co~tin~s and l~min~tes which can be utilized with a matrix having air voids are discussed in greater detail below.

W O 95/21063 21 6 ~ ~ 1 7 PCTAUS95101497 In certain embodiments, nonagglomerated air voids may be introduced by high shear, high speed mixing of the hydraulically settable mixture, with a foaming or stabilizing agent added to the mixture to aid in the incorporation of air voids. The high shear, high energy mixers discussed above are particularly useful in achieving this desired goal. Suitable foaming and stabilizing agents include commonly used surfac-tants. One ~;ullclltly l~lcrellcd surfactant is a polypeptide alkylene polyol, such as Mearlcrete~ Foam Liquid.
In conjunction with the surfactant, it may be nPcess~ry to stabilize the entrained material using a stabilizing agent like Mearlcel 3532(~), a synthetic liquid anionic 10 biodegradable solution. Both Mearlcrete(E~) and ~earlcel~) are available from the Mearl Corporation in New Jersey. Another foaming and stabilizing agent is vinsol resin. In addition, the rheology-modifying agent can act to stabilize the entrained air.
During the ellll~ of air the atmosphere above the high speed mixer can be saturated with a gas such as carbon dioxide, which has been found to cause an early false 15 setting and create form and foarn stability ofthe hydraulically settable lnixlulc. The early false setting and foam stability is thought to result from the reaction of CO2 and hydroxide ions within the hydraulically settable lllixlule to form soluble sodium and potassium carbonate ions, which in turn can interact with the al--min~te phases in the cement and accelerate the setting of the llliXlUl~;.
Foam stability helps .. ~ the dispersion, and prevents the agglomeration, of the air voids within the uncured hydraulically settable mixture. Failure to prevent the coalescence of the air voids actually decreases the insulation effect, while greatly decreasing the strength, of the cured hydraulically settable lllixlule. Raising the pH, increasing the concentration of soluble allcali metals such as sodium or ~ol~ssiulll, adding 25 a stabilizing agent such as a polys~c~ rifle rheology-modifying agent, and carefully adjusting the concentrations of surfactant and water within the hydraulically settable mixture all help to increase the foam stability of the mixture.

W O 95/21063 2 ~ 7 PCTrUS95/01497 Air voids may alternatively be in*oduced into the hydraulically settable nli~Lule by adding an easily oxidized metal, such as aluminum, mQgneSium~ zinc, or tin into a hydraulic mixture that is either naturally ~lkQlin~, such as a cementitious or calciurn oxide co~ g mixture, or one that has been made ~lkQline, such as those co~ il,illg gypsum or another lower alkaline hydraulic binder. This reaction results in the evolution of tiny hydrogen bubbles throughout the hydraulically settable mixture. Adding a base such as sodium hydroxide to, and/or he~ting, the hydraulically settable mixture increases the rate of hydrogen bubble generation.
During the process of forming andlor hardening the hydraulically settable mixture, it is often desirable to heat up the hydraulically settable mixture in order to increase the volume of the air void system. Heating also aids in rapidly removing significant amounts of the water from the hydraulically settable mixture, thereby increasing the green strength of the formed product.
If a gas has been incorporated into the hydraulically settable mixture, heating the mixture to 250C, for example, will result (according to the ideal gas equation) in the gas increasing its volume by about 85%. When heating is a~lop,;ate, it has been found desirable for the heating to be within a range from about 1 00C to about 2500C. More ,L~llly, if p~opelly controlled, heating will not result in the cracking ofthe structural matrix of the sheath or yield imperfections in the surface texh~re of the sheath.
In other applications, where viscosity ofthe hydraulically settable mixture is high, such as is required in certain forming processes, it is much more difficult to obtain adequate numbers of air voids through high shear mixing. In this case, air voids may alternatively be introduced into the hydraulically settable mixh re by adding an easily oxidized metal, such as al~minllm, m~ ium, zinc, or tin into a hydraulic mixh~re that 25 is either n~hlr~lly ~lk~lint~ (such as a hydraulic cement or calcium oxide COIQ;~.ig mixture) or one that has been made ~lk~line (such as those CO--~Q;-~ g gypsum or another ~lk~line hydraulic binder).

W O9S/21063 2 1 ~ O 1 1 7 PCTAUS9~/01497 This reaction results in the evolution of tiny hydrogen bubbles throughout the hydraulically settable mixlu~c. Adding a base such as sodium hydroxide to, and/or heating (as described below), the hydraulically settable mixture increases the rate of hydrogen bubble generation.
It may further be desirable to heat the mixture in order to initiate the chemical reaction and increase the rate of formation of hydrogen bubbles. It has been found that heating the formed product to telllpcl~lulcs in the range of from about 50C to about 1 00C, and preferably about 75C to about 85OC, effectively controls the reaction and also drives off a significant amount of the water. Again, this heating process does not result in the introduction of cracks into the matrix of the formed product. This second method of introducing air voids into the structural matrix can be used in conjunction with, or in place of, the introduction of air through high speed, high shear mixing in the case of low viscosity hydraulic llliXLul~ s used in some forming processes.
Finally, air voids may be introduced into the hydraulically settable mixture during the forming process by adding a blowing agent to the IlliXLUIC, which will expand when heat is added to the llliXLu~c. Blowing agents typically consist of a low boiling point liquid and finely divided calcium carbonate (talc). The talc and blowing agent are uniformly mixed into the hyaraulically settable nlixLulc and kept under ~ies~ulc while heated. The liquid blowing agent pcllclldl~s into the pores of the individual talc particles, which act as points from which the blowing agent can then be v~oli;~cd upon thermal expansion of the blowing agent as the plcs~ule is suddenly reduced.
During the forming process, the ~lixlul c can be heated while at the same time it is collll,lcssed. While the heat would nnrrn~lly cause the blowing agent to vaporize, the increase in plcs~ule prevents the agent from ~ol~illg, thereby t~lllpoldl;ly creating an equilibrium. When the plC~ C iS released after the follllillg or extrusion of the m~t~ri~l, the blowing agent vaporizes, thereby e~r~ntling or "blowing" the hydraulically settable m~t~ri~l. The hydraulically settable material eventually hardens with very finely Wog5/21063 21 G ~ PCT/US95/01497 dispersed voids throughout the structural matrix. Water can also act as a blowing agent as long as the mixture is heated above the boiling point of water and kept under pressure of up to 50 bars.
Air voids increase the insulative properties of the hydraulically settable sheaths 5 and also greatly decrease the bulk density and, hence, the weight of the final product.
This reduces the overall mass of the resultant product, which reduces the amount of m~tçri~l that is required for the m~nuf~cture ofthe sheaths and which reduces the amount of material that will ultimately be discarded in the case of disposable ch~,th.c G. Set Accelerators.
In some cases it may be desirable to accelerate the initial set of the hydraulically settable mixture by adding to the lllixlule an applo~l;ate set accelerator. These include Na2CO3, KCO3, KOH, NaOH, CaCl2, CO2, triethanolamine, alllmin~tçc, and the inorganic alkali salts of strong acids, such as HCl, HNO3, and H2SO4. In fact, any compound which 15 increases the solubility of gypsum and Ca(OH)2 will tend to accelerate the initial set of hydraulically settable mixtures, particularly cementitious lllix~ s.
The amount of set accelerator which may be added to a particular hydraulically settable mixture will depend upon the degree of set acceleration that is desired. This in turn will depend on a variety of factors, including the mix design, the time interval 20 between the steps of mixing the colllpollents and forming or extruding the hydraulically settable mixture, the tell.i)el~l~e of the mixlu-e, and the identity of the set accelerator.
One of ordill~ y skill in the art will be able to adjust the amount of added set accelerator according to the parameters of a particular m~mlf~rtllring process in order to o ptillli~t; the setting time of the hydraulically settable llli~lule. The amount of set accelerator will be 25 included in an amount less than 2% of the hydraulically settable binder by weight.

wo 95/21063 2 16 ~ 1 1 7 PCT/USg5/01497 III. Formin~ the Markin~ Implements with a Hydr~ lly Settable Sheath and a Markin~ Core.
There are many methods of forming the marking implements of the present invention from hydraulically settable mixtures. Most methods generally involve 5 substantial mechanical mixing of the materials and water, and formation by either extrusion or by molding. ~nother method involves the compaction of hydraulically settable m~tPri~l~ into a desired shape and then hydrating the mixture without substantial mechanical mixing of the materials. After the m~rking implements are formed through one of these methods the m~rking implements can be subjected to several other 10 processing steps, such as, h~ting, applying a coating, and l~min~ting the sheath.
The combination of hydraulic binders, aggregates, fibers, and (optionally) air voids results in a composition that can be formed into sheaths having roughly the same thickness as conventional sheaths made from wood or paper. In addition, the composition can be formed into suitable shapes for sheaths with both removable m~rking 15 cores and m~rking cores which are fixedly retained within the sheath.
It is generally possible to increase the strength of the sheath while decreasing the density of the sheath by using lightweight aggregates which contain air voids. This allows for a stronger, more continuous hydraulically settable binder matrix holding the particles together. The amount of ag~l~gal~s in the ~ lule partially det~rmin~s the 20 ability of the sheath to adhere to the m~rking core in a m~rking implement, such as a pencil, without the use of adhesives. Additionally, the amount of aggregates in the mixture partially ~let~rmines the porosity of the m~rking implements. The porosity of pencils having a hydraulically settable sheath is de~ign~d to permit the use of traditional pencil ~ e,lers to sharpen the pencils with a hydraulically settable sheath. The 25 aggregates utilized in such pencils must be small enough to avoid creating a large open pore by cutting off the surface of an aggregate in a pencil sharpener.

WO 95/21063 21~ ~ ~ 17 PCT/US95/01497 In order for the m~l~ri~l to exhibit the best l,rop~l lies of high tensile strength and toughness, the fibers can be unidirectionally or bidirectionally aligned or stacked according to the present invention, instead of being randomly dispersed, throughout the structural matrix. It is often preferable for the fibers to be laid out in a plane that is 5 longitudinally parallel to sheath.
Such ~lignment of fibers can be achieved by any number of techniques such as by jiggering, ram-pressing, pull-trusion, hot pressing, extrusion, or calentlering the hydraulically settable mixture. Generally, the fibers are oriented in the direction of the flow of material during the molding or extrusion process. By controlling the flow 10 patterns of the material during the molding or extrusion process, it is possible to build a sheath having the desired fiber orientation.
These processes also result in near zero porosity in terms of relatively large, continuous and unwanted air pockets which usually occur during normal concrete manufacture. This greatly increases the colllplcs~ e and tensile strengths of the 15 hydraulically settable material and reduces the tendency of the matrix to split or tear when the sheath is exposed to external merll~nical forces. Such undesirable air voids will be minimi7~d by evacuating the material before forming. Minimi7~tion of the undesirable air voids is particularly i~ olL~ll when m~mlf~cturing m~rking implements, such as pencils, which require a secure bond between the m~rking core and the 20 hydraulically settable sheath.
The undesirable discolllilluilies and voids in typical cern~ntitious products should not be confused with the finely dispersed non-connected micro-pockets of air (or other gas) that may be intentionally introduced into the hydraulically settable structural matrix by the direct introduction of gas, the use of a high shear mixer, or the addition of reactive 25 metals. Undesired voids or discollLinuilies are large and randomly dispersed, and offer little in terms of altering the pl.)p.,.lies, such as the bulk specific gravity of the sheath, WO 95/21063 21 6 ~1 1 7 PCT/US95/01497 while at the same time greatly red~lcing the integrity of the structural matrix and reducing its strength characteristics.
In contrast, the intentionally introduced gas bubbles or voids are generally uniformly and finely dispersed throughout the hydraulically settable mixture. The use 5 of voids enables the m~nllf~cture of lightweight sheaths without substantially reducing the strength of the underlying hydraulically settable structural matrix. In addition, the sheaths of the present invention can be designed to have cushioning characteristics.
Sheaths with cushioning characteri~tics can conform to the grip ofthe individual utili7inp~
the m~rking implement.
In order for the hydraulically settable mixtures of the present invention to be effectively formed, it is important that the hydraulically settable colllposilion be form stable in the green state; that is to say, the formed product must rapidly (preferably in three seconds or less) be able to support its own weight. Further, it must harden sufficiently that it can be quickly ejected from a mold. Otherwise, the cost of molding may make the process uneconomical. In addition, the surface of the formed article carmot be too sticky, as that would make it difficult to remove from the forming device, to handle and stack the formed articles.
By altering the quantities of cement, water, aggregates, fibers, and rheology-modifying pl~tiri~ing agents, it is possible to control the rheology, or flow plo~el ly, of the hydraulic paste. For example, when ram-pressing, jiggering or injection molding is used, it may often be preferable to start with a relatively highly viscous hydraulically settable lllixlule which will be highly form stable in the green state; the res~llting molded product will then ~ its shape after being formed, even before being dried or hardened.
When extrusion, calen~l~ring, pull-trusion, or hot pressing is used, the hydraulically settable mixture is preferably less viscous and has a lower yield stress so that it will be more workable and flow easier. Because sheaths formed by these methods 216011~

will usually be heated in order to remove much of the water in order to achieve a drier, more form stable product, it will not be necessary for the hydraulically settable mixture to have as high a yield stress or initial form stability as in other molding processes.
Nevertheless, even these less viscous hydraulically settable mixtures are able to 5 achieve rapid form stability when heated, making the manufacturing processes using them commercially acceptable and capable of mass producing the products. This is important because the longer the product remains in the mold, the higher the cost of m~nnf~cturing in most cases.
Whether a more or less viscous hydraulic paste is required, it is generally 10 desirable to include as little water as is nPcess~ry to impart the requisite rheology for a particular molding process. One reason for . ~ g the water is to control the capil-lary action of the water in the hydraulically settable mixture, as this may cause stickiness of the hydraulically settable mixture, which in turn can cause problems in demolding the mixture from the mold. Minimi7in~ the amount of water elimin~tes the free water and 15 reducesthechemicaland1ll~c~ icaladherenceofthem~teri~ltothemold. Hence,the capillary action and related surface tension of the water should be minimi7Pd if possible in order for there to be quick release of the hydraulically settable mixture during the molding process.
Furthermore, the resulting hydraulically settable products are stronger if less 20 water is used. Of course, adding more water initially will require that more water be removed from the hydraulic lllixlull during the drying or hardening process, thereby increasing manufacturing costs.
In order to obtain a hydraulically settable ~rixlu~c having the a~prupl;ate plopt.lies of workability and green strength, it is hll~oll~ll to adjust the water content 25 in combination with the use of a rheology-modifying agent and, optionally, a di~c.~i~,t within the hydraulically settable ",ixlu,c. As discussed above, there are a variety of suitable rheology-modifying agents.

WO 95/21063 21 ~ 01 1 7 PCT/US95/01497 The rheology-modifying agent increases the yield stress and makes the mixture more plastic so that it can be deformed and molded and then m~int~in its shape upon release ofthe molding ple~ e. This allows the molded product to with~t~n(l forces such as gravitational forces (that is, it can support its own weight without extern~l support) as S well as forces involved in demolding the product from the mold and subsequent h~ntlling of the sheath before it has become subst~nti~lly hardened.
There are several modifications to conventional molding processes which are preferably employed in order to ease the m~mlf~cturing process. For example, it is frequently desirable to treat the mold with a releasing agent in order to prevent sticking.
10 Suitable releasing agents include silicon oil, Teflon~, Deleron~, and UHW~.
Preferably, the mold itself will be made of stainless steel and/or coated with a material having a very slick finish, such as Teflon~), Deleron(~), or chrome plating polished to about O. 1 RMS.
The same effect can be achieved from the use of frictional forces. By spinning 15 the head of the molding app~dlus against the interior and/or exterior surfaces of the cemPntitious m~tPri~l, any chemical and mechanical adherence (i.e., stickiness) to the mold can be overcome.
During the process of forming and/or curing the cçm~ontitious lllixlule, it is often desirable to heat up the cementitious mixture in order to control the air void system by 20 allowing for proper control of the porosity and the volume in the sheath. However, this heating process also aids in making the cçnnentitious lllixlule form stable in the green state (immediately after forming) by allowing the surface to gain strength quickly. Of course, this heating aids in rapidly removing significant amounts of the water from the hydraulically settable lllixlule. The result of these advantages is that the use of the 25 heating process can ease the m~mlf~.turing of the ~h~th~
If a gas has been incol~oldled into the hydraulically settable lnixlu e, heating that rnixture to 250C will result (accoldillg to the gas-volume equation) in the gas increasing WO 95/21063 2 1 f~ ~) 1 17 PCT/US9S101497 its volume by about 85%. When heating is appropriate, it has been found desirable for that heating to be in the range from about 100C to about 2500C. More importantly, when properly controlled, heating will not result in the formation of cracks within the structural matrix of the sheath or imperfections in the surface texture of the sheath.
In fact, the process of adding CO2 gas to the hydraulically settable mixture during the molding process can help the molded product to quickly gain stability. From the foregoing disclosure, it will be al)pal cnl that this can be accomplished by the addition of a CO2 gas or CO2 generating material, such as an easily oxidized metal like zinc or aluminum, wherein the CO2 generating process can be accelerated by the addition of a base and/or heat.

A. Mechanical Mixin~ of the Hydraulically Settable Materials.
The mixing system used to prepare the hydraulically settable material used for forming the sheaths of the present invention includes a mixer, a handler, and usually an extruder system. The materials are loaded into a hopper where they are metered by weight and fed into a mixer for the creation of a hydraulically settable mixture. As previously discussed, the hydraulically settable mixture is microstructurally engineered to have certain desired ~ropc~lies. Consequently, the metering of the bulk m~teri~l~ is regulated to ensure proper proportioning according to design specifications of the hydraulically settable mixture.
The mixing method is subst~nti~lly the same for sheaths formed by molding and by extrusion. The composition of the mixtures will, however, vary. After the mixtures are plopl~ly blended the ll~ixlul~S can be utilized to form the sheaths by any of the above methods.
A method of ~lcp~;llg the desired ll~ixlule includes the steps of (a) mixi~g a powdered hydraulically settable m~teri~l and water in order to form a paste or mixture and optionally ~ltili7.ing a disl cl~ll, (b) blending a fibrous m~t~ri7~1 (such as cellulose WO 95/21063 21 ~ ~ ~ 1 7 PCT/US9S/01497 fiber or from other sources such as glass, plastic, or metal) into the paste under high shear energy mixing to form a mixture in which the fiber is well dispersed; (c) adding a rheo-logy-modifying agent (such as methylhydroxyethylcellulose) to the llliXIUle such that the resultant nlixlule develops a more plastic-like rheology; and (d) combining one or more 5 aggregates into the mixture under normal low shear energy mixing so as to impart the desired l.r~l lies to the mixture. In alternative embodiments, other additives such as air dining agents and reactive metals can be incorporated into the mixture so as to obtain a mixture with desired plop~,.lies. The amount of water included in the lnixlule has an effect on the time duration necessary for mixing the components under high shear 10 mixing. Mixtures with low amounts of water typically require longer mixing periods than mixtures with high amounts of water.
High shear energy mixing is used for the addition of fibrous m~tPri~l to insure that the fibrous materials are well dispersed throughout the mixture. This results in a more uniformly blended lllixlure, which improves the con~i~tçncy of the uncured mixture as 15 well as increasing the strength of the final cured product.
The addition of fibrous m~t~ri~l~ by normal cement mixing techniques results in the conglomeration of the fibrous materials, leading to deformities in the resulting sheaths or articles. Standard mixers, such as drum mixers, combine the components of the desired nlixlure by applying low energy stirring or rotating to the components. In 20 contrast, high shear energy mixers are colllpal~ble to heavy duty blenders and are capable of rapidly blending the mixture so as to apply high ~h~ring forces on the particles of the hydraulically settable materials and the added fibrous m~teri~l~ without tl~m~ging the fiber. As a result, the fibrous m~tçri~l~ are uniformly dispersed throughout the mixture, thereby 1~ ...;U;.~g a homogenous structure for the subsequent ~heatll~. Fine particulate 25 aggle~es of relative high strength, such as sand, silica, or alumina, can also be blended using a high speed mixer. Plasticizers, sl-rf~ct~nt~, and stabilizers can also be added.

W O 95/21063 21 ~ ~ 1 17 PCTAUS95/01497 Nevertheless, in the case of lightweight aggregates such as perlite, pumice, or exfoliated rock, it is usually best to use a low speed mixer to avoid breaking the aggregate into a powder. In addition, the flocculation of the hydraulically settable mixture using Tylose~) is usually performed under low shear mixing conditions.
S In one embodiment, the m~t~ri~l~ utilized in the mixture are automatically and continuously metered, mixed, de-aired and extruded by a twin auger extruder appaldlus.
A twin auger extruder app~dlus has sections with specific purposes such as low shear mixing, high shear mixing, v~c~ ming and pumping. A twin auger extruder ~pa~dLIls has dirr~l~;llL flight pitches and orientations enabling the sections to accomplish their specific purposes. It is also possible to premix some of the components in a vessel, as needed, and pump the premixed components into the twin auger extruder apparatus. The preferable twin auger extruder a~p~dlus utilizes uniform rotational augers wherein the augers rotate in the same direction. Counter rotational twin auger extruders, wherein the auger rotate in opposite directions, accomplishes the same purposes. A pugmil may be utilized as well for the same purposes.
In another embodiment, a cement mixer capable of both high and low shear mixing, such as the RV- l l mixer, available from EIRICH of Germany, is used to meter and mix the m~teri~l~ in a batch mode. A simple mixer can typically supply mixedhydraulically settable ~ lul~s for downstream production lines used to form the .Che~th~ The mixer can handle up to 13 cubic feet of material per batch and, ~s--ming a six minute mix cycle, is capable of producing 4,000 pounds of hydraulically settable mixture per hour ~sllming 31 pounds per cubic foot.
In an alternative embo-liment high energy mixers described in U.S. Patent No.
5,061,319 entitled "Process for Producing Cement Building Material", U.S. Patent No.
4,944,595 entitled "AlJp~dlus for Producing Cement Building Material", U.S. Patent No.
4,552,463 entitled "Method and Appalalus for Producing a Colloidal Mixture" and U.S.
Patent No. 4,225,247 entitled "Mixing and Agitating Device" which were previously W O 95/21063 21 ~ O 1 1 7 PCT~US95/01497 incorporated here in by specific reference, can be used for mixing the hydraulically settable mixture. High shear energy mixtures within the scope of these patents are available from E. KHASHOGGI INDUSTRIES in Santa Barbara, California.
The internal components of the mixer are generally carbide hard coated for extended life, thereby resisting the abrasion expected from the aggregates and cement.
The mixtures, however, within the scope of the present invention result in less abrasion than many hydraulically settable mixtures due to the low pressure utilized in processing and also due in part to the excess water that provides a high degree of lubrication when any pressure is applied.

B. Methods for Manufacl-.r; .~ the Sheaths from Mechanically Mixed Hydraulically Settable Materials.
Several dirr~lelll mrthotl~ of m~mlf~r,tl-ring the m~rking implement with s}. . iths formed from hydraulically settable llli~ es are within the scope of the present invention.
The sheaths can be formed by ntili7ing various combinations of these dirr~lellt methods which enhances the ability to design a variety of m~rking implements. Manufacturing m~rking implements with sheaths formed from hydraulically settable materials through these methods enables the optimization of the rheology of the mixture through the forn~ing process selected and permits h~n~lling of the formed sheath shortly after forming due to the level of form stability.
The methods of m~mlf~rt~lrinE most m~rkin~ implements with hydraulically settable sheaths formed from merh~nically mixed hydraulically settable materials can be categorized into two broad groups: formation by molding and formation by extrusion.
An additional method involves the use of sheets formed from hydraulically settable m~t~ri~l~ which are wrapped around a m~rking core to form m~rking implements such as china m~rk~rs WO 95/21063 PCT/US9~/01497 2l~oll~ 58 Formation by molding usually requires de-airing of the mixture before the step of actually forming the mixture into a sheath. De-airing the mixture can be accomplished by extruding the mixture. Consequently, the mixture may be extruded before it is molded. Similarly, de-airing is usually a prestep to forming sheets from hydraulically 5 settable mixtures.

1. Formation of Sheaths by Extrusion~ De-airin~ by Extrusion and Formation of Markin~ Implements by Co-extrullin~ a Markin~ Core and A Sheath.
Extrusion of hydraulically settable mixtures has several different uses within the scope of the present invention. Extrusion provides a useful method for forming sheaths and for forming sectioned sheaths. Extrusion can also be utilized as a prestep to forming sheaths by de-airing a hydraulically settable sheath. Extrusion also permits the formation of a marking implement in single step by co-extruding a hydraulically settable sheath around a m~rkinp~ core.
To form a m~rkin~ implement by extruding a hydraulically settable mixture into a sheath a m~rking core must be inserted into sheaths. Similarly, forming a m~rking implement from parts of a sheath or sections of a sheath requires that the parts or sections be joined around a m~rking core. An example of forming a m~rkin~ implement with a sectioned sheath is provided by extruding slats shaped as a halved sheath with a half circle groove similar to the shape of conventional wood slats utilized to from pencils with a wood sheath. After the extruded slats are formed, the slats can be joined in pairs around a m~rking core. Additionally, such slats can be extruded as a set of adjacent slats and paired with another set of extruded ~ c~nt slats to sandwich a m~rking core.
Extrusion is particularly useful for forming m~rking implements with a hydraulically settable sheath and a m~rkin~ core in ess~nti~lly one step. To form a m~rking implement by extrusion in one step, the m~rking core and the sheath are co-extruded. Formation of m~rkinE implements by co-extrusion is conventionally utilized in forming pencils and ink markers with plastic sheaths and lead or filament winding m~rking cores. The contact between the marking core and hydraulically settable sheath can result in an adhesiveless bond between the m~rking core and the sheath, this is particularly useful when it is desirable for the m~rking core to ~. fixedly retained within 5 the sheath as in pencils.

(a) Extrusion Variables.
The sheaths of the m~rking implements shown in FIGS. 1, 2, 3, 4, 5, and 6 can be formed by extruding a hydraulically settable mixture. The m~rking implements shown generally at 10 in FIGS. 1, 2, 3, 4, 5, and 6 have a hydraulically settable sheath 12 and a m~rking core 14. The sheaths shown in FIGS. 1, 2, 3, 4, 6 can be integrally formed by extrusion. The sheaths shown in FIGS. 1, 2, 3, 4, 5, and 6 can be formed in sections or parts by extrusion. The m~rking core shown in FIG. 1 is a traditional pencil, in FIG.2 the m~rking core is a cosmetic pencil core, in FIG. 3 the m~rking core is a traditional pen marker fil~ment, in FIGS. 4 and 5 the m~rking core is an ink cartridge, and in FIG. 6 the m~rking core is a pencil lead.
A conventional piston extruder can be utilized to extrude the hydraulically settable lllixlulc through a die. The shape of articles extruded from the lllixlulc is determined by the cross-sectional shape of the die. The lllixlulc can be extruded into articles having a variety of shapes. The shape of the extruded article depends on whether the extrusion process is utilized as the forming step or a prestep to forming the sheath of a m~rking implement. When utilized to form the sheath of a m~rking implement, the shape of the extruded m~rking implement also depends on which embodiment of the m~rking implement is being produced.
The shape of the die should be configured to minimi7~ the specifi urface area of the extruded llli~l~c, thereby minimi7ing the e~ lllent of air. It is desirable to 21~0117 minimi7~ the e~ d~lllent of air to avoid creating a defective or non-homogenous structural matrix.
The amount of pressure applied in extruding the mixture depends on several factors. High pressure extruding can assist in the production of high strength sheaths.
5 Typically, the lower the concentration of water, the greater the strength of the extruded article. However, as the concentration of water decreases, the workability of the llliXlUIe also decreases. In part, this is because there is no longer sufficient water to surround the particles and reduce their frictional forces. Accordingly, the mixture becomes more difficult to position and shape.
When high pressures are applied to hydraulically settable mixtures with low concçntr~tion of water, the space between the particles is decreased. As these interstitial spaces decrease, the water exi~ting within the lnixlule becomes more effective in encasing the particles and reducing their frictional forces. Accordingly, as pressure is applied to a mixture, the mixture becomes more fluid or workable and, thus, less water 15 needs to be added. In turn, the decrease in the concentration of water, increases the strength of the resulting product. In application to the present invention, the higher the pressure exerted by the extruder, the lower the amount of water that needs to be added to the lllixlul~ to make it workable. Also, internal lubricants can be added to ease extrusion even when very dry, similar to the use of such lubricants in powder 20 compaction.
Although high pressures are generally desirable, they also have a negative effect in the production of lower bulk density sh~th~, lightweight ~h~th~ To produce a lightweight sheath, low density aggregates (such as perlite or hollow glass spheres) are typically added to the mixture. As the p,~ s~ exerted by the extruder is increased, these 25 aggregates are crushed, thereby increasing the density of the aggregate and the density ofthe reslllting sheath. Crushing the ag~gdle also decl~dses the in~ ting effect ofthe aggregates since they no longer contain air pockets.

21~117 In the preferred embodiment, a negative pressure is applied to the mixture before it is extruded into a sheath or an article as a prestep to forming the article into a sheath.
This can be accomplished by either ~tt~ching a vacuum to the extruder or by a conventional vacuum auger which can be used to feed the mixture to the extruder. This 5 negative pressure removes air trapped in the mixture. Failure to remove such air can result in the extruded article having a defective or non-homogenous structure matrix.
However, in some embo-liment~, a UlliÇo~ dispersion of small air voids in the mixture may be desirable; and, thus, the negative p.es~ule is not needed.
Trapped air can, however, be an effective means of decreasing the density of the 10 sheath, consequently certain mixtures may be designed to include entrained air at a certain percentage. Accordingly, a formed sheath or article having trapped air pockets positioned within its walls will be less dense and will also have a lower K-factor.
It will be understood that the extrusion of hydraulically settable binder through the die will tend to unidirectionally orient the fibrous materials of the hydraulically 15 settable mixture so that they are substantially planer, or parallel to, the extrusion flow direction.
Continuous fibers or fil~m~nt winding such as Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers can also be coextruded with the sheath to str~ngth~rl the sheath and to decrease the amount of nPce~ fiber. Disks within the extruder rotating 20 in opposite directions can be utilized for co-extruding the continuous fibers to achieve a crisscrossing pattern of fiber overlay. Controlling the rotational speed and the fu. ~v~d - extrusion speed perrnits control of the angle of the fibers. Controlling the angle permits optimal elasticity and tensile strength to be achieved. Additionally, the space bt~w~e.l the fibers can be altered to achieve varying strengths. By ~ ,fly spacing the fibers and 25 yet achieving a desired strength, the amount of fiber utilized can be limite~l 21~0117 (b) Perpendicular Extrusion.
Conventional perpendicular extrusion is the preferred method of producing m~rking implements with a hydraulically settable sheath and a m~rking core in a single step. This method of forrning m~rking implements in a single step can be utilized to forrn 5 the embodiment of the present invention as shown in FIGS. 1, 2, 3 and 4.
Perpendicular extrusion is accomplished by extruding the hydraulically settable mixture by either piston extrusion or auger extrusion. The m~rking core is introduced perpendicularly to the flow of the extruded ~ and the ~ Luleis then extruded with the m~rking core centrally located within in it. The hydraulically settable mixture has 10 been found to adhere less when a piston extruder process is used than when an auger extruder process is used.
The m~rking core is introduced perpendicularly to the flow of the mixture within a perpendicular extruder by a m~rking core feeder such as a hydraulically operated reciprocating piston or any other suitable means for receiving a m~rking core and for 15 ejecting it axially. The m~rking core can be introduced continuously or sequentially into the extruder. Leads, cosmetic cores and filaments can be in the form of a continuous strand while ink cartridges are introduced sequentially.
The m~rking core is advanced out of the m~rking core feeder within the perpendicular extruder into a chamber co..~inillg the hydraulically settable mixture and finally through a die orifice. As the m~rking core exits the die orifice it is ~nl~ced by the hydraulically settable mixture forming a sheath. The cross-sectional shape of the die orifice generally determines the shape of the sheath, however a sizing jig in an evacuated chamber may also be utilized to render the diameter of the sheath more uniform. When a continuous m~rking core is utilized it is necessary to cut the advancing continuous m~rking implement into desired len~hc.
A bond results b~w~en the m~teri~lc compri.cing the sheath and the m~rkinp core, which is ideal for creating pencils. Adhesives can also be utilized when n~cess~ry to improve the strength of the bond. To m~nllf~ture m~rking implements with m~rking cores which do not adhere to the sheath, the m~rking core receives a coating which is insoluble in water and prevents adhesion or the m~rking core can be intruded after the sheath has hardened or partially hardened.

(c) Initial Hardenin~.
Once formed, the hydraulically settable mixture is allowed to harden in the desired shape ofthe hydraulically settable sheath. To economically produce the inventive sheath, it must be rapidly hardened to a point where it has sufficient strength to be 10 packaged and shipped without substantial deformation.
Hardening of the sheath may be accomplished by exposing the sheath to heated air, such as in a conventional tunnel oven. The application of the heated air drives off a portion ofthe water in the hydraulically settable llliXIule, thereby il..,l~ h~g the frictional forces between the particles and, thus, increasing the strength of the resulting sheath.
15 Furthermore, the application of heated air to the sheaths increases the reaction rate of the cement, which provides early strength to the sheath through curing. Accordingly, hardening results from both an increase in the friction forces between the particles and curing of the hydraulically settable llli~
In the pl. f~ d embo-limPnt, the sheath is h~delled only to the extent that it has 20 sufficient strength for p~c~ ing and transport without deformation. Ideally, the hardened sheath retains a small amount of unreacted water that permits the sheath to continue to cure, and thus increase in strength, during the period of time it is transported and stored prior to use.
In yet another embotlim~nt the air is blown over the sheath to increase the rate 25 at which the hydraulically settable lllixlul~e dries, thereby il~leashlg the rate of hardening.

21~0117 Also, the air can be applied through an autoclave capable of regulating the humidity, pressure, and temperature in the environment in which the sheath is cured.
Increasing the humidity and temperature assists in producing more complete hydration of the hydraulically settable mixture, thereby producing a stronger sheath.
S In any event, the temperature in the tunnel oven should preferably not exceed 250 C in order to prevent cracking of the hydraulically settable matrix or the destruction of fibrous or plastic additives. Preferred temperatures might range between 20 C and 250 C, more preferably between 30 C and 200 C, and most preferably between 20 C and 250 C.
The dwell time within the tunnel oven depends on the temperature in the tunnel, as well as the thickness of the sheath to be dried. In the case of a sheath 1 mm thick and a drying tunnel t~lllp~,ld~ule of 200 C, the sheath will preferably remain within a tunnel oven for period of 45 seconds.
In summary, the following conclusions can be drawn with respect to the drying l S of the hydraulically settable product:
1) The higher the telllpeld~ule, the shorter the drying time.
2) The higher the air speed, the shorter the drying time.
3) Once a majority of the water is removed from a sheath, exposing the sheath to t~lllpeldlul~s above 250OC will burn the fibers in the mixture, thereby decreasing tensile strength of the fibers and ~h~th~
4) The thinner the m~tteTi~l wall of the sheath, the shorter the drying time.
5) The higher the telllp~ldlule, the lower the tensile strength of the sheath.

6) Air speed and total time in the oven have less effect on the tensile strength of the sheath.

2. Formation of Marking Implements by Moldin.~.
Molding can be utilized to form the embodiment of the present invention as shown in FIGS. 1, 2, 3, 4, 5 and 6. M~m-f~chlring the sheaths depicted in FIGS. 1, 2, 3, 5 4, 5, and 6 can be accomplished by a variety of possible molding approaches within the scope of the present invention, such as: injection molding, direct molding, wet sheet molding, dry sheet molding and blow molding. The sheaths can be formed by conventional molding processes known in the art of molding, lltili7.ing such devices as split molds, multiple parting, progressive dies and multi-cavity molds.
Most molding systems, however, are utilized with thermoforming materials such as plastic while the hydraulically settable materials of the present invention are thermosetting. Thermoforming entails shaping a heated m~tçri~l and allowing it to cool while thermosetting entails shaping a m~t~ri~l and allowing it to cure. The processes and equipment utilized within the scope of this invention are modified on the basis of this distinction. Additionally, the molding processes and equipment are modified to allow chemical activation of the hydraulically settable simultaneously or following forming.
Another modification is the use of less pressure in forming sheaths from hydraulically settable materials than is nPcç~.c~ry in forming sheaths from convention materials. Less ples~ule is needed due to the free flowing nature of the hydraulically settable m~tçri~l~
resulting from the high amount of water in the mixlu,c.
Before molding, however, the hydraulically settable mixture must first be mixed and rheologically prepared into the desired con~ tçncy in p~palalion for the molding - process. Extrusion of the hydraulically settable nlixlul~ is desirable because certain extruders can be utilized as a continuous metçring, mixing and de-airing device that enh~nces the ability to alter many dirr~le.l~ plop~llies of the ~llixlule and the final product.

216011~ -3. The Injection Moldin~ and Direct Moldi~ Processes.
(a) Positionin~.
After the hydraulically settable mixture has been prepared as discussed above, the next step in the injection molding and direct molding processes is positioning the 5 hydraulically settable mixture between a set of dies for subsequent shaping of the hydra-ulically settable sheath. The dies comprise a male die having a desired shape and a female die having a shape subst~nti~lly complementary to that of the male die.
Accordingly, as the hydraulically settable mixture is pressed between the dies, the hydra-ulically settable mixture is formed into a sheath having the complementary shape of the 1 0 dies.
Injection molding utilizes a vacuum auger to inject or feed the hydraulically settable mixture between the dies. The vacuum auger applies a pressure dirre~ ial to the hydraulically settable mixture as the mixture is being transferred for positioning between the dies. This plcs~ulc dirrelclllial removes air trapped in the hydraulically 15 settable mixture. Failure to remove such air (unless the air is desired to create voids to impart lightweight characteristics) can result in the sheath having a defective or nonhomogeneous matrix.
Injection molding can also utilize an extruder positioned to move towards the molding a~dldlus in a piston action, extrude into the molding a~dlus and then move 20 away from the molding app~dlus. This arrangement can be useful for extruding and molding at di~lclll lelll~cldlules to avoid plugging the extruder with a lllixlule that has hardened due to the heat of the molds. The piston action of this a~l,~dlu~ es the heat transfer from the mold to the extruder and results in a safe manner of production.
After the mixture has been extruded, the processing of the nlixlule under injection 25 molding and direct molding both involve positioning the hydraulically settable nlixlulc between the male die and the female die. The male die is partially inserted into the female die such that a gap rli~t~n~e is created bclwcell the dies. The "gap distance" is ~ 216~117 defined as the ~i~t~nr.e one die must travel with respect to the other die for mating of the dies. The dies are "mated" when they are inserted into one another so as to form a mold area between the dies. The "mold area" defines the desired shape of the sheath and is the - area that the hydraulically settable nlixlule is pushed into when the dies are mated.
When the dies are positioned so as to have a gap distance, a cavity remains between the dies. This cavity comprises the mold area between the dies, and a second area also between the dies which corresponds to the gap distance. Once the cavity is formed, the hydraulically settable nlixlule can be positioned into the cavity, and thus between the dies, by being injected through a hole in one of the dies or through the gap 1 0 distance.
In the pl~felled embodiment, the female die is positioned vertically above the male die. The hydraulically settable lllixlule is then injected between the dies through an injection port extentling through the female die. The arrangement of having the female die above the male die is plefcll~d since once the hydraulically settable sheath is formed and the dies are s~aldl~d~ the force of gravity assists in in~nring the hydraulically settable sheath remains on the male die. This is beneficial as it is easier to subsequently remove the sheath from the male die without der~llllh~g the sheath.
Before positioning the hydraulically settable lllixlul~, it is preferable to minimi7r the gap rli~t~nre between the dies so as to limit the movement of the hydraulically settable mixture during the final pressing or mating of the dies. ~inimi~ing themovement of the mixture decreases the chance of irregularities in the final sheath as a - result of dirrel~lllial flow in the hydraulically settable lllixlule. The gap ~ t~nre between the male die and the female die is typically in a range of about 2 mm to about 5.0 cm, with 2 mm to about 3 cm being ~ r~led and 2 mm to about 1 cm being most preferred.
Another method of positioning the hydraulically settable lllixLul~ belwæn the dies is performed while the dies are still fully separated. The method comprises forming a portion ofthe hy-lr~nlir~lly settable m~t~ri~l into a mass, the portion being sufficient to W O 95/21063 2 1 ~ O 1 17 PCTrUS95/01497 create the sheath, then placing the mass between the dies, typically by resting the mass on the top of the male die. Subsequently, as the dies are mated, the mass is pressed between the dies.
In an alternative embodiment, a template is used to position the hydraulically 5 settable mass. In this embodiment, the male die has a base with a circumference; and the template has a passage with a pclhllclel substantially complimentary to the circumference of the base of the male die.
The method comprises forming a portion ofthe hydraulically settable mixture into a mass having a diameter sufficiently large to span the passage of the template. The mass 10 is then placed on the template so as to span the passage. Finally, the template is placed between the male die and the female die such that the passage is complementarily aligned with the dies. Thereby, as the dies are pressed together, the male die travels through the passage of the template in order to press the hydraulically settable ~ lule between the dies.
The above method can further include the step of depositing the template onto the male die such that the template becomes positioned about the base of the male while the mass independently rests on the male die. Subsequently, as the dies are pressed together, the mass is again pressed between the dies. Additional benefits relating to the use of the template will be ~ cllc~ecl hereinafter with respect to the step relating to removing the 20 sheath from the dies.

(b) Formin~ and Molllin.~.
The next step in the m~nllf~ctllring process is pressing the hydraulically settable mixture between the male die and the female die in order to mold the hydraulically 25 settable mixture into the desired shape of the hydraulically settable sheath.
The pl~ iWC exerted by the dies forrns the hy l~lllic~lly settable mixture into the desired configuration for the sheath. Accordingly, the ples~ ; must be sufficient to actually mold the hydraulically settable mixture between the dies. Furthermore, it is preferable that the pressure be sufficient to produce a sheath with a uniform and smooth finished surface.
The aI unt of pressure applied to the hydraulically settable lllixlulc also affects the strength of the resulting sheath. Research has found that the strength of resultant product is increased for mixtures where the cement particles are close together. The greater the pressure used to press the cement mixture between the dies, the closer together the cement particles are pushed, thereby increasing the strength of the resulting sheath.
That is to say, the less porosity that there is in the hydraulically settable mixture, the higher the strength of the resulting product.
As high pres~ulcs are applied to hydraulically settable nlixlures with a low concentration of water, the space between the particles is decreased. Thus, the water existing within the mixture becomes more effective in enr.~ing the particles and re~luçing their friction force. In esserlre, as plcs~ule is applied to a hydraulically settable mixture, the llliXlUlC becomes more fluid or workable and, thus, less water needs to be added. In turn, the strength of the res-llting product is increased. In application to the present invention, the higher the pressure exerted by the dies, the lower the amount of water that needs to be added to the mixture.
Although a high IJleS~ iS generally desirable, it also has a negative effect. Toproduce a lightweight hydraulically settable sheath, low density ag~ gales (such as perlite or hollow glass spheres) are typically added to the llli~lule. As the pressure exerted by the dies is increased, these ag~g~les may be crushed, thereby increasing the density of the aggregate and the density of the resulting sheath, while decreasing the insulative effect of the aggregates.
Accordingly, the ples~ule applied by the dies should be optimized so as to m~imi7~ the strength, structural hlt~5l;ly, and low density of the hydraulically settable sheath. Within the present invention, the ~l~S~ul~ exerted by the male die and the female 21~0117 70 die on the hydraulically settable mixture is preferably within a range from about 50 psi to about 100,000 psi, more preferably from about 100 psi to about 20,000, and most preferably from about 150 psi to about 2000 psi. However, as discussed below, the amount of ~ressule will vary depending upon the t~ p~ ldl lre and time of the molding 5 process. Additionally, sheaths with a deep draw generally require an increase in velocity to decrease the time nececs~ry for pressing. The time must be decreased to m~int~in the necessary flow without drving the m~trri~l prematurely.
The step of pressing further includes expelling the air from between the dies when the dies are pressed together. Failure to remove such air can result in air pockets or 10 deformities in the structural matrix of the hydraulically settable sheath. Typically, air between the dies is expelled through the gap distance between the dies as the dies are pressed together.
In an alternative embodiment, the dies may have a plurality of vent holes çxten-ling through the dies so as to make them permeable. Accordingly, as the dies are 15 pressed together, the air between the dies is expelled through the vent holes. The vent holes thus prevent air pockets from forming within the cavity which could deform the hydraulically settable sheath.
The vent holes also prevent the creation of a vacuum within the cavity as the dies are separated, by allowing air to return into the cavity. Such a vacuum could exert an 20 undue force on the newly formed hydraulically settable sheath, thereby disrupting its structural hllegl;ly. Fur~ermore, vent holes permit the escape of excess stearn created during the heating process which will be rli~c~-~.se~l later. The vent holes can exist in either or both of the dies.

25(c) He~tin~ and Form Stability.
The next step in the m~nnf~r,ttlring process is heating the hydraulically settable mixture for a sufficient period of time to impart form stability to the hydraulically settable sheath. The preferred method for heating the hydraulically settable nlix~ulc com-prises heating the male die and the female die each to a respective temperature before pressing the hydraulically settable mixture.
Increasing the te~ tldlllre of the dies prior to the pressing step, serves several 5 functions. For ease in molding the hydraulically settable mixture into a sheath without crushing the aggregate, an excess of water is added to the mixture. By applying heated dies to the mixture, a portion of the water in the hydraulically settable mixture evaporates in the form of steam, thereby decreasing the volume percent of water and, thus, increas-ing the ultimate strength of the sheath.
Furthermore, as the water on the surface of the sheath evaporates, that portion of the hydraulically settable mixture rapidly becomes dry. The friction forces between the dry particles in the hydraulically settable mixture forrns a strong thin "shell" around the sheath which provides the hydraulically settable sheath with form stability.
The application of heat to the hydraulically settable lllix~ule also increases the rate of curing. As is ~1iec~ e(1 below, however, the dies remain pressed on the hydraulically settable mixture for such a short period of time that only a fraction of the hydraulically settable mixture reacts to become cured. A substantial arnount of strength required for form stability is thus a result of the friction forces and adhesion between the dry particles, as well as internal capillary forces. As a result, the sheath is still in the green state even after achieving form stability.
The ability to rapidly impart form stability to the hydraulically settable sheath in the green state is irnportant as it permits mass production of the ~heath~. Form stability allows the sheaths to be quickly removed from the pressing d~Udlus so that new sheaths can be forrned using the same pressing or molding eq~lirlnPnt Another purpose for increasing the telllpcld~ulc of the dies is to ~llillillli~
adherence of the hydraulically settable ~ lu c to the dies. As the steam is emitted from the hydraulically settable llli~lule, it creates a boundary layer bclwcen the dies and the 21~0117 --hydraulically settable mixture. This boundary layer provides a substantially uniform force that pushes the hydraulically settable mixture away from the die and, thus, prevents the hydraulically settable mixture from sticking to the dies.
Furthermore, experiments have determined that if the male die and female die 5 have a variance in telllpeldlulc, the hydraulically settable material will have a tendency to remain on the die with the lower tcnlp~ldlule when the dies are sepaldled.
Accordingly, one can select the die on which the hydraulically settable sheath is to remain on as the dies are sep~dled, by having the desired die have a lower temperature.
The respective temperatures ofthe dies are hlll,oll~ll to m~;~ irlg the speed of 10 the m~nllf~tllnng process and are dependent, in part, upon the duration that the dies are in contact with hydraulically settable m~ten~l. In general, it is desirable that the telll~c~dl~lre be as high as possible -- the higher the len~cldlule, the faster the drying on the surface of the ~hP~th~, the quicker the sheaths can be removed, and the more sheaths that can be made per unit time. The problem with higher tClll~ ldlUl~3, however, is that 15 if the hydraulically settable mixture becomes too hot, the water throughout the hydraulically settable llli~ e, as opposed to just on the surface of the sheaths, turns to steam. The sudden release in ples~ule associated within demolding can result in the cracking, or even explosion, ofthe molded sheath once the dies are separated. (However, this wdckillg can often be solved by faster closing and opening speeds of the press.) Moreover, the faster the hydraulically settable material cures, the greater the likelihood of a deformity forming within the hydraulically settable sheath as a result of difr~lelllial flow. That is, as the dies are pressed together, the hydraulically settable m~tPn~l flows into the desired shape. However, once the hydraulically settable mixture on the surface of a sheath starts to dry, the drier cement has dirr~l~nt flow properties than 25 the .~~ii.~g wet hydraulically settable m~tPn~l This dirrelclllial in flow plopellies can result in dcrol,llilies such as agglolllcldles, voids, cracks, and other irregularities in the structural matrix of the hydraulically settable sheath.

Accordingly, the interrelationship between time and temperature is that the )cldl lre of the dies can be increased as the time that the dies are in contact with the hydraulically settable mixture is decreased. Furthermore, the temperature can be increased as the gap distance between the dies is decreased. However, there are limits 5 to how high the temperature can go before the hydraulic mixtures become damaged.
To achieve the above desired objectives, it is preferable to heat the female and male die to a temperature within the range from between about 50OC to about 200C, more preferably to between about 75C to about 160~C, and most preferably to between about 120C to about 140C. For reasons previously ~ c~l~se~l it is desirable to have the l O hydraulically settable sheath remain on the male die after separation of the dies. Accord-ingly, the male die preferably has a lower telllp.,ldlulc than the female die. The tellll)eld~ulc variance between the female die and male die should preferably be in the range from about 10C to abc~lt 30C.
The duration in which the heated male die and the heated female die are both in 15 contact with the hydraulically settable material (i.e., the time that the dies are mated) is preferably within the range from about 0.05 seconds to about 30 seconds, more preferably between about 0.7 seconds to about 10 seconds, and most preferably between about 0.8 seconds to about 5 seconds.
In an ~ltPrn~tive embodiment, the step of heating the hydraulically settable sheath 20 furt~her includes exposing the hydraulically settable sheath to heated air after the dies are sep~r~te l but before the sheath is removed from the die, that is, while the hydraulically settable sheath is supported on the male die. Exposure to heated air insures that the sheath is form stable before it is removed from the die.
In another ~ltPrn~tive embotlim~nt, the step of heating the hydraulically settable 25 lllixlule can be accomplished by exposing the hydraulically settable llli~Lu~e to microwaves, x-ray waves and infrared waves.

(d) Remov;n.~.
After the molded article has achieved some form stability, the newly formed hydraulically settable sheath is removed from the dies. In the preferred embodiment, when the dies are separated, the newly formed hydraulically settable sheath remains on the male die. In one embodiment, the male die and the female die are rotated as they are separated so as to prevent the hydraulically settable sheath from adhering to the dies.
Once the dies are separated, heated air can be blown over the sheath for a few seconds (as previously discussed) to further increase form stability. The hydraulically settable sheath can then be removed from the male die without deformation. In the preferred embodiment, a standard process known as airveying is used to remove the hydraulically settable sheath from the male die. Airveying is a process in which a negative pressure is applied to the sheath for sucking the sheath from off the die. The sheath then travels through a "U" shaped tube that deposits the sheath.
The airveying process is preferable due to its gentle h~nt11ing of the form stable sheaths and its low o~ -g and capital costs. Heating air which is present to drysheaths may be used to provide the bulk air transport carrying the sheaths through the length of the tubes. The air ducts are simply ports in the male die through which air can be injected to provide a ulliro,lll force to push the sheath offthe male die. Such air ducts have ~.hs~ lly the same size, shape, and position as the vent holes previously discussed.
In one embodiment, the air ducts and vent holes may be one and the same. The air inserted in the air ducts must be low enough not to damage the ~h~th~ It is envisioned in the preferred embodiment that air ducts are located on the male die to help eject the sheaths from the male die and into the tubes.
In an alternative embo~lim~nt the hydraulically settable sheath can be mechanically removed from the male die by simply picking up the sheath. Such a process, however, ~ uiles exceptional care so as not to deform the sheath. The preferred WO 95/21063 2 1 ~ 01 1 7 PCT/US95/01497 _ method for mechanically removing the hydraulically settable sheath incorporates using a template.
The template is circumferentially located at the base of the male die and is - removable. The hydraulically settable sheath is loaded onto the template via the lip of the hydraulically settable sheath by either lifting the template or lowering the male die.
When the sheath is removed from the dies, the sheath is form stable due to its dried surface. However, the sheath will still have green cement between its walls and, thus, it will not have reached its maximum strength. In such a condition, the hydraulically settable sheath is strongest in compression along its vertical axis. Accordingly, the benefit of using the template is that the force applied for removing the sheath is applied along the strongest axis of the sheath, thereby minimi7ing possible deformation to the sheath.

(e) Initial Hardenin~.
Once initial form stability has been achieved, the hydraulically settable product can be dried and hardened by the same various techniques described above with respect to the extrusion forming process.

C. Formation of the Sheaths by Powder Compaction of the Hydraulically Settable Materials.
The matrix of the sheath can be designed to be very dense lltili~ing powder compaction techniques as set forth in detail in co-pending application Serial No.
07/981,615, entitled "Methods of M~nllf~rt lrc and Use For Hydraulically Bonded - Cement" filed November 25, 1992, in the names of Harnlin M. J~nnings, Ph.D., Per Just Andersen, Ph.D., and Simon K. Hodson which is a contin-l~tion-in-part of patent application Serial No. 07/856,257, filed March 25, 1992 in the names of Harnlin M.
Jçnningc, Ph.D. and Simon K. Hodson, and entitled "Hydraulically Bonded Cement 21(~117 Compositions and Their Methods of l\/l~nllf~rh-re and Use" (now abandoned), which was a file wrapper continuation of patent application Serial No. 07l526,23 1 filed May 18, 1990 in the narnes of Hamlin M. Jenning~, Ph.D and Simon K. Hodson, and entitled "Hydraulically Bonded Cement Compositions and Their Methods of Manufacture and 5 Use" (also abandoned). For purposes of underst~n~ling such compaction techniques and their methods of use, the disclosure of the aforesaid applications are incorporated by specific reference.
Powder compaction employs the manipulation and positioning of hydraulically settable binders into a desired configuration before hydrating the hydraulically settable l 0 binders with water. The hydraulically settable binder compositions are hydrated without substantial mechanical mixing of the hydraulically settable binder and water. These methods can be utilized to form the embodiment of the present invention as shown in FIGS. 1,2,3,4,5and6.
The benefit of positioning the powdered hydraulically settable binder into a 15 desired configuration prior to hydration is that aggregates may be placed within the matrix of the sheath without subjecting the aggregates to hostile and ~l~m~ging mixing forces usually associated with forming a hydraulically settable paste.
After the powdered hydraulic cement has been deliberately positioned into a pred~ d configuration, the hydraulically settable binder is hydrated. Hydration is 20 accomplished by diffusion of water (both gaseous and/or liquid) into the preconfigured sheath. Utilizing high pressures, the water is able to s~lcces~fully penetrate the preconfigured sheath and chemically react with the hydraulically settable binder. The hydration may be in an autoclave which is a useful vessel for altering pressure and Ic~ cldlule to conveniently control the hydration condition. Additionally, carrier gases 25 may be utilized which aid the process.
There are a number of di~lclll processing techniques capable of deliberately positioning the powdered hydraulically settable binder particles prior to hydration in the wo 95/21063 21 6 01 1 7 PCT/US95/01497 shape of a sheath. The cement processing techniques suitable for such use include modified and adapted solids processing techniques, such as pressure compaction processes, slip casting, plastic forming processes, vibratory p~c~ing processes, warm pressing and pneumatic-mechanical impaction.
Dry pressing is a ~uleS~ule compaction process con~i~ting of comp~cting powders between die faces in an enclosed cavity. Slip casting processes are particularly useful for manufacturing thin-walled sheaths. These processes involve shaping the sheath bycasting a liquid suspension of the powdered hydraulically settable binder in a porous mold. Water is utilized in the ~ ellsion which is poured into a porous mold. The mold draws the liquid from the slurry and builds up a deposit of particles on the mold wall.
Drying the slurry allows the article to shrink for easier release with an a~rol l;ate water content. The rem~ining slurry is poured out of the mold resulting in an article having an outer configuration which reproduces the inner configuration of the mold.
Additionally, continuous isostatic pressing can be utilized to form sheaths fromthe hydraulically settable materials. Continuous isostatic pressing involves thecc,lllplession of a mixture within a çh~mh~r toward a die and colllplession in a direction normal to the flow towards the die. Continuous isostatic presses can be obtained from Handle of Germany.
In a powder compaction process intern~l lubricants may be added to impart a plasticizing effect. After the lllixLu~e has been plasticized, it may be manipulated by conventional plastic forming processes such as extrusion, jiggering, wet pressing, and injection molding. Vibratory pacl~ing and pressing processes utilize vibrations with a suitable amplitude and can result in 100% of theoretical packing density which is the highest conceivable p~rlring density achievable v~ith a given powder size distribution.
Aggregates commonly utilized in the cement industry are utilized with the powdered hydraulically settable binder prior to hydration. It is preferable to include a plurality of dirrelelllly sized aggregates capable of filling interstices between the aggregates and the powdered hydraulically settable binder so that greater density can be achieved. The other mixture components may also be mixed with the powdered hydraulically settable binder prior to hydration.
The density of the resulting sheath can be decreased by utili7in~ lightweight 5 aggregates with the powdered hydraulically settable binder. Additionally, the density of the resulting sheath can be decreased by co~ lcsshlg powdered hydraulically settable binder with a solid material, such as ice, dry ice, frozen aqueous solutions, or certain salts which will later melt, volatilize, evaporate, or dissolve leaving voids in the final sheath.
The result of these compaction techniques is the manufacture of sheaths which 10 have high tensile strength and have a low porosity. The sheaths formed by this process may be subjected to heating, the use of coatings, and l~min~tes, printing and assembly.

It is within the scope of this invention to utilize powder compaction in conjunction with the other methods disclosed for forming the ~he~th.~ For example, it 15 may be desirable to form a portion of a sheath by a powder compaction techniques and form another portion of a sheath by a molding technique. Additionally, it is within the scope of this invention to utilize powder comp~ction techniques to form l~min~tes with multiple layers formed from hydraulically settable materials and with other m~teri~

D. Formation of the Sheaths by Wrappin~ a Sheet formed from Hvdr~rlir~lly Settable Materials around a Markin.~ Core.
Sheets forrned from hydraulically settable materials can be utilized to from a sheath around a m~rking core. The sheets can be w~alJped by convoluting the sheet or 25 by spiral winding the sheet. Such sheets are utilized in forming m~rking implements as shown in FIGS. 7 and 8. The sheath in FIG. 7 is a series of convoluted sheets which can be removed through the use of a string and the m~rking core can be a variety of m~teri~lc This configuration is particularly useful with m~rking cores which cannot be sharpened in a conventional pencil sharpener, such as china marker cores which are very useful for writing on substances such as glass. The sheath in FIG. 8 is a single convoluted sheet with overlapping ends and the mArkin~ core can be substances such as crayons and oil pastels.
The sheets are formed ~Itili7ing techniques as set forth in detail in co-pendingapplication Serial No. 08/101,500 entitled "Methods and Apparatus for Manufacturing Moldable Hydraulically Settable Sheets Used in Making Containers, Printed Materials, and Other Objects" filed August 3, 1993, in the names of Per Just Andersen, Ph. D., and Simon K. Hodson and in co-pending application Serial No.08/101,630 entitled "Sheets Made from Moldable Hydraulically Settable Materials and Methods for Manufacturing such Sheets" filed August 3, 1993, in the names of Per Just Andersen, Ph. D., and Simon K. Hodson. For purposes of disclosure, these applications are incorporated herein by specific reference.

E. Final Proce~in~ of the Sheath.
The hydraulically settable sheaths may also be subjected to several processing steps before the m~rking implement is finally completed. The proces~ing steps may include coating the .cheAth~, applying printing or other indicia, and assembling the mArking implements.
1. Co~Rngs and L~minates.
The surface charAct~ri~tics of the sheaths can be altered in a number of ways, such as coating the sheaths and creating lAminAtes Utilization of these techniques may increase the tensile strength of the sheath, w~ of the sheath, and provide a smoother, glossier surface or scuff~ isl~ll surface and help prevent fiber "fly away". Additionally, they may also provide protection against nonneutral materials, such as saliva which can be slightly AlkAlin~.

~ 1 6 ~ 80 Some coatings can be applied to the surface of the product during the forming process, in which case the process is an "on-machine" process. In an on-m~rhine process, the coating may be applied as a liquid, gel, or even a thin film sheet. It may be preferable to apply the coating after the hydraulic product has been formed and dried to 5 at least a limited extent, in which case the process is an "off-machine" process.
The object of the coating process is usually to achieve a uniform film with minimum defects on the surface of the product. The selection of a particular coating process depends on a number of substrate variables, as well as coating formulation variables. The substrate variables include the strength, wettability, porosity, density, 10 smoothness, and uniformity of the matrix of the product. The coating formulation variables include total solids content, solvent base (including water solubility and volatility), surface tension, and rheology.
The coatings may be applied to the sheaths using any coating means known in the art including blade coating, puddle co~ting, air-knife coating, Dahlgren coating, gravure 15 coating, powder coating, sp~lltering, chemical plasma deposition, a high energy electron beam evaporation process and printing. The amount of coating can be controlled by the volume of the spray or the dwell time of the sheaths under the spray or both. Coatings may also be applied by spraying the sheath with any ofthe coating m~teri~l~ listed below or by dipping the sheath into a vat co.~ g an ~rol.l;ate coating m~tçri~l. Finally, 20 coatings may be coextruded along with the sheath components in order to integrate the coating process with the extrusion process.
Ap~lopl;ate organic coatings include edible oils, melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylates, polyamides, hydroxypropylmethyl-cellulose, polyethylene glycol, acrylics, polyulet~ e, polyethylene, polylactic acid, 25 Biopol~ (a polyhy~xyl .llyl~Le-hydroxyvalerate copolymer), ~ hes, soybean protein, polyethylene, and synthetic polymers including biodegradable polymers, waxes (such as beeswax or petroleum based wax), elastomers and llliXLllleS thereof. Biopolg) is WO 95/21063 2 1 G ~1 1 7 PCT/US95/01497 m~nllf~tured by ICI in the United Kingdom. Appropriate inorganic coatings include sodium silicate, calcium carbonate, aluminum oxide, silicon oxide, kaolin, clay, ceramic and mixtures thereof. The inorganic co~ting.c may also be mixed with one or more of the organic co~tingc set forth above.
S An FDA approved paint can also be utilized as a coating. Many FDA approved coating materials are also useful depending on the application involved. In some cases, it may be preferable for the coating to be elastomeric or deformable. In such cases, a pliable, possibly elastomeric, coating may be pler.,lled.
An example of a particularly useful coating is sodium silicate which is FDA-approved and acid resi~t~nt Many silicate based coatings provide acid resistant barriers which are also impermeable. Orthosilicates and siloxanes are particularly useful for sheath coatings due to their tendency to fill the pores of the hardened hydraulically settable matrix. Additionally, useful coatings are obtained from colloidal silica in organic polymer dispersions, films and fibers. These coating compositions provide water i,npc~ eable barriers and an increase in hardness and durability. It is generally mnecesc~ry to protect the sheath from basic sllbs~ es, but i~l~,leased resistance to basic substances can be provided by an a~propl;ate polymer or wax coating.
Biodegradable plastics provide particularly useful coatings. Biodegradable plastics, such as polylactic acid and Biopol, are insoluble in water and acidic solutions.
Another useful coating material is calcium carbonate, which is acid resistant and also allows the printing of indicia on the surface of the sheaths.
It may also be desirable to spray the m~rking implement with CO2 to impart added strength and to improve the surface appeal~lce and form stability. This type of process is known for hll~&lling strength and for improving surface a~eal~lce and form stability. The process is described in U.S. Patent No. 5,232,496 entitled "Process for Producing Improved Building Material and Product Thereof" and issued August 3, 1993, in the names of Hamlin M. Jenning.~, Ph.D.. and Simon K. Hodson.

WO 95/21063 117 PCT/US9~/01497 A useful method of forming an aluminum oxide or silicon oxide coating within the scope of this invention involves the treating of the hydraulically settable sheath with an aqueous solution having an a~lop~iate pH level to cause the formation of alnminllm oxide or silicon oxide on the sheath due to the composition of the sheath.
T ~min~tes include multiple layers of sheets andlor coatings with at least one layer formed from hydraulically settable m~t~ri~lc T ~ çs enable the production of sheaths having an interior with a layer or coating with dirr.,lel" properties from the layer or coating on the exterior of the sheath.

2. Printin~.
Another optional step in the m~nl-f~cturing process is applying print or designsto the sheath through the use of a conventional printer, such as an offset, Van Dam, laser, direct transfer contact, and thermographic IJlhlle~. Additionally, methods include lltili7ing a relief printinp~ intaglio printing, stencil printing and hot ~ hlg. F..c.cçnti~lly any hand or mechanical means can be used. Of coarse, hydraulically settable products such as those disclosed herein are particularly well suited for such a use. In addition, decals, labels or other indicia can be attached or adhered to the sheaths using known methods in the art. Furthermore, as mentioned above, it is within the scope of the present invention to coat the sheaths with a govPrnment approved co~ting, most of which are cu~lc;lllly used and well adapted for placing indicia thereon. In order to speed up the drying process, the sheaths can be passed through a second drying tunnel in order to increase the rate of drying of the ink.

3. Assembly of Markin~ Implements.
The assembly involved in m~nuf~ctllring the m~rking implements within the scope of the present invention varies based on the particular m~rking implement being _ manufactured. The amount of assembly involved also varies with the method of formation and whether the sheath was integrally formed or formed in sections or portions.
Sheaths formed by extrusion, molding and other forming processes can be manufactured as an integrally formed sheath or as sections or portions of a sheath.
5 Sheaths which are integrally formed and sheaths assembled from portions or sections of sheaths can receive a m~rkin~ core by insertion or intrusion to form a m~rking implement. Marking implements can also be formed by joining sheath sections or portions around a m~rkin~ core.
Sume m~rking implements within the scope of this invention whicl are 10 manufactured with a hydraulically settable sheath may have structures formed from conventional materials. Such structures include clips for pocket attachments, protective caps and covers, means for ~ffi~in~ the m~rking core in a secure manner within the sheath, means for moving the m~rking core within the sheath, erasers and me, for co~ g erasers. These structures can be formed from conventional materials such as 15 metal, plastic, rubber and wood or from hydraulically settable m~t~ri~l.c For example, an eraser can be ~ ched to the hydraulically settable sheath by crimping a metal ring as utilized with conventional pencils or the sheath can be configured ~ - receive the eraser without a metal ring by inserting an eraser into an end of the sheath and crimping the sheath around the eraser.

IV. Examples of the Pr~Ç~ d Embodiments.
To date, numerous tests have been pclro~ ed co,~ ;lIg the ~ro~ lies of sheaths of var,ving composition. Below are specific examples of hydraulically settable compositions which have been created according to the present invention.

216~)117 Example 1 A m ~rking implement was formed by extruding a hydraulically settable mixture around a m ~rking core, the mixture contained the following components:
Portland White Cement 1.00 kg Water 1.60 kg Glass balls 0.9052 kg Tylose~ 4000 0.20 kg Fiber 0.04 kg The resulting m ~rking implement formed from this mixture had a density of .23 g/cm3.

Fx7mple 2 A m ~rking implement was formed by extruding a hydraulically settable mixture around a m ~rking core, the mixture contained the following components:
Portland White Cement 2.00 kg Water 1.60 kg Glass balls 0.9052 kg Tylose~ 4000 0.20 kg Fiber 0.08 kg The resulting m ~rking implement formed from this mixture had a density of .62 g/cm3.

Example 3 A m ~rking implement was formed by extruding a hydraulically settable mixture around a m ~rking core, the mixture contained the following components:
Portland White Cement 3.00 kg Water 1.60 kg Glass balls 0.9052 kg Tylose~9 4000 0.20 kg Fiber 0.12 kg The resulting m ~rking implement formed from this mixture had a density of .85 g/cm3.

WO 9S/21063 21 ~ ~1 1 7 PCTrUS95/01497 Example 4 A m~rking implement was formed by extruding a hydraulically settable mixture around a m~rking core, the mixture contained the following components:

Portland White Cement 4.00 kg Water 1.60 kg Glass balls 0.9052 kg Tylose~ 4000 0.20 kg Fiber 0.16 kg The resulting m~rking implement formed from this mixture had a density of .95 g/cm3, 10 which is approximately the same density as conventional wood pencils.

Example 5 A m~rking implement was formed by extruding a hydraulically settable mixture around a m~rking core, the mixturc contained the following components:

Portland White Cement 1.00 kg Water 1.60 kg Perlite 1.98 kg Tylose~ 4000 0.20 kg Fiber 0.04 kg Example 6 A m~rking impl~omtq,nt was formed by extruding a hydraulically settable mixture around a m~rking core, the ~ lulc contained the following components:

Portland White Cement 2.00 kg Water 1.60 kg Perlite 1.98 kg Tylose@ 4000 0.20 kg Fiber 0.08 kg -Example 7 A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:
Portland White Cement 3.00 kg Water 1.60 kg Perlite 1.98 kg Tylose~ 4000 0.20 kg Fiber 0.08 kg Example 8 A marking implement was formed by extruding a hydraulically settable mixture around a marking core, the mixture contained the following components:
Portland White Cement 4.00 kg Water 1.60 kg Perlite 1.98 kg Tylose~ 4000 0.20 kg Fiber 0.08 kg V. Summarv.
From the fu~egoing, it will be app-~c,aled that the present invention provides novel compositions and methods of m~nllf~.tllring marking implements with a hydraulically settable sheath and a malLIlg core for marking, writing, drawing, coloring, painting or applying cosm~tics in the manner that pencils, pens, me~h~nical pencils, ink m~ke~, and cosm~tic pencils and the like are used. The hydraulically settable sheaths formed thereby can take the place of almost any marking implement now produced from plastic, wood, paper or metal.
The present invention provides novel compositions and methods of m~nllf~ctllringmarking implements with a Illalkillg core and hydraulically settable sheaths produced at - 216~117 relatively low cost which are tough, durable, flexible, and can be either disposable or reusable.
The present invention further provides novel compositions and processes which are much more environmentally sound in their m~nllf~rture than other she~th.~, made 5 from plastic, wood, paper or metal. The raw materials utilized as starting material in the m~nuf~rtllre of hydraulically settable sheaths may be obtained from the earth, decreasing the use of wood and petroleum products. Additionally, sheaths can be m~nuf~ctured from recycled hydraulically settable materials, without the by products associated with other recycled materials.
Further, the present invention provides novel compositions and processes for m~rking implements with a hydraulically settable sheath which are essentially compri~ed of the same compounds as the earth, and are similar to dirt and rock, and therefore pose little or no risk to the environment when discarded. Additionally, disposal of hydraulically settable sheaths does not create lm~ightly garbage which does not degrade, 15 or which only very slowly degrade over time in l~ntlfill~
The present invention further provides novel hydraulically settable m~rking implements with a m~rking core and hydraulically settable sheaths which do not adhere to the forming a~lus and m~int~in their shape without external support during the green state and rapidly achieve sufficient strength so that the molded m~rkin,~ implements 20 can be handled using ordinary methods.
The present invention may be embodied in other specific forms without departing from its spirit or essçnti~l characteristics. The described embo-limçnt~ are to be considered in all respects as illustrative only, and not restrictive. The scope of the invention is, therefore, inrlic~ted by the appended claims rather than by the foregoing 25 description. All changes which come within the meaning and range of equivalency of the claims are to be embraced wit~h~n their scope.

216~117 What is claimed and desired to be secured by United States Letters Patent is:

Claims (78)

1. An article of manufacture comprising:
a marking implement having a marking core and a sheath for retaining therein the marking core, the sheath having a hydraulically settable matrix formed from a hydraulically settable mixture comprising a hydraulically settable binder, water and a rheology modifying agent, wherein the hydraulically settable binder is selected from the group consisting of portland cement, microfine cement, slag cement, calcium aluminate cement, silicate cement, phosphate cement, white cement, high-alumina cement, magnesium oxychloride cement, and aggregates coated with microfine cement particles.

2. An article of manufacture as defined in claim 1, wherein the marking core is selected from the group consisting of a graphite-clay lead, a colored lead, a cartridge containing a marking fluid and having means for dispensing the marking fluid, an absorbent filament saturated with marking fluid and the absorbent filament is connected to a reservoir containing a marketing fluid, a solid cosmetic product in contact with the sheath, a crayon, an oil pastel, a china marker, and a predetermined amount of marking fluid retained within the sheath and dispensed therefrom by means for dispensing the marking fluid.

3. An article of manufacture as defined in claim 1, wherein the hydraulically settable matrix has a tensile strength to density ratio in the range from about 1 MPa-cm3/g to about 300 MPa-cm3/g.

4. An article of manufacture as defined in claim 1, the hydraulically settable matrix having a maximum thickness of about 10 mm.

5. An article of manufacture as defined in claim 1, the hydraulically settable matrix having a maximum thickness of about 5 mm.

6. An article of manufacture as defined in claim 1, the hydraulically settable matrix having a maximum thickness of about 2 mm.

7. An article of manufacture as defined in claim 1, wherein the hydraulically settable matrix can achieve form stability in less than about 60 seconds.

8. An article of manufacture as defined in claim 1, wherein the hydraulically settable matrix can achieve form stability in less than about 30 seconds.

9. An article of manufacture as defined in claim 1, wherein the hydraulically settable matrix can achieve form stability in less than about 10 seconds.

10. An article of manufacture as defined in claim 1, wherein the hydraulically settable matrix can achieve form stability in less than about 2 seconds.

11. An article of manufacture as defined in claim 1, wherein the hydraulically settable binder is included in a range from about 5% to about 90% by weight of the hydraulically settable mixture.

12. An article of manufacture as defined in claim 1, wherein the water is included in an amount up to about 10% by weight of the hydraulically settable mixture.

13. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises a fibrous material.

14. An article of manufacture as defined in claim 1, wherein the fibrous material is selected from the group consisting of abaca fiber, glass fiber, cellulose, hemp, metal, carbon, ceramic, silica, and plastic fibers.

15. An article of manufacture as defined in claim 1, wherein the fibrous material comprises continuous fibers.

16. An article of manufacture as defined in claim 1, wherein the fibrous material is selected from the group consisting of Kevlar, polyaramite, glass fibers, carbon fibers and cellulose fibers.

17. An article of manufacture as defined in claim 1, wherein the fibrous material is included in a range from about 0.2% to about 50% by volume with respect to the hydraulically settable mixture.

18. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent increases the plastic characteristics of the hydraulically settable mixture during a forming process and imparts form stability to the hydraulically settable matrix after forming.

19. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent comprises a polysaccharide based material, including polysaccharides and any derivative thereof.

20. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent comprises a cellulose based material, including cellulose and any derivative thereof.

21. An article of manufacture as defined in claim 1, wherein the rheology modifying agent is a starch based material, including starches and any derivative thereof.

22. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent comprises a protein based material, including proteins and any derivative thereof.

23. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent comprises a synthetic material selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides, ethylene oxide polymers, synthetic clay, latex, and mixtures thereof.

24. An article of manufacture as defined in claim 1, wherein the rheology-modifying agent is included in an amount within the range from about 0.5% to about 50%
by weight of the hydraulically settable mixture.

25. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material.

26. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of perlite, mica, clay, kaolin, micro spheres, hollow glass spheres, porous ceramic spheres, and calcium carbonate.

27. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of vermiculite, diatomaceous earth, exfoliated rock, sodium silicate macrospheres, exfoliated rock, lightweight concrete, tabular alumina, aerogel, lightweight expanded clay, expanded fly ash, expanded slag, pumice, and mixtures thereof.

28. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of glass beads, metals, polymers, ceramic, alumina and cork.

29. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of sand, calcite, bauxite, dolomite, granite, quartz, gravel, rock, limestone, unreacted cement particles, sandstone, gypsum, silica, ground quartz, and mixtures thereof.

30. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of seeds, starches, gelatins, and agar-type materials

31. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material selected from the group consisting of hollow glass spheres and plastic spheres.

32. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises an aggregate material included in an amount within the range from about 0.5% to about 50% by weight of the hydraulically settable mixture.

33. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises means for creating a discontinuous phase of finely dispersed, nonagglomerated voids within the hydraulically settable matrix.

34. An article of manufacture as defined in claim 1, wherein the hydraulically settable mixture further comprises a dispersant.

35. An article of manufacture as defined in claim 1, further comprising a coating on at least a portion of the surface of the hydraulically settable matrix.

36. An article of manufacture as defined in claim 35, wherein the coating comprises a material selected from the group consisting of edible oils, melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyacrylate, hydroxypropylmethylcellulose, polyethylene glycol, acrylics, polyurethane, polylactic acid, starch, soy bean protein, polyethylene, synthetic polymers, waxes, elastomers and mixtures thereof.

37. An article of manufacture as defined in claim 35, wherein the coating comprises a material selected from the group consisting of sodium silicate, calcium carbonate, aluminum oxide, silicon oxide, clay, kaolin, ceramic and mixtures thereof.

38. An article of manufacture as defined in claim 1, the hydraulically settable matrix having high green strength immediately after being formed.

39. An article of manufacture for marking, writing, drawing, coloring, painting, painting, or applying cosmetics, comprising:
a marking core; and a sheath for retaining therein the marking core, the sheath having a hydraulically settable matrix formed from a hydraulically settable mixture compris-ing:
hydraulic cement and water in an amount resulting in a hydraulic cement to water ratio within the range of from about 0.01 to about 4;
a fibrous material having a concentration in the range of from about 0.2% to about 50% by volume with respect to the hydraulically settable mixture, wherein the fibrous material has an aspect ratio of greater than 100:1;
a rheology-modifying agent having a concentration in the range of from about 0.5% to about 50% by weight of the hydraulically settable mixture, wherein the rheology-modifying agent increases the plastic characteristics of the hydraulically settable mixture during the molding process and imparts form stability to the shaped hydraulically settable mixture as it cures into the hydraulically settable matrix; and an aggregate material having a concentration up to about 80% by weight with respect to the hydraulically settable mixture.

40. An article of manufacture as defined in claim 39, wherein the hydraulic cement comprises a portland cement.

41. An article of manufacture for marking, writing, drawing, coloring, painting, painting, or applying cosmetics, comprising:
a marking core; and a sheath for retaining therein the marking core, the sheath having a hydraulically settable matrix formed from a hydraulically settable mixture compris-ing:
gypsum binder and water in an amount resulting in a gypsum to water ratio within the range of from about 0.01 to about 4;
a fibrous material having a concentration in the range of from about 0.2% to about 50% by volume with respect to the hydraulically settable mixture, wherein the fibrous material has an aspect ratio of greater than 100:1;
a rheology-modifying agent having a concentration in the range of from about 0.5% to about 50% by weight of the hydraulically settable mixture, wherein the rheology-modifying agent increases the plastic characteristics of the hydraulically settable mixture during the molding process and imparts form stability to the shaped hydraulically settable mixture as it cures into the hydraulically settable matrix; and an aggregate material having a concentration up to about 80% by weight with respect to the hydraulically settable mixture.

42. A method of manufacturing a marking implement the method comprising the steps of:
mixing a hydraulically settable binder, water and a rheology modifying agent to form a hydraulically settable mixture, wherein the hydraulically settable binder is selected from the group consisting of portland cement, microfine cement, slag cement, calcium aluminate cement, silicate cement, phosphate cement, white cement, high-alumina cement, magnesium oxychloride cement, and aggregates coated with microfine cement particles;

forming the hydraulically settable mixture into a sheath having a hydraulically settable matrix, the sheath being formed to retain a marking core; and allowing the hydraulically settable matrix of the sheath to harden.

43. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath imparts form stability to the hydra-ulically settable matrix.

44. A method of manufacturing as defined in claim 42, further comprising the step of positioning a marking core within the sheath.

45. A method of manufacturing as defined in claim 44, wherein the marking core is removable.

46. A method of manufacturing as defined in claim 44, wherein the marking core is fixedly retained within the sheath.

47. A method of manufacturing as defined in claim 44, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur simultaneously.

48. A method of manufacturing as defined in claim 44, wherein the step of forming the hydraulically settable mixture into a sheath and the step of positioning a marking core within the sheath occur sequentially.

49. A method of manufacturing as defined in claim 44, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of:

extruding the hydraulically settable mixture into parts of a sheath; and assembling the parts into a sheath.

50. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath is performed by extruding the hydraulically settable mixture into a sheath.

51. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath is performed by coextruding the hydraulically settable mixture and a marking core, the sheath being formed from the hydraulically settable mixture around the marking core.

52. A method of manufacturing as defined in claim 42, further comprising the step of de-airing the hydraulically settable mixture.

53. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by molding the hydraulically settable mixture into a sheath.

54. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by molding the hydraulically settable mixture into a part of a sheath.

55. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of:
fashioning a sheet from the hydraulically settable mixture; and convoluting the sheet around the marking core.

56. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath comprises the steps of:
fashioning a sheet from the hydraulically settable mixture; and spiral winding the sheet around the marking core.

57. A method of manufacturing as defined in claim 42, wherein the step of forming the hydraulically settable mixture into a sheath is accomplished by powder compaction of the hydraulically settable mixture.

58. A method of manufacturing as defined in claim 42, wherein the water is included in an amount within the range of from 5% to about 10% by weight of the hydraulically settable mixture.

59. A method of manufacturing as defined in claim 42, further including the step of adding a fibrous material to the hydraulically settable mixture.

60. A method of manufacturing as defined in claim 59, wherein the fibrous material is included in an amount within the range from between about 0.2% to about 50% by volume of the hydraulically settable mixture.

61. A method of manufacturing as defined in claim 42, wherein the rheology-modifying agent increases the plastic-like consistency of the hydraulically settable mixture.

62. A method of manufacturing as defined in claim 42, wherein the rheology-modifying agent is included in the range from about 0.5% to about 50% by weight of the hydraulically settable mixture.

63. A method of manufacturing as defined in claim 42, wherein the rheology-modifying agent includes a polysaccharide material.

64. A method of manufacturing as defined in claim 42, wherein the rheology-modifying agent includes a protein material.

65. A method of manufacturing as defined in claim 42, wherein the rheology-modifying agent includes a synthetic organic material.

66. A method of manufacturing as defined in claim 42, further including the step of adding an aggregate material to the hydraulically settable mixture.

67. A method of manufacturing a as defined in claim 66, wherein the aggregate material is included in an amount up to about 80% by weight of the hydraulically settable mixture.

68. A method of manufacturing as defined in claim 42, further including the step of adding a dispersant to the hydraulically settable mixture.

69. A method of manufacturing as defined in claim 42, wherein the hydraulically settable binder and water are mixed in a high energy, high shear mixer.

70. A method of manufacturing as defined in claim 42, further including the step of introducing air voids into the hydraulically settable mixture, thereby forming air voids in the resultant hydraulically settable matrix.

71. A method of manufacturing as defined in claim 42, further including the step of passing the sheath through a drying tunnel in order to remove a significant amount of the water within the hydraulically settable mixture.

72. A method of manufacturing as defined in claim 71, wherein the removal of a significant amount of the water increases the form stability of the hydraulically settable matrix.

73. A method of manufacturing as defined in claim 71, wherein the removal of a significant amount of the water is accomplished through the use of waves having a wavelength within the range from about the wavelength of microwaves to about the wavelength of x-rays.

74. A method of manufacturing as defined in claim 42, further including the step of coating at least a portion of the surface of the hydraulically settable matrix of the sheath.

75. A method of manufacturing as defined in claim 74, wherein the coating on at least a portion of the surface of the hydraulically settable matrix of the sheath is coated with a material selected from the group consisting of sodium silicate, orthosilicates, siloxanes, colloidal silica in organic polymer dispersions, colloidal silica in films, colloidal silica in fibers, biodegradable plastics, calcium carbonate, acrylics, polyacrylates, polyurethanes, melamines, polyethylene, synthetic polymers, hydroxypropylmethyl-cellulose, polyethyleneglycol, kaolin, clay, Zein?, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, ceramics, waxes and paint.

76. A method of manufacturing as defined in claim 74, wherein the coating on at least a portion of the surface of the hydraulically settable matrix of the sheath is coated with carbon dioxide.

77. A method of manufacturing a marking implement the method comprising the steps of:
mixing a hydraulically settable binder, water and a rheology modifying agent to form a hydraulically settable mixture, wherein the hydraulically settable binder is selected from the group consisting of portland cement, microfine cement, slag cement, calcium aluminate cement, silicate cement, phosphate cement, white cement, high-alumina cement, magnesium oxychloride cement, and aggregates coated with microfine cement particles;
forming the hydraulically settable mixture into a sheath having a hydraulically settable matrix, the sheath being formed to retain a marking core;
positioning a marking core within the shealth; and allowing the hydraulically settable matrix of the sheath to harden.

78. A method of manufacturing a marking implement the method comprising the steps of:
mixing gypsum, water and a rheology modifying agent to form a hydraulically settable mixture;
forming the hydraulically settable mixture into a sheath having a hydraulically settable matrix, the sheath being formed to retain a marking core; and allowing the hydraulically settable matrix of the sheath to harden.