US2918737A - Hollow plastic shoe heel - Google Patents

Description

Dx. 29, 1959 c. L. BEM. 2,918,737

HOLLOW PLASTIC SHOE: HEEL Filed Jan. 15, 1958 52 53 .Vlg 57 I @5g (J El 50 54 CARL L. BEAL` 56 I ATTORNEY United States Patent O HOLLOW PLASTIC SHOE HEEL Carl L. Beal, Huntington, N .Y.

lAlapli'cation'January 15, 1958, Serial No. 709,015

6 Claims. (Cl. 36-34) This invention relates lto plastic heels for ladies shoes `'arid'especially `to a novel construction of such plastic rhlels'and to the manufacture of such plastic heels from plastic `compositions, including slim high plastic heels for ladies dress shoes, as well as lower types of heels.

A high quality ladies dress shoe needs to retain the "trimappearance of a new shoe throughout its useful klife. To maintain such a new appearance throughout the life of a shoe, the slim high heel must be strong "enough to prevent breakage, to show no distortion and not to lbecome loosened or pulled away from the area of theshoe bottom'to which the heel is attached.

Fromthe standpoint of appearance, a slim high heel iforladies shoes made from `plastics is preferable, for

the iheel, being integral with the plastic of the heel, may

be highly polished toa mirror-like smoothness, yielding `a. heel of` a `desirable appearance that is retained through- `outthelite of the shoe.

Nevertheless, the manufacture of such slim high heels `froin plastics has not heretofore been entirely satis- "factory, largely because the essential strength characterist'ics of a slim high heel above indicated have not been `'obtainable in any plastic heel previously produced. The general practice heretofore has been to make a tall slim Vhighplastic heel by pressureinjection molding of plastics i`ri`multiple"cavity molds, which method is not only exipensivefbut also such an injection molded plastic heel "bends-progressively with service wear at the slender 'ibottom Aportion under the repeated and continual loads `placed-"on the plastic heel in walking and standing, un- `til the heel `becomes `so distorted as to be useless and need be replaced, aidefect known in the industry as creepx `A primerequirement of a plastic heel for high quality 'ladies"shoes, and especially for tall slim high plastic v"heelsfor'la;dies"'dress shoes, is that the slender lower portion `of the heel be'capable of retaining its new ap peairanc'e throughout the useful life of the shoe, of withst'ariding any tendency to bend or creep and, further, of withstanding the lateral bending stresses in every directin whichare :continuously imposed on such a heel by Vnormal use and periodically withstanding the lateral stressesof unusual magnitude imposed on such a heel lby'stubbing the heel against obstructions and/ or by catching the bottom of the heel in openings of various kinds infthesurfaces on which the wearer of shoes may from time to time need to walk, with the result that the lower isl'ender part `of the slim high plastic heel either bends, 'breaks or chips, or becomes so bent or otherwise dis- "torted as to require replacement.

An object of the invention of this application is to provide a slim high plastic heel of superior quality, one that possesses in ahigh degree all the desirable charac- `i"teristics of a slim high plastic heel for ladies dress shoes, including strength throughout the heel and particularly Dixit-the lower slim ground-contacting portion of the heel, ermness of attachmentto the shoe, and an extremely atltrattative appearancafwhich `characteristics endure for the useful life of the shoes to which the novel `plastic heel of this application is attached.

Another object of this invention is to provide a slim high hollow plastic heel having an integral wall structure defining an interior closed hollow space, the slim lower portion of the wall structure having embedded therein fibrous reinforcing elements which extend substantially vertically in the lower ground-contacting p0rtion of the heel.

A further object of this invention is to provide a slim high hollow plastic heel having an integral wall structure defining an interior closed hollow space, the slim lower portion of the wall structure `having `embedded therein vertically disposed ibrous reinforcing means-and the upper shoe-contacting wall portion having embedded therein a plate-like fastening retaining insert.

A still further object of this invention is to Vprovide a novel and economical method for the production of the novel slim high plasticheels of this application.

Other objects will be apparent from the following speciiication and the accompanying drawing, it being understood that variations and modifications are to be included within the scope of this invention as herein described and claimed.

Fig. l is a cross-sectional View of the lower part of a two-part heel mold, showing the initial step in the production of the slim high plastic heel, a owable plastic composition being within the lower mold part up to a level indicated by line A-Ag Fig. 2 is a fragmentary cross-sectional view of the lower mold part of the two-part mold of Fig. 1, taken on line 2 2 of Fig. 5, showing fibrous rods inserted into and vertically disposed within the owable plastic composition oi Fig. l, which causes the plastic composition to rise to a level indicated by line B-B;

Fig. 3 is a, cross-sectional View of a two--part heelmold taken on line 3--3 of Fig. 5, showing added plastic composition in the lower mold part to a level C--C, and also showing the cover part of the two-part mold in place to close the heel mold preparatory to gyrational heating;

Fig. 4 is a plan view of the plate-like insert, shown'in Fig. 3 attached to the cover part of the mold;

Fig. 5 is a cross-sectional View taken on line 5 5 of Fig. 2;

Fig. 6 is a cross-sectional View of the finished slim high plastic heel within the two-part heel mold;

Fig. 7 is a cross-sectional view of they linishedheel, removed from the mold;

Fig. 8 is a cross-sectional view of a modilied form of the slim high plastic heel of this invention; g

Fig. 9 is a cross-sectional view on line 9--9 of Fig `8;

Figs. l0, ll, l2 and 13 are each cross-sectional views to illustrate modifications of the plastic heel, each view being taken in a plane similar to that of Fig. 9;

Fig. 14 is a diagrammatic View of one form of apparatus for impregnating with plastic composition fibrous rovings, shaping the plastic impregnated fibrous rovings into rod form, and setting the plastic composition of the brous rod elements;

Fig. 15 is a cross-sectional View of the `brous roving on line 15-15 of Fig. 14;

Fig. 16 is a fragmentary plan View of the brous roving of Fig. l5, adjacent the cross-section line 15-15 of Fig. 14;

Fig. 17 is a fragmentary elevation taken as indicated by line 17-17 of Fig. 14;

Figs. 18 and 19 are views in cross-section and in elevation, respectively, of one size of fibrous rods; Figs. 20 and 2l, and Figs. 22 and 23 being similar Views of other sizes of brous rods.

Referring to the drawing, in all -Vfigures "of `whichi'the -to be produced therein.

Isoftening temperature of about 400 F. or higher.

3 same reference numeral indicates the same element, the finished plastic heel 40 is shown in Fig. 6 within a mold 30, before the opening of the mold and the removal of the yheel 40, and in Fig. 7 after being removed from the mold The mold 30 is preferably made of a good heat-conducting material, such as a metal, and as shown is a two-part mold, and although the mold 30 may be made of a wide variety of materials, a two-part metal mold is vpresently preferred.

As illustrated, the mold 30 consists of a one-piece lower mold part 31 and a tightly fitting cover part 32, although the lower mold part 31 may be made of two or more sections where ready removal of the finished heel indicates this to be desirable. The inner wall Surfaces 33 of the lower mold part 31 are of a size and shape to form the exposed surfaces of the plastic heel Thus, the lower mold part 31 has a rear and side wall arcuate inner surface 34, a forward instep wall inner surface 35, and a bottom inner surface 36. The dimensions and contours of such inner surfaces 34, 35 and 36, are designed for each size and style of heel, as is understood by those skilled in this art.

The cover mold part 32 has a concave inner surface 36 of a shape to form the upper shoe-contacting portion of the heel to a contour fitting closely the portion of the shoe to which the heel is to be attached, and has a pin 37 secured centrally thereof so as to support an insert,

later to be described, in proper position during the production of the plastic heel.

,relatively slender ground-contacting wall portion 43, an

upper concave shoe-contacting wall portion 44, a rear and side arcuate wall portion 45 and a front or forward instep wall portion 46. The upper wall portion 44 has embedded therein a fastening insert 47 and a hole 4S, vleft in the upper wall 44 and insert 47 upon removal of the pin 37 on which is mounted fastening insert 47 during the production of the heel 40, as will be more fully hereinafter described. The plastic of which the plastic heel is made is a tough, rigid, resilient plastic of medium hardness and may be produced by any suitable process, although the plastic composition hereinbelow described seems at present to be a most satisfactory composition.

The relatively slender ground-contacting wall portion 43 of the plastic heel 40 has embedded therein a number of vertically disposed fibrous rods 50, or rod-like bundles 50 of continuous length fibers 51, which in a tall needle heel may be a single fibrous rod 50 as shown in Figs. 8 and 9, but in general from 3 up to 60 vertically disposed fibrous rods 50 arranged in either regular or haphazard arrangement, as indicated in Figs. to 13, are employed.

vIn the fibrous rod 50, the individual continuous length fibers 51 are each substantially parallel to each other, although there may be some intertwining of the fibers 51 during the production of the fibrous rods 50.

The rod 50 with its substantially parallel continuous length fibers S1 may be made from a number of continous length liber rovings 52, the preferable characteristics of the individual fibers being a width (diameter) of from about 5 to 50 microns, and, when tested at 70 F. and 65% relative humidity, a high tensile strength of the order of about 85,000 to 400,000 or more pounds per square inch and an ultimate elongation of less than about 25%, and also a high resistance to heat, as an initial it is to be understood that the numerical values hereinabove given are preferred ranges, and that somewhat higher and lower numerical values may be employed. A number of continuous length fibers having these characteristics are listed in the Fiber Chart, pages 580 to 584 of Modern Plastics Encyclopedia, 1957 edition, published by Breskin Publications, Inc., 575 Madison Avenue, New York City, which fibers are here incorporated by referenee.

. Applicant has discovered that glass fibers of about 5 to 40 microns in width (diameter) having, when tested at 70 F. and 65 relative humidity, a tensile strength of about 200,000 to about 350,000 pounds per square inch and an ultimate elongation of from about 2.5 to about 4.0%, and having an initial softening temperature of from about 1300 to about 1550 F., or more, is one of the preferable fibers for the production of the rods 50 of this application.

Another continuous length fiber, that has in use proven to be highly satisfactory for the production of the rods 50, is a high tenacity fiber of Daeron, a polyester condensation polymer of ethylene glycol and either terephthalic acid or methyl terephthalate. High tenacity Daeron, manufactured by Du Pont, is about 15 to 25 microns in width (diameter) and has, when tested at 70 F. and 65 relative humidity, a tensile strength of about 100,000 to 125,000 pounds per square inch and an ultimate elongation of about l0 to 13%, and also has an initial softening point of about 455 F. i

Still another continuous length fiber, that has proven to be satisfactory for the production of rods 50, islu'gh tenacity nylon, a polyamide condensationrpolyrner of hexamethylene diamine and either adipic or sebacic acid. High tenacity nylon fiber, as manufactured by 13u Font, has a width of about 15 to 45 microns, and has, when tested at 70 F. and 65% relative humidity, a tensile strength of about 85,000 to 114,000 pounds per square inch and an ultimate elongation of about 15 to 23% and also has an initial softening temperature of aboutAOQ F.

The continuous length fibers 51 of the rodsMSlare normally marketed in the form of roving 52,` that is, loosely associated generally parallel fibers with af, specified number of ends, or fibers, in each roving" 52, as shown in Figs. l5 and 16. Glass fiber roving isfnow generally available in "60 ends, that is, 60 fibers to a roving 52, or multiples or fractions of 60 ends. `Generally l0 to 480 end rovings are adequate for the roving 52 employed in the invention of this application. Thus, applicant has demonstrated that a glass roving having 240 to 480 ends is desirable where only one vertically disposed fibrous rod or fibrous bundle 50 is used in the bottom portion of the plastic heel 40, as in a needle heel of Fig. 8. Where from 3 to 6 rods are employed, a 120 to 240 end roving is satisfactory; where from 6 to 10 rods are used, a 60 to 120 end roving; where 10 to 20 rods are used, a 30 to 60 end roving; and where 30 to 60 rods are used, a l0 to 30 end roving. It will be understood that the number of ends, or individual continuous fibers, in a roving is a matter of choice and that applicant does not limit his invention to any particular number of ends, or continuous fibers, in any roving employed in the invention of this application.

The conversion of the roving 52, comprising the loosely associated continuous fibers 51, to a rod or rod-like bundle 50 of continuous length fibers 51, may be carried out in any of the several known ways. As illustrated, diagrammatically in Fig. 14, a roll 53 of roving 52, supported on a suitable rotatable drum 54, is first saturated with a plastic composition 55, preferably of the same plastic composition, but which may be of a different fluidity, as that of which the wall structure 41 of the heel 40 is made, by passing the roving 52 through the flowable plastic composition 55 contained in a tank 56, the roving 52 passing around the rollers 57, 58 and 59, these rollers directing the roving 52 into and out of the flowable plastic composition 55 in the tank 56. After leaving the tank 56, the plastic saturated roving 52 is passed through a frustro-eonical forming member 60, having a cylindrical outlet opening 61 at its apex, which open- .ing shapes the plastic-impregnated roving 52 intov u rodsurplus plastic that is removed from the roving 52 during the shaping operation is drained back on the downwardly slanting lip 62 of the forming member 60 intoV the tank 56. Thereafter, the impregnated roving 52, now shaped into a rod 50, is passed through an oven 65, where the plastic composition 55 is solidified to some extent so as to produce a self-sustaining continuous rod 50 which is carried away by rolls 66 for storage and subsequent use inthe production of individual rods 50. The rod 50 may have one end 67 pointed to facilitate its placement in the plastic of the lower heel portion 43, as will be hereinafter described. However, the rod 50 may have a square cut end 68 at each end of the rod 50.

The plastic heel 40 is preferably made in the mold 30 by what is sometimes called gyrational casting from a suitable flowable plastic composition capable of being distributed over the inner surfaces of the closed mold 30 during the gyration of the mold 30 and further capable of being converted into a rigid resilient solid plastic, as by gelling and solidifying the flowable plastic composition by heat transferred through the walls of the mold 30 while the iiowable plastic composition is distributed bythe gyrational movements over theinner surfaces of the mold 30. The gyratio-n and heating may be carried out simultaneously, when the mold 30, containing the plastic composition and wall embedded elements, as more fully hereinafter described, has been closed, or the closed mold 30 with a iiowable plastic composition and reinforcing rods 50 therein, may be first gyrated to distribute the iiowable `plastic composition within the mold 30, and then heat applied to the outer surfaces of mold 30 while continuing the gyration of the mold 30. lt is also within the scope of this invention to add to the plastic composition a delayed gelling and/or solidifying agent having the properties of solidifying the plastic composition during gyration but without application of heat to the mold. However, the time cycle of the gyrational casting operation is shortened where heat is applied to the mold 30 during gyrationand for` that reason heating of the mold 30 during the gyrational period is preferred.

Applicant has discovered novel plastic compositions which` havecharacteristics especially adapting them for theproduction of plastic` heels: by gyrational casting and whichare the` subject matter of other pending applications. Each of these plastic compositions, which applicanthasrtermed a.rigisol, may be employed in the invention of this application. Gne of the rigisols found tobelsatisfactory for the production of the plastic heels of this application consists of a dispersion of finely dividedparticles` of polyvinyl chloride resin in a liquid mixture of a piasticizer anda liquid dispersant capable oflbeingconvertedinto a rigid plastic by heating, such as a polymerizable monomer. When such a plastic composition is heated inside of a closed gyrating mold, the plastic composition is first distributed over the inner surfaceof the mold, then is gelled in that position, and thereafter` the plastic composition rapidly becomes a medium-hard resilient plastic product having a closed hollow spacexinside the product.

By way ofillustration, a flowable plastic composition, or rigisol, of the following composition may be employed:

Constituents: Parts by weight 1. High molecular weight dispersion-type polyvinyl lchloride resin 100 6 The constituents of the above formula` are thoroughly intermixed by stirring and/ or by grinding. The resulting composition is a iiowable plastic liquid composition of low viscosity capable of being converted into a rigid plastic by heating.

The high molecular weight dispersion-type polyvinyl chlorides, which have been found satisfactory in carrying out the invention of this application, are finely divided or minute particle sized resins, such as as produced by the polymerization of vinyl chloride in aqueous emulsion, the particle size normally ranging from 0.1 to 10.0 microns` Thus, the high molecular weight dispersion-type polyvinyl chloride resins marketed by B. F; Goodrich Chemical Company as Geon 202 and Geon 121, dispersiontype resins having a particle size ranging between about 0.1 and 4.0 microns, or a dispersion-type high molecular weight polyvinyl resin marketed by Naugatuck Chemical Company as Marvinol VR-lO, having an average par.- ticle size of about 6.2 microns. It may be preferable, however, to use a mixture of two or more dispersiontype polyvinyl resins in varying proportions, since a mixture of the particle sizes of the different dispersion-type resins gives a lower viscosity composition.. In practice, equal parts of Geon 121 and of Marvinol VR-l() have given satisfactory results. It is to be understood that other makes of the dispersion-type high molecular weight polyvinyl resins also may be employed, such as Bakelite QYNV, Exon 654, Marvinol VR-50, and the like.

The liquid dispersant is one capable of being hardened by heat and/or chemical action, the dispersion-type polyvinyl resin being first dispersed in the dispersant, with other constituents, and then hardened by heat and/or chemical action. The dispersant is preferably a polymerizable acrylic monomer, preferably a methacrylate diester of an ethylene glycol, such as triethylene glycol dimethacrylate, marketed by Specialty Resins, Inc., as monomer SR #205, or ethylene glycol dimethacrylate, marketed by The Borden Company as EGD, or a commercial acrylic monomer marketed by Carbide and Car.- bon Corporation under the trade name MG-l, comprising chiefly diethylene glycol dimethacrylate, and having a viscosity of 12.2 centipoises at 25 C., a specific gravity at 25 C. of 1.078, and a refractive index at 30 C. of 1.459, or other like dispersants.

The plasticizer may also be chosen from a variety of plasticizers known to plasticize high molecular weight polyvinyl chloride resins, as di(2-ethylhexyl)phthalate, dicapryl phthalate, dioctyl sebacate, di(2-ethylhexyl)iso sebacate, di(2-ethylhexyl)succinate, and the like.

Thecatalyst may likewise be any one of the recognized catalysts for the hardening or solidification of the acrylic monomer, such as benzoyl peroxide, acetyl peroxide,- lauroyl peroxide and the like.

The colorant of the above flowable plastic composition, or rigisol, may be any one of numerous natural and/ or synthetic organic or inorganic pigments, and blends thereof, which impart to the plastic heels 4t) of this application, either bright colors or more subdued tints and pastel shades, to match the colors of the shoes to which the heels are applied. Thus, for black heels, finely divided carbon black gives excellent jet black plastic heels; for white heels, finely divided titanium dioxide has high tinctorial strength and gives excellent white plasticheels; and any color, tint or shade can he produced in plastic heels by employing the well known red, blue, yellow, green, orange and scarlet pigments, and blends thereof, such as are listed on pages 367 to 373 of Modern Plastics Encyclopedia, 1957 edition, published by Breskin Publications, Inc., 575 Madison Avenue, New York City.

While the heel 40 with the fibrous rods 50 embeddedin the lower` part thereof may be produced in other ways, a `preferred method of producing the heel 40isi1lus-j tratedinFigs. l to 6.

'Into the lower heel mold part 31 is poured a measured quantity of a suitable iiowable plastic composition 70 :of the characterhereinabove more fully described, as to Ialevel indicated by the dotted line A-A of Fig. 1, the ylevel of which may vary considerably, as from one-fourth 'to one-half the distance from the bottom 36 of the mold -part 31 to the front edge of the flange 38 of the mold part 31, the amount of the plastic compositio-n depending "on the desired service characteristic of the heel being produced. Next, a number of librous rods 50, from one to 60 or more, or, as shown in Fig. 5, 6 rods, are thrust down into the plastic composition 70 so as to be embedded therein, which operation raises the level of the plastic composition to a level indicated by the dotted line 'B-B of Fig. 2. Then, a further measured amount of a suitable plastic composition 71 is placed in the lower mold part 31 to a predetermined level, as level C-C of 3. The plastic composition 71 may be the same as the plastic composition 70, or may be a plastic composition of lower viscosity than that of the plastic composition 70. The amount of the plastic composition 71 may Ialso vary but is such as to produce a sufficiently thick @wall structure, when distributed within the mold 3) during the gyrational movements o-f the mold, and to leave a closed central space 42 of optimum size within the plastic heel 4i).

-1 f The cover part 32 may have, or may not have, a platelike insert 47 attached to and spaced from the inner sur vface 36' of the cover part 32 by the centrally disposed pin 37. In some instances it may be desirable to omit the insert 47, in which case the upper wall 44 of the plastic heel 40 will not contain an insert but will be adequate for certain types of plastic heels, as in the plastic heel of Fig. 8.

Normally, it is desirable to have the insert 47 embedded in the upper wall 44, as in Figs. 6 and 7. In this case, 4before closing the mold 30, the cover part 32 is made ready for the casting operation by supporting a fastening insert 47 on the pin 37 so as to bring the upper surface of the insert 47 generally parallel to and spaced from the inner surface 36 of the cover part 32 a distance approximately of the thickness of the wall structure 41 at its thinnest portion as shown in Fig. 3, so that the plastic composition 71 during gyrational casting will completely iill the space between the upper surface of insert 47 and the inner surface 36 of the cover part 32, as shown in Fig. 6, and will form on the lower face of the insert 47 a plastic layer somewhat thinner than that of the wall structure 41 at its thinnest portion, since the insert 47 shields somewhat the plastic composition 71 beneath the insert 47 from the heat transmitted through the cover part 32, when the mold 3i) is subjected to heat.

As has been above indicated, the cover mold part 32, either with or without the fastening insert 47 supported from the cover part 32 by the pin 37, is clamped tightly to the lower mold part 31 containing the plastic composition 70 to level C-C, and the vertically disposed fibrous `rods 50 embedded in the plastic composition in the lower slender portion of the heel 40, all as shown in Fig. 3. The ycharged and assembled mold 30 is then ready to be gyrated by any suitable mechanism.

Experience has demonstrated that the flowable plastic composition 70 in the lower mold part 31, with the fibrous rods 50 embedded therein, is not disturbed but remains in place during the gyrational movements of the mold 30, where iiowable plastic compositions 7) and 71 of the character hereinabove described are employed, and that where a relatively low viscosity plastic composition 71 is employed in order to secure a more ready distribution of the plastic composition between the insert 47 and the inner surface of the cover mold part 32, a plastic composition 70 of higher viscosity than that of plastic. composition 71 is advisable. In either case, where a period of time elapses between the charging of they mold 30 and the starting of the gyrational mover ments, the mold 30 should be preferably kept during that period in the upright position, shown in Fig. 3. t

Gyrational casting, as the name implies, comprehends movements of the mold 30 in a variety of ways. Thus, the charged and assembled mold 30 of Fig. 3 may be rotated about a single axis, or simultaneously about two or more axes, or may be oscillated through a wide angle in one or more planes, or may be moved in irregular or zigzag paths, the purpose of any such gyrating movements of the mold 30 being to spread the flowable plastic composition 71 over the inner surfaces of the mold 30 and into the space between the inner surface of the cover part 32 and the fastening insert 47, so as to fill that space. The gyration is accompanied by heating, as by gyrating the mold 30 in a chamber containing a liuid heating medium, such as heated air, gas o1 steam. The temperature of the heating medium is such that the heat transferred through the mold 30 to the plastic composition, which has been distributed over the inner surfaces of the mold 30 and around the insert 47 during the heat-up period, is converted into a tough rigid solid hollow plastic heel 40, such as is shown in Fig. 6 of the drawing. The mold 30 is then cooled, as by passing it through a cold water spray, and when the mold 30 and the tough rigid plastic of the cast heel 40 have been cooled somewhat, the mold parts 31 and 32 are opened, the cover part 32 removed, taking with it the pin 37, leaving the heel 40 with an opening 48 made by removal of the pin 37. The cast plastic heel 40 is then removed from the lower mold part 31 of the mold 30, with the fibrous rods 50 firmly embedded in, and an integral part of the lower wall 43 and the fastening insert 47, where present, firmly embedded in the shoe-contacting wall 44 of the heel 40, as shown in Figs. 7 and 8.

Where the insert 47 is employed, it may be made ofl a variety of materials. Thus, fibrous sheets or slabsof various types have been found to be eective. These may range from soft cardboard to wall boards and other fibrous bodies. The insert 47 in Figs. 3, 4, 6 and 7 is a fibrous sheet insert, such as cardboard. Again, the in-v sert 47 may be made of plywood or cross-plied fiber boards, or of a metal sheet, such as aluminum and aluminum alloys, copper and copper alloys. A sheet iron and tinned sheet iron insert has also proven to be effective in certain cases.

While the fastening insert 47 of the finished heel 40 serves primarily as an anchoring means for the fasteners employed in securing the heel 40 to the shoe, it may also be desirably employed to modify the properties of the rigid plastic in the region of the heel penetrated lby the fasteners. Thus, it has been found in certain cases to be advantageous to embody in the preformed insert 47, by incorporation into the insert 47 in course of its construction or later by impregnation, or otherwise, or by coating the insert 47 on its upper surface with, a material that eXerts a softening iniiuence on the plastic of the heel contiguous to the insert 47. Such a material may be a solid or liquid plasticizer, or both, that, during the heating of the mold 30 and its plastic composition contents, migrates into portions of the plastic composi tion contiguous to the insert, and thus makes the rigid plastic in the nailable top of the heel softer but tougher, less brittle and more readily penetrated by vthe fasteners which attach the heel to the shoe, thus reducing any tendency to crack or split the rigid plastic of the heel during the driving of the fasteners. It is to be understood, however, that satisfactory attachments of the heel 40 to a shoe may be attained without the embodiment of a plasticizer on or in the insert 47.

As an example of the use of solid plasticizers in the production of inserts having the plasticizer distributed throughout the insert, powdered dicyclohexyl phthalate, a commercial solid plasticizer having a melting point of about 58`65` C., is added to paper pulp atthe beater in proportions ranging from l to 40 weight percent of the dry ber weight, and thoroughly admixed therewith. Sheets of a thickness of heavy cardboard are made therefrom on apaper-makingmachine and sections of the size and shape of the insert 47 for any desired size heel are cut from said cardboard either as a single board section or a plurality of'plied-up sections to be utilized as an insert 47. Upon gyrational casting and heating of the mold 30` to the temperature necessary for conversion of the plastic composition to a hard tough rigid plastic, that is, from 300 to 500 F., or higher, the dicyclohexyl phthalate plasticizer fuses and migrates into contiguous portions of the plastic, producing a tougher and less brittle plastic portion inthe region of the insert. Other plasticizers which are solid at normal temperatures may be similarly employed, such as triphenyl phosphate, glycerol monostearate, N-ethyl p-toluenesulfonamide, and the like.

Plasticizers which are liquid at normal temperatures, such as didecyl phthalate, tricresyl phosphate, and the like, may serve a like purpose by impregnating or coating the insert 47 with the liquid plasticizer before attaching the insert 47 to the cover part 32 of the mold 30. If desired, only the side of the insert 47 facing the inner surface 36 of the cover mold part 32 may be coated with the plasticizer. Upon the heat formation of the plastic solid about the plasticizer-treated insert 47, the plasticizer will migrate into the contiguous portions of the plastic heel, producing aless brittle and tougher rigid plastic adjacent the insert.

Plasticizers, both solid and liquid, which are useful in the invention of this application, are described in the Plasticizers Chart of the Modern Plastics Encyclopedia,` 1957 edition, pages 598 to 613, published by Breskin Publications, Inc., 575 Madison Avenue, New York 22, N.Y., which plasticizers are incorporated in this application by reference.

The marked superiority of the tall slim plastic heels of this application over similar plastic heels of the prior art resides primarily in superiority of the quality of the plastic heels in strength and particularly the high resistance of the slender bottom portion of the heel to bending creep and distortions that in a relatively short time make prior art plastic heels useless.

This marked superiority of the tall slender plastic heels of this application over the prior injection mo-lded plastic heels is due in part to the wall strength imparted to the plastic heels of this invention by the wall inserts, such as the vertically disposed fibrous rods embedded in the slender portion of the heel and the plate-like insert embedded in the shoe-contacting wall of the plastic heel of this application, and also in part to the central closed hollow space within the integral wall structure of the plastic heel herein disclosed, which construction imparts to the plastic heel of this application greater resiliency and hence a greater capacity for withstanding progressive bending or creep and also for withstanding impacts of the magnitude that bend and break injection molded heels.

The superiority of the plastic heels of this application over the injection molded commercial plastic heels is clearly indicated by the data obtained in the following tests, in which the plastic heel of Fig. 7, a 31/2 inch heel, made as hereinabove described was test compared with injection molded commercial plastic heels of the same size and shape. For this test, a bending force was applied one-half inch from the bottom surface of the heel. The heels tested were A. The heel of Fig. 7, a 31/2 inch heel, made as herein described;

B. A heel of same size and shape injection molded from cellulose acetate; and

C. A heel of same size and shape injection molded from cellulose acetate butyrate.

Pounds Per Sq. In.

Heel Effect of Bending Force From the above tests, the marked superiority of the plastic heel A, the plastic heel of this application, is clearly evident.

Further, the manufacture of tall slim plastic heels for ladies shoes by the high pressure injection of a heatsetting plastic composition into multiple cavity molds requires expensive high pressure injection machinery as well as expensive multiple cavity high pressure molds, that is, molds that will withstand the high plastic pressures within the molds necessary for multiple cavity injection molding. On the other hand, the plastic heels of this application may be made inlightweight, thin-walled inexpensive molds made either by casting or by stamping or drawing sheet metal into the shape of the mold parts by processes now perfected for making such drawn metal parts, since the gyrational molding of this invention is carried out at atmospheric or relatively low pressures with the lightweight mold gyrated in heated chambers at relatively low pressures.

The invention of this application may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the embodiments hereinabove set forth are, therefore, to be considered in all respects as illustrative and not restrictive, and all modications coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

What is claimed is:

1. A strong resilient hollow plastic heel comprising an integral one-piece hollow heel-shaped body having a relatively thick shoe-contacting top portion, a vertical portion integral with an extending downwardly from said top portion and tapering inwardly and downwardly from the said top portion, said vertical portion having walls tapering inwardly and downwardly from the perimeter of said top portion to form within said body a closed central cavity, the walls defining said cavity converging downwardly to a thick ground-contacting portion, and at least one vertically positioned rod embedded within the plastic of the said ground-contacting portion, each rod comprising a bundle of longitudinally extending fibers, the individual iibers of each bundle having a width of from 5 to 50 microns, a tensile strength of about 85,000 to 400,000 or more pounds per square inch, an elongation of less than about 25%, and an initial softening temperature of not less than about 400 F.

2. A strong resilient hollow plastic heel comprising an integral one-piece hollow heel-shaped body having a relatively thick shoe-contacting top portion, a vertical portion integral with and extending downwardly from said top portion and tapering inwardly and downwardly from the said top portion, said vertical portion having walls tapering inwardly and downwardly from the perimeter of said top portion to form within said body a closed central cavity, the walls defining said cavity converging downwardly to a thick ground-contacting portion, and at least one vertically positioned rod embedded within the plastic of the said ground-contacting portion, each rod comprising a bundle of longitudinally extending fibers, the individual fibers of each bundle being a glass fiber having a tensile strength ranging from about 200,000 to about 350,000 pounds per square inch, an ultimate elongation of less than 4%, and an initial softening temperature of not less than l300 F.

3. A strong resilient hollow plastic heel comprising an integral one-piece hollow heel-shaped body having a relaentwarf tively thick shoe-contacting top portion, a Vertical portion.

integral with and extending downwardly from said top portion and tapering inwardly and downwardly from the said top portion, said vertical portion having walls tapering inwardly and downwardly from the perimeter of said top portion to form within said body a closed central cavity, the walls defining said cavity converging downwardly to a thick ground-contacting portion, and at least one vertically positioned rod embedded within the plastic of the said ground-contacting portion, each rod cornprising a bundle of longitudinally extending fibers, the individual fibers of each bundle being a synthetic polyester fiber made from the polycondensation of ethylene glycol and methyl-terephthalate having a tensile strength of about 100,000 to about 125,000 pounds per square inch, an ultimate elongation of to 15%, and an initial softening temperature of not less than about 455 F.

4. A strong resilient hollow plastic heel comprising an integral one-piece hollow heel-shaped body having a relatively thick shoe-contacting top portion, a vertical portion integral with and extending downwardly from said top portion and tapering inwardly and downwardly from the said top portion, said vertical portion having walls tapering inwardly and downwardly from the perimeter of said top portion to form within said body a closed central cavity, the walls defining said cavity converging downwardly to a thick ground-contacting portion, and at least one vertically positioned rod embedded within the plastic of the said ground-contacting portion, each rod comprising a bundle of longitudinally extending fibers, the individual fibers of each bundle being a high tenacity nylon fiber having a tensile strength of from about 85,000 to about 114,000 pounds per square inch, an ultimate elongation of about to 23%, and an initial softening temperature of not less than about 400 F.

5. A strong resilient hollow plastic heel comprising an integral one-piece hollow heel-shapedlbody having a relatively thick shoe-contacting top portion, a vertical portion integral with and extending downwardly from said top portion and tapering inwardly and downwardly fromv the said top portion, said vertical portion having walls tapering inwardly and downwardly from the perimeter of said top portion to form within said body a closed lcentral cavity, the walls defining said cavity converging downwardly to a thick ground-contacting portion, and a plurality of vertically positioned rods embedded within the plastic of the said ground-contacting portion, each rod comprising a bundle of longitudinally extending fibers.

6. A hollow plastic high heel for a womans shoe comprising an integral one-piece plastic body portion having an angularly disposed comparatively thickbroad shoecontacting top portion, the vertical portion of said heel extending integrally from said top portion and tapering inwardly and downwardly from the perimeter of the top portion to form a central cavity, the walls defining said cavity converging into a solid ground-contacting por- .tion for more than half the instep height of said heel, and flexible reenforcing means for the said ground-conrtacting portion, said means comprising at least one vertically positioned exible rod embedded within and surrounded by the plastic of the said ground-contacting portion, each rod comprising a bundle of longitudinally extending iibers.

References Cited in the file of this patentv UNITED STATES PATENTS 2,308,103 Pearson Jan. 12, 1943 2,379,793 Eenigenburg July 3, 1945 2,709,280 Beneke May 3l, 1955 2,807,099 Dickman Sept. 24, 1957 2,851,796 Ronci Sept. 16, 1958

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