EP0251673A1 - Nassverfahren zur Herstellung einer Struktur aus einzeln versteiften Fasern - Google Patents
Nassverfahren zur Herstellung einer Struktur aus einzeln versteiften Fasern Download PDFInfo
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- EP0251673A1 EP0251673A1 EP87305611A EP87305611A EP0251673A1 EP 0251673 A1 EP0251673 A1 EP 0251673A1 EP 87305611 A EP87305611 A EP 87305611A EP 87305611 A EP87305611 A EP 87305611A EP 0251673 A1 EP0251673 A1 EP 0251673A1
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- EP
- European Patent Office
- Prior art keywords
- fibers
- crosslinking
- crosslinked
- individualized
- fiber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
- D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
- D21H11/20—Chemically or biochemically modified fibres
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/009—Fibre-rearranging devices
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/34—Construction or arrangement of spraying pipes
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
Definitions
- This invention is concerned with individualized, stiffened fibres and processes for forming such fibers into wet-laid structures.
- Fibers stiffened in substantially individualized form and various methods for making such fibers have been described in the art.
- the term "individualized, stiffened, crosslinked fibers" refers to cellulosic fibers that have primarily intrafiber chemical crosslink bonds. That is, the crosslink bonds are primarily between cellulose molecules of a single fiber, rather than between cellulose molecules of separate fibers.
- Individualized, crosslinked fibers and other individualized, stiffened fibers are generally regarded as being useful in absorbent product applications. In general, three categories of processes have been reported for making indivualized, stiffened fibers by forming intrafiber crosslink bonds.
- Dry resilience specifically refers to the ability of an absorbent structure to expand upon release of compressional force applied while the fibers are in a substantially dry condition.
- Wet resilience specifically refers to the ability of an absorbent structure to expand upon release of compressional force applied while the fibers are in a moistened condition.
- wet resilience shall be observed and reported for an absorbent structure moistened to saturation.
- aqueous solution crosslinked fibers Processes for producing aqueous solution crosslinked fibers are disclosed, for example, in U.S. Patent No. 3,241,553, issued to F. H.Steiger on March 22,1966.
- Individualized, crosslinked fibers are produced by crosslinking the fibers in an aqueous solution containing a crosslinking agent and a catalyst. Fibers produced in this manner are hereinafter referred to as "aqueous solution crosslinked" fibers. Due to the swelling effect of water on cellulosic fibres, aqueous solution crosslinked fibers are crosslinked while in an uncollapsed, swollen state. Relative to dry crosslinked fibers, aqueous solution crosslinked fibers as disclosed in U.S. Patent No. 3,241,553 have greater flexibility and less stiffness, and are characterized by higher fluid retention value (FRV). Absorbent structures made from aqueous solution crosslinked fibers exhibit lower wet and dry resilience than pads made from dry crosslinked fibers.
- FRV fluid
- Crosslinked fibers as described above are believed to be useful for lower density absorbent product applications such as diapers and also higher density absorbent product applications such as catamenials.
- such fibers have not provided sufficient absorbency benefits, in view of their detriments and costs, over conventional fibers to result in significant commercial success.
- the wet-laid structures containing individualized, stiffened fibers may be made according to a process which includes the steps of: a) providing a slurry containing individualized, stiffened fibers; b) depositing the slurry of fibers on a foraminous forming wire; c) directing at least one stream of fluid upon the fibers such that the fluid disperses flocculations of fibers and also inhibits the formation of additional flocculations of the fibers; and d) setting the fibers into a sheeted form while the fibers are in a substantially unflocculated condition.
- the step of setting the fibers into sheeted form may be performed by pressing the fibers against the forming wire with a screened roll, such as a cylindrical Dandy Roll.
- a screened roll such as a cylindrical Dandy Roll.
- a plurality of streams fo fluid having sequentially decreasing volumetric flow rates are directed upon the fibers.
- the individualized, stiffened fibers may also be mixed with conventional, unstiffened fibers or highly refined, unstiffened fibers while in slurry form.
- Individualized, stiffened fibers made from cellulosic fibers of diverse natural origin are applicable to the invention.
- Digested fibers from softwood, hardwood or cotton linters are preferably utilized. Fibers from Esparto grass, bagasse, kemp, flax, and other lignaceous and cellulosic fiber sources may also be utilized as raw material in the invention.
- the fibers may be supplied in slurry, unsheeted or sheeted form. Fibers supplied as wet lap, dry lap or other sheeted form are preferably rendered into unsheeted form by mechanically disintegrating the sheet, preferably prior to contacting the fibers with the crosslinking agent. Also, preferably the fibers are provided in a wet or moistened condition.
- the fibers are never-dried fibers. In the case of dry lap, it is advantageous to moisten the fibers prior to mechanical disintegration in order to minimize damage to the fibers. Also applicable to the present invention are individual fibers of synthetic origin which tend to flocculate in solution due to fiber chemisty, geometry or a combination of these or other factors.
- the optimum cellulose fiber source utilized in conjunction with this invention will depend upon the particular end use comtemplated. Generally, pulp fibers made by chemical pulping processes are preferred. Completely bleached, partially bleached and unbleached fibers are applicable. It may frequently be desired to utilize bleached pulp for its superior brightness and consumer appeal. In one novel embodiment of the invention, hereinafter more fully described, the fibers are partially bleached, crosslinked, and then bleached to completion. For products such as paper towels and absorbent pads for diapers, sanitary napkins, catamenials, and other similar absorbent paper products, it is especially preferred to utilize fibers from southern softwood pulp due to its premium absorbency characteristics.
- any individualized, stiffened fibers which flocculate in solution are intended to be within the scope of this invention. These include the fibers made according to the dry crosslinking processes and nonaqueous solution crosslinking processes disclosed in the Background of The Invention. Also contemplated are individualized, stiffened fibers treated with resins or other polymeric compounds as exemplified in U.S. Patent No. 3,819,470, issued to Shaw, D. L., et al, on June 25, 1974 and U.S. Patent No. 3,756,913, issued to Wodka, E. A., September 4, 1973. This invention is believed to be most useful for individualized stiffended fibers which have twisted, curled configurations. Processes for making such fibers with monomeric crosslinking agents are discussed below.
- Crosslinking agents applicable to the present development which are preferred included C2 - C8 dialdehydes, as well as acid analogues of such dialdehydes wherein the acid analogue has at least one aldehyde group, and oligomers of such dialdehydes and acid analogues. These compounds are capable of reacting with at least two hydroxyl groups in a single cellulose chain or on proximately located cellulose chains in a single fiber.
- the dialdehyde crosslinking agents described above will be present, or may react in a variety of forms, including the acid analogue and oligomer forms identified above. All such forms are meant to be included within the scope of the preferred embodiments.
- crosslinking agent refers to that particular crosslinking agent as well as other forms as may be present in an aqueous solution.
- Particular crosslinking agents contemplated for use with the invention are glutaraldehyde, glyoxal, and glyoxylic acid.
- Glutaraldehyde is especially preferred, since it has provided fibers with the highest levels of absorbency and resiliency, is believed to be safe and non-irritating to human skin when in a reacted, crosslinked condition, and has provided the most stable, crosslink bonds.
- the crosslinking agent is contacted with the fibers in a liquid medium, under such conditions that the crosslinking agent penetrates into the interior of the individual fiber structures.
- other methods of crosslinking agent treatment including spraying of the fibers while in individualized, fluffed form, are also within the scrope of the invention.
- the fibers will also be contacted with an appropriate catalyst prior to crosslinking.
- the type, amount, and method of contact of catalyst to the fibers will be dependent upon the particular crosslinking process practiced. These variable will be discussed in more detail below.
- the crosslinking agent is caused to react with the fibres in the substantial absence of interfiber bonds, i.e., while interfiber contact is maintained at a low degree of occurrence relative to unfluffed pulp fibers, or the fibers are submerged in a solution that does not facilitate the formation of interfiber bonding, especially hydrogen bonding. This results in the formation of crosslink bonds which are intrafiber in nature. Under these conditions, the crosslinking agent reacts to form crosslink bonds between hydroxyl groups of a single cellulose chain or between hydroxyl groups of proximately located cellulose chains of a single cellulosic fiber.
- crosslinking agent reacts with the hydroxyl groups of the cellulose to form hemiacetal and acetal bonds.
- the formation of acetal bonds believed to be the desirable bond types providing stable crosslink bonds is favored under acidic reaction conditions. Therefore, acid catalyzed crosslinking conditions are highly preferred for the purposes of this invention.
- the fibers are preferably mechanically defibrated into a low density, individualized, fibrous form known as "fluff" prior to reaction of the crosslinking agent with the fibers.
- Mechanical defibration may be performed by a variety of methods which are presently known in the art or which may hereinafter become known. Mechanical defibration is preferably performed by a method wherein knot formation and fiber damage are minimized.
- One type of device which has been found to be particularly useful for defibrating the cellulosic fibers is the three stage fluffing device described in U.S. Patent No. 3,987,968, issued to D. R. Moore and 0. A. Shields on 0ctober 26, 1976.
- the fluffing device described in U.S. Patent No. 3,987,968 subjects moist cellulosic pulp fibers to a combination of mechanical impact, mechanical agitation, air agitation and a limited amount of air drying to create a substantially knot-free fluff.
- the individualized fibers have imparted thereto an enhanced degree of curl and twist relative to the amount of curl and twist naturally present in such fibers. It is believed that this additional curl and twist enhances the resilient character of absorbent structures made from the finished, crosslinked fibers. It is also believed that this additional curl and twist enhances the degree of flocculation of the individualized, crosslinked fibers.
- defibrating the cellulosic fibers include, but are not limited to, treatment with a Waring blender and tangentially contacting the fibers with a rotating disk refiner or wire brush.
- a Waring blender tangentially contacting the fibers with a rotating disk refiner or wire brush.
- an air stream is directed toward the fibers during such defibration to aid in separating the fibers into substantially individual form.
- the fibers s are preferably mechanically treated while initially containing at least 20% moisture, and preferably containing between about 40% and 60% moisture.
- Mechanical refining of fibers at high consistency or of partially dried fibers may also be utilized to provide curl and twist to the fibers in addition to curl or twist imparted as a result of mechanical defibration.
- the fibers made according to the present invention have unique combinations of stiffness and resiliency, which allow absorbent structures made from the fibers to maintain high levels of absorptivity, and exhibit high levels of resiliency and an expansionary responsiveness to wetting of a dry, compressed absorbent structure.
- the crosslinked fibers are characterized by having water retention values (WRV's) of less than 60, and preferably between 28 and 45, for conventional, chemically pulped, papermaking fibers.
- the WRV of a particular fiber is indicative of the level of crosslinking and the degree of swelling of the fiber at the time of crosslinking.
- individualized, crosslinked fibers may be produced from such a process by providing a quantity of cellulosic fibers, contacting a slurry of the fibers with a type and amount of crosslinking agent as described above, mechanically separating, e.g., defibrating, the fibers into substantially individual form, and drying the fibers and causing the crosslinking agent to react with the fibers in the presence of a catalyst to form crosslink bonds while the fibers are maintained in substantially individual form.
- the defibration step apart from the drying step, is believed to impart additional curl.
- Subsequent drying is accompanied by twisting of the fibers, with the degree of twist being enhanced by the curled geometry of the finber.
- fiber “curl” refers to the geometric curvature of the fiber about the longitudinal axis of the fiber.
- “Twist” refers to a rotation of the fiber about the perpendicular cross-section of the longitudinal axis of the fiber.
- individualized, crosslinked fibers within the scope of the invention having an average of about 6 (six) twists per millimeter of fiber have been observed.
- Maintaining the fibers in substantially individual form during drying and crosslinking allows the fibers to twist during drying and thereby be crosslinked in such twisted, curled state. Drying fibers under such conditions that the fibers may twist and curl is referred to as drying the fibers under substantially unrestrained conditions. On the other hand, drying fibers in sheeted form results in dried fibers which are not twisted and curled as fibers dried in substantially individualized form. It is believed that interfiber hydrogen bonding "restrains" the relative occurence of twisting and curling of the fiber.
- the fibers may be contacted with the crosslinking agent and catalyst.
- the fibers are contacted with a solution which initially contains both the crosslinking agent and the catalyst.
- the fibers are contacted with an aqueous solution of crosslinking agent and allowed to soak prior to addition of the catalyst.
- the catalyst is subsequently added.
- the crosslinking agent and catalyst are added to an aqueous slurry of the cellulosic fibers.
- the cellulosic fibers, crosslinking agent and catalyst are preferably mixed and/or allowed to soak sufficiently with the fibers to assure thorough contact with and impregnation of the individual fibers.
- any substance which catalyzes the crosslinking mechanism may be utilized.
- Applicable catalysts include organic acids and acid salts. Especially preferred catalysts are salts such as aluminum, magnesium, zinc and calcium salts of chlorides, nitrates or sulfates. One specific example of a preferred salt is zinc nitrate hexahydrate.
- Other catalysts include acids such as sulfuric acid, hydrochloric acid and other mineral and organic acids. The selected catalyst may be utilized as the sole catalyzing agent, or in combination with one or more other catalysts. It is believed that combinations of acid salts and organic acids as catalyzing agents provide superior crosslinking reaction efficiency.
- crosslinking agent and catalyst utilized will depend upon the particular crosslinking agent utilized, the reaction conditions and the particular product application contemplated.
- the amount of catalyst preferably utilized is, of course, dependent upon the particular type and amount of crosslinking agent and the reaction conditions, especially temperature and pH. In general, based upon technical and economic considerations, castalyst levels of between 10 wt. % and 60 wt. %, based on the weight of crosslinking agent added to the cellulosic fibers, are preferred. For exemplary purposes, in the case wherein the catalyst utilized is zinc nitrate hexahydrate and the crosslinking agent is glutaldehyde, a catalyst level of 30 wt. %, based upon the amount of glutaraldehyde added, is preferred.
- aqueous portion of the cellulosic fiber slurry or crosslinking agent solution is also added as a catalyst. It is additionally desirable to adjust the aqueous portion of the cellulosic fiber slurry or crosslinking agent solution to a target pH of between pH 2 and about pH 5, more preferably between pH 2.5 and pH 3.5, during the period of contact between the crosslinking agent and the fibers.
- the cellulosic fibers should generally be dewatered and optionally dried.
- the workable and optimal consistencies will vary depending upon the type of fluffing equipment utilized.
- the cellulosic fibers are dewatered and optimally dried to a consistency of between 30% and 80%. More preferably, the fibers are dewatered and dried to a consistency level of between 40% and 60%. Drying the fibers to within these preferred ranges generally will facilitate defibration of the fibers into individualized form without excessive formation of knots associated with higher moisture levels and without high levels of fiber damage associated with lower moisture levels.
- dewatering may be accomplished by such methods as mechanically pressing, centrifuging, or air drying the pulp. Additional drying is preferably performed by such methods, known in the art as air drying or flash drying, under conditions such that the utilization of high temperature for an extended period of time is not required. Excessively high temperatsure at this state of the process may result in the premature initiation of crosslinking. Preferably, temperatures in excess of 160°C are not maintained for periods of time in excess of 2 to 3 seconds. Mechanical defibration is performed as previously described.
- the defibrated fibers are then heated to a suitable temperatsure for an effective period of time to cause the crosslinking agent to cure, i.e., to react with the cellulosic fibers.
- the rate and degree of crosslinking depends upon dryness of the fibers, temperature, amount and type of catalyst and crosslinking agent and the method utilized for heating and/or drying the fibers while crosslinking is performed.
- Crosslinking at a particular temperature will occur at a higher rate for fibers of a certain initial moisture content when accompanied by a continuous air through drying than when subjected to drying/heating in a static oven.
- Those skilled in the art will recognize that a number of temperature-time relationships exist for the curing of the crosslinking agent.
- the maximum level of crosslinking will be achieved when the fibers are essentially dry (having less than 5% moisture). Due to this absence of water, the fibers are crosslinked while in a substantially unswollen, collapsed state. Consequently, they characteristically have low fluid retention values (FRV) relative to the range expressable to this invention.
- the FRV refers to the amount of fluid calculated on a dry fiber basis, that remains absorbed by a sample of fibers that have been soaked and then centrifuged to remove interfiber fluid. (The FRV is further defined and the Procedure For Determining FRV, is described below.)
- the amount of fluid that the crosslinked fibers can absorb is dependent upon their ability to swell upon saturation or, in other words, upon their interior diameter or volume upon swelling to a maximum level.
- FRV data described herein shall be reported in terms of the water retention value (WRV) of the fibers.
- Other fluids, such as salt water and synthetic urine, may also be advantageously utilized as as fluid medium for analysis.
- the FRV of a particular fiber crosslinked by procedures wherein curing is largely dependent upon drying, such as the present process will be primarily dependent upon the crosslinking agent and the level of crosslinking.
- the WRV's of fibers crosslinked by this dry crosslinking process at crosslinking agent levels applicable to this invention are generally less than 50, greater than 25, and are preferably between 28 and 45.
- Bleached SSK fibers having between 0.5 mole % and 2.5 mole % glutaraldehyde reacted thereon, calculated on a cellulose anhydroglucose molar basis, have been observed to have WRV's respectively ranging from 40 to 28.
- Southern softwood Kraft (SSK) fibers prepared by dry crosslinking processes known prior to the present invention have levels of crosslinking higher than described herein, and have WRV's less than 25. Such fibers, as previously discussed, have been observed to be exceedingly stiff and to exhibit lower absorbent capabilities than the fibers of the present invention.
- cellulosic fibers are contacted with a solution containing a crosslinking agent as described above. Either before or after being contacted with the crosslinking agent, the fibers are provided in a sheet form.
- the solution containing the crosslinking agent also contains one of the catalysts applicable to dry crosslinking processes, also described above.
- the fibers, while in sheeted form, are dried and caused to crosslink preferably by heating the fibers to a temperatsure of between about 120°C and 160°C. Subsequent to crosslinking, the fibers are mechanically separated into substantially individual form.
- This is preferably performed by treatment with a fiber fluffing apparatus such as the one decribed in U.S. Patent No. 3,987,968 or may be performed with other methods for defibrating fibers as may be known in the ast.
- the individualized, crosslinked fibers made according to this sheet crosslinking process are treated with a sufficient amount of crosslinking agent such that between 0.5 mole % and 3.5 mole % crosslinking agent, calculated on a cellulose anhydroglucose molar basis and measured subsequent to defibration are reacted with the fibers in the form of intrafiber crosslink bonds.
- Another effect of drying and crosslinking the fibers while in sheet form is that fiber to fiber bonding restrains the fibers from twisting and curling with increased drying.
- absorbent structures made the relatively untwisted fibers made the sheet curing process described above would be expected to exhibit lower wet resiliency and lower responsiveness to wetting of a dry absorbent structure.
- crosslinking processes applicable to the present invention is nonaqueous solution cure crosslinking processes.
- the same types of fibers applicable to dry crosslinking processes may be used in the production of nonaqueous solution crosslinked fibers.
- the fibers are treated with a sufficient amount of crosslinking agent such that between 0.5 mole % and 3.5 mole % crosslinking agent subsequently react with the fibers, wherein the level of crosslinking agent reacted is calculated subsequent to said crosslinking reaction, and with an appropriate catalyst.
- the crosslinking agent is caused to react while the fibers are submerged in a solution which does not induce any substantial levels of swelling of the fibers.
- the fibers may contain up to 30% water, or be otherwise swollen in the crosslinking solution to a degree equivalent to fibers having a 30% moisture content.
- the crosslinking solution contains a nonaqueous, water-miscible, polar diluent such as, but not limited to, acetic acid, propanoic acid, or acetone.
- Preferred cataysts include mineral acids, such as sulfuric acid, and halogen acids, such as hydrochloric acid.
- Other applicable catalysts include salts of mineral acids and halogen acids, organic acids and salts thereof.
- Crosslinking solution systems applicable for use as a crosslinking medium also include those disclosed in U.S. Patent No. 4,035,147, issued to S. Sangenis, G. Guiroy, and J. Quere, on July 12, 1977.
- the crosslinking solution may include some water or other fiber swelling liquid, however, the amount of water is preferably insufficient to cause a level of swelling corresponding to that incurred by 70% consistency pulp fibers (30% aqueous moisture content). Additionally, crosslinking solution water contents less than 10% of the total volume of the solution, exclusive of the fibers are preferred. Levels of water in the crosslinking solution in excess of this amount decrease the efficiency and rate of crosslinking.
- Absorption of crosslinking agent by the fibers may be accomplished in the crosslinking solution itself or in a prior treatment state including, but not limited to, saturation of the fibers with either an aqueous or nonaqueous solution containing the crosslinking agent.
- the fibers are mechanically defibrated into individual form. This mechanical treatment may be performed by methods previously described for fluffing fibers in connection with the previously described dry crosslinking process.
- a mechanical treatment which causes the moist cellulosic fibers to assume a curled or twisted condition to a degree in excess of the amount of curl or twist, if any, of the natural state of the fibers. This can be accomplished by initially providing fibers for fluffing which are in a moist state, subjecting the fibers to a mechanical treatment such as those previously described methods for defibrating the fibers into substantially individual form, and at least partially drying the fibers.
- the relative amounts of curl and twist imparted to the fibers is in part dependent upon the moisture content of the fibers. Without limiting the scope of the invention, it is believed that the fibers naturally twist upon drying under conditions wherein fiber to fiber contact is low, i.e., when the fibers are in an individualized form. Also mechanical treatment of moist fibers initially causes the fibers to become curled. When the fibers are then dried or partially dried under substantially unrestrained conditions, they become twisted with the degree of twist being enhanced by the additional amount of curl mechanically imparted.
- the defibration fluffing steps are preferably practiced on high consistency moist pulp or pulp which has been dewatered to fiber consistency of 45% to 55% (determined prior to initialization of defibration).
- the fibers should be dried to between 0% and 30% moisture content prior to being contacted with the crosslinking solution, if the defibration step has not already provided fibers having moisture contents within that range.
- the drying step should be performed while the fibers are under substantially unrestrained conditions. That is, fiber to fiber contact should be minimized so that the twisting of the fibers inherent during drying is not inhibited. Both air drying and flash drying methods are suitable for this purpose.
- the individualized fibers are next contacted with a crosslinking solution which contains a water-miscible, nonaqueous diluent, a crosslinking agent and a catalyst.
- the crosslinking solution may contain a limited amount of water.
- the water content of the crosslinking solution should be less than 18% and is preferably less than 9%.
- a bat of fibers which have not been mechanically defibrated may also be contacted with a crosslinking solution as described above.
- crosslinking agent and acid catalyst utilized will depend upon such reaction conditions as consistency, temperature, water content in the crosslinking solution and fibers, type of crosslinking agent and diluent in the crosslinking solution, and the amount of crosslinking desired.
- the amount of crosslinking agent utilized ranges from .2 wt % to 10 wt % (based upon the total, fiber-free weight of the crosslinking solution).
- Preferred acid catalyst content is additionally dependent upon the acidity of the castalyst in the crosslinking solution.
- catalyst content including hydrochloric acid, between .3 wt % and 5 wt % (fiber-free crosslinking solution weight basis) in crosslinking solutions containing an acetic acid diluent, preferred levels of glutaraldehyde, and a limited amount of water. Slurries of fibers and crosslinking solution having fiber consistencies of less than 10 wt % are preferred for crosslinking in conjunction with the crosslinking solutions described above.
- the crosslinking reaction may be carried out at ambient temperatures or, for accelerated reaction rates, at elevated temperatsures preferably less than 40°C.
- the fibers may be contacted with, and crosslinked in, the crosslinking solution.
- the fibers are contacted with the solution which initially contains both the crosslinking agent and the acid catalyst.
- the fibers are allowed to soak in the crosslinking solution, during which time crosslinking occurs.
- the fibers are contacted with the diluent and allowed to soak prior to addition of the acid catalyst.
- the acid catalyst subsequently is added, at which time crosslinking begins.
- Other methods in addition to those described will be apparent to those skilled in the art, and are intended to be within the scope of this invention.
- the crosslinking agent and the conditions at which crosslinking is performed are chosen to facilitate intrafiber crosslinking.
- the crosslinking reaction it is advantageous for the crosslinking reaction to occur in substantial part after the crosslinking agent has had sufficient time to penetrate into the fibers.
- Reaction conditions are preferably chosen so as to avoid instantaneous crosslinking unless the crosslinking agent has already penetrated into the fibers.
- Periods of reaction during which time crosslinking is substantially completed over a period of about 30 minutes are preferred. Longer reaction periods are believed to provide minimal marginal benefit in fiber performance. However, both shorter periods, including substantially instantaneous crosslinking, and longer periods are meant to be within the scope of this invention.
- the fibers are drained and washed.
- a sufficient amount of a basic substance such as caustic is added in the washing step to neutralize any acid remaining in the pulp.
- the fibers are defluidized and dried to completion.
- the fibers are subjected to a second mechanical defibration step which causes the crosslinked fibers to curl, e.g.., fluffing by defibration, between the defluidizing and drying steps.
- the curled condition of the fibers imparts additional twist as previously described in connection with the curling treatment prior to contact with the crosslinking solution.
- the term “defibration” shall refer to any of the procedures which may be used to mechanically separate the fibers into substantially individual form, even though the fibers may already be provided in such form. "Defibration” therefore refers to the step of mechanically treating the fibers, in either individual form or in a more compacted form, to a mechanical treatment step which a) would separate the fibers into substantially individual form if they were not already in such form, and b) imparts curl and twist to the fibers upon drying.
- This second defibration treatment after the fibers have been crosslinked, has been found to increase the twisted, curled character of the pulp. This increase in the twisted, curled configuration of the fibers leads to enhanced absorbent structure resiliency and responsiveness to wetting.
- a second defibration treatment may be practiced upon any of the crosslinked fibers described herein which are in a moist condition.
- a second defibration step is possible without necessitating an additional drying step. This is due to the fact that the solution in which the fibers are crosslinked keep the fibers flexible subsequent to crosslinking even though not causing the fibers to assume an undesirable, highly swollen state.
- Fibers having higher FRV's correspond to fibers which have been crosslinked while in a more swollen state relative to fibers crosslinked while in a less swollen state, all other factors being equal.
- FRV fluid retention value
- Fibers having higher FRV's correspond to fibers which have been crosslinked while in a more swollen state relative to fibers crosslinked while in a less swollen state, all other factors being equal.
- partially swollen, crosslinked fibers with increased FRV's have greater wet resilience and responsiveness to wetting than fibers which have been crosslinked while in an unswollen state. Fibers having this increase in wet resilience and responsiveness to wetting are more readily able to expand or untwist when wetted in an attempt to return to their natural state.
- Numerical FRV data described herein in connection with partially swollen crosslinked fibers shall be water retention values (WRV). As the WRV increases beyond approximately 60, the stiffness of the fibers is believed to become insufficient to provide the wet resilience and responsiveness to wetting desired to support a saturated absorbent structure.
- the fibers are first soaked in an aqueous or other fiber swelling solution, defluidized, dried to a desired level and subsequently submersed in a water-miscible crosslinking solution containing a catalyst and crosslinking agent as previously described.
- the fibers are preferably mechanically defibrated into fluff form subsequent to defluidization and prior to additional drying, in order to obtain the benefits of enhanced twist and curl as previously described.
- Mechanical defibration practiced subsequent to contacting the fibers with the crosslinking agent is less desirable, since such defibration would volatilize the crosslinking agent thus, possibly leading to atmospheric contamination by, or high air treatment investments due to, the crosslinking agent.
- the fibers are defibrated and then presoaked in a high concentration solution of crosslinking agent and a fiber-swelling diluent, preferably water.
- the crosslinking agent concentration is sufficiently high to inhibit water-induced swelling of fibers.
- aqueous solutions of the crosslinking agents of this invention preferably, glutaraldehyde, have been found to be useful solutions for presoaking the fibers.
- the presoaked fibers are defluidized and submerged in a crosslinking solution containing a water-miscible, polar diluent, a catalyst, and a limited amount of water, and then crosslinked as previously described.
- the crosslinked fibers may be defluidized and subjected to a second mechanical defibration step prior to further processing into a sheet or absorbent structure.
- Presoaking the fibers with crosslinking agent in an aqueous solution prior to causing the crosslinking agent to react provides unexpectedly high absorbency properties for absorbent pads made from the crosslinked fibers, even relative to pads made from crosslinked fibers of the prior described nonaqueous solution cure processes wherein the fibers were not presoaked with a solution containing crosslinking agent.
- the crosslinked fibers formed as a result of the preceding dry crosslinking and nonaqueous solution crosslinking processes are the product of the present invention.
- the crosslinked fibers of the present invention may be utilized directly in the manufacture of air laid absorbent cores. Additionally, due to their stiffened and resilient character, the crosslinked fibers may be wet laid into an uncompacted, low density sheet which, when subsequently dried, is directly useful without further mechanical processing as an absorbent core.
- the crosslinked fibers may also be wet laid as compacted pulp sheets for sale or transport to distant locations.
- the individualized, crosslinked fibers may be dry laid and directly formed into absorbent structures, or wet laid and formed into absorbent structures or densified pulp sheets.
- Attempts to sheet individualized, crosslinked fibers by conventional pulp sheeting methods have been found to result in the formation of a plurality of clumps of flocculated fibers.
- a novel process for sheeting individualized, crosslinked fibers which tend to flocculate in solution has been developed, wherein a slurry containing individualized, crosslinked fibers are initially deposited on a foraminous forming wire, such as a Fourdrinier wire in a manner similar to conventional pulp sheeting processes.
- a foraminous forming wire such as a Fourdrinier wire
- these fibers are deposited on the forming wire in a plurability of clumps of fibers.
- At least one stream of fluid, preferably water is directed at the deposited, clumped fibers.
- a series of showers are directed at the fibers deposited on the forming wire, wherein successive showers have decreasing volumetric flow rates.
- the showers should be of sufficient velocity such that the impact of the fluid against the fibers acts to inhibit the formation of flocculations of the fibers and to disperse flocculations of fibers which have already formed.
- the fiber setting step is preferably performed with a cylindrical screen, such as a dandy roll, or with another apparatus analogous in function which is or may become known in the art. Once set, the fibrous sheet may then be dried and optionally compacted as desired.
- the spacing of the showers will vary depending upon the particular rate of fiber floccing, line speed of the forming wire, drainage through the forming wire, number of showers, and velocity and flow rate through the showers. Preferably, the showers are close enough together so that substantial levels of floccing are not incurred.
- the fluid showered onto the fibers also compensates for the extremely fast drainage of individualized, crosslinked fibers, by providing additional liquid medium in which the fibers may be dispersed for subsequent sheet formation.
- the plurality of showers of decreasing volumetric flow rates facilitates a systematic net increase in slurry consistency while providing a repetitive dispersive and inhibiting effect upon flocculations of the fibers. This results in the formation of a relatively smooth and even deposition of fibers which are then promptly, i.e., before reflocculation, set into sheeted form by allowing the fluid to drain and pressing the fibers against the foraminous wire.
- Pulp sheets containing stiffened, crosslinked fibers preferably contain between 5% and 90% uncrosslinked, cellulosic fibers, based upon the total dry weight of the sheet, mixed with the individualized, crosslinked fibers. It is especially preferred to include between 5% and 30% of highly refined, uncrosslinked cellulosic fibers, based upon the total dry weight of the sheet.
- Such highly refined fibers are refined or beaten to a freeness level less than 300 ml CSF, and more preferably less than 100 ml CSF.
- the uncrosslinked fibers are preferably mixed with an aqueous slurry of the individualized, crosslinked fibers. This mixture may then be formed into a densified pulp sheet for subsequent defibration and formation into a absorbent pads.
- the incorporation of the uncrosslinked fibers eases compression of the pulp sheet into a densified form, while imparting a surprisingly small loss in absorbency to the subsequently formed absorbent pads.
- the uncrosslinked fibers additionally increase the tensile strength of the pulp sheet and to absorbent pads made either from the pulp sheet or directly from the mixture of crosslinked and uncrosslinked fibers.
- the blend of crosslinked and uncrosslinked fibers may be first made into a pulp sheet and then comminuted to form an absorbent pad or formed directly utilized as an absorbent pad.
- the fibers, if comminuted, may be air-laid or wet-laid as previously described.
- Wet-laid sheets or webs made from the individualized, crosslinked fibers, or from mixtures also containing uncrosslinked fibers will preferably have basis weights of less than 800 g/m2 and densities of less than 0.60 g/cm3. Although it is not intended to limit the scope of the invention, sheets having basis weights between 300g/m2 and 600 g/m2 and densities between 0.15 g/cc and 0.3 g/cc are especially contemplated for direct application as absorbent cores in disposable articles such as diapers, tampons, and other catamenial products.
- Fibers having basis weights and densities higher than these levels are believed to be most useful for subsequent comminution and air-laying or wet-laying to form a lower density and basis weight structure which is more useful for absorbent applications.
- Other applications contemplated for the fibers of the present invention include low density tissue sheets having densities which may be less than 0.10 g/cc.
- the absorbent structures made by the process described are useful for a variety of absorbent articles including, but not limited to, tissue sheets, disposable diapers, catamenials, sanitary napkins, tampons, and bandages wherein each of said articles has an absorbent structure containing the individualized, crosslinked fibers described herein.
- tissue sheets disposable diapers, catamenials, sanitary napkins, tampons, and bandages wherein each of said articles has an absorbent structure containing the individualized, crosslinked fibers described herein.
- a disposable diaper or similar article having a liquid permeable topsheet, a liquid impermeable backsheet connected to the topsheet, and an absorbent structure containing individualized, crosslinked fibers is particularly contemplated.
- Such articles are described generally in U.S. Patent 3,860,003, issued to Kenneth B. Buell on January 14, 1975.
- a sample of 0.3 g to 0.4 g of fibers is soaked in a covered container with 100 ml distilled or deionized water at room temperature for between 15 and 20 hours.
- the soaked fibers are collected on a filter and transferred to an 80-mesh (opening 0.177mm) wire basket supported 38mm. above a 60-mesh (opening 0.25mm) screened bottom of a centrifuge tube.
- the tube is covered with a plastic cover and the sample is centrifuged at a relative centrifuge force of 1500 to 1700 gravities for 19 to 21 minutes.
- the centrifuged fibers are then removed from the basket and weighed.
- the weighed fibers are dried to a constant weight at 105°C and reweighed.
- a sample of individualized, crosslinked fibers is extracted with 0.1N HCI at 60°C for one hour.
- the extract is separated from the fibers, and the same extraction/separation procedure is then repeated for each sample an additional three times.
- the extract from each extraction is separately mixed with an aqueous solution of 2,4-dinitrophenylhydrazone (DNPH).
- DNPH 2,4-dinitrophenylhydrazone
- the reaction is allowed to proceed for 15 minutes after which a volume of chloroform is added to the mixture.
- the reaction mixture is mixed for an additional 45 minutes.
- the chloroform and aqueous layers are separated with a separatory funnel.
- the level of glutaraldehyde is determined by analyzing the chloroform layer by high pressure liquid chromatography (HPLC) for DNPH derivative.
- the chromatographic conditions for HPLC analysis utilized were - Column: C-18 reversed phase; Detector: UV at 360 mm; Mobile phase 80:20 methanol: Flow rate: 1 ml/mm.; measurement made: peak height.
- a calibration curve of peak height and glutaraldehyde content was developed by measuring the HPLC peak heights of five standard solutions having known levels of glutaraldehyde between 0 and 25 ppm.
- Each of the four chloroform phases for each fiber sample was analyzed by HPLC, the peak height measured, and the corresponding level of glutaraldehyde determined from the calibration curve.
- the glutaraldehyde concentrations for each extraction were then summed and divided by the fiber sample weight (dry fiber basis) to provide glutaraldehyde content on a fibers weight basis.
- This example discloses a preferred process for making individualized, crosslinked fibers.
- the individualized, crosslinked fibers were made by a dry crosslinking process.
- a quantity of never dried, southern softwood kraft (SSK) pulp were provided.
- the fibers had a moisture content of 62.4% (equivalent to 37.6% consistency).
- a slurry was formed by adding the fibers to a solution containing a selected amount of 50% aqueous solution of glutaraldehyde, 30% (based upon the weight of the glutaraldehyde) zinc nitrate hexahydrate, demineralized water and a sufficient amount of 1N HCl to decrease the slurry pH to 3.7.
- the fibers were soaked in the slurry for a period of 20 minutes and then dewatered to a fiber consistency of 34% to 35% by centrifuging.
- the dewatered fibers were air dried to a fiber consistency of 55% to 56% with a blow through dryer utilizing ambient temperature air.
- the air dried fibers were defibrated utilizing a three-stage fluffing device as described in U.S. Patent 3,987,968.
- the defibrated fibers were placed in trays and cured at 145°C in an essentially static drying oven for a period of 45 minutes. Crosslinking was completed during the period in the oven.
- the crosslinked, individualized fibers were placed on a mesh screen and washed with 20°C water, soaked at 1% consistency for one (1) hour in 60°C water, screened, washed with 20°C water for a second time, centrifuged to 60% fiber consistency, defibrated in a three stage fluffer as previously described, and dried to completion in a static drying oven at 105°C for four (4) hours.
- the fibers had between 0 mole % and 3.3 mole % glutaraldehyde reacted in the form of crosslink bonds.
- the corresponding WRV's varied between 51% and 28%.
- the purpose of this example is to exemplify a process for making wet-laid sheets containing individualized, crosslinked fibers.
- a 0.55% consistency slurry of a blend of fibers containing 90% individualized, crosslinked fibers made according to the crosslinking process described in Example 1 and 10% conventional, uncrosslinked fibers having a freeness of less than 100 CSF were deposited in flocculated, clumped fibers on a conventional 84-mesh Fourdinier forming wire.
- the papermaking flow rate out of the headbox was 430 kg/min.
- a series of five streams of water of sequentially decreasing flow rates were directed upon the fibers.
- the five streams of water provided a cumulative flow ratio 85 kg water/kg bone dry (b.d.) fiber.
- the showers were all spaced within an approximately 1 meter long area parallel to the direction of travel of the forming wire.
- Each stream of water was showered onto the fibers through a linear series of 1/8" (3.2 mm) ID circular aperatures spaced 1/2" (12.7 mm) apart and extending across the width of the forming wire.
- the aproximate percentage of flow, based upon the total flow rate, and velocity of flow through the aperatures for each of the showers was as follows: shower 1-37% of total flow, 170 m/min.; shower 2-36% of total flow, 165 m/min.; shower 3-13% of total flow, 61 m/min.; shower 4-9% of total flow, 41 m/min.; shower 5-5% of total flow, 20 m/min.
- the fibers were set by treatment with a cylindrical, screened roll known in the art as a Dandy Roll.
- the Dandy Roll pressed the fibers, which at the time of setting were in a high consistency slurry form, against the forming wire to set the fibers to form a wet sheet.
- the sheet was similar in appearance to conventional fibrous pulp sheets.
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Biochemistry (AREA)
- Absorbent Articles And Supports Therefor (AREA)
- Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
- Paper (AREA)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US87967386A | 1986-06-27 | 1986-06-27 | |
US879673 | 1993-05-06 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0251673A1 true EP0251673A1 (de) | 1988-01-07 |
EP0251673B1 EP0251673B1 (de) | 1992-02-26 |
Family
ID=25374645
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP87305611A Expired - Lifetime EP0251673B1 (de) | 1986-06-27 | 1987-06-24 | Nassverfahren zur Herstellung einer Struktur aus einzeln versteiften Fasern |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0251673B1 (de) |
AU (1) | AU612322B2 (de) |
CA (1) | CA1306894C (de) |
DE (1) | DE3776820D1 (de) |
FI (1) | FI90678C (de) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5124197A (en) * | 1989-07-28 | 1992-06-23 | Kimberly-Clark Corporation | Inflated cellulose fiber web possessing improved vertical wicking properties |
WO2000065146A1 (en) * | 1999-04-26 | 2000-11-02 | Weyerhaeuser Company | Crosslinkable cellulosic fibrous product |
WO2010059888A2 (en) * | 2008-11-20 | 2010-05-27 | Nalco Company | Application of retention, drainage and formation (rdf) chemical aids after a headbox of a papermaking process |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4822453A (en) * | 1986-06-27 | 1989-04-18 | The Procter & Gamble Cellulose Company | Absorbent structure containing individualized, crosslinked fibers |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB149416A (en) * | 1919-05-10 | 1920-08-10 | Leon Thiry | Improvements in machines for the manufacture of paper, cardboard and the like |
US3455778A (en) * | 1965-12-13 | 1969-07-15 | Kimberly Clark Co | Creped tissue formed from stiff crosslinked fibers and refined papermaking fibers |
US3470064A (en) * | 1965-04-06 | 1969-09-30 | Feldmuehle Ag | Spray receiving device for a papermaking machine |
DE3217805A1 (de) * | 1982-05-12 | 1983-11-17 | Metallgießerei und Armaturenfabrik Heinrich Stamm, 6520 Worms | Formationsspritzrohr zur erzeugung von turbulenzenergie in einer suspension bei der karton- oder papierherstellung, sowie verfahren zur herstellung eines solchen formationsspritzrohres |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3224926A (en) * | 1962-06-22 | 1965-12-21 | Kimberly Clark Co | Method of forming cross-linked cellulosic fibers and product thereof |
IL82913A (en) * | 1986-06-27 | 1990-11-05 | Buckeye Cellulose Corp | Twisted,stiffened cellulosic fibers and absorbent structures made therefrom |
US4822453A (en) * | 1986-06-27 | 1989-04-18 | The Procter & Gamble Cellulose Company | Absorbent structure containing individualized, crosslinked fibers |
-
1987
- 1987-06-16 CA CA000539775A patent/CA1306894C/en not_active Expired - Lifetime
- 1987-06-24 DE DE8787305611T patent/DE3776820D1/de not_active Expired - Lifetime
- 1987-06-24 EP EP87305611A patent/EP0251673B1/de not_active Expired - Lifetime
- 1987-06-26 AU AU74760/87A patent/AU612322B2/en not_active Ceased
- 1987-06-26 FI FI872843A patent/FI90678C/fi active IP Right Grant
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB149416A (en) * | 1919-05-10 | 1920-08-10 | Leon Thiry | Improvements in machines for the manufacture of paper, cardboard and the like |
US3470064A (en) * | 1965-04-06 | 1969-09-30 | Feldmuehle Ag | Spray receiving device for a papermaking machine |
US3455778A (en) * | 1965-12-13 | 1969-07-15 | Kimberly Clark Co | Creped tissue formed from stiff crosslinked fibers and refined papermaking fibers |
DE3217805A1 (de) * | 1982-05-12 | 1983-11-17 | Metallgießerei und Armaturenfabrik Heinrich Stamm, 6520 Worms | Formationsspritzrohr zur erzeugung von turbulenzenergie in einer suspension bei der karton- oder papierherstellung, sowie verfahren zur herstellung eines solchen formationsspritzrohres |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5124197A (en) * | 1989-07-28 | 1992-06-23 | Kimberly-Clark Corporation | Inflated cellulose fiber web possessing improved vertical wicking properties |
WO2000065146A1 (en) * | 1999-04-26 | 2000-11-02 | Weyerhaeuser Company | Crosslinkable cellulosic fibrous product |
US6572919B2 (en) | 1999-04-26 | 2003-06-03 | Weyerhaeuser Company | Crosslinkable cellulosic fibrous product |
WO2010059888A2 (en) * | 2008-11-20 | 2010-05-27 | Nalco Company | Application of retention, drainage and formation (rdf) chemical aids after a headbox of a papermaking process |
WO2010059888A3 (en) * | 2008-11-20 | 2011-11-03 | Nalco Company | Application of retention, drainage and formation (rdf) chemical aids after a headbox of a papermaking process |
Also Published As
Publication number | Publication date |
---|---|
FI90678C (fi) | 1994-03-10 |
AU7476087A (en) | 1988-02-04 |
DE3776820D1 (de) | 1992-04-02 |
FI90678B (fi) | 1993-11-30 |
EP0251673B1 (de) | 1992-02-26 |
FI872843A0 (fi) | 1987-06-26 |
FI872843A (fi) | 1987-12-28 |
AU612322B2 (en) | 1991-07-11 |
CA1306894C (en) | 1992-09-01 |
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