ABSORBENTS CONTAINING STIFFENED FIBERS AND SUPERABSORBENT MATERIALS

Abstract: Absorbent structures having a fluid acquisition/distribution layer (110) with an average dry density of less than about 0.30 g/cc, an average density upon wetting with 1.0 % NaCl aqueous solution of less than about 0.20 g/cc, and an average dry basis weight from about 0.001 to about 0.10 g/cm<2>; and a fluid storage layer (108) positioned beneath the acquisition/distribution layer (110) comprising at least about 15 % superabsorbent material. The fluid acquisition/distribution layer (110) comprises from about 50 % to 100 % chemically stiffened cellulosic fibers and from 0 % to about 50 % binding means.

Description: P -1- ABSORBEOTS CONTAINI G, STIFFENED FIBERS AND SUPERABSORBENT MATERIALS FIELD OF-THE INVENTION This invention relates to absorbent structures using both cellulosic fiber material and superabsorbent material. The absorbent structures can be used in a variety of absorbent articles such as disposable diapers, adult incontinence pads and briefs and the like which are required to handle relatively larg amounts of discharged body fluids, especially repeated discharges of relatively large amounts of fluid in relatively short amount of time. BACKGROUND OF THE INVENTION Absorbent webs which comprise entangled masses of fibers, i.e., fibrous webs, are well known in the art. Such webs ca -M ibe liquids, such as discharged body fluids, both by a absorption mechanism wherein fluid is taken up by the fibe material itself and by a wicking mechanism wherein fluid i acquired by, distributed through and stored in the capillar interstices between fibers. One means for improving th absorbency characteristics of such fibrous web structures is t incorporate therein superabsorbent material, such as as polymeri gelling material (also referred ^ to as hydrogel-forming materia superabsorbent polymers, etc.) which imbibe fluid. Th superabsorbent material serves to retain fluid such as discharge body liquids. An absorbent structure of this type wherei hydrogen-formin materials in particu ate form are incorporate into fibrous webs is disclosed in Weisman and Goldman; U.S. Patent 4,610,678; Issued September 9, 1986. The improvement in absorbency provided by incorporation o absorbent gelling materials has permitted the realization o 5 absorbent articles such as diapers which employ relatively thin absorbent cores and which are, therefore, relatively thin products. Thinner diapers are less bulky to wear and fit better under clothing. They are also more compact in the package, making the diapers easier for the consumer to carry and store. 10 Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor. One such absorbent core configuration which is useful for use as the absorbent structure in relatively thin absorbent articles is disclosed in U.S. Patent No. 4,765,780, issued August 23, 1988 15 (Angstadt). This patent discloses absorbent articles, such as diapers, which have a two layer absorbent core configuration wherein the core comprises an upper primary layer and a lower dusting layer. The primary layer is an airlaid web of hydrophilic fiber material with a -substantial amount of absorbent gelling 20 material admixed therewith. The dusting layer comprises hydrophilic fiber material and, preferably, contains no absorbent gelling material. Another absorbent core configuration is disclosed in eisman/Houghton/Gellert, U.S. Patent No. 4,673,402, issued June 25 If - 1987. This patent discloses absorbent articles having a dual layer absorbent core. In the dual layer configuration, the core comprises an upper primary layer which is an airlaid web of hydrophilic fiber material, optionally with a small amount of polymeric gelling agent particles admixed therewith. The core 30 also comprises an underlying insert layer which is an airlaid mixture of hydrophilic fiber material and a substantial amount of polymeric gelling agent particles. This insert layer is generally positioned toward the front of the absorbent article such that more than half of the polymeric gelling agent material in the 35. article is found, in. the front-half thereof. Absorbent articles having the particular dual layer configuration.of the '402 patent can be prepared in the form of especially thin, highly effective low leakage diaper products. Notwithstanding the existence of absorbent cores as describe above, there remains a need to provide absorbent cores wit improved effective absorbent capacity. One way to theoreticall do this would be to increase the level of polymeric gellin material in the absorbent core. Unfortunately, high levels o polymeric gelling material, (especially levels in excess of abou 15%) in fibrous webs typically used in absorbent cores tends t induce a phenomena referred to as gel-blocking. Gel-blockin occurs when the polymeric gelling material located in region first contacted with fluid increase in volume as a consequence o imbibing the fluid and forming the hydrogel. When polymeri gelling material concentration is too high, the hydrogel can bloc additional fluid from reaching other regions of the core havin unused absorbent capacity. The occurrence of gel blocking ca lead to leakage during usage of the absorbent article. Polymeric gelling materials have been developed which ca exhibit a reduced tendency to result in gel blocking. Suc materials are described in U.S. Patent RE 32,649, April 19, 1988 Brandt/Goldman/Inglin. However, these improved polymeric gellin materials, and other superabsorbent materials, are subject t performance limitations of the web of cellulosic fibers in whic particles of gelling material are distributed. In particular -ttpen-initial wetting, the cellulosic fibers become highly flexibl and the web tends to collapse to a higher density and consequently, exhibits smaller average pore size. Whereas, por size becomes smaller than the pore size in regions of the web no yet wetted, a capillary gradient is created which oppose efficient transport of.fluids to the dry areas of the absorben article. Another reason why many absorbent articles such as diaper are subject to leakage is inability to absorb second an subsequent discharges of fluid even if the first fluid discharg has been effectively absorbed. ' Leakage due to second an subsequent discharges is.especially prevalent during the night when Λser.S:-.commonly experiepce-irmultiple^-dischargesi efore bein attended to. One reason for the inability of many absorbent articles to adequately handle multiple discharges of fluid, in addition to the reasons discussed above, 1s the inability of the absorbent core to transport discharged fluid away from the region of discharge once the absorbent capacity of that region has been reached. After a discharge of fluid occurs, the fluid tends to remain situated in the region proximate to the discharge. The occurrence of successive voiding of fluid creates a driving force to laterally transport the previous fluid and newly discharged fluid. However, actual performance of the absorbent article is limited by the ability to have the fluid transported to the farther reaches of the core. In this regard, even in the absence of polymeric gelling material, the overall absorbent capacity o conventional absorbent diaper cores is generally incompletely utilized prior to failure, i.e., leakage, of the absorbent article. Yet another reason for leakage in conventional absorbent articles is the propensity of the cellulosic fibers conventionally utilized for fluid acquisition and distribution to collapse upon wetting, thus impairing permeability of the structures. It is an object of this invention to provide superabsorbent- containing absorbent structures which can circumvent the problems of gel blocking and wet collapse and which can utilize an increased proportion of their absorbent capacity. It is a further object of this invention to provide superabsorbent-containing absorbent structures which can acquire fluid rapidly in the region of discharge and transport the fluid over relatively large proportion of the absorbent structure storage area and, additionally, be capable of effectively acquiring and distributing discharged bodily fluid from second or other successive voiding. It is yet another object of this invention to provide absorbent structures which are capable of meeting the objects described above which are of a relatively thin design. One absorbent- structure which has been suggested is described in U.S. Patent No. 4,935,022, issued June 19, 1990 to Glen R. Lash and ÷becmard <β. - Thompson. This -^patent discloses disposable absorbent articles comprising a layered absorbent core positione between a backsheet and a topsheet, wherein the absorbent cor comprises an upper layer of stiffened, twisted, curled cellulos fibers and requires from about 3% to 15%, by weight, of larg particle absorbent gelling material and a lower layer o stiffened, twisted, curled cellulose fibers and from about 15% t 60%, by weight, of absorbent gelling material. The upper laye serves the principal purpose of acquisition and distribution o bodily fluid discharges. The stiffened, twisted, curled fiber are highly beneficial in this regard. The lower layer, which i necessarily smaller than the upper layer, is principally for flui storage. Another absorbent structure which has been proposed i described in U.S. Patent 4,798,603, S. C. Meyer et al., issue January 17, 1989, titled "Absorbent Article Having a Hydrophobi Transport Layer." As suggested by the title, this paten describes an absorbent article with a hydrophobic transport layer, made from known hydrophobic synthetic fibers. The transport laye is positioned between a topsheet and an absorbent body. Th absorbent body is necessarily more hydrophilic than the transpor layer. The purpose of the transport layer is to act as a insulating layer between the topsheet and the absorbent body, t reduce skin wetness. Regardless of whether the structure described therein meet this objective, the hydrophobic nature o tfee transport layer of U.S. Patent 4,798,603 would be expected t have limited fluid acquisition and fluid transport propertie due, at least in part, to the hydrophobicity of the layer. Thi would be particularly so for second and successive flui discharges after which any optional surfactants have been washe away. Notwithstanding the existence of absorbent articles of th type described above, there is a need to identify further improve configurations for absorbent articles which provide improved flui distribution and acquisition performance, especially with respec to successive fluid discharges. Accordingly, the present invention provides improve absorbent structures, and[elements /or use therein, as well a absorbent articles utilizing such structures, utilizing a multipl layer absorbent core that effectively and efficiently acquires th wearer's discharged body fluids upon initial and successiv discharges, transports acquired fluid, from both initial an successive discharges over a relatively large proportion of th absorbent structure surface area, and stores such discharge fluids. SUMMARY OF THE INVENTION The present invention provides an absorbent structure, which is particularly useful as the absorbent core in disposable absorbent articles such as diapers and incontinence briefs, and which comprises: a) a fluid acquisition/distribution layer having an average dry density of less than about 0.30 g/cc, an average density upon wetting to saturation with 1% NaCl aqueous solution, on a dry weight basis, of less than about 0.20 g/cc, and an average dry basis weight of from about 0.001 to about 0.10 g/cm2; and a fluid storage layer, positioned beneath the acquisition/distribution layer. The acquisition/distribution layer comprises a web of from about 50% to 100%, by weight, chemically stiffened cellulosic fibers and from 0% to about 50%, by weight, of a binding means. The binding means can be used to increase physical integrity of the web to facilitate processing and/or improve in-use performance, and/or increase effective average inter-fiber pore size of the web. As used herein, binding means refers to means incorporated integral to the layer o -#ttf#ened fibers, such as (but not limited to) nonstiffened cellulosic materials, synthetic fibers, chemical additives, and thermoplastic polymers. Tissue envelopes and other scrim external to the acquisition/distribution layer can also be used to enhance physical integrity in combination with, or in place of, said binding means. The storage layer comprises at least about 15%, by weight, of superabsorbent material and from 0% to about 85% of a carrier means for the superabsorbent material. The fluid acquisition/distribution layer should contain no more than about 6.0% of superabsorbent material. Preferably, the acquisition/distribution layer will be substantially free of superabsorbent material. For purposes herein, "substantially free" of superabsorbent material means less than about 2.0%, preferably less . than about 1.0%, more preferably zero o essentially zero percent superabsorbent material. As used herein, "essentially zero" percent superabsorbent material means lo amounts (less than about 0.5%) of superabsorbent material presen in the acquisition/distribution layer incidental to the contact o close proximity of the superabsorbent-containing storage laye with the acquisition/distribution layer. The fluid acquisition/distribution layer has a top surfac area which is at least.15% of the top surface area of the flui storage layer, but which is smaller than the top surface area o the fluid storage layer. The acquisition/distribution layer i preferably positioned relative to the fluid storage such that i the unfolded planar configuration of the article none of it surface area extends beyond the boundaries of the top surface are of the fluid storage layer. More " preferably th acquisition/distribution layer has a top surface area which i from about 15% to about 95%, most preferably from about 25% t about 90%, of the top surface area of the fluid storage layer. The absorbent structure can be advantageously utilized as th absorbent core in absorbent articles, e.g., disposable diapers an incontinence briefs, which also comprise a fluid pervious topshee and a fluid impervious backsheet affixed to the topsheet, wherei the absorbent core is disposed therebetween. The absorbent cor i& positioned such that the acquisition/distribution layer i located between the topsheet and the storage layer, and th storage layer is located between the acquisition/distributio layer and the backsheet. - The superabsorbent material used in the storage layer has a Absorbent Capacity of ajb least about 10 grams of Synthetic Urin (1.0% NaCl aqueous (distilled water) solution) per gram o superabsorbent material, measured aςcording to the test procedur hereinafter described. Suitable superabsorbent materia categories include polymeric absorbent gelling materials typically utilized in the form of discrete particles, an superabsorbent fibers, such as acrylate grafted fibers an superabsorbent modified cellulosic fibers. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 represents a perspective view of a diaper with an absorbent core having the multiple layer configuration of the present invention. The absorbent core shown has a rectangular-shaped acquisition/distribution layer and an hour glass-shaped storage layer. Figure 2 represents a perspective view of a diaper structure similar to Figure 1, but wherein the storage layer has a modified hour-glass shape. Figure 3 represents a direct view of an absorbent core useful for diaper applications, such as in Figures 1 and 2, wherein the core has a modified hour glass-shaped storage core and a similar hour glass-shaped acquisition/distribution layer. DETAILED DESCRIPTION OF THE INVENTION The absorbent structures of the present invention can be utilized in disposable products which are capable of absorbing significant quantities of body fluids, such as urine and water in body wastes. Such articles may be prepared in the form of disposable diapers, adult incontinence briefs, adult incontinence pads and the like. The absorbent articles herein generally comprise three basic structural components. One such component is a liquid impervious backsheet. On top of this backsheet is disposed an absorbent core which itself comprises two distinct layers, and which includes a sαperabsorbent material in one of the layers. " On top of this absorbent core and joined to the backsheet is a water pervious topsheet. The topsheet is the element of the article which is placed next to the skin of the wearer. As used herein, the term "joined" encompasses configurations whereby the topsheet is directly joined to the backsheet by affixing the topsheet directly to the backsheet, and configurations whereby the topsheet is indirectly joined to the backsheet by affixing the topsheet to intermediate,members which in turn are affixed to the backsheet. Preferably he topsheet and backsheet rare joined directly at the diaper.periphery by adhesive or other attachment means known in the art. Especially preferred absorbent articles of this invention ar disposable diapers. Articles in the form of disposable diaper are fully described in Duncan and Baker, U.S. Patent Re 26,151 Issued January 31, 1967; Duncan, U.S. Patent 3,592,194, Issue July 13, 1971; Duncan and Gellert, U.S. Patent 3,489,148, Issue January 13, 1970; and Buell, U.S. Patent 3,860,003, Issued Janua 14, 1975; which patents are incorporated herein by reference. preferred disposable diaper for the purpose of this inventio comprises an absorbent core; a topsheet superposed or co-extensiv with one face of the core, and a liquid impervious backshee superposed or co-extensive with the face of the core opposite th face covered by the topsheet. Both the backsheet and the topshee most preferably have a width greater than that of the core there providing side marginal portions of the backsheet and topshee which extend beyond the core. Frequently the backsheet and th topsheet will be fused together in these side marginal portions The diaper is preferably constructed in a shaped configurati such as, but not limited to, an hourglass shape. The backsheet of the articles herein can be constructed, f example, from a thin, plastic film of polyethylene, polypropylen or other flexible moisture impeding material which i substantially water impervious. Polyethylene, having an emboss caliper of approximately 1.5 mils, is especially preferred. The topsheet of the article herein can be made in part HffiipTetely of synthetic fibers or films comprising such material as polyester, polyolefin, rayon, or the like, or of natural fibe such as cotton. In nonwoven topsheets, the fibers are typicall bound together by a thermal binding procedure or by a polymeri binder such as polyacrylate. This sheet is substantially poro and permits a fluid to " readily pass therethrough into t underlying absorbent core." Another suitable type of topsheet comprises the topshee formed from liquid impervious polymeric material such as polyol fins. Such topsheets can have tapered capillaries of certai diameter and taper positioned in the topsheet to permit flow discharged fluid through the topsheet into the underlyi absorbent core Of tfie^rrticle. PCI7US91/00169 - 10 - The topsheets used in the articles of the present invention should be relatively hydrophobic in comparison with the absorbent core of said articles. Topsheet construction is generally disclosed in Davidson, U.S. Patent 2,905,176, Issued September 22, 1959; Del Guercio, U.S. Patent 3,063,452, Issued November 13, 1962; Holliday, U.S. Patent 3,113,570, Issued December 10, 1963, and Thompson, U.S. Patent 3,929,135; Issued December 30, 1975; which patents are incorporated herein by reference. Preferred topsheets are constructed from polyester, rayon, rayon/polyester blends, polyethylene or polypropylene. The topsheet can be treated with surfactant to make it more wettable and therefore relatively less hydrophobic, to thereby increase fluid flow through it at least upon initial wetting. However, the topsheet should still be more hydrophobic than the absorbent article element which receives fluids after passing through the topsheet. An absorbent core, which is preferably flexible, is positioned between the elongated backsheet and the topsheet to form the absorbent articles herein. This core essentially comprises both an upper fluid acquisition/distribution layer and a lower fluid storage layer. It should be understood that for purposes of this invention these two types of layers refer merely to the upper and lower zones of the absorbent core and are not necessarily limited to single layers or sheets of material. Thus both the fluid acquisition/distribution layer and the fluid storage layer may actually comprise laminates or-combinations of several sheets or webs of the requisite type of materials as hereinafter described. The storage layer can comprise a single sheet of essentially 100% superabsorbent material, as will be hereinafter described. As used herein, the term "layer" includes the terms "layers" and "layered." For purposes of this invention, it should also be understood that the term "upper" refers to the layer of the absorbent core which is nearest to and faces the article topsheet; conversely,, the term "lower" refers to the layer of the absorbent core whic , is nearest to and faces the article backsheet, Optionally, a fluid, pervious sheet (e.g., a tissue sheet) or other scrim is positioned, between the acquisition/distribution layer and the storage layer to increase integrity of t acquisition/distribution layer during processing and/or use. Su sheet or scrim can envelope all or part acquisition/distribution layer, or simply be positioned described above without necessarily enveloping t acquisition/distribution layer. Also, optionally, t superabsorbent material-containing storage layer can be envelop with a fluid pervious sheet, such as a tissue paper sheet, obviate user concerns with loose superabsorbent material. Acouisition/Distribution Laver One essential element of the absorbent structures hereof i an upper fluid acquisition/distribution layer which comprises combination of a hydrophilic fibrous material, described mo fully hereinafter. This fluid acquisition/distribution lay serves to quickly collect and temporarily hold discharged bo fluid. A portion of discharged fluid may, depending upon t wearer's position, permeate the acquisition/distribution layer a be absorbed by the storage layer r in the area proximate to t discharge. However, since fluid is typically discharged gushes, the storage, layer in such area may not absorb the fluid quickly as it is discharged. Therefore, the upp acquisition/distribution layer hereof also facilitates transpo of the fluid from the point of initial fluid contact to oth parts of the acquisition/distribution layer. In the context t*e- present invention, it should be noted that the term "flui means "liquid." As previously noted, the fluid acquisition/distribution lay 1s a web comprising stiffened cellulosic fibers. The acquisiti layer comprises from about 50% to 100% of these fibers and from to about 50% of a binding means. Suitable binding means a discussed below. The fluid distribution function of the acquisition/distrib tion layer is of particular importance in order to more ful utilize the capacit of the storage section. The presence substantial amounts of superabsorbent materials in t acquisition/distribution layer which swell upon contact wi fluids is believed to adversely affect this function of t acquisition/distribution layer. A variety of other factors relating to the fluid acqui sition/distribution layer of the absorbent structures herein c be of importance in determining the effectiveness of the resulti absorbent articles. These include shape, basis weight, densit permeability, capillarity and wicking ability, the type a structural integrity, and character of the fibrous materi utilized. As indicated, the acquisition/distribution layer of t core is preferably elongated. For purposes of this inventio this means that the acquisition/distribution layer, like t storage layer, is elongated if it is of unequal length and wid in the unfolded, flat configuration. The acquisition/distributi layer in the unfolded configuration can be of any desired shap for example, rectangular, trapezoidal, oval, oblong hourglass-shaped. The shape of the upper fluid acquisi tion/distribution layer of the core can, but need not necessaril correspond to the general shape of the storage layer. The t surface area of the acquisition/distribution layer will preferabl range from about 25% to about 90% of the top surface area of t storage layer, and also preferably will not extend beyond the ed of the storage layer at any outer boundary. T acquisition/distribution layer will typically have top surfa area less than about 80% of that of the storage layer. Preferably, there is a margin from the edge of t acquisition/distribution layer to the edge of the storage layer at least about 0.5 cm, preferably at least about 1.25 cm, in th regions proximate to where fluid is discharged during use. I diapers, this would correspond, for example, to the crotch regio 115 of Figure 2, particularly at the narrowest part of the stora core 106 in the central region 115. Additionally, especially fo absorbent articles to be worn by males, such a margin i maintained in the front waist region, exemplified as 112 in Figu 2, which area is to be worn on the front of the wearer. The fluid acquisition/distribution layer will generally hav an -average dry density of less than about 0.30 g/cm 3 , measure prior to- use, and an average density upon-wetting to saturatio with Synthetic Urine (1.0% NaCl aqueous solution, with distille water), on a dry weight basis, of less than about 0.20 g/cm 3 preferably less than about 0.15 g/cm 3 . Also, preferably, th average dry density and density upon wetting to saturation ar between about 0.02 g/cm 3 and 0.20 g/cm 3 , more preferably betwee about 0.02 g/cm 3 and about 0.15 g/cm 3 . The average dry basi weight of the acquisition/distribution layer of the absorbent cor will typically range from about 0.001 to about 0.10 g/cm 2 preferably from about 0.01 to about 0.08 g/cm2, more preferabl from about 0.015 to, about 0.04 g/cm 2 . Unless specificall indicated, all basis weights and density values are calculated o a dry basis (at equilibrium moisture levels no greater than abou 6%). Density and basis weight can be substantially unifor although nbnuniform density and/or basis weight, and densit and/or basis weight gradients, are meant to be encompassed herein Thus, the acquisition/distribution layer can contain regions o relatively higher or relatively lower density and basis weight preferably not exceeding the foregoing ranges. Average dr density and average dry density upon wetting to saturation wit Synthetic Urine (1.0% NaCl aqueous solution, with distilled water values are.calculated from basis weight of the dry layer and laye caliper. Dry caliper and caliper upon wetting to saturation ar measured under a confining pressure of 0.2 psi (1.43 kPa) Average density upon wetting to saturation is calculated from th dsy basis weight and saturation caliper. The saturation calipe is measured after the .layer is saturated (under unrestraine conditions) with the 1.0% NaCl aqueous solution and allowed t equilibrate. The acquisition/distribution layer of the absorben structures herein essentially comprises a web of hydrophili chemically stiffened cellulosic fibers. These cellulosic fiber are typically wood pulp fibers which have been stiffened with a intrafiber chemical stiffening agent. The fluid acquisition/distribution layer should contain n more than.about 6.0% of superabsorbent material. Preferably, th acquisition/distribution layer will be substantially free o superabsorbent material.. For purposes herein., "substantiall free" of superabsorbent material means less than about 2.0% preferably less than about 1.0%, more preferably zero o essentially zero percent superabsorbent material. As used herein "essentially zero" percent superabsorbent material means lo amounts (less than about 0.5%) of superabsorbent material presen in the acquisition/distribution layer incidental to the contact o close proximity of the superabsorbent-containing storage laye with the acquisition/distribution layer. If present in the acquisition/distribution layer, especiall if present in amounts greater than about 2.0%, superabsorben material in the form of particles of absorbent gelling materia may be of relatively large diameter (e.g., from about 400 to abou 700 microns in mass median particle size). Superabsorben particles having a mass median particle size less than 400 micron may also be employed. As discussed above, the articles of the present inventio employ chemically stiffened fibers. As used herein, the ter "chemically stiffened fibers" means any fibers which have bee stiffened by chemical means to increase stiffness of the fiber under both dry and aqueous conditions. Such means include th addition of chemical stiffening agents which, for example, coa and/or impregnate the fibers. Such means also include th stiffening of the fibers by altering the chemical structure of th fibers themselves, e.g., by cross-linking polymer chains. For exemplary purposes, polymeric stiffening agents which ca coat or impregnate cellulosic fibers include: cationic modifie starch having nitrogen-containing groups (e.g., amino groups) suc as those available from National Starch and Chemical Corp., Bridgewater, NJ, USA; latex; wet strength resins such a polyamide-epichlorohydrin resin (e.g., KymeneTM 557H, Hercules, Inc. Wilmington, Delaware, USA), polyacrylamide resin (described, for example, in U.S. Patent 3,556,932 issued January 19, 1971 t Coscia, et al.; also, for example, the commercially availabl polyacrylamide marketed by American Cyanamid Co., Stanford, CT, USA, under the tradename Parez™ 631 NC); urea formaldehyde an melamine formaldehydg resins,, .and polyethylenimine resins. general dissertation on wat strength resits.utilized in the pape art, and generally applicable herein, can be found in TAPP monograph series No. 29. "Wet Strength in Paper and Paperboard" Technical Association of the' Pulp and Paper Industry (New Yor 1965). The fibers utilised in the structures herein can also stiffened by means of chemical reaction. For example,crosslinki agents can be applied to the fibers which, subsequent application, are caused to chemically form intra-fiber crossli bonds. These .crosslink bonds can increase stiffness of t fibers. Whereas the utilization of intrafiber crosslink bonds chemically stiffen the fibers ii preferred, it is not meant exclude other types of reactions for chemical stiffening of t fibers. Fibers stiffened by crosslink ' bonds in individualized (i.e. fluffed) form are disclosed, for example, in Bernardin, U. Patent 3,224,926, Issued December 21, 1965; Chung, U.S. Pate 3,440,135, Issued April 22, 1969; Chatterjee, U.S. Pate 3,932,209, Issued January 13, 1976 and Sangenis et al., U. Patent 4,035,147, Issued July 12, 1977. More preferred fibers a disclosed in.Oean et al., U.S. Patent 4,822,453, issued April 1 1989, Dean et al., U.S. Patent 4,888,093, issued December 1 1989, and Moore et al., U.S. Patent 4,898,642, issued February 1990. All of these patents are incorporated herein by referenc In addition to being hydrophilic, these stiffened fibers remai stiff even upon wetting; thus webs made from them do not collaps » as dδ webs made from conventional unstiffened fibers when we This provides improved ability to acquire and distribute fluids second and subsequent discharges. In the more preferred stiffened fibers, chemical processi includes intrafiber crosslinking with crosslinking agents whil such fibers are in a, relatively dehydrated, defibrated (i. individualized), twisted, curled condition. Suitable chemic stiffening agents include monomeric crosslinking agents includin but not limited to, C2-C8 dialdehydes and C2-C8 monoaldehyd having .an acid functionality can be employed to form t crosslinking solution. These .compounds are capable of reacti with..at least. wo hydroxyl groups in a .single cellulose chain on. proxisately located ceHulose chains in a single fiber. Su crosslinking agents contemplated for use in preparing the stiffened cellulose fibers include, but are not liaited to, glutaraldehyde, glyoxal, foπ ldehyde, and glyoxylic acid. Other suitable stiffening agents are polycarboxylates, such as citric acid. The polycarboxylic stiffening agents and a process for making stiffened fibers froα thee are described in U.S. Serial No. 596,606, filed October 17, 1990, incorporated by reference herein. The effect of crosslinking under these conditions is to fora fibers which are stiffened and which tend to retain their twisted, curled configuration during use in the absorbent articles herein. Such fibers, and processes for Baking thea are described in the above incorporated patents. The preferred stiffened fibers are twisted and curled can be quantified by referencing both a fiber "twist count" and a fiber "curl factor". As used herein, the tera "twist count" refers to the number of twist nodes present in a certain length of fiber. Twist count is utilized as a aeans of βeasuring the degree to which a fiber is rotated about its longitudinal axis. The tens "twist node" refers to a substantially axial rotation of 180* about the longitudinal axis of the fiber, wherein a portion of the fiber (i.e., the "node") appears dark relative to the rest of the fiber when viewed under a aicroscope with transmitted light. The twist node appears dark at locations wherein the transmitted light passes through an additional fiber wall due to the aforementioned rotation. The distance between nodes corresponds to an axial rotation of 180 * . The nuπber of twist nodes in a certain length of fibers (i.e., the twist count) is directly indicative of the degree of fiber twist, which is a physical parameter of the fiber. The procedures for determining twist nodes and total twist count are described in the hereinbefore referenced U.S. Patent 4,898,642. The preferred stiffened cellulose fibers will have an average dry fiber twist count of at least about 2.7, preferably at least about 4.5 twist, diodes per aillineter. furthermore, the average wet fiber twist count of these fibers should preferabl be at least- bout 4.8, preferably at least about 3.0, and should also preferably be at least about 0.5 twist nodes per ailliueter less than the average dry fiber twist count. Even more preferably, t average dry fiber twist count should be at least about 5.5 twis nodes per millimeter, and the average wet fiber twist count shoul be at least about 4.0 twist nodes per millimeter and should als be at least 1.0 twist nodes per millimeter less than its avera dry fiber twist count. Most preferably, the average dry fib twist count should be at least about 6.5 twist nodes p millimeter, and the average wet fiber twist count should be least about 5.0 twist nodes per millimeter and should also be least 1.0 twist nodes per millimeter less than the average d fiber twist count. In addition to being twisted, the preferred fibers used i the acquisition/distribution layer of the absorbent structure a also curled. Fiber curl may be described as the fraction shortening of the fiber due to kinks, twists, and/or bends in t fiber. For the purposes of this invention, fiber curl is measur in terms of a two dimensional plane. The extent of fiber curli can be quantified by referencing a fiber curl factor. The fib curl factor, a two dimensional measurement of curl, is determin by viewing the fiber in a two dimensional plane. To determi curl factor, the projected length of the fiber as the longe dimension of a two dimensional rectangle encompassing the fibe L , and the actual length of the fiber, LA, are both measure The fiber curl factor can then pe calculated from the followi 'equation: Curl Factor - (LA/LR) - 1. An image analysis method that can be utilized to measure and LA is described in U.S. Patent 4,898,642. Preferably t fibers utilized in the layers of the absorbent core herein wil have a curl factor of at least about 0.30, and more preferabl will have a curl factor of at least about 0.50. The degree pf stiffening, dependent upon the type and amou of stiffening agent (i.e_., crosslinking agent) used, the degree dehydration of, he fibers,.during curing of the crosslinking agen and the curing time and. conditions, affect the ability of t fiber to.take up fluid and.th tendency of the fiber to swell. The fiber stiffness as it relates to resistance to fiber wall swelling can be quantified by referencing the water retention value (WRV) of the stiffened cellulosic fibers used in th absorbent articles herein. WRV is a measure of the amount o water retained by a mass of fibers after substantially all of the interfiber water has been removed. Another parameter which can be used to characterize the nature of the stiffened fibers formed b crosslinking fibers in relatively dehydrated form is that o alcohol retention value (ARV). ARV is a measure of the extent to which a fluid, e.g., isopropyl alcohol, which does not induce substantial fiber swelling, is taken up by the stiffened fibers. The ARV of the stiffened fibers is directly related to the extent that the fibers were swollen with the solution of crosslinking agent during the stiffening procedure. Relatively higher ARVs mean that the fibers were generally swollen to a relativel greater extent during crosslinking. Procedures for determining WRV and ARV are described in U.S. Patent 4,898,642. The WRV for the stiffened, twisted, curled fibers used in the present invention will preferably range between about 28% and about 50%. In more preferred embodiments, the WRV of the fibers can range from about 30% to 45%. Fibers having a WRV within these ranges are believed to provide an optimal balance of swelling-in¬ duced untwisting and fiber stiffness. The stiffened cellulose fibers preferred for use herein are those which have an ARV (isopropol alcohol) of less than about 30%. The limitation that such fibers have an ARV (isopropol alcohol) of less than about 30% is indicative of the relatively dehydrated, unswollen state of these fibers during the stiffening process. More preferably, the ARV (isopropol alcohol) of the fibers useful herein will be less than about 27%. The stiffened cellulose fibers herein having the preferred twist count, curl factor, WRV and ARV characteristics hereinbefore set forth, can be prepared by internally crosslinking such fibers in relatively dehydrated form while or after such fibers are being or have been dried " and " deflbrated' (1.e., "fluffed") as described in U.S. Patent 4,898,"6'42v ≥lt ^ds cnot, however, meant to necessarily exclude other hydrophilic, chemically stiffened fibers from this invention, such other fibers being described in (but n limited to) the previously incorporated U.S. Patents 3,224,92 3,440,135, 4,035,147, and 3,932,209. A characteristic of stiffened fibers, particularly t twisted, curled stiffened fibers is their ability to partial untwist and uncurl upon wetting. Thus, when formed into webs sufficient density, the webs can expand upon wetting to equilibrium wet density, which, when calculated, on a dry fib density, is less than the average dry density (prior to wetting This accounts for thβiaverage dry densities of up to about 0. g/cm 3 described above, in conjunction with lower average densiti upon wetting to saturation. Such webs which can expand up wetting are described in U.S. Patent 4,822,453. To the exte that it is desired to utilize this characteristic in absorbe article design, those of ordinary skill in the art will be able adjust the relative amount of stiffening agent used, and t extent to which twist and curl in the stiffened fibers imparted, to achieve the desired amount of expansion upon wettin The stiffened cellulosic fibers can be provided in web fo by various techniques, including airlaying and wetlaying. Airlaid Webs The stiffened cellulosic fibers can be airlaid to form t web of a desired density and basis weight. The stiffened fibe for use in the present invention can be airlaid according techniques well known to those skilled in the art of airlayi cellulosic fibers. In general, airlaying can be effected metering an air flow containing the fibers, in substantially d condition, onto a wire screen and, optionally, compressing t resulting web to the desired density. Alternately, the fibers c be airlaid to the desired density without compression. T airlaid web will comprise at least about 50% of stiffen cellulosic fibers, as described above, and can comprise up to a including 100% of said, fibers. The web can optionally conta binding means, such^as described below, or other option components, such as ' or ingredients modifying fluid handli properties (e.g.,' hydrophlic surface active agents), and t like. Wetlaid Webs In another embodiment, the stiffened cellulosic fibers rather than being airlaid to form the web, are wetlaid. Th wetlaid webs comprise from about 50% to 100% of the stiffene fibers and from 0% to about 50% of a binding means for increasin physical integrity of the web, to facilitate processing in the we and/or dry state, and to provide increased integrity upon wettin of the web during use. Preferably, the wetlaid webs will compris at least about 2% of a fibrous binding means or high surface are cellulose binding means (hereafter described). Chemical additive can also be used as binding means, and are incorporated into th acquisition/distribution layer at levels typically of about 0.2 to about 2.0%, dry web weight basis. Techniques for wetlaying cellulosic fibrous material to for sheets such as dry lap and paper are well known in the art. Thes techniques are generally applicable to the wet-laying of th stiffened fibers to form wetlaid sheets useful in the absorben structures of this invention. Suitable wetlaying technique include handsheeting, and wetlaying with the utilization o papermaking machines as disclosed, for instance, by L. H. Sanfor et al. in U.S. Patent 3,301,746. Due to the behavior of stiffene fibers, particularly their tendency to flocculate in aqueou slurries, certain processing modifications, hereafter described are preferably implemented when wetlaying with papermakin machines. In general, wetlaid webs can be made by depositing a aqueous slurry of fibers on to a foraminous forming wire, dewatering the wetlaid slurry to form a wet web, and drying th wet web. Preferably, the aqueous slurries of fibers for wetlayin will have a fiber consistency of between about 0.05% and abou 2.0%, preferably between about 0.05% and about 0.2%, total slurr weight basis. Deposition of the slurry is typically accomplishe using an apparatus known in the art as a headbox. The headbox ha an opening, known as a slice, for delivering the aqueous slurry o fibers onto the foraminous forming wire. The foraminous formin wire is often referred to in the art- as a fourdrinier wire. Th Fourdrinier-wire <:an be of construction and mesh size used for dr lap or other papermaking processing. Preferably, mesh sizes o about 70 to about 100 (Tyler standard screen scale) are used (All mesh sizes referred to herein shall be based upon the Tyle standard screen scaled unless otherwise specifically indicated. Conventional designs of headboxes known in the art for drylap an tissue sheet formation may be used. Suitable commerciall available headboxes include, for example, fixed roof, twin wire and drum former headboxes. Once formed, the wet web is dewatere and dried. Dewatering can be performed with suction boxes o other vacuum devices. Typically, dewatering increases the fibe consistency to betwelή about 8% and about 45%, total wet we weight basis, preferably between about 8% and about 22% Dewatering to consistencies above about 22% may requir wet-pressing and vsfless preferred. After dewatering, the web ca be, but is not necessarily, transferred from the forming wire to drying fabric which transports the web to drying apparatuses. Th drying fabric is preferably coarser than the forming wire, fo increased drying efficiency. The drying fabric preferably ha about 30% to about 50% open area and about 15% to about 25 knuckle area, such as a 31 X 253S (satin weave) fabric that ha been sanded to increase the knuckle area to within the preferre range. Wet microcontraction is preferably implemented durin transfer from the forming wire tp the fabric. We microcontraction can be accomplished by running the forming wir at a speed which is from about 5% to about 20% faster than th speed at which the fabric is being run. Drying can b accomplished with a thermal blow-through dryer or vacuum devic such as a suction box, although thermal blow-through drying i preferred. The wetlaid webs are preferably dried to completio (generally to fiber consistency between about 90% and about 95% by the thermal blow-through dryers. Blow-through drying i believed to efficiently dry webs of the stiffened fibers due t the high void volume of the webs. Steam drum drying apparatu known in the art, such as Yankee drum dryers,,can be used but ar less preferred. Drum dryers are believed to be less efficient fo drying webs of the stiffened fibers and can also compact the webs The dried webs are preferably not creped. As an alternative to drying as described above, the dewatere web can be removed from the forming wire placed on a drying scree and dried (unrestrained) in a batch drying process by, fo example, a thermal blow through dryer or a forced convection stea heated oven. The stiffened fibers have the tendency to flocculate, or for clumps, in aqueous solution. In order to inhibit flocculation, the aqueous slurry should be pumped to the headbox at a linea velocity of at least about 0.25 m/sec. Also, it 1s preferred tha the linear velocity of the slurry upon exit from the headbox slic is from about 2.0 to about 4.0 times the velocity of the formin wire. Another method for reducing flocculations of fibers in wetlaying process is described in U.S. Patent 4,889,597, issue December 26 t 1989, incorporated herein by reference, wherein jet of water are directed at the wetlaid fibers just after depositio on the forming wire. Binding Means Relative to conventional non-stiffened cellulosic fibers, th crosslinked, twisted, stiffened fibers as described above for lower tensile strength sheets, particular in the undrie condition. Therefore, in order to facilitate processing and t increase the integrity of the webs, particularly for wetlaid web (although binding means can also be used with airlaid webs), binding means can be integrally incorporated into or onto the web. Tfcis-can be done by adding the binding means to the fibers prio to web formation (wetlaid or airlaid web formations), by applyin the binding means (e.g., chemical additive binding means) to wetlaid web after deposition on the forming wire and befor drying, by applying binding means to a dry web (wetlaid), or combination thereof. Suitable binding means for addition to the stiffene cellulosic fibers prior to formation of the wet web from a pul slurry include, but are not limited to, a variety of cellulosi and synthetic fibrous materials. Such material includ nonstiffened cellulosic fibers (i.e., conventional cellulosic pul fibers), highly refined, npnsti inned, cellulosic fibers which are refined to Canadian.Standard Eεeeness (£SF) of less than about 20 CSF, more preferably from about 100 CSF to about 200 CSF (hig refined fibers being referred to herein as "crill", and h surface area cellulosic material such as expanded cellulose fib (hereinafter described). Various types of synthetic fibrous material can be used the synthetic fiber binding means. For the purposes hereof, use of "synthetic fibrous materials" as a binding means sh refer to the utilization of such fibrous materials, in the fi product, in fibrous form. (Preferably, the synthetic fibers of at least staple length, i.e., the fibers preferably having average length of at least about 1.5 cm). Any type of fibr material which is suitable for use in conventional absorb products is believed to be suitable for use in acquisition/distribution web of the present invention. Speci examples of sμch fibrous material include modified cellul fibers, rayon, polyester fibers such as polyethylene terephthal (DACR0N), hydrophilic nylon (HYDR0FIL) and the like. Other fib useful include cellulose acetate, polyvinyl fluori polyvinylidene chloride, acrylics, polyvinyl acetate, polya i (such as nylon), bicomponent fibers, tricomponent fibers, mixtu thereof, and the like. Hydrophilic fibrous materials preferred. Examples of suitable hydrophilic fibrous materi include hydrophilized hydrophobic fibers, such surfactant-treated or silica-treated thermoplastic fibers deriv fσr " example, from polyolefins such as polyethylene polypropylene, polyacrylics, polyamides, polystyrenes, po urethanes and the like. Hydrophobic synthetic fibers can also used, but are less preferred. Such synthetic fibers that can added to the web and utilized in the final web product in fibr form include rayon, polyethylene, polypropylene, etc. S fibers, when of a hydrophobic nature, are preferably present quantities of less, than about 30%, total web weight basis, s that the web remains substantially hydrophilic. Conventional nonstiffened fibers, crill, and synthetic fibers can also be u in airlaid webs. In one preferredembodiment wherein the acquisition/distri tion,layer is made.by,a wetlaying process, the-web comprises f about 85% to about 95% of the stiffened cellulosic fibers and fro about 5% to about 15% of crill, preferably from about 90% to abou 95% of the stiffened fibers and from about 5% to about 10% o crill, most preferably about 92% of stiffened fibers and about 8 crill. Suitable cellulosic fibers for use as crϋl includ chemically pulped wood fibers, Including softwood and hardwoo pulp fibers, preferably southern softwood fibers (e.g., Fole Fluff, The Procter & Gamble Cellulose Co., Memphis, Tennessee USA). All percentages of web components referred to herein unless otherwise expressly stated, are on a dry web total weigh basis. In another embodiment, the acquisition/distribution laye comprises the stiffened fibers and up to about 25% of high surfac area cellulosic material such as expanded cellulose fibers Preferably, the acquisition/distribution layer comprising a web o wetlaid stiffened fibers and high surface area cellulose wil comprise from about 85% to about 98% of the stiffened fibers preferably from about 90% to about 95%, and from about 2% to abou 15%, more preferably from about 5% to about 10%, of high surfac area cellulose. The high surface area cellulosic material use herein will typically have a surface area of at least about 1 m2/g > preferably at least about 20 m2/g» of cellulosic material Reference can be made to U.S. Patent 4,761,203, Vinson, August 2 1988, incorporated herein by reference, for a thorough discussio of expanded cellulose fibers. In general however, cellulosic fibers are multi-componen ultrastructures made from cellulose polymers. Lignin hemicellulose, and other components known in the art may also b present. The cellulose polymers are aggregated laterally to for threadlike structures called microfibrils. Microfibrils ar reported to have diameters of about 10-20 nm, and are observabl with an electron microscope. Microfibrils frequently exist in th form of small bundles known as macrofibrils. Macrofibrils can b characterized as a plurality^of microfibrils which are laterall aggregated to form a threadlike structure which is larger i diameter than a> microfibril, but substantially smaller than ceϋfflostfe 1 fiber. **fc general', a cellulesld-' ' ber' 1s made up of relatively thin primary wall, and a relatively thick seconda wall. The primary wall, a thin, net-like covering located at t outer surface of the fiber, is principally formed fr microfibrils. The bulk of the fiber wall, i.e., the seconda wall, is formed froa a combination of microfibrils a macrofibrils. See Pulp and Paper Manufacture, Vol. 1, Properti of Fibrous Raw Materials and Their Preparation For Pulping, ed. Dr. Michael ocurek, Chapter VI, "Ultrastructure and Chemistry pp 35-44,- published jointly by Canadian Pulp and Paper Indust (Montreal) and Technical Association of the Pulp and Pap Industry (Atlanta), 3rd ed., 1983. Expanded cellulose fibers th refers to microfibrils and macrofibrils which have be substantially separated from or disassociated from a cellulos fiber ultrastructure. High surface area cellulose can also be made from cellulos fibers by passing a liquid suspension of cellulose fibers throu a small diameter orifice, in which the suspension is subjected a pressure drop of at least 3000 psig and a high velocity sheari action, followed by a high velocity decelerating impact. Passa of the suspension through the orifice is repeated until substantially stable suspension is obtained. See U.S. Pate 4,483,743, Turbak et al., November 20, 1984, incorporated here by reference. A preferred process for preparing expanded cellulose fibe fs disclosed in the Vinson patent (ibid.), and involves impacti a fibrous material having a fibrillar ultrastructure (e.g cellulose fibers) with fine media to cause microfibrils a macrofibrils to separate froa said fibrous materi ultrastructure. The length of the high surface area cellulosic materi preferably ranges from about 20 to about 200 μm. Typically, for wetlaying, the high surface area cellulose provided as a damp pulp, generally at 15-17% solids, a preferably diluted to less than 4% solids content and processed a beater or disc refiner to break up ".entanglements. The hi surface areas/cellulose-nis then well mixed with the stiffen ibersr.in slurry iandittoe siurry is wetEJβidoaS'described above. blender, a deflaker or a refiner (e.g., single, cone, or double, disk refiner, or other equipment known in the art can be used to mix the stiffened fibers and high surface area cellulose. Preferably, fine mesh wires (e.g., 84M, (84 X 76, 5 shed weave)) are used for improved retention of the high surface are cellulose, rather than the more open wire conventionally used for the forming wire. Other binding means for increasing physical integrity of the acquisition/distribution layer and/or facilitating processing of webs, especially wetlaid webs, for use as the acquisition/distribution layer include chemical additives, such as resinous binders, latex, and starch known in the art for providing increased integrity to fibrous webs. Suitable resinous binders include those which are known for their ability to provide wet strength in paper structures, such as can be found in TAPPI monograph series No. 29, Wet Strength in Paper and Paperboard, Technical Association of the Pulp and Paper Industry (New York, 1965), incorporated herein by reference. Suitable resins include polyamide-epichlorohydrin and polyacrylamide resins. Other resins finding utility in this invention are urea formaldehyde and melamine formaldehyde resins. The more common functional groups of these polyfunctional resins are nitrogen containing groups such as amino groups and methylol groups attached to nitrogen. Polyethylenimine type resins may also find utility in the present invention. Starch, particularly cationic, modified starches may also find utility as chemical additives in the present invention. Such cationic starch materials, generally modified with nitrogen containing groups such as amino groups and methylol groups attached to nitrogen, may be obtained from Natural Starch and Chemical Corporation, located in Bridgewater, New Jersey. Other suitable binders include, but are not limited to, polyacrylic acid polyvinyl acetate. The level of chemical additive binders which are added will typically be from about 0.25% to about 2%, total web weight basis. Chemical additive-binders which-vare-hydrophilic, however, can be utilized in quantitiesr 4f< the. -chemical binder additives are added to the stiffene fibers in aqueous slurry, conventionally, nonstiffened cellulosϋc fibers or high surface area cellulose i preferably also present, to enhέnce retention of the chemical additive binder. Chemical additive binders can be applied t dried or undried webs by printing, spraying, or other method known in the art. Thermoplastic Reinforced Acquisition/Distribution Laver In another embodiment, the acquisition/distribution laye comprises an airlaid or wetlaid, preferably airlaid, web o stiffened cellulosic fibers wherein the web is reinforced wit from about 10% to about 50%, preferably from about 25% to abou 45%, more preferably from about 30% to about 45%, of thermoplastic binding material, wherein the thermoplastic bindin material provides bond sites at intersections of the stiffene cellulosic fibers. Such thermally bonded webs can, in general, b made by forming a web ^ comprising^the stiffened cellulosic fiber and thermoplastic fibers, which are preferably evenly distribute throughout. The we f-can be formed by either airlaying o wetlaying processes. O ce formed, the web is thermally bonded b heating the web until the thermoplastic fibers melt. Upo melting, at leas a portion of the thermoplastic material wil migrate to intersections of the stiffened cellulosic fibers due t interfiber capillary gradients. These intersections become bon sites for the thermoplastic material. The web is then cooled an migrated thermoplastic material bonds the stiffened cellulosi fibers together at the bond sites. Melting and migration of th thermoplastic material , to the stiffened cellulosic fibe intersections has the effect of increasing average pore size o the web, while maintaining the density and basis weight of the we as originally fojgned. This can improve distribution properties o the acquisition/distribution layer upon initial discharges due t improved fluid permeability, and upon subsequent discharges, du to the combined ability of the stiffened fibers to retain thei stiffness upon wetting and the. ability of the thermoplastic t remain bonded at the fiber intersection upon wetting and upon we compression. In net, "..the. thermally .bonded web retains it original overall volume^ but the volumetric regions previousl occupied by thermoplastic fibrous material becomes open to thereby increase average interfiber capillary pore size. Thermally bonded, thermoplastic-reinforced absorbent webs, utilizing conventional, unstlffened cellulosic fibers, are described in U.S. Patent 4,590,114, D. C. Holtaan, issued May 20, 1986, incorporated by reference herein and by Peter G. Bither in "Thermally Bonded Cores Add Value to Absorbent Products," Nonwovens World, November 1988, pp 49-55, both incorporated herein by reference. The processing techniques applied to make those are applicable herein. The thermoplastic binding material should be evenly distributed throughout the web. Subsequent to formation of a dry web, the web can be heated to a temperature to melt the thermoplastic fibers but not char or otherwise damage the stiffened cellulosic fibers. Upon cooling, at least some of the resolidified thermoplastic material will provide bond sites which secure stiffened, cellulosic fibers to one another at points of individual fiber intersections to form a stabilizing network of interfiber bond sides at the intersection of the stiffened cellulosic fibers. The thermoplastic binding materials useful for the acquisition/distribution layers herein include any thermoplastic polymer which can be melted at temperatures which will not extensively damage the cellulosic fibers. Preferably, the melting pofnf of the thermoplastic binding material will be less than about (135*C), preferably between about 75'C and about 175*C. In any case, the melting point should be no lower than temperatures at which the articles of this invention are likely to be stored, whereby melting point will be typically no lower than about 50*C. The thermoplastic binding aaterial aay, for example, be polyethylene, polypropylene, polyester, polyvinylchloride, polyvinylidene chloride. Other synthetic fibrous materials which can be utilized in thermally bonded webs are described above. Preferably, the thermoplastic -will preferably not significantly imbibe or absorb aqueous fluid. However, the surface -of the thermoplastic material .can be-hydrophilic or ■ tødrophobic; fAs. used -hereiny the terns ► "•hydrophilic" and P - 29 - "hydrophobic" shall refer to the extent to which the surfaces a wetted by water.) The surface of the thermoplastic can rendered hydrophilic by treatment of a hydrophobic thermoplasti binding material with a surfactant, such as a non-ionic or anioni surfactant, as by spraying the material with a surfactant or dipping the material " into the surfactant. Upon melting a resolidification, the surfactant will tend to remain at t surfaces of the thermoplastic. Suitable surfactants inclu non-ionic surfactants such as Brij 76 manufactured by I Americas, Inc. of Wilmington, r Delaware and the various material sold under the Pegosperse trademark by Glyco Chemical, Inc. Greenwich, Connecticut. Anionic surfactants can be also use Surfactants are applied to the fibers at a level .of from about 0. to about ^ 1 gram per square meter of thermoplastic bindi material. Hydrophilic materials become more desirable at high thermoplastic material levels, particularly above about 40% of t dry web. Thermoplastic fibers for use herein can be on the order about 0.1 cm to about 6 cm long, preferably from about 0.3 cm about 3.0 cm. A preferred type of thermoplastic fibrous material i commercially known and,-available as PULPEX™ (Hercules, Inc. Wilmington, Delaware, USA). PULPEX is a polyolefin materi having a very high surfaie area to mass ratio, which, in general is made by spraying molten polymer and gas through a nozzle into vacuum. PULPEX is available in both polyethylene and polyprop lene forms. The thermoplastic used can be hydrophilic or hydrophobic. As described above, thermoplastic binder-reinforced webs stiffened cellulosic fibers can be made by wetlaying or airlayi processes. Airlaid webs can be made by intermixing the cellulosi and thermoplastic fibers and then airlaying according to t techniques described above. The stiffened cellulosic fibers a thermoplastic fibers can be 1 intermixed, in an airlaid context, carding or by metering air strea s of the stiffened fibers a thermoplastic fibrous?material together and directing the combin system through a brush screen:deposition apparatus, or other w forming device. Such techniques are known in the art. Suitable equipment includes air forming systems available from Dan Webfor ing International Ltd. (Rlsskov, Denmark). A suitable method and apparatus for mixing cellulosic and thermoplastic fibers for subsequent airlaying are also described in U.S. Patent 4,590,114, Holtman, D. C, issued May 20, 1986, incorporated herein by reference. In wetlaying contexts, the thermoplastic fibrous material can be intermixed with the stiffened cellulosic fibers in the aqueous slurry prior to web formation. The thermoplastic is preferably melted by through-air bonding, however other methods such as infra red light, etc. are not meant to be excluded. In another variation, the web is subjected to by heat embossing on one or both faces of the web. This technique is described in further detail in U.S. Patent 4,590,114, which was previously incorporated into this specification. As discussed previously, scrims such as tissue sheets and other water pervious nonwoven sheets can be used as external support in addition to or in place of the binding means described above. Storage Layer A second essential element of the absorbent core is a lower fluid storage layer which comprises at least 15%, by weight, preferably at least 25%, of superabsorbent material (defined more fufly hereafter), and from 0% to about 85%, preferably less than about 75%, of a superabsorbent material carrier means. The principal function of the fluid storage layer is to absorb discharged body fluid from the upper acquisition/distribution layer and retain such fluid under the pressures encountered as a result of the wearer's movements. Thus, the storage layer is subjacent to and in fluid communication with the acquisition/distribution layer. Ideally the fluid storage layer will drain the upper layer of much of its acquired fluid load. As indicated 'hereinbefore, the storage layer comprises superabsorbent material such as, but-not necessarily limited to, discrete particles f -absorbent gelling material and superabsorbent fibrous material -such- as acryiate grafted fibers - 31 - and superabsorbent modified fibers. The superabsorbent material can be in any form which can be incorporated into a flexible web or sheet to form the storage layer. Superabsorbent materials are described in more detail below. The superabsorbent material, upon contact with fluids such as water or body fluids, absorb such fluids. (As used herein, the term "fluids" shall refer to liquids, as opposed to gases.) In this manner, fluid discharged into the acquisition/distribution layer and transported to the storage layer can be acquired and held by the superabsorbent material, thereby providing the articles herein with enhanced absorbent capacity and/or improved fluid retention performance. The superabsorbent materials intended to be encompassed in this invention are those which are capable of absorbing at leas about 10 grams, preferably at least about 15 g, more preferably a least about 20 g, of Synthetic Urine (SU - 1.0% NaCl aqueou solution) per gram of superabsorbent material, as determine according to the hereinafter described Absorbent Capacit procedures. The superabsorbent material utilized herein is typically in the form of discrete particles of absorbent gelling material. These particles will typically be distributed within a web o fibrous material as carrier means. The superabsorbent fibrous material can comprise synthetic or natural fibers. Suitabl fibrous carrier means are cellulose fibers, in the form of fluff, such as is conventionally utilized in absorbent cores. Modifie cellulose fibers such as the stiffened cellulose fibers described above can also be used, but are preferably not used, in th storage layer. Synthetic fibers can also be used and includ those made of cellulose acetate, polyvinyl fluoride, polyvinylidene chloride, acrylics (such as Orion), polyvinyl acetate, non-soluble polyvinyl alcohol, polyethylene, polypropylene, polyamides (such as nylon), polyesters, bicomponen fibers, tricomponent fibers, mixtures thereof and the like. Preferred synthetic fibers have a denier of from about 3 denie per filament to about 25 denier per filament, more preferably fro about 5 denier per filament-to about 16 denier per filament. Als preferably, the fiber surfaces are hydrophilic or are treated t be hydrophilic. The average dry density of the fluid storage layer comprising nonsuperabsorbent fibers as superabsorbent material carrier means will generally be in the range of from about 0.06 to about 0.5 g/cm 3 , and more preferably within the range of from about 0.10 to about 0.4 g/cm 3 , even more preferably from about 0.15 to about 0.3 g/cm 3 , most preferably from about 0.15 to about 0.25 g/cm 3 . Typically the basis weight of the lower fluid storage layer can range from about 0.02 to 0.12 g/cm2, more preferably from about 0.04 to 0.08 g/cm 2 , most preferably from about 0.05 to 0.07 g/cm2. As with the acquisition/distribution layer, density and basis weight need not be uniform throughout the storage layer. The storage layer can contain regions of relatively higher and relatively lower density and basis weight. Also as with the acquisition/distribution layer, density values for the storage layer are calculated from basis weight and layer caliper measured under a confining pressure of 0.2 psi (1.43 kPa). Density and basis weight values include the weight of the superabsorbent material.. Additionally, the storage layer can have a superabsorbent material gradient, such as with more superabsorbent material being present in regions of relatively high fluid handling requirements (i.e., near the region of fluid discharge) and less superabsorbent material at lower demand regions. The superabsorbent material which is employed in the storage layer of the absorbent core will most often comprise a substantially water-insoluble, slightly cross-linked, partially neutralized, polymeric absorbent gelling material. This material forms a hydrogel upon contact with water. Such polymer materials can be prepared from polymerizable, unsaturated, acid-containing monomers. Suitable unsaturated acidic monomers for use in preparing the polymeric gelling material used in this invention include those listed in Brandt/Goldman/Inglin; U.S. Patent 4,654,039, Issued March 31, 1987, and reissued as RE 32,649 on April 19, 1988, both incorporated herein by reference. Preferred monomers include acrylic acid, methacrylic acid, and 2-acrylamido- 2-methyl propane sulfonic acid. Acrylic acid itself is especially preferred fbr-preparation of ~ the polymericgelling agent material. The polymeric component formed from unsaturated, acid containing monomers may be grafted on to other types of polyme moieties such as starch or cellulose. Polyacrylate grafted starc materials of this type are also especially preferred. Preferred polymeric absorbent gelling materials which can b prepared from conventional types of monomers include hydrolyze acrylonitrlle grafted starch, polyacrylate grafted starch polyacrylates, maleic anhydride-based copolymers and combination thereof. Especially preferred are the polyacrylates an polyacrylate grafted starch. Whatever the nature of the basic polymer components of th hydrogel-forming polymeric absorbent gelling material particle used in both layers of the absorbent cores herein, such material will in general be slightly cross-linked. Cross-linking serves t render the hydrogel-forming polymer gelling agents used in thi invention, substantially water-insoluble, and cross-linking thus i part determines the gel volume and extractable polyme characteristics of the hydrogels formed from the polymeric gellin agents employed. Suitable cross-linking agents are well known i the art and include, for example, those described in greate detail in Masuda et al.; U.S. Patent 4,076,663; Issued Februar 28, 1978, incorporated herein by reference. Preferred cross linking agents are the di- or polyesters of unsaturated mono- o polycarboxylic acids with polyols, the bisacrylamides and the di or triallyl amines. Other preferred cross-linking agents ar N,N'-methylenebisacrylamide, trimethylol propane triacrylate an triallyl amine. The cross-linking agent can generally constitut from about 0.001 mole percent to 5 mole percent of the resultin hydrogel-forming polymer material. More preferably, th cross-linking agent will constitute from about 0.01 mole percen to 3 mole percent of the hydrogel-forming polymeric gellin material particles used herein. The slightly cross-linked, hydrogel-forming polymeric gellin material particles which may be used in the articles of th present invention are generally employed in their partiall neutralized form. For purposes of this invention, such material are considered partially eutralized when At least 25 mol percent, and preferably at least 50 mole percent of monomers used to form the polymer are acid group-containing monomers which have been neutralized with a salt-forming cation. Suitable salt- forming cations include alkali metal, ammonium, substituted ammonium and amines. This percentage of the total monomers utilized which are neutralized acid group-containing monomers Is referred to herein as the "degree of neutralization." Webs comprising absorbent gelling material particles and nonsuperabsorbent fibrous carrier means will typically have from about 10% to about 80%, more typically from about 20% to about 75%, polymeric gelling material and from about 20% to about 90%, more typically from about 25% to about 80%, carrier means. Such webs will typically be made by airlaying, wherein an airstream of the absorbent gelling material particles is metered into an airstream of the fibrous carrier means. It is also contemplated to provide a storage layer wherein particles of absorbent gelling material are laminated between two or more webs of fibrous material, such as exemplified in U.S. Patent 4,578,068, Kramer et al., issued March 25, 1986, incorporated herein by reference. As discussed above, superabsorbent fibers can be used instead of particles of absorbent gelling material. Superabsorbent fibers have been previously disclosed in the art. Superabsorbent fibers are described in Textile Science and Technology, Volume 7, Pronoy K\ Chatterjee, editor, Elsevier Science Publishers B.V. (The Netherlands), 1985, in Chapters VII and VIII (collectively pages 217-280), incorporated by reference herein. Synthetic and modified natural fibers, such as cellulosic fibers, can be used. The superabsorbent fibers for use herein should have an absorbent capacity of at least about 10 g Synthetic Urine per g superabsorbent material (dry weight basis), preferably at least about 15 g/g. One type of superabsorbent fiber comprise the polycarboxylate polymer-modified cellulosic fibrous pulps such as mildly hydrolyzed methyl acrylate-grafted softwood kraft pulps. These superabsorbent fibers are described in U.S. Serial No.07/378,154, filed July 11, 1989, titled "Absorbent Paper Comprising - 35 - Polymer-Modified Fibrous Pulps and Wet-Laying Process for th Production Thereof," by Larry N. Mackey and S. Ebrahi Seyed-Rezai, incorporated herein by reference. Other types of superabsorbent fibers can include crosslinke carboxymethyl cellulose and polymer grafted cellulose fibers Polymer grafted cellulose fibers include hydrolyze polyacrylonitHle, polyacryl1c esters, and polyacrylic an polymethacrylic acids. These superabsorbent fibers includin discussion of and references to processes for making them, can b found in-the Chatterjee's Vol. 7 of Textile Science and Technolog as previously incorporated herein by reference, include: A. H Zahran, et al., "Radiation Grafting of Acrylic and Methacryli Acid to Cellulose Fibers to Impart High Water Sorbency", J. o App. Polymer Science, Vol. 25, 535-542 (1980), which discusse radiation grafting of methacrylic acid and acrylic acid t cellulose fibers, as the title suggests; U.S. Patent 4,036,588, J L. Williams, et al., issued July 19, 1977, which describes th graft a vinyl monomer containing a hydrophili group onto cellulose-cdiitalning material, e.g., rayon yarn; U.S Patent 3,838,077, H. W Hόftiezer, et al., issued September 24 1974, which discltfses polyacrylonitrile-grafted cellulose fibers. The superabsorbent * fibers can be incorporated into webs o conventional or other nonsuperabsorbent fibers, such as i wet-laid webs as described above or in air-laid webs, and can als U8" " fδrmed into nonwoven Sheets. In another embodiment hereof, the storage layer comprise superabsorbent fibers which are formed into nonwoven sheets. Suc sheets can consist essentially of superabsorbent fibers wit substantially'zero percent carrier means, although such sheets ca include carrier means, -and such embodiments are not meant to b excluded. Nonwoven sheets made from superabsorbent fibers such a the non-acrylate Superabsorbent microfibers and superabsorben fibers useful for makinj such sheets are available from Arc Chemical Co. (Newtown Square, PA, USA), under the tradenam FIBERSORβTM and from Japan Exlan Co., Ltd. (Osaka, Japan) whic markets superabsorbent fibers comprising a polyacrylonitrile cor with a polyacrylic acid/polyammonium acrylate skin under the tradename LANSEAL™. The storage layer embodiments of the absorbent core wherein an airlaid web comprises the carrier means can be formed by air-laying a substantially dry mixture of fibers and absorbent gelling material particles and, if desired or necessary, densifying the resulting web. Such a procedure 1s in general described more fully in the hereinbefore referenced Weisman and Goldman; U.S. Patent 4,610,678; Issued September 9, 1986. Superabsorbent fibers can be airlaid with fibrous carrier means according to conventional airlaid web-forming processes. The superabsorbent fibers and fibrous carrier means can be blended by, for example, carding or Rando web formation. Within the storage layer of the absorbent core, the superabsorbent material can be uniformly distributed. Alternately, there may be regions or zones of the storage layer which have higher concentrations of superabsorbent material than do other regions or zones of the layers. As discussed above, the acquisition/distribution layer of the absorbent core preferably has a smaller, surface area (in an unfolded configuration) than the storage layer and, in fact, can have a surface area that is substantially smaller than, or equal to or greater than, the fluid storage layer. Generally, the surface area of the acquisition/distribution layer will range from about 25% to about 100%, preferably from about 30% to about 95%, more preferably less than about 90%, most preferably less than about 85%, of the surface area of the storage layer. In accordance with the present invention, the acquisition/distribution layer of the absorbent core should be placed in a specific positional relationship with respect to the topsheet and the storage layer of the absorbent article. More particularly, the acquisition/distribution layer of the core must be positioned so that it is effectively located to acquire discharged body fluid and transport said fluid to other regions of the core. Thus the acquisition/distribution layer should encompass the vicinity of the point of discharge of body fluids. These, areas MOUIS ioclude the crotch area and. jreferably for males, also the region where urination discharges occur in t front of the diaper. For a diaper, the front of the absorbe articles herein means' the portion' of the absorbent article whi Is intended to be placed on the front of the weare Additionally, for males, it is desirable for t acquisition/distribution layer to extend to near the front wai area of the wearer to- effectively acquire the relatively hi fluid load that occurs in the front of the male wearer, and compensate for directional variations of the discharges. corresponding absorbent article regions will vary depending up the design and fit of the absorbent article. acquisition/distribution layers 110 of diaper 100 as shown Figure 2, exemplify one embodiment wherein acquisition/distribution layer 110 is suitably positioned receive both bowel and urine discharges for both males females. For disposable baby diaper executions, acquisition/distribution layer of the core is preferably pos tioned relative to the elongated topsheet and/or the storage la such that the acquisition/distribution layer is sufficien enlongated to.extend to areas corresponding at least to about 5 preferably 75%, of the length of the storage layer. acquisition/distribution layer should have a width sufficient acquire gushes of body fluids without direct discharge of fl TWto-the storage layer. Generally, for diapers, such as shown Figures 1 and 2, the width will be at least about 5 cm, prefera at least about 6 co. As noted, for purposes of the present i vention, sections of the absorbent article can be defined reference to top surface areas of the unfolded absorbent arti found in front of a given point on the line which defines t length of the absorbent article. For purposes of deterπiniπg such acquisition/distributi layer positioning, the length of the absorbent article will taken as the normal longest longitudinal dimension of t elongated article backing sheet. This normal longest dimension the elongated backing sheet.can be defined with respect to t article-as i isrβpplied to;the wearer. When worn, the opposi ends of the back sheet are fastened together so that these joined ends form a circle around the wearer's waist. The normal length of the backing sheet will thus be the length of the line running through the back sheet from a) the point on the edge of the back sheet at the middle of the wearer's back waist, through the crotch, to b) the point on the opposite edge of the backing sheet at the middle of the wearer's front waist. The size and shape of the topsheet will generally correspond substantially to the back sheet. In the usual instance wherein the storage layer of the absorbent core generally defines the shape of the absorbent article, the normal length of the elongated article topsheet will be approached by the longest longitudinal dimension of the storage layer of the core. However, in some applications (e.g., adult incontinence articles) wherein bulk reduction or minimum cost are important, the storage layer would not take on the general shape of the diaper or incontinence structure. Rather the storage layer would be generally located to cover only the genital region of the wearer and a reasonable area proximate to the genital area. In this instance both the fluid acquisition/distribution layer and the storage layer would be located toward the front of the article as defined by the topsheet such that the acquisition/distribution and storage layers would typically be found in the front two-thirds of the article. The storage layer of the absorbent core can be of any desired shape consistent with comfortable fit including, for example, circular, rectangular, trapezoidal or oblong, e.g., hourglass- shaped, dog-bone-shaped, half dog bone shaped, oval or irregularly shaped. This storage layer need not be physically separated from the acquisition/distribution layer and can simply be a zone of superabsorbent material concentration in a continuous web of stiffened cellulose fiber material. More preferably, however, the storage layer of the absorbent core will comprise a separate web which can be used as an insert placed underneath the acquisl- ±ion/distribution layer. The acquisition/distribution layer can also be of any desired shape; consistent with;icorafortable fit and the sizing limitations discussed above. These shapes include, for example, circula rectangular, trapezoidal or oblong, e.g., hourglass-shape dog-bone-shaped, half dog bone shaped, oval or irregularly shape The acquisition/distribution layer can be of similar shape differing shape than the storage layer. Figures 1 and 2 each show diaper executions embodying t present Invention. Shown in each figure 1s a diaper 100 wi topsheet 104 and backsheet 102. Disposed between topsheet 104 a backsheet 102 is absorbent core 106 having storage layer 108 a rectangular acquisition/distribution layer 110. Although n shown, storage layer 108 has discrete particles of absorbe gelling material distributed throughout. Specifically referring to Figure 2, the absorbent core 106 shown as having a front region 112, a back region 114, and central region 115. As previously described, the front regi 112, corresponds to the end of the diaper 100 that would covering the front of the wearer when the diaper was in use, a the back region 114 would be covering the back of the user. absorbent core 106 of Figure 2, specifically the storage lay 108, has a modified hour-glass shape to provide enhanced fit a reduce i -use leakage. Figure 3 shows an absorbent core 106, that can be utilized conjunction with a disposable diaper, having a storage layer 1 of similar shape , to those of Figures 1 and Acquisition/distribution layer 111, however, is of a modifi hour-glass shape of substantially similar shape to the stora layer 108, though of smaller surface area. Further with respect to Figure 3, the absorbent core 106 h front region 112,- rear region 114, and central region 115. Fro region 112, front edge M<7 and, at rear region 114, has rear ed 119. Front edge 11.7 and, has rear edge 119. Front edge 117 a rear edge 119 are connected by storage layer side edges 122 a 123, corresponding to the central region 11 Acquisition/distribution layer 111 has front edge 116 in the fro region JJ2 and rear edge ,-418 1n the rear region 11 Acquisition/distribution layercside edges 120 and 121, conne front edge-116~and-rear edged 8 In preferred absorbent article embodiments, e.g., disposable absorbent diapers, the edges 116, 118, 120, 121 of the acquisition/distribution layer 111 will respectively be at least 0.5 cm., preferably at least 1.25 cm. inside the edges 117, 119, 122, 123 of the storage layer 108, particularly in central region 115. Superabsorbent Material Absorbent Capacity Test Method As discussed above, the superabsorbent materials for use in the present invention will preferably have an Absorbent Capacity of at least about 10 g, preferably at least about 15 g, more preferably at least about 20 g Synthetic Urine (1.0% NaCl aqueous solution, prepared using distilled water) per gram dry superabsorbent material. In general, the superabsorbent material is place within a tea bag, immersed in an excess of Synthetic Urine for a specified time, and then centrifuged for a specified period of time. The ratio of superabsorbent material final weight after centrifuging minus initial weight to initial weight is Absorbent Capacity. The following procedure can be used to determine Absorbent Capacity. The procedure is conducted under standard laboratory conditions. Using a 6 cm X 12 cm cutting die, the tea bag material is cut, folded in half lengthwise, and sealed along two sides with a T-bar heat sealer to produce a 6 centimeter by 6 centimeter tea bag square. The tea bag material utilized is grade 1234 heat scalable, obtainable from C. H. Dexter, Division of the Dexter Corp., Windsor Locks, Connecticut, USA, or equivalent. Lower porosity tea bag material should be used if required to retain fine superabsorbent materials. 0.200 grams plus or minus 0.005 grams of superabsorbent material is weighed onto a weighing paper and transferred into the tea bag, and the top (open end) of the tea bag is sealed. An empty tea bag is sealed at the top and is used as a blank. Approximately 400 milliliters of Synthetic Urine are poured into a 1,000 milliliter beaker. The blank tea bag is submerged in the Synthetic Urine. The tea bag containing the superabsorbent material (the sample tea bag) is held horizontally to distribute thejnaterial evenly throughout the tea bag. The tea baa; is laiώron the surface of the Synthetic. Urine; The tea bag is * - 41 - allowed to wet, for a period of no more than one minute, .and the submerged and soaked for 60 minutes. Approximately 2 minute after the first sample is submerged, a second set of tea bags, prepared identically to the first set of blank and superabsorben I material-containing tea bags, is submerged and soaked for 6 minutes in the same'manner as the " first set. After the prescribe soak time 1s elapsed, for each set of tea bag samples, the te bags are promptly removed (with'toήgs) from the Synthetic Urine. The samples are then centrifuged as described below. Th centrifuge u'sed_ is a Delux Dynac II Centrifuge, Fisher Model No. 05-100-26, obtainable 'from Fisher Scientific (Pittsburgh, PA, USA), or equivalent/ The centrifuge should be equipped with direct read tachometer and an electric brake. The centrifuge i further .equipped with " "a cylindrical insert basket having a approximately 2.5 inch (6.35 cm) high outer wall with an 8.43 Inch (21.425 cm) outer diameter, an 7.935 inch (20.155 cm) insid diameter, and 9 rows each of approximately 106 3/32 inch (0.23 cm) diameter circular holes equally spaced around th circumference of the outer wall, and having a basket floor wit six 1/4 inch (0.635 cm) diameter circular drainage holes equall spaced around the circumference of the basket floor at a distanc of 1/2 inch (1.27 cm) from the interior surface of the outer wall to the center of the drainage holes, or equivalent. The basket i mounted in the centrifuge so as to rotate ' , as well as brake, i τπrtson with the- centrifuge. The superabsorben material-containing tea -bags are positioned in the centrifug basket with a folded end of tfhe tea bag in the direction o centrifuge spin. The blank tea bags are placed to either side o the corresponding sample tea' bags. The superabsorben material-containing tea bag from the second set of tea bags mus be placed opposite-the superabsorbent material-containing tea bag from the first set of tea ' bags; and the second blank tea bag, opposite the first blank, to balance the centrifuge. Th centrifuge is started an -allowed to ramp up quickly to a stabl 1,500 rpm. -Once the centrifuge has been stabilized at 1,500 rpm, a timer is set for 3 minutes. After 3 minutes, the centrifuge i turned off and the brake is applied. The first superabsorben material-containing tea bag and first blank tea bag are remove and weighed separately. The procedure is repeated for the secon set of tea bags. The absorbent capacity (ac) for each of th samples is calculated as follows: ac - (Superabsorben material-containing tea bag weight after centrifuge minus blan tea bag weight after centrifuge minus dry superabsorbent material weight) divided by (dry superabsorbent material weight). Th Absorbent Capacity value for use herein is the average absorben capacity (ac) of the two samples. EXAMPLE I A disposable diaper is prepared comprising a thermally bonde polypropylene topsheet, a fluid impervious polyethylene backin sheet and a dual layer absorbent core positioned between th topsheet and the backing sheet. The dual layer absorbent cor comprises an hourglass-shaped storage layer positioned below rectangular shaped acquisition/distribution layer, as shown i Figure 1. The acquisition/distribution layer comprises stiffened, twisted, curled cellulose fibers and optionally a binding means. The storage layer comprises an air-laid mixture of conventional cellulosic fluff (Foley fluff, southern softwood kraft pulp, Th Procter & Gamble Cellulose Co., Memphis, TN, USA) and sodiu polyacrylate polymeric absorbent gelling material of the typ described in U.S. RE 32,649, reissued April 19, 1988, and havin aπ-Absorbent Capacity of about 30 g/g. The acquisition/distri¬ bution layer comprises a 92%/8% wetlaid mixture of stiffene fibers and conventional nonstiffened cellulosic fibers. Th nonstiffened fibers are also made from Foley Fluff; and ar refined to about 200 CSF. The stiffened, twisted, curle cellulosic fibers are made from southern softwood kraft pul (Foley fluff) and crosslinked with glutaraldehyde to the extent o about 2.5 mole percent on a dry fiber cellulose anhydroglucos basis. The fibers are crosslinked according to the "dr crosslinking process" as.described above.in U.S. Patent 4,822,453. The stiffened fibers, are similar,..to the fibers having th characteristics described in Table 1. Table 1 Stiffened. Twisted. Curled Cellulose (STCC1 Fibers Type - Southern softwood kraft pulp crosslinked with glutaralde hyde to the extent of mole percent on a dry fiber cellulos anhydroglucose basis Twist Count Dry - 6.8 nodes/mm Twist Count Wet » 5.1 nodes/mm Isopropol Alcohol Retention Value * 24% Water Retention Value - 37% Curl Factor » 0.63 The acquisition/distribution layer is a uniform, wetlaid we as described in Example II. The acquisition/distribution lay has an average dry density of about 0.06 g/cc. An average densi upon saturation with .Synthetic Urine, dry weight basis, of abo 0-07 g/cc, and an average basis weight of about 0.03 g/cm 2 . T storage layer comprises 50% by weight Foley fluff and 5 absorbent gelling material particles, has an average dry densit of about 0.24 g/cc and an average dry basis weight of about 0. g/cm 2 . The acquisition/distribution layer has dimensions of abo 7.6 cm X 22.9,cm and is positioned relative to the storage lay as shown in Figure 1. The storage layer has crotch width (at t most narrow part of the crotch) of about 8.9 cm, a width at t front waist area of about 21.6 cm, and a width at the rear (bac TTTist area of about 16.,5 cm. In an alternative embodiment, the storage layer compris about 15% of the absorbent gelling material particles and abo 85% of Foley fluff and has a basis weight gradient such that t front 60% of the storage core has a basis weight of about 0.1 g/cm 2 and a density of about 0.15 g/cc and the rear 40% of th storage core has a basis weight of about 0.04 g/cm 2 and a densit of about 0.06 g/cc. In a further embodiment, the storage core comprises about 2 of the absorbent gelling material particles and about 72% of Fol fluff, and has basis weight and' density gradients as describ immediately above. PCI7US91/00169 - 44 - EXAMPLE II This example exemplifies wetlaying of a web useful for use a an acquisition/distribution layer in the present invention. Th web comprises 92% stiffened fibers, as described in Example I an Table I, and 8% highly refined Foley fluff (crill) having freeness of about 200 CSF. A pulp slurry of the stiffened and nonstiffened fibers havin a fiber consistency of 0.1%-0.2% is pumped to a FORMAR papermakin machine at a linear velocity of 25 a s and at rate of about 9 liters/minute. The slurry is distributed by a fixed-roof forme headbox onto an inch wide (30.5 ca) 84M, 5 shed 12 forming wir moving continuously at a rate of 1.5 m/ainutes. Linear velocit of the pulp slurry upon exit from the headbox is froa 50 to 10 m/s. Flow and wire movement are regulated so that a uniform moist sheet having a dry basis weight of about 0.03 g/cm 2 and a average dry density of about 0.06 g/cc is foπoed. Shee consistency is increased to about 16%-22% by application of tw vacuum boxes from underneath the wire, such vacuum boxes operatin in sequence at 75 mm Hg and 100 mm Hg, respectively, with residence time for the sheet being subject to each vacuum box o about 1 second. The sheet is then removed froa the forming wir manually and dried, batchwise, in a forced convection steam heate oven for about 4 hours at about 110°C. XAMPL HI Absorbent cores are prepared as in Exaaple I, except that th acquisition/distribution layer is airlaid and comprises 100% o the stiffened fibers. EXAMPLE IV Absorbent cores are prepared as in Exaaple III except tha the acquisition/distribution layer is made froa an airlaid an thermally bonded thermoplastic-reinforced web comprising 55% o the stiffened fibers and 45% of PULPEX™ (Hercules, Inc., Wilmington, Delaware, USA) . polyethylene aicrofibers having an average length of about 0.3 cm. The acquisition/distribution layer is formed by metering airstrea s of the stiffened fibers and PULPEX, and then forming the web using conventional airlayin equipment. The web is thermally bonded by heating the web b through-air bonding, under unrestrained (i.e., uncompressed) conditions, and subsequently allowed to cool. WHAT IS CLAIMED IS:

Claims: 1. An absorbent article for acquisition, distribution, an storage of bodily fluids, said article characterized by: (a) a fluid pervious topsheet; (b) a fluid impervious backsheet affixed to said topsheet; and (c) an absorbent core disposed between said topsheet and said backsheet, said absorbent core having: (i) a fluid acquisition/distribution layer having an average dry density of less than 0.30 g/cc, a average density upon saturation with 1% NaCl aqueous solution, dry weight basis, of less than 0.20 g/cc, and an average dry basis weight of from 0.001 t 0.10 g/cm 2 , said acquisition/distribution laye comprising from 50% to 100%, preferably from 95% t 100%, dry weight basis, of chemically stiffene cellulosic fibers and from 0% to 50%, dry weigh basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath sai acquisition/distribution layer relative to sai topsheet, comprising at least 15%, by weight of sai storage layer, of superabsorbent material and from 0 to 85% of a carrier means for said superabsorben material; said fluid acquisition/distribution layer having no more tha 6.0% of superabsorbent material and having a top surface area whic is at least 15% of the top surface area of said fluid storage laye and which is smaller than the top surface area of said fluid storag layer. 2. An absorbent structure for acquisition, distribution, an storage of bodily fluids, said structure characterized by: (i) a fluid acquisition/distribution layer having a average dry density of less than 0.30 g/cc, a -47- average density upon saturation with 1% NaCl aqueo solution', dry weight basis, of less than 0. g/cc, an «an average dry basis weight of from 0.0 to 0.10 g/cm 2 , said acquisition/distribution lay comprising' from 50% to 100%, preferably from 95% 100%, dry weight basis, of chemically stiffen cellulosic fibers and from 0% to 50%, dry weig basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath sa acquisition/distribution layer comprising at lea 15%, by weight of said storage layer, superabsorbent material and from 0% to 85% of carrier means for said superabsorbent material; said fluid acquisition/distribution layer having no more th 6.0% of superabsorbent material and having a top surface area whi is at least 15% of the top surface area of said fluid storage lay and which is smaller than the top surface area of said fluid stora layer. 3. The absorbent article or structure of Claim 1 or Claim wherein said acquisition/distribution layer is substantially free superabsorbent material, has a top surface area which is at lea 25% of the top surface area of said storage layer and which is le ttøp 90% of the top surfate area of the said storage layer, has average density upon saturation with 1.0% NaCl aqueous solution, d weight basis, of between 0.02 g/cc and 0.15 g/cc, and has an avera basis weight of between 0.01 g/cm 2 and 0.08 g/cm 2 , and wherein sa superabsorbent material has an Absorbent Capacity of at least g/g. 4. The absorbent article or structure of any of Claims 1 3 wherein said acquisition/distribution layer comprises from 2% 50% of said binding means, wherein said binding means compris non-chemically stiffened cellulosic material. 5. The absorbent article or structure of any of Claims 1 to 4 wherein said binding means comprises highly refined cellulosic. fibers having a freeness of less than 200 Canadian Standard Freeness, and said acquisition/distribution layer comprises from 5% to 15% of said highly refined fibers. 6. The absorbent article or structure of Claims 1 to 4 wherein said binding means comprises high surface area cellulose, and said acquisition/distribution layer comprises from 2% to 15% of said high surface area cellulose. 7. The absorbent article or structure of any of Claims 1 to 6 wherein said acquisition/distribution layer is an airlaid web. 8. The absorbent article or structure of any of Claims 1 to 7 wherein said acquisition/distribution layer is a thermally bonded web comprising from 10% to 50% of thermoplastic material, said web being made by preparing a web of a blend of said stiffened fibers and from 10% to 50%, total web weight basis, of thermoplastic material, heating the web to melt the thermoplastic material, and cooling the web. 9. The absorbent article or structure of any of Claims 1 to 6 or Claim 8 wherein said acquisition/distribution layer is a wetlaid web. 10. The absorbent article or structure of any of Claims 1 to 9 wherein in said storage layer the carrier means for said superabsorbent material comprises a web of cellulosic fibers, and wherein said storage layer comprises from 15% to 75% of said superabsorbent material, said superabsorbent material having an Absorbent Capacity of at least 15 g/g. material and wherein said storage layer is substantially free of chemically stiffened cellulosic fibers. -49- 11. The absorbent article or structure of any of Claims 1 to 10 wherein in said storage layer the superabsorbent material comprises discrete particles of absorbent gelling material having an Absorbent Capacity of at least 20 g/g. ,12. The absorbent article or structure of any of Claims 1 to 10 wherein said storage layer comprises superabsorbent fibers.

Inventors: COOK JEFFREY TODD, LASH GLEN RAY, MOORE DANNY RAYMOND, YOUNG GERALD ALFRED, COOK, JEFFREY, TODD, LASH, GLEN, RAY, MOORE, DANNY, RAYMOND, YOUNG, GERALD, ALFRED
Applicants: PROCTER & GAMBLE, THE PROCTER & GAMBLE COMPANY
Application year: 1991
Main classification: A61F13
IPC codes: A61F13, A61L15