CA2069443C - Absorbents containing stiffened fibers and superabsorbent materials - Google Patents

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 % NaC1 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/cm2; 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

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FIELD OF THE INVENTION
This inventton relates to absorbent structures using both cellulosic fiber mat-rial and superabsorbent material The absorbent structures can be used in a variety of absorbent articles such as dtsposable dtapers adult incontinence pads and brtefs and the li~e whtch are rcquired to handle relatively large a~ounts of disch~rged body fluids espec1ally repeated discharges of relatively large amounts of fluid in relatively short amounts of time ~ACK6R~l~n OF THE INVF~TION
Absorb nt ~ebs ~htch co~prise ent-ngled masses of fibers i e f1brous ~ebs are ~ell kno~n in the art Such webs can ib~ibe liqu1ds such as discharged body flutds both by an absorption mechantsm wherein flutd is taken up by the fiber matertal itself and by a wicktng mech-nism wherein fluid is acqutred by dtstrtbuted through and stored in the capillary intersttces bet~ en fibers One me-ns for improving the absorbency characteristics of such fibrous web structures is to ;ntG~ ~G~ ate therein su~erabsorbent 0aterial such as as polymeric gelling material (also nefE~ ed to as hyd cgel-forming material supe n bsorbent polymers etc ) wh1ch imbtbe fluid The superabsorbent material se n es to retain fluid such as discharged body liquids An absorbent st.~ct~ _ of this type wherein hydroge~for~ing m~terials in parttculate form are inco w ~ated ~6~44 3 W 0 91/11163 P ~ /ussl/ool69 tnto ftbrous ~ebs is disclosed in ~eisman and &oldman; U.S. Patent 4 610 678; Issued Septe~ber 9 1986.
The i prove~ent in absorbency provided by incorporatjon of absorbent gelling m~teri~ls has permitted the realizatton of absorbent articles such as diapers which employ relattvely thin absorbent cores and ~htch are therefore relattvely thin products. Thinner diapers are less bulky to wear and ftt better under clothing. The~ are also more comp~ct in the package ~aking the dt~pers easier for the consumer to carry and store.
Compactness in pack~ging also results in reduced distribution costs for the ~anuf~cturer and distrtbutor.
One such absorbent core configuration which is useful for use as the absorbent structure in relatively thin absorbent art1cles is dtsclosed in U.S. Patent No. 4 765 780 issued August 23 1988 (Angstadt). This patent discloses absorbent arttcles such as diapers ~hich haYe a two layer absorbent core configuration wherein the core co~prises an upper primary layer and a lower dusting layer. The primary layer is an airlaid web of hydrophilic ftber miterial ~ith a ~substantial a~ount of absorbent gelling material admixed therewith. The dusttng layer comprises hydrophilic fiber o~terial and preferably contains no absorbent gelling mtteri~l.
Another tbsorb nt core configuration is disclosed in ~eisman/Houghton/6ellert U.S. Patent No. 4 673 402 issued June 1~ 1987. This p~tent discloses absorbent articles having a dual l~yer absorbent core. In the dual layer configuration the core co~prises ~n upper prim~ry layer which is an airlaid web of hydrophilic fiber material optionally with a small amount of polymeric gelling agent parttcles admixed therewith. The core ~o also comprises an underlying insert layer which is an airlaid mixture of hyd.ophilic fiber material and a substanttal amount of polymeric gelling agent particles. This insert layer is generally positioned towtrd the front of the absorbent article such that more th~n half of the poly~eric gelling agent material in the arttcle is found in the front half thereof. Absorbent articles having the particu1~r dual layer conftguration of the 402 Datent PCI~/US91/00169 ~O 91/11 163 can be prepared in the form of especially thin, highly effective, low leakage diaper products.
Notwithstanding the existence of absorbent cores as described above, there remains a need to provide absorbent cores with improved effective absorbent capacity. One way to theoretically do this would be to increase the level of polymeric gelling material in the absorbent core. Unfortunately, high levels of polymertc gelling material, (espectally levels in excess of about 15%) in fibrous webs typically used tn abso.bent cores tends to induce a phenomena referred to as gel-blocking. Gel-blocking occurs when the polymeric gelling material located in regions first contacted with fluid increase in volume as a consequence of imbibing the fluid and forming the hyd~ogel. ~hen polymeric gelling material concentration is too high, the hydrogel can block I5 additional fluid from reaching other regions of the core having unused absorbent capactty. The occu-,ence of gel blocking can lead to leakage during usage of the absorbent arttcle.
Polymeric gelling materials have been developed which can exhtbit a reduced tendency to result in gel blocking. Such materials are described in U.S. Patent RE 32,649, April 19, 1988, Brandt/Goldman/Inglin. However, these improved polymeric gelling materials, and other superabsorbent materials, are subject to performance limttations of the web of cellulosic fibers in which part~cles of gelling material are dtstrtbuted. In particular, ~en-initlal wetting, the cellulosic fibers become highly flexible and the web tends to collapse to a higher density and, consPq~ently, exhtbtts smaller average pore size. Whereas, pore stze becomes smaller than the pore size in regions of the web not yet wetted, a capillary gradient is created which opposes efftcient transport of fluids to the dry areas of the absorbent arttcle.
Another reason why many absorbent arttcles such as diapers are subject to leakage is inabillty to absorb second and subsequent discharges of fluid even if the first fluid discharge has been effectively absorbed. Lea~age due to second and subsequent dtscharges is especially prevalent during the night, ~hen ~users,-eo~monly e~peri~ mu~ipl~,rdtscharges before being 4 zn~9443 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, is the inability of 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 fluidtransported to the farther reaches of the core. In this regard, even in the absence of polymeric gelling material, the overall absorbent capacity of 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 an aspect 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 an object of an aspect of this invention to provide superabsorbent-containing absorbent structures which can acquire fluid rapidly in the region ofdischarge 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 an object of an aspect of this invention to provide absorbent structures which are capable of meeting the objects described above which are of a relatively thin deslgn.
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 Leonard R. Thompson. This patent discloses disposable 3 2 0 6 9 4 9 3 PCr/US9t/00169 absorbent articles comprising a layered absorbent core positioned between a bac~sheet and a topsheet, wherein the absorbent core comprises an upper layer of st1ffened, twisted, curled cellulose ftbers and requires from about 3% to 15X, by weight, of large S part1cle absorbent gelling matertal ant a lower layer of st1ffened, twisted, curled cellulose fibers and from about lS% to 60X, by weight, of absorbent gelling material. The upper layer serves the principal purpose of acqu1sitton and distribution of bod11y fluid discharges. ~he stiffened, twisted, curled fibers are highly benefictal in this regard. The lower layer, which is necessarily smaller than the upper layer, is principally for fluid storage.
Another absorbent structure which has been proposed is described in U.S. Patent 4,798,603, S. C. Meyer et al., issued lS January 17, 1989, titled ~Absorbent Article Having a Hydrophobic Transport Layer.~ As suggested by the title, this patent describes an absorbent arttcle with a hyd~ophobic transport layer, made from known hydrophobtc synthetic ftbers. The transport layer is posttioned between a topsheet and an absorbent body. The absorbent body is necessarily more hydrophilic than the transport layer. The purpose of the transport layer is to act as an insulattng layer between the topsheet and the absorbent body, to reduce skin wetness. Regardless of whether the structures described therein meet this objective, the hydrophobic nature of ~ transport layer of U.S. Patent 4,798,603 would be expected to have limited fluid acquisitton and fluid transport properties due, at least tn part, to the hyd~ophobicity of the layer. This would be parttcularly so for second and successive fluid dtscharges after whtch any optional surfactants have been washed away.
Notwithstanding the existence of absorbent articles of the type described above, there is a need to identtfy further improved configurations for absorbent arttcles which provide improved fluid distributton and acquisition performance, especially with respect to successive fluid discharges.
Accordingly, the present inventton provides improved absorben~ structures, and~ ments for use ~ere~n, as well as absorbent arttcles uttltzing such structures, uttllztng a multiple -6- 2 ~ 6 9 ~ ~ 3 layer absorbent core that effectively and efficiently acquires the wearer's discharged body fluids upon initial and successive discharges, transports acquired fluid, from both initial and successive discharges over a relatively large proportion of the absorbent structure surface area, and stores such discharged fluids.
SUMMARY OF THE INVENTION
Various aspects of the invention are as follows:
An absorbent article for acquisition, distribution, and storage of bodily fluids, said article comprising:
(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 about 0.30 g/cc, an average density upon saturation with 1% NaC1 aqueous solution, 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, said acquisition/distribution layer comprising from about 50% to 100%, dry weight basis, of chemically stiffened cellulosic fibers and from 0% to about 50%, dry weight basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath said acquisition/distribution layer relative to said topsheet, comprising at least about 15%, by weight of said storage layer, of superabsorbent material and from 0% to about 85%
of a carrier means for said superabsorbent material;
said fluid acquisition/distribution layer having no more than about 6.0% of superabsorbent material and having a top surface area which is at least 15% of the top surface area of said fluid storage layer and which is smaller than the top surface area of said fluid storage layer.
An absorbent structure for acquisition, distribution, and storage of bodily fluids, said structure comprising:
(i) a fluid acquisition/distribution layer having an average dry density of less than about 0.30 g/cc, an average density upon saturation with 1%
NaCI aqueous solution, dry weight basis, of less than about 0.20 g/cc, and an average --6a-dry basis weight of from about 0.001 to about 0.10 g/cm2, said acquisition/distribution layer comprising from about 50% to 100%, dry weight basis, of chemically stiffened cellulosic fibers and from 0% to about 50%, dry weight basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath said acquisition/distribution layer having no more than about 6.0% of superabsorbent material and having a top surface area which is at least 15% of the top surface area of said fluid storage layer and which is smaller than the top surface area of said fluid storage layer.
By way of added explanation, 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% NaCI 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 toincrease 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 ofstiffened 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 ,..

W O 91/11163 2 0 6 9 4 ~ 3 P~r/US91/00169 free~ of superabsorbent material means less than about 2.0X, preferably less than about 1.0%, more preferably zero or essentially zero percent superabsorbent material. As used herein, - ~essentially zero- percent superabsorbent material means lo~
amounts (less than about O.5X) of superabsorbent material present in the acquisitton/dlstribution layer incidental to the contact or close proximtty of the superabsorbent-containing storage layer with the acquisition/d~stributton layer.
The ftuid acquisition/d1stribution layer has a top surface area which is at least 15% of the top surface area of the fluid storage layer, but which is smaller than the top surface area of the fluid storage layer. The acquisition/distribution layer is preferably positioned relative to the fluid storage such that in the unfolded planar configuration of the article none of its surface area extends beyond the boundaries of the top surface area of the fluid storage layer. More preferably the acquisition/distribution layer has a top surface area which is from about 15% to about 95%, most preferably from aboùt 25X to about 90X, of the top surface area of the fluid storage layer.
zO The absorbent structure can be advantageously utilized as the absorbent core in absorbent articles, e.g., disposable diapers and incontinence briefs, which also comprise a fluid pervious topsheet and a fluid impervious backsheet affixed to the topsheet, wherein the absorbent core is disposed therebetween. The absorbent core ~s pDsitioned such that the acquisition/distribution layer is located between the topsheet and the storage layer, and the storage layer is located between the acquisit10n/distribution layer and the backsheet.
the superabsorbent material used in the storage layer has an Absorbent Capac~ty of at least about 10 grams of Synthetic Urine (l.OZ NaCl aqueous (distilled water) solution) per gram of superabsorbent material, measured according to the test procedure hereinafter described. Suitable superabsorbent material categories include polymeric absorbent gelling materials, typically utilized in the form of discrete particles, and superabsorbent fibers, such as acrylate grafted fibers and superabsorbent modified cellulosic fibers.

20694~3 W O 91/11163 PC~r/US91/00169 BRIEF OESCRIPTION Of THE DRA~INGS
Figure 1 represents a perspective vie~ of a diaper with an absorbent core having the multtple layer conftguration of the present invention. The absorbent core shown has a rectangular-shaped acquistt1cn/distribut10n layer and an hour glass-shaped storage layer.
Figure 2 represents a perspective vie~ of a dtaper structure similar to Figure 1, but wheretn the storage layer has a ~odtfied hour-glass shape.
Flgure 3 represents a direct view of an absorbent core useful for diaper applicattons, 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/dtstribution layer.
DETAILED OESCRIPTIOH OF THE INVENTION
The absorbent structures of the present invention can be utilized in disposable products which are capable of absorbing significant quantittes of body flu~ds, such as urine and water in body wastes. Such arttcles may be prepared in the form of dtsposable diapers, adult inconttnence brtefs, adult incontinence pads and the like.
The absorbent arttcles herein generally comprise three basic structural components. One such component is a liquid impervious backsheet. On top of thts backsheet is disposed an absorbent core which itself comprises two dtsttnct layers, and which includes a s~erabsorbent matertal in one of the layers. On top of this absorbent core and joined to the bac~sheet is a water pervious topsheet. The topsheet is the element of the arttcle which is placed next to the skin of the wearer. As used herein, the term ~oined~ encompasses configurattons whereby the topsheet is directly joined to the backsheet by affixing the topsheet directly to the backsheet, and conftgurattons whereby the topsheet is indtrectly jotned to the backsheet by aff~xing the topsheet to intermedtate members whtch in turn are affixed to the backsheet.
Preferab1yj-the topsheet and back~heet -are joined dtrectly at the 3~ diaper per-tphery by adhesiYe or ot~her attach0ent means kno~n in the art.

Especially preferred absorbent articles of this invention are disposable diapers.
Articles in the form of disposable diapers are fully described in Duncan and Baker, U.S. Patent Re 26,151, Issued January 31, 1967; Duncan, U.S. Patent 3,592,194, Issued July 13, 1971; Duncan and Gellert, U.S. Patent 3,489,148, Issued January 13, 1970;
and Buell, U.S. Patent 3,860,003, Issued January 14, 1975. A preferred disposable diaper for the purpose of this invention comprises an absorbent core; a topsheetsuperposed or co-extensive with one face of the core, and a liquid impervious backsheet superposed or co-extensive with the face of the core opposite the facecovered by the topsheet. Both the backsheet and the topsheet most preferably have a width greater than that of the core thereby providing side marginal portions of the backsheet and topsheet which extend beyond the core. Frequently the backsheet and topsheet will be fused together in these side marginal portions. The diaper is preferably constructed in a shaped configuration such as, but not limited to, anhourglass shape.
The backsheet of the articles herein can be constructed, for example, from a thin, plastic film of polyethylene, polypropylene, or other flexible moisture impeding material which is substantially water impervious. Polyethylene, having an embossed caliper of approximately 1.5 mils, is especially preferred.
The topsheet of the article herein can be made in part or completely of synthetic fibers or films comprising such materials as polyester, polyolefin, rayon, or the like, or of natural fibers such as cotton. In nonwoven topsheets, the fibers are typically bound together by a thermal binding procedure or by a polymeric binder such as polyacrylate. This sheet is substantially porous and permits a fluid to readily pass therethrough into the underlying absorbent core.
Another suitable type of topsheet comprises the topsheets formed from liquid imperious polymeric material such as polyolefins. Such topsheets can have tapered capillaries of certain diameter and taper positioned in the topsheet to permit flow of discharged fluid through the topsheet into the underlying absorbent core of the article.

' ' -lo- 7. ~ 6 ~ 4 4 3 The topsheets used in the articles of the present invention should be relativelyhydrophobic 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. 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 l~rnin~tes 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 basorbent core which 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 W O 91/11163 2 0 6 9 4 4 3 P(~r/usgl/00l69 layer and the storage layer to increase integrity of the acquisition/distribution layer during processing and/or use. Such sheet or scrim can enve10pe all or part of - acquisition/distribution layer, or simply be posit10ned as S described above without necessaril~ enveloping the acquisition/distribution layer. Also, optionally, the superabsorbent material-containing storage layer can be enveloped with a fluid pervious sheet, such as a tissue paper sheet, to obviate user concerns with loose superabsorbent material.
Ac~uisition/Dtstribution LaYer One essential element of the absorbent structures hereof is an upper fluid acquisition/distribution layer which comprises a combination of a hydrophilic fibrous material, described more fully hereinafter. This fluid acqutsit10n/distribution layer serves to quickly collect and temporarily hold discharged body fluid. A portion of discharged fluid may, depending upon the wearer's position, permeate the acquisition/distribution layer and be absorbed by the storage layer in the area proximate to the discharge. However, since fluid is typically discharged in gushes, the storage layer in such area may not absorb the fluid as quickly as it is discharged. Therefore, the upper acquisition/distribution layer hereof a7so facilitates transport of the fluid from the point of initial fluid contact to other parts of the acquisition/distribution layer. In the context of t~ ~resent invention, it should be noted that the term ~fluid-means ~liquid.~
As previously noted, the fluid acquisition/distribution layer is a web comprising stiffened cellulosic fibers. The acquisition layer comprises from about 50% to 100% of these fibers and from 0%
to about SOX of a binding means. Suitable bindin~ means are dtscussed below.
The fluid distribution functton of the acquisition/distribu-tion layer is of particular importance in order to more fully utilize the capacity of the storage ~ection. the presence of ~5 substantial a~ounts of super~hso.bent materials in the acquisition/distribution layer whtch swell upon contact ~ith 20~94~

fluits is believed to adversely affect this funct10n of the acquisition/distribution layer.
A variety of other factors relating to the fluid acqui-sition/distribution layer of the absorbent structures herein can S be of importance in determining the effect1veness of the result1ng absorbent art~cles. These include shape, basis we19ht, dens1ty, permeabil1ty, captllarity and wicking ability, the type and structural tntegrtty, and character of the fibrous material utilized. As indicated, the acquisition/dlstribution layer of the I0 core is preferably elongated. for purposes of this invention, this means that the acquisttion/distribution layer, like the storage layer, is elongated if it is of unequal length and width in the unfoldet, flat configuration. The acquisition/distribution layer in the unfolded configuration can be of any desired shape, lS for example, rectangular, trapezoidal, oval, oblong or hourglass-shaped. The shape of the upper fluid acquisi-tlon/distribution layer of the core can, but need not necessarily, correspond to the general shape of the storage layer. The top surface area of the acquisition/distribution layer will preferably range from about 25X to about 90Z of the top surface area of the storage layer, and also preferably will not extend beyond the edge of the storage layer at any outer boundary. The acquisitlon/distribut10n layer will typically have top surface area less than about 80X of that of the storage layer.
Preferably, there is a margtn from the edge of the acquisit10n/distrtbution layer to the edge of the storage layer of at least about 0.5 cm, preferably at least about I.25 cm, in the regtons proximate to where fluid is discharged during use. In diapers, th1s would correspond, for example, to the crotch region 115 of Figure 2, particularly at the narrowest part of the storage core 106 in the central region 115. Addltionally, especially for absorbent art1cles to be worn by males, such a margin is maintained in the front waist region, exemplified as 112 in Figure 2, which area is to be worn on the front of the wearer.
The fluid acquisit10n/distr1but10n layer will generally have an -average dry density of less than about 0.30 g/cm3, measured pr10r to- u~e, and an aver~ge denstty upon~ ttng to saturation W O 91/11163 2 ~ 6 ~ ~ ~ 3 pc~r/us9t/oo169 with Synthet1c Urine (1.0% NaCl aqueous solution, with dlstilled water~, on a dry weight basis, of less than about 0.20 g/cm3, preferably less than about O.lS g/cm3. Also, preferably, the average dry density and density upon wettlng to saturation are between about 0.02 g/cm3 and 0.20 g/cm3, more preferably between about 0.02 g/cm3 and about 0.15 g/c~3. The average dry basis weight of the acquisitton/distributton layer of the absorbent core will typically range from aboùt 0.001 to about 0.10 g/cm2, preferably fro~ about 0.01 to about 0.08 g/cm2, more preferably from about O.OlS to about 0.04 g/cm2. Unless specifically indicated, all basis weights and density values are calculated on a dry basis (at equilibrium moisture levels no greater than about 6%). Density and basis weight can be substantially unifor~
although nonuniform density and/or basis weight, and density and/or basis weight gradients, are meant to be encompassed herein.
Thus, the acquisition/distribution layer can contain regions of relatively higher or relatively lower density and basis weight, preferably not exceeding the foregoing ranges. Average dry density and average dry density upon wetting to saturation with Synthetic Urine (1.0% NaCl aqueous solution, with distilled water) values are calculated from basis weight of the dry layer and layer caliper. Dry callper and caliper upon wetting to saturation are measured under a confining pressure of 0.2 psi (1.43 kPa).
Average density upon wetting to saturation is calculated from the ~5 d~ basis weight and saturation caliper. ~he saturation caliper is- measured after the layer is saturated (under unrestrained conditions) with the 1.0% NaCl aqueous solution and allowed to equilibrate.
The acquisition/dlstribution layer of the absorbent structures herein essentially comprises a web of hydrophilic chemically stlffened cellulosic fibers. These cellulosic fibers are typically wood pulp flbers which have been stiffened with an intrafiber chemical stlffening agent.
The fluid acquisition/distribution layer should contain no 3S more than about 6.0% of superabsorbent material. Preferably, the acquisitlon~distribution layer will be substantla11y free of superabsorbent ~ateriat. For purposes herein, ~substantia1ly W O 91/11163 2 0 6 9 4 4 3 PC~r/US91/00169 free~ of superabsorbent material means less than about 2.0~, preferably less than about 1.0%, more preferably zero or essent1ally zero percent superabsorbent matertal. As used herein, ~essentially zero~ percent superabsorbent material means lo~
S a~ounts (less than about 0.~%) of superabsorbent matertal present in the acquisitlon/dtstribution layer incidental to the contact or close proximity of the superabsorbent-containing storage layer wtth the acquisttion/dtstribut~on la~er.
If present in the acquisition/dtstributton layer, especially if present in amounts greater than about 2.0X, superabsorbent material in the form of particles of absorbent gelling material may be of relatively large diameter (e.g., from about 400 to about ~00 microns in mass median particle size). Superabsorbent part kles having a mass median part kle size less than 400 microns lS may also be employed.
As discussed above, the articles of the present invention employ chemically stiffened fibers. As used herein, the tenm ~che~ically stiffened fibers~ means any fibers ~hich have been stiffened by chemical means to increase stiffness of the fibers under both dry and aqueous conditions. Such means include the addition of che~ical st~ffening agents which, for exa~ple, coat and/or impregnate the fibers. Such means also include the sttffening of the fibers by altering the chemical structure of the fibers themselves, e.g., by cross-linking polymer chains.
2S For exemplary purposes, polymeric stiffening agents which can coat or impregnate cellulostc fibers include: cationic modified starch having nitrogen-containing groups (e.g., amino groups) such as those available from Nattonal Starch and Chemical Corp., Bridgewater, NJ, USA; latex; wet strength resins such as polyamide-epichlorohydrtn resin (e.g., KymeneTM 557H, Hercules, Inc. Wilmington, Oelaware, USAJ, polyacrylamite resin (described, for example, in U.S. Patent 3,556,932 issued January 19. 1971 to Coscia, et al.; also, for example, the commercially available polyacrylamide marketed by Amertcan Cyana~id Co., Stanford, CT, ~SA, under the tr~de~ame ParezTM 631 NC); urea fon0aldehyde and mela~iae forma]dehy~ resins,~ and polyethyleni~ine resins. A
gQnor~l tisser.~tto~ on ~t str~n~th r~sins u~izeJ in the paper art. ~nd l~n~r~l 1 v ~rlnl ~ e~

-15- ~ $ ~ ~
monograph series No. 29. "Wet Strength in Paper and Paperboard", Technical Association of the Pulp and Paper Industry (New York, 1965).
The fibers utilized in the structures herein can also be stiffened by means of chemical reaction. For example, crosslinking agents can be applied to the fiberswhich, subsequent to application, are caused to chemically forrn intra-fiber crosslink bonds. These crosslink bonds can increase stiffness of the fibers. Whereas the utilization intrafiber crosslink bonds to chemically stiffen the fibers is preferred, it is not meant to exclude other types of reactions for chemical stiffening of the fibers.
Fibers stiffened by crosslink bonds in individualized (i.e., fluffed) form are disclosed, for example, in Bernardin, U.S. Patent 3,224,926, Issued December 21,1965; Chung, U.S. Patent 3,440,135. Issued April 22, 1969; Chatterjee, U.S. Patent 3,932,209, Issued January 13, 1976 and Sangenis et al., U.S. Patent 4,035,147, Issued July 12, 1977. More preferred fibers are disclosed in Dean et al., U.S. Patent 4,822,453, issued April 18, 1989, Dean et al., U.S. Patent 4,888,093, issued December 19, 1989, and Moore et al., U.S. Patent 4,898,642 issued February 6, 1990. In addition to being hydrophilic, these stiffened fibers remain stiff even upon wetting;
thus webs made from them do not collapse, as do webs made from conventional unstiffened fibers when wet. This provides improved ability to acquire and distribute fluids in second and subsequent discharges.
In the more preferred stiffened fibers, chemical processing includes intrafiber crosslinking with crosslinking agents while such fibers are in a relatively dehydrated, defibrated (i.e., individualized), twisted, curled condition. Suitable chemical stiffening agents include monomeric crosslinking agents including, but not limited to, C2-C8 dialdehydes and C2-C8 monoaldehydes having an acid functionality can be employed to form the crosslinking solution. These compounds are capable of reacting with at least two hydroxyl groups in a single cellulose chain or on proximately located cellulose chains in a single fiber. Such crosslinking agents contemplated for use in pl~pa~ g the stiffened cellulose fibers include, but are not limited to, glutaraldehyde, glyoxal, formaldehyde, and glyoxylic acid. Other suitable stiffening agents are polycarboxylates, such as cikic acid. The polycarboxylic stiffening agents and a process for making stiffened fibers from these are described in U.S. Serial No. 596,606, filed October 17, 1990. The effect of crosslinking under these conditions is to form 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 making them 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 term "twist count" refers to the number of twist nodes present in a certain length of fiber. Twist count is utilized as a means of measuring the degree to which a fiber is rotated about its longitudinal axis. The term "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 microscope 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 of 180~. The number 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 mentioned 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, nodes per millimeter.
Furthermore, the average wet fiber twist count of these fibers should preferably be at least about 1.8, preferably at least about 3.0, and should also preferably be at least about 0.5 twist nodes per millimeter less WO 91/11163 2 0 ~ 9 ~ 4 3 PCI~/US91/00169 than the average dry fiber twtst count. Even more preferably, the average dry fiber twist count should be at least about 5.5 twist nodes per mtlltmeter, and the average wet fiber twist count should - be at least about 4.0 twtst nodes per mtlttmeter and should also be at le-st l.0 twtst nodes per mtlltmeter less than its average drr ftber t~tst count. Most preferably, the average dry fiber twtst count should be at least about 6.~ twtst nodes per milltmeter, and the average wet f~ber twtst count should be at least about S.0 twist notes per milllmeter and should also be at least l.0 twist nodes per mtllimeter less than the average dry ftber twist count.
In addttion to being twisted, the preferred fibers used in the acquisitlon/distribution layer of the absorbent structure are also curled. Fiber curl may be described as the fractional shortening of the fiber due to kinks, twists, and/or bends in the f~ber. For the purposes of this inventton, ftber curl is measured in tenms of a two dimension~l plane. The extent of fiber curling can be quanttfied by referenctng a ftber curl factor. The fiber curl factor, a two dimensional measurement of curl, is determined by viewing the ftber in a two dimensional plane. To determine curl factor, the projected length of the fiber as the longest dtmension of a two dimensional rectangle encompassing the fiber, LR, and the actual length of the fiber, LA, are both measured.
The ftber curl factor can then be calculated from the following 1~qu~t~on:
Curl Factor ~ (LAJLR) - 1.
An image analysis method that can be uttltzed to measure LR
and LA is described in U.S. Patent 4,898,642. Preferably the ftbers uttlized in the layers of the absorbent core herein will have a curl factor of at least about 0.30, and more preferably will have a curl factor of at least about 0.50.
The degree of sttffentng, dependent upon the type and amount of sttffening agent (~.e., crosslinking agent) used, the degree of dehydrat10n of the ftbers during curing of the crosslinking agent, and the curing ttme and condtttons, affect t~he abiltty of the ftber to.take up fluid an~ the tendeoc~ of the f{ber to swell.

20~ 9 4~3 W o 91/11163 P~r/US91/oo169 The fiber stiffness as it relates to resistance to fiber wall swelling can be quanttfied by referencing the water retention value (WRV) of the sttffened cellulos1c ftbers used in the absorbent art1cles heretn. ~RV is a measure of the amount of water reta1ned by a mass of ftbers after substantially all of the interftber water has been removed. Another para~~ter ~h1ch can be used to charactertze the nature of the stiffened ftbers fonmed by crosslinktng f~bers in relat~vely dehydratad form is that of alcohol retentton value (ARV). ARV ~s a measure of the extent to which a fluid, e.g., isopropyl alcohol, which does not induce substant1al fiber swelling, is taken up by the stiffened fibers.
The ARV of the sttffened fibers is directly related to the extent that the fibers were swollen with the solution of crosslinking agent during the stiffening procedure. Relattvely higher ARVs mean that the f1bers were generally swollen to a relatively greater extent durinQ crosslinking. Procedu-es for determining ~RV and ARV are descrtbed in U.S. Patent 4,898,642.
The WRV for the sttffened, twtsted, curled fibers used in the present invent10n will preferably range between about 28% and about 50%. In more preferred embodiments, the ~RV of the fibers can range from about 30Z to 45X. Fibers having a ~RY within these ranges are believed to provtde an opttmal balance of swelling-in-duced untwisttng and ftber st1ffness.
The sttffened cellulose ftbers preferred for use herein are those whtch have an ARV (isopropol alcohol) of less than about 30X. The limitatton that such ftbers have an ARV (isopropol alcohol) of less than about 30X is indtcative of the relatively dehydrated, unswollen state of these fibers during the stiffening process. More preferably, the ARV (~sopropol al~ohol) of the fibers useful here~n will be less than about 27%.
The st1ffened cellulose f~bers herein having the preferred ~wist count, curl factor, WRV and ARV charactertstics hereinbefore set forth, can be prepared by internatly crossl1nking such fibers in relativelr dehydrated form wh~le or after-such ftbers are bein~
-35 or have been drted~~n~-deftbrated-(~.e., ~n uffed~) as described in U.S. Patent 4,898~ t ~s -mnot, ho~: ve., meant to necessartly exclude other hydrophtl1c, chemically st1ffened fibers from this invention, such other fibers being described in (but not limited to) the previously referred to U.S. Patents 3,224,926, 3,440,135, 4,035,147 and 3,932,209.
A characteristic of stiffened fibers, particularly the twisted, curled stiffenedfibers is their ability to partially untwist and uncurl upon wetting. Thus, when formed into webs of sufficient density, the webs can expand upon wetting to an equilibrium wet density, which, when calculated, on a dry fiber density, is less than the average dry density (prior to wetting). This accounts for the average dry densities of up to about 0.30 g/cm3 described above, in conjunction with lower average densities upon wetting to saturation. Such webs which can expand upon wetting are described in U.S. Patent 10 4,822,453. To the extent that it is desired to utilize this characteristic in absorbent article design, those of ordinary skill in the art will be able to adjust the relative amount of stiffening agent used, and the extent to which twist and curl in the stiffened fibers is imparted, to achieve the desired amount of expansion upon wetting.
The stiffened cellulosic fibers can be provided in web form by various 15 techniques, including airlaying and wetlaying.
Airlaid Webs The stiffened cellulosic fibers can be airlaid to form the web of a desired density and basis weight. The stiffened fibers for use in the present invention can be airlaid according to techniques well known to those skilled in the art of airlaying 20 cellulosic fibers. In general, airlaying can be effected by metering an air flow cont~ining the fibers, in substantially dry condition, onto a wire screen and, optionally, compressing the resulting web to the desired density. Alternately, the fibers can be airlaid to the desired density without compression. The airlaid web will comprise at least about 50% of stiffened cellulosic fibers, as described above, and can comprise up 25 to and including 100% of said fibers. The web can optionally contain binding means, such as described below, or other optional components, such as or ingredients modifying fluid handling properties (e.g., hydrophilic surface active agents), and the like.

3 91/11163 2 0 6 ~ 4 ~ 3 P{~r/USsl/00169 ~etlald Webs In another embodiment, the st1ffened cellulosic fibers, rather than being airlaid to form the web, are wetlaid. The wetlaid webs comprtse from about SOX to lOOX of the stiffened f~bers and fro~ OX to about SOX of a b1nd1ng means for increasing phystcal integr1ty of the web, to fac11itate processing in the wet and/or dry state, and to prov1de increased integr1ty upon wetting of the web during use. Preferably, the wetla1d webs will co0prtse at least about 2% of a fibrous b1nd1ng means or h1gh surface area cellulose bind1ng means (hereafter described). Chemical additives can also be used as binding means, and are incorporated into the 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 form lS sheets such as dry lap and paper are well known in the art. These techniques are generall~ applicable to the wet-laying of the sttffened fibers to form wetlaid sheets useful in the absorbent structures of th1s invent10n. Su1table wetlaying techniques include handsheet1ng, and wetlay1ng w1th the utilization of papermaking machines as dtsclosed, for instance, by L. H. Sanford et al. in U.S. Patent 3,30l,746. Due to the behavior of stiffened fibers, particularly their tendency to flocculate in aqueous slurries, certain process1ng modifications, hereafter described, are preferably imple~ented when wetlaying with papermaking ~ch~nes. In general, wetlaid webs can be made by depositing an aqueous slurry of fibers on to a foraminous forming wire, dewatering the wetlaid slurry to form a wet web, and drying the wet web. Preferably, the aqueous slurries of fibers for wetlaying will have a fiber consistency of between about 0.05% and about 2.0%, preferably bet~een about O.OS% and about 0.2%, total slurry weight bas1s. Depostt10n of the slurry ts typically accomplished using an apparatus known in the art as a headbox. The headbox has an opening, known as a sllce, for delivering the a~ueous slurry of fibers onto the foraminous formtng wire. -The fora~inous forming wire is often referred to in the art as a fourdr~nier wire. The Fou,dli..ierYwire can be of-construction and mesh size used for dry lap or other papenmak1ng processing. P.~ft~ably, mesh sizes of W 0 91/llt63 2 0 ~ ~ ~ 4 3 P(~r/US91/00169 about 70 to about 100 (Tyler standard screen scale) are used.
(All mesh stzes referred to herein shall be based upon the Tyler standard screen scale, unless otherwise speciftcally indicated.) Conventlonal destgns of headboxes known in the art for drylap and S ttssue sheet formatlon may be used. Suitable commercially avatlable headboxes include, for example, fixed roof, twin wire, and drum former headboxes. Once formed, the wet web is dewatered and drted. Oewatering can be performed wtth suctton boxes or other vacuum devices. Typically, dewatering increases the fiber conststency to between about 8% and about 45%, total wet web weight basis, preferably between about 8X and about 22%.
Dewatering to consistencies above about 22% may require wet-pressing and is less preferred. After dewatering, the web can be, but is not necessarily, transferred from the forming wire to a drytng fabric whtch transports the web to drytng apparatuses. The drying fabrtc is preferably coarser than the forming wire, for increased drying efficiency. The drying fabrtc preferably has about 30X to about 50X open area and about 15% to about 25%
knuckle area, such as a 31 % 25 3S (satin weave) fabric that has been sanded to increase the knuckle area to withtn the preferred range. Wet mtcrocontract10n is preferably implemented during transfer from the formtng wtre to the fabric. ~et mlcrocontraction can be accompltshed by running the forming wire at a speed whtch is from about 5% to about 20% faster than the 5p~ d at whtch the fabrtc is being run. Drying can be acco~plished with a thenm-l blow-through dryer or vacuum device such as a suctton box, although thermal blow-through drying is preferred. The wetlaid webs are preferably drted to completion (generally to f~ber consistency between about 90% and about 95%) by the thermal blow-through dryers. Blow-through drytng is believed to efficiently dry webs of the stiffened fibers due to the htgh votd volume-of the webs. Steam drum drying apparatus kno~n in the art, such as Yankee drum dryers, can be used but are less preferred. Drum dryers are belteved to be less eff~ctent for drytng webs of the sttffened fibers and can also compact the webs.
The drted webs ~rc p~fe~bly not cre~ed.

w o 91/11163 2 0 6 9 4 4 3 PCT/US91/00169 As an alternative to drytng as described above the dewatered web can be removèd from the for0ing wire placed on a drying screen - and dried (unrestrained) in a batch drytng process by for example a ther0al blow through dryer or a forced convection steam S heated oven.
The sttffened fibers have the tendency to flocculate or form clumps in aqueous solutton. In order to inhtbit flocculation the aqueous slurry should be pu~ped to the headbox at a linear veloctty of at le~st ~bout 0.25 ~/sec. Also lt ts preferred that the linear velocitr of the slurry upon extt from the he~hox slice is from about 2.0 to about 4.0 times the veloc1ty of the forming wire. Another method for reducing flocculattons of fibers in a wetlaying process is described in U.S. Patent 4 889 597 issued December 26 1989 incorpor~ted herein by reference wherein jets lS of water are directed at the wetlatd ftbers iust after deposition on the forming wire.
B1ndtno Means Relattve to convention~l non-sttffened cellulosic fibers the crosslinked twtsted sttffened ftbers as descrtbed above form lower tenstle strength sheets parttcular in the undried condttion. Th~.efo,e in order to factlttate processing and to increase the integrtty of the webs parttcularly for wetlaid webs (~lthough bindtng ~eans c~n also be used with airlaid webs) a btndtng ~e~ns can be integrall~ incGr~c.ated into or onto the web.
~s-can be done by add1ng the btndtng means to the fibers prior to web formatton (wetl~td or airlald web format~ons) by applying the btndtng means (e.g. che~ic~l addtttve btndtng means) to a wetlatd web after deposition on the forming wire and before drytng by applying bindtng means to a dry web (wetlaid) or a combtnatton thereof.
Suttable binding me~ns for add1tton to the stiffened cellulosic ftbers prtor to fon~atton of the wet web from a pulp slurry include but are not limited to a variety of cellulosic and synthettc fibrous m~terials. Such material include 3~ nonsttffened cellulosic ftbers (t.e. conventtonal cellulosic pulp fibers) htghly refined n~nstiff4nedt cellulosic fibers which are reftned to ~anad~an Standar~ En en~s~ (LSF) a~ less than~about 200 W O 91/11163 2 ~ P ~ /US91/00169 CSF, more preferably from about 100 CSF to about 200 CSF (highly refined fibers being referred to herein as ~crill~, and hiQh surface area cellulosic material such as expanded cellulose fibers ~ (hereinafter described).
Various types of synthet1c f~brous matertal can be used in the synthettc fiber btndtng means. For the purposes hereof, the use of ~synthetic fibrous materials~ as a bindtng me~ns shall refer to the utilizatton of such fibrous matertals, in the final product, in fibrous form. (Preferably, the synthetic fibers are of at least staple length, i.e., the fibers preferably having an average length of at least about 1.5 cm). Any type of fibrous material which is suitable for use in conventional absorbent products is believed to be suitable for use in the acquisition/distribution web of the present invention. Specific examples of such fibrous material include modified cellulose fibers, rayon, polyester fibers such as polyethylene terephthalate (DACRON), hydrophilic nylon (HYOROFIL) and the like. Other fibers useful include cellulose acetate, polyvinyl fluoride, polyvtnylidene chloride, acrylics, polyvinyl acetate, polyamides (such as nylon), bicomponent fibers, trtcomponent fibers, mixtures thereof, and the like. Hydrophllic fibrous materials are preferred. Examples of suitable hydrophilic fibrous materials include hydrophllized hydrophobic fibers, such as surfactant-treated or stlica-treated thermoplastic fibers derived, r8~ - example, from polyolefins such as polyethylene or polypropylene, polyacryllcs, polyamides, polystyrenes, poly-urethanes and the ltke. Ilydrophobic synthettc fibers can also be used, but are less preferred. Such synthetic fibers that can be added to the web and utllized in the final web product in fibrous form include rayon, polyethylene, polypropylene, etc. Such fibers, when of a hydrophobic nature, are preferably present in quanttties of less than about 30X, total web weight basis, such that the web remains substantially hydrophtlic. Conventionally, nonstiffened fibers, crtll, and synthetic fibers can also be used in airlaid webs.
In one preferred l~mbodiment wheretn t~e acquisition/distribu-t~on~1ayer is-m~de,by,a.~etl~yttng ~rocess, the web comprises from ~ n ~ ~ ~ 4 ~

about 85% to about 95% of the stiffened cellulosic fibers and from about 5% to about 15% of crill, preferably from about 90% to about 95% of the stiffened fibers and from about 5% to about 10% of crill, most preferably about 92% of stiffened fibers and about 8% crill. Suitable cellulosic fibers for use as crill include chemically pulped wood fibers, including softwood and hardwood pulp fibers, preferably southern softwood fibers (e.g., Foley 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 weight basis.
In another embodiment, the acquisition.distribution layer comprises the stiffened fibers and up to about 25% of high surface area cellulosic material such as expanded cellulose fibers. Preferably, the acquisition/distribution layer comprising a web of wetlaid stiffened fibers and high surface area cellulose will comprise from about 85% to about 98% of the stiffened fibers, preferably from about 90% to about 95%, and from about 2% to about 15%, more preferably from about 5% to about 10%,of high surface area cellulose. The high surface area cellulosic material used herein will typically have a surface area of at least about lOm2/g, preferably at least about 20m2/g, of cellulosic material. Reference can be made to U.S. Patent 4,761,203, Vinson, August 2, 1988 for a thorough discussion of expanded cellulose fibers.
In general however, cellulosic fibers are multi-component ultrastructures made from cellulose polymers. Lignin, hemicellulose, and other components known in the art may also be present. The cellulose polymers are aggregated laterally to formthreadlike structures called microfibrils. Microfibrils are reported to have diameters of about 10-20 nm, and are observable with an electron microscope. Microfibrils frequently exist in the form of small bundles known as macrofibrils. Macrofibrils can be characterized as a plurality of microfibrils which are laterally aggregated to form a threadlike structure which is larger in diameter than a microfibril, but substantially smaller than a cellulosic fiber. In general, a cellulosic fiber is made up of a -25- ~ a ~
relatively thin primary wall, and a relatively thick secondary wall. The primary wall, a thin, net-like covering located at the outer surface of the fiber, is principally formed from microfibrils. The bulk of the fiber wall, i.e., the secondary wall, formed from a combination of microfibrils and macrofibrils. See Pulp and Paper Manufacture, Vol. 1, S Properties of Fibrous Raw Materials and Their Plepal~ion For Pulping, ed. by Dr.
Michael Kocurek, Chapter VI, "Ultrastructure and Chemistry", pp 35-44, publishedjointly by C~n~ n Pulp and Paper Industry (Montreal) and Technical Association of the Pulp and Paper Industry (Atlanta), 3rd ed., 1983. Expanded cellulose fibers thus refers to microfibrils and macrofibrils which have been substantially separated from or disassociated from a cellulosic fiber ultrastructure.
High surface area cellulose can also be made from cellulosic fibers by passing aliquid suspension of cellulose fibers through a small diameter orifice, in which the suspension is subjected to a pressure drop of at least 3000 psig and a high velocity shearing action, followed by a high velocity decelerating impact. Passage of thesuspension through the orifice is repeated until a substantially stable suspension is obtained. See U.S. Patent 4,483,743, Turbak et al., November 20, 1984.
A preferred process for plepa~ g expanded cellulose fibers is disclosed in the Vinson patent (ibid.), and involves impacting a fibrous material having a fibrillar ultrastructure (e.g., cellulose fibers) with fine media to cause microfibrils and macrofibrils to separate from said fibrous material ultrastructure.
The length of the high surface area cellulosic material preferably ranges from about 20 to about 200 ,um.
Typically, for wetlaying, the high surface area cellulose is provided as a damp pulp, generally at 15-17% solids, and preferably diluted to less than 4% solids content and processed in a beater or disc refiner to break up entanglements. The high surface area cellulose is then well mixed with the stiffened fibers in slurry and the slurry is wetlaid as described above. A 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 thestiffened 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 of wire.
Other binding means for increasing physical integrity of the acquisition/distribution layer and/or facilitating processing of webs, especially wetlaid 1, -26- ~ 4 ~
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). 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 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 cont~ining 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 whichare hydrophilic, however, can be utilized in quantities. If the chemical binder additives are YVo 91/11163 2 0 6 9 4 4 3 P(~r/USsl/00169 added to the stiffened fibers in aqueous slurry, conventtonally, nonstiffened cellulosic fibers or high surface area cellulose is preferably also present, to enhance retentton of the chemical addtt1ve btnder. Chemical addtttve btnders can be applted to drted or undrted webs by prtnttng, spr~ytng, or other methods known tn the art.
ThermoDlasttc Retnforced Acauisitton/Otstrtbutton ~aYer In another embodtment, the acqutsltton/d1stribution layer comprises an airlatd or wetlald, preferably airlaid, web of st1ffened cellulosic ftbers wheretn the web is retnforced with from about l0X to about 50%, preferably from about 25% to about 45%, more preferably from about ~0% to about 45%, of a thermoplastic binding material, wherein the thermoplastic bindtng material provides bond sites at intersections of the stiffened lS cellulosic fibers. Such thermally bonded webs can, in general, be made by forming a web comprising the sttffened cellulosic fibers and thenmoplast1c fibers, whtch are preferably evenly distributed th.oughout. The web can be for0ed by e1ther airlaying or wetlaying proçesses. Once formed, the web is thermally bonded by heating the web unt11 the thenmoplast1c ftbers melt. Upon melttng, at least a portton of the thermoplasttc material will migrate to intersecttons of the sttffened cellulosic fibers due to interf1ber capillary gradients. These intersections become bond sttes for the then~oplasttc matertal. The web is then cooled and mn~rfated thermoplastic material bonds the sttffened cellulosic f~bers together at the bond sttes. Melt1ng and migration of the thensoplasttc mater1al to the st1ffened cellulosic fiber tntersecttons has the effect of increasing average pore size of the web, whtle ma1ntaining the density and basis weight of the web as originally formed. Thts can improve dtstrtbutton properties of the acquisition/dtstribution layer upon intttal dtscharges due to imp~ovEd flutd permeabtltty, and upon subsequent discharges, due to the combined ability of the stiffened ftbers to retain their sttffness upon wetttng and the ability of the thermoplastic to rematn bonded at the ftber intersectton upon wetttng and upon wet co~pFessi.on. In net, the. thQ~al]y boDded web retains its ortgt~al oY~ral1 Yolume~ but ~Ae volu~st~ic -regtons previously occupied by thermoplastic fibrous material becomes open to thereby increase average interfiber capiilary pore size.
Thermally bonded, thermoplastic-reinforced absorbent webs, utilizing conventional, unstiffened cellulosic fibers, are described in U.S. Patent 4,590,114, D.C. Holtman, issued May 20, 1986, and by Peter G. Bither in "Thermally Bonded Cores Add Value to Absorbent Products," Nonwovens World, November 1988, pp 49-55. 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 point of the thermoplastic binding material will be less than about (135~C), preferably between about 75~C and about 1 75~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 material may, 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 hydrophobic. (As used herein, the terms "hydrophilic" and W O 91/11163 2 0 6 S 4 4 3 pc~r/us9l/oo169 ~hyd~ophobtc~ shall refer to the extent to ~htch the surfaces are wetted by water.) The surface of the thermoplastic can be rendered hydrophilic by treatment of a h~d~ophobic thermoplastic binding material ~ith a surfactant such as a non-ionic or anionic surfactant as by spraying the 0aterial with a surfactant or by dipping the matertal into the surfactant. Upon melting and resolldificatlon the surfactant will tend to remain at the surfaces of the thermoplastic. Suitable surfactants include non-tontc surfactants such as Bri~ 76 manufactured by ICI
Amertcas Inc. of ~il0ington Delaware and the various materials sold under the Pegosp~.se trade~ark by Glyco Chemtcal Inc. of Greenwich Connecticut. Anionic surfactants can be also used.
Surfactants are applted to the fibers at a level of from about 0.2 to about 1 gra~ per square meter of thermoplastic binding material. Hydrophilic materials beco~e 00re desirable at higher thermoplastic material levels particularly above about 40% of the dry web.
Thermoplastic fibers for use herein can be on the order of about 0.1 cm to about 6 cm long preferably from about 0.3 cm to about 3.0 cm.
A preferred type of thermoplastic fibrous material is commercially known and avatlable as PULPEXTM (Hercules Inc.
~ilmington Oelaware USA). PULPEX is a polyolefin material having a very high surface area to mass ratio which in general 2S lS made by spraying molten polymer and gas through a noz~le into a vacuum. PULPEX is available in both polyethylene and polypropy-lene forms.
The thermoplasttc used can be hydrophtlic or hydrophobic.
As described above thenmoplasttc binder-reinforced webs of stiffened cellulosic fibers can be 0ade by ~etlaying or airlaying processes. Airlaid webs can be 0ade by inter~ixing the cellulosic and thermoplastic fibers and then airlaying according to the techniques described above. The sttffened cellulosic fibers and thermoplastic fibers oan be intermixed in an airlaid context by cardtng or- by metering air ~treams of the sttffened fibers and thermopla~tic f~brou~slrteqi~t together and directtng the combined ~stem-th.uugh a br~sh scree~-depm ~ ~10n ~a.~tus or other web forming device. Such techniques are known in the art. Suitable equipment includes air forming systems available from Dan Webforming International Ltd.
(Risskov, 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. 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 previously referred to U.S. Patent 4,590,114.
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 fully 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 storagelayer 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 of absorbent gelling material and superabsorbent fibrous material such as acrylate grafted fibers W O 91/11163 ~ 4 13 P(~r/US91/00169 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 mater1als are described in more detail below. The superabsorbent material upon contact with fluids such as water or body flutds absorb such fluids. (As used herein the tenm ~fluids~ shall refer to liquits 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 im~oved fluid retentlon performance.
The superabsorbent materials intended to be encompassed in thts invention are those which are capable of absorbing at least about lO grams preferably at least about 15 9 more preferably at least about 20 g of Synthetic Urine (SU - 1.0% NaCl aqueous solution) per gram of superabsorbent material as detenmined according to the here1nafter descr1bed Absorbent Capac1ty procedures.
The superabsorbent material utllized herein is typically in the form of discrete part1cles of absorbent gelling material.
These particles will typically be distr1buted within a web of fibrous material as carrter means. The superabsorbent fibrous material can compr1se synthettc or natural f1bers. Suitable f~brous carrter means are cellulose f~bers in the form of fluff such as is conventionally utilized in absorbent cores. Modified cellulose flbers such as the st~ffened cellulose f~bers described above can also be used but are preferably not used in the storage layer. Synthet1c fibers can also be used and include those made of cellulose acetate polyvtnyl fluoride polyvtnylidene chlortde acryl1cs (such as Orlon) polyvinyl acetate non-soluble polyvinyl alcohol polyethylene polypropylene polyam1des (such as nylon) polyesters bicomponent f~bers tricomponent fibers mtxtures thereof and the like.
Preferred synthetic fibers have a den1er of from about 3 denier per filament to about 25 denter per filament more preferably from a h ut 5 denier per filament-to about l~-den1er per filament. Also preferably the fiber surfaces are hydrophiltc or are treated to be hyd~vph~l~c.

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/cm3, and more preferably within the range of from about 0.10 to about 0.4 g/cm3, even more preferably from about 0.15 to about 0.3 g/cm3, most preferably from about 0.15 to about 0.25 g/cm3. 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/cm2, 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. Alsoas with the acquisition/distribution layer, density values for the storage layerare 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/lnglin; U.S. Patent 4,654,039, Issued March 31, 1987, and reissued as RE 32,649, on April 19, 1988. Preferred monomers include acrylic acid, methacrylic acid, and 2-acrylamido-2-methyl propane sulfonic acid.
Acrylic acid itself is especially preferred for preparation of the polymeric gelling agent material.

The polymeric component formed from unsaturated, acid-containing monomers may be grafted on to other types of polymer moieties such as starch or cellulose. Polyacrylate grafted starch materials of this type are also especially preferred.
Preferred polymeric absorbent gelling materials which can be prepared from conventional types of monomers include hydrolyzed acrylonitrile grafted starch, polyacrylate grafted starch, polyacrylates, maleic anhydride-based copolymers and combinations thereof. Especially preferred are the polyacrylates and polyacrylate grafted starch.
Whatever the nature of the basic polymer components of the hydrogel-forming polymeric absorbent gelling material particles used in both layers of the absorbent cores herein, such materials will in general be slightly cross-linked. Cross-linking serves to render the hydrogel-forming polymer gelling agents used in this invention substantially water-insoluble, and cross-linking thus in part determines the gel volume and extractable polymer characteristics of the hydrogels formed from the polymeric gelling agents employed. Suitable cross-linking agents are well know in the art and include, for example, those described in greater detail in Masuda et al.; U.S. Patent 4,076,663; Issued February 28, 1978. Preferred cross-linking agents are the di- or polyesters of unsaturated mono- or polycarboxylic acids with polyols, the bisacrylamides and the di- or triallyl amines. Other preferred cross-linking agent are N,N' - methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine.
The cross-linking agent can generally constitute from about 0.001 mole percent to 5 mole percent of the resulting hydrogel-forming polymer material. More preferably, the cross-linking agent will constitute from about 0.01 mole percent to 3 mole percent of the hydrogel-forming polymeric gelling material particles used herein.
The slightly cross-linked, hydrogel-forming polymeric gelling material particleswhich may be used in the articles of the present invention are generally employed in their partially neutralized form. For purposes of this invention, such materials are considered partially neutralized when at least 25 mole -34- ~ 4 ~
percent, and preferably at least 50 mole percent of monomers used to form the polymer are acid group-cont~ining 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-cont~ining 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 amterial and from about 20% to about 90%, more typically from about 25% to about 80%, carrier means. Such webs will typiclaly be made by airlaying, wherein an airstream of the absorbent gelling material particles is metered inot an airstream of the fibrous carrier means.
It is also contemplated to provide a storage layer wherein particles of absorbent gelling material are l~rnin~ted 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.
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). 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 fibers 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 "Absorbentpaper Comprising Polymer-Modified Fibrous Pulps and Wet-Laying Process for the Production Thereof," by Larry N.
Mackey and S. Ebrahim Seyed-Rezai.
Other types of superabsorbent fibers can include crosslinked carboxymethyl cellulose and polymer grafted cellulose fibers. Polymer grafted cellulose fibers include hydrolyzed polyacrylonitrile, polyacrylic esters, and polycrylic and polymethacrylic acids. These superabsorbent fibers including discussion of and references to processes .~

for making them, can be found in the Chatterjee's Vol. 7 to Textile Science and Technology; A.H. Zahran, et al., "Radiation Grafting of Acrylic and Methacrylic Acid to Cellulose Fibers to Impart High Water Sorbency", J. of App. Polymer Science, Vol.
25, 535-542 (1980), which discusses radiation grafting of methacrylic acid and acrylic acid to cellulose fibers, as the title suggests; U.S. Patent 4, 036,588, J.L. Williams, et al., issued July 19, 1977, which describes the graft copolymerization of a vinylmonomer containing a hydrophilic group onto cellulose-containing material, e.g., rayon yarn; U.S. Patent 3,838,077, H.W. Hoftiezer, et al., issued September 24, 1974, which discloses polyacrylonitrile-grafted cellulose fibers.
The superabsorbent fibers can be incorporated into webs of conventional or other nonsuperabsorbent fibers, such as in wet-laid webs as described above or in air-laid webs, and can also be formed into nonwoven sheets.
In another embodiment hereof, the storage layer comprises superabsorbent fibers which are formed into nonwoven sheets. Such sheets can consist essentially of superabsorbent fibers with substantially zero percent carrier means, although such sheets can include carrier means, and such embodiments are not meant to be excluded.
Nonwoven sheets made from superabsorbent fibers such as the non-acrylate superabsorbent microfibers and superabsorbent fibers useful for making such sheets are available from Arco Chemical Co. (Newtown Square, PA, USA), under the tradename FIBERSORBTM and from Japan Exlan Co., Ltd. (Osaka, Japan) which markets superabsorbent fibers comprising a polyacrylonitrile core with a polyacrylic acid/polyammonium acrylate skin under the tradename LANSEALTM.
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 is in general described more fully in the hereinbefore noted 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 -36- ~ 3 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 ~ess 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 would include the crotch area and preferably for wo 91/11163 2 0 6 9 4 4 3 Pcr/usg~ 69 m~les also the region nhere urin~tion discharges occur in the front of the di~per. For ~ ti~per the front of the absorbent articles herein ~e~ns the portion of the absorbent article which is intended to be pl~c d on the front of the ~earer.
S Addttionally for ~~les it is desirable for the acquisition/distribution l~rer to extend to ne-r the front waist area of the ~e~rer to effectivel~ acquire the relatively high fluid load that occurs in th- front of the male wearer and to compensate for direction~l v~ri~tions of the discharges. The corresponding absorbent ~rticle regions ~ill vary depending upon the design and fit of the absorbent article. The acquisition/distribution l~ers llO of diaper lO0 as shown in Figure 2 exe~plif~ one e~boJioent wherein the acquisition/distribution l~er llO is suitably positioned to receive both bo~el ~nd urine discharges for both males and females.
For dispos~blc b4br di~per executions the acquisition/distribution l~er of the core is preferably posi-tloned relative to the elong~ted topsheet and/or the storage layer such that the acquisition~tistribution l~yer is sufficiently enlongated to extend to ~re~s co..~sp~nt~ng ~t least to about SOX
preferably 75X of the lenSth of the storage layer. The acquisition/distribution l~er should h~ve a width sufficient to acquire gushes of bod~ fluids Yithout direct discharge of fluid ~ntcrthe stor~ge l~er. 6ener~11y for diapers such as shown in F~gures l and 2 the ~idth ~ e ~t le~st about 5 cm preferably ~t le~st about 6 c~. As no:ed for purposes of the present in-vent10n sections of the ebsorbent article can be defined by reftlence to top surf~ce are~s of the unfolded absorbent article found in front of a given point on the line which defines the length of the absorbent ~rticle.
For purposes of deterciining such acquisition/distribution layer positioning the length of the absorbent article will be taken as the noro~l longest longitudin~l dimension of the elongated art~cle b~c~ing sheet. This nono~l longest dimension of the elong~te~ b-c~i~g she~t~c~n be defi~ned with respect to the ~rt~cl~s it ~s~ppl~ed to~the-~e~rer.~ ~hen ~orn the opposing W091/11163 ~,~69 ~3 PCI/US91/00169 ends of the b~ck sheet are fastened together so that these joined ends for~ ~ circle around-the ~earer s waist. The nor~al length of thc b~c~ing sheet will thus be the length of the line running through the back sheet fro~ a) the polnt on the edge of the bac~
shect at the ~tddle of the ~earer's bac~ ~atst through the crotch to b) the point on the oppostte edge of the backlng sheet ~t the ~iddle of the ~earer s front ~alst. The st~e and shape of the topsheet will generall~ cc-~cspond substanttall~ to the back sheet.
In thc usual instance wherein the storage la~er of the ~bsorbent core generally defines the shape of the absorbent article the noroal length of the elong~ted artlcle topsheet will be appro~ched by the longest longitudinal dimension of the storage l~rer of the core. Ho~ever in so~e applications (e.g. adult inconttnence ~rticles) ~herein bulk reJuction or ~inimum cost are i~port~nt the storage larer would not ta~e on the general shape of the ti~per or incontinence structure. R~thcr the storage layer ~ould be generallr located to cover onlr the genit~l region of the ~earer and ~ reasQn~ble are~ proxi~Rte to the genital area. In this inst~nce both the fluld acqulsttton/dlstribution layer and the storage l~rer ~ould be locateJ to~ard the front of the article as defined b~ the topsheet such that the acquisition/distribution ~nd stor~ge larers would typically be found in the front t~o-thirds of the ~rtlcle.
~ e storage layer of the absorbent corc can be of an~ desired sh~pe conststent ~ith co~fortable flt includtng for ex~mple clrcular rect~ngular trapezoidal or oblong e.g. hourglass-shaped. dog-bone-shaped half dog bone shaped oval or irregularl~
shaped. Thts storage l~yer need not be ph~sicall~ separated from the acquisition/distrlbution la~er and c~n si~ply be a zone of su~e.~bso.bent mater1al concentrat10n in a continuous web of stlffcned cellulose f1ber oaterial. More prefer~bl~ ho~ever the storage l~er of the absorbent core wlll comprise a separate web ~blch can be used as an insert placed underne~th the acquis1-~tDn/dtstributton layer.
Ihe ~cquisit~on~d~strtbut~on la~er can ~lso be-of an~ desired ~ha~ oonststent~it~ ~uo~fortable-flt and the slzlng lt~itations WO 91/11163 2 0 6 ~ ~ 4 3 PCI/US91/00169 dlscussed above. These shapes include, for example, circular, rectangular, trapezoidal or oblong, e.g., hourglass-shaped, dog-bone-shaped, half dog bone shaped, oval or irregularly shaped.
The acquisition/dlstributlon layer can be of simllar shape or dlffering shape than the storage layer.
Figures 1 and 2 each show d1aper executlons embodylng the present inventlon. Shown in each figure ts a dlaper 100 w~th topsheet 104 and bac~heet 102. Dlsposed between topsheet 104 and backsheet 102 is absorbent core 106 havlng storage layer 108 and rectangular acquisition/dlstributlon layer 110. Although not shown, storage layer 108 has dtscrete particles of absorbent gelling material distributed th-oughout.
Specifically referring to flgure 2, the absorbent core 106 is shown as having a front reglon 112, a back reglon 114, and a central region 115. As previously descrlbed, the front region 112, corresponds to the end of the dlaper 100 that would be covering the front of the wearer when the dlaper was in use, and the back reglon 114 would be coverlng the back of the user. The absorbent core 106 of Figure 2, speclf~cally the storage layer 108, has a modlfled hour-glass shape to provide enhanced fit and reduce in-use leakage.
Figure 3 shows an absorbent core 106, that can be utilized in conjunction with a disposable diaper, having a storage layer 108 of simllar shape to those of Flgures 1 and 2.
~qutsitlon/d~strlbutton layer 111, ho~e~Ye" is' of a modified hour-glass shape of substantlally stmllar shape to the storage layer 108, though of smaller surface area.
Further with respect to Figure 3, the absorbent core 106 has front region 112, rear region 114, and central region 115. Front region 112, front edge 117 and, at rear reglon 114, has rear edge 119. Front edge 117 and, has rear edge 119. Front edge 117 and rear edge 119 are connected by storage layer side edges 122 and 123, correspondlng to the central region 115.
Acquisltion/dlstribution layer lll;has front edge 116 in the front region 112 and rear edge ~lB ln the rear regton 114.
Acquls~tlon~distr~butlon layer:side- edges 120 and 121, connect front edge ~6 and rear edgel~8.

206!~443 WO 91/11163 PCI'/US91/00169 In preferred absorbent artlcle embodtments, e.g., d~sposable absorbent diapers, the- edges 116, 118, 120, 121 of the acquisltlon/dlstributlon layer 111 wlll respectlvely be at least 0.5 cm., preferably at least 1.25 cm. lnstde the edges 117, 119, 122, 123 of the storage layer 108, partlcularly in central region 115.
S~ rabsorbent Materlal Absorbent CanacitY Test Method As dlscussed above, the superabsorbent mater1als for use in the present lnvent10n wtll preferably have an Absorbent Capaclty of at least about lO 9, prefer-bly at least about lS g, more preferably at least about 20 9 Synthetlc Urlne (l.~X NaCl aqueous solution, prepared using distilled water) per gram dry superabsorbent material. In general, the superabsorbent matertal is place within a tea bag, immersed in an excess of Synthettc lS Urine for a specified time, and then centrifuged for a specifled per10d of time. The ratio of superabsorbent materlal final weight after centrtfug~ng minus init1al wetght to initlal weight is Absorbent Capactty. The following ploced~.e can be used to determine Absorbent Capacity. The prDcedu~e is conducted under standard laboratory condltions.
Using a 6 cm X 12 cm cuttlng die, the tea bag material is cut, folded ln half lengthwise, and sealed along two sides with a T-bar heat sealer to produce a 6 centlmeter by 6 centimeter tea bag square. The tea bag matertal utillzed is grade 1234 heat ~e~lable, obtainable from C. H. Dexter, Division of the Oexter Corp., ~lndsor Locks, Connecticut, USA, or equivalent. Lower porosity tea bag material should be used if required to retain flne superabsorbent materials. 0.200 grams plus or minus 0.005 grams of superabsorbent matertal is we~ghed 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. Approxtmately 400 mill~ltters of Synthetlc Urine are poured into a 1,000 milliliter beaker. The blank tea bag is sub~erged in the Synthettc Urine. The tea bag containing the superabsorbent mater~al (the sample tea-bag) ts held horizontally to distribute th~-matertal evenly througbsut the tea bag. The tea bag is lald;on the su~face of the-Synthettc ~r~ne. ~he tea bag is w o 9l/11163 2 0 ~ 3 P ~ /US9l/00169 ~

allowed to wet, for a pertod of no more than one minute, and then sub~erged and soaked for 60 minutes. Approximately 2 minutes after the first sample is submerged, a second set of tea bags, ~ prepared 1denttcally to the first set of blank and superabsorbent mater1al-contatntng tea bags, is submerged and soaked for 60 mtnutes in the same manner as the first set. After the prescribed soak time is elapsed, for each set of tea bag samples, the tea bags are promptly removed (wtth tongs) from the Synthetic Ur1ne.
The samples are then centrtfuget as described below. The centrifuge used is a Delux Oynac II Centrtfuge, Fisher Model No.
05-100-26, obtainable from Fisher Scientific (Ptttsburgh, PA, USA), or equivalent. The centrtfuge should be equipped with a dtrect read tachometer and an electric brake. The centrifuge is further equipped with a cylindrtcal insert basket having an lS approximately 2.5 inch (6.35 cm) high outer wall with an 8.435 inch (21.425 cm) outer dtameter, an 7.935 inch (20.l55 cm) inside d1ameter, and 9 rows each of approximately 106 3/32 inch (0.238 cm) dtameter ctrcular holes equally spaced around the circumference of the outer wall, and having a basket floor with stx l/4 inch (0.635 cm) dtameter ctrcular drainage holes equally spaced around the circumference of the basket floor at a distance 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 is mounted in the centrtfuge so as to rotate, as well as brake, in ~ntson w~th the centrifuge. The superabsorbent m~tertal-containing tea bags are posttioned in the centrifuge basket with a folded end of the tea bag in the d~rection of centrifuge spin. The blank tea bags are placed to either side of the corresponding sample tea bags. The superabsorbent material-containing tea bag from the second set of tea bags must be placed opposite the superabsorbent material-containing tea bags from the first set of tea bags; and the second blank tea bag, opposite the first blank, to balance the centrifuge. The centrtfuge is started and allowed to ramp up quickly to a stable 1,500 rpm. -~nce the centrtfuge has been stabilized at l,500 rpm, a t1mer 1s set for 3 minutes. After 3 minutes, the centrtfuge is turned off and the brake is applied. The f~rst superabsorbent 20~4~3 w o 91/11163 p(~r/us91/oo169 ~aterial-containing tea bag and first blank tea bag are removed and weighed separately. The procedure is repeated for the second set of tea bags. The absorbent capacity (ac) for each of the samples is calculated as follows: ac ~ (Superabsorbent matertal-containtng te- bag wetght after centr1fuge minus blank tea bag weight after centrtfuge mtnus dry superabsorbent matertal weight) dtvided by (dry superabsorbent material weight). The Absorbent Capactty value for use heretn is the average absorbent capac1ty (ac) of the two samptes.
FYAMPLE I
A disposable diaper is prepared comprtstng a thermally bonded polypropylene topsheet a flutd impervtous polyethylene backing sheet and a dual layer absorbent core positioned between the topsheet and the backtng sheet. The dual layer absorbent core comprises an hourglass-shaped storage layer positioned below a rectangular shaped acqutsitton/d1strtbut10n layer as shown in F~gure l.
The acquisition/dtstrtbut10n layer comprises stiffened twlsted curled cellulose fibers and opttonally a binding means.
The storage layer comprises an atr-latd mtxture of conventional cellulostc fluff (Foley fluff southern softwood kraft pulp The Procter ~ Gamble Cellulose Co. Me~phts TN USA) and sodium polyacrylate polymertc absorbent gelling material of the type described in U.S. RE 32 6~9 retssued Aprtl l9 1988 and having arr-Abso,bent Capactty of about 30 9/9. The acq~isition/dlstri-button layer comprtses a 92%~8X wetla~d mixture of st1ffened f1bers and conventtonal nonsttffened cellulosic fibers. The nonsttffened fibers are also made from Foley Fluff; and are reftned to about 200 CSF. The sttffened tw1sted curled cellulosic fibers are made from southern softwood kraft pulp (Foley fluff) and crosslinked wtth glutaraldehyde to the extent of about 2.5 mole percent on a dry fiber cellulose anhydroglucose basts. The fibers are crosslinked according to the ~dry crosslinking process~ as descrtbed above in U.S. Patent 4 822 453.
The stiffened fibers are stmtlar~ to the fibers having the char~ctertstics descrtbed in Table l.

-w o 91/11163 2 ~ 6 ~9 4 -13 p(~r/ussl/oo169 -Table 1 Stlffened. Twisted. Curled Cellulose (STCC) Fibers Type ~ Southern softwood kraft pulp crossllnked with glutaralde-= hyde to the extent of mole percent on a dry fiber cellulose anhydroglucose basis Twist Count Ory ~ 6.8 nodes/mm Twlst Count Wet ~ 5.1 nodes/m~
Isopropol Alcohol Retentlon Value ~ 24X
~ater Retention Value - 3~X
Curl Factor ~ 0.63 The acquisitlon/dlstribution layer ls a unlform, wetlaid web as described in Example II. The acquisitlon/dlstribution layer has an average dry density of about 0.06 g/cc. An average density upon saturation with Synthetic Urlne, dry welght basis, of about 0.0~ g/cc, and an average basis welght of about 0.03 g/cm2. rhe storage layer comprtses 50% by wetght foley fluff and 50%
absorbent gelling material partlcles, has an average dry density of about 0.24 g/cc and an average dry basts weight of about 0.5 g/cm2 .
~he acquisltlon/dlstribution layer has dtmensions of about 1.6 cm X 22.9 cm and ls positloned relattve to the storage layer as shown in figure l. The storage layer has crotch width (at the most narrow part of the crotch) of about 8.9 cm, a width at the front watst area of about 21.6 cm, and a width at the rear (backJ
- ~R~s~ area of about 16.5 cm.
In an alternatlve embodiment, the storage layer comprises about 15% of the absorbent gelllng matertal part~cles and about 85X of Foley fluff and has a basis welght gradlent such that the front 60% of the storage core has a basis weight of about 0.11 g/cm2 and a density of about 0.15 g/cc and the rear 40Z of the storage core has a basis weight of about 0.04 g/cm2 and a density of about 0.06 g/cc.
In a further embodlment, the storage core comprises about 28X
of the absorbent gelling material part kles and about 72% of Fole~
fluff, and has basis weight and dens1ty gradlents as described immedlately above.

W o 91/11163 p(~r/us91/oo169 FYA~PLE r I
Thts example exe~pl-tfies wetla~ing of a ~eb useful for use as an acquisitton/dtstrtbutton la~er in th- present invention. ~he web comprises 92X sttffene~d fibers as descrtbed in Example I and Table I and 8X htghly refined Fole~ n uff (crtlt) having a f-eeness of about 200 CSF.
A pulp slurry of the sttffened and nonsttffened fibers having a f~ber conststency of O.IX-0.2% is pu ped to ~ fOR~AR papen~aking machine at a linear veloctty of 25 ~/s and ~t r-te of about 95 I0 ltters/mtnute. The slurry is distributed b~ ~ fixeJ-roof former he~dbox onto an inch wide (30.5 c~) 84~ 5 shed 12 fon~ing ~ire ~oving continuously at a rate of I.5 ~-inutes. Linear velocity of the pulp slurry upon exit froo the he~o~ is froo 50 to 100 m/s. Flow and wire movement are regulated so that a unifor~
motst sheet having a dr~ basis weight of about 0.03 9/C~2 and an average dry density of about 0.06 g/cc is fonoed. Sheet consistency is increased to about 16~-22S br application of two vacuum boxes fro~ underne~th the ~ire such v~cuu~ boxes operating in seq~nce at 75 mm Hg and 100 ~ Hg respectively with a residence tt~e for the sheet betng sub~ect to e~ch v~cuu~ box of about 1 :econd. The sheet ts then removed fro the fon~ing ~ire manually and dr1ed batchwtse in a forced con~ectton steao heated oven for about ~ hours at about 110~C.
f~AMPLF III
2S Absorbent cores are prep~red as in Exa ple I except that the acqutsition~dtstrtbutton la~er is airlatd and co~prises lOOX of the sttffened fibers.
EXAMPLE IV
Absorbent cores are prèpared as in Exa~ple III except that the acquisltion/dtstributton la~er is ~de fro an airlaid and thermally bonded thermoplastic-reinforced ~eb comprising 55X of the stiffened ftbers and 45X of PULPEXT~ (Hercules Inc.
~tlmtngton Oelaware USA) polyeth~lene microfibers having an average length of about 0.3 cm. The acquisitton/distribution layer is formed by metering airstre~s of the stiffened fibers and PULPEX and then forming the web ustng conv~..ttonal atrlaying equtp~ent. The we~ is ther~allr bonded b~ he~ttng the ~eb by through-air bonding, under unrestrained (i.e., uncompressed) conditions, and subsequently allowed to cool.

Claims (30)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An absorbent article for acquisition, distribution, and storage of bodily fluids, said article comprising:
(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 about 0.30 g/cc, an average density upon saturation with 1% NaC1 aqueous solution, 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, said acquisition/distribution layer comprising from about 50% to 100%, dry weight basis, of chemically stiffened cellulosic fibers and from 0% to about 50%, dry weight basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath said acquisition/distribution layer relative to said topsheet, comprising at least about 15%, by weight of said storage layer, of superabsorbent material and from 0% to about 85% of a carrier means for said superabsorbent material;
said fluid acquisition/distribution layer having no more than about 6.0% of superabsorbent material and having a top surface area which is at least 15% of the top surface area of said fluid storage layer and which is smaller than the top surface area of said fluid storage layer.

2. An absorbent article as in Claim 1, wherein said acquisition/distribution layer is substantially free of superabsorbent material, has a top surface area which is at least about 25%. of the top surface area of said storage layer and which is less than about 90% of the top surface area of the said storage layer, has an average density upon saturation with 1.0% NaC1 aqueous solution, dry weight basis, of between about 0.02 g/cc and about 0.15 g/cc, and has an average basis weight of between about 0.019 cm2 and about 0.08 g/cm2, and wherein said superabsorbent material has an Absorbent Capacity of at least about 15 9/9.

3. An absorbent article as in Claim 2, wherein said acquisition/distribution layer comprises from about 2% to about 50% of said binding means, wherein said binding means comprises non-chemically stiffened cellulosic material.

4. An absorbent article as in Claim 3, wherein said binding means comprises highly refined cellulosic fibers having a freeness of less than about 200 Canadian Standard Freeness, and said acquisition/distribution layer comprises from about 5% to about 15% of said highly refined fibers.

5. An absorbent article as in Claim 3, wherein said binding means comprises high surface area cellulose, and said acquisition/distribution layer comprises from about 2% to about 15% of said high surface area cellulose.

6. An absorbent article as in Claim 2, wherein said acquisition/distribution layer is an airlaid web.

7. An absorbent article as in Claim 2, wherein said acquisition/distribution layer is a thermally bonded web comprising from about 10% to about 50% of thermoplastic material, said web being made by preparing a web of a blend of said stiffened fibers and from about 10% to about 50%, total web weight basis, of thermoplastic material, heating the web to melt the thermoplastic material, and cooling the web.

8. An absorbent article, as in Claim 4, wherein said acquisition/distribution layer is a wetlaid web.

9. An absorbent article, as in Claim 5, wherein said acquisition/distribution layer is a wetlaid web.

10. An absorbent article as in Claim 2, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material. said superabsorbent material having an Absorbent Capacity of at least about 15 g/g.
material and said storage layer is substantially free of chemically stiffened cellulosic fibers.

11. An absorbent article as in Claim 4, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

12. An absorbent article as in Claim 5, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

13. An absorbent article as in Claim 6, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

14. An absorbent article as in Claim 7, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

15. An absorbent article as in Claim 2, wherein said storage layer comprises superabsorbent fibers.

16. An absorbent structure for acquisition, distribution, and storage of bodily fluids, said structure comprising:
(i) a fluid acquisition/distribution layer having an average dry density of less than about 0.30 g/cc, an average density upon saturation with 1% NaC1 aqueous solution, 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, said acquisition/distribution layer comprising from about 50% to 100%, dry weight basis, of chemically stiffened cellulosic fibers and from 0% to about 50%, dry weight basis, of a binding means for said fibers; and (ii) a fluid storage layer, positioned beneath said acquisition/distribution layer relative to said topsheet, comprising at least about 15%, by weight of said storage layer, of superabsorbent material and from 0% to about 85% of a carrier means for said superabsorbent material;
said fluid acquisition/distribution layer having no more than about 6.0% of superabsorbent material and having a top surface area which is at least 15% of the top surface area of said fluid storage layer and which is smaller than the top surface area of said fluid storage layer.

17. An absorbent structure as in Claim 16, wherein said acquisition/distribution layer is substantially free of superabsorbent material, has a top surface area which is at least about 25% of the top surface area of said storage layer and which is less than about 90% of the top surface area of the said storage layer, has an average density upon saturation with 1.0% NaC1 aqueous solution, dry weight basis, of between about 0.02 g/cc and about 0.15 g/cc, and has an average basis weight of between about 0.019 cm2 and about 0.08 g/cm2, and wherein said superabsorbent material has an Absorbent Capacity of at least about 15 g/g.

18. An absorbent structure as in Claim 17, wherein said acquisition/distribution layer comprises from about 2% to about 50% of said binding means, wherein said binding means comprises non-chemically stiffened cellulosic material.

19. An absorbent structure as in Claim 18, wherein said binding means comprises highly refined cellulosic fibers having a freeness of less than about 200 Canadian Standard Freeness, and said acquisition/distribution layer comprises from about 5% to about 15% of said highly refined fibers.

20. An absorbent structure as in Claim 18, wherein said binding means comprises high surface area cellulose, and said acquisition/distribution layer comprises from about 2% to about 15% of said high surface area cellulose.

21. An absorbent structure as in Claim 17, wherein said acquisition/distribution layer is an airlaid web that comprises from about 95% to 100% of said stiffened fibers.

22. An absorbent structure as in Claim 17, wherein said acquisition/distribution layer is a thermally bonded web comprising from about 10% to about 50% of thermoplastic material, said web being made by preparing a web of a blend of said stiffened fibers and from about 10% to about 50%, total web weight basis, of thermoplastic material, heating the web to melt the thermoplastic material, and cooling the web.

23. An absorbent structure, as in Claim 19, wherein said acquisition/distribution layer is a wetlaid web.

24. An absorbent structure, as in Claim 20, wherein said acquisition/distribution layer is a wetlaid web.

25. An absorbent structure as in Claim 17, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material having an Absorbent Capacity of at least about 15 g/g.
material and said storage layer is substantially free of chemically stiffened cellulosic fibers.

26. An absorbent structure as in Claim 19, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

27. An absorbent structure as in Claim 20, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

28. An absorbent structure as in Claim 21, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

29. An absorbent structure as in Claim 22, wherein said carrier means for said superabsorbent material comprises a web of cellulosic fibers, and said storage layer comprises from about 15%
to about 75% of said superabsorbent material, said superabsorbent material comprising discrete particles of absorbent gelling material having an Absorbent Capacity of at least about 20 g/g.

30. An absorbent structure as in Claim 17, wherein said storage layer comprises superabsorbent fibers.