CA2079134C

CA2079134C - Enhanced core utilization in absorbent products

Info

Publication number: CA2079134C
Application number: CA002079134A
Authority: CA
Inventors: Richmond R. Cohen
Original assignee: Hercules LLC
Current assignee: FIBERVISIONS LP
Priority date: 1991-09-30
Filing date: 1992-09-25
Publication date: 1997-12-02
Anticipated expiration: 2012-09-25
Also published as: EP0536941B2; EP0536941B1; JP3749267B2; EP0536941A3; CA2079134A1; US5334177A; DE69215186D1; DK0536941T3; JPH05228175A; MX9205581A; US5330457A; EP0536941A2; DE69215186T2; DE69215186T3; DK0536941T4

Abstract

A core component for use in a fluid-absorbing article, such as a diaper, incontinence pad, catamenial device or the like is described, which core component has a plurality of core zones comprising a zone of vulnerability positioned in said core component for maximum potential exposure to wetting, and at least one additionalcore zone arranged in an area of reduced potential exposure to initial wetting and in direct or indirect fluid receivable relation from the zone of vulnerability. The zone of vulnerability has a wadding component comprising synthetic fiber of filament and has a greater average pore size than the average pore size of the wadding component in the at least one additional core zone. When two or more additional core zones are used, the average fractional value of fiber volume-to-fiber surface area and the average pore size within the wadding components of the additional core zones decrease invalue from zone to zone with increased distance from the zone of vulnerability and with reduced risk of initial wetting. The zone of vulnerability may be further characterized by having a greater average liquid-solid contact angle than the average liquid-solid contact angle in the additional core zones. A fluid absorbing article and a method for increasing fluid receptivity, fluid storage efficiency, and reduced rewet characteristics utilizing the core component of the invention are also described.

Description

3 ~

The present invention relates to a fluid-absorbing core component, a fluid-absorbing article utili7ing such component, and a method for making a fluid-absorbing 5 core component.
It is generally recognized that success in the marketplace with fluid-absorbing articles such as disposable diapers, i.lconlinence g~~ ltS or pads, cat~meni~l devices and the like, depends substantially on functional efficiency of the article, as well as comfort to the wearer, a~pe~u~ce and price of the article.
In general, such articles have an efficient fluid-ret~ining core component, usually comprising one or more layers of absoll~cnl material such as wood pulp, rayon, gauze, tissue or the like, and, in some cases, superabsorbent particulate matter or powder (SAP). To protect clothing, and ~ullounding areas from being wetted and stained by fluids retained in a core co~ unent, such articles are generally backed by a 15 fluid-i~ vious backing component. They also usually possess a nonwoven-type fabric or coverstock material, which defines, at least, the body-contacting surface of the fluid-absorbing article. The nollwo~en coverstock material, along with optional e.l..~di~te acquisition layers, are relied on to control fluid flow and insulate the wearer from continuous contact with moisture already retained in the core. The facing 20 or coverstock must be pervious to fluids on its body-conta~;lu~g side to promote rapid transfer of each fluid insult directly into the fluid absorbent core component while, itself, rem~ininE~ soft, dry and esse~ti~lly nonabsorbent to aqueous fluids.
The art describes various constructions for core components. Radwanski et. al.
in U.S. Pat. No. 4,767,586 describes disposable diapers cont~ining nonwoven webs of 25 cellulosic fiber produced using ~u~lillll)osed layers of material in selected areas. It describes that webs of cellulosic fiber (i.e., for paper making) may be used in different fiber compositional areas. Drummond in U.S. Pat. No. 2,751,962 describes producing fibrous products in which coarse and fine denier fiber are incolporated into an integral web.

2 ~ 7 ~ ~ 3 ~ --Marshall et. al. in U.S. Pat. No. 4,931,357 described forming fibrous material from webs formed of different staple mixtures fed through separate lickerins feedably arranged in parallel axial relation over a conveyor screen or belt. The fiber feed is oriented on the belt by use of baffles to define separate lateral and vertical fiber cross-sections within the resulting web. The web, as shown, is folded over to form a cylindrical-shaped component having a homogeneous external layer.
Anderson in U.S. Pat. No. 4,223,677 describes an absorbent fibrous core structure in which absorbent fibers of less than about 6.35 mm in length are graded by length through the thickness of the absorbent structure.
It is recognized that additional improvements to fluid-absorbing articles are needed to enhance the comfort of the wearer of such articles. Such improvements may include increasing the overall efficiency and liquid acquisition rate of the core component itself, and improving fluid flow control, especially back flow or rewet properties, by varying the make up of core component.
There is a need for a fluid-absorbent core component which has increased fluid receptivity and fluid storage efficiency, and reduced rewet characteristics. There is also a need for a core component which is capable of avoiding the creation of local areas of over-saturation upon insults to the core. It is an object of the invention to provide a core component for use in a fluid-absorbing article which has enhanced fluid retention and control The core component of the present invention has improved fluid control. The core component for use in a fluid-absorbing article has a plurality of zones characterized by: (a) a zone of vulnerability positioned in said core component for maximum potential exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic . ~
r ,~"

~ ~ 7 ~

fiber or filament; and (b) at least one additional core zone in the core component having a wadding component and arranged in the core component in an area of reduced potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability; wherein the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size than the average pore size of the wadding components in the at least one additional core zone and (2) a higher average fractional value of fiber volume-to-fiber surface area than the average fractional value of fiber volume-to-fiber surface area within the wadding component of the at least one additional core zone.
Furthermore, the core component for use in a fluid-absorbing article can have for enhanced fluid retention and control having a plurality of zones characterized by: (a) a zone of vulnerability positioned in said core component for m~i mum potential exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic fiber or filament; and (b) a plurality of additional core zones in the core component each having a wadding component and arranged in the core component in an area of reduced potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability; wherein (A) the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size than the average pore size of the wadding components within the additional core zones and (2) a higher average fractional value of fiber volume-to-fiber surface area than the average fractional value of fiber volume-to-fiber surface area within the wadding components of the additional core zones; and (B) the average fractional value of fiber volume-to-fiber surface area and the average pore size within the wadding components of said additional core zones decrease in value from zone to zone relative to increased geometric distance from said - 2a -zone of vulnerability and corresponding decreased potential exposure to initial wetting.
The present invention also provides a method for the preparation of a core component for use in a fluid-absorbing article comprising laying down a zone of vulnerability positioned in the core component for maximum exposure to initial wetting and at least one additional core zone characterized in that the zones are comprised of fiber or filament possessing different average pore sizes and average fractional values of fiber or filament volume to fiber or filament surface area, and the at least one additional core zone is arranged in direct or indirect fluid-receivable relation to the zone of vulnerability and in areas of reduced exposure to initial wetting; and further characterized in that the at least one additional core zone has a smaller average pore size and average fractional value of fiber or filament volume to fiber or filament surface area than the respective average pore size and average fractional value of fiber or filament volume to fiber or filament surface area in the zone of vulnerability; and in that when two or more additional core zones are used the degree of difference in the average pore size and average fractional value of fiber or filament volume to fiber or filament surface area between the additional core zones increase in relation to increased distance from the zone of vulnerability and to reduce risk of initial wetting.
The core component for use in a fluid-absorbing article can also have for enhanced fluid retention and control having a plurality of zones characterized by: (a) a zone of vulnerability positioned in said core component for maximum exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic fiber or filament; and (b) a plurality of additional core zones in the core component each having a wadding component and arranged in the core component in areas of reduced - 2b -~, B

~ ~ 7 ~

potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability;
wherein the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size and greater average liquid-solid contact angle than the average pore size and average liquid-solid contact angle of the wadding components within the additional core zones and (2) a higher average fractional value of fiber volume to fiber surface area then the average fractional value of fiber volume to fiber surface area within the wadding components of the additional core zones; and wherein the average fractional value of fiber volume to fiber surface area, the average liquid-solid contact angle, and average pore size within the wadding components of said additional core zones decrease in value from zone to zone in general proportion to increased geometric distance from said zone of vulnerability and corresponding decreased exposure to initial wetting.
The improved core component of the invention achieves a capillary gradient through the layers of the structure to effect fluid migration away from the fluid-receiving portion of the core component, i.e., the zone of vulnerability, and through the core component in radial, lateral or axial direction. The invention recognizes that a capillary gradient is achieved in several ways: (1) by varying from zone to zone through the core component the denier of the synthetic fiber or filament in the wadding component; (2) by varying the concentration of the fibers in the fiber mix in ~' each zone of the core co.n~oll~,nl whc.cill the fiber mL~ conl~ls one fiber which has a higher average surface area and a lower average volume than the other ffber in the mi~; or (3) by varying both the denier of the s~ ,tic fiber and the concentration of the fibcrs in the fiber mi~. In these ways the average volume to surface area ratio and 5 the average pore sizc chnngcs from zone to zone. If the concentradon of the fibers in the fibcr mi~ rh~ l~s, in addition to ~ nge~ porc size, the averagc liquid-solidcontact angle from zone to zone also ~ -gcs.
To achieve the desired capillary gra1i~nt, the zonc of vulnerability and additional core zones cn~u~ lSS a variety of fiber mi~ces and core COIllpv~
10 sll lc~ s. The zone of vulnerability is usefully .,hal~ct~ d by having a greater average pore size than thc avclagc pore size of the more wettable a~ ition~l core zones a.langcd in direct or indirect fluid-l~ ceiv '~le relatdon from the zone of vulnerability, and may ~d litionslly have a greater a~cr~gc liquid-solid contact angle than the average liquid-solid contact angle of the more ...:t~':le additional core zones 15 ~l~lged in direct or indirect fluid-l~,cciv~}le relation from such zone of vulnerability.
The zone of vulnerability is furtner usefully charact.,.iLcd by ~ltili7ing s~llth.,t;c fiber or filament having an a~,.~C rl ~ ction~l value of fiber volume-to-fiber surface area, "volume to surface area" (c.g., cc/cm2) higher than the cG..G~ndi,lg average volume to surface area value within the w~rling cG~ cn~s of the ~lition ' core zones 20 ~-~hlgcd in direct or indirect fluid-receivable relation to the zone of vulnerability.
In the nd-liti.~nsl core zones the a~c.~, volume to surface area fractional value, the a~,.~c pore size, and g~.ne~lly the a~G.~g~, liquid-solid contact angle, within ~d~d l~g con~ lts of individual ~liti~ -' core zones dc~,.easc in value relative to increased ~ t~ ~IfX from the zone of vulnerability and relative to de~leased 25 potential GApGsul~ to initial wetting. For P~ 'e, the dcs~ cd values preferaUy decreasse in value in general l)n,~,lion to inclcased ge~ ;C ~ e from the zone of ~rulnerability, and in general plopollion to dGcreasGd potential e~pos~lle to initial wetting. For ~ 03CS of the present in~,enlioll, the average value of the volume to surface area for fiber or fibrillated film in the zone of vulnerability within the above-indicated pa~ .. rt~.~ can vary from about 1 cc/20,000 cm2 to about 1 cc/500 cm2 or higher, and the coll~-vpon-1ing average volume to surface area value within coll~ g ad-liti,~ core zones can usefully va~y from about 1 cc/2S,000 cm2 toabout 1 cc/40,t)00 cm2 or lower.

2 ~

In ~ s~ c~s..~g suitable structures of the core CV~ VnC,nl of the invention, a core colllpv~nl laying on a flat surface, with a backing sheet nn~ c;t1~l the core component and a cv~ ock on top will be utilized for illustration. Then, the corecolllpone.ll can be de,ccril~d with reference to its ~, y and z a~es described below.
5 The y-a~is is a.l,ill~rily chosen as the a~is across the core COIll~)OnC~ in the direction which would co.~ ond to the direction from one leg cuff to a second leg cuf~ The~-a~is is described as the a~cis perpendicular to the y-a~cis. The core colll~oncnl is described as having a "top" which defines a portion of the core component which lcce,~cs thc initial wetting, and is in the plane of the i~ and y a~is, designated the ~c-y 10 plane; and a "bottom" which defines the portion of the core col~ t ~dj~cent to a fluid-L~ vious ~a~lri~ The distance from the top to the bottom of the core COIllpOlle,nl defines the ~ L~.css of the corc colll~ol~nl and describes a z-a~is from the top surface. "Radial" shaU refer to the ~e~ tcr around the zone of vulnerability in the ~c-y plane. "Lateral" shall refer to the ~ and y directions from the zone of 15 vulnerability in the ~c-y plane. "A~cial" shall refer to the z-a~cis through the core colllpol~nl. Fluid migration in the core conl~>one.lt of the invention from the zone of vulnerability to the a~-lition~l corc zones shall be dcselibcd as being generally in the radial direction (i.e., in the ~-y plane to the pe- ;~ ter around the zone of vulnerability), lateral direction (i.e., in the direction of the i~ or y a~cis in the ~c-y 20 plane), or a~ial direction (i.e., through the core COIll~)llCnt in the di~ n of the z-a~is). The ~l-liti--r~al core zones which is the rulll,c~t in gCOI..~ ~;c distance from the zone of vulnerabil~y is said to be the o~lt~m--)st ~1iti,~ core zone.
Figure 1 is a s~ ;c top plan view of a fluid absorbing article showing the core compo~ of the invention in hidden outline. Figures 24 are scl~ ql;~ cross-2S section views of altemative embo~ , of the core cc,ll,i)ullc~lt of the ~l~e.lliOIl taken along line 2-2 of Figure 2. Figures 5A, SB and SC e~cen~li~ pn~,s;~ive steps lC.~)lCS~ a ~uitabb t~ u~ for forming the core zones of thc corc CUI~ C-lt of the invention. Figures 6-7 are schematic top plan views of altemative embo~ of the Lv~ tioll.
One embodimcnt of thc instant invention is shown in sclu-~ ~l;c top plan view in Figurc l in usc in a fluid absolb~g ~.sonal article in the general form of an open diaper l, showing core con,~o"~l 4 in hidden oudine, c~ hc~l 2, leg seal cuffs 3, and adhesive tabs (not nu,llbe~ d). The fluid-impervious backing COIll~)n~ [ iS not ~ 9 ~ 3 . s shown in the figure. Co~el~hc~,l 2 is preferably one forrncd from a plurality of bonded polyolefin resin fiber or fibrillated film co.~ g webs (not shown) such as treated polypropylene (PP) or polyethylene (PE) staple inclut~ing copolyrners and havinghomoge.leous or mi~ed denier per fil~m~nt (dpf) values of a mono- or bicolll~ne,ll-5 type fiber. Heat-sealed or cc...~nte~ thereto is a highly hydrophobic water-ble leg seal cuff 3, ~ fcl~-bly a topically treated polyolefin nonwo~cll m~teri~l, and a core colll~nc.-t 4 visible through non-woven covel~lle~l 2, pl~fcrably in a lecl~t~gular or oval forrn. The core colll~nelll of the invendon is normally utilized in the form of a rectangular, circular, or oval-shapcd body of loosely bonded 10 (or unbonded) wadding, conl~lisillg fiber bundles, slivers, fibrillated film and the like, of limited structural strength.
The zone of vulnerability has, as a plinl~uy absol~ltll material, a waddillg colll~ll~"ll COIll~liSillg sylltll~,tic fiber or fil~rnent such as polyester or polyolefin-co.~ ;..g fiber inclusi~., of poly~ltt~ylene or polyethylene, or copolymers thereof, in an e~;live amount, here defined as about 25%-100% and pl~fc~a~ly about 50%-100%
bascd on the total weight of the zone. The zone of vulnerability can also include, as desired, up to about 75%, pl~fe~abl~ 0% to about 50%, of an r l~lhion~1 fiber colll~ollc.ll having a higher fiber surface area and a lower volume, such as cellulose-based fiber. It preferably also conlaills su~cl~s~ t matter. A useful c~ 1;0n 20 for the zone of vulnerability, for e~ample, in~lit~ .s a polyolefin/cellulose-based staple fiber miAlure having a ratio, by weight, of 100~ abuul 259b/0~ aboul 75%, plcfe. bly 100~ aboul 50%/0%-about 50%, and up to about 10% of superabsorbent powder or particulate matter (SAP).
The fl~ ition~1 core zones have wadding COnl~ ,nlS which c-....l.. ;~< fiber 25 mi~tures of ~ylltll~,lic fiber or fil~nt and an a~ ;vn~l fiber type, or the additional fiber type alone. Ihe ad~1ition~l fiber p~f~lably has a higher fiber surface area and a lower volume ~an that of the syl.ll.cl;c fiber, for e~mrl~, such as ccllulose-based fiber. Suitable ~iiti~r-~ core zones contain from about 25% to 100%, preferably about 50% to 100% of an additional fiber type, and up to about 75%, plt~.ably up to 30 about 50% syl~ ,lic fiber.
One ç~. , l of such a core co...l>ol~nl follows: the zone of vulnerabilit~
COI--l~-;~S about 50% ~y~ ic fiber or filament, and about 509to cellulose-based fiber;
a first ~ additional core zone conl~llses about 20% ~ylltllctic fiber and about ~ 7~

80% cellulose-based fiber; and an outermost additional core zone cc.ln~liscs 100%
cellulose-based fiber. Superabsorbent particulate matter (SAP) is pnfe.~bly added to each zone. For e~carnple, if 10% SAP is added to the zone of vulnerability the fiber pc.celltage by weights would change to about 45% ;~lllh~,~iC fiber and 45% cellulose S based fiber, the balance pc.cc.llage by weight in SAP. Similarly, the first additional core zone cont~in.~ 10% ~ylltl.elic fiber, 70% cellulose-based fiber and 20% SAP; the oule.~llo~l core zone contains 0% ~llth~ lic fiber, 50% cellulose-based fiber and 50%
SAP.
Herein the term "denier" shall have its art recognized definition, i.e., it shall 10 mean a meas~r~ of fil~mrnt or thread thickness e~cpressed as grams per 9000 meter length. A suitable fluid absorbent w~d~iing conl~llc.ll within the zone of vulnerability, for present luul~scs, col~ ises homog~n~ous or mi~ed monocolllpolKn or bicolll~ ~e"~ ~ylltll~ lic fiber or fil~mPnt, usefully one having an ave.agc dpf value within a range of about 3 to about 50 dpf, preferably about 10.040Ø Synthetic ffber 15 or fil~nt in the w~ddii~g colllponcnls within the fluid l~,ce;v7~1e addition~ core zones COIIl~l~C fiber or filarnents having average dpf values within a range of about 1-about 40 dpf, preferably 2.0-40. Such fiber or filament may be crimr,ed or U~r~ ~d~
as desired.
For pull,oses of the present invention, the term "synthetic fiber" refers to staple 20 fiber, fil~n~nt, or fibrillated film selected from the group consi~tirlg of polyolef~, polyester and nylons. Suitably the fibers or films fo,llling the zones of the core COIll~)ullCnl are l.locliLcd for conventicn~l processing steps (i.e., cutting, Clu~ g and carding) and for control of flow-through ~ro~.lics, by topical tre~ with modifiers or by the inrlu~ion of suitable modifiers within the spun melt itself to 25 ,llcrease ll~dlu~hilic or ~ ;c properties. Such s~ - b!- ffber processing is disclosed, for instance, in U.S. Pat. No. 5,033,172 of Jarnes H. E~ on in which one or more N,N-polyalko~ylated 10-22 carbon fatty amines with up to 60% of 10-22 carbon fatty acid amides are incorporated in the spun melt, and/or treated in acconlance with U.S. Pat. No. 5,045,387 of A. C. Scllmsl7 in which an e~f~live 30 amount of a modifier colll~silion colllpli;,ing at least one of (a) a colll~llcnl col-la;..;.~g lko~ylated ricinoleate with up to about 159to, by weight of nlodirlcr colll~siliun, of an 18 carbon fatty acid; (b) a coll~ ding h~d~ug~ cd derivativeof (a); and (c) a polyalko~ylated pol~dillle~llylsilo~cane, having up to about 80% by 2~

weight of modifier composition, of one or more of conl~lulll (a), (b), or combination thereof is topically applied onto hydrophobic polyolefin fiber or Coll~SlX)ndillg fibrillated film.
Also useful, for ~ul~)OSGS of the present invention, is the above-indicated S incorporation of strategically positioned art-recogll~zed su?eldbsol~llt powder or particulate matter within the core zones to ilnpl~ùvc liquid 1,~l~ and favor more even and rapid distribution of fluids. Such col~ Gn~s are natural absorbents such as guar gum"c: th~n gum, or chitin, or are ~y..~ sin~-~l by the polylllGI~alion of acrylic acid, acrylate esters, vinyl alcohol, ethylene o~ide, acrylamide, and other vinyl 10 IllOllOlllG.~. One of r.ulllGro~.s cumlllelcially available products of this ty-pe is Sumikagel~9 S-50 ( a product of Sumitomo Colll~l~).
ReÇe"i,lg again to the Figures, Figures 2-4 l~p~senl ~1iagr~mm~tic cross-sections of several ~ le variations of core co,l~ollcnl 4 taken along line 2-2 of Figure 1, in which the respective zones of vulnerability are ~ livdy shown as (a), 15 (a ), and (a ), and the l~,s~ctive additional core zones as (b) and (c), (b ) and (c ), and (b ) and (c ). If desired, the number of ~ 1ition~1 core zones can be con~,nielllly incleased to si~ or more, for e~ample ten, and is preferably in the range of one to SL~
additional core zones. In high volume or collllnc..;ial production a core colll~having one to three additional core zones may be ~ c. ble, with those having one 20 ~cldition~1 core zone generally being the simplest to ...~.. ,r~- ~Ul~i. The zones are shown in cross-section in ;,.~ tle, semi-col-~e~ ;c confi~u,.~tiull (Fig. 2), in stacked hori7ont~l conÇ,y,u,~tion (Fig. 3), and in verticaVcontignous configuration (Fig. 4).
The core zones may bc shaped generally as rectangular he~ rirons and positioned in adjacent parallcl pl.~ n~ to one another. In each case from the zone of 25 vulnerability, design -:d by wl~ lled or primed "a", through additional core zones ~lesign~ted by wlyli llcd or primed "b" and "c," the zones are ~;La~ elized as having prû~ s~i~ely decreased a.,e~.ge volume to surface area ratio values, pore size and potentially dec~sscd average liquid-solid contact angles relative. As previouslydescribed, these ch~t~ ;cs are ob~ai,led, for i~t~lnf~e~ by varying the fiber mi~ so 30 as to lower the average dpf of the ~ylllh~,lic fiber, and by v~g thc average liquid-solid contact anglc by illcl~asillg the conc~ntr~ n of one or more suppk ..f ~ lbers, pr~;~rabl~ ~lbers having a lowcr average volume and a highcr average fibcr surface area, such as a ccllulosc-based fiber.

2~313~

In Figure 2, (a) ~pr~sents a centrally located zone of vulnerability, preferablyone cont~ining about 25%-100%, preferably about 50%-100% of a sylllh~ lic thermoplastic fiber preferably topically or ot~le.wise treated for wo~ g and retained hydrophilic l,r~ ies. Such fiber, as above noted, can be a spun and treated S polyolefin resin, resin mi~c or copolymers thereof (i.e., PP/PE) having relatively high average dpf values within the above-indicated range, and colllbi.lcd with about 0%-about 75%, preferably 0%-about 50%, by weight of ccllulose-based fiber, and SAP
powder or particulate matter as above described.
Additional core zones, (b) and (c) of Figure 2, in that order, l~l~s~.ll 10 individual homogeneous zones co.-.l.. icing fibrous absorbent material having a progl~ s~iv~ly smaller average fber volume and higher average fiber surface area and a pro~l~ssively smaller average pore size, and, if the conccnt,ttion of fibers in the fiber mi~c also change, a lowcr average liquid-solid contact angle as the relativc geolll~llic disla.~ce from zone (a) incleascs. Zones (a) (b) and (c) can be individually bonded (or 15 wlbonded), or bonded "in toto" using coll~nlional bond;.lg ~e~tmiques The embodiment illu;,ll~ted in Figure 2 dç ~.on~l.ates a structure in which fluid migration from the zone of vulnerability occurs in both the lateral and a~ial directions. The embodiment illus~ d in Figure 3 d~ o~ lrates fluid migration in the a~ial direction.
The embodiment illustrated in Figure 4 demon~trates fluid migr~tjon in the lateral 20 direction.
The c llb~3i~e~ illustrated in Figures 6 and 7 ~on.~lrate fluid migration in the radial dil~ ion. A particularly ~~ble e,ll~3;...- -.1 for the core colll~llcnl of the in~ e.lli.,n is shown in schematic top plan view in Figure 6 in which a zone of vulnerability (a ) is radially s.-lf~wlded by a single ~ 1itionql core zone (b ). The 25 top and bottom of zonc of vulnerability (a ) are not surrounded by the additional core zone (b ), and a bottom view of this configuration (not shown) would show essçrlti~lly the same configuration as that shown in Figure 6.
Figure 7 illustrates an ~ " e.llbo~ ll in s. I.e ~ ;c top plan view of the radial configuration in which another -1-1hiQn~ core zone (c ) is addcd to the 30 structure in which additional core zone (c ) is formed radially around additional core zone (b ). I~e radial configurations illustra~ed in Figures 6 and 7 also ~~co....~.odate any number of -'~liti~n~l core zones, prerc.~ly from one to si~ additional core zones, preferably one or two additional core zones, and most preferably one additional core zone.
Encouraging fluid migration in several directions is achie~cd by con-bil~g the structures described. An ~ltern~ive embodiment of the radial configuration in Figure S 6, for e~cample, CG.~ L ;ng a first radial structure upon a second radial structure (not shown) in which the zone of vulnerability of the second radial structure has a reduced ~~ nlage by weight of syl~ lic fiber than the pe.cenlage by weight of synthetic fiber in the zone of vulnerability of the fi~t radial structure to create a gradient in both the radial and a~cial direction.
Figure 5A r~p~se.lls, in schematic cross-section view, a step or stage in a process suitable for producing zoned core col.l~nellls within the scope of the present invention, in which a contin~lous fle~cible screen or belt S is ~ Wt~ d from movable support çk~ 9 having end-wise attached flanges 10 slideably resting on co~ li. g support flanges 11 at the top of a "U" shaped pclrorated forming trough 15 6 folllling an upper surfacc of suction bo~c 7. As shown, one core layer, CGll~ ~l,onding, for instance, to additional core zone (c) of Figure 2 has been formed from an air e~ d fiber mi~c 12 supplied from above (see arrows) through twin çrins a~iaUy arranged in n~.-chin-, direction and a mi~ing zone (not shown). Thee.~ led fiber is shown to be adhered to the colles~n)ndi,lg "U" shaped fle~ible screen 20 or belt 5 with the aid of a partial vacuum obtained through vacuum e~haust pipe 8 on the reverse side of the belt and trough 6.
An ~ hionsl core zone, here rel.le3~ ted in Figure SB as layer (b), is coll~e.~i~.lll~ applied at a dowlls~ station, using dil~,lcnl fiber, or fibcl/~liculate mi~cturcs to obtain a core zone of higher fiber volume and lower fiber surface area 25 (i.e., a nnm~ri~slly higher volume to surface area value) and a larger average pore size, and potentially a larger average liquid-solid contact angle than laid down in zone (c).
Figure 5C s~ slly Icpn3ellls a cross-section at a further dOw,l,llcalll station in which the zone of vulnerability or (a) core zone is formed. As shown, the 30 air~ntr~in~ d fiber or particulate matter making up such zone is applied from above in the general manner of the previous u~ l stations as shown in Figures SA and SB, ho..~r, the (a) zone can also be sepdl~tely laid down "in toto" as a cornpiled fiber or fil~ nt mass as webs, or even as fibriUated film, and the entire wa~l-ling optionally 2 ~ 9 !j; ~

bonded together using sonic, therm~l, laser or similar co~ ional bonding techniques (not shown).
The dim~n~ions of each core zone vary according to the fluid-absorbing article and the size of the particular article in which the core co.~ l is utili7~-1 ForS e~c~mrlç, the size of each zone depends upon the structure of the core Cc~ )oll~nl and the number of additional core zones utili7e-1 A suitable zone of vulnerability has a meter within the range of about S cm to about 10 cm. The zone of vulnerability ranges in thickness from about 2 mm to about 2 cm. The additional core zones range in thir~n~ss from about 2 mm to about 2 cm. Additional core zones sulluullding the 10 zone of vulnerability in the radial or lateral direction l~lcs~-ll illCl'c-n~l~ from the zone of vulnerability in the ~c-y plane. The inert,.l~ of the ~A~lition~1 core zones range in size from about O.S cm to about 20 cm.

EXAMPLE I
A. Three test diaper cores, id<-~l;l;cd as T-l, T-2 and T-3 and having the 15 general semi-co~-~e ~;c conl;g,l.alioll as desclibed in Pigure 2, are formed from se~lu~ ly-applied mi~tures of air e.lLI~u~d 18 dpf (0.75 inch staple) poly~lu~llene and cellulose fluff pulp fiber (ob~ained from Ceorgi~ier Wood Pulp softwood bleached Kraft from l l l Rainier Co.). The mi~ctures are applied at five s~alale stations onto a movable screen or belt in the I~ er g~n~ ly described with respect 20 to Figures SA-SC. The resulting unbollded zones are scqu~ ly laid down in about l"-thick layers having the following con~e--t.~ions (in weight percent) of poly~rc,pylene/cellulose: 0/100, 10/90, lS/85, 2sns and S0/S0 (zone of vulnerability).
The test cores, in toto, contain 23 weight perce~ , (23 wt. %) polyln~,~ylene staple with a density of about 0.045 grn,/cc. The test cores are then topped with 25 id~-nti~l poly~iv~ylene l~lwo~cn co~ lock and tested for Liquid Acquisition and Rewet chara~,~- ;.~l;CS (Table I) using a p~ driven GATS (Gl~vil~ ic AbsGfl~ncy Testing System) with GATS II test eqnirn-~nt from M/K Systems Inc. ofDanvers, Massa~ sct~. A raised (lS cm) liquid reservoir is fee'~ly COn~lf~ted bytubing (for upward flow) be,le~l. a single-holed simple platform. The test core and a 30 weighted cove,i,twk are placed thereon above the hole under 0.1 psia. A flow valve is opened for one (1) second and reservoir weight loss l~cor~d. The reservoir loss (gm) divided by time, provides initial acquisition rate data.

2 ~ 7 The rewet test is effected by obtaining an 80% core saturation using as ~ylllL. tic urine, a 53 dyne/cm dilute saline~ r~ l solution obtained from Pluronic~9 lO-R-8 surf~ct~nt from BASF Inc. After five (5) minutes the test core is removed and covered with a second preweight dry bonded core and pressed (0.5 psi) for two (2) 5 ~ cg, the increase in weight of the dry-bonded core is reported as rewet in grams.
As a control, E~cample L~ is repeated but using identic~l polypropylene/cellulose staple mi~ctures at each zone application station to obtain unifu~ ly-distributed fiber mi~c throughout the core at a density of about 0.045 grn/cc and a total content of polypropylene staple of about 23 wt. %. The control cores, 10 i(l- ~.l;r;ed as C-l, C-2 and C-3, are tested for Acquisition Rate and Rewet Plo~llies as before and the results reported as an average in Table I below.
As a further control, three cores, idc~ ed as C4, C-5 and C-6 are plcparcd using 100 weight percent of the same batch cellulose as that used in the previous ç~mple in each zone to obtain a core of about the sarne density and weight. These 15 control cores are id~ntir~lly tested for Acquisition Rate and Rewet P'lu~llics and the results reported as an a~c.agc in Table I below. As a c~ ;.con for Acquisition Rate, it is noted that m-~ n;~dcd flow is 10.7 r~second.
Table I

Acquisition Rate Rewet Core Sample #mUsecond (av.) (grn) (av.) T-1, T-2, T-3 9.7 7.9 C-l, C-2, C-3 8.8 8.0 C4, C-5, C-6 8.1 9.9 B. E~cample IA is l~ ~cat~ d in core sarrlples T4, T-5 and T-6, using 15 dpf 0.75" polyester staple in place of polypl~*ylene staple. The cores are identically 25 tested as before and the averaged test results reported in Table ~[ below.
E~ample LA is l~cat~d with control cores C-7, C-8 and C-9, in which the same total ~llou-lls of polyester (PET) and identie~l weight ~r~.ll~ge of PET/cellulose as used in T4, T-5 and T-6 are applied at each zone to obtain a Ulli[~ l staple d~ ulion through the cores. The cores are tested as before and the 2 ~ 7 ~

averaged test results reported in Table II below as a~e.ages. Again, it is noted that m~imllm w~illlpeded flow rate is 10.7 rnl.sec.
Table II

q~ ion Rate Core Sample # ml/~cond (av.) T4, T-5, T-6 10.5 C-7, C-8, C-9 8.7 E~amples IA and IB are repeAted but with the ad~1ition of 5 weight percent of Sumikagel~D S-50 (SAP) within the zone of vulnerability and S weight percent within the outcnnost zone (the first laid down in Figure SA). Rewet ~lete....;nAI;ons arc 10 carried out as before and thc averaged test results rcported in Table m as average values in con~p~;.son with E~carnple L~ and IB values.

Table m Rewet Rewet Core Sample # (no SAP)(grn) (with SAP)(grn) T-l, T-2, T-3 7.9 5-5 C-l, C-2, C-3 8.0 6.3 2 ~ 7~
.

EXAMPLE II
Test diaper cores, ide~ ed as T-7, T-8, and T-9 and having the general radial configuration as described in Figure 6, are formed from mL~ctures of air entrained 20 dpf (0.75 inch staple) poly~r~ylene and cellulose fluff pulp (obtained from S Georgianier Wood Pulp bleached Kraft from ITT Rainier Co.). Thc following concentrations (in weight percent) of polyp,u~ylene/cellulûse: 0/100 and 50/50 (zone of vulnerability) are utilized. A first additional core zone co~ lising an appro~.iullat~ ly one (1) inch layer of 100% cellulose is formed, and a hole of appro~imately 1-1/2 to 2" in ~ nn~t~r is pu~l~;hed and lcinlo.~ed from a central area of 10 the additional core zone. A second layer of the 50/50 col-re~ ution is formed, and a generally circular form of appro~cimately 1-1/2 to 2 inches in diameter, l~lese ~ g the zone of vulnerability, is .e.no~cd frorn the second layer. The circular form is inlaid into the hole pl~n~h.-d in the first layer to form a core colllpon~,nt with a zone of vulnerability and one additional core zone.

The test cores, in toto, contain 33 weight ~crce.ltage (33 wt. %) poly~l~ylene staple with a density of about 0.05 gm/cc. The test cores are then topped with i(ientiç~l poly~l~ylene nonwoven coverstock and tested for Liquid Acq~iQition (Table I) using a ~.es;,~i-drive GATS (Clavilll~llic Absoll~.l~;y Testing System) with GATS
II test e(~ l from M/K Systems Inc. of Danvers, ~f~QQ~ Q,etts, as described in 20 E~cample I.

As a control, the e~mple above is ~p~axd but using identi~l poly~fo~lene/cellulose staple ll~lu~s at each zone application station to obtainullifollllly-disllibul~d fiber mi7c throughout the core at a density of about 0.05 gm/cc and a total content of pol~prvpylene staple of about 33 wt. ~o. The control cores, 25 i~lPntifi~ as C-10, C-ll and C-12 are tested for Acquisition Rate as before and the results reported as an average in Table IV below.

As a further control, three cores, icl~ ;l;Pd as C-13, C-14 and C-15 are ~ pal~d using 100 weight percent of the same batch cellulose in each zone to obtain a core of about the same density and weight. These control cores are identically tested 30 for ~qllicition Rate and the results reported as an a~ ge in Table IV below. As a 2 ~ 3 4 comparison for Acqui~ition Rate, it is noted that m~iml-m "~ 3ed flow is 10.7 rnl/second.
TABLE IV

Core Sample # Acquisition Rate ST-7, T-8, T-9 9.16 mVsec (av.) C-10, C-ll, C-12 7.81 ml/sec (av.) C-13, C-14, C-15 7.35 mVsec (av.)

Claims

1. A core component for use in a fluid-absorbing article having a plurality of zones characterized by:
(a) a zone of vulnerability positioned in said core component for maximum potential exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic fiber or filament; an (b) at least one additional core zone in the core component having a wadding component and arranged in the core component in an area of reduced potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability;
wherein the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size than the average pore size of the wadding components in the at least one additional core zone and (2) a higher average fractional value of fiber volume-to-fiber surface area than the average fractional value of fiber volume-to-fiber surface area within the wadding component of the at least one additional core zone.

2. A core component as claimed in claim 1 wherein the wadding component in the zone of vulnerability is characterized by a greater average liquid-solid contact angle than that of the wadding component of the at least one additional core zone.

3. A core component for use in a fluid-absorbing article for enhanced fluid retention and control having a plurality of zones characterized by:
(a) a zone of vulnerability positioned in said core component for maximum potential exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic fiber or filament; and (b) a plurality of additional core zones in the core component each having a wadding component and arranged in the core component in an area of reduced potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability;

wherein (A) the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size than the average pore size of the wadding components within the additional core zones and (2) a higher average fractional value of fiber volume-to-fiber surface area than the average fractional value of fiber volume-to-fiber surface area within the wadding components of the additional core zones; and (B) the average fractional value of fiber volume-to-fiber surface area and the average pore size within the wadding components of said additional core zones decrease in value from zone to zone relative to increased geometric distance from said zone of vulnerability and corresponding decreased potential exposure to initial wetting.

4. A core component as claimed in claim 3 wherein the wadding component in the zone of vulnerability is characterized by a greater average liquid-solid contact angle than the average liquid-solid contact angle of the wadding components within the additional core zones and the average liquid-solid contact angle within the additional core zones decreases in value from zone to zone relative to increased distance from said zone of vulnerability and corresponding decreased potential exposure to initial wetting.

5. A core component as claimed in claim 1 wherein the core component contains one additional core zone to the zone of vulnerability.

6. A core component as claimed in claim 5 wherein the wadding component in the zone of vulnerability is further characterized by a greater average liquid-solid contact angle than the average liquid-solid contact angle of the wadding component within the additional core zone.

7. A core component as claimed in any of the preceding claims 1 - 6 further characterized in that the additional core zone is positioned about the zone of vulnerability in semi-concentric configuration.

8. A core component as claimed in any of claims 1 - 6 further characterized in that the zone of vulnerability and the additional core zone form generally rectangular hexahedrons in adjacent parallel placement to one another.

9. A core component as claimed in any of claims 1 - 6 further characterized in that the additional core zone is positioned in radial configuration around the zone of vulnerability.

10. A core component as claimed in any of the preceding claims further characterized in that the wadding component of the zone of vulnerability comprises about 25%-100% by weight of polyolefin or polyester staple fiber or filament.

11. A core component as claimed in claim 10 wherein the wadding component of the zone of vulnerability comprises about 50% to 100% by weight of polyolefin or polyester staple fiber or filament.

12. A core component as claimed in any of claims 1-10 further characterized in that the zone of vulnerability comprises about 25% to 100% of polyolefin or polyester staple fiber or filament and about 75% to 0% by weight cellulose-based fibers.

13. A core component as claimed in any of the preceding claims further characterized in that the zone of vulnerability comprises from about 0% up to about 50% by weight of a cellulose-based fiber.

14. A core component as claimed in any of claims 1-10 further characterized in that the zone of vulnerability comprises about 25% to about 75% of polyolefin or polyester staple fiber or filament and about 75% to about 25% by weight cellulose-based fibers.

15. A core component as claimed in any of the preceding claims wherein the additional core zone comprises cellulose-based fibers.

16. A core component as claimed in any of the preceding claims wherein the additional core zone contains from about 25% to 100% by weight of a cellulose-based fiber.

17. A core component as claimed in claim 15 wherein the additional core zone contains from about 50% to 100% by weight of a cellulose-based fiber.

18. A core zone as claimed in claims 3 or 4 wherein the zone of vulnerability comprises about 25% to 100% of polypropylene or polyethylene fiber or filament and 0% to about 75% by weight of cellulose-based fiber and wherein eachadditional core zone comprises about 25% to 100% of cellulose fiber, and 0% to about 75% by weight of synthetic fiber or filament, and wherein each additional core zone has a greater amount of cellulose-based fiber than the additional core zones geometrically closer to the zone of vulnerability.

19. A core component as claimed in any of the preceding claims further characterized in that the wadding components within the zone of vulnerability comprise fiber or filament having an average dpf value within a range of about 3 to about 50 dpf and wadding components within the additional core zone comprise fiber or filament having average dpf values within a range of about 1 to about 40 dpf.

20. A core component as claimed in claim 19 wherein the wadding components in the zone of vulnerability comprise fiber or filament having an average dpf value within a range of about 10.0 to about 40.0 dpf and wadding components within the additional core zone comprise fiber or filament having average dpf values within a range of about 2.0 to about 40.

21. A core component as claimed in any of the preceding claims further characterized in that the zone of vulnerability or the additional core zone contains superabsorbent.

22. A core component as claimed in claim 21 wherein the additional core component has up to 10% by weight superabsorbent.

23. A core component as claimed in any of the preceding claims wherein the additional core zones contain from about 20% to about 50% by weight of superabsorbent.

24. A core component as claimed in any of the preceding claims further characterized in that the additional core zone is bonded to at least one adjacent additional core zone or the zone of vulnerability.

25. A core component as claimed in any of claims 1-6 further characterized in that the at least one additional core zone is in lateral contact with said zone of vulnerability.

26. A core component as claimed in claims 1-6 further characterized in that at least one additional core zone is positioned so as to permit radial fluid migration from the zone of vulnerability to the at least one additional core zone.

27. A core component as claimed in any of the preceding claims further characterized in that the fiber or filament comprising the wadding components within the zone of vulnerability and additional core zones are of constant length.

28. A core component as claimed in any of claims 1-27 further characterized in that the average value of the fiber or fibrillated film volume to fiber or fibrillated film surface area in the zone of vulnerability is in the range of about 1 cc/20,000 cm2 to about 1 cc/500 cm2, and the average value of the fiber or fibrillated film volume to fiber or fibrillated film surface area in the additional core zone is in the range of about 1 cc/25,000 cm2 to about 1 cc/40,000 cm2.

29. A core component for use in a fluid-absorbing article as claimed in any of the preceding claims further characterized in that the zone of vulnerability comprises about 50% by weight synthetic fiber and about 50% by weight of cellulose-based fiber, and that a first additional core zone is arranged in radial configurationabout the zone of vulnerability, and a second additional core zone comprising about 100% cellulose-based fiber is arranged adjacent to and in radial configuration around the first zone of vulnerability.

30. A method for the preparation of a core component for use in a fluid-absorbing article comprising laying down a zone of vulnerability positioned in the core component for maximum exposure to initial wetting and at least one additional core zone characterized in that the zones are comprised of fiber or filament possessing different average pore sizes and average fractional values of fiber or filament volume to fiber or filament surface area, and the at least one additional core zone is arranged in direct or indirect fluid-receivable relation to the zone of vulnerability and in areas of reduced exposure to initial wetting; and further characterized in that the at least one additional core zone has a smaller average pore size and average fractional value of fiber or filament volume to fiber or filament surface area than the respective average pore size and average fractional value of fiber or filament volume to fiber or filament surface area in the zone of vulnerability;
and in that when two or more additional core zones are used the degree of difference in the average pore size and average fractional value of fiber or filament volume to fiber or filament surface area between the additional core zones increase in relation to increased distance from the zone of vulnerability and to reduce risk of initial wetting.

31. A method as claimed in claim 30, further characterized in that the zone of vulnerability has an average liquid-solid contact angle greater than that of the at least one additional core zone and that when two or more additional core zones are used the degree of difference in average liquid-solid contact increases in relation to increased distance from the zone of vulnerability and to reduced risk of initialwetting.

32. A method for the preparation of a core component for use in a fluid-absorbing article as claimed in claims 30 or 31 further characterized by the step of laying the additional core zones about the zone of vulnerability in semi-concentric arrangement, or in lateral configuration about the zone of vulnerability, or in axial configuration beneath the zone of vulnerability, or in radial configuration around the zone of vulnerability.

33 A fluid-absorbing article comprising, in combination, the fluid-retaining core component of any of claims 1-29 arranged within at least a fluid permeable coverstock and a fluid impervious backing layer.

34. A core component for use in a fluid-absorbing article for enhanced fluid retention and control having a plurality of zones characterized by:
(a) a zone of vulnerability positioned in said core component for maximum exposure to initial wetting, said zone of vulnerability having a wadding component comprising synthetic fiber or filament; and (b) a plurality of additional core zones in the core component each having a wadding component and arranged in the core component in areas of reduced potential exposure to initial wetting and in direct or indirect fluid-receivable relation from said zone of vulnerability;
wherein the wadding component in the zone of vulnerability is characterized by (1) a greater average pore size and greater average liquid-solid contact angle than the average pore size and average liquid-solid contact angle of the wadding components within the additional core zones and (2) a higher average fractional value of fiber volume to fiber surface area than the average fractional value of fiber volume to fiber surface area within the wadding components of the additional core zones; and wherein the average fractional value of fiber volume to fiber surface area, the average liquid-solid contact angle, and average pore size within the wadding components of said additional core zones decrease in value from zone to zone in general proportion to increased geometric distance from said zone of vulnerability and corresponding decreased exposure to initial wetting.