CA2237154A1 - Liquid-absorbent article and method and apparatus for manufacturing the absorbent article - Google Patents

Abstract

A liquid-absorbent article having a high absorption capacity and a short fluid penetration time. The liquid-absorbent article has a porosity gradient along the Z direction (the thickness) established by superposing layers of absorbent material having different average pore sizes. In one embodiment the porous network of each absorbent layer is a combination of inter-particle and intraparticle interstices. In another embodiment the absorbent layers have different average particle sizes. The liquid-absorbent article is well-suited for use as an absorbent component of a disposable absorbent product, such as a sanitary napkin, a diaper, an incontinence pad, an adult brief, a wound dressing, a nursing pad, a tampon pledget, or as desiccant for packaging materials to keep goods dry during shipping or storage. The invention also extends to a novel method and apparatus for manufacturing the liquid-absorbent article.

Description

CA 02237l~4 1998-0~-08 WO97/13484 PCT/CAs6/00626 TITLE LIOUID ABSORBENT ARTICLE AND ~ L~O~ AND APPARATUS FOR
MANUFACTURING THE ABSORBENT ARTICLE
.

FIELD OF THE INVENTION

The lnvention relates to the art of manufacturin~
structures for absorbinq body exudate. More specifically, the lnvention relates to a hiqhl~ absorbent article that has a porosity ~radlent alonq the directlon of fluid mi~ration there throuqh. The lnvention also extends to a method and apparatus for manufacturln~ the absorbent artlcle.

BACKGROUND OF THE INVENTION

Many dlsposable absorbent products use absorbent cores made prlmarily of cellulosic pulp fluff materlal. Such cores are generally soft, flexlble and absorbent but tend to be bulk~ and thlck and have poor wicking propertles. In addition, cellulosic pulp fluff materlal has poor structural stabillty which may cause the absorbent core to collapse when saturated with liquid.

An absorbent structure that has poor wickinq, proPerties usually increases the likellhood of failure of the absorbent product to hold and contain body liquids. Body exudate will be localized to a certain area of the poorly wickinq absorbent medium, causing localized saturation whereby excess liquid may overflow throuqh an external surface of the absorbent product.
This overflow may contact the user's garment and cause stai.ns or contact the user's body and cause wet discomfort or rash. It is therefore desirable to provide an absorbent core for disposable absorbent products which can wick away body liquids from the CA 02237l54 l998-05-08 Point of contact with the absorbent core and spread it throuah the absorbent core. The imProved wlckinq pronerties of such an absorbent core provide the capacitY for liquids to travel bY
capillarY pressure throuahout the entire absorbent volume. Thls permlts the use of thlnner cores, since more absorbent volume can be made avallable for absorbina body liquids by such wickin~
action. Thinner absorbent cores may also prove to be more comfortable for the user and less unsiahtly or obvious when worn under clothes. Absorbent cores comprisinq sphagnum moss are described, for example, ln the followinq US Patents, the sub~ect matter of which is incorporated hereln by reference, ln their entirety:

PATENT #INVENTOR(s) DAT~ OF ISSU~ ll 4,170,515Lalancette et October 9, 197g al.
4,215,692Levesque Auaust 5, 1980 4,226,237Levesque October 7, 1980 4,305,393 Nauven December 15,1981 4,473 440 Ovans September 25, 1984 4,507,122Levesque March 26. 1985 4,618,496Brasseur October 21, 1986 4,676,871Cadleux et al. June 30. 1987 4,9g2,324 Dubé Februarv 12, lg91 5,053,029 Yana I October 1, l9gl .
In accordance wlth the teachlna of these Patents, an absorbent str~lcture comPrislnq sPhaqnum moss as a Primarv absorbent component ls formed as a sheet by alr or wet laylna of Partlcles. The sheet ls calendered to obtain a relatively thln, CA 022371~4 1998-0~-08 i.e. from about 0.025 to about 0.~5 centimeters (cm) thic'~ and relativelv dense i.e. from about 0.1 to about 1.0 qrams per ~ cublc centimeter (q/cc~ structure. Such absorbent sphaanum moss sheet ma~ be processed to lncrease its flexibllity for enhancin~
its comfort potential bY sub~ectinq the sheet to mechanical tenderl~lng such as a perf-embossinq or a mlcro-corruaatinq process.

The sphaqnum moss sheet thus formed has a larqe proportlon of extremely tiny pores and caplllaries allowing the sheet to absorb and retaln a verY hi~h amount of liquid. The sphaqnum moss pores swell as they absorb liquid, however, this swelling does not cause a loss of capacity for further admittin~ llquid.
Rather, the swelling contributes to the ability of the absorbent medlum to retain the liquld while generally maintainlng the structural integrity of the absorbent structure in use.

The wicking properties of the above-described sphagnum moss sheet provide the ability for the sheet to be hlghly absorbent while remaining relatively thin.

Although sphagnum moss has certain highly deslrable llquid-absorption propertles, it manifests less than ideal fluld-acquisition rates. To overcome this difficulty it is common practice to provide a hi~hly permeable, fibrous, liquid transfer layer on the sphagnum moss layer, whose function ls to quickly collect the body exudate and then meter the liquid to the sphagnum moss material. Liquid discharged on such composite absorbent structure will rapldly ingress the transfer layer due to its highly porous network. From the transfer layer, liquid migrates toward the sphaqnum moss layer by capillary pressure as CA 02237l54 l998-05-08 WO97/13484 PCT/CAs6/00626 a result of the substantlal difference in wlckina PoWer between the different materlals. The llquid mlaration ls well-controlled, occurrln~ at the rate of acceptance of the spha~num moss.

ComPound absorbent structures includin~ transfer and reservoir layers are costly to produce because the raw materlal for manufacturinq the transfer layer ls expenslve. Another drawback is the undesirable bulk increase of the dlsposable absorbent artlcle resultlnq from the use of a thick transfer layer.

Hence, there ls a need in the industrY to Provlde a sphaqnum moss absorbent core havlng a signlflcantly lmproved llquid acquisltion rate, thus allowln~ to employ a thlnner transfer layer and possibly ellmlnate the transfer layer altogether.

SUMMARY OF THE INVENTION

It is an ob~ect of this lnvention to provide an absorbent article having a hi~h liquld-acqulsltlon rate and a hlqh absorption capaclty.

Another ob~ect of thls lnventlon is to Provide a disposable absorbent product, such as a sanltary napkln, a diaper, an incontlnence pad, an adult brief, a wound dressing, a nursinq pad, a tampon pledget, or a desiccant for packaglng materials, which utllizes a spha~num moss absorbent core having a significantly improved llquld acquisition rate.

Another ob~ect of thls lnventlon ls to provlde a novel method and apparatus for manufacturing a liquid-absorbent article CA 022371~4 1998-0~-08 WO97/13484 PCT/CAs6/~0626 ~ which utllizes a sPhaqnum moss absorbent core havina a siqnificantl~ improved liquid acquisltion rate.
.

As embodied and broadly described herein, the present invention provldes a liquid-absorbent article comprisinq absorbent particulate material and further comprisin~ first and second zones in lntimate fluid communicative relat~onshlp each zone having a multiplicity of inter-partlcle and intra-particle interstices admittinq passa~e of liquid, said first zone havina a larger average interstlce size than said second zone, whereby said second zone manifests a hiqher capillary attraction than sald first zone. For purposes of the present lnvention, the terminology "particle" shall mean fibrous as well as non-flbrous materials, i.e., any small unlt of materlal wlthout limitations of shape. Thus, a fiber that is characterized as havin~ a geometrlcal extension along a preferential direction will be considered a Partlcle. Hence, "partlculate material" includes materials made of fibers, partlcles having non-fibrous ldentity, or a combination of both.

As used herein the terminology "inter-particle interstices"
refers solely to the lnterstlces defined between the partlcles, while "intra-partlcle interstices" refers to an open cellular structure inside the particles, such as the lumen in sphagnum moss leaves. The terminolo~y "average interstice size" as used herein refers to both the intra-particle interstices and the inter-particle interstices. There exist many different porous materials which are capable of providing intra-particle interstices and thus are considered suitable for use ln the manufacture of the li~uid-absorbent article of the present invention. Suitable materials include, for examPle, sphaqnum, CA 02237l~4 lsss-o~-os perlite, vermiculite, ex~anded claY, exPanded rlce, crushed foam, zeollte, and combinations thereof are suitable ~or use in the present invention. Sphaanum, however, is the preferred material for use in the present lnventlon due to lts hl~hly absorbent nature.

Asused herein thetermlnoloqY "lntimatefluid-communicative relationshlp" refers to a conditlon in which llquld in one of the zones can easilY mlqrate toward the other zone. This condit~on ls achleved when the zones are co-formed or when they have been formed as discrete elements and then ~oined to one another b~
means to create an interface providing a path of comparatively low resistance to the miqration of llquld. Suitable means for ~olnlna the zones include, but are not llmited to, adheslve, thermobondinq, needle punchin~, and the like, and comblnations thereof.

It has now been dlscovered that absorbent structures havinq a poroslty ~radlent of the type broadly deflned above, provide a slqnlflcant advanta~e to absorbent products. The first zone has an open network that rapldly admlts the discharge of body exudate lnto the absorbent structure. The second zone has a less o~en network which provldes a strongcapillary attractlon differentlal between the two zones, whereby the llquld ls preferentially drawn toward the second zone where lt ls permanently entrapped. The lncrease in the fluld take-up rate of the provided by the absorbent structure of the present lnventlon permlts a dlsposable absorbent product to utillze a thinner transfer layer wlthout lncreaslng the rlsk of failure by overflow leakage. For some appllcations, the transfer layer may even be dlspensed wlth.

CA 022371~4 1998-0~-08 wo97ll34s4 pcTlcAs6l~o626 - The average interstice size of a qiven zone of the llquld-absorbent articlP may be controlled bY one or more of the ~ following expedients:

A) ad~ustin~ the Proportion between inter-partlcle lnterstices and intra-particle interstices in the liquld-absorbent material. For example, an lncrease in the relatlve amount of particles having lntra-particle interstices in the li~uid-absorbent material, wheretn the lntra-particle interstices are smaller than the inter-particle interstices, will cause the averaqe interstice size of the liquid-absorbent material to dlminlsh. For example, spha~num moss has lumen (i.e.
intra-partlcle lnterstlce) whose average size is typically below 66-microns. Accordingly, a relative increase in the amount of sphagnum moss in the liquld-absorbent material wlll result in a reduction in the average interstlce size.
Conversely, a relative decrease in the ratio intra-particle interstlces/inter-partlcle interstices, results in an increase ln the average lnterstlce slze.

B) ad~ustlng the slze of the lnter-particle interstices of the material. In general, the size of lnter-particle lnterstices is proportional to the size of the part1cles.
Hence, the lncorporatlon of coarse partlcles into a li~uid-absorbent material will result in a liquid-absorbent article having larger lnterstices than would be obtalned by the use of fine particles. This allows one to regulate the average interstice size by varying the average particle size of the material.

CA 022371~4 1998-0~-08 C) combinina steps A and B. For example. the averaae interstlce size of a material may be lncreased bv lntroducin~ in the absorbent material non-~orous partlcles that are relativel~ larqe. The non-porous character of the partlcles lncreases the ratlo inter-particle interstices/intra-partlcles lnterstices while the coarseness of the partlcles augments the averaqe lnter-particle size.

~) applylnq mechanical compresslon to brlnq the partlcles closer to one another, thus decreasing the average interstice size. The compresslon may affect both the inter-particle interstice and the lntra-particle interstice sizes.

Thus, anyone of the steps A to D applled alone or in combination can be used to control the average interstice size of lndivldual zones of the llquld-absorbent to optlmlze the porosity gradient in the li~uid-absorbent product.

Underone exemplary embodlment,the liquid-absorbent product includes a lower layer made of sphagnum moss material on top of which ls inte~rally formed an upper layer that combines spha~num moss and debonding component. The purpose of the debonding component is to lncrease the avera~e lnterstlce slze in the sphagnum moss network and provide therein interstlces that are slgnlflcantly larger than the lnterstlces of the lower layer. For the purpose of this speclfication "debondlng component" shall mean any material which is capable of reducing the cohesiveness of a glven particulate liquid- absorbent material, such as an agent actln~ chemicall~ to reduce the bonds unltlng the particl~s CA 02237l~4 l998-0~-08 of the material to one another, or a physlcal seParator that forcibly malntalns the Particles in a sPaced apart relationship, hence increasing the average interstice slze of the network. One example of a suitable debondln~ component manifestin~ a physical separator activity is cross-linked cèllulosic fibers.

Suitable cross-linked cellulosic fi~ers for use in this inventlon are dlsclosed ln US Patent 4,853,086, assigned to Weyerhaeuser Company, dated Au~ust 1, 1989, which describes a method for manufacturinq cross-llnked cellulosic fibers which conslsts of sPrayinq a wet or partially dry web of ~ellulosic fibers with an aqueous solution of glycol and dialdehyde. The dlsclosure of thls patent is lncorporated hereln by reference in its entirety.

Under another exemplary embodiment, the poroslty qradient is obtalned by formingthe various layers of the llquid-absorbent sheet from sphagnum moss particles having dlfferent dimensions.
More particularly, the upper layer is formed of sphagnum moss particles that are relatively coarse i.e. larqer than the particles in the lower layer. When those particles are amalgamated together durln~ the formation process of the absorbent sheet, large inter-particle interstices remaln between them. In contrast, the lower la~er is formed primarily of fine sphagnum moss particles that, due to their smaller size, flt closer to one another to provide lnter-particle lnterstices of lesser dimensions.

A hybrid structure combinin~ the features of the two previously described embodiments is the most preferred. The characterizing feature of this variant is the inclusion of CA 02237l~4 1998-0~-08 debondlng component lnto the upper laver of coarse sphaanum moss Particles. A~ain, the debondinq comPonent may be a chemical a~ent or a physical separator such as cross-linked flbers. Preferably, the layer of coarse sPha~num moss particles has a particle slze median value in the range from about 2000 mlcrons to about 500 microns. Preferably, the fine layer of spha~num moss particles has a particle slze median value ln the range from about 500 mlcrons to about 150 microns.

The layer of coarse sphagnum moss particles having a median particle of about 2000 microns has slgnificantly more inter-particle interstlces ln the slze range from about 600 microns to about 120 microns, by comparison to a fine layer of sphagnum moss where no separatlon has been made between coarse and flne sphagnum moss partlcles, and thus has a lesser amount of inter-particle interstlces in the size range from about 600 microns to about 120 mlcrons than the coarse sphagnum layer. In a preferred embodlment, the coarse layer of sphagnum moss has at least about 55% of lnter-partlcle lnterstices (in term of interstlce count rather than lnterstlce volume) havlng a slze ln the range from about 600 mlcrons to about 120 mlcrons, more preferably at least about 60~ of inter-particle interstlces in that range and most preferably at least about 63% of inter-partlcle lnterstices in that range. For purposes of thls speciflcatlon, any lnterstice in spha~num moss material havln~
a size ln excess of 66 mlcrons ls considered to be an inter-particle lnterstice rather than an intra-partlcle lnterstlce, since the intra-partlcle lnterstlces (lumen) on the sphagnum leaves are substantlally smaller than 66 microns.

As embodied and broadly descrlbed herein, the invention also CA 022371~4 1998-0~-08 W097/13484 PCT/CA96/~0626 provldes a liquld-absorbent artlcle includinq first and second zones ln fluid-communiCatiVe relationship, said first zone and sald second zone lncludlna sphagnum moss partlcles, said flrst zone havlnq a lar~er proportion of inter-particle interstices (ln terms of lnterstlce count rather than lnterstlce volume) ln a slze range from about 600 microns to about 12~ microns than said second zone.

Under this embodiment, the absorbent artlcle is not necessarllv an inteqrally formed structure. The varlous zones whlch preferably form indlvldual layers of the artlcle may be dlscrete elements that are united wlth adhesive or by another suitable means.

As embodied and broadly described herein, the invention also provldes a liquid-absorbent article including first and second zones in fluld-communicative relationship, sald flrst zone including sphagnum moss particles having a flrst partlcle size median value, sald second zone havlng a second particle slze medlan value.

As embodied and broadly descrlbed hereln, the lnvention also provldes a disposable absorbent product, comprislng:

- an absorbent component of particulate material said absorbent component including upper and lower layers ln lntlmate fluid communicative relationship, each zone havlng a multipliclty of lnter-particle and lntra-partlcle lnterstices admitting passage of liquid, said first zone havlnq a larger average interstice size than sald second zone, whereby sald lower zone manlfests a higher capillary attraction than said upper laYer in CA 022371~4 1998-0~-08 order to induce llquid absorbed in said upper laYer to mlqrate toward said lower laver; and - a body contacting, liquld-pervious cover LaYer superposed to said absorbent component.

As embodled and broadly descrlbed hereln, the lnventlon further provldes a method for manufacturing a llquid absorbent component, said method comprlsing the steps of:

- Providinq a first zone of partlculate materlal havinq a multiplicity of lnter-particle and lntra-partlcle lnterstices, sald flrst zone havin~ a flrst averaqe lnterstlce slze;

- provldlng a second zone of partlculate materlal havlng a multipliclty of inter-partlcle and lntra-partlcle lnterstices, said second zone having a second average lnterstice slze, sald flrst lnterstlce size beinq larger than said second lnterstlce slze; and - establlshlng an lntimate fluid communlcative relatlonship between said zones to allow liquid in said flrst zone to migrate toward sald second zone.

In a most preferred exemplary embodiment, the first and the second zones include sphagnum moss and are manufactured by a co-formlng process whlch lncludes the followlng steps:

A) laying ln a superposed relationshlp and ln physlcal contact a first slurry layer of partlculate materlal and a second slurry layer of particulate material to form a CA 02237l~4 1998-0~-08 laminated composlte slurry laYer, the flrst and the second slurry layers includln~ ~effectlve amounts ofl sphagnum moss partlcles, l) the first slurrY layer constltutlnq a precursor phase of a the flrst zone;

ll) the second slurry la~er constltutlnq a precursor phase of the second zone;

B) extractln~ fluidlzin~ medlum from the laminated composite slurry layer to form a lamlnated composlte web including the flrst zone and the second zone in a superposed condltlon and intimately unlted to one another.

The co-forming process broadly described above ~reatly slmpllfies the manufacture of the llquid-absorbent artlcle ~n accordance with the lnvention because the formatlon and bonding of the layers ls accompllshed ln a slngle operatlon. A further advantage of this method resldes ln the stren~th of the bond between the layers whlch ls hlghly reslstant to delamlnatlon. As a result, the liquld-absorbent article can withstand viaorous mechanical worklng wlthout looslng lts structural lntegrity.
Further, the bond is such as to establish the desirable lntlmate fluld-communicative relatlonshlp allowlng fluldto easllymigrate from the upper layer towards the lower layer.

In a most preferred embodlment, the slurrles forming the respective layers of the llquld-absorbent artlcle are lald in a superposed relatlonshlp on a continuously advancing Fourdrinier wire to form the lamlnated composlte slurry layer. The CA 02237l~4 1998-0~-08 Fourdrlnler wire is passed over a vacuum slot establishinq a pressure dlfferential across the laminatedcomposlte slurry laYer to extract water therefrom. The resulting web is drled, calendered and cut lnto dlscrete absorbent components. If deslred, the web may be sub~ected to mechanical working, such as perf-embosslng or mlcro-corru~atlng, in order to increase its flexibillty for a better comfort potential.

The composltlon of the indlvidual slurry layers determ~nes the final structure of the liquid-absorbent sheet. When the poroslty ~radlent ls achieved solely by the lnclusion of debonding component in the upper layer, the selected debondlng component is added to the slurr~ before laying the slurry on the Fourdrinier wire.

Under the embodiment that requires separation of the sphagnum moss in coarse particles and fine particles, the manufacturing process beqins by preparln~ a mother slurry containing sphagnum moss particles of varying sizes. The slurry is then subjected to a classiflcation step to separate the mother slurry in at least two slurry fractions according to the size of the sphagnum moss particles. The slurry fractions are then laid in a superposed relationship on a Fourdrinier wire as described above.

Under the hybrid embodlment the spha~num moss particle separation is followed by the addition of debonding component in the slurry fraction containing the coarse sphagnum moss particles.

In a possible variant, the layers of the absorbent article CA 022371~4 1998-0~-08 are formed as discrete elements that are ultimately united bY
adheslve bondln~ or by any other suitable agency to form a laminated structure havin~ strata ofdlfferent average interstice slzes. In an exemplary embodiment the layers are manufactured bY
separating a mother slurry of sphaqnum moss lnto coarse and fine fractions, and then layln~ the fractions separately to form the lndividual layers. After the usual post-formatlon treatments, such as dryin~, pressing, calenderlng, etc., the layers are unlted to one another in a superposed relationshlp.

Ob~ectively, the manufacture ofthe llquld absorbent artlcle conducted by assembllng together discrete absorbent layers is perhaps less deslrable than the inteqral formatlon approach, prlmarlly because additional manipulatlons are requlred to complete the manufacture of the absorbent artlcle. In addition, the lnterface between the discrete layers provides a llquid path of somewhat hlgher resistance than when the layers are inte~rally formed. Still, thls embodlment exhlblts slgnlflcantly lmproved liquid-absorbent properties by comparlson to prlor art structures and lt thus suitable for many applications.

As embodled and broadly descrlbed hereln, the lnventlon further provides a method for manufacturlng a laminated liquid-absorbent article, comprlsing the steps of:

- providlng a body of particles suspended ln fluld, such as llquid or gas, said partlcles havln~ varying dlmenslons ?

- separatlng sald body of particles ln at least two fractions, referenced as a first fraction and a second fractlon, said flrst fraction having a higher partlcle slze median value CA 022371~4 1998-0~-08 than sald second fraction:

- extractlnq fluidizlnq medium from sald fractions to form a flrst absorbent layer and a second absorbent layer respectlvel~, sald first absorbent layer havlnq a hlc~her averaqe inter-particle interstice size than said second absorbent layer, whereby said second absor~ent layer manifests a hi~her capillary attraction than said flrst absorbent layer;

- establishlnc~ a llc3uid-communlcative relationship between sald layers, whereby lic~uid lntroduced in said flrst layer is lnduced to ml~rate toward said second layer under the effect of caplllary attractlon.

In the most preferred embodiment, the llquid communlcative relatlonshlp between the absorbent layers ls created by co-formatlon, such as wet laylng the slurry fractlons in a superposed relationshlp, as descrlbed earller. Thls approach produces an lntegrally formed llquld-absorbent article. In a variant, the absorbent layers may be formed separately from one another and then assembled by adheslve bondlng or the llke to establish the llquid-communicatlve relatlonship between them.

As embodled and broadly described hereln, the lnventlon also provides an apparatus for manufacturing a hlghly absorbent structurally lnte~ral artlcle havln~ superposed liquld-absorbent layers unlted ln an intimate fluid-communicatlve relatlonshlp, sald apparatus comprlslng:

- a classlfler for separatlnc~ partlcles suspended ln fluldlzing medium into at least two slurry fractlons in CA 02237l~4 1998-0~-08 accordance to size of sald partlcles, a first slurrY fraction havinq ~ larqer partlcle size median than ~ 5econd slurrv fraction, sald classlfier havins first and second outlets for discharqin~ sald flrst and second slurry fractions, respectively;

- a foraminous member;

- first and second headboxes in a flui~ communlcative relationship with said flrs and second outlets respectively for discharqing said flrst and second slurry fractlons in a superposed relationshlP on said foraminous member to form a lamlnated composlte slurry layer; and - means for establlshing a pressure dlfferentlal across said laminated composite slurry layer to extract fluidlzlng medlum from sald first and second slurry fractlons in order to form respectlve flrst and second porous networks lntimately united to one another, sald second porous network manlfestlng a hlqher capillary attraction than said first porous network to induce liquld absorbed in said flrst porous network to mlgrate toward sald second porous network.

The fluld absorbent article ln accordance with the present lnvention ls sultable for use in disposable absorbent products including, but not limited to sanltary napkins, diapers, urinary pads, adult briefs, wound dressln~, nurslng pads, tampon pledgets, or as desiccants for packa~in~ materials to keep goods dry during shipplng or storage.

BRIFF DESCRIPTION OF THE DRAWING~

- Flgure 1 is a fra~mentary, perspect iV'? view of a sanitary CA 02237l54 l998-05-08 napkln incorporating the ll~uld-absorbent article accordinq to the lnvention:

- Figure 2 is a fraqmentarY perspectlve view of the llquid-absorbent artlcle accordinq to the present invention that ls characterlzed by a non-uniform porosity distributlon:

- Flqure 3 ls a schematlc representation of an apparatus for manufacturing the comPound, structurally lnteqral, llquld-absorbent artlcle ln accordance wlth the lnventlon;

- Flgure 4 ls a flowchart of the process for manufacturing the llquld-absorbent artlcle in accordance with the invention;

- Fl~ure 5 ls a flowchart of the process for manufacturing the liquld-absorbent article in accordance wlth a variant;

- Flgure 6 ls a flowchart of the process for manufacturinq the llquld-absorbent article in accordance wlth a further variant;

- Flgure 7 ls a perspectlve vlew of a llquid-absorbent artlcle manufactured by assembllng ln a superposed relationshlp separately formed dlscrete absorbent layers; and - Flgure 8 is a porosity dlstrlbution graph of the llquid-absorbent article and some of lts component layers.

DETAILED DESCRIPTION OF ~K~RED EMBODIMENTS

Referring now to Flgure l of the annexed drawlngs, the CA 022371~4 1998-0~-08 WO97113484 PCT/CA96/~0626 reference numeral 10 desianates comprehenslvelya sanltary napkin constructed in accordance with the principles of the present invention. The sanltary napkin 10 comprises an envelope l~
definlng an lnternal space recelvin~ an absorbent component 56 that lncludes sphagnum moss. The envelope 12 lncludes a li~uid permeable cover layer 16 made of a non-woven fabric or any other suitable porous web or apertured fllm, and a liquid impervlous backin~ layer 18, made of polyethylene fllm for exampl~. The cover and backlng layers 16 and 18 are heat-sealed to one another along their mar~inal portlons. To attach the sanitary naPkln l~
to the wearer's underpants, the llquld impervlous backlng layer 18 ma~ be provided with adhesive zones covered wlth a Peelable backlng ~not shown ln the drawings).

The absorbent component 56 is a dual-layer structure featurlng a porosity gradient along the Z dlrectlon. Preferably, a transfer layer (not shown ln the drawlngs) of known constructlon is provlded overthe absorbent component wlth a vlew of further enhancing the ll~uid acquisltion rate of the sanitary napkln.

The structure of the absorbent component 56 is shown ln Flgure 2. It comprlses a central core 58 containing prlmarily sphagnum moss and having a porosity gradient along the Z
directlon (the thlckness). The central core 58 is constituted by an upper layer 60a and a lower layer 60b intermlxed at the lnterface to provide an intimate llquid-communlcative relationship between them. Layer 6~a has a larger average lnterstlce size than layer 60b.

The central core 5~ is confined between relnforcing laYers CA 022371~4 199X-0~-08 62 and 64 of flbrous material. The purpose of the relnforcinq layers is twofold. First, they stren~then the core 58, there~y provlding a unitlzed absorbent structure capable of maintalnlna lts lntegrlty even when saturated wlth liquld. Second, the laYers 62 and 64 reduce dustlng by preventing free sphagnum moss particles within the absorbent structure from belng released outslde. Kraft wood pulp materlal has been found hiqhly satlsfactory for manufacturin~ the reinforcing layers 62 and 64.
It is also posslble to use other materials, such cotton linters or ground wood among others, ln admlxture wlth or ln substitutlon to the Kraft wood pulp material.

The detailed composltlon of the llquld-absorbent component 56 will be best understood from the following descrlptlon of the apparatus and the process for manufacturlng such absorbent component. Referrlng to Figure 3, the apparatus designated comprehensively by the reference numeral 18, comprlses an endless, fluld-pervlous Fourdrlnler wlre 26 which is mounted on rollers 28 to provide a horizontally extendlng run 30 that is continuously advanced forward to support and convey a slurry of sphagnum moss and cellulosic flbers throu~h various processing stations.

Headboxes 32, 34, 66 and 36 arranged ln a spaced apart relatlonshlp along the path of travel of the wlre 26 are provided to lay on the wlre 26 slurry ln sheeted form. The headbox ban~.
deposlts on the wire 26 four (4) layers of slurry ln a superposed relatlonshlp to form a laminated slurry web. More speclflcally, the headboxes 34 and 66 lay slurrles contalnlng sphagnum moss whlle the headboxes 32 and 36 dellver slurrles of fibrous material such as Kraft wood pulp or any other sultable substance.

CA 022371~4 1998-0~-08 WO97/13484 PCT/CAg6/~0626 - The preparation of the sphagnum moss slurry layers suppliedto headboxes 34 and 66 is lllustrated by the flowchart of Fl~ure 4. The mother slurry prepared by dlspersin~ raw sphaqnum moss material in water is wet classlfied at steps 68 and 70 to retain only the partlcles having a size in the range from about 74 microns to about 2000 microns. The screened fraction ls diluted with water to render the slurry more manageable and supplied to a dual-stage classifier station 72 ln order to separate the sphagnum moss partlcles ln a fine fractlon and a coarse fraction.
The classifler station 72 comprises a primary centrifuqal classifier 74 to perform an initial separatlon of the spha~num moss particles on the basls of slze. ~ centrifu~al classifier available from Hymac Limited under any one of commercial designations RB 200, RB 150XC or RB 80X has been found satisfactory.

The centrlfugal classifler 74 is calibrated to produce a re~ect stream having a partlcle size median in the range from about 2000 mlcrons (10 mesh) to about 500 microns(35 mesh) that ls dlrected at headbox 66. The particle size median value is defined as the slze of the particles havin~ the hi~hest fre~uency when the sphagnum moss particles are classified according to slze.

It is preferred to add a fibrous component, such as polyester flbers and~or Kraft wood pulp at step 76 prlor to supplyin~ the slurry to headbox 66 that forms the layer 60a of the central core 58. Sultable flbrous components may lnclude such materials as Kraft wood pulp, cross-linked cellulosic fibers, mechanical wood pulp, natural or synthetic textile fibers such as rayon, polyester, nylon, acrylic and the like, and mixtures CA 02237l~4 1998-0~-08 thereof. The flbrous components are qenerally added to the headbox in an amount from 2 to 20~ by wel~ht of the absorkent sheet 10, preferably from 2% to 6%. As used herein, th- term mechanical wood pulp is meant to include qround wood pulp, thermo-mechanlcal pulp and refiner wood pulp. Ground wood pulp ls essentially trees and branches whlch have been debarked, cleaned and ~round into particulate matter. Reflner wood pulp differs from ~round wood pulp only in that the ~rindin~ step utilizes a refiner, i.e. a dlsc-like devlce well-known in the art and havin~ metalllc rlbs at the peripheral sections thereof whlch last contact the wood particles and help separate the wood fibers without excesslvely dama~ing them. Thermo-mechanlcal wood pulp ls slmllar to refiner pulp wlth the exceptlon that the wood particles are heated in the refiner, usually with steam, to aid in separatlng the wood fibers. The common characteristic of these mechanlcal pulps ls that no attempt has been made to separate the flbers by chemlcal means although they may later, after belng reduced to fine partlculate matter, be subiected to a desired chemical treatment, such as bleaching. Preferably, when mechanical wood pulp is used in a sphagnum moss slurry, such mechanlcal pulp has a Canadian Standard Freeness (TAPPI test method T-227), in a range of from about 60 to 750 and preferably from about 400 to 600.

The Kraft wood pulp, also usable in combination wlth sphagnum moss, is essentially chemically treated, long fibred wood pulp such as sulphite and sulphate wood pulps.

Preferably, a debonding component is added to the slurry supplied to headbox 66 in an amount which is effectlve to increase the lnter-partlcle lnterstlces in the liquid-absorbent CA 022371~4 1998-0~-08 - product. Sultable debondlng agents include, but are not llmltedto fibrous materials which are effective for reducing the ~ coheslveness of the partlcles ln the liquld-absorbent product.
These fibrous materials preferablv have a length of from about 0.6 cm to about l.9 cm, preferably about l.3 cm and a denier of from about 1.0 to 5Ø Preferred debondin~ components whlch have been found to be particularly effective in opening-up a sphagnum moss network ln order to allow a faster llquld acquisition are cross-linked cellulosic fibers. In a preferred embodiment, cross-llnked cellulosic flbers are lncorporated into the slurry in an amount effective to reduce the cohesiveness of the sphagnum moss partlcles in the ll~uld-absorbent product, i.e., open-up the sphagnum moss network. The exact amount of cross-linked fibers can vary widely, depending on the nature and particle size of the sphagnum moss partlcles, and is preferably ln the range from about 5% to about 75% based on the weight of sollds in the slurry. The slurry of coarse sphagnum moss partlcles may also contain an effectlve amount of a chemical debonding a~ent, of a type known in the art, which can be used either in comblnation or ln substltutlon to the cross-llnked celluloslc flbers.

The accepts stream of the centrifugal classifler 74 that contains sphagnum moss particles of smaller size ls supplled to a 60 mesh stationary screen 78 of the type descrlbed ln Canadlan patent appllcatlon 2,057,654 assl~ned to Johnson & Johnson Inc.
lald open on June 14, l9g3 which ls lncorporated herein by reference in its entirety. The screen 78 features a system of ~ets directed at the screen plate to prevent the screen apertures from clogglng. The re~ects stream that contains particles larger than about 150 microns (100 mesh~ are discarded. The accepts having an avera~e particle size ln the ran~e from about 500 CA 022371~4 1998-0~-08 WO97/13484 PCT/CAs6/00626 microns (35 mesh) to about 150 microns tl00 mesh) are directed to head~ox 34 to form layer 60b of the central core 58.

It ls preferred that a stationary screen operating on the prlnclple of a sieve be used ln the second stage 78 than a centrifugal classifler because it allows a better process control. Slmllarly, a statlonary screen, may be substltuted to the centrlfugal classifier 74. Such statlonary screen is ldentlcal to screen 78 described above wlth the exception that screening apertures of 6.35 mm could be used rather than 60 mesh perforatlons.

At the completlon of the classlflcatlon stage, a flbrous component may be added to the slurry, as shown as step 80.

In a varlant, the slurry fractions supplled to the headboxes 34 and 66 are prepared on the production llne illustrated ln Flgure 5. The dlfference wlth the set-up of Fl~ure 4 resides ln that no cross-linked celluloslc flbers are added to the flow of coarse sphagnum moss particles. In a further variant shown ln Flgure 6, no separatlon of the sphagnum moss particles is made. The slurry from the screening system 68 and 70 is split ln two parts havin~
approxlmately the same sphagnum moss particle size distrlbution.
To create the poroslty gradlent ln the flnal product, cross-llnked fibers or another debondln~ component ls added to one of the slurry fractlons from whlch the layer 60a ls made.

In a flrst embodlment of the present invention, as lllustrated ln Flgure 3, a slurry cf Y~raft wood pulp layer havlna a conslstency of about 0.2% by welght of sollds ls first lald down on the wire 26 from the headbox 32 in order to ~orm the bottom Kraft reinforcln~ layer 64. The slurry flow rate is selected to deliver on the wire 26, 15 qrams of sollds per square meter. The Kraft slurry passes under the headbox 34 which delivers on top of the Kraft layer a slurry of flne sphaqnum moss particles prepared wlth the installatlon of Fiqure 4. The slurry has a spha~num moss content ln the range from about 80~,to 10 by weight of solids ln the slurry and contains polyester fibers up to 20% by welght.

A speclfic formulatlon that has been found satisfactorv is reproduced below:

CONSTITUENT PROPORTION BY WEIGHT
OF SOLIDS IN THE SLURRY
sphficn~:~mnEEIpartlcle $~
E~emed.ac i!l the ranceC!o~50~mcrQr~E
LC 15~ ~ -rQQEI, pQl jester f lber6 6 . ! 7 eraf~ ~QerE

The consistency of the sphagnum moss slurry fraction is set at 0.5% by welght of sollds. The flow rate of the slurry fractlon is selected to dellver 178 grams of solids per square meter on the wire 26.

The headbox 66 delivers the slurry fraction of coarse sphagnum moss partlcles lntermlxed wlth cellulosic cross-linked flbers. Thls slurry fractlon has a consistency of 0.5~ by weight of solids, a flow rate to deliver 182 grams of solids per square meter on the wire 20. The coarse particles slurry contains CA 02237l54 l998-05-08 WO97/13484 PCT/CAs6/00626 sPhaqnum moss ln the ranqe from about 20% to 60% by wel~ht of solids in the slurry, cross-linked cellulosic fibers in the ranqe from about 5% to about 75% by welqht and polyester flbers up to 20% by wel~ht.

Example l.

A llquid absorbent article was manufactured h~ving the followlng formulatlon and poroslty distrlbution proflle as described below:

CONSTITUENT PROPORTION BY WEIGHT
OF SOLIDS IN THE SLURRY
spha~r.smm~sEpa;t1c1eE
Ipart,c:eE!zemed:ar.!r,th- 54.39 rcl'!~:e frOIII 2e~ ~.cror.E ~c c~
.-:rrons !
croEs-';nkEdce1'~!os:c':berc ~Q.
~.rECtflber~ ~,~9i polles er flberE 1.~

Interstlce Size Percentage of (mlcrons) interstlces (%) Z980 0.3 596 9.5 l99 24.6 ll9 13.7 7.6 CA 02237l54 l998-05-08 Interstice Size ' Percentage of (microns) interstlces (%) 66 4.5 c 66 39~7 For comparlson purposes, the porosity distribution of the lndlvidual layers of the llquid-absorbent artlcle of this example was determlned and provlded ln the followlng tables.
The method for measuring the porosity dlstribution profiles is dlscussed herelnafter in the section entltled "Test procedures". For laYer 60a (containin~ the coarse sphaanum moss partlcles, the lnterstice slze and percentage of lnterstlces are as follows:

Interstice Size Percentage of ~microns) interstices (~) 2980 0.6 596 14.9 199 39.3 119 14.0 4.7 66 2.g c 66 23.6 For layer 60b (containlng the fine sphagnum moss partlcles)l the interstice size and percentage of lnterstlces are as follows Interst~ce Size ~ Percentage of (microns)interstices (%) 2980 0.6 596 9.g l99 17.0 ll9 18.0 9.0 66 5.0 < 66 40.6 The poroslty dlstrlbution profiles for the entire liquid-absorbent artlcle and lts indivldual layers are also reported in a chart shown ln Flgure 8. It ls particularly lnteresting to note that the layer 60a (coarse sphagnum particles) had a significant amount of interstices ln the slze range from about 600 microns to about l20 microns. In a preferred embodlment, layer 60a should have at least about 50%
of lnterstlces in the range 600 - 120 mlcrons, more preferably at least about 60% and most preferably ~in the embodlment shown) at least about 63%. In contrast, the layer 60b had less interstices in thls size range (41% in the embodiment shown).

ExamPle 2.

A second example of a formulatlon for the sphaqnum moss slurry layers delivered from the headboxes 34 and 66 ls as follows. Thls formulatlon was prepared ln accordance wlth the manufacturlng process shown in Figure 5 and contained sphaqnum moss ln the range from about 68~ to 100% by welqht of sollds in the slurry, polyester fibers up to 20% by weight and Kraft CA 02237l54 l998-05-08 wood pulp fibers up to 30~ by weiqht. The slurry fractlons coarse/flne differed primarily by the particle size of the spha~num moss material. In this example, the slurry fraction of primarily fine sphagnum moss particles was as follows CONSTITUENT PROPORTION BY WEIGHT
OF SOLIDS IN THE SLURRY
cpkacnu~ Q9E l~aar~!~'e ElZ~
~edlac ~ t're raGae from 5g0 ~Cro!l~ t~ 15~ ro!ls P~.7 p~ ~ ieEtC~ erE
F.ra~t ROOd ~ p flbers I Q~ ?

The slurry fraction of primarily coarse sphagnum moss particles was as follows:

CONSTITUENT PROPORTION BY WEIG~T
Epkaonilm mcss ~l7~rticle rn~e medlaE ;n t~e ranoe ~ro.q, _00;~' IEi''rO!~6 ~A 50Ç~ C',~7~
.~1 oroQ5 !
polyeCter Clber9 2 . 7 ~.r6ft RGOd ~ D f~berE 5.55 Example 3.

A third example of a formulation for the sphagnum moss slurry layers delivered from the headboxes 34 and 66 is as follows. This formulation was prepared in accordance with the manufacturlng process shown ln Figure 6. In this example, both slurry fractions have approximately the same sphagnum moss particle slze dlstribution.

The lower slurrY layer delivered from the headbox 34 had a spha~num moss content ln the range from about 80% to 100% by weight of sollds ln the slurry and contalned polyester fibers up to 20% by weight. The speclfic formulatlon is as follows:

CONSTITUENT I PROPOSITION BY WEIGHT
OF SOLIDS IN THE SLURRY I
EDhaar!u~ mosC p7 D~ E~ cr flberE ~ 7 ~.ra't YOOd ~ul~ fibe.~
The upper slurry fraction dellvered from the headbox 66 contalns spha~num moss ln the range from about 20~ to about 60% by welght of solids in the slurry, cross-linked celluloslc fibers in the range from about 5~ to about 75% by weight and polyester fibers up to 20~ by weight. A speclfic formulatlon ls reproduced below:

CONSTITUENT PROPORTION BY WEIGHT
OF SOLIDS IN THE SLURRY
~D~:aar;~ 08~ 4 CrnEE- H~ked ce H u lo E~~
flberE i4 Del:ester flbe!r ~.3~

A flnal Kraft wood pulp slurry layer was lald from the head~ox 36 on the spha~num moss slurry ln order to form the reinforclng top layer 62. Thls final layer was ldentical ln terms of consistency and composltion to the bottom Kraft wood CA 02237l~4 1998-0~-08 pulp layer 64 prevlously deposited except that the flow rate was such as to deposit on a s~uare meter of the wire 26 fi~e grams of sollds.

The resultln~ laminated slurry layer Kraft~Sphagnum Sphagnum/Kraft was then passed over a vacuum slot 50 to extract water under the influence of a pressure dlfferential establlshed across the slurry layer. It was necessary to regulate the resldence tlme of the slurry layer over the vacuum slot 50 and the vacuum lntenslty in order to control the denslty of the final product. Generally, decreased vacuum and lncreased speed wlll result ln a less dense product.
Conversely, lncreased vacuum and decreased speed will produce a denser product.

The web leavlng the dewatering statlon 50 passed through a drler 52 whose purpose was to elevate the temperature of the web to evaporate resldual water. The drier 52 is of a well-known constructlon and does not re~ulre a detalled descrlptlon hereln.

It may be envlsaged to add between the drler 52 and the vacuum slot 50 a press sectlon (not shown in the drawlngs) to mechanically express water from the web, as lt is well-known to those skllled ln the art, ln order to reduce the water contents ln the web as much as posslble before lt ls processed ln the drler 52.

Downstream of the drier 52 a calenderln~ station S4 is provlded whlch mechanlcally compresses the drled product ln order to densify the sphagnum moss material for enhancing lts drylng power. If desired, the calenderlnq statlon 54 may be followed by a perf-embosslng statlon (not shown in the drawinqs) provlded to tenderize the web by mechanical worklnq.
This treatment softens the sphagnum moss structure for enhancing its comfort potentlal. The calenderin~ operation is described ln detail in the lnternatlonal applicatlon PCT/CA92/00308 filed on July 20, 1992 in the name of Johnson &
Johnson Inc. The contents of thls applicatlon ls lncorporated hereln by reference.

An alternative to the perf-embossin~ techni~ue is the mlcro-corrugatlng operatlon which ls similar to the perf-embosslng except that no perfor~tions are performed. The llquid-absorbent structure is solely subjected to an embosslng operatlon to create closely spaced hinge llnes. The mlcro-corrugatlng operatlon is described ln US patents granted to Personal Products Company 4,596,567 and 4,559,05 issued on June 24, 1986 and December 17, 1988 respectlvely.
The contents of these patents ls lncorporated herein by reference.

If deslred, the absorbent artlcle under the second embodiment may be treated wlth re-wetting agent. Preferably, an RL Thorowet re-wetting agent ~available from Clough Chemicals~ ls added to the mother slurry prior to the screening step in an amount of 0.3% by welght of solids ln the absorbent artlcle. Subsequently, a G-60 Thorowet re-wettlng agent ~avallable from Clough Chemicals) is delivered on the Kraft/Sphagnumt Sphagnum/Kraft lamlnated slurry layers, prlor the dewaterlng stage in an amount of 0.8% by welght of sollds -CA 022371~4 1998-0~-08 in the absorbent article. Most preferably, the G-60 Thorowet re-wettin~ a~ent is delivered on the top Kraft layer in a foamed condltlon, as described ln the Canadian Patent application 2,057,693 in the name of Johnson & Johnson Inc.
and laid open on June 14, l9g3. The dlsclosure of this patent application is incorporated herein by reference.

A variant of the liquid-absorbent article ls illustrated in Fi~ure 7. This variant is characterized in that the layers 60a and 60b are formed as dlscrete entltles and then unlted to form a compound li~uid-absorbent structure, rather than bein~
integrally formed. The layers are manufactured by following the process steps lllustrated in Fi~ure 4 wlth the exceptlon that headboxes 34 and 66 deposit the fine and the coarse slurry fractlons on separate Fourdrlnier wires (not shown in the drawlngs). Each slurry fraction ls then sub~ected to lndependent post-formation treatments, such as pressing, drying, calenderlng, etc. The resulting absorbent layers are then unlted to one another ln a superposed relatlonshlp by adheslve or any other suitable agency.

Sanitary napkins constructed with the liquid-absorbent article 56 as the absorbent core are found to possess a very high liquid-absorption capacity and a comparatively high llquid-penetration rate which reduces the risk of failure when a large quantity of body exudate is suddenly released on the sanltary napkln.

The propertles of the llquld-absorbent article 56 and of the sanitary napkin manufactured wlth such absorbent article are compared to control samples ln a series of tests.

CA 022371~4 1998-0~-08 LI~UID-ABSORBENT ARTICLE CONTROL

The control is an integrally formed sheet containlng a central core of sphagnum moss havin~ a unlform poroslty dlstribution and united to two outer layers of Kraft wood pulp. The central core contalns 76.92% by welght of sollds ln the control sheet of sphagnum moss, 3.69% of polyester flbers and 7.38% of Kraft wood pulp. Each of the top and bottom Kraft layers represent 4.61% of the control by weight of sollds. The control sheet also contalns 0.92% by weight of sollds of G-60 Thorowet re-wetting agent and 0.4% by weiqht of solids of RL
Thorowet re-wettin~ agent that are applied as dlscussed earller. The basls weight of the control sheet ls of 325 grams per meter squared.

SANITARY NAPKIN CONTROL

The sanltary napkln control ls manufactured by placlna on the absorbent artlcle as descrlbed above cut ln the form of a 10 centlmeter (cm) by 10 cm square, a transfer layer of ldentlcal dlmenslons. The specific transfer layer used has a basls wel~ht of 120 grams per meter squared and it ls available from James Rlver Corporatlon under the brand deslgnatlon Alrtex 397. Finally, a 10 cm by 10 cm embossed hydrophlllic apertured fllm ls placed over the transfer layer.
The apertured fllm is known ln the trade as wettable Reticulon and it ls used to manufacture the cover layer of a sanitary napkin commerclallzed by Johnson & Johnson ln Germany under the trademark Silhouette Ultra.

In a first set of tests the liquid-absorbent article CA 022371~4 1998-0~-08 prepared by the process of Fl~ure 4 ls tested aqainst the llquld absorbent article control to assess the followlng characteristlcs ltest procedures are described ln detall later):

a) Capacity;
b) Capillary pressure (lst load), c) Capillary pressure (2nd load);
d) Penetratlon tlme (synthetic menstrual test liquld with protein having a viscosity of 25 centipoise ( cps );
e) Penetration tlme (synthetlc menstrual test llquld wlth proteln having a vlscosity of 100 cps)l and f) Stain area In a second set of tests the llquid absorbent article prepared by the process of Figure 4 is incorporated in a sanitary napkln constructlon as the absorbent core. Thls conslsts of placlng on the liquld absorbent artlcle the transfer layer and the cover layer used in the sanitary napkin control. The resultlng product ls then tested agalnst the sanitary napkin control to assess the following characteristics (test procedures are described in detail later):
g) Penetratlon tlme (menstrual test liquid wlth protein having a viscosity of 100 cps);
h) Re-wet/wet back; and i) Liquid dlstrlbution;
EXPERIMENTAL DATA FROM TESTS A TO F

CAPILLARY CAPILLARY PBNETRaTION p~7Tp~rroN SHBBT
CAPACITYPRBSSURB PR~SSURB TIaE 151 .TIML 16~ STRAIN
SA~IPLL ARBA
l~l padl11st loadl~2nd loadl 25 cps 100 cp8 lcal1 Invention 35.6 ~6~3 21.5 8.3 166 12.71 Co~trol 36.3 55.6 0 gO.3 > 60~ 18.39 !~

~IPLRIKL~TAL DlTA YR0~ TLSTS G AJD H
Sa~PLB PBNETRaTION ~BTBACR 1%1 TI~B lsl 100 cps InYention 165 353 Control 287 453 ~IPLRIYL~TAL DATA YR0~ rLsr I

8A~PLE LIQUI~ ~ISTRIBUTION ~1 lnYentlon CoYer 0.0 Transfer Larer 5.1 Absorbent Core 9~.9 control Cover 3.~
Transfer Layer ~S.6 Absorbent Core ~g.o ~l CA 022371~4 1998-0~-08 T~ST PROCEDURES
CAPACITY
Purpose to determine the absorption capaclty of an absorbent material.

Test procedure a disk of ~0 mm diameter ls cut from a sheet of the material to be tested. The dry welqht of the disk is measured and recorded. The dlsk is deposlted on the porous plate of a GATS (Gravimetric Absorbency Test System) lnstrument (a "coarse" or "medlum" frltted dlsk havlng 90 mm dlameter available from Canadal~ide Inc., has been found satlsfactory). Test fluld ls allowed to ingress the sample through the porous plate for a period of 15 mlnutes. The wetted sample is removed from the porous plate and weighted to determlne the amount of test fluld uptake. The absorption capacity is expressed in terms of volume of fluld absorbed (cublc centimeters (cc) or mllliliters (ml)) per gram of absorbent materlal. For ease of reference, however, the absorption capaclty ls reported in the above test results in mllliliters per pad of absorbent materlal in the form of a sheet of 20 cm X 5 cm havlng a wel~ht of 4 ~rams (~).
Test fluid: l% NaCl solutlon CAPILLARY PRESSURE
Purpose to determlne the capillary attractlon developed by an absorbent materlal on a fluid.

Test procedure the instrument dlsclosed ln the US patent 5,361,627 assigned to Johnson & Johnson Inc that was issued on November 8, l994 is used for this purpose. A sample of the CA 022371~4 1998-0~-08 material to be tested ln the form of a rectanqle 5 cm b~ 20 cm ls lald on a horizontal sup~ort surface. For a first load test 3 cc of test fluld is dePosited on the vlr~ln sample and the sensor of the lnstrument ls placed ln contact wlth the absorbing surface of the sample. After 30 minutes from the fluld dlscharge the pressure reading ln mllllmeters of mercury ~mmHg) is recorded.~For a second test load the sensor is removed an additional load of 3 cc of test fluid is dlscharged and the sensor is placed again in contact with the absorbln~ surface of the sample. The pressure readinq is taken 30 mlnutes after the second 3 cc fluid discharge.
Test fluld: synthetlc menstrual liquld wlth protein having a viscoslty of 25 cps.

STAIN AREA
PurPose: to determlne fluid mlgration proflle of test fluid ln a sample material.
Test Procedure a samPle of the absorbent material in the form of a rectan~le 10 cm X 10 cm is lald on a flat surface and 1 cc of test fluid is dlscharged ln the center of the absorbent surface. After the li~uld has disappeared the surface area of the stain ls measured and recorded. A comparatively small surface area lndicates that the absorbent material has a good wicking power in the Z direction ~vertical~.
Test fluid synthetic menstrual fluid with protein havlng a viscoslty of 25 cps.

PENETRATION TIME
PurPose: to determine the penetratlon time of an absorbent material by measuring the time requlred to completely absorb a finlte amount of fluid.

CA 022371~4 1998-0~-08 Test procedure the time reaulred for a 5 cm X 20 cm sample to absorb 5 cc of test fluid fed to the sample from an overhanqlnq burette at l.5 cm from the absorblng surface of the sample. The penetratlon time ls recorded when all free ll~uld has dlsappeared from the surface of the sample.
Test fluld: synthetic menstrual fluid with proteln havln~ a vlscoslty of elther 2~ c~s or 100 cps.

RE-WET/WETBACK
PurPose: the purpose of thls test ls to assess the propensity of a fluld present ln an absorbent materlal under pressure to wet back an adjacent surface ln contact therewlth.
Test Procedure: the sample materlal to which has been dellvered 10 cublc centlmeters of test fluld ls allowed to rest 15 mlnutes and lt is covered wlth a NuGauze brand pad. A
pressure of 10.48 kPa ls applled over the NuGauze pad. After 3 mlnutes, the amount of fluld (mass) captured by the pad ls measured and reported in percentage on the basls of the dry wel~ht of the pad.
Test Fluld: synthetic menstrual fluld wlth protein having a vlscosity of l00 cps.

LIOUID DI~ ~UTION
Purpose: to determlne the fluid distrlbutlon proflle ln a multl-layered absorbent structure.
Test procedure: the dry wel~ht of each layer of the absorbent structure ls recorded. The absorbent structure ls then assembled and lald on a flat surface. 5 cc of test fluld ls deposlted on the absorbent surface of the structure. After 20 mlnutes followlng the test fluld dlscharge each layer of the absorbent structure is wei~hted to determlne the lndlvidual CA 02237l54 l998-05-08 WO97/13484 PCTtCA96/00626 amount of fluld take-u~.
Test fluid: svnthetlc m~nstrual flu1d wlth ~roteln havin~
vlscos~t~ o~ 10~ cPs.
POROSITY nI~TR~ TI~N
Pur~ose: to determlne the PorositY distrih-lt1OrJ Profi.le ln an absorbent: structure, Test Procedure: A GAT~ ~rav.imetric Absor~ency Test .~vstem! is used to determlne the amount of li~uid retained ln thf~ samPle at different hvdrostatic neaative Pressures.

The results are then converted to interstice slze valuec:
uslnq a known formula. The GATS apParatus uses a "medlum"
frltted dlsc (CANADAWID~) havlnq a 90 mm d1ameter. ~he fr~tted disc is ln liquld communication with a vertical burette contalninq test llquld. The vertical distance ~etween the meniscus in the burette and the top surface of the fritted disc on which the sample is dePoslted def1nes the hvdrostati~
pressure exerted on the sample. To maintain the hYdrostatic pressure constant durin~ the entire test Procedure the burette is continuously replenished with liquid at the same rate at which the ll~uid ls beln~ absorbed by the samPle~
Prior to inltiatin~ the test procedure the wei~ht of the sample which is ln the form of a 90 mm dlsc 1s corrected at 12% relative humidity (RH). This is effected by first measurin~ the dry welqht of the sample (after drYin~ the sample at 150 degrees Celslus for 15 mlnutes) and then lts wei~ht when humld (after allowlnq the sample to reach equllibrium) to determine its level of humldity .

CA 02237l54 l998-05-08 WO97/13484 pcTlcAs6loo626 Pr -> Corrected weiaht at 12% RH
P -~ weiaht of humid samPle P, -~ nrv weiqht ~,~,_ ~h ~ ; 100 The corrected weiaht at 12~ RH is:
~ ~Hj c Q ~

The amount of llauld absorbed bv the samPle ls then measured for the followinq neaatlve hvdrostatlc Pressures -45 cm, -40 cm, -35 cm, -25 cm! -15 cm, -5 cm and -1 cm. For the -4~ cm measurement the samPle ls Placed on the frltted dlsc under a 50 a compresslve weiqht, The sample remains on the fritted disc for 15 minutes. The amount of test liquid pick-up ls measured by subtractinq P from the welqht o~ the wet sample (Pjc rr ) . The hel~ht of the liquld in the burette ls raised to -40 cm and the samPle placed back on the fritted disc for another 15 mln. The amount of addltlonal liquid plck-up ls calculated by subtractinq from P~r~ the weiqht of the sample at -40 cm, The same procedure ls followed for the remalninq hydrostatlc pressures. The proportion of liquid Pick-up at each hydrostatic pressure is translated in Percenta~e of interstices by usinq the followinq table which establlshes a correspondence CA 02237l54 l998-05-08 between the hYdrostatic pressure and lnterstice size:

-1 cm -~ 2980 microns -5 cm -> 596 mlcrons -15 cm -> l99 microns -25 cm -> 119 mlcrons -35 cm -~ 85 microns -40 cm -~ 74 microns -45 cm -> 66 mlcrons By "interstice slzes" 15 meant the equlvalent lnterstlce diameter.

The above table establishing the relationship between the hydrostatlc pressure and the interstlce size is obtalned from the followin~ formula:

~= 2y. cosA
r . d . g.

Where: h -~ hydrostatic pressure helqht (cm) a -~ 73 dynes/cm cosA -> assumed to be l r -~ interstlce radius (mlcron) d -~ denslty of test liquld (l.OOg/cc) g -> gravity (980cm/ms'); and The test results clearly demonstrate the advantages of the liquid absorbent article ln accordance with the inventlon.
Note partlcularly the dramatic improvement in penetration time CA 022371~4 1998-0~-08 WO 97tl3484 PCT/CA96/00626 and capillary pressure over the control. The abllltY of such llquid absorbent art~cle to manifest a powerful capillary attractlon is particularly useful in sanitary napkin constructlons for the purpose of desorbin~ the ad~acent liquld absorbing layers. For instance, the results of test I (llquld dlstrlbution) show that the llquld absorbent article ln accordance wlth the lnvention collects vlrtually all the li~uld discharged on the sanltary napkin, totally desorbing the cover layer and leavlng only a small amount of liquid ln the transfer layer. In contrast, the control has a less favorable fluld distrlbution pattern, with only 48 % of the total liquid discharge being contained in the absorbent core.

Another lnteresting polnt is the signlflcant reductlon of wet-back in light of the penetration time lmprovement. These two parameters are usually consldered by the prlor art as lncompatlble obiectlves in that an lmprovement of one entails a negatlve effect on the other. Much to the contrary, the present lnvention demonstrates the possibility of improving both parameters without creatlng any significant drawbacks.

Applications of the product and methods of the present lnventlon for sanltary and other health-care uses can be accomplished by any sanltary protectlon, lncontlnence, medlcal and absorbent methods and technlques as are presently or prospectlvely known to those skilled ln the art. Thus, lt ls intended that the present application covers the modlficatlons and variatlons of thls lnventlon provided that they come wlthln the scope of the appended claims and their equlvalents.

Claims (52)

WE CLAIM:

1. A liquid-absorbent article of particulate material including first and second zones in intimate fluid communicative relationship, each zone having a multiplicity of inter-particle and intra-particle interstices admitting passage of liquid, said first zone having a larger average interstice size than said second zone, whereby said second zone manifests a higher capillary attraction than said first zone.

2. A liquid-absorbent article as defined in claim 1, wherein said second zone incudes sphagnum moss.

3. A liquid-absorbent article as defined in claim 2, wherein said first zone includes sphagnum moss.

4. A liquid-absorbent article as defined in claim 3, wherein said first zone has a larger sphagnum moss particle size median than said second zone.

5. A liquid-absorbent article as defined in claim 4, wherein said first zone has a sphagnum moss particle size median in the range from about 2000 microns to about 500 microns.

6. A liquid-absorbent article as defined in claim 5, wherein said second zone has a sphagnum moss particle size median in the range from about 500 microns to about 150 microns.

7. A liquid-absorbent article as defined in claim 1, wherein said article is in the form of a sheet.

8. A liquid-absorbent article as defined in claim 7, wherein said zones constitute superposed layers of said sheet

9. A liquid-absorbent article as defined in claim 3, wherein said first zone includes debonding component.

10. A liquid-absorbent article as defined in claim 9, wherein said debonding component constitutes a physical separator for maintaining sphagnum moss particles in a spaced apart relationship.

11. A liquid-absorbent article as defined in claim 10, wherein said debonding component has a fibrous identity.

12. A liquid-absorbent article as defined in claim 9, wherein said first zone includes cross-linked cellulosic fibers in the range from about 5% to about 75% by weight of solids in said first zone.

13. A liquid-absorbent article as defined in claim 1, further comprising a fibrous component selected from the group consisting of rayon, polyester, nylon, acrylic, Kraft wood pulp, mechanical wood pulp, cotton liners and mixtures thereof.

14. A liquid-absorbent article as defined in claim 1, wherein said article is mechanically tenderized for increasing a softness and flexibility of said article.

15. A liquid-absorbent article as defined in claim 1, wherein said article is mechanically tenderized by a method selected from the group consisting of perf-embossing and micro-corrugating.

16. A liquid-absorbent article as defined in claim 7, comprising a reinforcing layer.

17. A liquid-absorbent article as defined in claim 16, wherein said reinforcing layer provides an outer surface of said article.

18. A liquid-absorbent article as defined in claim 17, wherein said article includes a pair of reinforcing layers in a spaced apart relationship providing respective main outer surfaces of said article, said first and second zones being located between said reinforcing layers.

19. A liquid-absorbent article as defined in claim 16, wherein said reinforcing layer includes Kraft wood pulp fibers.

20. A liquid-absorbent article as defined in claim 3, wherein said first zone has a higher proportion of inter-particle interstices in a size range from about 600 microns to about 120 microns than said second zone.

21. A liquid-absorbent article as defined in claim 3, wherein said first zone has at least about 55%
inter-particle interstices having a size in the range from about 600 microns to about 120 microns.

22. A liquid-absorbent article as defined in claim 3, wherein said first zone has at least about 60%
inter-particle interstices having a size in the range from about 600 microns to about 120 microns.

23. A liquid-absorbent article as defined in claim 3, wherein said first zone has at least about 63%
inter-particle interstices having a size in the range from about 600 microns to about 120 microns.

24. A liquid-absorbent article as defined in claim 1, wherein said article is integrally formed.

25. A liquid-absorbent article as defined in claim 1, wherein said zones are discrete entities united in a face-to-face relationship.

26. A liquid-absorbent article including first and second zones in fluid-communicative relationship, said first zone and said second zone including sphagnum moss particles, said first zone having a larger proportion of inter-particle interstices in a size range from about 600 microns to about 120 microns than said second zone.

27. A liquid-absorbent article as defined in claim 26, wherein said zones are integrally formed.

28. A liquid-absorbent article as defined in claim 27, wherein said zones constitute superposed layers of said article.

29. A liquid-absorbent article including first and second zones in fluid-communicative relationship, said first zone including sphagnum moss particles having a first particle size median value, said second zone including sphagnum moss particles having a second particle size median value, said first particle size median value being larger than said second particle size median value.

30. A liquid-absorbent article as defined in claim 29, wherein said first zone has a sphagnum moss particle size median in the range from about 2000 microns to about 500 microns.

31. A liquid-absorbent article as defined in claim 30, wherein said second zone has a sphagnum moss particle size median in the range from about 500 microns to about 150 microns.

32. A liquid-absorbent article as defined in claim 29, wherein said article is in a configuration of a sheet, said zones constituting superposed layers of said sheet.

33. A disposable absorbent product, comprising:

- an absorbent component of particulate material, said absorbent component including upper and lower layers in intimate fluid communicative relationship, each zone having a multiplicity of inter-particle and intra-particle interstices admitting passage of liquid, said first zone having a larger average interstice size than said second zone, whereby said lower zone manifests a higher capillary attraction than said upper layer in order to induce liquid absorbed in said upper layer to migrate toward said lower layer; and - a body contacting, liquid-pervious cover layer superposed to said absorbent component.

34. A disposable absorbent product as defined in claim 33, further comprising a liquid-impervious layer underneath said absorbent component for preventing liquid captured by said absorbent component to egress said disposable absorbent product.

35. A disposable absorbent product as defined in claim 33, wherein said product is selected from the group consisting of sanitary napkin, diaper, adult incontinence brief, urinary pad, wound dressing, nursing pad and desiccant for packaging materials.

36. A method for manufacturing a liquid absorbent component, said method comprising the steps of:
- providing a first zone of particulate material having a multiplicity of inter-particle and intra-particle interstices, said first zone having a first average interstice size;
- providing a second zone of particulate material having a multiplicity of inter-particle and intra-particle interstices, said second zone having a second average interstice size, said first interstice size being larger than said second interstice size; and - establishing an intimate fluid communicative relationship between said zones to allow liquid in said first zone to migrate toward said second zone.

37. A method for manufacturinq a highly absorbent structurally integral sheet having superposed liquid-absorbent layers united in an intimate fluid-communicative relationship, said method comprising the steps of:
- laying in a superposed relationship and in physical contact a first slurry layer of particulate material and a second slurry layer of particulate material to form a laminated composite slurry layer, said first and second slurry layers including effective amounts of sphagnum moss particles, i) said first slurry layer constituting a precursor phase of a first porous network having a multiplicity of inter-particle interstices and intra-particle interstices admitting passage of liquid, said first porous network having a first average interstice size, ii ) said second slurry layer constituting a precursor phase of a second porous network having a multiplicity of inter-particle interstices and intra-particle interstices admitting passage of liquid, said second porous network having a second average interstice size, said first average interstice size being larger than said second average interstice size;
- extracting fluid medium from said laminated composite slurry layer to form a laminated composite web including superposed layers of said first porous network and said second porous network which are intimately united to one another, said second porous network manifesting a higher capillary attraction than said first porous network to induce liquid absorbed in said first porous network to migrate toward said second porous network.

38. A method as defined in claim 37, wherein said first slurry layer has a larger sphagnum moss particle size median than said second slurry layer.

39. A method as defined in claim 38, wherein said first slurry layer has a sphagnum moss particle size median in the range from about 2000 microns to about 500 microns.

40. A method as defined in claim 38, wherein said second slurry layer has a sphagnum moss particle size median in the range from about 500 microns to about 150 microns.

41. A method as defined in claim 37, comprising the step of incorporating in said first porous network an effective amount of debonding component.

42. A method as defined in claim 41, comprising the step of incorporating said debonding component in said first slurry layer.

43. A method as defined in claim 42, wherein said debonding component has a fibrous identity.

44. A method as defined in claim 43, comprising the step of incorporating in said first slurry layer cross-linked cellulosic fibers in the range from about 5% to about 75% by weight of solids in said first slurry layer.

45. A method as defined in claim 37, further comprising the step of incorporating in said laminated composite slurry layer a fibrous component selected from the group consisting of rayon, polyester, nylon acrylic, Kraft wood pulp, mechanical wood pulp, cotton linters and mixtures thereof.

46. A method as defined in claim 37, comprising the steps of:
- laying one of said slurries on a foraminous member;
- laying the other of said slurries on said one slurry to form said laminated composite slurry layer; and - establishing a pressure differential across said laminated composite slurry layer to extract fluidizing medium therefrom.

47. A method as defined in claim 37, comprising the steps of:
- providing a mother slurry of sphagnum moss particles;
and - classifying the sphagnum moss particles in said mother slurry in fractions according to size to provide said first and second slurry layers.

48. A method for manufacturing a laminated liquid-absorbent article, comprising the steps of:
- providing a body of particles suspended in fluid, such as liquid or gas, said particles having varying dimensions;
- separating said body of particles in at least two fractions, referenced as a first fraction and a second fraction, said first fraction having a higher particle size median value than said second fraction;
- extracting fluidizing medium from said fractions to form a first absorbent layer and a second absorbent layer respectively, said first absorbent layer having a higher average inter-particle interstice size than said second absorbent layer, whereby said second absorbent layer manifests a higher capillary attraction than said first absorbent layer;
- establishing a liquid-communicative relationship between said layers, whereby liquid introduced in said first layer is induced to migrate toward said second layer under the effect of capillary attraction.

49. An apparatus for manufacturing a highly absorbent structurally integral article having superposed liquid-absorbent layers united in an intimate fluid-communicative relationship, said apparatus comprising:
- a classifier for separating particles suspended in fluidizing medium into at least two slurry fractions in accordance to size of said particles, a first slurry fraction having a larger particle size median than a second slurry fraction, said classifier having first and second outlets for discharging said first and second slurry fractions, respectively;
- a foraminous member;
- first and second headboxes in a fluid communicative relationship with said first and second outlets respectively for discharging said first and second slurry fractions in a superposed relationship on said foraminous member to form a laminated composite slurry layer; and - means for establishing a pressure differential across said laminated composite slurry layer to extract fluidizing medium from said first and second slurry fractions in order to form respective first and second porous networks intimately united to one another, said second porous network manifesting a higher capillary attraction than said first porous network to induce liquid absorbed in said first porous network to migrate toward said second porous network.

50. An apparatus as defined in claim 49, wherein said particles include sphagnum moss, said classifier station producing the first slurry fraction with sphagnum moss particle size median in the range from about 2000 microns from about 500 microns.

51. An apparatus as defined in claim 49, wherein said particles include sphagnum moss, said classifier station producing the second slurry fraction with a sphagnum moss particle size median in the range from about 500 microns to about 150 microns.

52. A liquid-absorbent article as defined in claim 1, wherein said zones include material selected from the group consisting of perlite, vermiculite, expanded clay, expanded rice, crushed foam, zeolite and sphagnum moss.