AU1004499A - Absorbent materials having improved absorbent property and methods for making the same - Google Patents

Description

I-'UUI11 2WS1' Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE

SPECIFICATION

STANDARD

PATENT

Application Number: Lodged: Invention Title: ABSORBENT MATERIALS HAVING IMPROVED ABSORBENT PROPERTY AND METHODS FOR MKING THE SAME The following statement is a full description of this invenltionl, including the best method of performing it known to us

C

C

C.

C

ABSORBENT MTRIALS HAvT.NG 1INTROVED ABSORLBENT PROPERTY ANDI fETHODS FOR MAKING TH-E SANT FIELD OF ThE INVENTION The present invention relates to absorbent materials which, upon contacting liquids such as water or body fluids, swell and imbibe such liquids. More specifically, the present invention relates to absorbent materials having at least one improved absorbent property to after swelling. The present invention has particular applicability to absorbent articles such as diapers. adult incontinence pads, sanitary napkins. and the like.

BACKGROUND OF THE MhJENTION Water-insoluble, water-swellable. hydrogel-forming absorbent polymers are capable s of absorbing large quantities of liquids such as wter. body fluids urine, blood.

menstnial fluid), industrial fluids and household fluids and are fuirther capable of retaning such absorbed liquids under moderate pressures. The absorption characteristics of such polymer materials make them especially useftl for incorporation into absorbent articles such as disposable diapers, adult incontinence pads and briefs. and catamenial products such as ~n sanitaiy napkins, and the lik.

The development of highly absorbent members used in such absorbent articles arc the subject of substantial commercial intercst. A highly desired characteristic for such products is thinness. For example, thinner diapers a=e less buk to wws. fit better under clothing, and are less noticeable. 'Dey ame also morm comnpact in the package. making the diapers easier for the corusunser to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor, including less shelf spa"e required in the store per diaper Unit.

The ability to poid thinner absorbent articles such as diapers has been contingent on the ability to develop reladivly thin absorbent cores or nstrces that can acquire and store large quantities of discharged body fluids, in particulax urine. In this regard. t use Of certain absorbent polymers often referred to as 'hydrogels," sunas ets' orf "hydrocolloid' materia has been particularly important Se, for example, US. Patent 3.699.103 (Hape CIL al). issue June 13. 1972. and U.S. Patent 3.77D.731 (Ha2rmon). issued June 20. 1972. that disclose the use of such absorbent polymers (hereafter 'hydragel-forming 3i absorbent polymers) in absorbent articles. Indeed, the development of thinner diapers has been the direct cnqeceof thinner absorbent cores that take adv~antage of the ability of 2 these hydrogel-rorrning absorbent pohmer to sort) lnrgc quantitiezs of discharged body fluids. tYpically when used in Combiontion with a fibrous matrix. Sec. for example. U.S.

Patent 4.673.402 (Wei.'nvn et at). issued Jun-, 16, 1937 atid U.S. Patent 4.935.022 (Lash et al), issued June 19. 1990. dth~ disclose dual.In~er core structure s *1 C)risingafbosatx and hydrogel-fortning absorment polymers useful in fashioning thin. compact. nonibulky diapes.

in the meantinie. prior abioi'bent structures have generally comprised relatively low amounts iiess; than about 50% bf weigh!). of these hydrogcl-fir-n bobn pc~ymncrs. See, for example U.S. Patem 4.334,1135 (Alemany ct al), issu 13vy 30. 1989 (preferably from about 9 to about. 50% hydrogel-form-ing abs-orbent polymer in thi'- ibrous* matrix). There avc several reasons for this. The hydrogel-fortniing ab~sorbent polymers employed in prior absorbent 'sructurts have generally tnot had an absorption rate that would allow them to quickly absorb bcdy. fluids, especially in 'gush* sinuations. This has ncesitated the inclusion of fibers, typically wod pulp fibers, to serve as temnporary Is reservirs to hold the discharged fluids until absorbed by the hydrogel-forming absorber-( More importantly, many of the known hydrogel-fonning absorbent polymers eXhibited gel blocking when they are uscd.in absorbent articles in a high corleenuation. 'el bldcking' occurs when particles of the hydroget-forming absorbent polymer are wened and o ti partcles swell so as 1o inhibit flidd transmission to other regions of the absorbent strcture Wetting of these other regions of the absorbent member therefore takes place via a Very slow diffission proces. In practical terms, this means acquisition of fluids by the absertieml stucture is much slower than the rate at which fluids ame discharged. especially in gush sipuations. Leakage from the absorbent article can take place well before the particles 25 i of hydrogel foriming atvirbent poiymesr in the absorbent member are fully saturated or before thefluid can difus or wiek pas t 'eblocking' particles into the rest of the absorbent member. ,Gel blocking can be a palticularly: acute problem if the panticles of htydrogel forinn. absorbent polymecr do not have adequate gel strength and deform. or spread under StrMS on=e the particles s-ACll with absorbed fluid. See: U.S. Patent 4.334i735 (Alcrmany Ct 3so al). issued May 30,.1989.

Thsglbokn hrmnhas typically ne~cessitated the Use Of a fibrous matrix in which are dispmrsd the particles of hydrogel-runing absorbent polymer.: This fibrous -matrix the paruics of hydrogel-farming absorbent polyme separsed from one another. This librous matrix also prorvides Mepillay strur that allows fluid to reach the, 3$ hydro el-form~ing absorbent Polymer locate in regionis remote fi the Initial fluid.

discharge pont. See U.S. Pateng48, .3 (Alesnny Ct a!.issued May370. I9 Howvever. 4

AA

dispersing the hydrogel-forming absorbent polymer in a fibrous matrix at relatively low concentrations in order to minimize or avoid gel blocking may lower the overall fluid storage capacity of thinner absorbent structures. Using lower concentrations of these hydrogelforming absorbent polymers limits somewhat the real advantage of these materials, namely t heir ability to absorb and retain large quantities of body fluids per given volume.

In general, increasing the gel strength of hydrogel-o-rming absorbent polymers can contribute to decrease gel blocking. Gel strength relates to the tendency of the hydrogcl formed from these polymers to deform or flow" under usage stresses. Gel strength needs to be such that the hydrogel formed does not deform and fill to an unacceptable degree the to capillary void spaces in the absorbent structure or article, thereby inhibiting the absorbent capacity of the stucture/article, as well as the fluid distribution through the stucture/article.

High gel suength usually obtained by crosslinking. It is believed that crosslinking increases the resistanct to deformation of hydrogel-forming absorbent polymer surfaces. However.

crosslinking has a deep impact on the absorbent capacity of a hydrogel-forming absorbent is polymer. In general, absorbent capacity or "gel volume" has inverse power-law dependence on the level of crosslinking. That is. high cmsslinking level results in high gel strength but low gel volume. Gel volume is a measure of the amount of vater or body fluids that a given amount of hydrogel-fonning polymer can absorb. It is required that gel volume is sufficiently high in order that the hydrogel-forming polymer can absorb significant amounts v of the aqueous body fluids encountered during use of the absorbent article.

Another important factor that has to be considered is the liquid permeability of hydrogel-forming absorbent polymers. It has been discovered that the permeability or flow conductivity of the gcl laycr formed by swelling in the presence of body fluids is extremely important when these absorbent polymers are used in absorbent cores or members at a high s concentration in localized or throughout regions thereof. It should be noted that lack of the liquid permeability or flow conductivity of absorbent polymers may directly impact on the ability of resultant gel layers to acquire and distribute body fluids.

Yet another important factor of hydrogel-forming absorbent polymers is the level of extractable polymer material present therein. See U.S. Patent 4.654.039 (Brandt et al).

3o issued March 31. 1987 (reissued April 19. 1988 as Re. 32,649). Many hydrogel-forring absorbent polymers contain significant levels of extracable polymer material. This extractable polymer material can be leached out from the resultant hydrogel by body fluids urine) during the time period such body fluids remain in contact with the hydrogel- S. forming absorbent polymer. It is believed such extracted polymer material can alter both the "s chemical characteristics osmolarity) and physical characteristics viscosity) of the body fluid to such an extent that the fluid is more slowly absorbed and more poorly held by 7 1 .'treC a..

I the hydrogcl. This polymer contaminated fluid is also more poorly transported through the absorbent member. Such a situation can contribute to undesirable and premature leakage of body fluid from the absorbent article. Thus it is desirable to use hydrogel-forming absorbent polymers with lower levels of extractable polymer material.

A further important factor that has to be considered in order to take full advantage of the high concentration of hydrogel-forming absorbent polymers in thinner absorbent articles is the wet integrity of the region or regions in the absorbent member that comprise these polymers. By "good wet integrity" is meant that the region or regions in the absorbent member having the high concentration of hydrogel-forming absorbent polymer have to sufficient integrity in a partially wet. andlor wetted state such that the physical continuity of the hydrogel formed after swelling in the presence of body fluids is not substantially disrupted or altered, even when subjected to normal use conditions. During normal use.

absorbent cores in absorbent articles are typically subjected to tensional and torsional forces of varying intensity and direction. These tensional and torsional forces include bounehing in is the crotch area, stretching and twisting forces as the person wearing the absorbent article walks, squats, bends, and the like. If wet integrity is inadequate, these tensional and torsional forces may cause a substantial alternation and/or disruption in the physical continuity of the hydrogel. Such alternation could minimize or completely negate any advantageous fluid distribution (permeability/flow conductivity) property of the hydrogelo farming absorbent polymer. Such alernation and/or disruption may also cause the gel to mobilize and bring about the disclosure of the gel to the surface of absorbent article.

therefore cause the so called "gel-on-skin" problem.

Still another important factor of hydrogel-forming absorbent polymers used in thinner absorbent article is the jelly/mushy feel when touching and handling the absorbent I is article after usage. When hydrogel-forming absorbent polymer is dispersed in region or regions at a high concentration, the swollen gel formed by absorbing body fluids is a gel layer that the particulate is mobile and the gel layer is collapsed when subjected to forces such as pushing, squeezing, etc. when handling the absorbent article after usage. This is why absorbent articles having high concentration of hydrogel-forming absorbent polymer i 0 o give users or consumers "wet/mushy" fel when touching or handling them from outside.

S Therefort one object of the present invention is to prevent gel blocking phenomena caused in absorbent articles while maintaining required absorbent capacity.

S Yet another object of the present invention is to prevent leakage of swollen absorbent materials from absorbent articles.

is Still another object of the present invention is to improve the jelly/mushy feel of absorbent artciles after usage.

7, Yet another object of thc prcscnt inventioni is to provide thinner ibsorbent articles.

Still another object of the present invention is to provide thinner absorbent disposable articles such as diapers. sanitary napkins. tampons. and the like.

SUMMINARY OF THEl INVENTION Briefly stated, the present invention relates to absorbent materials. In one aspect of the invention. an absorbent material comprises a mixture of a plurality of absorbent gelling particles; comprising a water-insoluble, water-swell[able polymer. and an absorbent property modification polymer reactive with at least one componcnt included in a wine, wherein the mixtur is made by applying a solution contidning an organic solvent.

water and the absorbent property modification polymer onto the phuality of absorbent gelling particles, wherein the weight ratio of the organic solvent to -the water is at least 50:50. and (ii) removing a portion of the organic solvent and water from the applied Is absorbent getting particles.

The present invention further relates tn absorbent articles. In another aspect of the invention, an absorbent article comprises: a liquid pervious topshect; a liquid impervious backshct: and an absorbent core positioned betweeni the topsheet and thc backsheet. whcreint the absorbent core comprises the above described absorbent material.

present invention further relates to methods for making absorbent materials. In yet another aspect of the invention, a method for making an absorbent material comprises the steps of: preparing a solution containing an organic solvent. water and an absorbent property modification polymer reactive with at least one component included in a urine.

wherein the weighit ratio of said organic solvent to said water is at least 50:50; applying 33 an amount of the solution onto a plurality of absorbent gelling particles comprising a waterinsoluble. water-swellable polymer and removing a portion of the organic solvent and water from the applied absorbent gelling particles.

BRIEF DESCRIPTON OF THE DRAWINGS Figure I is a schematic view of an apparatus for measuring the Gel Bulk Density (GBD) value of the absorbent materials.

Figure 2 is a seltrnaic view of an apparatus for measuring the Saline Flow Conductivity (SFC) value of the absorbenitrmaterials.

3 represents an enlarged sectonal view of the piston/~cylinlder assembly shown in Figure 2.

C

AA

Figure 4 represents a plan %icw of the bottom or th- pito hC-sd fromn the pistonlcylinder assemnbly shoun in Figure 3.

Figure 5 is a schermtic view of an apparatus for measurng tbte Mal Burst Strength (BBS) value of the absorbent materials.

Figure 6 is a schematic view of an apparatus for preparing a predetrmitned laver Of the swvollen absorbent materials.

Figure 7 is a schematic Nicw of an apparatus for measuring the Compression Recovery (CR) value of the absortbent riaterials.

Figure: 8 is a graph showing the relationship between the comprcssioroeovcty load and the compression depth in the CR res.

Figure 9 is a graphi showing one example of che relationship between the compressiort'reeovery load and the compression depth in the CR test.

Figure 10 is a graph showing a comparison example of the relationsltip between the curnpi-ssion/recoyery load and the comnprssion depth in the CR test.

DETAILED DESCRIPTON OF THEl INVENTION A. Definitions As used herein, the ternm 'body fluids' includes urine, blood. menses and vaginal X discharges.

-As used herein, the tecrm 'absorbent core' refers to the componcnt of the absorbent *article that is primarily responsible for fluid handling properties of the article, including acquiring. transporting, distributing and storing body fluids. As such, the absorbent core typica~lly does not include the topsheet or backsheet of the absorbenit article.

23As used herein, the term "absorbent member refers to the components of the absorbent core that typically provide one or more fluid handling properties. fluid acquisition. fluid distribution, fluid ransportaton. fluid storage, etc. The absorbent mecmber cani comprise the entire absorbent core or only a portion Of inlie absorbent core. the absorbent core can comprise one or more absorbent members.

As used herein, the term 'region' refers to portions or setions of the absorbent member.L As use herein, the termi 'layer* refers to an absorbent member whose primaiy dimension is X-Y. along its length and width. howkever. it should be noted that the layer has thickness- 33 16a As used herein, the terms "comprises", "comprising", "includes" and "including" are to be taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or "more other features, integers, steps, components or groups thereof.

;t .y B. Absorbent Mwerrials of the Invention Absorbent maiterials of the present invention are capable of absorbing larg: quantities of liquids such as waebody fluids. industrial fluids and household fluids and are capable ofrrEtaining such liquids und-r moderate pressure. In particular. absorbent materiAs included in ihc absorbent members of the presecnt invention ;,ill swell generally isotropically and absorb rapidly tire liquids.

Briefly stated- an absorbent material of the present invention comprises a mixtture of a plurality of absorbent gelling particles comprising a water-insoluble. A1cr-swcllablc polymer, and an absorbent property modification polymer reactive with at least one to component included in a urine, wherein the mixture is made by applying a solution containing an organic solvent. water and the absorbent property modification poly-mer onto (he plurality Of absorbent gelling particles, wherein the weight ratio of the organic solvent to the water is at least 50:50. and Cii) removing a portion of the organic solvent and water from the applied absorbent gelling particles. The process for making the maixtur will be ts described in detail in the "Process for Making Absorbent Materials* scction.

In the mixture, the absorbent property modification polymer is. to be on at lea= a portion of the surf~ce area oftthc absorbent gelling particles, preferably most preferably 4 more than 90% of thc all surface area of the absorbent gelling particles- In preferred embodiments, there is less covalent bonds between the absorbent property modification polymer and the absorbent gelling particles. In a most preferred embodiment, there is no chemiical bonds betwen the absorbent property modification polymer and the absorbent gelling particles. In such embodiments, most of the absorbent property modification pelytner is only associated to the absorbent gelling particles via intermolecular interactions such as electrostatic interaction, hydrogen bonding interaction, and is van der Waals interactions. Therefore, the existence of the absorbent property modification polymer on the absorbent gelling particles gives little effect to the gel volume of the absorbent gelling particims Preferably, the existece of the absorbent property modification polymer cauises less than 10% change of the gel volume of the resultant absorbent mauterial.

2; This can be also achieved by less amount of chemaical and/or physical bondings between the absorbent property modification polymer and the absorbent gellinrg particles.

If there are certain chemical bonds betw~een the absorbent property modification polymer and the absorbenit gelling particles, it is preferred that the typ and extnt of such chemical bonds have little effect on the gel volume of the resultant absorbent material- The decrease in gel volume due to the association of the absorbent property modification Polymer with the absorbent gelling particles is preferred to be less than 101/. Preferably, almost all functional groups of the absorbent property modification polymer are not used for bonding Lhe absorbent property modification polymer to the absorbent polymecr of the 02 material. These unused funtctiornal groups ate preferably used for the bonds among the absorbent gelling particles after an application of a urine.

Consequently. the absorbent getting particles can be sonancgusly conneccu'c through the absorbe nt property modif ication polymer in response to an application of u un Consequently. when the absorbent mater:3l is provided in the region at a high concentration more dha the absorbent nmaterial is flormed into a porous aggregate of the swollen particles after an application of a urine.

It should be noted that the unused functional groups of the absorbent property to modification polymer of the absorbent material can be als rcactive %ith the extractable componcrnts included in the hydrogel-forrning absorbent polymers. More specifically, the absorbent property modification polymer is capable of trapping the ecxuacied components which may cause a charge of the characteristics of the body fllui& Thereforc, the presence of U the absorbent property modification polymer can lower the level of the extractable 13 components of the absorbent Material.

a Absorbent materials of the present invention have at lea= one improved absorbent property. The absorbent property can be improved by changing at least ont physical property after swelling ofthe absorbent material. The -physical property' herein used includes porosity. liquid permeasbility. wet integrity. and recovery properTy .o when subjected to extrnal forces, of in absorbent material after swelling by absorbing liquids.

The porosity of an absorbent mraterial after swelling is evaluated by conducting the Gel Bulk Density (GBD) test. The liquid permcability of an absorbent material after swellting can be evaluated by conducting the Saline Flow Conductivity (SFC) test. The wet 23 integrity of an absorbent mnaterial after swelling is evaluated by conducting the Bail Burst Stregth (BBS) test. The recovery property of an absorbent material after swelling is evaluated by conducting the Compression Recovmy (CR) test. The tesv methods for ev-aluating these: properties as well as rte gel volume and extractable components w4ill be described in detail in te Test Meslsods section.

me0 hIn such anp io ted on presertyithattihen the absorbent mat eial wel byobn 4~mmbe ha sinon a pect e of obn poet thet wrhetinetin the absorbent material w ell bso y absorbing a urine and is formed into a precletermined layer of the swollen absorbent matterial under a predeterminsed load the layer of the swollen absorbent ataterial has a Gel Bulk **Density (GBD),.2lue of below 0.9i ror 3 in the GBD test.

GBD is an important physical property after swelling of' the absorbent mterials of the present inventon- This is to show their gel burlk dcasity when swollen with body fluids

I

so as to form a hydrogtl zone or lavc.. T1his density is defiried herein in terms of the GBD value of the abso rbent unaterial. GBD measures the weight per unit volume of 3 Zel laver formed from the vwollen absoirbent material, including voids inherent in the gel laver. In other words. GBD is 3 measure of the porosity of swollen absorbent materials. It is anticipated that GBD value has a relationship wvith the SFC value described hcreitefC.

The GBD value of the absorbent materials of the present invention is below about 0.95 g/eM3. preferbly below about 0.9 &lcm 3 and most preferably beow about 0.35 g/cm3.

Typically. these GBD values arc in the range of from about 0.5 to about 0.9 gicra. more ty-pically from about 0.1 to about 0.3 glcm3_ In another aspect of the present inventicn. the absorbent material used in the absorbent member has such an improved property that when the absorbent material swells by absorbing a urine and is formed into a predetermined layer of the swollen absorbent material.

the layer of the swollen absorbent material has a Saline Flow Coniductivity (SFC) value of at lea=s 20 x 10- 7 cm 3 scefg in the SFC tesi- SFC is another important phytical property after swelling of the absorbent m-aterials of the present invention. T his is to show their liquid permeability or flow conducuvrty w hen swollen with body fluids so as to form a hydrogcl zone or layer. SFC measres the ability of a swollen absorbent mavterial to transport saline fluids tberethrough. In other words. it shows the ability of a gcl layer formed from the swollen absorbent material to transport liquids- The SFC value of the absorbent materials after swe-lling of the present invention is at least about 20 x 10-7 crn~scl/g. preferably at least about 40 x l0,7 crn 3 sen/g. and nfos, preferably at least about to0 x 10-7 em 3 secijg Typically. these SFC values are in the rxnge 737 10- cr. sc/jg.

It is believed that when an absorbent material is present at a high conccntintiott in an absorbent memrber and then swells to form a hydrogel under usage pressures. the bounidisies; of the hydrogel come into contact and interstitil voids in this highenucentration region become generally bounded by hydrogel. Whe-n this occurs. it is believed the porosity znd/or the permeability or flow conductiv.ity properties of this region are generally reflective of the porosity and/or the permeability or flow conductivity properties of a hydnmgcl 7one or layer formed from the swollen absorttert material alorx- It is further beieved that increasing the: porosity and/or the perrmezbility of thes swollen highconcentrationl regions to levels that approachs or even exceed corrventina acuisitioiditrbution rmaterials. such as wood-pulp fluff, can prov.ide superior fluid s handcling properties for the absorbent member and absorbent core. thiiS decasing incidents Oat.

I. *a.

t

I

of leakage, especially at high fluid loadings. (Higher SFC values also are reflective of the ability of the formed hydrogel to acquire body fluids under normal usage conditions.) hi yet another aspect of the present invention, an absorbent material has such an i improved absorbent property that when the absorbent material swells by absorbing a urine I and is formed into a predetermined layer of the swollen absorbent material, the layer of the swollen absorbent material has a Ball Burst Strength (BBS) value of at least 30 gf in the BBS test.

BBS is another important physical property after swelling of the absorbent materials of the present invention. This is to show their bursting peak load when swollen with body to fluids so as to form a hydrogel zone or layer. BBS measures the force (or peak load) required to produce rupture of a gel layer formed from the swollen absorbent material.

BBS values of the absorbent materials after swelling of the present invention is at least about 30 gf in the BBS test preferably at least about 50 gf, and most preferably at leas Sabout 100 gf. Typically, these BBS values are in the range of from about 0O to about 400 gf, is more typically from about 100 to about 300 gf.

It is believed that when a conventional absorbent polymer is present at high concentrations in an absorbent member and then swells to form a hydrogel. the hydrogel is pushed by the usage pressures applied thereto and may move towards a edge portion of the absorbent member or core. and the absorbent article. When this occurs, a leakage of the S hydrogel may be caused from the edge portion of the absorbent article. thus, a "gel-on-shin" problem is caused by using a conventional absorbent polymer Since the absorbent materials of the present invention have improved wet integrity, in other words, bondings among the swollen absorbent particles of the absorbent material are more strength, and the individual swollen gel particles are not mobile, the leakage of swollen absorbent materials from 2s absorbent articles can be prevented.

S n still another aspect of the present invention, an absorbent material has such an improved absorbent propery that when the absorbent material ,wells by absorbing a urine and is formed into a predetermined layer of the swollen absorbent material, the layer of the swollen absorbent material has a Compression Recmvey (CR) value of at least 15% in the CR test.

S CR is another important physical property after swelling of the absorbent materials of the present invention. This is to show their compression recovery when swollen wiLh body fluids so as to form a hydrogel zone or layer. CR measure the ability of the extent that an absorbent material at wet sate has returned to its original shape/state when subjected to S. external forces M U M t i-i -i CR values of the absorbent materials after swelling of the present invention is preferably at least about 20%. and most preferably at least about 30%. Typically, these CR values are in the range of from about 20 to about 80%. more typically from about 30 to about s It is believed that when a conventional absorbent polymer is present at a high concentration in an absorbent member and then swells to form a hydrogel. the hydrogel looks and feels jelly and mushy. In particular. when a user and/or consumer touches the absorbent article from the outside, the absorbent article gives such undesirable feeling to the user and/or consumer. Since the absorbent materials of the present invention have such to improved CR values, the undesirable feeling jeliy/mushy feel) to the user and/or consumer can be prevented.

In a preferred embodiment, an absorbent material of the present invention can be formed in a porous structure. As used herein, the terms "porous strcure" mean a structure forming walls surrounding and defining cellular voids of absorbent polymers when is substantially dry. In general a porous structure of absorbent material can provide the porous absorbent material with low density and/or high specific surface area. Under microscopic observations, walls formed in a porous absorbent material, for example, show the sponge-like appearance and/or the withered leaf-like appearance. Preferred examples of porous structures of absorbent materials and processes therefor disclosed in the co-pending U.S.

o application serial No. 197.913. entitled "Absorbent Materials Having Modified Surface Characteristics And Methods For Making The Same". Attorney Docket No. JA-80U, filed February 17. 1994. incorporated herein by reference.

25 C. Composition Materials Used in Absorbent Materials 1. Absorbent Property Modification Polymers Absorbent property modification polymers used in the present invention are reactive with at least one component included in a urine.

The term reactive" used herein means that a substance compound or ion) has 3s an ability of interacting with another substances to cause changes in chemical and/or physical properties. Therefore. absorbent property modification polymers used in the present invention have an ability of interacting with at least one component included in a urine. In a preferred embodiment, the absorbent property modification polymer has an ability of interacting with a phosphate ion of urine through electrostatic interaction.

3a A practical method for determining whether an absorbent property modification polymer is reactive with at least one component included in a urine or not is mixing an i "1' i i 9 r E ''i a id

:-P

;-FI

-i ~J1-~ a

L

i i! :i r o r r r Ici~ rrco rrce S I ~sb~ss~8a~asla~a~ -12 aqueous solution of the absorbent property modification polymer with a urine. If the resultant mixture solution becomes cloudy, the absorbent property modification polymer can be determined as reactive with at least one component included in the urine.

The term "urine" used herein should be understood in general. A typical example S of content of normal urine" is disclosed in the book entitled "Textbook of Medical Physiology' by Arthur C. Guvyon Saunders Company, 1991. page 304). which is incorporated herein by reference. It should be noted that Jayco Synthetis Urine is used for all measurements described hereinafter. In general, a urine contains an anion having at least two ionic charge numbers, such as a phosphate ion. a sulfate ion, and carbonate ion.

to In preferred an embodiment, the absorbent property modification polymer can render the absorbent gelling particles spontaneously connective through the absorbent property modification polymer in response to an application of a urine.

The term "connective" used herein means that a plurality of materials has an ability of connecting with each other. Therefore, the absorbent gelling particles of the absorbent ts material can have an ability of connecting with each other after urine is applied to the absorbent material.

In a more preferred embodiment, the absorbent property modification polymer is a cationic polymer which can be reactive with at least one component included in a urine.

Preferably. the cationic polymer is capable of having an electrostatic interaction with an -o acidic group such as a carboxyl group of absorbent polymer. Therefore. in a further preferred embodiment, the cationic polymer is capable of bonding to both the anion included in a urine and the absorbent polymer.

Preferred cationic polymers can include polyamine or polyimine materials which are reactive with at least one component included in a urine. The polyamine material 2. preferably used in the present invention is selected from the group consisting of polymers having primary amine groups polyvin''anmine. polyallyl amine); polymers having secondary amine groups polycthylencimine); and polymers having tertiary amine groups poly N. N-dimcthylalkyl amine).

Practical examples of the cationic polymer are, for example., polyethyleneimine. a modified polyethyleneimine which is crosslinked by cpihalohydrine in a range soluble in :wa;er, polvarine. a modified polvamidoamine by graft ofethylenimine. polyetheramine.

polyvinylamine, polyalkvlamine, polyamidopolyamine. and polyallylamine.

S In preferred embodiments, a cationic polymer has at least 500 of the molecular c* weight in average, more preferably 5.000. most preferably 10.000 or more. Cationic polymers having 500 or more of the weight-average molecular weight used in the present invention are not limited to polymers showing a single maximum value (a peak) in a grgai^M^8m ^^Ba^B«B«B^z 13 molecular weight analysis by gel permeation chromatography, and polyme rs hiaving a weight-averagc molecular weight of 500 or more may be used even if il exhibits a plural maximum value (peaks).

A preferable amount of the cationic polymer is in a range of from about 0.05 to parts by weight against 100 parts by weight of the absorbent polymer particle, more preferably from about 0.3 to 10 parts by weight. and most preferably from about 0.5 to parts by weigh:.

2. Absorbent Gelling Particles Chemical Composition The water-insoluble. water-swellable absorbent polymers useful in ithe present irtvcntdon are commonly referred to as 'hydrogcl-forming'. 'hvdrocolloids". or .superabsorbent' polymers and can include polysacchauides such as casboxymethyl swach.

carboxymethyl cellulose, and hydro.'tyropyl cellulose-, nonionic typcs such as polyvinyl alcohol. arnd polyvinyl ethers:. cationic types such as polyvinyl pyridine. polyvinyl morpholinione. and N.N-dimcthylaminoethyl or N.N-diethylaminopropyl. acrylates and mcthacrylates. and the respective quaternary salts thereof. Typically. hydlogel-fort'itg absorbent polymers useful in the present invention havc a multiplicity of anionic. functional t groups, such as sulfontic acid, and more typically carboxy. groups. Examples of polymcrs; suitable for use herein include those which are prepared from polymerizable. unsaturated.

acid-containing monomers. Thus, such monomers include the olcftnically unsaturated acids .L and anhydrides that contain at least one carbon to carbon olefinie double bond. Marc specifically, these monomers can be selcecd from olcfinically unsaturaed carboxylic acids and acid anhydrides oleftnically unsaturated sutfonic acids, and mixtures thereof.

Some non-acid monomers can also be included, usually in minor amounts, in 5 prepring the hydrogel-forrting absorbent polymers herein. Such non-acid monomers ea~n include, for exmple. the water-soluble or water-dispersible esters of the acid-containing monomers as well as monomers that contain no carboxylic or sulfonic acid groups at all.

Optional non-acid monomers can thus include monomers containing the following types of 305 functional groups: carboxyliC acid or stlfonic acid esters. hydroxyl groups. amtide-groups. amino groups. nitrile groups. quaternary ammonium salt groups. aryl groups phenyl groups, such as those derived from styrente monomer). These non-acid monomers are wellknown materials and are described in greater deail, for example. in U.S. Patent 4.076,663 (Masda et al). issued February 28, 1978. and in U.S. Patent 4,062,817 (Westerrnan). issued ts December 13. 1977. both of which are incorporated by reference.

*5J4S 14i 0; .0;

C

S

C C Olefinically unsaturated ccrboxylic acid and carboxwlic acid anhydridc monomers include the acrylic acids typified by ncrylic acid i iseif. niethacrylic acid. ethacryvi acid.

chloroacrylic acid. a-eyarsoacrylic acid. -methylacrylic acid (crolortic acid), .phenylacrylic acid. -acrylo.\ypropionic acid. sorbic acid. -chlorosorbic acid. angelic acid. cinna~mic acid. p- 3 chlorocinnamic acid. *stervlacrylic acid. itaconic acid. citroconic acid. mesaconic acid.

glutaconic acid. aconitic acid. malcie acid. fumaric acid. tricarboxycthvlcnc and malcic acid anhydride.

Olefinicall unsaturated sulfonic acid monomers include aliphatic or aromatic iiinyl sulfonic acids such as vinylsulfonic acid. ally[ sulfonic acid, vinyl toluene sulfonic acid and 1o styrene sulfonic acid: acrylic and meshacrylic sul-fonie acid such as sulfoethyl acrylate.

suLfoethyl methacrylate. sulfbpropyl aesylate. sulfopropyl methactylate. 2-hvdroxv-3rnethacryloxyropyl sulfionic acid and 2-acrylamide-2-methylpropanc sulfonic acid.

Preferred hydrogel~fortning absorbent polymers for use in the presenCrt invention contain carb-oxy groups. These polymers include hydrolyzed staxch-aczylonitrile graft is copolymers. partially .neutralized hydrolyzed starch-acrylonufile graft copolymers. starhacrylic acid graft copolymners. partially neutralized stach-acrylic acid graft copolymers.

saponified vinyl acetate-acrylic eaicr copolym ers. hydrolyzed acrylontitrile or acrylamnide copolymers. slightly network crosslinked polymers of any of thc foregoing copolymers.

partially neutralized polyaerylic acid, and slightly nctwork crosslinked polymers of partially o neutralized polyacrylic acid. These polymers can be used either solely or in the form of a mixture of two or more different polymers. Examples of these polymer materials are disclosed in U.S. Patent 3.661.875. U.S. Patent 4.076.663. U.S. Patent 4.093.776. U.S.

Patent 4.666.983. and U.S. Patent 4.734.478.

Most preferred polymer materials for use in making the hydrogel-fonning absorbent 25 polymers are slightly network erosslinked polymers of' partially neutralized polyacrylic acids anid stamb derivatives thereof. Most preferably, the hydrogel-formaing absorbent polymers comprise from about 50 to about 95% preferably about 753%1 neutralized, slightly network crosslinked. polyacrylic acid poly (sodium acrvlate/acrylic acid) Net-work crosslinig renders the polymer substantially water-insoluble and, in pan,. determines the 30 absorptive capacity and exractble polymer content characteristics of the hydrogel-forening absorbent polymers. Processes for network erosslinkirig these polymers and typical network crosslinking agents ame described in g reaer detal in U.S. Patent 4.076,663..

Further. surface crosslinced hydrogcl-forining absorben -olymrics ca.n be preferably used in the present invention. They have a higher, 3-.il of crossliniting in the 33 vicinity of the surface than in the interior. As used herein, "sur~cc" describes the outer.

facing boundaries of the particle, fiber. etc. For porous hydrogel-formting absorbent 7 .13) polymers porous partnicles. etc.). exposed internal boundaries can also be included. B% a higher level of crosslittking at the surface. it is meant that the level of fujnctional crosslinks for the hydi'ogeL-fortmng nbsorbent polymter in the vicinity of the surface is generally higher than the level of functionail crosslinits for the polymer in the interior.

3The gradation in crosslinking from surface to interior can vary, both in depth and profile. Thus, for example, the depth or surface erosslinking can be shallow. with a relatively sharp transition to a lower level of crosslinking. Alternatively, for example. the depth of surface crossliaking can be a significant flaction ortwhc dimensions of the hydrogelforming absorbent polymer, with a broader transition.

to Depending on size, shaKe porosity as well as functional considerations. t~he degreeand gradient of surface crosslinking can vary within a given hydrogel- formiing absorbent polymer. For particulate hydrogel -forming absorbent polymers, surface crosslinking can vary' with particle size, porosity. etc. Depending on variations in surface:volunie ratio within the hydrogcl-formning absorbent polymer between small and large particles), it is not 13 unusual for the overall level of crosslinking to vary within the maaterial be greater for srmaller particles).

Surface crosslinking is generally accomplished after the finalI boundaries of the hydrogel-formirig absorbent polymer are essentially established by grinding. eatniding.

foaming. etc.) However, it is also possible to effect surface crosslinking concurrent with the .0 creation of final boundaries. Furthermore, some additional changes in boundaries can occur even after surface crosslinks are introduced.

A number of processes for introducing surface crosslinks are disclosed in the art.

These include those wbere: a di- or poly-functional reagent(s) glycerol. 1.3dioxolan-2-one. polyvalent metal ions. polyquaternay amines) capable of rectidng with existing functional groups; within the hwdrogel-formning absorbent polymer is applied to the suriface of the hydrogel-fornting absorbent polymer, (ii) a di- or polyfunctiorial reagent that is capable of reacting with other added reagents and possibly existing functional groups witltn the hydrogel-formiing absorbent polymer such as to increae the level of crosslinking at the surface is applied to the surface the addition of monomer plus crosslinker and the 30 initiation of a second polymerization reaction)-. (iii) no additional polyfunctional reagents are added, but additional reaction(s) is induced amongst existing components within the hydrogel-Formning absorbent polymer either during or after the priry polyierization proccess such as to generate a higher level of erosslinking at or near the surface heating to induce the formaton of anhtydride and or esits crosslinks between existing polymer carboxylic acid andfor hydroxyl groups and suspension polymerization processes wherein the crosslinker is inthcrently presnt at higher levels near the surface); and (iv) other materials t I4 r.C

~JI

-16are added to the surface such as to indue a higher level of crosslinking or otherw4ise reduce the surface defoermabiliry of the resultant hydrogel. Combinations of these surface crosslinking processes either concurrently or in sequence can also be employed. In addition to crosslinking reagents, other components can be added to the surface to aid/eonrol the distribution of crosslinking the spreading and penetration of the surface crosslinking reagents.) Suitable general nmethiods for carrying out surface crosslinking of hydrogel-forming absorbent polym~ers according to the present invention are disciksed in U.S. Patent 4.541.871 (Obayashi). issued September 17. 1985; published PCIT application W097JI6565 (Stanley).

to published October 1. 1992. published PCT~ application W090/08789 (Tal), published August 9. 1990: published PCT application W093105080 (Stanley), published March 18. 1993: U.S.

Patent 4.824.901 (Alexander). issued April 25. 1989; U.S. Patent 4.789.861 (Johnson).

issued January 17. 1989; U.S. Patent 4.587,308 (Mdakita). issued May 6, 1986; U.S. Patent 4.734.478 (Tsubakimoto). issued March 29. 1988:. U.S. Patent 5.164.459 (Kimura et. al.).

issued November 17, 1992: published Germ~an patent application 4.020,780 (Dalunen).

published August 29. 1991: and published European patent application 509.708 (Gartner).

published October 21. 1992: all of which are incorporated by reference.

While the hydrogel-fon~ning absorbent polymer is preferably of one type homogeneous). mixtures of polymers can also be used in the present invention. For example.

rn ixtures of starch-acrylic acid graft copolymiers and slightly network crosslinked polymers of partially neutralized polyacrylic acid m-n be used in the present invention.

Physical Forms The absorbent gelling particles used in the present invention can have a size, shape zi andfor morphology varying over a wide range. The absorbent gelling particles do not have a large ratio of greatest dimension to smallest dimension granules. flakes, pulverulents.

inerparticle aggregates, interparticle erosslinked aggregates, and the like) and can be in the form of fibers. foarms, and the like. The hydrogcl-forming absorbnt polymers can also comprise mnixtures with low levels of one or more additives such as for example powdered o silica. surfactants. glue, binders, and the like. The components in this mnixnire can be physically and/or chemically associated in a form such that the hydrogel-formaing polymer component and the non-hydrogel-forming polymer additive are not readily physically separabie.

The hydrogel-forring absorbent polymers can be essentially non-porous or have 31 substantial interna porosity- -iT-r For panicles as described above. panicle size is defined as the dimension determined by sieve size analysis. Thus. for example. a panicle that is retained on a U.S.A.

Standard Testing Sieve with 710 micron openings No. 25 U.S. Series Alternate Sieve Designation) is considered to have a size greater than 710 microns; a panicle that passes j through a sieve with 710 micron openings and is retained on a sieve with 500 micron openings No. 35 U.S. Series Alternate Sieve Designation) is considered to have a panicle size between 500 and 710 microns; and a panicle thai passes through a sieve with 500 micron openings is considered to have a size less than 500 microns. The mass median panicle size of a given sample of hydrogel-forming absorbent polymer particles is defined as o1 the panicle size that divides the sample in half on a mass basis. one-half of the sample by weight will have a panicle size less than the mass median size and one-half of the sample will have a paricle size greater than the mass median size. A standard particle-size plotting method (wherein the cumulative weight percent of the particle sample retained on or passed through a given sieve size opening is plotted versus sieve size opening on probability paper) is is typically used to determine mass median particle size when the 50% mass value does not correspond to thzesize opening of a U.S.A Standard Testing Sieve. These methods for determining panicle sizes of the hydrogel-forning absorbent polymer panicles are further described in U.S. Patent 5.061.259 (Goldman et. al). issued October 29. 1991. which is incorporated by reference.

:o For particles of hydrogel-forming absorbent polymers useful in the present invention, the panicles will generally range in size from about I to about 2000 microns.

more preferably from about 20 to about 1000 microns. The mass median particle size will generally be from about 20 to about 1500 microns, more preferably from about 50 microns to about 1000 microns, and even more preferably from about 100 to about 800 microns.

Within these size ranges. it can be preferable to choose either larger or smaller particles depending on the need for faster or slower absorption kinetics. For example, for non-porous particles, the swelling rate will generally decrease with increasing particle size.

It can also be preferable to choose either larger or smaller particles or narrower size cuts S(fractions) of larger or smaller particles from the bulk polymer in order to increase the gel 3 layer permeability increase the Saline Flow Conductivity (SFC) value). For particles of some hydragel-forming absorbent, polymers, it has been found that narrower size range cuts containing generally larger particle sizes within the above specified size ranges have higher 'SFC values without any significant degradation in other hydrogel-forming absorbent polymer propenies such as Performance Under Pressure (PUP) capacity and level of 35 extractable polymer. Thus. for example, it can be useful to use a size cut having a mass median size in the range of from about 500 to about 710 microns wherein only minimal mass S- j

_I

fractions of the particulates have sizes either greater than about 710 microns or less than about 500 microns. Alternaivel. a broader size cut wherein the particles generally have a size in the range of from about 150 microns to about 800 microns can be useful.

D. Process for Making Absorbent Materials As previously described. the mixtures of absorbent materials of the present invention can be made by applying a solution containing an organic solvent. water and the absorbent property modification polymer onto the plurality of absorbent gelling particles, wherein the weight ratio of the organic solvent to the water is at least 50:50. and (ii) removing a portion of the organic solvent and water from the applied absorbent gelling particles. More preferably, the weight ratio of the organic solvent to the water is from about 70:30 to about 93:2.

As used herein, the term 'apply onto' means that the absorbent property is modification polymer will be on at least a portion of the surface area of the absorbent gelling particles. Preferably. the absorbent property modification polymer is applied onto all of the surface of the absorbent gelling panicles.

In a case where the absorbent property modification polymer is in the form of a small particle or powder, the absorbent property modification polymer can be applied by any .o of various techniques and apparatus used for applying a material to another material. In another case where the absorbent property modification polymer is in the form of a liquid.

the absorbent property modification polymer can be applied by any of various techniques and apparatus used for applying a liquid to a material. As a result, absorbent materials of the c present invention can be obtained in the forms of the above described mixtures.

25 In a preferred embodiment, an absorbent property modification polymer a ctionic polymer or a polyamine or polyimine material) which is reactive with at least one component included in a urine is dissolved into a solvent to make a solution. The absorbent property modification polymer can be dissolved in the solvent by any of various techniques Sand apparatus used for dissolving a material to a solvent known in the an. In more preferred so embodiments. an organic solvent is used as the solvent. Preferably, the concenuation of the absorbent property modification polymer in the solution by weight is from about 0.05% to S 60%. more preferably, from 0.5% to In preferred embodiments an absorbent property modification polymer which is insoluble in an organic solvent can be used. In more preferred embodiments. a polar organic S s solvent is used as the solvent. In such embodiments, a mixtur solvent of a hydrophilic organic solvent and water is used as the solvent for the absorbent property modification

I-:

polymrer. Nots-limiting e.v~isiples of tlie preferred organic solventr includcs: the low molecular weight alcohols such as methanol. ethanol, or propanol. acetone: dimCthIet~afrrnamfidc(DSA)- dimethylsulfoside(DMSOl: lhem'c~methylphosphoric triamidc(N.fT): and mixtures thereof. In alternative preferred emnbodimcnts. non-polar solvents such as hexane. toluene. xylene. and benzene can be used as one of the organic solvent.

After preparing the solution. the solution is applied onto the absorbent gelling particles thereby making a intermittent mixture. More specifically, an amount of the solution is applied onto the absorbent gelling particles. The solution can be applied by any a0 of various techniques and apparatus used for applying a solution to a tlutrial including coating, dumping. pouring, dropping. spraying, acomizing. condensing. or immersing the liquid mixture onto the absorbent gelling particles. Thus, in die intcrtittncnt mixture the solution will be on at least a portion of the surface area of the absorbent gelling particles.

Preferably, the solution will be on all of the surface of the absorbent gelling particles.

Th 7e amount of the absorbent property modification polymer which is sufficient to effect an enhancement of the physical properties of the absorbent material can vay on a number of faciors such as the chcmical composition of the absorbent polymer and the physical forms of the absorbent gelling particles. particle size of the absorbent particles.

and the chemical composition and molecular weight of the absorbent property modification 4 :0 polymer, as well as on the applying method thereof.

In pref'erred embodiments, the weight ratio of the absorbent property modification polymer to the absorbent gelling particles is from about 0.05:100 to about 20:100. more preferably from about 0.5:100 to about 5:100.

After makng the intermittent mixture, at least a portion of the solvent is removed from the intermittent mixture. Preferably, at least about SV0%, more preferably more than I 95%. ams preferably about 100O'. of the solvent is removed from the intermittent maixtur.

The removal of the solvent can be made by any of various techniques and apparatus used for separating or removing liquids from liquid-solid mnixtures, including evaporation, filtration.

wasingor a combination thereof.

In a preferred embodiment. the physical property modification polymer is applied onto the absorbent gelling particles after the treatment of the surface crosslinking of the absorbent gelling paiteles On the other hand, in another embodiment the physical property modification polymer is applied onto the absorbent geiling particles before the treatment of the surface crosslinking of the absorbent gelling particles. *In addition, in a futrther 4.:31 embodiment the application of the physical property modificationt polymer and the treatment of the cross linking can be carried out at the same time. It should be noted that in some embodiments the physical property modification polymer can be used as a cross linking agent.

In preferred embodiments. the resultant absorbent materials can have a number of sh;apes and sizes. For e.'cmplc. the absorbent materials can be typically in the form of particles, sheets, films. cylinders, blocks, fibers, filaments, or other shaped elements. Mare preferably. the absorbent material is particulate.

E. Absorbent Articles Using T7he Absorbent Materials The absorbent mnaterinls according to the present invention can be used for many purposes in many fields of use. For example. the absorbent materials can be used for packing contaiiners; drug delivery devices: wound cleaning devices: burn treatment devices-.

ion e"change column materials; construction nuaterials-; agncultrual or horticultural materials such as seed sheets or wter-retentive materials: and industrial uses such as sludge is or oil dewatering agents. materials for the prevention of dew forniation. desiccants. and humidity control materials.

Because of the unique absorbent properties of the absorbent materials of the presnt invention. they are especially suitable for use as absorbent cores in absorbent articles.

especially disposable absorbent articles- As used herein, the term 'absorbent article' refers :0 to articles which absorb and contain body fluids and more specifically refers to articles which are placed against or in proximity to the body of the wearer to absorb and contain the various fluids discharged from the body-. Additionally. 'disposable" absorbent articles are those which arc intended to be discarded after a single use the original absorbent article in its whole is not intended to be laundered or otherwise rested or reused as an absorbent article.

although certain materials or all of the absorbent article can be recycled, reused. or conmposted).

In general. an absorbent article comprises: a liquid pervious topshcrt which is located adjacent to the wearces body: a liquid impervious baekshct which is located distant fronm the wears body and adjacent to the vicares clothig. and an absorbent care positioned between the topsheet and the backsheel- The absorbent core comprises at least one or the above described absorbent mraterials. In a prefen-ed embodimen, the absorbent core is one of the abovi: described absorbent memnbers. Preferably. the absorbent core further compise a substrate web wherein the absorbent material is artached to the substrate web.. Alitnatively, the absorbent- core further compnises an envelope web encasing the absorbent material. In a further alternti~tve embodiment. the absorbent core fujrther 1 comprises two layered tissues wheireir. the ab~wrbeflt mnatenal is distnbuted between the two lavered tissues- In more preferred embodiments. the absorbent material in the absorbent Core has a basis weight of from about 60 9/m 2 to about 1500 SIm2. more preferably from about 100 2 to about 1000 V/rn. most preferably from about 150 gIm2 to about 500 gim2 of the absorbent amterial.

In some preferred cmbodirntiS. the absorbent core or absorbent memnbcr can further comprise fibers or fluff pulp (fibrous or fiber matierial), more specifically. nonabsorberit-gclling fibers. Such fiber materia can be used as reinforcing members in the to absorbent core. improving fluid handling of the corm as well as a co-absorbent -Atl the absorbent polymers, Preferably, the absorbent care or member inicludes from ab~out 410% to about 100% by weight of the absorbent material and from about 60V. to about 0% by weight of such noft-absnrbent-gellitlg ftber material distributed within the absorbent mtrial.

In a preferred embodiment, the absorbent material is in a concetrauto of at least more preferablyv frm about 60 to 100% by weight in at leas one region of the core or absorbent member. In a more preferred embodiment. the absorbent member comprises fibrous matrix~ wherein the absorbent material is distributed in the fibrous matrix.

Any type of fiber maiterial which is suitable for use in convenlUtinl absorbent products can be- used in the absorbent core or absorbent member herein. Slxaafie examples of such fiber material include cellulose fibers, improved cellulose fibers, rayon.

polypropylenec. and polyestier fibers such as polythylene tcrephthalate

(DACRON).

hydrophilic nylon (HYDROFIL). and The like- Examples of other fiber materials for use in the present invention in addition to some already discussed are hydrophilized, hydrophobic fibers such as surfactantE-treated or silica-tmeted thermoplastic fibers derived, for example.

2s from polyolefins such as polyethylene or polypropylene. polyacrylims palyamides.

polyrryrens. polyireihaies and the like. In fact- hydrophilized hydrophobic fibers which arm in and of themselves not ver absorbent and which, theirefore, do not provide webs of sufficienit absorbent capacity to be useful in conventinal absorbent structures. are suitable for use in the absotbent core by virtue of their good wicking properties. This is because, in 3o the absorbent core herein, the ivicking propensity of the fibers is as impotant. tf not more important. than the absorbent capacity of the fiber material itself due to the high rate of fluid uptake and lack of gel blocking properties of the absorbent core Synthetic fibers arc generally preferred for use herein as the fiber component of the absorbent core. Most preferred are polyolefin fibers. preferably polyethylene fibers.

cellulosic fiber materials which can be usefuL- in certain absorbent cores or absorbent member herein are chernically stiffened cellulorsie fibers Preferred chemically 5

S

7 Lom -22stiffened cellulosic fibers are the stiffened. twisted. curled cellulosic fibers which can be produce-d by internally crosslinking Cellulose ibers -Aith a crosslinking agent. Suitable stiffened. t%%isted. curled cellulose fibers uiseful as the hydrophilic fiber mauterial herein are described in greater detail in U.S. Pntent 4.888.093 (Dean CE al). issued Decmber 19. 1939; U.S. Patent 4.889.595 (Herman ci al). issued December 26. 1989-. U.S. Patent 4.889.596 (Schoggen ct al). issued December 26. 1989; U.S. Patent 4.889.597 (Bourbon CE 31). issued December 26. 1989-. and U.S. Patent 4.998.647 (io-ore et al). issued February 6. 1990. all of which art incorporated by reference.

A preferred embodiment of the disposable absorbent article is a diaper. As used toherein, the term 'diaper" refers to a ga-ment generally worn by infants and incontinent persons that is worn about the lower torso of the wearer. A preferred diaper configuration for a diaper comprising an absorboent core is described generally in U.S. Patent 3.860.003 (Buell), issued January 14. 1975. which is incorporated by reference. Altern~atively preferred configurations for disposable diapers herein are also disclosed in U.S. Patent 4,808.178 Is (Aziz et al). issued February 28. 1989-. U.S. Patent 4.695.278 (Lawson), issued September 22. 1987; U.S_ Patent 4.816.025 (Foremnan). issued March 28. 1989; and U.S. Parent 5.15 1.092 (Buell et issued September 29. 1992. all of which are incorporated by reference.

Another preferred embodiment of the disposable absorbent article is a cai~amnenial o0 product. Preferred cacamenial products comprise a formed-film. aperttrd lopsheet as disclosed in U.S. Patent 4.285.343 (McNair). issued August 25. 1981; U.s. Patent 4.608.047 (Martingly). issued August 26. 1986-: and U.S. Patent 4.687.478 (Van Tilburg). issued August 18. 1987. all of which are incorporated by referec.c Preferred1 catamentiat products can comprise wings, side flaps% and other strtctures i% and elements, as described in co-pending. eomonly-assigned U.S. application serial No.

9&'.071. to Yisuko Mania, entitled -Absorbent Article Haying Elastcized Side Flaps'.

Attorney Docket No. IA-09RM. file November 30. 1992. incorporated herein by reference.

It should be understood, however, that the present invention is also applicable to other absorbent articles known commercially by other names, such as incontinent briefs.

3o adult incontinent products. training pants,diaper inserts, facial tissues, Paper towtls, and the SF.. Test Methods Sy-nthetic Urine 3. 1he specific synthetic urine used in the test methods of the present invention is r-efered to herein as 'Synthetic Urine'. The Synthetic Urine is cormmonly known as layco

PORN

4 Or 13yen Synthetas Urine and is aviilble from 13veo Pharm3Cac ias ComPany Of Camp Hill. Pcnnswvz-nia- The formula for the Synthetic Unnec is: 3.0 &1l of KCIL 2.0 g/l of Na2SOL; 0.85 &q of (NH-I)H2PO-t; 0-15 g/1 (NHS)2HPO4: 01[9 EA of CaC12 and 0.23 gfl or MgCI2. All of the chemi-.als are of reagent grade. The pH of the Synthetic Urine is in the 3 range of 6.0 to 6.4.

L Gel Bulk Density (GBD) Test This test determines the gel bulk densicv (GBD) of an absorbent material that is swo~lcn in Jayco synthetic urine- The GBID is the -weight per untit volume of a swollen to absorbent material, including voids inherent in the swollen gel material as tested.

The objective of this test is to assess the porosity of an absorbenit material at wet state. GBD of an absorbent material is used as a measure of the gel porosity of an absorbent material alter sweliling in Jayco synthetic urine. Ge-l porosity here means the voids fraction in the swollen absorbent material or the fraction volume of the bulk gel layer that is not 13 occupied by gel. An absorbent matuerial that has tower GEID is likely to have more voids, in other words, to have higher porosity at wet state.

Apparatus A suitable GBD measuremencrt apparatus is shown in Figure 1. This apparatus comprises a cylinder 1 10, a cup-like pistol 140, a weight 130 tiat fits inside the pistol 140.

o0 and a flat-bottomed TEFLON tray 120. The cylinder 110 is bored from a transparent LEXAN rod (or equivalent, for example Acrylic rod) and has an inner diameter of 6.00 cm (area =28.27 em 2 with a wall thickness of approximately 0.5 cM and a height of approximatecly 5.0 cm- The bottom of the cylinder is faced with a No. 400 mash stainlesssteel screen 150 that is biaxially stretched to tautness prior to attachmeint. The piston 140 is is in the. form of a TEFLON cup and is machined to fit into the cylinder 110 within light tolerances. Stainless weight 130 is machined to fa within the pistol 140. The combined wight of piston 140 and weight 130 is 199 g. which corresponds to a pressue of 0.Ipsi for an area of 28.27 cm 2 The thickness of the gel layer 160 in cylinder 1 10 is measured to an accuracy of 3a about 0.05 mm- Any method having the requisite accuracy can be used, as long as the weights are not removed and the gel laver is not additionally disturbed during the thickness measurement. Using a cliper gauge Digimatic Caliper. Mitoya Corp.. Kyoto. or equivwalent) to measure the gap berween the top of the TEFLON pistol 140 and the top of the cylinder 110. relative to this gap wvith no absorbent maten~al in the cylinder is acceptable.

33 The GED measurement is performed at room tentpcrarure. Jayo synthetic urine is used in this test

I

PC.

Procedure U 9 g aliquot of absorbent material is added to the cylinder 110 and dispersed evenly on the screen 150. For most absorbent materials. moisture content is typically less than For these, the quantity of absorbent material to be added can be determined on a wet-weight s (as is) basis. For absorbent material having a moisture content greater than about the added absorbent material weight should be corrected for moisture the added absorbent should be 0.9 gm on a dry-weight basis). Care is taken t' prevent the absorbent material from adhering to the cylinder walls. Pistol 140 is inserted into cylinder 110 and positioned on top of the absorbent material 160. Weight 130 is then positioned in pistol 140.

to The piston/cylinder apparatus with the absorbent material is then transferred to a flat-bottomed TEFLON tray 120. 18 Milliliters of Jayco synthetic urine is added to the tray 120. Time is recorded as soon as Jayco urine is poured in to the tray 120. Jayco synthetic urine from the uay passed through the stainless screen 150 and is absorbed by the absorbent material 160. As the absorbent material absorbs fluid, a gel layer is formed in the cylinder is 110. After a time period of 30 minutes, the thickness of the gel layer is determined.

Consequently, the predetermined layer of the swollen absorbent material for the GBD measurement has been prepared. The gap between the top of the TEFLON pistol 140 and the top of the cylinder 110 is measured Relative to this gap with no absorbent material in the cylinder (Lc) is also measured. This difference between Le and Ls is the thickness of o the absorbent material gel layer The piston/cylinder apparatus with swollen gel is weighted (Ws).

The GBD is calculated according to the equation: GBD (Ws Wc)(28.27 x Lg) Where GBD is the gel bulk density value (glcm 3 Ws is the total weight of the Zs pistoncvylinder apparatus with swollen gel We is the weight of pistol/cylindcr without absorbent material and Lg is the thickness of the swollen gel layer (cm).

2. Saline Flow Conductivity (SFC) Test This test determines the Saline Flow Conductivity (SFC) of the gel layer formed o from hydrogel-forming absorbent polymer that is swollen in Jayco synthetic urine under a confining pressure. The objective of this test is to assess the ability of the hydrogel layer formed from a hydrogel-forming absorbent polymer to acquire and distribute body fluids when the polymer is present at high concentrations in an absorbent member and exposed to usage mechanical pressures. Darcy's law and steady-state flow methods are used for is determining saline flow conductivity. (See, for example, "Absorbency," ed. by P. K.

i 1 r t rir

I

r r i

P,

~as~i~s~a~s~ia~ s~Be~~ 1 -21 Chatterjec. Elsevicr. 1985. Pages 42-43 and "Chemical Engineering Vol. 11. Third Edition.

I. M. Coulson and I. F. Richardson. Pergnmon Press. 1978. Pages 125-127.) A predetermined layer of swollen absorbent material used for SFC measurements is formed by swelling an absorbent material in Jayco synthetic urine for a time period of s minutes. The hydrgel layer is formed and its flow conductivity measured under a mechanical confining pressure of 0.3 psi (about 2 kPa). Flow conductivity is measured using a 0.118 M NaCI solution. For a hydrogel-forming absorbent polymer whose uptake of Jayco synthetic urine versus time has substantially leveled off. this concentration of NaCI has been found to maintain the thickness of the hydrogel layer substantially constant during the Io measurement. For some hydrogel-forming absorbent polymers. small changes in hydrogellayer thickness can occur as a result of polymer swelling, polymer deswelling, and/or changes in hydrogel-layer porosity. A constant hydrostatic pressure of 4920 dyne/cm 2 (5 cm of 0.1 1M NaCI) is used for the measurement.

Flow rate is delermined by measuring the quantity of solution flowing through the is hydrogel layer as a function of time. Flow rate can vary over the duration of the measurement. Reasons for flow-rate variation include changes in the thickness of the hydrogel layer and changes in the viscosity of interstitial fluid, as the fluid initially present in intersitial voids (which. for example. can contain dissolved extractable polymer) is replaced with NaCI solution. If flow rate is time dependent, then the initial flow rate.

0: typically obtained by extrapolating the measured flow rates to zero time, is used to calculate flow conductivity. The saline flow conductivity is calculated from the initial flow rate.

dimensions of the hydrogel layer, and hydrostatic pressure.

A suitable apparatus 610 for this test is shown in Figure 2. This apparatus includes a constant hydrostatic head reservoir indicated generally as 612 that sits on a laboratory jack 2 indicated generally as 614. Reservoir 612 has lid 616 with a stoppered vent indicated by 618 so that additional fluid can be added to reservoir 612. An open-ended tube 620 is inserted through lid 616 to allow air to enter reservoir 612 for the purpose of delivering fluid at a constant hydrostatic pressure. The bonom end of tube 620 is positioned so as to maintain fluid in cylinder 634 at a height of 5.0 cm above the bottom of hydrogel layer 668 (see Figure 3).

Reservoir 612 is provided with a generally L-shaped delivery tube 622 having an inle 622a that is below the surface of the fluid in the reservoir. The delivery of fluid by tube 622 is controlled by stopcock 626. Tube 622 delivers fluid from reservoir 612 to a piston/cylinder assembly generally indicated as 628. Beneath assembly 628 is a support is screen (not shown) and a collection reservoir 630 that sits on a laboratory balance 632.

r o r r Ir~i re r~t I r I o~r rre rrt s i;Z Ilrj i: cj ii Ir i i-~l: il

I

I

1 F 1C 26- Referring to Figure 2. assembly 628 basically consists of a cylinder 634. a piston generally indicated as 636 and a cover 637 provided-with holes for piston 636 and delivery tube 622. As shown in Figure 7. the outlet 622b of tube 622 is positioned below the bottom end of tube 620 and thus will also be below the surface of the fluid (not shown) in cylinder 634. As shown in Figure 3. piston 636 consists of a generally cylindrical LEXANI' shaft, 638 having a concentric cylindrical hole 640 bored down the longitudinal axis of the shaft.

Both ends of shaft 638 are machined to provide ends 642 and 646. A weight indicated as 648 rests on end 642 and has a cylindrical hole 648a bored through the center thereof.

Inserted on the other end 646 is a generally circular Teflon piston head 650 having an annular recess 652 in the bottom thereof. Piston head 650 is sized so as to slidablv move inside cylinder 634. As particularly shown in Figure 4. piston head 650 is provided with four concentric rings of twenty-four cylindrical holes each indicated generally as 654. 656.

658, and 660. As can be seen in Figure 4. concentric rings 654 to 660 fit within the area defined by recess 652. The holes in each of these concentric rings are bored from the top to is bottom of piston head 650. The holes in each ring are spaced by approximately 15 degrees and offset by approximately 7.5 degrees from the holes in adjacent rings. The holes in each ring have a progressively smaller diameter going inwardly from ring 654 (0.204 inch diameter) to ring 660 (0.111 inch diameter). Piston head 650 also has cylindrical hole 662 bored in the center thereof to receive end 646 of shaft 638.

a As shown in Figure 3. a frined circular glass disc 664 fits within recess 652.

Attached to bottom end of cylinder 634 is a No. 400 mesh stainless steel cloth screen 666 hat is biaxially stretched to tautness prior to attachment. The sample of hydrogel-forming absorbent polymer indicated as 668 is supported on screen 666.

Cylinder 634 is bored from a transparent LEXAN' rod or equivalent and has an u inner diameter of 6.00 cm (area 28.27 cm2). a wall thickness of approximately 0.5 cm. and a height of approximately 6.0 cm. Piston head 650 is machined from a solid Teflon rod. It has a height of 0.625 inches and a diameter that is slighty less than the inner diameter of cylinder 634. so that it fits within the cylinder with minimum wall clearances, but still slides freely. Recess 652 is approximately 56 mm in diameter by 4 mm deep. Hole 662 in the M center of the piston head 650 has a threaded 0.625 inch opening (18 threadsinch) for end 646 of shaft 638. Fritted disc 664 is chosen for high permeability Chemglass Cat No.

CG-20140. 60 mm diameter. X-Coarse Porosity) and is ground so that it fits snugly within o eee e" rcss 652 of piston head 650. with the bottom of the disc being flush with the bottom of the piston head. Shaft 638 is machined from a LEXAN rod and has an outer diameter of as 0.875 inches and an inner diameter of 0.250 inches. End 646 is approximately 0.5 inches long and is threaded to match hole 662 in piston head 650. End 642 is approximately an

M~

~:i ri inch long and 0.623 inches in dimcter,. forming an annular shoulder to support the stainless steel weight 643. Fluid passing through the hole 640 in shaft 638 can directly access the friuted disc 664. The annular stainless steel weight 648 has an inner diameter of 0.625 inches. so that it slips onto end 642 of shaft 638 and rests on the annular shoulder formed therein. The combined eight of fritted glass disc 66. piston 636 and weight 648 equals 596 g. which corresponds to a pressure of 0.3 psi for an area of 28.27 cm. Cover 637 is machined from LEXAN® or its equivalent and is dimensioned to cover the top of c-linder 634. It has an 0.877 inch opening in the center thereof for shaft 638 of piston 636 and a second opening near the edge thereof for delivery tube 622.

The cylinder 634 rests on a 16 mesh rigid stainless steel support screen (not shown) or equivalent. This support screen is suficienty permeable so as to not impede fluid flow into the collection reservoir 630. The support screen is generally used to support cylinder 634 when the flow rate of saline solution through assembly 628 is greater than about 0.02 g/sec. For flow rates less than about 0.02 gfsec, it is preferable that there be a continuous I fluid path betwecn cylinder 634 and the collection reservoir.

The 0.118 M NaCI solution is prepared by dissolving 6.896 g NaCI (Baker Analyzed Reagent or equivalent) to 1.0 liters with distilled water.

An analytical balance 632 accurate to 0.01 g Mettler PM4000 or equivalent) is typically used to measure the quantity of fluid flowing through the hydrogel layer 668 when the flow rate is about 0.02 gsec or greater. The balance is preferably interfaced to a computer for monitoring fluid quantity versus time.

The thickness of hydrogel layer 668 in cylinder 634 is measured to an accuracy of about 0.1 mm. Any method having the requisite accuracy can be used, as long as the weights are not removed and the hydrogel layer is not additionally compressed or disurbed S during the measurement. Using a caliper gauge Manostat 15-100-500 or equivalent) to measure the vertial distance between the bottom of the stainless steel weight 648 and the top of cover 637 relative to this distance with no hydrogel layer 668 in cylinder 634 is acceptable.

The SFC measurement is performed at ambient temperature 20°-25C) and is 36 carried out as follows: 0.9 g aliquot of hydrogel-forming absorbent polymer (corresponding to a basis weight of 0.032 g/cn 2 is added to cylinder 634 and distributed evenly on screen 666. For most hydrog-forming absorbent polymers. moisture content is typically less than For these, the quantity of hydrogel-forming absorbent polymer to be added can be determined on 3s a wt-wtight (as is) basis. For hydmgcl-forming absorbent polymers having a moisture content grter than about 5, the added polymer weight should be corrcted for moisture 5 ,r .rr o C goo :ih ir i-i% r.- ;;i i i ae

~E~B~BSS~

-28the added polymer should be 0.9 g on a dry-weight basis) Care is taken to prevent hydrogcl-forming absorbent polymer froin adhering to the cylinder walls. Piston 636 (minus weight 6-4) with disc 664 positioned in recess 652 of piston head 650 is inserted into cylinder 634 and positioned on top of the dry hydrogel-forming absorbent polymer 668. If S necessary. piston 636 can be turned gently to more-uniformly distribute the hydrogclforming absorbent polymer on screen 666. Cylinder 634 is the covered with cover 637 and weight 648 is then positioned on end 642 of shaft 638.

A fritted disc (coarse or extra coarse) having a diameter greater than that of cylinder 634 is positioned in a wide/shallow flat-bottomed container that is filled to the top of the o fritted disc with Jayco synthetic urine. The piston/cylinder assembly 628 is then positioned on top of this fritted glass disc. Fluid from the container passes through the frilted disc and is absorbed by the hydrogel-forming absorbent polymer 668. As the polymer absorbs fluid, a hydrogel layer is formed in cylinder 634. After a time period of 60 minutes, the thickness of the hydrogel layer is determined. Care is taken that the hydrogel layer does not lose fluid or is take in air during this procedure.

The piston/cylinder assembly 628 is then transferred to apparatus 610. The support screen (not shown) and any gap between it and the piston/cylinder assembly 628 is presaluratcd with saline solution. If the fritled funnel 718 of the PUP apparatus 710 is used to support cylinder 634. the surface of the frited funnel should be minimally elevated :o relative to the height of the fluid in the collection reservoir, with valves between the fritted funnel and the collection reservoir being in the open position. (The frined funnel elevation S should be sufficient such that fluid passing through the hydrogel layer does not accumulate in the funnel.) The SFC measurement is initiated by adding NaCI solution through hole 640 in 2s shaft 638 in order to expel air from piston head 650 and then turning stopcock 626 to an open position so that delivery tube 622 delivers fluid to cylinder 634 to a height of 5.0 cm above the bottom of hydrogel layer 668. Although the measurement is considered to have been initiated (to) at the time NaCI solution is first added, the time at which a stable hydrostaic pressure, corresponding to 5.0 cm of saline solution, and a stable flow rate is a attained (t s is noted. (The time t s should typically be about one minute or less.) The quantity of fluid passing through hydrogel layer 668 versus time is determined gravimetrically for a time period of 10 minutes. After the elapsed time. piston/cylinder assembly 628 is removed and the thickness of hydrogel layer 668 is measured. Generally the change in thickness of the hydrogel layer is less than about S is t In general. flow rate need not be constant. The time-dependent flow rate through the system. Fs is determined, in units of g/sec. by dividing the incremental weight of fluid ;i -29.

passing through the systenm (it grains) by incremental time (in seconds). Only data collected for times betweeni is and 10 ininutes is used for flowv rate calculations. Flow rate results between is and 10 minutes is used to calculate a value for F, the initial flow rate through the hydrogel liver. Fs tt=0) is calculated by extrapolating the resuls Of a leastsquares fit of Fs versus time to t=O.

for a layer having a very high prmea~bility a flow rate greater than -2 g/sec).

it may not be practical to collect fluid for the full 10 minute time period. For flow rates greater than 2 sec. the time of collection can be shortened in proportion to the flow rate.

For some hydiogel-forming absorbent polymers having extremely low permeability.

to absorption of fluid by the lwdrogel competes with transport of fluid through the hydrogel layer and either there is no flow of fluid through the hydrogel layer and into the reservoir or.

possibly, there is a net absorption of fluid out of the PUP reservoir. For these extremely low permeability hydrogel layers, it is optional to extend the time for Jayco SynUrinc absorption to longer periods 16 hours).

Int a separate me-asurement. the flow rate through apparatus 610 and the pistonicylindcr assembly 628 (Fa) is measred as desetibed above, except that no hydrogcl layer is present. If F2 is much greater than the flow rate through the system when the hydrogel layer is present. Fs. then no correction for the flow resistancc of the SFC apparatus and the pision/cylinder assembly is necessary. In this limit, Fg -Fs. where Fg is the V contribution of the hydrogel laver to the flow rate of the system. However if ths requirement is not satisfied, then the follow-ing correction is used to calculate the value of Fg from the values of Fs and Fa: Fg =(FaxFsY1(FaFs) The Saline Flow Conductivity of the hydrogel layer is ealculated using the :j following eq~uation: K (Fg(t4J)x'LO)I(xAxP).

where Fg(t 0 O) is the flow rate in gssc determined from regression analysis of the flow rte results and 'any correction due to assembly/apparatus flow resistance, L 0 is the inutial thickness of the hydroget layer in em. is the density of the liaCI solution in g/crn 3 A is the 22 arao tehdogllyr ne 2 P is the hydrostatic pressur in dynelem and the saline flow conductivity. K. is in units of cm see/g.

The average of three determinations should be 3. Ball Burst Strength (BBS) Test 13This test determines the ball burst strertgtltCBlS) of an absorbent matesal at wet state. BBS of an absorbent' matetial is the force (peak load. ins gramns) required to produce rrr it rupture of an absorbent material gel layer that is swollen in Jayco synthetic urine under procedures specified in this test method. BBS of an absorbent material is used for evaluation of the wet integrity of an absorbent material that is swollen in Jayco synthetic urine.

Sampling apparatus SA suitable sampling apparatus for BBS measurement is shown in Figure 5. This apparatus comprises an inner-cylinder 270 which is used to contain an absorbent material laver 260. an outside-cylinder 230. a TEFLON flat-bottomed tray 240. an inner-cylinder cover plate 220. and a stainless weight 210. The inner-cylinder 270 is bored from a transparent LEXAN rod (or equivalent. for example Acrylic rod) and has an inner diameter o of 6.00 cm (area 28.27 cm 2 with a wall thickness of approximately 0.5 cm. and a height of approximately 1.50 cm. The outside-cylinder 230 is bored from a transparent LEXAN rod (or equivalent, for example Acrylic rod) and has an inner diameter that is slightly larger than the outside diameter of the inner-cylinder 270. so that the inner-cylinder 270 fits within the outside-cylinder 230 and slides freely. Outside-cylinder 230 has a wall thickness of is approximately 0.5 cm. and a height of approximately 1.00 cm. The bonom of the outsidccylinder 230 is faced wit' No. 400 mesh stainless-steel screen 250 that is biaxially stretched to tautness prior to attachment. Inner-cylinder cover plate 220 is made of glass plate with a thickness of 0. cm and a weight of 500 g. Stainless weight 210 has a weight of 1700 g.

Burst tester A Tensile Tester with a burst test load cell (Intelect-I-STD Tensile Tester. made by Thwing-Albert Insrument Co.. Pennsylvania) is used for this test. Referring to Figure this apparatus comprises a circular sample lower clamp platen 280 that is mount on a stationary crosshcad 310 provided at the top of a dual screw instrument. a force sensing load S cell 330 equipped with a polished stainless steel ball-shaped probe 290, a moving crosshead 320. and a upper clamping platen 300 that is used to clamp a sample 260 pneumatically.

Lower clamp platen 280 is mount on the stationary crosshead 310. The force sensing load cell 330 is equipped with the probe 290. Both lower clamp platen 280 and upper clamp platen 300 have a diameter of 115mm. a thickness of 2.9mm. and a circular opening so 18.65mm in diameter. Polished stainless steel ball-shaped probe 290 has a diameter of 15.84mm. The moving crosshead 320 moves up. causing the probe 290 to contact and penetrate the sample 260. When the probe 290 penerate the sample 260. the test is considered complete. and the test reslt data arc displayed and rcorded.

Procedure s Referring to Figure 5. inner-cylinder 270 is inserted into outside-cylinder 230. 1.4 g aliquot of an absorbent material is added to the inner-cylinder 270 and dispersed evenly on cc V C C 4 Itcsg~gSaa -31the 400 mesh stainless screen 250 of the bottom via g:ntly shaking and/or tapping of the assembled cylinders. The assembled cylinders with absorbent material are transferred to TEFLON lint-bottomed tray 240. and inner-cylinder cover plate 220 is positioned cnto inner-cylinder 270. 42.0 Milliliters of Jayco synthetic urine is applied to TEFLON flat- S botomed tray 240. Jayco synthetic urine from TEFLON lat-bottomed tray 240 passes through the stainless screen 250. All of the applied urine is absorbed by the absorbent material 260 for 5 minutes. Then tle stainless weight 210 is placed onto the inner-cylinder cover plate 220. After further 25 minutes. stainless weight 210 and inner-cylinder cover plate 220 are removed. Consequently. the predetermined layer 260 of the swollen absorbent o1 material for the GBD measurement has been prepared. The inner-cylinder 270 with the absorbent material gel layer 260 is immediately transferred to the Burst Tester for BBS test.

Referring to Figure 6. inner-cylinder 270 with an absorbent material gel layer 260 is positioned on lower clamp platen 280 and is fixed pneumatically with upper clamping platen 300. Using a break sensitivity of 10.00 g and a test speed of 5.00 inch/minutes and is Initiating the test by pressing the Test switch. The moving crosshead 320 moves up until polished stainless steel ball-shaped probe 290 penetrate absorbent material gel layer 260. After a sample burst is registered, moving crosshead 320 returns to start position. The BBS is expressed as peak load grams. The average of three determinations should be reported. -o 4. Compression Recovery (CR) Test This test determines the recovery from compression of an absorbent material that is swollen in Jayco synthetic urine. Recovery of compression (RC) is the extent that an absorbent material at wet state has returned to its original shape when subjected to the compression under procedures specified in this test method. RC of an absorbent material is s used for evaluation of the wet integrity of an absorbent material that is swollen in Jayco synthetic urine, and is related to the ability of an absorbent material at wet state to ret me its original shape after being subjected to tensional and torsional forces of varying intensity and direction during normal use. RC is also related to the tightness or snugness of an absorbent material at wet stale.

"o Sampling apparatus A suitable sampling apparatus for RC measurement is similar to the apparatus used s* in the BBS test (as shown in Figure 5) but is higher in height than the latter. The apparatus "for RC measurement comprises an inner-cylinder 270 which is used to contain an absorbent material layer 260. an outside-cylinder 230. a TEFLON flat-bottomed tray 240. an inner-" 35s cylinder cover plate 220. and a stainless weight 210. The inner-cylinder 270 is bored from a transparent LEXAN rod (or equivalent, for example Acrylic rod) and has an inner diameter Elio7 32 of 6.00 cm (area 28.27 cm 2 llh a wall thickness of approximately 0.5 cm. and a height of approximately 2.00 cm. The outside-cylinder 230 is bored from a transparent LEXAN rod (or equivalent. for example Acrylic rod) and has an inner diameter that is slightly larger than the outside diameter of the inner-cvlinder 270. so that the inner-cylinder 270 fits within S the outside-cylinder 230 and slides freely. Outside-cylindcr 230 has a wall thickness of approximately 0.5 cm. and a height of approximately 1.00 cm. The bottom of the outsidecylinder 230 is faced with a No. 400 mesh stainless-steel screen 250 that is biaxially stretched to tautness prior to attachment. Inner-cylinder cover plate 220 is made of glass plate with a thickness of 8.00cm and a weight of 530g. Stainless weight 210 has a weight of o1 1672g.

Compression Tester A Handy-type Compression Tester (KES-G5, made by Kato Tech Co.. Ltd.. Kyoto) is used in this method. Referring to Figure 7. the mechanical pan of this apparatus comprises a compression plate 310. a load indicator 350 that is connected to compression I plate 310. a drive mechanism 360. and a specimen stand 320. A load indicator 350 is capable of showing the total load (gflcm 2 carried by the test specimen. A compression plate 310 is circular plate with a area of 2.00cm 2 a thickness of0.40 cm. A driving mechanism 360 is capable of imparting to the compression plate 310 a uniform and steady controlled compression/recovery rate (cm/sec.).

Procedure Inner-cylinder 270 is inserted into outside-cylinder 230. 2.8 g aliquot of an S. absorbent material is added to the inner-cylinder 270 and dispersed evenly on the 400 mesh stainless screen 250 of the bottom via gently shaking and/or tapping of the assembled cylinders. The assembled cylinders with absorbent material are tansferred to TEFLON flats bottomed tray 240. and inner-cylinder cover plate 220 is positioned onto inner-cylinder 270.

56 Milliliters of Jayco synthetic urine is added to TEFLON flat-bottomed tray 240. Jayco synthetic urine from TEFLON flat-bottomed tray 240 passes through the stainless screen 250. All of the applied urine is absorbed by the absorbent material 260 for 5 minutes. Then the stainless weight 210 is placed onto the inner-cylinder cover plate 220. After nrther 25 o minutes. stainless weight 210 and inner-cylinder cover plate 220 are removed.

~Consequently. the predetermined layer 260 of the swollen absorbent material for the GBD measurement has been prepared. The inner-cylinder 270 with the absorbent material gel layer 260 is immediately transferred to the Compression Tester for RC test.

Inner-cylinder 270 with an absorbent material gel layer 260 is immediately .s positioned on specimen stand 320 of the Handy-type Compression Tester as shown in Figure 7. Compression plate 310 is positioned on to absorbent material gel layer 330 suriac but L: i-i:i~T~ wAithout compressing lte specimen (0 gf/cm 2 load at 0 cm compression depth). The compression depth is selcted itt tile range from 0 to 1.00 cmi. the comprcssiontccOveTT rate is selected at 0 .01 cm/sec. and the Load sensitivitV is selected at 10 gf. Start the test by pushing start switch of the Tester- Drive mechanism 360 drives compression plate 3 10 to s compress an absorbent material gel layer 330 at a speed of 0.01 cmjsec. till the con.pression depth reaches 1.00 cm. and thien tile compression plate 3 10 returns at the tame speed as compression to the original position. The load (gf/cm 2 and depth (cm) are recorded by using a XCY.Recordcr. Compression recovery (CR) is expressed as the percentage Of recovery work (gfctm2) to compression work (gfcnt/cm 2 As showns in Figure 8. recovery work to crsod o the area (5r) that is enclosed by the recovery curve. AB ln n o~f~ asis. Compression woark corresponds to the area that is enclosed by the compression curve.

AB line and horizontal axis, and is equal to the total area of Sc Sr. where Sc corresponds to the area that is enclosed by the compression curve, and the recovery curve. Therefore.

RC

can be calculated [rom tile following equation: Is RC -Sr(Sc +Sr) X The average of three determiniationts should be reported, Gel Volume Gel volume of a hydrogcl4forming absorbent polymer is defined as its free-swell absorbenlt capacity when swollen in an excess of Jayca synthetic urine. It provides a measure of the maximum absorbent capacity of the polymer under condition~s of use where the pressure-s on the polymer are relatively low. For most hydrogel-form~ing absorbent polymers.

gel volume is determined by the method described in U.S. Reissue Patent 32,649 (Branldt et al). reissued April 19. 1933 (herein incorporated by reference) but using the Jayco Synithetic is Urine described above. All of the chemicals are of regent grade The pH of the synthetic urine is in the rage of 6.0 to 6.4. The gel volume is calculated on a daty-weight basis. The dry weight msed in the gel volume calculation is deterinend by oven drying the hydrogelforming absorbent polymer at 105*C for three hours.

Ao 6. Exlrtactable Component The percentage of extsractable polymer in caaboxylic acid based hydrogel-forining polymers is determiuned by the Extractable Polymer Content DEittlilatiofl Carboxylic Acid Based FHvdrogel.Forming Polymers method described in U.S. Reissue Patent -32.649 (Brandt et reissued April 19. 1988 (herein incorporated by referenic), but usin g 0.91/ saline 35 solution, filtering the supernatant through a Whatanan 0.7 micron GFIF glass anierofiber filter Catalog 01825-125) or equivalent, and calculating the extractable polymer on a C.

*OC*

S 4 Nt, now drvy-weight basis- It is also noted that in U-S- Reissue Patent 32.649 thZt V. should refer to the volume of base and Vb should rcfer to the volumie of acid.

G. Ectamples of Absorbent Materials PRECURSOR PARTICLE EXAMPLE An aqueous monomer solution is prepared contsisting of 4O g of partiailv neutralized acrylic acid having a 75 mol% portion thereof neutralized with caustic soda. 3.7 g of NXN'methylene-bis-acrylamide. and.6000 g of waler. The aqueous monomer solution to is led into the reaction vessel, which is subsequently purged with nitrogen gas to remove the remaining entrapped -ir from the reaction system. Then. the mixt-ure was sfirrcri and heated to about 45'C. and a solution of 20.Sgof 2.2-azo-bis-(2-amidinopropafle)-dihydlochloflde in 100 g of water is added thereto as a polymerization iniitiator. Polymerization begins about mninutes after the addition of the polymerization initiator. With the progress of the is polymerization, the aqueous monomer solution gives rise to a soft water-containing gel. The inner temperature of the reaction system is kept at 80 90*C for hours to lfurther complete the polymerization. A swollen absorbent getting polymer is formed. The resultant swollen absorbent getting polymer thus obtained is spread on a standard 950 size metal gauge and dried with a hot air at 150'C The dried parliCleS are pulverized with a ltanmcr type crusherc ni and sifted with a standard 020 sieve (850 microns) to obtain particles that pass through the standard #20 sieve. As a result, dry white precursor absorbent gelling particles are obtained.

Exmple I A solution is prepared consisting of 250 g of polyallyarninc solution wAitha is concent~ration of 10%h by weight (PAA-C. supplied from Ninto Boseki Co. Ltd., Tokyo). '1600 g of ethanol. The solution is applied to 2500 g of the precursor particles made in accordance with the Precursor Particle Extample in a 20-liters evaporator flask. The prccursor particles have a particle size such that the precursor particles pass through a standard #20 sieve (850 microns) and ame retaned on a standard N100 sieve (150 mictrons). The mixture is s thoroughly mixed with a spatula until all of the prcur atce r etdwt h bv solution-. The solvent included in the resultant -mixtuxr is evaporated with: a rotary evaporator (EYELA N-I I M~e. available from TOKYO RDLAKDWA CO.. LTD.. Tokyo) at 0 C The resultant product is vacuum dried at 100 OC: for 3 hours. The dried absorbent material is pulverized with a hammer rtp crusher and sifted with a standard 920 sieve (850 Is microns) to obtain particles that pass through the standard 020 sieve. As a result, dry white particles of the resultanit absorbent material (Ey- 11) aeobtainedL In comparison of the

ON

properies of the precursor particles nd (lie absorbent mnterial (Ex- z1). the gel volume.

BBS v-alue and RC value of the precursor particles are 4.t0gig. 17 d and 99/. respectively.

while the gel volume. BBS v-alue and RC valuc or the absorbent nntenal (Ex. 0 1) are 39-2 gig. 160 gf and 62% respectively.

Example 2 Absorbent gelling particles obtained from commeria sources are used in this example. 25DO Gram of Aquatic CA L76lf (lot 4N22-029) supplied from Nippon Shokubai Co. Ltd.. Osaka. Japan. i~r t;!a-cd in a 20-liters rotary evaporator flask. L761f is a to surface-crosslinked absorbent gelling particle. A solution consisting of 250 g of polyally-amine solution %Iiih a concentration of 10% by weight (PAA-C. supplied from Nitto Boseki Co. Ltd-. Tokyo). 1600 g of ethanol is applied to the flask. The mixture is thoroughly mnixed with a spaiula until all of the precursor particles are wetted with the above solution.

The solvent included in the resultant mi.,ture is evaporated with a rotary evaporator (EYELA 1) N-1I type, available from TOKYO RIKAKIKAI CO.. LTD.. Tokyo) at 60 0 C. The rcsWltn 6 product is vacuum dried at 100 OC for 3 hours. The dried absorbent material is pulverized wuith a hammer type crusher and sifted with a standard 020 sieve (1150 microns) to obtain particles that pass through the standard #20 sieve. As a result, dry while particles of the resultant absorbent material (Ex. M2) are obtained. The CR curve for the absorbent material S is shown in Figure 9. By conrast, the CR curve for L761f is show in Figure 10. A comparison table for showing the properties of these materials is summarized in Table I below: Table I Sample Gel GBD F B CR Extractable L76Lf 37-5 1.09 4 7 12.3 36.2 0.75 t 2.1 138 S1 8.9 Example 3 Absorbent gelling particles obtained from comrueresal sour=s art used in tllis example. 100 Gram of Aqualie CA 1-7617 (lotE# 4E28-012) supplied from Nippon Shokubai Co. Ltd.. Osaka. japan. is placed in a Kitchen-typ Mixer. A solution is prepared contsisting 3o of 10 g of potyallyamine solution w~ith a concentration of 10% by wight (PAA-C. supplied from Nitto Boseki Co. Lid. Dsaka). and 20 g of ethanol- After 2 portion of the solution is

RI

-36.

sprayed onto the absorbentt getting particles with a spraver (rtype 24-182.01- ava3ilable from luchi Seicido Co.- Ltd-. Osaka)- the mi'xcr is opera ted ror aperod of about 4 minutes. Then more solution is spryed. and the mixer is operted 2gain for another 4minutes. Repeating the sprivingimixing tiocesses till all the solution ar.- sprayed on to the absorbeit Sellinga patice..The esutan miture is dried wi2h n un oven- at about 160-C for about 3 hours. The dried particles are pulverizcd wvith a harmer cype crusher and sifted w-ih a prpriso h eutn bobn otr E.13 nsoni alsndard 1120 sieve (850 microns) to abtain particles that paiss through the stndard sieve. As a result-d.%-white particles of the rcsultant absorbeti material arc obtained-, The -proertes fth rml~n[absrbet mteril (x.-03)are ho~ inTabe 2

C

AVI,

Sample Gel olunic L76Ir 36.4L Ex. #3 35.0

GBD

1-07m~ IS7 Table 2 SFC BBS CR Etaa~ (10-7cm' (g %)cight 91 21 I iL 45 124~ 55

I

Claims (15)

1. An absorbent material having an improved absorbent property, including a mixture of a plurality of absorbent gelling particles including a water- insoluble, water-swellable polymer, and an absorbent property modification polymer reactive with at least one component included in a urine, characterised in that said mixture is made by applying a solution containing an organic solvent, water and said absorbent property modification polymer onto said plurality of absorbent gelling particles, wherein the weight ratio of said organic solvent to said water is at least 50:50, and (ii) removing a portion of said organic solvent and water from the applied absorbent gelling particles.

2. The absorbent material of Claim 1 characterised in that said organic solvent is a polar organic solvent.

3. The absorbent material of Claim 1 or 2 characterised in that the weight ratio of said organic solvent to said water is from 70:30 to 98:2.

4. The abscrbent material of any one of Claims 1 to 3 characterised in that said absorbent property modification polymer is a cationic polymer. The absorbent material of Claim 4 characterised in that said absorbent property modification polymer is a polyamine or polyimine material.

6. The absorbent material of any one of Claims 1 to 5 characterised in that said at least one component included in a urine is an anion having an ionic charge number of at least two, and said cationic polymer is reactive with said anion in a urine.

7. The absorbent material of Claim 6 characterised in that said anion is a phosphate ion, a sulfate ion, or a carbonate ion, and said cationic polymer is reactive with said phosphate ion, sulfate ion, or carbonate ion in a. urine. r~oi r r r ro c re 1; rii r r rrre IlI .1~ n~2

8. The absorbent material according to any one of Claims 1 to 7 characterised in that said absorbent modification polymer is a polyamine is selected from the group consisting of polymers having primary amine groups; polymers having secondary amine groups; polymers having tertiary amine groups; and mixtures thereof.

9. The absorbent material of any one of Claims 1 to 8 characterised in that said organic solvent is selected from the group consisting of a methanol, an ethanol, a propanol, an acetone, a dimethylformamide (DMF), a dimethylsufoxide (DMSO), and a hexylmethylphosphoric triamide (HMPT). The absorbent material of any one of Claims 1 to 9 characterised that, when said absorbent material swells by absorbing urine and is formed into a layer of the swollen absorbent material under a load of predetermined weight, said layer of the swollen absorbent gelling particles has a Gel Bulk Density (GBD) value of below 0.95 g/cm 3 in the GBD test, a Saline Flow Conductivity (SFC) value of at least 20 x 10-7 cm3sec/g in the SFC test, a Ball Burst Strength (BBS) value of at least 30 gf in the BBS test, and a Compression Recovery (CR) value of at least 15% in the CR test.

11. An absorbent article including: liquid pervious topsheet; a liquid impervious backsheet; and an absorbent core positioned between said topsheet and said backsheet, characterised in that said absorbent core includes at least one absorbent material of any one of Claims 1 to 10 in said absorbent core.

12. The absorbent article of Claim 11 characterised in that said absorbent core includes at least one absorbent material of any one of Claims 1 to 10 in a S.:io concentration of from 60 to 100% by weight in said absorbent core. IT roo

13. A method for making an absorbent material having an improved absorbent property, characterised in that it includes the steps of: preparing a solution containing an organic solvent, water and an absorbent property modification polymer, reactive with at least one component included in a urine, wherein the weight ratio of said organic solvent to said water is at least 50:50; applying an amount of said solution onto a plurality of absorbent gelling particles including a water-insoluble, water-swellable polymer; and removing a portion of said organic solvent and water from the applied absorbent gelling particles.

14. The method of Claim 13 characterised in that said organic solvent is a polar organic solvent. The method of Claim 13 or 14 characterised in that the weight ratio of said organic solvent to said water is from 70:30 to 98:2.

16. The method of any one of Claims 13 to 15 characterised in that said at least one component included in a urine is an aniun having an ionic charge number of at least two, and said cationic polymer is reactive with said anion in a urine.

17. The method of Claim 16 characterised in that said anion is a phosphate ion, a sulfate ion, or a carbonate ion, and said cationic polymer is reactive with said phosphate ion, sulfate ion, or carbonate ion in a urine. S 18. The method of any one of Claims 13 to 17 characterised in that said j cationic polymer is a polyamine or polyimine material. l 1 l 41

19. The method of Claim lb characterised in that said polyamine is selected from the group consisting of polyr,.ers having primary amine groups; (b) polymers having secondary amine groups; polymers having tertiary amine groups; and mixtures thereof. The method of any one of Claims 13 to 19 characterised in that said organic solvent is selected from the group consisting of a methanol, an ethanol, a propanol, an acetone, a dimethyformamide (DMF), a dimethylsufoxide (DMSO), and a hexymethylpphosphoric triamide (HMPT). DATED this 29th day of December, 1998 THE PROCTER GAMBLE COMPANY S WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA S LCG/JGC:BA DOC 024 AU1608195.WPC t c sf 'f 1 i:: F*.