Hydrogel-forming polymer compositions for use in absorbent structures

Claim 2

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of (a) from about 50 mole percent to 99.999 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers; and (b) from about 0.001 mole percent to 5 mole percent of a cross-linking agent; wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

Claim 3

A hydrogel-forming polymer composition according to claim 1 wherein (a) said composition has a degree of neutralization of at least about 50%; (b) said composition has a gel volume of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer; (c) the hydrogel formed from said composition has a gel strength such that the hydrogel exhibits a shear modulus of from about 2500 to 92,000 dynes/cm 2 ; (d) said composition has an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer; and (e) said composition has an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer.

Claim 4

A hydrogel-forming polymer composition according to claim 2 wherein (a) said acid-group containing monomers are selected from acrylic acid, methacrylic acid, and 2-acrylamido-2-methylpropane sulfonic acid, and combinations thereof; and (b) said cross-linking agent is selected from (i) di- and polyvinyl compounds; (ii) di- and polyesters of unsaturated mono- and polycarboxylic acids with polyols; (iii) bisacrylamides; (iv) carbamyl esters obtained by reacting polyisocyanates with hydroxyl group-containing monomers; (v) di- and polyallyl ethers of the polyols; (vi) di- and polyallyl esters of polycarboxylic acids; (vii) esters of unsaturated mono- and polycarboxylic acids with mono-allyl esters of polyols; and (viii) di- and triallyl amines

Claim 5

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of: (a) from about 75% to 99.99% mole percent of polymerized acrylic acid monomers; and (b) from about 0.01% to 3% mole percent of a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine; wherein said composition has at least 50% of its acrylic acid groups neutralized with sodium cations and is substantially free of graft polymerized polymer moieties, and further wherein said polymer composition has a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

Claim 6

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of: (a) from about 75% to 99.99% mole percent of polymerized acrylic acid monomers; and (b) from about 0.01% to 3% mole percent of a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine; wherein said composition has at least 50% of its acrylic acid groups neutralized with sodium cations and is substantially free of graft polymerized polymer moieties, and further wherein said polymer composition has a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

Claim 7

A hydrogel-forming polymer composition according to claim 4 wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0.

Claim 8

A hydrogel-forming polymer composition according to claim 4 wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0; and wherein the relationship between gel volume, v, and shear modulus, s, is defined by the equation: log s≧-2.494 log v+8.090.

Claim 9

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of (a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers; and (b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent; wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0.

Claim 10

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of (a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers; and (b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent; wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0.

Claim 11

A hydrogel-forming polymer composition according to claim 7 wherein (a) said composition has a degree of neutralization of at least about 50%; (b) said composition has a gel volume of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer; (c) the hydrogel formed from said composition has a gel strength such that the hydrogel exhibits a shear modulus of from about 2500 to 92,000 dynes/cm 2 ; (d) said composition has an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer; and (e) said composition has an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer.

Claim 12

A hydrogel-forming polymer composition according to claim 8 wherein (a) said acid group-containing monomers are selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and combinations thereof; and (b) said cross-linking agent is selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate, and triallyl amine.

Claim 13

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of (a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers; and (b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent; wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0; and further wherein the relationship between gel volume, v, and gel strength as measured by shear modulus, s, is defined by the equation: log s≧-2.494 log v+8.090.

Claim 14

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of (a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers; and (b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent; wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0; and further wherein the relationship between gel volume, v, and gel strength as measured by shear modulus, s, is defined by the equation: log s≧-2.494 log v+8.090.

Claim 15

A hydrogel-forming polymer composition according to claim 10 wherein (a) said composition has a degree of neutralization of at least about 50%; (b) said composition has a gel volume of at least about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer; (c) the hydrogel formed from said composition has a gel strength such that the hydrogel exhibits a shear modulus of from about 2500 to 92,000 dynes/cm 2 ; (d) said composition has an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer; and (e) said composition has an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer.

Claim 16

A hydrogel-forming polymer composition according to claim 11 wherein (a) said acid group-containing monomers are selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and combinations thereof; and (b) said cross-linking agent is selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine.

Claim 17

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel or hydrogel-forming polymer material suitable for use in absorbent products, said process comprising (a) preparing a reaction mixture consisting essentially of from about 5% to 35% by weight of unsaturated, polymerizable, acid group-containing monomers in the free acid form, from about 0.001 mole percent to 5 mole percent, based on moles of polymerizable monomers, of a cross-linking agent and from 0 mole percent to about 5 mole percent, based on the moles of polymerizable monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties; (b) subjecting said aqueous reaction mixture to polymerization conditions which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polymer material which, upon subsequent neutralization to a degree of neutralization of at least 50% and upon subsequent drying, has or would have, a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer; and a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation: e≦0.23v-3.0; and (c) neutralizing at least a portion of the acid groups of the polymer material formed in the aqueous reaction mixture with salt-forming cations to form a partially neutralized polymer material having a degree of neutralization of at least about 25%.

Claim 18

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel or hydrogel-forming polymer material suitable for use in absorbent products, said process comprising (a) preparing a reaction mixture consisting essentially of from about 5% to 35% by weight of unsaturated, polymerizable, acid group-containing monomers in the free acid form, from about 0.001 mole percent to 5 mole percent, based on moles of polymerizable monomers, of a cross-linking agent and from 0 mole percent to about 5 mole percent, based on the moles of polymerizable monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties; (b) subjecting said aqueous reaction mixture to polymerization conditions which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polymer material which, upon subsequent neutralization to a degree of neutralization of at least 50% and upon subsequent drying, has or would have, a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer; and a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation: e≦0.23v-3.0; and (c) neutralizing at least a portion of the acid groups of the polymer material formed in the aqueous reaction mixture with salt-forming cations to form a partially neutralized polymer material having a degree of neutralization of at least about 25%.

Claim 19

A process according to claim 13 wherein (a) the acid groups of the polymer material formed in the aqueous reaction mixture are neutralized with salt-forming cations to form a polymer material having a degree of neutralization of at least about 50%; (b) said neutralized polymer material has a gel volume of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer; (c) said neutralized polymer material forms a hydrogel having a gel strength such that said hydrogel exhibits a shear modulus of about 2500 to 92,000 dynes/cm 2 ; and (d) said neutralized polymer material has an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer and an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer.

Claim 20

A process according to claim 14 wherein (a) said acid group-containing monomers are selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methyl propane sulfonic acid, and combinations thereof; and (b) said cross-linking agent is selected from (i) di- and polyvinyl compounds; (ii) di- and polyesters of unsaturated mono- and polycarboxylic acids with polyols; (iii) bisacrylamides; (iv) carbamyl esters obtained by reacting polyisocyanates with hydroxyl-group containing monomers; (v) di- and polyallyl ethers of polyols; (vi) di- and polyallyl esters of polycarboxylic acids; (vii) esters of unsaturated mono- and polycarboxylic acids with mono-allyl esters of polyols; and (viii) di- and triallyl amines.

Claim 21

A process according to claim 15 wherein the aqueous reaction mixture comprises (a) from about 8% to 24% by weight of the acid group-containing monomers; (b) from about 0.01 mole percent to 3 mole percent of the cross-linking agent; and (c) from about 0.001 mole percent to 0.5 mole percent of the free radical initiator; and wherein the polymerization conditions to which said reaction mixture is subjected include a polymerization temperature of from about 5° C. to 40° C.

Claim 22

A process according to claim 16 wherein the free radical initiator comprises a peroxygen compound or comprises a redox initiator system formed by combining a peroxygen compound with a reducing agent.

Claim 23

A process according to claim 17 wherein the peroxygen compound initiator is selected from sodium, potassium, and ammonium persulfates, caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxides, t-butyl diperphthalate, t-butyl perbenzoate, sodium peracetate and sodium percarbonate, and wherein the redox initiator system comprises the combination of any of said peroxygen compound initiators with a reducing agent selected from sodium bisulfite, L-ascorbic acid and ferrous salts.

Claim 24

A process according to claim 18 wherein the initiator, or a component thereof, is incrementally added to the aqueous reaction mixture only in such amounts as are sufficient to promote complete polymerization of the acid group-containing monomers and cross-linking agents.

Claim 25

A process according to claim 13 which comprises the additional step of drying the polymer material produced in said aqueous reaction mixture.

Claim 26

A process according to claim 20 wherein said drying step is accomplished either by subjecting said polymer material to a temperature of from about 40° C. to 150° C. for a period of time sufficient to form a semi-solid mass of hydrogel-forming polymer material, by treating said polymer material with a dewatering solvent or by removing water from said polymer material via azeotropic distillation.

Claim 27

A process according to claim 13 wherein the aqueous reaction mixture is suspended in the form of droplets in a water-immiscible organic solvent, and wherein said droplets are subjected to polymerization conditions using inverse suspension or inverse emulsion polymerization procedures.

Claim 28

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel-forming polymer material suitable for use in absorbent products, said process comprising (a) preparing a reaction mixture consisting essentially of from about 8% to 24% by weight of polymerizable acrylic acid monomers in the free acid form, from about 0.01 mole percent to 3 mole percent, based on total moles of polymerizable monomers, of a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine, and from about 0.001 mole percent to 0.5 mole percent, based on the total moles of acrylic acid plus cross-linking agent monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties; (b) subjecting said aqueous reaction mixture to polymerization conditions, including a temperature of from about 5° C. to 40° C., which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polyacrylic acid-based polymer material having, upon subsequent neutralization and drying, a gel volume, v, of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that said hydrogel formed from said polymer material exhibits a shear modulus, s, of from about 2500 to 92,000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer, a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation: e≦0.23v-3.0, and a relationship between gel volume, v, and shear modulus, s, defined by the equation: log s≧-2.494 log v+8.090; and (c) neutralizing at least a portion of the carboxyl groups of said polyacrylic acid-based polymer material formed in the aqueous reaction mixture with sodium cations to form a partially neutralized polymer material having a degree of neutralization of at least about 50%.

Claim 29

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel-forming polymer material suitable for use in absorbent products, said process comprising (a) preparing a reaction mixture consisting essentially of from about 8% to 24% by weight of polymerizable acrylic acid monomers in the free acid form, from about 0.01 mole percent to 3 mole percent, based on total moles of polymerizable monomers, of a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine, and from about 0.001 mole percent to 0.5 mole percent, based on the total moles of acrylic acid plus cross-linking agent monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties; (b) subjecting said aqueous reaction mixture to polymerization conditions, including a temperature of from about 5° C. to 40° C., which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polyacrylic acid-based polymer material having, upon subsequent neutralization and drying, a gel volume, v, of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that said hydrogel formed from said polymer material exhibits a shear modulus, s, of from about 2500 to 92,000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer, a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation: e≦0.23v-3.0, and a relationship between gel volume, v, and shear modulus, s, defined by the equation: log s≧-2.494 log v+8.090; and (c) neutralizing at least a portion of the carboxyl groups of said polyacrylic acid-based polymer material formed in the aqueous reaction mixture with sodium cations to form a partially neutralized polymer material having a degree of neutralization of at least about 50%.

Claim 30

An absorbent structure suitable for use in disposable absorbent articles, said absorbent structure comprising: (a) from about 50% to 98% by weight of said structure of hydrophilic fiber material; and (b) from about 2% to 50% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry, hydrogel-forming polymer material; wherein said polymer material has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer material, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming material.

Claim 31

An absorbent structure suitable for use in disposable absorbent articles, said absorbent structure comprising: (a) from about 50% to 98% by weight of said structure of hydrophilic fiber material; and (b) from about 2% to 50% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry, hydrogel-forming polymer material; wherein said polymer material has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties; and further wherein said polymer material, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming material.

Claim 32

An absorbent structure according to claim 24 wherein said hydrogel-forming polymer material (a) has a degree of neutralization of at least about 50%; (b) has a gel volume of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer; (c) forms a hydrogel material which exhibits a shear modulus of from about 2500 to 92,000 dynes/cm 2 ; (d) has an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer; and (e) has an extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer.

Claim 33

An absorbent structure according to claim 24 wherein the hydrophilic fiber material comprises from about 65% to 90% by weight of said structure and wherein said polymer particles comprise from about 10% to 35% by weight of said structure.

Claim 34

An absorbent structure according to claim 24 which has a density of from about 0.06 to 0.3 grams/cm 3 .

Claim 35

An absorbent structure according to claim 24 wherein said polymer material, prior to neutralization, comprises polymerized monomers selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methyl propane sulfonic acid and combinations thereof, cross-linked with a cross-linking agent selected from (a) di- and polyesters of unsaturated mono- and polycarboxylic acids with polyols, (b) bisacrylamides and (c) di- and triallyl amines.

Claim 36

An absorbent structure according to claim 28 wherein said absorbent structure has a density of from about 0.09 to 0.18 g/cm 3 , a basis weight of from about 0.02 to 0.12 g/cm 2 and wherein said absorbent structure comprises a mixture of wood pulp fibers and polymer particles having a particle size of from about 50 microns to 1 mm.

Claim 37

An absorbent structure according to claim 24 wherein, for the hydrogel-forming polymer particles, the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0.

Claim 38

An absorbent structure according to claim 24 wherein, for the hydrogel-forming polymer particles, the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0; and wherein the relationship between gel volume, v, and shear modulus, s, of the hydrogel formed from said particles is defined by the equation: log s≧-2.494 log v+8.090.

Claim 39

An absorbent article comprising: (a) a liquid impervious backing sheet; (b) a liquid pervious, relatively hydrophobic topsheet; and (c) an absorbent core comprising an absorbent structure according to claim 24 positioned between said backing sheet and said topsheet.

Claim 40

A diaper article comprising: (a) a liquid impervious backing sheet; (b) a relatively hydrophobic, liquid pervious topsheet; and (c) an absorbent core positioned between said backing sheet and said topsheet, said absorbent core comprising an absorbent structure which consists essentially of (i) from about 65% to 90% by weight of said structure of hydrophilic fiber material; and (ii) from about 10% to 35% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry hydrogel-forming polymer material comprising polymerized acrylic acid monomers, cross-linked with a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine; wherein said polymer material has at least 50% of its acrylic acid groups neutralized with sodium cations and is substantially free of graft polymerized polymer moieties, and further wherein said hydrogel-forming polymer material has a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, after 16 hours in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

Claim 41

A diaper article comprising: (a) a liquid impervious backing sheet; (b) a relatively hydrophobic, liquid pervious topsheet; and (c) an absorbent core positioned between said backing sheet and said topsheet, said absorbent core comprising an absorbent structure which consists essentially of (i) from about 65% to 90% by weight of said structure of hydrophilic fiber material; and (ii) from about 10% to 35% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry hydrogel-forming polymer material comprising polymerized acrylic acid monomers, cross-linked with a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine; wherein said polymer material has at least 50% of its acrylic acid groups neutralized with sodium cations and is substantially free of graft polymerized polymer moieties, and further wherein said hydrogel-forming polymer material has a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm 2 , an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, after 16 hours in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

Claim 42

A diaper article according to claim 33 wherein the absorbent core comprises an hourglass-shaped absorbent structure formed from an air-laid mixture of hydrophilic fiber material and hydrogel-forming polymer particles.

Claim 43

A diaper article according to claim 33 wherein the polymer-containing absorbent structure comprises an insert positioned underneath an upper layer of the diaper core, which upper layer is hourglass-shaped and consists essentially of wood pulp fiber material and from 0% to about 8% by weight of particles of hydrogel-forming polymer material.

Claim 44

A diaper article according to claim 33 wherein, for said polymer particles, the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0.

Claim 45

A diaper article according to claim 33 wherein, for said polymer particles, the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation: e≦0.23v-3.0 and wherein the relationship between gel volume, v, and shear modulus, s, of the hydrogel formed from said particles is defined by the equation: log s≧-2.494 log v+8.090.