Absorbent materials and absorbent articles incorporating such absorbent materials
View Patent ↗An absorbent material formed at least in part of a cross-linked polymer. The absorbent material has a centrifuge retention capacity as determined by a Centrifuge Retention Capacity Test of at least about 20 g/g and a gel bed permeability under load as determined by a Gel Bed Permeability Under Load Test of at least about 300×10 −9 cm 2 or a free swell gel bed permeability as determined by a Free Swell Gel Bed Permeability Test of at least about 2,500×10 −9 cm 2 . The cross-linked polymer may comprise either at least about 75 weight percent anionic polymer or at least about 75 weight percent cationic polymer. In one embodiment, the cross-linked polymer is surface treated with a water soluble non-cross-linked polymer having a potential for becoming charged opposite that of the cross-linked polymer.
1. A surface treated absorbent material comprising a superabsorbent material consisting essentially of a superabsorbent polymer consisting of
a) at least about 75% by weight of the superabsorbent polymer of an anionic polymer comprising functional groups selected from carboxyl groups, sulfonate groups, sulphate groups, sulfite groups, and phosphate groups; and
b) an internal crossliniking agent based on the polymerizable unsaturated acid group containing monomer, wherein the superabsorbent polymer has a degree of neutralization of greater than about 25%; wherein elements a) and b) are polymerized and prepared into superabsorbent polymer particles and further comprising the following surface additives to form surface treated superabsorbent polymer particles
i) from about 0.5% to about 5% by weight of surface crosslinking agent based on the superabsorbent polymer composition; and
ii) from about 0.63% to about 5% by weight of a non-cross linked cationic polymeric coating based on the superabsorbent polymer composition; wherein the superabsorbent material having a gel stiffness index of at least about 0.8.
2. A surface treated absorbent material as set forth in claim 1 wherein the surface treated absorbent material has a gel bed permeability (GBP) under load as determined by a Gel Bed Permeability Under Load Test of at least about 200×10 −9 cm 2 .
3. A surface treated absorbent material as set forth in claim 2 wherein the surface treated absorbent material has a gel bed permeability (GBP) under load as determined by the Gel Bed Permeability Under Load Test of at least about 400×10 −9 cm 2 .
4. A surface treated absorbent material as set forth in claim 2 wherein the surface treated absorbent material has a gel bed permeability (GBP) under load as determined by the Gel Bed Permeability Under Load Test of at least about 300×10 −9 cm 2 .
5. A surface treated absorbent material as set forth in claim 1 wherein the superabsorbent material has a centrifuge retention capacity (CRC) as determined by a Centrifuge Retention Capacity Test of at least about 20 g/g.
6. A surface treated absorbent material as set forth in claim 1 wherein the superabsorbent material has a centrifuge retention capacity (CRC) as determined by a Centrifuge Retention Capacity Test of at least about 25 g/g.
7. A surface treated absorbent material as set forth in claim 1 wherein the cationic polymer is polyvinyl amine.
8. A surface treated absorbent material as set forth in claim 1 wherein the superabsorbent material has a gel stiffness index of at least about 0.85.
9. A surface treated absorbent material as set forth in claim 1 wherein the surface treatment is applied to substantially the entire outer surface of the superabsorbent material.
10. A surface treated absorbent material as set forth in claim 1 wherein the surface treatment further comprises in the range of about 0.5 to about 5 grams weight of water per 1 gram weight of superabsorbent material.
11. A surface treated absorbent material as set forth in claim 1 wherein the surface treated absorbent material has a free swell gel bed permeability as determined by a Free Swell Gel Bed Permeability Test of at least about 2,000×10 −9 cm 2 .
12. A surface treated absorbent material as set forth in claim 11 wherein the surface treated absorbent material has a gel bed permeability (GBP) under load as determined by a Gel Bed Permeability Under Load Test of at least about 200×10 −9 cm 2 .
13. A method of making a surface treated absorbent material comprising a superabsorbent material consisting essentially of a superabsorbent polymer consisting of
a) at least about 75% by weight of the superabsorbent polymer of an anionic polymer comprising functional groups selected from carboxyl groups, sulfonate groups, sulphate groups, sulfite groups, and phosphate groups; and
b) an internal crosslinking agent based on the polymerizable unsaturated acid group containing monomer, wherein the superabsorbent polymer has a degree of neutralization of greater than about 25%; wherein elements a) and b) are polymerized and prepared into superabsorbent polymer particles and further comprising the following surface additives to form surface treated superabsorbent polymer particles
i) from about 0.5% to about 5% by weight of surface crosslinking agent based on the superabsorbent polymer composition; and
ii) from about 0.63% to about 5% by weight of a non-cross linked cationic polymeric coating based on the superabsorbent polymer composition; wherein said method comprising: solubilizing a water soluble cationic polymer in water to form an aqueous solution; and applying the aqueous solution to the outer surface of a superabsorbent material having a gel stiffness of at least about 0.8 and comprising a cross-linked polymer comprising at least about 75 weight percent anionic polymer.
14. A method as set forth in claim 13 further comprising removing water from the aqueous solution following application of the solution to the superabsorbent material to thereby leave cationic polymer on the surface of the superabsorbent material.
15. A method as set forth in claim 13 wherein the concentration of cationic polymer is in the range of about 0.05 to about 10 weight percent of the superabsorbent material.
16. A method as set forth in claim 13 wherein the solubilizing step comprises solubilizing the cationic polymer in at least about 0.5 to at least about 10 grams weight of water per 1 gram weight of superabsorbent material.
17. A method as set forth in claim 13 wherein the step of applying the aqueous solution to the outer surface of the superabsorbent material comprises mixing the aqueous solution and superabsorbent material together until the superabsorbent material has absorbed at least a portion of the aqueous solution.