Method for the secondary cross-linking of hydrogels with 2-oxotetrahydro-1,3-oxazines

• US 6,657,015 B1
• Filed: 05/17/2001
• Issued: 12/02/2003
• Est. Priority Date: 11/26/1998
• Status: Expired due to Term

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Riegel, Ulrich, Daniel, Thomas, Weismantel, Matthias, Frenz, Volker, Engelhardt, Fritz
• Primary Examiner(s): WILSON, DONALD R
• Application Number:
  US09/831,382
• Time in Patent Office: 929 Days
• Field of Search: 525/329.9, 525/375
• US Class Current: 525/329.9
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 8/30 Introducing nitrogen atoms or nitrogen-containing groups
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 2333/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking

Abstract

Liquid-absorbent polymers are prepared by a process for the gel and/or surface postcrosslinking of water-absorbent polymers by the polymer being treated with a surface postcrosslinking solution and being postcrosslinked and dried during and after the treatment by raising the temperature, wherein the crosslinker comprises a compound of the formula I

where R¹ is hydrogen, C₁-C₄-alkyl, C₁-C₄-hydroxyalkyl, trialkylsilyl or acetyl and R², R^2′, R³, R^3′, R⁴, R^4′ are each independently hydrogen, C₁-C₁₂-alkyl, C₂-C₁₂-alkenyl or C₆-C₁₂-aryl, dissolved in an inert solvent, and are used in hygiene articles, packaging materials and nonwovens.

Claims

1. A process for the gel or surface postcrosslinking of water-absorbing polymers, comprising treating polymers with a surface postcrosslinking solution containing a crosslinker, and postcrosslinking and drying by increasing the temperature, wherein the crosslinker comprises a compound of the formula I

wherein R¹ is hydrogen, C₁-C₄-alkyl, C₁-C₄-hydroxyalkyl, trialkylsilyl or acetyl;

R², R^2′

, R³, R^3′

, R⁴, R^4′

are each independently hydrogen, C₁-C₁₂-alkyl, C₁-C₁₂-alkenyl or C₆-C₁₂-aryl, dissolved in an inert solvent.

2. The process of claim 1, wherein the water-absorbing polymer is selected from the group consisting of a polymeric acrylic acid, polymeric acrylic esters, graft copolymer of acrylic acid and a water-soluble polymer matrix, and a graft copolymer of acrylic esters and a water-soluble polymer matrix.

3. The process of claim 1, which further comprises a catalyst comprising an acid or an anhydride thereof when the polymers are treated with the surface postcrosslinking solution.

4. The process of claim 3, wherein the catalyst is selected from the group consisting of boric acid;

sulfuric acid;

hydroiodic acid;

phosphoric acid;

tartaric acid;

acetic acid;

toluenesulfonic acid;

an acidic salt thereof;

a polymeric form of boric acid;

a polymeric form of sulfuric acid;

a polymeric form of phosphoric acid; and

an anhydride of boric acid, sulfuric acid, phosphoric acid, tartaric acid, acetic acid, or toluenesulfonic acid.

5. The process of claim 1, wherein the inert solvent is water, a mixture of water with monohydric alcohol is from 10 to 90% by weight of the alcohol, or a mixture of water with a polyhydric alcohol is from 10 to 90% by weight of the alcohol.

6. The process of claim 1, wherein the crosslinker is in an amount of from 0.01 to 5% by weight, based on the mass of the water-absorbing polymer.

7. The process of claim 1, wherein the crosslinker is in an amount of from 0.01 to 1% by weight, based on the mass of the water-absorbing polymer.

8. The process of claim 1, wherein the crosslinker is in an amount of from 0.05 to 0.5% by weight, based on the mass of the water-absorbing polymner.

9. The process of claim 1, wherein the postlinking and drying temperature is from 50 to 250°

C.

10. The process of claim 1, wherein the postlinking and drying temperature is from 50 to 200°

C.

11. The process of claim 1, wherein the postlinking and drying temperature is from 100 to 180°

C.

12. The process of claim 1, wherein the crosslinker is 2-oxotetrahydro-1,3-oxazine.

13. The process of claim 1, wherein the crosslinker is N-methyl-2-oxo-tetra hydro-1,3-oxazine.

14. The process of claim 5, wherein the monohydric or polyhydric alcohol is selected from.the group consisting of methanol, ethanol, isopropanol, ethylene glycol, 1,2-propanediol, and 1,3-propanediol.

15. The process of claim 1, wherein the postcrosslinking solution is in an amount of from 1 to 20% by weight based on the mass of the water-absorbing polymer.

16. The process of claims 1, wherein the postcrosslinking solution is in an amount of from 0.5 to 10% by weight based on the mass of the water-absorbing polymer.