Postcrosslinking of water-absorbing polymers

• US 20070161759A1
• Filed: 02/18/2005
• Published: 07/12/2007
• Est. Priority Date: 02/24/2004
• Status: Active Grant

• Current Assignee: BASF AG (BASF SE)
• Original Assignee: BASF AG (BASF SE)
• Inventors: Riegel, Ulrich, Daniel, Thomas, Elliott, Mark, Weismantel, Matthias, Hermeling, Dieter
• Granted Patent: US 7,981,969 B2
• Time in Patent Office: Days
• US Class Current: 525/375
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking

Abstract

The invention concerns a process for producing water-absorbing polymer, which comprises a base polymer A being mixed with a first aqueous solution B of at least one surface postcrosslinker and a second aqueous solution C of at least one polyvalent cation and thermally treated, wherein said base polymer A is based on at least 50% neutralized acid-functional monomer and said solutions B and C are metered wholly or partly concurrently through separate nozzles whereby a water-absorbing polymer having a high saline flow conductivity value is obtained.

Claims

1. A process for producing a water-absorbing polymer comprising a base polymer A being mixed with a first aqueous solution B of at least one surface postcross-linker and a second aqueous solution C of at least one polyvalent cation and thermally treated, wherein said base polymer A is based on an at least 50% neutralized acid-functional monomer and said solutions B and C are metered wholly or partly concurrently through separate nozzles, the concentration of the at least one surface postcrosslinker on said base polymer A being in the range from 0.01% to 0.5% by weight and the concentration of the at least one polyvalent cation on said base polymer A being in the range from 0.001% to 0.5% by weight, based in each case on said base polymer A.

2. The process of claim 1 wherein said solutions B and C are metered concurrently through separate nozzles.

3. The process of claim 1 wherein said solution B comprises a cosolvent.

4. The process of of claim 1 wherein said solution B of said surface postcrosslinker comprises an oxazolidone.

5. The process of claim 1 wherein said solution B comprises at least two mutually distinct surface post-crosslinkers.

6. The process of claim 1 wherein said solution B comprises at least one surface postcrosslinker different from a polyol and at least one polyol.

7. The process of claim 1 wherein said base polymer A has a deagglomerating assistant added to it.

8. The process of claim 7 wherein said deagglomerating assistant is sorbitan monococoate, sorbitan monolaurate, or a mixture thereof.

9. The process of claim 7 wherein said deagglomerating assistant is added to said aqueous solution B or to said aqueous solution C.

10. The process of claim 7 wherein the deagglomerating assistant is metered such that the surface tension of an aqueous extract of the swollen water-absorbing polymer after addition of said deagglomerating assistant is at least 0.065 N/m.

11. The process of claim 1 wherein the concentration of the at least one surface postcrosslinker in said solution B, based on said solution B, is not more than 30% by weight.

12. The process of claim 1 wherein the concentration of the at least one surface postcrosslinker on said base polymer A, based on said base polymer A, is in the range from 0.1% by weight to 1% by weight.

13. The process of claim 1 wherein the concentration of the at least one polyvalent cation in said solution C, based on said solution C, is not more than 12% by weight.

14. The process of claim 1 wherein the concentration of the at least one polyvalent cation on said base polymer A, based on said base polymer A, is in the range from 0.001% by weight to 0.5% by weight.

15. The process of claim 1 wherein the concentration of the at least one polyvalent cation on said base polymer A, based on said base polymer A, is in the range from 0.02% by weight to 0.1% by weight.

16. The process of claim 1 wherein the ratio of said solution B to said solution C is in the range from 10:

1 to 1;

10.

17. The process of claim 1 wherein the total amount of said solutions B and C is in the range from 2.5% to 6.5% by weight, based on said base polymer A.

18. The process of claim 1 wherein said base polymer A is a partially neutralized and crosslinked polyacrylic acid.

19. The process of claim 1 wherein said base polymer A has a pH in the range from 5.6 to 6.2.

20. The process of claim 1 wherein said solutions B and C are sprayed onto said base polymer A and the average diameter of the sprayed drops is in the range from 50 to 100 μ

m.

21. A water-absorbing polymer prepared by the process of claim 1, said polymer having a saline flow conductivity of not less than 80×

10<sup>−

7</sup> cm³s/g and comprising not less than 80% by weight of particles between 150 and 600 μ

m in size.

22. The polymer of claim 21 comprising not less than 80% by weight of particles between 150 and 500 μ

m in size.

23. The polymer of claim 21 comprising not less than 95% by weight of particles between 150 and 500 μ

m in size.

24. The polymer of claim 21 having a saline flow conductivity of not less than 100×

10<sup>−

7</sup> cm³s/g.

25. The polymer of claim 21 having a saline flow conductivity of not less than 120×

10<sup>−

7</sup> cm³s/g.

26. The polymer of claim 21 having a centrifuge retention capacity of not less than 24 g/g and an absorbency under load at 4830 Pa of not less than 21 g/g.