Production process for water-absorbing agent

• US 6,265,488 B1
• Filed: 02/21/1999
• Issued: 07/24/2001
• Est. Priority Date: 02/24/1998
• Status: Expired due to Term

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Nakamura, Masatoshi, Fujino, Shinichi, Nagasuna, Kinya
• Primary Examiner(s): Wilson, Donald R.
• Application Number:
  US09/253,858
• Time in Patent Office: 884 Days
• Field of Search: 525/119, 525/329.5, 525/329.7, 525/384
• US Class Current: 525/119
• CPC Class Codes: B01J 20/267 Cross-linked polymers
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 2810/20 leading to a crosslinking, either explicitly or inherently
• CPC Class Codes: C08F 8/00 Chemical modification by after-treatment graft polymers, block polymers, crosslinking with unsaturated monomers or with polymers C08F251/00 - C08F299/00; of conjugated diene rubbers C08C

Abstract

The invention provides a process for producing a water-absorbing agent by using a crosslinking agent of high molecular weight, wherein the water-absorbing agent is excellent with good balance in respect to the absorption capacities under no load and under a heavy load and can display excellent absorption properties even if the weight percentage of the water-absorbent resin (resin concentration) is high when the water-absorbent resin is used for materials such as hygienic products. In a production process for a water-absorbing agent comprising the steps of mixing a water-absorbent resin with a crosslinking agent and heating the resultant mixture wherein the water-absorbent resin has a carboxyl group; the invention is characterized in that the crosslinking agent has a group reactable upon the carboxyl group, an average molecular weight of 500 or more, and a repeating structural unit of general formula (1) below:

—[(CH₂CH₂O)_m—CH₂—CH(OH)CH₂—O]—  (1)

wherein m is an integer of 1 to 10.

Claims

1. A production process for a water-absorbing agent comprising the steps of mixing a water-absorbent particulate resin with a crosslinking agent and heating the resultant mixture, wherein the water-absorbent particulate resin has a carboxyl group;

with the process being characterized in hat the crosslinking agent has a group reactable upon the carboxyl group, all average molecular weight of 500 or more, and a repeating structural unit of general formula (1) below;

2. A production process according to claim 1, wherein the group, reactable upon the carboxyl group, in the crosslinking agent is an epoxy group.

3. A production process according to claim 2, wherein the crosslinking agent has 2 or more epoxy groups.

4. A production process according to claim 1, wherein the average molecular weight of the crosslinking agent is 1,000 or more.

11. A production process according to claim 1, wherein the water-absorbent particulate resin has a water content in the range of about 1 to about 400%.

15. A production process according to claim 1, wherein particles of the water-absorbent particulate resin have irregular pulverized shapes.

5. A production process for a water-absorbing agent, comprising the steps of mixing a water-absorbent particulate resin with a crosslinking agent and heating the resultant mixture, wherein the water-absorbent particulate resin has a carboxyl group;

with the process being characterized in that the crosslinking agent has an average molecular weight of 500 or more and is shown by general formula (2) below;

6. A production process according to claim 5, wherein R is a glycidyl group.

7. A production process according to claim 5, wherein m is 1.

8. A production process according to claim 5, wherein the average molecular weight of the crosslinking agent is 1,000 or more.

12. A production process according to claim 5, wherein the water-absorbent particulate resin has a water content in the range of about 1 to about 400%.

16. A production process according to claim 5, wherein particles of the water-absorbent particulate resin have irregular pulverized shapes.

9. A production process for a water-absorbing agent having an absorption capacity of 20 (g/g) or more under a heavy load, comprising the steps of mixing a water-absorbing particulate resin with a crosslinking agent and heating the resultant mixture, wherein the water-absorbent particulate resin has a carboxyl group;

with the process being characterized in that the crosslinking agent is a polyepoxy compound which has at least two epoxy groups and at least two hydroxyl groups and an average molecular weight of 1,000 or more.

13. A production process according to claim 9, wherein the water-absorbent particulate resin has a water content in the range of about 1 to about 400%.

17. A production process according to claim 9, wherein particles of the water-absorbent particulate resin have irregular pulverized shapes.

10. A production process for a water-absorbing agent, comprising the steps of mixing a water-absorbent particulate resin with a surface-crosslinking agent and heating the resultant mixture, wherein the water-absorbent particulate resin has a carboxyl group, and wherein the surface-crosslinking agent includes at least two epoxy groups or at least two hydroxyl groups;

with the process being characterize in that the surface-crosslinking agent has no cationic group and in that the resultant water-absorbing agent displays a crosslinking absorption property index of 1,000×

10, or more, wherein 1he index is defined by the following equation;

14. A production process according to claim 10, wherein the water-absorbent particulate resin has a water content in the range of about 1 to about 400%.

18. A production process according to claim 10, wherein particles of the water-absorbent particulate resin have irregular pulverized shapes.