Method for production of hydrophilic resin

• US 6,998,447 B2
• Filed: 03/29/2002
• Issued: 02/14/2006
• Est. Priority Date: 06/10/1992
• Status: Expired due to Fees

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Irie, Yoshio, Kajikawa, Katsuhiro, Hatsuda, Takumi
• Primary Examiner(s): Lipman, Bernard
• Application Number:
  US10/108,572
• Publication Number:
  US 20020161132A1
• Time in Patent Office: 1,418 Days
• Field of Search: 525/329.7, 525/329.9, 525/330.2, 528/503
• US Class Current: 525/330.2
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 20/04 Acids, Metal salts or ammonium salts thereof
• CPC Class Codes: C08L 33/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof

Abstract

In the production of an acrylate polymer by the steps of preparing a water-soluble unsaturated monomer having a ratio of neutralization in the range of 30 to 100 mol % and containing 50 to 100 mol % of an acrylate and then polymerizing the monomer, a method for the production of a hydrophilic resin which comprises using a water-soluble unsaturated monomer having a β-hydroxy propionic acid (salt) content of not more than 1,000 ppm. The hydrophilic resin obtained by this method exhibits excellent physical properties and has only a small residual monomer content. Further, a residual monomer content neither occurs nor increases in any using conditions.

Claims

1. A method for the production of a hydrophilic resin which comprises preparing a mixture solution of a water-soluble unsaturated monomer or monomer mixture containing 50 mol % or greater of aciylic acid partially or completely neutralized in an amount of 30 to 100 mol % to form an alkali metal and/or ammonium salts, 1 to 1,000 ppm of β

-hydroxy propionic acid or a salt thereof and, optionally, a first cross-linking agent, polymerizing the mixture solution, drying the gel polymer thus obtained, and then cross-linking a surface region of the polymer by treating said polymer with a second cross-linking agent having at least two groups capable of reacting with a functional group within the molecular unit of said polymer.

2. A method according to claim 1, wherein said water-soluble unsaturated monomer or monomer mixture contains 50 to 0 mol % of at least one unsaturated monomer selected from the group consisting of hydrophilic unsaturated monomers and hydrophobic unsaturated monomers.

3. A method according to claim 1, wherein said mixture solution contains not more than 300 ppm of β

-hydroxy propionic acid or a salt thereof.

4. A method according to claim 1, wherein said alkali metal salt is at least one member selected from the group consisting of sodium salts and potassium salts.

5. A method according to claim 1, wherein said hydrophilic resin has a cross-linked structure.

6. A method according to claim 1, wherein said second cross-linking agent is at least one member selected from the group consisting of polyhydric alcohols, polyepoxy compounds, polyamines, polyaziridines, polyaldehydes, polyisocyanates, polyoxazolines, alkylene carbonates, and polyvalent metals.

7. A method according to claim 5, wherein said partially neutralized or completely neutralized acrylic acid is an acrylic acid alkali metal salt and an acrylic acid ammonium salt and said polymer or the dry product thereof has been subjected to a heat treatment.

8. A method according to claim 7, wherein acrylic acid ammonium salt accounts for 10 to 40 mol % of the neutralized acrylic acid.

9. A method according to claim 7, wherein the temperature of said heat treatment is in the range of 150°

to 250°

C.

10. A method according to claim 7, wherein said heat treatment is carried out at the step of drying said polymer.

11. A method according to claim 1, said method resulting in a final polymer product obtained by drying having a residual monomer content below 300 ppm.

12. A method according to claim 1, wherein said β

-hydroxy propionic acid salt is sodium β

-hydroxy propionate.

13. A method according to claim 2, wherein said hydrophilic unsaturated monomers are selected from the group consisting of methacrylic acid, 2-(meth)acryloyl ethane sulfonic acid (salt thereof), 2-(meth)-acrylamide-2-methyl propane sulfonic acid and salts thereof, methoxy polyethylene glycol (meth)acrylate, N,N-dimethylamino ethyl (meth)acrylate, acrylamide, and mixtures thereof.

14. A method according to claim 2, wherein said hydrophobic unsaturated monomers are selected of the group consisting of styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, stearyl (meth)acrylate, lauryl (meth)acrylate and mixtures thereof.

15. A method according to claim 1, wherein said hydrophilic resin is an absorbent resin.

16. A method according to claim 1, wherein said hydrophilic resin is an absorbent resin which has a cross-linked structure.

17. A method according to claim 1, wherein said polymer has not more than 40 ppm of latent residual monomer claculated by the following formula:

latent residual monomer? {(residual monomer of the polymer after heating at 180°

C. for 3 hours)—

(residual monomer of the polymer before heating)).

18. A method according to claim 1, wherein said mixture solution of the water-soluble unsaturated monomer or monomer mixture is subjected to polymerization within 24 hours after the preparation.

19. A method according to claim 1, wherein the acrylic acid is purified by distillation and is used for neutralization or preparation of the water-soluble unsaturated monomer or monomer mixture within 24 hours after the distillation.

20. A method according to claim 1, wherein said first cross-linking agent is a polymerizable unsaturated groups and the first cross-linking agent is used in the range of 0.005-5 mol % to said water-soluble unsaturated monomer based on the monomer.

21. A method according to claim 15, wherein the absorbent resin is a powder having an average diameter in the range of 300-600 μ

m.

22. A method according to claim 1, wherein said hydrophilic resin has a cross-linked structure and said second cross-linking agent comprises at least one polyhydric alcohol.

23. A method according to claim 1, wherein said hydrophilic resin has a cross-linked structure and said second cross-linking agent is at least one member selected from the consisting of polyhydric alcohols, polyglycidyl compounds, polyamines and alkylene carbonates.

24. A method according to claim 1, wherein said hydrophilic resin has a cross-linked structure and the treatment with said second cross-linking agent occurs at a temperature in the range of 150 to 250°

C.

25. A method according to claim 1, wherein said mixture solution of the water-soluble unsaturated monomer or monomer mixture is subjected to polymerization by radical polymerization initiator within 24 hours after preparation.