Process for continuous production of water-absorbent resin product

• US 7,193,006 B2
• Filed: 12/02/2003
• Issued: 03/20/2007
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Kajikawa, Katsuhiro
• Primary Examiner(s): Seidleck; James J.
• Assistant Examiner(s): Asinovsky; Olga
• Application Number:
  US10/724,895
• Publication Number:
  US 20040110006A1
• Time in Patent Office: 1,204 Days
• Field of Search: 524/500, 524/501, 524/502, 525/41, 528/480, 528/502.R
• US Class Current: 524/500
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 3/005 Processes for mixing polymers
• CPC Class Codes: C08J 3/12 Powdering or granulating
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

There is disclosed a process for continuous production of a water-absorbent resin product by which the water-absorbent resin product having high properties can continuously be produced easily and inexpensively with stable constant quality. In addition, there is disclosed a water-absorbent resin product having high properties and being stable in quality. The process comprises the following steps of: (A) measuring a water-absorbent resin by its predetermined property and/or its predetermined component content, wherein the water-absorbent resin comes being continuously produced via a classification step and/or a surface-modifying step; (B) separating a predetermined amount of water-absorbent resin (a) from the water-absorbent resin that comes being continuously produced, wherein the water-absorbent resin (a) is a water-absorbent resin which displays not less than a definite value and/or a water-absorbent resin which displays not more than a definite value as to the predetermined property and/or the predetermined component content in accordance with results of the aforementioned measurement; and (C) mixing at least a portion of the aforementioned separated predetermined amount of water-absorbent resin (a) into a water-absorbent resin that comes being continuously produced via a classification step and/or a surface-modifying step on the same or another production line.

Claims

1. A process for continuous production of a water-absorbent resin product, wherein the water-absorbent resin comes being continuously produced via a classification step and a surface-modifying step following a step of polymerizing a monomer and a step of drying, wherein the water-absorbent resin has a mass-average particle diameter of 200 to 700 μ

m (according to JIS-standardized sieves) after the classification, and contains particles of not smaller than 1,000 μ

m (according to JIS-standardized sieves) in the range of less than 5.0 mass %,

which comprises the following steps of;

(A) measuring a water-absorbent resin by its predetermined property and/or its predetermined component content after the classification step and/or a surface-modifying step;

(B) separating a predetermined amount of water-absorbent resin (a) from the water-absorbent resin that comes being continuously produced, wherein the water-absorbent resin (a) is a water-absorbent resin which displays not less than a definite value and/or a water-absorbent resin which displays not more than a definite value as to the predetermined property and/or the predetermined component content in accordance with results of the aforementioned measurement; and

(C) mixing at least a portion of the aforementioned separated predetermined amount of water-absorbent resin (a) into a water-absorbent resin that comes being continuously produced via a classification step and/or a surface-modifying step on the same or another production line, wherein the water-absorbent resin (a) is mixed without being substantially modified.

2. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the mixing in the aforementioned step (C) is carried out on the way of the production line.

3. A process for continuous production of a water-absorbent resin product according to claim 1,

further comprising the step of changing a production condition in accordance with results of step (A).

4. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the aforementioned water-absorbent resin which is measured by its predetermined property and/or its predetermined component content is a water-absorbent resin product that is finally obtained via the surface-modifying step.

5. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the aforementioned predetermined property and/or the aforementioned predetermined component content is at least one member selected from the group consisting of absorption capacity without load, absorption capacity under load, liquid permeability, and particle diameters.

6. A process for continuous production of a water-absorbent resin product according to claim 5, wherein the particle diameters of the water-absorbent resin having a mass-average particle diameter of 300 to 600 μ

m and having particles of 850 to 150 μ

m (according to JIS-standardized sieve) in an amount of 95 to 100 mass % are measured by a laser diffraction scattering method.

7. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the water-absorbent resin has particles of 850 to 150 μ

m (according to JIS-standardized sieve) in an amount of 95 to 100 mass %.

8. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the mixing in step (C) is carried out in a dry manner.

9. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the yield of the water-absorbent resin per line is not less than 20 t (metric tons)/day.

10. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the water-absorbent resin contains a carboxyl group, and the surface-modifying step is carried out by dehydration-reactable crosslinking agent which can react with the carboxyl group by dehydration esterification and/or dehydration amidation.

11. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the amount of the water-absorbent resin (a) separated in the step (B) and mixed to the water-absorbent resin is not larger than 10 mass % relative to the entirety.

12. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the amount of water-absorbent resin (a) separated in the step (B) is 20 to 0.001 mass % relative to the total amount of the water-absorbent resin as produced.

13. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the obtained water-absorbent resin satisfy the following:

(1) a mass-average particle diameter of 300 to 600 μ

m;

(2) a residual monomer content of not higher than 500 ppm;

(3) an absorption capacity of not less than 25 g/g without load;

(4) an absorption capacity of not less than 20 g/g under a load of 1.9 kPa or 4.9 kPa; and

(5) a fine powder (smaller than 150 μ

m) content of less than 5.0 mass %.

14. A process for continuous production of a water-absorbent resin product according to claim 6, wherein the laser diffraction scattering method is carried out in the dry measurement.

15. A process for continuous production of a water-absorbent resin product according to claim 1, wherein the water-absorbent resin (a) in step (C) is mixed without surface treatment and/or granulation.