Water-absorbent resin powder and production process therefor

• US 20010025093A1
• Filed: 02/22/2001
• Published: 09/27/2001
• Est. Priority Date: 02/29/2000
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Fujino, Shinichi, Kanto, Teruyuki, Hatsuda, Takumi, Harada, Nobuyuki
• Granted Patent: US 6,576,713 B2
• Time in Patent Office: Days
• US Class Current: 526/210
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 3/12 Powdering or granulating
• CPC Class Codes: C08J 3/122 Pulverisation by spraying
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

The present invention provides a production process for a water-absorbent resin powder which is excellent in particle diameter distribution and properties, wherein the production process not only inhibits adhesion and aggregation in the production steps, but also is excellent in energy efficiency, drying efficiency, and productivity. The production process for a water-absorbent resin powder comprises the steps of: polymerizing an aqueous monomer solution containing a crosslinking agent; heat-drying the resultant crosslinked hydrogel polymer; and pulverizing the resultant dry polymer; wherein: the dry polymer resultant from the heat-drying step is forcibly cooled before or during the pulverization step; and the water-absorbent resin powder has an average particle diameter of 200 to 600 μm after the pulverization step wherein the total ratio of particles having particle diameters of not larger than 150 μm and particles having particle diameters of not smaller than 850 μm in the water-absorbent resin powder is not more than 15 weight % of the water-absorbent resin powder.

Claims

1. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer; and

pulverizing the resultant dry polymer;

wherein;

the dry polymer resultant from the heat-drying step is cooled before or during the pulverization step; and

the water-absorbent resin powder has an average particle diameter of 200 to 600 μ

m after the pulverization step wherein the total ratio of particles having particle diameters of not larger than 150 μ

m and particles having particle diameters of not smaller than 850 μ

m in the water-absorbent resin powder is not more than 15 weight % of the water-absorbent resin powder.

2. A production process for a water-absorbent resin powder according to

claim 1

, which further comprises the step of surface-crosslinking the water-absorbent resin powder after the pulverization step.

3. A production process for a water-absorbent resin powder according to

claim 2

, wherein:

the temperature of the heat-drying step is in the range of 110 to 230°

C.;

the temperature of the forcible cooling step following the heat-drying step is in the range of 85 to 35°

C.; and

the temperature of the surface-crosslinking step following the pulverization step is in the range of 110 to 230°

C.

4. A production process for a water-absorbent resin powder according to

claim 1

, wherein the dry polymer has a solid content of 93 to 97 weight %.

5. A production process for a water-absorbent resin powder according to

claim 1

, which further comprises the steps of laminating the crosslinked hydrogel polymer into a definite thickness of 1 to 20 cm in particulate form and then drying it.

6. A production process for a water-absorbent resin powder according to

claim 1

, which further comprises the step of recycling heat obtained by forcibly cooling the dry polymer.

7. A production process for a water-absorbent resin powder according to

claim 1

, wherein the water-absorbent resin powder has a bulk density of not less than 0.65 g/ml after the pulverization step.

8. A production process for a water-absorbent resin powder according to

claim 1

, which further comprises the step of forcibly heating or heat-retaining the resultant water-absorbent resin powder after the pulverization step.

9. A production process for a water-absorbent resin powder according to

claim 1

, which further comprises the step of adding an aqueous liquid to the water-absorbent resin powder obtained after the pulverization step following the forcible cooling step.

19. A water-absorbent resin powder, which is obtained by the production process as recited in any one of

claims 1

to

18

, and exhibits an absorption capacity of not less than 25 g/g under a load (1.96 kPa).

20. An absorbent article, which comprises the water-absorbent resin powder as recited in

claim 19

.

10. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer; and

pulverizing the resultant dry polymer;

with the production process further comprising the steps of;

forcibly cooling the dry polymer after the heat-drying step; and

recycling the resultant heat in order to utilize it for forcible heating in a production process for a water-absorbent resin.

11. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer;

pulverizing the resultant dry polymer; and

adding an aqueous liquid to the resultant powder in a mixer;

wherein;

the temperature of the heat-drying step is in the range of 110 to 230°

C.;

the dry polymer is cooled into the range of 80 to 35°

C. before the addition of the aqueous liquid; and

the dry polymer is adjusted so as to have a bulk density of not less than 0.65 g/ml after the pulverization step.

12. A production process for a water-absorbent resin powder according to

claim 11

, wherein the forcible cooling of the dry polymer is carried out before the pulverization step.

13. A production process for a water-absorbent resin powder according to

claim 11

, wherein the aqueous liquid contains a crosslinking agent.

14. A production process for a water-absorbent resin powder according to

claim 11

, wherein the aqueous liquid is an aqueous polyhydric alcohol solution.

15. A production process for a water-absorbent resin powder according to

claim 11

, wherein the water-absorbent resin powder has an average particle diameter of 200 to 600 μ

m wherein the total ratio of particles having particle diameters of not larger than 150 μ

m and particles having particle diameters of not smaller than 850 μ

m in the water-absorbent resin powder is not more than 15 weight % of the water-absorbent resin powder.

16. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer;

pulverizing the resultant dry polymer; and

adding an aqueous liquid to the resultant powder in a mixer;

wherein;

the temperature of the heat-drying step is in the range of 110 to 230°

C.;

the dry polymer is cooled into the range of 80 to 35°

C. before the addition of the aqueous liquid;

the mixer is a stirring mixer having an internal wall temperature of not lower than 40°

C.; and

the mixture resultant from the addition of the aqueous liquid is reheated into the range of 110 to 230°

C.

17. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer; and

pulverizing the resultant dry polymer;

wherein;

the dry polymer is forcibly cooled after the heat-drying step;

the step of pulverizing the dry polymer is carried out so as to form a water-absorbent resin powder having a bulk density of not less than 0.65 g/ml; and

the cooled water-absorbent resin powder is further surface-crosslinked.

18. A production process for a water-absorbent resin powder, which comprises the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer; and

pulverizing the resultant dry polymer;

wherein;

the dry polymer is forcibly cooled after the heat-drying step;

the step of pulverizing the dry polymer is carried out so as to form a water-absorbent resin powder having a bulk density of not less than 0.65 g/ml; and

an aqueous liquid is further added to the cooled water-absorbent resin powder in a stirring mixer having a heated internal wall.

21. A water-absorbent resin powder, which is obtained by a process including the steps of:

polymerizing an aqueous monomer solution containing a crosslinking agent;

heat-drying the resultant crosslinked hydrogel polymer;

pulverizing the resultant dry polymer; and

adding an aqueous polyhydric alcohol solution to the resultant powder in a mixer wherein the aqueous polyhydric alcohol solution does not contain any volatile organic solvents;

wherein the resultant water-absorbent resin powder has the following properties;

(1) the bulk density is not less than 0.65 g/ml;

(2) the average particle diameter is in the range of 200 to 600 μ

m;

(3) the total ratio of particles having particle diameters of not larger than 150 μ

m and particles having particle diameters of not smaller than 850 μ

m in the water-absorbent resin powder is not more than 10 weight % of the water absorbent resin powder; and

(4) the absorption capacity under a load (1.96 kPa) is not less than 25 g/g.

22. An absorbent article, which comprises the water-absorbent resin powder as recited in

claim 21

.