Method for producing particulate water absorbing agent containing water absorbent resin as main component

• US 20110039961A1
• Filed: 03/31/2009
• Published: 02/17/2011
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Kanzaki, Shuji, Matsumoto, Koji
• Granted Patent: US 8,912,298 B2
• Time in Patent Office: Days
• US Class Current: 521/63
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: B01J 19/0086 Processes carried out with a view to control or to change the pH-value; Applications of buffer salts; Neutralisation reactions
• CPC Class Codes: B01J 2219/00006 Large-scale industrial plants
• CPC Class Codes: C07C 51/41 Preparation of salts of carboxylic acids C07C51/093 - C07C51/34 take precedence preparation of soap C11D
• CPC Class Codes: C07C 51/50 Use of additives, e.g. for stabilisation
• CPC Class Codes: C08F 2/10 Aqueous solvent
• CPC Class Codes: C08F 2/48 by ultraviolet or visible light
• CPC Class Codes: C08F 20/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08J 2333/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• CPC Class Codes: Y10T 137/4673 Plural tanks or compartments with parallel flow
• CPC Class Codes: Y10T 137/469 Sequentially filled and emptied [e.g., holding type]
• CPC Class Codes: Y10T 137/86187 Plural tanks or compartments connected for serial flow

Abstract

An apparatus (2) includes: a first tank (4); a line mixer (6); a second tank (8); a cooling jacket (10); a first tube (12); a second tube (14); and a third tube (16). In the first tank (4), (i) sodium persulfate serving as a polymerization initiator and (ii) water are fed so as to obtained an aqueous solution. The aqueous solution is continuously taken out and transferred via the first tube (12) to the line mixer (6). Between the first tank (4) and the line mixer (6), water is injected into the first tube (12). The water and the sodium persulfate aqueous solution are stirred together in the line mixer (6). This stirring decreases a concentration of the aqueous solution. The resulting aqueous solution is continuously fed to the second tank (8) via the second tube (14). The aqueous solution is then continuously taken out via the third tube (16) and is continuously added to an acrylic acid (salt) aqueous solution. This provides a production method which allows a high-quality water absorbing agent to be obtained with a compact apparatus.

Claims

1. A method for producing a particulate water absorbing agent containing a water absorbent resin as a main component,

the method comprising the steps of:

(1) mixing, with an aqueous solution of a monomer for a water absorbent resin, a liquid containing a polymerization initiator;

(2) polymerizing the monomer so as to obtain a hydrogel;

(3) drying the hydrogel so as to obtain a dried polymer; and

(4) adding, to either the aqueous solution of the monomer or the polymer, a liquid containing a modifier,

either the liquid containing the polymerization initiator or the liquid containing the modifier being obtained through the steps of;

(a) providing at least two kinds of liquids; and

(b) continuously feeding the at least two kinds of liquids to a tank either separately or together while continuously taking out a mixture solution of the at least two kinds of liquids from the tank.

2. The method according to claim 1, wherein, in the step (b), the mixture solution in the tank is circulated via a circulation loop.

3. The method according to claim 2, wherein the mixture solution is cooled or heated in the circulation loop.

4. The method according to claim 1, wherein the mixture solution is cooled or heated in the tank.

5. The method according to claim 1, wherein one of the at least two kinds of liquids provided in the step (a) is an aqueous solution.

6. The method according to claim 1, wherein, in the step (a), (i) an aqueous solution of the polymerization initiator comprising at least one kind of polymerization initiator and (ii) water are provided.

7. The method according to claim 6, wherein:

the aqueous solution, provided in the step (a), of the polymerization initiator has a concentration of not less than 20 mass % but not more than 50 mass %; and

the aqueous solution of the polymerization initiator has a concentration of not less than 1 mass % but not more than 25 mass % after the aqueous solution is diluted through the step (b).

8. The method according to claim 6, wherein the polymerization initiator is contained in an amount of not less than 0.001 part by mass but not more than 2 parts by mass with respect to 1 mole of the monomer.

9. The method according to claim 1, wherein, in the step (a), (i) a liquid including at least one kind of surface cross-linking agent serving as the modifier and (ii) water are provided.

10. The method according to claim 9, wherein the at least one kind of surface cross-linking agent is contained in an amount of not less than 0.001 part by mass but not more than 10 parts by mass with respect to 100 parts by mass of a solid content of the polymer.

11. The method according to claim 1, wherein, in the step (a), the modifier comprises a surface cross-linking agent, and the modifier is further used after surface cross-linking performed by the surface cross-linking agent.

12. The method according to claim 11, wherein the modifier is contained in an amount of not less than 0.0001 part by mass but not more than 10 parts by mass with respect to 100 parts by mass of a solid content of the polymer.

13. The method according to claim 1, wherein the modifier comprises at least one selected from the group consisting of a surface cross-linking agent, a surface active agent, a chelating agent, a deodorant agent, an antibacterial agent, a reducing agent, and an anti-coloring agent.

15. The method according to claim 1, wherein:

in the step (b), a flow rate is controlled to satisfy 0.95≦

x/y≧

1.05, where x is an amount of the at least two kinds of liquids fed to the tank and y is an amount of the at least two kinds of liquids taken out from the tank; and

the at least two kinds of liquids is stored in the tank in an amount which is controlled so that the amount is not less than 10% but not more than 90% of a capacity of the tank.

16. The method according to claim 1, wherein:

the water absorbent resin comprises a polyacrylic acid water absorbent resin and/or a polyacrylic acid salt water absorbent resin; and

the polymerization is a continuous kneader polymerization or a continuous belt polymerization.

17. The method according to claim 1, wherein the water absorbing agent is continuously produced at not less than 1000 kg/hr per one line or per one plant.

18. The method according to claim 1, wherein at least one dehydration esterification surface cross-linking agent selected from the group consisting of an oxazolidinone compound, an alkylenecarbonate compound, a polyhydric alcohol compound, and an oxetane compound is added to the dried polymer as the modifier.

19. The method according to claim 1, wherein a plurality of covalent bonding or ionic bonding surface cross-linking agents are added as the modifier to the dried polymer either simultaneously or separately.

20. The method according to claim 1, wherein the polymerization initiator is a water-soluble pyrolytic polymerization initiator which is used in combination with a reducing agent.

21. The method according to claim 1, wherein:

the particulate water absorbing agent contains a polyacrylic acid-based water absorbent resin and/or a polyacrylic acid salt-based water absorbent resin as the main component; and

(i) an absorbency against pressure of the particulate water absorbing agent for physiological saline under a pressure of 4.8 kPa falls within a range from 15 g/g to 35 g/g, and/or (ii) a liquid permeability of the particulate water absorbing agent is not less than 30 (×

10<sup>−

7</sup>·

cm³·

s·

g<sup>−

1</sup>).

14. A method for producing a particulate water absorbing agent containing a water absorbent resin as a main component,

the method comprising the steps of:

(1) mixing, with an aqueous solution of a monomer for a water absorbent resin, a liquid containing a polymerization initiator;

(2) polymerizing the monomer so as to obtain a hydrogel; and

(3) drying the hydrogel so as to obtain a dried polymer,

the liquid containing the polymerization initiator being obtained through the steps of;

(a) providing at least two kinds of liquids; and

(b) continuously feeding the at least two kinds of liquids to a tank either separately or together while continuously taking out a mixture solution of the at least two kinds of liquids from the tank.

22. The method according to claim 14, wherein:

in the step (b), a flow rate is controlled to satisfy 0.95≦

x/y≧

1.05, where x is an amount of the at least two kinds of liquids fed to the tank and y is an amount of the at least two kinds of liquids taken out from the tank; and

the at least two kinds of liquids is stored in the tank in an amount which is controlled so that the amount is not less than 10% but not more than 90% of a capacity of the tank.

23. The method according to any one of claim 14, wherein:

the water absorbent resin comprises a polyacrylic acid water absorbent resin and/or a polyacrylic acid salt water absorbent resin; and

the polymerization is a continuous kneader polymerization or a continuous belt polymerization.

24. The method according to claim 14, wherein the water absorbing agent is continuously produced at not less than 1000 kg/hr per one line or per one plant.

25. The method according to claim 14, wherein the polymerization initiator is a water-soluble pyrolytic polymerization initiator which is used in combination with a reducing agent.

26. The method according to claim 14, wherein:

the particulate water absorbing agent contains a polyacrylic acid-based water absorbent resin and/or a polyacrylic acid salt-based water absorbent resin as the main component; and

(i) an absorbency against pressure of the particulate water absorbing agent for physiological saline under a pressure of 4.8 kPa falls within a range from 15 g/g to 35 g/g, and/or (ii) a liquid permeability of the particulate water absorbing agent is not less than 30 (×

10<sup>−

7</sup>·

cm³·

s·

g<sup>−

1</sup>).