Water absorbent resin composition and production method thereof

A method for producing a water absorbent resin composition, comprising:

• adding a solution of an aqueous multivalent metal compound (B) to a particulate water absorbent resin (A) with a cross-linked surface, said particulate water absorbent resin (A) having a cross-linking structure obtained by polymerizing an unsaturated monomer containing an acid group;
• and mixing the solution of the aqueous multivalent metal compound (B) with the particulate water absorbent resin (A),
• wherein the particulate water absorbent resin (A) contains 95 wt % or more of the particles whose particle diameter is less than 850 μm and not less than 106 μm, and a weight average particle diameter of the particles is less than 500 μm and not less than 300 μm, and a logarithmic standard deviation (σζ) of a particle size distribution of the particulate water absorbent resin (A) is 0.45 or less, and a water-soluble component of the particulate water absorbent resin (A) is 35 wt % or less, and
• an amount of a multivalent metal component contained in the solution of the aqueous multivalent metal compound (B) is 0.001 wt % to 10 wt % with respect to the particulate water absorbent resin (A), and
• a concentration of the aqueous multivalent metal compound (B) in the solution is 0.40 or more with respect to a saturated concentration of the aqueous multivalent metal compound (B) in the solution, and
• at least one of a temperature of the particulate water absorbent resin (A) is 50° C. or higher and lower than 100° C., and a temperature of the solution of the aqueous multivalent metal compound (B) is 30° C. or higher and lower than 100° C., and wherein an extraction rate of the multivalent metal component around the surface of said particulate water absorbent resin is 7.6 wt % to 14.8 wt %.

A method for producing a water absorbent resin composition, comprising:

• mixing a particulate water absorbent resin (A) having a cross-linking structure obtained by polymerizing an unsaturated monomer containing an acid group, a solution of an aqueous multivalent metal compound (B), and an organic surface cross-linking agent (C);
• and heating a mixture that has been obtained in the mixing step at 150 to 300° C. so as to cross-link a surface of the particulate water absorbent resin (A),
• wherein the particulate water absorbent resin (A) contains 95 wt % or more of the particles whose particle diameter is less than 850 μm and not less than 106 μm, and a logarithmic standard deviation (σζ) of a particle size distribution of the particulate water absorbent resin (A) is 0.45 or less, and
• an amount of a multivalent metal component contained in the solution of the aqueous multivalent metal compound (B) is 0.001 wt % to 10 wt % with respect to the particulate water absorbent resin (A), and
• a concentration of the multivalent metal component contained in a mixed solution including the solution of the aqueous multivalent metal compound (B) and the organic surface cross-linking agent (C) is at least 1.80 wt %, and wherein an extraction rate of the multivalent metal component around the surface of said particulate water absorbent resin is 7.6 wt % to 14.8 wt %.

A method for producing a water absorbent resin composition, comprising:

• heating a precursor (D) obtained by mixing a particulate water absorbent resin (A) having a cross-linking structure obtained by polymerizing an unsaturated monomer containing an acid group, a solution of a multivalent metal compound (B), and an organic surface cross-linking agent at 150° C. to 300° C. so as to cross-link a surface of the particulate water absorbent resin (A),
• wherein the particulate water absorbent resin (A) contains 95 wt % or more of the particles whose particle diameter is less than 850 μm and not less than 106 μm, and a logarithmic standard deviation (σζ) of a particle size distribution of the particulate water absorbent resin (A) is 0.45 or less, and
• an amount of a multivalent metal component contained in the solution of the multivalent metal compound (B) is 0.001 wt % to 10 wt % with respect to the particulate water absorbent resin (A),
• a concentration of the multivalent metal component contained in a mixed solution including the solution of the multivalent metal compound (B) and the organic surface cross-linking agent is at least 1.80 wt %, and
• a humidification blocking ratio (wt %) of the precursor (D) is 80 wt % or less, and wherein an extraction rate of the multivalent metal component around the surface of said particulate water absorbent resin is 7.6 wt % to 14.8 wt %.