Particulate water absorbing agent and manufacturing method of same

1. A particulate water absorbing agent, comprising 70 to 99.9 wt % of a polyacrylic acid- or polyacrylate-based water absorbing resin, 0.001 to 0.5 wt % of a water-soluble organic chelating agent, and 0.01 to 2 wt % of one or more water-soluble inorganic phosphorous compounds;

wherein the polyacrylic acid- or polyacrylate-based water absorbing resin is surface crosslinked with an organic crosslinking agent;

wherein after being exposed to a temperature of 70±1° C. and a relative humidity of 65±1% for 7 days, said particulate water absorbing agent shows an L value of 78 or greater as measured according to Hunter's Lab color system; and

wherein either:

(1) (i) the water-soluble organic chelating agent contains at least one selected from the group consisting of organic polyvalent phosphoric acids and amino polyvalent phosphoric acids and (ii) the one or more water-soluble inorganic phosphorous compounds reside locally on a surface of the polyacrylic acid- or polyacrylate-based water absorbing resin or

(2) (i) the water-soluble organic chelating agent contains at least one amino polyvalent carboxylic acid, (ii) at least one water-soluble inorganic phosphorous compound is selected from the group consisting of phosphorus acid, hypophosphorus acid, triphosphoric acid, salts thereof, and phosphate and (iii) the one or more water-soluble inorganic phosphorous compounds reside locally on a surface of the polyacrylic acid- or polyacrylate-based water absorbing resin.

2. The particulate water absorbing agent of claim 1 , wherein at least one of (a) to (c) below applies:

(a) said particulate water absorbing agent contains 0 to 5 mass % particles that are 150-μm or smaller, having a mass-average particle diameter (D50) of 200 to 600 μm, and exhibiting a particle size distribution having a logarithmic standard deviation (σζ) of 0.20 to 0.40;

(b) said particulate water absorbing agent has an absorption capacity against pressure (AAP) for a 0.90 mass % aqueous solution of sodium chloride under 1.9 kPa or 4.9 kPa for 60 minutes of at least 20 (g/g); and

(c) said particulate water absorbing agent has a 0.69mass % saline flow conductivity (SFC) of at least 5 (cm 3 ·sec·10 −7 ·g −1 ).

3. The particulate water absorbing agent of claim 1 , wherein the water-soluble organic chelating agent is contained inside the water absorbing resin.

4. The particulate water absorbing agent of claim 1 , comprising 0.001 to 5 wt % polyvalent metal salt.

5. The particulate water absorbing agent of claim 1 , comprising 0.0001 to 3 mass ppm iron content (expressed in terms of Fe 2 O 3 ).

6. A urine, faeces, or blood absorbing article, comprising the particulate water absorbing agent of claim 1 .

7. A particulate water absorbing agent, comprising 70 to 99.9 wt % of a polyacrylic acid- or polyacrylate-based water absorbing resin, 0.001 to 0.5 wt % of a water-soluble organic chelating agent, and 0.01 to 2 wt % of one or more water-soluble inorganic phosphorous compounds;

wherein the polyacrylic acid- or polyacrylate-based water absorbing resin is surface crosslinked with an organic crosslinking agent;

wherein after being exposed to a temperature of 70±1° C. and a relative humidity of 65±1% for 7 days, said particulate water absorbing agent shows an L value of 78 or greater as measured according to Hunter's Lab color system; and

wherein (i) the water-soluble organic chelating agent contains at least one amino polyvalent carboxylic acid, (ii) at least one water-soluble inorganic phosphorous compound is selected from the group consisting of phosphorus acid, hypophosphorus acid, triphosphoric acid, salts thereof, and phosphate and (iii) the one or more water-soluble inorganic phosphorous compounds reside locally on a surface of the polyacrylic acid- or polyacrylate-based water absorbing resin.

8. A particulate water absorbing agent, comprising 70 to 99.9 wt % of a polyacrylic acid-or polyacrylate-based water absorbing resin, 0.001 to 0.5 wt % of a water—soluble organic chelating agent, and 0.01 to 2 wt % of one or more water-soluble inorganic phosphorous compounds;

wherein the polyacrylic acid- or polyacrylate-based water absorbing resin is surface crosslinked with an organic crosslinking agent;

wherein after being exposed to a temperature of 70±1° C. and a relative humidity of 65±1% for 7 days, said particulate water absorbing agent shows an L value of 78 or greater as measured according to Hunter's Lab color system; and

wherein (i) the water-soluble organic chelating agent contains at least one selected from the group consisting of organic polyvalent phosphoric acids and amino polyvalent phosphoric acids, (ii) at least one water-soluble inorganic phosphorous compound is selected from the group consisting of sodium dihydrogenphosphate, potassium dihydrogenphosphate, and ammonium dihydrogenphosphate and (iii) the one or more water-soluble inorganic phosphorous compounds reside locally on a surface of the polyacrylic acid- or polyacrylate-based water absorbing resin.

9. A method of manufacturing a particulate water absorbing agent, comprising the steps of:

polymerizing an aqueous solution of a monomer composed primarily of an acrylic acid or acrylate;

drying a water-containing gel-like crosslinked polymer obtained by the polymerizing step;

surface crosslinking a dry powder obtained in the drying step with an organic surface crosslinking agent; and

adding a polyvalent metal salt after the surface crosslinking step; said method further comprising the steps of:

adding a water-soluble organic chelating agent in the polymerization or to the aqueous solution of a monomer being polymerized; and

adding one or more water-soluble inorganic phosphorous compounds selected from the group consisting of phosphoric acid, sodium dihydrogenphosphate, potassium dihydrogenphosphate, and ammonium dihydrogenphosphate after the drying step but before the step of adding the polyvalent metal salt.

10. The method of manufacturing of claim 9 , further comprising the step of adding a surfactant.