Patent ID: 8481664

Claim:
A particulate water absorbing agent which comprises a water absorbing resin having a constitutional unit derived from acrylic acid and a salt thereof, and has: (a) permeability potential under pressure (PPUP) being 50 to 100%; (b) yellowness index (YI) being 0 to 10, and rate of change of yellowness index (ΔYI) being 100 to 150% as measured with a coloring acceleration test for 14 days in an atmosphere of the temperature being 70±1° C. and the relative humidity being 95±1%; and (c) particles of smaller than 150 μm specified by standard sieve classification accounting for 0 to 5% by weight, weight average particle diameter (D50) specified by standard sieve classification being 200 to 550 μm, and logarithmic standard deviation (σζ) of particle size distribution specified by standard sieve classification being 0.20 to 0.40, wherein permeability potential under pressure (PPUP) is specified by the following formula: PPUP(%)=(AAP:5.0 g)/(AAP:0.90 g)*100 wherein (AAP: 0.90 g) is the absorbency against pressure measured with 0.90 g of the particulate water absorbing agent for a 0.90% by weight aqueous sodium chloride solution under a pressure of 4.8 kPa for 60 min; and (AAP: 5.0 g) is the absorbency against pressure measured with 5.0 g of the particulate water absorbing agent for a 0.90% by weight aqueous sodium chloride solution under a pressure of 4.8 kPa for 60 min.