Patent ID: 8198209

Claim:
A water absorbing agent containing water absorbing resin particles with an internal crosslinking structure obtained by polymerization of a water-soluble unsaturated monomer, the agent satisfying conditions (a) to (d) below: (a) the agent contains water-insoluble inorganic particles at an amount of from 10 ppm to 1,900 ppm, inclusive, relative to the agent, wherein the water-insoluble inorganic particles include silicon dioxide, and the silicon dioxide has, on a surface thereof, residual silanol groups at a concentration from 0.7 to 1.7 SiOH/nm 2 ; (b) the agent contains 5 mass % or less water absorbing resin particles which have such a size that they can pass through a sieve having a mesh opening size of 150 μm; (c) the agent has an absorbency against a pressure of 4.83 kPa (AAP) of 18 g/g or more; and (d) the water-insoluble inorganic particles reside on a surface of the water absorbing resin.