Patent ID: 8182916

Claim:
A particulate water absorbing agent comprising a water absorbent resin as a principal component, wherein the absorbent resin has a cross-linked structure including a constitutional unit derived from an unsaturated carboxylic acid and/or a salt thereof and is obtained by a surface crosslinking treatment around the surface thereof with a surface crosslinking agent, said water absorbing agent comprising particles having a particle size of 300 to 850 μm and particles having a particle size of smaller than 300 μm, wherein the amount of residual monomer is not lower than 0 but not higher than 500 ppm, and residual monomer index (RMI) calculated by the following formula (1): RMI=| RM 1 −RM 2 |/RM A (1) wherein, RM 1 represents the amount of residual monomer of the water absorbing agent having a particle size of smaller than 300 μm among the particles constituting the water absorbing agent; RM 2 represents the amount of residual monomer of the water absorbing agent having a particle size of 300 to 850 μm among the particles constituting the water absorbing agent; and RM A represents the amount of residual monomer of the water absorbing agent, is not greater than 0.30.