Patent ID: 7582705

Claim:
A production method of a particulate water absorbing agent comprising the step of adding a surface treatment agent, containing (A) a surface cross-linking agent and (B) a surfactant or a powder lubricant as essential components, to a water absorbent resin, having a cross-linking structure, so as to cross-link a surface of the water absorbent resin, wherein: an amount of the surfactant or the powder lubricant added ranges from 0.0005 weight parts or more to 0.012 weight parts or less with respect to 100 weight parts of the water absorbent resin, and a surface tension of a supernatant liquid obtained in 4 minutes after dispersing 0.5 g of the particulate water absorbing agent in 50 ml of physiological saline whose temperature is 20° C. is 55 mN/m or more.