Patent ID: 8383746

Claim:
A water absorbing resin, comprising a water-soluble unsaturated monomer as a repeat unit for a major chain, 90 mol % or more, based on the total monomers making up the resin, of an acrylic acid and/or salt thereof, the resin having an internal crosslinking structure and exhibiting a weight-average molecular weight Mw of 360,000 to 1,000,000 daltons and an intrinsic viscosity IV of 2.1 to 6.0 dL/g where the weight-average molecular weight Mw and the intrinsic viscosity IV are measured after treatment under set 2 of hydrolysis conditions, in which treatment 20 mg of the water absorbing resin is left in 10 grams of a 0.1 mol/L aqueous solution of sodium hydroxide at 80° C. for 3 weeks, and the water absorbing resin regulates a thermally decomposing radical initiator content index for a water-containing gel to 40 to 100.