Water-absorbent resin and production process therefor

A production process for a water-absorbent resin, which comprises the steps of:

• carrying out polymerization, involving crosslinking, of an aqueous solution of a water-soluble unsaturated monomer including acrylic acid (salt);
• and carrying out fine division to obtain a resultant hydrogel,
• wherein the polymerization, involving crosslinking, is aqueous solution polymerization, and the resultant finely divided hydrogel is obtained by the fine division after static polymerization on a moving belt,
• with the production process being characterized in that:
• (A) the water-soluble unsaturated monomer contains furfural in an amount of 11 to 1,000 weight ppm (relative to the monomer);
• (B 1) the polymerization is initiated at a temperature of the aqueous solution of a water-soluble unsaturated monomer before a polymerization initiator is added of not lower than 30° C. and/or (B2) the water-soluble unsaturated monomer before a polymerization initiator is added further contains a transition metal in the range of not more than 5 ppm relative to the monomer in terms of its cation;
• and
• (C) the resultant finely divided hydrogel has a weight-average particle diameter of 0.3 to 4 mm, and the ratio of coarse gel particles having particle diameters of not smaller than 10 mm is not more than 5 weight % of the finely divided hydrogel.

A production process for a water-absorbent resin, which comprises a polymerization step that includes the steps of:

• carrying out polymerization, involving crosslinking, of an aqueous solution of a water-soluble unsaturated monomer including acrylic acid (salt);
• and at the same time obtaining a finely divided hydrogel,
• wherein the polymerization, involving crosslinking, is reversed-phase suspension polymerization, and the resultant finely divided hydrogel is obtained at the same time as the suspension polymerization in a hydrophobic organic solvent,
• with the production process being characterized in that the water-soluble unsaturated monomer contains furfural in an amount of 11 to 1,000 weight ppm (relative to the monomer).