Water absorbing agent, water absorbing article and method for production of water absorbing agent

A water absorbing agent comprising:

• a water absorbent resin which has a cross-linked structure including a constitutional unit derived from an unsaturated carboxylic acid and/or a salt thereof and which is obtained by a surface crosslinking treatment around the surface thereof with a surface crosslinking agent;
• and a sulfur-containing reducing agent,
• wherein absorption capacity without load (CRC) for a physiological saline solution is not less than 32 g/g,
• absorption capacity under a high load of 4.8 kPa (AAP 4.8 kPa) for a physiological saline solution is not less than 20 g/g,
• content of sulfur based volatile component as an atmospheric concentration specified by a gas detector tube is not less than 0 but not higher than 2.5 ppm.

A method for the production of a water absorbing agent which comprises:

• a first step of obtaining a hydrogel polymer by polymerizing an aqueous solution of a monomer including an unsaturated carboxylic acid and/or a salt thereof in the presence of a crosslinking agent;
• a second step of obtaining a water absorbent resin precursor which is in powder form and includes particles having a particle size of 300 to 850 μm and particles having a particle size of smaller than 300 μm as main components by drying said hydrogel polymer followed by pulverization and classification to adjust the particle size distribution,
• a third step of obtaining a water absorbent resin by heating a mixture of said water absorbent resin precursor and a surface crosslinking agent, which can form an ester bond around the surface of said water absorbent resin precursor,
• a fourth step of adding by spraying an aqueous solution that includes a sulfur-containing reducing agent to said water absorbent resin, and
• a fifth step of subjecting the mixture of the water absorbent resin and said aqueous solution to a heat treatment under an airflow of not lower than 40° C. but not higher than 120° C.