Method for producing particulate water absorbing agent containing water absorbent resin as main component

A method for producing a particulate water absorbing agent containing, as a main component, a water absorbent resin whose surface is cross-linked,

• the method comprising the steps of:
• (1) mixing, with an aqueous solution of a monomer for a water absorbent resin, an aqueous solution containing a polymerization initiator;
• (2) polymerizing the monomer so as to obtain a hydrogel;
• (3) drying the hydrogel so as to obtain a dried polymer;
• (4) cross-linking a surface of the water absorbent resin;
• (5) adding, to the hydrogel or the dried polymer, a liquid containing a modifier, and
• (6) producing the liquid containing the modifier by a method comprising the steps of:
• (a) providing at least one kind of liquids in at least one tank;
• (b) removing the at least one kinds of liquid from the at least one tank and mixing the at least one kind of liquid with a liquid separately prepared by a mixing device provided in a tube connecting the at least one tank to a storage tank to produce a mixture solution thus obtained;
• (c) continuously taking out a part of the resulting mixture solution from the storage tank while continuously feeding the resulting mixture solution to the storage tank,
• the modifier being a surface cross-linking agent which is used in the step (4),
• in the step (a), the at least one kind of liquid provided in the at least one tank being a stock solution of the surface cross-linking agent, and
• in the step(b), the liquid separately prepared being water and the step of said mixing being performed with use of the water to dilute the stock solution of the surface cross-linking agent removed from the at least one tank wherein the water absorbing agent is continuously produced at not less than 1000 kg/hr per one line or per one plant.