Method for producing water absorbent resin

A method for producing a surface-crosslinked particulate poly(meth)acrylic acid (salt)-based water-absorbing resin, said method comprising the steps of:

• (i) preparing a (meth)acrylic acid (salt)-based aqueous monomer solution;
• (ii) polymerizing the (meth)acrylic acid (salt)-based aqueous monomer solution;
• (iii) carrying out gel-crushing of a crosslinked hydrogel polymer generated during or after the polymerization to obtain a particulate hydrogel;
• (iv) drying the particulate hydrogel to obtain a dried polymer;
• (v) pulverizing and/or classifying the dried polymer to obtain a particulate water-absorbing resin before surface-crosslinking;
• and
• (vi) surface-crosslinking the particulate water-absorbing resin before surface-crosslinking, wherein
• in the step (i) and/or the step (ii), water-soluble polyalkylene glycol having a weight average molecular weight of not more than 2000 is added to the aqueous monomer solution so that a total amount of the water-soluble polyalkylene glycol added in the step (i) and/or the step (ii) is 0.01 mass % to 1 mass % relative to a total mass of a monomer included in the aqueous monomer solution,
• the crosslinked hydrogel polymer has a centrifuge retention capacity of not more than 31 g/g and not less than 20 g/g, and
• the surface-crosslinked particulate poly(meth)acrylic acid (salt)-based water-absorbing resin obtained by said method satisfies (1) to (4) below:
• (1) a centrifuge retention capacity (CRC) of not less than 20 g/g and not more than 35 g/g;
• (2) an absorption against pressure (AAP), measured under a load of 0.7 psi, of not less than 25 g/g;
• (3) a saline flow conductivity (SFC) of not less than 15 (×10−7 cm3 sec/g);
• and
• (4) a free swell rate (FSR) of not less than 0.33 g/(g×s).