Method for producing polyacrylic acid (salt)-based water absorbent resin powder
From a view point of reduction in an out of spec product after surface crosslinking, particularly, when an alkylene carbonate compound is used as a surface crosslinking agent, influence by an air temperature is great, and it is necessary to reduce ethylene glycol which is produced as a byproduct, and there is provided a process for producing a polyacrylic acid (salt)-based water absorbent resin powder, comprising a step of polymerizing an aqueous acrylic acid (salt)-based monomer solution, a step of drying the resulting polymer, an optional grinding•classifying step, and a surface crosslinking step, wherein in the surface crosslinking step, (1) a surface crosslinking agent containing an alkylene carbonate compound and a polyhydric alcohol compound is mixed into a water absorbent resin powder, the mixture is heat-reacted and, further, simultaneously with, or separately from the mixing, an ion reactive surface crosslinking agent is mixed, and/or (2) mixing treatment of mixing a surface crosslinking agent solution into a water absorbent resin powder containing at least one or more kinds of ion reactive surface crosslinking agents is performed two or more times.
1. A polyacrylic acid (salt)-based surface crosslinked water absorbent resin powder, wherein the polyacrylic acid (salt)-based surface crosslinked water absorbent resin powder has a saline flow conductivity (SFC) retention after a paint shaker test at 800 cycle/minute for 20 minutes of 80% or more, and comprises 100 to 1000 weight ppm of ethylene glycol, 1000 to 10000 weight ppm of a C3-C6 polyhydric alcohol, and a polyvalent metal cation or polyvalent cationic polymer, and an internal gas bubble ratio is 0.5% or more.
2. The water absorbent resin powder according to claim 1 , wherein an absorption capacity without load is 25 to 35 g/g, and saline flow conductivity is 45 to 150·10 −7 cm 3 s g −1 .
3. The water absorbent resin powder according to claim 1 , further comprising at least any one a-hydroxycarboxylic acid (salt), and a surfactant.
4. The water absorbent resin powder according to claim 1 , wherein
said water absorbent resin powder has a saline flow conductivity (SFC) after a paint shaker test at 800 cycles/minute for 20 minutes of 30×10 −7 cm 3 ·sec/g or more.