Super absorbent polyacrylic acid (salt)-based resin powder, method for manufacturing same, and method for evaluating same
The present invention provides polyacrylic acid (salt)-based water-absorbing resin powder having an excellent fluid retention capacity under pressure, an excellent water absorption speed, and an excellent liquid permeability and a method for producing the polyacrylic acid (salt)-based water-absorbing resin powder. The earlier-described objects are attained by: a method for producing water-absorbing resin powder which includes adding an inorganic compound to a crosslinked hydrogel polymer obtained in a polymerization step of polymerizing a polyacrylic acid (salt) and performing crushing in specific gel-crushing conditions; and the resultant water-absorbing resin powder.
1. Polyacrylic acid (salt)-based water-absorbing resin powder comprising a polyacrylic acid (salt) as a main component, wherein some particles of said polyacrylic acid (salt)-based water-absorbing resin powder include an inorganic compound internally present therein, said polyacrylic acid (salt)-based water-absorbing resin powder satisfying the following physical properties (1) to (4):
(1) a water absorption time according to a vortex method (Vortex) is 42 seconds or less or a free swell rate (FSR) is 0.28 g/(g·s) or more;
(2) a percentage of water-absorbing resin powder having a particle size of 150 μm or more and less than 850 μm is 90 weight % or more;
(3) a gel particle's collapse rate at swelling is 10 weight % or less;
(4) an internal gas bubble ratio defined by the following equation is 0.1% to 2.5%:
Internal gas bubble ratio (%)=(true density−apparent density)/true density×100.
2. The polyacrylic acid (salt)-based water-absorbing resin powder according to claim 1 , further satisfying any one or more of the following physical properties (5) to (9):
(5) a fluid retention capacity under pressure (AAP) is 20 g/g or more;
(6) a saline flow conductivity (SFC) is 10×10 −7 ·cm 3 ·s·g −1 or more;
(7) a percentage of water-absorbing resin powder having a particle size less than 150 μm is 5 weight % or less;
(8) a percentage of water-absorbing resin powder having a particle size of 850 μm or more is 5 weight % or less; and
(9) a centrifuge retention capacity (CRC) is 10 g/g or more.
3. The polyacrylic acid (salt)-based water-absorbing resin powder according to claim 1 , wherein said polyacrylic acid (salt)-based water-absorbing resin powder is surface-crosslinked with a covalently bonding surface-crosslinking agent.
4. The polyacrylic acid (salt)-based water-absorbing resin powder according to claim 1 , wherein said inorganic compound is in the form of inorganic particles, the inorganic particles being a polyvalent metal salt.