Particulate water-absorbing agent
The present invention provides a particulate water-absorbing agent which has an excellent fluid retention capacity under pressure and an excellent liquid permeability. Each of the following values of the particulate water-absorbing agent of the present invention falls within a certain range: a ratio represented by “centrifuge retention capacity/Ln (water-soluble component amount)”; a molecular weight distribution of the water-soluble component; a weight average molecular weight after a hydrolysis treatment; and a branching density after the hydrolysis treatment.
1. A particulate water-absorbing agent comprising a polyacrylic acid (salt)-based water-absorbing resin as a main component, said particulate water-absorbing agent satisfying (a) through (d) below:
(a) EXI represented by the following Formula (1) is not less than 11.5:
EXI=centrifuge retention capacity/Ln (water-soluble component amount) (1),
(b) a molecular weight distribution of a water-soluble component is 1.0 to 4.8÷
(c) a weight average molecular weight after a hydrolysis treatment is 450,000 Da to 1,800,000 Da, and
(d) a branching density after the hydrolysis treatment is not more than 0.100,
said hydrolysis treatment being a treatment carried out by allowing said particulate water-absorbing agent to swell in a 0.9 weight% aqueous sodium chloride solution, removing the water-soluble component so as to obtain a gel, and allowing 600 mg of the gel to stand still in 10 mL of a 0.1 N aqueous sodium hydroxide solution at 80° C. for 3 weeks.
2. The particulate water-absorbing agent according to claim 1 , wherein
a weight average molecular weight of the water-soluble component is 200,000 Da to 1,000,000 Da.
3. The particulate water-absorbing agent according to claim 1 , wherein
a fluid retention capacity under pressure is not less than 20 g/g.
4. The particulate water-absorbing agent according to claim 1 , wherein
a saline flow conductivity is not less than 10×10−7·cm3·s·g−1.
5. The particulate water-absorbing agent according to claim 1 , wherein
a water absorption time is not more than 42 seconds.
6. The particulate water-absorbing agent according to claim 1 , wherein
a free swell rate is not less than 0.28 g/(g·s).
7. The particulate water-absorbing agent according to claim 1 , wherein
a branching degree after the hydrolysis treatment is not more than 2.5.
8. The particulate water-absorbing agent according to claim 1 , wherein
said particulate water-absorbing agent is surface-crosslinked with use of a covalent bonding surface-crosslinking agent.
9. The particulate water-absorbing agent according to claim 1 , further comprising:
a polyvalent metal salt.
10. The particulate water-absorbing agent according to claim 1 , wherein
particles having particle diameters of less than 150 μm are contained at a proportion of not more than 5 weight%.