Process for production of water-absorbing resin particles, water-absorbing resin particles, water-stopping material, and absorbent article
The present invention provides a method for producing water-absorbing resin particles having high equilibrium swelling capacity, a high water-absorption rate or high initial swelling capacity, and an appropriate particle size that achieves good handling performance; water-absorbing resin particles obtained by the method; and a water blocking material and an absorbent article which include the water-absorbing resin particles. The present invention is a method for producing water-absorbing resin particles, which comprises: preparing a hydrogel polymer by reversed-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon solvent in the absence of an internal crosslinking agent but in the presence of a surfactant with an HLB of 8 to 12; carrying out a post-crosslinking reaction of the hydrogel polymer whose moisture content is adjusted to 30 to 110 mass % based on a water-soluble ethylenically unsaturated monomer component that composes the hydrogel polymer.
1. A method for producing water-absorbing resin particles, which comprises:
preparing a hydrogel polymer by reversed-phase suspension polymerization of a water-soluble ethylenically unsaturated monomer in a hydrocarbon solvent in the absence of an internal crosslinking agent but in the presence of a surfactant having an HLB in a range from 8 to 12; and
carrying out a post-crosslinking reaction of the hydrogel polymer, whose moisture content has been adjusted so as to form a first-dried gel, to in a range from 30 to 110 mass % relative to a water-soluble ethylenically unsaturated monomer component that forms the hydrogel polymer,
wherein a ratio (A:B) is in a range from 99:1 to 70:30, where A is a moisture content (A) of the first-dried gel and B is a moisture amount (B) added with a post-crosslinking agent for the post-crosslinking reaction.
2. The method according to claim 1 ,
wherein the surfactant having the HLB in a range from 8 to 12 is at least one compound selected from the group consisting of sorbitan fatty acid esters, polyglycerine fatty acid esters, and sucrose fatty acid esters.
3. The method according to claim 1 ,
wherein the post-crosslinking agent is a glycidyl ether compound.
4. The method according to claim 1 ,
wherein an amount of the post-crosslinking agent is in a range from 0.0001 to 1 mol % relative to a total molar amount of the water-soluble ethylenically unsaturated monomer.
5. The method according to claim 1 ,
wherein an amount of the post-crosslinking agent relative to a total molar amount of the water-soluble ethylenically unsaturated monomer is in a range satisfying formula (1):
(−0.0002 Z+ 0.023)≦ Y ≦(−0.0002 Z+ 0.050) (1)
wherein Y represents an amount (mol %) of the post-crosslinking agent, and
Z represents the moisture content (mass %) of the hydrogel polymer upon mixing with the post-crosslinking agent.
6. Water-absorbing resin particles obtained by the method according to claim 1 .
7. The water-absorbing resin particles according to claim 6 ,
wherein equilibrium swelling capacity of the water-absorbing resin is in a range from 10 to 28 mm,
a water-absorption rate of the water-absorbing resin is in a range from 1 to 20 seconds, and
a median particle size of the water-absorbing resin is in a range from 80 to 400 μm.
8. An absorbent article, which comprises:
a liquid-permeable sheet;
a liquid-impermeable sheet; and
an absorber sandwiched between the liquid-permeable sheet and the liquid-impermeable sheet, the absorber including the water-absorbing resin particles according to claim 6 .
9. A water blocking material, which comprises:
two or more liquid-permeable sheets; and
an absorber sandwiched with the two or more liquid-permeable sheets, the absorber including the water-absorbing resin particles according to claim 6 in an amount from 30 to 300 g/m 2 .