Water-absorbent resin powder and production method thereof
The present invention addresses the problem of providing; a water absorbent resin powder having a reduced amount of fine powder generated and a reduced amount of fine powder recovered; and a production method for the water absorbent resin. The production method of the present invention includes a drying step and a fine powder granulation step. The drying step is for obtaining a dried polymer by drying a particulate water-containing gel crosslinked polymer which is obtained using an acid group-containing unsaturated monomer as a main component. The fine powder granulation step is for obtaining a fine powder granulated product by adding a binder and an adhesion control agent to a fine powder made of a water absorbent resin. In this production method, the obtained fine powder granulated product is recovered in the drying step or in any step before the drying step.
1. A method of producing a water-absorbent resin powder, the method comprising:
a drying step of drying a particulate hydrogel crosslinked polymer which is obtained using an acid group-containing unsaturated monomer as a main component to obtain a dried polymer, and
a fine powder granulation step of adding a binder and an adhesion controlling agent to fine powder formed of a water-absorbent resin to obtain a fine powder granulated product,
wherein the fine powder granulated product is recovered after the gel crushing step and before the drying step, or during the drying step;
wherein the adhesion controlling agent is added in a form of aqueous solution; and
an added amount of the adhesion controlling agent is from 0.02 mass % to 1.0 mass % relative to the solid content of the fine powder formed of the water-absorbent resin;
wherein a stirring dryer having one or more of heating means selected from a group of a ventilation heating type, an outer wall heating type and a tubular heating type in the drying step;
wherein a temperature of the fine powder granulated product and the particulate hydrogel cross-linked polymer is in a range of 50° C. or more to 100° C. or less; and
a temperature difference between the fine powder granulated product and the particulate hydrogel cross-linked polymer is within 30° C.
2. The method according to claim 1 , wherein the adhesion controlling agent is a surfactant.
3. The method according to claim 1 , wherein a drying method is stirring drying in the drying step.
4. The method according to claim 1 , wherein
a main component of the fine powder is a poly (meth) acrylic acid (salt)-based crosslinked polymer, and
a mass average particle diameter of the fine powder is less than 150 μm.
5. The method according to claim 1 , further comprising:
a surface crosslinking step of surface crosslinking the particulate hydrogel crosslinked polymer and/or particulate dried polymer; and
a sizing step of adjusting the particle size of the dried polymer and/or surface-crosslinked dried polymer;
wherein the fine powder is obtained in the sizing step.
6. The method according to claim 1 , wherein the fine powder granulated product contains a surface crosslinked fine powder.
7. The method according to claim 1 , wherein an added amount of the water vapor relative to the fine powder is, per unit time, in a range of 1% by mass or more to 100% by mass or less.
8. The method according to claim 1 , wherein a solid content of the fine powder granulated product is in a range of 30% by mass or more to 80% by mass or less.
9. The method according to claim 1 , wherein an atmospheric dew point in an interior of a dryer is in a range of 60 to 100° C. in the drying step.
10. A water-absorbent resin powder obtained by the production method according claim 1 .
11. The water-absorbent resin powder according to claim 10 , wherein
the water-absorbent resin powder contains a water-absorbent resin fine powder granulated product containing an adhesion controlling agent;
the adhesion controlling agent is a surfactant; and
a content of the surfactant in the water-absorbent resin fine powder granulated product is larger relative to an average content of the surfactant in the water-absorbent resin powder.
12. The water-absorbent resin powder according to claim 10 , wherein
a proportion of particles having a particle diameter of less than 150 μm contained in the water-absorbent resin powder is 15% by mass or less.