Patent ID: 11970585
Assignee: NIPPON SHOKUBAI CO., LTD.
Field: Chemical engineering (Chemistry)
Classification: CPC C  B | IPC C

Claim 0:
1. A method for producing a water absorbent resin comprising:
i) a polymerization step of polymerizing an aqueous monomer solution to obtain a hydrogel crosslinked polymer;
ii) a gel crushing step of crushing the hydrogel crosslinked polymer, the step being performed in the middle of and/or after the polymerization step i);
iii) a drying step of drying the hydrogel crosslinked polymer after the gel crushing step ii);
iv) a crushing step of crushing a dried polymer after the drying step iii);
v) a classifying step of removing fine powder from the dried polymer after the drying step iii); and
vi) a fine powder recycling step of recycling the fine powder removed in the classifying step v) before the drying step iii),
wherein the fine powder recycling step vi) includes:
vi-1) a granulation step of mixing the removed fine powder and an aqueous liquid to obtain a granulated gel, wherein the aqueous liquid is added in an amount of 10 parts by mass or more and less than 100 parts by mass relative to 100 parts by mass of the fine powder, a mixing time of the aqueous liquid and the fine powder is 1 second or more and 3 minutes or less;
vi-2) a granulated gel adding step of adding the granulated gel to the hydrogel crosslinked polymer in at least one step of and/or between the steps i) to iii) until completion of drying in the drying step iii); and
vi-3) a gel mixing step of mechanically mixing the hydrogel crosslinked polymer and the added granulated gel in at least one step of and/or between steps from the granulated gel adding step vi-2) to completion of drying in the drying step iii),
wherein, in the granulated gel adding step vi-2),
a temperature difference between a temperature of the granulated gel and a temperature of the hydrogel is 40° C. or less,
a time period from addition of the granulated gel to the hydrogel to the start of the mechanical mixing is within 5 minutes,
a solid content of the granulated gel is in a range of 50 mass % or more to 90 mass % or less, and
a temperature of the granulated gel is in a range of 50° C. or more to 100° C. or less.