METHOD FOR PRODUCING A WATER-ABSORBENT RESIN
First Claim
1. A method for producing a water-absorbent resin by a multi-stage reversed-phase suspension polymerization to polymerize a water-soluble ethylenically unsaturated monomer, wherein the first stage polymerization comprising at least the following steps:
- (A) performing a primary dispersion in the absence of surfactants by stirring to mix an aqueous solution of a water-soluble ethylenically unsaturated monomer containing a water-soluble radical polymerization initiator in a petroleum hydrocarbon dispersion medium in which a hydrophobic polymeric dispersion agent is dispersed or dissolved;
(B) performing a secondary dispersion by adding a surfactant to the resultant dispersion liquid; and
(C) performing a radical polymerization to obtain water-absorbent resin particles in a hydrous gel state which disperse in the petroleum hydrocarbon dispersion medium; and
the second stage polymerization comprising at least the following steps;
(D) precipitating at least a part of the surfactant;
(E) stirring to mix the aqueous solution of the water-soluble ethylenically unsaturated monomer of the second stage polymerization containing a water-soluble radical polymerization initiator therein to be absorbed and aggregated in the polymerized gel at the first stage; and
(F) performing a radical polymerization again;
wherein the aqueous solution of the water-soluble ethylenically unsaturated monomer is added in step (A) to the petroleum hydrocarbon dispersion medium at an addition rate V of 0.30 [min−
1] or less defined by the following Equation (I);
V=F×
A/T wherein V;
Addition rate [min−
1], F;
Average linear flow rate from nozzle [m/min], A;
Cross-sectional area of nozzle [m2], and T;
Total amount [m3] of aqueous monomer solution added to a polymerization reaction tank.
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Abstract
A method for producing a water-absorbent resin having a further reduced odor as compared with a water-absorbent resin obtained by a conventional method as well as a water-absorbent resin produced by the same method, by maintaining the addition rate V from the pouring nozzle for the aqueous solution of the water-soluble ethylenically unsaturated monomer in a polymerization reaction tank not more than 0.30 [min−1], in the first stage polymerization step which is within the step of the conventional method upon performing multi-stages such as two or more stages of reversed-phase suspension polymerizations in a method for producing a water-absorbent resin, and thereby by being able to reduce the amount of the petroleum hydrocarbon dispersion medium remaining in the above water-absorbent resin.
4 Citations
20 Claims
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1. A method for producing a water-absorbent resin by a multi-stage reversed-phase suspension polymerization to polymerize a water-soluble ethylenically unsaturated monomer, wherein the first stage polymerization comprising at least the following steps:
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(A) performing a primary dispersion in the absence of surfactants by stirring to mix an aqueous solution of a water-soluble ethylenically unsaturated monomer containing a water-soluble radical polymerization initiator in a petroleum hydrocarbon dispersion medium in which a hydrophobic polymeric dispersion agent is dispersed or dissolved; (B) performing a secondary dispersion by adding a surfactant to the resultant dispersion liquid; and (C) performing a radical polymerization to obtain water-absorbent resin particles in a hydrous gel state which disperse in the petroleum hydrocarbon dispersion medium; and the second stage polymerization comprising at least the following steps; (D) precipitating at least a part of the surfactant; (E) stirring to mix the aqueous solution of the water-soluble ethylenically unsaturated monomer of the second stage polymerization containing a water-soluble radical polymerization initiator therein to be absorbed and aggregated in the polymerized gel at the first stage; and (F) performing a radical polymerization again; wherein the aqueous solution of the water-soluble ethylenically unsaturated monomer is added in step (A) to the petroleum hydrocarbon dispersion medium at an addition rate V of 0.30 [min−
1] or less defined by the following Equation (I);
V=F×
A/Twherein V;
Addition rate [min−
1], F;
Average linear flow rate from nozzle [m/min], A;
Cross-sectional area of nozzle [m2], and T;
Total amount [m3] of aqueous monomer solution added to a polymerization reaction tank.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification