To obtain a water-absorbing resin with a high water absorption rate by dispersing inert gas bubbles in an aq. soln. of a mixture of a water-soluble unsatd. monomer and a water-soluble cross-linking monomer and conducting the copolymn. of the monomers at a specified ratio of the vol. of the soln. contg. the bubbles to the vol. of the soln. before dispersing the bubbles therein.
An aq. monomer soln. with a concn. of 15-50wt.% is prepd. by mixing 100 pts.wt. water-soluble unsatd. monomer (e.g. acrylic acid or sodium acrylate), 0.001-2 pts.wt. water-soluble cross-linking monomer, a fluorine-based cationic surfactant in an amt. of 0.0001-10wt.% of the sum of the monomers, and a certain amt. of water. The soln. is stirred at a high speed in an nitrogen atmosphere to homogeneously disperse a large amt. of nitrogen bubbles having an average bubble size of 10-500μm in the soln. When the vol. of the soln. contg. the bubbles reaches 1.02-5 times that of the soln. before dispersing the bubble, a redox catalyst comprising Na2S2O8, an aq. soln. of NaHSO3, etc., in an amt. of 0.001-5wt.% of the sum of the monomer is added to the soln. and the monomers are copolymerized at 20-110°C. The resultant spongy hydrogel polymer is thermally dried and ground to give the a water-absorbing resin.
MIYAKE KOJI
MOTONO YOSHIHIRO
TAWARA HIDEYUKI
