W/O-TYPE POLYMER EMULSION AND USE THEREOF

PURPOSE:To provide a W/O-type polymer emulsion composed of a specific polymer, a specific oil-soluble surfactant, water, a hydrophobic liquid and a phase-inversion promoting surfactant at specific ratios, having low shape-keeping viscosity and excellent water-solubility, dispersion stability and storage stability and useful as a yield-improving agent for paper-making, etc. CONSTITUTION:This W/O-type polymer emulsion is composed of (A) 25-50wt.% (based on the total emulsion) of a polymer containing one or more kinds of water-soluble vinyl monomers of the formulas I to III (R is H or methyl; R is H or 1-3C alkyl; R is H or 1-8C alkyl; R is R or carboxyl; M is H, univalent to trivalent metal ion, etc.) as constituent units, (B) 30-50wt.% of water, (C) 10-30wt.% of a hydrophobic liquid such as n-paraffin, (D) 0.1-8wt.% of oil- soluble surfactants containing (i) one or more kinds of oil-soluble surfactants having an HLB of 2-6 and (ii) one or more kinds of oil-soluble surfactants having an HLB of 8-15 and (E) 0.1-8wt.% of a phase-inversion promoting surfactant such as polyoxyethylene lauryl ether. The particle diameter of the polymer in the emulsion is