Japan Synthetic Rubber Co., Ltd.

Fujio Sakurai

Hiroshi Tadenuma

Kiyoshi Kasai

Nobuo Kawashima

Polymer particles prepared by polymerizing polymerizable monomers by seed polymerization, with far more excellent polymerization stability than conventional seed polymerization processes, in the presence of a polymer emulsion comprising low molecular weight polymer particles, radically polymerizable in an aqueous system. The polymer particles are present in an amount of 0.5-30 parts by weight (on solid basis) per 100 parts by weight of polymerizable monomers, have a weight average molecular weight of 500-10,000 and are prepared by emulsion polymerization or soap-free polymerization. The seed polymerization is carried out by initially charging less than 30% by weight of said polymerizable monomers to the polymerization mixture, and after the polymerization conditions are established, by continuously or intermittently adding the remaining portion of said polymerizable monomers to the reaction system.

Process for preparing polymer particles

Hollow polymer particles having at least two polymer layers, wherein (1) the particles have an average particle diameter in the range of 0.15 to 20 micrometers, (2) each of the particles has an average equivalent hollow diameter/equivalent particle diameter in the range of 0.2 to 0.8, (3) the proportion of a toluene-insoluble portion of the particles is 20 to 90% by weight, (4) the polymer particles have a melt flow rate at 180.degree. C. under 10 kgf/cm.sup.2 of 0.1 to 1 g/10 min., (5) the inside layer of the two polymer layers is composed of a crosslinked polymer and (6) the outside layer of the two polymer layers is composd of a non-crosslinked polymer. This invention also provides hollow crosslinked polymer particles wherein the proportion of a toluene-insoluble portion of the particles exceeds 85% by weight, the melt flow rate of the polymer particles at 180.degree. C. under 10 kgf/cm.sup.2 is less than 0.2 g/10 min., and the outside layer is composed of a crosslinked polymer. The hollow polymer particles are useful, for example, as a pigment, and for a paper coating composition and a general-purpose coating composition.

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Yokkaichi, Japan

Fujio Sakurai