Mitsubishi Yuka Badische Company, Ltd.

Shinya Ohgi

Hiroshi Matsui

Naoto Taga

A process for producing expandable styrene-based polymer beads is disclosed, which comprises adding a low temperature polymerization initiator that is decomposable to the half at a temperature of from 50.degree. to 80.degree. C. for a period of 10 hours to an aqueous medium having suspended therein blowing agent-containing expandable styrene-based polymer small particles whose particle sizes have been adjusted so as to have a particle size distribution falling within a mean particle size .+-.20% in a proportion of at least 1/2 the amount required for polymerization of a styrene-based monomer to be added to the system, adding a blowing agent to the system in an amount enough to inhibit expansion of said expandable styrene-based polymer small particles while the system is heated to a temperature for first stage polymerization, continuously or intermittently adding thereto a styrene-based monomer to which the rest, if any, of said low temperature polymerization initiator and a high temperature polymerization initiator that is decomposable to the half at a temperature of from 80.degree. to 120.degree. C. for a period of 10 hours have been added, adding a blowing agent to the polymerization system in an amount required for desired expansion of the resulting expandable styrene-based polymer beads, effecting first stage polymerization at a temperature ranging from a temperature 10.degree. C. lower than the decomposition temperature of said low temperature polymerization initiator for obtaining a half-life of 10 hours to a temperature 20.degree. C. higher than said decomposition temperature, and subsequently effecting second stage polymerization at an elevated temperature of from 100.degree. to 150.degree. C. The process makes an effective use of expandable styrene-based polymer small particles obtained by suspension polymerization in the presence of a blowing agent whose particle size is unsuitable for use as expandable beads. The resulting expandable styrene-based polymer beads have a desired particle size with a narrow particle size distribution.

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Mie, Japan

Shinya Ohgi