Patent ID: 6506807
Filing Date: 2003-01-14
Classification: B29C,C08J

Abstract:
A batch process for preparing pre-expanded particles of a thermoplastic resin comprising:charging particles of a thermoplastic resin and an aqueous dispersion medium containing, as a dispersing agent, a slightly water-soluble inorganic compound and a surface active agent into a closed pressure vessel, the amount of said slightly water-soluble inorganic compound being from 0.15 to 2.0 parts by weight per 100 parts by weight of said particles of thermoplastic resin, heating the resulting aqueous dispersion of the resin particles to a temperature of not less than the softening point of said thermoplastic resin in said vessel, releasing said aqueous dispersion of the resin particles containing a blowing agent consisting essentially of water in an amount sufficient to expand said resin particles in an expansion ratio of 3 to 40 from said closed vessel into an atmosphere of lower pressure than the inner pressure of said closed vessel, thereby expanding said particles, separating the produced pre-expanded particles and subsequently drying them without washing, recovering said aqueous dispersion medium containing the slightly water-soluble inorganic compound and the surface active agent, and recycling the recovered aqueous dispersion medium to said closed pressure vessel as a dispersion medium for a subsequent batch process.