Process for preparing expanded product of thermoplastic resin

摘要

A process for preparing an expanded product of a thermoplastic resin is herein disclosed which comprises a gas dissolving step of adding supercritical carbon dioxide and/or nitrogen as an blowing agent to a thermoplastic resin, and melting it in the thermoplastic resin, a cooling step of cooling the resulting molten resin composition under a pressure not less than a critical pressure of the blowing agent, a nuclei forming step of discharging the molten resin composition from a die(4)to lower the pressure to a level not more than the critical pressure, and an expansion controlling step of cooling an expanded product of the thermoplastic resin to a level not more than a glass transition temperature or a crystallization temperature of the resin to control a cell diameter of the expanded product, wherein the process comprises a shear rate adjusting section (12) having a function of generating a shear rate in the range of 10<2> to 10<4> sec<-1> and having a sectional area A, and a flow velocity distribution adjusting section (13) having a function of lowering the shear rate and having a sectional area B, and B/A is in the range of 1.3 to 20, whereby a cell diameter and a cell density are controlled. According to this process, the expanded product of the thermoplastic resin can be obtained which has an excellent surface appearance, a high strength, and cells of a fine average cell diameter and a uniform average cell density and in which carbon dioxide and/or nitrogen is used as the blowing agent.