Pre-expanding process and apparatus for the same.

摘要

A process for preparing pre-expanded particles of a thermoplastic resin which comprises; heating under an elevated pressure an aqueous dispersion comprising thermoplastic resin particles (2) containing a volatile foaming agent and an aqueous medium (3) in a pressure vessel (1); releasing the dispersion from the pressure vessel (1) into a space within a sealed low-pressure vessel (7) wherein the pressure is lower than that in the pressure vessel (1), whereby expanding the thermoplastic resin particles (2) to give pre-expanded particles (8); and simultaneously recovering the foaming agent volatilized from the thermoplastic resin particles by discharging the foaming agent out of the space in the low-pressure vessel (7) with controlling the pressure in the low-pressure vessel (7) to substantially a given pressure. According to the process, the release of the volatile foaming agent into the air is prevented.