Abstract
In this paper, the equivalency between the foaming time and foaming temperature of the cell density, the number of cells per unit volume remaining in the foamed plastics, will be discussed. The foaming was carried out by the following method. The blowing agent was soaked into the solid resin at high pressure under temperature lower than the glass transition temperature of the resin. After the blowing agent reached its saturation state, cell nucleation and cell growth were induced by heating various foaming temperatures higher than glass transition temperature and various foaming times after decompression. Finally, cell growth was halted by cooling. Concretely, using a device that can accurately control temperature and the decompression rate, polystyrene (PS) and polycarbonate (PC) resins which are amorphous resins were foamed under various the foaming temperatures and the foaming times by the above-mentioned method. The following results were obtained. (1) Cell density of foamed PS and PC plastics shows time and temperature dependence as the cell density becomes large when foaming temperature is low and foaming time is short. (2) Equivalency is maintained between the foaming time and foaming temperature dependence of the cell density of PS and PC foamed plastics, and they can be expressed with one master curve respectively. That is, the time-temperature equivalent law is held about cell density. (3) These results seem to become one technique to select the foaming condition of foamed plastics having required cell densities.