In this paper, the correlation between the cell density (the number of cells per unit volume remaining in the foamed polymethylmethacrylate (PMMA) resin) with the decompression time and foaming temperature will be discussed. The foaming was carried out by the following method. The solid PMMA resin was soaked in a blowing agent under high pressure at a temperature higher than the glass transition temperature of the resin. After the foaming agent reached its saturation state, cell nucleation and cell growth were induced by decompression at the elevated temperature. Cell growth was then halted by cooling. Using a device that could accurately control temperature and decompression rate, PMMA resins were foamed under various foaming temperatures and decompression times by the above-mentioned method. The following results were obtained.
(1) The cell density of the foamed PMMA increases when the decompression time is shortened at low foaming temperatures but decreases when the decompression time is lengthened at high foaming temperatures.
(2) The correlation between the cell density of foamed PMMA and the decompression time and foaming temperature can be expressed with a master curve, i. e., a time-temperature equivalence can be derived.
(3) The time-temperature shift factor obtained from the master curve shows Arrhenius type of activation behavior, similar to the viscoelastic behavior of the material.
(4) Based on these correlation, it is possible to predict the necessary foaming conditions to achieve arbitrary cell densities.
抄録全体を表示