Study on Foam Injection Molding of Thermoplastic Elastomer by Supercritical Fluid

Abstract

Foam injection molding is a molding method that generates cells in the resin by dissolving carbon dioxide and chemical foaming agent. Foam injection molding makes it possible to reduce weight of products and material by generating cells in the resin. However, this technique may cause a problem defective molded product was a defects known as short-shot if the amount of resin that is filled into the mold is insufficient. Therefore, in this study, we studied to prevent the molding defects such as short shot, and to clarify molding conditions and factors to achieve stable molding process in continuous molding. Foam injection molding with a thermoplastic elastomer and supercritical carbon dioxide was carried out. We considered molding conditions and factors that prevented molding defects such as short-shot and could realize a stable molding process. We have revealed the following results. When carbon dioxide gas was injected at a pressure lower than the critical point, weight of the resin was constant and the weight of the molded product was stable. Therefore, we could achieve a stable molding process, and prevent short-shot. However, in this case, it is necessary to use a gas having a high-solubility into the resin.