Method of manufacturing foamed thermoplastic resin profiles

Abstract

A method for producing foamed thermoplastic resin profiles with an outer skin layer of increased hardness and an inner foam structure which may be used in place of wooden articles. The outer skin has a smooth surface and a good appearance, and the inner portion enclosed by the skin has a uniform foam structure. Also, with this method an improved foaming efficiency can be obtained. The method comprises a step of melting and kneading a mixture consisting of a thermoplastic resin and a foaming agent without causing the gasification of the foaming agent, a step of heating the melted and kneaded mixture obtained in the previous step to cause the gasification of the foaming agent without agitating the mixture and under a pressure sufficient to supress the substantial foaming of the mixture, thereby forming an expandable melted resin mixture containing microbubbles which are prevented from gathering and uniting, and a third step of causing the melted resin obtained in the previous step to expand while cooling the resin by leading the resin to a foaming die under low temperature and low pressure conditions.