Novel Foam Injection Molding Technology Using Carbon Dioxide-Laden Pellets

Injection molding of foamed components typically uses chemical blowing agents (CBAs) or physical blowing agents (PBAs) to produce a cellular or microcellular structure. A CBA can be easily and directly mixed with plastic pellets and fed into the molding machine through the hopper while a generally finer, microcellular structure can be realized using PBAs. The PBA route is accomplished by injecting more environmentally benign gases into the machine barrel to form a single-phase polymer-gas solution that subsequently foams during molding. This article proposes a new foam injection molding technology that enables the ease of processing of the CBA method with the foaming characteristics of a PBA, but in a cost-effective fashion. In this article, the manufacturing method and theoretical background for producing plastic pellets loaded with carbon dioxide as well as the resulting part characteristics are described. Using the proposed technique, lightweight injection molded parts with a cellular structure, good dimensional stability, and a good surface quality can be produced. POLYM. ENG. SCI., 51:2295-2303, 2011. (C) 2011 Society of Plastics Engineers