Effect of key process variables on microstructure of injection molded microcellular polystyrene foams

The effect of control factors as key process variables on injection molds of microcellular plastics were investigated experimentally in this paper. The continuos foam processing system was constructed using screw preplasticating type injection mold machine, which is capable of supplying blowing agent, plasticity, kneading and keeping of retention time for gas/polymer solution. The propriety of foam processing system constructed in this study was verified. Control factors that affect cell nucleation and growth by injection molding were classified and some of them were considered in this study. In order to investigate cell morphology and cell structure, microcellular polystyrene samples were produced under various ranges in control factors by using the above processing system. In particular, the effect of injection velocity, mold temperature, retention time, plunger stroke and dwelling pressure on cell morphology of microcellular polystyrene were examined and discussed. It was found that cell size decreases and cell density increases with an increase in injection velocity. Cell size decreases about linearly with an increase in injection velocity and becomes about half size for five times of velocity. An increase rate of cell density is about ten times to five times of injection velocity.