Measurement on Viscosity of Polystyrene Melts Dissolved with Supercritical Nitrogen Fluid During Microcellular Injection Molding

摘要

The purpose of this study is to investigate the rheological behavior of PS melt dissolved SCF of nitrogen during Microcellular Injection Molding process applied with Gas Counter Pressure (GCP) technology. The application of gas into the mold cavity prior to the melt filling provides a counter force against the melt front advancement, restricting the foaming process during the melt filling stage. A slit cavity is designed to measure the pressure drop of polystyrene mixed with 0.4wt% supercritical nitrogen fluid under different mold temperatures (185, 195, and 205°C), injection speeds (5, 10, and 15mm/s) as well as counter pressures (50, 100, 200, 300 bars). It was found that the T_g can be reduced from 96°C to 50°C when the applied GCP is 300 bar. In addition, compared to conventional injection molding, melt viscosity is reduced by up to 30% when GCP is increased from 50 to 200 bar. The non-nucleation mixture melt obtained by using a GCP of 300 bar has 32~49% lower viscosity.