Effects of Process Conditions on the Mechanical Properties of Microcellular Injection Molded Polycarbonate Parts

In the supercritical fluid (SCF) microcellular injection molding process, the polymer melt is first mixed with controlled SCF, followed by cavity filling, creating millions of micron-sized voids within the solidified parts. Benefits associated with this microcellular foaming process include significant reductions in part weight, processing temperature, clamping force, shrink/ warpage, dimensional instability, and cooling/cycle. The purpose of this study is to examine the effects of process conditions on the mechanical properties of PC parts, injection molded via microcellular foaming. The thickness of tensile test specimens was 2.5 and 1.2mm. For Izod impact tests, a specimen of 3.2mm thickness was used. On average, the weight of parts was reduced by 40%. Melt temperature can be lowered by about 20—30°C (from 320 to 290°C) and cycle time reduced by 40—70%. Higher injection rates resulted in a more uniform foaming structure. In addition, the supercritical fluid microcellular process did not reduce the tensile strength of the molded parts; instead, the impact energy values increased slightly over parts molded by convectional injection molding.