Controlled orientation of reflective pigment and optical property characterization of injection-molded polypropylene

The aims of the research reported were to explore the possibility of removi ng surface weld lines from highly reflective aluminum pigmented polypropyle ne injection moldings. Moldings were optically characterized and their char acteristics attributed to pigment orientation present in the samples. Conve ntional injection molding and two novel molding techniques were employed fo r this investigation, Shear Controlled Orientation Injection Molding (SCORI M) and Bright Surface Molding (BSM). Further, the two techniques, SCORIM an d BSM, were used in series and termed SBM to remove surface weld lines. The use of SBM enabled the re-orientation of the pigment in order to induce a uniform direction for the "flip-flop" effect where flow fronts have impinge d from different directions. These moldings were then quantitatively charac terized using a gonio-spectrophotometer. Their different reflective surface characters were then related to the angle of orientation induced by the re spective processing technologies used.