Improvement of Appearance of Injection Molded Products made of Polypropylene Containing Bright Flakes by Induction Heating and Cooling Injection Mold Equipped with Melt Flow Control System

Abstract

In polymer injection molding, to achieve surface appearance resembling metallic coating without painting the molded product, bright material such as aluminum flake is sometimes mixed into the resin. In such cases, the generation of weld lines which appear as lines with different gloss and coloring are formed at the flow front meeting area of molded products and the vicinity areas. In this study, we used an electromagnetically induced heating and cooling injection mold equipped with system to control the melt flow to mold polypropylene containing aluminum flakes. As a result, it was clarified that weld lines with inconsistent coloring can be reduced by controlling the melt flow while heating the mold. We also measured the light reflectance of the molded products and confirmed that the color inconsistency is due to the orientation of the aluminum flakes around the flow front meeting area.