Orientation of two dimensional fillers and surface appearance in an injection molded article

Painting and coating impart metallic textures to plastic surfaces but increase manufacturing cost. Therefore, developing a single-step molding method such as injection molding by using plastics containing aluminum (Al) flake (i.e. two-dimensional flat plate) that imparts metallic textures to plastic products is beneficial. Unlike one-dimensional fillers, such as fibers, two-dimensional fillers exhibit complex orientation during molding. In this paper, the orientation of two-dimensional fillers was analyzed, and their surface appearances during the injection molding of various shapes, such as holes, slits and ribs, were predicted. During normal flow, the Al flakes oriented parallel to the flow direction near the skin region of the product, whereas those near the core region and the weldline oriented perpendicular to the flow direction or flow direction. Al flake orientations at the bottom surface of ribs were irregular, causing flow marks. These predicted surface appearances were compared with those of actual injection molded product, and the simulations showed good agreement with the experimental results.