Influence of Resin Flow State on Aluminum Flake Orientation in a Metallic-Like Resin Product Manufactured Through Injection Molding

A potential method for predicting the orientation of aluminum flakes in a metallic-like product without a coating was examined. To achieve this goal, injection molding test of a thin product was carried out with a metallic-like resin that contained aluminum flakes. Furthermore, the flow state of the base material (polypropylene) of the metallic-like resin during molding was calculated via computer simulations, and the results were compared to the experimental results. The reflectance and orientation of the product were measured as functions of the gate shape and injection speed. The reflectance of the product made with the metallic-like resin was measured with a spectrophotometer, and the orientation of the aluminum flakes was measured via X-ray computed tomography (CT). The reflectance changed according to differences in the gate shape and injection speed. In addition, the orientation of the aluminum flakes changed with the distance from the surface of the product. The shear rate of the base material was calculated immediately after the resin completely filled the mold, and the results correlated well with the orientation of the flakes. The results suggest that it is possible to predict the orientation of aluminum flakes within metallic-like resins.