Observation of Two-Dimensional Shaped Aluminum Flake Orientation During Injection Molding and Its Orientation Mechanism

Use of injection molding with pearl resin containing aluminum (Al) flakes to give a metallic texture on the molded product is increasing. An Al flake has a flat plate shape, and this two-dimensional shaped additive shows a complex orientation. In this study, the orientations of two-dimensional Al flakes were observed in injection molded specimen. Specimen containing holes, slots, and ribs had weldlines and flowlines (or flow marks). The orientations of Al flakes in the normal flow region, weldlines, and flowlines (or flow marks) were observed by scanning electron microscope and optical microscope. This paper proposes orientation mechanisms of two-dimensional additives. Under the conditions of normal flow, the aluminum flakes were oriented parallel to the flow direction in the skin layer and were perpendicular to the flow direction in the core layer. At weldlines (or flow marks), the aluminum flakes were oriented perpendicular to the flow direction, while an irregular orientation occurred under ribs, showing flowlines (or flow marks).