2022 年 34 巻 6 号 p. 223-230
Surface quality is an important issue for plastic automotive parts. Weld lines are one of several types of surface defects, but it is known that weld lines can be improved by controlling the confluence angles of the flow of resin in the die. Additionally, surface grooves that occur at confluence points during molding become smoother after the application of primer in the painting process. However, even after the painting process, there are quality defects that appear in the vicinity of weld lines that look like scratches, and urgent efforts are being made to develop technologies to reveal and control the causes of occurrence. Concerning improvement in the visual surface quality of bumpers and other external components, when light hits the raised resin confluence areas after the painting process, shadowing causes them to look like defective scratches. In this paper, in order to improve the visual quality of parts after painting, we investigated the surface profile using automotive composite PP material. As a result of our investigations we found these defects that are classified as ridges look like slight, connected scratches, and that the elongation and orientation of rubber and talc contained in the composite material affects the raised areas and their size. Therefore, in order to clarify the mechanism of the ridges, the process of elongation and orientation of the rubber flowing in the mold was quantified by SEM observation and binarization of the rubber orientation. The results showed that the orientation of the rubber in the skin layer affected the ridges.