Orientation of flake pigments in injection-molded polymer: Numerical simulation and its application to appearance prediction

• Published in: Powder technology 2023-10, Vol.428, p.118848, Article 118848
• Main Authors: Sasayama, Toshiki, Okamoto, Hirotaka, Kawada, Jumpei, Sato, Norikazu, Ishibashi, Takuya
• Format: Article
• Language: English
• Subjects: Appearance defect; Flake pigment; Injection molding; Numerical simulation
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2023.118848

A particle-level simulation of flake pigment orientation in injection molding was proposed to predict appearance defects caused by disturbed flake orientations. The effects of fountain flow and resin solidification were considered in order to reproduce the formation process for the orientation near the product surface, which has a large impact on the product appearance. In addition, an efficient method using a reverse-time calculation to predict the orientation in a surface layer was developed. The proposed method was verified by applying it to two types of center-gated disks, with different numbers of obstacles consisting of a hole and a thin-walled area, which were injection molded using polypropylene and aluminum flakes. For both disks, the proposed simulation reasonably predicted the location of the flow line defects generated downstream of the obstacles. We also performed an X-ray micro-computed tomography analysis to reveal the characteristic orientation distribution in the flow line. [Display omitted] •The orientation of flake pigments in injection molding was simulated.•An efficient simulation scheme was developed.•The location of the flow line defects caused by misaligned flakes was reasonably predicted.•X-ray micro-computed tomography analysis revealed the orientation distribution in the flow line region.