Occurrence of Surface Defects in TPO Injected Foam Parts

The occurrence of surface defects in TPO injected foam parts has been investigated. Unlike typical flow marks such as tiger stripes that affect the surface quality of injected bulk parts, jetting and silver streaks are the major problems encountered with the TPO foamed parts. Systematic experiments are performed to study the effect of rheological properties and key injection parameters, such as melt temperature, mold cooling, and injection speed on the occurrence of the surface defects. Premature cell nucleation before the injection of the melt into the mold is believed to be the main cause of the surface defects. Therefore, methods that avoid injection of a two-phase mixture into the mold and force cell nucleation to take place strictly in the mold are considered to improve the surface quality of the parts.