Co‐injection molding of reinforced polymers

Abstract Co‐injection molding of calcium carbonate filled polypropylene, short glass‐fiber‐filled polypropylene, or unfilled high‐density polythylene melts is studied using a mediumsize injection‐molding machine and a center‐gated disc mold. Injection molding is carried out under non‐isothermal conditions. Order of injection of the melts, injection speed, and mold temperature is changed in order to understand the mold filling in general and to investigate the type of skin/core structure and mechanical interlocking of the phases in the moldings. It is found that the order of injection is not significant in obtaining a skin/core structure but it is important in obtaining extensive phase interlocking, which is reduced if the flow rafe and the mold temperature are low. Presence of fillers appears to result in more mechanical interlocking of the phases.