Apparatus and process for injection molding a thermoplastic resin article

摘要

The present invention provides an apparatus for injetion molding a void plastic article, characterized by that a liquid foaming agent is injected through an injection pin (25) into the injected plastic material in a mold cavity of a plastic injection mold unit (20). The injection pin (25) is assembled with the void forming apparatus which is mounted at a location of a movable mold section (22) or of a stationary mold section (21). The liquid foaming agent is injected through an injection pin (25) into the injected plastic material in a liquid state without preheating the liquid foaming agent. The void forming apparatus consists of an injection pin (25) and an injection cylinder (24). The void forming apparatus carries out periodically reciprocal movement into the mold cavity so that the injection pin (25) may enter the cavity when a liquid foaming agent is injected into plastic material, and that the injection pin (25) may return to its original position. A feeding meter (28) is installed in front of the void forming apparatus. The feeding meter (28) measures a predetermined amount of a liquid foaming agent and supplies the liquid foaming agent into the injection cylinder (24). More than one void forming apparatus (24, 25) may be mounted at locations of a movable mold section (22) or of a stationary mold section (21) in a accordance with the shape of a molded article. The liquid foaming agent is injected through the injection pin (25) immediately after the total amount of the molten plastic material for an article is injected by a molding machine or after most of the molten plastic material for an article is injected by a molding machine. Furtheron there is provided a process of injection molding for forming a plastic article. <IMAGE>