Process for injection molding a preform of a polyester resin

摘要

When a desired preform is to be molded from a molding material which is a polyester resin composed of a blend of PET and PEN by compressing and melting the molding material by the rotation of a screw in a heating cylinder and injecting and filling the molten material into a mold, a plastication zone 13 for the molding material is formed between a compression zone 12 of the injection screw 2 and a metering zone 14 at an end of the screw. In the plastication zone 13, the molding material is subjected to melting, relaxation, kneading and relaxation steps in order to melt and remove an unmolten material until the molten material reaches the metering zone 14. To prevent a molded article from becoming opaque and the production of a gel-like unmolten granular material when a polyester resin composed of a blend of PET and PEN is used as a molding material.