METHOD FOR MANUFACTURING BIAXIALLY STRETCHED POLYESTER CONTAINER SHOWING PREVENTED WHITENING AT BOTTOM PORTION

摘要

PROBLEM TO BE SOLVED: To provide a method for preventing whitening of a bottom portion and generation of a white line in a method for manufacturing a biaxially stretched polyester container comprising a process of injection-forming a polyester into a bottom-possessing prefoam having a substantially non-crystalline sidewall portion and a process of biaxially stretching blow-forming the bottom-possessing prefoam in the temperature range of stretching the polyester by use of an injection machine equipped with a nozzle tip with a valve stem. SOLUTION: A method for manufacturing a biaxially stretched polyester container which prevents whitening at a bottom portion comprises a process of injection-molding a polyester into a bottom-possessing prefoam having a substantially amorphous sidewall portion and a process of biaxially stretching and blow-molding the bottom possessing prefoam in a temperature range for stretching the polyester, wherein a die for injection-molding the bottom- possessing prefoam is equipped with a gate portion comprising a straight cylindrical portion and a taper portion having a diameter increasing toward a cavity connected to the cylindrical portion and the injection machine is equipped with a nozzle tip having a reciprocatable valve stem fittable in the cylindrical portion, the fitting-in amount of the cylindrical portion and the valve stem during cutting the prefoam gate being 0.05 to 0.19 time the diameter of the cylindrical portion.