BOTTLES WITH GRADATION PATTERNS AND PROCESS FOR INJECTION MOLDING OF PREFORMS

摘要

Synthetic resin bottles exhibiting high-grade gradation of color density and decoration which could not be attained in the prior art are provided by injecting a chief material resin and a color resin into a preform while changing gradually and vertically the thickness of the color resin layer constituting the preform by utilizing the gradual thickness reduction phenomenon of the color resin layer caused by the flow of the chief material resin in a preform molding unit and subjecting the preform to biaxial orientation blow molding. According to the process, a preform having a gradation of thickness of a color resin layer is formed by injecting a multilayer molten resin fluid while gradually reducing the thickness of a color resin layer constituting the fluid toward the upstream or downstream end by controlling the injection pattern including feed initiation timing of the chief material resin and the color resin, feed termination timing thereof, pressure, and speed profile, and then the perform is subjected to biaxial orientation blow molding to give a bottle whose body exhibits a gradation of color density or color shade.