Synthetic resin bottle having a gradation pattern, and process for injection molding the preform for use in such a bottle

摘要

SYNTHETIC RESIN BOTTLE HAVING A GRADATION PATTERN, AND PROCESS FOR INJECTION MOLDING THE PREFORM FOR USE IN SUCH A BOTTLE 5 Abstract There is disclosed a process for injection molding a preform in the shape of a test tube to be used in biaxial drawing and blow molding, which comprises: flowing molten synthetic resins through at least three layer-forming channels consisting of a cylindrical inner flow channel (15), a middle flow channel 1o (16), and a cylindrical outer flow channel (17); flowing the resins through a confluence (18) disposed downstream of these layer-forming channels and through a joined flow channel (19); passing the resins through a gate disposed at a position opposed to center of bottom (107); and 15 injecting the resins into mold (1) to form a preform; and which also comprises: supplying the inner flow channel (15) and the outer flow channel (17) with a main resin for the preform (101) from at least one loader (A) at a predetermined time span, pressure, or velocity; 20 supplying the middle flow channel (16) with a colored resin from another loader (B) at a predetermined pressure and/or velocity during a predetermined time within said time span; allowing the colored resin to join the main resin from the inner flow channel (15) and the outer flow channel (17) at a confluence (18) in such a manner that the 25 layer of colored resin is sandwiched between the two layers of the main resin; forming a multi-layered molten resin fluid having an intermediate layer of the colored resin between the layers of main resin within the joined flow channel (19) over a certain span of time; adjusting injection pattern including the time of starting and ending the 30 supply of colored resin, pressure and/or velocity profiles; and reducing the thickness of this intermediate layer at an upstream or downstream point of the flow gradually in the upstream or downstream direction so as to form a color-gradated portion caused by the change in thickness.