Patent ID: 8889053

Claim:
An injection molding method for a preform using an injection molding apparatus comprising a mold apparatus for injection-molding a bottomed tubular preform having a neck with an opening portion at an upper end thereof, a body continuous with the neck, and a bottom continuous with the body and larger in wall thickness than the body, comprising a neck mold for forming an outer surface of the neck; an injection cavity mold for forming outer surfaces of the body and the bottom of the preform; and an injection core mold for forming at least an inner surface of the preform, wherein the injection core mold includes an inside core mold, inserted into the injection cavity mold, for forming the inner surface of the preform, and an outside core mold, having a leading end portion clamped by the neck mold, for forming an upper end surface of the preform and holding the inside core mold slidably in accordance with a change in a pressure within an injection space, and the mold apparatus further comprises regulation means for regulating movement of the inside core mold toward an outside of the injection cavity mold, the method comprising: injecting a raw material continuously into the injection space to charge the raw material into the injection space while moving the inside core mold from a first position to a second position; and then cooling the raw material within the injection space to solidify the raw material, while holding the inside core mold at the second position by continuing injection of the raw material into the injection space.