Patent ID: 8691128

Claim:
An expansion injection molding process comprising charging a thermoplastic resin which has been plasticated and which contains expanding gas dissolved therein into a cavity defined by a fixed mold and a movable mold, and then moving the movable mold to enlarge the volume of the cavity to obtain expanded resin molded article, wherein the movable mold is moved toward the fixed mold, whereby a sealing member arranged on at least one of a pair of facing surfaces facing each other outside the cavity of the fixed mold and movable mold is brought into contact with the other facing surface or a sealing member arranged thereon, the sealing member arranged on one of the pair of facing surfaces does not slide against a surface of the other facing surface or a sealing member arranged on the other facing surface during the movement of the movable mold, whereby the cavity is brought into a gas-sealed state; thereafter, the movable mold is moved further toward the fixed mold while the sealing member is compressed, whereby the volume of the cavity is reduced while the gas-sealed state is maintained, whereby the gas pressure in the cavity is increased to a pressure higher than the atmospheric pressure; thermoplastic resin is injected into the cavity in which the gas pressure has been increased, wherein when the thermoplastic resin is injected into the cavity in which the gas pressure has been increased, the gas pressure in the cavity is not further substantially increased by draining the gas in the cavity through a gas passageway; during or after the injection of the thermoplastic resin into the cavity, the gas pressure in the cavity is released; and thereafter, the movable mold is moved apart from the fixed mold, whereby the cavity volume is enlarged, whereby the thermoplastic resin in the cavity is expanded.