Method of injection molding thermoplastic resin using supercritical fluid and injection molding apparatus

A method of injection molding for producing an article of which a surface has no foam using an injection molding apparatus comprising

• a mold and a plasticizing cylinder having a screw, the plasticizing cylinder injecting molten resin of thermoplastic resin into the mold by the screw, the method comprising:
• measuring a filling amount of the molten resin in the plasticizing cylinder;
• introducing a supercritical fluid into the molten resin in the plasticizing cylinder simultaneously with moving back the screw by a predetermined distance without rotating the screw from a position of the screw at the time of completing the measuring;
• detecting a pressure of the molten resin;
• determining, based on the pressure, an injection start position for the screw;
• and
• advancing the screw from the injection start position to inject the molten resin into the mold without applying a counter pressure to the mold,
• wherein the determining of the injection start position for the screw includes pressurizing the molten resin by advancing the screw in a direction that the molten resin is injected into the mold and depressurizing the molten resin after the pressurizing of the molten resin so that a differential pressure between the pressure of the molten resin in the plasticizing cylinder and a pressure inside the mold is 1 MPa to 5 MPa thereby producing the article of which the surface has no foam.