Patent ID: 6773640
Filing Date: 2004-08-10
Classification: B29C,B29D

Abstract:
A process for injection-foaming a thermoplastic resin using an injection molding machine having a two-stage compression screw within a cylinder and to which a physical foaming agent is fed at a point of the cylinder, wherein the screw comprises a first stage and a second stage, and wherein the screw moves forward and backward in the cylinder, comprising:(1) feeding the physical foaming agent into the cylinder from a storage tank at a pressure lower than storage pressure by a pressure difference between the storage tank and the injection molding machine cylinder; (2) feeding the foaming agent to the cylinder at a point within a range from the starting point of the second stage of the screw to a point determined by nine times the outside diameter of the screw in the direction of injection at the time the screw is caused to advance most forward in the direction of injection, wherein a hollow area in which there is no resin, is present at the second stage of the screw, and wherein the foaming agent is supplied to the hollow area; and (3) obtaining a foam by reducing the pressure in a cavity of the mold in the injection molding machine to a predetermined pressure, injecting the resin into the cavity, and then expanding the volume of the cavity.