Patent ID: 6652254
Filing Date: 2003-11-25
Classification: B29C,Y10S

Abstract:
An apparatus for use in practicing an injection molding process for producing molded articles of thermoplastic resin which comprises the gas impregnation step of supplying a carbon dioxide gas from a gas supply opening to a thermoplastic resin rendered molten by the rotation of a screw within a molding machine cylinder to impregnate the molten resin with the carbon dioxide gas, and the molding step of obtaining an expansion-molded article from the gas-impregnated molten resin,the injection molding apparatus being characterized in that the screw for use in the gas impregnation step comprises a resin melting portion disposed at an upstream position for rendering the resin molten, a molten resin nonfilled-up portion integral with a downstream side of the resin melting portion for making the resin lower than the carbon dioxide gas at the gas supply opening in pressure, and a gas impregnation portion integral with a downstream side of the molten resin nonfilled-up portion for supplying the inert gas and impregnating the molten resin with the carbon dioxide gas wherein the resin melting portion of the screw comprises a solid transport part disposed at an upstream position and having a small screw shaft diameter, a compression melting part integral with a downstream side of the power transport part and having a screw shaft diameter gradually increasing downstream, and a molten resin transport part integral with a downstream side of the compression melting part and having a large screw shaft diameter, wherein the gas impregnation portion comprises a tapered part gradually increasing in screw shaft diameter from a downstream end of the molten resin nonfilled-up portion, and a solid cylinder part downstream from the tapered part, wherein the screw has a gas inlet channel formed in an upstream end thereof, and a gas supply channel communicating with the gas inlet channel and extending through the screw longitudinally thereof, the gas supply opening being located at the upstream end of the solid cylinder part of the gas impregnation portion and positioned between adjacent screw flight portions and close to the downstream flight portion, the gas supply channel being provided with a check valve, the lengths of the screw parts and portions having the following relationships with a cylinder diameter D: length L1 of the solid transport part=5D-10D, length L2 of the compression melting part=3D-6D, length L3 of the molten resin transport part=1D-4D, length L4 of the molten resin nonfilled-up portion=0.1D-2D, and length L5 of the gas impregnation portion=4D-10D.