Injection molding process and injection molding apparatus for thermoplastic resin molded articles

An injection molding apparatus for use in practicing an injection molding process for a thermoplastic resin molded article including the blowing agent incorporating step of supplying through a blowing agent supply opening a blowing agent to a resin melted by rotating a screw within a cylinder of an injection molding machine and mixing the blowing agent with the molten resin for incorporation, and the injection molding step of measuring out an amount of the blowing agent-incorporating molten resin obtained and thereafter injecting the measured-out resin into a mold cavity to prepare an expansion-molded article,

• the injection molding apparatus for a thermoplastic resin molded article being characterized in that the screw has a blowing agent inlet formed in a rear end portion thereof and a blowing agent supply channel extending through the screw longitudinally thereof and communicating with the inlet, the blowing agent supply opening being formed in a surface of the screw and opened to an enlarged incorporating zone forming portion defined as having a deeper screw groove relative to a remaining portion of the screw, the supply opening being in communication with the inlet through the supply channel and the enlarged incorporating zone forming portion being further defined by front and rear screw flights having an increased pitch relative to remaining ones of screw flights of the screw.

An injection molding apparatus for use in practicing an injection molding process for a thermoplastic resin molded article including the blowing agent incorporating step of supplying through a blowing agent supply opening a blowing agent to a resin melted by rotating a screw within a cylinder of an injection molding machine and mixing the blowing agent with the molten resin for incorporation, and the injection molding step of measuring out an amount of the blowing agent-incorporating molten resin obtained and thereafter injecting the measured-out resin into a mold cavity to prepare an expansion-molded article,

• the injection molding apparatus for a thermoplastic resin molded article being characterized in that the screw has a blowing agent inlet formed in a rear end portion thereof and a blowing agent supply channel extending through the screw longitudinally thereof and communicating with the inlet, the blowing agent supply opening being in communication with the inlet through the supply channel,
• the screw having front and rear flights of an increased pitch and/or a reduced shaft diameter and thereby being provided with an enlarged incorporating zone forming portion to form an enlarged incorporating zone which is greater than a space between flights which are positioned rearwardly of the flights, the blowing agent supply opening being opened to the incorporating zone,
• the blowing agent supply opening or the blowing agent supply channel inside the screw being provided with a check valve for preventing the molten resin from ingressing into the supply channel from the supply opening.