Method for multilayer molding of thermoplastic resins and multilayer molding apparatus

A multilayer-molding apparatus for manufacturing a multilayer-molded product that contains a multilayer of a plurality of types of thermoplastic resins, one layer of which is foamed and composed of at least one thermoplastic resin selected from a plurality of types of thermoplastic resins, the apparatus comprising:

• a plurality of injection-molding machines, at least one of which being a two-stage screw injection molding machine, that plasticize and inject a plurality of thermoplastic resins as molding materials, each of the plurality of two-stage screw injection-molding machines has a reduced screw-flight clearance at a boundary between a first stage and a second stage;
• a mold that has a cavity as a molding space to be filled with the thermoplastic resins injected by the plurality of injection-molding machines;
• a clamping apparatus that can clamp the mold and open or close the mold to increase or decrease a volume of the cavity;
• and
• a unit for supplying a foaming gas to the two-stage screw at a pressure of 0.1 MPa or more but less than 1.0 MPa and a unit for supplying a bubble-nucleating agent for use in the foaming,
• wherein reducing a screw-flight clearance at the boundary between the first stage and the second stage of the two-stage screw results in sealing performance of the two-stage screw at the foaming gas supply pressure of 0.1 MPa or more but less than 1.0 MPa, a pressure at which desired plasticizing capacity can be maintained and sufficient foaming can be achieved at the reduced screw-flight clearance.