Abstract: Molten synthetic resin material containing foaming agent in an amount of 0.05 to 5 percent by weight is injected into a pre-pressurized mold cavity in a mold which is closed by a relatively low clamping force having a coefficient in the range of 10 to 40, said coefficient being represented as a ratio of clamping force to maximum injection shot volume. The above injection step is carried out for at least 3 seconds. After the injection step has been initiated, the pre-pressurized mold is released to atmosphere during the injection step at the soonest. At least two molds may be used to be alternately charged with said material.

Abstract: A multi-layered article molded according to the present invention has in its cross-section a triple-layered structure consisting of two surface layers and a core layer interposed between said surface layers, said triple-layered structure being injection molded in a single shot from two kinds of thermoplastic synthetic resins to be formed into the surface and core layers, respectively, said core layer having a thickness less than one half of the entire thickness of said article.

Abstract: Foamable synthetic resin materials are plastified and injected into a mold cavity in an amount less than the volume of mold cavity and a body of gas under pressure is charged in the mold cavity in such manner that it is enclosed by said resin materials. When the injected resin materials sets at least at its outer surface layer, the gas is discharged out of the mold cavity so that the foamable resin materials can be expanded in the hollow portion formed by the pressure of the charged gas. Said foamable resin materials may be surrounded by unfoamable resin materials in the mold cavity.

Abstract: An apparatus for injection molding synthetic resin materials comprises means for injecting the material to be molded, mold means having a cavity for receiving the material from said injecting means, entrance passage means connecting said injecting means with the cavity of said mold means and valve means disposed in said entrance passage means for closing it to shut off the flow of material in said entrance passage means, said valve means having a fluid passage communicating at its one end with only the cavity of said mold means when said valve means is closed, said fluid passage having the opposite end thereof adapted to connect with another source of pressurized fluid.

Abstract: A method of producing foamed thermoplastic resin articles having smooth and glossy surfaces free from swirl marks and hair cracks, which comprises melting a thermoplastic resin containing a condensable blowing agent and an organic chemical blowing agent, injecting, in full shot, the molten resin into a mold cavity to which a pressurized gas is being applied during said injection, terminating the application of the pressurized gas to the mold cavity, enlarging the volume in said molded cavity by movement of a mold wall, and thereafter cooling and solidifying the resin to form the foamed articles.

Abstract: A first thermoplastic resin for forming the shell of an article is charged into the front portion of an injection cylinder and a second thermoplastic resin for forming the core of the article is charged into the rear portion of the injection cylinder. Both resins are substantially separated, being in contact only a central area of the cross-sectional plane of the injection cylinder. These thermoplastic resins are injected in a mass into a mold cavity with the second resin enveloped by the first resin, and finally solidified in the mold cavity resulting in a molded article having sandwich construction. Various sandwich articles can be obtained easily by means of a single injection molding machine. The process also allows repeated injection operations without exposure of the core material on the surface of the molded article.