| 摘要 |
PURPOSE:To obtain a highly accurate molded product by introducing a foaming substance into the cavity of a molded, injecting a thermoplastic resin into the cavity to fill the mold, foaming the foaming substance, and generating inner pressure to prevent the generation of a sink or the like. CONSTITUTION:A mold 1 is set to temp. lower than the softening point of a molding resin and a foaming substance 3 is set to the central part of a cavity 2 corresponding to the thick-walled part of the molding resin. As the foaming substance, a substance generating gas such as steam, carbon dioxide or nitrogen at temp. equal to or higher than the softening point of the resin is pref. Subsequently, a molten resin 4 is injected into the cavity 2 to fill the cavity 4. At this time, the foaming substance 3 is involved by the molten resin 4 and foamed (or gasified) by heating to form a hollow part 5. By this constitution, inner pressure is generated in the molten resin and, when the resin 4 is cooled to be contracted in volume, the generation of transfer inferiority such as a sink can be prevented. |
