| 摘要 |
PURPOSE: To provide a thermoplastic resin molded item which has improved smoothness of surface, uniform gloss, external surface appearance having no sink, and high expansion ratio by providing such a condition that the interior of a mold is maintained under a predetermined pressure before and after injection of a molten resin containing a foaming agent. CONSTITUTION: The interior of a mold is pressurized beforehand and the mold is depressurized to form a vacuum simultaneously with injection or a little later and the vacuum is maintained, while the pressure in the mold is kept and measured so that amount of next molding shot is stored in a cylinder and after the lapse of a cooling time, the pressure is raised to normal pressure to take out a molded item. That is, the interior of the mold which is sealed beforehand is maintained at a pressure exceeding 1atm. and is put into reduced pressure below 1atm. simultaneously with a start of injection molding or a little later. As a result, a thermoplastic resin molded item having high expansion ratio can be provided. |
