| 摘要 |
<p>When interconnected cells are formed in molded foam, the rigidity is poor even when the thickness is uniform. Therefore, foam is desired which has the highest possible expansion ratio while also having fine independent cells of uniform size. In the injection molding process, thermoplastic resin containing dissolved nitrogen at a supercritical state as a physical foaming agent is injected into a mold cavity with a variable volume, and the volume of the cavity is expanded to obtain molded foam. In this process, the inner surface temperature of the mold cavity at the beginning of injection is heated to a range from -20°C to +20°C, which is the deflection temperature under load of the molded material. After the cavity has been injected with a predetermined amount of resin, it is subjected to holding pressure for a predetermined amount of time. After the pressure inside the mold cavity has been maintained at a pressure which does not allow cells to develop and grow, the volume of the cavity is increased and the inner surface temperature of the mold cavity is cooled to a predetermined temperature to obtain an injection-molded foam having fine, uniform independent cells with a narrow cell size distribution in the direction of thickness, and having a high expansion ratio.</p> |
