Importance

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Abstract

A predetermined amount of melted thermoplastic resin of raw material is injected into a molding space which is previously set to a temperature higher than that at which the resin beings to harden under atmospheric pressure and which has a capacity larger than a volume of a product. The injected resin is cooled in the molding space and pressurized before the resin is cooled to the temperature at which the resin begins to harden under atmospheric pressure. When pressurized, the glass transition temperature of the thermoplastic resin is shifted to a higher temperature so that the thermoplastic resin hardens in slight reduction of the temperature. The resin is cooled in the pressurized state until the resin possesses the dynamic rigidity under room temperature and atmospheric pressure. While the thermoplastic resin is further cooled to the extraction temperature, the pressure applied to the resin is controlled until a further increase of the dynamic rigidity due to the cooling ceases and the dynamic rigidity of the thermoplastic resin in the cooling is maintained to that under room temperature and atmospheric pressure.

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First Claim