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A method for manufacturing molded products of polyethylene terephthalate by injection molding a material containing polyethylene terephthalate as the principal component characterized by using virgin and/or waste polyethylene terephthalate of average molecular weight of more than 10000 to which poly

A method for manufacturing molded products of polyethylene terephthalate by injection molding a material containing polyethylene terephthalate as the principal component characterized by using virgin and/or waste polyethylene terephthalate of average molecular weight of more than 10000 to which polymer such as nylon and/or inorganic fillers can be added as required, and molding said material under the following molding conditions by a general type or vent type molding machine: (a) Control of a temperature of a cylinder of the molding machine in the range of melting temperature of resin plus/minus 35°C., and (b) Control of the staying hour of resin in the cylinder to be within 15 minutes.

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A method of manufacturing molded products from material selected from the group consisting of polyethylene terephthalate having an average molecular weight more than about 10,000 (I.V. about 0.39), a combination of said polyethylene terephthalate as the primary component and a second polymer compone

A method of manufacturing molded products from material selected from the group consisting of polyethylene terephthalate having an average molecular weight more than about 10,000 (I.V. about 0.39), a combination of said polyethylene terephthalate as the primary component and a second polymer component selected from the group consisting of polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene, polybutylene terephthalate, polyamide 6, polyamide 66, polyamide 7, polyamide 11, polyamide 12, cotton, hemp, and rayon in an amount of from 5% to 60% by weight, or a blend of said polyethylene terephthalate as the primary component and an inorganic material selected from the group consisting of boron nitride, glass fiber, glass balls, glass powder, feldspar, quartz, aluminum oxide, marble, metal fibers, metal powder and metal whiskers, and a mixture of said polyethylene terephthalate as the primary components with said polymer component and said inorganic material, by one of injection or extrusion means in a molding machine having a screw conveyor cylinder provided with controllable heating means, a hopper at one end of said cylinder, and a discharge means at the other end of said cylinder selected from at least one of a nozzle, die, and adapter, comprising: (a) providing said material with a water content of less than about 1.0% by weight; (b) maintaining the inside wall temperature of said cylinder within a range of plus or minus 35°C. of the melting temperature of the material; (c) keeping the temperature of a first portion of the inside wall of said cylinder located adjacent said one end lower than the melting temperature of said material and sufficient to achieve substantially complete dehydration or negligible hydrolysis and heat deterioration of the material prior to the material reaching a second portion of the inside wall of the cylinder in the direction of travel of material; (d) controlling the temperature of the second portion of said inside wall of said cylinder which extends from a position intermediate its opposite ends to said other end at a temperature higher than the melting temperature of said material, while controlling the temperature difference between said first and second portions of said inside wall below 70°C.; (e) bringing the temperature of said molding temperature to a predetermined maximum at the outlet zone adjacent said discharge means; (f) controlling the temperature of the inside of the cylinder by directly measuring the actual temperature of the molding material as it passes through the one of the nozzle, die and adapter of the molding machine; and (g) controlling the residence of time of said molding material in said cylinder in response to the cylinder temperature so that the residence time is reduced as the temperature is increased whereby the residence time of said material in said cylinder is less than about 23 minutes.