Patent EA-000662-B1 (EA)
Title: Process for molding a preform of a polyester resin and apparatus for injection mouding
Inventor: NAKAJIMA HISASHI
IPC: B29C48/09
Filed: 1996-08-13
Abstract: 1. A process for injection molding a preform of a polyester resin comprising the steps of compressing and melting a molding material which is a polyester resin composed of a blend of polyethylene terephthalate and polyethylene naphthalate by rotation of a screw within a heating cylinder, and injecting and filling the molding material into a mold to mold a desired preform, wherein a plastication zone is divided into a melting section, a melting relaxation section, a kneading section and a kneading relaxation section. 2. The process for injection molding a preform of a polyester resin according to Claim 1, wherein the relaxation of the molding materialis carried out by expanding a gap between the heating cylinder and a screw shaft portion of the screw of obtaining forming material. 3. The process according to Claim 1, wherein the blend of polyethylene terephthalate and polyethylene naphthalate contains 90 to 10 % by weight of polyethylene terephthalate and 10 to 90 % by weight of polyethylene naphthalate. 4. A process according to Claim 1 or 3, wherein the polyethylene naphthalate is a copolymer composition containing 8.0 mol% of terephthalate and 92.0 mol% of 2,6-naphthalene dicarboxylate. 5. An injection screw for injecting and/or plasticating a polyester resins, said screw being arranged in a heating cylinder so as to be rotationally, forward and backward movable, wherein said screw comprises a material feed zone, a compression zone, a plastication zone and a metering zone in order, said plastication zone has operation sections of a melting section, a melting relaxation section, a kneading section and a kneading relaxation section wherein the diameter of the screw shaft in the melting relaxation section and in the kneading relaxation section less than that of the screw shaft in other sections, and the kneading relaxation section has a portion devoid of flight. 6. An injection screw according to Claim 5, wherein the screw is an injection screw of an in-line screw type injection unit. 7. An injection screw according to Claim 5, wherein the screw is an injection screw which is plastication screw of a screw-plunger type. 8. An injection screw according to Claim 5, wherein the screw is a plastication screw and an injection screw of a screw-screw preplasticator type injection unit. 9. An injection screw according to any Claim 5-8, wherein a part of said front screw flights is made double flights so as to set a narrower pitch than that of the rear screw flights. 10. An injection screw according to any Claim 5-9, wherein the diameter of the screw shaft at said relaxation sections is 70 to 80 % reduced diameter of the screw shaft of the melting section. 11. A process for stretch blow molding a polyester resin comprising the steps of: molding a preform, releasing the preform from a cavity mold and a core mold of an injection mold with a mouth portion thereof held by a lip mold in an early stage in which the inside of the preform is not completely cooled and still at a high temperature and the shape of the preform is kept by a skin layer formed on the surface by cooling; transferring the preform to a blow mold; and stretching the preform in an axial direction in the blow mold before the surface temperature of the preform is elevated by internal heat and reaches the peak temperature and at the same time blowing air to mold it into a hollow molded article such as a thin-wall vessel, wherein the polyester resin is the blend of polyethylene terephthalate and polyethylene naphthalate and molding a preform is carried out in accordance with an injection molding process of any one of Claims 1 to 4. 12. A process for stretch blow molding a polyester resin comprising the steps of: molding a preform cooling the preform until the shape of the preform is fully kept; releasing the preform from a cavity mold and a core mold of an injection mold with a mouth portion thereof held by a lip mold; transferring the preform to a temperature conditioning section to adjust the temperature of the preform to a molding temperature; transferring the preform to a blow mold; and stretch blow molding the preform into a hollow molded article such as a thin-wall vessel, wherein the polyester resin is the blend of polyethylene terephthalate and polyethylene naphthalate and molding a preform is carried out in accordance with an injection molding process of any one of Claims 1 to 4.