Abstract: A process for preparing a fired-retardant polyamide, which comprises polymerizing a carboxylic acid component consisting essentially of at least one naphthalene-dicarboxylic acid selected from the group consisting of naphthalene-2,7-dicarboxylic acid and naphthalene-2,6-dicarboxylic acid and/or its amide-forming derivative, and a halogen substituted-carboxylic acid and/or its amide-forming derivative, and an aliphatic diamine, the amount of said naphthalene dicarboxylic acid and/or its derivative being at least 40 mol% of the total acid component, and the amount of said halogen-substituted carboxylic acid being such that the halogen atom content of the polyamide is at least 0.13% by weight.

Abstract: Fiber-forming polyamides are prepared by poly-condensing naphthalene-2,7-dicarboxylic acid and a straight-chain aliphatic diamine containing 4 to 13 carbon atoms and 15 to 50 mol% of another carboxylic acid and/or another diamine as a copolymerizing component.

Abstract: A method for stabilizing a polyester at least 80% of the recurring units of which in terms of number consist of tetramethylene terephthalate units or tetramethylene-2,6-naphthalate units, by incorporating into said polyester 0.001 to 10% by weight, based on the weight of the polyester, of at least one compound of the following formula (I) ##SPC1##This application is a continuation-in-part of application Ser. No. 548,988, filed Feb. 10, 1975, which in turn is a divisional application of Ser. No. 417,918 filed Nov. 21, 1973, now U.S. Pat. No. 3,904,578.

Abstract: A zip fastener made of a monofilament of 200 to 20,000 denier composed of a polymethylene terephthalate containing at least 85 mole % of trimethylene terephthalate, tetramethylene terephthalate or hexamethylene terephthalate as a recurring unit, said monofilament having an intrinsic viscosity of 0.35 to 3.5 and a circularity of not more than 1.01. The monofilament is prepared by melt-extruding the polymethylene terephthalate in the form of a filament, passing the extruded filament through an air gap, passing it through a cooling bath of an inert quenching liquid held at a temperature of about 60.degree. to 100.degree.C., then passing it through a cooling zone at a temperature of below 35.degree.C., and then drawing the filament.

Abstract: In a process of preparing aromatic polyesters from (A) aromatic dicarboxylic acids and (B) diphenols by the solid phase polymerization method, the speed of the solid phase polymerization reaction can be enhanced to a marked degree by copolymerizing (C) an aliphatic dihydroxy compound, and in this case the amounts in which the components (B) and (C) are used, based on (A), being 70 - 105 mol % of (B) and 1 - 50 mol % of (C), with the total amount of (B) and (C) corresponding to 100 - 130 mol % of (A).

Abstract: A thermally stable extrusion-molded article characterized by (1) consisting of a substantially linear polyester in which at least 90 mol% of the total recurring units consist of tetramethylene 2,6-naphthalate units, (2) having a density not in excess of 1.318, and (3) being in the unstretched state.This article is prepared by extruding a melt of a substantially linear polyester in which at least 90 mol% of the total recurring units consist of tetramethylene 2,6-naphthalate units into the form of a molded structure, and cooling the extruded molded structure to room temperature, wherein during the period in which the extruded molded structure is cooled from at least 75%C. to room temperature, the cooling of the molded structure is performed rapidly so that the density of the molded structure does not exceed 1.318.

Abstract: A process for preparing a shaped article by melt-extruding a polyester containing tetramethylene naphthalene-2,6-dicarboxylate or hexamethylene naphthalene-2,6-dicarboxylate as a main recurring unit, wherein the extrudate is exposed to a temperature of 75.degree. to 450.degree.C. for 1 to 180 seconds immediately after extrusion.

Abstract: An aromatic polyester resin composition with inhibited coloration comprising (1) 100 parts by weight of an aromatic polyester resin composed mainly of tetramethylene arylcarboxylate units and polymerized by a titanium compound catalyst, (2) 5 to 100 parts by weight of a polycarbonate resin and (3) a coloration inhibiting amount of at least one phosphorus compound, and a method for inhibiting the coloring phenomenon of a resin composition comprising the polyester resin (1) and polycarbonate resin (2).

Abstract: An electrically insulating material composed of an unstretched film of a substantially linear polyester at least 85 mol% of the recurring units of which consist of a hexamethylene naphthalene-2,6-dicarboxylate unit and which has an intrinsic viscosity, as measured on its ortho-chlorophenol solution at 35.degree.C., of at least 0.3.