Abstract: Disclosed are a polyester mainly composed of an aromatic dicarboxylic acid as an acid component and an aliphatic diol as a diol component, wherein the content of an antimony element in the polyester is from 50 to 350 ppm, the number of metallic antimony particles having a diameter of 0.5 &mgr;m or more is 30,000 or more per 100 mg of polyester, the ratio of the number of fine particles having a diameter of 0.5 &mgr;m to less than 0.6 &mgr;m is 70% or more, and the L value in hue is 80 or more; a stretch blow molded product formed of the polyester; and a method for producing a polyester mainly composed of an aromatic dicarboxylic acid as an acid component and ethylene glycol as a diol component which comprises adding a preliminary mixed catalyst solution of an antimony compound and a trivalent phosphorus compound as a catalyst, the catalyst solution having a haze of 10% or less, at a stage showing an acid value of 1,000 eq/ton or less before initiation of melt polymerization.

Abstract: A polyester which is characterized in that(1) it comprises ethylene terephthalate units as the main constituting component,(2) its intrinsic viscosity is from 0.6 to 0.9 dl/g,(3) the content of an antimony element is from 0.8 to 2.0 mmol/kg,(4) the temperature-rising crystallization peak temperature (Tc.sub.1) is at least 160.degree. C., and the temperature-dropping crystallization peak temperature (Tc.sub.2) is at most 170.degree. C. or non-existent, and(5) the number (N.sub.1) of spherulites when it is heated from room temperature to 120.degree. C. and maintained for 10 minutes is at most 1.times.10.sup.-2 /.mu.m.sup.2, and the number (N.sub.2) of spherulites when it is cooled from 300.degree. C. to 200.degree. C. and maintained for 2 minutes is at most 1.times.10.sup.-3 /.mu.m.sup.2.

Abstract: A process for producing polyethylene terephthalate comprises the following steps 1 and 2:1 a moisture conditioning step of contacting a polyethylene terephthalate having an intrinsic viscosity of from 0.5 to 1.5 dl/g, a density of at least 1.37 g/cm.sup.3 and a cyclic trimer content of at most 5,000 ppm, with water to bring the water content of the polyethylene terephthalate to from 1,000 to 5,000 ppm, and2 a heat aging step of holding the moisture-conditioned polyethylene terephthalate obtained by the above moisture conditioning step, in a state where its water content is maintained at a level of at least 1,000 ppm.

Abstract: A copolyester comprising a dicarboxylic acid component comprising (a) 80 to 99.5 mol % of terephthalic acid or an ester forming derivative thereof and (b) 0.5 to 4.5 mol % of a phenylenedioxy diacetic acid or an ester forming derivatives thereof and a diol component is described. Hollow containers and stretched film produced from the copolyester are further described. The copolyester has a high transparency, superior gas barrier property, mechanical strength, water resistance and heat resistance. In addition, since the copolyester has a low oligomer content, it scarcely contaminates a mold used in molding process, which leads to a high productivity. The molded article produced from the copolyester can be used widely as packaging materials including various films, sheets and containers. Moreover, since a molded article having superior properties is obtained form the copolyester alone, it is possible to manufacture various packaging materials without using a complicated apparatus and complicated process.