Abstract: A polyester composition comprising 0.005 to 10% by weight compound oxide particles having a volume average particle meter of 0.005 to 2 .mu.m, a relative standard deviation .sigma. of the particle diameter of not more than 0.3, and composed mainly of silicon (Si), aluminum (Al) and at least one alkali metal (M), wherein the contents of the silicon, aluminum and alkali metal satisfy the following requirements: 10 wt. %.ltoreq.Si.ltoreq.45 wt. %, 3 wt. %.ltoreq.Al.ltoreq.30 wt. % and 0.5 wt. %.ltoreq.M.ltoreq.20 wt. %, respectively. The polyester composition, particularly when formed into films, has excellent surface evenness, running ability and abrasion resistance, and such films are suitable particularly for magnetic recording media and other applications.

Abstract: A biaxially stretched polyester film for forming a container, characterized by being formed of a polyester substantially consisting of an ethylene terephthalate unit and an ethylene naphthalate unit, the refractive index in the direction of thickness of the film being 1.5 or greater. This film is not only excellent in the formability during formation into cans or the like, but has excellent properties in taste property, particularly, the taste property after the retorting, and may be suitably used for containers produced by forming process and, particularly, for metallic cans.

Abstract: A polyester composition comprises a polyester component (a) and polymer particles (b). At least an outermost layer of the polymer particles (b) is of a polymer having hydroxyl groups. The composition can be made into a film especially suitable for use as a substrate in a magnetic recording medium.

Abstract: A biaxially stretched polyester film for forming a container, characterized by being formed of a polyester substantially consisting of an ethylene terephthalate unit and an ethylene naphthalate unit, the refractive index in the direction of thickness of the film being 1.5 or greater. This film is not only excellent in the formability during formation into cans or the like, but has excellent properties in taste property, particularly, the taste property after the retorting, and may be suitably used for containers produced by forming process and, particularly, for metallic cans.