Abstract: A polyester which is prepared by using a germanium compound as the polymerization catalyst, in which the Young's modulus E.sub.MD in the machine direction and the Young's modulus E.sub.TD in the transverse direction satisfy the requirements of E.sub.MD .gtoreq.350 kg/mm.sup.2, E.sub.TD .gtoreq.350 km/mm.sup.2 and E.sub.MD .times.E.sub.TD .gtoreq.250,000 kg.sup.2 /mm.sup.4, the refractive index n.sub.ZD in the thickness direction satisfies the requirement of 1.480.gtoreq.n.sub.ZD .gtoreq.1.492, and the maximum roughness Rt of at least one surface satisfies the requirement of Rt.gtoreq.100 nm, is valuable as a base film for a magnetic recording medium. A laminate structure of a polyester layer A and a polyester layer B is also used as a base film for a magnetic recording medium, in which the above requirements of E.sub.MD, E.sub.tD and n.sub.ZD are satisified, fine particles are incorporated in the layer B, the outer surface of the layer A satisfies the requirement of Rt .gtoreq.

Abstract: The present invention relates to an easily-adhesive polyester film comprising a polyester base film and a coating layer formed on one surface of the polyester base film, the coating layer comprising a mixture composed mainly of a higher fatty acid wax and a copolyester comprising as one comonomer component an alkali metal salt of an ester-forming aromatic sulfonic acid.The film of the present invention has excellent adhesiveness and has an improved anti-blocking property, and the film of the present invention is valuable as a base film for a magnetic recording medium, a capacitor or a photographic film.