Abstract: A biaxially oriented laminate polyester film for magnetic recording medium, which is a laminate film comprising a base layer (A) formed of a polyester resin and a coating layer (B) which exists on one surface of the base layer (A) and contains a binder resin, added fine particles and a surfactant, wherein the base layer (A) is a biaxially oriented film which substantially contains no fine particles added or contains 0.001 to 0.1% by weight of added fine particles having an average particle diameter of 0.005 to 0.3 &mgr;m, the coating layer (B) has a surface having a central plane roughness (SRa) of 5 nm or less, the surface of the coating layer (B) has protrusions having a major diameter of 0.05 &mgr;m or more in a density of 80,000 pieces/mm2 or less and has extra-large protrusions having a major diameter of 10 &mgr;m or more in a density of 20 pieces/cm2 or less.

Abstract: An aromatic polyester film, which comprises an aromatic polyester comprising 2,6-naphthalenedicarboxylic acid as the main dicarboxylic acid component and 1,3-propanediol as the main diol component and having a density of at least 1.310 g/cm3. A laminated film comprising another polyester layer can be formed from this aromatic polyester film. An aromatic polyester containing a small amount of a sulfonic acid phosphonium salt used as one of the aromatic polyesters forming this laminated film is excellent in electrostatic casting properties and resistance to the contamination of an electrostatic wire, and an aromatic polyester containing an inorganic anti-fungus agent is used for antifungal application.

Abstract: A polyalkylene naphthalate for a film, which comprises a naphthalenedicarboxylic acid component as a main dicarboxylic acid component and an aliphatic glycol component as a main glycol component, and contains (a) an antimony compound and (b) a quaternary phosphonium sulfonate compound unit having an ester-forming functional group in such amounts that satisfy the following expressions (1) and (2): 0<Sb≦80  (1) 0<S/Sb≦0.4  (2) wherein Sb and S are the molar ratios (mmol %) of the antimony compound and the quaternary phosphonium sulfonate compound unit having an ester-forming functional group to the total of all the dicarboxylic acid components forming the polyalkylene naphthalate, respectively. The film of the present invention has excellent surface flatness and is suitable for use as a base film for a magnetic recording medium. It is also excellent in high-speed winding properties and can be formed into a film stably and produced industrially advantageously.