Biaxially oriented polyester film for a magnetic recording medium

Abstract

A biaxially oriented polyester film for a magnetic recording medium, which is formed from a polyester composition comprising at least one member of fine particulate agglomerates selected from the group consisting of alumina fine particulate agglomerates and fine particulate agglomerates of a composite oxide comprising alumina and other metal oxide(s) in a proportion of 0.05 to 1% by weight of the polyester, the fine particulate agglomerates having an average particle diameter of 0.005 to 0.5 .mu.m and having been surface-treated with an alkali metal salt of a polyvalent carboxylic acid; and other inert fine particles different from the above fine particulate agglomerates and having an average particle diameter of 0.2 to 2.0 .mu.m in a proportion of 0.05 to 5% by weight of the polyester; and a biaxially oriented laminate polyester film for a magnetic recording medium comprising a polyester film layer of the above polyester composition as at least one surface layer.

Dependencies are inferred from the claim text.