| abstract |
Polyester film prepared from a polyester produced by using a germanium compound as a polymerization catalyst and having a Young's modulus in the longitudinal direction, E MO , and a Young's modulus in the transverse direction, E TD , satisfying the following conditions: E MD ≥ 350 kg/mm 2 , E TD ≥ 350 kg/mm 2 , E MD x E TD ≥ 250 000 kg 2 /mm 4 ; having a refractive index in the thickness direction, n ZD , satisfying the following condition:1.480 ≤ n ZD s 1.492 and having a maximum roughness, R 1 , of at least one side surface satisfying the following condition: R t ≤ 100 nm, is useful as a base film for a magnetic recording medium. A laminate composed of polyester layer A and polyester layer B may be prepared, which have E MD , E TD and n ZD satisfying the above-described conditions, which contains fine particles in layer B, and which have an outer surface of said layer A with R t ≤ 100 nm and an outer surface of said layer B with 30 ≤ R t ≤ 150 nm. A thin-film ferromagnetic metal magnetic recording medium prepared from this polyester film shows good workability and less drop-out, undergoes markedly reduced marring in contact with a magnetic head, and does not damage a magnetic head. |