| abstract |
A biaxially oriented laminated polyester film comprising a first polyester surface layer having (a1) a central line average roughness RaA of 1 to 7.9 nm, (b1) a 10-points average roughness RZA of 15 to 400 nm and (c1) an RZA/RaA ratio of 11-51, and a second polyester surface layer having (a2) a central line average roughness RaB which is greater than RaA and is 5 to 40 nm, (b2) a 10-points average roughness RZB of 75 to 600 nm and (c2) an RZB/RaB ratio of 20 or less, and satisfying the relationship between the first polyester surface layer and the second polyester surface layer, which is represented by the following expressions, RaAxRaB<50 (1) RZAxRZB=130 to 3,000(2). This biaxially oriented laminated polyester film is excellent in lubricity, high-speed take-up properties, processability and electromagnetic characteristics when used for a magnetic film, and is particularly useful as a base film for a magnetic recording medium. |