| abstract |
(57) [Problem] To provide a base film excellent in durability of an MR head during recording and reproduction of a magnetic recording tape, and excellent in running property of a film and durability of a film surface on a magnetic surface side. SOLUTION: This is a biaxially oriented polyester film having a large number of fine projections formed on a background portion of the surface, and the fine projections have a total projection number of 3,000,000 to 1 having a projection height of 3 to 5 nm. The average grain size is 1 when the number of protrusions / mm 2 is 3 nm and the height threshold of the protrusions is 3 nm. 0-100 nm. This biaxially oriented polyester film is a monolayer film or a laminated film of two or more layers. |