PURPOSE: To obtain a polyester film as a magnetic recording medium, which is excellent in scratch resistance, fits for repeated use and meets the requirements for higher image quality, by a method wherein the surface roughness of at least one side of film and the height and number of projections per unit area of the surface of the film are provided.
CONSTITUTION: The surface of the film concerned is set to have the center-like mean surface roughness Ra of 10-30nm and, at the same time, the three-dimensional mean surface roughness SRa of 15-55nm. If the surface roughness of film is smaller than the above-mentioned range, the frictional coefficient of the resultant film becomes larger and if the surface roughness of film is larger than the above-mentioned range, unsatisfactory image quality results. Further, the number of projections having the height of 200-400nm is set to be 1,100 or more per 0.1nm2 and the number of projections having the height of 400-600 is set to be 600 or less per 0.1nm2. If the former is not more than 1,100, unsatisfactory usage durability results. If the latter is not less than 600, poor image quality results. The film concerned can be obtained by adding 0.01-1.5vol.% of inactive particle having the average particle diameter of 0.1-1.0μm.
TSUCHIBUCHI MASANOBU
MOGI MASAHIKO
