Polyester films for magnetic recording medium.

摘要

There is provided a polyester film useful for production of a magnetic recording medium excellent in runnability, electromagnetic conversion characteristics and storage stability. In the polyester film, a continuous thin film which contains a resin as a matrix and acts as a primer layer for a magnetic layer is coated on one surface of a support film composed of a polyester. According to one embodiment thereof, the surface of the continuous thin film has (A) small protuberances each containing particles with an average particle size of less than 0.06 micrometer as a nucleus and having a height of 13 nm or less, (B) large protuberances each containing particles with an average particle size of 0.06 micrometer or more as a nucleus and having a height of 30 nm or less, and (C) micro-protuberances composed of a matrix resin alone, the numbers, per mm<2> of the film, of these protuberances satisfying the formulas, An = 1.0 x 10<4> - 1.0 x 10<8>/mm<2>, Bn = 0 - 4 x 10<4>/mm<2>, and Cn /mm<2> wherein An is the number of the small protuberances, Bn is the number of the large protuberances, and Cn is the number of the micro-protuberances, the fine surface roughness Ra of the continuous thin film portion composed of the matrix resin alone being 1.10 nm or less, and the surface roughness Ra of the overall continuous thin film being 1 to 10 nm.