BIAXIALLY ORIENTED POLYESTER FILM

To stably provide a biaxially oriented polyester film that is excellent in runnability and windability and further excellent in dimensional stability and when used as a magnetic recording medium, serves as a high-density magnetic recording medium having a smooth magnetic layer with a small dimensional change due to environmental change of temperature and humidity or due to storage and having less occurrence frequency of missing pulse.SOLUTION: The biaxially oriented polyester film is such that on at least one outermost layer surface of the biaxially oriented polyester film, projections whose cut end at a height of 60 nm has an area of 1 μm2 or more are 50/mm2 or less in number and the number of projections having a height of 30 nm or more is 15,000 to 200,000/mm2.SELECTED DRAWING: None 【課題】走行性や巻き取り性に優れ、さらには寸法安定性に優れた二軸配向ポリエステルフィルムであって、磁気記録媒体とした際に平滑な磁性層を有すると共に温度や湿度の環境変化や保存による寸法変化が小さい、ミッシングパルスの発生頻度の少ない高密度磁気記録媒体となる二軸配向ポリエステルフィルムを安定に提供すること。【解決手段】二軸配向ポリエステルフィルムの少なくとも一方の最外層表面において、高さ６０ｎｍにおける突起の切り口の面積が１μｍ２以上の突起が５０個／ｍｍ２以下、高さ３０ｎｍ以上の突起個数が１．５万〜２０万個／ｍｍ２である二軸配向ポリエステルフィルムとする。【選択図】なし