BIAXIALLY ORIENTED LAMINATED POLYESTER FILM AND MAGNETIC RECORDING MEDIUM

PROBLEM TO BE SOLVED: To provide a biaxially oriented laminated polyester film which exhibits excellent electromagnetic conversion characteristics when used for a magnetic tape having high density and high capacity, and which is excellent in the productivity of a base film and, in particular, used as a base suitable for a magnetic recording medium of an application type digital recording system.SOLUTION: The biaxially oriented laminated polyester film is provided which has a layer structure of two or more layers and contains a heat-resistant thermoplastic resin of 0.3 mass% or more and 10 mass% or less. When an A layer denotes a layer positioned at the outermost layer on the side of applying a magnetic layer and a B layer denotes another layer, a difference between the content of the heat-resistant thermoplastic resin on the surface A side and that on the other surface B side is 0.5 mass% or more and 10 mass% or less. A difference between the content of the heat-resistant thermoplastic resin of the A layer and that of the B layer is 0.3 mass% or more and 5 mass% or less. On the surface A side, a three-dimensional center line surface roughness is 1.2-3 nm and a root mean square roughness is 1.5-5.5 nm, and on the surface B side, a three-dimensional center line surface roughness is 8-13 nm and a root mean square roughness is 11-17 nm.SELECTED DRAWING: None 【課題】高密度、高容量の磁気テープに用いた場合の電磁変換特性が良好で、かつベースフィルムの生産性にも優れ、特に塗布型デジタル記録方式の磁気記録媒体用途に好適なベースとなる二軸配向積層ポリエステルフィルムを提供する。【解決手段】２層以上の層構成を有し、耐熱性熱可塑性樹脂を０．３質量％以上１０質量％以下含有する二軸配向積層ポリエステルフィルムであって、磁性層を塗布する側の最表層に位置する層をＡ層、他方の層をＢ層としたとき、表面Ａ側と他方の表面Ｂ側の耐熱性熱可塑性樹脂の含有量差が０．５質量％以上１０質量％以下。Ａ層とＢ層の耐熱性熱可塑性樹脂の含有量差が０．３質量％以上５質量％以下。表面Ａ側の３次元中心線表面粗さが１．２〜３ｎｍ、二乗平均平方根粗さが１．５〜５．５ｎｍ、表面Ｂ側の３次元中心線表面粗さが８〜１３ｎｍ、二乗平均平方根粗さが１１〜１７ｎｍとする。【選択図】なし