Patent ID: 6670030
Filing Date: 2003-12-30
Classification: G11B,Y10S,Y10T

Abstract:
A biaxially oriented laminate polyester film for magnetic recording medium, which is a laminate film comprising a base layer (A) formed of a polyester resin and a coating layer (B) formed on one surface of the base layer (A), characterized in that:(1) the base layer (A) substantially contains no added fine particles or contains 0.001 to 0.1% by weight of added fine particles having an average particle diameter of 0.005 to 0.3 &mgr;m, (2) the coating layer (B) contains a binder resin, added fine particles and a surfactant, the added fine particles having an average particle diameter of 10 to 50 nm and being contained in an amount of 0.5 to 30% by weight, and the coating layer (B) having a thickness of 3 to 40 nm, (3) the coating layer (B) has a surface which satisfies the following surface characteristics (a) to (d): (a) the surface has 80,000 pieces/mm2 or less of protrusions having a major diameter of 0.05 &mgr;m or more when measured on the basis of a surface photograph taken and enlarged at a magnification of 5,000 with a scanning electron microscope, (b) the surface has 1 to 40 pieces/&mgr;m2 of protrusions, measured on the basis of a surface photograph taken and enlarged at a magnification of 35,000 with a scanning electron microscope, (c) the surface has 10 pieces/cm2 or less of extra-large protrusions having a major diameter of 10 &mgr;m or more, and has 5 pieces/cm2 or less of the extra-large protrusions having a height of 100 nm or higher, and (d) the surface has a central plane average roughness (SRa) of 5 nm or less and (4) wherein the base layer (A) contains (a) at least one compound selected from the group consisting of an alkali metal compound, an alkaline earth metal compound and a manganese compound, (b) a phosphorus compound and (c) at least one compound selected from the group consisting of a germanium compound, a titanium compound and an antimony compound in an amount ratio satisfying the following expressions (1) to (6) simultaneously: 25&lE;M&lE;250â€ƒâ€ƒ(1) 0.1&lE;(M/P)&lE;6.0â€ƒâ€ƒ(2) 0&lE;Ti&lE;12.5â€ƒâ€ƒ(3) 0&lE;Ge&lE;110â€ƒâ€ƒ(4) 0&lE;Sb&lE;50â€ƒâ€ƒ(5) 0.3Ti+Ge)&lE;110â€ƒâ€ƒ(6), wherein M is a content (ppm) of a total of an alkali metal element, an alkaline earth metal element and a manganese element from the compound (a), P is a content (ppm) of a phosphorus element, Ti is a content (ppm) of a titanium element, Ge is a content (ppm) of a germanium element and Sb is a content (ppm) of an antimony element, in the polyester.