Biaxial ausgerichteter Polyesterfilm für magnetische Aufzeichnungsmedia

摘要

A biaxially oriented polyester film for magnetic recording media improved in slipperiness, shaving resistance and scratch resistance by protrusions formed on the film surface, namely, a polyester film for magnetic recording media wherein the film is a biaxially oriented polyester film which contains (I) heat resistant high molecular particles having an average particle size of 0.3 to 1.5 mu m in 0.001 to 0.5 % by weight of the polyester, and (II) alumina particles having an independent existence rate of 80 % or more and an average particle size of 0.06 to 0.2 mu m in 0.05 to 1.0 % by weight of the polyester and/or colloidal silica particles having an independent existence rate of 80 % or more and an average particle size of 0.3 mu m or less in 0.05 to 2.0 % by weight of the polyester; wherein the distribution curve, in the range where the height (x : mu m) is 0.05 mu m or more and the number of the protrusions (y : per mm<2>) is 30 protrusions/mm<2> or more, of protrusions formed on the film surface satisfies the following formula A