Biaxially oriented polyester film for magnetic recording media

Abstract

The present invention relates to a biaxially oriented polyester film for magnetic recording medium having a thickness of thinner than 7 μm and satisfying the formula 1 ≤ P - ( α ⁢ ⁢ t + α ⁢ ⁢ h ) 10 ≤ 10 wherein αt (×10−6/° C.) is the thermal expansion coefficient of the film in transversal direction, αh (×10−6/%RH) is the humidity expansion coefficient in transversal direction and P (ppm/g) is the transversal shrinkage of the film under the load (grams) applied to the film in machine direction. It has thin film thickness, excellent dimensional stability and small dimensional change in the direction of width (transversal direction) especially under a load in the direction of the length of the film (machine direction) and useful as a magnetic recording medium, especially a digital data storage tape generating little error in magnetic recording and reproduction, free from the generation of error rate caused by track shift and having excellent output characteristics.

Dependencies are inferred from the claim text.