POLYESTERSUBSTRATFILM FUER MAGNETISCHE AUFZEICHNUNGSTRAEGER.

摘要

A biaxially stretched polyester base film having many fine protrusions on its surface, characterized by having the following properties: (a) in a distribution curve representing the relation between the number of protrusions (y/mm2) and the height of protrusions (x in mu m) on the surface of said film which are measured in a region having at least 20 protrusions/mm2, that part of the distribution curve at which the protrusion height (x) is larger than its peak value crosses the line of log10 y=-18x+3.7, (b) when the number of protrusions (y) on the film surface is at least 20/mm2, no protrusion exists which has a height (x) of at least 0.13 mu m, (c) said film has a surface roughness (Ra) of not more than 0.012 mu m, (d) said film has a Young's modulus in the longitudinal direction of at least 650 kg/mm2, and (e) when heat-treated at 70 DEG C. for 1 hour under no load, said film has a heat shrinkage in the longitudinal direction of not more than 0.1%.