Patent ID: 7871691

Claim:
An oriented polyester film stretched in at least one direction, comprising as a major component of a substrate layer polyethylene-2,6-naphthalene dicarboxylate and having a film thickness of from 12 to 250 μm, characterized in that (1) a coefficient of linear thermal expansion αt at a temperature of from 30 to 100° C. is from 0 to 10 ppm/° C. in both longitudinal and width directions of the film, (2) a thermal shrinkage rate at 100° C. for 10 minutes is 0.05% or less in both longitudinal and width directions of the film, wherein the film has a thermal shrinkage rate at 150° C. for 30 minutes of 2.0% or less in both the longitudinal direction and the width direction, and wherein the film has a total light transmittance of the film of 85% or more and a haze of 1.5% or less, wherein the film has a coated layer at least on one surface of the substrate layer, and wherein the film has a ten-point average roughness Rz on an outer surface of the substrate layer of from 2 to 30 nm, and a ten-point average roughness Rz on an outer surface of the coated layer of from 50 to 150 nm.