Patent ID: 6946192

Claim:
A transparent, biaxially oriented polyester film comprising: (A) a base layer, at least 80% by weight of which is composed of a thermoplastic polyester; and (B) at least one outer layer having a thickness of from 0.2 to 6 μm, wherein the outer layer is composed of a polymer, or of a mixture of polymers comprising: at least 40% by weight of ethylene 2,6-naphthalate units; ethylene terephthalate units, wherein the ethylene terephthalate units are present in an amount up to 40% by weight; and optionally up to 60% by weight of units from cycloaliphatic diols, aromatic diols, cycloaliphatic dicarboxylic acids, aromatic dicarboxylic acids, or a combination thereof, wherein the glass transition temperature (T g 2 value) of the polyester film is above the T g 2 value of the base layer but below the T g 2 value of the outer layer, and at least one film surface has a surface tension of from 35 to 65 mN/m or has been provided with a functional coating of thickness from 5 to 100 nm or both.