Polyester film coated with metal adhesion promoting copolyester

An oriented self-supporting plastic film having a continuous copolyester polymeric coating on one or both sides thereof, said film prepared by melt extruding a substantially amorphous plastic film and thereafter orienting the film by stretching in one or two directions and heat setting the film, said copolyester coating being applied to said film as an aqueous dispersion prior to stretching in one direction or subsequent to stretching in one direction but prior to stretching in two directions, said copolyester coating consisting essentially of the polyester condensation product of the following monomers or their polyester forming equivalents:

• (A) about 65 to 95 mole percent of isophthalic acid;
• (B) about 0 to 30 mole percent of at least one aliphatic dicarboxylic acid of the formula HOOC(CH.sub.2).sub.n COOH, wherein n ranges from about 1-11;
• (C) about 5 to about 15 mole percent of at least one sulfomonomer containing an alkali metal sulfonate group attached to a dicarboxylic aromatic nucleus;
• and
• (D) stoichiometric quantities of about 100 mole percent of at least one copolymerizable aliphatic or cycloaliphatic alkylene glycol having about from 2 to 11 carbon atoms,
• said film exhibiting improved adhesion to a metal coating applied by vapor deposition techniques onto one or both of said copolyester coated sides.