Polyester compositions and use thereof in extrusion coating

A method of coating a metal substrate comprising:

• (a) heating the metal substrate to a temperature of about 120.degree. C. to about 250.degree. C. to provide a preheated metal substrate;
• (b) heating a solid, thermoplastic coating composition to a temperature of about 1800C to about 240.degree. C. to melt the coating composition and provide a molten coating composition, said coating composition comprising:
• (i) about 50% to about 100%, by total weight of the composition, of a polyester having a weight average molecular weight of about 10,000 to about 35,000, a glass transition temperature of about -30.degree. C. to about 120.degree. C., a melt viscosity of about 75 to about 150 Pa.s at 240.degree. C., a melt flow index of about 20 to about 200 g/10 min at 200.degree. C., and a softening point of about 120.degree. C. to about 200.degree. C., and
• (ii) 0% to about 15%, by total weight of the composition, of a modifying resin selected from the group consisting of an epoxy or phenoxy resin having an epoxy equivalent weight of about 500 to about 3,000, an acrylic resin having a weight average molecular weight of about 15,000 to about 100,000, a polyolefin resin having a weight average molecular weight of about 15,000 to about 1,000,000, and mixtures thereof;
• (c) extruding the molten coating composition onto a surface of the preheated metal substrate to provide a layer of molten coating composition about one to about 40 microns thick on the preheated metal substrate and provide a coated metal substrate;
• (d) allowing the coated metal substrate to cool;
• and
• (e) heating the cooled coated metal substrate of step (d) at a temperature of about 300.degree. C. to about 550.degree. C. for about 5 to about 30 seconds.