Coating composition having improved release properties and the process for making the same

Abstract

A protective coating composition and a method for coating a metal substrate are provided. The composition and method are particularly suitable for coating can ends. The coating composition includes a film-forming polymer that includes an epoxy-based resin, a lubricant system, and a solvent or water component or mixture of solvent and water. The lubricant system includes a first surface modifier that reduces the coefficient of friction and a second surface modifier that reduces the abrasion of the cured coating.

1 . A coating composition which comprises:
 from about 10% to about 50% solids based on the weight of the coating composition, the solids comprising:
 an epoxy-based resin; 
 from about 0.1% to about 20% by weight lubricant compound which comprises:
 a first surface modifier; 
 a second surface modifier that is different from the first surface modifier; and 
 
   wherein the coefficient of friction (COF) of the coating composition when dried is less than about 0.15.   
     
     
         2 . The coating composition of  claim 1 , wherein the coating composition comprises:
 from about 50% to about 99.5% by weight epoxy-based resin;   from about 0.25% to about 16% by weight of the first surface modifier; and   from about 0.25% to about 16% by weight of the second surface modifier.   
     
     
         3 . A coating composition which comprises:
 an epoxy-based resin;   a lubricant system that comprises:
 at least about 0.1% by weight based on the weight of the total solids, a first surface modifier selected from the group consisting of carnauba wax, petroleum waxes, paraffin wax, microcrystalline waxes, semicrystalline waxes, silicones, beeswax, candelilla, japan wax, ouricury wax, Douglas-fir bark wax, rice-bran wax, jojoba, castor wax, and bayberry wax; hydrogenated castor oil; high molecular weight acids and alcohols; mineral waxes, monton wax, peat wax, ozokerite, ceresin; and mixtures of the above; and 
 at least about 1% by weight based on the weight of the total solids, a second surface modifier selected from the group consisting of polyolefins and polyolefin copolymers, polypropylene, modified polypropylenes, polyethylene and modified polyethylenes; polytetrafluoroethylene; Fischer-Tropsch waxes, and mixtures of the above. 
   
     
     
         4 . The coating composition of  claim 3  wherein the coating composition comprises from about 50% to about 99.8% epoxy-based resin. 
     
     
         5 . The coating composition of  claim 3  wherein the coating composition comprises from about 0.25% to about 16% of the first surface modifier and from about 0.25% to about 16% of the second surface modifier. 
     
     
         6 . The coating composition of  claim 5  wherein the lubricant system is present in a dispersion having an average particle size distribution that ranges from about 0.5 to about 5 microns. 
     
     
         7 . The coating composition of  claim 5  wherein the first surface modifier comprises at least one of carnauba wax and silicone. 
     
     
         8 . The coating composition of  claim 7  wherein the second surface modifier comprises polyethylene. 
     
     
         9 . The coating composition of  claim 3  wherein the first surface modifier comprises carnauba wax and the second surface modifier comprises polyethylene. 
     
     
         10 . The coating composition of  claim 3 , further comprising, by weight, from about 0.1% to about 40% cross-linker. 
     
     
         11 . The coating composition of  claim 3 , wherein the lubricant system further comprises at least one of a surfactant and a dispersing polymer. 
     
     
         12 . The coating composition of  claim 3 , wherein the coefficient of friction of the coating when dried is less than about 0.1. 
     
     
         13 . The coating composition of  claim 3 , wherein the epoxy-based resin is in an epoxy-acrylic resin. 
     
     
         14 . The coating composition of  claim 9 , wherein the epoxy-based resin is in an epoxy-acrylic resin. 
     
     
         15 . A method for coating a metal substrate, which comprises:
 applying a coating composition to the metal substrate;   heating the metal substrate and coating composition until the coating is cured to produce a cured coating film having a film weight that ranges from about 1 mg/in 2  to about 8 mg/in 2 ;   wherein the cured coating film comprises, by weight, based on the total solids in the coating composition, from about 50% to about 99.5% epoxy-based resin;   from at least about 0.1% of a first surface modifier;   from at least about 0.1% of a second surface modifier; and   wherein the cured coating film has a coefficient of friction that is less than about 0.15.