Coating compositions for packaging articles such as food and beverage containers
An article, comprising a food or beverage container ( 20 ), or a portion thereof, that includes a metal substrate ( 30, 32 ) and a coating ( 34 ) disposed on at least a portion of the metal substrate ( 30, 32 ). The coating ( 34 ) is preferably formed from a coating composition that comprises an emulsion polymerized latex having a first-stage emulsion polymerized copolymer and a second-stage emulsion polymerized copolymer.
1. A method of making an inside spray coating composition for food or beverage containers, the method comprising:
emulsion polymerizing first-stage monomers in an aqueous carrier to produce a first-stage copolymer comprising water-dispersing groups;
emulsion polymerizing second-stage monomers, wherein at least 5% by weight of the second-stage monomers are chemically different from the first-stage monomers, in the presence of the first-stage copolymer to form a second-stage copolymer, wherein the second-stage copolymer is chemically different from the first-stage copolymer, and wherein the second-stage copolymer comprises a curing group configured to react with the first-stage copolymer during a curing step; and
formulating the coating composition for a spray coating application, wherein the coating composition is substantially free of one or more, or all, of structural units derived from each of (meth)acrylamide-type monomers and bisphenol A, and wherein the coating composition spray-applied onto an interior of a 12 ounce two-piece drawn and ironed aluminum beverage can and cured at 188° C. to 210° C. (measured at the can dome) for 60 seconds provides an inside spray beverage can coating with an average film thickness of about 0.7 mg/in 2 to about 4.0 mg/in 2 , and the can coating exhibits a global extraction result of less than 50 ppm as measured according to the extraction procedure in 21 C.F.R. § 175.300, paragraphs (d)-(e).
2. The method of claim 1 , wherein the coating has an average film thickness of about 0.9 mg/in 2 to about 2.1 mg/in 2 .
3. The method of claim 2 , wherein the first-stage copolymer has an acid number greater than about 80 milligrams potassium hydroxide per gram of first-stage copolymer.
4. The method of claim 1 , wherein the first-stage copolymer has an acid number greater than about 40 milligrams potassium hydroxide per gram of first-stage copolymer.
5. The method of claim 4 , wherein the curing group comprises an oxirane group.
6. The method of claim 5 , wherein second-stage monomers comprise greater than 5% to less than 40% by weight of monomer having an oxirane group.
7. The method of claim 1 , wherein the first-stage copolymer has an acid number greater than about 100 milligrams potassium hydroxide per gram of first-stage copolymer.
8. The method of claim 1 , wherein the curing group comprises an oxirane group, an isocyanate group, an azlactone group, an oxazoline group, a cyclocarbonate group, or a combination thereof.
9. The method of claim 1 , wherein the curing group comprises an oxirane group, and wherein the second-stage monomers comprise glycidyl methacrylate.
10. The method of claim 9 , wherein second-stage monomers comprise greater than 5% to less than 30% by weight of glycidyl methacrylate.
11. The method of claim 1 , wherein the first-stage copolymer has a glass transition temperature of greater than 30° C. and wherein the second-stage copolymer has a glass transition temperature of greater than 30° C.
12. The method of claim 1 , wherein each of the first- and second-stage copolymers are substantially free of styrene.
13. The method of claim 1 , wherein the coating has an initial metal exposure of less than 3 mA.
14. The method of claim 1 , wherein the first-stage monomers are present in an amount of greater than 30% by weight and less than 100% by weight relative to the total weight of first-stage monomers and second-stage monomers.
15. The method of claim 14 , wherein the first-stage monomers are present in an amount greater than 0% by weight of less than 75% by weight relative to the total weight of first-stage monomers and second-stage monomers.
16. The method of claim 1 , wherein the coating composition has a total solids content of greater than about 15% to less than about 25%, based on the total weight of the coating composition.
17. The method of claim 16 , wherein the coating composition includes greater than about 50% by weight of latex emulsion copolymers, based on the entire weight of the total solids in the coating composition.
18. The method of claim 17 , wherein the first-stage copolymer has an acid number greater than 40 milligrams potassium hydroxide per gram of first-stage copolymer, and wherein the first-stage monomers are present in an amount of greater than 30% by weight and less than 100% by weight relative to the total weight of first-stage monomers and second-stage monomers.
19. The method of claim 17 , wherein the first-stage copolymer has a glass transition temperature of greater than 30° C. and wherein the second-stage copolymer has a glass transition temperature of greater than 30° C.
20. The method of claim 1 , wherein the coating composition includes greater than about 50% by weight of latex emulsion copolymers, based on the entire weight of the total solids in the coating composition.
21. The method of claim 1 , wherein the coating composition includes a phenoplast resin.