Coating compositions for packaging articles such as food and beverage containers
An article, comprising a packaging article such as food or beverage container ( 20 ), or a portion thereof, that includes a substrate ( 30, 32 ) and a coating ( 34 ) disposed on at least a portion of the substrate ( 30, 32 ). The coating ( 34 ) is preferably formed from a coating composition that comprises a latex emulsion having a first-stage copolymer, a second-stage copolymer, and a linkage interconnecting the first-stage copolymer and the second-stage copolymer prior to curing.
1. An article, comprising a food or beverage container, or a portion thereof, including:
a metal substrate; and
a coating disposed on at least a portion of the metal substrate, wherein the coating is formed by curing a coating composition having an emulsion polymerized latex that is a reaction product of a method comprising:
providing a first-stage copolymer having step-growth-functional groups;
grafting a linkage monomer to one of the step-growth-functional groups on the first-stage copolymer to provide a pendant linkage group on the first stage copolymer;
emulsion polymerizing a plurality of second-stage monomers, chemically different from the first-stage monomers, in the presence of the first-stage copolymer to form a second-stage copolymer chemically different from the first-stage copolymer; and
linking the second-stage copolymer to the first-stage copolymer with a linkage derived from the pendant linkage group to produce an interconnected network of the first-stage copolymers and the second-stage copolymers, wherein the coating composition is substantially free of one or more of structural units derived from each of bisphenol A, bisphenol F, bisphenol S, any diepoxides thereof, formaldehyde or formaldehyde-forming materials, (meth)acrylamides, styrene, or combinations thereof.
2. The article of claim 1 , wherein providing the first stage copolymer comprises emulsion polymerizing a plurality of first-stage monomers to form the first stage copolymer.
3. The article of claim 1 , wherein the step-growth-functional groups comprise acid-functional groups, alcohol-functional groups, amine-functional groups, or combinations thereof.
4. The article of claim 3 , wherein the step-growth-functional groups comprise acid-functional groups, and wherein the acid-functional groups comprise carboxylic acid-functional groups, anhydrides thereof, salts thereof, or combinations thereof.
5. The article of claim 1 , wherein the linkage monomer comprises an ethylenically-unsaturated oxirane-functional monomer.
6. The article of claim 5 , wherein the linkage monomer comprises glycidyl acrylate, glycidyl methacrylate, or a mixture thereof.
7. The article of claim 1 , wherein the first-stage copolymer comprises at least one structural unit produced from a polymerizable surfactant monomer.
8. The article of claim 1 , wherein the second-stage copolymer further comprises at least one functional group comprising an oxirane group, an isocyanate group, an azlactone group, an oxazoline group, a cyclocarbonate group, or a combination thereof.
9. The article of claim 1 , wherein the second-stage monomers comprise one or more (meth)acrylates, one or more ethylenically-unsaturated aromatic monomers, or combinations thereof.
10. The article of claim 1 , wherein at least about 5 wt % of the first-stage monomers are chemically different from the second-stage monomers.
11. The article of claim 1 , wherein the second-stage copolymer in the cured coating further comprises a curing group reacted with a step-growth-functional group of the first-stage copolymer.
12. The article of claim 1 , wherein the linkage linking the first and second copolymers includes at least one ester linkage, and is connected to the second-stage copolymer with a carbon-carbon covalent bond.
13. The article of claim 1 , wherein the copolymer linkage has a structure selected from the group consisting of:
wherein the carbonyl groups are directly bonded to backbone carbon atoms of the first-stage copolymer and the second-stage copolymer, and wherein, optionally, each hydrogen atom of the CH 2 and CH groups is independently substituted with a C 1 -C 3 alkyl group.