Systems and methods for laminating can end stock
Improved aluminum can end stock (CES) is disclosed. The CES includes an adhered polymer coating exhibiting low feathering and high performance in various acid tests. The low feathering and resistance to acid tests is accomplished by incorporating a copolymer adhesion promoter film to an aluminum alloy before lamination. In some cases, the metal strip is pretreated with a conversion layer, which can include compounds of trivalent chromium (Cr(III)) and phosphates or titanium and zirconium.
1. A process for preparing can end stock, comprising:
cleaning a metal strip, wherein cleaning the metal strip includes removing or reducing native oxide or hydroxide species from a first side of the metal strip so that a remaining metal oxide or hydroxide layer, if present, is 1 nm thick or less;
applying a copolymer adhesion promoter solution to the first side of the metal strip having the remaining metal oxide or hydroxide layer, if present, thereon, wherein the copolymer adhesion promoter solution comprises a vinyl phosphonic acid-acrylic acid copolymer;
drying the copolymer adhesion promoter solution to provide a copolymer adhesion promoter film on the first side of the metal strip;
curing the copolymer adhesion promoter film on the first side of the metal strip;
laminating a polymer film to the copolymer adhesion promoter film on the first side of the metal strip to produce a laminated metal strip; and
annealing the laminated metal strip at an annealing temperature.
2. The process of claim 1 , wherein the metal strip is a 1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, or 8xxx series aluminum alloy.
3. The process of claim 1 , wherein the polymer film comprises a polyester film.
4. The process of claim 3 , wherein the polymer film comprises a polyethylene terephthalate (PET) film.
5. The process of claim 1 , wherein applying the copolymer adhesion promoter solution comprises bar coating, roller coating, spray coating, or dip coating.
6. The process of claim 1 , wherein the copolymer adhesion promoter solution is an aqueous copolymer adhesion promoter solution.
7. The process of claim 1 , wherein drying the copolymer adhesion promoter solution is performed for up to 30 seconds.
8. The process of claim 1 , further comprising:
applying a conversion layer before applying the copolymer adhesion promoter solution; and
curing the conversion layer.
9. The process of claim 8 , wherein the conversion layer comprises compounds of chromium III phosphate or titanium/zirconium.
10. The process of claim 1 , wherein cleaning the metal strip comprises immersing the metal strip in a mixture of sulfuric acid and hydrofluoric acid.
11. The process of claim 1 , wherein laminating the polymer film comprises:
heating a temperature of the polymer film to at least 200° C.;
contacting the polymer film with the copolymer adhesion promoter film on the first side of the metal strip; and
maintaining the temperature of the polymer film for from 1 second to 30 seconds.
12. The process of claim 1 , wherein annealing the laminated metal strip includes raising a temperature of the polymer film to at least 230° C.
13. The process of claim 1 , further comprising applying a layer of lacquer or another polymer film to a second side of the metal strip, wherein the first side of the metal strip corresponds to an interior-facing side of a can end formed from the metal strip, and wherein the second side of the metal strip corresponds to an exterior-facing side of a can end formed from the metal strip.
14. The process of claim 1 , wherein the applying step comprises depositing the copolymer adhesion promoter solution, wherein the copolymer adhesion promoter solution comprises an aqueous solution containing an adhesion promoter from 0.08 wt. % to 0.45 wt. %.
15. A process for preparing can end stock, comprising:
cleaning a metal strip, wherein cleaning the metal strip includes removing or reducing native oxide or hydroxide species from a first side of the metal strip so that a remaining metal oxide or hydroxide layer, if present, is 1 nm thick or less;
applying a copolymer adhesion promoter solution to the first side of the metal strip having the remaining metal oxide or hydroxide layer, if present, thereon, wherein the copolymer adhesion promoter solution comprises a vinyl phosphonic acid-acrylic acid copolymer;
drying the copolymer adhesion promoter solution to provide a copolymer adhesion promoter film on the first side of the metal strip;
laminating a polymer film to the copolymer adhesion promoter film on the first side of the metal strip to produce a laminated metal strip; and
annealing the laminated metal strip at an annealing temperature.