Two-coat single cure powder coating
View Patent ↗Methods and systems for coating metal substrates are provided. The methods and systems include sequential application of low flow and high flow powder coatings followed by a single heating step to provide a cured coating. The methods and systems include a marker that allows coating uniformity to be monitored and assessed during application. The described methods provide coatings with optimal surface smoothness and edge coverage.
1. A method, comprising:
providing a metal substrate;
applying a primer coating comprising a first powder coating composition including a carboxyl-functional polyester binding resin, wherein the first powder coating composition has flow of no more than about 40 mm;
applying a topcoat comprising a second powder coating composition with flow of at least about 40 mm; and
heating the metal substrate with the primer coating and topcoat applied thereon in a single step, without multiple heating cycles, to form a continuous corrosion-resistant coating with 20-degree gloss of at least 50%.
2. The method of claim 1 , wherein the first coating composition has a flow of about 15 mm to 40 mm.
3. The method of claim 1 , wherein the first coating composition has a flow of about 20 to 35 mm.
4. The method of claim 1 , wherein the second coating composition has flow of greater than about 50 mm.
5. The method of claim 1 , wherein the second coating composition has flow of greater than about 70 mm.
6. The method of claim 1 , wherein the second coating composition has flow of greater than about 75 mm.
7. The method of claim 1 , wherein the cured coating has edge coverage equal to at least 2% of face coverage.
8. The method of claim 1 , wherein the cured coating has edge coverage equal to about 10% of the face coverage.
9. The method of claim 1 , wherein the metal substrate is unprimed, clean blasted, or pretreated.
10. The method of claim 1 , wherein the first coating composition and second coating composition are heated in a single step at a temperature of about 180° C. to 200° C.
11. The method of claim 1 , wherein the first coating composition and second coating composition are heated in a single step at a temperature of about 140° C. to 170° C.
12. The method of claim 1 , wherein the first coating composition and second coating composition are heated in a single step at a temperature of about 120° C. to 135° C.
13. The method of claim 1 , wherein the first coating composition is applied only to one or more edges of the substrate.
14. The method of any claim 1 , wherein the second coating composition is applied only to one or more edges of the substrate.
15. The method of claim 1 , wherein the first coating composition and the second coating composition are applied only to one or more edges of the substrate.
16. The method of claim 1 , wherein the first coating composition is applied at a film build of about 20 to 40 micron.
17. The method of claim 1 , wherein the second coating composition is applied at a film build of about 25 to 35 micron.