Two-coat single cure powder coating

Abstract

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.

What is claimed is: 
     
         1 . A method, comprising:
 providing a metal substrate;   applying a primer coating comprising a first powder coating composition including a polymeric 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 corrosion-resistant coating having a surface smoothness on the Powder Coating Institute (PCI) scale of at least 4.   
     
     
         2 . The method of  claim 1 , wherein the polymeric binding resin includes a carboxyl-functional polyester binding resin. 
     
     
         3 . The method of  claim 1 , wherein the first coating composition has a flow of about 15 mm to 40 mm. 
     
     
         4 . The method of  claim 1 , wherein the first coating composition has a flow of about 20 to 35 mm. 
     
     
         5 . The method of  claim 1 , wherein the second coating composition has flow of greater than about 50 mm. 
     
     
         6 . The method of  claim 1 , wherein the cured coating has edge coverage equal to at least 2% of face coverage. 
     
     
         7 . The method of  claim 1 , wherein the polymeric binder is made with epoxy, polyester, polyurethane, polyamide, acrylic, polyvinylchloride, nylon, fluoropolymer, silicone, or combinations thereof. 
     
     
         8 . 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 degree C. to 200 degree C. 
     
     
         9 . 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 degree C. to 170 degree C. 
     
     
         10 . The method of  claim 1 , wherein the first coating composition is applied only to one or more edges of the substrate. 
     
     
         11 . The method of any  claim 1 , wherein the second coating composition is applied only to one or more edges of the substrate. 
     
     
         12 . The method of  claim 1 , wherein the corrosion-resistant coating having a surface smoothness on the PCI scale of at least 5. 
     
     
         13 . The method of  claim 1 , wherein the corrosion-resistant coating comprises 20-degree gloss of at least 27%. 
     
     
         14 . The method of  claim 1 , wherein the first powder coating composition and second powder coating composition comprise different polymeric binders selected from a group comprising, carboxyl-functional polyester resin and epoxide-functional compounds, carboxyl-functional polyester and polymeric epoxy resins, carboxyl-functional polyester resins and hydroxyalkyl amides (HAA), hydroxyalkyl urea (HAU) and blocked isocyanates or uretdiones, hydroxyl functional polyester resins and blocked isocyanates or uretdiones, epoxy resins and amines, epoxy resins and phenolic-functional resins, epoxy resins and carboxyl-functional curatives, carboxyl-functional acrylic resins and polymeric epoxy resins, hydroxyl functional acrylic resins and blocked isocyanates or uretdiones, unsaturated resins and free radical reactions. 
     
     
         15 . A kit for coating a substrate comprising:
 a first container comprising a sprayable primer coating comprising a polymeric binding resin, wherein the first powder coating composition has flow of no more than about 40 mm;   a second container comprising a sprayable topcoat comprising a second powder coating composition with flow of at least about 40 mm,   wherein the sprayable topcoat when applied to the sprayable primer coating and cured in a single step, without multiple heating cycles, results in a corrosion-resistant coating having a surface smoothness on the Powder Coating Institute (PCI) scale of at least 4.   
     
     
         16 . The kit of  claim 15 , wherein the first powder coating composition and second powder coating composition comprise different polymeric binders selected from a group comprising, carboxyl-functional polyester resins and epoxide-functional compounds, carboxyl-functional polyester and polymeric epoxy resins, carboxyl-functional polyester resins and hydroxyalkyl amides (HAA), hydroxyalkyl urea (HAU) and blocked isocyanates or uretdiones, hydroxyl functional polyester resins and blocked isocyanates or uretdiones, epoxy resins and amines, epoxy resins and phenolic-functional resins, epoxy resins and carboxyl-functional curatives, carboxyl-functional acrylic resins and polymeric epoxy resins, hydroxyl functional acrylic resins and blocked isocyanates or uretdiones, unsaturated resins and free radical reactions. 
     
     
         17 . The kit of  claim 15 , wherein the polymeric binding resin includes a carboxyl-functional polyester binding resin. 
     
     
         18 . The kit of  claim 15 , wherein the corrosion-resistant coating comprises 20-degree gloss of at least 27%. 
     
     
         19 . The kit of  claim 15 , further comprising instructions to first apply the sprayable primer coating and subsequently applying the sprayable topcoat to a substrate and then in a single step curing both the sprayable primer coating and the sprayable topcoat. 
     
     
         20 . The kit of  claim 15 , wherein the first coating composition has a flow of about 15 mm to 40 mm.