Based on the coating method, the production processes for color-coated steel sheets are primarily categorized into roller coating, curtain coating, powder coating, and film lamination. Among these, roller coating is the most widely used. Roller coating processes typically involve configurations such as "one-coat, one-bake," "two-coat, two-bake," or "three-coat, three-bake" to meet specific coating thickness requirements, with the "two-coat, two-bake" method being the most common. A standard continuous production line for this process includes the following steps: uncoiling, head cropping, alkaline degreasing/cleaning, chemical conversion treatment (phosphating/passivation), drying, application of the primer, curing, application of the topcoat, curing, cooling, and recoiling.
Pretreatment is designed to enhance coating adhesion and corrosion resistance; it primarily consists of alkaline degreasing and the formation of a chemical conversion layer. While traditional processes utilize phosphating followed by chromate passivation, the current trend-driven by environmental considerations-is to adopt chromium-free treatment solutions. The coating system for color-coated sheets generally comprises a primer and a topcoat. Primers, typically based on epoxy or polyester resins, serve to provide corrosion protection and improve adhesion. Topcoats-which may consist of polyester, polyvinyl, acrylic, fluorocarbon (such as PVDF), or silicone-modified resins-primarily provide decorative properties and weather resistance. Curing methods for the coatings include convection (hot air) heating, infrared heating, and induction heating. Electron-beam curing (EBC) is an emerging technology that enables the formation of a film almost instantaneously at room temperature.