Selection of Coating Thickness for Color Coating Rolls
Microscopically speaking, the coating is a hollow structure. Water and corrosive media (chloride ions, etc.) in the air will penetrate through the weak part of the coating, causing corrosion under the film, and then the coating will foam and peel off.
In addition, even with the same coating thickness, the secondary coating is denser than the primary coating. According to foreign reports and related corrosion test results, the front coatings above 20 microns can effectively prevent the invasion of corrosion media. Because of the different anti-corrosion mechanism of primer and top coat, not only the total film thickness, but also the thickness of primer (> 5 micron) and top coat (> 15 micron) are required respectively. Only in this way can the corrosion resistance of different parts of the coated steel plate be balanced.
PVDF products require thicker coatings because of the need to provide longer service life guarantees. The requirement of back coating depends on the use. Sandwich board only needs a layer of adhesive primer. Formed steel plate is required to be coated with two layers, at least 10 micron in thickness, because of indoor corrosion environment.