On the microcosmic point of view, the coating is an empty tissue. Air, water, corrosive medium (chloride ion, etc.) will be penetrated through the weak part of the coating, causing corrosion under the film, and then coating bubbles and spalling. In addition, even the same coating thickness, the two coating is denser than the first coating. According to the results of foreign reports and related corrosion tests, the positive coating is more than 20 mu m to prevent the invasion of corrosion medium effectively. As the anticorrosion mechanism of the primer and topcoat is different, the thickness of the total film is not only required, but also the thickness of the primer (> 5 mu) and the top coat (> 15 mu m) is required respectively. Only in this way can the color coating steel be guaranteed. The corrosion resistance of different parts of the plate is balanced.
Class PVDF products require thicker coating because they provide longer service life. The requirement for the back coating depends on the application. The sandwich panel only requires a layer of adhesive primer, and the formed steel plate is also required to be coated w