Microscopically, the coating is a long empty structure. […]
Microscopically, the coating is a long empty structure. Water in the air, corrosive media (chloride ions, etc.) will invade through the weak part of the coating, causing corrosion under the film, and the coating will foam and flake 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 coating can effectively prevent the intrusion of corrosive media by more than 20μm. Due to the different anti-corrosion mechanism of the primer and topcoat, not only the total film thickness but also the primer is required. The thickness of 5μm) and topcoat (≥15μm) is the only way to ensure that the corrosion resistance of different parts of the painted steel plate is balanced.
Color coated roll
PVDF products require a thicker coating because of the longer lifespan. The requirements for the backside coating depend on the application. The sandwich panel requires only one layer of bondable primer. The profiled steel sheet is also required to be coated with two layers due to the indoor corrosive environment and has a thickness of at least 10 μm.