1. Coating
Due to the uneven mixing of the paint or the large difference in the viscosity of the paint in different barrels, the paint extends from the feed port side to the return port in the tray, and a color difference band appears. In addition, changing the paint color, especially the two colors with large color contrast, will cause color difference due to unclean cleaning.
Second, the substrate
The difference in the size of the spangle of the substrate will also affect the chromatic aberration, and many small pits of different sizes will be formed at the grain boundary, which will affect the chromatic aberration of the board surface. For light colors, the color difference is particularly obvious, and it is best to use a spangle-free or small spangle substrate.
3. Chemical coating treatment
Improper chemical coating process will cause the chemical coating film to be too thick, and the board temperature will be insufficient after drying. If the coating roller is damaged, yellow spots will form after drying, resulting in color difference of the color coated board, especially the light color is obvious.
Fourth, film thickness
The film thickness stability has a great influence on the color difference of the color-coated board. The adjustment methods of film thickness mainly include: coating viscosity, adjusting the gap between the sticking roll and the coating roll of the roll coater, changing the roll speed of the coating roll and the sticking roll, adjusting the coating roll and the strip steel support roll. pressure, etc.
5. PMT
PMT represents the peak temperature the strip needs to reach when the coating is fully cured. The stability of PMT has a great influence on the color difference of color-coated boards. Changes in strip specifications will cause PMT changes, local high or low temperatures will affect PMT changes, uneven substrate thickness will cause PMT changes, and seasonal changes in furnace temperature changes will also cause PMT changes.
6. Cooling water
Atomization cooling, the cooling water is not replaced in time, when the volatiles of the organic solvent in the furnace gas are cooled and condensed, and the cooling water is brought to the board surface, after being squeezed by the squeeze roller, it will cause color difference on the board surface. During production, the cooling water should be kept overflowing properly, so that the condensed volatiles can be overflowed and removed in time, so as to avoid the color difference of the board surface.