Q. I am responsible for the various finishing operations at my plant. My company is experiencing a variation in adhesion results among different colors of the same paint system from the same supplier.
Specifically, the black paint seems to have poorer adhesion than the other colors. Is there something inherent in black pigment, or in other materials or processes used to make black paint, that prevents it from adhering as well as other colors do? The paint we are using is a baking enamel applied over chrome at around 25µ dry film thickness. T.B.
A. If the paint is the same, except for its color, the process and materials used should be essentially the same. The main difference would be the color pigments used to produce the specific colors. However, there will be slight differences in the formulation owing the variations in oil absorption values and bulking values of the different color pigments. These differences will result in different pigment volume concentrations. Oops, I just remembered this is not a forum for paint chemists!
Simply stated, the subtle differences mentioned above should not grossly affect paint adhesion. Instead, I would look at other factors.
In your investigation, consider the following:
1) Check the supplier to ensure you are getting the same paint in all colors.
2) Did the adhesion problem with black paint just start? If these adhesion problems with the black paint are new, you could have gotten a bad batch of paint.
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3) Are you applying all the paint colors within the same time frame after chrome plating? It is my understanding that because of the nature of chrome plating, it should be painted within 8 hours after plating.