Q: We are having a problem with one of our texture powder coatings. It is a light color and has areas where it looks like you can see the substrate through it. We do a mil thickness check, and we get a reading of 2.5 +. We have also done a MEK rub test on the area that looks light and passed (with no drop in the reading after).
We are concerned since we have a customer returning product because it looks light. Any ideas?
A: This is an age-old problem with textured powders, especially white or light colored ones. And it’s important to qualify the descriptor textured. In this case, we’re talking about a very structured or grainy surface consisting on a micro scale of high peaks and deep valleys. Some might call these coatings “dry texture” or even “anti-skid” coatings. We are not referring to “mini-tex,” “hammertones,” “rivers,” or “veins.”
You mention that your film thickness readings are over 2.5 mils. This measurement is a good place to start, but you have to take into consideration that the film gauge is measuring the tallest peaks. The “valleys” are significantly thinner than this reading.
Consequently, 2.5 mils is probably too thin to provide complete coverage and opacity. I recommend that you increase the thickness of the coating by applying more powder to your parts (that seems rather obvious).
Increasing the thickness of a highly textured powder is easier said than done. This may involve slowing down your line, lowering the current on the gun(s), and possibly preheating the parts. Once you find the film thickness range that provides acceptable hiding, use this as the specification for this particular powder coating.
Keep in mind that incomplete coverage not only affects cosmetics such as color and appearance but also influences durability, particularly corrosion resistance.