Q: My problem is that a customer wants a white powder paint very white. However, all those that we have applied are too yellowish. Is there a solution?
A: Thanks for the question, this is a common problem. Your customer requests a very white powder. While “very white” is a relative term, I think I can still provide some guidelines to allow you to provide the whitest finish for your situation.
First of all, the chemistry of the powder coating affects whiteness. For example, hybrid and especially epoxy-type powders tend to yellow upon baking. Powder types less prone to yellowing include polyesters, polyurethanes, and acrylics. Formulating technique also affects the yellowing of these chemistries. The choice of pigment, crosslinker, and additives can significantly influence yellowing resistance. So be sure to evaluate more than one version of these types of powders.
Overbaking (high temperature and/or extended time) exacerbates this problem. Furthermore, the quality of your oven affects whiteness. Gas ovens cause more yellowing than electric or infrared types. Incorrectly adjusted gas/air mixtures also cause more yellowing. It is imperative to keep your oven burner adjusted properly and to avoid overbake conditions.
If your customer requires an extremely highly reflective white powder for an application that involves lighting fixtures, then a specifically formulated powder is required. These products incorporate special grades of titanium dioxide (white pigment), as well as quite possibly an optical brightener and antioxidant.