Poor Paint Adhesion on Anodized Surfaces

Q. I just read your July 2007 column. I have run into this paint adhesion issue on top of anodize before. Not having your paint background I assumed it was something we were doing in the anodize process. I looked into the nickel acetate seal we were using and it was loaded with wetting agents and surfactants to remove any smut that was generated in the anodize process. So, I changed the seal to sodium dichromate and our paint adhesion issues went away. We also tried an “old” formulation of nickel acetate that didn’t have the organics, and it passed as well. We even went back to the original seal and found that the longer we used that seal the worse the paint adhesion became. I’m not sure it helps but just thought I’d share it. A. F.

 

A. You’re referring to M. C.’s question “Pretreatment of Aluminum.” As an organic chemist, I’m not completely familiar with the subtle differences in the anodizing process. I leave that to the “wizards”— you know, the folks who wear the conical hats with the moon and stars embroidered on them. I am surprised to learn that wetting agents and surfactants would be allowed to remain on anodized surfaces.

Organic materials of these types can be considered contaminants to the painting process and could interfere with paint adhesion. I can’t help wondering whether a final rinse would remove these contaminants, which could certainly have caused M. C.’s problems. Eliminating them or using anodized aluminum having more compatible surfaces adds a third answer to M. C.’s question.

Thank you, A. F. I learned something new.