Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2008

Powder Coat Paint Adhesion Problem on a Zinc Die Casting

Q: My customer tested our parts and said they had fatty acid amides on the surface and that is why the coating fails adhesion test. I don't know where this amide came from and if they are pre-treating with iron phosphate why is it not removing this substance? Here is what they are using:

Cleaner is Chemfos ATP-31FRS from PPG Chemfil
Temperature is ambient
Time the part is with the cleaner is 80 secs.
Powder paint is Hybrid from IVC Powder in Grand Rapids
No specific colour as they all have the same adhesion problem.

What is you opinion and recommendations?

A: Fatty acid amides are chemicals, but despite trying to research this on the Internet I was not able to identify a substance that one would find in a zinc die casting or painting operation. It is possible that your customer's laboratory identified such a substance using an analytical technique such as FTIR, but that in itself is not sufficient to claim that its presence was the root cause of the failure.

Can you ask your customer to get back to you with some examples of fatty acid amides? If your customer can send me the (presumably) FTIR scan, I will send it to a colleague for a second opinion interpretation. Please bear in mind that some scans are ambiguous and the spectroscopist often needs to stretch to name the compound.

Is the fatty acid amide present as a trace amount or in significant quantity?

There are several questions that need to be answered before one can blame the paint failure on this compound.

I work for Exponent Failure Analysis and if you would like to pursue this I will need to do so through the company.

I look forward to hearing from you.

Regards,

Ron Joseph