Fading Color

Q. I work in quality control for a facade company and have some questions about the boiling adhesion test for powder coating. We recently received some powder coated materials from a Chinese company for one of our projects. The coating is a polyester grey in color. On the left, we have some materials that have gone through 2 hrs boiling adhesion test in a pressure cooker. Although it has perfectly good adhesion, it is significantly different in color compared with the materials that have not been tested yet. We have not seen this before and don’t understand why it happened.

In short, my questions are:

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1) Should we be concerned about this? Would it affect the color and gloss retention after a few years or any other resistance? We are running some accelerated weathering tests (QUV (B) Rays + Humidity) on it right now, but I’d love to have some answers before my project is all done and on the building itself. (We still need another 20 days to have some answers!)

2) Why does this happen? I had the same colored materials earlier and they were perfectly fine. S.Y.

A. Did the water turn color? It appears that the powder is losing pigment from the solvency of the water and the heat. They may have changed the pigment and the new yellow will not take hot water exposure for the boiling test. I have never seen this before. It may be okay in sunlight, but you should check your QUV B at every 100-hr interval and you should know if you are OK at around 300 hr.

If you do not see this color change after 500 hr, you have good color stability.