Q: What could cause a slick glossy appearance in a black wrinkle powder coating? I have tried a few different manufacturers with similar results. Granted, I have different substrate thicknesses, but issues are not limited to the thicker materials and surrounding areas.
I have been told that the black wrinkle begins its “crawl” at a particular temperature and cannot be interrupted during this process or the “slick” undercoating (or what is there before the crawl) will be left.
This is a very time-consuming powder that unfortunately has to be used on certain product lines in order to match outsourced products. I have tried a few different primers to help with no avail. What do you think could be the prominent issue?
A: From what you describe, this is most probably a polyester-based wrinkle. The wrinkle surface is created by a carefully controlled chemical reaction between the polyester resin and a unique curing agent. This chemical reaction requires a very specific catalyst to make this happen.
Since the wrinkle surface is driven by a chemical reaction, the curing conditions affect the degree of wrinkling. Hence, a severe undercure will cause the “slick glossy” or “wet look” appearance you describe.
Severe undercure can be ascertained by a simple solvent rub test (acetone or MEK will do). If the coating is easily removed with 10-20 double rubs of a solvent-soaked rag, then the coating did not see enough heat (time and temperature).
Another condition that influences wrinkling is pH (acidity/alkalinity). The catalyst used to create the wrinkle is acid based and, consequently, a substrate surface with high alkalinity will retard the acid catalyst and cause a glossy spot. High alkalinity can occur from substrate contamination, especially from poor rinsing of chemical cleaners.
The concept of wrinkle powder over a primer is an interesting proposition. I have seen wrinkle failure with polyester wrinkle powders applied over fillers. This was with repair fillers (first it was old fashioned Bondo® and next high-temperature filler) and probably occurred due to an alkaline nature of the filler.
Many fillers contain high levels of calcium carbonate, which is alkaline in nature. As for primers – it’s possible that the surface of the primer is alkaline. This could retard the catalysis and cause a glossy instead of wrinkled surface.
I recommend that you try the wrinkle powder over different primers and other more standard powder coatings. If you think the end use of the products you are coating will perform acceptably with a single coat of wrinkle powder, this may be your best bet.