david.t2

Topic: Opaque bloom on powder coating

Hi

Having a major problem with an opaque film or bloom on coated panels when baked.Can partly remove it by polishing but not completely.

Have maintained oven and tried different powders but still the same

Any ideas ?

Regards

David

Val R DeBrunce

Re: Opaque bloom on powder coating

Good Day - Have you tried increasing the oven temperature?  I'd try increments of 25F until I was roughly 50F above the supplier's recommended tmeperature.  How about more time at any given temperature?  Again, I'd increase the time in intervals of 10 minutes, until I was at twice the supplier's recommended time for cure.  Last but not least, I'd combine more time at higher temperatures.

DustinGebhardt

Re: Opaque bloom on powder coating

I had a similar problem that was traced back to trace amounts of water trapped in the base coating that came out during cure and ruined the final part.  We fixed this by pre-baking the parts with a normal cycle, minus powder of course.

-Dustin Gebhardt,
CEF
Plating Engineer
Danaher Tool Group
Gastonia, NC

PaulBradleyTrimite

Re: Opaque bloom on powder coating

Could be several things;

1.  Bloom that can form from some polyesters or hybrids if baked lower than 340F.  Check your oven to make sure that the oven temperature is what you think it is.  If problem persists when the oven is at 350-400F then contact powder supplier.

2. Ventilation - powder coatings (in particualr smooth coatings) contain a small amount of benzoin which evaporates during baking - this is the whitish or yellowish deposits you sometimes see around the entrance/exits.  If the oven doesn't ventilate well then benzoin (or benzil as it becomes in the oven) looks for something cold to condense on - parts that are cooling down as they exit the oven are ideal!

3. Off gloss powders can contain some wax matting agents.  This becomes visible as a bloom in dark colors.  Ask your supplier to change formula and stop using a wax matting agent.