How to Control Gloss at 60° and 85° Angles
Hi Joe,
My team and I are currently trying to make a powder that is very low in gloss when measured at the 60° and 85° angles (approx. less than 1.6 and 4.0 gloss units respectively). Can you elaborate on how to control the gloss at these angles? Would the solution lie in the formulation itself, the process, or a little bit of both?
Regards,
Jeremy T. Francis
Cleveland, OH
Hi Jeremy,
It looks like you guys are trying to push the boundaries of powder coating technology. That's awesome. Achieving extremely low gloss, aka dead matte finishes, in any coating technology is a formidable task. I think it is trickier in powder than liquid coatings. That said, it is possible, and some powder producers have commercialized products that exhibit this range of low gloss. The U.S. military has called for products possessing 60⁰ gloss <1.0 gloss units and 85⁰ gloss <3.5 gloss units. Check out US MIL-PRF 32348. The camo green spec calls for a 60⁰ of <1.0 GU and the spec for black is even lower at <0.6 GUs. So commercial powder coatings exist in this gloss range. They are premium products and not all powder suppliers have them in their portfolios.
A very important question revolves around the expected (or specified) performance of the powder coating. Color will impact the gloss as lighter colors exhibit higher gloss due the greater reflectivity of bright pigments and alternately darker colors absorb more light and are somewhat easier to develop lower gloss. Therefore - what color(s) do you seek? And just as important, what film performance is required? UV resistance? Mechanical flexibility? Chemical resistance? Corrosion resistance? These requirements will dictate the base chemistry of the powder coating.
You also mentioned process. Process influences gloss, but not nearly as much as formulation. Higher temperature bake usually pushes gloss down a bit. Film thickness has an effect - too thin equals more texture and possibly film incontinuity, whereas thicker films are typically smoother.
If you have any follow-up questions, just let me know.
Best of luck,
Joe
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