Metallic Pigments in Powder Coatings
Dear Joe,
A question….
Is it possible to create that liquid look with a metallic pigment in a powder coating? I’ve heard a lot of grumbling among powder coat companies that it’s just not possible. What research has your lab completed on the topic, if any, and do you have any positive results you can share with your beloved fans? If not, do you think it will take new technology on the resin/pigment suppliers part to achieve the liquid look in powder, or a new type of gun, or maybe both?
…or are we all just a little to “pie in the sky” to think it’s possible.
Thanks,
Tenacious K.
Somewhere in Massachusetts
Hey Karen,
Yep, this is a problem and has to do with rheology, viscosity and open time of a curing binder system. Metallics tend to orient themselves randomly in a viscous powder binder. The metal flakes are distributed onto particles via bonding or worse, just mixed into the bulk powder. Electrostatic application doesn't help either. The charging characteristics of a metal flake are vastly different than a nodular organic particle.
Consequently the "lay-down" of the flakes is indeed random. Then the only time the flakes can "lay down" to establish any degree of regular orientation is in the oven after the powder melts, coalesces and is fluid. The vast majority of powders are thermosetting, so soon after the powder melts it starts to build molecular weight and therefore increased viscosity. Low-viscosity binders (some epoxies and polyurethanes) are somewhat better but never approach the low viscosity of a solventborne paint.
Hence a powder technologist's tale of woe regarding metallic flake orientation and matching a liquid metallic coating’s appearance.
Peace,
Joe Powder
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