This month we seem to have a number of questions from offshore powder coating formulators. First, I must tell all my readers that I am an engineer and not a chemist. However, these questions are pretty basic, so I have no problem answering them. For the future, anyone having questions about how to formulate powder coatings should look to another source for answers, as I may not know the answer. Having said that, anyone who has questions about powder coating formulations that they may be using has come to the right place.
We produce powder coatings. What is the optimum powder coating particle size required for good leveling? How do you achieve the best bell-shaped curve during powder particle size testing? M. A.
Most powder coatings are shipped where 80% of the material has a particle size of 20-40 microns. Purchasing a sophisticated sieving system to remove fine and oversized particles will ensure that your bell curve is exactly where you want it.
Finer powders normally produce a smoother cured finish. However, if the powder coating is too fine, it can be very difficult to fluidize, spray and charge. Smoothness also can be controlled by the gel time of the powder coating formulation. Adjusting the gel time will not affect the application equipment, but can cause sags in the coating if not applied to the optimum film thickness.