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Powder Paint Attributes

What are the attributes of uncured powder paint that will determine how well it will fluidize in our paint hopper? What about attributes that determine the ability of the paint to cover or hide the substrate at a given coating thickness? How can I measure these attributes, say on an incoming inspection basis at the receiving dock, to prevent loading up the paint hopper with "bad paint"?

brack c [last name deleted for privacy by Editor]
- Columbus, Georgia, US
2000

For fluidization- particle size & shape, powder particle surface attributes(affected by chemistry and additives (waxes) and the use of "post-add" dry flow agents are some of the controlling factors for fluidization. Unfortunately, I've never seen a really good (quick, easy, and relatively inexpensive) test for directly measuring fluidization. Your best bet is to get a small fluidizing hopper (available from spray equipment manufacturers) and visually check it. Follow the same procedures for conditioning the powder before use as you would on your line.

Hiding power is a function of the pigments and loading in the powder formulation and can be measured as a contrast ratio by spraying over a black and white panel at a given film build and measuring color over the black and white sections with a spectrophotometer (color computer). Since the spectrophotometers are expensive (if you don't already have one) I'd suggest getting some of the black and white panels (Lenetta is our supplier of these panels) and simply doing a visual evaluation of the minimum film-build required to get the same visual look over the black and white sections.

You should look at the ASTM test methods that are available for powder coating testing. They are a wonderful starting point for establishing test methods of your own or for setting up test methods with your supplier.

Greg Walls
- Reading, Pennsylvania
2000