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Take a powder…

SpecialChem / Dec 19, 2007

Powder coatings have evolved continuously for more than half a century (or much longer if we include cosmetic applications). The original system in which thermoplastic polyamide or vinyl powders are applied by fluidised bed is now reduced to a niche product in a market dominated by spray-applied thermoset powders, with radiation-curing also occupying a significant market position. Various proposals have been put forward for processes which avoid these problems, but they have not so far had a major impact.How effective pigment dispersion is in an extruder depends on the type of pigment. Tests on dispersion of an iron oxide and blanc fixe in a commercial polyester powder, using an oxygen plasma to expose the particles within a cured coating, revealed quite efficient dispersion, with a mean particle size of 0.8 µm for the iron oxide and 2.1µm for the blanc fixe;1 but the situation with organic pigments is more problematic, and likely to lead to reduced optical efficiency. Conversely, the shear developed is too high for many effect pigments.

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