A Novel Method to Formulate Pigmented Powder Coatings by Ultrafine Powders

Powder coatings are a green alternative to conventional solvent-borne liquid coatings, but they have the intrinsic drawback of color-matching and adjustment in production with the conventional extrusion process. In this study, an industrially applicable approach to formulate color powder coatings utilizing ultrafine powders, i.e., a powdery blending and pressing method, was invented. This novel method was validated by comparing samples prepared by the Method 1 conventional extrusion method with an extra ultramarine pigment at 3%; Method 2 powdery blending and pressing of the original coatings and the same coating with 6% ultramarine pigment utilizing regular (coarse) powder coatings; and Method 3 utilizing ultrafine powder coatings for the two coatings with the same formulations as Method 2. The coating powders were prepared to have similar particle sizes and particle size distributions, with three commonly used coating binders, namely polyester-epoxy hybrid, polyester/TGIC (triglycidyl isocyanurate), and polyurethane (PU). The powders prepared by Methods 1 and 3 had similar flow abilities in terms of angle of repose (AOR) and avalanche angle (AVA). The performance of the new coatings by Method 3 was close to or better than the ones prepared by Method 1 in terms of the specular gloss, DOI (distinctness-of-image), reflection haze and color values, being superior to Method 2. The coatings via ultrafine powders also exhibited a comparable ultramarine particle distribution in the coating cross-sections as the conventional ones, whereas the ones via regular powders had an inferior pigment dispersion. The new method can greatly enhance the production efficiency and reduce the cost of powder coatings with compound colors, especially for small batch manufacturing.