Characterization of orange pigments in decorative outdoor coatings and their weather fastness

The shades of decorative coatings for façades are currently changing from white and pale to more chromatic ones. This also imposes a phase-out of heavy-metal pigments based on cadmium and lead, which cover the full range of yellow, orange, and red shades, and show excellent performance. The substitute pigments have many limitations regarding heat stability, colour strength, opacity, light fastness, or dispersibility. While all components of the final coating contribute to these properties, we have studied here the stability of four orange pigments suitable to replace the pigments with heavy metals in water-based coatings for outdoor applications in a different binder system (acrylate styrene with different amount of silicone resin, vinyl acetate versatate and acrylate based polymer). The accelerated weathering tests show that the stability of all samples strongly depends on the applied coating base and is systematically higher in white coating bases, especially when combined with pigment pastes prepared without a binder. The pigment chemistry, being inorganic, hybrid, or organic plays a role, but the stability of the coating gradually depends on the other components.