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Surface Treatment Effects on Humidity Resistance for Coated Mica Pigments in Waterborne Coatings

SpecialChem / Apr 9, 2003

Since their introduction in the late 1970s, mica pigments have become a staple in the automotive and high-performance coatings industries. They began what has become known as the "effect pigment" industry. Coated mica pigments, also known as pearlescent or interference pigments, have a structure consisting of a mica platelet surrounded by a thin layer of titanium dioxide (TiO2) or iron oxide. Color generated by thin film interference can be likened to the colors observed from a soap bubble. Analogous to the film of a soap bubble, a metal-oxide film interacts with light, causing reflection of certain wavelengths. By carefully controlling the thickness of the film, the observed specular reflection is of a particular color. For TiO2, which itself absorbs no visible light, a white reflection is observed from the thinnest film, followed by gold, red, blue and, finally, green reflection from the thickest film. For iron oxide, which has a reddish orange color due to light absorption, the observed reflections begin with gold. At non-specular angles, the absorption color is observable and becomes stronger as the film thickness increases.

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