Journal of the Japan Society of Colour Material

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We have successfully prepared titanium dioxide flakes as a novel iridescent material and investigated their optical characteristics, etc.
Muscovite raw stone was pulverized by a wet process using a ball mill, and classified by elutriation to prepare five types of mica substrate particles with different average particle sizes. These mica substrate particles were coated with the fine particles of titanium dioxide by the method of thermal hydrolysis with titanyl sulfate until the interference color became a second-order yellow green. The fine particle layer of titanium dioxide could be efficiently removed from the particles of mica substrate by immersion of the particles in an aqueous solution of 10 wt % sodium hydroxide for 72 h after washing, drying, and heating. In this case, the fine particle layer of titanium dioxide could be efficiently removed by using the coarse mica particles with an average particle size of 240 μm.
The removed titanium dioxide flakes from the mica substrate particles were used as a starting material, and the fine particles of titanium dioxide were again coated on the flakes by the method of neutralization precipitation in an aqueous solution of titanium tetrachloride. The iridescence of the resulting flakes changed from yellow green to yellow, purple, violet, blue, and green, as the amount of titanium tetrachloride added was increased. In addition, these titanium dioxide flakes had a strong surface activity and thus exhibited a photochromic property and an ultraviolet scattering effect. However, the surface activity could be reduced by a surface treatment with aluminum sulfate and zirconium oxychloride. An exposure test conducted in the prefecture of Okinawa also showed that the surface-treated titanium dioxide flakes exhibited satisfactory weather resistance.

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