Photochromic Pearl Pigments -Photochromism of Ferric-Oxide-Doped Pearl Pigments

Abstract

Photochromism of titanium oxide (TiO2) particles and TiO2-mica doped with metals or metal oxides has been examined. Their coloration, which was evaluated by DE under UV, was, however, low for security applications. To improve their photo properties, we studied doping conditions, especially in terms of the particle size of ferric oxide (Fe2O3) to pearl pigments. Pigments obtained by doping nanoparticles of Fe2O3 retained their pearl luster, and their coloration under UV irradiation was deeper than that of doped TiO2 or TiO2-mica. These photochromic pigments have good repeated cycling property. Silk screen printing using one of these pigments exhibited clear contrast between the UV irradiated area and the rest. Therefore, these pigments can be applied to security inks and printings with both overt and covert characteristics.