Metal-dielectric pure red to gold special effect coatings for security and decorative applications

Abstract

Because of high color saturation and fewer layers, metal-dielectric thin film has been used for years in the field of special effect coatings such as security and decorative applications. In the application of red color, purple red and orange red metal-dielectric thin films have already been realized, however, pure red thin film has not been achieved. In this paper, color target optimization method is adopted to eliminate the blue second order reflect peak (460 nm–470 nm) and compress the red first order reflect peak (675 nm), consequently, a seven-layer metal-dielectric pure red thin film is designed and fabricated. The chromaticity coordinate is (x,y) = (0.635,0.32) at normal incidence, which is located in pure red region, and the gold color target coordinate is (x,y) = (0.52,0.45) at 45°. The final base structure is Air/1.5Cr/230SiO2/6.3Cr/225SiO2/8.9Cr/213SiO2/100Al/Glass, where the numbers refer to layer thicknesses in nanometers. As the observation angle is increased from 0° to 45°, the thin film varies from pure red to gold. Remote plasma sputtering technique is used to fabricate the multilayer thin film. Finally, pure red thin films are demonstrated for the automobile coatings and optically variable ink applications, and the practical color effects are presented.