Fabrication of anti-counterfeiting patterns with angle-dependent colors by silkscreen printing and UV-curable photonic crystal inks

Photonic crystal (PC) pattern with angle-dependent colors is a promising anti-counterfeiting material as it can show unique visual effects without physical or chemical stimuli. Although various methods have been reported to fabricate PC patterns, few of them offer a complete solution for the fast, low-cost, and mass production of these materials. Here, delicate PC patterns are fabricated by silkscreen printing of photo-curable SiO2/monomer PC inks on the substrate, followed by ultraviolet irradiation to fix the PC structures. The PC inks composed of acrylic, acrylamide, and alkene monomers can be quickly cured in the air. They can also produce PC marks with noticeable angle effects, uniform color distribution, and good mechanical and chemical stabilities. Meanwhile, the silkscreen stencils with different mesh numbers are investigated to achieve the best color intensity and high printing resolution. Finally, as a demonstration of the anti-counterfeiting functions, the as-prepared monochromatic PC pattern changes color with the incident/viewing angle, while the bicolor pattern reversibly switches to a "quasimonochromatic " pattern or is alternately revealed under different angles.