Influence of different application methods of special inks on thermochromic and fluorescence effect in screen printing

Abstract

Printing inks with special effects are commonly utilized in graphic technology for the purposes of added value and anti-counterfeiting methods of printed products. Thermochromic liquid crystal-based inks (TLC) and ultraviolet (UV) visible (daylight invisible) fluorescent printing inks (UVF) can be used in smart packaging - as additional security features, indicators, markings, etc. In this research, TLC ink and UVF ink with red pigment have been applied on the printing substrate as a hybrid ink system, with the aim of obtaining a functional printed product with combined added value. Two suitable paper substrates were screen-printed using two methods: overlaying the prepared UVF ink on the printed TLC ink; and by mixing the UVF red pigment directly into the TLC ink before printing. Thickness, roughness, surface free energy and adhesion parameters of printed layers were analysed. Spectral reflectance of the UVF ink, as well as thermochromic effect of TLC ink were measured. Microscopy was used to display the visual colour play effect and the effect of luminescence. Results of the research have enabled the evaluation of hybrid TLC-UVF effect obtained by screen printing technique, using different ink application methods. Analysis of the properties of obtained prints can be used for the optimization and applicability recommendation of screen-printed TLC-UVF special inks.