Photochromic Responses and Stability of Functional Inks Applied on Sustainable Packaging Materials

Photochromism refers to a reversible colour change induced by the irradiation of photochromic materials with ultraviolet (UV) or visible light that reverts to the original colour after the light source is removed. This effect arises from chemical transformations between two isomers with different absorption spectra, involving processes like proton transfer, chemical-bond formation, and isomerisation. These photochromic inks, appearing as crystalline powders with micro-sized particles, require dissolution in a suitable matrix to achieve the colour change. Photochromic inks are used in security, as functional coatings for paper and packaging, in the fabric industry, and in other ways. This study examines the influence of varying concentrations of micro-sized photochromic pigments and different ink-coating thicknesses on the photochromic effect on sustainable paperboard substrates. Artificial ageing was performed to assess the photochromic response and lightfastness in relation to pigment concentration, ink-coating thickness, and the influence of the paperboard substrates. The results of this research could contribute to enhancing knowledge on employing photochromic inks for diverse packaging applications.