Investigation of a Hydrochromic Ink Used As a Safety Feature

Hydrochromic inks change their colour by impact of water or moisture. Depending on the ink's components, this colour change process can be reversible or irreversible. Here, focus is on irreversible colour changes, without any re-change of the ink's color. Moisture is monitored in several technical processes, in the paper or plastics industry and in printing companies. Humidity that deviates from the norm can cause problems in technical processes and even lead to production breakdowns. Particularly in the case of electronic components, the humidity of the surrounding air should not be too humid (oxidation) or too dry (diffusion). The aim of this research project is to develop a hydrochromic ink for piezoelectric inkjet printing that serves as a security feature. The functionality of the developed hydrochromic ink and the theoretical background will be discussed. Furthermore, the identification of a suitable solvent will be discussed and criteria for the identification will be shown. Furthermore, suitable oxidizing agents will be identified. The resulting ink will be printed and tested regarding to its light fastness. Furthermore, the characteristic properties such as the colour change behavior will be analyzed.