Accelerated photodegradation of dye-based ink-jet printing inks in an aqueous solution and on a substrate

When studying the process of photodegradation, we often deal with the durability of the individual ink colour components, the durability of the printing material or the durability of the ink on the printing material. Less frequently, ink degradation in the solution is compared to the print. However, it is essential to consider all the crucial external and internal factors that influence the photodegradation process in the context of the durability of printed materials. When studying photodegradation, external factors such as light, temperature and humidity are relatively easy to control. On the other hand, the control of internal factors in the photodegradation process is much more complex since the internal factors are related to the composition of the ink used, the substrate and the physical and chemical processes between them. The study aims to analyse the complex degradation process of prints made with an ink-jet printer compared to the degradation of the same inks in an aqueous solution. The study included two types of paper and an ink-jet printer using dye-based inks. A high-pressure mercury lamp was used to irradiate and accelerate the degradation process, and a specially adapted reactor was used to irradiate solutions and prints. The results showed how short-wave UV radiation significantly influences the changes of the printing material, ink and prints. In some cases, the difference between the ink stability in solution and ink stability on the printing material can be observed. The effect of paper on the durability of the print is, however, negligible in the case of short-wave UV radiation. The process of photodegradation of the paper under UV radiation was mainly manifested by the loss of specific surface and optical properties.