Leuco dyes applied in thermochromic pigment and inks

leuco dye based thermochromic inks are specialized dynamic inks that change color when exposed to different temperatures, i.e., below their activation temperature they are colored and above their activation temperature they are clear or slightly colored. They are usually blended with some other pigments (non-heat sensitive pigment) change from one color to another. The activation temperature is defined as the temperature above which the ink has almost achieved its final clear or light color end point. The color starts to fade at approximately 4˚C below the activation temperature and will be in between colors within the activation temperature range. Leuco dye-based thermochromic inks can be made to change color at temperatures ranging from -15°C to 60°C. The ink’s temperature can be chosen when it is ordered.

There are some important factors, which should be considered before starting to work with leuco dye-based thermochromic inks: the ambient temperature (20°C) (non-heated state of e.g. the printing lab); temperature sensitivity of the inks; and the properties of the inks. The ambient temperature at the printing lab at the Swedish School of Textiles at the University of Borås, where this study was carried out, was 20°C. Tempreture sensitivity of the chosen inks were 27°C and 15°C. The inks were reversible and water-based. Therefore, the most desirable printing effect was achieved by printing them on cellulosic fabric. White plain cotton-weaved fabric was used as a background. The method used was silk-screen printing and the size of the silk- screen mesh was 43 threads per centimeter.