The properties of printing substrates required for thermochromic liquid-crystal printing inks

Abstract

The color change of thermochromic liquid-crystal (TLC) printing inks occurs inside the microcapsules containing thermo-responsive material. It starts at the defined activation temperature (t_A) and occurs in several degrees wide region above the t_Awhere the color changes throughout the whole visible spectrum, with the effect known as “color play”. Previous research showed that the “color play” effect of TLC printing ink is clearly visible if the ink is printed on a black substrate but on the white one no color can be observed. The presented research aims to answer what optical density (D) of the substrate is needed for clear observation of the “color play” effect. The results show that mentioned effect of the TLC ink is observable if it is printed on grey substrate with Dof at least 0.72. The research also shows that samples printed on uncoated black paper result in stronger temperature dependent optical properties of TLC printing ink compared to the samples printed on coated black paper. This effect is related to drying mechanism of TLC printing ink and absorption properties of printing substrate.