Abstract
In this study, the interactions between different solvents (benzene, acetone, cyclohexanone, various alcohols and water) and thermochromic printing ink were investigated. Thermochromic printing ink was printed on metal surface. Components of thermochromic printing inks are polymeric microcapsules and classic yellow offset printing ink. Below its activation temperature, dye and developer within the microcapsules form a blue coloured complex. Therefore, thermochromic print is green. By heating above the activation temperature, blue colour of the complex turns into the leuco dye colourless state and the green colour of the prints turns into the yellow colour of the classic offset pigment. The results of the interaction with various solvents show that the thermochromic print is stable in all tested solvents except in ethanol, acetone and cyclohexanone. In ethanol, the green colour of the print becomes yellow. SEM analysis shows that microcapsules are dissolved. In acetone and cyclohexanone, the green colour of the print turns into blue, and the microcapsules become significantly more visible. Thus, the yellow pigment interacts with examined ketones. Based on the obtained interactions it can be concluded that the microcapsules have more polar nature than the classical pigment particles. Solvent-thermocromic print interactions were analysed using Hansen solubility parameters that rank the solvents based on their estimated interaction capabilities.
Highlights
The thermochromic ink composition includes a thermochromic microcapsules and an ink vehicle
Thermochromic prints are stabile in all solvents besides acetone, cyclohexanone and ethanol (Figure 4a)
It can be concluded that the yellow pigment, since it is soluble in cyclohexanone, is not non-polar but it contains functional groups which interact with polar interactions but the proportion of dispersion interactions is higher which can be attributed to the structure of the coloured organic compounds
Summary
The thermochromic ink composition includes a thermochromic microcapsules and an ink vehicle. Thermochromic prints are stabile in all solvents besides acetone, cyclohexanone and ethanol (Figure 4a). After interaction with acetone and cyclohexanone the colour of the print was changed to blue. Since the colour of the print was changed to blue, it can be assumed that a yellow pigment (or yellow offset ink) was dissolved in acetone.
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