PCL NANOMODIFIED COATING FOR THE PROTECTION OF THERMOCHROMIC PRINTS ON PACKAGING

In graphic industry, thermochromic inks are used primarily in development of "smart" packaging for different applications, such as indicators of the product's current temperature or an out-of-boundary temperature reading. Thermochromic inks change their colouration with the change of temperature. During storage and transportations of products, as well as during their use, the packaging may come into contact with various chemicals, which may bring into question the chemical stability and therefore the functionality of thermochromic sensor. Polycaprolactone (PCL) is a biodegradable polymer which can find usage in various applications due to its good characteristics. The aim of this work was to determine the effect of a coating made of the biodegradable PCL polymer, and a PCL coating with the addition of zinc oxide or titanium dioxide, on the chemical stability and colorimetric properties of an offset thermochromic ink based on leuco dyes. For this purpose, full-tone prints of thermochromic ink were made on the printing substrate, appropriate coatings were applied to them, and the resulting samples were tested for chemical stability to water, soap, and ethanol according to ISO 2836:2021 standard. The results show that the coatings have no significant negative impact on the colorimetric values of the prints compared to uncoated prints, and the chemical stability of the thermochromic prints is significantly improved in the case of exposure to ethanol, especially a strong, 96% ethanol solution.