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Mechanical and chemical resistance of thermochromic packaging prints

Thermochromic inks are temperature-sensitive materials that change colour due to a temperature change. These inks are mostly printed on smart packaging applications where they are used in a form of temperature indicators. The colorants in these inks are microencapsulated which makes the prints obtained with these inks more sensitive to abrasion in comparison to the prints obtained with conventional inks. Thermochromic prints are also very sensitive to adverse environmental conditions, such as exposure to UV light, heat and certain chemicals and solvents. Abrasion and chemical resistance of thermochromic prints obtained on metallized label papers are discussed in this paper. For that purpose, two thermochromic UV screen inks were printed on two types of metalized papers that are commonly used as food packaging labels. The prints thus obtained were then subjected to a rub test in accordance with standard method BS 3110. Rub test was performed using Hanatek RT4 Rub and Abrasion Tester. The degree of rubbing was assessed by visual inspection and by detection of the colorimetric changes on the prints after their exposure to rubbing. Assessment of prints' resistance to various liquid agents (water, ethanol and citric acid) was done in accordance to standard method ISO 2836. Evaluation of chemical degradation on prints was done by the spectrophotometric measurements. The results of conducted research showed good rub resistance of these inks, as no rubbing was detected, but poor resistance to all liquid agents they were exposed to. Exposure to ethanol, particularly, caused severe damage to the prints. The bleeding of the colorants from the prints was also detected. However, even though the prints were not able to completely withstand exposure to specific liquid agents which was demonstrated by their optical deterioration, the thermochromic effect was still present in them after resistance tests were conducted.

thermochromic inks, metallized label paper, rub resistance, chemical resistance

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