Jamnicki Hanzer Sonja, Kulčar Rahela, Vukoje Marina, Marošević Dolovski Ana
Faculty of Graphic Arts, University of Zagreb, 10000 Zagreb, Croatia.
Polymers (Basel). 2023 Feb 27;15(5):1208. doi: 10.3390/polym15051208.
Thermochromic inks, also known as color changing inks, are becoming increasingly important for various applications that range from smart packaging, product labels, security printing, and anti-counterfeit inks to applications such as temperature-sensitive plastics and inks printed onto ceramic mugs, promotional items, and toys. These inks are also gaining more attention as part of textile decorations and can also be found in some artistic works obtained with thermochromic paints, due to their ability to change color when exposed to heat. Thermochromic inks, however, are known to be sensitive materials to the influence of UV radiation, heat fluctuations, and various chemical agents. Given the fact that prints can be found in different environmental conditions during their lifetime, in this work, thermochromic prints were exposed to the action of UV radiation and the influence of different chemical agents in order to simulate different environmental parameters. Hence, two thermochromic inks with different activation temperatures (one being cold and the other being body-heat activated), printed on two food packaging label papers that differ in their surface properties were chosen to be tested. Assessment of their resistance to specific chemical agents was performed according to the procedure described in the ISO 2836:2021 standard. Moreover, the prints were exposed to artificial aging to determine their durability when exposed to UV radiation. All tested thermochromic prints showed low resistance to liquid chemical agents as the color difference values were unacceptable in all cases. It was observed that the stability of thermochromic prints to different chemicals decreases with decreasing solvent polarity. Based on the results obtained after UV radiation, its influence in terms of color degradation is visible on both tested paper substrates, but more significant degradation was observed on the ultra-smooth label paper.
热致变色油墨，也称为变色油墨，在各种应用中变得越来越重要，这些应用范围从智能包装、产品标签、安全印刷和防伪油墨到诸如热敏塑料以及印在陶瓷杯、促销物品和玩具上的油墨等应用。由于它们在受热时能够变色，这些油墨作为纺织品装饰的一部分也越来越受到关注，并且在一些用热致变色涂料制作的艺术作品中也能找到。然而，已知热致变色油墨是对紫外线辐射、热波动和各种化学试剂的影响敏感的材料。鉴于印刷品在其使用寿命期间会处于不同的环境条件下，在这项工作中，热致变色印刷品受到紫外线辐射作用和不同化学试剂的影响，以模拟不同的环境参数。因此，选择了两种具有不同活化温度（一种是冷活化，另一种是体温活化）、印在两种表面性质不同的食品包装标签纸上的热致变色油墨进行测试。根据ISO 2836:2021标准中所述的程序对它们对特定化学试剂的抗性进行评估。此外，将印刷品进行人工老化处理，以确定它们在受到紫外线辐射时的耐久性。所有测试的热致变色印刷品对液体化学试剂的抗性都很低，因为在所有情况下色差数值都不可接受。观察到热致变色印刷品对不同化学物质的稳定性随着溶剂极性的降低而降低。基于紫外线辐射后获得的结果，在两种测试的纸质基材上都可以看到其在颜色降解方面的影响，但在超光滑标签纸上观察到的降解更为显著。
