Recent Advances on Thermochromic Inks for Security Applications

ABSTRACT In the security printing industry, high complexity stimuli‐responsive functional inks have been used to develop anti‐counterfeit elements, such as authentication markers and encrypted patterns. Through these applications, they create more reliable products, reduce economic losses, help retain brand identity, and assist in identifying counterfeit products. Thermochromic inks, owing to their temperature‐responsive color‐shifts, have gained considerable interest in the last decade as functional inks in a variety of fields. Here, we outline the different types of thermochromic materials, their properties, development scales, and how they have been previously applied, with a focus on their use as security inks for anti‐counterfeit elements. Despite promising functional properties, thermochromic materials are hindered from use by low stability, generally high toxicity, and a lack of printing optimization. In recent years, however, efforts have been made to enhance their durability and sustainability, along with an improved understanding of their thermochromic transitions and novel ink formulations, granting great promise for more diverse and specialized applications. Additionally, their integration alongside other functional materials has promoted the development of multilevel high‐security elements with potential for future anti‐counterfeit technologies. In this review, we highlight recent advancements in property enhancement, sustainable development, and scalability of thermochromic security inks.