“Smart color-changing packaging” refers to packaging that can respond to environmental factors such as light, temperature, and humidity by changing color. This feature is used for various functions, including anti-counterfeiting, monitoring, and indication. The color-changing function of most smart packaging is often achieved through printing inks, leading to the development of various smart inks. Using color changes in ink as an indicator to monitor product quality or environmental conditions has broad application prospects in the packaging industry.
Thermochromic Materials:
Thermochromic materials are often used as time-temperature indicators (TTIs), applied to quality monitoring of temperature-sensitive and perishable products such as food and vaccines. Common types include enzyme-based, diffusion-based, and polymer-based TTIs. However, these are mostly in gel or liquid states, limiting their practical application. Incorporating color-changing materials into ink systems to create printable TTIs can partially resolve the inconvenience of using traditional TTIs.
Ink Formulation:
By combining leuco dyes (such as Leucocrystal Violet, LCV) with photo-acid generators (PAGs), where protons produced by PAGs interact with the leuco dyes to gradually develop color, the dyes can replace pigments in inks, achieving an irreversible color change effect. The types and proportions of ink binders and solvents significantly affect the color-changing properties and overall performance of the ink. Binders ensure the uniform flow of ink and enhance adhesion, while solvents dissolve the binders or color-changing components, altering ink viscosity and affecting the depth of the color change.
