Thermochromic Products predominantly change color in response to temperature fluctuations. There are two primary types of Thermochromics: Liquid Crystals and Leuco Dyes. The most famous Thermochromic application, the “mood” ring of the 1970’s, was a Liquid Crystal.
Today, Liquid Crystals are used in many products, including forehead thermometers, room and refrigeration thermometers, and other applications including food quality indicators. While Liquid Crystal Thermochromics are extremely capable materials, they are difficult to work with and require highly specialized manufacturing techniques.
The other type of Thermochromic is called a Leuco Dye. It is commonly used in manufacturing and control processes, advertising, consumer packaging, product labels, security printing, novelty applications such as temperature sensitive plastics and mugs, promotional items, toys, and textiles. Thermochromic Permanent Change Ink is a high temperature activated, permanent change pigment used in metalworking, annealing, welding, and riveting for quality purposes.
Thermochromic Liquid Crystals
Liquid Crystals are generally used for higher precision applications since the temperature response point can be tightly engineered. Forehead thermometers, medical devices and game pieces are just a few of the more common applications.
Leuco Dyes are less precise and easier to work with. They are commonly used for packaging, product labeling / graphics, toys, and quality / process control applications.
Chromazone is a combination of Leuco Dyes (also known as Color Formers), Color Developers and Melt Materials blended then microencapsulated. This produces an aqueous slurry which changes from color to colorless as the temperature rises. When temperature decreases, the color returns.
These microcapsules are individual systems of the chromogenic material containing a polymeric wall with particle sizes ranging from sub-micron to 6 microns depending on the product.
While they can withstand most standard mixing and application procedures, the reaction can be disrupted by several external influences such as high exposure to UV light, presence of polar solvents, very high temperatures, or excessive shear.
The visible color change of Chromazone pigments occur over a temperature range of approximately 3°C to 5°C and shows a thermal hysteresis. This indicates that the color starts fading before reaching the relevant response temperature. To return to full color, a significantly lower temperature is required.
Kromagen is also a combination of Leuco Dyes, Color Developers and Melt Materials blended then micronized to reduce particle size. They are then blended into a carrier forming an aqueous concentrate, which changes from a translucent off-white to a permanent color, when heated above its rating.
Again, this reaction can be disrupted by several external influences such as high exposure to UV light, presence of polar solvents, and excessive shear.
The visible color change of Kromagen is generated over a 5°C to 10°C range. Color does not fade when temperature decreases.
Chromazone and Kromagen can be used for added security, to create interactive packaging, to show process temperatures have been achieved, or to add changes to toys, labels, games, or packaging.