Newly developed thermochromic pigments can be incorporated directly into commercially available resins during processing. This means that completely new product groups are coming within reach.
Thermochromic systems change colour with a temperature change. Depending on product requirements, this can occur reversibly or irreversibly. Quite a few organic thermochromic systems are already on the market. In order to colour plastics throughout, the various components of the thermochromic system must be incorporated during processing. To date, however, the high temperatures and pressures during plastics processing have resulted in decomposition of the colourant systems. As a consequence, through pigmenting of large moulded parts or film was not possible.
At the Fraunhofer Institute for Applied Polymer Research (Fh-IAP), the chromogenic polymers research group headed by Dr. Arno Seeboth has developed a system that combines the characteristics of a microcapsule with those of a micelle. This protects the thermochromic system from the surrounding processing conditions. The resultant thermochromic composite is suitable for extrusion at temperatures up to 240°C. This now makes direct incorporation of thermochromic pigments possible in commercially available resins.
There are a great many possible applications for these through-coloured thermochromic plastics. Initial developments are focussing on highly stressed machine components that change colour upon reaching a critical temperature. Packaging materials the colour of which signals at a glance whether the proper storage conditions have been maintained could become an additional quality attribute in the pharmaceutical and food processing industries. Last but not least, thermochromic plastics will likely make household and leisure environments more colourful.