ChromaZone is a combination of Leuco Dyes (also known as Colour Formers), Colour Developers and Melt Materials all blended together and then microencapsulated. This produces an aqueous slurry which changes from colour to colourless as the temperature rises and with decreasing temperature the colour returns.
These microcapsules are individual systems of this chromogenic material with a polymeric wall with particle sizes ranging from sub-micron to 6 microns in size depending on product. Graphic 1 explains the principle of the reaction.
Whilst 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 colour change of ChromaZone pigments occurs over a temperature range of approximately 3 to 5ºC and additionally shows a thermal hysteresis. This means that the colour starts fading before reaching the relevant response temperature and to return to full colour a significantly lower temperature is required. Graphic 2 shows this effect.
Kromagen is also combination of Leuco Dyes, Colour Developers and Melt Materials all blended together and then micronized to reduce particle size. This is then blended into a carrier forming an aqueous concentrate which changes from a translucent off white to a colour permanently 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 colour change of Kromagen is generated over a 5 to 10°C range and colour does not fade when temperature decreases.
ChromaZone & Kromagen can be used for added security, to create interactive packaging, show that process temperatures have been achieved or to add something different to toys, labels, games or packaging.