THERMOCHROMIC INKS
These heat sensitive inks offer security to a wide range of applications from Passport booklets to Tax Stamps and Certificates. Although the ink can be manufactured to react at a variety of heat levels, it is most commonly set close to normal human body temperature. This allows for authentication using only the warmth of an individual’s finger tips. The fact that there is no need for equipment like UV lamps or detectors adds to the strength and versatility of this overt feature.
Thermochromic inks are coloured below the specified temperature and become transparent when this temperature is exceeded. It is possible to add a visible, non-changing colour to increase the range of effects, for example; by using a 27°C blue thermochromic ink and adding yellow, it is possible to achieve a green colour below 27°C and yellow above 27°C.
Printing Methodology
Thermochromic inks can be printed via wet or dry offset, letterpress, gravure, flexo and screen processes. It should be noted that Thermochromic inks printed in offset generally produce light pastel shades and should not be used to print intricate designs. Full opacity is only possible by screen printing these inks.
PHOTOCHROMIC INKS
These inks change colour when they are exposed to either ultra-violet (UV) or natural daylight. They are colourless in their natural state and when illuminated they produce their visible colour. Photochromic inks are reversible, meaning that they will revert to their colourless state when the light source is removed. The change in colour is more immediate and spectacular when using a 365nm UV lamps compared to direct sunlight.
The dramatic nature of the colour change and the possibility to achieve the effect without the use of electronic equipment makes it perfect for securing documents like certificates, tickets and tax stamps.
Photochromic inks are produced in three standard colours; Invisible to Blue, Invisible to Purple and Yellow to Green where Invisible to Purple gives the best contrast between the colourless and coloured state.
Printing Methodology
Photochromic inks can be printed using offset, flexo, gravure and screen processes.
