Thermochromic materials change colour at specific temperatures. One use is where they are integrated into a special ink and printed onto plastic films to create thermometers or as an indicator of temperatures.
In many cases the thermomchromic materials are based on liquid crystal technology.
How does it work.....?
At specific temperatures the liquid crystals change position and produce an apparent change of colour. The liquid crystal material is micro-encapusulated. This means that it is contained inside microscopic spherical capsules that are usually just 10 microns in diameter. It takes billions of these capsules mixed with a suitable base to make thermomchomic ink for printing or plastics that can be used in injection moulding. The pigments are made by us to produce a specific colour change to translucent at a chosen change-over target temperature. We make them in the most popular colours and target temperatures e.g. 15°C, 25°C, 27°C, 31°C, 47°C but we can produce many others to order. Please contact us for details.
So in principle.....?
A 31°C thermochromic ink appears coloured at normal room temperature but at 31°C target temperature the colour would then disappear. As an example, if a black thermochromatic ink is applied to a white surface, the surface changes from black to white at the target temperature. When the temperature falls, the pigment colouring re-appears. Another example is when a 50°C yellow ink is applied to something red, the surface colour would change from yellow to red at 50°C. This is used practically in a similar way in the hot warning label sold by Colour Changing Products http://www.colourchanging.co.uk/thermometers/hot-warning-labels/hand-hot-indicators-50a-c/prod_254.html.
Of course, a thermochromic pigment changes colour at the target temperature, so bear in mind that this change will occur if the ambient or contact temperature is the same or more than the target temperature of the pigment. Where this works well and gives the desired result, is in the case of a 15°C target temperature. For example, the blue 15°C often chosen where a translucent pigment is used to illustrate cold temperatures by chenging colour to blue. It is utilised in the production of fun clothing for cold weather and on lager cans to show when the beer is at the desired cool temperature.
As a guide, here are examples of uses for the activation temperatures but can vary depending on users requirements:
Touch Activated Liquid Crystal Ink will change colour within the visible spectrum when rubbed or touched. Typical temperature range at 25-30°C.
Cold Activated Thermochromic Ink is used on labels and packaging to create a colour change when cooled. Typical temperature Translucent to Colour at 15°C
Touch Activated Thermochromic Ink is intended to temporarily vanish when rubbed or touched to reveal an image or another colour printed beneath. It is often called ‘rub and reveal’. Colour to Translucent Typical temperature at 31°C.
High Temperature Thermochromic Ink is designed to change colour just below the pain threshold that alerts users to a health and safety hazard and/or quality issue - Too Hot! Colour to Translucent Typical temperature at 43-47°C, with higher specialised ranges being used at 70°C and above.
As with all our products, we recommend that relevant data information is observed and a small test area is fully trialled before buying in large quantities.