Types of thermochromic inks and their applications
Thermochromic inks are products based on pigments which are sensitive to temperature. In their reverisble versions, the colour fades together with the temperature increase, and appears along wth the temperature decrease. In the irreversible version, after reaching a set temperature, the colour becomes visible and remains irreversible.
Applications of reversible thermochromic inks
Securing authenticity and originality
Reversible thermochromic inks are used in printing such products where it is key to ensure their authenticity and originality. All kinds of tickets, coupons, lotteries, securities, packagings secured against counterfeiting etc. belong to this group. A small marker, printed with a thermochromic ink, discolours under the influence of set temperature, e.g. after contact with a heat of human body. The marker, fading when touched, informs the inspecting person that this product is original.
Markers of reaching or decrease of a set temperature
Another way to use reversible thermochromic inks is printing markers of reaching or decrease of a set temperature. These are used in printing labels and packaging of cooling beverages such as alcohols, energy drinks or carbonated drinks. At the moment when the marker reaches appriopriately low temperature, it turns into a specific colour, informing that the product is properly cooled down. The same applies to the markers of reaching or maintaining a sufficiently high temperature. When the marker on the product, which requires to be heated up, starts to colour or changes its colour, it means that the product is cooling down, and the marker informs about the undesirable cooling of that product.
Marketing and board games
Thermochromic inks with a reversible effect have also found their wide use in products used in marketing and many kinds of games and activities. Although these inks in general have poor opacity, when the ink is applied thickly enough on the substrate, it is possible to obtain coverage. Then, these inks can hide a drawing, an image, a sign, numbers or text on the substrate. The ink, when the temeprature increases to the set value, becomes transparent, revealing what was hidden underneath. This gives abundant possibilities for creative use in all kinds of games, interactive activities and marketing „tricks”.
Applications of irreversible thermochromic inks
Irreversible thermochromic inks are a kind of inks used slightly less often by the recipients, however the solutions they offer have application in a few quite significant industries. They are used in printing the markers of reaching high temperature by a product. It is important to note here that, due to their nature, irreversible thermochromic inks – contrary to the reversible ones – are used for indicating high temperatures above 70°C.
Medicine and food products
Irreversible thermochromic inks are used for printing markers for autoclaves or in sterilisation of surgical devices and instruments. The ink, after reaching set temperature of 130 °C, discolours irreversibly, indicating that the temperature required for the process to properly take place has been reached. Similar markers are used in packaging of food products which are to be heated up to a sufficient temperature together with ther packaging. The marker, after reaching a set temperature, indicates that food is heated up to a desired degree.
Marking of overheating of machinery and devices
Another way to use irreversible thermochromic inks is marking of overheating of machinery and devices in these areas of insductry where excessive friction and hyperthermia of parts or mechanisms of production equipment is common. A marker, visible to the machinery operators, can inform in time about defective operation of a machine element by changing its colour from transparent to colored after reaching a critical temperature. This inexpensive warning system can help avoid many malfunctions and accidents in industrial facilities.
There is also a very common way of using irreversible thermochromic inks in our everyday lives. They are used as coatings of so-called thermal papers, used in printing by using thermal printers. The most commonly used material with an irreversible thermochromic ink coating are receipts printed in cash registers, fiscal printers, ATMs and many other places. The transparent coating on a paper is exposed to a narrow beam which generates a specific temperature. This beam „burns out” letters, numbers, pictures etc., irreversibly activating selected parts of a thermal coating.
Thermochromic liquid crystal inks
There are also lesser known types of thermochromic inks, which role can increase in this area of industry. The first type are thermochromic liquid crystal inks, which turn different colours in different temperatures. For example, when a product reaches 30°C, they become red, then yellow at 32°C, green at 34°C, blue at 38°C, purple at 39°C and after exceeding 40°C they return to black.
Two-range thermochromic inks
Another noteworthy thermochromic ink worth mentioning is a two-range thermochromic ink. When the product reaches one temperature value (e.g. 30°C), it permanently discolours until cooling it down to an abruptly different temperature value, e.g. – 10°C. This solution can be useful for marking products which should not reach recommended temperature before arriving to the target customer, e.g. during temperature control in a supply chain. They can also be used in marking labels of cold meats, delicatessen, ice cream, deep frozen products and many, many more.
Interval thermochromic inks
Interval thermochromic inks are inks which retain their colours in a set range of temperatures (e.g. 30° C – 50°C) and discolour when the temperature goes above or below that range. The change of colours of interval thermochromic inks is reversible, which means that they can be coloured and discoloured multiple times by maintaining or going beyond a specific temperature interval. The change in a colouring-discoloration cycle takes place in a range of several degrees, similarly to other reversible thermochromic inks. Interval thermochromic inks can serve as indicators of maintaining temperature of the product at a set range. If the temperature goes below this range, the ink will discolour and the same will happen when the temperature exceeds that range.
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