Inkjet Inks

Color changing T-shirt are a novelty and they come in several formats and types of color activation. Color changing T-shirt are a novelty and they come in several formats and types of color activation.

Color changing Inks

There are several mechanisms in which color changing of an ink can occur, in this article we cover specifically two, photochromic and thermochromic. The first meaning that a specific light type (wavelength) triggers the ink and changes its color, thermochromic means that color change will occur depending on the temperature it has been designed to activate.


Color-changing-Inks

Photochromic T-shirt on its passive state (left) and activated by UV Light (right) (colourchange.com)


Photochromic inks are invisible under artificial light and will appear visible once exposed to outdoor sunlight or UV / black light. These inks can be applied to papers and boards or to textiles. This type of inks and dyes change their molecular structure from a clear or white color and darken revealing its true color (on exposure to specific types of light of enough intensity, most commonly ultraviolet (UV) light sources, (UV light in the range of 300 to 360 nanometers).


Color-changing-Inks

Photochromic pigment of different colors activated by a concentrated UV-light source (nanomatrixsecure.com)


Photochromic dyes are reversible, when placed into sunlight or a UV-Light source they become activated, in an “excited” state, and depending on the manufacturer it takes from 10 to 20 seconds to allow the photochromic compound to turn into a darker color. In the absence of activating light when the UV light source fades, the effect is reversed and they return to their clear state after 5 minutes or less.


Color-changing-Inks

Photochromics are great on white t-shirts but not limited to be used on it (sfxc.co.uk)


Thermochromic ink or fabrics change color in response to temperature fluctuations, meaning heat will enable it to change color at its designated temperature, color change activation occur at temperatures from -10°C up to +70°C, they usually are reversible, changing either way as the ink warms or cools. There are two primary types of thermochromic coatings: liquid crystals and leuco dyes.


Color-changing-Inks

Thermochromic fabric, color change is activated by body temperature.


Liquid crystals dyes rely on liquid crystals contained in tiny capsules. The liquid crystals are cholesteric, this refers to the arrangement of molecules, which means that its molecules arrange themselves in a very specific helical structure. These structures reflect certain wavelengths of light. As the liquid crystals heat up, the orientation of the helices changes, which causes the helices to reflect a different wavelength of light. To our eyes, the result is a change in color. As the crystals cool down, they reorient themselves into their initial arrangements and the original color returns.

Leuco dye inks, are a darker color when cooler than their temperature activation point, and lighter in color or virtually clear when warmer than their activation point, temperature uses of these inks generally fall into three areas: cold, body temp and hot.


Color-changing-Inks

A black thermochromic ink (with body temp activation) screen printed over and obscuring a litho printed image or words, can become clear and reveal the litho image when it is touched or rubbed. (sfxc.co.uk)


A black thermochromic ink with a higher activation temperature can be screen printed onto a coffee coaster, so that the thermochromic ink becomes clear when heated by a hot mug, revealing the message or branding also printed on the coaster.


Color-changing-Inks

Heat-sensitive vans shoes will change color temporarily when exposed to body heat and return to original color at room temperature (vans.com)


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