Clevertex - Grado Zero Espace Srl

softeners. These are said to be able to destroy the thermochromic properties. The microcapsules have
a diameter between 8 and 15µm. They are applied on the textile substrate by means of silkscreen
printing or transfer printing. The ink consists of small capsules in an aqueous binding resin. Since the
thermochromism involves reflected light, the effects are best seen against a dark background, which
soaks up the light transmitted by the liquid crystal. Only those wavelengths that are reflected by the
liquid crystals are observed, and not those that are reflected by the substrate. All the colours, which
are not reflected by the print layer, will be absorbed. The temperature at which the colour change
should start can be adapted and varies between – 30°C and + 70°C. The temperature at which the
colour change occurs can be set accurately to 1°C.
While the changes in colour may be striking and relatively sensitive to temperature, opportunities to
take advantage of this technology for textile coloration are limited by the necessity of using dark
substrates as well as the requirement that the liquid crystal systems must be microencapsulated [3].
The American company C.T.I. commercialises thermochromic textile screen inks under the tradename
DynaColor. The inks are available in various colours and activation temperatures. The colour
change is reversible, so that the original colour will be restored upon cooling.
Thermochromic pigments
In 1988, Toray Industries Inc. developed a multicolour fabric Sway ® on the basis of thermochromic
organic pigments. This fabric enabled 64 colour hues in temperature intervals of 5°C in the
temperature range -40°C and +80°C. They used the technology of microencapsulation of four
thermochromic pigments, which were capable of changing colour from white into pink, blue into black,
yellow into blue, and pink into grey. Depending on the end use, colour changes were designed to
occur between 11-19°C for ski wear and 13-22°C for women’s clothing [140].
In the late 1980ties and early 1990ties, the Generra Sportswear Company, which manufactured tshirts
with numerous colour change choices, bought the right from the Japanese Matsui-Shikiso
chemical company to print cotton fabrics with thermochromic organic pigments with negative
thermochromism. This process was commercialised under Hypercolour ® .
Today, organic thermochromic pigments are mostly used for embroidery on apparel and for thermal
printing.
Photochromism
The photochromic microcapsule reacts on contact with ultraviolet rays so a typical end use has been
towelling and beach wear in the textile sector. These products are extremely active in the range of
200-320nm, which is the harmful portion of UV rays. By absorption of light the chemical structure is
changed, creating the appearance of colour. However, if the light is intercepted, the textile goods will
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