Dynamic colorimetric properties of mixed thermochromic printing inks

Colorimetric description of thermochromic printing inks

2017

The dynamic colour of three commercial reversible thermochromic inks were studied. Thermochromic printing inks change their colour according to a change in temperature. The two types of thermochromic inks are based on leuco dyes and liquid crystals. The thermochromic effect achieved by liquid crystals is quite different from the effect achieved with leuco dyes. Leuco dyes change from a coloured to a colourless state, or from one colour shade to another due to structural changes inside leuco dye molecules under assistance of developer. Liquid crystal inks change colour continuously throughout the spectrum, producing iridescent colours starting from red and shifting to blue part of the spectrum with temperature. The colour change results from the way light interacts with special arrangement of liquid crystal molecules to produce coloured reflection by interference, and with the variation of this structure with temperature. In this paper we will present differences between two types of...

Dynamic Colour Possibilities and Functional Properties of Thermochromic Printing Inks

Acta Graphica, 2012

Thermochromic printing inks change their colour regarding the change in temperature and they are one of the major groups of colour-changing inks. One of the most frequently used thermochromic material in printing inks are leuco dyes. The colour of thermochromic prints is dynamic, it is not just temperature-dependent, but it also depends on thermal history. The effect is described by colour hysteresis. This paper aims at discussing general aspects of thermochromic inks, dynamic colorimetric properties of leuco dye-based thermochromic inks, their stability and principle of variable-temperature colour measurement. Thermochromic material is protected in round-shaped capsules. They are much larger than pigments in conventional inks. The polymer envelopes of pigment capsules are more stable against oxidation than the binder. If these envelopes are damaged, the dynamic colour is irreversibly lost. Our aim is to analyse the colorimetric properties of several reversible screen-printed UV-cur...

Colorimetric properties of reversible thermochromic printing inks

Dyes and Pigments, 2010

The colorimetric properties of three, leuco dye-based thermochromic inks at 31 °C activation temperature were studied. The inks had similar pigment particle size distribution and comparably thick microcapsule shells with similar stability against oxygen plasma etching. The colour of the inks was dependent on temperature as well as the thermal history of the sample, which gives rise to colour hysteresis. The area of the observed hysteresis loop in CIELAB colour space determines how different colours appear on the sample when decolourisation and colourisation processes are compared. The largest colour difference achieved for the same sample that arose because of different thermal history and temperature were determined. Four characteristic temperatures were ascribed to the two chemical reactions causing colour hysteresis. The stability of the decolourised state at cooling <activation temperature was confirmed as >10 h. The reversibility of the thermochromic effect diminished approximately linearly with the highest heating temperature.

Dynamic Colour Possibilities and Functional Properties of Thermochromic Printing Inks Authors

Thermochromic printing inks change their colour regarding the change in tem-perature and they are one of the major groups of colour-changing inks. One of the most frequently used thermochromic material in printing inks are leuco dyes. The colour of thermochromic prints is dynamic, it is not just temperature-dependent, but it also depends on thermal history. The effect is described by colour hysteresis. This paper aims at discussing general aspects of thermochromic inks, dynamic colorimetric properties of leuco dye-based thermochromic inks, their stability and principle of variable-temperature colour measurement. Thermochromic material is protected in round-shaped capsules. They are much larger than pigments in con-ventional inks. The polymer envelopes of pigment capsules are more stable against oxidation than the binder. If these envelopes are damaged, the dynamic colour is irreversibly lost. Our aim is to analyse the colorimetric properties of several revers-ible screen-printed UV-...

Spectroscopic evaluation of the colour play effect of thermochromic liquid crystal printing inks

Coloration Technology, 2016

Colour changes of a thermochromic liquid crystal (TLC) ink printed on a black substrate are clearly observed by the naked eye, and therefore it is reasonable to expect that every approach recommended for colour measurements of samples with solid colour would be appropriate. In addition, the published spectroscopic analyses of TLC inks do not provide any guidance or limitations for the measurement geometry. On the other hand, our study demonstrates that spectroscopic measurements of such samples are not so straightforward. When using the most simple and commonly used measurement equipment with a directional illumination and viewing approach, the temperature-dependent spectral features resolve in a narrow spectral region that gives only a small part of the colour play effect. Detection of the entire effect requires the use of integrating spheres, which spatially integrate the radiant flux reflected on a sample in any direction; better results are obtained by spheres of larger diameter. The comparision of spectroscopic and colorimetric results obtained when different measurement geometries are applied on the same sample may demonstrate certain properties of the liquid crystal material inside microcapsules and help in understanding some details of the optical properties of the ink layer.

Dynamic colour of chromogenic materials

2010

Este libro ha sido debidamente examinado y valorado por evaluadores ajenos a la Universidad de Alicante, con el fin de garantizar la calidad científica del mismo.

Light fastness of liquid crystal-based thermochromic printing inks

Dyes and Pigments

Thermochromic inks are known for their poor stability against UV light, appearing differently in leuco dye-based and liquid crystal-based ink types. The leuco dye-based inks lose the colour contrast between the coloured and discoloured states but the temperature at which the colour changes stays the same. These inks retain thermochromic functionality, i.e. the relation between colour and temperature, as long as the colour contrast between both states remains visible. Liquid crystal-based inks reflect a narrow band of light with wavelengths equal to the pitch length of the helical structure formed in the chiral-nematic mesophase. While the length of this helix depends on temperature, the wavelength of the reflected light shifts across the spectrum. This unique thermochromic effect is also called the colour play effect and is used for visual determination of temperature. However, the helical structure is highly sensitive to UV light which changes the temperature-related colours; consequently, such an ink loses its thermochromic functionality. Almost complete deterioration of the colour play effect occurs on unprotected samples in less than 60 days of exposure to natural indoor daylight and after 10 h under the artificial daylight. UV-protective foil or UV filter protects the ink against detrimental effects of UV light and keeps its functionality even after 10 h of exposure but the colour play effect is shown at lower temperatures.

Identifying a Unique Communication Mechanism of Thermochromic Liquid Crystal Printing Ink

Crystals, 2021

Thermochromic liquid crystal materials are commonly used in printing inks, opening up a wide range of possible applications. In order to ensure and control the most accurate application, the occurrence of the so-called colour play effect, i.e., the appearance of iridescent (rainbow) colours as a function of temperature, must be determined precisely. For this purpose, the temperature-dependent reflection of a sample must be measured using a spectrometer with an integrating sphere. The same values should be obtained for each sample containing the same thermochromic liquid crystalline material, irrespective of the spectrometer used, integrating sphere, layer thickness and the surface properties of the substrate. To describe this intrinsic property of the thermochromic liquid crystal material, the term communication mechanism might be considered. The research has shown how this mechanism is obtained experimentally.

Colorimetric changes of thermochromic ink printed on smart textile materials exposed to different heat transfer methods

TEKSTİL VE KONFEKSİYON

This research aims to determine the influence of heat and printing substrate type on the colorimetric properties of the thermochromic ink printed on various textile materials while subjected to heating simulating realistic conditions of usage. The results of the research can be used as a recommendations for the development of a smart temperature indicators for textile packaging. Four specific groups of textile materials were used as printing substrates and magenta leuco thermochromic water-based screen printing ink (activation temperature 31°C) in order to analize resulting colorimetric properties. Experiment based on analysis of resulting color differences confirmed that the screen thread count influences the rate of the material color change. Namely, the higher the thread count the faster the color change i.e. the sample returns faster from the discolored to the colored state. It was also confirmed that the lower the fabric weight of the material is, the sample returns faster from discolored to the colored state. In addition, this article presents a comparison of the contact and contactless method of sample heating at the same temperature. It was shown that the samples were cooled slower and consequently changed the colorimetric values after the contact method.