THE COLOURIMETRIC PROPERTIES OF SMART TEXTILE PACKAGING TEMPERATURE INDICATORS

Chromatic materials are materials that change colour under the influence of external factors such as heat, light, solvents, pressure, electricity, friction, etc. Materials that change colour due to heat change are called thermochromic materials, and they are usually used for temperature indicators during the storage and transport of products packaged in heat-sensitive packaging such as frozen foods and pharmaceuticals. This paper presents the research on the colourimetric properties of yellow and blue thermochromic inks that can be used to produce temperature indicators of smart textile packaging. The activation temperature of these inks is 31 °C, so the measurements and printing of the samples were carried out under controlled conditions same for all samples. Samples are made up of four specific groups of textile materials, printed with screen printing technique, with two different screen mesh size. The paper presents the study of the parameters (colour tone, time, temperature, screen mash size and type of material) influence on the colourimetric properties of the temperature indicators. After heating the samples for 90 secs in the multi-purpose device, COLO DRYS53A at the temperature of 50 °C, the temperature of the sample was decreased to 24 °C. During the cooling process CIELAB values of thermochromic inks were measured for every 10 sec. The research has shown that the use of yellow thermochromic ink is not suitable for printing temperature indicators due to small colour differences during measurement in the cooling process, which has been shown on all types of materials and using all types of screen mesh sizes. The blue ink proved to be usable, but the packaging material type greatly influenced the change in the CIELAB values of the measured colour. The best results for the application of thermochromic blue indicator showed a sample that is 100% cotton material and has less surface mass, printed with screen mash size 54 l/cm. The procedure for determining the most suitable sample was based on the comparison of the colour difference increase during the 60-sec measurement obtained by the formula CIEDE2000. The results for this material have shown that the colour difference rise curve has the most similar trend relative to the reducing curve of the measured temperature in the given 60-sec measurements. So, the material is most suitable from the aspect of determining the packaging material or the packaged product temperature