ŚƚƚƉƐĚŽŝŽƌŐϭϬϮϰϴϲϳ'Z/ͲϮϬϮϮͲƉϴϰ KƌŝŐŝŶĂů ƐĐŝĞŶƚŝĨŝĐ ƉĂƉĞƌ DYNAMICS OF THERMOCHROMIC COLOR CHANGE OF PRESSURE SENSITIVE LABELS FACESTOCK MADE FROM ENVIRONMENTALLY FRIENDLY MATERIALS Rahela Kulčar , Dorotea Maretić, Marina Vukoje , Ivan Malenica University of Zagreb, Faculty of Graphic Arts A Abstract: To maintain a circular economy and better sustainability, it is important to minimize the use of synthetic polymers. Nowadays, agricultural and industrial wastes or by-products are increasingly being used as raw materials in industrial processes. It has been determined that agro-industrial wastes have a high potential of cellulose fibers, which makes them an excellent resource for paper production. Recently, potential resources from non-wood raw materials for paper production, as well as cheap raw materials, have become the interest of various researchers. Since our main focus is on the study of thermochromic inks (TC) and the influence of substrate characteristics on their dynamic color change, this paper will examine the possibilities of a commercially available offset TC ink printed on several environmental friendly pressure sensitive labels (PSL) facestock compared to commonly use in PSL production. For the purpose of this study, a commercially available TC ink with an activation temperature (TA) of 29°C was used. The effect of color change, from blue to colorless, was measured through one heating and cooling cycle at several selected temperatures at six different PSL materials. Three fiber-based facestock of PSL used in this research are produced with 15% agroindustrial byproducts, 40% post-consumer recycled paper and 45% virgin wood pulp to form a high-quality natural paper. In addition, one material made from biogenic polymers facestock and two materials commonly used in labels production were used as well. The results of this research show that TC ink printed on alternative materials has a similar trend of color change and may be a good choice. Also, the influence of the color of fiber-based paper substrates on the change of TC color was noticed, which indicates the importance of colorimetric analysis of paper and TC ink before their printing. Key words: ƉƌĞƐƐƵƌĞ ƐĞŶƐŝƚŝǀĞ ůĂďĞůƐ ĨĂĐĞƐƚŽĐŬ ƚŚĞƌŵŽĐŚƌŽŵŝĐ ŝŶŬƐ ĞĐŽͲĨƌŝĞŶĚůLJ ŵĂƚĞƌŝĂůƐ ƐƉĞĐƚƌŽƉŚŽƚŽŵĞƚƌŝĐ ŵĞĂƐƵƌĞŵĞƚƐ ϭ /EdZKhd/KE Pressure sensitive labels (PSL), also known as self-adhesive labels, have gained great popularity due to their simplicity and user-friendly role (Medeiros et al., 2019). As AWA predict globally, PSL label material industry is expected to grow (Labels&Labeling, 2021). The PSL is an integrated part of the product packaging. It is very important that the label and the product packaging are made of the same materials and have the same structure. Such mono-material packaging enables recycling and reuse. Paper as a substrate for the production of labels represents more than 50%, and 20% is the siliconized part (PP and PE). When choosing an appropriate label material, it is important to choose an adhesive that will not adversely affect the recycling or reuse process of the product in any way (Huhtamaki, 2020). Each PSL from a roll consists of three basic parts: facestock (paper, foil), adhesive and liner. The paper used as facestock can be coated, uncoated, white, colored, smooth, structured and may contain some special characteristics such as security fibers. The correct selection of each part of the label is defined by various parameters. Some of the parameters are where the label will be placed and used and general information about its use such as application surface, application speed, room temperature of use and the temperature of the product itself, humidity, etc. The most common printing techniques for PSL are UV flexo printing, UV offset, UV letterpress, digital UV inkjet and electrophotography (Marošević Dolovski, 2016; Tesařová et al., 2020). The PSL can also provide additional value by using interesting structures, designed by a hot or cold stamping process, spot varnishes etc. It is also possible to insert RFID tags or NFC and use labels for security purposes. The life cycle of a label is defined by several conditions such as printing, handling, use and deciding whether the label is to be recycled or treated as waste. All materials from which the label is made depend on various external influences such as weather and storage conditions, methods and , , ϳϲϭ