###### Abstract
Distinctive limitations of TLC ink in printing, handling, and combining with other printing materials puts a great challenge in development of temperature--sensitive applications and other hybrid systems. For the purpose of this research, a hybrid printing ink systems with dual functional properties obtained in combination of two special effect printing inks, i.e., TLC printing ink and UV-visible fluorescent printing inks, are proposed. UV-visible fluorescent pigments/inks used in this research are invisible in the daylight, only being visible when exposed to UV radiation. Because of their original properties, they belong to a group of luminescent materials; i.e., they have the possibility of absorbing the UV radiation, and re-emitting photons of a different radiation. The effect of fluorescence lasts only as long as the primary radiation acts, after which it stops almost immediately [16; 17; 18]. This characteristic gives them an original application and in the last decades, they have been used in the decorative and packaging industry for highlighting markers, in document security applications, and the tagging of postage stamps, etc. [19; 20; 21; 22]. UV-visible (daylight invisible) fluorescent inks (UVF) can be used in different printing processes. Most commonly, they are used in a screen-printing technique by mixing the UV fluorescent pigment with the transparent base. Furthermore, UV fluorescent inks can be used in the form of a varnish in flexography, offset printing techniques, and in relief printing [23; 24; 25]. Research published before showed the possibilities of printing with UVF inks on paper substrates using the screen-printing technique by addition of silicon dioxide (SiO\({}_{2}\)) and titanium dioxide (TiO\({}_{2}\)) nanoparticles into the UVF inks. Inks were prepared by the addition of fluorescent pigment into a transparent base. Results of that research showed that the addition of nanoparticles does not cause any significant change in the visibility of the fluorescence effect. The research also addressed the influence of the aging process on the stability of fluorescent prints and concluded that the addition of nanoparticles could have a positive impact on the fading of the UVF prints and on the observed chemical and mechanical characteristics of printed coatings [26]. To observe the influence of the addition of SiO\({}_{2}\) and TiO\({}_{2}\) nanoparticles in the varnish used in flexography, the fluorescent varnish was printed on polyester substrate, woodfree uncoated paper, and 100% recycled packaging paper [27; 28]. Results demonstrated the possibilities of achieving fluorescent phenomena by application of fluorescent inks on different printing substrates with different surface properties. The authors in [25] investigated the effects of ink media on the fluorescence properties of fluorescent dyes used in the offset-printing technique. The effect of fluorescence was observed in digital electrophotographic printing processes as well [29]. Having in mind that the fluorescence effect can be used in different applications; research on this phenomenon is interesting from different aspects. It demands a complex approach in studying the interactions of fluorescent material with other materials in contact to meet the specific printing requirements and ensure their optimal functional application. This research proposes a new functional printing ink with dual functional properties that could be used as a common hybrid system in the proposed combination. It includes pure TLC printing ink, as well as two hybrid ink systems based on the combination of TLC and UV-visible fluorescent pigments/printing inks, printed on two types of black uncoated paper substrates. The combination of these materials could be used in the development of functional packaging, security applications, and brand protection, as well as all other applications with special requests for temperature monitoring (TLC) and possible hidden information (UVF).