Improving the security of conventional and UV luminescent flexographic prints by modification of the pritning inks using nanoparticles
With the development of the graphic technology and growing needs of the market, the protection of the printed product from counterfeiting has become more sophisticated and increasingly used, with the demand for maintained print quality. Conventional process black (PB) and UV luminescent (UVL) flexographic inks modified by addition of different concentrations of nanoparticles of silicon dioxide (SiO2), rutile and anatase titanium dioxide (TiO2), and zinc oxide (ZnO) were used in this research. The addition of nanoparticles to these inks had a purpose of protecting PB and UVL inks from counterfeiting without significantly affecting the optical and colorimetric properties of printed motives.
The results of the research have showed that nanoparticles do not affect the spectral reflectance of UVL inks observed under UV radiation significantly, nor the visual effect of UV luminescence. Also, nanoparticles had a negligible effect on the optical and colorimetric properties of PB inks observable through a slight increase in color lightness after the addition of nanoparticles. Indirect detection of nanoparticles through their interaction with PB and UVL inks was possible by FTIR-ATR spectroscopy which showed changes in the spectra of PB and UVL inks with nanoparticles compared to nanoparticle-free inks in the fingerprint range, as well as in the characteristic bands at higher wavenumbers for UVL ink. This research opened the possibility of expanding the use of nanoparticles of different types and concentrations for process, spot, luminescent and other special and conventional inks in the field of graphic technology.
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