The article is devoted to the study of the intermolecular adhesive interaction of alcohol-soluble flexographic inks with the surface of printing elements of photopolymer printing plates. DuPont Cyrel DPR photopolymer flexographic printing plates with the thickness 1.14 mm and alcohol-soluble printing inks of White and Magenta of Polistar series are used for the study. To assess the adhesive interaction, the indicator of the relative adhesion work is used, which is calculated by the value of the cosine of the surface wetting angle of the photopolymer plate printing elements with the ink. Projections of liquid drops on the printing plate surface are recorded with a digital camera. The obtained digital images are analysed with the help of the application “Analysis of the Kinetics of Liquid Spreading”, which is developed at Ukrainian Academy of Printing.
In the work, the interaction of the printing plate surface with inks with different types of pigments (inorganic titanium oxide and organic azopigment) is studied and the difference in their adhesive interaction is established. This can be explained by the fact that each printing ink of the same series is characterized by a different ability to structure, which, in turn, affects their rheology. The surface energy of photopolymer printing plates is researched and its change after the print run is determined. Testing of surfaces with distilled water (ASTM D5946 – 09) shows a decrease in surface energy by 3 mN/m during the print run, which is explained by the mutual diffusion of organic ink solvents and components of the photopolymer composition. Accordingly, there is a change in the number of active functional groups on the plate surface and, as a result, the adhesive interaction begins to decrease. The results of the study show that in the case of using the ink based on titanium oxide pigment, the sensitivity of the adhesive interaction in the printing system is somewhat greater than in the case of using purple ink.
Keywords: flexographic solvent inks, photopolymer plate, wetting contact angle, surface energy, adhesion.
doi: 10.32403/0554-4866-2024-1-87-133-139
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