Modifying the qualitative properties of print by surface treatment of flexographic printing plate

Abstract

In the fast-pace technology development in graphic industry, modern flexography has found its domain mostly in the packaging sector and it is increasingly of interest for functional printing. Functional printing has a relatively low market value but greater interest in research. Due to the new qualitative requirements, workflows and materials used in flexography had to be updated and improved. The application of digitally controlled processes and procedures has taken the place of the analogue production, together with the new methods of material processing and improvements of the materials themselves. This research focuses on the functional modification of photopolymer flexographic printing plate’s properties with the aim of achieving optimal output quality. During the transfer of the printing ink from the anilox to the printing plate and then to the printing substrate, surface properties of the printing plate influence the quality of the print. Therefore, surface properties of the printing plate should be compatible with the used printing ink and the printing substrate, which is especially important when using new formulations of inks and experimenting with different printing substrates and applications, for example in functional printing. In this research, samples of photopolymer flexographic printing plates were exposed to UV-ozone treatment in order to modify the surface properties of the photopolymer material. Results have displayed significant changes in surface free energy of the photopolymer material when the printing plate samples were exposed to the UV-ozone for periods up to 5 minutes. In order to analyze the quality of the prints produced with UV-ozoned flexographic printing plates, test prints were produced. Prints produced with printing plates with longer UV-ozone treatment have displayed the qualitative changes in the reproduction of fine printed elements, i.e. the width of fine lines, coverage values, ink volume on print and the definition of the shape and edges of printed elements. Changes of named properties of the print are significant for conventional, and in many cases for functional printing. Performed research proved that the functional modification of flexographic printing plates with the aim of improving the print quality is possible. The UV-ozone treatment is a procedure where the printing plate is exposed to significantly higher energy than with conventional UVA and UVC tubes. Therefore, the duration of the UV-ozone treatment must be precisely adjusted in order to maximize the quality of the print, while at the same time maintaining printing plate’s functionality.