engleski

Surface properties of flexographic printing plates related to UVC post-treatment

Flexography is a printing technique mostly used in packaging printing. Flexographic printing plates are made of photopolymer materials, formulated to meet mechanical and qualitative requirements in the graphic reproduction process. The printing plate making process includes three exposures to UV radiation, and post-treatment with exposure in the UVC wavelength range. The post- treatment has to be performed in order to terminate the photopolymerisation process. During the transfer of the printing ink from the printing plate to the printing substrate, the surface properties of the printing plate strongly influence the quality of the imprint. The aim of this paper is to determine the influence of the UVC post-treatment of a flexographic CtP printing plate on its surface properties by analysing contact angle, surface free energy and energy-dispersive X-ray spectroscopy (EDS). The results indicate that UVC post-treatment influences the printing plate’s physico-chemical surface characteristics by changing the contact angle and the surface free energy components. This could result in a negative influence on the process of printing ink transfer from the printing plate to the printing substrate. EDS analysis shows that the changes in contact angles of probe liquids and surface free energy are caused by the increase of oxygen concentration in the surface layer of the printing plate, while Fourier transform infrared spectroscopy (FTIR) analysis points specifically to an increased ratio of carbonyl and hydroxyl bonds. Therefore, the duration and intensity of UVC post-treatment must be strictly controlled and regularly monitored in order to avoidunwanted changes of surface properties of the flexographic printing plate and, onsequently, of its behaviour in the printing process.

flexography ; photopolymer ; CtP ; UVC post-treatment ; contact angle ; surface free energy ; EDS ; FTIR

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