The influence of micro- rasterization modes of flexographic printing plates on the imprint quality

Experimental studies are performed in the manufacturing conditions of the company “Poly Pak” (Lviv). Photopolymer printing plates for flexographic printing technology DuPont Cyrel DPR (DigiFlow technology, the company “Repro Studio Dialog”), Flint Group nyloflex ACE (NExT technology, the company “Laser Flex”), MacDermid LUX ITP (LUX technology, the company “Alef Inc”), Asahi AFP–TOP (the company “Continent”), 1.14 mm thick are used for the experimental studies. A digital camera with 150x magnification (Du Pont Microflex MS 1320) is used to analyse the reproduction quality of raster dots and control elements on the printing plate and the imprint, as well as the generated microstructures on the printing elements. Qualitative characteristics of imprints are assessed using an eXact spectrodensitometer (X-Rite Pantone).

As a result of experimental studies, the optimal types of microstructure and laser operating modes for DPR (WSI boost 320) and ACE (WSI boost 250) plates are determined, which is confirmed by micro photographing the surface of the plates and imprints. Based on the analysis of monochrome test imprints, rasterization algorithms for DPR plates (C31 WSI_FADE55_P +) and ACE plates (HD11–C18 MCWSI_P06_P +) are established as such that provide the optimal combination of high optical imprint density, tone transfer correctness, image contrast and small details reproduction. Based on a comprehensive analysis of the quality of full-colour test imprints (optical density, compression, tone reproduction range, image contrast, quality of the die and small image details reproduction), it is found that the studied plates can be placed like that according to qualitative parameters: DuPont Cyrel DPR > Flint Group nyloflex ACE > MacDermid LUX ITP > Asahi AFP-TOP.

It is experimentally proved that the use of micro rasterization of the printing elements surface of flexographic printing plates with a systematic approach to the selection of microstructures used can significantly increase the optical density of the imprints, the uniformity and saturation of the die and the quality of gradation transfer. Regularities of dependencies of flexographic printing imprint quality on the type of microstructure of the printing element surface, laser operating modes and the used technologies of printing plate exposure are established.

Based on the analysis of the experimental research results, practical recommendations are formed for the effective use of the studied printing plates in the flexographic printing processes by selecting the optimal modes of their manufacturing and operation.

Keywords: flexographic printing technology, flexographic printing plates, printing elements with flat top, micro rasterization, imprint quality, optical density, compression.

doi: 10.32403/1998-6912-2021-2-63-42-51