Telegina T. Technological quality assurance of printing on high-speed flexographic presses

The dissertation work is dedicated to improving flexographic packaging printing technology on high-speed presses. The study is based on the analysis of the interaction between printing equipment parameters, packaging substrate properties, and ink rheological characteristics. The influence of these factors on the densitometric, colorimetric, and performance characteristics of imprints has been established, enabling the optimization of the technological process, ensuring color reproduction stability, reducing printing defects, and increasing Overall Equipment Effectiveness (OEE). As a result of the conducted theoretical and experimental studies, a scientific and applied problem has been resolved, and the following new results have been obtained: For the first time:  a method has been developed for evaluating the quality of a white ink layer on film materials. This method involves the instrumental measurement of opacity, a microscopic assessment of layer continuity under standard D50 illumination, and the determination of the number of pinholes per unit area, alongside their sizes and distribution uniformity on the imprint surface. This approach enabled the establishment of a stable, asymmetric regularity: with every 100 m/min increase in printing speed, a reduction in white ink layer opacity (by 1.4%) is accompanied by a decrease in the mass of the dry residue (by 22%) on the imprint. This phenomenon is explained by the reduction of contact time within the printing couples and an increase in the Capillary number, which leads to incomplete release of the anilox roller cells.  a generalised model of ink transfer regularities within the «anilox–printing plate–substrate» system has been proposed. This model prioritises the factors influencing imprint optical density into three levels: the first level comprises cell volume, anilox roller line screen, and the type of the «plate–substrate» contact system; the second level includes the anilox roller cell angle; and the third level consists of the printing plate mounting base hardness (which determines process stability but is not a dominant factor in transfer). This model will enable a substantiated selection of optimal flexographic technological process parameters to ensure predictable imprint quality;  the influence of printing speed on the manifestation of the bouncing effect has been determined using a newly developed methodology. This methodology involved obtaining single-colour imprints within a speed range of 100 to 600 m/min (in 100 m/min increments) from an original test plate, where the printing and non-printing elements were positioned at the edges and in the centre of the plate. This approach enabled the identification of the local nature of the defect's manifestation and confirmed that the micro-geometry of printing elements is the most sensitive indicator of the bouncing effect. This effect is driven by height differences among plate elements and vibration processes within the printing couples during high-speed operation, which cause a momentary increase in specific pressure within the contact zone, subsequently leading to ink displacement beyond the boundaries of the printing element, distortion of its area, and deterioration of image sharpness. Keywords: flexographic printing, film, flexible packaging, anilox roller, ink transfer, printing speed, printing plate, geometric parameters, raster, printing press, densitometric indicators, imprints, print quality indicators, hierarchical model, equipment efficiency.