Abstract
The intensive use of flexographic printing for packaging decoration and the increased consumer demands for it require an in-depth study of the factors that influence the prints’ quality. In this paper, we examined the test prints obtained at a flexographic proofer. Images on cardboard were printed by the environmentally friendly inks made by a Ukrainian manufacturer. The effect of the cardboard surface layer on the microgeometry of the prints created by cyan, yellow, black, and magenta inks has been shown. It has been established that the roughness parameter Ra for a two-layer coated cardboard is reduced by 3 times as compared to the uncoated cardboard. The photographs of the microstructure of the prints’ surface, their profile demonstrate a significant effect of the chalked coating on the image quality. It has been confirmed that the ink layer smooths out the micro-roughness of the print surface. However, when printed on the uncoated cardboard, the ink particles penetrate deeper into the structure and do not completely smooth out its micro-roughness. If the size of the printing element is smaller than the size of the cell on a raster roller, it falls into this cell and the ink is applied beyond the boundaries of the image. As a result, a spot of an arbitrary shape is formed on the print instead of a raster dot of a certain size, that is, the so-called "inverse tone transfer" occurs. We have measured the densitometric indicators of prints (optical density, gray balance), which significantly affect the quality of the product. Based on a Harrington's desirability function, the maximum permissible values of optical density, evenness of printing, contrast, dot gain of raster elements, and trapping, have been calculated. According to the generalized optimization criterion, a comprehensive index of the prints’ quality has been determined, which could ensure the predicted quality of a would-be run of the printed products, and would make it possible to adjust the printing process if necessary
Highlights
There is a tendency in the market of printing production towards the intensive use of flexographic printing techniques
Changing the anilox roller adjusts the dosage of the ink that is fed to the photopolymer printing plate and to the printed material from it [2]
The following tasks were set: ‒ to determine a change in the topography of the surface and structure of the printed material and the prints on it; ‒ to examine the densitometric quality indicators of flexographic prints; to optimize single indicators by using a Harrington desirability function
Summary
There is a tendency in the market of printing production towards the intensive use of flexographic printing techniques. This relates to the rapid development pace of the packaging industry, the introduction of innovative technologies, the reduction in the costs of products printed in large numbers [1]. There are problems related to the correct reproduction of elements in the image with different complexity of the pattern, which affects the stability of the printing process, as well as obtaining high-quality prints. The use of various materials for printing flexographic images requires the study into their surface structure before and after the application of the ink and is of paramount importance for obtaining prints with the appropriate optical and operational characteristics
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