This study characterizes and compares the parameters of the quality reproduction of fine elements in flexography on coated and uncoated paper as well as on OPP film (oriented polypropylene). A monochrome test form was created and printed using cyan UV ink. The analysis of results confirms the importance of interaction between the printing substrate and ink; it also indicates identical line and text deformations on the print. Quality reproduction on coated paper is higher in relation to OPP film for all the research parameters. The ink penetrates significantly more and with more irregularity into the pores and throats of the uncoated paper, which results in less homogeneous elements, and in such way that it loses its original shape. In coated paper and OPP film, the ink spreads more on the substrate area which gives it a significantly more homogeneous shape. However, due to the surface spread of the ink, the biggest changes in the size of fine elements are noticeable in the OPP film. The scientific contribution of this paper is based on the comparison of print quality parameters of fine elements, which can contribute to the optimization of the production process and quality of the final graphical product.

Flexographic printing plate is used for the transfer of image onto a printing substrate. The surface of printing plate is stretched lengthwise when the plate is mounted on plate cylinder. As a result, the print length on the impression is always longer than the actual length of the plate. Prepress must compensate for this difference in length. The result of wrong plate distortion is different print length in flexography compared to the processes that follow printing. The aim of this paper is to research the influence of repeat length in printing and polymer plate thickness on the factor distortion. The distortion factor values were calculated using the derived formulas. Regardless of the repeat length in printing, the value of the thickness factor for a particular printing plate is constant. However, the values of the distortion factor decrease with the increasing thickness of the polymer plate and the decreasing of the total plate cylinder circumference.

This study characterizes and compares the dot properties in flexography on coated and uncoated paper and on OPP film, with the use of conventional AM screening technology and photopolymer plate with flat top dots. A monochrome test form was created and printed with cyan ink on three different printing substrates. For the study of the dot deformation, microscopic images were taken from the prints and analyzed using ImageJ software. The primary area of the study are highlight tones since the reproduction of small dots is synonymous with high quality reproduction. All significant parameters of the dot deformation were evaluated, including the dot geometry, dot sharpness and uniformity of density. The image analysis showed that dot deformation is the result of spreading and penetration of the ink. The microscopic snapshots of the test areas on the prints show that ink penetrates significantly into the pores and holes of the uncoated paper, resulting in a non-homogeneous dot, thus losing its original shape. On coated paper and OPP film, the ink spreads more on the surface of the printing substrate and in such way gives a more homogeneous dot shape.

This paper researches the issues related to the print quality in flexography, especially the influence of the print run and inadequate printing settings on dot deformation. Dot deformation can lead to inconsistencies in print quality, such as a loss of highlight tones or an unpredictable increase in tonal value. This research was conducted on two concrete examples of flexible packaging printed on transparent films. All significant parameters of dot deformation were evaluated, including dot coverage, dot sharpness and the uniformity of the ink density. The increase in the coverage values in the midtones was linear throughout the entire print run, while in the light tones, it was more logarithmic. The overall percentage deviations from the reference value were 6.3% in the midtones and 52.6% in the light area. The increase in dot coverage was due to the wear of the polymer plate, which caused the side shoulders of the dot to become a part of the printing surface. An analysis of the ink density showed a much more homogeneous shape of the dot at the beginning of the print run. The correct ratio of the anilox roller line screen to the line ruling of the printing plate is important in order to ensure a minimum dot size in print.

Abstract:The top dot shape is an important element of plate dot geometry which has a significant effect on dot formation on the prints. There are several key parameters that can affect individual dot deformation: nip engagement, line ruling and dot geometry. The main question is how these parameters affect dot deformation. This paper researches the issues regarding print quality in highlights, especially dot formation on print at lighter and higher pressure which leads to inconsistency in the printing process like loss of highlight detail and unpredictable dot gain. The purpose of this research is to improve the understanding of the effect of nip engagement on dot deformation and to determine how top dot shapes affect dot formation. A test image was printed with cyan UV ink on aluminium foil on the pre-printed opaque white ink with plates of different types of top dot shapes, round and flat. The images were taken from the prints and analysed by using ImageJ software. All the important parameters of dot formation including uniformity of density, dot sharpness and dot roundness were evaluated. The results highlight the importance of the top dot shape in plate dot geometry which has a significant effect on print dot formation.