Determining the Print Quality Due to Deformation of the Halftone Dots in Flexography

Abstract

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.

The Influence of Anilox Roller Lines on the Ink Impression on Different Polymer Substrates in Flexo Printing

“…Mariappan et al researched in their paper the dynamics of liquid transfer between nanoporous stamps and solid substrates [25]. The research by Valdec et al comprises the comparison of the most important quality parameters of graphic reproduction in accordance with the ISO 12647-6 standard for three types of printing substrates: uncoated and coated paper and OPP film [26], as well as the influence of printing substrate on quality of line screen and text reproduction in flexography [27,28]. Zhang et al determined by an analysis that the ink penetration depth into the substrate can theoretically predict the quality of printed material [29].…”

The Impact of Underlying Opaque White Coating Parameters on Flexographic Print Quality

“…The hardness of the polymer plate in combination with the selection of the mounting adhesive tape has a significant influence on the adherence of the ink and, thus, on the opacity of the opaque white ink [19]. This choice can affect the level of "mottle" effect and the appearance of pinholes.…”

Influence of the Polymer Plate Thickness on the Plate Distortion Factor in Flexography

“…Therefore, there is an interaction between the circumference of the outer surface of the plate towards the circumference of the anilox roller and the printing substrate. If this compression is too high (nip engagement > 150 µm), the surface of the plate will be outside the print diameter, so a slurring effect will occur at the places of contact between the plate and the printing substrate due to faster circumferential speed of the plate surface [14]. Otherwise, if the compression is too low (nip engagement < 20 µm) slurring also occurs due to lower circumferential speed of the plate surface [15].…”