# Determining the Print Quality Due to Deformation of the Halftone Dots in Flexography
## 2 Tone Reproduction in Flexography  
Dot coverage is expressed as a percentage and typically varies from 1% up to 100%. Low coverages less than 10% are commonly called highlight areas; coverages between 10% and 25% are referred to as light tones; coverages between 25% and 60% are referred to as midtones; and high coverages between 60% and 100% are referred to as shadows [13]. The reproduction of highlight tones at low line rulings is a great challenge for the flexographic printing process, and that is exactly what will be the subject of this research. The flexo break effect creates a visible rough transition due to the loss of dots at lower tonal values [14]. The ratio of the dot size on the polymer plate to the cell size of the anilox roller has a direct impact on the quality of a reproduction [15]. Depending on the type of screening technologies, line rulings, the ability of the printing process and the type of material, the minimum dot size that can be maintained on the polymer plate and in the printing process is determined [16]. The minimum isolated dot size indicates what the ability of the plate system to reproduce a self-sustaining single printing dot without the presence of surrounding dots that help sustain it with their shoulders is [17]. The relationship between the plate dot size and the anilox roller line screen can be shown through three specific situations [18] shown in Figure 1. The ink film thickness is more homogeneous when a larger number of cells support one dot (situation 1). When the dot is supported by the cell wall of a single anilox cell, it is wetted by a maximum amount of ink (situation 2), and when the dot is smaller than the cell, it sinks into the cell and is covered with too much ink (situation 3), which is the so-called \"dot dipping\" effect [19]. There are several options for solving the problem of the \"dot dipping\" effect by manipulation with the prepr  
Figure 1: Three specific situations of the relationship between the plate halftone dot and the anilox cell size. Decrease the line ruling on the printing plate. This increases the minimum dot size on the printing plate and thus optimizes the ratio to the cell size of the anilox roller. The print quality is generally reduced;
* Use an anilox roller of a higher line count, if available. This leads to a smaller cell opening size and hence a better adjustment to the minimum size of the dot;
* Increase the size of the minimum dot by using a \"bump-up\" curve in the prepress. This means keeping the same line ruling of the polymer plate, which also reduces the tonal range on printouts;
* Apply advanced hybrid screening technologies that, via a different approach, allow better reproduction of highlight tones [20]. Pressure in printing is a parameter that significantly affects ink transfer, and that will also be a subject of research in this paper. The printing pressure can be adjusted at three points: (1) between the doctor blade and the anilox roller, (2) between the anilox roller and the printing plate and (3) between the printing plate and the printing cylinder (Figure 2). A change in the pressure between the printing plate and the printing cylinder has the greatest impact on the tonal value increase and thus on the print quality [21]. Research of the influence of the printing pressure has shown that the percentage of ink transfer increases with an increase in the printing pressure [22], and once the ink transfer reaches its maximum, there is no further increase in ink transfer regardless of a further increase in the printing pressure [23]. Light (also known as kiss) pressure is very important for quality reproduction because it prevents the \"halo\" effect and optimizes the tonal value increase (TVI). Light pressure is the lowest possible pressure at which the ink is transferred from all printing surfaces to the printing substrate [24].