# Determining the Print Quality Due to Deformation of the Halftone Dots in Flexography
## 4 Results
### Dot Deformation Caused by Incorrect Printing Settings  
In this chapter, the dot deformation in the highlight tones caused by the use of an inappropriate anilox roller and inadequate printing pressure is analyzed. For the analysis of this, microscopic images were used that showed two states: a print with visible deformations of the dot (Figure 9, left images) and a good quality print or correct reproduction (Figure 9, right images). Figure 8: 2D dot profile in three stages of printing. On microscopic images, dot deformations in a black color, visible as a dirty print, can be easily detected. However, the cause is related to defining the anilox roller line screen, (i.e., defining the minimum dot in the print). The minimum dot is the smallest dot that can be well reproduced in a defined printing process [34]. Using the data from Table 1, which shows the technical characteristics of the printing process, it is possible to determine the relationship between the dot size on the printing plate and the cell size of the anilox roller, which is very important for the reproduction of highlight tones. Based on a line ruling of 133 lpi and an output resolution of 2540 dpi, the dot size in the highlight tones up to 5% coverage was calculated by using the following formula [31]:  
\[d_{D}=\sqrt{\frac{A_{D}}{25\pi\times L^{2}}}\times 10^{3}=\frac{1}{5L}\sqrt{ \frac{A_{D}}{\pi}}\times 10^{3} \tag{3}\]  
where \(A_{D}\) is the dot area as a percentage, \(d_{D}\) is the diameter of the dot in microns, \(L\) is the plate line screen in lines per millimeter and \(10^{3}\) is the factor for converting millimeters to microns. The specifications of the anilox roller, in addition to the line screen specification, were defined by the size of the cell opening and the size of the cell wall. There are standard values for the wall thickness, depending on the anilox line screen. The values are inversely proportional (i.e., the higher line screen of the anilox roller, the smaller cell wall thickness). The total cell size in microns is calculated by using the following formula [31]:  
\[\text{Anilox Cell Size}=\frac{2.54}{\text{lpi}}\times 10^{4} \tag{4}\]  
Figure 9: Display of the deformation of dots on the print at two states of printing. where lpi is the plate line screen in lines per inch and \(10^{4}\) is the factor for converting centimeters to microns. The values calculated on the basis of the abovementioned formulas are shown in Table 3. The reproduction with the full tonal range must satisfy the values of the anilox line screen for a minimum dot of 1% coverage. The table shows that at all the tonal values of 1-5% coverage, the dot diameter on the printing plate was larger than the size of the cell opening. Otherwise, there was an effect whereby the dots on a flexo plate dipped into the cells of the anilox roller (dot dipping effect), and an increased transfer of ink onto the printing substrate took place. Furthermore, the characteristics of the printing process should be compared with the values from Table 3. It was noticed that only the line screen of the anilox roller for the black color was too low, while other anilox rollers were in accordance with the specifications. According to the data listed in Table 3, the anilox roller line screen for the black color of 340 cells/cm (860 cpi) was sufficient for quality reproduction of the minimum dot of 2% coverage. A dot of 1% coverage at 133 lpi (22 \(\upmu\)m) was smaller than the anilox cell opening at 340 c/cm (26 \(\upmu\)m). The dot was dipped in the cell and too much ink was transferred onto the printing substrate. In addition, with the top of the dot, the ink was also transferred with the side parts of the dot (dot shoulders), thus creating very pronounced black spots on the print in the highlight tones (Figure 9, left). The quality of the reproduction was significantly reduced and unacceptable, which was visible in the form of a darker halo around the dot.