# Determining the Print Quality Due to Deformation of the Halftone Dots in Flexography
## 4 Results
#### 4.1.1 Analysis of Dot Coverages  
Five areas with flat tones in highlights and midtones on the prints were selected, and the dot diameters were determined by measurements through three stages of printing. The area below 5% coverage was not analyzed, because a different mechanism of dot deformation occurred in this area. The measurement was performed on images and captured on prints at 200\(\times\) magnification and a 1280 \(\times\) 1024 resolution. A Dino-Lite AM4000 digital microscope with a resolution of 1.3 megapixels and in-built LED light was used for this purpose. ImageJ 1.47 software was used for processing and analysis of the microscopic images. It was necessary to set a correspondent size ratio before measuring, based on known values at the same magnification. A ratio of 500:1 was set for image analysis (i.e., 500 pixels amounted to 1 mm), which gave the image a size of 2.56 \(\times\) 5.12 mm. The measurement results of the dot diameters at three stages of printing are shown in Table 2, and they were obtained as the average values of five measurements. For the needs of a more detailed analysis and comparison, the corresponding values of the dot coverages in percentages for all cases were calculated. Figure 3: Appearance of dot deformations in specific stages (no. of print runs). Based on the measured values of the dot diameters at the line ruling of 133 lpi, the corresponding value of the surface coverage as a percentage was calculated according to the following formula [31]:  
\[A_{D}=25\pi(d_{D}\times L)^{2} \tag{1}\]  
where \(A_{D}\) is the dot area as a percentage, \(d_{D}\) is the diameter of the dot in microns and \(L\) is the plate line screen in lines per millimeter. To convert the screen frequency from lines per inch to lines per millimeter for the output resolution of 2540 dpi, the following formula was used:  
\[L=\frac{lpi}{25.4} \tag{2}\]  
where \(lpi\) is the plate line screen in lines per inch. After the printing of the entire print run, there was an increase in the dot diameter in all five selected areas. The increase in the dot diameter in relation to the reference value was to amount of 12% in the midtones and up to 28% in the light tones (Table 2). However, to determine the deformation of the dot through the entire print run, it was necessary to analyze the changes in coverage by the stages of printing. The graph shows that the changes in coverage in the midtones were linear throughout the entire print run, while in the light tones, it was more logarithmic (Figure 4). That means a significant change in the light tones occurred from the beginning of the print to one-fifth of the print run (Stage II of printing). However, the changes in coverage in the third stage of printing (print run from 100,000 to 500,000 prints) was higher in the midtones compared with the light tones. The second part of the graph (orange bar), which indicates a print run of 100,000-500,000 prints, shows results opposite to those for the first part of the graph. Namely, a slightly larger increase in coverage in the midtones was recorded compared with the light tones (from 10.4% in the midtones to 1.1% in the light tones) (Figure 6). The percentage deviation of the coverage value at Stage III compared with Stage II was 17.5% in the midtones and up to 7.4% in the light tones. In the first part of the print run (100,000 prints), a significant increase in coverage occurred in the light tones. The halftone dots in the light areas were isolated from each other and thus more susceptible to wear compared with the midtone areas, where the dots were connected on all sides. In the second part of the print run (from 100,000 to 500,000 prints), there was a slightly larger increase in coverage in the middle tones. However, it is very interesting to look at the percentage distribution within the entire increase in coverage. At 9.7% of the surface coverage (halftone dot No. 5), 82% of the increase occurred by the second stage of printing, and the remaining 18% happened by the end of the print run.