# Influence of Printing Substrate on Quality of Line and Text Reproduction in Flexography
## 3 Experimental Methodology
* Flexo printing machine: Nilpeter FB4200;
* Printing speed: 60 m/min;
* Flexo ink: PULSE SLM 318 UV cyan;
* UV curing: UV Lamp-Mercury Wavelength, 600 WPI output power (Watts Per Inch);
* Printing width: 330 mm;
* Printing length: 490.00 mm;
* Anilox line count: 405 l/cm (1020 lpi);
* Anilox cell volume: 3.1 BCM (Billion Cubic Microns);
* Plate mounting tape: 3M E315, 0.38 mm thickness, Medium Soft;
* Substrate: uncoated paper, coated paper, OPP film. The amount of ink delivered by anilox roller is controlled by a pattern of small precisely sized dimples, or cells. Cell volumes are typically expressed in billion cubic microns per square inch (BCM/in\({}^{2}\)). The power and the position of the UV lamps did not change for the whole printing experiment. The distance to the printing substrate is constant across the entire web width and adjusted in line with manufacturer's instructions and recommendations. Specification of the three chosen printing substrates:  
* Uncoated, white, machine-finished label paper HERMA white (601), grammage 72 g/m\({}^{2}\), opacity 83% (abbreviation UCTD). * White label paper, semi-gloss coated on one side HERMA extracoat (242) grammage 80 g/m\({}^{2}\), opacity 86%, area gloss 30% (abbreviation CTD). * White, high gloss, opaque OPP (Oriented Polypropylene) label film Treofan decor-LWD, thickness 38 um, unit weight 23.5 g/m\({}^{2}\), opacity 82%, gloss 65%, one side corona treated by the film manufacturer, surface tension of 40 dyne/cm. (abbreviation OPP film). In order to be able to compare the results of the research, it is important for the printing experiment to take place under controlled printing conditions. Each of the chosen substrate types belongs to an individual quality group regarding their characteristics. The control of CIELCH cyan values on prints for three groups of printing substrates is the basis for color matching of prints with target values and allowed tolerances in accordance with ISO 12647-6 [31]. Color matching with the mentioned standard is based on the difference in the color tone \(\Delta t_{ab}\), based on CIELCH values for the solid tones of the process colors. Due to the analysis of deformation in fine elements, it is necessary to capture the chosen areas on the prints of all the three printing substrates. Digital Microscope Dino-Lite AM4000 is used for this purpose, with a resolution of 1.3 pixels and in-built LED light which enables a better display of the captured object. Samples for the analysis are captured with 200\(\times\) magnification and 1280 \(\times\) 1024 resolution. The software ImageJ 1.47 was used for processing and analysis of the microscopic images; different image analysis techniques were used for evaluation. Measurement results must be shown in real values (mm, \(\upmu\)m,... ). Therefore, it is necessary to set a correspondent ratio based on known values at the same magnification while doing the measuring. A ratio 500:1 is set for image analysis, i.e., 500 pixels amounts to 1 mm, which gives the image size of 2.56 mm \(\times\) 5.12 mm. When evaluating the area and the perimeter of fine elements in the ImageJ software, the threshold method of image processing was used. Thresholding is a method where the image converts from color or grayscale mode into a binary image mode. Then, the red threshold color in the image was used to measure the area and perimeter of the evaluated elements. The following values of color threshold in HSB color space were used: in positive shapes (Hue 0-255; Saturation 80-255; Brightness 125-255), and in negative shapes (Hue 0-255; Saturation 80-255; Brightness 185-255). The measured results for the particular imprints do not depend on the number of measurements and are valid for the specific measurement condition, especially color threshold settings. However, during the printing process, additional deformations of fine elements occur, which would certainly give different results, and are not the subject of research in this paper.