# Influence of Printing Substrate on Quality of Line and Text Reproduction in Flexography
## 3 Experimental Methodology  
The goal of this study is to determine the influence of printing substrate on quality reproduction of fine elements such as thin lines and small text sizes in order to compare quality reproduction parameters and optimization of the production process. The study was conducted by evaluating the most important parameters of line and text quality reproduction, and those are line edge noise, line sharpness and uniformity of density. The research framework describing the purpose and process of research is shown in Figure 2.  
The experimental part of this paper begins with the creating of a test image designed to enable the evaluation of the quality reproduction in fine elements, by using acceptable and validated scientific methods and research techniques. The test image was not newly designed. Instead of that, a standard test form Kodak_NX_Target_v10 provided by the equipment supplier in 1-bit iff document was used. The test image is monochrome, and all evaluated elements of the testing image have a solid tone, that is, 100% surface coverage. A part of the test form, which served for the analysis of fine elements, contains the following elements (Figure 3):  
* serif text 2-12 pt in positive and negative shape
* line width 1-128 pixels at 2400 ppi in positive and negative shape (0.01-1.36 mm)  
Figure 2: Research framework. The positive version of the shape used dark colors for the front elements on a light background, and the negative versions of the shape used light colors for the front elements on a dark background. The following parts of test image are used for the analysis of fine elements: 85 um and 170 um line thickness, and 6 pt and 8 pt text size. The flexographic photopolymer printing plate used for this research was the Kodak Flexcel NX plate (hardness acc. to DIN 53505: Shore A is 73) without advanced DigiCap NX patterning of the surface on the polymer plate. The characteristics of Flexcel NX platemaking technology [27] include a flattened top of the halftone dot which requires a light impression and, in such way, enables quality transfer of ink from the printing plate to the printing substrate [28]. Plate-making process specification:  
* CtP device: Kodak Trendsetter NX;
* Resolution: 2400 dpi;
* Photopolymer: Kodak Flexcel NX Digital Plate;
* Plate thickness: 1.14 mm;
* Base layer thickness: 0.125 mm;
* Line ruling: 150 lpi;
* Screen angle: 37.5\({}^{\circ}\);
* Screening type: conventional AM, Euclidean dot shape. A six-color flexo printing machine Nilpeter FB4200, max printing width 420 mm, was used for printing. Printing was performed using the principle \"from Roll to Roll\", with a printing speed of 60 m/min, applying UV cyan ink. UV links have a number of good printing properties: almost 100% of transferred color is used for creating ink film; smaller anilox volume is needed in comparison with water inks; the ink does not change consistency; due to lower viscosity there is less color bleeding; the ink can remain in the inking system for a longer time without requiring to be cleaned. The optimal anilox line screen for printing is determined in line with halftone screen and minimum dot size [29]. During the printing process, a substrate passes between the plate cylinder and the impression cylinder. The space between them must be optimal to give the proper printing pressure [30]. The gap value or the nip engagement between the plate cylinder and impression cylinder for the lightest printing pressure is one three-thousandth of an inch, or 75 um (0.0762 mm). The next level of pressure is a higher pressure, and the gap value is one six-thousandth of an inch or 150 um (0.1524 mm). During the printing experiment, the test form was printed on three different printing substrates while other printing parameters, i.e., speed, pressure level, anilox roller characteristics and UV curing system settings, were kept to constant. Printing specification:  
Figure 3: The part of the test form for analysis of line and text print quality in positive and negative shape.