# Influence of Printing Substrate on Quality of Line and Text Reproduction in Flexography
###### Abstract
analyzed the influence of surface roughness of cardboard as a printing medium on printing properties of environmentally friendly inks, and in their research they presented the effect of the surface layer of cardboard on the microgeometry of prints formed by cyan, yellow, black and magenta inks [18]. [PERSON] et al. investigated colorimetric changes of the water-based flexographic ink printed on three types of hemp-based printing substrates subjected to artificial ageing [19], and it was proven that the most stable prints under the influence of light were made with black ink. The application of both instruments and measurement standards together has contributed substantially to the improvement of print quality in flexography. As flexographic printing technology fast evolved over the last two decades, the application of an increasing number of substrate materials of different characteristics and types of printing ink, many critical print quality issues such as sharpness, line quality and text quality and micro and macro uniformity often become worse. The quantification of these parameters requires a completely different approach to determining print quality based on image analysis systems or image analyzers. This specific metrics can determine the effect of surface structure of the printing substrate on print quality of fine elements which cannot be determined by standard methods. In order to obtain a broader perspective of quality reproduction, in addition to standard evaluation methods, more space is being given to image analysis. The ability to measure image structure characteristics such as sharpness and line edge noise, as well as other fine detail deformations is what contributes to an image analysis system, while also distinguishing it from a conventional densitometer or spectrometer [20]. Therefore, during the evaluation of the quality reproduction these parameters need to be analyzed as well. The goal of this paper is to research the influence of printing substrate on quality reproduction of the lines and text based on image analysis and visual evaluation in precisely defined conditions for three chosen printing substrates. The obtained results will show the importance of interaction between the three types of printing substrate and printing ink, and the influence on the print quality parameters. Parameters of Quality Reproductions of the Fine Elements in the Process of Image Analysis Evaluation  
A typical system for image analysis consists of a high-resolution digital camera or microscope which captures areas of interest and of a specialized software which analyzes quality reproduction characteristics based in a digital image. Microscopes with a high-resolution optical model (5 um per pixel or 5080 ppi) are applied in different methods of research for displaying fine elements invisible to the naked eye. The evaluation of quality reproduction in line with the ISO13660 standard is based on the following three parameters (Figure 1): line width, ragedness and blurriness [21]. Line width: The evaluation is determined based on the average line width on the print in relation to the theoretically defined line width. Blurry line edges, disproportionally distanced from the full line color, are included in the evaluation process into the total width, which can significantly influence the change of the line width. Data on widening or narrowing of the line can be obtained by evaluating its area. Line edge noise: This characteristic is also called line raggedness. Line raggedness is a shift of a black and white line boundary relative to the ideal boundary line. The ideal boundary line is the best fitted line passing through most of the edge dots. Dispersion or the appearance of dots near the edge of the full line is the result of bleeding of the colors during the printing process. Data on line raggedness can be obtained by evaluating its perimeter.