# Influence of Printing Substrate on Quality of Line and Text Reproduction in Flexography
###### Abstract  
This study characterizes and compares the parameters of the quality reproduction of fine elements in flexography on coated and uncoated paper as well as on OPP film (oriented polypropylene). A monochrome test form was created and printed using cyan UV ink. The analysis of results confirms the importance of interaction between the printing substrate and ink; it also indicates identical line and text deformations on the print. Quality reproduction on coated paper is higher in relation to OPP film for all the research parameters. The ink penetrates significantly more and with more irregularity into the pores and throats of the uncoated paper, which results in less homogeneous elements, and in such way that it loses its original shape. In coated paper and OPP film, the ink spreads more on the substrate area which gives it a significantly more homogeneous shape. However, due to the surface spread of the ink, the biggest changes in the size of fine elements are noticeable in the OPP film. The scientific contribution of this paper is based on the comparison of print quality parameters of fine elements, which can contribute to the optimization of the production process and quality of the final graphical product. flexography; line and text quality; image analysis; ink spreading; printing substrate +
Footnote †: journal: Medical  
hand, if the pressure is too high, dots will be squeezed more and can be deformed [7]. [PERSON] et al. investigated how different pressures in flexographic printing and smoothness of the paper affect the printed line width and legibility of the printed typographic elements of 4 pt size [8]. Printouts were obtained on five different printing substrates made of recycled paper and was found that the smoothness of the paper is directly related to ink spreading on the surface of the print. The composition and the surface characteristics of the printing substrate significantly influence the ability of the ink to penetrate into its structure [9]. Coated glossy or matte papers are harder to absorb the ink than the uncoated ones because they are less porous and less permeable [10]. Therefore, the ink spreads more over the surface of the printing substrate, and the ink layer on the printing surface is more uniform. [PERSON] et al. analyzed the print quality of edible inks on a coated printing substrate in the technique of flexographic and screen printing [11]. It is important for the ink to adhere well to the printing substrate [12], which is directly influenced by the texture of the printing surface or treating the surface of PET films in order to decrease the surface tension [13]. [PERSON] et al. in their work researched the dynamics of liquid transfer between nanoporous stamps and solid substrates [14]. Although many types of printing substrates (plastics, film and foil) are widely used for flexible packaging, paper-based materials remain popular due to their good printing characteristics [15]. The most important properties for the packaging material are: the gas barrier property, mechanical, thermal, rheological, optical and physical properties. The entire process of flexography consists of a large number of influential parameters that need to be standardized for specific printing conditions [16]. This research comprises the comparison of the most important quality parameters of graphic reproduction in accordance with the ISO 12647-6 standard for three types of printing substrates: uncoated and coated paper and OPP film. [PERSON] et al. found that by analyzation, the ink penetration depth into the substrate can theoretically predict the quality of printed matter [17], and presented the mechanism of interaction between the ink and paper based on two models, static penetration and dynamic diffusion. The common way of evaluating the quality of graphic reproduction consists of an objective evaluation of the color and tone in the printed image using the spectrometric and densitometric measurement methods. [PERSON] et al.