Opaque white ink is highly important when printing on transparent substrates. The purpose of the white ink is to completely or partially cover the content of the packaging as well as to ensure the printing of other colors over it according to the appropriate printing specifications. The main goal of this study was to research the impact of anilox roller volume of opaque white on its opacity, and, consequently, on opacity, as well as the CIELAB values of colors that are printed over it. The research was conducted in three printing stages, during which the volume of the anilox roller was increased in linear steps of 3 cm³/m² while other parameters remained constant. The analysis of white ink covering properties was carried out on microscopic print images using ImageJ software. The results showed that a linear increase in the anilox roller volume resulted in an exponential change in white ink opacity as well as the opacity of color samples. It was also determined that a volume increase of 6 cm³/m² was required to visually notice color difference. Namely, medium lightness colors more strongly reacted to changes in white ink opacity compared to light and dark colors.

The food industry has recognized the important role that multi-layered, flexible packaging materials play and it uses them extensively within the packaging processes. Trends within food processing and packaging continuously encourage manufacturers to develop new technologies which extend a product’s shelf-life. The samples that were the subject of research described in this paper are retort stand-up pouches made of multi-layered flexible material, the layers of which have been bonded with a laminating process that aims to both extend a product’s shelf-life and stability, permitting the final processing of the finished product under aggressive regimes. It is intended that packaging, when subjected to graphic reproduction and high pressure processing, shall remain unchanged in all aspects, in particular the visual aspect that is the subject of the research. The samples were printed on polyester film (PET) using a rotogravure printing technique and laminated on aluminum (Al), oriented polyamide (OPA) and finally on inner polypropylene (PP) layers. The sample was monitored for the Vegeta Blue spot colorimetric difference in the CIE L*a*b* space throughout the individual graphic reproduction phases and the final high pressure processing (HPP) of the finished product. The goal is to determine the size of the spot color colorimetric difference (Δ????????∗) in relation to the defined formula and the established standard. On the basis of measured results, guidelines and recommendations for the correction and quality assessment of spot color reproduction throughout the entire process were defined, with the goal to minimize any deviation to the lowest possible level.

Flexographic printing plate is used for the transfer of image onto a printing substrate. The surface of printing plate is stretched lengthwise when the plate is mounted on plate cylinder. As a result, the print length on the impression is always longer than the actual length of the plate. Prepress must compensate for this difference in length. The result of wrong plate distortion is different print length in flexography compared to the processes that follow printing. The aim of this paper is to research the influence of repeat length in printing and polymer plate thickness on the factor distortion. The distortion factor values were calculated using the derived formulas. Regardless of the repeat length in printing, the value of the thickness factor for a particular printing plate is constant. However, the values of the distortion factor decrease with the increasing thickness of the polymer plate and the decreasing of the total plate cylinder circumference.