The packaging and labels graphic industry is dominated by several main printing techniques, namely flexography, offset, gravure and digital printing. Each technique is suitable for a particular type of graphic product and differs in the way ink is transferred to the printing substrate and by the type of image carrier employed. Depending upon the printing process, the printing ink is transferred to the substrate either directly or indirectly. High-quality prints in analogue technologies are based on ink transfer from printing plate to printing substrate, while digital printing is based on inkjet or statical ink transfer directly to the printing substrate. Since the development of digital commercial printing in the mid-1990s, devices have emerged that can reproduce almost the same quality in any required application. Digital printing has created a revolution in the printing industry, where inkjet printing and electrophotography printing are fast-growing digital printing techniques. Inkjet printing is one of the most popular non-impact printing technologies, where printing is performed without

Nowadays, there is a strong initiative to use recycled or biodegradable materials in all aspects of production including the graphic industry. In this study, paper was used as a material fulfilling the two of mentioned properties. Under laboratory conditions, papers were made of 70% pulp from recycled wood fibres with an addition of 30% straw pulp (wheat, barley or triticale). Considering the importance of the possibility of printing such media based on their end use, the influence of fibre type on vapour barrier properties was studied and overall migration to hydrophilic and fatty food simulants was measured. Analyses were performed on digital, flexographic, and offset prints obtained by printing laboratory papers with UV-curable black ink. It was found that prints produced using the offset technique, in which the ink remains on the surface of the paper, had lower overall levels of migration compared to other printing techniques. The paper produced appears to have the potential to be used as a secondary food packaging material.

Traditional papermaking is based on the use of an aqueous suspension consisting of cellulose fibres obtained by processing wood, non-wood plants or waste paper. With growing environmental concerns regarding deforestation and CO2 production, the paper industry has been always looking for new sources of non-wood pulp that would produce papers of similar quality to those made from wood pulp. Cereal straw from wheat, barley or triticale crops that remains on fields as a residue after grain harvesting has proven to be a good substitute for virgin wood fibres needed in the production of recycled paper. In this study, the quality of printed text on recycled paper with added straw pulp is evaluated mainly based on the line and edge characteristics of the printed letters. For this purpose, three types of laboratory paper substrates were first prepared using recycled wood pulp with the addition of 30% wheat, barley, or triticale straw pulp. The same letter pattern was printed with black ink on each paper substrate at a standard size of 12 pt with two common typefaces: Arial and Times New Roman. The quality of the printed letters was assessed through the measured print quality parameters such as blurriness, raggedness, fill and contrast. The resulting measurements were compared with the results obtained on the reference and control samples made exclusively from recycled wood pulp as a substrate from laboratory and commercial production. In terms of fill and contrast values, the uniformity of lines printed on the recycled papers with added straw pulp is the same or very similar to the reference and control papers. Letters printed in Arial (sans-serif) typeface show slightly better reproduction quality than letters printed in Times New Roman (serif) typeface. The measured parameters blurriness and raggedness of all laboratory-made paper substrates (with and without straw pulp) had similar values between 0.17 mm and 0.20 mm, resulting in a very similar reproduction quality compared to the reference paper substrate.

Even though most information is digitized today, paper as a printing substrate is still essential. The quality of the paper depends on whether it has the properties required for its intended use, which will fundamentally rely on the raw materials used. Nowadays, the production of paper and board is increasingly focused on alternative non-wood raw materials. In this context, the main objective of this research is to improve the quality of prints on laboratory-made papers with supplementary barley pulp by coating the surface of the papers with titanium dioxide coating. Since laboratory-made papers were not subjected to the bleaching process and no additional surface treatments were used, TiO2-based coating proved to be one of the ways to improve the quality of the prints on such substrates. In this study, it was concluded that TiO2-based coating did not affect the colorimetric values of the black prints to the extent that it affected the colorimetric values of the magenta prints. However, density of printed inks was increased up to 14% for prints on laboratory-made papers with higher amount of barley pulp and TiO2-based coating in two layers.

Surface characteristics of printing substrates are of the utmost importance to all types of paper that interact with ink. During all types of printing processes, the behaviour of the liquid phase (ink or dye) on the paper is directly defined by the paper cellulose-based surface. The printed ink spreads and penetrates more into paper fibres when the paper surface is rougher and more permeable. Contact angle measurements by sessile drop method are considered the most appropriate for determining the paper sheet surface energy. Paper as hydrophilic material has a high absorption rate resulting in a low contact angle. The objective of this study was to evaluate the surface free energy of laboratory-made papers containing straw pulp obtained from residues after the harvest of the most cultivated cereals in Croatia (wheat, barley and triticale). The obtained surface free energy results are promising for straw pulp usage in the manufacture of printing paper.