The influence of MFC and NFC addition in uncoated paper on flexography optical print quality

摘要

Nanocellulose is a natural nanomaterial that can be obtained in many different ways with chemical procedures (Saito et al., 2006, Saito et al., 2009), mechanical procedures (Correia et al., 2016) or with the use of appropriate microorganisms (Jozala et al., 2016). Due to its properties, it is increasingly used in paper-making as a filler in fibre suspensions and coatings, particularly in order to improve mechanical, physical and barrier properties of the products. As far as the influence of nanocellulose on the printing properties of papers is concerned, most studies describe the influence of nanocellulose addition in coatings. According to CEPI in 2017 (CEP1, 2017), the production of mostly uncoated packaging grades was estimated to increase by around 3.7% compared to 2016. These types of paper are potentially very suitable for the nanocellulose addition according to the requirements (as low mass as possible, with the highest possible mechanical strength). The effect of NFC and MFC addition on optical printing properties of uncoated papers has not been studied in details yet and that was one of the motivations to conduct this research. Some research regarding printability which is overlapping with optical print quality was done mainly for offset and inkjet printing technologies. Nunes et al., (2015) studied the influence of cellulose nanofibrils in the coating on inkjet printability and their results prove that the printing quality, quantified through colour gamut area and by the black optical density, was increased with the use of NFC which was obtained by TEMPO-mediated oxidation and mechanical homogenisation.