Water uptake

This study was addressed to flexographic printing of paper by water-based inks. In a multicolour press a water containing ink is transferred to a dampened surface in printing units after the first printing unit. The aim of this study was to investigate the relation between print quality (mottling, print density, average reflectance, absolute ink amount and dot gain) and pre-treatment of the surface by water and heat. In particular, the experimental set-up was chosen in order to mimic the affects of aqueous ink applied in a former printing units and subsequent air-drying units. The effects, as well as the mechanisms behind, of water transferred in a former printing unit and subsequent drying on surface properties, ink transfer and ink setting were studied. The investigated substrates were two liquid packaging board grades and one white top liner grade. The surfaces of the substrates possessed hydrophobic properties, i.e. water contact angle >100°. The printing trials were performe...