Some convertibility effects on printability of paper and paperboard

摘要

In this work, paper and paperboard were characterized to study the influence of base-substrate properties, extrusion-coating and corona treatment on printability of LDPE-coated paper and paperboard. Printing was performed using water-based flexographic ink on two different commercial base-substrates: commercially LDPE-extruded and printed wrapping paper and laboratory LDPE-extruded and printed paperboard. Characterization of substrates and evaluation of print quality was performed visually and with conventional measurement methods. Ink spreading and ink distribution on the substrate was analyzed using contact angle measurements in combination with microscopy methods and profilometry. The results obtained show that corona treatment improves ink adhesion and ink spreading on a LDPE surface, but at the same time leads to an increase in surface roughness and higher dot-gain. Better print quality was evident for corona treated samples. The results obtained from microscopy studies showed that the grammage variations of the base-substrate and variations in LDPE layer influence compressibility of the substrate and may cause defects in print quality in the form of an uneven ink film distribution and a mottled print with uncovered areas. Uneven grammage distribution, a varying formation and a high surface roughness with exposed fibre on the top side of the base-substrate have a large influence on the compressive behaviour of the substrate, which in turn may influence both distribution of the LDPE layer and print quality. A higher surface roughness in most cases require the use of a higher nip pressure and ink volume to obtain a good ink coverage, which in turn may result in an uneven ink film distribution.