Nanocellulose in pigment coatings : Aspects of barrier properties and printability in offset

Abstract: Papers are coated in order to improve the properties of the surface, to improve printability and to include new functionalities like barriers properties. Typical coating formulation contains a high number of components, some are made from minerals and others are manufactured from petroleum. The barrier properties of today's paper based packages are plastics and/or aluminum             foil. Environmentally friendly substitutie of these nonrenewable materials are needed.  Nanocellulose is a promising material                 and of a growing interest as an alternative to petroleum-based materials, since nanocellulose films/coatings have been shown to have excellent mechanical and barrier properties.   This project aimed to evaluate nanocellulose in combination with minerals in paper coatings. The project had two approaches. One was to evaluate the barrier properties of MFC coatings with mineral included. The second part was about coatings for           printing matters, and evaluation of the possibility to replace petroleum-based binders in the coating color with MFC. Barrier properties were evaluated by measuring the air permeability of the coatings. The properties of the coating affecting the         printability in offset printing examined was the surface energy, the gloss, the roughness of the coatings, the strength and the offset ink setting.   Carboxymethylated nanocellulose formed denser films and had superior barrier properties compared with enzymatically pretreated nanocellulose. Adding of minerals did not affect the barrier properties of the MFC coatings to a significant extent.         Therefore, minerals cannot be added to enhance the barrier but it can be added to reduce the cost of the coating process without losing any barrier properties.                                 The print quality depends on how the ink interacts with the coating. These coatings did have a relatively high surface energy, which is preferable for printing with waterborne ink. It was also shown that the absorption abilities increased when the amount of MFC was increased. However, offset printing demands high surface strength and addition of MFC in the coating color                     drastically decreased the strength. This means that the coatings produced in this work are not strong enough and thereby not           suitable for offset printing. However other printing technologies put lower demand on surface strength and are still possible.