Keywords: dispersion coating, barrier, WVTR, Cobb, paperboard
Summary:The inherent properties of paper-based packaging means that it is not a naturally good barrier against the ingress of water, water vapour and gases. The development of water-based barrier coatings paperboard has been stimulated by the need to substitute for wax treatment and to replace extrusion coatings or laminated board. Nowadays the use of barrier dispersion coatings is a well-established method to provide improved barrier properties to the paperboard, in particular lowering the oxygen transition rate (OTR) and water vapour transition rate (WVTR) through the paperboard. However, the final barrier performance of the coated board is to high extent dependent on the properties of the baseboard. In this work, we demonstrate use of different precoatings to provide different pre-conditions for the final application of the barrier coatings. All coatings were applied on a pilot coater at a speed of 300-380 m/min with two baseboard at different grammages (210 g/m2 vs 350 g/m2) in combination with two different styrene acrylate/GCC precoating formulations, i.e. open/porous- vs closed/less-porous precoatings. The different types of precoatings did not have a significant impact on OTR barrier. The decrease in OTR was mostly related to the total grammage of the barrier coating applied. On the other side, the type of precoating had a significant impact on the direct water uptake and WVTR barrier, where closed/less-porous precoatings applied at low grammages (6 gsm) provided the best WVTR barriers and lowest Cobb 60 values. In addition, increased grammage of the open precoatings resulted in increased direct water uptake what could be related to increased total pore volume of the precoating layers.