Effect of blank pre-conditioning humidity on the dimensional accuracy and rigidity of paperboard trays

Abstract

Abstract Optimization of storage conditions is essential for successful converting of paperboard. This paper investigates the effect of blank moisture content on the dimensional accuracy and rigidity of press-formed paperboard trays. The trays were manufactured from uncoated, pigment-coated and extrusion-coated paperboards and multi-layer materials using fixed process parameters. Because of the different layer structures and coatings, the paperboards showed different hygroscopic behavior. Prior to converting trials, the bursting strength of paperboards under different moisture conditions was assessed. It was found that the moisture content has only a minor influence on bursting strength, but moisture affects blank curling tendency and dimensional accuracy of the tray. A high blank moisture content led to a loss of the dimensional stability and load-bearing capacity of trays, although based on earlier knowledge it is evident that the moisture content should be high for successful press-forming. As expected, a low blank moisture content increased the prevalence of ruptures in forming but the resulting trays were stiffer and their dimensional accuracy was better. It was suggested that the increased stiffness is related to a more efficient moisture removal during the press-forming, so that the fiber network is more effectively consolidated due to e. g. the formation of hydrogen bonds.