Combined Modeling And Experimental Studies To Optimize The Balance Between Fold Crack Resistance And Stiffness For Multilayered Paper Coatings - Part 1: Introduction And Modeling Studies

Fold-crack resistance is a key coated paper quality that influences the functionality and appearance of the final product. Cracking at the fold may lead to strength reduction and the appearance of a visible crack at the folded surface. It is well known that bending stiffness and fold cracking are closely related, with a higher stiffness leading to higher risk of fold cracking. The aim of this study was to optimise the balance of stiffness and fold cracking for multilayered paper coatings. This paper is Part 1 of a combined modeling and experimental study to assess the relationship between fold-crack resistance and bending stiffness in coated papers. The objective of the work was to suggest ways to optimize coated paper to maximise fold-crack resistance as well as bending stiffness. Models were developed to calculate bending stiffness, predict the onset of failure, and based on this prediction, calculate the residual load carrying capacity of coated paper. The model parameters included the number of coating layers, the individual layer thickness, and the mechanical properties of the coating layers in both tension and compression. The modeling work suggested that the best possibility to optimize the balance between fold cracking and bending stiffness was seen for triple coated paper. The use of a thin, stiff bottom coating layer, combined with a thick, lower-stiffness middle layer and a thin, stiff top coating layer gave the best balance. The simulations showed that a thin stiff bottom layer can be allowed to crack with a thick middle layer acting as a buffer to absorb the crack. This enables the use of a stiff top coating layer which contributes the most to the overall stiffness of the multilayered coated paper.