An experimental and computational study of laminated paperboard creasing and folding

Laminated paperboard is often used as a packaging material for products such as toys, tea and frozenfoods. To make the paperboard packages appealing for consumers, the fold lines must be both neat and undamaged. The quality of the folds depends on two converting processes: the manufacture of fold lines (creasing) and the subsequent folding. A good crease contains some delamination, initiated during creasing, to reduce the bending stiffness and to prevent the board from breaking during folding. However, for boards of high grammage breaking of the top layer is nevertheless a frequent problem. The mechanisms that operate in the creasing zone during creasing and folding, and that may thus result in breaking of the top layer, are studied in this contribution on the basis of idealized small-scale creasing and folding experiments. However, since experimental observations are only limited means to study the paperboard’s behavior, a mechanical model is proposed to obtain more detailed insight. Although the material and delamination descriptions used in the mechanical model are both relatively straightforward, comparisons between the model and the experimental data show that the model predicts the paperboard’s response well. The mechanical model shows – in combination with experimental strain fields – that multiple delaminations are initiated in the shear regions. Moreover, only the mechanical model reveals the mechanism that is responsible for the failure of the top layer if a crease is too shallow. Finally, the model also demonstrates that not only delamination but also plastic behavior must occur during creasing if breaking of the top layer is to be avoided.