Wet creping of paperboard

We describe a wet creping approach, applicable not only for softwood kraft papers in the grammage range of 30–120 g/m2 but also for 300 g/m2 CTMP board. Creping of board requires a certain level of deformability in the material, which is controlled by its solids content. The concept was tested at laboratory scale using a device on which temperature, blade angle and line load could be adjusted. The sample density was decreased by creping due to smallscale delamination of the structure, leading to separate inner layers with a wavy appearance. The strain at break was remarkably increased and agreed well with the theoretical estimate based on the crepe ratio and the breaking strain of the uncreped sample. Simultaneously, tensile strength was reduced by creping. In terms of tensile strength and stretch, 60–70 % solids content during creping was optimal for the tested board.