Single Sided Lamination Curl against the Flatness Filling Lines Need
Single-sided lamination curl is controlled by balancing nip heat, reverse dampening, decurling bar tension, and conditioning board to filling line humidity.
Substrate Z Direction Shear
Internal Strength
Resistance of a paper or board material to forces that would cause it to delaminate or split between its internal layers. Measuring substrate z direction shear is fundamental for predicting how the material will behave during the printing and folding stages. A low value indicates that the internal fibre bonds are weak, which can lead to structural failure under stress.
Printing Stress
Tacky inks used in offset lithography apply a heavy vertical force to the surface of the sheet as it leaves the blanket. If the substrate z direction shear is insufficient, the ink will pull the top layer of the board away from the rest of the sheet. This defect ruins the print and can contaminate the ink rollers with debris.
Converters must select materials with high internal bond strength for jobs that involve heavy ink coverage or high speed production.
Scoring Performance
Bending and folding also place stress on the internal structure of the board. A material that lacks substrate z direction shear will often crack or delaminate at the crease, resulting in a weak carton corner. Mills control this property by managing the fibre length and the amount of internal sizing added during the wet end of the paper machine.