Sheet Distortion
Dimensional instability in paperboard occurs as a physical deviation from a flat plane, resulting from moisture gradients or structural tension. This deformation, known as board curl, typically arises during the drying phase of manufacturing or during subsequent storage in uncontrolled atmospheres. It can occur across the machine direction, along the machine direction, or diagonally across the sheet.
The severity of the deviation dictates whether the substrate remains usable for high-speed printing and converting processes where flat sheets are required.
Moisture Influence
Fiber expansion and contraction under variable relative humidity drive the physical warping of the substrate. When board curl is caused by uneven moisture absorption between the top and bottom plies, it creates unequal dimensional forces that bend the sheet toward the drier side. Multi-ply boards are highly susceptible to this effect due to differences in furnish composition and refining levels between the liners and the middle plies.
Managing ambient humidity in warehouse and pressroom environments remains the primary method for preventing this imbalance.
Finishing Impact
Press feeding issues represent the most immediate operational consequence of distorted stock. Distorted sheets fail to register correctly in high-speed sheet-fed offset presses or die-cutters, leading to frequent feeder trips and machine stoppages. This downtime reduces converting efficiency and increases material waste.
