Managing Paperboard Hygroexpansion and Moisture Balance in Converting Operations
Targeting 5.5 to 6.5 percent board moisture and maintaining 50 percent relative humidity prevents hygroexpansion fan-out, registration drift, and score cracking.
Delamination Stress
Structural Integrity
Internal bond strength defines the threshold where fibrous materials resist separation under perpendicular load. Delamination stress occurs when these forces exceed the internal cohesive energy holding paper plies or coating layers together. Converting operations like high speed folding or aggressive adhesive application expose substrates to these forces.
If the bond energy remains lower than the applied tension, the material experiences catastrophic separation or surface picking.
Application Threshold
Manufacturing variables determine how much load a sheet carries before failure occurs. Calendering intensity and fibre refining stages directly adjust the internal bonding density of a substrate. Excessive coating weight on a weak base sheet increases the risk of layer detachment during vacuum feeding on a press.
Producers monitor these values to confirm that materials withstand the mechanical rigors of automated cartoning. Uniformity across the web allows converters to calibrate their machinery to specific tension limits without causing structural damage.
Mechanical Consequence
Rupture propagation follows a path through the weakest region of the cross section once initial failure begins. Energy dissipation through fibre tearing consumes more force than simple inter ply separation, which provides a measure of relative material toughness. Surface treatments that improve printability occasionally degrade the integrity of the base layer if the chemical formulation reacts poorly with the sizing agents.
Controlled testing confirms that high internal bond levels prevent substrate failure during complex forming operations.