Caliper Reduction
Industrial practice in packaging design focuses on minimizing the raw material weight of paperboard while preserving its physical volume and rigidity. Through boxboard downgauging, converters decrease the thickness of the board substrate without altering its overall structural capacity. This structural adjustment relies on high-yield chemical pulps and multi-ply forming technologies that concentrate denser fibres in the outer layers to maintain the bending moment.
The target caliper is achieved by optimizing the press section of the paper machine. High-yield pulp provides the required bulk to offset the reduction in total fibre weight. Mill trials confirm that a ten percent reduction in basis weight can be implemented without loss of protective performance if the multiply structure is carefully managed.
Stiffness Maintenance
The physical strength of multi-ply board depends on the distance between the top and bottom linerboard layers. When executing boxboard downgauging, maintaining the cross-direction bending stiffness is essential for carton performance during high-speed packing. Using mechanical pulp in the middle ply provides the necessary bulk to keep these outer layers apart.
This configuration maximizes the moment of inertia. A decrease in basis weight without bulk compensation will lead to bulging and failure of the carton during palletized storage.
Runnability Constraint
High-speed packaging lines impose strict limits on the mechanical variation of paperboard substrates. If boxboard downgauging is carried too far, the reduced stiffness causes feeding errors and jams in the folder-gluer machine. Converting lines require a minimum board resistance to withstand the pressure of the filling nozzles.
This boundary is defined by the stiffness profile.
