Calibrating Crease Channel Width for Matte Laminated Folding Cartonboard
Matte laminated boxboard demands channel width expansion of twelve to eighteen percent over raw stock formulas to absorb film strain and prevent score rupture.
Neutral Bending Axis
Stress Equilibrium
The theoretical plane within a sheet of material that experiences zero axial stress when subjected to a bending force represents the boundary between tension and compression. When paperboard is bent, the fibres on the outer side of the curve are stretched while those on the inner side are compressed, leaving the neutral bending axis unstressed. In a perfectly symmetrical and homogeneous sheet, this axis lies exactly in the middle of the board’s thickness.
Any shift in this plane’s position alters the amount of force needed to initiate a fold.
Crease Mechanics
Structural changes during the creasing step deliberately displace this line to control the folding behavior. When the board is scored, the pre-damage to the internal plies shifts the neutral bending axis toward the outer liner. This shift protects the surface from cracking by reducing the tensile stress on the outer printed plies.
The board then folds easily along the designated crease line without ruining the graphics.
Stiffness Optimization
Ply configuration determines the initial location of this stress-free zone. By placing stronger pulp in the outer plies and bulkier pulp in the center, manufacturers keep the neutral bending axis in the middle of the sheet. This design maximizes bending stiffness while minimizing total weight.