Converting Fault
Bending paperboard along a pre-formed crease can result in structural failure if the fibers or surface coating rupture. The score line splitting is a defect where the outer plies of the board crack along the bend line during carton erection. This issue occurs when the board is too dry or when the creasing tooling is incorrectly sized.
It degrades the visual appearance of the printed packaging and exposes the grey or brown interior fibers of the board. Proper moisture management in the storage area and correct tooling setup prevent this degradation from occurring.
Causal Factor
Low moisture content reduces the elasticity of the cellulose fibers, which makes them highly brittle. When the board folds, the outer surface is stretched beyond its tensile limit, which causes the fibers to tear. This problem is compounded by heavy ink and varnish layers that do not stretch.
Additionally, using a creasing rule that is too narrow or a matrix that is too shallow will over-stress the sheet and initiate splits.
Structural Remediation
Adjusting the creasing matrix to a wider dimension reduces the strain on the outer fibers. This change distributes the bending stress over a larger area, which prevents the surface from cracking.
