Optimizing Score Line Geometry for Low-Fibre-Length Recycled Substrates
Low-fibre recycled board requires widening female matrix channels to 1.8 times caliper and reducing penetration depth to prevent top-liner rupture.
Crease Line Geometry
Structural Profile
Mechanical impressions embossed into paperboard determine the specific paths along which carton panels fold during high-speed assembly. This physical configuration, referred to as crease line geometry, is defined by the width of the crease groove and the depth of the rule penetration. Standard creasing systems use a steel rule to force the paperboard into a groove in a polyurethane matrix, creating a controlled delamination of the internal layers.
This internal shear allows the board to bend without tearing the outer liners.
Folding Resistance
Measurement of the bending moment shows how the thickness of the crease governs the force required to fold each panel. Incorrect crease line geometry leads to high folding resistance, which can prevent automated packaging lines from sealing cartons correctly or cause the panels to bow. When the groove is too narrow, the board undergoes compressive failure rather than controlled delamination.
Conversely, an overly wide groove produces loose, poorly defined folds.
Operational Tolerance
High-speed filling lines require tight tolerances on the dimensions of the crease to prevent jamming. Adjustments of less than fifty micrometres in rule depth can make the difference between a clean fold and a split board. Correct crease line geometry minimizes springback forces, ensuring that glued flaps remain secure under continuous line speeds.