Dynamic Fracture Mechanics of Multi Layer Paperboard Creasing under Rapid Shear Loading
Rapid shear creasing requires tailored interply delamination toughness to prevent liner fracturing while reducing folding torque on high-speed lines.
Score Line Stiffness Ratio
Stiffness Proportion
The relationship between the bending resistance of an unbroken board panel and the stiffness of its creased fold determines carton folding behavior. This measurement, known as the score line stiffness ratio, compares the force required to bend a pre-creased crease to that of the raw board. A low ratio indicates a highly compliant crease that will fold easily and reliably.
Erecting Machine Performance
Automated carton erecting lines require consistent spring-back resistance to operate without jam-ups. When the score line stiffness ratio is too high, the carton panels bulge or fail to square up properly because the crease resists folding. This resistance can cause the carton flaps to push open before the adhesive has fully cured.
If the ratio is too low, the cartons lack structural integrity and can collapse when stacked on pallets or store shelves. Automated machinery requires a well-balanced ratio to avoid stops, as excessive stiffness ruins the alignment of the flaps while too little stiffness prevents the carton from standing upright.
Substrate Variable
Achieving the correct ratio depends on the fiber length and moisture content of the starting paperboard. Drier board is more brittle and has a different score line stiffness ratio, which necessitates adjusting the depth of the creasing rules. Variations in these properties are managed by checking the creases at regular intervals during production.