Polymer Film Micro Fracture Mechanisms under High Strain Shear in Folding Boxboard Creases
High strain shear during boxboard creasing causes polymer film micro fractures when local elongation exceeds film yield capacity along the outer bend radius.
Rule Radius
Tool Specification
The curvature on the tip of a creasing rule used in die-cutting machines determines the profile of the hinge formed in the board. The rule radius defines the shape of this rounded edge and directly influences how the paperboard fibres are deformed during the creasing stroke. It is a critical parameter for tool makers and converters.
Material Compression
A larger rule radius spreads the compressive force over a wider area, whereas a smaller radius concentrates the stress. The selected radius must match the thickness and stiffness of the paperboard grade being processed. This matching ensures the board is compressed but not severed.
Die-Cutting Quality
Selecting the correct rule radius prevents the outer layers of the paperboard from cracking when the carton is folded. If the radius is too small, it can slice the board, while a radius that is too large can result in a weak, poorly defined crease. Packaging designers use this specification to optimize foldability on automated packaging lines, ensuring that boxes square up correctly and do not pop open during gluing.
This parameter is therefore key to maintaining both structural reliability and aesthetic quality. It is a core factor in creasing rule mechanics.