Structural Rupture
Structural failure in the top liner of paperboard occurs when the tensile stress of folding exceeds the internal bonding strength of the fibres. Visual signs of a creasing fracture typically appear as a visible crack along the outside of a fold, compromising both the aesthetic quality and the physical integrity of a carton. This failure results from insufficient ply bond strength or excessive stiffness in the outer coating layer.
Board Ductility
Fibre length and moisture content determine how well a material withstands the mechanical force of a creasing matrix. If the board is too dry, creasing fracture becomes more frequent because the cellulose fibres lose their natural flexibility and snap under tension. The creasing rule must displace the internal structure to create a hinge without breaking the surface.
Adjusting the humidity of the storage environment or the depth of the crease profile can mitigate the risk of surface cracking during high-speed conversion.
Visual Integrity
Printed surfaces often show the most damage when the underlying substrate fails. When creasing fracture occurs, the white fibres of the board become visible through the ink or varnish layer. This disruption creates a ragged edge that prevents the clean closure of the packaging.
Coatings that lack sufficient elasticity fail to bridge the gaps created by the ruptured board surface.
