Dynamic Crease Stiffness Reduction Ratios under Ultra High Speed Packaging Line Strain Rates
Dynamic crease stiffness reduction ratios must be evaluated under operational strain rates of 1000°/s to 5000°/s to prevent high-speed cartoning line jams.
Viscoelastic Breakdown
Structural Degradation
Irreversible structural degradation of polymer networks and fiber matrices occurs when mechanical stresses exceed material elastic limits during converting operations. The phenomenon viscoelastic breakdown describes the permanent disruption of hydrogen bonding and cellulose fiber entanglement caused by severe shear and compressive forces. Creasing rules force paperboard past its yield point, inducing permanent plastic deformation along score lines.
The thermodynamic boundary applies to mechanical deformation zones within fiber webs under high-rate loading.
Mechanical Rupture
High strain rates during die-cutting force amorphous cellulose regions and hemicellulose binders to undergo rapid shear slipping. Fiber plies delaminate locally, dissipating strain energy and preventing catastrophic tensile failure of outer liner coatings. When viscoelastic breakdown occurs, the board loses its internal elastic memory, preventing springback after ninety-degree folding.
Inadequate energy dissipation during compression causes brittle fiber fracture and top liner cracking along score ridges. High moisture content lowers the glass transition temperature of lignin and hemicellulose, accelerating plastic yield under creasing tools. Temperature increases inside high-speed press nips further modify polymer mobility and shear behavior.
Hinge Formation
Insufficient force fails to initiate ply delamination, leaving score lines stiff and prone to springback. Controlled viscoelastic breakdown enables clean panel folding on high-speed packaging machinery.