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.
Strain Rate Sensitivity Exponent
Deformation Rate
Polymer and fibre network mechanics describe how material yield stress increases when deformation forces are applied at elevated velocities during high-speed converting. Within dynamic mechanical analysis, the strain rate sensitivity exponent quantifies the degree to which a substrate’s deformation resistance depends on the speed of applied mechanical strain.
Viscous Response
Paperboard and polymeric coatings exhibit viscoelastic behavior, combining instantaneous elastic strain with time-dependent viscous flow during mechanical deformation. At high strain rates typical of rotary die cutting and rotary scoring, polymer chains and inter-fibre bonds have insufficient time to relax, causing the apparent yield strength of the material to rise significantly. A higher exponent value indicates that material resistance increases sharply as converting line speeds accelerate, requiring proportional increases in die impact force.
Higher required forces accelerate tool wear and increase the likelihood of brittle surface fracturing along crease lines. Determining this strain parameter enables packaging engineers to model board behavior across varying production speeds.
Converting Velocity
High-speed cartoning machines expose paperboard creases to deformation rates exceeding several hundred percent per second during box erection. Understanding rate-dependent material response aids in selecting substrate formulations that resist cracking at high production velocities. Optimizing polymer formulations maintains flexible score performance across fast packaging lines.