Calculating Matrix Depth Ratios for Co-Extruded Film Laminates under Pressure
Matrix depth ratios dictate counter-die selection by balancing polymer yield strain against substrate compaction to preserve layer integrity under pressure.
Plastic Yield Stress
Transition Threshold
The critical mechanical stress level at which a material transitions permanently from recoverable elastic deformation to permanent plastic strain governs carton scoring. Plastic yield stress establishes the threshold force required to induce irreversible molecular or fiber displacement within paperboard and barrier polymers. In packaging substrate evaluation, this mechanical limit dictates the energy required to create lasting hinge scores that will not spring open after release.
Crease Permanence
Board scoring requires exceeding internal yield thresholds while keeping outer liner stresses below their ultimate tensile limits. When creasing rules compress paperboard into a counter matrix, localized shear stresses exceed the plastic yield stress of the internal plies. This initiates permanent fiber rearrangement, shear delamination, and cell-wall collapse.
If applied stress remains below this yield threshold, the board deforms elastically and recovers its original shape, resulting in poorly defined, stiff scores.
Matrix Resistance
Extrusion-coated polymers feature their own yield criteria that dictate their response to die scoring and folding. Polymers possessing low plastic yield stress deform smoothly around paperboard hinges without tearing, whereas brittle polymers fracture under equivalent score strain. Sourcing boards with optimized fiber bonding balances low folding resistance against high panel stiffness.
Precise yield stress control ensures predictable carton formation on high-speed packaging machinery.