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.
Elastic Springback
Viscoelastic Recovery
The instantaneous and time-dependent dimensional recovery exhibited by a folded or deformed fibrous web measures its resistance to permanent set. Elastic springback quantifies the degree to which scored paperboard returns toward its initial planar orientation after folding forces are removed. This mechanical reaction originates in the unyielded elastic zones of outer cellulose fibers and internal polymer coating layers that store strain energy during deformation.
Residual Stress
Bending moments applied during scoring and folding establish internal tensile and compressive stress gradients across the sheet thickness. Elastic springback manifests when these internal stresses fail to relax completely through plastic yield or inter-ply shear delamination. Board with elevated stiffness and moisture contents below five percent exhibits pronounced springback, complicating automated packaging assembly.
Inadequate crease depth amplifies springback force, causing cartons to bow outwardly along panel faces.
Gluer Stability
High-speed packing and cartoning lines require consistent fold angles to maintain reliable adhesive bonding. Carton flaps displaying excessive springback can rupture partially cured hot-melt or cold-emulsion glue seams during discharge from folder-gluer compression belts. Setting counter-die tooling to deliver deep, clean ply delamination optimizes the hinge ratio and minimizes springback force.
Reliable carton squaring on filling lines depends directly on controlling this mechanical property.