Dispersion Barrier Coating Mechanics under Crease Stresses in Flexo Converting
Flexographic dispersion barrier coatings retain water and grease resistance under crease stresses only when coating elongation capacity matches board strain.
Crease Stresses
Deformation Physics
Mechanical forces induced during the localized bending of folding boxboard generate distinct tensile and compressive fields across the substrate thickness. The resulting crease stresses determine whether paperboard folds cleanly along scored lines without surface cracking or liner rupture. During scoring, male creasing rules compress the board into female channels, initiating controlled internal delamination between fiber plies.
This structural breakdown reduces bending stiffness along the crease line while preserving tensile strength on the outer printed liner. The stress distribution depends heavily on board moisture content and fiber orientation relative to the fold axis.
Force Analysis
Plies under tension on the outer radius of a fold risk cracking when localized tensile load exceeds fiber elongation limits. Internal shear forces promote delamination, which allows the board to form a smooth bead inside the fold rather than buckling outwards. Excessive compressive load on the inner ply leads to unsightly surface ruptures and compromised carton squareness.
Converting Tolerance
Tooling dimensions must match board caliper precisely to control delamination depth and peak bending torque. Incorrect channel width alters the stress profile, increasing glue line springback during carton assembly. High-speed cartoning machines require low bending moments to maintain reliable feeding and accurate square folding.