Tensile Strain Measurement in Recycled Paperboard Grades
Recycled paperboard strain measurement requires direct optical extensometry under ISO 1924-3 to isolate true sheet elongation from clamp slippage.
Coat Ply Fracture
Failure Mechanism
Structural failure within the layered composition of a coated board occurs when the pigment layer separates from the underlying fibrous base. While coat ply fracture usually happens during folding or creasing, it represents a breakdown of the adhesive bond between the mineral coating and the substrate surface. This defect appears as a visible crack or peeling that exposes the raw fibres beneath the finished surface.
High pigment loads or insufficient binder levels often increase the risk of such failures.
Bending Stress
Bending forces applied during the conversion process generate tensile stresses that exceed the internal bond strength of the coating layer. If the coating is too brittle, coat ply fracture emerges as a series of jagged ruptures along the axis of the fold. This rupture differs from simple fibre breakage because it specifically involves the delamination of the chemical application.
Starch or latex distribution within the coating formulation provides the necessary elasticity to resist these forces.
Resulting Defect
Resulting defects on a finished package often stem from the loss of surface continuity during the die-cutting stage. When coat ply fracture occurs on a printed area, the white base sheet becomes visible and disrupts the graphic design. Ink absorption also changes at the site of the fracture.