Polymer Laminate Surface Energy and Foil Adhesion Dynamics
Foil adhesion succeeds when polymer film surface energy exceeds forty-two dynes per centimeter and sizing chemistry matches the polar surface component.
Interfacial Shear Failure
Adhesive Breakdown
Mechanical separation along the boundary between two bonded plies or between a coating and a substrate occurs when parallel forces exceed the bond strength. This phenomenon, known as interfacial shear failure, occurs when the internal cohesive strength of either layer is greater than the adhesion between them. It represents a weakness in the bond that can cause the package to split or peel.
Shearing Force
When a carton is folded, the outer plies of the paperboard are subjected to tension while the inner plies experience compression. This creates a shearing action that can cause interfacial shear failure if the adhesive or the internal sizing is inadequate. If this failure happens during the folding step, the structural integrity of the carton is lost, leading to soft folds and weak corners.
Substrate Influence
Testing this resistance involves applying a measured shear force to the bonded area to determine the point of separation. A clean separation at the interface indicates a poor adhesive bond, whereas a fiber-tearing break shows that the adhesive bond was stronger than the paperboard itself. Achieving a fiber-tearing bond is the standard for secure packaging closure.
Packaging designers use these shear values to select appropriate adhesives for coated surfaces. This measurement ensures that the sealed areas will withstand the stresses of shipping and handling.