Internal Rupture
Structural failures involving the internal separation of a material rather than a break at the interface signify a weakness in the base substance. Skin layer cohesive failure occurs when the internal strength of a coating or a polymer ply is lower than the force applied to it during processing or use. This results in the material splitting apart and leaving a residue on both surfaces.
Mechanical Stress
High peel forces or aggressive adhesives often trigger this type of breakdown in paper or film skins when the bond to the next layer is stronger than the layer itself. In the case of skin layer cohesive failure, the problem lies within the formulation or the curing process of the layer rather than the surface treatment. This is distinct from adhesive failure where the bond at the surface breaks cleanly.
It often indicates that the polymer chains are not sufficiently entangled or the binder level is insufficient to hold the pigment load. Mechanical stresses from nip rollers can also initiate these internal fractures if the material is brittle.
Quality Control
Microscopic examination of the failed area reveals the nature of the rupture and helps identify the point of weakness. Preventing skin layer cohesive failure requires increasing the molecular weight of the resins or adding reinforcing agents to the mix. Consistent testing ensures that the surface remains intact.
