Coating Adhesion
Polymer layers applied to paper substrates must withstand mechanical stress during subsequent converting operations. Cross hatch adhesion measures this bond strength through a standardized lattice pattern cut into the dried film. Operators score the coated surface with parallel blades in two perpendicular directions to create a grid of small squares.
A specific pressure sensitive tape adheres firmly over the cut zone before manual removal at a rapid uniform angle. The amount of coating remaining within the grid area defines the resistance to delamination under mechanical force.
Test Parameter
Blade spacing dictates the severity of the evaluation based on total film thickness. Substrates carrying layers under fifty micrometers require a one millimeter grid interval. Films exceeding that dimension demand a two millimeter separation to maintain accurate mechanical stress ratios.
Cutting tools must maintain sharp edges to prevent tearing the underlying fibrous substrate instead of shearing the coating cleanly. Environmental conditioning prior to testing removes humidity variables that soften water based latex binders during evaluation.
Failure Mode
Delamination typically occurs at the interface between the pigment layer and the cellulosic base paper. Poor primer application creates microscopic voids where moisture vapor concentrates during thermal drying cycles. Poor anchor coat chemistry prevents covalent bonding across the phase boundary between synthetic polymers and natural fibers.
Finished cartons subjected to creasing and folding experience intense shear forces that exploit these interfacial weaknesses. Substrates failing the rating threshold require adjustments to binder ratios or corona treatment energy levels before production resumes.
