Quantifying Surface Elevation Variance along Score Lines Using Optical Profilometry
Optical profilometry quantifies score elevation variance down to sub-micron resolution, identifying die wear and coating micro-fractures before carton assembly.
Coating Micro-Cracking
Surface Fissure
Microscopic fracturing of pigment or polymer binders on the surface of coated paperboard arises from mechanical strain during converting operations. The occurrence of coating micro-cracking is common on the outer surface of folds, where the board is subjected to high tensile force. These tiny cracks do not necessarily penetrate the entire board but they disrupt the visual uniformity of the printed surface.
Deformation Vulnerability
The susceptibility of the surface to fracturing depends heavily on the ratio of binder to pigment in the coating formulation. If a sheet exhibits coating micro-cracking, it indicates that the coating layer is too brittle or that the drying temperature during manufacture was too high. High clay or calcium carbonate content reduces the overall flexibility of the dry film.
Structural Assessment
Detecting these superficial failures requires high-magnification optical microscopy or dye penetration tests. When coating micro-cracking occurs on printed packaging, it exposes the unprinted white base paper beneath, creating unsightly white lines along the folded edges of the finished box. This effect is especially noticeable on dark solid print designs where it severely detracts from the aesthetic value of the brand.
Applying specialized varnishes can sometimes mask these defects but the root cause must be addressed through adjustments in coating formulation or creasing geometry.