Designing Counter Die Relief Profiles for Laminated Folding Boxboard
Counter die relief profiles for film laminated folding boxboard require expanding channel widths by twenty percent to prevent outer film shear tearing.
Score Fold Whitening
Surface Integrity
Optical contrast loss occurs when mechanical pressure disrupts the internal coating or fibre structure of a folded substrate. Score fold whitening characterizes this degradation by the appearance of a distinct pale line along a crease where the surface finish fails to maintain continuity under stress. High opacity stocks with heavy clay coatings face this risk more frequently than lighter finished papers because the coating layer lacks the necessary elastic binder to accommodate a tight bend radius.
Converting lines often observe this effect after a folder-gluer operation creates a permanent deformation in the sheet.
Folding Resistance
Performance limits for this defect depend on the ratio of binder content to pigment volume in the applied coating formulation. Manufacturers adjust the latex levels to improve the flexibility of the surface without compromising the ability of the material to hold ink during printing. Low binder concentrations lead to brittleness at the crease, which exposes the raw fibre underneath and scatters light in a way that produces the signature white cast.
Calendering settings during production also influence the density of the sheet, providing an additional safeguard against surface rupture during post-press processing.
Correction Method
Operators mitigate the risk by modifying the width of the score channel to match the caliper of the board being processed through the machine. Wider channels reduce the sheer force applied to the outer surface of the fold, preventing the coating from fracturing even when using heavy weight stocks. Adjusting the score profile compensates for the inherent stiffness of the fibre matrix, ensuring the structural transition remains smooth enough to protect the decorative finish from visible damage.
Mechanical tension reduction at the fold point decreases the probability of visual defects on high value packaging products.