Dynamic Optical Displacement Calibration Protocols across Folding Boxboard Converting Lines
Dynamic blue-laser displacement calibration eliminates light-penetration drift, securing exact FBB crease metrics and stopping false sheet rejection.
Specular Bleedthrough
Optical Defect
Light that penetrates the thin top layer of a coated board and reflects off the grey or brown plies underneath reduces the perceived brightness and contrast of the printed image. This phenomenon, termed specular bleedthrough, occurs when the opacity of the coating formulation or the top fibre ply is insufficient to block the underlying stock. The defect degrades print quality by muting highlights and altering the appearance of critical brand colors.
Sheet Structure
Preventing this issue requires a carefully designed board structure with a high-opacity top ply and a dense, uniform clay coating. Kraft boards with recycled middle plies are particularly susceptible, as the dark fibres can show through if the top liner weight is too low. In such cases, papermakers must increase either the titanium dioxide content in the coating or the basis weight of the bleached chemical pulp layer.
Selecting a board with a guaranteed opacity level ensures that the white areas of the packaging remain bright and vibrant after printing.
Quality Control
Densitometers and spectrophotometers measure the reflection values to detect any drop in top-sheet brightness before the board is sent to the printing press. This testing helps avoid printing on defective sub-standard board.