Air Coupled Ultrasonic Guided Wave Measurement for Board Crease Integrity
Air-coupled ultrasonic guided waves quantify paperboard crease ply delamination and micro-cracking non-destructively, preventing box compression failure.
UV Varnish Cracking
Coating Defect
Fracture of a cured ultraviolet layer when the underlying substrate is bent is a common finishing problem. Avoiding uv varnish cracking requires a balance between film hardness and flexibility. This issue appears as fine white lines or flaking along the fold of a brochure or carton.
It creates a poor finish that can snag or peel away.
Chemical Interaction
Excessive curing speed results in a brittle film that cannot stretch with the board fibres. Managing uv varnish cracking involves adjusting the photoinitiators and monomers in the formula. If the board absorbs the varnish too deeply, the resulting composite layer becomes too rigid to withstand the mechanical stress of the folder gluer.
Applying a primer or using a varnish with higher elastic properties can prevent these failures on heavy grammage stocks.
Environmental Factor
Low ambient temperature in the warehouse makes the polymer chains in the coating more rigid and susceptible to breaking. When the temperature drops, uv varnish cracking becomes more likely because the film cannot deform. Storing printed work in a climate controlled environment ensures the coating remains stable.
Testing the brittle point of the cured film on a sample fold allows the printer to adjust the lamp intensity or the coating weight before starting a full production run.