Adhesion Failure
The separation of the outer ply of a multi-ply board from the underlying layers occurs when the internal bond strength is lower than the tension applied during printing or converting. This liner splitting is a common defect in high-speed offset printing where the tack of the ink pulls the surface away from the core. It results in a complete destruction of the board’s structural integrity at the point of failure.
This defect often results in the immediate stoppage of a print run to prevent damage to the blankets.
Mechanical Cause
Insufficient starch or poor fibre entanglement at the ply-bond interface during the papermaking process creates a weak plane within the material. When the grippers or the ink rollers exert a vertical force, the weakest link gives way. This problem is often aggravated by dry conditions that make the fibres more brittle.
Prevention Strategy
Reducing the ink tack or slowing down the press can sometimes mitigate the risk of this failure. Mills monitor this property using the Scott Bond test to ensure that the internal layers are fused strongly enough for demanding jobs. A board with a high surface strength but a weak core is particularly susceptible.
