Surface Strength
The maximum printing speed at which a liquid ink can be applied to a coated paperboard surface without causing the mineral coating layer to rupture or pull away from the underlying paper base is a fundamental material threshold. This threshold, known as coating pick velocity, determines how fast a press can run before paperboard surface failure occurs. It defines the boundary where the tacky printing ink exerts a lifting force that exceeds the internal cohesive strength of the surface coating.
Measurement Method
Standard testing involves an accelerating print tester that applies a fluid of known tack to a sample strip at increasing speeds. During this evaluation of coating pick velocity, the tester registers the exact point where the first pick or rupture of the surface is observed. This measurement allows board mills to adjust the binder level in their kaolin or carbonate coating formulations.
Operators utilize these values to establish the maximum running limits on commercial multi-color offset presses without risking mechanical surface failure.
Production Effect
High-speed offset presses require paperboard with a high resistance to surface picking to prevent frequent stops for plate cleaning. When the coating pick velocity is too low, particles of the coating accumulate on the rubber blanket. This accumulation results in visible print defects.
