Surface Rupture
Surface failure occurs when fibers or coating fragments are pulled from a paper substrate during the separation of the ink film from the printing plate. In high-speed offset lithography, print picking causes unprinted white spots and accumulates debris on the blanket cylinder, which degrades the image quality over time. This defect occurs when the pulling force exerted by the splitting ink film exceeds the surface strength of the paper.
The resistance of the paper to this force is known as its pick resistance.
Ink Tack
As the ink tack increases or the press speed accelerates, the hydrodynamic forces generated during the splitting of the ink film rise significantly. This increase in force triggers print picking if the paperboard coating has insufficient binder content or if the base paper has weak internal fiber bonding. For example, a heavy coverage area with a tacky cyan ink might pull off microscopic portions of the clay coating, which then adhere to the printing plate.
This continuous accumulation of coating particles requires the press operator to stop the run and wash the blanket, which reduces overall productivity. The problem is particularly severe in colder print shops where ink viscosity is naturally higher.
Mitigation Strategy
Lowering the print speed or reducing the ink tack with additives are common remedies used on the press floor. By selecting paperboards with higher binder levels, converters can prevent print picking during demanding, high-speed multi-pass printing runs.
