Capillary Absorption Kinetics in Lightweight Coated Virgin Graphic Papers
Capillary absorption kinetics in lightweight coated virgin papers depend on pigment packing geometry, binder distribution, and sub-micron pore radii.
Offset Litho Picking
Surface Damage
Printing defects occur when the tack of the ink exceeds the surface strength of the paper, causing fibers or coating particles to be pulled away. Known as offset litho picking, this phenomenon leaves small white spots on the printed image and can lead to the buildup of debris on the printing blanket. This ruins the quality of the finished work.
Force Equilibrium
The likelihood of the defect depends on the speed of the press and the viscosity of the ink. As offset litho picking is more common in the first printing units where the ink is tackiest, printers must carefully select the substrate and ink combination. The internal bond strength of the paper is the primary resistance factor.
Production Troubleshooting
Frequent cleaning of the blankets is necessary when this issue appears, which reduces the efficiency of the print run. Solutions include reducing the press speed or adding a tack reducer to the ink. However, these changes can affect the drying time and the color density of the print.
Choosing a paper with a higher pick resistance rating is the most effective long-term solution. Testing with a wax pick test or an IGT printability tester provides a quantitative measure of the surface strength. This data helps in selecting the right material for demanding jobs.
Picking resistance often improves with increased binder content in the coating.