Virgin Hardwood Pulp Sizing Chemistry and Fibre Hydrogen Bonding Properties
Virgin hardwood sizing requires balancing high surface hydroxyl density against AKD and ASA steric interference to maintain internal bond and Cobb holdout.
Offset Lithography Holdout
Surface Acceptability
Surface pore structure and sizing level govern the absorption rate of oil-based inks applied to paperboard substrates. Offset lithography holdout measures the resistance of a coated board surface to the penetration of ink vehicles and varnish solvents. Proper holdout maintains ink pigment on the sheet surface, maximizing gloss and color density.
Capillary Absorption
High-speed offset lithographic presses transfer thin ink films onto paperboard under high nip pressure. Offset lithography holdout depends on pore size distribution and hydrophobic surface coatings that restrict capillary absorption of ink oils. Low holdout allows ink vehicles to drain rapidly into the substrate, causing ink strike-through and dull appearance.
Excessive holdout prevents vehicle absorption entirely, leading to ink set-off and smudging on stacked printed sheets. Paper mills balance kaolin clay particle orientation and latex binder ratios to achieve controlled pore structures. Testing with standardized oil absorption methods verifies ink vehicle resistance prior to press runs.
Rheology Boundary
Printability metrics evaluate ink vehicle absorption on coated paperboard substrates. Offset lithography holdout testing does not apply to water-based flexographic inks or dry toner electrophotographic processes. Testing procedures cease when solvent drying mechanisms shift from absorption to ultraviolet curing.
Measurement loses validity when ambient pressroom humidity alters base sheet pore dimensions.