Lead Time Each Added Pass Buys between Approval and Pallet
Each added pass adds 24 to 48 hours of lead time through mandatory inter-pass drying, thermal stabilization, tooling lead times, and offline queue staging.
Oxidative Polymerization
Chemical Drying
Oil-based printing inks require a chemical reaction to transform from a liquid state into a solid, abrasion-resistant film. Oxidative polymerization describes the process whereby the unsaturated fatty acids in vegetable oils react with atmospheric oxygen to form a cross-linked polymer network. This drying mechanism is critical for offset inks printed on paperboard substrates, as it ensures the ink layer does not rub off during folding or stacking.
Catalytic driers, such as cobalt or manganese salts, are added to the ink formulation to accelerate this reaction.
Oxygen Availability
Adequate exposure to fresh air is essential for the ink film to dry completely through its entire thickness. Oxidative polymerization is a relatively slow process that can take hours or even days, during which the printed sheets must be protected from heavy pressure. If the oxygen supply is restricted, the ink remains tacky and can cause set-off or blocking in the delivery pile.
Air circulation within the print shop is designed to supply a steady stream of oxygen to the sheets.
Surface Cure
Highly absorbent paperboard can pull the solvent oils away from the surface too quickly, leaving the pigment unbound. Ink drying must be balanced with the absorption rate of the substrate. Correct paperboard porosity ensures that the solid ink film cures with high gloss.