Pore Network Structure Modulating Offset Ink Vehicle Absorption Rates
Narrow coating pore throats below 0.05 micrometres maximize capillary pressure, driving rapid ink vehicle separation and set speed on offset press.
Ink Tack Buildup
Tack Evolution
The progressive increase in the cohesive stickiness of an ink film during the printing process alters the force required to separate the printing plate from the paper substrate. Operators monitor ink tack buildup to ensure that the cohesive forces do not exceed the surface strength of the paperboard during a long press run. An uncontrolled increase in tack can lead to fiber tearing or coating pick.
Solvent Loss
As the offset ink is distributed through the roller train, the volatile solvents begin to evaporate and the liquid vehicle starts to penetrate the paper surface. This rapid extraction of the light oils causes the remaining ink resins to polymerize and concentrate on the surface. Consequently, the viscosity and tack of the ink film rise rapidly within the first few seconds of printing.
If the ink chemistry is mismatched with the substrate’s porosity, the tack builds up too quickly and causes the paper fibers to pull apart in the printing nip.
Press Management
Pressroom technicians regulate the temperature of the roller chilled-water system to control the evaporation rate of the solvent. Adding a small amount of reducing oil or gel to the ink can also slow down the setting rate and limit tack development. This control keeps the ink stable and prevents print defects during high-speed production.