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.
Heatset Blistering
Surface Disruption
Moisture trapped within the core of a coated paper sheet can expand rapidly and rupture the surface when exposed to the high temperatures of a drying oven. Printers identify this thermal defect as heatset blistering, which typically occurs on double-sided coated papers printed on high-speed web offset presses. The result is the formation of small, unsightly bubbles on the printed surface that ruin the graphics.
Moisture Expansion
The drying oven of a web offset press heat-sets the ink by evaporating the solvent carrier at temperatures that often exceed one hundred degrees Celsius. If the paperboard or paper has high moisture content and the coating layer is too dense, the steam cannot escape through the surface pores. This trapped steam builds up pressure until it physically separates the paper plies or lifts the coating.
It occurs most frequently in heavily printed areas where the ink film acts as an additional barrier to moisture escape.
Moisture Management
Control of the paper’s moisture content during manufacture is the primary defense against this drying defect. Mills keep the moisture level below a critical percentage for grades destined for heatset web offset printing. Printers can also reduce the drying oven temperature to allow the steam to escape more gradually without causing a rupture.