Capillary Absorption Testing Standards in Coated Printing Substrates
Substrate capillary absorption speeds govern ink setting rate, dryer energy consumption, and cross-web print defect thresholds across high-speed converting runs.
Pore Radius Distribution
Microstructure Metric
Analytical void space measurements describe the volume allocation of microscopic channels within paper coating layers and fibre networks. Characterized through mercury intrusion porosimetry or nitrogen adsorption, pore radius distribution defines the relative frequency of narrow capillaries and large inter-particle voids in coated paperboard. The metric applies to coated printing papers, barrier substrates, and absorbent towel stocks.
It fails to predict fluid transport when swelling fibres alter internal network geometries upon contact with water.
Capillary Mechanics
Capillary pressure scales inversely with pore radius, making narrow voids the primary drivers of rapid initial liquid absorption. Fine ground calcium carbonate pigments create narrow pore structures that exert strong capillary suction on ink solvents. Coarse pigments and plate-like kaolin clays form larger inter-particle voids that permit high total void volume but generate lower capillary pressure.
Pigment packing, latex binder migration, and calender nip pressure modify the ratio of small to large pores across the coating thickness. Narrow pores accelerate ink vehicle setting, whereas larger pores allow rapid ink pigment penetration that can lower printed image density. Mercury porosimetry forces liquid mercury into voids under incrementally increasing pressure, calculating pore radiuses from the Washburn equation.
Understanding void dimensions allows paper technicians to engineer coating colors for precise print performance.
Coating Optimisation
Paper coating development relies on void structure profiling to optimize ink drying and surface strength balance. Coating mills measure pore structures to maintain uniform holdout characteristics across paperboard grades. Structured pore networks prevent binder migration during high-temperature dryer passage.
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.