Mineral Coating Pigment Packing Micro Geometry and Pore Volume Distribution
Pigment micro-geometry and particle packing dictate coat pore volume distribution, controlling ink vehicle absorption rate, print gloss, and coat strength.
Void Volume Distribution
Pore Size Dispersity
Volumetric allocation and dimensional scale of interconnected air channels and capillary pores within a consolidated mineral coating define its internal void structure. In coated paper and packaging board, void volume distribution dictates ink solvent absorption kinetics, dry optical scattering efficiency, and fluid barrier performance. Mercury intrusion porosimetry and nitrogen gas adsorption quantify the fractional volume of micropores, mesopores, and macropores distributed across the coating layer.
A narrow distribution of uniform mesopores generates powerful, predictable capillary suction, which stabilizes ink setting during high-speed lithographic and flexographic printing runs.
Performance Impacts
Optical brightness and opacity depend on the concentration of voids sized near half the wavelength of visible light, which scatters light efficiently. If the void volume distribution shifts toward excessively large macropores, ink pigments penetrate too deeply into the coating layer, causing significant loss of print density and visual strike-through. A distribution biased toward fine micropores accelerates ink solvent separation while filtering resin molecules onto the surface, which enhances print gloss but risks ink set-off in the delivery stack.
In barrier coatings, minimizing total void volume is essential to block water vapor, oxygen, and liquid oil transmission.
Calendering Influence
Thermomechanical finishing directly modifies the internal pore network. Calendering compresses larger macropores first, narrowing the overall void distribution and decreasing total pore volume while preserving internal light scattering. Formulators manipulate the initial distribution by blending coarse calcium carbonates with fine platy clays and adjusting binder volume fractions.
Porosity measurements lose structural significance if the test method crushes fragile mineral networks during sample preparation.