Mineral Pigment Morphology Effects on Capillary Pressure and Vehicle Separation
Mineral pigment shape dictates coating pore diameter, where narrow platelet networks accelerate ink vehicle separation and induce print chalking.
Platy Kaolin
Pigment Geometry
Hydrated aluminum silicate minerals refined into thin, tabular particle shapes provide opacity and barrier properties to paper and board coatings. Industrial paper coating formulations incorporate platy kaolin to form overlapping particle structures that align parallel to the substrate surface during blade metering. Particles exhibit high aspect ratios, with diameters significantly larger than their thickness.
This flat shape blocks light transmission, enhances sheet gloss, and creates tortuous diffusion pathways for liquids and gases.
Coating Application
Blade coaters align plate-like mineral particles under high shear rates, constructing an impervious coating layer over raw paperboard fibers. Utilizing platy kaolin in topcoat formulations improves print holdout, preventing offset ink vehicles from draining prematurely into the porous paper base. The overlapping plate geometry covers surface fiber peaks efficiently, yielding smooth printing surfaces at lower total coat weights than spherical calcium carbonate pigments.
Converter operations benefit from improved barrier properties against oil and grease penetration in folding carton applications. Higher gloss values achieved after supercalendering enhance graphic reproduction quality for high-end packaging applications.
Rheology Constraint
High aspect ratio particle concentrations increase coating color viscosity at elevated solids content, causing blade bleeding or streaks during high-speed coater operations. Shear thinning behavior breaks down if particle aspect ratios exceed runnability limits.