Mercury Intrusion Porosimetry ISO 15901 Dynamic Surface Absorption Inspection Protocols
ISO 15901-1 porosimetry paired with dynamic sorption testing qualifies coating pore structures to prevent back-trap mottle and ink setting failures on press.
Coating Structure Clearance
Application Geometry
Metering geometry in blade and rod coaters determines the physical gap through which wet pigment suspension passes onto a moving paper web. Coating structure clearance defines the spatial separation between the metering element and the substrate surface under dynamic hydrodynamic pressure. High-speed liquid application relies on this dimension to establish the initial wet coat weight prior to capillary absorption into the base stock.
Liquid shear stress inside this zone frequently exceeds one million reciprocal seconds, which alters the rheological behavior of clay and calcium carbonate formulations. The physical threshold stops applying once the wet layer settles and liquid filtration into the fibre network commences.
Fluid Mechanics
Hydrodynamic force generated within the fluid wedge exerts an upward lift on the metering blade during reel production. Coating structure clearance adjusts dynamically as base sheet roughness and web tension fluctuate across the machine width. Lower gap dimensions increase shear forces, forcing tabular kaolin particles to orient parallel to the paper plane.
Higher gap values allow random orientation, which increases pore volume but reduces surface gloss after supercalendering. Dewatering rate accelerates when the base sheet exhibits high air permeability, shortening the time available for fluid levelling before immobilisation.
Defect Limit
Excessively tight settings cause streak formation when large agglomerates lodge against the metering edge. Coating structure clearance must exceed the ninety-nine percentile particle diameter of the slurry to prevent continuous scratches.