Surfactant Diffusion Rate Impact on Air Entrainment Thresholds in Curtain Coaters
Surfactant diffusion kinetics govern dynamic surface tension within millisecond curtain residence times, dictating high-speed air entrainment speed thresholds.
Gurley Porosity
Permeability Measurement
Air resistance through paper and paperboard substrates governs ink absorption, coating holdout, surface strength and vacuum handling performance during converting operations. Physical testing standard TAPPI T460 defines Gurley porosity as the time required for one hundred cubic centimeters of air to pass through a specific substrate area under constant pressure. Higher air resistance time indicates a dense, tightly closed sheet structure.
Low values correspond to porous, highly permeable fibrous networks.
Test Procedure
Standard testing apparatus clamping holds a circular paper specimen between two cylinders while an inner cylinder falls under its own weight. This displacement forces ambient air through a fixed surface area of one square inch. Measuring Gurley porosity provides mill technicians with feedback on refining degree and pressing density.
Densely refined fibers create long tortuous pathways for air flow, yielding high Gurley values above fifty seconds. High porosity values correlate with reduced penetration of barrier coatings into the paperboard matrix during fluid application.
Converting Property
Suction cup material handling equipment requires minimum air resistance to lift heavy packaging boards without loss of vacuum. Uncoated porous papers with low Gurley porosity permit excessive air leakage through the sheet thickness. Insufficient air resistance results in sheet feeding failures on automatic folding carton machinery.