Substrate Holdout and Pinhole Formation in Inline Flexographic Coating
Substrate holdout and pinhole control require matching anilox coat weight delivery to sheet absorbency while regulating dynamic wetting and surface skinning.
Bendtsen Porosity
Structural Measurement
Measurement of the air permeability of paper and board provides data on the structural uniformity of the sheet. This property, known as Bendtsen porosity, measures the rate of air flow through a specified area of the paper under a constant pressure difference. Substrates with high values allow air to pass through easily, indicating a highly porous and open fibrous network.
Controlling this property is necessary for optimizing ink absorption on printing presses, where uneven porosity can lead to blotchy ink coverage or mottled finishes across the surface.
Test Method
Clamping the paper specimen between a flat glass plate and a circular metal head with a defined force initiates the standardized test procedure. The apparatus forces air through the paper at a pressure of one point forty-seven kilopascals, measuring the resulting flow rate in milliliters per minute. In this test, Bendtsen porosity values increase when the sheet structure is less dense.
Regular calibration of the capillary flowmeters ensures the reliability of the measurements.
Print Performance
Absorption of ink solvents during the printing process relies heavily on the void structure of the paper. High Bendtsen porosity can lead to excessive ink penetration, causing print problems like strike-through on thin paperboards. Low porosity may cause ink smear due to slow drying times.