Surface Topography
Airflow measurement provides a quantified assessment of the tactile and functional evenness of a paper surface. Practitioners utilize bendtsen smoothness to determine how readily a substrate accepts ink or maintains contact with a printing plate. The method records the rate of air escaping between a flat glass plate and the paper sample under a specific pressure.
A higher flow rate indicates a rougher surface with more voids.
Testing Mechanism
Standardized equipment applies a constant air pressure of 1.47 kilopascals through a measuring head with a narrow circular edge. Because bendtsen smoothness relies on the seal created against the fibres, any structural deviation in the sheet thickness impacts the result. The value is expressed in millilitres per minute.
Rougher boards might show values exceeding 500 millilitres per minute, whereas high quality coated grades often fall below 50 millilitres per minute. Sensitivity of the equipment makes regular calibration of the rotameter tubes essential for maintaining data integrity across different shifts at the paper mill.
Conversion Outcome
Uniformity in the surface profile ensures consistent ink transfer and prevents mottled appearances in solid print areas. While bendtsen smoothness offers a rapid check for mill production, it does not account for the compressibility of the sheet under high pressure printing nibs. Low values generally correlate with better varnish gloss and sharper halftone dot definition.
Boards intended for high speed rotogravure require lower air leakage values than those used for basic offset lithography.
