Grade Substitution Shipped under an Unchanged Product Name
Unannounced paper grade substitution alters structural fiber bonding and surface chemistry, demanding dockside physical and chemical testing before press loading.
Bendtsen Roughness ISO 8791
Surface Topography
Measurement of paper texture relies on the volume of air leaking between a flat glass plate and a specimen under specific pressure. The bendtsen roughness iso 8791 method quantifies this flow in millilitres per minute to define the tactile and visual quality of the substrate. It applies to most paper and board products except those with very high air permeability or extreme surface irregularities.
Airflow Mechanism
A constant pressure difference is maintained across the measuring head which rests on the paper sample. Because no sheet is perfectly flat, air escapes through the microscopic valleys between the glass ring and the fibre network. The rate of this escape increases as the surface becomes more irregular.
High readings indicate a coarse profile while low readings suggest a smooth surface suitable for fine detail.
Print Interaction
Smoothing treatments at the mill adjust the final reading to meet specific ink transfer requirements. Lithographic printing often requires a low bendtsen roughness iso 8791 value to ensure uniform contact between the blanket and the paper. If the surface is too coarse, ink fails to reach the deepest recesses of the grain.
Such failure creates a mottled appearance in solid areas and breaks up the clarity of halftone dots. Proper calibration of the measurement equipment prevents erroneous grading of stock destined for high speed presses.