Paper and board roughness / smoothness testing

There are several test methods for measuring the roughness or smoothness of paper including surface profiling and lateral air flow measurement.

Profilometry method

Contact or stylus profilometers such as Pira's portable Handysurf E-35B move a loaded diamond probe across the surface and record the vertical movement of the stylus caused by the irregularities. Several relevant standards have been published, including ISO 3274.

Air leakage methods

The most common method of testing smoothness or roughness in the paper and board sector is by one of three air leakage methods.

Bendtsen roughness is achieved by clamping the test piece between a flat glass plate and a circular metal head and measuring the rate of airflow in ml/minute between the paper and head. The Bendtsen technique is designed to work in the range 30-1500 ml/minute. Applicable test methods are BS 4420, ISO 8791/2, DIN 53108 and SCAN P21. Pira is UKAS, ISO 17025 accredited to BS 4420.

Bekk smoothness is again measured by the air leak method but, unlike the Bendtsen method, air is drawn across the surface of the test piece under a partial vacuum. Applicable standards are ISO 5627, Tappi T479 and DIN 53107.

Parker print-surf roughness - designed specifically for measuring the surface roughness of printing papers under simulated printing press conditions. The instrument contains an internal gas flow restrictor whose pressure drop versus flow characteristics is closely controlled. The air flow is calculated by comparing the pressure drop across the measuring head and the paper test surface with that across the flow restrictor. Applicable standards are BS 6563, ISO 8791/4, Tappi T555 and SCAN P76.