Coefficient of Friction (CoF) / Slip coefficient testing

The coefficient of friction of a material is the ratio of the force acting between the material surfaces to the pulling force. A lower friction coefficient indicates a lower resistance to the sliding motion - measurements are usually made material surface against itself, as CoF values can vary with surface finishes and contamination on test surfaces.

There are two components of friction, static and dynamic. Static friction is the force required to initiate movement between the two surfaces, whereas dynamic friction (often called kinetic friction) is the force required to maintain motion between the surfaces.

The coefficient of friction, or the slip, is a critical property of all materials which run on high speed printing and packaging lines. Some examples where coefficient of friction is routinely specified include photocopier papers, cartons and flowrapping films.

Slip coefficient = 1/coefficient of friction

Some applications where a high coefficient of static friction is desirable include sacks, bags and corrugated cases which need to resist sliding when stacked.

Pira use an RDM horizontal plane instrument to measure both static and dynamic coefficients of friction in accordance with British and International standard BS ISO 8295 and ASTM D1894 for plastic films and sheeting. Uncoated writing and printing papers are tested to Tappi T549, corrugated and solid fibreboard are tested to Tappi T816 and general paper and board to British and International standard BS ISO 15359.

Our UKAS, ISO 17025 accredited testing is performed to the ASTM standard D1894.