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 such as photocopier papers and cartons.
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.
Smithers Pira use an RDM horizontal plane instrument to measure both static and dynamic coefficients of friction in accordance with International standard ASTM D4917 for paper. 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.
Smithers Pira is UKAS, ISO 17025 accredited for testing to ASTM D4917.