Meaning
Measured friction values provide a ratio between the force required to move a surface and the pressure pushing those surfaces together. In polymer film production, coefficient of friction determines how easily a web travels over rollers or through packaging equipment. A high value indicates a sticky surface that may cause jams, while a low value suggests a slippery material.
This measurement is divided into static friction, for the force to start movement, and kinetic friction, for the force to maintain it. Precise control of these values is necessary for high-speed automated packaging.
Surface Interaction
Contact between two plastic films or a film and a metal plate involves microscopic surface roughness. Slip agents are added to the resin to bloom to the surface and create a lubricating layer. This layer fills the valleys and coats the peaks of the surface profile.
The resulting reduction in resistance allows for smoother handling and prevents the film from stretching or tearing during conversion.
Additive Influence
Loading levels of slip and antiblock agents directly dictate the final friction results. Small changes in the parts-per-million of oleamide can shift the value from a tacky zero point eight to a slippery zero point two. Moulders must monitor these levels because excessive additives can interfere with printing and heat sealing.
The migration of these chemicals is time-dependent, meaning the value often changes as the material ages.
Measurement Standard
Laboratory testing follows protocols like iso 8295 to ensure accuracy and repeatability across different production lots. A sled of known weight is pulled across the test material at a specific speed. The force is recorded by a load cell and converted into a dimensionless number.
Consistent testing environments are required because temperature and humidity can alter the surface characteristics and the recorded values.
