Meaning
Surface interaction metrics define the resistance to sliding motion between a polymer and another material once movement has already begun. The dynamic coefficient of friction is a dimensionless value calculated as the ratio of the sliding force to the normal force. In film extrusion, this value determines how easily a web moves over rollers or through packaging machinery.
This reading differs from the static value, which measures the force required to initiate motion from a standstill.
Slip Performance
Additives known as slip agents migrate to the surface of a part to lower the resistance during contact. Measuring the dynamic coefficient of friction allows moulders to verify that these additives have reached the correct concentration at the surface. Lower values prevent the sticking and jerking motion known as stick-slip, which can cause surface defects.
This property is highly sensitive to the temperature of the contact surfaces during the test.
Winding Tension
Film manufacturers rely on consistent surface properties to produce flat, stable rolls of material. If the dynamic coefficient of friction is too high, the film may wrinkle or stretch as it moves through the winder. Conversely, excessively low values cause the roll to telescope or collapse during handling.
Controlling this variable ensures that the film maintains its integrity through subsequent printing and laminating steps.
Surface Degradation
Continuous sliding over metal surfaces can wear away the top layer of the polymer or the slip agent coating. Monitoring the dynamic coefficient of friction over a long production run identifies when the surface properties begin to drift due to heat or abrasion. Changes in this value often signal the need for cleaning the rollers or adjusting the additive loading in the melt.
A stable reading confirms that the material will perform predictably in the end-user’s high-speed packaging equipment. Consistent friction values support high efficiency in downstream conversion processes.
