Slip additives reduce friction between films, and between film and equipment, thereby facilitating movement through converting and downstream packaging operations. Slip additive effectiveness is measured in terms of the static or kinetic Coefficient of Friction (COF), a dimensionless number that represents the resistance to sliding of two surfaces in contact with each other. COF is equal to the force necessary to slide one surface over another divided by the force perpendicular to the contacting surfaces.
COF = (Force to cause sliding of film surfaces)/(sled weight)
ASTM D 1894-73 is a standard test to determine the COF of plastic films. In general, COF values over 0.50 are considered to be non-slip surfaces and values less than 0.20 are viewed as high-slip surfaces that can be prone to roll telescoping.
Slip additives range from traditional amide slips to newer specialty non-migratory grades that can meet requirements to perform well at higher temperature, provide improved reliability, and hold COF steady before and after laminating.