Most polyolefin exhibit a degree of thickness and hence can’t be readily processed into packaging films without the presence of additives to ease their ability to separate and slide. Slip agents are used in conjunction with antiblocking agents to reduce the coefficient of friction. They are designed to be miscible with the molten polymer, but to separate out as the polymer crystallizes forming a very thin surface layer. It is possible for some of this surface film of antislip agent to be lost by transfer to metal rollers during processing.
Effectiveness of slip is normally determined by coefficient of friction (COF). COF is a ratio of the force required to slide one layer of film across another, relative to the force exerted on it.