Anti-block Additives

Abstract

Anti-blocking is a term used to describe measures to prevent film sheets to stick together. Polyolefin films tend to adhere to each other due to strong van der Waals interaction or electrostatic charges when being in close contact (adjacent layers). The higher the temperature, pressure, and contact/processing time, the higher the tendency to stick to each other.

To avoid the adherence of layers due to a close contact, particulate matter is introduced into the film in a highly diluted concentration. By that measure a micro-rough surface is created, and contact area of film layers is minimized; the distance between the layers is maximized and adherence suppressed. Minerals used for that application should have little to no impact on the mechanical properties of the film; must not deteriorate transparency, haze, color, gloss of the film; and should be compatible with the film-processing process. Several minerals are used for this purpose: talc, calcined kaolin, cristobalite, precipitated silica, diatomaceous earth, mica, calcium carbonates, calcium sulfate (anhydrite), magnesium carbonate, magnesium sulfate, and feldspars.

Organic alternatives used for anti-blocking or anti-stick are amides, fatty acid amides, fatty acids, salts of fatty acids, silicones, or others. They work with different mechanisms compared to the inorganic anti-blocking additives, migrating to the film surface upon cooling and forming a release layer. Sometimes combinations of inorganic and organic anti-blocking additives are used. Organic additives typically have lower anti-blocking ability in comparison to the inorganic ones but better slip effect.

This entry summarizes the mechanisms of anti-blocking and subsumes results from literature on that subject with an emphasis on the mineral anti-blocking additives.