Flat film extrusion: cast film

Flat film extrusion, commonly referred to as "cast film" or "film casting", is one of the processes used to manufacture films (with thicknesses ranging from 10 to 300 µm). Flat film extrusion is preferred when the polymer is low-viscosity and not well suited to sheath blowing operations (as in the case of polyamides), when the product is to be coated on a substrate (low-density or high-density polyethylene, polypropylene, polyethylene terephthalate), or when the film is to be beaded (as in the case of polypropylene or polyethylene terephthalate). In recent years, the demands of the film market have led to intensive developments in flat film extrusion technology, resulting in a mature production process for the manufacture of dimensionally accurate films from a very wide range of polymer materials.

Films produced by flat extrusion are mainly used in the packaging market. These may be food packaging or packaging for technical products, both of which require the development of sophisticated, highly technical films, either in terms of the number of associated materials, or the relative thicknesses of the layers obtained. Coextrusion, for example, is an increasingly popular technique for flat film extrusion, with systems exceptionally capable of up to 11 layers, but generally limited to 5.

This article is essentially limited to the single-layer film extrusion process. The flat film extrusion process is renowned for its excellent optical and dimensional properties. Cooling by means of a thermostatically controlled roll enables high production speeds (several hundred meters per minute) to be achieved, and has a significant influence on the morphologies obtained in the film.