Traditionally the films we know come from oil processing. However, today we can mention other raw materials such as cellulose, starch and sugars. These are classified as renewable sources and are typically used to make biodegradable and compostable films.
Le pellicole più comunemente utilizzate sono: il polipropilene (PP), il polietilentereftalato (PET) e il polietilene (PE). Examples of compostable films are cellulose acetate and PLA.
The production of traditional films is similar to each other. It starts with granules that are introduced into extruders or heated hollow cylinders that house a worm screw inside. The extruder has the task of homogenizing and melting all the components. The compound obtained is pushed through a die which provides a continuous “plate” or “tube” of semi-melted polymer.
Thanks to the operation of “orientation” or stretching of the sheet both longitudinally and transversally, the appearance, thickness and properties we know are given to the film. In the image below an example of sequential orientation. From left to right, it is possible to appreciate in order: the granule loading hopper (resin), the actual extruder (Twin-screw extruder), the die (T-die), first orientation station in the machine direction ( Machine direction stretcher) and the second station of orientation in the transverse direction (Transverse direction stretcher). The operation ends with the wrapping of the film (Winder)
The film can receive further processing such as corona treatment, application on one side of acoating,metallization.