Films can be simple but can also be quite complicated and sophisticated.
Films range from monolayer to multilayer coextruded films.
Coextrusion is an efficient and delicate production process. Today the number of layers in coextrusion range from 2 up to 11 layers.
Specialty films may even contain more than hundred layers.
Coextrusion of different polymers requires proper understanding of the flow behaviour and rheology once the materials get into contact with each other in the die.
The main production processes for films are:
In the cast film process, the polymer is cast on a chill roll. This allows rapid cooling of the melt. By "playing" with the chill roll temperature, it is possible to influence the film morphology.
Cast film are used for thermoforming applications.
Conventional blown film is widely used for film production. It is flexible as it is is possible to change the blow-up ratio.
Cooling is less efficient in comparison with cast film. This implies that films are more crystalline and are commonly used for lidding and pouch films.
Water quenched films
An upcoming technology for the the production of barrier films. The technology for the commercial production of multilayer barrier films was introduced by Brampton Engineering in the 90's. Today there are several machine suppliers offering this technology.
Rapid quenching by direct water contact results in a morphology that makes the films highly transparant and ideal for thermoforming.
Biaxially oriented films
Basically, there are 2 processes for the production of bioriented or stretched films: double bubble and tenter frame. The tenter frame process can be sequentially or simultaneously.
The main reason for stretching is increasing the crystallinity of the films which will result in improved transparency, mechanics and barrier.
Double bubble film
Double bubble stretching can be used for the production of bioriented films but is also used for the production of:
Double bubble films is sometimes also referred to as triple bubble films when an annealing step is applied after the orientation.
The Extrusionists - version 1.3 - September 2016