Advanced Thermoforming, 2nd Edition

Chapter 44Flexible Films

Written in cooperation with Claudia Müller and Peter Brass, Südpack Verpackungen GmbH & Co. KG, Ochsenhausen, Germany

44.1 FLEXIBLE PACKAGING MATERIAL

Flexible films are often multilayer films of polyamide/polyethylene, and they are chiefly used for thermoforming purposes. These films are processed on forming, filling, and closing machines to create vacuum packs. As described earlier in the book, multilayer films are composite films that combine the properties of their respective film layers:

Polyamide

• High barrier against oxygen and aromatic chemicals
• High thermal resistance
• High mechanical properties
• Good thermoformability

Polyethylene

• High water vapor barrier
• Sealability

Multilayer films consisting of polyamide/polyethylene can be produced as flat films by coextrusion, extrusion coating, or lamination, or as blow film by coextrusion.

As a rule, the thicker the polyamide layer, the deeper the film can be formed. Unlike rigid parts, parts made from flexible films are not dimensionally stable (Table 44.1). Subsequent to the forming procedure, the film is subject to a certain resilience, which is also referred to as immediate shrinkage. The free shrinkage and mold shrinkage phenomena intermingle, with free shrinkage playing a more important role in the dimensional changes during the processing of flexible films. The term “mold shrinkage” applies only when one talks about rigid parts.

Table 44.1 Flexible Films

Source: Courtesy of Südpack Verpackungen ...