This section discusses barrier films as are used in the packaging industry for manufacturing film covers. Unlike films which are only used for covering goods, barrier films meet far more demanding requirements with respect to water vapor permeability because their thickness is more homogenous. In the packaging sector, and in particular in the field of corrosion protection using the desiccant method, two different types of film are used:
- Polyethylene films (PE films)
- Aluminum composite films
5.3.1 Polyethylene films (PE films)
Two different types of PE films are distinguished:
||Density approx. 0.92 ... 0.94 g/cm³
||Density approx. 0.94 ... 0.96 g/cm³
Films used in packaging are generally made of low-density polyethylene. The temperature range in which they can be used can be given as approx. +40 °C through approx. -20 °C under given testing conditions (DIN 55 530, 1986-01 water vapor permeability WVP).
When heat sealing the films, you should ensure that appropriately adapted equipment is used. Consult the manufacturer for details on the temperature, time and pressure to be used when sealing the films.
5.3.2 Aluminum composite films
The technical properties of aluminum films (strength, water vapor permeability WVP) are described in TL 8135-0003, Edition 9 and in DIN 55 531, 1988-09. Compliance of the aluminum composite films with the standards named above is indicated by printed markings on the film. In addition, the necessary heat-sealing conditions (temperature, time and pressure) are shown. The temperature range in which aluminum composite films can be used can be derived from the testing conditions and can be assumed to be -35 °C through +70 °C.
The most important property of both types of film with regard to shipping is their water vapor permeability. You will find guideline values for this in section 4.4.4.
The most important processing notes for aluminum composite films are printed on the tested films.
Figure 34: Example of processing notes on aluminum composite film