Aluminum foil and metallized PET Film (MPET): Applications & Differences
Aluminium foil has been used for more than 100 years especially in the packaging industry. But meanwhile a serious competitor has entered the arena. Metallized PET film covers an ever-growing range of applications, making it one of the fastest growing segments in the flexible packaging market.
At first sight, the two types of films are similar. However, they offer very different properties, making each of them more or worse suitable depending on the applications.
Properties of aluminum foil
Aluminium foil is usually made of pure aluminium, with an aluminium content of at least 99%. In a series of passes through rolling mills the aluminium reaches the desired thickness.
Very thin foils are double-rolled together in the last step and later, separated again This process produce two kind of natural finishes: the outer side of the foil touching the mill work rolls gets a “bright” finish, while the side contacting the other aluminium foil (foil-to-foil) gets a “matte” finish.
The aluminium is solidified by the cold rolling, becoming hard and brittle. Nevertheless, a subsequent thermal treatment in an annealing furnace makes the films soft and flexible again.
Food packaging made of Aluminium
Chocolate wrapping made of Aluminium foil
Aluminium foils with a thickness of about 12-20 μ possess barrier properties. This means that those foils are impermeable to water and gases. Thinner foils cannot guarantee the same 100% barrier properties. However, they also offer barrier properties and ensure that food stays fresh longer because of its light protection.
Aluminium foil is easily deformable without losing its barrier properties.
aluminium foil is physiologically harmless to food. However, acidic, alkaline and salty foods should not be in contact with the film. Aluminum foil is light and resistant to water, water vapor, grease and gas, it reflects light, heat and UV rays and does not charge electronically. Moreover, it is fire resistant and easy to recycle.
For packaging, it is rarely used pure aluminum foil. In most cases, the aluminum foil is laminated with plastic films (eg PET, PE, or PP) or paper. One then speaks of aluminum composite films. Composite films have some advantages over pure aluminum foils, for example, higher resistance to rusts and/or stiffness. In addition, aluminum foil can be painted and printed to meet the requirements of modern packaging.
Aluminium bands can be deep-drawn to produce containers or trays and cans. It then keeps the deep-drawn shape. Aluminum can be bent and folded without losing its barrier properties.
Properties of PET-met film
Aluminium coffee capsules
Coffee capsules are also made of Aluminium
In contrast to aluminum foils, which are made entirely of light metal, metallized PET foils are plastic foils which are only evaporated with aluminium powder in a high vacuum. For this process, it is used pure aluminium in powder form with an aluminium content of at least 99,98%. The films produced this way obtain a metallic shine and thereby achieve a special optical effect.
In addition to the optical effect, the aluminum vaporization serves in particular to improve its barrier effects against vapours, gases and aromas in comparison to non-metallized plastic film. Overall, the metallized PET films are less gas-tight than “real” aluminum foil, but more tear resistant, more flexible and lighter. Also, they are less sensitive to corrosion and not as winkle-prone as pure aluminium foil.
You can see through PET-met foils,
not through aluminum foils.
PET-met films are made of only 1% of the aluminum that would have been needed for an aluminum foil. Therefore, PET-met is especially interesting as a cost-effective and more environmentally friendly alternative to aluminum.