Metallised film

Metallised films (or metallized films) are polymer films coated with a thin layer of metal, usually aluminium. They offer the glossy metallic appearance of an aluminium foil at a reduced weight and cost. Metallised films are widely used for decorative purposes and food packaging, and also for speciality applications including insulation and electronics.

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History

Manufacture

Metallisation is performed using a physical vapour deposition process. Aluminium is the most common metal used for depsotion, but other metals such as nickel or chromium are also used. The metal is heated and evaporated under vacuum. This condenses on the cold polymer film, which is unwound near the metal vapour source. This coating is much thinner than an metal foil could be made, in the range of 0.5 microns ^[1]. This coating will not fade or discolour over time. While oriented polypropylene and PET are the most common films used for metallisation, nylon, polyethylene and cast polypropylene are also used ^[2].

Properties

Metallised films have a reflective silver surface similar to aluminium foil. The coating also reduces the permeability of the film to light, water and oxygen. The properties of the film remain, such as higher toughness, the ability to be heat sealed, and a lower density at a lower cost than an aluminium foil. This gives metallised films some advantages over aluminium foil and aluminium foil laminates. It was thought that metallised films would become a replacement for aluminium foil laminates, but current films still cannot match the barrier properties of foil. Some very high barrier metallised films are available using EVOH, but are not yet cost effective against foil laminates ^[3].

Table 1. Comparison of Metallised PET and aluminium foil

Uses

Decoration

  Metallised films were first used for decorative purposes as Christmas tinsel ^[1], and continue to be used for items such as wrappers and ribbons. The metallic helium filled novelty balloons given as gifts are made of metallised PET.

Packaging

Both metallised PET and PP have replaced foil laminates for products such as snack foods, coffee and candy, which do not require the superior barrier of aluminium foil. Metallised nylon and polyethylene are used in the meat export market.

Metalised films are used as a susceptor for cooking in microwave ovens. An example is a microwave popcorn bag.

Many food items are also packaged using metallised films for appearance only, as these produce a package with greater sparkle when compared to competing products that use printed paper or polymer films.

Insulation

Metallised PET films are used in NASA's spacesuits to make them radiation resistant and keep astronauts warm, and in proximity (aluminized) suits used by AR-FF fire fighters for protection from the high amount of heat relase from fuel fires. Silver emergency blankets used to conserve a shock victim's body heat also used metalised films.

Electronics

Metallised films are used as a dilectric in the manufacture of capacitors.

See also

• Popcorn bag

References