Metallised film - AbsoluteAstronomy.com

Metallised films are polymer films coated with a thin layer of metal, usually aluminium. They offer the glossy metallic appearance of an aluminium foil

Aluminium foil

Aluminium foil is aluminium prepared in thin metal leaves, with a thickness less than , thinner gauges down to are also commonly used. In the USA, foils are commonly gauged in mils. Standard household foil is typically thick and heavy duty household foil is typically .The foil is pliable, and...

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.

Manufacture

Metallisation is performed using a physical vapour deposition

Physical vapor deposition

Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...

process. Aluminium is the most common metal used for deposition, 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 a metal foil could be made, in the range of 0.5 micrometres . This coating will not fade or discolour over time. While oriented polypropylene

Polypropylene

Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...

and PET

Polyethylene terephthalate

Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

are the most common films used for metallisation, nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

, polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

and cast polypropylene are also used .

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

EVOH

Ethylene Vinyl Alcohol, commonly abbreviated EVOH, is a formal copolymer of ethylene and vinyl alcohol. Because the latter monomer mainly exists as its tautomer acetaldehyde, the copolymer is prepared by polymerization of ethylene and vinyl acetate to give the ethylene vinyl acetate copolymer...

, but are not yet cost effective against foil laminates .

Table 1. Comparison of Metallised PET and aluminium foil

	Moisture (g/m².day)	Oxygen (mL/m².day)	UV light (%transmittance)
PET film, 12.7μm	31	465	91
Metallised PET	0.8	1.2	5
Aluminium foil 6μm .	0	0	0

Decoration

Metallised films were first used for decorative purposes as Christmas tinsel , 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. The controlled permeation

Permeation

Permeation, in physics and engineering, is the penetration of a permeate through a solid, and is related to a material's intrinsic permeability...

extends shelf life

Shelf life

Shelf life is the length of time that food, drink, medicine, chemicals, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption...

.

Metallised films are used as a susceptor

Susceptor

A susceptor is a material used for its ability to absorb electromagnetic energy and convert it to heat . This energy is typically radiofrequency or microwave radiation used in industrial heating processes, and also occasionally in microwave cooking...

for cooking in microwave oven

Microwave oven

A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...

s. An example is a microwave popcorn bag

Popcorn bag

A microwave popcorn bag is an engineered, enhanced, sealed paper bag in which un-popped popcorn is sold for the purpose of cooking popcorn in a microwave oven. These bags and their contents are sometimes referred to as microwave popcorn...

.

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 are used by AR-FF fire fighters for protection from the high amount of heat released from fuel fires. Silvered emergency blankets are also used to conserve a shock victim's body heat. These reflective materials might also be used as part of industrial and commercial insulation (for example, insulated shipping container

Insulated shipping container

Insulated shipping containers are a type of packaging used to ship temperature sensitive products such as foods, pharmaceuticals, and chemicals. They are used as part of a cold chain to help maintain product freshness and efficacy...

s.)

Insulating blankets made with Metallised PET were also used as insulation in aircraft until safety concerns resulted in their deprecation. In particular, it was found to be a major cause of the in-flight fire of Swissair Flight 111

Swissair Flight 111

Swissair Flight 111 was a Swissair McDonnell Douglas MD-11 on a scheduled airline flight from John F. Kennedy International Airport in New York City, United States to Cointrin International Airport in Geneva, Switzerland...

on September 2, 1998.

Electronics

Metallised films are used as a dielectric in the manufacture of a type of capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

used in electronic circuits.