PET film (biaxially oriented) 172928 225448726 2008-07-13T19:20:22Z 201.103.179.45 [[Image:Myla32rp.jpg|thumb|right| metallized boPET film, 32 layers of ~15 µm thickness each]] Biaxially-oriented [[polyethylene terephthalate]] (boPET) [[polyester]] film is used for its high [[tensile strength]], [[chemical]] and [[Shape|dimensional]] [[stability]], [[Transparency (optics)|transparency]], [[reflective]], gas and aroma barrier properties and [[electricity|electrical]] [[Electrical insulation|insulation]]. A variety of [[Company (law)|companies]] manufacture boPET and other polyester films under different [[Brand|trade names]]. In the US and Britain, the most well-known trade names are '''Mylar''' and '''Melinex'''. ==History and manufacture== Biaxially oriented PET film was developed in the mid-1950s, originally by [[DuPont]] and [[Imperial Chemical Industries|ICI]]. In 1960 and 1964 [[NASA]] launched the [[Echo satellite]]s, {{convert|100|ft|m|-1}} diameter balloons of metallized {{convert|0.005|in|mm|2}} thick boPET film. The [http://www.ampef.com/technology2.html manufacturing process] begins with a film of molten [[Polyethylene terephthalate|PET]] being [[Plastics extrusion|extruded]] onto a chill roll, which quenches it into the amorphous state. It is then biaxially oriented by drawing. The most common way of doing this is the sequential process, in which the film is first drawn in the machine direction using heated rollers and subsequently drawn in the transverse direction, i.e. [[orthogonality|orthogonally]] to the direction of travel, in a heated oven. It is also possible to draw the film in both directions simultaneously, although the equipment required for this is somewhat more elaborate. Draw ratios are typically around 3 to 4 in each direction. Once the drawing is completed, the film is "heat set" or [[crystal]]lized under tension in the oven at temperatures typically above 200 °C. The heat setting step prevents the film from shrinking back to its original unstretched shape and locks in the molecular orientation in the film plane. The orientation of the polymer chains is responsible for the high strength and stiffness of biaxially oriented PET film, which has a typical [[Young's modulus]] of about 4 GPa. Another important consequence of the molecular orientation is that it induces the formation of many crystal nuclei. The crystallites that grow rapidly reach the boundary of the neighboring crystallite and remain smaller than the wavelength of visible light. As a result, biaxially oriented PET film has excellent clarity, despite its [[semicrystalline]] structure. If it were produced without any additives, the surface of the film would be so smooth that layers would adhere strongly to one another when the film wound up, similar to the sticking of clean glass plates when stacked. To make handling possible, microscopic inert inorganic particles are usually embedded in the PET to roughen the surface of the film. Biaxially oriented PET film can be [[aluminium|aluminized]] by [[evaporation|evaporating]] a [[Thin-film_deposition|thin film]] of metal onto it. The result is much less permeable to gasses (important in [[Modified atmosphere|food packaging]]) and reflects up to 99% of light, including much of the [[infrared]] spectrum. For some applications like food packaging, the aluminized boPET film can be laminated with a layer of [[polyethylene]], which provides sealability and improves puncture resistance. The polyethylene side of such a laminate appears dull and the PET side shiny. Metallized [[nylon]] (or "foil") [[balloon]]s used for floral arrangements and parties are often mistakenly called "Mylar", one of the trade names for boPET film. Other coatings, such as conductive [[indium tin oxide]] (ITO), can be applied to boPET film by [[sputter deposition]]. ==Uses for boPET film== Uses for boPET polyester films include, but are not limited to: '''[[Flexible Packaging]] and food contact applications''' * Laminates containing metallized boPET film protect food against oxidation and aroma loss, achieving long shelf life. Examples are coffee "foil" packaging and pouches for convenience foods. * Attractive glossy or matte surfaces on the outside of packages are achieved using boPET film. * White boPET film is used as lidding for dairy goods such as [[yoghurt]]. * Clear boPET film is used as lidding for fresh or frozen ready meals. Due to its excellent heat resistance, it can remain on the package during microwave or oven heating. * Roasting bags '''Covering over paper''' * A clear overlay on a [[map]], on which notations, additional [[data]], or copied data, can be drawn without damaging the map * Metallized boPET is used as a mirror-like decorative surface on some book covers, T-shirts, and other flexible cloths. * Protective covering over buttons/pins/[[badge]]s * The glossy top layer of a [[Polaroid Corporation|Polaroid]] [[SX-70]] photographic print * As a backing for very fine [[sandpaper]] * boPET film is used in bagging [[comic books]], in order to best protect them during storage from environmental conditions (moisture, heat, and cold) that would otherwise cause paper to slowly deteriorate over time. This material is used for [[archival quality]] storage of documents by the [http://lcweb.loc.gov/preserv/supply/specific.html Library of Congress] *For protecting the spine of important documents, such as [[medical records]]. '''Insulating material''' * An [[Electrical insulation|electrical insulating]] material * As base material for audio or video [[magnetic tape|magnetic recording tape]]s * [[Thermal insulation|Insulation]] for houses and tents in ''cold'' environments, covering the inner walls with the metallized surface facing ''inward'', thus reflecting heat ''back into'' the space * [[Thermal insulation|Insulation]] for houses and tents in ''hot'' environments, covering the outer walls with the metallized surface facing ''outward'', thus reflecting heat ''away from'' the space * Five layers of metallized boPET film in [[NASA]]'s [[spacesuit]]s make them [[radiation]] resistant and keep astronauts warm. * Metallized boPET film "[[Space blanket|emergency blankets]]" conserve a [[Shock (medical)|shock]] victim's body heat. * As a thin strip to form an airtight seal between the control surfaces and adjacent structure of aircraft, especially [[glider]]s. * Light insulation for [[indoor gardening]]. * [[Wildland]] fire shelters. * Proximity(aluminized) suits used by AR-FF fire fighters for protection from the high amount of heat relase from fuel fires. * Aluminized boPET films are no longer used as thermal/acoustic insulation in aircraft since they were found to have been a factor in the [[Swissair flight 111|Swissair Flight 111 crash]]. The [http://lessons.air.mmac.faa.gov/l2/SA111/accident accident investigation] showed that the aluminum layer prevents the film from self-extinguishing in a fire under the conditions in aircraft. '''Solar and marine applications''' * [[Solar sail]]s as an alternative [[spacecraft propulsion|means of propulsion]] for [[spacecraft]] such as [[Cosmos 1|Cosmos 1]] * Metallized boPET [[Sun|solar]] curtains reflect sunlight and heat away from windows. * Aluminized, as an inexpensive [[solar eclipse]] viewer, although care must be taken, because invisible fissures can form in the metal film, reducing its effectiveness. * High performance [[sail]]s for [[sailboat]]s and [[hangglider]]s '''Electronic / acoustic applications''' * Very thin boPET film is often used as the [[diaphragm material]] in [[electrostatic loudspeaker]]s and [[Microphone#Electret capacitor microphones|electret microphones]]. * boPET film has been used in the production of [[banjo]] & [[drumhead]]s since 1958 due to its durability and acoustical properties when stretched over the bearing edge of the drum. They are made in single- and double-ply versions, with each ply being between 2 [[Thou (unit of length)|mils]] and 10 mils (0.05 – 0.25 mm) in thickness, with a [[clear]] or [[opaque]] surface, originally used by the company [[EVANS]]. * boPET film is used as the substrate in practically all [[magnetic tape|magnetic recording tape]]s. * Metallized boPET film, along with other plastic films, is used as a [[dielectric]] in foil [[capacitor]]s. *Clear boPET bags are used as [[packaging]] for audio media such as [[compact discs]] and [[vinyl records]]. '''Graphic arts''' * Often [[engineering plans]] or [[architectural drawing]]s are plotted onto sheets of boPET film. The boPET sheets become legal documents from which copies or [[blueprint]]s are made. boPET sheets are more durable and can withstand more handling than [[bond paper]]. * [[Overhead transparency film]] for [[photocopiers]] or [[laser printers]] (boPET film withstands the high heat). '''Other''' * For materials in [[kite flying|kite]]s * Covering [[glass]] to decrease probability of shattering * In theatre effects as [[confetti]]. * As the adhesive strip to attach the string to a [[teabag]] * One of the many materials used as Windsavers or valves for [[valved harmonicas]] * As a light diaphragm material separating gases in hypersonic shock and expansion tube facilities * On California farmland, highly reflective aluminized PET film ribbons are tied to the plants to create shimmers from the sun for an effect similar to a [[scarecrow]]. ==External links== *''Plastics: Background Information for Teachers''. by The American Plastics Council [http://www.teachingplastics.org/hands_on_plastics/intro_to_plastics/teachers.html (HTML format)] or [http://www.teachingplastics.org/hands_on_plastics/pdf/teachers.pdf (PDF format) - 1.9MB)], which includes the "[[Recycling Symbol|chasing arrow]]" recycling symbols (PET is #1) and a description of plastics. * Links to most manufacturers of boPET films are available at the [http://www.ampef.com/ AMPEF website] [[Category:Plastics]] [[Category:Dielectrics]] [[Category:Reflective building components]] [[de:Polyethylenterephthalat]] [[pt:Filme PET (poliéster)]] [[ru:Майлар]]