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Foil is a very thin sheet of rolled aluminium supplied in its pure form (‘commercial purity’) or in a variety of alloys and tempers which give a wide choice of tensile properties.
The thickness of foil ranges from the thinnest currently produced commercially at about 0.0065 mm (or 6.5 µm) to the defined upper limit of 0.2 mm (or 200 µm). Material thicker than 0.2 mm is defined as sheet or strip.
What are its Attributes?
• Abundance - aluminium is plentiful with no danger of world depletion.
• Barrier efficiency to light, gases, oils and fats, volatile compounds and water vapour
• Temperature resistance from deep-freeze to oven processing
• Heat conductivity and reflectivity
• Electrical conductivity
• Strength and durability
• Compatibility with foods and pharmaceuticals
• Ease of lamination and coating
• Flexibility
• Formability and non-returning dead-fold
• Decorative potential, brilliant or matt surface
• Printability by flexo, gravure and offset litho
• Non-toxicity
• Low weight
• Recyclability
• Corrosion resistance
• Cost-effectiveness - optimum performance yet resource economy
Technical Properties
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Specific gravity
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2.7
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Weight
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At 6.35 µm foil weighs 17.2 g/m2
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Melting point
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660°C
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Electrical conductivity
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37.67 m/mm2d (64.94% IACS)
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Electrical resistivity
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2.65 µΩ.cm
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Thermal conductivity
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235 W/m.K
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Thickness
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Foil is defined as metal measuring 0.2mm (or 200 µm and below)
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Surface finish
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Above 40µm aluminium foil has a brightly polished surface on both sides imparted by the rolling cylinders. Below 40µm one side has a matt finish due to the process of rolling two layers of foil simultaneously. If specified by the customer, foil can be supplied below 40µm thickness with both surfaces bright. Other surface finishes such as etched, grained or embossed can be supplied to meet particular customer needs.
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Impermeability
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The molecular structure of the metal provides a high performance barrier even at thicknesses under 6.5µm, the foil commonly used in liquid cartons. Alufoil is normally used with a supporting laminate of film or paper materials which further enhance the strength and barrier performance of the metal layer. A pouch laminate made up of 12 µm PET/7µm alufoil/50µm LDPE has a WVTR’* of less than 0.2 g/m2/day compared with a 12 µm PET/60µm LDPE laminate for which the WVTR is 1.5 g/m2/day.
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Corrosion Resistance
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The naturally-occurring surface oxide on all aluminium in the presence of oxygen in the atmosphere acts as a shield and renders foil substantially corrosion resistant. Aluminium is also chemically resistant in contact with substances in the pH range 4 to 9.
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Compatibility with food and chemicals
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Non-reactive except to substances of high acidity or alkalinity (see Corrosion Resistance). Resistant to most common compounds in solution.
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Formability
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Aluminium is very malleable and can be deformed considerably without losing its barrier integrity.
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Dead fold
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When fully annealed, aluminium foil retains no 'temper' and therefore retains its shape when deformed.
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Non-absorbency
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Non-absorbent and proof against grease, oil, water and other liquids.
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Hygiene
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Foil is sterile following annealing, and does not harbour or support the growth of bacteria.
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Toxicity
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Aluminium is present in many fresh vegetables and is non-toxic in amounts and compounds normally encountered. The metal does not accumulate in the body and is non-reactive with virtually all foods, drugs and cosmetics.
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Taste, odour
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Tasteless and odour-free, alufoil imparts no detectable taste or odour to foodstuffs.
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Opacity
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Foil is a solid metal. It transmits no light and is a total barrier to light including the UV spectrum.
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Reflectivity
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Reflects approximately 98% of radiant heat and light.
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Non-magnetic
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Aluminium is insignificantly magnetic and therefore provides excellent electrical shielding.
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Recyclability
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Aluminium is easily recycled. Plain aluminium foil can be compacted and re-melted. Laminated aluminium is processed to separate the supporting layers and the aluminium residue is reused in other applications. In addition, the energy contained in the thin foil component of a laminate can be recovered in the form of heat.
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*Water Vapour Transmission Rate.
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