Aluminium, the third most abundant element on the earth’s crust after oxygen and silicon, is extracted from an ore called Bauxite. The ore is refined to make ‘alumina’, a pure aluminium oxide. The aluminium metal is then produced from alumina by passing an electric current through it in a process called ‘electrolytic reduction’. The resulting silvery metal is the basis of a wide range of alloys made by adding small amounts of other metals to provide the specific characteristics needed for each application. For most alufoil packaging virtually pure aluminium is used but increasingly alloys are being ‘tailored’ in order to add strength and allow for reductions in thickness for the same performance.
Alufoil is a very thin sheet of aluminium ranging from about 0.006 mm to the upper ISO defined limit of 0.2 mm (200 µm). It is produced by first rolling heated ingots (hot rolling) down to coils of thickness between 2 and 4 mm. The coils are then successively cold rolled to the required foil thicknesses. A second foil rolling method, continuous casting, bypasses the ingot stage and converts molten metal directly into a thick strip which is immediately rolled into the coil from which the foil is then rolled.
To obtain the very thinnest foils, two layers are rolled simultaneously. This ‘double rolling’ results in the difference between the two surfaces – matt and polished – the matt side being the inner side during double rolling. The two layers of alufoil are then separated. The resulting large reels are slit to the widths needed for further processing for the required end use – flexible packaging, foil containers, lidding foils, household foil, heat exchanger foil, laminations for heat insulation materials, etc.
From plain aluminium foil many material specifications are produced. Packaging converting companies make an enormous variety of alufoil-based products by coating and laminating with other materials, printing, embossing, etc. Using plain foil in thicker gauges specialist manufacturers produce containers for fresh and cooked foods. Plain foil is also familiar in most domestic and professional kitchens. Its unique combination of properties – impermeability, flexibility, strength, ductility, recyclability, corrosion resistance, conductivity and compatibility with other materials – qualify aluminium foil for an infinite variety of uses, see Markets.