February 28, 2008

Characteristic of Aluminum Foils

Aluminum foil is used where the ultimate in protection from moisture or oxygen is required. It is also noted for the attractive appearance of its reflective surface. If it is used for its barrier properties alone, foil is best put on the inside of the package or buried in the walls of the container, to protect it from damage. It is very vulnerable to scratching and abrasion when it is exposed. Lacquer or varnish will help to protect it, and such coating can be tinted to produce some beautiful effects, so that almost any metallic color can be achieved. Various matte or embossed texture is also available.

Aluminum foil in the softest temper will dead fold with no spring back. This facilitates forming it into any desired shape. Unfortunately, it also makes it wrinkle easily, so that great care must be used in handling to avoid spoiling its smooth surface. Since aluminum is very ductile, it can be stretched quite a bit if the proper tools are used. Pouches are sometimes made in this way for bulky items by forming pockets to conform to the shape of the product. However, aluminum has rather poor tensile strength and tears rather easily. For most applications it is usually laminated to paper, both to reduce cost and to give it the stiffness and tensile strength necessary for handling on packaging machinery.

Character of aluminum foil is generally smooth and shiny, but it is possible to get embossed or brushed textures which are very attractive. Gauge of 0.001 inch and below are usually produced by pack rolling; that is, two layers are put through the rolls together. This produces a glossy finish on one side and a satin finish on the other where the two sheets are in contact. The superior barrier properties of metal foil put it in a class by itself. In appearance foil has a luster and color that add glamour to any package. On the debit side it is higher in cost than the commonly used papers and films, especially because it must often be laminated to paper to make it usable.

Aluminum foil in gauges above 0.0007 inch is impermeable to moisture and gases. Thinner gauges have pinhole that make the foil permeable to a slight degree. Chemical resistance to solvents and grease is good, but resistance to water is only fair. Resistance to acids, except very mild acids, and to alkalis is poor unless it is protected with a coating of wax or lacquer. Aluminum foil is unaffected by sunlight or by temperatures up to 550 oF. 

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