Aluminum foil on reel.In addition to the alloy, the material temper also has an influence on the properties of the aluminum. A distinction is made here between “soft” and “hard” aluminum, as well as the intermediate forms “quarter hard”, “semi hard” and “three-quarter hard”.
After (several times) rolling operations, the aluminum is in a hard condition. If the rolls are then heated for several hours in an oven, the material is transformed to a soft state. In addition, rolling oil residues also evaporate on the film. This is particularly important for the production of laminates, because oil residue is degrading or preventing the adhesion of the adhesive. For laminates, mainly soft aluminum is used. This also applies to coatings – most of the lacquers also do not adhere to films with oil residues.
If, however, aluminum foil is to be used in the “hard” state for laminates and lacquered films, the films can also be degreased chemically. The aluminum foil is “washed” by a bath in chemical substances instead of heating the foil in the oven.