In the case of paper/PE/aluminum complex, the most difficult part to obtain a good adhesion is aluminum. In fact, the surfaces of the apparently smooth aluminum ribbons, if examined at the electronic almicroscope, present numerous imperfections. These are caused by the used laminating systems that leave on the surfaces of the oil that, although not too high, penetrate the imperfections thus inhibiting the adhesion.
In addition, the aluminum strips can be contaminated by contact with paper and inking printing. A system must therefore be used to perfectly clean the surfaces and create the bonds necessary for the adhesion. The most effective system is flame treatment. Which guarantees the superficial cleaning and the necessary adhesion until obtaining a wettability with distilled water.