The two main methods of surface pretreatment for aluminum boxes mentioned in professional materials are chromic acid passivation and phosphating, which mainly prevent corrosion on the surface of the aluminum box and improve its adhesion to other materials. These pre-treatment methods have been widely applied in the metal reprocessing industry, not just for the needs of lamination. For example, when spraying or painting, passivation and phosphating pre-treatment must be carried out on the surface of raw aluminum. Otherwise, it is difficult to reprocess or decorate the surface of raw aluminum due to its low tension and easy corrosion.
The surface of the aluminum box is coated with film after powder spraying, which is a further treatment based on the original passivation or phosphating technology, with the aim of making film coating more convenient. The reasons are as follows:
1. After the surface of the aluminum box is treated, if it is not sprayed, the surface must be reprocessed in a short period of time, such as film coating, painting, etc. Otherwise, the treated surface will become ineffective (oxidized or corroded by air);
2. The visible surface of the window profile (such as the window slot after opening) is not sprayed, and the comparison between the coated and non coated areas is obvious. Bare aluminum gives a feeling of low grade. However, the overall cost of aluminum windows has also increased due to the early spraying treatment, but this does not affect the use of high-end projects. Technically, it should also be noted that before surface powder spraying, chromate passivation or phosphating treatment should be carried out on the surface of the aluminum box to increase the adhesion fastness between the spraying layer and the substrate. Moreover, since the coating adhesive used is polyurethane adhesive, it is recommended that the main raw material for surface powder spraying should be polyester.
After the aluminum box is pre treated using the above method, it can be coated with film. All subsequent steps and processes are the same as other substrate coating, including the factory and corresponding mechanical equipment. However, it should be noted that the connectivity between the aluminum box and the adhesive used in UPVC requires testing by the customer or consultation with the adhesive supplier (based on actual experience, the two are basically compatible). The only difference between aluminum and UPVC profile lamination is that aluminum, as a metal, dissipates heat quickly. During lamination, attention should be paid to temperature control (the required temperature is about 55 degrees), and the aluminum box should not have sharp edges during lamination.
4. The packaging and storage of aluminum boxes after lamination are the same as those of other substrates after lamination.
