Vacuum aluminum plating is to heat and melt aluminum metal to evaporation under vacuum, and aluminum atoms condense on the surface of polymer materials to form an extremely thin aluminum layer. Vacuum aluminum plating requires that the surface of the substrate be smooth, flat and uniform in thickness; Stiffness and friction coefficient are appropriate; The surface tension is greater than 38dyn/cm2; It has good thermal performance and can withstand the heat radiation and condensation heat of the evaporation source; The moisture content of the substrate is less than 0.1%. Commonly used aluminized substrates include polyester (PET), polypropylene (PP), polyamide (PA), polyethylene (PE), polyvinyl chloride (PVC) and other films, and the process requirements; The vacuum degree shall not be lower than 103pa to avoid brown stripes or uneven thickness of aluminum layer; Control the system tension and turn on the cooling system to avoid stretching deformation of the film when heated; Accurately control the coiling speed (280 ~ 320m/min), aluminum feeding speed (0.4 ~ 0.7m/min? 2mm aluminum wire) and evaporation boat heating current to obtain the required aluminum layer thickness (100 ~ 300A °); A certain amount of primer can be coated on the film in advance and fully dried, and then vacuum aluminized to improve the adhesion between the aluminum layer and the film. Then a certain amount of protective resin is coated on the aluminum film to prevent the oxidation and deterioration of the aluminum layer. The aluminized film formed by this process is friction resistant and not easy to deteriorate.
Common quality problems and solutions of vacuum aluminizing are as follows:
1. Brown stripes appear on the film surface
① Solution to low vacuum: clean the aluminum feeding, evaporation device, cooling system, unwinding, coiling device and guide roller in the vacuum chamber; Check the vacuum pumping system; Reduce ambient humidity.
② The film releases gas. Solution: film pre drying; Extend the vacuum pumping time.
③ Too much aluminum spraying. Solution: increase the speed; Reduce evaporation boat current; Reduce the aluminum feeding speed.
④ There are impurities in the evaporation boat. Solution: clean the evaporation boat and heat shield plate.
⑤ The evaporation boat is aging. Solution: replace the evaporation boat.
2. Holes appear in the film during aluminum plating
① The aluminum material in the evaporation boat is too full. Solution: reduce the aluminum feeding speed; Increase the evaporation boat current.
② There is a short circuit between the evaporation boats in the vacuum chamber. Solution: eliminate the short circuit.
③ Impurity splashing in vacuum chamber
Solution: clean the vacuum chamber wall, aluminum feeding evaporation device, cooling drum, unwinding, coiling device and guide rollers.
3. The film is stretched during aluminum plating
① The substrate tension is too high. Solution: adjust the unwinding and coiling tension control system to appropriately reduce the tension.
② The cooling system is not working properly. Solution: check the cooling system and eliminate the fault.