According to the application, there are mainly degreasing, sandblasting, wire drawing, polishing, and oxygen grease.
1. Degreasing: In order to make the surface of the aluminum substrate have a certain degree of ink affinity, the oil layer and oil stains on the surface need to be removed, which can be wiped with cotton yarn dipped in gasoline. Alkaline solution can also be used for chemical degreasing, such as sodium sulphate 30-50 g/l, sodium phosphate 40-60 g/l, sodium silicate 10-15 g/l, immersion in temperature 60-70 degrees for 2-5 Deoil in minutes.
2. Sandblasting: Sandblasting is to improve the adhesion between the ink and the metal material. A special sandblasting machine is usually used for spraying. River sand can be used after being filtered through a sieve.
3. Wire drawing: also known as twisting, which is to process fine straight lines on the surface of the aluminum plate by mechanical friction. It is a relatively new surface decorative treatment process, which can overcome defects such as scratches on the aluminum surface. Increase the utilization rate of materials. There are two types of wire drawing: thick wire and thin wire. Generally, a stainless steel wire brush with a diameter of 0.1 mm or a scouring cloth belt brush is used, or a nylon abrasive belt can be used for processing.
4. Polishing: To overcome the surface defects of aluminum-based materials and improve the surface finish. Polishing is divided into mechanical polishing and chemical polishing. Mechanical polishing uses cloth wheel polishing machine. Chemical polishing is mostly performed in acid solution, such as sulfuric acid 15%, nitric acid 10%, temperature 90-100 degrees, and time is 2-3 minutes.
5. Oxidation: The polished surface of the aluminum plate has the remaining polishing soap, which should be wiped off by dipping in gasoline, and then chemically degreasing, then immersed in a nitric acid solution (1:1 ratio of nitric acid and water), and then taken out after 10 minutes. Then put it into an oxidation tank for electrochemical oxidation. Oxidation solution formula: 160-200 g/ml nitric acid, temperature 10-20 degrees, time 30 minutes.
The oxidized aluminum plate is fully washed and dried, and an oxide layer with uniform pores is formed on the surface, that is, an oxide film, which should avoid dirt pollution. The oxidized aluminum plate is best to be printed immediately. If it cannot be printed immediately, it should be wrapped with a soft paper septum or placed directly on the drying rack. The storage time should not exceed one week.
The oxide layer on the surface of the aluminum plate can absorb dyes, moisture and other salts, so do not touch the surface with your hands or oily objects during screen printing. When the ink is printed on the oxide layer, the ink penetrates into the pores. The heating of the next process is to accelerate the ink penetration into the pores until all the pores on the surface covered by the ink are filled.
The ink printed on the surface seldom spreads or does not spread, which can ensure the accuracy and clarity of text and patterns.
6. Sealing: Its function is to seal the ink firmly in the pores, never overflow or spread. For the parts that are not covered by ink, the function of sealing is to fill the gaps of the oxide film, make it impermeable, and strengthen the corrosion resistance of the surface. Generally, nickel sulfate solution is used for sealing. Recipe: 10-12 ml of nickel Chinese acid, temperature 80-90 degrees, 10-15 minutes. After sealing the hole, touch the surface with your hands or other oily things and wash it off with normal detergent. In today's screen printing of metal signs or non-metal plates, more printing inks can be used, but it is not easy to choose suitable inks (paints).