Electrophoretic coating has the characteristics of high weather resistance, high corrosion resistance, high transparency, good decoration, environmental protection and safety, and has become an important means of aluminum profile processing in China. This paper introduces the current situation and development trend of electrophoretic coating of aluminum profiles in China, and discusses the preparation, technology and management of electrophoretic coating.

1. Current Situation and Development Trend of Electrophoretic Coating of Aluminum Profile

1.1 Current situation of electrophoretic coating of aluminum profile in China

After nearly 20 years of development, China's aluminum industry has formed a complete industrial system and become one of the technological industries of the national economy. The output of primary aluminum has reached more than 2.5 million tons, accounting for the third place in the world. There are more than 1000 aluminum processing enterprises, and the production capacity has reached 3.5 million tons/year. It can produce 18 categories of belt, shape, bar, wire, forging, powder, etc., more than 200 kinds of alloys, more than 2400 varieties, especially the output of aluminum profiles has increased 100 times to 1 million tons per year.

Electrophoretic coating of aluminum profiles in China began in the mid-1980s. In the following 10 years, only a few manufacturers had production lines, such as Xifei Aluminum Profile Factory and Qinhuangdao Aluminum Company. The reasons for the slow development of electrophoretic coating are: ① the price is too high. At that time, electrophoretic coating was imported, and the sales price was 8000 to 10000 yuan/ton higher than that of ordinary profiles. ② The industrial level is low. The manufacturing of aluminum profiles is a comprehensive technology. Its quality is directly related to factors such as melting casting, extrusion, mold and process surface treatment, and environmental conditions. Any defects in the process will be exposed under the transparent characteristics of electrophoretic coatings.

At present, after technological transformation, the aluminum profile industry has moved towards the development period of medium and high-grade profiles, and the production and management technologies have made considerable progress. With the improvement of people's living standards and the diversification of market demand, the development of aluminum profile surface treatment technology has been promoted, from a single ancient copper material to a new generation of wood grain treatment technology with such technological means as powder coating, fluorocarbon coating, organic and inorganic dyeing, electrophoretic coating, mechanical and chemical polishing, Three stage electrolytic multi-color coloring and micro arc oxidation coloring technology are also in trial production. The appearance of aluminum profiles includes imperial gold, golden yellow, champagne, imitation stainless steel and various colors, as well as special effects such as mirror, sandstone, matt, pearlescent, etc. There are a wide variety of designs and colors. Among many surface treatment technologies, electrophoretic coating is the most promising one. Therefore, in recent two years, aluminum profile electrophoresis technology has made rapid development. The number of production lines has soared from 30 in 1997 to more than 100, and the production capacity has grown from more than 40000 tons to 300000 tons, but the actual output is still between 100000 and 150000 tons per year, accounting for only 10% - 15% of the total output of aluminum profiles in China.

1.2 Features of electrophoretic coating aluminum profiles

First, the aluminum profile is anodized and electrolytic colored before electrophoretic coating, with double-layer protection. With high transparency, high metal texture, high corrosion resistance and high weather resistance, it is more decorative than spray painting and powder spraying. It is loved by users and has been widely used in home decoration, with a huge potential market. Secondly, the process is easy to implement. As long as several grooves and aluminum oxidation are added to the production line of, the coloring process will form a production line. Water soluble electrophoretic coating is safe and can realize closed circuit circulation, which is beneficial to environmental protection.

1.3 Several aspects for attention in the development of electrophoretic coating of aluminum profile industry

① Develop new sections to promote the new development of aluminum profiles. In the past five years, the output of aluminum profiles in China has always been around 1 million tons per year. This is related to the fact that profiles are only used for construction and a small number of industrial profiles, with few sections and limited application. There are more than 700000 kinds of aluminum products in the world. There is no statistics on the number of aluminum products in China, but the types of aluminum profiles are far less than the existing types abroad, which cannot be ignored. China should make great efforts to develop industrial profiles, from a small number of heating and cooling hubs to mechanical and automotive structural parts. This is a promising field; The development of household appliances, aluminum profiles for daily use, household appliance components, lamps, kitchenware, bathroom appliances, and aluminum profiles for daily use is almost blank. People of insight should make great efforts in this field; Profiles for packaging containers, aviation, transportation and chemical industry are also expanding space.

② The key to the development of electrophoretic coating technology is to develop the processing technology of aluminum profiles and improve the qualification rate of electrophoretic materials. The high cost of electrophoresis profiles stems from the low qualification rate. If the qualification rate is lower than 80%, there will be no profit or even loss. On the contrary, if the qualification rate reaches more than 90%, there will be huge profits. Therefore, this is the key factor restricting the development of electrophoresis technology. The high transparency of the electrophoretic paint makes the melting and casting shrinkage cavity, the black, black lines, coarse crystals caused by ash, the mold extrusion coarse lines, bumps and scratches, the combination mold coarse crystal lines, black spots and white spots; Flowers, stripes and water marks caused by oxidation and coloring process, dust burrs and nodules caused by environmental conditions, and defects caused by electrophoresis process, such as low penetration rate, high yin and yang surface and porosity, are all exposed. Therefore, the comprehensive technical level of aluminum processing must be systematically improved.

③ Improve the quality of electrophoretic paint and expand the variety of electrophoretic paint. The profile electrophoretic coatings in China are mainly acrylic electrophoretic coatings and polyurethane electrophoretic coatings, which are mainly transparent, and their quality is inferior to imported products in hardness and transparency. Improve localization, further reduce costs, and increase color varieties such as matt, matt, sand, pearlescent and other effects of electrophoretic paint.

2. Electrophoretic coating and coating process for aluminum profiles

2.1 Anodic electrophoretic coating for aluminum profile

Because acrylic resin has excellent weather resistance, abrasion resistance, colorless and transparent resin, and excellent decorative property, the coating performance can be adjusted by formula. The main chain of acrylic resin is composed of carbon carbon bond, which has high chemical resistance. The alkaline electrophoretic paint with large water content will not decompose and has good stability. Therefore, the acrylic type anodic electrophoretic paint occupies the mainstream of aluminum profile electrophoretic paint.

At present, there is also a kind of opaque polyurethane electrophoretic paint with excellent performance and simple process. Because the use of colored opaque polyurethane electrophoretic paint can eliminate anodic oxidation, coloring and sealing processes, which is conducive to cost saving.

With the wide application of electrophoretic coatings on aluminum profiles and electroplated products, in order to meet the different needs of various products, the variety of electrophoretic coatings has increased sharply. At present, in addition to acrylic anode electrophoretic coatings, polyurethane negative and positive electrophoretic coatings, there are functional antibacterial, insulating, self-lubricating electrophoretic coatings, and decorative matt, matt, pearlescent electrophoretic coatings.

2.2 Principle and characteristics of electrophoretic coating

2.2.1 Features of electrophoretic coating

Since the application of electrophoretic coating and coating in a wheel coating line of Ford Motor Company in the 1930s, its application has developed rapidly in the past 40 years. Electrophoretic coating is widely used in automobile industry because of its advantages of safety, high efficiency, high quality and environmental protection. Due to the excellent performance of electrophoretic coatings, transparent acrylic and polyurethane electrophoretic coatings have been successfully used for the decoration and protection of metal surfaces since the 1970s, such as the protection of bronze signs, the decoration and protection of stainless steel and electroplating products.

The traditional surface treatment process of aluminum profiles is oxidation, coloring and sealing treatment. When this aluminum conversion film is used outdoors for a long time, especially in acid rain or marine environment, it is easy to corrode and has poor durability. Therefore, since the 1970s, people have tried to improve the decorative performance and service life of aluminum profiles for building by coating. At present, The successful industrial applications include electrophoretic coating, powder coating, fluorocarbon coating, etc. As electrophoretic coating is a water-based coating, aluminum materials can be directly electrophoretic after pretreatment and washing, and the electrophoretic coating has high transparency, which not only has high decorative properties, but also can highlight the metallic luster of aluminum profiles. Therefore, architectural aluminum profiles have increasingly used electrophoretic coating.

Electrophoretic coating occupies an important position in the surface treatment process of aluminum profile due to its transparency, high metal texture, high weather resistance and corrosion resistance. It is more decorative than other spraying processes of aluminum profile (such as painting, powder spraying, etc.), because it highlights the metal texture of aluminum itself, the safety, environmental protection, easy automation of water-based electrophoretic coating and the high quality of coating, It makes the electrophoretic coating process of aluminum more widely used, and is the development direction of decorative profiles and electroplated parts coating.

Compared with other coating methods, electrophoretic coating has the following advantages:

① Easy to realize automatic production: because electrophoretic coating is carried out in water-based electrophoretic tank, similar to anodic oxidation and electrolytic coloring processes, the treatment time is short, and it is easy to realize the flow line operation of the entire process.

② Uniform and dense coating: Due to the high penetration of electrophoretic coating, profiles with complex shapes can also obtain uniform coating. The film thickness can be controlled by adjusting the electric quantity.

③ High utilization rate of coatings: due to low viscosity, less workpieces are taken out, and electrophoresis workpieces can be washed with water. The utilization rate of electrophoresis coating coatings is up to 95% or more due to the utilization of recovery devices.

④ Safety and environmental protection: due to the water dilution, low solids and low solvent content of electrophoretic coating, it is an environmentally friendly coating, which avoids the risk of fire and ensures the health of workers.

⑤ Good coating quality: acrylic resin is cured with amino resin, which ensures high decoration and corrosion resistance of the coating film. At the same time, because the resin is highly transparent, it effectively highlights the metal texture, and can also obtain matt, sand, pearl and other decorative effects as required.

⑥ Compared with the common electrolytic coloring sealing process, it is time-saving and manpower saving, and the resin film does not need to seal the hole at the same time, which avoids cracks and other problems caused by poor sealing.

⑦ The thickness of the coating film can be freely controlled, which is generally controlled at 7 μ m and 12 μ m at home and abroad.

⑧ Because the electrophoresis layer is transparent and bright, it requires high quality aluminum ingots, smooth extrusion material surface, few mechanical defects, and strict management of oxidation and coloring process, because any minor defects and stains will be exposed under the lacquer.

⑨ High requirements for electrophoresis process management to improve the yield.

2.3.3 Aluminum profile electrophoresis process equipment

① Electrophoresis tank: aluminum profile electrophoresis tank is mostly designed as a rectangular tank, and its internal size depends on the size of the hanging crane. The tank body is made of 4-6 mm steel plate, lined with polypropylene or epoxy glass fiber reinforced plastic, and an overflow tank is required.

② Power supply: the DC requirement is 0-250 V adjustable, and the current is calculated according to 50 A/m2, about 2000 A/slot. The ripple factor of the power supply must be less than 6%. The larger the ripple, the greater the probability of pores in the electrophoretic coating.

③ Electrode: during anodic electrophoresis, aluminum profile is used as anode, and stainless plate or aluminum plate is used as cathode plate. The cathode area is twice the total area of the workpiece. Plate diaphragm: polypropylene fiber cloth is used.

④ Heat exchange system: it can ensure the stability of bath liquid temperature.

⑤ Pre preparation tank and automatic addition system: the pre preparation tank can complete the preparation of electrophoresis tank solution to ensure that normal parameters are reached; The automatic addition system can supplement the amount of electrophoretic paint consumed by each tank of aluminum profile, ensure that the solid content of electrophoretic tank solution is within the process range, and ensure the consistency of film thickness.

⑥ Ion exchange treatment (IR) system: during anodic electrophoresis, the cathode pH value will continue to increase. The use of ion exchange resin system can remove impurities anion and cation in the tank solution, so that the pH value of the tank solution is stable. If the reverse osmosis device (RO) is added, the R0 closed circuit system can be realized, which is conducive to environmental protection and process control.

⑦ Baking system: radiation convection type is mostly used. Anode electrophoresis paint film needs to be baked at 140 ℃.

3. Summary

Due to the reduction of electrophoretic coating and coating cost, the electrophoretic coating of aluminum profiles has developed rapidly. Many large aluminum profile factories in China have been on the electrophoretic line to meet the market demand for high-quality profiles. The weatherability, corrosion resistance and decorative properties of electrophoretic profiles exceed those of traditional oxidized and colored closed profiles; Compared with powder spraying and painting profiles, it highlights the texture of metal and has better decoration. At present, if electrophoretic profiles can be improved in the following aspects, they will have a larger market share.

Improvement of aluminum ingot processing technology; The improvement of electrophoresis management level; Acrylic paint film has higher hardness and transparency, and domestic paint manufacturers are making improvements in this regard to reach the level of similar products abroad; The application scope of aluminum profile products is expanded; More products are decorated and protected by electrophoretic coating; Reduction of baking temperature of electrophoretic coating.

To sum up, the development of electrophoretic coating of aluminum profiles in China is entering a new period. With the development of urban construction in China, the improvement of residents' decoration level and the expansion of application fields, electrophoretic profiles with their high quality, high decoration and corrosion resistance, good film forming performance, safety and environmental protection of electrophoretic process, Electrophoretic coating of aluminum profiles will develop more rapidly in China.

Guangzhou Tuoshen Surface Treatment Co., Ltd., the spraying manufacturer, is preferred for purchasing spraying, Spray processing Factory, trustworthy