Aluminum electrophoretic coating technology and development

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 for the processing of aluminum profiles in China. This article describes the current status and development trend of electrophoretic coating of aluminum profiles in China, discusses the preparation of electrophoretic coatings and electrophoretic coating process and management.

1. Current status and development trend of electrophoretic coating of aluminum profiles

1.1 The status of electrophoretic coating of aluminum profiles in China

After nearly 20 years of development, China's aluminum industry has formed a complete industrial system and has become one of the national economy's technology industries. 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 1,000 aluminum processing companies and the production capacity has reached 3.5 million tons per year. It can produce 18 types of belts, types, rods, wires, forgings, and powders, more than 200 kinds of alloys, more than 2400 varieties, especially aluminum production has increased by 100 times to 1 million tons/year.

China's electrophoretic coating of aluminum profiles 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 as follows: 1 The price is too high. At that time, the electrophoretic coating was imported, and the sales price was 8000-10,000 yuan/ton higher than that of ordinary profiles. 2 The industrial level is low. The manufacture of aluminum profiles is an integrated technology. Its quality is directly related to factors such as casting, extrusion, mold and process surface treatment, and environmental conditions. Any defects in the process will be transparent to the electrophoretic coating. Exposed under the characteristics.

At present, the aluminum profile industry has undergone technological transformation and has been moving towards the development of middle-to-high-end profiles. The production and management technologies have made great progress. With the improvement of people’s living standards and diversified market demands, the development of aluminum surface treatment technology has been promoted. From a single bronze material to powder coating, fluorocarbon coating, organic and inorganic dyeing, electrophoretic coating, and machinery And chemical polishing and other technological means, a new generation of wood grain processing technology, three-stage electrolytic multi-coloring and micro-arc oxidation coloring technology are also trial production. The appearance of aluminum profiles includes gold, golden, champagne, imitation stainless steel and various colors, as well as special effects such as mirror surface, sandstone, matt, and pearlescent. It is a variety of colors and colors. Among the numerous surface treatment technologies, electrophoretic coating is the most applicable technology with the most potential for development. Therefore, in the past two years, electrophoresis technology for aluminum profiles has made rapid progress. The production line has increased from 30 in 1997 to more than 100, and the production capacity has increased from 40,000 tons to 300,000 tons. However, the actual output is still between 10 and 150,000 tons/year, which only accounts for the total output of aluminum profiles in China. 10% - 15%.

1.2 Characteristics of electrophoretic coating aluminum profiles

First, after the anodized and electrolytically colored aluminum profiles are electrophoretically coated, there is double protection. With high transparency, high metal texture, high corrosion resistance and high weather resistance, it is more decorative than spray paint and powder coating. It is deeply loved by users and has been widely used in home decoration. The potential market is extremely large. Second, the process is easy to implement, as long as several slots are added to the production line and aluminum is oxidized, and the coloring process forms an assembly line. Water-soluble electrophoretic coating is safe and can realize closed circuit circulation, which is conducive to environmental protection.

1.3 Several aspects that should be paid attention to in the development of electrophoretic coating in aluminum 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 about 1 million tons/year, and it has been stagnating. This is related to the fact that profiles are limited to construction and a small number of industrial profiles, with few sections and applications. There are more than 700,000 kinds of aluminum products in the world. There are no statistics on the number of species in China. However, the types of aluminum profiles are far less than those existing in foreign countries. This cannot be ignored. China should work hard to develop industrial profiles, from the current small amount of heating and cooling hubs to mechanical and automotive structural parts. This is a very promising area; the development of household appliances, aluminum profiles for daily use, home appliances, lighting, kitchen utensils, bathroom appliances, aluminum profiles for daily use, almost blank, people of insight should make great achievements in this area; Packaging containers, aviation, transportation and chemical profiles are also expanding space.

2 The development of aluminum profile processing technology to improve the pass rate of electrophoretic materials is the key to the development of electrophoretic coating technology. The high cost of electrophoresis profiles stems from the low pass rate. If the pass rate is less than 80%, there will be no profit or even a loss. On the contrary, there is a huge profit if the passing rate is more than 90%. Therefore, this is a key factor that restricts the development of the electrophoresis process. The high transparency of the electrophoretic paint makes the casting shrinkage shrinkage, the black, black lines, coarse crystals caused by the ash, the mold squeezing coarse pattern, bump scratches, the combination of mold coarse crystal lines, dark spots and white spots; , markings, water marks, environmental conditions caused by dust burr, nodulation and electrophoresis process caused by low rate of penetration, yin and yang surface and high porosity of the rickets are revealed, we must systematically improve the comprehensive level of aluminum processing technology.

3 to improve the quality of electrophoretic paint, expand the type of electrophoretic paint. The electrophoretic coatings of our country's profiles are mainly acrylic electrophoretic paints and polyurethane electrophoretic paints. They are mainly translucent, and their quality is inferior to imported products in hardness and transparency. Improve the localization, further reduce the cost, increase the color of the varieties such as matt, extinction, sand surface, pearlescent and other effects of electrophoretic paint.

2, aluminum electrophoretic coating and coating process

2.1 Aluminum electrophoretic coating

Because acrylic resin has excellent weather resistance, abrasion resistance, the resin is colorless and transparent, and it has excellent decorative properties. The properties of the coating can be adjusted by formula. The main chain of acrylic resin is composed of carbon-carbon bonds, which has high chemical resistance. Alkaline electrophoretic paint liquids with large water content will not decompose and have good stability. Therefore, acrylic type electrophoretic coatings occupy aluminum profiles. The mainstream of electrophoretic coatings.

There is also a class of opaque polyurethane electrophoretic paints with excellent performance and simple process, because the use of colored opaque polyurethane electrophoretic paint can eliminate anodizing, coloring, and sealing processes, which is beneficial to cost savings.

With the wide application of electrophoretic coatings in aluminum profiles and electroplating products, the variety of electrophoretic coatings has increased dramatically to meet the different needs of various products. Currently, there are functionalities in addition to acrylic anode electrophoretic coatings, polyurethane electropositive and cationic electrophoretic coatings. Antibacterial, insulating, self-lubricating electrophoretic coatings, etc., as well as decorative matt, matt, pearl electrophoretic coatings.

2.2 Electrophoretic coating principle and characteristics

2.2.1 Electrophoretic coating features

Since the 30th century, electrophoretic coatings and paintings were used on a wheel coating line of Ford Motor Co., and its application has been rapidly developed in the past 40 years. Because electrophoretic coating uses water-based coatings, it has the advantages of safety, high efficiency, high quality, and environmental protection, and has been widely used in the automotive industry. 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 copper signs, the decoration and protection of stainless steel and electroplated products, and as a final protective decoration. The most representative and most widely used is the electrophoretic coating of architectural aluminum profiles.

The traditional aluminum profile surface treatment process is oxidation, coloring, and sealing treatment. This aluminum conversion film is prone to corrosion and has poor durability when it is used outdoors for a long time, especially in acid rain or marine environments. , People try to use paint coating method to improve the decorative aluminum building materials and the service life, at present, has been successful industrialization of electrophoretic paint, powder coating, fluorocarbon paint and so on. Since the electrophoretic coating is a water-based coating, the aluminum material can be directly electrophoresed after being washed by the pretreatment. The electrophoretic coating has a high transparency, and both the high decorativeness and the metallic luster of the aluminum profile itself can be highlighted. Therefore, the architectural aluminum profile has been increasingly used. Electrophoretic coating.

Electrophoretic coating has an important position in the aluminum surface treatment process because of its transparency, high metal texture, high weather resistance and corrosion resistance, and it is more than other spraying processes of aluminum profiles (such as spray paint, powder coating, etc.) High decorativeness, because it highlights the metal texture of aluminum itself, the safety of waterborne electrophoretic coating, environmental protection, easy automation and high quality of coating, so that the electrophoretic coating process of aluminum has a wider range of applications. The development direction of decorative profiles and plating parts.

Electrophoretic coating has the following advantages over other coating methods:

1 Easy to realize automatic production: Since the electrophoretic coating is carried out in an electrophoresis bath, similar to the anodizing and electrolytic coloring processes, the processing time is short, and it is easy to realize the assembly line operation of the entire process.

2 uniform and dense coating: due to the high throwing power of the electrophoretic coating, the shape of the complex shape can also obtain a uniform coating film, and the film thickness can be controlled by adjusting the power.

3 The utilization rate of the paint is high: due to the low viscosity, the workpiece is brought out less, and the electrophoresis workpiece can be washed with water. The utilization of the recovery device makes the utilization rate of the electrophoretic coating paint up to 95%.

4 Safety and environmental protection: Due to the water dilution of the electrophoretic coating, the solid content is low, and the solvent content is low, it is an environmentally friendly coating, and the danger of fire is eliminated, and the health of workers is also guaranteed.

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

6 Compared with the conventional electrolytic coloring and sealing process, it has the characteristics of time saving and labor saving. The resin film does not need to be sealed at the same time, and cracks and other defects caused by the bad sealing are avoided.

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

8 Because the electrophoretic layer is transparent and bright, aluminum ingots are required to have high quality, smooth surface of the extruded material, less mechanical defects, and strict management of the oxidation coloring process, because any minor flaws and stains will be exposed under bright paint.

9 The requirements for the management of the electrophoresis process are high to increase the yield.