Development Status of Chinese Passenger Cars in Painting Technology

The passenger car manufacturing industry in China has developed rapidly in recent years, and new materials and new processes have been widely used; by cooperating with well-known foreign passenger car companies, the quality of luxury passenger car painting has also been improved. This article describes the status of the application of paint and coating technology and equipment for domestic and foreign passenger cars.

With the demand of the Chinese bus market and the growth of the national economy, the development process of the passenger car manufacturing industry has accelerated. New materials, new processes, and new technologies are widely used in passenger cars. In the past 10 years, China has successively introduced luxury passenger cars of different levels, which has led to a fundamental shift in the passenger car manufacturing industry. Through the joint venture and technical cooperation between foreign well-known passenger car companies and domestic passenger car companies, on the basis of introduction and digestion, the advantages of Chinese passenger car manufacturing are brought into play, the coating technology level and coating quality of luxury passenger cars are close to the international level, and passenger car products are thus improved. Grade.

The development of medium-sized passenger cars and mid-range passenger car manufacturing in China mainly depends on their own strength, such as Yangzhou Yaxing, Zhengzhou Yutong, Dandong Huanghai, Liaocheng Zhongtong, and Xiamen Kinglong Bus Company. In Nanjing, where passenger car painting production is relatively large, Iveco IVECO and Shenyang Jinbei have introduced painting lines. Luxury passenger car manufacturing has developed rapidly on the basis of introducing and digesting foreign advanced passenger car painting technology and equipment. Ankai Automobile Co., Ltd. and Germany KASSBOHRER company technical cooperation, to achieve 12-meter S215HDSETRA luxury passenger car mass production. In order to meet the demand of the domestic passenger transport market, the S315HD luxury passenger car with a higher level has been introduced and pilot-scaled this year, and a new factory that has been simultaneously built has been put into production. The coating production line adopts the German coating process technology and the advanced equipment and equipment are complete. Among the companies that have cooperated with foreign companies are Anhui Jianghuai JAC Corporation and Yanbian Bus Company, which have respectively introduced modern 9-12m luxury buses from South Korea and Dutch Bofa Buses from Liaocheng Bus Company. The IRIZAR luxury coaches of the Tianjin Bus Company, the German Mercedes-Benz coaches of the Yangzhou Bus Company, the Japanese Isuzu Bus Company of the Guangzhou Coach Company, and the Swedish Volvo Buses of Xi'an and Shanghai are all used for joint venture projects and have all reached mass production. At present, some of the paint lines have been built, and some are being reconstructed. Looking at the overall technical level of passenger car painting at home and abroad, the development trend of painting in China's passenger car manufacturing industry is promising. Here are some overviews.

Bus materials and coating applications

The main body material of passenger cars is steel or aluminum profiles. The body skin material is mainly made of steel plate, galvanized steel plate, alloy aluminum plate, engineering plastics and glass fiber reinforced plastic, etc.; the body side skin and skin welding adopts tension-tensioned prestressed group welding process or tensioned-up prestressed adhesive welding process, front and rear circumferences. The arc and plane are welded or glued together. The use of glass fiber reinforced plastic covers for the front and rear enclosures, wheel guards, luggage compartments, bumpers and other materials of passenger cars is a new technology developed in recent years. The application of FRP skins on passenger cars replaces traditional steel skins, reduces welding distortion, reduces weight, reduces costs, and is conducive to type change and mass production, especially for applications on medium-to-high-end passenger cars.

To meet the different levels of passenger cars, to adapt to the diversity of body materials coating, passenger car paint application research and development speed up. At the beginning of this century, the implementation of the bus market scale and the environmental protection law focused on the development of environmentally friendly automotive coatings and the reduction of harmful gas emissions and energy-saving measures. In the 21st century, which is called the environment-oriented new century, environmental protection has attracted worldwide attention. In countries with strict environmental regulations in Europe and the United States, passenger cars paint earlier to develop low-VOC (volatile organic compound) coatings for water-based coatings and painting equipment, and have been successfully applied in the production line extensively, and have begun to study new coating applications. Water-based coatings have reached the spray application level in Germany and Japan. Powder coatings have already been applied to passenger car parts, but they also face problems such as thinning of the coating. 2K-High Solids Low Temperature Curing Coatings include primers, midcoats, topcoats, on all kinds of passenger cars. Especially the application of high-end luxury passenger cars is very extensive.

The use of phosphating primers and epoxy primers can meet the requirements for corrosion resistance and adhesion of various materials; the use of polyurethane intermediate coatings and epoxy intermediate coatings can meet the requirements of filling and polishing.

Acrylic and polyurethane topcoats are used to achieve good UV resistance, anti-aging and vividness. Domestic high-temperature coatings are more commonly used in the coating of passenger vehicles under medium-sized vehicles to achieve electrophoretic and mechanized coatings.
Passenger car painting anti-corrosion technology and application of topcoat decoration

Passenger car requirements for coating functions are broadly divided into: protection functions (protection, sun protection, waterproof, oxidation prevention, salt spray, acid rain, anti-scrubbing, stone attack, anti-pollution substances) and decorative functions (color, Brightness, smoothness, three-dimensionality, etc.).

The pre-paint treatment and primer layer are the basis of the coating and directly affect the corrosion resistance and service life of the body. Due to the needs of market competition, there are large-scale bus companies in the world investing in improving the service life of the car body, and a new paint coating line consisting of dip and spray phosphating pretreatment and cathodic electrodeposition coating processes is newly established. German SETRA, Mercedes-Benz, South Korea Hyundai, France Renault and other passenger car skeleton body primer has been used cathodic electrodeposition coating. The coating method is still a 21st century coating process with advanced coating, high material utilization, and popularization in terms of quality, cost, pollution, and efficiency. The cathodic electrophoresis has a high throwing power, and the coating has good corrosion resistance, and can ensure the service life of the vehicle body is more than 10 years. In addition, there is a step-by-step intermittent coating production method based on the current status of small-scale coating production of passenger cars. General use of split phosphating, cathodic electrophoretic coating primer, and then welding body assembly assembly process program; or the overall body of the passenger car skeleton in the degreasing, phosphating shower room degreasing phosphating, and then coated paint. This will not only reduce investment and operating costs, but also achieve the annual replacement of the new electrophoretic paint bath solution 2 to 3 times the process requirements, so that parts of the surface of the outer and crevices to obtain a high quality primer coating.

The use of galvanized steel plates, aluminum plates and aluminum profiles, glass steel and other materials instead of ordinary steel plate body, and with a special primer for galvanized sheet and aluminum plate, is an international development trend of passenger car body manufacturing materials, not only can greatly improve The cracks in the body cavity cannot be coated with the corrosion resistance of the paint surface, and the body's weight can be reduced. The SETRA luxury large passenger car produced by Ankai Automotive Co., Ltd. imported the above-mentioned body materials and painting process from Germany to ensure the service life of the vehicle body was more than 10 years.

The coating of the undercoat, especially the midcoat, directly determines the appearance quality of the topcoat. The strong anti-corrosion performance of the underbody coating and the good adhesion, easy polishing, and the selection of the coating for the penetration resistance of the topcoat are the preconditions for passenger car painting. At present, it has attracted the attention of the passenger car industry. The defects on the surface of the car body are usually scraped and polished by putty. The car body primer and the middle coating are grinded and polished with a putty ash, respectively, and then sprayed with a primer, a center coat, a water mill, or a primer. After the atomic ash was ground, the spray coating was dry ground.

The luxury passenger car topcoat is made of 2K low-temperature drying paint mainly composed of acrylic polyurethane and acrylic with good weather resistance, gloss and color retention, and good UV resistance. Passenger car topcoats are generally classified into three types. Single-layer solid color topcoat: Solid color topcoats account for more than 50% of the top coat of passenger cars. It is the basic coating for topcoats; double-layer metallic paint coating: metallic flash paint as a luxury passenger car The main body paint has been widely used; three layers of pearl paint: the coating is more difficult, the bus main color spray paint forms include: gradient spray, color combination spray and the main paint monochrome spray.

The following are several forms of passenger car pattern spraying and spray painting. The use of large-scale computer photo inkjet film: computer photo inkjet film process is suitable for the production of complex clear and vivid picture patterns; the use of paint spray pattern: paint spray pattern, usually with colorful solid paint spray pattern for more, there is color Stable and subtle metal paint spray pattern; use color sticky film to make patterns: spray paint on the stick to form a pattern, and then transfer it to the body. The luxury passenger cars are bulky, have a large coating area, have many layers for spraying, are well-used in materials, are meticulous in processes, elegant in pattern, and are lean in painting. Therefore, they use an intermittent flow coating method.

Passenger car painting equipment and process application

With the increase in the demand for passenger cars, the added value of the appearance and function of the coating film and various requirements for the environmental load, the application of new materials, new processes and new technologies will be promoted, and the painting equipment and painting construction system will be changed. It has promoted the adjustment and transformation of existing passenger car painting equipment and the rational investment in new equipment, thereby expanding the scale of production.

In terms of process improvement, the wet-on-wet process that simplifies the baking process, the two-coat-bake (2C1B), and the three-coat-bake (3C1B) process scheme are used. The application of high-solids low-temperature curing coatings solves the problem of high energy consumption. In the aspect of drying, high-heat drying methods such as ultraviolet rays and high-frequency drying are gradually adopted. Spraying equipment is commonly used in water-spraying spray booths and drying chambers as well as space-saving spray drying chambers. The painting method is mainly manual spraying, and it also uses door-type mechanical spraying. Sprayers use high-pressure airless sprayers, electrostatic rotary cup sprayers, pressurized tank sprayers, and various types of tank spray guns.