At present, it is mainly sprayed by hand, generally using an air Spray Gun or a portable electrostatic Spray Gun. The new portable electrostatic Spray Gun used is cable-free, and adopts air atomization method or air-assisted atomization electrostatic Spray Gun, which has the advantages of high paint utilization rate, safety and reliability, and can reduce the labor intensity of workers.
In small batch production, the manual spraying of air atomization spraying equipment is basically used. In order to prevent the viscosity of the paint from changing with the change of temperature, affect the atomization effect of the paint during spraying, and cause fluctuations in the appearance and quality of the paint film, the paint storage tank should be equipped with a constant temperature device. In order to solve the problems of low paint utilization rate and more spraying of paint mist during air spraying, more environmentally friendly low-pressure high-flow (HVLP) and medium-pressure medium-flow air spraying equipment has been used.
The wet-on-wet process is often used in multi-layer coating, that is, after the first coat is sprayed, it is not directly dried, but only dried for about 5 minutes, so that the coating film is surface dry, and then sprayed with the second coat or even For the third coat, it is a process of drying and leveling for 5-10 minutes and then drying together. Using this process can enhance the bonding force between coatings, save energy and greatly shorten working hours, and improve production efficiency. At present, the wet-on-wet process has been widely used in the coating of primers and topcoats. However, it should be noted that the wet-on-wet process is mainly suitable for condensation-polymerized thermosetting baking paints such as epoxy resins, amino resins, and acrylic resins, but not for oxidative polymerization-type coatings such as alkyd resins. For example, in the coating of high-end automobile bodies, in order to obtain a more wonderful decorative effect, metallic flash paint or pearlescent paint is used as the top coat layer. It is composed of two spraying and drying of the base paint and the varnish "wet on wet".
In order to improve the decorative effect of the coating film, a large number of metallic flash color coatings have been used in the coating of automobiles and motorcycles. Metal flash color paint is formed by adding 3%~10% aluminum powder to base materials such as melamine and acrylic resin. However, in the past, the brightness of the metallic flash color topcoat film obtained by electrostatic spraying is obviously lower than that obtained by other spraying methods of non-electrostatic spraying. The research shows that the reason for this result is related to the reflectance of the damaged light caused by the vertical arrangement of the aluminum flakes in the coating film on the surface of the coated object under the action of the electric field. In addition, because metal aluminum is a good conductor of electricity, the volume resistance of the metal flash color paint is low. After the high voltage of 60,000 to 80,000 volts is connected during electrostatic painting, it will cause leakage through the grounded paint circuit, which will not form High voltage, so electrostatic spraying method cannot be used to spray metallic glitter paint for a long time in the past. At present, this problem has been well solved by improving the process. Specific measures include: lengthening the length of the paint supply insulation pipe, increasing the air pressure of the spray pattern; spraying in two thin layers, improving the structure of the electrostatic Spray Gun, adjusting the paint formula, construction viscosity and coating process, etc.
At present, the coating process of double-coat metallic flash color topcoat used on the car body painting line usually adopts the 2CIB method (two coats and one drying), in which the thickness of the metallic base paint is 15-20 µm, and the thickness of the clear coat is 20 µm. ~30µm. When using electrostatic painting, the metal base color paint film should be as thin as possible (about 15µm), and the primer should be sprayed as little as possible under the premise of meeting the hiding power, while the varnish paint film is relatively thicker, about 30~35µm, so that A coating film with high gloss can be obtained. Spray in two coats during automatic electrostatic spraying of metal base paint. The film thickness of the first pass is 10~12µm, and the second pass adjusts the metallic feeling, the film thickness is 3~5µm, and a good ratio needs to be found in practice. One process is to use an air-atomized electrostatic Spray Gun for two passes, and the other process is to use high-speed cup-type automatic electrostatic spraying for the first pass of the base coat, and the second pass for the base coat to use automatic air spraying by a manipulator. After spraying the base paint, let it dry for 3~5 minutes and then use a high-speed cup-type automatic electrostatic spraying machine to spray the finish varnish.