Electrophoretic coating

For continuous production of pass-through electrophoretic coating equipment, the workpiece consists of a continuous production line by means of a hanging conveyor and other processes (pre-treatment-drying), which are suitable for mass production.
Definition Electro-coating is a coating method in which particles such as pigments and resins suspended in an electrophoresis liquid are directionally migrated and deposited on the surface of one of the electrodes by an applied electric field. The principle of electrophoretic coating was invented in the late 1930s, but the development of this technology and industrial application is after 1963, electrophoretic coating is a special coating film formation method developed in the past 30 years, is a water-based coating The most practical construction process. It is water-soluble, non-toxic, easy to automate and control, and is widely used in automotive, building materials, "target=_blank> building materials, hardware, home appliances and other industries.
The electrophoretic coating process is to put the workpiece and the corresponding electrode into the water-soluble paint. After the power is connected, the physico-chemical action generated by the electric field is used to make the resin and the pigment filler in the paint on the surface of the object to be coated. A coating method for uniformly depositing a deposit to form a water-insoluble paint film. Electrophoretic coating is an extremely complex electrochemical reaction process, which includes at least four processes of electrophoresis, electrodeposition, electroosmosis and electrolysis. Electrophoretic coating can be divided into anodic electrophoresis (the workpiece is anode, the coating is anionic) and cathodic electrophoresis (the workpiece is cathode, the coating is cationic) according to the deposition performance; DC electrophoresis and AC electrophoresis can be divided according to the power supply; There are constant voltage and constant current methods. At present, the anodic electrophoresis of the DC power supply constant voltage method is widely used in the industry.

Electrophoresis is the electrophoretic coating on the yin and yang electrodes. Under the action of voltage, the charged coating ions move to the cathode and form an insoluble matter with the alkaline action generated on the surface of the cathode, which is deposited on the surface of the workpiece.
The production process consists of four processes:

1) Electrolysis (decomposition)

In the cathode reaction, the initial reaction is electrolysis, and hydrogen and hydroxide ions OH are formed. This reaction causes the cathode surface to form a highly alkaline boundary layer. When the cation and the hydroxide act as water-insoluble substances, the coating film is deposited. The equation is : H2O→OH+H

2) Electrophoresis (migration, migration)

The cationic resin and H+ move toward the cathode under the action of an electric field, and the anion moves toward the anode.

3) Electrodeposition (precipitation)

On the surface of the workpiece to be coated, the cationic resin and the surface of the cathode are alkaline, neutralized to precipitate no deposit, and deposited on the workpiece to be coated.

4) Electroosmosis (dehydration)

The coating solid and the coating film on the surface of the workpiece are translucent and have a plurality of capillary pores. The water is drained from the cathode coating film, and under the action of the electric field, the coating film is dehydrated, and the coating film is adsorbed on the surface of the workpiece. And complete the entire electrophoresis process.
Process Features Features of Electrophoretic Surface Treatment Process:

The electrophoretic paint film has the advantages of fullness, uniformity, smoothness and smoothness of the coating. The hardness, adhesion, corrosion resistance, impact performance and penetration performance of the electrophoretic paint film are obviously superior to other coating processes.

(1) Using water-soluble paint, using water as the dissolution medium, saving a lot of organic solvents, greatly reducing air pollution and environmental hazards, safety and hygiene, while avoiding the hidden dangers of fire;

(2) High coating efficiency, small coating loss, and the utilization rate of the coating can reach 90% to 95%;

(3) The coating film has uniform thickness, strong adhesion, good coating quality, and uniform and smooth paint film can be obtained in various parts of the workpiece such as inner layer, depression, weld seam, etc., and other coating methods are solved for complex shape workpieces. Painting problem

(4) High production efficiency, automatic continuous production can be realized in construction, and labor efficiency is greatly improved;

(5) The equipment is complex, the investment cost is high, the power consumption is large, the temperature required for drying and curing is high, the management of coating and painting is complicated, the construction conditions are strict, and wastewater treatment is required;

(6) Only water-soluble paints can be used. The color cannot be changed during the painting process, and the stability of the paint storage is not easy to control.

(7) The electrophoretic coating equipment is complex and has high technology content, which is suitable for fixed color production.
Equipment composition (1) tank body

(2) Stirring cycle system

(3) Electrode device

(4) Paint liquid temperature adjusting device

(5) Coating replenishing device

(6) Ultrafiltration device

(7) Ventilation device

(8) Power supply device

(9) Water washing device after swimming

(10) Paint storage device

Electrophoretic coating can generally be divided into continuous production of pass-through and intermittent fixed type.

For continuous production of pass-through electrophoretic coating equipment, the workpiece consists of a continuous production line by means of a hanging conveyor and other processes (pre-treatment-drying), which are suitable for mass production.

For batch production of fixed electrophoretic coating equipment, the workpiece is composed of a monorail electric hoist or other type of conveyor, and other processes (pre-treatment-drying) constitute a batch coating production line, suitable for medium-volume coating production.

In the coating engineering electrophoresis voltage, time, temperature, anode-anode area ratio, the solid content of the paint liquid and the PH value of the paint liquid affect the quality of the coating. In practice, the above parameters are determined according to the customer's process parameters.

Cathodic electrophoresis coating metal is not easy to oxidize at the cathode. Compared with anodic electrophoresis, the coating is more common. The ultrafiltration system tank is not polluted, the bath maintenance is simple, and the coating has anti-corrosion effect.

The coating is cured in a curing oven. Curing ovens can be divided into continuous and intermittent types.

The temperature profile of the curing process has a large effect on the quality. It is generally necessary to use the furnace temperature tracker (model SMT-4 or SMT-7-32-300-K) produced by Beijing Saiweimei High-Tech Co., Ltd. to periodically check the temperature curve of the baking process. Make sure the temperature profile meets the process requirements.

The vehicle cathodic electrophoretic coating production line has caused no small fluctuations in the passenger car coating industry in China. Zhongda Coating (Jiangsu Zhongda Industrial Coating Environmental Protection Co., Ltd.) is the only coating company listed in China and the first one. A Sino-foreign joint venture of a domestic large-scale passenger car cathodic electrophoretic coating production line.



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