What is the best treatment method of electrophoretic fluid?

Electrophoretic coating technology, methods and skills

The so-called electrophoretic coating is a coating technology that the coated object is immersed in water-soluble coating as an anode (anodic electrophoresis), and a corresponding cathode is set, and a direct current is applied between the two electrodes, so that the coating is evenly coated on the coated object through the physical and chemical action generated by the current.

Electrophoretic coating must use electrophoretic paint, usually also called water-soluble coating. Electrophoretic paint and distilled water must be diluted in a certain proportion before use.

Electrophoretic coating usually includes four simultaneous processes:

1. electrophoresis: under the action of DC electric field, colloidal particles with positive and negative charges move in positive and negative directions, which is also called swimming.

2. Electrolysis: redox reactions are carried out on the electrodes respectively, but redox phenomena are formed on the electrodes.

3. Electrodeposition: Due to electrophoresis, charged colloidal particles moving near the anode release electrons on the surface of the template and deposit precipitates in an insoluble state, thus forming a paint film.

4. Electroosmosis: Under the action of electric field, the solid phase does not move and the liquid phase moves. Electroosmosis makes the water contained in the paint film gradually drain out of the paint film, and finally forms a dense paint film with extremely low water content and high resistance, which can hardly pass current.

5. Iron red epoxy electrophoretic paint is an example: electrophoretic paint consists of modified epoxy resin, butanol, ethanolamine, talcum powder and iron red. After mixed with distilled water, electrophoretic paint is separated into positively charged cations and negatively charged anions under the action of DC electric field, and undergoes a series of complex physical, chemical, colloidal chemical and electrochemical changes.

Methods and skills of electrophoretic coating

(1) The process flow of electrophoretic coating on metal surface is as follows: pre-cleaning → online → degreasing → water washing → derusting → water washing → neutralization → phosphating → water washing → passivation → electrophoretic coating → tank cleaning → ultrafiltration water washing → drying → offline.

(2) The substrate and pretreatment of the coated object have great influence on electrophoretic coating. Generally, the castings are derusted by sand blasting or shot blasting, the floating dust on the workpiece surface is removed by cotton yarn, and the impurities such as steel shot remaining on the surface are removed by 80 # ~ 120 # sandpaper. The steel surface is degreased and derusted, and when the surface requirements are too high, the surface is phosphatized and passivated. The ferrous metal workpiece must be phosphatized before anodic electrophoresis, otherwise the corrosion resistance of the paint film is poor. Zinc phosphate film is generally used for phosphating treatment, and the thickness is about 1 ~ 2 microns, which requires fine phosphate film and uniform crystallization.

(3) In the filtration system, one-stage filtration is generally adopted, and the filter has a mesh bag structure with a pore size of 25 ~ 75 microns ... Electrophoretic coating is transported to the filter by a vertical pump for filtration. Considering the replacement cycle and paint film quality, the filter bag with the aperture of 50μm is the best, which not only meets the paint film quality requirements, but also solves the problem of filter bag blockage.

(4) The circulating quantity of electrophoretic coating circulation system directly affects the stability of bath solution and the quality of paint film. With the increase of circulation, the precipitation and bubbles of bath solution decrease; However, the aging of the bath is accelerated, the energy consumption is increased, and the stability of the bath becomes worse. It is ideal to control the circulation times of bath solution at 6 ~ 8 times /h, which not only ensures the quality of paint film, but also ensures the stable operation of bath solution.

(5) With the extension of production time, the anode diaphragm impedance increases and the effective working voltage decreases. Therefore, the working voltage of the power supply should be gradually increased according to the voltage loss in production to compensate for the voltage drop of the anode diaphragm.

(6) The ultrafiltration system controls the impurity ion concentration brought by the workpiece to ensure the coating quality. During the operation of this system, it should be noted that once the system is put into operation, it must run continuously, and intermittent operation is prohibited to prevent the ultrafiltration membrane from drying up. After drying, the resin and pigment adhere to the ultrafiltration membrane, which can not be thoroughly cleaned, which will seriously affect the water permeability and service life of the ultrafiltration membrane. The effluent rate of ultrafiltration membrane decreases with the extension of operation time, and it should be cleaned once after 30 ~ 40 days of continuous operation to ensure the ultrafiltration water needed for soaking and washing.

(7) Electrophoretic coating method is suitable for a large number of production lines. The renewal period of electrophoresis bath solution should be within 3 months. Taking an electrophoresis production line with an annual output of 300,000 steel rings as an example, it is extremely important to manage the bath scientifically. Regularly test the parameters of the bath, and adjust and replace the bath according to the test results. Generally, the bath parameters are measured according to the following frequencies: PH value, solid content and conductivity of electrophoresis solution, ultrafiltrate and ultrafiltration cleaning solution, cathode (anode) solution, circulating cleaning solution and deionized cleaning solution once a day; Yan Jibi, organic solvent content, laboratory cells tested twice a week.

(8) For the management of paint film quality, we should always check the uniformity and thickness of the paint film, and the appearance should not have pinholes, sagging, orange peel, wrinkles and other phenomena, and regularly check the physical and chemical indicators such as adhesion and corrosion resistance of the paint film. The inspection cycle is subject to the manufacturer's inspection standards, and generally each batch needs to be tested.

The application of electrophoretic coatings and waterborne coatings marks the great progress of coating industry.

Electrophoretic coating has the advantages of fast construction speed, mechanization, automatic continuous operation, reduced labor intensity, uniform paint film and strong adhesion, and can obtain uniform, flat and smooth paint film for parts that are not easy to be coated or poorly coated by general coating methods, such as the above-mentioned rib weld. The utilization rate of the coating is as high as 90%-95%. Because the electrophoretic coating takes water as solvent, it has the advantages of incombustibility, non-toxicity and convenient operation. The dried paint film after electrophoresis has excellent adhesion, and its rust resistance, corrosion resistance, weather resistance and other properties are better than ordinary coatings and general construction methods.