Application of electrophoretic coating technology on body
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Electrophoretic 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.
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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 has been widely used in automobiles, building materials, hardware, home appliances and other industries.
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The automobile body generally adopts two coating (electrophoresis + topcoat) or three coating (electrophoresis + topcoat) coating process, and the product structure is complex and the quality requirement is high. Therefore, the general requirements for cathodic electrophoretic coatings for automotive bodies are:
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1. The swimming speed is high, especially the inner and outer cavity film thickness of the car body is as small as possible. Generally, the inner cavity film thickness is required to be greater than 10 μm. The Ford box method and the four box method are used to evaluate the throwing power of the electrophoretic coating.
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2. The working fluid has good stability. Generally, the automobile body coating line is automatic continuous production. The electrophoresis tank is a few tens of tons smaller, and the larger one is several hundred tons. Therefore, the working fluid of the electrophoretic coating is required to have good stability. That is, the working fluid is not degraded for a long time under the specified process conditions, and the sample coating performance of the swimming coating is qualified.
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Coating performance requirements:
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1. Good anti-corrosion performance (resistance to salt spray is more than 840h, heat and humidity resistance is above 240h);
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2. Good mechanical properties (adhesion, impact strength, nostalgia, anti-shock performance);
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3. The surface flatness is good (low roughness, Ra is generally 0.3~0.4μm), because the decorative appearance of the car body is relatively high, the surface flatness of the base coat is not good, which directly affects the decorativeness of the top coat, especially The new intermediate coating and topcoat coating process developed in recent years (3C1B and double-base paint coating process) has stricter requirements on the surface roughness of the electrophoretic paint film (Ra≤0.2μm);
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4. It has good compatibility with the top coating. When spraying the middle coating or topcoat on the electrophoretic coating, it should meet the requirements of adhesion between the coating and resistance to stone strike.
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