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240 Landmarks TopProduction > Anion electrodeposition coating
 Anion electrodeposition coating
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 In conventional corrosion-prevention painting methods, air spraying could not apply coat in every corner, and dipping required a lot of time and effort to handle drips.
 In 1963, Ford announced reported the advantages of using electrodeposition coating, and announced that its application to vehicles was being discussed. Toyota Auto Body Co., Ltd. started development for applying electrodeposition coating to automobiles from early 1964. In the autumn of that year, the company built a test plant, and then in April 1965, it completed Japan's first electrodeposition coating body line equipment in the Kariya Plant and started mass-production.
 When DC voltage of approximately 100 V is applied with electrodeposition paint as the cathode and the coated object as the anode, resin and pigment components move to the anode (anion electrodeposition coating). The components that reach the anode form a paint film in the anode direction, losing their negative charge. The film becomes highly condensed to about 90% due to dehydration by the voltage (the electro-osmotic effect). When the film is washed with water after the coating, the paint remains because it is insoluble, and any free paint is removed.
 Electrodeposition coating greatly improves corrosion prevention performance including closed cross sections and keeps paint loss very low.
(1)Film thickness can be easily controlled by time and voltage, therefore, variations of film thickness can be substantially reduced. Moreover, the paint film is without drips and flows.
(2)Anion electrodeposition coating is applicable to edges, corners, the inside of boxes, and spot welding portions.
(3)It is a low concentration paint dipping method that reduces the amount of paint taken out of the tank by each body.
 Coating cannot be performed after one month of operation. This is caused by accumulated amine which is a neutralizer for dissolving resin in water in the tank. The problem can be solved by constantly removing amine by replacing the paint in the tank as well as introducing ion exchange equipment as a permanent measure.
 This coating is applied to surface coating in addition to primer coating. At the beginning, the electrodeposition film was not dried and wet-on-wet application of a water-based paint was adopted. However, the moisture content in the film was unstable, resulting in defects in the paint appearance. The process was revised to perform surface coating after the electrodeposition film was dried.

 In June 1965, the electrodeposition technology was applied to a passenger vehicle line for the Corona hardtop RT50.
 The electrodeposition paint was changed from a conventional maleic oil paint to a synthetic resin paint (polybutadiene electrodeposition paint) in 1971 aiming at improved corrosion prevention performance for inner and outer panels.
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Storage location:TOYOTA AUTO BODY CO., LTD., HEAD OFFICE, FUJIMATSU PLANT, TECHNICAL ADMINISTRATION DIV. (100 Kanayama, Ichiriyama-cho, Kariya, Aichi 448-8666)
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Year manufactured:1965
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Manufacturer:Toyota Auto Body Co., Ltd.
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Classification:Design drawings, literature
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Current status:In storage: not open to the public
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Company name:Toyota Auto Body Co., Ltd.
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Familiar name:Anion electrodeposition coating (ED coating)
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Installation vehicle:Corona Hardtop (RT50)
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Year of manufacture:1965.4
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Collaboration:Toyota Motor Corporation
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Structure, type, measure, means, etc.:Painting process: ① Attach auxiliary electrode (8 types) ② Auxiliary electrode short circuit test ③ Attach positive electrode, etc. ④ ED coating ⑤ Wash with water + air blow ⑥ Remove auxiliary electrode and positive electrode ⑦ Air blow ⑧ Repair coating ⑨ ED paint baking
ED coating method: paint concentration (heating residue): 14.0±1.0%; voltage: 55-80 V; film thickness: 20-30 μ (body side surface); paint pH: 7.8±0.3; conveyer speed: 1.6 m/min; paint temperature: 23±2℃ (first temperature control range); liquid circulation: 1 cycle/h;
Other process conditions: ⑤ Washing spraying pressure: 1.0±0.2 kg/c㎡; ⑤ Air blow pressure: 1.5±0.2 kg/c㎡;⑦ Air blow pressure: 4.0±0.5 kg/c㎡;⑨ Baking: body temperature 160±10 ℃, retention time 25±5 min;
Paint: Esubia TS-4 (Black): Shinto Paint Co., Ltd.
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Points of interest, topicality:Anion electrodeposition coating for an automotive body line mass-production system was developed and used for the first time in Japan.
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Features: Paint film thickness can be easily controlled by time and voltage, and uniform film thickness can be obtained compared with conventional corrosion prevention methods such as air spraying and dipping. Moreover, edges, corners, inside boxes, and spot welding portions can be appropriately painted without drips on paint films.
 It is a low concentration paint dipping method that can reduce the amount of paint taken out of the tank by each body, consequently paint loss is low.
 Corrosion prevention performance was dramatically improved, including that of closed cross sections.
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Reference materials:Toyota Shatai 50 Nenshi (Dai 4 Sho, Toso Seisan Hoshiki No Hensen To Seisansei Kojo)
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