Cathodic Electro Deposition

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for Automobile


By Yoshiaki 0YABU,** Nobuo FURUNO,*** Yoji HIRASAWA*** and Hiroshi OMORI **** Synopsis The earlier electrodeposition processwas mainlypursuitedfor the quality control in terms of mass production. However, the coating efficiency was picked up to be a serial problemfrom a standpoint of the harmony between natural circumstancesand human's living-life conditions and the recovery usage of the paint was earnestlysearched. This trend led to the development in various technicalfields. The second impetus on further improvementof electrodeposition paint was due to oil crisis in 1973. The new technology relating to save-energy was developed. In thepaint industries, the further improvedanti-corrosive performance was strongly demanded. This demand also involvedthe developmentof new materials for automobile bodies and even the design of bodiesstructure. In this report, the introduction of electrodeposition process into automobile industries in Japan is hystrically reviewedand the electrodeposition mechanismand the mechanism which deposited materials from the coating film are briefly explained. As the demandfor anti-corrosiveperformance is increased, the coating system in which the anodic oxidation and the dissolutionfrom the object metal can not occur, was aimed and recentlyit was rapidly accepted as the superior system. On the other hand, there is an oppositeopinionfor this trend on the basis of the metal analysis detectedin the deposited film. The characteristics of cationic electrodeposition,in particular, the superior corrosion resistance with regard to the metal dissolution in the wholeelectrodeposition processis explained. In Chapter III, throwingpower which is characteristic for electrodeposition processis described. It is referred that throwingpower is not necessarily determined by the paint performance. Even the electrodeposition coating system, the areas into which the paint liquid does not intrude can not be coated. And it is pointed out that the design of bodiesstructure is inevitablynecessaryas well as the improvement paint performances. of In Chapter IV, the role of the main component,vehicleresin, is introduced. The deviceswhich disperse resin into solvent` water', and factors which determine the polarity of electrodeposition explained. And the are typical resin structure is shown. The paint performanceis greatly effected by the vehicleresin, but it is also deeplyrelated how thepaint is produced and how it is coated. Therefore, it is inferred that thepaint performances are relativelyestimated. In Chapter V, the whole system of electrodepositioncoating process is given. The so-called ` closed-loopsystem' which is remarkably characteristic in electrodeposition process, and which is suitably fitted for mass production of automobile bodies is explained. Besides, the pH control technologyof paint bath and the possibility on its future development are referred. Thefurther improvement the recycleusage technology f paint of o is pointed out and the possibility to replyfor the social needssuch as saveenergyand lesspolution is explained. In Chapter VI, thepresent status of electrodeposition processand various technicalproblemsare explained. The summary of this review and authors' views for future development are given in thefinal chapter.


Introduction The development of the electrodeposition coating

technology in automobile bodies industry commenced around 1964 in Japan. In those days, dip coating of water-borne paint was applied to automobile parts after metal pretreatment, and it was confirmed when voltage was applied, the vehicle was deposited at the electrode. This was the beginning of electrodeposition coating. However, the essential point of this technology was not properly comprehended, while the unpublished work was progressing. Before 1963, the small products to which latex emulsion was mainly applied had been produced industrially. In Great...
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