Cathodic electropainting

The development of new paint technology has mandated further improvements in the performance of non-chrome rinses. Greater use of a final water rinse in treatment applications has taken place particularly with the advent of anodic and cathodic electropainting which require the use of a deionized rinse to prevent paint contamination. High solids paints which tend to be more... 

Fig. 8.24 The principles of cathodic electropainting, (a) A divided cell, (b) Detail of the anode box. (c) A general arrangement, showing the electrical connections. (Courtesy ICI Ltd, Paints Division.)...

Thorgaard, S. Btihlmann, P. 2007. Cathodic electropaint insulated tips for electrochemical scanning tunneling microseopy. A a/. Chem. 79 9224-9228. 

After rinsing and dry-off, the primer is applied. In most modern plants this means electrodeposition of the primer (Section 14.1). The most widely used primers are cathodic. The body shell is made the cathode and current flows between it and inert anodes in the electropaint bath. The paint is formulated so that the resin is basic and, when neutralised with an acid such as lactic acid, becomes positively charged. The most widely used resins are epoxy-amine adducts ... 

Electrophoretic paints consist of ionic oligomers dispersed in an organic solvent and usually diluted with water to form an emulsion used for deposition. When cathodic current (for a cationic paint) is driven through a tip connected to a two-electrode cell containing the electropaint solution, the oligomers migrate to the tip and deposit on the surface due to reactions with the reduction... 

As can be deduced from the discussion in the previous section, the processes that occur during electropainting give rise to an accumulation of hydrogen ions at the anode and hydroxyl ions at the cathode. If a polymer which is stabilised by the existence of carboxyl ions along the chain approached the anode, the carboxyl ions will be neutralised and the polymer will precipitate out of solution onto the anode. Similarly, if a polymer stabilised by acid-neutralised amino groups approaches the cathode, then this will be precipitated out by the hydroxyl ions. 

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