Method for the cathodic electro-dipping process, and use of nitric acid and/or nitrous acid for neutralising coating baths

摘要

The anode plates of cathodic electro-dipping baths are strongly attacked by halide ions. This was previously prevented by adding salts such as, for example, copper nitrate. The object of the invention is to provide a method which protects the anode continuously without the addition of troublesome accompanying substances. The cathodic electro-dipping process is carried out in an aqueous coating bath containing a basic or amphoteric film former which, by neutralisation with acid, can be transferred into an aqueous solution or dispersion, neutralisation being achieved by using free nitric acid and/or nitrous acid, and/or the process being carried out in the presence of an electrodialysis membrane which was loaded with nitric acid and/or nitrous acid. Cathodic electro-dipping processing of surfaces of electrically conductive substrates connected as the cathode.