If an aqueous dip coating is deposited in a bath on electrically conductive work-pieces by applying a DC voltage, this is referred to as electro dip coating. Depending on the polarity of the work-piece, a distinction is made between anodic electro-coating (ADC) and cathodic dip coating (CDC). The process is mainly used for bulk goods, e.g. in car and truck series production.
In the automotive industry, cathodic deposition systems have largely been used since the mid-1970s.
The aqueous paint contains only low concentrations of organic solvents and consists mainly of binder and pigment paste The resins of the binder are converted into ions in their chemical structure by reaction with acids or bases. Thus they are water-soluble and can be deposited as cationic (in the case of cathodic dip painting) resins on the correspondingly polarised work-piece.
In cathodic dip painting, the component is negatively polarised (cathode), while anode plates are located in the area of the basin wall. The contacted, fully immersed work-piece attracts the charged paint particles and builds up a very uniform coating film on its entire surface. For this it is important that the composition of the paint bath is permanently controlled and that it is adjusted to the desired deposition and system conditions during bath maintenance. The coated components are then cross-linked and cured in the furnace at an object temperature of between 185 and 200°C. The coating is then applied to the components and the coating is applied to the surface. Typical layer thicknesses in the range of 8 - 35 µm can be achieved. Different plant technologies allow components to be either individually suspended from racks or coated as bulk material in drums.
The design and quality of the coating produced therefore depend primarily on the relevant control variables in an adapted system technology: