An E-coat paint solution consists of an emulsified polymer system in de-ionised water. When a D.C. voltage is applied to the tank through a positive (anode) and negative (cathode) electrode, electrolysis occurs where hydrogen is produced at the cathode and oxygen is produced at the anode. There is a simultaneous pH change which in turn results in a controlled precipitation of the polymer onto the appropriate electrode. The deposition electrode can either be the cathode or anode depending on the E-coat technology being utilised.
The very earliest commercialisation of this technology in the 1960’s involved anodic technology, where the part to be coated is made the anode. In this case the pH of the coating bath is slightly alkaline. One major disadvantage of anodic coating is that because oxygen is formed at the anode during deposition, certain substrates may be attacked. In fact, anodic coating is aggressive to the substrate. It is therefore not possible to coat brass, silver and to some degree zinc parts anodically because the appearance of the metal is adversely affected.
However, anodic coating is still widely employed for application onto aluminium extrusion alloys and castings, stainless steel and phosphated steel.
Cathodic deposition takes place in acid bath conditions and depending on the formulation can be anything between 4-6 pH. Because of its passive deposition the cathodic process does not affect the metal surface, making it by far the most versatile method of application.
