Process features:

In anodic coating, paint film is deposited on the anode; in this case, the anode is the piece that must be painted, that is connected to the positive side of the rectifier. So, paint has negative charge.

In cathodic coating, the cathode is the piece that must be painted, and paint has positive charge.

With these different processes (anodic/cathodic coatings) and their application systems, films and paints with different properties are got.

Property	Cathodic	Anodic
Salt fog resistance till 240 hours	yes	yes
Salt fog resistance till 1000 hours	yes	no
UV resistance	no/yes*	no/yes*
Alkali resistance	yes	no
Penetration power	very good	good
Set of colors	little	good
Chemical resistance	yes	little

*There are specific products to fulfil these requirements.

Cathodic system - CED:

• no piece dissolution
• base polymers are corrosion-proof and also saponification-proof
• the phosphates-coating is unassailable

Anodic system - AED

• the anodic dissolution of piece that must be painted is a co - reaction that traps metallic ions of the film (corrosion points)
• acid polymers are easy to saponify, so there is low chemical resistance and low alkali resistance too
• the coating process can give problems to adhesion between phosphates and metallic support

For such reasons, these two processes are employed for particular applications:

• CED are usually employed when high resistance to corrosion is required
• AED instead are employed if main properties of the film are more important than corrosion resistance. Acrylic products are especially used because their very good resistance to UV rays makes possible to get a wide set of colors

Composition and components of paint:

An ED bath is 80-90% water. Other components are resins, pigments, and a little quantity of organic solvents and additives.