E-Coat also know as Electrocoat , electrophoretic paint, EDP or electrodeposited paint.

Description

E-coat is an electrodeposited semi-gloss black epoxy paint providing high corrosion and chip resistance while retaining tight build tolerances on fabricated parts. A uniform thickness maintains hole sizes and dispenses with the need to mask threads etc.

E-coat is widely specified by automotive manufacturers for under bonnet and under body corrosion protection on steel componentry.

How The Process Works

Electrodeposition works much like a plating process. The parts (cathode) to be coated serve as one electrode and the auxiliary electrodes (anode) serve as the oppositely charged pole as displayed by the following diagram.

fig.1 ecoat tank

Upon application of a direct current the charged polymers migrate electrophoretically to the electrode of the opposite charge, become insoluble, and form an insulating film which limits further deposition. When positively charged polymers deposit on the cathode it is referred to as cationic or cathodic electrocoating.

Process Properties

• the cationic process is epoxy based.
• can be used as a primer or a one coat finish.
• gives very high levels of corrosion protection.
• e-coat has great throwing power ( the ability to coat recessed areas such as the inside of
  tubes, cavities and channels in fabricated metal components).
• coats all conductive metals including stainless steel and aluminium.
• uniform thickness builds over the entire component.
• smooth finish, with no dags or runs and high chip resistance.
• the system is alkaline in nature making it an inherent corrosion inhibitor.
• unlike anodic systems cationic systems have very little substrate dissolution giving far greater
  corrosion protection.
  

Important component design & presentation considerations.

Silicone

Under no circumstances can any silicone based products be used on components to be
e-coated eg. anti-spatters for welding, some of these contain silicone. At very low levels (parts per million) silicone in an e-coat plant will contaminate the paint tank.

Cleaning

Use as little oil as possible in the production of parts, only water soluble oils and advise presentations to ensure compatability.

Unlike zinc plating lines which have many powerful cleaning stages, E-Coat plants have only limited dedicated cleaning systems to prevent contamination of the paint system by heavy
alkalis and acid ions. They are similar in nature to pre-paint cleaning systems and are not designed to remove heavy oils, rust and mill scale. Lanolin based oils for example will react with cleaners and cause mapping under the coating. The cleaner the presentation of your part the better the end product.

Metals

As with cleaning the same principals exist, the better the presentation the better the end product. Cold rolled and pickled and oil steels should be free of mill smuts, which can be rolled into the surface at the slitting stage if rollers are not cleaned after running hot rolled sheet.

Designing components.

Because the process involves the components being immersed in many stages of varying
solutions parts should be designed so that they will not create air pockets which will result in bare areas of uncoated steel.

Parts also must be designed so that they do not carry over solution into the next stage of the process, this can cause problems with the end product when it reaches the oven curing stage, as well a causing plant contamination.