Origin:
Even though E-coat has been with us since the 1930's, it is mainly due to interest and capitol investment in the 1970's by the automobile industry for primers that made it popular. Since then, the technology has found its way into more decorative and functional (non primer) single coat application like CLEARCLAD.

Timeline:

Process Mechanism:
E-coat is an emulsion of organic resins and de-ionized water which is in a stable condition. The E-coat solution also comprises of solvents and some ionic components. When a DC voltage is applied across two immersed electrodes the passage of current is accompanied by electrolysis of water. This results in oxygen gas being liberated at the anode (positive electrode) and hydrogen gas liberated at the cathode (negative electrode). The liberation of these gases disturbs the hydrogen ion equilibrium in the water immediately surrounding the electrodes. This results in a corresponding pH change and this in turn de-stabilizes the paint components of the solution and they coagulate onto the appropriate electrode.

Electrophoresis is a well documented process whereby electrically charged particles in a conductive medium will migrate to the electrode bearing the opposite charge under the influence of DC voltage. Although many technical descriptions of electropaint ascribe electrophoresis to the deposition process it is not the predominant mechanism. However it is very common to refer to eletropaint as "Electrophoretic"

Application:
An unfinished product is immersed in a bath containing the electrophoretic paint emulsion and then an electric current is passed through both the product and the emulsion. The paint particles that are in contact with the product adhere to the surface as described in the above mechanism and build up an electrically insulating layer. This layer prevents any further electrical current passing through resulting in a perfectly level coating even in the recessed parts of complex shaped objects. The product is then removed from the paint bath and baked in an oven.

Due to the insulating nature of the deposit as described above, it is possible to accurately control the thickness over the part. Whereas with plating and anodizing thickness is controlled by amp/time relationship.

E-coat vs. electroplating and anodizing - amp/time relationship

With E-coat, the thickness is controlled by voltage. The time is not as critical as once the part is coated and insulated no more coating will take place. Depending on surface area and complexity of the parts, most coating is accomplished within 2 minutes. this highlights one of the big equipment differences. Plating and anodizing require low voltage and high amperage rectification. E-coat requires high voltage and low amperage (1sq. ft. draws 1.5 amps max) rectification. 

Electrocoating is a method of painting which uses electrical current to deposit the paint. The process works on the principal of "opposites attract". An E-coat system applies a DC charge to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and the paint is deposited on the part, forming an even, continuous film over every surface until the coating reaches the desired thickness.

The electrocoat process can be divided into four distinct steps:

1. Pretreatment cleaning and phosphating cycle.
2. Electrocoat bath cycle.
3. Post rinse cycle.
4. Baking and curing cycle.

Electrocoating Advantages:

1. Uniform coating thickness over all areas including sharp corners, recesses and areas     
    that would be hard to reach with spray painting.

2. Electrocoating is automatic and labor saving, requiring little maintenance.

3. Electrocoating saves the costs and operating expenses of air supply systems, fire protection equipment, respiratory hazards and costly cleanup. The paint material is water based and non-toxic

4. Approximately 95% utilization of paint with no overspray, drip or drain losses.

5. Complete paint coverage -no touch up required.

6. parts may be racked on the conveyor, one on top of the other with no concern for dripping.

7. Primers applied by electrocoating come out smooth and may be top coated without sanding.

Electrocoat Details:
The system offers better uniformity, higher density and less permeable coating than spray applications, saving up to 50% on coating materials. It is environmentally friendly, reducing emissions up to 70% and achieving nearly 100% coating utilization. Electrocoating also eliminates expenses associated with over spray cleanup and disposal.

Dial Your Coating:
The main factors controlling film thickness are the applied voltage and the film resistance. Increasing the coating voltage or lowering the specific film resistance causes an increase in film thickness. You simply dial in the desired coating thickness. The electroplating process will continue until the organic film deposited provides an electrical insulating resistance which prevents further current flow. When the coated parts are removed from the bath, they are rinsed in permeate and deionized water to remove non-deposited paint particles.