E-Coating

So, what is E-coat?

Like “Powder Coating – the basic explanation”, E coating is similar to powder but, it is a liquid dip application. The parts get inspected and racked to fit in our line. Heated, agitated degreaser soak for 15 minutes, is the first step. After rinsing with de-ionized water, parts go into the zinc phosphate soak tank for a few minutes, then another de-ionized water rinse. Next, the rack is grounded to the application (paint) tank and the voltage is turned on. The liquid paint pigment is electrified up to 480 volts (like a hair dryer that falls into the tub). The paint creeps around the part until the ground is completed. At that point, no more paint will stick to the part. This is how we create the uniform epoxy 1 mil finish.

After the paint pigment coated part is moved into the rinse tanks, the parts are dried and moved to the curing oven. 400 degrees for 20 minutes, cooling and inspection and the parts are ready to go. The black pigment mix we use is considered an inner-cabinet, under-hood or buried application finish – Unless you are using it as a primer for powder. This non-cosmetic finish has no UV inhibitors.

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 some solvent and some ionic components. When a D.C. 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.

– Cathodics electropaints are stable except at high (alkaline) pH. Anodics are stable except at low (acid) pH

– Electrolysis of water causes the cathode to become alkaline and the anode to become acid

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 D.C. 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 electropaint as “Electrophoretic”

ecoating process

E-coat advantages:

  1. Excellent corrosion resistance (works fantastic on aluminum)
  2. Uniform, 1 mil thick epoxy surface finish
  3. Being 1 mil thick, most threads do not need masking or plugging
  4. E-coat finish is very resistant to many chemicals (see attachment)
  5. Can be used as a primer for powder coating to create an extremely durable finish

E-Coating 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 goods. The product is then removed from the paint bath and baked in an oven.

How does this compare to plating

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;

With e-coat the thickness is controlled by voltage. 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 easily accomplished with 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 (1 sq. ft. draws 1.5 amps max) rectification.