Substrate surfaces are commonly prepared for electrocoating by cleaning, conversion coating, sealing, drying, and cooling. During electrocoating, an electrical charge (direct current or DC) is applied to during immersion in a waterborne paint bath. During the process, the part becomes the cathode (in cathodic e-coat baths) and there are a number of anodes spaced evenly throughout the tank. Paint molecules then travel to the substrate and adhere to the surface. Adequate bath agitation is necessary during the process to prevent bath separation and to ensure a uniform concentration of bath constituents. Coating thickness can be precisely controlled, and is dependent on immersion time, bath temperature, process voltage, and bath chemistry. Substrates are typically immersed for 90 to 360 seconds at a bath temperature between 60 to 80°F (15 to °C). The DC power supply voltage typically ranges from 90 to 500V.

The electrocoating process may be anodic or cathodic, depending on the charge applied the substrate. Although the processes are virtually the same, properties of the resultant coating are dissimilar. Anodic systems, which were the first to be used for electrocoating, apply paint to positively charged substrates. The negatively charged pigment and resin particles deposit onto the substrate (anode). One disadvantage of this process is that substrate metals dissolve and become incorporated into the coating, which affects surface properties. Cathodic electrocoating deposits paint onto negatively charged substrates and offers several advantages over anodic electrocoating. For example, metal dissolution of the substrate does not occur, cathodic electrocoating has the ability to deposit over contaminants, corrosion resistance is improved, and a better color consistency occurs over welded areas.

After the electrocoating process is complete, excess paint is removed from the substrate by immersing or spraying the part with a permeate rinse (consisting of the ultrafilter permeate of the e-coat bath itself) and then a DI water rinse. The rinse is collected and separated to recover paint and recycle a portion of it back to the electrocoating bath.

After the coated substrates have been rinsed, they are then baked to cure and cross-link the coating. Baking is typically performed with a gas-heated convection oven, although some industries employ fresh-air-type heaters. Baking temperatures are commonly between 250 to 375°F with a baking time between 15 to 30 minutes.

Because of the uniformity of the applied coating, and excellent adhesion properties, the corrosion protection offered by e-coat systems is extremely high on both steel and aluminum substrates. Virtually all automobile manufacturers currently utilize an e-coat primer prior to application of the standard automotive paint finish. Corrosion testing performed by the National Defense Center for Environmental Excellence (NDCEE) has demonstrated exceptional performance when used as a primer in combination with both aerospace and chemical agent resistant coating (CARC) topcoats.

The DOD specification for electrocoat primers is MIL-P-53084. The material is also approved for CARC systems.

The capital costs for an electrocoating system varies depending on the system configuration, but is generally in the range of $0.5 million to $1.5 million.

Operational Cost:

Paint purchase costs are the major operational cost element for most painting processes. Paint costs for an electrocoating system are estimated at $205,200 per year, versus $273,600 per year for conventional solvent paint. Adding in other operational costs (labor, energy, disposal, etc.) brings the total annual operating cost for electrocoating to $363,200 per year, versus $439,800 per year for conventional painting. Table 1 compares the various operational costs for electrocoating versus conventional solvent painting.

Table 1: Annual Operating Cost Comparison for Electrocoating and Conventional Solvent Painting at 12M ft2 per Year

Operational Cost Category	Dollars per Year
	Electrocoating	Solvent Painting
Material:	$205,200	$273,600
Labor & Clean-up:	$59,000	$118,000
Maintenance:	$17,000	$17,000
Energy:	$22,000	$21,200
Disposal:	$10,000	$10,000
Depreciation (10 Yrs – Straight Line):	$50,000	$--
Total Operational Costs:	$363,200	$439,800
Net Annual Savings:	$76,600

Payback Period:

The calculated payback period for investment in the equipment/process: <8 years (basis: $0.5M system with $0.1M installation cost)

Annual Savings:

The calculated annual savings for electrocoating: $76,600

Economic Analysis Summary:

Electrocoating reduces operating costs through a reduction in raw material costs, waste disposal, permitting, and emissions control requirements.

However, it should be noted that this particular economic analysis was performed for a high-volume production facility. Facilities processing a relatively small amount of parts per year may have significant difficulty in justifying an e-coat system. This is due to the high fixed costs (capital and operating) associated with e-coat.

In general, e-coat is one of the most cost-effective technologies available when a high-volume production line is considered. Small job -shops and other facilities processing a low annual amount of square footage coated will see a higher cost per unit surface area.