Electrocoating is a widely used technology that has provided excellent levels of performance on a diverse assortment of industrial metal objects for more than 30 years. Electrocoat technology has evolved dramatically since the early 1960's, when it was first commercialized as an automobile body primer. Today, more than 98 pct of all car bodies produced globally use an electrocoat primer. New end uses for electrocoat are found annually, for example: automotive parts and accessories; appliances; heat exchangers; decorative plated objects; and heat-sensitive components.
Current commercially available electrocoat systems use processes and materials that are both environmentally friendly and economically efficient. Electrocoat is an "environomic" coating solution for many finishing needs. Major advantages of the electrocoat process include:
- Total coverage of complex parts with film uniformity
- Material transfer efficiencies routinely in the 95 to 99 pct range
- Highly automated, closed-loop systems with excellent productivity and low operating costs
- Fast line speeds and high part-racking densities
- Low air and wastewater emissions
- Totally enclosed systems leading to cleaner and safer paint operations
Electrocoat products can be segmented into anodic or cathodic, and epoxy or acrylic. Table I illustrates common end uses for the four categories of electrocoat. The industry's research and development activities have fostered many exciting developments during the past 30 years. Some of the significant advancements include:
- Environmentally optimized operating processes
- Near zero VOC and HAPS electrocoat and pretreatment products
- Lead-free cathodic electrocoat with corrosion protection equal to prior leaded products
- Cathodic acrylic coatings with corrosion and UV protection as a single-coat finish
- Two-coat electrocoat systems for ultimate primer/topcoat performance
- Exceptional coverage of sharp metal edges
- Advances in material handling and application equipment.
The environmental impact of electrocoat is, in many cases, substantially less than that of other coating processes. Transfer efficiency typically exceeds 90 pct with electrocoat, a performance that is difficult to match with liquid or powder spray methods. Closed-loop rinsing and recovery of dragout with little or no permeate to drain greatly reduces wastewater emissions and BOD/COD levels. Conductivity can be controlled easily in both anodic and cathodic systems using automated equipment.
The pretreatment processes continue to evolve into more environmentally friendly applications. Better equipment design and improved chemicals are leading to minimized waste treatment demands, elimination of heavy metals and optimized water use without sacrificing performance.
New electrocoat products offer the end user a variety of options to meet increasingly stringent air, water and waste disposal regulations. HAPS-free electrocoat products, both anodic and cathodic, are available today. Near-zero-VOC systems are also available, with volatile content as low as 0.1 lb/gal or less. Several systems have demonstrated the ability to operate without solvent additions to the electrocoat tank.
Today, a major area of product development is lead-free cathodic epoxy electrocoat. Until now, lead-free electrocoats were not able to offer the same performance as leaded coatings, particularly over substrates without optimal pretreatment. The latest generation of lead-free cathodic epoxy offers the same performance as the prior leaded coatings and is approved by the domestic automotive manufacturers for use on small parts.
Cathodic acrylic electrocoats are capable of providing the best combination of corrosion resistance, exterior durability and color control. The appliance market is experiencing the commercialization of single-coat white cathodic acrylic to replace previous applications of primer and topcoat, leading to economic advantages for the end user. New low-VOC and HAPS-free acrylics are in the marketplace, targeted at high-performance applications with improved environmental characteristics.
An exciting recent development is the use of the two-coat electrocoat process for extreme performance environments. The first coat is a conductive epoxy electrocoat, which, when baked, provides a surface that can receive a second coat of acrylic electrocoat. The two-coat system is capable of providing long-term exterior durability and corrosion resistance in excess of 2,000 salt spray hours. The photographs represent a current two-coat electrocoat application.
With the tendency of coatings to flow away from sharp edges while still in the liquid phase, corrosion protection of objects such as body panel edges and fins on radiators has proven difficult. Advances in cathodic epoxy electrocoat formulations have resulted in the ability to control film thickness over sharp objects, greatly enhancing corrosion resistance.
Developments in material handling systems continue to lead to more efficient line designs and less capital cost intensity. A variety of system layouts is available for consideration, including monorail and programmable hoist options. Flexible conveyors provide more efficient use of space with monorail designs. Material handling system suppliers continue to work towards improving the economics associated with electro-coat operations.
The use of the electrocoat process to provide excellent coating finishes over a variety of metal surfaces has been widely recognized during the past 30 years. Significant advancements in both anodic and cathodic electrocoat technologies have generated a palette of coating products that are both environmentally friendly and economically efficient. Electrocoat has become the "environomic" coating solution of choice for many product end uses today and future developments to increase the added value nature of electrocoating are in process.
|TABLE I Electrocoat Product Categories|
|ELECTROCOAT TYPE||PROPERTIES||END USES|
|Anodic Epoxy||Low Cure
|Anodic Acrylic||Color Control
|Metal Office Furniture
Wire Screen and Hangers
|Cathodic Epoxy||Corrosion Resistance
|Automobiles and Parts
|Cathodic Acrylic||UV Durability
|Lawn and Garden
Automotive Wheels and Trim Appliance