Typical clear-coated aluminum extrusions.

Electrodeposition, also known as electrocoat or e-coat, is one of the most cost-effective finishing technologies available due to its high transfer efficiency, ability to densely load parts on the production line, and automated process. While electrocoat systems often are significantly more capital intensive than other coating systems, they offer the opportunity to quickly achieve a return on investment based on the cost-effectiveness of the e-coat operation. However, the selection of colors traditionally has been limited, and clear e-coats with the required performance in areas such as chemical resistance, hardness, abrasion, gloss and clarity have been difficult to find. As a result, electrodeposition coatings have largely been relegated to being used as black primers in a small number of applications.

Recently, new electrodeposition clear coatings have been developed to meet the needs of a variety of markets. These coatings can be tinted with dyes, traditional pigments and specialty pigments to provide a substantial range of colors and effects, and new pigments can allow for effects and finishes that were previously only achievable with powder or liquid coatings. With these new options, finishing professionals in a range of markets now can consider e-coat as a viable technology.

An aluminum running board with a clear coating.

Clear Coating Markets

In the traditional decorative market, clear coatings are used on brightly plated cabinetry hardware, ornate fixtures and frames, and perhaps jewelry and associated personal items such as pens, medals, money clips or belt buckles. On the industrial side, with much higher volumes, clear coatings can be found on industrial and institutional hardware and plumbing fixtures. For most of these applications, the clear coating requirements are largely the same. The coating must have excellent clarity, good durability, perspiration resistance, high hardness, corrosion resistance and impact resistance, as well as other properties. In general, the coating requirements are difficult to achieve with one formulation.

In the automotive market, clear coatings (aside from exterior topcoats) are used for trim, wheels and accessories on both interior and exterior pieces. A Class “A” finish and superior functional properties are required, including hardness, corrosion, long-term weathering and durability, chemical resistance and abrasion resistance.

The aluminum extrusion market tends to be driven more by performance in certain geographical regions, but elsewhere a superior appearance is what sells. For example in the U.S., clear coatings for exterior extrusions must meet certain American Architectural Manufacturers Association (AAMA) specifications for architectural markets before even being considered for an application. In Asia, however, appearance drives the decision makers, and the performance specifications are less stringent.

Extrusions are made in a variety of shapes, colors and finishes. The colors and finishes are achieved either through mechanical or chemical treatment of the extrusion metal or through coatings applied after forming. High gloss and durability are key factors for extrusion coatings.

In the consumer electronics market, which encompasses computers, cell phones, PDAs, iPODs, MP3 players and TVs, appearance and functionality are the key drivers for clear coatings. This market, perhaps more than any other, is driven by style. Today’s consumers are looking to “personalize” their products to reflect their individual personality, social status, or even emotion, and this personalization is being accomplished with unique finishing or styling of the product. For example, cell phones can be purchased with additional interchangeable covers that are painted with various colors and designs that reflect the personal desires of the consumer. Even though appearance is one of the major drivers in this market, the coating performance requirements are similar to those in the markets mentioned previously. Some of the more difficult requirements for the consumer electronics market include hardness, abrasion resistance and chemical resistance.

The new e-coat pigment technology was used on the tip of this muffler. The faded blue piece around the muffler is anodized.

New E-Coat Options

Each of the four markets just described has its own unique performance criteria. For example, the chemical resistance requirement for decorative hardware is four cycles of perspiration, while chemical resistance in the automotive trim industry primarily means withstanding carwash detergents.

Basic similarities also exist across the market segments. For example, hardness is a requirement for all markets with slight variations accepted for each. Thus, a coating formulated to give a minimum 4H pencil hardness would likely satisfy most, if not all, industrial applications. If this approach of formulating a coating to meet most of the high-end requirements for a select set of applications is followed, the probability of the coating having broad application use is greatly increased. Granted, the development of one “super” coating that can meet all needs is an unrealistic goal; however, the concept of formulating a coating to meet a fair number of requirements is reasonable.

This approach was taken in formulating the new electrodeposition clear coatings. The initial target was to develop a clear coating that would provide a high level of performance for properties such as chemical resistance, hardness, abrasion, gloss and clarity. For applications requiring a higher level of performance in a particular area, the coating can be optimized through formulation adjustments to meet the specific needs. The new electrodeposition clear coatings can be tinted with dyes, traditional pigments, and specialty pigments to expand the range of options even further.

In the area of color, a new pigment technology has been developed for electrodeposition coatings that allows for effects and finishes that were previously only achievable with powder or liquid spray technology. The substrate finish continues to show through and, in many cases, adds to the final overall desired effect. For example, a brushed aluminum part will tend to look like it has been anodized with a color, particularly in applications where a lower-gloss coating can be used. Tint colors include blue, green, yellow, orange, red, magenta, champagne, gold and opal, and these colors can be blended to achieve almost any color in the spectrum. Black and white tints are also possible, but they produce opaque finishes. The only color that cannot be produced is silver; the grinding process used to create the tints causes the silver mica pigments to lose their effectiveness.

The transparent, tinted e-coat finishes have the appearance and clarity of a dyed coating with the superior durability of an opaque pigmented coating. The ability to achieve this type of finish opens new possibilities for decorative applications such as intricate three-dimensional parts, large volumes of small parts and metal finishing processes. In these and other applications, e-coat’s uniform and thin coating can preserve surface shapes such as engravings, which might be obscured with powder or liquid coatings. In addition, these transparent color coatings can be used to reduce manufacturing costs by allowing the use of a substitute metal such as coated zinc in place of brass, or by using a coating instead of anodizing (provided the organic coating meets the performance specifications) to achieve a more consistent color batch-to-batch or lot-to-lot.

The Future is Clear

The future for electrodeposition is clear - and colorful. These new technologies will allow finishing professionals to meet the physical property demands of the decorative, automotive, aluminum extrusion and consumer electronics markets while also creating new style effects. The new coating options will also allow electrodeposition coatings to be expanded to new markets. One example is the eyeglass frame market, which traditionally has been served with liquid spray technology. Other markets that are being explored include cosmetics packaging, medical equipment, sporting goods, cycling, bathroom furniture, lighting fixtures and tools. As with the consumer electronics market, these markets are driven by consumers looking for appearance and style, with the underlying requirement that the coating must perform to the individual application needs. The new clear e-coat is designed to meet these and other coating specifications.

Electrodeposition technology is no longer just for black primer markets. As the finishing industry embraces new developments, further advances beyond clear and color will allow additional markets to take advantage of this flexible, cost-effective finishing method.

For more information about electrodeposition coatings, visit www.electrocoat.org.