Automotive The underhood segment of the automotive industry was the first to use powder coatings to a large extent. During the early 1970s thin-film epoxy powders found use as corrosion-resistant coatings on coil springs. These springs required a coating that provided flexibility, as well as protection, to the substrate in a hostile environment. Typical processing of coil springs included cleaning and an ironphosphate pretreatment, after which about 2 to 4 mils of an epoxy powder were electrostatically applied. oFinally, a convection cure of about 300 F for 20 minutes finished the parts. When this process was successfully implemented, these parts exhibited excellent field durability. If the pretreatment process was compromised and the cleaning or phosphatizing steps were ineffective, the painted part performance would be greatly diminished. Failures such as gross adhesion loss and poor corrosion resistance could occur. In the early days, powder was positioned in the market as a very high-quality coating. Some might have considered it to have such high quality that the cleaning and pretreatment was not so crucial to the finished part’s quality and durability. Pretreatment of powder-coated parts is as important to the finished-part performance as it is for other coatings, such as electrocoats. Powder has been used extensively as a protective finish to provide corrosion and chemical resistance for many underhood components. Stamped steel brackets, tubing and castings of all kinds are commonly coated. To achieve optimum adhesion, pretreatments vary according to the type of metal. Perhaps one of the more surprising uses for powder coatings is on engine blocks and cylinder heads. For the past five years, OEM engines have had epoxy powder coatings applied to cast-iron blocks and heads. Specialized coating lines must process these parts to handle the massive weight of the parts and the curing ovens used to crosslink the powder. Even though an engine block can weigh upwards of 300 pounds and be a tremendous heat sink, the process is still very economical to the engine manufacturer. Organic powder coatings have been used extensively in the automotive industry since the early 1970s. This article will discuss the growth of powder coatings in this market from first application s to current and future uses. The old process of painting an engine involved sending an assembled engine through a liquid paint booth. Much masking had to be done to prevent oversprayed paint from getting into the intake manifold and the flywheel area. Pretreatment and cleaning of the engine were difficult at best. The liquid epoxy coating was a low-bake cure product that did not have significant crosslink density. Finished-part performance was not very good for all of these reasons. Powder coating these castings offers many advantages to the engine maker. The blocks and heads are painted immediately after the casting process, which helps keep the parts clean prior to painting. Also, there is a significant texture in the raw casting, which greatly aids the mechanical adhesion of the powder to the block. For these two reasons, it is often not necessary to chemically clean and pretreat these castings to achieve the desired corrosion performance. Certainly, the powder finish has a much higher quality than the liquid coatings because of the much higher molecular weight of the resins used in the paint. That, coupled with the crosslink density achieved in the massive curing ovens, gives outstanding finished-part durability. The ability to recover the oversprayed powder during application also results in a significant savings over the liquid alternative. All of the coating work takes place in transit as the castings move from the foundry to the engine assembly plant. This serves to reduce transportation costs, since the parts must move on this path anyway. Painted parts arrive at the engine assembly plant ready to be machined. The coating has enough integrity to survive this machining process. At that point, the blocks and heads are ready to be assembled. The in-plant painting process can be removed completely, eliminating costly process equipment and reducing VOC emissions and paint-waste disposal issues. In modern vehicle design, the engine compartment has been “tidied up” and the engine itself has been decorated. With the prevalence of fuel injection, cast-aluminum intake manifolds occupy a prominent place in the engine compartment. For several years, powder coatings have been Paint & Coatings Industry 49 used as decorative and protective coatings on manifolds and valve covers. They highlight the casting and give it a more uniform appearance than is possible with a raw casting. The coatings are durable enough to have the manifold retain its appearance for many years of field service. Often, these coatings have a texture that also hides defects in the cast substrates. Interior Trim Parts While most automotive interior trim materials are made of some type of plastic, this is still a large market for powder coatings. The primary reason for this is that most truck interior seating requires the use of a steel platform that raises the seat about 6 to 9 inches above the floor. The truck and van market currently represents 50% of the North American automotive market. Typically, a truck seat has a cold rolled steel platform made from stampings. It might require three or more stampings to be assembled to form one platform. These platforms are currently coated with just a single coat of powder, which provides corrosion, chip and mar resistance. The common requirements for these finishes are uniform color and consistent low-gloss appearance. Typically, there are four colors involved in a vehicle program: gray, beige, red and blue. While the shades can vary from program to program, the gloss is becoming consistent throughout the o industry, averaging about 4 gloss on a 60o gloss meter. Generally speaking, polyester chemistries have replaced epoxy chemistry for interior applications. It might be arguable that seat risers do not see much UV exposure, but other applications, such as speaker grilles, are at or above the beltline and could see more UV exposure. Powders are regarded as the optimal finishing material for interior seating components. Powders are still limited from the job of finishing plastic substrates because the curing temperatures powders need are above the distortion temperature of plastic substrates. Exterior Trim Parts Powder coatings have been used for 15 years to finish exterior trim parts for the automotive market. A real boon to the use of powders was the “black out” look. Hang-on or add-on parts such as door handles and moldings needed a finish that was as durable as the body coating materials, since they would be added to the vehicle in the assembly plant. Further, these addon parts would need to be finished at supplier or custom-coating plants all over the country. Polyesterurethane powders were developed in smooth, lowgloss finishes that did two things well: they met the appearance requirements and provided excellent durability on the finished part. The first application commercialized for automotive exterior trim parts was a low-gloss, black, 30o gloss powder for door handles made of zinc diecastings. A finish was needed that would be attractive and also cover the edges and curvature of the casting in an economical yet durable way. One of the first specifications in this market was FBMS l-43, a GM specification. It called out a specific process for cleaning, priming and topcoating zinc castings. Polyesterurethane powders were specified as the topcoat. For steel and aluminum moldings, the same powder topcoats were used, often without the need for primers. These coatings still are in widespread use today and represent the best overall value for appearance, durability and cost for exterior trim parts finishing needs. Currently, black is the dominant color for powder finishes for exterior trim parts. Different OEM’s might have subtly different shades of black, which vary in their degrees of jetness. They also differ in the gloss specifications, which range from 12 to 20 to 30 to 90+. One of the major issues in this market is gloss retention after weathering. While polyester-urethane coatings provide very good overall performance,o after about 18 to 24 months of 5 South Florida black box exposure, these coatings lose more than 50% of their initial gloss. The FBMS 1-43 specification allowed the part to be “polished black” to restore the lost gloss. Today’s customers want the add-on parts to have the same durability as the newer basecoat/clearcoat body finishes, Customers don’t want to polish the handles-they want them to be more durable in the first place. Acrylic powders have been proposed to offer better weathering characteristics. This is a logical progression in the powder market since automotive basecoat/ clearcoat topcoat systems are in acrylic chemistries. The market for acrylic powders has emerged in the last two years. Where OEM customers have demanded better performance, GMA acrylic powders are now commercially available for several applications, These are predominately high-gloss black powders. This chemistry offers powders that have exterior weathering properties comparable to current BC/CC systems in a one-coat system. The cost per pound of these materials is approximately double that of polyester-urethane powders, which has caused these powders to be specified only where the increased material costs are not an issue. Speculation abounds that an interim quality powder - something that is a mid-grade in cost and performance could find a place in the market. Acrylicurethanes should indeed fill that gap, they offer increased Florida gloss retention and are at a mid-point in cost between polyester-urethane and GMA acrylic powders. These formulations are sometimes called hydroxyl functional acrylics. Wheels Powder coatings have found an important home in the aluminum wheel industry Since the Detroit community first started using large quantities of cast aluminum wheels as a design tool, powder has grown steadily with the market. In 1983, most of the manufacturers of cast aluminum wheels were located in Southern California. At that time the market for wheels was almost exclusively in the aftermarket. Those customers took exceptional care of their cars and were very particular about their appearance. The environment in which these wheels lived was not very severe - no real winters, which meant no road salt that would accelerate c o r r o s i o n o f the wheels. In fact, most wheels sold to the aftermarket had no protective clearcoat at all. Powder earned its place in this market only when Detroit wanted to buy millions of wheels, put them into service all over the United States and warrant them to their customers. The first coating system used by the aluminum wheel industry as a protective clearcoating was a solventborne clear. One can imagine that the Southern California Air Resources Board would strictly limit the use of such a paint in the Los Angeles area. As Detroit increased demand for these wheels, the industry searched for an alternative coating system to comply with these air quality regulations. The next step was to use a waterbased clear. While it was a reduction, these water-based coatings still contained VOCs. Despite the increasing demand for wheel production, the air quality permits limited the number of wheels the manufacturers could finish. Production was actually restricted because of these regulations, One alternative was for manufacturers to purchase credits from an “air broker.” An air broker obtained VOC emission rights from companies that were not using their full allotments. These rights were transferred to the purchasing company as a way to comply with the regulations. This was obviously not a value-added cost, but simply a way to meet the market demand for aluminum wheels. The answer was to eliminate the root cause of the problem: VOCs in clearcoating material. Clear powders were first used on OEM aluminum wheels during the 1984 model year. Powders were an answer to the wheel manufacturers’ dilemma, but there were other advantages. The powders reduced rejected wheels because runs and sags were avoided on complex shaped wheels. Also, powders could be easily applied thicker than liquids. This provided much better edge coverage, a major concern in corrosion protection. Metallic-colored powder basecoats soon followed. Powders were able to decorate the wheels with attractive colors while still enhancing their overall corrosion resistance and durability. Even today, a powder basecoat plus a powder clearcoat paint system is recognized as the most durable and highest quality paint finish for aluminum wheels. The primary quality issue in the aluminum wheel finishing market today is filiform corrosion resistance. This phenomenon is the finger-like white corrosion usually found only on clear-coated, bright machined surfaces. This problem has been extensively studied by the OEMs, and the emerging trend is that clear acrylic powders offer better filiform corrosion performance than the typical polyester TGIC clear. 5 4 S e p t e m b e r 1 9 9 4 It is further understood that the pretreatment process for the clear machined surfaces is critical to successful performance against filiform corrosion. The cost/benefit calculations have continued in an attempt to determine the best fix to this answer. As in the exterior trim parts market, the material cost of switching from polyester TGIC clear to acrylic can mean a premium of 80% or more. Another major issue in the market is the growing trend towards very bright metallic wheel basecoat colors. The aluminum pigments used to achieve these colors have been available only in paste form, which is not readily adaptable to dry powder formulations. Therefore, water-based liquids have emerged as an important technology to achieve these bright metallic looks. Two factors might change this trend. The first - continuing VOC reduction regulations happened 10 years ago in the clearcoat market. The second is new technology to produce these bright appearances in powder. The end result might also allow powder to supersede liquid coatings in this area, as it has in the rest of the Steel wheels are suffering in growth due to the popularity of aluminum wheels. Most are supplied directly to assembly plants with a weatherable acrylic electrocoat finish, since wheel covers will protect them for most of their lives. About the only other color commonly seen in the OEM steel wheel market is a silver. One-coat powders with sufficient weatherability are on the horizon now. When perfected, this market will also discover the many benefits of a powder topcoat to replace the liquids now in widespread use. Bodies Twenty years ago in the United States, powder was applied to automobile bodies on a “production trial” basis. Ten years ago, powder was used on a “full production” basis as a powder primer-surfacer. Today, at least three automotive assembly plants are using powder as both a primer-surfacer and a black-out coating material. Numerous others are using powder as a chip-resistant coating on rocker panels and leading edges of sheet metal - areas most prone to paint chipping. The use of primer-surfacer seems to be growing in importance and value again. The purpose of this layer is to protect the underlying electrocoat primer from ultraviolet degradation and to optimize the chip resistance of the topcoat paint system. In a case where this process must be added to an assembly plant, powder can be a very economical alternative to liquid spray primers, due largely to the environmental friendliness of powder. it is easier to permit an automotive assembly plant to use powder than it is to allow liquid paint. The ultimate automotive application would be to use powder as the final protective and decorative clearcoating for the body. The trend of basecoats followed by clearcoats has become the state of the art in body finishing. It will be much easier for powder to become the substitute for liquid clears than for the colors. Powder application systems that can change colors rapidly and efficiently according to the demands of the automotive body painting market have not yet been perfected. Therefore, powder makes the most sense as a topcoat, as long as every car is painted the same color. That is the allure of a clear powder. Powder coatings have found a significant place in the automotive coatings market. If the powder coatings industry successfully addresses the issues of appearance and economics, growth would be sustainable at rates well above those of other technologies.