Clear topcoats are used to protect an automobile’s finish from environmental factors such as dirt, acid rain and ultraviolet rays. The current industry standard for clear topcoats is conventional solventborne liquid coatings. However, because these coatings emit VOCs at their application stage, alternative coating systems have been developed. Powder, waterborne and high-solids coatings are alternatives that offer several benefits. The benefits for powder coating include the elimination of VOC emissions, the ability to collect and recycle overspray, no sludge waste, and the elimination of the need for solvent capture systems or incineration.
There are several common types of powder coatings (polyester, super durable polyesters, polyester urethanes, and melamine urea) used in the automotive industry that provide adequate performance for specific applications other than clearcoats. Some manufacturers that demand better clearcoat performance, however, are using glycidyl methacrylate (GMA)-based coatings, which offer formulators and end users the highest levels of clarity, durability, weatherability, smoothness and chemical resistance.
Key Industry PlayerAnderson Development Co., Adrian, MI, and its parent, Mitsui Chemicals, a worldwide leader in technology-based chemical products, are forerunners in GMA resin technologies for powder coating applications. Jack Georgal, director of Marketing at Anderson, says powder coatings are attractive to the auto industry because they do not emit the harmful VOCs that liquid paints do.
“Reducing VOC emissions is a top priority for the auto industry today,” Georgal says. “Because the GMA powder coating process does not use solvents, virtually no VOCs are emitted into the atmosphere. Reducing VOCs keeps with the automotive industry’s commitment to becoming ‘green.’”
Using the principle of “opposites attract,” the powder coating application method uses electrostatically charged particles that are sprayed onto electrically grounded parts. The charged powder particles adhere to the parts and are held in place until they enter a baking oven, where they are melted and fused into a finished part. Because these dry powders do not run or drip, they produce a smooth, superior-quality finish.
Georgal points to the Big Three’s development of the low emission paint consortium (LEPC) as an example of the industry’s concern about VOC problems. Although the LEPC has documented many successes with powder coating technologies, he says the industry has been slow to implement change because of the financial costs to overhaul current systems and perceptions that the technology has not yet been perfected.
“Mitsui and Anderson have spent more than 10 years developing and refining resins for powder clear topcoat applications,” Georgal says. “We offer the resin technology needed to efficiently and cost-effectively implement GMA powder coatings on a wide-scale basis today.”
Poised for a Break OutFerro Corp., a specialty chemical company in Cleveland, uses GMA resins in automotive powder coating formulations. Champ Bowden, the automotive market manager for industrial coatings at Ferro, says GMA clearcoats are the primary top coating for aluminum wheels and are starting to penetrate the industry for us in clear top coatings for automotive bodies.
“The excellent appearance and performance properties of GMA acrylics have made them our resin system of choice for powder clearcoats for the automotive industry,” he says.
Marshall Leininger, OEM product manager for powder clearcoats and waterborne coatings at Seibert Powder in Cleveland, says that the company selected a GMA acrylic resin system as the backbone of its automotive powder clear products for several reasons, but primarily because of the long successful history of the technology. He adds that the long history of these systems should reduce the perceived risks of implementing powder clearcoats in today’s OEM coatings.
“We like to call it a new old technology,” he says. “GMA acrylics have been in the automotive arena for nearly 30 years and have demonstrated excellent long-term weathering characteristics as well as the clarity, smoothness, and chemical resistance required by the automotive OEMs.”
Dr. Paul Pettit, global technical director for PPG Industries, says acrylic powder coatings, such as GMA, are poised to break out of the small niche markets that they historically occupied due to new resins and formulation technology.
“With the advances in technology, combined with the need for higher performance in many markets,” Pettit says, “acrylic powders can and will offer cost-competitive options to alternative technologies for these new opportunities.”
Pettit notes that powder acrylic technology was first introduced to the marketplace during the 1970s with several automotive companies experimenting with pigmented monocoat topcoat powders.
“Nissan actually commercialized acrylic powder coatings in Japan and used them for a number of years to coat some of their pickup trucks,” Pettit says. “The coatings offered a higher level of durability, but following these experimental projects there was only limited activity to develop and commercialize acrylic color and clear powder for automotive applications.”
Georgal says that’s because the U.S. affiliate shifted to a basecoat/clearcoat system, which offered use of existing liquid application equipment and eliminated the problem of color change difficulties with six different colored topcoat powders.
Georgal notes an interesting experiment Anderson was able to conduct with two black 1981 Datsun (the former name of Nissan) pickup trucks, which were manufactured within a month of each other.
“We found the trucks in a junkyard and paid $300 for their cab roofs,” Georgal says. “We washed and then polished sections of each roof with a common automotive polish and found that the surface finishes were restored to an 88% gloss. The experiment demonstrated the excellent weatherability and chemical resistance of coatings formulated with GMA resins.”
Commercial ApplicationsPPG’s Pettit says Harley Davidson was one of the first companies to use acrylic powder clear topcoats to protect the finishes on motorcycles. He explains that Harley Davidson switched to acrylic clearcoat technology because of its excellent durability, chemical resistance and appearance. Since then, he adds, new acrylic powder technology, with improved formulations, resin chemistry and powder manufacturing processes and application, enabled BMW to construct the first commercial powder clear line at its plant in Dingolfing, Germany.
“The development of powder clear technology for the BMW line resulted in an acrylic powder with excellent thin film appearance, good recyclability, and excellent long-term durability,” Pettit says. “Based on this outstanding achievement, BMW has received numerous awards and accolades for technical excellence.”
Georgal says the concept for the BMW plant in Germany was pitched in the early 1990s, commitment was achieved in 1996 and commercialization took place in 1998. Today, powder clear topcoats are exhibited on BMW’s Five and Seven Series vehicles.
“BMW went out on a limb to prove that this new, non-polluting technology works,” Pettit says. “In the U.S., one of the main reasons the auto industry has been cautious about this GMA powder coatings is perceived weaknesses in the technology. BMW is showing the world the concept of powder clearcoats is a viable and effective option.”
Pettit adds that BMW has a program in place to monitor the performance of the finishes and that reports have indicated outstanding customer satisfaction.
Technological ChallengesPaul Prucnal, manager of powder coatings technology at Anderson Development, says that while GMA powder clearcoats have come a long way, there is still some work to be done to raise their performance level to that of 2K Urethane, the liquid standard by which GMA powder coatings are compared in the industry.
One challenge is eliminating the yellowing that sometimes appears on white cars coated with GMA powder clearcoats, and a second is achieving smoothness and thickness that is equal to liquid coatings.
“We’re continually working on developing new resins to attain the desired application features,” Prucnal says, “and we are confident that we will be able to work out solutions for the few remaining bumps that remain in the road of GMA powder clearcoats.”
The Dow Chemical Co. has made manufacturing high-quality GMA resins easier by supplying high-quality raw materials.
“Dow has been a leader in supplying GMA monomer that exhibits quality and consistency,” Carlo Spaniol, Dow global market manager for packaging, auto and photocure applications, says. “In producing GMA resins, adjustments are needed based on the purity of the GMA monomers. High-quality GMA monomers mean fewer adjustments and a more stable process, which translates into a higher quality product and better results.”
Dow’s acrylic monomers — GMA, as well as hydroxyethyl acrylate (HEA) and hydroxypropyl acrylate (HPA) — provide consistent quality and unique chemical resistance and weatherability in the production of resins used in a variety of high-performance coating applications, including automotive coatings, according to Spaniol.
“Industry wide, Dow is the only company with plants 100% dedicated to the production of GMA, HEA and HPA,” Spaniol says. “We see great potential in the future of the paint and coatings industry and are committed to supplying our customers with the products they need to achieve success.”
ConclusionAlthough automakers have been conservative about adopting this new technology, many industry experts believe that the case for wide scale implementation of GMA powder clear topcoat systems is strengthening on a daily basis.
“Originally, environmental friendliness was the driving force behind the push for alternative coating technologies,” Georgal says. “However, many other benefits have become apparent to the industry, including application friendliness and performance. All of these benefits are positive factors that will eventually push GMA powder coatings to the forefront of the industry.”
For more information about GMA monomers, visit www.dow.com; call Dow’s Customer Information Group at 800/441.4369 in North America or 1-517/832.1426 outside North America (mention element number 1-A2THX).