Coils, powders, and other beneficial approaches to painting. (WIP).

"Cut costs. Reduce emissions. Save weight. Make the top coat more durable." The challenges facing paint companies that supply the auto industry are often at odds with each other, and usually require new coating technologies applied using tried-and-true methods.

There are Four layers to a typical OEM paint job: electro-coat, primer/surfacer, base (color) coat, and clear coat, and the sum total measures just 0.1-mm. thick. In terms of weight, the breakdown, according to the folks at BASF Automotive [Southfield, MI], looks like this: electro-coat, 2 kg--3 kg; primer/surfacer, 1.2 kg--1.7 kg; base coat, 0.6 kg--1.2 kg; and clear coat, 1.5 kg--1.8 kg. That means the average vehicle in the fleet has 12 lb--17 lb of covering on its body, with the lightest layer being the one that gives it its color. And OEMs want to bring this down in an effort to cut vehicle weight and cost. According to Dennis Taljan, director, Decorative Product/Technology/Management, PPG Industries (Troy, MI), "The weight and cost of the finish are paramount to the OEMs, yet consumers want coatings that are more colorful and durable." And while these concerns would appear to be diametric opposites, the paint industry is moving forward on developing technologies that meet these conflicting needs.

Coil coating is one way in which automakers and coating suppliers can control emissions, film thickness, and cost. It significantly reduces paint usage because it has a 99.5% paint transfer efficiency, zero VDC [volatile organic compound) emissions, and greatly reduces in-plant floor space requirements. "The coating line moves at 500 ft./min, and the cure time is 24 seconds for coil coated steel," says Robert White, director, Substrate Protection Systems, Automotive Coatings, PPG Industries. "Compared to painting a formed part, this process cleans the surface better, allows for better preparation and coating, coats both sides of the sheet in one pass, and has better edge-to-edge film control." The A- and B-pillar covers on the previous generation of the Ford Expedition and the windshield base molding of the first generation Chrysler Sebring convertible used steel coated by PPG. The company also has produced many prototype parts--including four-layer (base coat, paint, mica-flake, clear coat) door panels for Chrysler's now-defunct Prowler--and suggests the process is well--suited for many current applications, especially for producing ready-for-assembly roof sections. (The SMART car is the only current application for coil-coated roof panels, though other programs are under development. BASF (coating) and Arvin-Meritor (forming and assembly) collaborate to produce the coil--coated module, which includes an integrated fabric sunroof.) Unfortunately, the range of colors, including metallics, is in need of further development. This limits its application, and many OEMs are taking a wait-and-see attitude as development continues. "None of them want to be the first to use it in a large volume application," says White, "even though most of the large appliances on the market have used this technology for years." Undaunted, PPG says there is a low-cost, low-exposure way for automakers to begin using coil-coated panels.

"If you planned it properly," says White, "you could use coil-coated steel for an entire vehicle as long as you controlled the color palette." While development work is focused on increasing the number of colors available, and reducing appearance harmony issues (coil-coated panels often have a smoother finish and richer appearance due to the lack of "orange peel" and uniformity of the coating), its use might require tighter logistical control, including the batch-build of like-colored vehicles. The reason is simple. A steel coil weighs 40,000 lb., while the average body-in-white tips the scales at or below 1,000 lb. This suggests OEMs would be required to build vehicles in batches of 40 before swapping out coils and colors. However, since this is supposed to be a low-cost, low-exposure example, White suggest that OEMs would be better served by using the coil-coat technology to build, "a modular spaceframe structure with bolt-on panels. This," he says, "would let them stamp a complete set of panels From a single coil, and draw the color needed from inventory as needed."

Because spot welding has the potential to seriously mar the painted surFace, inner and outer panels would be held together via a combination oFadhesive bonding and self-piercing rivets. In what sounds like a precursor to the Saturn program, PPG says that prototypes were built by GM using this technology in the late 1 980s, though at the time the color palette was limited to Four colors: black, white, blue and red. This was a major stumbling block, despite some significant advantages to be had from using coil-coated steel. "Because you can completely eliminate the paint facility,' says White, "you can radically alter the plant Footprint, and eliminate a number oF processes." But with most automakers unwilling to throw out known processes and technologies in Favor oF an unproven but potentially profitable production method, the Fully coil-coated car, when it arrives, probably will Follow White's low-exposure recipe: a nodular spaceFrame niche model designed around the technology's process capability.

Aware of automakers' reticence to scrapping existing painting technology, DuPont Automotive [Troy, MI] has introduced an ultraulow emissions coating technology that can be applied using existing equipment. The "Super Solids" technology is designed to the reduce VOC levels and improve the durability oFthe clear coat. Currently in use at DaimlerChrysler's Newark, Delaware, assembly plant, where the Dodge Durango SUV is built, Super Solids increases the solids content oF the clear coat From 50% to 65%, which reduces VOCs by reducing the volume oF solvents used. DF course, iF it was only a case oF decreasing the solvents and increasing the solids, everyone would be doing it.

According to Robert Matheson, manager, Strategic Technology, DuPont PerFormance Coatings, "We changed the nature oF the oilgomersuthe small polymer chains with Few structural unitsuand gave them structure by changing their reactivity with each other." In other words, DuPont lowered the molecular weight but kept the structures intact, which means less solvent is necessary to thin and disperse the coating because the new chemistry is much less sticky." Thus this high-solids coating flows like a liquid through current sprayers. And with minor modifications to the in-plant equipment, DuPont says it's possible to spray clear coat with a solids content over 80% As a result, OEMs can avoid spending the approximately $20 million necessary to replace an existing liquid spray line with one that applies powder coatings. Also, the Super Solids technology has a total energy and emissions inventory similar to powder coating.

In a similar vein, BASF's Integrated Paint Process [1FF] cuts costs and emissions by eliminating the primer/surFacer step, and the oven time that goes with it. AFter electro-coating, the vehicle is sprayed with two color base coats, and this is immediately Followed by a powder-slurry clear coat. Dnly then is it sent to the curing oven. Because the IPP clear coat is a powder dispersed in water, it's possible to apply this powder-slurry mixture via a standard production spray system, and place it directly atop the uncured color coats. According to Frank McKulka, president, NAFTA II Region, BASF Automotive (Southfield, MI), "This process reduces coating consumption by 20%, eliminates one step in the process, and reduces the energy necessary to cure the Finish." A vehicle painted this way--the Mercedes A-Class is a prime example--spends five minutes in a 175[degrees]F oven rather than 30 minutes in a 320[degrees]F curing oven, a significant energy and time reduction.

PPG's Dennis Taljan, however, suggests eliminating the primer/surfacer layer may cause problems unrelated to the paint to arise. "This is the layer OEMs love to hate," he says. "It costs money, adds weight, requires energy to cure, and eliminating it would make their lives much simpler. But you often Find that, when you take it out, there has been a negative impact on sound levels." Which leaves OEMs with the choice of living with the increased noise, adding sound absorbers, or bringing the primer/surfacer layer back into the painting process. "We expect to sell a lot of Audio Guard to OEMs that insist on eliminating this layer," says Taljan.

Audio Guard is a PPG-developed spray-on acoustic coating designed to be applied by robots during the assembly process, and currently used on some Jeep models. Rather than add asphalt melt sheets and other sound attenuators to the inner panels of the body-in-white, OEMs program robots to spray consistent coatings of Audio Guard on pre-determined areas of the structure. Reprogramming the robots allows a quick alteration in the geometry, thickness, and placement of the coating, so a number of different models and trim levels can be handled by the same application robots. Adds Taljan, "You can replace the separate sheets--which can vary dramatically from trim level to trim level and model to model--with a single Formulation of Audio Guard and multiple parameters for the robots, while greatly reducing the level of dust and dirt in the air." The latter, he says, often ends up on the vehicle surface, and is responsible for the majority of off--line paint repairs.

Because the application is concentrated to the problem area, PPG claims it reduces the amount of material necessary to dampen the noise, and thus reduces vehicle weight. In addition, the material adds reinforcement to the panels on which it is sprayed. The epoxy thermoset---a water-based variant is nearing introduction--is applied as a solid, not a mist, has near-zero VOCs, and can be delivered at a rate of one gallon every 30 seconds. In the future, the Audio Guard coating will be used as an underbody coating, seam sealant, and structural reinforcement. And a variant is under development that can bond metals and composites. "If you can reduce the cost to the OEM by increasing the use and functionality of a single coating," says Taljan, "everybody wins."

RELATED ARTICLE: Taking a Powder

Sitting on the sidelines, despite its greater coverage and recovery rates, is powder coating. Switching to a powder coating system requires a complete tear-out of existing spray systems, and their replacement with a dedicated powder-coat line, It's a cost that, not surprisingly, automakers aren't ready to take, especially when their intransigence has forced coating suppliers to improve their existing products and adapt new technologies to old spray methods. Nevertheless, this hasn't stopped development of powdercoat technologies, despite their greater up-front costs.

Both Dupont and PPG supply powder clear coats to BNW, which are used on the 5- and 7-Series, and many auto plants use powder primer coating technology. Grabbing the color coat and switching it over to powder deposition, however, has been a tough sell thus far. Boosting the efficiency of the entire process while drastically reducing emissions levels may put powder over the top. ""Normally, about 30% of the powder is over spray, and a good bit of that is never recovered," says Rick Tansey, technical manager, Automotive Powder Coating, PPG. Recovering this lost material currently requires purging the paint line between colors so the powder can be collected with minimum contamination. Yet, collecting approximately 98% of the over spray in a so-called "reclaim coat," following it with a color top coat, and topping it off with a powdered clear coat--a process PPG calls "P2Zero"--eliminates the need for a mixing room, paint waste, and exhaust air treatment systems; significant cost centers in an assembly plant. Floo r space requirements are reduced as well. But, because this technology requires a new paint line, it's best used in greenfield sites where it can be integrated into the production process and plant footprint.

Undaunted, Behr and PPG have developed the Dynamic Flex Coat system to provide automakers with a custom, on-the-fly paint capability. The powder dispersal bell is fed by multiple color lines, mixes the pigments in the atomizer, and sprays a color palette of approximately 160 colors, which can be changed as the paint bell travels around the vehicle. Custom paint effects, two-tone finishes, and unique colors can be created in one step. An internal PPG/Behr study showed the process could cut painting costs by nealy 11/unit, but would--again--require a dedicated, though compact, facility, and an automaker ready to adopt a novel painting technology delivered by a single supply source.