Marked technology advances in resin chemistry and analytical methods lead toward increasingly higher solids content in automotive clearcoats.

DuPont Aims for Higher Ground with ‘Super' Clearcoat Technology;BASF Sees Bright Future for UV

With the recent commercial introduction of its "Super Solids" automotive-clearcoat technology, DuPont Performance Coatings has taken the initial step toward realizing a technical objective conceived way back in the same decade that the first Chevrolet Corvette rolled off the assembly line.

Unfortunately for DuPont in the otherwise happy-days 1950s, the seminal attempt to formulate a 100%-solids automotive finish met an inglorious fate more akin to the demise of another icon of the era -- the Edsel -- than that of the ‘Vette, still zipping along in the early 21st century.

But thanks to marked technology advances in resin chemistry and analytical methods in the intervening years, DuPont this time around is cruising confidently toward its goal of increasingly higher solids content in automotive clearcoats. And the company again sees a 100%-solids coating as being within reach in the very near future.

That's the bullish opinion voiced by Robert Matheson, Technical manager for Strategic Technology at DuPont Performance Coatings, who led efforts to develop the Super Solids technology in a program that began more than 10 years ago.

DuPont last year took the Super Solids technology from the R&D lab to the assembly line with a commercial introduction at DaimlerChrysler's Newark, DE, auto-production plant. Application of the Super Solids clearcoat on the Dodge Durango made at the Newark plant has significantly reduced VOC emissions, bringing the facility into compliance with new regulations affecting the site, Matheson says.

At Newark, the Super Solids clearcoat is being applied at about 63% solids content, with VOCs at about 2.9 lb/gal. Matheson says. But he says DuPont is well on its way to formulating a two-component clearcoat system with a solids content of 88% and a VOC level of 1.2 lb/gal, with trials at auto-assembly facilities under way. "We're confident it will work," he says.

Looking further down the road, Matheson says DuPont is on the fast track to meet its long-term objective of a 100%-solids finish, with laboratory work currently under way and a trial product anticipated by as early as the end of this year.

DuPont's Super Solids technology is among several recent notable technology developments to emerge from the R&D think tanks of the major automotive OEM coatings manufacturers. Also receiving rave reviews in automotive-industry circles are BASF's "DynaSeal" and "Integrated Process" technologies, while PPG Industries Inc. has captured a number of industry awards with a series of product innovations ranging from new electrodeposition coatings to highly durable clearcoats.

Advances in resin chemistry achieved by the coatings makers themselves have played a major role in many of these technology developments, with the developments spanning a number of resin types.

DuPont’s Super Solids clearcoat is applied to Dodge Durangos at DaimlerChrylser’s Newark, DE, assembly plant.

Super Solids Success Based on Functionality of Oligomers

For DuPont, the development of low-molecular-weight but highly functionalized resin systems held the key to the successful formulation of very high-solids coatings that offered reduced emissions, application with conventional equipment and a strong performance profile in terms of durability and resistance to chemicals, environmental etch, scratching and marring.

"The old wives' tale that low-molecular-weight resin materials are bad for properties is false," Matheson says. "What is true is that low-molecular-weight film-forming ingredients of zero or inadequate functionality are catastrophically bad for properties."

This premise drove the research team headed by Matheson to focus on ways to modify the oligomers that make up resin systems to increase reactivity in ways that could enhance performance properties, while still retaining the low molecular weight needed to allow the coating to be applied as a conventional liquid finish.

Matheson says the origins of the Super Solids technology dates back to the late 1980s, when DuPont sought to assess whether "non-paint" options such as laminating and in-mold color plastic auto parts would emerge as alternatives to existing automotive-finishing technologies. The consensus was that paint would remain the most economical technology for most automotive finishing applications, he says.

Around 1991, DuPont launched a strategic technology group to focus on various finishing options expected to emerge as solutions to the challenge of lower emissions without sacrifice in performance. Powder coatings, waterbornes and higher solids were viewed as the primary candidates. DuPont is active in all three areas, and in the 1990s renewed its quest for increasingly higher solids content. Clearcoats became the focus of this R&D program, although other components of the automotive-finishing spectrum are also being targeted, Matheson says.

The Super Solids odyssey actually began with an extensive review of DuPont's first quest for a 100%-solids paint nearly 50 years earlier, Matheson says. A year of study of that "famous failure," as Matheson describes it -- work devoted to essentially recreating the R&D process involved -- showed that the idea then as now was to take solventborne paints to their highest solids limit. The resins and all other liquid components were designed to be reactive and film-forming. Back then, the primary incentive was economic -- to get the most applied material for the money.

While the objective appeared to offer great promise, Matheson says the analytical tools of that day and age did not permit adequate detection of variability in the paint's chemistry. The resin chemistry employed in the 1950s was something called "vinyl dioxalane" catalyzed to create a thermoset crosslinked polyester. Any chance for success was killed by batch-to-batch variations in the resin, making performance unpredictable.

With the mass spectrometry and infrared tools available in the 1990s, such variations could be accurately gauged, Matheson says. Using these advanced analytical tools, DuPont researchers this time around focused on the development of resins characterized by low molecular weight but possessing high levels of reactivity and high functionality.

Besides the original DuPont project in the 1950s, Matheson says the research team also reviewed a development program conducted in the 1980s at Ford Motor Co. that produced a durable, non-brittle, low-VOC monocoat using highly functional oligomers. Making a very high-solids paint that would not be brittle was viewed as a major challenge, he says.

Continued development focused on refining the product and determining the primary properties sought in the coating. Low molecular weight of the resin, a necessary characteristic in view of the increased solids content, actually was found to provide greater miscibility of the various polymer components needed to generate the crosslinking that delivers important performance properties.

"When we realized that, we moved into hybrid crosslinking," Matheson says. Thus, the resin system combines melamine, urethane and silane components, all synthesized at a much lower molecular weight than the norm.

"This really opens up a very powerful door. We found we can increase solids and improve film properties, tailoring them to give hardness, etch and chemical resistance, adhesion, and durability," Matheson says. The silane functionality is critical to the chemical resistance, exterior durability and the needed low viscosity, while the urethane component adds toughness. The melamine also boosts durability, adhesion and recoatability.

At the DaimlerChrysler plant in Delaware, the decision to make the conversion to the Super Solids clearcoat alone allowed the plant to meet new emissions requirements that are based on a total coating process. That process includes a low-VOC electrocoat, a powder primer, waterborne basecoat, and the Super Solids clearcoat, Matheson says. "And they could use existing equipment, with no capital investment."

DuPont also is looking to market OEM primers and aftermarket refinish products based on the Super Solids technology, with a refinish clearcoat nearing commercial application. In the OEM primer segment, Matheson sees the technology as posing a strong challenge to waterbornes and powders, based on both performance and environmental criteria. DuPont actually offers all three types of primer systems, as automakers have tended to pursue different tracks to achieve various performance and environmental objectives.

Solids-content levels in DuPont’s automotive coatings have increased markedly over the past 50 years, and exceed 60% with DuPont’s Super Solids clearcoat technology. A nearly 90% solids clearcoat is undergoing application trials.

BASF Looks to UV As Shining Light in Automotive-Coatings Future

At BASF Coatings, UV-cure advances have recently grabbed the spotlight with the company's introduction of the DynaSeal coating, a dual-cure (UV/thermal) sealer designed for application to sheet-molded composite (SMC) materials used in automotive vehicles.

The problem addressed by the DynaSeal system is the porosity of SMC substrates and the resulting "outgassing" of volatiles -- moisture or solvents -- that can occur when the coating is baked.

"Basically we're using the crosslinking density provided by UV coatings to eliminate the ability of vapor to travel out of the substrate, by creating a barrier," says T.J. Lepkowski, Product Marketing manager at BASF Corp's coatings business in Southfield, MI.

The DynaSeal resin system employs urethane, acrylic or polyester oligomers that react under the application of UV light to create the dense crosslink matrix that provides the desired barrier effect. In addition to crosslink density, the technology allows a thinner film build and can boost production rates due to the rapid cure rate, with the UV cure requiring a fraction of a second and the thermal-bake time also reduced from what's normally required. Lepkowski says the technology has reduced SMC porosity defects by 75%.

The DynaSeal technology is being used for automotive fender panels produced by Meridian Automotive, a Kansas City-based supplier to Ford assembly plants in Kansas City and St. Louis.

Taking UV curing technology to a starring role in automotive OEM finishes, however, will not happen at the speed of light, Lepkowski says. UV curing of three-dimensional parts and substrates of various shapes presents a challenge, and the distances from curing lamps also must be kept within certain parameters. That's where the role of thermal cure comes in with the DynaSeal technology -- providing complete cure in all substrate areas.

BASF sees the relatively humble beginnings for DynaSeal as a first step toward more ambitious objectives in the automotive field. "One reason it was brought to market this way is to make the industry comfortable with this technology," Lepkowski says. BASF also is at work on a UV clearcoat, which Lepkowski sees as having potential to find its way to the marketplace "three to five years out." The technology offers the potential for excellent resistance properties, he says.

Taking a realistic view, however, Lepkowski says UV technology won't get a great deal of attention "until the economy turns around." BASF operates a UV pilot lab in Germany where the process is being employed to finish body panels and auto bodies. "It's very positive," he says of the performance results being seen. The coatings can be sprayed at 100% solids, but 60-70% solids are more realistic in the short term due to rheology issues, he says.

Also in recent years, BASF has successfully developed the commercial application of its "Integrated Process" automotive-finishing system at a Mercedes-Benz assembly plant in Rastatt, Germany. The process is designed to reduce costs and emissions by removing a bake step following application of the primer.

With the Integrated Process, two waterborne basecoats are applied, with one of the layers serving as a primer-surfacer. Then a "powder slurry" clearcoat -- a powder coating finely dispersed in water -- is applied, followed by a thermal bake. BASF calls the process "wet on wet on wet" and says it is working to expand its use to other auto-assembly plants.

BASF is focusing considerable R&D attention on UV-cure coatings for automotive applications.

New Substrates, Environmental Issues Seen as Major ‘Drivers'

Taking a glance toward the future, DuPont's Matheson says coatings suppliers will be challenged to develop finishes for lightweight aluminum and plastic substrates, particularly if hydrogen-powered and fuel-electric "hybrid" vehicles gain momentum in a marketplace increasingly shaped by oil-conservation needs. Automakers also are looking to keep processing and capital outlays to a minimum.

Waterbornes and powder clearcoats continue to draw considerable R&D attention, but technical issues remain, among them film thicknesses in the case of powder and cost factors with waterbornes due to the need for stainless-steel application equipment and slower dry times that can drag efficiencies down.

Matheson says no clear-cut "winner" has emerged in the race for the dominant automotive-clearcoat technology, as automakers and their coatings suppliers pursue waterborne, powder and high-solids avenues. "It's going to be a complex situation in the clearcoat picture involving alternative technologies," he says.

But DuPont figures its ultra high-solids entry in the clearcoat derby is sure to outdistance its ancestor of some 50 years ago. After all, one Edsel per century is enough.