Carmakers opt for “greener” paints
Automakers are developing new paint technologies that are good for business and reduce VOC emissions.
Despite various emissions-control technologies, automobile painting operations are a significant source of volatile organic compounds (VOCs). But the new technologies that large auto manufacturers are adopting to lower costs and improve their products are also reducing harmful VOC emissions.
Under the Clean Air Act, the U.S. EPA and state agencies regulate VOCs emitted from paint refinishing at body shops and car dealers, because these facilities do not necessarily have emissions-control technologies, says Jose Gomez, a technical development manager at the California Air Resources Board (CARB). No upper limits have been set for VOCs emitted from auto manufacturing, and automakers are mandated to use the best available pollution-control technologies at new plants, says David Miller, a department manager in paint engineering and maintenance at a Nissan plant in Tennessee. Regulations do not require an update of the technologies unless a plant is to be modified significantly, Miller says.
Standard pollution-control systems capture solvent fumes and burn them off with natural gas, but that takes a lot of energy and results in CO2 emissions, says Mark Wherett, an environmental engineer at Ford. A standard-sized Ford plant that uses this process emits ~800 t/yr of CO2 and ~4.5 million g/yr of VOCs.
The nonprofit Ecology Center estimates that U.S.-based automobile plants emit ~1800 g of VOCs for each vehicle manufactured. These emissions can be reduced with evolving paint technologies, says Charles Griffith, director of the Ecology Center’s auto project team. According to the team’s analysis, 900 g/vehicle is an achievable goal for the auto industry. Although most major manufacturers, including Toyota, Ford, Mazda, and Nissan, already use water-based and high-solid paints at plants built since the mid-1990s to keep their emissions in check, newer technologies could cut emissions even more. However, outfitting existing manufacturing plants with newer technologies is expensive, and “engineers will meet the minimum standards most cost-effectively,” Griffith says.
But the latest technologies that some companies have developed to cut costs and improve product lines have environmental benefits.
Last year, Mazda established a three-layer wet-paint technique at all of its Japanese plants. The process combines three painting stages—paint primer, base coat, and clear coat—into one, saving the company energy and paint costs by reducing the number of painting steps. It has brought VOC emissions down by 45% to 35 g/m2 of vehicle area painted. This meets the EU standard for refinish coatings, which are more stringent than those in the U.S.
Mazda is also setting up a new base-coating process that involves immersing a vehicle in a paint tank and subjecting it to an electric current to make the paint stick to the surface. This technology cuts VOCs emitted during base-coat painting by half, down to 32 t/yr, and provides better rust protection.
Ford, which has a business alliance with Mazda, plans to use the three-layer wet-paint process at its next-generation plants by 2010. The new plants will generate electricity by burning fumes from solvent-based paints to run a Stirling engine. The technique cuts CO2 emissions to an eighth of the present amount and reduces VOCs by 25%, says Wherett, who was a lead developer of the process. The method also uses less heat energy than it takes to burn the VOCs, and generates 50 kW of electricity, saving the company energy costs. But adapting plants to the new technology is expensive, he says, so they will be converted only if it makes economic sense.
At Toyota’s North American plants, VOC emissions are as low as 20 g/m2. The company uses water-based paints in addition to efficiency measures such as reducing the amount of paint solvent used for cleaning and reusing solvents.
Japanese automotive companies seem to be taking the lead in new paint technologies, but the reason why is unclear, says Dimitri Stanich, a spokesperson for CARB. “The Japanese have been more innovative in terms of other environmental technologies, hybrids in particular,” he says. “So it could be as simple as they have better technology or as benevolent as they want to do something for the environment.”
Automakers have made strides in improving VOC emissions with new paint technologies, but painting remains a significant source of VOCs, according to Griffith, and improvements usually occur only at recently updated plants. “There are lots of older ones out there that tend to have much worse emissions.” To achieve lower VOC emissions, automakers need to find out how they can “more quickly bring the bottom rung of these facilities up to a standard with the higher performing facilities.”
