Finishing Pollution Prevention Options
Process changes and product reformulations can help reduce the emission of volatile, sometimes toxic, chemicals. Product redesign, a pollution prevention option that addresses issues of waste at the earliest possible moment – the conceptualization of a product – can eliminate the emissions to air as well as the generation of hazardous/solid waste and wastewater.

Process Changes
"Block painting" is an industry term used to describe a painting practice that minimizes the frequency of color changes in finishing operations. Simply stated, the term refers to painting many vehicles of the same color before changing colors. Block painting, by minimizing color changes, reduces the wastes generated during purging and cleaning the application equipment to accommodate color changes.

Transfer efficiency is a parameter that measures the performance of painting and coating operations. It is the amount of paint that remains on the part compared with the quantity of paint used; the more material that adheres to the part, the better the transfer efficiency. Paint that is not delivered to the part surface -- instead sticking to floor grates or walls, or being removed by ventilation air flowing through the paint booths -- is waste and represents poor performance. By increasing the transfer efficiency of the application process, the consumption of paint is decreased. Methods that have been successfully employed to increase transfer efficiency include the use of electrostatic spray guns and the reconfiguration of vehicle body parts and spray guns. Electrostatic spray guns impart a charge to the paint particles. The electrically charged particles are attracted to the vehicle part, thus improving the transfer efficiency of the system. The reconfiguration of vehicle body parts and spray guns can also enhance transfer efficiency by increasing the amount of paint directed at the parts. Both methods try to maximize the amount of paint that is applied to and remains on the parts.

Product Formulations
Paint formulations continue to evolve to meet a variety of environmental and performance goals. Initially containing high quantities of solvents (i.e., high-solvent, low-solids), paint formulations have changed and now include (1) high-solids, low-solvent formulations, (2) water-borne formulations, and (3) powder coatings. High-solids, low-solvent formulations reduce VOC emissions by 50 percent or more, when compared with high-solvent formulations. Water-borne formulations can reduce VOC emissions even further. Containing less than 5 percent solvent, they are an improvement over high-solids, low-solvent formulations, which contain as much as 15 percent solvent. Similar spray techniques can be used to apply both products, but stainless-steel piping within the painting system is required to eliminate the potential for rust if water-borne formulations are used. Water-borne formulations for color coats and low-solvent clear coats are successfully being used in a number of assembly facilities across the country.

At this time, General Motors, Ford, and Chrysler (now DaimlerChrylser), through the United States Council for Automotive Research (USCAR), are cooperatively developing and evaluating the use of powder coatings and other low-emission technologies for color and clear-coat applications. Powder coatings are applied as a solid to the vehicle body, which is then oven-cured. Less than 1 percent solvent is present in powder coatings, and the application and curing processes are almost pollution free. As of yet, powder-coating techniques have not been successfully applied to finish coatings at full production volumes in the United States. In Germany, BMW and Mercedes Benz have successfully implemented powder coatings for finishing operations.

As paint formulations shift from solvent-based to water-borne and powder coatings, solvents can be eliminated from cleaning and purging operations. Water often can be used to clean and purge equipment that applies water-borne coatings, further decreasing emissions of VOCs into the air. This change in purging practices also may reduce the generation of hazardous waste. Powder coatings offer even greater pollution prevention potential. Blown air or a vacuum system is all that is required to clean and purge powder-coating equipment. Powder coatings thus eliminate volatile air emissions and any liquid waste stream that may be generated by other cleaning and purging processes.

Product Redesign
Plastic parts offer a unique pollution prevention opportunity when considering painting and coating operations. Colored plastic resin can be used to produce parts (e.g., bumper facia), thus eliminating the need for painting. Product redesign strategies that utilize mold-in color plastics eliminate the need not only for finishing, but also for priming. For exterior surfaces, a clear coat may be needed to achieve the gloss and scratch-resistant characteristics expected in an automotive coating. Mold-in color plastics, currently are used in some interior and exterior parts, from interior door panels and steering column shrouds, to bumpers. This design option can minimize or eliminate VOC emissions and wastes that originate from the painting and cleaning/purging operations.

Pollution Control
As part of an effective environmental management scheme, pollution control technologies, if used, must be efficiently operated. Although not the first choice within the waste hierarchy, control technologies can protect human health and the environment from potentially harmful materials. Industry must be held accountable for the efficient operation of these processes, while encouraged to implement pollution prevention options that may obviate such controls.

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