Characterization of automotive paints: an environmental impact analysis☆
Introduction
Advances in automotive paint research have led to the development of waterborne and powder-coating formulations that provide alternatives to solvent-based paint for primer surfacers, basecoats, and clearcoats. This is an important step towards cleaner automotive paint operations, especially considering that among all manufacturing processes for vehicle production, the painting operation contributes most to the direct environmental emissions.
The painting operation continues to be an area for increasingly stringent environmental standards. In this regard, it is necessary to examine the broader environmental issues associated with the entire production and use of the materials involved in the painting operation. Life cycle assessment (LCA) tools contribute quantitative results to the decision process, and are increasingly used for the evaluation of the environmental emissions associated with the manufacturing, use and end of life of materials and processes. The main goal of such an analysis is to identify the sources that contribute the most to adverse environmental impact and to provide the necessary information that allows the design and manufacturing engineers to choose among alternatives. LCA is based on industrial ecology principles, taking into account all energy and material flows throughout the production, use and end of life of a product [1].
Previous studies that address paint life cycle analysis (LCA) have not considered a thorough life cycle evaluation of the different coating materials that are commonly used in automotive painting; the studies are more focused on the processes that the materials go through during application to the vehicle [2], [3], [4]. For example, a recent study has used LCA approach to investigate the facility and management operations of the painting process in an assembly plant [2]. Dobson [3] compares two painting scenarios of water-based painting and solvent-based painting, and reports on their associated environmental impacts including solid waste, energy consumption, and air emissions. Life cycle simulation of automotive painting processes is also reported by Matthias and Manfred [4]. This study shows very limited data on the energy required for the production of powder, waterborne and solventborne clearcoats. For energy consumption, powder production is shown to be more energy intensive than others (201, 225, 226 and 299 MJ/vehicle for water, 1k, 2k and powder clearcoats, respectively); the large difference is primarily due to the film thickness of 65 μm assumed for powder compared to 35 μm for other liquid clearcoats.
Many different coatings are used in automotive assembly plants to provide the desired protection and finish for the vehicle. In this study, we used the LCA methodology to assess the environmental impact of most commonly used automotive paint materials including: solvent-based and powder primers, water-based basecoat, and solvent-based and powder clearcoats. A complete life cycle analysis of the above paint materials were carried out using commercial state of the art software considering national average electricity production. The analysis evaluates emissions from the production of materials on a per kilogram basis as well as the necessary quantities used on a typical sport utility vehicle. We followed the EPA SETAC (Society of Environmental Toxicology and Chemistry) guidelines in which a complete inventory of all materials that includes resource extraction and energy requirements is considered [5]. For the materials production, we have obtained energy and emissions information from paint manufacturers, literature, and patents.
We also evaluated the total environmental impact of the materials used for painting of a vehicle, considering three different painting scenarios:
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Scenario 1: solventborne primer–waterborne basecoat–solventborne clearcoat.
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Scenario 2: powder primer surfacer–waterborne basecoat–solventborne clearcoat.
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Scenario 3: powder primer surfacer–waterborne basecoat–powder clearcoat.
Scenarios 1 and 2 are common in US (e.g. General Motors’s Hamtramck and Moraine plants, respectively). Scenario 3 is the future goal for automotive paint operations and is currently being investigated by the low emission paint consortium (LEPC) of the USCAR. In these scenarios, we assumed a sport utility vehicle (e.g. Chevy Blazer). The overall LCA of the materials are described for all the scenarios to allow the comparison of more traditional coatings (Scenario 1) with alternative coatings based on powder. The results of the analysis provide the energy and water requirements as well as the air, water, and solid waste emissions per job.
Section snippets
LCA of the materials
Table 1 summarizes the nomenclature used for each material. We considered two different powder primer formulations from two suppliers: DuPont and Seibert. Both primers are used at General Motors, one is based on acrylic (DuPont) and the other on polyester chemistry (Seibert). For the waterborne basecoat, we considered two different colors: white and pewter from DuPont. These two colors hold supplier’s highest selling volumes. The clearcoats included an acrylic powder from Seibert and a
Material requirements
To estimate the amount of the paint required per job for each coat application, we have used the parameters shown in Table 3. Scenario 2 is currently in operation for Chevy Blazer production at a GM plant. The surface area for each coating application at that GM plant is applied to each scenario as appropriate. Table 3 also includes actual gallons per job used for different coatings. It is seen that in most cases, the estimated values are in very good agreement with actual values with the
Energy consumption
The energy consumption for the synthesis of 1 kg of each coating is shown in Table 4. The results show that the production of the acrylic primer coatings is more energy intensive than the polyester ones. This is because the energy required to produce 1 kg of glycidyl acrylic polymer resin (322 MJ) is much higher than that for polyurethane (114 MJ). Note that 1 kg of powder acrylic primer uses 0.72 kg of resin.
The pie charts, presented in Fig. 1, show the relative contributions to the energy consumed
Total life cycle environmental assessment of coating manufacturing
In this section, we present the total life cycle environmental impacts associated with the manufacturing of the materials (primer, basecoat, and clearcoat) needed for painting of a vehicle (SUV) in each of the painting scenarios: SP1–WB1–SC1, PP2–WB1–SC1, PP2–WB1–PC2 (see Table 1 for nomenclature). The environmental assessment will include energy and water requirements as well as air, water, solid waste, and carbon dioxide equivalent emissions.
Overall environmental performance of scenarios
The LCA analysis of the three different paint scenarios has revealed some trends in their environmental emissions for manufacturing of the materials. Fig. 14 summarizes the environmental performance of material production for the three scenarios in a single chart. The attributes considered are energy, water consumption, solid wastes, CO2-equivalent emissions, VOC, CO, NOx, SOx and PM. For each attribute, the basis is taken to be that for the SP1–WB1–SC1 scenario and those of the other scenarios
Conclusions
Life cycle assessment was used to evaluate the environmental impact associated with the manufacturing of different automotive coatings. The findings show that the production of acrylic primer coatings is more energy intensive than the polyester ones, powder or solventborne. This is due to the high energy consumption of the methacrylate resin, which is the largest constituent of the acrylic powder. Overall environmental performance for production of the polyester primer (solventborne and powder)
References (15)
- P. Schulze (Ed.), Measures of Environmental Performance and Ecosystem Condition, National Academy of Engineering,...
- The President’s Council on sustainable development eco-efficiency task force, Auto Team Report, March 1, 1996. website:...
- D.I. Dobson, Life cycle assessment of painting processes: putting the VOC issue in perspective, Prog. Org. Coat. 27...
- H. Matthias, S. Manfred, Life-cycle engineering of powder coating technology in comparison to other painting...
- A technical framework for life cycle assessment, SETAC Workshop Report, Smugglers Notch, VT, August 18,...
- The Boustead Model, Version 3, January...
- Personal communication with Buck McKinney, DuPont Automotive Finishes and Peter Gribble Seibert Powder and Coatings,...
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The 26th Annual International Conference on Organic Coatings is organizing an international conference on Waterborne, High Solids, and Powder Coating Technologies. The author has been accepted to speak at this international conference, which is a highly technical conference. The presentation will publicize our efforts towards implementation of powder coatings for automotive applications and GM will benefit by gaining more technical knowledge from the participants of the conference. The presentation by the author will contain no patentable or proprietary information. This material has been cleared and the R&D number is 9011.
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World Wide Facilities, General Motors.