Pollution Prevention and the Use of Low-VOC/HAP Coatings at Wood Furniture Manufacturing Facilities

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1 Pollution Prevention and the Use of Low-VOC/HAP Coatings at Wood Furniture Manufacturing Facilities Amy M. Marshall and Jennifer L. Spaight Midwest Research Institute, 5520 Dillard Rd., Suite 100, Cary, NC Julian W. Jones U.S. Environmental Protection Agency, Air Pollution Prevention and Control Division (MD-61), Research Triangle Park, NC ABSTRACT Midwest Research Institute, under a cooperative agreement with the Air Pollution Prevention and Control Division of the U.S. Environmental Protection Agency's (EPA s) National Risk Management Research Laboratory, is conducting a study to identify wood furniture and cabinet manufacturing facilities that have converted to low-volatile organic compound/hazardous air pollutant (VOC/HAP) coatings and to develop case studies for those facilities. The case studies include (1) a discussion of the types of products each facility manufactures; (2) the types of low- VOC/HAP coatings each facility is using; (3) problems encountered in converting to low- VOC/HAP coatings; (4) equipment changes that were required; (5) the costs associated with the conversion process, including capital costs associated with equipment purchases, research and development costs, and operating costs such as operator training in new application techniques; (6) advantages/disadvantages of the low-voc/hap coatings; and (7) customer feedback on products finished with the low-voc/hap coatings. The primary goals of the project are (1) to demonstrate that low-voc/hap coatings can be used successfully by many wood furniture manufacturing facilities, and (2) to assist other wood furniture manufacturing facilities in their conversion to low-voc/hap coatings, in particular facilities that do not have the resources to devote to extensive coatings research. This paper discusses the progress of the project and pollution prevention options at wood furniture manufacturing facilities and the regulatory requirements [e.g., the National Emissions Standards for Hazardous Air Pollutants (NESHAP) for Wood Furniture Manufacturing Operations] that these facilities face. INTRODUCTION Midwest Research Institute, under a cooperative agreement with the U.S. Environmental Protection Agency, is conducting a study to accelerate development and market penetration of low-voc/hap wood furniture coatings. Types of low-voc/hap coatings include waterborne, ultraviolet (UV)-cured, high-solids, and powder coatings. The primary goals of this project are to demonstrate that these coatings can be used successfully by many wood furniture manufacturers and to provide a resource to the wood furniture industry. This resource will be in the form of a compilation of case studies developed as a result of visits to wood furniture and cabinet manufacturing facilities which have converted to low-emitting coating technologies. The case studies include a discussion of the issues involved in each facility s conversion. Costs, problems, 1

2 emissions/waste reductions, and facility and customer satisfaction are considered in each case study. In addition to the use of low-voc/hap coating technologies, many facilities choose to implement other pollution prevention activities as well. Reductions in emissions and waste from these activities are also considered in each case study. The following sections provide a profile of the wood furniture manufacturing industry, an overview of the emission sources in the wood furniture manufacturing industry, and a discussion of the regulatory requirements to which the industry is subject. Pollution prevention options for the wood furniture industry are then described. A summary of the case studies that have been written is provided, and facility experiences with waterborne, UV-cured, and powder coatings are related. PROFILE OF THE WOOD FURNITURE INDUSTRY The wood furniture industry can be divided into three main sectors: cabinets, office and institutional furniture, and residential furniture. There are over 10,000 wood furniture manufacturing facilities in the United States, consisting mainly of small companies with fewer than 50 employees. Many of these facilities are concentrated in the Southeast and California. Facilities in North Carolina, Virginia, Tennessee, and California accounted for 55 percent of the residential furniture segment s employment in Indiana, North Carolina, California, and New York accounted for 55 percent of the wood office furniture segment s employment in the same year. 2 Emissions from these facilities are largely uncontrolled because it is usually not economical for them to install air pollution controls. Their exhaust streams are characterized by a high volumetric flow and low VOC concentration due to the large amount of fresh air that is usually used in manual spray operations. For the same production level, the VOC emissions are greater for high-end furniture (higher quality and price) than for low-end furniture. The manufacture of high-end furniture often entails a series of as many as 15 finishing steps, with multiple applications for some finishes. A typical long finishing sequence for high-end furniture might involve application of stain, toner, washcoat, glaze or filler, sealer, highlights, and topcoat, as well as intermediate sanding, rubbing, and drying steps. A short finishing sequence for low-end furniture usually involves application of stain, sealer, and topcoat. Since more finishing steps are performed for high-end than for low-end furniture, more solvent is used for the former. Because the majority of the solvents consumed by the industry are VOCs, solvent usage is approximately equal to VOC emissions. The consumption of solvents in coatings used in the wood furniture industry for the year 1989 was estimated at 135,000 tons (122,850 Mg). 3 The wood furniture and fixtures industry s coating usage accounts for about 15 percent of all product finishes (not including architectural coatings or special purpose coatings) consumed by the coating industry. 3,4 WOOD FURNITURE INDUSTRY EMISSIONS There are many sources of VOC/HAP emissions in the wood furniture industry. These sources include: finishing operations (spray booths, flashoff areas, ovens); cleaning operations; mixing operations; touch-up and repair operations; and gluing operations. Finishing operations typically account for the largest portion of the facility-wide VOC emissions. Typical pollutants emitted include alcohols, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), toluene, and 2

3 xylene. Acetone, although not considered a VOC, also is emitted by the industry in large quantities. Finishing materials are usually applied in booths using various types of application equipment. The types of spray guns used to apply wood furniture finishes include: conventional air; airless; air-assisted airless; electrostatic; and high-volume, low-pressure (HVLP). Application may be manual or automatic, but the majority of spray booths are operated using manual finishing techniques. Most spray booths are equipped with dry filters to control particulate (paint droplets) generated by overspray. Finishes also may be applied using techniques such as roller, curtain, and dip coating. It is assumed that all solvent in the applied finish evaporates during the finishing process, either as the coating is applied or as it dries or cures. Therefore, finishing emissions are calculated by multiplying the amount of coatings used by their VOC/HAP content. Emissions of VOC/HAP are generated from cleaning operations if an organic solvent is used to clean application equipment, spray booths, or other equipment. Organic solvent is generally necessary to clean equipment that has been used to apply solvent-borne and UV-cured coatings, while hot water may be often be used to clean equipment that has been used to apply waterborne coatings. Spray guns are usually cleaned by sending solvent or water through the gun and atomizing the liquid into the booth ventilation system. This practice is common unless dedicated coating supply lines and spray guns are used for each color or type of coating. If a facility is using powder coatings, there are typically no cleaning emissions. Some VOC emissions may occur during mixing operations if volatile materials, such as thinning solvent, are used or if material is spilled. Touch-up and repair operations are a source of VOC emissions if solvent is used to strip a piece of furniture or perform spot rework. Figure 1 depicts emission and waste sources from coating and cleaning operations. 5 Gluing operations can potentially be as large a source of emissions as finishing operations, depending on the type of glue used. In the past, glues containing methylene chloride were widely used and could account for a significant portion of a facility s HAP emissions. In recent years, wood furniture plants have transitioned to waterborne, hot melt, or low-voc/hap adhesives as alternatives. WOOD FURNITURE INDUSTRY REGULATORY REQUIREMENTS In 1995, the EPA promulgated National Emission Standards for Hazardous Air Pollutants (NESHAP) for the wood furniture manufacturing industry. The NESHAP applies to wood 3

4 furniture manufacturing facilities that emit 10 tons (9.1 Mg) or more per year of one HAP or 25 tons (22.75 Mg) or more per year of any combination of HAPs. Facilities emitting 50 or more tons (45.5 or more Mg) per year of HAPs were required to comply with the standards by December 1997, while facilities emitting less than 50 tons (45.5 Mg) per year of HAPs were required to comply by December Facilities using less than 250 gallons (946 L) of finishing materials per month and facilities performing incidental wood furniture manufacturing operations (such as a hobby shop at a military base) are exempt from the NESHAP. The NESHAP requires facilities to implement work practice standards and provides pollution prevention alternatives as compliance options. Facilities can implement low-hap coating and gluing technologies rather than installing an air pollution control device. However, many facilities subject to the NESHAP simply reformulated their solvent-borne coatings to include solvents that are considered VOCs but not HAPs. In 1996, the EPA issued a Control Techniques Guideline (CTG) Document, which outlined methods of reducing VOC emissions from wood furniture finishing operations. 6 States must implement rules that require wood furniture manufacturing facilities located in ozone nonattainment areas to control VOC emissions to levels at least as stringent as those given in the CTG. The CTG recommended the use of waterborne topcoats or high-solids sealers and topcoats as reasonably available control technology (RACT). Many states have promulgated their own VOC regulations that wood furniture manufacturing facilities must follow. In some cases, these rules are more stringent than the levels recommended in the CTG. California, in particular, has some of the most stringent VOC regulations in the United States. Under the current ozone National Ambient Air Quality Standards (NAAQS), there are few nonattainment areas in the United States. However, EPA finalized a new ozone NAAQS in 1997 that will cause many more counties to be classified as ozone nonattainment areas in the year Furniture companies in these counties will have VOC control requirements starting in 2004, with compliance determinations beginning in Therefore, many furniture facilities will be required to either control or prevent their VOC emissions, as well as their HAP emissions. POLLUTION PREVENTION IN THE WOOD FURNITURE INDUSTRY Pollution prevention is the use of materials, processes, or practices that reduce or eliminate the creation of pollution or wastes at the source. Pollution prevention is also called source reduction and includes practices that reduce the use of hazardous materials, energy, water, and other resources. Instead of controlling pollution with an add-on control device, for instance, the facility would institute work practices that prevent the pollution from being generated or reduce the amount generated. In addition to any emissions reductions achieved, pollution prevention practices can also serve to reduce operating costs, reduce permit fees, reduce liability and fire risk, improve employee morale, and enhance a company s image. The pollution prevention practices typically implemented in the wood furniture manufacturing industry to reduce volatile emissions include: Use of low-voc/hap coatings and glues; Use of more efficient application equipment; 4

5 Reduction in the number of coating steps; Housekeeping measures, such as keeping containers of coating, solvent, glue, or cleaning rags covered; Recycling of cleaning, finishing, and gluing materials; Using heat to adjust viscosity, instead of thinning solvent; Using coating supply lines dedicated to a particular color; and Implementation of an operator training program. Other pollution prevention options, including recycling programs for waste wood, packing materials, and empty containers, exist for reducing facility-wide waste and emissions. Laundering cleaning or wiping rags, instead of disposing of them after one use, is also a means of reducing waste if they are not contaminated by solvent. Use of more efficient application equipment will also result in less waste (because booth filters will need to be changed less often) and less coating usage. Because the quantity of VOC emitted is directly related to the amount of coating used, common pollution prevention measures involve reformulation of the coatings and glues. Reformulation to higher-solids or waterborne coatings will reduce the amount of solvent in the coating, may reduce the volume of coating required per piece, and will therefore reduce VOC emissions. Converting to UV-cured or powder coatings will further serve to reduce volatile emissions, but implementing these types of coatings and their associated application equipment is not always cost-effective, especially for smaller companies. Simple housekeeping measures, such as keeping containers of coating covered and minimizing spills, also serve to reduce VOC emissions. Recycling cleaning solvent will cut down on cleaning emissions, as will reformulation of cleaning solvent. Using coating supply lines and spray guns dedicated to particular coatings and colors will also reduce cleaning emissions because lines will not need to be flushed when a different color of finish must be applied. Depending on the types of materials used, coating and gluing materials also can be recycled. Use of more efficient application equipment, such as HVLP spray guns, automatic spray, or flat line finishing, will serve to reduce emissions associated with coating overspray (more coating is applied onto the piece). However, an operator training program should be implemented as well, to ensure that the operators are using the equipment correctly. Operators should be instructed in proper application technique and appropriate equipment settings, such as pressure. Although most surface coating regulations require facilities to use finishes with low VOC or HAP contents, some in the industry have been concerned about having to move away from conventional, solvent-borne, nitrocellulose-based finishes that have been used for many years. One reason is because many furniture companies that tried waterborne coatings in their early stages of development found that they did not perform as well as solvent-borne coatings. 5

6 Specifically, there were problems related to appearance, grain raise, and dry time. In addition, conversion to UV-cured systems is often viewed as capital intensive. To address these concerns, Midwest Research Institute and EPA initiated a cooperative agreement to find facilities that were using low-emitting coatings successfully and to provide information on their experiences to the industry. The types of case studies completed and the typical issues associated with the use of waterborne, UV-cured, and powder coatings are discussed below. CASE STUDIES COMPLETED Table 1 presents a summary of the case studies completed at the time this paper was prepared. The table divides the facilities by product (furniture or cabinets/components) and by the low- VOC/HAP coating technology implemented. One plant, in particular, had implemented waterborne, UV-cured, and powder coatings at the same facility. Therefore, that plant accounts for three entries in the table. Efforts were made to compile case studies for a broad range of facilities, products, and coating technologies. Case studies were written for facilities ranging in size from 2 to 900 employees with products ranging from coated panels used as casegood components to high-end furniture and cabinets. Facilities in ozone nonattainment areas also were visited. All of the case studies will ultimately be compiled and published as a final project report. FACILITY EXPERIENCE WITH WATERBORNE COATINGS Waterborne coatings are generally a less costly method of reducing VOC/HAP emissions than UV-cured or powder coatings, and therefore are the most appealing to smaller shops. Capital investment ranges from nominal to several thousand dollars to purchase stainless steel lines and equipment. The average facility studied replaced several gun or pump components, but not the entire line. The cost of the waterborne coatings themselves tended to be slightly higher per gallon than the solvent-borne coatings used traditionally, but many facilities found that the higher solids content of the waterborne coatings provided better coverage and found that they could use a smaller volume of coating per piece. However, other facilities reported that either additional or thicker coats of the waterborne material were required to achieve the desired appearance. The appearance of products finished with waterborne coatings is often the main hurdle to overcome. Pieces finished with waterborne stains were often described as being muddy, or lacking the depth of a solvent-borne stain. Pieces that receive only a sealer and/or topcoat may appear as having a green tint in the wood, instead of the amber tint associated with solvent-borne coatings. However, working with the coating supplier to adjust the formulation often solved any appearance issues. Waterborne coatings are generally applied using spray guns, although dipping, roll coating, and wiping also are used. Application of waterborne coatings by spray gun requires a different operator technique than that used to apply solvent-borne coatings. Several facilities noted it was easier to train an employee who had never sprayed coatings before than one who had used the spray equipment with solvent-borne coatings for years. The waterborne coatings often have to be applied sparingly to achieve the desired finish. 6

7 Another difficulty often associated with waterborne coatings is grain raise. The water in the coatings is absorbed by the wood, causing it to swell. Grain raise results in a finish that is rougher feeling and rough looking. However, most facilities have found that, with the proper combination of coatings, equipment, and sanding, grain raise can be minimized to an acceptable level. One facility chose to use only a waterborne topcoat instead of a full waterborne system (waterborne stain, sealer, and topcoat). Waterborne coatings often require a longer drying time than typical solvent-borne coatings because the water in the coating does not evaporate as quickly as the solvent does. Larger facilities often install infrared ovens for use between coating steps to shorten drying times. Smaller facilities that use the same spray booth (with no oven) for each coating step, in more of a batch process, generally found that by the time they were ready to apply the next coating, or package the product, the piece was dry. In addition to VOC and HAP reductions, the main advantages cited by facilities that have switched to waterborne coatings include: elimination of the smell associated with solvent-borne coatings; reduction of fire risks and associated ease of storage (an explosion-proof storage room is not required); low capital investment; a more durable finish; and reductions in permit and license paperwork and/or fees. Overall, the majority of the facilities were pleased with their waterborne finishes. Coating suppliers played a key role in the success of the coating system. Facilities had the most success when the coating suppliers were willing to provide the individual attention necessary to formulate the system to facility-specific needs and eliminate any problems. The adjustment period from solvent-borne to waterborne coatings (the period of testing and refining the coating system and the application technique) varied from facility to facility, but was generally several months. FACILITY EXPERIENCE WITH UV-CURED COATINGS Installation of a UV-cured coating line typically requires a large capital investment, often millions of dollars. This large up-front cost limits many smaller facilities from implementing a UV-cured coating system. However, once the system is in place, it is generally a very cost-effective method of production because transfer efficiency can be up to 100 percent and the lines are typically automated, requiring few operators. The finishing line can be a flat line or a spray line. Coatings applied on a flat line, using roll coaters or curtain coaters, can contain up to 100 percent solids (meaning all of the coating components cure to form the final film) and have little or no emissions. This type of coating may also be sprayed, but water or solvent is often added to reduce the viscosity of the coating for 7

8 easier application. Spray booths for UV-curable coatings are generally enclosed and automated, often with electronic eyes to sense when the product is present and reduce overspray. Most facilities found that the increased automation of a UV line decreased the number of operators required. However, one cabinet manufacturing facility did not decrease the number of operators on the line when it switched to an automated spray UV line from hand spraying traditional solvent-borne coatings. Because of the detail present in their products (e.g., raisedpanel doors), hand-sanding and touch-up is performed between automated coating steps. At this facility, these manual steps limit the line speed and require the same number of operators on the line as the previous system. Another advantage of UV lines is the decrease in the amount of floor space required. A curing oven follows the coating applicator and contains varying numbers of UV lamps, often at different intensities and positions, that cure the coating in a matter of seconds. Since the cure time is so short, pieces can be assembled and stacked immediately after they are coated. Additional floor space for large curing ovens or areas for drying the product are eliminated with this type of coating system. A UV-cured finish is more durable than the typical solvent-borne finish. However, rework of pieces with finishing defects is very difficult; the product must be sanded to bare wood and refinished, with care taken not to sand through a veneer, or reduce the thickness of the board below the coating line s tolerance. One component manufacturer stated that they sell those pieces as shop-grade panels instead of reworking them. Rework is more of a problem for the retail sales people than for the manufacturing facility. Retail stores commonly touch up pieces that have finishing blemishes, which is very easy with solvent-borne coatings because the new coating tends to melt into the old coating layer. With UV-cured finishes, this type of repair cannot be done. Damaged pieces must be sent back to the manufacturer for repair. Equipment used to apply UV-curable coatings is also difficult to clean. The coatings are viscous and sticky. In addition, they must be kept away from direct light to prevent them from curing in or on the equipment. Many facilities allow the coating to remain in the supply lines and coating reservoirs when not in use, and they cover the equipment to prevent the coating from curing. Flat line equipment (e.g., applicator rolls) is generally easier to clean than spray equipment. The appearance of a UV-cured finish is typically aesthetically pleasing. High-gloss finishes can be easily achieved by applying either multiple coats or thicker coats. The clarity and depth of the finish is comparable to traditional nitrocellulose-based coatings. Overall, case study facilities found the transition to a UV-cured coating line to be fairly smooth. Minor problems were encountered, but quickly overcome. The end result is a quality finish that is equivalent to the solvent-borne finishes previously used, often at a lower operating cost and higher production rate. FACILITY EXPERIENCE WITH POWDER COATINGS One facility studied under this project had implemented a powder coating line to coat office furniture components. The facility plans to phase out the use of pigmented waterborne coatings 8

9 and rely on the powder coating line for all but a few specialty colors or small jobs. The substrate coated is medium-density fiberboard (MDF). The powder coating line consists of four stages: preheating, coating, curing, and cooling. The components to be coated are first hung from grounded metal hooks and preheated before entering the spray booth. Automatic spray guns are used to apply the coating, and all overspray is reclaimed with a cyclone and reused. Only one coating step is necessary; it is followed by a curing stage in a long infrared (IR) oven and a cooling stage. Coating changes take a matter of minutes because the facility purchased two spray booths that can move into and out of the coating line interchangeably. The entire line is 550 feet (168 meters) long. Several variables affect the quality and performance of the final finish, particularly board moisture, temperature, and thickness. The facility has experienced problems with the coating adhering to the areas around the metal hooks from which the boards hang on the line. They have also had problems with coating adhesion when areas of the board are too thin and do not retain the heat from the preheating step. For example, they mill out an area on cabinet doors to attach hinges. If that area becomes too thin, the coating will not adhere to it (although this is not a significant concern if the hinge covers the bare area). The facility cites the following advantages of the powder coating system: no VOC emissions; no lost overspray; good color consistency; very durable finish; and high capacity. Because the line is automated, only seven operators are required. The line moves at about 10 feet (3 meters) per minute, and the IR ovens take only 1 minute to heat up. Production on the powder coating line is almost twice that on the waterborne line, and the powder coating line is much more compact. The facility spent about $2 million and 4 years developing the powder coating system, so this technology may be cost-prohibitive for small facilities at this time. Because this type of line is not in widespread use for wood coating, facility personnel had to work closely with the coating and equipment suppliers in developing their powder coating line. This type of line is most suitable for flat components finished with pigmented coatings. SUMMARY The goal of this project is to produce a case study document that will assist the wood furniture manufacturing industry as it moves toward low-voc/hap coatings. Facilities that do not have the resources to devote to extensive coatings research should benefit from the information provided in the case studies. Plans call for making available the final project report and associated 9

10 technical reference information on EPA s Internet site after all case studies are completed. The information will be accessible through the Wood Furniture NESHAP Implementation site, located at Outreach efforts through environmental conferences, trade associations, trade magazines, state regulatory agencies, state small business assistance programs, and an EPA-sponsored low-voc wood coating technology fair are planned during 1999 to disseminate this information. REFERENCES 1. U.S. Department of Commerce, Economics and Statistics Administration Census of Manufactures: Household Furniture. 2. U.S. Department of Commerce, Economics and Statistics Administration Census of Manufactures: Office, Public Building, and Miscellaneous Furniture; Office and Store Fixtures. 3. SRI International. The U.S. Paint Industry Data Base. Prepared for the National Paint and Coatings Association, September SRI International. Chemical Economics Handbook: Paint and Coatings Industry; SRI International: Menlo Park, California, April Northeast Waste Management Officials Association and Northeast States for Coordinated Air Use Management. Wood Furniture: The Clean Air Act Amendments of 1990 and Pollution Prevention Opportunities, September U.S. Environmental Protection Agency. Guideline Series: Control of Volatile Organic Compound Emissions from Wood Furniture Manufacturing Operations. EPA 453/R (NTIS PB ). Office of Air Quality Planning and Standards, Research Triangle Park, NC. April

11 Table 1. Breakdown of Case Studies by Coating Type and Industry Segment Coating Type Household and Office Furniture Manufacturers Cabinet and Component Manufacturers High Solids Coatings 2 2 Waterborne Coatings 8 3 UV-cured Coatings 4 3 Powder Coatings

12 Figure 1. Emission and Waste Sources from Coating and Cleaning Operations. 5 12

13 Furniture Piece Coating Inputs Cleaning Inputs Air Emissions -Leaks -Coating Transfer to Smaller Containers -Uncovered Containers -Spills Solid and/or Hazardous Waste -Empty Coating Containers Air Emissions -Coating on Furniture* -Overspray* -Used Rags -Used Adsorbents -Spills -Uncovered Containers -Flushing Guns and Lines with Coating on Startup Solid and/or Hazardous Waste -Used Rags -Used Adsorbents Air Emissions -Coating on Furniture Coating Materials Rags and Adsorbents Coating Application Cleaning** Spray Booth Flashoff Cleaning Solvent Strippable Spray Booth Coating Air Emissions -Leaks -Coating Transfer to Smaller Containers -Uncovered Containers -Spills Solid and/or Hazardous Waste -Empty Solvent Containers Air Emissions -Gun/Line Cleaning -Metal Filter Cleaning (if used) -Uncovered Containers -Spills -Application of Strippable Spray Booth Coating Solid and/or Hazardous Waste -Used Solvents -Disposable Filters (if used) -Dried Overspray/Lacquer Dust -Strippable Spray Booth Coating * Quantity dependent on application equipment and other factors ** Frequency dependent on coating type and application equipment Drying Oven Sanding Number of repetitions dependent on number of coating steps Provided by and posted with permission of Julian W. Jones. 13