Increasingly stringent limits on emissions loom for makers of coatings for wood building products.

When it comes to the environmental track record of industrial coatings for wood building products, the prevailing attitude of the EPA might appear to reflect the old adage, "What have you done for me lately?"

At least, that's one view being heard from the ranks of companies that manufacture such coatings - and who are currently facing the challenge of a major new regulatory initiative from the EPA.

The EPA recently issued a proposed emission standard for HAPs from surface-coating processes for wood building products. The industry and the agency are currently engaged in discussion and debate over certain provisions in this regulation. But when this rule is finalized in a year or so, coatings formulators and manufacturers no doubt will be asked, "how low can you go in terms of formulating with ever more miniscule levels of certain HAPs and still make a product that does the job?"

The dilemma, says G.M. Currier, Akzo Nobel vice president of Research & Development for Industrial Wood Coatings, is that the coatings industry has already pursued an extensive reformulation program over the last 20-plus years that has produced a dramatic transition from solventborne coatings to low-emission technologies such as waterbornes and ultraviolet (UV)-cure coatings.

"The one thing I have questioned is the idea of taking an industry that's paid its dues years ago and pushing it to new (emission) lows," Currier says. "These are some of the least-polluting coatings - coatings that have gone to waterborne, UV and other technologies. And now we're being asked to contribute more. It's trying to get blood out of a turnip.

"The industry will comply with the regulation, but the bottom line is that it's going to cost the consumer. And the question is, was it worth what they've gained? For what it's going to cost the consumer, they're (the EPA) going to get very little," Currier says.

The types of coatings targeted by the new HAP regulation - formally termed a National Emission Standard for Hazardous Air Pollutants (NESHAP) - are a range of factory-applied coatings and finishes for:

  • Doors and windows;
  • Flooring;
  • Interior wall paneling and tileboard and other interior panels; and
  • Exterior siding, doorskins and "miscellaneous."
The proposed rule is one of a series of HAP emission regulations affecting industrial coating processes that have recently been enacted or proposed. Final regulations have been issued for coating processes involving boat manufacturing, metal coil and large appliances, and proposed rules have been issued for paper and other web coating; metal furniture; fabric coating; and miscellaneous metal parts and products. Proposed rules are scheduled to be issued in the near future for plastic parts; autos and light-duty trucks; and metal cans.

The proposed HAP emission regulation for wood building products has run into criticism from the coatings industry on several fronts, including the rule's unconventional provision for measurement of HAP content in the coating material. The proposal calls for a calculation based on pounds of HAP per gallon of coating solids, a weight-to-volume method that industry representatives say would be difficult to use and likely to result in inaccuracies. The National Paint & Coatings Association is urging the EPA to adopt the widely accepted method that is based on pound of HAP per pound of weight solids.

Even the laboratory device reputed to provide volume solids values for a calculation of HAPs content based on the weight-to-volume method presents a puzzle, industry sources say. The device is something called a "helium pycnometer."

"There's not adequate equipment out there to be able to measure this," Currier says. "It's like setting the speed limit without having a speedometer on your car. And it may be more difficult to measure with the low-solids coatings of the type used in this industry."

In comments submitted to the EPA, the NPCA said measurement methods that could be used to determine HAP solids per gallon of solids are "flawed due to inaccuracies and high cost." The pycnometer itself can cost up to $20,000, the association said.

Currier sees this measurement method as the biggest negative in the proposed HAP rule for wood building products, although the HAP content limits themselves are by no means a walk in the park. The proposed rule includes separate limits for existing and new emission sources that go as low as zero pounds of HAP per gallon of coating solids for new emission sources. For existing sources, the limits range from a low of 0.01 lb. HAP/gal. solids for "other interior (stock) panels" to 1.53 lb. HAP/gal. solids for interior wall paneling and tileboard.

Detailed information on the proposed rule and other regulations affecting industrial coating processes is available on the EPA website located at http://www.epa.gov/ttn/atw/ eparules.html, and on several other related sites. A site specifically related to the wood building products regulation is located at www.epa.gov/ttn/atw/wbldg/wbldgpg.html.

The NPCA has submitted extensive comments on the proposed wood building products regulation. Among the points made by the association are the following.

  • Greater clarification of the rule's overlap with regulations involving other surface-coating processes is needed, along with provisions for flexibility to address such overlap. Specifically, those overlap issues involve coating processes for wood furniture, plywood and composite wood products, and plastic parts. In addition, provisions for flexibility are needed to address finishing processes involving separate building-product categories in cases where the process is similar or identical.

  • Additional clarification and flexibility also are needed for alternative compliance options. These compliance approaches include coatings material-specific HAP levels, a facility-wide HAP averaging system, and the use of add-on emission-abatement systems. Exemptions for low-volume noncompliant materials are also suggested.

  • The proposed rule requires zero HAP coatings in several cases, without establishing minimum or trace levels, raising the question of exactly what constitutes "zero" HAP content. A truly "zero" limit would be "impossible to comply with."

  • The rule should allow the use of formulation data as a basis for determining HAP content levels as opposed to actual testing under methods that could result in questionable readings - at least until issues related to test methods are adequately addressed.
Under the EPA timetable for the HAP regulations on surface-coating processes, the wood building products rule is expected to be finalized late next year, with the rule becoming effective approximately three years later. Currier, while questioning the cost-benefit rationale of further HAP restrictions, says he sees the measure as causing relatively modest reformulation rather than radical formula revisions, since the industry has already made great strides in moving away from conventional solventborne coatings.

Summarizing some of this evolution, Currier says coating processes for flooring have moved heavily to UV-cure systems, while waterbornes are being used for other major building-product categories such as wall panels, exterior siding, doorskins, and others. Solventbornes, however, remain a high-volume material for wood "joinery" - windows and frames for windows and doors - and continue to be used for some hardboard and tileboard applications. Waterbornes currently appear to be the leading substitution candidates for these applications, since UV curing is a less-viable option due to the need to coat three-dimensional substrates.

A key challenge for the industry, Currier says, will be pressure to slash emissions of formaldehyde, which are generated during thermal cure of coatings based on phenol, melamine and urea resins. These chemistries have served as workhorse resins in many wood building product coatings.

"The bottom line is that you're probably going to have to go away from low- to no-formaldehyde-containing coatings," Currier says. Also a likely outcome is the replacement of some commonly used coalescent solvents that are listed as HAPs, such as glycol ethers. "You would replace the small amounts of HAPs with non-HAPs, or switch to systems where you don't need coalescing solvents. I think the industry is up to this task," Currier says.

Currier envisions fewer compliance issues for finishing of wood panels used in applications such as cabinets, where UV-cure materials are providing excellent performance and appearance properties and no formaldehyde headaches. In this end-use segment, conversion to an available technology is an option for the noncompliant-coatings user, albeit at a retrofitting cost.

In speculating about the potential for emerging technologies, Currier sees promise for UV-cure waterborne finishes, where the applicator would have the ability to keep film thicknesses low even in spray-overlap areas, due to lower solids content.

"The industry is going to have to change. Maybe we will see a switch to waterborne with UV curing and use existing ovens to remove the water. But there will be an economic impact, because new chemistries are not as cheap. There will be a price to be paid to get to these (emission) levels."