Mr. Bruce Moore
U.S. Environmental Protection Agency
OAQPS/ESD/CCPG (MD-13)
Research Triangle Park, NC 27711

Re: Comments on the Planned Rulemaking for Miscellaneous Metal Part Coating Operations

Dear Mr. Moore:

The Fluoropolymers Division of the Society of the Plastics Industry, Inc. (SPI) is pleased to submit written comments to the Environmental Protection Agency (EPA) on planned federal regulations and/or guidelines for controlling emissions of Hazardous Air Pollutants (HAPs) and Volatile Organic Compounds (VOCs) from stationary sources that coat miscellaneous metal parts and plastic parts.

The Society of the Plastics Industry, Inc. (SPI) is a trade association of nearly 2,000 members representing all segments of the plastics industry in the United States. SPI's business units and committees are composed of plastics processors, raw material suppliers, machinery manufacturers, moldmakers, and other industry-related groups and individuals. Founded in 1937, SPI serves as the "voice" of the plastics industry. Members of SPI's Fluoropolymers Division (FPD) are manufacturers and users of fluoropolymer resins, and include manufacturers and users of coatings systems that use fluoropolymers to impart significant and unique performance benefits to finished goods.

In several draft documents and at various stakeholders meetings, EPA has solicited public input. In particular, during a February 4, 1998, stakeholders meeting, EPA specifically requested input from industry on possible categories of specialty coatings. EPA stated that

specialty coatings might be considered separately because they are used in significantly smaller quantities, or because they have special performance criteria such as corrosion protection or safety considerations. Specialty coatings could be given separate standards, or they might be exempt.

Fluoropolymer coatings are uniquely qualified as specialty coatings that should be treated in a separate, distinct category in this rulemaking. In the comments that follow, we provide an overview of this category which we call extreme-performance fluoropolymer (EPFP) coatings.

Our comments provide a description of the industry, including details about the extreme performance demands our products and processes are designed to meet, and suggest a regulatory limit that represents the lowest emission that these type of sources are capable of meeting by the application of control technology that is reasonably available considering technological and economic feasibility.

Introduction - What Are Extreme-performance Fluoropolymer Coatings?

Extreme-performance fluoropolymer (EPFP) coatings are formulated systems based on fluoropolymer resins and often contain "bonding" matrix polymers dissolved in non-aqueous solvents as well as other ingredients. Coatings are typically used when one or more critical performance criteria are required. For example, these coatings are used when the application requires:

• a nonstick, low-energy surface
• dry film lubrication
• outstanding resistance to chemical attack
• an extremely wide operating temperature range
• superior electrical insulating properties, or
• that the surface comply with government (e.g., USDA, FDA, DOD MILSPEC) or third-party specifications (e.g. NSF) for health, safety, reliability, or performance.

One distinctive characteristic of coatings is that, once applied to the surface, they are not air-dried. Instead, they undergo a curing process that typically requires high temperatures, chemical reaction, or other specialized technology. In the absence of the high-temperature cure process, the film does not form properly and the coating will fail.

How Are Extreme-performance Fluoropolymer Coatings Different from Paints?

Unique engineering characteristics distinguish EPFP coatings from ordinary paints and finishes. EPFP coatings are formulated to operate under extreme conditions. Extreme conditions include exposure to corrosive chemicals, temperature extremes (cryogenic to 500 F / 260 C), and tremendous pressures (up to 150,000 psi / 10,555 kg/cm²). Coating failure under any of these conditions may result in the failure of the system using the coated component. Because EPFP coatings are frequently used in critical industrial, automotive, aerospace, and medical applications, coating failure could lead to catastrophic results.

By comparison, "ordinary" finishes typically function at or near ambient conditions and are required to meet only one or two performance criteria, such as protecting metal from chemical attack or steel from rusting. If an ordinary finish fails, a slow process of degradation may occur. Seldom will the degradation of an ordinary finish cause a catastrophic failure of a critical component in an industrial, automotive, aerospace, or medical application simply because design engineers do not specify the use of ordinary finishes on critical components.

III. Unique Characteristics of Extreme-performance Fluoropolymer Coatings

Extreme-performance fluoropolymer coatings are formulated to provide one or more of the following unique properties:

1. Easy-to-clean, nonstick surface;

2. Dry film lubrication - which provides lubrication without oil or grease - coefficient of friction as low as 0.02, the lowest coefficient of friction of any solid;

3. Chemical resistance - withstands prolonged exposure to strong acids, bases, and solvents even at temperature extremes;

4. Wide temperature operating range - from cryogenic conditions to +500 F / +260 C;

5. Superior electrical insulation in thin films essential to critical medical applications;

6. FDA, USDA, and NSF compliant formulations available - e.g., cookware, bakeware, food processing, pharmaceutical applications;

7. Mandated by many MILSPECs and civilian aircraft/aerospace manufacturers;

8. Noncombustible - will not burn without an external source of oxygen;

9. Environmental corrosion resistance against sunlight, ultraviolet radiation, saltwater, and acid rain;

10. Pliability - the ability of fluoropolymer coatings to bend freely and repeatedly without cracking, peeling, or separating from the substrate;

11. Suitable for use in selected applications involving radiation;

12. Machinability - allows fluoropolymer coatings to be machined, ground, or polished to achieve critical tolerances;

13. Excellent adhesion to conventional, exotic, and noble metals, as well as ceramics and composites;

14. Wear resistance - even when subjected to pressures of 150,000 psi / 10,555 kg/cm²; and

15. Nonwetting surfaces - a critical property in analytical laboratories and medical applications;

In medical applications, EPFP coatings are used on endoscopy devices, surgical wires, heart monitor leads, shunts used to repair aneurisms, needles which measure electrical impulses in the nerves and brain, scalpel blades, needles to measure blood gases and diseased cells in blood, and drug dispensers. EPFP coatings are also required in many health and safety applications regulated by the U.S. Department of Agriculture (USDA) and the Food and Drug Administration (FDA), as well as mandated by third-party standards organizations such as the National Sanitation Foundation (NSF).

EPFP coatings also meet specific demands in the aerospace industry and are mandated in numerous U.S. Department of Defense (DOD) procurement specifications (MILSPECs). For example, in aircraft applications, EPFP coatings are used on control surface actuators, control surface bearings, emergency backup valves, jet engine bearings, "O" rings, seals, fuel delivery systems, and thermal barriers. In spacecraft applications, EPFP coatings are used in fuel sensors, chemical isolators, chemical barriers, bearing surfaces, bearing cases, self-extinguishing electrical insulators, valve surfaces, cryogenic seals, actuators, repair devices for leaking metal seals, and nonarcing electrical guides. Attachment 1 to this letter contains a few examples of third-party specifications that EPFP coatings are designed to meet.

EPFP coatings also are used in critical automotive and industrial applications, and even in consumer products when specific characteristics are demanded. Some examples include antilock brake system (ABS) components, seat belt latches, natural gas pumping and compressor stations, oil and gas actuator systems, and "fire safe" valves. In addition to critical "must-function" applications, there are hundreds of other useful applications which benefit from the unique properties of EPFP coatings. Examples include coated saw blades (low friction), knives (easy cut, easy clean), camera parts (lubrication, corrosion protection), gaskets (easily removed because of nonstick properties), and faucets (lubrication, corrosion protection). Attachment 2 to this letter contains a wide range of examples of critical EPFP applications.

The application process begins with surface preparation of the item to be coated (cleaning, roughening of the surface) followed by application of the fluoropolymer coating to the item. Because these coatings are most often formulated to yield a thin-film, functional surface (typically 0.001 inch / 0.0254 mm or less), the most common method of application is via various air spraying techniques.

Following application, the coating must be cured, typically by means of high-temperature baking, chemical reaction, or other specialized technology. To get the required performance from the finished coating, and in some cases to control the rate of curing, most EPFP coatings are not air dried.

Why Are Specific Organic Solvents Essential for Extreme-performance Fluoropolymer Coatings

The organic bonding polymers used in EPFP coatings are insoluble in water. In order to introduce them into a solution that can be applied, they must be dissolved in a liquid carrier. The only liquids in which many of these polymers will dissolve are organic solvents (i.e., water will not dissolve them). While many breakthroughs in polymer chemistry have been achieved in recent years in terms of relatively low-performance, ordinary finishes in aqueous formulations, the use of organic solvents remains essential to the application of EPFP coatings.

The alternative to dissolving organic polymers in solvents is to disperse finely divided particles into water. The disadvantage to this approach is that it requires the individual particles to melt and flow together during the curing process. Many of these polymers will not melt and flow to form a continuous film without the presence of some solvent. The absence of solvent makes it difficult, if not impossible, to form a continuous film, which is absolutely necessary to achieve optimum performance from an EPFP coating.

An additional benefit of solvent-borne formulations is that they do a good job of "wetting" the surface during application. Wetting the surface helps to develop the adhesion of the coating to the substrate and the physical, chemical, and mechanical properties in the final film.

A fundamental reason for using solvent-borne formulations is that specific solvents allow the curing rate to be controlled. For example, depending upon the solvents used in the formulation, the coating can be made to cure in stages and not form a film too quickly. This prevents the liquid carrier or other volatile compounds from becoming trapped in the coating's film. If volatile components are trapped the coating's film, they will rupture the surface during the curing process and cause voids or pinholes to appear in the film. Pinholes result in inferior performance and create the potential for rapid failures of the coated component to occur because the substrate is exposed to the extreme conditions that the coating was intended to protect against.

Comparison of Solvent-borne to Waterborne Extreme-performance Fluoropolymer Coatings

In contrast to the chemistry of solvent-borne EPFP coatings, waterborne coatings involve dispersing, not dissolving, polymers in a formulation of solvents and water. (It is essential to understand that solvent-borne coatings, by comparison, have the critical polymer components in solution, i.e., dissolved in a solvent or solvents). In solvent-borne coatings, the solvents evaporate during the curing process and a continuous film is formed.

Waterborne fluoropolymer dispersions consist of finely divided solids suspended in an aqueous carrier. In order for waterborne coating dispersions to form a film, the suspended solids must melt and flow together. While waterborne fluoropolymer dispersions may be adequate for some applications, they do not achieve comparable performance to solvent-borne fluoropolymer coatings - especially when continuous film barriers are needed to ensure protection against corrosive environments.

Why Won't Waterborne or Aqueous CCoatings Do the Job?

Sometimes, if only one performance property is critical, a waterborne fluoropolymer coating will work. Often, however, high-tech applications demand not one, but many properties, and only solvent-borne fluoropolymer coatings can do the job. While waterborne fluoropolymer coatings (and, to some extent, fluoropolymer powder coatings) offer excellent performance, these coatings are usually eliminated for critical high-tech applications due to one or more of the following reasons:

Cure temperature limitations. Waterborne fluoropolymer coatings typically require curing temperatures of 750 F / 399 C. Many composites and other materials cannot be cured at such high temperatures. Most solvent-borne coatings can be cured at much lower temperatures, such as 600 F / 316 C. This is of critical importance when the temper of a metal must be maintained.

Abrasion resistance. Most solvent-borne coatings are highly abrasion-resistant materials. This characteristic is due to the hardness of the bonding polymers and the thin coating thickness. Waterborne fluoropolymer coatings tend to be softer and lack the abrasion resistance of the solvent-borne coatings.

Adhesion. Solvent-borne fluoropolymer coatings provide better adhesion to a broader range of substrates than waterborne fluoropolymer coatings. Also, the multiple layers of some waterborne fluoropolymer coating systems are more likely to disbond (separate) from the substrate than solvent-borne fluoropolymer coatings.

Rust contamination. Waterbone and aqueous primers and coatings can cause rust on steel and ferrous metals. Rust may compromise adhesion and can cause catastrophic failure of key components.

Dry film characteristics. Waterborne fluoropolymer coatings may leave pinholes (imperfections) which provide locations where electrical current, corrosion, or wear may begin to attack the underlying component.

Thinness. Some solvent-borne fluoropolymer coatings are applied as thin as 0.0001-0.0002 inch / 0.00254-0.00508 mm. Typical waterborne fluoropolymer coatings, which are applied in thicknesses in the range of 0.01 inch / 0.254 mm exceed the thickness allowed for many critical applications.

What Types of Facilities Apply Extreme-performance Fluoropolymer Coatings?

It is estimated that there are fewer than 200 job shop coaters in the United States that apply EPFP coatings. They are located throughout the 50 states, although concentrated in the Northeast, Gulf Coast, and West Coast, and generally serve all industry segments. With a few exceptions, companies that apply EPFP coatings are small, family-owned job shops. They employ from 5 to 70 personnel and have annual sales ranging from $500,000 to $6.5 million. The typical coater, however, employs between 5 and 15 employees and has sales ranging from $500,000 to $2.5 million.

The coatings industry is a mature one, involving companies that have years of experience in a range of coatings materials and technologies. In most cases, these companies apply EPFP coatings as only part of their business. Indeed, EPFP coatings are only used when mandated by the customer's specifications or the performance requirements of the application. For other applications, many of these companies use coatings that are low-VOC, high-solid, or powder coatings, and occasionally even ordinary coatings.

Why Can't Coaters Use Emission Control Devices to Reduce VOC Emissions?

As a result of their small size, relatively low emission of VOCs, and selection of low-VOC coatings when appropriate, most job shop coaters are not required under the Clean Air Act to install emission control devices. In fact, for most of these companies, add-on pollution control devices would be prohibitively expensive, technically infeasible, or both.

EPA has recognized that the best achievable control (BAC) or reasonably available control technology (RACT) for many types of coating operations are changes in product formulation or coating technique rather than emission controls. For example, in the recently-issued Control Techniques Guideline (CTG) for the aerospace industry, EPA acknowledged that product substitution is the preferred method of emission reduction because it requires less energy and produces less waste than control devices. EPA also has recognized that specialty coatings typically have relatively low usage and that, as a result, reformulation of specialty coatings would not result in significant air quality benefits. Indeed, as EPA itself said in the Aerospace CTG

Specialty coatings typically have relatively low usage, so reformulation to lower VOC content does not produce significant air quality benefits nor is it feasible for the paint suppliers.

Generally speaking, coating suppliers have targeted high-volume materials for reformulation; accordingly, low-VOC formulations for many specialty coating applications are not available. In the case of fluoropolymer coatings, performance is the single most important issue in selecting the particular coating used. Although comprehensive figures for the volume of EPFP coatings used annually in the United States are not available, EPFP coatings represent a small fraction of all materials used to coat metal and plastic parts. Finally, cost is a major consideration. Because EPFP coatings cost many times more than conventional coatings, they are only used when specified by the customer for performance reasons. Furthermore, application of EPFP coatings is carefully controlled to obtain maximum return on the investment in raw materials.

What Is the Typical VOC Content of a Solvent-borne Extreme-performance Fluoropolymer Coating?

Some liquid formulations of fluoropolymer coatings are available with no VOC content. As described above, however, such coatings frequently cannot meet the specifications required for the extreme performance demanded by many applications.

Most solvent-borne formulations of fluoropolymer coatings used for extreme-performance applications contain no more than 890 g/L (7.4 lb/gal) of VOCs. These limits are consistent with the limits for specialty coatings established in other regulatory schemes for stationary sources.

EPA also has recognized that the lowest available VOC limits for some specialty coatings in various industry sectors are higher than the 420 g/L (3.5 lb/gal) limit recommended in the existing Miscellaneous Metal Parts Control Techniques Guideline (CTG). For example, the new CTG for the aerospace sector contains limits for some specialty coatings that are as high as 1230 g/L, although most are in the 600 to 840 g/L (5.0 to 7.0 lb/gal) range. The recently issued federal regulation covering automobile refinish coatings similarly contains higher limits for some performance-driven specialty coatings. These coatings, most of which do not need to meet the extreme demands for which fluoropolymer coatings are specified, have regulated limits of 550 to 840 g/L (4.6 to 7.0 lb/gal). Several states and localities have also recognized that some extreme performance specialty coatings deserve separate classification due to performance considerations and the relatively small environmental benefit to be achieved by attempting to further control these sources. For example, California's South Coast and Bay Area Air QualityManagement Districts - areas with some of the most extreme ozone problems and the most stringent VOC regulations in the Nation - both exempt "solid film lubricants" entirely from the requirements in their regulations. Although the EPFP applications described in this letter are technically "solid film lubricants," we present below a more precise definition of EPDP for purposes of a federal CTG or regulation.

Recommended VOC Limits for Extreme Performance Fluoropolymer Coatings

SPI recommends that a CTG or federal regulation for surface coating of miscellaneous metal parts include a specific category for extreme performance fluoropolymer coatings. To that end, we recommend the following definition:

Extreme-performance fluoropolymer coatings: Extreme-performance fluoropolymer coatings are formulated systems based on fluoropolymer resins which often contain "bonding" matrix polymers dissolved in non-aqueous solvents as well as other ingredients. Extreme-performance fluoropolymer coatings are typically used when one or more critical performance criteria are required including, but not limited to, a nonstick, low-energy surface; dry film lubrication; outstanding resistance to chemical attack; an extremely wide operating temperature range; superior electrical insulating properties, or that the surface comply with government (e.g., USDA, FDA, DOD MILSPEC) or third-party specifications (e.g. NSF) for health, safety, reliability, or performance. Once applied to a substrate, extreme-performance fluoropolymer coatings undergo a curing process that typically requires high temperatures, chemical reaction, or other specialized technology.

SPI also recommends that a CTG or regulation for this source category should, for simplicity, contain a single VOC limit for extreme performance fluoropolymer coatings. The recommended level is 890 g/L (7.4 lb/gal) of VOCs.

IV. Conclusion

SPI appreciates the opportunity to comment on the planned rulemaking. We look forward to working with EPA in further refining the regulatory structure. SPI and the members of the Fluoropolymer Division remain available to discuss this letter, to respond to any questions you may have on these issues, or to arrange for visits to representative facilities. In the meantime, please do not hesitate to call if you require any additional documentation or if we can be of assistance in any way.

Respectfully submitted,

Lewis R. Freeman

Vice President, Government Affairs

Sample Third Party Specifications for Extreme-Performance Fluoropolymer Coatings

Naval Air Systems Command AS 4171

Naval Sea Systems Command, Source Control Drawing 5184307

Mil-C 8175B

Missile Command Specification, MID 19350D

General Dynamics GD 10108

General Electric, Aircraft Equipment Division, A10334

General Motors Corporation, GM 6070-M

Saudi Arabian Oil Company, CM-E-V-S M00-DS-037.0

Parker Hannifin ESS-36

North American Rockwell RA0108-008

These are selected examples of specifications used in the industry. Members report hundreds of different specifications which require these coatings. Additional examples can be provided on request.

Extreme-Performance Fluoropolymer Coatings - Product Examples

Trademark names (selected):

Teflon®
Silverstone®
Excaliber®
Xylan®
Ultralon®
Dykor®

Medical applications:

surgical wires
heart monitor leads
screens that repair aneurism
needles to measure electrical impulses in brain and nerves
scalpel blades
needles to measure blood gases and diseased cells in blood
drug dispensers
endoscopy unit/suture stapling device
hypodermic needles
catheter wires
intramuscular needles

Aircraft applications:

control surface actuators
control surface bearings
emergency backup valves
jet engine parts
"o" rings and gaskets
seals
fuel delivery systems
bearings
thermal barriers

Spacecraft applications:

fuel sensors
chemical isolators
chemical barriers
bearing surfaces
bearing cases
self-extinguishing electrical insulators
valve surfaces
seals
cryogenic seals
actuators
repair devices for leaking metal seals
non-arching electrical guides

Heavy industrial

Corrosion-resistant nuts and bolts for chemical/water contact
Fiberoptic cable connectors
Emergency shut-off valves and blow-out preventors
Chemical-resistant tank linings
Sub-sea oil production equipment
;Substitute for environmentally unfriendly cadmium plating on fasteners in the petrochemical and oil industries

Selected Extreme-Performance Fluoropolymer Coating Success Stories

Angioplasty Catheter

During the production of angioplasty catheters, heat is used to join the angioplasty balloon to extruded tubing. In order to maintain the accuracy of the extruded bore and to prevent tearing of the balloon itself, a PTFE-coated wire mandrel is used. The PTFE-coated wire is placed on the ID of the extrusion up to where the balloon and extrusion meet. Once the weld is cooled the wire is removed. Without the release provided by the PTFE coating, melted plastic sticks to the wire and threatens the integrity of the weld.

Solid Rocket Fuel Mold

The mold is coated with a fluoropolymer coating, which allows the mold to release from the surface of the cured solid fuel.

Military Aircraft Ejector Seats

Fluoropolymer coatings have replaced cadmium plating, which was corroding and causing ejection failures. A tertiary benefit is that the fluoropolymer coating replaces cadmium, which is environmentally unfriendly.

Commercial Bakeware

Fluoropolymer coatings are applied to commercial bakeware pans to provide a permanent non-stick surface. The use of the fluoropolymer coating eliminates the need for silicone glazing, which is a solvent-intensive and environmentally unfriendly process. It also reduces the use of oil in the baking process.

Industrial Dryer Rolls

Fluoropolymer coatings are applied to industrial dryer rolls to provide a non-stick, corrosion resistant surface. Fluoropolymer coatings replace the use of chrome plating, which is an environmentally unfriendly process.

Firesafe Actuater Valve/Blowout Preventors

In the petroleum industry, valves are coated with fluoropolymers to ensure that they can be quickly closed in the event of a fire or other emergency. Relief valves, which are in standby mode for extended periods, are coated with fluoropolymers to ensure that they activate when needed to relieve pressure in emergencies.