For those who keep their eyes on construction trends, the increased use of residential metal roofing has been apparent for several years. Along with that growth has been the development of new products and new features that better meet the needs of today's homeowners. A leader in the development of new technologies in residential metal roofing has been Classic Products Inc., Piqua, Ohio.

Classic Products was started in 1980 with a focus on manufacturing aluminum shingle roofing systems for commercial and residential applications. Its products are apparent on thousands of restaurants, convenience stores and other buildings across the country. Starting in the late 1980s, though, the company started to focus on residential metal roofing systems. Through Classic Products' ability to bring increased technology to the residential marketplace, its business is now almost entirely residential. The company sells its products through independent dealers across the United States as well as in several other countries.

The company historically has produced its roofing systems from pre-painted aluminum. The preferred coatings used are PVDF II finishes sold under the trade names of Kynar* and Hylar**, which are popular for their overall durability as well as fade and chalk resistance. Classic Products has been an innovative leader in these finishes by being one of the first manufacturers to offer multi-hued finishes.

While Classic Products has based its reputation on aluminum roofing systems, the company began seeing certain market conditions arise in the mid 1990s, which caused it to start the development of a steel roofing system. This was due to several severe hailstorms in the central United States that had caused insurance companies to begin recommending not "metal" roofing but "steel" roofing to their clients.

According to company president Todd Miller, "The decision to pursue a steel product created a bit of a problem for us because we had always worked very hard to sell the rust resistance of aluminum roofing.

"So, when we started developing a steel roofing system, we wanted to develop something truly revolutionary in terms of corrosion resistance and aesthetics. One thing we knew for certain was that if we produced a heavily formed product such as a shake profile, we needed more corrosion resistance than can be achieved with pre-painted steel. We needed a product which started with a good base material but then was made even better with a post-coat finish applied after the panels are formed," Miller says.

At this point, the company had noted the increasing popularity of steel roofing shingles which had "stone" coatings. This technology consists of taking aggregate granules similar to those normally used on asphalt and fiberglass shingles and bonding them to steel. These finishes are noted for their beauty and texture. To homeowners, they offer a "bridge" of sorts from asphalt and fiberglass shingles to steel roofing.

Classic Products, however, was concerned about the long-term durability of stone coatings. The company also wanted to differentiate itself from other manufacturers. Knowing the durability of polyvinylidene fluoride (PVDF) finishes from its pre-painted raw materials, Classic's new product development team came up with the idea of applying a PVDF powder coat to its steel shingles after the panels were formed. Ideally, the powder coat would have heavy texture to it and would be a "blend" of several colors. This would help in competing against the popular stone coatings. Classic took this idea to Morton International who was at that time involved in pre-paint finishes but also owner of Morton Powder Coatings in Reading, Pa. Morton Powder Coatings is now owned by Rohm & Haas. The resulting finish is a powder coat called ThermoBond by Classic Products, which is applied to steel roofing panels after they have been formed from galvanized steel with a pre-painted PVDF II finish.

PVDF Powder Development

Fluoropolymer coatings, including PVDF powder coatings, have proven to weather for 5 to 20 years with an approximate dry film thickness of 1.2 mils using liquid PVDF technology, e.g., Kynar 500. Seventy percent Kynar 500 coatings are produced by one powder manufacturer,(Rohm and Haas Powder Coatings), and five liquid suppliers. Kynar 500 PC resin-based powder coating was initially manufactured prior to 1989 as a result of the company's expertise in thermoplastic powder coatings. Currently, Rohm and Haas Powder Coatings markets Kynar 500 PC resin-based powder coating system to the architectural community for roofing panels, window and door extrusions, wall and curtain panels, guard rails, and fascia accessories.

This powder coating system is formulated to meet or exceed the performance criteria established by the AAMA 2605 10-yr specification guidelines. The key to Kynar's success can be found in its basic foundation, which is the carbon/fluorine bond, one of the strongest chemical bonds.

The coating thickness creates a barrier coat and contributes to long-term corrosion resistance, color and gloss retention. Rohm and Haas Powder Coatings has developed technology which allows the Kynar 500 PC PVDF flouropolymer resin system to be formulated into a powder coating and applied with a dry film thickness of 2 to 4 mils. This provides two to three times the barrier coat vs. the liquid system for continued long-term performance.

The coating film hardness is a significant factor to consider when considering PVDF powder coatings over PVDF liquid systems. ASTM D3363 defines "Gouge Hardness" as "the hardest pencil that will not cut through the film to the substrate for a distance of at least 1/8 inch."

PVDF Powder Coatings offer superior mar resistance and do not contain VOCs (volatile organic compounds) or HAPs (hazardous air pollutants) vs. liquid PVDF coatings. PVDF coatings exhibit superior characteristics as a barrier coating to water vapor transmission to the substrate, when compared to other paint systems. By increasing the barrier coat (dry film thickness) with PVDF Powder Coatings and an approved primer, this will contribute to the elimination of the transmission of moisture to the substrate, helping to prevent filiform corrosion.

Miller says there were a number of challenges when they started applying the PVDF powder to their products. "First, this was the first time we'd ever done any coating in our factory. Second, the blending of colors and the attempt to achieve a coating with a consistent appearance from panel to panel let alone from run to run proved to be a real challenge," he says.

Classic Products purchased a used powder coating line and, along with a great deal of support from the powder manufacturer, jumped feet-first into its new product line. Over time, the company developed the right "recipe" of powder application and baking, which ensured good adhesion between the powder and the steel's original pre-painted PVDF II finish. With the assurance of the pre-painted finish beneath the powder, the company learned that they did not have to worry about 100 percent perfect powder coverage; letting some of the base coat show through was found to make the end product even more distinctive.

"In essence, we're trying to create a heavily textured, multi-hued look that by traditional powder coating standards would be unacceptable. However, for our application, it is just what we need," says Miller. "We still fight some issues with keeping the finish texture the same form run to run. As a result, we are currently developing our own proprietary powder delivery system for the spray guns. Once this new system has been completed, we anticipate that we will be producing a very consistent product with no concerns for mixing lots from one run to the next. Right now, however, we do maintain control over production lots and do not mix between them," he says.

Classic Products has named its powder-coated roofing system TimberCreek Shake. It is a system of 12" x 48" interlocking roofing panels and matching pre-formed accessories. The roofing panels are produced on a 275-ton stamping press from 0.017" thick G90 galvanized steel pre-painted with PVDF II. Classic has developed six blends of the ThermoBond powder ranging from grays and browns to green. The company also has found some opportunities to create custom color blends to better satisfy their customers.

According to Miller, TimberCreek Shake has been very well-received by the roofing market. "It truly does combine the beauty of stone coat systems with the incredible durability of Kynar/Hylar finishes. Many homeowners who have seen the ThermoBond finish have fallen so in love with it that they have had us apply it to our aluminum roofing shakes as well. It is our feeling that, over time, we will see additional metal roofing manufacturers begin to use this technology as well. As metal roofing gains popularity in the residential marketplace, we are seeing a rapidly increasing consumer demand for products which are increasingly beautiful and durable."

Potential for the Future

Architectural grade PVDF coatings have the best track record (and test data) for outdoor durability and weathering resistance of the fluoropolymer resin systems used in North America. In addition to excellent weatherability, PVDF coatings have exceptional flexibility, abrasion and corrosion resistance, plus low surface-friction and dirt-retention properties.

The overriding trend or goal for powder coatings, including PVDF powder offerings, is to provide a coating system at least equal in performance to liquid coatings without sacrificing ease of application and environmental advantages. This can be broken down into to several key areas where PVDF powder coating technology advances are evolving: weatherability (exterior durability), thinner films, greater appearance offerings, and improving cost effectiveness. Also, with the emergence of alternative non-chrome pretreatment chemistries that will meet the physical performance requirements of the AAMA 2605-02 10 year performance requirements, PVDF powder coatings technology development may ultimately contribute to sustainable, energy-related benefits with the inherent significant environmental enhancements.

In addition to providing similar weatherability results as liquid PVDF technology without the use of solvents, the resulting harder PVDF powder coating will, theoretically, result in less handling damage in the field. Research and development research continues with resin melt-flow properties as well as with powder particle size control and powder delivery. Reclaimability of PVDF powder overspray is easily managed and achieved similar to alternative powder resin chemistries, e.g., polyesters. Appearance development efforts have successfully achieved several metallic looks employing micas while a primary focus has been on smoothness and clarity. The smoothness of most PVDF powder coating colors is not, however, equal to PVDF liquid systems at thinner films, i.e., at or below 2.0 mils.

The key to 70 percent PVDF powder coatings success can be found in its basic chemical foundation. The carbon/fluorine bond that is the basis of this technology is one of the strongest chemical bonds known to man and is sustains its resistance to UV degradation. It has been reported through extensive analytical analysis that the 70 percent PVDF formulation, which is regulated by license, has more than twice the fluorine content compared to that of any alternative fluoropolymer chemistry, e.g., FEVE. A 70 percent PVDF containing coating also has excellent non-staining characteristics and since its coefficient of friction is extremely low, heavy rains can help wash and keep the coated surface clean.

Advantages

• Outdoor weatherability
• Chemical resistance
• Broad temperature operating range
• Flexibility
• Abrasion resistance
• Surface release properties
• Environmentally sound: No VOCs or HAPs; non hazardous waste; reclaimable field touchup identical to liquid PVDF systems

Disadvantages

• Higher initial material cost
• Use of primer recommended
• Three coat applications require extra line processing
• Metallic offsets

limited

Typical End-Use Applications

• Roofing panels
• Monumental-type structures
• Exterior wall panels
• Aluminum extrusions

Cool Metal Roofing and PVDF Powder Development

Most conventional roofing materials absorb some amount of solar radiation, which causes the surface temperature to elevate. This heat can be transferred to the interior of the building and accelerate the deterioration of those roofing materials. Cool roofing material will reduce these problems and these materials are defined by their reflectance and emissivity measured as either a percentage or a value between 0 and 1. Various standards are utilized and different labeling standards have different requirements. Energy Star, LEED (Leadership in Energy and Design) administered by the U.S. Green Building Council, and the CCRC (Cool Roof Rating Council) rating systems have different criteria and each one means something different and some areas of the country may require that the PVDF powder coating system be tested under one or more of these programs. Cool roofing is a topic that has gained increased exposure in the architectural community and it is widely believed that energy efficiency holds a significant growth.

There is opportunity in metal roofing in the coming years. Combining energy efficiency with the environmental benefits of powder coatings that can comply with the various standards cited and remain competitive with alternative PVDF liquid technology is moving closer to reality.

For more information:

For more information on Rohm and Haas, call 414-443-9230 or visit www.rohmhaas.com. For more information on Classic Products, call 800-543-8938 or visit www.classicroof.com.

^{*Kynar is a registered trademark of Arkema.}

**Hylar is a registered trademark of Solvay Solexis.