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Top Quality Finishes for Architectural Metal: The Right Chemistry for High-performance, Long-lasting Building Envelopes

Today's building designers continue to challenge manufacturers of building envelope components to provide unorthodox shapes, styles and colors. Simple straight lines, corners and smooth surfaces are being replaced with curvatures, textures and complexities. At the same time, architects and building owners expect the envelope components to hold up in blistering heat, humidity, urban grime, acid rain, corrosive salt and abrasion over decades of exposure.

Metal has rapidly become the material of choice for exterior use due to its rugged durability, design versatility and aesthetic possibilities. Metal roof and wall components, extrusions and preformed shapes can be bent, crimped and twisted to meet the most challenging building design requirements. They can also save energy, increase property values and hold their beauty far longer than other building materials.

For all its performance advantages and beauty, however, metal doesn't necessarily have a tough skin and is only available in a single color. To satisfy a designer or owner's needs, architectural metal must be coated with a rugged protective finish that not only beautifies with color but also doesn't chalk; lose its color and sheen; or pit, chip and age for a long time.

 

Weatherability Is Paramount

Color creates a mood and makes that desired first impression quickly and more effectively than almost any other architectural component. But while architects like to use color to create a statement or image with a building, retaining its beauty and vibrancy can be very difficult. Exterior paints naturally degrade from exposure to heat, humidity and harmful ultraviolet rays. Sunlight can quickly turn brown to tan, red to pink or a deep blue to sky blue. Deterioration can also be evident in the loss of gloss and adhesion, as well as the appearance of chalking. More than 95 percent of architects in a recent national survey considered weatherability as "critical" or "very important" to specifying for metal roof and wall panels. Nearly nine out of 10 of these same architects rated Kynar 500 PVDF resin-based metal coatings as "good or excellent" in terms of weatherability and color retention and said they prefer coatings formulated with Kynar 500 PVDF resins. Additional results from the survey can be found at www.kynar500.com/ma.

A key reason for this strong brand preference among architects is the Kynar 500 resin-based coating's outstanding resistance to film degradation. The high-performance chemistry behind these premium exterior finishes is transparent to UV rays and, when combined with durable pigments, creates a coating system that prevents color from fading. Coatings formulated with Kynar 500 resins also withstand extended exposure to water, humidity, temperature, UV rays, oxygen and atmospheric pollutants.

 

Green Building Solutions

With energy codes becoming more rigorous, cool roofing is becoming a more popular means of energy-efficient building. Sustainable design calls for the reduction in energy consumption as a cost savings to the building owner and as a direct reduction in the greenhouse gas emissions at the power plant generating the energy for the building.

The choice of roofing material has the greatest impact on the energy conservation of a building. Cool metal roof systems, which feature a finish such as a Kynar 500 PVDF resin-based coating, can reduce energy consumption by up to 40 percent as part of a total system design (as reported by the Oak Ridge National Laboratory, Oak Ridge, Tenn.).

Kynar 500-based painted metal roofing, which offers advanced resistance to UV degradation, can achieve solar reflectance of over 70 percent. Reflected solar energy allows the roof surface to remain cool, which means less heat is transferred into the building. As a result, use of cool metal roofing products featuring Kynar 500 PVDF-based paints is one proven way to limit the urban heat island effect.

Kynar 500 PVDF-based coatings offer superior long-term color retention, allowing the building owner to enjoy the original color specified over the life of the building with little to no change over time. Unlike conventional products, which are regularly destructed by UV energy, heat and moisture, colors in a Kynar 500-based paint system remain rich and vibrant due to the resin's resistance to UV solar radiation. With restoration not being required as often as it is with competitive products, environmental impact is reduced. The reduction in restoration and reconstruction results in lower amounts of VOCs emitted into the atmosphere. These features of a Kynar 500 PVDF system make it a sustainable green building product.

 

The Kynar Technology Platform

Kynar 500 PVDF, or polyvinylidene fluoride, homopolymer is universally known within the architectural community as a weatherable coating resin. All coating systems contain a specific resin that acts as the first line of defense against weathering. Ultimately, the resin determines robustness. The durability found in PVDF is a result of the chemical composition of the resin relying on the carbon-fluorine molecular bond-one of the strongest bonds known. It is the C-F bond that provides the resilience, color and gloss retention for which Kynar 500 PVDF-based coatings are so well known.

The structure of PVDF contains alternating carbon/fluorine and carbon/hydrogen bonds, which provide a polarity that enables the formulation of a practical coating that resists environmental degradation and dirt retention. This structure enables PVDF to resist oxidation, photochemical deterioration, fading, chalking, cracking and airborne pollutants. Thus, PVDF has a balance of properties that make it particularly suitable for use in coatings, especially for architectural uses.

The National Coil Coating Association, Cleveland, rates the performance of PVDF coatings very favorably to the other common paint systems used in the metal construction industry. A portion of its Comparative Properties and Performance Chart, shown in Table 1 (above), illustrates that PVDF coatings, such as resin-based Kynar 500 paint systems, excel in most every category of importance to a building owner. In all cases, NCCA used the opinions of industry experts to accurately capture the performance of each technology. The properties are measured using recognized standards and test methods from West Conshohocken, Pa.-based ASTM International and Schaumburg, Ill.-based American Architectural Manufacturers Association.

 

Strong Performance Record

Kynar 500 PVDF resin-based coatings have been thoroughly analyzed since they were first introduced to the market over 40 years ago. Coatings made with this fluoropolymer are time tested in harsh climates, internationally evaluated and rewarded by being the product of choice for architects and designers who specify durable prepainted metal components in the construction industry.

The performance of Kynar 500 PVDF resin-based coatings compared to other common paint systems used in the metal construction industry is illustrated in Figure 1 (above). The superior resistance to fade exhibited by the Kynar 500 resin-based coating is obvious after 17 years of exposure at an independent test-fence facility in southern Florida. It is difficult to retain dark colors over time, and yet even in the dark color used, fading was insignificant with the Kynar 500 resin-based coating.

 

In other colors, the performance of Kynar 500 PVDF-based paint finishes is noted in Figure 2 (above).

 

Taiyo Steel Performance Study

Customers of Kynar 500 PVDF resin-based coatings in other parts of the world have agreed with the excellent performance seen in North America. To test the weatherability of its precoated metal products, Taiyo Steel of Funabashi, Japan, established an exposure test fence by using the south-facing wall of a new plant it was building. Thirty-three-foot- (10-m- ) high steel panels were coated with acrylic, polyester, silicone polyester and Kynar 500 PVDF resin-based coatings in 1981. After 14 years, the Kynar 500 resin-based coating was the only system that kept its original appearance.

 

Quality Control Through Licensing

The number and variety of building components that are commonly protected with Kynar 500 resin-based coatings continue to grow. Examples include spandrel panels, wall panels, curtainwalls, metal roof systems, storefronts, column covers, entranceways, louvers, mullions, window and doorframes, metal trim and fascia. When specifying a Kynar 500 resin-based paint system for ultimate performance on a building project, the following terminology should be used: "The final coating for aluminum, galvanized steel or aluminized steel shall be a factory-applied, oven-baked finish based on 70 percent KYNAR 500 polyvinylidene fluoride resin."

Product consistency, quality and availability are managed on a worldwide basis through a rigid licensing program. A license is granted only to quality coating companies and only after a rigorous testing program is completed. This program encompasses both outdoor exposure testing and extensive laboratory testing. The license grants the licensee the right to identify their products formulated from Kynar 500 PVDF resins with the Kynar 500 trademark. Licensees must use nothing less than 70 percent Kynar 500 PVDF resin. This minimum establishes the base level of performance for licensed Kynar 500 resin-based coatings that the industry has come to expect.

 

Chip Bisignaro is business manager for Arkema Inc., Philadelphia.

www.arkema-inc.com; www.kynar500.com/ma