New Technologies in Coatings

A building’s exterior surfaces experience rigorous, day-to-day durability challenges. Metal is generally available in only a single color. To be both functional and pleasing to the eye, metal must be coated, which beautifies with color and resists any chalking, pitting, chipping or premature aging.

It can be a daunting task to determine which coatings for metal architecture roof and wall panels will be the best choice to maintain a building’s longevity, but there have been many new technologies available to the metal construction industry in recent years.

The three types of factory-applied high-performance coatings for aluminum are Polyvinylidene fluoride (PVDF) paint, powder coat and anodize. All three processes offer a long-lasting finish on building materials and surfaces, but each has its own characteristics for application.

“Anodized aluminum offers three main characteristics: its uniform, extremely hard surface protects the substrate from deterioration; its protective chemical resistance provides excellent wear and abrasion resistance with minimal maintenance in most environments; and it’s 100 percent recyclable and poses no health risks,” says Tammy Schroeder, LEED Green Associate and senior marketing specialist at Linetec, Wausau, Wis. “High-performance PVDF paint and/or powder coatings offer the benefits of protection against weathering, aging and pollution; design versatility with endless color options; and the capability of field touch-up and job-site repainting. PVDF finishes are inherently inert and have the ability to withstand long-term ultraviolet radiation, which results in excellent color/gloss retention and chalk resistance. PVDF finishes also resist acids, alkalis, oils and dirt pick-up.”

Environmental impetus

The green movement is a driving force in new coating technologies today. Unlike wet painting and liquid finishes, which require solvents, powder coating applications use an electrostatic charge to transfer the powder to an item. As a result they have a much lower impact on our environment. Powder coatings emit zero or near-zero volatile organic compounds (VOC). Thus, there is no longer a need for finishers to buy costly pollution control equipment. Since powder coating overspray that does not adhere to the part can be retrieved and reused, this eliminates the waste commonly found in liquid finishing processes, making the entire powder coat process environmentally green.

Elimination of VOCs and reduction of waste saves money and helps companies comply more easily and economically with the U.S. Environmental Protection Agency regulations.

Flurospar SR Classic II spray applied coatings are the newest products to the Fluropon coatings product line from Minneapolis-based Valspar, and are considered to be some of the most environmentally responsible coatings available to the aluminum building products industry today.

“This new, eco-friendly product is formulated with solar reflective (SR) pigments that keep building components cooler than bare aluminum or anodized aluminum,” says Schroeder. “They decrease the amount of heat absorbed by a building resulting in energy savings and they help mitigate urban heat island effect. While programs currently focus on roof temperatures, aluminum extrusions and wall panels coated with Flurospar SR Classic will also reduce surface temperature.”

For anodize finishes, one of the most significant developments has been the eco-friendly anodize. “Linetec has had this technology installed for the past three years and 95 percent of our customers have made the transition,” Schroeder says. “Eco-friendly anodize utilizes an etch process designed to dissolve a thin layer on the surface of the aluminum to develop a smooth, uniform finish that helps hide small defects, such as die lines, flow lines, minor corrosion and scratches, that may occur on the aluminum surface of architectural products.”

The eco-friendly anodize process gives manufacturers the ability to now use secondary billet in their extrusion process. It reduces landfill waste from conventional anodize etch processes by 75 to 80 percent and its low gloss level reduces glare in bright sunlight.

In spite of governmental pressure, new regulations and a concerned public, the push to go green in the metal architecture arena is not as powerful as some would like it to be. “Being in the greenest of coating alternatives for metal in the architectural industry’s recent ‘green movement’ and VOC compliance has done nothing substantial to [the] industry in my opinion,” says Shivie Dhillon, marketing and technology director at Sundial Powder Coatings, Sun Valley, Calif. “All day I hear about green, green, green but even the government doesn’t take advantage of powder coating.”

Reflective coatings

Hundreds of years ago white lime paint was used to help keep homes cooler. It was the science behind solar reflectance that helped make this happen.

A cool roof reflects and emits the sun’s heat back to the sky instead of transferring it to the building below. According to the Cool Roof Rating Council “Coolness” is measured by two properties, total solar reflectance (TSR) and thermal emittance. Both properties are measured from 0 to 1 and the higher the value, the “cooler” the roof.

All coating technologies can be “cool” with formulation techniques that reflect UV light. These formulation techniques can yield cool roof coatings with a minimum 25 percent TSR to meet the EPA’s Energy Star Requirements. Many colors are greater than 25 percent.

“Studies have shown when these cool roof coatings are used it reduces energy consumption,” says Andrew Blake, president of Beckers Industrial Coatings-Americas, Elk Grove Village, Ill. “The green movement and energy savings in using cool roofs has spurred cool roofs to be required by architects, builders, building owners and consumers. Cool roofs earn credits under LEED and many new buildings being built today are trying to attain certain LEED accreditation. Cool metal roofs help architects and building owners to earn credits towards LEED accreditation.”

“The Cool Technology Paint Systems available on Alucobond offer longer lasting color life and chalk resistance,” says Tom Seitz, sales manager at 3A Composites USA Inc., Mooresville, N.C. “Corrosion, chemical and resistance to humidity are also improved. Cool Technology has the potential to provide energy savings to cool your building due to the solar reflectance of the paint. The technology keeps the surface of the building cooler. Cool Technology on the vertical walls along with the roof can provide a complete building envelope.”

Additional emphasis is being placed on the SR index system. “Selecting exterior aluminum components coated in a high SR system, such as Fluropon SR fluoropolymer coatings or Duranar Ultra-Cool infrared (IR) reflective fluoropolymer coatings, can be of assistance, particularly in hot climates,” says Schroeder. “High-solar reflectance (albedo) and high-emittance coatings play an important role in resisting heat absorption and keeping buildings cooler, which reduces energy consumption used by air-conditioning systems.”

In March 2011, PPG Ideascapes Industries Inc., Pittsburgh, issued a white paper titled “Energy Savings in High-Rise Buildings Using High-Reflective Coatings.” The study showed that when IR reflectance coatings are increased from 5 to 70 percent for metal wall, window frame and roof, total building energy costs are reduced by 1 percent in cold-weather cities such as Ottawa, Boston and Chicago, and by up to 4 percent in warm-weather cities such as Mexico City and Phoenix. In the cooler climates, there is a trade-off between increased heating load and decreased cooling load, but reflective coatings still yield a small advantage. In hot climates, such as Atlanta and Phoenix, significant energy savings can be achieved.

Water-based coating

Cold spray metal coating technology has been on the scene since the mid 1990s. It requires a solvent-based product which requires a catalyst to cure it and takes up to 24 hours to cure. Solvents have a foul smell prohibiting in situ applications and forcing people to be removed from it during application.

Auckland, New Zealand-based Metalier International has developed a water-based coating the company claims to be the first to be marketed to the world. “Smooth-finished cold spray metal coatings are sprayed on using compressed air and high-volume, low-pressure (HVLP) guns,” says Mary Whaley, international operations manager of Metalier International. “After curing, the sprayed surface is then polished using orbital sanders or a bristle system. The solvent product not only takes 24 hours or so to cure, it takes a long time to polish. Most solvent product sellers advise the avoidance of high-polished finishes as they are just so time consuming to achieve. With Metalier’s water-based coatings high polishes are speedily and easily achievable opening up other options for designers.”

Another advantage of water-based technology for metal panel coatings is the finishing ease means less consumable usage like sandpaper. Acetone and gun cleaners no longer need to be used because guns and other tools wash up in water. There is no smell and the binder isn’t sticky like solvent-based binders.

“The availability of a water-based coating means architects and designers can now specify metal coatings in situations where the solvent products are unsuitable,” Whaley says. “A cheaper metal substrate can be transformed with the addition of copper, bronze or brass (for example). And we have teamed with a U.S. manufacturer of a 100 percent UV-stable nano-based clear coat to ensure our finishes remain as pristine as the day they were completed.”

Looking old is new

In recent years, the metal architecture industry has witnessed a greater interest in finishes that look old. “Many iron/steel components are much more attractive if coated with a
‘gunmetal’ finish with a silvery/black color tone which is more compatible than black paint with other adjacent materials, such as stone and wood,” says Mark Ruhland, vice president of Birchwood Casey, Eden Prairie, Minn. “In the parlance of one operator, the clients want ‘living finishes’ that have character, like they have hung in the barn for 40 years. These finishes might look rustic to some viewers, but, in most cases, the response is natural. Clients want a natural-looking finish that can age naturally to produce an even more attractive finish over time.”

Besides the aged look of iron and steel components, many architects want an oil-rubbed bronze finish on copper-based alloys or the green patina finish on copper components. Since copper has long been regarded as a natural material with inherent corrosion resistance, it is an ideal material for many applications. “Copper is capable of taking on an attractive chemical finish, then developing its own natural patina finish over many years of service,” Ruhland says. “In this way, the copper finishes become more visually warm and attractive as they age.”

Textures and colors

Pigment and paint manufacturers have studied the performance of high reflectance colors and are now including a complete rainbow of reflective colors, besides just white.

“Now architects have a whole range of cool colors to specify for painted metal walls and roofs from many paint manufacturers,” says Jay Kahn, global commercial development manager, Alcoa Architectural Products, Eastman, Ga. “This is only the beginning of improved energy efficiency from cool paint. Several universities and government laboratories have begun testing on dirt deposits on cool paints. Early studies show a significant reduction in reflective performance with a thin layer of dirt build up. With the hydrophilic surface and organic deposit destroying performance of EcoClean, Alcoa believes we may offer a major long-term performance improvement in helping cool painted metals maintain their intended performance levels.”

There is increasing interest in multi-chromatic pigmented coatings that provide novel color effects, such as exhibiting a color change relative to the exposure angle. “Valspar Kameleon PVDF system is an example of one of our product lines that offers this performance,” says Bill Simser, director of marketing-coil & extrusion, Valspar. “This line of product specifically targets novel aesthetic appearance.”

Interest in textured coatings is prompting new technologies too. “There are several ways to accomplish this goal such as solid texture particles or wrinkled appearance,” says Simser. “Valspar’s Hardcoat PVDF is an example of a textured solid particle coating. The wrinkle finish is more prevalent in Europe where Valspar Novacoil polyesters and polyurethanes are examples. These lines offer both appearance differentiation and handling advantages.

“We continue to invest in the development of technologies to improve weathering performance, primarily in polyester and siliconized polyester chemistries. North America remains focused on both siliconized modified polyesters and PVDF chemistries where Europe and Australia have interest primarily in polyester and polyurethane chemistries.”

Linetec continues to work on new technologies, textures and colors for the architectural market. “Most recently developed is our copper anodize,” says Schroeder. “This exclusive, copper anodize finish offers our customers the look of rich, real copper without such shortcomings as salt run-off stains, galvanic corrosion and patina. Linetec’s new copper anodize process is a unique, consistent and repeatable process. It involves using actual copper to color the aluminum, while isolating the copper in the coating.”