PERFORMANCE CHARACTERISTICS OF PRE-PAINTED METAL

What contributes to the excellent performance of pre-painted metal? Beyond the core of treated metal, it comes down to enhancements and formulations of the coating. Just as custom finishes and coloring are possible, so too can the performance characteristics be customized and worked into a coating formulation.

There are also industry guides developed by the National Coil Coating Association (NCCA), which is an established trade organization dedicated to the growth of coil-coated products. NCCA has developed a series of technical manuals referred to as “Toolkits” (www.coilcoating.org/toolkits). Specifically, Toolkit #26 focuses on the long-term performance of metal building panels and metal buildings. It notes that there are three principal factors that influence that performance: 1) the choice of materials, 2) the environment in which the products are placed, and 3) the variability of coating processes. By following the guidance contained in these documents, manufacturers can achieve consistent, high-quality results, and specifiers can identify acceptable tolerances and performance parameters.

• Pigment performance: While the resin choice (PVDF, SMP, or polyester) is the single biggest determinant of overall performance, all coil coatings are baked at temperatures that are much higher than those of other industrial coatings. Therefore coil coatings topcoats, including the pigments selected, need to provide heat-resistance and -tolerance qualities. Then, once the finished products are installed on buildings, the pigments must be able to hold up by providing exceptional weathering performance properties for 20–40 years or longer. This includes providing resistance to chalking and fading of the pigment colors. Pigments can be selected to meet these requirements plus enhance some of the other qualities of the paint coatings, such as hardness, corrosion resistance (particularly in primer systems), chemical resistance, resistance to degradation from ultraviolet radiation, and the reflectivity of solar radiation.
• Environmental performance: Different project locations bring different environmental conditions that will warrant different types of coatings as well as attention to the selection of the base metal and pre-treatments. For example, some products may be placed in remote locations with aggressive UV light conditions, corrosive salt spray, or higher-than-typical temperature exposure. Others may be in industrial locations with the presence of chemicals. Metals and coatings can be selected to address any or all of these environmental conditions. In urban locations, there may be concerns about smog, so it is useful to know that some highly specialized coatings are shown to be smog eating. In places prone to graffiti, pre-painted steel can be selected that limits adhesion or penetration, making graffiti removal much easier than with other materials.
• Water performance: Materials used on building exteriors will encounter water in the form of rain, sleet, melting snow, ice, or other weather related conditions. Pre-painted metal products remain clean because metal inherently sheds water better than other materials.

Overall, virtually every geographic location and project type can benefit from some aspect of pre-painted metal performance. In the western United States, lightweight metal roofing and wall panels reduce seismic mass and offer noncombustible, high temperature resistance in the case of wild fires. In the storm-prone southern United States, pre-painted metal products are extremely resistant to uplift from hurricane winds. In the humid eastern United States and elsewhere, mold growth is not supported on metal, while resistance to rust or decay from water is based on the choice of substrate metal and coating process. In the Midwest, where hail is often a concern, resistance to hail storms can be factored into the strength of the metal as well as the durability of the coating. In short, regardless of the conditions or locations, pre-painted metal has been successfully used to create an appropriate solution.

GREEN BUILDING CONTRIBUTIONS OF PRE-PAINTED METAL

Like most other building components, pre-painted metal manufacturers have developed products that can contribute to the green and sustainable nature of buildings. Indeed, many have helped building designs achieve certification under the LEED program, ENERGY STAR programs, and the Living Building Challenge, among others. Some of the ways they do that include the following:

• Cool roofing: There are several national programs that recognize the significance of keeping roof temperatures cool and offer ways to measure and document the relative heat or coolness of different types of roofing. These include the ENERGY STAR Roofing Products Labeling program (www.energystar.gov) (due to sunset in 2021) and the Cool Roof Ratings Council (CRRC). Pre-painted metal roofs have been tested under these programs and shown to provide significant solar infrared reflectance and thermal emittance, both of which can reduce the surface temperature of a roof. This is achieved primarily through the use of solar-reflective (SR) pigments in the coating. These roofs reflect heat emitted by the sun back into the atmosphere. This lowers the temperature of the roof and reduces the amount of heat transferred into the building, which decreases energy consumption.

• Energy performance: Cool roofing impacts the energy performance of a building in two ways. First, it reduces the creation of “heat islands,” which have been shown to increase ambient outdoor air temperatures noticeably compared to green or more natural areas. Second, by reflecting away the heat, the cooling load of a building is often reduced, such that air-conditioning runs less, using less energy.

  Standing-seam metal roofing panels provide an ideal substrate for installing electricity generating solar panels (i.e., photovoltaic or PV panels). Solar pre-painted panels can be easily attached to the upright standing seams using non-penetrating clamps. Further, the long life of a metal roof will outlast the life of the solar panels, thus eliminating costs and complications of reroofing with a solar array in place. All of these energy-related attributes help the natural environment by reducing the air pollution caused by the demand placed on power generation plants and lowering the local air temperature in urban areas, which helps to minimize the formation of smog.

• Materials and resources: There are several ways that pre-painted metal contribute in this category.
  • Life cycle assessment: Attributes such as environmental impacts, health impacts, and end-of-service-life options are all routinely part of such a life-cycle assessment, and pre-painted metal products have been subjected to them. Contributing to a favorable assessment is the fact that metal wall and roofing products demonstrate significant longevity. For example, it is common for metal roofing to last 50 to 60 years or longer, while other roofing would last only one-third to one-half as long.
  • Material transparency: There is an ongoing movement to create greater transparency in the makeup of all building products and materials. The careful avoidance of harmful elements and ingredients helps in this regard. For example, there are pre-painted products with a greatly reduced usage of Chromium 6 content. This helps make them compliant with the Living Building Challenge Red List requirements.
  • Recycled content: The fact that a high recycled content of the metal is common in pre-painted metal is a significant green aspect of the products. Further, the ability to recycle at the end of its use is noteworthy.

• VOC reduction: Historically, volatile organic compounds (VOCs) played a large role in the coating industry because they contain properties that assist in applying coatings to a surface. However, since VOCs are recognized for playing a significant role in contributing to the generation of ground-level ozone, urban smog, negative health effects, and environmental issues, their use is being reduced. To mitigate the harmful effects of VOCs, modern coil-coating processes incorporate a thermal oxidizer that destroys the VOC gasses released during the coating process and prevents them from entering the atmosphere. The energy generated during this process is returned to the facility in the form of heat, where it can be used to preheat fresh air entering the baking ovens or to heat part of the facility. This results in products that are more environmentally friendly, even before they leave production. Once the pre-painted metal products are shipped, there is no need for on-site paints or coatings, so no other VOCs should need to be introduced.

In general, there are multiple ways that pre-painted metal products currently contribute to green and sustainable buildings. There are also new and innovative initiatives being developed. One intriguing technology is the use of coil coatings that can react with pollutants in the air surrounding it. The chemical reaction creates a harmless transformation into water vapor, inert gas, and some dust that can be washed off of the surface and remain clean. Stay tuned, as there is more to watch for on the sustainability front.