Metal panels come in a wide variety of colors and types of coatings. The technology in coatings makes sure that they not only look nice, but also protect the metal panels from moisture and pollution. Before deciding on which type of coating is right for your next metal panel project, here are the basics of what’s involved in the coatings and the types of aesthetic options available.
Understanding the types of coatings and their characteristics can help you create a lasting impression
Photo courtesy of Sherwin-Williams Coil Coatings
“Coatings are formulated specifically to protect the substrate and withstand, in this case, extreme weather conditions,” says Jeff Alexander, vice president of sales for Minneapolis-based Sherwin-Williams Coil Coatings. “All while protecting the substrate and maintaining the beautiful aesthetic of the metal building products.”
Consideration for metal panel coatings have to do with where the project is located, how the sun exposure and weather elements will affect the building products, and the requirement of added corrosion protection. Additionally, the type of color and visual effect of the coating, as well as whether the desired color is part of the brand/styling of the building, are also important.
“Performance considerations could include exposure to corrosion causing substances such as salt air and industrial output, and heavy or inconsistent ultraviolet (UV) exposure,” says Michelle Vondran, technical manager at NS BlueScope Coated Products–North America, Kalama, Wash. “These factors will influence the type of paint system. Integration considerations include color choice, gloss levels or other finish options to improve the way a metal panel integrates with other building materials and the environment.”
“The advancement of coating formulations not only offers protection but a wide range of design options that include a full range of color and texture possibilities,” adds Alexander. “Further, when the coating is factory applied it is more consistent, more durable and more environmentally friendly than other alternatives. The appeal of prepainted metal includes mechanical strength, corrosion resistance and an excellent base substrate upon which to apply advanced coatings.”
The ingredients in a coating typically include 15 percent pigments, 35 percent resins, 50 percent solvents, and 1 percent additives. (Image courtesy of Sherwin-Williams Coil Coatings)
Parts of a Coating
When choosing the right coatings, it is important to understand the ingredients and the role they play in the overall system of the coatings. There are three parts to every coating: pigment, resin and solvents. Additives may be added to fine tune or improve a coating’s performance characteristics.
“Each of the three main components of paint can be modified based on specific end use,” Vondran says. “This modification process must take into consideration the application process to ensure the right adhesion, formability, color and gloss is created. Other considerations include end use requirements, cost, and desired warranty coverage. Many attributes of a paint are trade-offs and paint mixes must be balanced to achieve certain characteristics.”
Pigments
Pigments supply the color and opacity to hide the substrate and to achieve nice even color across the entire surface. There are two key types of pigments: organic and inorganic. “Pigments are tiny particles of color that are blended according to specific formulations, says Alexander. “Pigments not only add color, they can also provide opacity to hide the substrate and they can improve corrosion resistance. Your color selection will determine if organic or inorganic pigments—or both—are needed.”
“Organic pigments are typically derived from plants whereas inorganic pigments are metallic compounds or oxides that are further processed to provide excellent color stability,” adds Vondran. “Organic pigments are usually brighter than inorganic pigments and can provide a cleaner or more distinctive look. However, organic pigments are less durable and fade faster when exposed to UV light, a key consideration for exterior building design. For some high visibility applications, the use of a clear coat over the top of finishes with bright organic pigments can help reduce color fade.”
Resins
Resins are the glue or binder that hold the coating together and impart the majority of the performance properties of the coating. “They provide the coating’s physical and chemical attributes and determine how effectively the paint will adhere to a surface, flex and form, and weather,” explains Vondran. “The resin chemistry is also the paint type name; polyester, silicone polyester, acrylic, epoxy, PVDF, etc.”
“Resins hold pigments in place and protect them from damage by exposure to sunlight and rain,” says Kristen Blankenship, business development manager at AGC Chemicals Americas Inc., Exton, Pa. “Some resins are inherently glossy and translucent allowing for truer or cleaner colors. Others may be inherently lower in gloss and offer a satin finish. Some resins have chemistry that makes them more susceptible to UV degradation and therefore are only offered in earth-tone colors.”
Solvents
Solvents are the thinner that make the pigment and resin easier to apply and provide application properties that result in a nice smooth surface. “Solvents are used only to transfer paint from the equipment to the part that is painted and don’t offer any long-term advantage to the cured paint film,” explains Scott Moffat, global marketing director, specialty markets, industrial coatings at Pittsburgh-based PPG Industries Inc.
Photo courtesy of Steelscape
Types of Coatings
Coatings are generally described by using the name of the type of resin used. There are three primary resin-based coating systems used for finishing sheet metal: polyester, silicone-modified polyester and fluoropolymers. In terms of performance, the paint systems range from good (Polyesters) to better (SMPs) to best (PVDF), however, Richard King, product manager at Steelscape, Kalama, says the performance comes at a cost premium that may not be justified for all applications and panel types.
Polyester
Polyester coatings include a wide class of resins that are custom formulated for different end uses. From good weathering, flexibility, hardness to corrosion-resistance, polyester coatings can be tailored with a combination of properties, making it a multipurpose coating, explains Alexander, with typical uses in interior liner panels, doors and trim, to exterior rainware, window cladding and more. “Polyesters offer low-cost finishes with a range of design options,” adds Blankenship. “They are best for interior applications or low- sun environments.”
Silicone-Modified Polyester (SMP)
Silicone-modified polyester products are incredibly durable in tough conditions given the carbon-silicone bond is one of the strongest bonds in nature. SMPs offer a harder surface, better color retention, and better weather resistance than polyester. According to Alexander, the two-coat system is ideal for a number of commercial and residential metal roofing, wall panels and other exterior products. SMPs are a cost-effective choice if a more durable finish is needed, notes Blankenship.
Fluoropolymers
There are two types of fluoropolyers that are most widely used in architectural systems: polyvinylidene fluoride (PVDF), and fluoroethylene vinyl ether (FEVE).
PVDF is commonly known as 70% PVDF coatings, which represents just the resin, with the remaining 30% being made up of acrylic. Kynar and Hylar are the brand names of the 70% PVDF resin using in the coating. “PVDF coatings represent a significant advancement in paint technology with superior weathering characteristics,” says Alexander. “They have long been recognized for their excellent chalk and fade resistance and are flexible in nature allowing for the forming of a wide variety of shapes.”
“Fluoropolymers like PVDF and FEVE offer the highest performance in exterior environments,” says Blankenship. “They resist color fade, chalking and gloss loss for decades. Both PVDF and FEVE can be used for low to satin gloss finishes while FEVE can be used for higher gloss finishes a well. Though fluoropolymers come at a higher price point, their life cycle cost is often much lower than other finishes. Long-life coatings have significantly longer maintenance intervals. They require less maintenance and fewer repaints over the life of the asset making them a sustainable choice for the environment.”
Photo courtesy of Sherwin-Williams Coil Coatings
Visual Effects
Prepainted metal is available in thousands of different color options. “To produce a specific-colored coating, colored pigments are selected and blended together,” Alexander says. “Coating manufacturers have a variety of pigments from which to choose, and the color selection will determine if organic or inorganic pigments—or both—are needed.” In addition to colors, there are a variety of visual effects that can be achieved with metal panel coatings.
Gloss and Sheen
Gloss is a unit of measurement that specifies how much reflectance a coating will have. “The way light reflects off the surface of an object is an indication of its gloss level,” explains Alexander. “Similar to interior paints, metal coatings are available in various gloss levels from matte, low gloss, standard and high gloss.”
The way in which a finish reflects light can be considered part of its aesthetic properties. “These attributes are naturally considered aesthetic properties of a finish,” explains Blackenship. “As an organic coating ages, it may break down at the chemical (microscopic) level. Depending on the resin system, this process may happen at different rates. The microscopic chemical breakdown evolves into macroscopic degradation and erosion of the bulk finish itself. The first indication of this process is a change in gloss. Once this process, also called photochemical degradation, starts it follows an exponential curve. The integrity of the finish weakens reducing its barrier properties. This can result in corrosion formation, chalking, and color fade. It is important to consider gloss as more than an initial number, but a property that is indicative of the performance of a coating over its life.”
When it comes to the different types of coatings, Moffat explains that polyesters have a wide gloss range, while PVDF fluoropolymers only offer a gloss range of 10-40 degrees, and FEVE fluoropolymers are available with full gloss ranges. “Low-gloss coatings hide metal and paint defects and have always been the preferred level of gloss,” he says. “Gloss will change the look of the coating dramatically even with the same base color.”
Micas and Metallics
In addition to solid colors, coatings with a pearlescent shimmer can offer different visual effects. “Mica and metallics are a blend of mica and aluminum pigmentation that add varying degrees of sparkle to the surface to produce a metallic luster look,” explains Alexander. “Micas and metallics sparkle and add life to the coating,” adds Moffat. “Sunlight and angles accentuate the effect. They are the most popular commercial coating but the hardest for color control. Application variables can change color on micas and metallics based on how these pigments reflect by orientation in the paint film.”
Color-Shifting Effects
To achieve color-shifting effects, coated flakes are added to the coating formulation that cause a color-shift due to light reflectivity. “Color-shifting pigmentation works when viewed from different angles or under changing light sources,” says Alexander. “There is a wide range of color shift which can be achieved from dramatic, red to a green, or more subtle a white to a cream. As with mica/metallics it is well known in the auto industry and becoming more popular in architectural products.”
Prints and Textures
Prints are an effect that mimics natural materials, and can reflect antique styles, patina aesthetics or natural metals, stonework and wood. “To create a print effect, a one-color basecoat and then a one- or two-color tint coat is applied on top that has some opacity,” says Alexander. “Coil coaters use a special print roller, such as a roto gravure, that has a pattern template. The pattern is rolled on the top of the primary basecoat to create the desired effect.”
According to Moffat, textures have become more popular because of the look it provides. One way to add texture to a prepainted metal is by adding texture within the coating. Another way is to use an additive, which creates the textured effect during the curing process. “A textured coating is performance you can see and feel, adding a nice distinctive finish to any project,” says Alexander.
Photo courtesy of PPG Industries Inc.
Cool Coatings
Cool coatings are solar-reflective pigments that have been altered both physically and chemically to reflect infrared radiation while still absorbing the same amount of visual light. “Certain pigments reflect light better than others, mainly used on metal roof panels and referred to as cool roof coatings,” explains Alexander. “A cool roof is one that reflects the heat emitted by the sun back into the atmosphere, keeping the temperature of the roof lower and thereby reducing the amount of heat transferred into the building below, resulting in a cooler building, which means less energy used and lower energy bills.”
According to King, with most coatings available with solar reflective cool pigments, lighter colors will always outperform darker colors for solar resistance. “In certain environments where this is critical to lower cooling costs and achieve building efficiency needs, such as those outlined by LEED, this may limit color selection. The best way to validate this is to understand the Solar Reflective Index (SRI) needs for a project then validate suitable colors on a product color card.”
