The Evolution of Coil Coatings and Paint Systems for Metal

Numerous Finishes Redefine What Is Possible for Fabricators and Designers

There are various options for applying paint to metal. In the field, it is common to see spray or brush applications, while in the factory, methods such as spray, powder coating, or coil coating can be utilized. However, for today's metal architecture performance requirements, products like metal composite materials almost exclusively use the coil coating process to achieve finishes that are nearly flawless and durable.

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Coil coating is a method where a metal coil is coated in a continuous process before fabrication. The metal coil passes through an uncoiler, a line-loading accumulator, and then undergoes processing and painting according to specifications. Afterward, it moves through a finish line exit accumulator and is finally rewound on a recoiler. This method finishes and cures the coils continuously. Although traditionally applied to aluminum substrates, this procedure can also be used for other metals, such as steel.

According to the National Coil Coating Association, prepainted metal outperforms post-painted surfaces over time. With robust quality assurance programs, coil-coated metal has a significant advantage in terms of consistency. Continuous manufacturing also leads to lower costs and environmentally friendly practices, minimizing waste, enhancing efficiency, and capturing VOCs.

Methods of Coating

The application of paint to metal has evolved beyond the traditional spray systems, which are now more common in single-sheet batch processes. Continuous coil coating manufacturing employs either a roll coating or a die coating method. Reverse roll coating, commonly used in metal manufacturing, applies paint with two rolls moving in opposite directions. A metering roll loads and transfers paint to an applicator roll, which then coats the substrate. This technique allows for precise control over paint thickness but can leave the panel prone to "roping" marks, which are striations that appear at the edges of the brush similar to a ship's wake.

Die coating, on the other hand, is a precision coil coating process that retains the advantages of high-volume, continuous coating while offering even greater paint control. Paint is directly applied to the substrate through a slot die extrusion system.

Paint thickness is meticulously controlled in a single, seamless application. Both the paint system and the coil must meet stringent quality standards during the die coating process. The outcome is the smoothest coating achievable along with improved sustainability due to waste reduction.

Paint Systems

Over the years, paint systems have evolved as the industry has demanded more from finishes than what polyester and urethane paints could deliver. The only paint systems capable of meeting the most widely referenced architectural performance specifications established by AAMA are fluoropolymers. Their unique chemical composition provides exceptional weather resistance and durability.

The first generation of fluoropolymer paint, introduced in the 1980s, was polyvinylidene fluoride (PVDF). This system requires an additional acrylic resin to formulate PVDF into a coating, typically comprising 70 percent PVDF and 30 percent acrylic resin. As the PVDF ratio decreases, paint performance also diminishes. Although thermoplastic, meaning it melts at high temperatures, PVDF does not undergo chemical cross-linking, rendering it susceptible to remelting. PVDF has a relatively low-gloss finish, with a 60-degree gloss meter limiting it to a range of 30 to 40. The addition of acrylic also restricts color options, and achieving bright colors can be challenging.

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The second generation of fluoropolymer paint, introduced in the 2000s, is fluoroethylene-vinyl ether (FEVE). This paint system is thermoset and chemically cross-links the fluorocarbon components, preventing remelt under high pressure and temperature. FEVE is a clear resin that produces brighter and more vibrant finishes, achieving gloss rates as high as 70.

Advancements in coil coating and paint systems have resulted in a nearly limitless palette of finishes that can endure for decades. The introduction of metal composite material (MCM) into the architectural landscape represents another revolutionary innovation. MCM is versatile, easily fabricated into complex shapes without the weight or issues such as oil canning that occur with solid plate metal. Over the last 40 years, these advancements have significantly redefined the capabilities available to fabricators and designers.

Jim Moses is the technical services manager at Mitsubishi Chemical Composites America's ALPOLIC MCM division in Chesapeake, Va. With over 40 years of experience in manufacturing, engineering, and operations within the construction industry, he is an active member of various industry associations.

This article was featured in Metal Construction News.

High-speed coil-coated products, also known as prepainted products, can significantly aid a company's environmental sustainability, efficiency, and cost reduction journey. Coil coating has been practiced since the 1960s and is currently used worldwide.

Kloeckner Metals, through its Coil Coated Services Group, can facilitate improvements whether (a) optimizing a current coil coating user's incoming product or (b) managing a post paint-to-prepaint conversion project. Coil coated products can possess both aesthetic and functional attributes.

The variety of industries we serve is almost unlimited; however, we currently cater to the following sectors with products engineered specifically to meet their needs: automotive, transit, appliances, agricultural equipment, building products, boats, clean rooms, cold storage facilities, coolers, elevators, escalators, food and beverage, garage doors and opener shells, general metal cabinetry, HVAC systems, utility trailers, and Tonneau covers.

Kloeckner takes pride in offering our clients the best in coil coating equipment and capabilities. Allow our experts to assist you with all your coil coating needs.

Contact us to discuss your requirements for custom painted aluminum coil for gutters factory. Our knowledgeable sales team is ready to help you identify the options that best suit your needs.