Coil Coating and Its Applications

Coil coating is the process of continuously and highly automated coating of metal. A metal coil approximately 1.8 metres (72 inches) wide is unwound at a speed of 213 metres per minute in a single continuous process, both top and bottom surfaces are cleaned, chemically treated, primed, baked, coated, baked again, rewound for shipment and packaged. To explain this process in more detail, the metal coil is first placed on a recoiler or unwinder where the metal is observed for defects. The metal is then cleaned and chemically treated while being prepared for painting. Brushes can be used to physically remove contaminants from the surface, or the metal surface can be abraded with cover sanders to further treat it. In addition to making it corrosion resistant, pre-treatments can be used to provide a bond between the metal and coating. The type of chemical treatment varies depending on the type of metal used. After drying, the strip generally enters a coating chamber where a primer layer is created on both sides of the surface. A collection cylinder transfers the coating liquid from the pan to the applicator roller. The liquid is then pumped back to the pan and transferred to a feedback tank where it is re-mixed and filtered.3

The direction of rotation of the applicator roller plays a role in determining the coating type. Reverse roll coating, where the applicator roller rotates in the opposite direction to the strip, is used for applying thick coatings. Direct roll coating, rotating in the same direction as the strip, is used for thinner coatings of 0.5 mil or less.

The paint layer then enters an oven where the coating is cured at high temperatures for 15 to 30 seconds. The strip exits the oven and is cooled with air and water. Most technical specifications require two coats (primer and topcoat) on each side of the surface, which is why a second coating chamber and oven pass are required. The fully painted sheet then exits the second oven, cools before inspection and rewinding. Since the process ensures a continuous passage of metals, there is flexibility in metal coating and coating types. Organic and inorganic substances such as polyesters, epoxies, vinyls, plastisols, acrylics, water-borne emulsions, fluorocarbons, dry lubricants, surface treatments and primer combinations can be applied. Painted coils can be patterned, embossed or printed to create special visual effects. Coil coating provides controls that are nearly impossible to achieve in most other painting processes. Working with a flat surface provides mechanical cleaning in addition to spray cleaning. The flat sheet also allows perfect control of both the pre-treatment and paint coating weights to within a tenth of a mil or less, depending on the equipment applied and paint system. These advantages, along with economic and environmental benefits, make coil coating the right choice for many manufacturers.

Financial Advantages of Coil Coating

Coil coating means a product that is pre-painted or pre-coated and ready for use in production. Working with pre-painted parts, or outsourcing the painting operation, has many advantages, including: • Cost reduction, • Reduced capital expenditures, • Reduced environmental compliance costs, • Improved quality, • Simplified processes. In today's business environment, the ability to increase profits by raising prices is nearly impossible. Business analysts agree that the best way to increase profits is through outsourced services or reducing internal operating costs. Capital expenditures for in-house painting, the investments required for environmental compliance, personnel costs for staff working in this area and many other related cost factors make it logical for companies to outsource this operation. Paint shops are subject to changing environmental standards and strict health regulations. Outsourcing metal processing and coating operations can eliminate all these problems and costs. Coil coating, also called pre-coating, is an ideal outsourcing solution.

Who Needs It?

• Any business working with sheet metal converted into painted or coated parts or products for decorative or corrosion protection purposes. • Any business considering updating or replacing its paint line. • Any manufacturing operation facing production bottlenecks resulting from painting operations. • Any company limited by facility capacity or capital.

Can Painted Metal Be Formed?

Yes, in fact, painted or coated metal (prepainted metal) can be formed with a superior finish compared to post-painting. This is because post-painted surfaces may contain dirt and oil residue, uneven application and other defects. Prepainted metal, on the other hand, means savings in cost, time and difficulties before production, and obtaining a beautiful and flawless surface after forming.

How Can Prepainted Metal Be Joined?

Painted metal can be easily joined using adhesives, fasteners or welding and can protect the surface more beautifully and flawlessly than unpainted metal. This is because painted metal is coated with consistent thickness on both top and bottom layers, flawlessly from edge to edge. Painted metal can be joined extremely well.

Corrosion Resistance

Research has proven that prepainted parts perform better over time than post-painted surfaces due to their overall superior finish. Prepainted metal, even with cut edges, corrodes significantly less than painted metal without exposed edges. The U.S. National Coil Coating Association (NCCA), a major paint manufacturer, and the North American Zinc-Aluminum Coaters Association (NamZAC) compared the corrosion resistance of a prepainted sample with samples painted with three different types of paint. This test compared a prepainted part with cut, that is exposed edges, with different parts painted with e-coat, powder paint and spray paint. The parts were made of hot-dip galvanized steel and exposed to the same environment. Measurements taken over 16, 44 and 68 months showed that the corrosion resistance of prepainted parts was significantly better than post-painted parts in terms of consecutive and post-film thickness. The reason prepainted parts are superior to post-painted ones is that the prepainted metal surface is uniformly cleaned, pre-treated and painted as a flat surface, thus edge-to-edge and side-to-side variation is nearly eliminated. In addition, the prepainted section has two coats (primer and topcoat) and each is tightly bonded to the metal compared to a painted part, which typically has only a single paint coat. In most cases, the prepainted section also has paint on the back (one or two coats). Uniform pre-treatment and paint on the back of a part increases the part's corrosion resistance by increasing long-term durability.

Can Prepainted Metal Be Transported Without Damaging Its Surface?

Painted metal can be stored as coils for long periods, transported by forklifts and shipped by flat-bed trucks. Painted metal can be successfully stored and transported without surface damage while maintaining its flawless finish. Storage of painted coils is also a simple process. Coils should be stored in a temperature-controlled warehouse. For successful on-site storage, it is sufficient to package and use waste layers and end caps. Of course, as an additional precaution, it is beneficial to minimize storage time. The contents of each package should be specified in an external salt spray receipt to minimize damage from packaging. General labels can also be attached to panel packages explaining proper handling and storage practices. Storage and transportation of painted rolls is easy.

Can Prepainted Metal Meet Special Design and Aesthetic Needs?

It is possible to create special visual effects in painted coils. Patterning operations are possible on painted metal, providing designers with very broad possibilities.

End Uses

There are countless end-use possibilities for prepainted metal.

Construction

In particular, architects are increasingly using painted metal to meet their design vision in commercial and residential installations. The ability of painted metal to be formed into virtually any shape, its superior long-term durability due to excellent resistance to weather conditions, endless aesthetic color and texture options and positive environmental benefits make it an excellent choice for both interior and exterior building applications.

Roofing

Painted metal roof panels are produced in many shapes with a wide range of products to meet any design requirement. Metal roof profiles are generally divided into two main categories: standing seam and formed panels. Standing seam panels can be formed in almost any length and are available in both exposed and hidden fastening systems. Formed painted roof systems transform metal roofing into profiles that resemble clay tile, slate, cedar shakes, shingles and more. In addition to beauty, longevity and functionality, painted metal examples also exist in "cool" infrared reflective pigment technology. This technology helps reduce building interior temperatures, saving energy spent on cooling.

Walls and Panels

Prepainted metal is an excellent choice for interior and exterior wall panels. Metal wall panels are available in ribs, insulated (foam-backed), composite and various architectural styles in many different profiles.

Drainage

The ability of painted metal to be formed in virtually any type of bend imaginable makes it a popular choice for the production of gutters. A wide range of parts needed for rainwater systems is provided.

Garage and Entrance Doors

The ability of painted metal to be stamped with deep embossed and detailed shapes, its resistance to weather conditions, economic benefits and environmental advantages provide garage and entrance door manufacturers with broad options.

Interior Spaces

Painted metal is widely used in interior building design. Sometimes it is used as a base layer, sometimes the metal itself is the main focus of the design. Ceiling tiles, ceiling grids, wall panels and column covers are among the uses of prepainted metals for interior spaces.

Automotive

The use of pre-primed base layers in automotive production, along with certain in-process materials, also prevents excessive paint waste.

Trailer Van Panels

The truck and trailer industry successfully uses prepainted coatings in various colors that perform beautifully over many years.

White Goods

The use of prepainted metal in white goods is common. It responds to many different needs such as glossy black, heat-resistant white, RoHS-compliant coatings.

HVAC

For the HVAC industry, the use of painted coils means not just a better product appearance, but numerous economic advantages such as higher product quality and performance, greater productivity and cost elimination. In conclusion, the coil coating process is a proven method for applying high-performance coatings to metal. Uniform cleaning of metal coils, pre-treatment and painting as a flat surface providing a secure bond to the metal, make it possible to achieve an excellent coating process.

References • The National Coil Coating Association. • The Fabricator, What you should know about stamping coated coil, July 29, 2008. • European Coil Coating Association, The Coil Coating Process. • European Coil Coating Association, Product Advisor. • Paint & Coatings Industry, Bottom-Line Benefits of Using Prepainted, Coil Coated Metal. June 1, 2007. • Jörg Sander, 2014. Coil Coating, European Coatings Tech Files, European Coatings.