Prepainted Metal Can Provide Cost And Quality Benefits To Manufacturers
CLEVELAND, OHIO -- Using prepainted metal is a solution for many manufacturers that use sheet metal that is fabricated into parts or products that are post painted either for decorative or corrosion protection purposes.
With this technology, large coils of metal sheet stock (including cold-rolled steel, hot dip galvanized, electro galvanized, zinc-steel, aluminum, stainless steel, copper, and brass) can be coated in a continuous, highly automated process prior to fabrication. During this continuous process, the metal coil is unwound, the top and bottom sides are cleaned, chemically treated, primed, ovencured, topcoated, oven-cured again, and then rewound for shipment. The variety of coatings available is almost unlimited and includes: polyesters, polyurethanes, epoxies, vinyls, plastisols, acrylics, water-borne emulsions, zinc-rich coatings, fluorocarbons, dry lubricants, and treatment and primer combinations.
Coil Coated Metal Joining and Forming
Prepainted coils can be rewound, drawn, formed, bent and blanked. In addition, the prepainted metals can be fastened with bolts, screws, rivets, Tog-L Locks, etc. They can also be lockseamed, adhesive bonded, and, in some cases, welded.
The fact is that prepainted metal can be formed and shaped with a finish that is actually superior to post-paint. This is because post-painted surfaces often suffer from dirt and oil residue, uneven application, and other imperfections. Because coil coated steel and aluminum is cleaned, primed and painted and cured in one process, the bond created between the substrate and the coating is superior to that of post-painted bonds, and it can endure even very intricate forming demands. For example, many wood windows are clad with prepainted aluminum on the outside which includes multiple bends. Also, screen frame is generally made from prepainted aluminum which is extensively formed and very durable.
Prepainting and Design
Another question is whether the prepainting process can accommodate special design and aesthetic needs. Prepainted coils can be printed, striped, textured and embossed to create special visual effects. In many ways, coil coating has limitless design possibilities, many of which are virtually impossible with post-painted metal.
Prepainted Metal and Cut-Edge
Manufactured products with prepainted cut-edge actually holds up better over time than post-painted surfaces, due to prepaint’s overall superior surface. It may be hard to believe, but it’s true: prepainted metal with cut-edges corrodes significantly less than post-painted metal with no exposed edges.
The NCCA along with the help of PPG Industries, Inc. and the North American Zinc-Aluminum Coaters Association (NamZAC) worked together to compare the corrosion resistance of prepainted metal louvers on air conditioning units to those coated with three types of post-paint.
Prepainted louvers with exposed cut edges were tested in the field along side three sets of metal louvers, one with a post-painted electrocoat, a second with a powder finish and a third with a spray finish. The parts in all instances were made of hot dipped galvanized steel and louvers were exposed to the same environment over time in Daytona Beach, Florida.
Comparisons made after 16 months, 44 months, and 68 months of exposure to the elements showed prepainted parts were repeatedly and significantly better than the post-painted parts in terms of the corrosion resistance, uniformity of treatment and film thickness.
The reason that the prepainted parts outperformed each of those with a post-painted application is due to the fact that prepainted metal sheet is uniformly cleaned, pretreated and painted as a flat surface, so the edge to edge and side to side variability is virtually eliminated. In addition, the prepainted part also has two coats of paint, tightly bonded to the metal as compared to a post painted part, which generally has only one coat of paint. In most cases, the prepainted part has paint (one or two coats) on the backside as compared to the post painted part which at best has a minimal amount of overspray. Uniform pretreatment and paint on the back side of a part increases the corrosion resistance of the part, enhancing long-term durability.
The study findings conclude that with proper selection of paint and substrate, a prepainted part should provide a superior, cost-effective product in corrosion resistance, appearance, and durability as compared to parts painted using other paint application methods.
Handling Prepainted Coils
Can prepainted metal be handled without harming the surface?
Prepainted metal can be shipped on flatbed trucks, moved using toe motors, stored as coils for long periods -- and still retain a more beautiful and flawless surface than post-painted metal. Prepainted metal can be handled successfully, without marring the surface. The National Coil Coating Association can help manufacturers with techniques on proper handling of prepainted metal coils.
Prepainted metals offer many cost savings and quality benefits over in-house painting, including avoiding costs associated with complying to environmental regulations. Even when joined, formed, cut and handled, coil-coated metals offer superior quality over post-painted alternatives. Manufacturers can get help with analyzing if prepainted metals are right for their products, and can get a free cost comparison form, by visiting www.coilcoatinginstitute.org or call the NCCA at 216-241-7333.
