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On the Road with Prepaint

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Prepainted metal is all around us. You are probably familiar with its many uses in the building and construction and appliance markets, but you may not be aware that prepainted metal is also important in the transportation sector.

Think “transportation,” and your mind typically leaps to cars and trucks—and from there to the beautiful body panels that are an aesthetically important part of these vehicles. Spoiler alert: Painted automotive body panels require specialized coatings and application techniques and, as a result, are not ideally suited to the use of prepainted metal. Nonetheless, there are plenty examples of coil-processed material used in the transportation sector.

But the transportation market doesn’t just include cars and trucks; it also covers the trailer portion of a tractor-trailer. The walls of a trailer (as seen below) are usually made of prepainted aluminum, a preferred substrate for this application. It has the necessary strength and rigidity and light weight to make it highly roadworthy.

Cargo trailers are another important segment of the transportation industry in which prepainted metal may be used. Like its much larger cousin, the cargo trailer must be lightweight yet strong, and its walls must be similarly constructed.

The coatings for these types of applications need to provide exceptional resistance to staining, scratching, and the damaging effects of sunlight.

License plates

You probably don’t think much about the license plate on your car, motorcycle, or RV, but you might know that the plates are often made by inmates in prisons. And before the material becomes a license plate, it typically goes through a coil line to be cleaned and treated and then sent to state facilities to be laminated. The pretreatment process provides corrosion resistance and aids in the conversion of the surface of the aluminum to maximize the adhesion of the laminate to the aluminum substrate. The highway patrol is thankful for that help in reading the plate numbers!

The need for speed

As you might imagine, bringing 17 million cars, trucks, and SUVs to market each year in the U.S. involves vast quantities of metal. With the additional volume of metal used for trailers, RVs, and buses, you’re looking at millions of square feet of metal, which favors the coil coating process. Three key aspects of a modern coil coating line are speed, efficiency, and sustainability. Coil coating lines can process thousands of square feet of metal each minute, with essentially no waste. All VOCs are captured and destroyed, and the heat generated in the process is recirculated into the facility. Because the coil coating process is environmentally friendly, prepainted metal is a good fit for the transportation segment.

Although fully painted body panels are a consideration for the future, there are two key areas where coil processing is playing an increasingly important role. The first of these involves pre-primed metal. Typically, we think of coil coated metal as a finished product (i.e., it is primed and topcoated), and a pre-primed coil, although painted, is often considered a material that first will be “processed,” and indeed often has additional coating post-applied. Regardless of the semantics, pre-primed metal from a coil coating line provides much-needed corrosion resistance to bus frames, body panels, and other parts of car, trucks, buses, etc., that eventually get a finish coat of paint applied (usually sprayed) by the OEM manufacturer. A pre-primed supply of metal to the OEMs promotes the cost effectiveness of the coil coating process. And did you know that coil-coated primers are available that may be welded? These conductive primers allow for resistance welding while maintaining long welding-tip life.

The next time you pass a Ford F-150 on the road, remember this.

Who hasn’t heard of the aluminum components used on Ford’s F-150 truck? The story is much more than “aluminum instead of steel.” It starts with a special alloy of aluminum, but the alloy has the same problem that all aluminum metal has: It forms an oxide layer very quickly, and this oxide layer presents a multitude of problems. (NOTE: The oxide layer is—on a positive note—the reason why aluminum is so corrosion resistant.) One issue is that this oxide layer creates poor adhesive bonding, and adhesive bonding is a critical requirement for the F-150’s use of aluminum. This concern, however, has been overcome by processing the aluminum on a coil coating line, first to clean and remove the oxide layer, and then to add a specialized pretreatment that provides enhanced adhesive bond durability along with an oxide stabilizer. This pretreatment layer is constantly challenged during the initial fabrication (stamping, hydroforming) process and during the final assembly of the body panels or the truck cab, and yet—because of the controlled processing on a coil coating line—the material stands up to the challenge of the manufacturing process.

So, as you wind down the highway, look around you and think about how prepaint is keeping all of those vehicles on the road—longer and stronger!

David Cocuzzi

NCCA Technical Director

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