In Part One, we discussed The Hidden Strength of a prepainted metal system (the base metal, the metallic layer, the pretreatment and primer). In Part Two, we examined The Visible Beauty of prepainted metal: color, gloss, texture. Strength and beauty—not to mention durability and sustainability—are important features, but the coil-coating industry also offers The Functional Capability that sets prepainted metal apart from other products, and most of this functionality can be built into the coil-coated topcoat. This topcoat layer, compared to the base metal, is thin—about 2% to 4% of the total thickness of the prepainted article. But what an incredible layer it is! In addition to providing the aesthetic properties (color, gloss, texture, etc.), coil-coating topcoats can be formulated to provide many functional properties.
The Functional Capability
Infrared (IR) Reflectance
An important energy-saving feature these days is to provide roofing materials that reflect a great deal of the infrared radiation from the sun back into outer space, which keeps the roof cool and lowers energy bills. “Cool roofing” is cool because of the topcoat layer. All of the infrared reflectance is built into this thin layer. Pigments are carefully chosen so they provide the desired color as well as excellent IR reflectance properties. White pigments, of course, are inherently IR reflective, but consumers are more inclined to want colorful building product materials. Prepainted metal can offer the consumer an extensive color palette that is also IR reflective.
If bare metal (think about a shiny, bare galvanized roof) is exposed to the sun, it will reflect much of the IR radiation—just like IR reflective paints—but shiny metal has very low thermal emittance. What does that mean, and why is it important? If you’ve ever picked up a shiny wrench that was lying around on a hot, sunny day, you have experienced the effect of low thermal emittance. That wrench is hot! Way hotter than the surrounding air temperature because it cannot release the absorbed heat, and that is because shiny metal has a low thermal emittance (TE). Thermal emittance is the measure of an object’s ability to release heat that it has absorbed. Low TE means low heat release; high TE means very effective heat release. IR-reflective prepainted metal—in addition to reflecting a great deal of IR radiation—also has a high thermal emittance. Even when the roof absorbs some of the IR energy from the sun, it also readily emits this built-up heat back into outer space. Cool!
Water beads up on hydrophobic surfaces. This property can be beneficial in many applications, and coil-coating paint formulators know how to build in this property to a topcoat. Hydrophobic surfaces help water run off the prepainted metal, and as a result, the part stays cleaner.
When water sheets off of something, such as glassware in a dishwasher, problems associated with water beads—especially spotting as these beads dry—are eliminated. To create a condition where water beads are not formed and the water instead sheets off the surface, the paint surface should be hydrophilic (as opposed to hydrophobic, discussed above). There are times when you might want water to bead up (and run off), but sometimes a water sheeting effect might be desired. Prepainted metal can offer either feature!
Coil coatings can even be functionalized to react with pollutants and clean the surrounding air. This is not simple technology, but it is being utilized with prepainted metal. Imagine a large metal building that not only looks beautiful but is also cleaning the air at the same time! This same technology has the additional advantage of creating a hydrophilic surface that stays clean even under the most polluted conditions.
We all recognize the problem, and coil-coated metal has the solution. Coil-coated metal products make the removal of graffiti a snap.
The Final Word
In Part One, we asked, “When you look at a piece of prepainted metal, what do you see?” Now you know that prepainted metal is far more than beautifully colored panels. It is designed to provide decades of aesthetics with topcoats that resist fading (The Visible Beauty), substrates that resist corrosion (The Hidden Strength), and various means to provide a functional benefit (The Functional Capability).
For more information on prepainted metal, visit: www.coilcoating.org.
David A. Cocuzzi
NCCA Technical Director