Road Markings
Of all the standard driving safety devices—seat belts, air bags, antilock brakes—many of us take these for granted.
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The familiar bright white or yellow lines are made from coating materials that juggle two priorities: drying time and durability. Minimizing drying time, of course, is critical for reducing traffic interruptions. Durability is essential for surviving constant sunlight, in particular ultraviolet radiation, as well as temperature fluctuations, road flexing, and physical abuse from vehicles, says David S. Entrekin, technical director for Future Labs, which tests highway safety products.
There are three classes of road-marking coatings, all of which use similar pigments. White markings typically contain titanium dioxide. Yellow lane lines were historically colored with lead chromate, but the pigment has been phased out for toxicity reasons. A big challenge for manufacturers of road-marking material has been to develop pigments that effectively mimic lead chromate’s color and stability to withstand high-temperature application methods and daily exposure to UV light, says Fred Gelfant, vice president of research and development at Epoplex. As such, firms in the road-marking industry don’t divulge their formulas for yellow paint, except to say that the color comes from organic molecules.
The pigment needs to be applied to the road by means of a quick-drying, liquid medium that must go on as thinly as possible—typically less than 1 mm thick—while also being long-lasting. On the least durable end is latex paint, which lasts only a year or two. Akin to latex paint used for building exteriors, road paint contains pigment, a polymer resin—often an acrylic—and water for the solvent. As the water evaporates, the paint dries and the polymer coalesces.
Visit “What’s That Stuff” to read more about the chemistry of the pigments, polymers, and reflective spheres that keep you safe.
Excerpted with permission, Chemical & Engineering News
Copyright © 2010 American Chemical Society