Polyurethane clearcoat

Small scratches in a car’s skin will soon heal themselves

Automotive coatings: increasingly resistant despite less solvent. Environmentally friendly PU clearcoats containing only small amounts of volatile organic compounds have already progressed beyond the laboratory stage.

Rotating above the paint is a brush like the ones used in many car washes. What the brush does to the paint, however, would plunge any driver into a deep depression: the “wash solution” contains sharp-edged quartz sand in addition to water. The operator of a car wash like this one would normally soon be bankrupt. But in this case, the rough treatment of the car’s paint is helping to make car buyers more satisfied.
Bayer MaterialScience, one of the largest plastics manufacturers in the world, is using the laboratory car wash to test how sensitive coatings formulations are to scratching. As Thomas Klimmasch, an engineer and co-developer of the laboratory car wash, explains, “Scratch resistance is almost entirely a function of the topmost layer, the clearcoat, which is only a few hundredths of a millimeter thick. This “skin” of an automobile also protects the layers below from the other mortal enemies of a top-notch automotive finish: the strong UV radiation of the sun and acid rain. Polyurethane (PU) clearcoats are especially resistant. These coatings can be recognized by their particularly high brilliance and their “wet look”-it seems like you are looking at a wet, shiny surface.
The experts at Bayer MaterialScience are working to further increase the scratch resistance of PU clearcoats. “The major difficulty with this is that scratch resistance and acid resistance are virtually opposing coating properties,” says Dr. Markus Mechtel, a chemist at Bayer MaterialScience.