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Small scratches in a car

Bayer MaterialScience AG : 15 February, 2005  (Company News)
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 carís 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. But the Bayer team has found a solution to this dilemma using new coating raw materials. These can be used to formulate clearcoats which form especially hard layers due to the strong crosslinking of their molecules yet are not brittle and are thus self-healing.

Summer temperatures allow small surface scratches to flow back together. The buyer of a car having such a skin will enjoy a vehicle that not only retains its youthful good looks longer but also has a higher resale value.

Environmentally friendly PU clearcoats containing only small amounts of volatile organic compounds have already progressed beyond the laboratory stage. 'We have developed waterborne two-component PU clearcoats that are suitable for online applications. Their property profile is every bit as good as that of the solvent-based PU coatings typically used today,' says Mechtel.

Laboratory tests are not the final word when it comes to UV stability, weather stability and chemical resistance, however. The decisive long-term outdoor tests are performed in Jacksonville, USA. As Klimmasch explains, 'The air there is very salty, the climate hot and humid and there are long periods of intense sunshine.' All this makes the Florida port city a nightmare for car owners - which is precisely why it is a Mecca for the coatings industry.

One word of advice: pick light colors when buying a car if you want your baby to have a long-lasting shine. According to Mechtel, 'While not any less susceptible to scratching, they donít show scratches and such as easily.'
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