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Smart coatings

Scratch disappears under UV light

It seems like everything is becoming smart these days: smart phones, smart watches, smart cars, smart drugs. There are even smart coatings (paints and finishes).

I’ve blogged about one already, a coating that uses nanotechnology to create an air barrier that causes liquids such as pee to bounce off walls and cover the perpetrator’s shoes. There are also coatings that are corrosion resistant, that change colors when hit with different stimuli, that are self-cleaning and that are anti-microbial. But the most interesting of these smart coatings, in my opinion, are the ones that are self-healing.

It used to be, especially with automotive coatings, that you could remove light scratches by heating the surface. Lacquers are evaporative coatings that aren’t very resistant to heat; they flow when heated. But lacquers are high in solvent content, so they began giving way to enamels in the 1970s due to increasingly strict environmental laws. Enamels are reactive (cross-linking) coatings that don’t flow when heated. So it became no longer possible to fix light scratches with heat.

(This method of fixing scratches in lacquer works better with cars than with furniture because of the sheen differences. Cars tend to be finished with a high gloss while most furniture is finished with a flatter satin sheen. When you heat a satin finish to the point of flowing, you change its sheen from satin to gloss. So the repaired area is obvious and not easy to disguise.)

In the last couple of decades, researchers at several universities, including Illinois and Southern Mississippi, have been working on ways to repair scratches in cross-linked coatings, such as polyurethane, using heat or UV light. Check out this Youtube video from Case Western Reserve University.

The day may come (fairly soon, actually) when a scratch caused by someone keying your car heals itself simply by sitting out in the sun for a short time. Also, scratches on cross-linked furniture finishes may be made to heal without changing the sheen.

— Bob Flexner


Editors note: Bob Flexner’s blog will be on the PWM shop blog until the end of March and will then move to the Flexner on Finishing blog here…

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