Aug. 28, 1998 New Polymer Tests Show How "Micro-Scratches" Develop, Damage Clear Coats
BOSTON, Mass.--Two polymer researchers have developed a new way to show how "micro-scratches" tinier than a human hair, can hurt your car's clear coating, a step forward toward developing an improved generation of polymer coatings that will resist scratches. The new test methods were described here today (Aug. 27) at the national meeting of the American Chemical Society, the world's largest scientific society.
Dupont researchers Li Lin and Greg Blackman described how the new method permits them to examine tiny scratches as they develop in real time. Similar to the minuscule scratches that can occur when you wash your car, the micro-scratches are extremely tiny. "A human hair laid up against one of these scratches would dwarf it," Blackman says.
The combination of many of these tiny scratches allows light to scatter over the coating, making the damage visible to the human eye, and leading to what the two researchers call an "objectionable appearance" that doesn't meet the auto industry's goal that cars retain their visual appeal for 10 years.
Examining the mechanical properties of the polymer during the formation of such small scratches, or swirl marks as they are often called, required an analytical device that was not commercially available. Lin developed a unique micro-scratch tester that was then coupled with an atomic force microscope and a video camera, thereby allowing real-time examination of scratches as they developed.
One surprising finding for the scientists was that in the early stages of scratch formation there is no loss of material, or debris formation. Rather, small cracks appear and create voids in the surface of the coating, which cause the scattering of light.
Based on their work, new coatings that Blackman describes as "significantly better" already have been applied to some cars for field testing. The analytical device developed by Lin has been licensed for development by CSEM Instruments (Centre Suisse d'Electronique et de Microtechnique SA) of Switzerland.
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