Improving automative coating
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"Clearcoats” applied over layers of automotive paint not only enhance automobile appearance, but also serve as a first line of defense against attack from moisture, acid rain, and ultraviolet radiation. Defects in these coatings can seriously compromise appearance and performance, and are costly to repair.
As a result, clearcoat manufacturers, such as PPG Industries, are seeking to improve the formulation of their coatings to perform these tasks better. As part of a Cooperative Research and Development Agreement with PPG Industries, Sandia has developed an optical instrument capable of mapping the surface of automotive clearcoats as they form to better understand the processing operation.
Successful development of advanced coatings requires a fundamental understanding of the interplay among the coating formulation, the application method, and processing conditions. Thus, characterization tools that can provide information about coating properties throughout the processing protocol are of extreme interest.
Optical profiler
Known as an optical profiler, it is loosely based upon known technology but has been optimized to provide a digital three-dimensional profile of both wet and dry clearcoats.
The profiler can operate at a distance so that measurements can be made looking into an oven for characterization of the coatings during thermal processing. The profiler features a wide field of view, submicron depth resolution, and fast acquisition times. The Sandia team has also developed a measurement technique that enables the profiler to be used for measurement of the surface tension of wet films during processing.
Such measurements have not previously been possible. In the new technique, a pulse of air from a tiny nozzle creates a small, circular depression in the coating, and the surface-tension-driven leveling that follows is measured. The leveling data, when combined with information about the coating viscosity, offer a new perspective on the behavior of the surface tension.
The new tool enables PPG to understand the behavior of coatings in ways that were not previously possible. Visualization and measurement of surface topography during processing allow investigation of processes such as leveling and re-flow.
In addition, researchers can observe the onset and evolution of defects, such as those known in the industry as “craters” and “orange peel.” They anticipate that the surface tension information provided by the profiler will enable them to tailor coatings to simultaneously achieve improved appearance and chemical resistance, and ultimately lead to improved, defect-resistant coating technologies.
The research/development team is led by Michael B. Sinclair of Sandia, and P. Kamarchik and R. Stiger of PPG Industries, Allison Park, Pennsylvania.
Technical Contact: Mike Sinclair, mbsincl@sandia.gov, (505) 844-5506
Media Contact: Nigel Hey nigel@nasw.org, (505) 898-6679