Automotive clearcoats characterized in search for improvement
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omotive clearcoats characterized in search for improvement
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n the automotive industry, four layers of coatings on the car body are typically used, each with 10–30 µm thickness, in order to provide protection from UV rays, scratches, and corrosion of the metallic frame, and for aesthetic purposes including color. The top coating, called clearcoat, is of particular importance since a strong clearcoat will also protect and maintain the performance of the underlying coatings. Currently, the automotive industry uses the Crockmeter and the Amtec-Kistler Carwash tests to assess the scratch resistance of their coatings. These tests simulate scratching conditions during usage of a car. The clearcoats are then classified based on their physical appearance. But scratch mechanics is a complex intertwining of viscoelasticity, plastic flow, and fracture, and industry seeks a better understanding of
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because higher charge-carrier density led to stronger lateral surface potential that forced the surface electrons apart. Mingyang Li of Sun Yat-sen University, China, who is not involved in the work, says, “The capability of imaging the charge transport on semiconductor surfaces with
excellent resolutions could verify the simulated motions of photocarriers during photo-reactions. The manipulation of the photo-induced electron distribution might also be used to improve the performance of photoelectrochemical cells.” Tianyu Liu
these different regimes in order to improve the coating formulations. This is the task tackled by research teams from Eastman Chemical Company, Hyundai-Kia America Technical Center, the National Institute of Standards and Technology, and Anton Paar USA Inc.; they published their results in a recent issue of Progress in Organic Coatings (doi:10.1016/j.porgcoat.2018.09.011). For their study, the researchers chose commercially available clearcoats and experimental coatings based on solvent or waterborne chemistry, and with tunable cross-linking density. Each formulation was coupled with a specific underlying basecoat to test its compatibility and adhesion. “Scratch has been often viewed as a surface issue as opposed to a bulk or interface issue in the coatings industry,” says Linqian Feng, the corresponding author of the study. “The nanoscratch methods specified in the automotive industry today do not necessarily probe the whole depth of the clearcoat where the
interface with the basecoat becomes a major consideration.” After being sprayed onto a steel plate, the dual coats were submitted first to industrial scratch tests. Then, using diamond tips of 1 µm, 50 µm, and 200 µm diameter and increasing loadings, the researchers used a tribometer and a nano-scratcher to examine the deformation regimes occurring during scratching. The loading conditions were similar to those occurring under a scratch from a brush, a key, or a cart. The researchers observed that the clearcoats deformed elastically at low scratch loads. As the severity of the scratch increased, the coatings deformed plastically, fract
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