Evaluation of high resistance to environmental corrosion for excellent car-coating treatment
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Evaluation of high resistance to environmental corrosion for excellent car-coating treatment Kiyotaka Mori, Takashi Okada, Kazuya Oguri, Kageyoshi Sakamoto, and Yoshitake Nishi Department of Materials Science, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-12, Japan (Received 3 January 1997; accepted 6 October 1997)
Using a scanning laser microscope and mercury porosi-meter, we evaluate the effects of an excellent car-coating treatment on resistance to environmental corrosion after aging for three years. The treatment maintains the clear surface. The effect can be explained mainly by the contact angle of sessile drops.
I. INTRODUCTION
Automobiles are necessary in a contemporary human life. However, automobiles have exhausted many environmental problems. A clean energy, being in fashion, an electric automobile, has a high potential to solve the problem within a field of internal combustion engine. An extension of car body span may contribute to the extension of the life of the automobile itself. It also contributes to the environmental problem being brought about by automobiles. The car body surface is damaged by environmental pollution such as acid rain at all times.1,2 Indeed it is unquestionable that the environment causes a short life of the automobile. A car-coating treatment that is resistant to the environment has been developed by Clean Excel Ltd. When the automobile is in a collision, the excellent car coating prevents scratching. Since the surface layer consists of silicone polymer-like rubber, the coated paint shows superelasticity. The effect has been confirmed even for three years after treatment.3 In addition to the mechanical resistance, the coated paint simultaneously shows resistance to environmental corrosion. The coating material contains a silicone polymer. The silicone polymer, used in this study, has siloxane bond as a principal chain and methyl bond as a functional group. The water repellent of silicon polymer is contributed by the hydrophobic methyl group whose critical surface tension is very low. Although the other polymers also have the methyl group, the silicone polymer shows the strongest water repellent. Zisman has reported that the methyl group is oriented toward the surface in the case of siloxane (see Fig. 1).4 Although the C–C is covalent bonding, the Si–O shows covalent and ionic bonding. Since the oxygen atoms in the CH3 –Si–O combine with a paint, the exposed surface is made up entirely of hydrophobic methyl groups. In regards to photoresistance, their bonding forces are an important factor. Since the bonding force of the Si–O is larger than the energy of ultraviolet ray in the sunlight, the siloxane is chemically stable. On the other hand, the J. Mater. Res., Vol. 13, No. 1, Jan 1998
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bonding force of the C–C forming the principal chain of the other polymer is smaller than it. Thus, the polymer consisting of the C–C is chemically unstable. For these reasons, the si
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