Characterization of colloidal particles formed in plastic coating solution at room temperature
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Characterization of colloidal particles formed in plastic coating solution at room temperature Yasuhiro Matsuda, Ryo Akao, Masaki Nakazawa, Hideyo Ando, Shigeru Tasaka
Ó American Coatings Association 2020 Abstract The structure of solution of methyltrimethoxysilane (MTMS), which is used for hard coating for plastic materials through its sol–gel reactions, was investigated by light scattering, atomic force microscopy, infrared spectroscopy, and X-ray diffraction. Although hard films can be formed only after heating the MTMS solution and no significant increase in viscosity can be found at room temperature, colloidal particles were detected in the solution by light scattering immediately after adding the catalyst. Particles with a size comparable to that determined by light scattering were observed by atomic force microscopy. The change induced by the growth of the particles was measured for 4 weeks. The infrared spectroscopy and X-ray diffraction for the solutions changed gradually, which supports the formation and growth of the colloidal particles. These results indicate a very slow reaction of MTMS and structural change in the solution even at room temperature, which can affect successful coating of plastic materials using MTMS. Keywords Methyltrimethoxysilane, Colloidal particles, Hard coating, Light scattering, Infrared spectroscopy
Y. Matsuda (&), R. Akao, M. Nakazawa, S. Tasaka Department of Applied Chemistry and Biochemical Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan e-mail: [email protected] H. Ando DOKEN Co. Ltd., Shinshiro, Japan
Introduction Plastic materials are increasingly used in industry and daily life. Plastics with high transparency and mechanical strength, such as polycarbonates and poly(methyl methacrylate), have attracted interest as alternates of inorganic glass because of their lightness. However, the surfaces of these plastics sometimes lack mechanical strength even if they have enough strength in their bulk phases. To enhance surface mechanical strength, such plastic materials are usually coated with hard films. Hard coating with silicon alkoxide reagents via sol–gel processes is one of the most frequently used methods to enhance the surface mechanical strength because the films have both good adhesive properties and high mechanical strength which are originated from the organic and inorganic hybrid structure.1 Methyltrimethoxysilane (MTMS) is an organic silane reagent of which the chemical structure is shown in Fig. 1. It has been used for hard coating since Dow Corning established a fundamental technology for hard coating using a hydrolysis reaction of MTMS with colloidal silica.2 Crack-free gel films can be obtained by using MTMS and 3-glycidylmethoxytrimethylsilane with fast condensation and slow ring-opening reactions.3–6 There have been reports about hard coating with some other silicon alkoxides. Methyltriethoxysilane and tetraethoxysilane form films as hard as a 2H pencil on a polycarbonate plate.7 Single-capped trialkoxysilanes
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