Preparation of Water-Repellent Coating Solutions from Tetraethoxysilane and Methyltriethoxysilane by Sol-Gel Method

Water-repellent coating solutions were prepared by sol-gel method using tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) as precursors. The solutions were spin-coated on a cold-rolled steel sheet and thermally cured to prepare a non-fluorine water-repellent coating films. The effects of molar ratios of MTMS/TEOS, water concentration and ammonia concentration on the hydrophobic properties of the coating films were studied. The contact angle of water on coating films prepared by varying the molar ratio of MTMS/TEOS to 1 similar to 20 showed a maximum value of 108 degrees when the MTMS/TEOS molar ratio was 10. With increasing water content, the coating films showed the larger contact angles and the better the water repellency. As the amount of ammonia added was increased, the contact angles of coating films were increased, showing the better the water repellency. It is considered that the larger the amount of ammonia added, the larger the size of the silica particles generated, which increases the surface roughness of the silica particles, thereby increasing the water repellency.