To prevent the storage of water droplet on the surface of a fin by providing a boehmite film having a specific thickness on the surface of an aluminum base material and a water repelling film formed by coating with a predetermined amount of fluorine or silicon water repelling paint having a specific contact angle.
A boehmite film having a thickness of 0.1μm or more is formed on the surface of an aluminum base material, and the surface is coated with fluorine or silicon water repelling paint of 0.1 to 10mg/dm2 at a contact angle of 90° or more when a smooth surface is coated with the film to form a water repelling film. In this case, the contact angle is the angle θ1 formed between the tangential line 3 and the surface 2 of the member when the line 3 is drawn from the point of contact of the surface of a water droplet 1 with the surface 2 of the member. As the paint becoming 90° or more of the angle, water repelling agent having perfluoroalkyl group is preferable. Thus, the water repellency of the surface is improved to make it possible to suppress the frost.
OTA YOSUKE
KAMIYA KENICHI
SAKURAI MASANORI
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