To lastingly obtain a superior hydrophilic property at an initial stage for a relatively long time by forming a covering layer where the contact angle of deionized water is specified on the surface of a metal plate, and at the same time by maintaining change in the contact angle at a specific value or less even after drying/wetting repetition treatment.
On a covering metal plate for a heat exchanger, a covering layer where the contact angle of deionized water at initial 20°C is set to 20 degrees or less is formed. Even after drying/wetting repetition treatment for performing drying at 20°C after dipping into flowing water is repeated for ten times, change in the contact angle is maintained at 5 degrees or less. The covering metal plate is obtained, for example, by forming paint coating containing hydrophilic polymer on an aluminum plate. Also, an additive agent is prepared as a hydrophilic composition (paint) by blending polymer, water, and an arbitrary additional constituent or the like as needed under various conditions. Furthermore, when the additive agent is used for manufacturing a precoat fin material for the heat exchanger, it is applied onto a fin base made of aluminum and a foundation coating for beating and drying.
ASAI HARUO
TANAKA HIDEKI
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