PURPOSE: To improve the weather resistance of the joined part of different kinds of steel sheets having potential difference and to produce a significant rust preventing effect by sealing the joined part with a urethane sealer.
CONSTITUTION: A cold rolled steel sheet 1 and a surface treated steel sheet 2 having potential difference are joined by spot welding or other method. The steel sheet 2 may be a galvanized steel sheet. Before the joining, the surfaces of the steel sheets 1, 2 to be joined are coated with an adhesive 6 or the like as required. An electrodeposition paint film 3 as an undercoat is then formed on the entire surface of the joined steel sheets 1, 2 with electrodeposition part and the joined part of the steel sheets 1, 2, that is, the joint is sealed with a urethane sealer 4. The sealer 4 is desirably prepd. by blending 100pts.wt. polyurethane resin with 20pts.wt. polyamide resin.
MINAMI TATSURO
KONO HIROBUMI
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