| 摘要 |
PURPOSE:To manufacture an organic composite clad steel tube excellent in corrosion resistance and spot weldability by successively forming organic composite cladding constituted of a chromate film, silica and an organic high polymer resin on the surface of a galvanized steel under specified conditions. CONSTITUTION:On the surface of a steel sheet 1 subjected to zinc or zinc alloy plating 2, a chromate film 3 having Cr<+6> content by >=70% to the total Cr content and coating weight by 5 to 500mg/m<2> expressed in terms of Cr is formed. An organic composite film 4 essentially consisting of silica and an organic high polymer resin (such as an epoxy resin) 7 and in which the ratio of the dry weight of the silica to the organic resin 7 is regulated to 10 to 100 pts.wt. silica to 100 pts.wt. resin is formed. At this time, the size of the average primary particles 6a of the silica is regulated to 5 to 30nm, the silica is condensed into the shape of a plane having 0.2 to 2mum average thickness and 5 to 300mum average size in the resin layer 4, the silica planar condensed body 8 is almost uniformly distributed on the plane of the steel sheet and the coating weight of the resin layer 4 is prescribed to 0.1 to 3g/m<2> by dry weight. |
