PURPOSE: To obtain an organic composite coated steel sheet which is superior in corrosion resistance, spot welding properties and cationic electrodeposition painting, by a method wherein two layers of a chromate layer and silica and an organic resin layer are provided on a zinc or zinc alloy plated steel sheet.
CONSTITUTION: A steel sheet 1 having a zinc or zinc alloy layer 2 possesses a chromate film 3 having a quantity of Cr6+ of not exceeding 70% to a quantity of the whole Cr and coating build-up of 5-500mmg/m2 in terms of Cr on the surface. The first resin layer 4 containing mainly a silica and polymeric organic resin is possessed in the upper layer of the chromate film 3 and the second resin layer 5 containing the silica and polymeric organic resin is possessed on the first resin layer 4. In the organic composite coated steel sheet, a dry weight ratio (P1) between the silica and polymeric organic resin in the first resin layer 4 and a dry weight ratio (P2) between the silica and polymeric organic resin in the second resin layer 5 are different from each other.
HAMAHARA KYOKO
SUJITA SHIGEKO
MUKAI RYOICHI
MOCHIZUKI KAZUO
