PURPOSE: To form an electrodeposition coating film excellent in corrosion resistance without impairing the stability of an electrodeposition coating compsn. used by incorporating a specified amt. of zinc oxide coated with an inorg. siloxane compd. and/or an org. acrylic compd. into the compsn.
CONSTITUTION: A paste is obtd. by adding an inorg. siloxane compd. (having siloxane bonds in the main chain and a number-average mol.wt. of 140-2,000) and/or an org. acrylic compd. (having a wt.-average mol.wt. of 15,000-70,000 and a number average mol.wt. of 10,000-30,000) to an active zinc oxide having a particle size of 0.01-0.1 um and a specific surface area of 40-100m2/g and dispersing them in each other with a dispersing machine. The paste is compounded into an electrodeposition coating compsn. in an amt. of 0.5-10 pts.wt. based on 100 pts.wt. solid resin content of the compsn., which is then diluted with deionized water to a 5-40wt.% concn., and adjusted to a pH of 5. 5-9.0 to provide an electrodeposition bath. A 10-40μm-thick coating film is formed at a bath temp. of 15-35°C under a voltage applied of 100-400V, and baked.
KUME MASAFUMI
HAISHI HIDEHIKO
