| 简介 |
PROBLEM TO BE SOLVED : To provide a method for improving corrosion-resistance in a method for forming a multilayer coated film unnecessarily requiring pretreatment of zinc phosphate by applying voltage in two stages using an aqueous cationic electrodeposition coating composition.
SOLUTION : In the method for forming a multilayer coated film including an immersion process of immersing an object to be coated into an electrolytic-decomposition corrosion-resistant metal salt (A), a substrate resin having a cationic group (B) and an aqueous cationic electrodeposition coating composition containing a curing agent (C), an electrolytic decomposition process of applying voltage of below 50 V in the aqueous cationic electrolytic composition by using the object to be coated as a cathode, and an electrodeposition coating process of applying the voltage of 50-450 V by using the object to be coated as a cathode, three of a rare earth metal salt lower in sedimentation pH of the electrolytic-decomposition corrosion-resistance metal salt (A) contained in the aqueous cationic electric-deposition corrosion-resistance coating composition (a1) a rare-earth metal salt having a deposition pH being lower than that of zinc, (a2) a zinc salt and (a3) a metal salt higher in sedimentation pH than that of zinc.
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