| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for forming a multilayer coating film which uses a chemical conversion treatment agent having a reduced load to the environment, and also, capable of forming a chemical conversion treatment film having excellent corrosion preventability and in which an electrodeposition coating material composition having excellent pigment settling stability and throwing power is used, and which can remarkably reduce coating cost as well. SOLUTION: Disclosed is a method for forming a multilayer coating film involving: a chemical conversion treatment film forming stage where a chemical conversion treatment film is formed on the object to be coated using a chemical conversion treatment agent; an electrodeposition coating film forming stage where the object to be coated with the chemical conversion treatment film formed is immersed into a cation electrodeposition coating material composition, so as to form an electrodeposition coating film. The cation electrodeposition coating material composition used in the electrodeposition coating film forming stage comprises an electric conductivity control agent composed of an amino group-containing compound having an amine value of 200 to 500 mmol/100 g, the cation electrodeposition coating material composition has an electric conductivity of 900 to 2,000μS/cm and a coating material solid content concentration of 0.5 to 9.0 wt.%, and further, the chemical conversion treatment agent comprises zirconium ions and tin ions, and whose pH is 1.5 to 6.5. The concentration of the zirconium ions is 10 to 10,000 ppm, and also, the concentration ratio of the tin ions to the zirconium ions is 0.005 to 1 expressed in terms of mass. COPYRIGHT: (C)2009,JPO&INPIT
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