Novel Composite Chemical Conversion Coating Film, Multiple Layered Coating Film Using the Same and Process for Forming Multiple Layered Coating Film

摘要

The present invention relates to a composite chemical conversion coating film containing a crystalline continuous coating film that is formed on a metal substrate. The present invention also relates to a process for forming a multiple layered coating film including (A) the first step of immersing an untreated metal substrate in an aqueous solution containing nitrate of a rare earth metal and forming a crystalline continuous coating film containing a rare earth metal compound with a deposition amount of 1 mg/m² at lower limit and 110 mg/m² at upper limit by cathode electrolysis and (B) the second step of coating an electrodeposition coating composition containing an organic acid or inorganic acid salt of a rare earth metal by cathode electrodeposition. According to the present invention, provided is a multiple layered coating film that forms extremely less amount of a composite chemical conversion coating film and an electrodeposition coating film in order in comparison with a pretreatment step and a cationic electrodeposition coating step by a conventional chemical coating solution and an electrodeposition coating composition; that is, a novel composite chemical conversion coating film with high economic efficiency and environmental conservation property is provided by expressing superior adhesion to a coating film and corrosion resistance equal to or more than a conventional step.