Multi-layer coating film forming method

摘要

A multilayer coating film forming method utilising the two coat one bake method which comprises coating a substrate with a cationic electrodeposition coating composition (A) containing a blocked polyisocyanate compound as a crosslinking agent to form a non-cured electrodeposition coating film. This is then coated with a water based intercoat coating composition (B1 or B2) followed by heat curing of both films simultaneously. Both Intercoat compositions (B1, B2) comprise a hydroxyl group and carboxyl group containing base resin, and a blocked polyisocyanate crosslinking agent. However B1 also contains a fine aluminium powder and a titanium oxide white pigment, whereas B2 contains an alicyclic epoxy compound. The crosslink-curing reaction of the non-cured electrodeposition film may be controlled so as to take place earlier than the crosslink-curing reaction of the non-cured intercoat coating film. The electrodeposition coating composition (A) may be a lead-free composition, and may contain a bismuth-containing compound.