Lead-free cationic electrodeposition coating composition, and electrodeposition coating process

Abstract

The present invention provides a lead-free cationic electrodeposition coating composition which contains an aqueous medium, a binder resin composed of a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in the aqueous medium, a neutralizing acid in order to neutralize the cationic epoxy resin, an organic solvent, and a metal catalyst, wherein the electrodeposition coating composition has a volatile organic content of 1% by weight or less, a metal ion content of 500 ppm or less, a neutralizing acid amount of 10 to 30 mg equivalent based on 100 g of binder resin solid content. The lead-free cationic electrodeposition coating composition has high throwing power, and exert a little influence on the environment due to its low VOC, low metal ion content, and reduced consumption of a coating composition itself.

1 - 9 . (canceled) 
     
     
         10 . A lead-free cationic electrodeposition coating composition which comprises an aqueous medium, a binder resin composed of a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in the aqueous medium, a neutralizing acid in order to neutralize the cationic epoxy resin, an organic solvent, and a catalyst releasing metal ion,
 wherein the electrodeposition coating composition has a nonvolatile content of 22 to 35% by weight, a volatile organic content of 1% by weight or less, a metal ion content of 500 ppm or less, and a neutralizing acid amount of 10 to 30 mg equivalent based on 100 g of binder resin solid content,   wherein the coating composition is capable of forming an electrodeposition coated film having a film resistance of 1000 to 1500 kΩ·cm 2  based on a film thickness of 10 to 20 μm,   wherein the metal ion is one or more selected from the group consisting of cerium ion, bismuth ion, copper ion, zinc ion, molybdenum ion and aluminium ion, and   wherein the neutralizing acid is one or more selected from the group consisting of acetic acid, lactic acid, formic acid and sulfamic acid.   
     
     
         11 . The lead-free cationic electrodeposition coating composition according to  claim 10  which further comprises a pigment in a ratio of 1/9 or less by weight based on a resin solid contained in the coating composition. 
     
     
         12 . The lead-free cationic electrodeposition coating composition of  claim 10 , wherein the metal ion is one or more selected from the group consisting of cerium ion, copper ion, zinc ion, molybdenum ion and aluminium ion. 
     
     
         13 . An electrodeposition coating process comprising:
 dipping a substrate to be coated in an electrodeposition coating composition which comprises an aqueous medium, a binder resin composed of a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in the aqueous medium, a neutralizing acid in order to neutralize the cationic epoxy resin, an organic solvent, and a catalyst releasing metal ion, and which has a nonvolatile content of 22 to 35% by weight, a volatile organic content of 1% by weight or less, a metal ion content of 500 ppm or less, and a neutralizing acid amount of 10 to 30 mg equivalent based on 100 g of binder resin solid content; and   conducting electrodeposition coating using the substrate as a cathode, thereby forming a coated film having a thickness of 10 to 20 μm and a film resistance of 1000 to 1500 kΩ·cm 2  on a surface of the substrate,   wherein the cationic epoxy resin is an oxazolidone ring-containing amine-modified epoxy resin,   wherein the metal ion is one or more selected from the group consisting of cerium ion, bismuth ion, copper ion, zinc ion, molybdenum ion and aluminium ion, and   wherein the neutralizing acid is one or more selected from the group consisting of acetic acid, lactic acid, formic acid and sulfamic acid.   
     
     
         14 . The process of  claim 13 , wherein the metal ion is one or more selected from the group consisting of cerium ion, copper ion, zinc ion, molybdenum ion and aluminium ion.