Resin based post rinse for improved throwpower of electrodepositable coating compositions on pretreated metal substrates

Abstract

Disclosed are methods for treating metal substrates, including ferrous substrates, such as cold rolled steel and electrogalvanized steel. The methods include (a) contacting the substrate with a pretreatment composition including a group IIIB or IVB metal and an electropositive metal, (b) contacting the substrate with a post rinse composition and (c) electrophoretically depositing an electrodepositable coating composition to the substrate, wherein the post rinse composition improves the throwpower of the subsequently applied electrodepositable coating composition. The present invention also relates to coated substrates produced thereby.

We claim: 
     
         1 . A method for coating a substrate comprising:
 (a) contacting the substrate with a pretreatment solution comprising a group IIIB metal and/or a group IVB metal and an electropositive metal;   (b) contacting the substrate with an anionic resin-based post rinse composition comprising an anionic resin; and   (c) electrophoretically depositing a cationic electrodepositable coating composition onto the substrate.   
     
     
         2 . The method of  claim 1 , wherein said cationic resin comprises a phosphitized epoxy resin. 
     
     
         3 . The method of  claim 1 , wherein step (a) occurs before step (b) and wherein step (b) occurs before step (c). 
     
     
         4 . The method of  claim 1 , wherein said group IIIB metal and/or a group IVB metal comprises zirconium. 
     
     
         5 . The method of  claim 1 , wherein the throwpower of the cationic electrodepositable coating composition is increased by at least 6% compared to the throwpower of said cationic electrodepositable coating composition applied to the substrate without step (b). 
     
     
         6 . The method of  claim 1 , wherein said group IIIB metal and/or group IVB metal comprises a group IIIB metal compound and/or a group IVB metal compound. 
     
     
         7 . The method of  claim 6 , wherein said group IVB metal compound comprises a zirconium compound 
     
     
         8 . The method of  claim 1 , wherein step (b) comprises:
 immersing the substrate in a bath comprising the anionic resin-based post rinse composition;   removing the substrate from said bath; and   rinsing the substrate with water.   
     
     
         9 . The method of  claim 1 , wherein step (b) comprises:
 spraying the substrate with the anionic resin-based post rinse composition; and   drying the anionic resin-based post rinse composition onto the substrate prior to step (c).   
     
     
         10 . A substrate coated according to the method of  claim 1 . 
     
     
         11 . A method for coating a substrate comprising:
 (a) contacting the substrate with a pretreatment solution comprising a group IIIB and/or a group IVB metal and an electropositive metal;   (b) contacting the substrate with an cationic resin-based post rinse composition comprising a cationic resin; and   (c) electrophoretically depositing an anionic electrodepositable coating composition onto the substrate.   
     
     
         12 . The method of  claim 11 , wherein said cationic resin comprises a trisaminoepoxy resin. 
     
     
         13 . The method of  claim 11 , wherein step (a) occurs before step (b) and wherein step (b) occurs before step (c). 
     
     
         14 . The method of  claim 11 , wherein said group IVB metal comprises zirconium. 
     
     
         15 . The method of  claim 11 , wherein said group IIIB metal and/or group IVB metal comprises a group IIIB metal compound and/or a group IVB metal compound. 
     
     
         16 . The method of  claim 15 , wherein said group IVB metal compound comprises a zirconium compound 
     
     
         17 . The method of  claim 11 , wherein step (b) comprises:
 immersing the substrate in a bath comprising the cationic resin-based post rinse composition;   removing the substrate from said bath; and   rinsing the substrate with water.   
     
     
         18 . The method of  claim 11 , wherein the throwpower of the anionic electrodepositable coating composition is increased by at least 6% compared to the throwpower of said anionic electrodepositable coating composition applied to the substrate without step (b). 
     
     
         19 . The method of  claim 11 , wherein said cationic resin comprises an amine adduct of an epoxy resin. 
     
     
         20 . A coated substrate coated according to the method of  claim 11 .