Process for the preparation of binder dispersions capable of being cathodically deposited using crosslinking agents based on polyisocyanates blocked by amino groups

Abstract

The invention relates to a process for the preparation of aqueous dispersions to be further processed to electrocoating paints with baking temperatures below 160° C. and baking times of ≦30 minutes, which dispersions contain modified epoxide-amine adducts as binders and polyisocyanates blocked by amino groups as crosslinking agents. In this process, polyepoxides and compounds which contain one or more, preferably 2, hydroxyl groups per molecule are converted at higher temperatures and in the presence of catalysts to epoxide-containing intermediates. A solvent or a mixture of solvents is then added with external cooling and the solution is then caused to boil under reflux, if necessary by application of a vacuum, until the temperature of the solution drops to 95° C. to 20° C. Amines are then added onto the epoxide groups which are still present in a free state in the epoxide resin and either a dispersion is prepared after the addition of the crosslinking agent by adding a water-acid mixture or the products are first dispersed and the crosslinking agent is added subsequently.

1 - 6 . (canceled)  
     
     
         7 . A process for the preparation of aqueous dispersions which are used for the preparation of aqueous electrocoating paints capable of being cathodically deposited and heat-curable at temperatures below 160° C. and baking times of <30 minutes which contain modified epoxide-amine adducts as binders capable of being cathodically deposited and polyisocyanates blocked by amino groups as crosslinking agents, comprising the steps of: 
 (1) reacting 
 (A) polyepoxides and  
 (B) compounds which contain at least one hydroxyl group attached to an aromatic and/or (cyclo)aliphatic molecular fragment per molecule, in the presence of a catalyst in an amount from about 0.1 to 2% by weight based on components (A) and (B) at elevated temperatures, to furnish an epoxide-containing intermediate (C);  
   (2) adding a solvent (D) with external cooling, and causing the resultant resin solution to boil under reflux, until the temperature of the solution drops down to 95° C. to 20° C.;    (3) adding primary and/or secondary amines (E) to react with the epoxide groups which are still present in a free state in the epoxide resin;    (4) dispersing these reaction products in a water-acid mixture, and    (5) admixing the crosslinking agent (F).    
     
     
         8 . The process as claimed in  claim 16 , wherein the polyisocyanates are aliphatic polyisocyanates.  
     
     
         9 . The process as claimed in  claim 16 , wherein the polyisocyanates are aromatic polyisocyanates.  
     
     
         10 . The process as claimed in  claim 16 , wherein substances are used as solvents in stage (2) which are nonreactive with the epoxide groups still present in the resin.  
     
     
         11 . The process as claimed in  claim 16 , wherein the resin solution in stage (2) is cooled to a temperature from about 50° C. to about 95° C.  
     
     
         12 . The process as claimed in  claim 16 , wherein the volatile solvent is removed in vacuo at temperatures below 65° C. after preparation of the aqueous dispersion.  
     
     
         13 . A process for the preparation of aqueous dispersions which are used for the preparation of aqueous electrocoating paints capable of being cathodically deposited and heat-curable at temperatures below 160° C. and baking times of ≦30 minutes 
 which contain modified epoxide-amine adducts as binders capable of being cathodically deposited and polisocyanates blocked by amino groups as crosslinking agents, comprising the steps of:    (1) reacting 
 (A) polyepoxides and  
 (B) compounds which contain at least one hydroxyl group attached to an aromatic and/or (cyclo)aliphatic molecular fragment per molecule, in the presence of a catalyst in an amount from about 0.1 to 2% by weight based on components (A) and (B) at elevated temperatures to furnish an epoxide-containing intermediate (C);  
   (2) adding a solvent (D) with external cooling, and causing the resultant resin solution to boil under reflux, until the temperature of the solution drops down to 95° C. to 20° C.;    (3) adding primary and/or secondary amines (E) to react with the epoxide groups which are still present in a free state in the epoxide resin;    (4) mixing a crosslinking agent (F) with these reaction products, and    (5) dispersing these reaction products in a water-acid mixture.    
     
     
         14 . The process as claimed in  claim 16  wherein the elevated temperature is approximately 100° C.-180° C.  
     
     
         15 . The process as claimed in claim  22  wherein the elevated temperature is approximately 100° C.-180° C.  
     
     
         16 . The process as claimed in claim  22  wherein substances are used as solvents in stage (2) which are non reactive with the epoxide groups still present in the resin.  
     
     
         17 . The process as claimed in claim  22 , wherein the resin solution in stage (2) is cooled to a temperature from about 50° C. to about 95° C.  
     
     
         18 . The process as claimed in claim  22 , wherein the volatile the solvent is removed in vacuo at temperatures below 65° C. after preparation of the aqueous dispersion.  
     
     
         19 . A process for electrocoating a substrate comprising: 
 (a) preparing an aqueous dispersion containing modified epoxide-amine adducts as binders and polyisocyanates blocked by amino groups as crosslinking agents, comprising the steps of: 
 (1) reacting 
 (A) polyepoxides and  
 (B) compounds which contain at least one hydroxyl group attached to an aromatic and/or (cyclo)aliphatic molecular fragment per molecule, in the presence of a catalyst in an amount from about 0.1 to 2% by weight based on components (A) and (B) at elevated temperatures to furnish an epoxide-containing intermediate (C);  
 
 (2) adding a solvent (D) with external cooling, and causing the resultant resin solution to boil under reflux, until the temperature of the solution drops down to 95° C. to 20° C.;  
 (3) adding primary and/or secondary amines (E) to react with the epoxide groups which are still present in a free state in the epoxide resin;  
 (4) mixing a crosslinking agent (F) with these reaction products, and  
 (5) dispersing these reaction products in a water-acid mixture;  
   (b) preparing an electrocoating bath comprising the aqueous dispersion of step (a) and additional agents selected from the group consisting of pigments, catalysts, and accelerators;    (c) electrodepositing a film on the substrate in the electrocoating bath of step (b); and    (d) curing the deposited film at temperature less than 160° C. for a time less than about 30 minutes.    
     
     
         20 . The process as claimed in claim  28 , wherein the resin solution in step (a)(2) is refluxed under vacuum.  
     
     
         21 . The process as claimed in claim  28 , wherein the resin solution in step (a)(2) is cooled to a temperature from about 50° C. to about 95° C.