Electrocoating composition

Abstract

Cathodic electrocoating composition with improved edge protection and coating appearance are provided. An exemplary cathodic electrocoating composition includes an aqueous carrier, a film forming binder dispersed in the carrier and including an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent; a pigment paste; a water-soluble cellulose ether; and a cationic microgel dispersion which is prepared by a process comprising dispersing in aqueous medium a mixture of a cationic polyepoxide-amine reaction product which contains amine groups selected from the group consisting of primary amine groups, secondary amine groups, and mixtures thereof and a polyepoxide crosslinking agent and heating the mixture to a temperature sufficient to crosslink the mixture to form the cationic microgel dispersion. The water-soluble cellulose ether may be hydroxyethyl cellulose.

What is claimed is: 
     
         1 . A cathodic electrocoating composition comprising:
 an aqueous carrier;   a film forming binder dispersed in the carrier, wherein the binder comprises an epoxy-amine adduct and a blocked polyisocyanate crosslinking agent;   a pigment paste;   a water-soluble cellulose ether; and   a cationic microgel dispersion which is prepared by a process comprising dispersing in aqueous medium a mixture of a cationic polyepoxide-amine reaction product which contains amine groups selected from the group consisting of primary amine groups, secondary amine groups, and mixtures thereof and a polyepoxide crosslinking agent and heating the mixture to a temperature sufficient to crosslink the mixture to form the cationic microgel dispersion.   
     
     
         2 . The composition of  claim 1  wherein the water-soluble cellulose ether is hydroxyethyl cellulose. 
     
     
         3 . The composition of  claim 1  wherein the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da. 
     
     
         4 . The composition of  claim 1  wherein the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da, and wherein the hydroxyethyl cellulose is present in amounts of from about 0.05 to 0.8 percent by weight, the percentage by weight being based on weight of resin solids of the composition. 
     
     
         5 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; 
 the hydroxyethyl cellulose is present in amounts of from about 0.05 to 0.8 percent by weight, the percentage by weight being based on weight of resin solids of the composition; and 
 solids from the cationic microgel dispersion is present in amounts of from about 0.5 to 8 percent by weight, the percentage by weight being based on weight of resin solids of the composition. 
 
     
     
         6 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; 
 the hydroxyethyl cellulose is present in amounts of from about 0.075 to 0.15 percent by weight, the percentage by weight being based on weight of resin solids of the composition; and 
 solids from the cationic microgel dispersion is present in amounts of from about 1.5 to 2.5 percent by weight, the percentage by weight being based on weight of resin solids of the composition. 
 
     
     
         7 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; and 
 the composition has a cationic microgel dispersion weight solids to hydroxyethyl cellulose weight solids ratio of from about 10:1 to about 55:1. 
 
     
     
         8 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; and 
 the composition has a cationic microgel dispersion weight solids to hydroxyethyl cellulose weight solids ratio of from about 15:1 to about 25:1. 
 
     
     
         9 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; 
 the composition includes from about 0.02 to about 0.2 percent hydroxyethyl cellulose solids, based on total solids of the composition; 
 the composition includes from about 1 to about 3 percent microgel dispersion solids, based on total solids of the composition; and 
 the composition has a cationic microgel dispersion weight solids to hydroxyethyl cellulose weight solids ratio of from about 15:1 to about 25:1. 
 
     
     
         10 . The composition of  claim 1  wherein:
 the water-soluble cellulose ether is hydroxyethyl cellulose having a molecular weight of from about 250,000 to about 1,500,000 Da; 
 the composition includes from about 0.05 to about 0.15 percent hydroxyethyl cellulose solids, based on total solids of the composition; 
 the composition includes from about 1 to about 3 percent microgel dispersion solids, based on total solids of the composition. 
 
     
     
         11 . The composition of  claim 1  wherein:
 the pigment paste includes pigment; 
 the pigment has a pigment to binder weight ratio of from about 2:1 to about 6:1; 
 the cathodic electrocoating composition has a pigment to binder weight ratio of from about 0.15:1 to about 0.4:1. 
 
     
     
         12 . The composition of  claim 1  wherein the pigment paste contains from about 45 to about 65 percent by weight solids. 
     
     
         13 . The composition of  claim 1  wherein the cationic microgel dispersion has a resin solids content of from about 5 to about 40 percent by weight. 
     
     
         14 . A method for coating an electrically conductive substrate, comprising
 (1) dipping the electrically conductive substrate into an electrodeposition bath comprising the cathodic electrocoating composition as claimed in  claim 1 ;   (2) connecting the substrate as a cathode;   (3) applying a current to the substrate to deposit a film on the substrate;   (4) removing the substrate with the deposited film from the electrodeposition bath; and   (5) baking the deposited coating film.   
     
     
         15 . A method for preparing a cathodic electrocoating composition, the method comprising:
 dispersing in aqueous medium a mixture of a cationic polyepoxide-amine reaction product which contains amine groups selected from the group consisting of primary amine groups, secondary amine groups, and mixtures thereof and a polyepoxide crosslinking agent to form a mixture and heating the mixture to a temperature sufficient to crosslink the mixture to form a cationic microgel dispersion.   preparing an epoxy amine adduct of an epoxy resin;   preparing a crosslinking agent for the epoxy amine adduct;   blending the epoxy amine adduct with the crosslinking agent to form a film forming binder;   forming an emulsion from the film forming binder and an aqueous carrier;   combining the cationic microgel dispersion and a water-soluble cellulose ether with the emulsion; and   forming a pigment paste and blending the pigment paste with the emulsion to form an electrocoating bath.