Electrocoating composition

1 . An improved aqueous cathodic electrocoating composition having a binder resin and a crosslinking agent; wherein the improvement is the use of a bismuth-sugar solution to provide a catalytic amount of a bismuth compound dispersed in the electrocoating composition, and wherein:

the electrocoating composition comprises an aqueous dispersion;

the composition is configured to achieve full crosslinking when cured at a low bake temperature of less than 130° C.;

the bismuth compound is bismuth subnitrate;

the bismuth-sugar solution comprises a polyhydroxy compound that is a sugar alcohol;

the bismuth-sugar solution consists essentially of water, bismuth subnitrate, and the sugar alcohol;

the bismuth-sugar solution provides the bismuth compound in an amount of at least 3% by weight based on the weight of the binder resin; and

the aqueous dispersion is configured to exhibit stability without sedimentation for at least two weeks at ambient temperature and pressure.

2 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein:

the sugar alcohol is sorbitol;

the bismuth-sugar solution has a bismuth content of at least 230 g/L;

the bismuth-sugar solution has a pH of 1.5 to 3.0;

the bismuth-sugar solution is a clear solution comprising a water-soluble bismuth-polyhydroxy complex;

the bismuth-sugar solution is free of lactic acid, dimethylolpropionic acid, and amino acids; and

the composition is free of bismuth lactate and bismuth dimethylolpropionate.

3 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the bismuth-sugar solution has a bismuth content of at least 220 g/L.

4 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the bismuth-sugar solution has a bismuth content of at least 240 g/L.

5 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the bismuth-sugar solution provides the bismuth compound in an amount of 3%-5% by weight, based on the weight of the binder resin.

6 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the bismuth-sugar solution provides the bismuth compound in an amount of 3%-4% by weight, based on the weight of the binder resin.

7 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the binder resin is an epoxy amine adduct that is the reaction product of a polyepoxide resin and an amine selected from the group consisting of diethanolamine, N-methylethanolamine, N-phenylethanolamine, and combinations thereof; and

the crosslinking agent is a blocked polyisocyanate selected from the group consisting of blocked hexamethylene diisocyanate, blocked cyclohexamethylene diisocyanate, blocked toluene diisocyanate, blocked methylene diphenyl diisocyanate, and combinations thereof.

8 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the composition is free of any catalyst other than the bismuth compound.

9 . The improved aqueous cathodic electrocoating composition of claim 1 further comprising at least one pigment selected from the group consisting of titanium dioxide, carbon black, iron oxide, clay, and combinations thereof, wherein the pigment to binder weight ratio is from 0.2:1 to 0.4:1.

10 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the aqueous cathodic electrocoating composition is free of pigment.

11 . The improved aqueous cathodic electrocoating composition of claim 10 , wherein the composition has an MEQ-acid value of less than 40 mmol 44 mmol per 100 g of resin solid content.

12 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein:

the sugar alcohol is selected from the group consisting of dulcitol, sorbitol, xylitol, mannitol, and combinations thereof;

the bismuth-sugar solution has a pH of from 1.0 to 4.0;

the bismuth-sugar solution has a density of from 1.0 g/mL to 2.0 g/mL;

the binder resin is an epoxy amine adduct that is a reaction product of a polyglycidyl ether of bisphenol A and diethanolamine; and

the crosslinking agent is a blocked polyisocyanate.

13 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the aqueous dispersion has an average particle size diameter of the binder phase of from 0.1 to 10 microns.

14 . The improved aqueous cathodic electrocoating composition of claim 1 , further comprising at least one additive selected from the group consisting of wetting agents, surfactants, defoamers, light stabilizers, anti-crater agents, flow aids, dispersion stabilizers, adhesion promoters, corrosion inhibitors, and combinations thereof.

15 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the composition has a solids content of from 10 to 30 percent by weight when formulated as an electrocoating bath.

16 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the composition has an MEQ-acid value of less than 39 mmol per 100 g of resin solid content; and the composition has an electrical conductivity of less than 1500 μS/cm at 20° C.

17 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein curing at the low bake temperature of less than 130° C. comprises curing at no more than 120° C.

18 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the sugar alcohol is sorbitol.

19 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein the bismuth-sugar solution has a pH of from 1.5 to 2.5 and a density of from 1.3 g/mL to 1.5 g/mL.

20 . The improved aqueous cathodic electrocoating composition of claim 1 , wherein;

the composition is free of bismuth lactate and bismuth dimethylolpropionate; and

the composition has an MEQ-acid value of less than 39 mmol per 100 g of resin solid content.