Waterborne polyurethane coating compositions

1. An aqueous polyurethane coating composition comprising:

(a) a water-dilutable hydroxy-functional polyester resin;

(b) a water-dilutable aminoplast resin; and

(c) a water-dilutable polycarbonate-polyurethane resin,

wherein the aqueous polyurethane coating composition comprises

(i) 50% to 99% by weight, on a solids basis of the water-dilutable hydroxy-functional polyester resin and a water-dilutable aminoplast resin; and

(ii) 50% to 1% by weight on a solids basis of the water-dilutable polycarbonate-polyurethane resin, the weight percents totaling 100%; and

wherein the weight ratio on a solids basis of the hydroxy-functional polyester resin to the aminoplast resin is from 50:50 to 90:10; and

wherein the polycarbonate-polyurethane resin is non-functional.

2. The aqueous polyurethane coating composition of claim 1 , wherein the hydroxy-functional polyester resin component (a) has a weight average molecular weight of 500-100000, a hydroxyl number of 16.5 to 264 mg KOH/g and an acid number of 5 to 125 mg KOH/g.

3. The aqueous polyurethane coating composition of claim 1 , wherein the aminoplast resin component (b) comprises a melamine-formaldehyde condensation product.

4. The aqueous polyurethane coating composition of claim 1 , wherein the polycarbonate-polyurethane resin component (c) is characterized by a glass transition temperature of between −60° C. and 0° C.

5. The aqueous polyurethane coating composition of claim 1 , wherein the polycarbonate-polyurethane resin component (c) is characterized by a viscosity at 25° C. of less than 500 mPa·s in an 38% to 42% solids aqueous dispersion.

6. The aqueous polyurethane coating composition of claim 1 , comprising:

60% to 75% by weight on a solids basis of the water-dilutable hydroxy-functional polyester resin; a water-dilutable aminoplast resin; and

40% to 25% by weight on a solids basis of the water-dilutable polycarbonate-polyurethane resin, wherein the weight percents total 100% by weight.

7. The aqueous polyurethane coating composition of claim 1 , wherein the weight ratio on a solids basis of the hydroxy-functional polyester resin to the aminoplast resin is from 50:50 to 90:10.

8. The aqueous polyurethane coating composition of claim 1 , further comprising a an additional polyol resin selected from the group consisting of water-dispersible hydroxy-functional polyether-polyurethane resins and water-dispersible hydroxy-functional polyacrylic resins.

9. A glass substrate at least partially coated with the coating composition of claim 1 .

10. A glass container at least partially coated with the coating composition of claim 1 .

11. The aqueous polyurethane coating composition of claim 1 , wherein the aminoplast resin component (b) comprises an oligomeric methylated melamine-formaldehyde condensation product comprising imino groups, methoxymethyl groups, and methylol groups.

12. The aqueous polyurethane coating composition of claim 11 , wherein an equivalent ratio of methylol groups and alkoxylmethyl groups of component (b) to hydroxyl groups of component (a) is at least 0.05:1.

13. The aqueous polyurethane coating composition of claim 1 , wherein the polycarbonate-polyurethane resin component (c) comprises a reaction product of a polycarbonate polyol and a polyisocyanate selected from the group consisting of 4,4′-diisocyanatodicyclohexylmethane, isophorone diisocyanate, 1,6-hexamethylene diisocyanate, and 1-methyl-2,4(2,6)-diisocyanatocyclohexane.

14. The aqueous polyurethane coating composition of claim 13 , wherein the polycarbonate polyol has a number average molecular weight range 500 to 6000.

15. The aqueous polyurethane coating composition of claim 1 , further comprising a silane-functional adhesion promoter.

16. The aqueous polyurethane coating composition of claim 15 , wherein the adhesion promoter is selected from the group consisting of γ-mercaptopropyl-trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylsilane hydrolysate, 3-glycidyloxypropyltriethoxysilane, and combinations of any thereof.

17. A substrate at least partially coated with the coating composition of claim 1 .

18. The substrate of claim 17 , wherein the coating exhibits microhardness of no greater than 90 N/mm 2 , direct impact strength of at least 100 in-lbs, and reverse impact strength of at least 160 in-lbs.