Low temperature curing coating composition containing sag control agent and use thereof

1. A coating composition comprising:

100 parts of a crosslinkable component comprising a film forming acrylate-polyester having a hydroxyl crosslinkable functional group; and

a crosslinking component comprising an alkylated melamine crosslinking activator having a crosslinking functional group that reacts with the hydroxyl crosslinkable functional group, the crosslinking activator comprising:

90 to 99 wt % of an alkylated melamine that is essentially unreactive to 1,6-hexamethylene diisocyanate; and

0.2 to 5 wt % of a polyurea sag control agent formed by reacting benzylamine and 1,6-hexamethylene diisocyanate in the presence of the alkylated melamine,

wherein said coating composition produces a cured sag-free coating layer having a gloss at 60° of 95 measured when the coating layer has a sag-free wet coating thickness of about 12 mils.

2. The coating composition of claim 1 , wherein the alkylated melamine comprises an alkylation group selected from C1-C10 alkyls.

3. The coating composition of claim 1 further comprising a pigment, a solvent, an ultraviolet light stabilizer, an ultraviolet light absorber, an antioxidant, a hindered amine light stabilizer, a leveling agent, a rheological agent, a thickener, an antifoaming agent, a wetting agent, a catalyst, or a combination thereof.

4. The coating composition of claim 1 , wherein the crosslinking component further comprises a polyisocyanate having two or more free isocyanate functional groups.

5. The coating composition of claim 4 , wherein the weight ratio of alkylated melamine:polyisocyanates is in a range of from about 1:0.1 to about 1:10.

6. A process for forming a sag-free coating layer on a substrate, the process comprising the steps of:

applying a coating composition over the substrate to form a sag-free wet coating layer having a wet coating thickness in a range of from about 12 to about 36 mils, wherein the coating composition comprises:

100 parts of a crosslinkable component comprising a film forming acrylate-polyester having a hydroxyl crosslinkable functional group; and

a crosslinking component comprising an alkylated melamine crosslinking activator having a crosslinking functional group that reacts with the hydroxyl crosslinkable functional group, the crosslinking activator comprising:

90 to 99 wt % of an alkylated melamine that is essentially unreactive to 1,6-hexamethylene diisocyanate; and

0.2 to 5 wt % of a polyurea sag control agent formed by reacting benzylamine and 1,6-hexamethylene diisocyanate in the presence of the alkylated melamine; and

curing the sag-free wet coating layer at a temperature in a range of from 15° C. to 60° C. to form the sag-free coating layer that has a gloss at 60° of 95 measured when the coating layer has a sag-free wet coating thickness of about 12 mils.

7. The process of claim 6 , wherein the coating composition further comprises a pigment, a solvent, an ultraviolet light stabilizer, an ultraviolet light absorber, an antioxidant, a hindered amine light stabilizer, a leveling agent, a rheological agent, a thickener, an antifoaming agent, a wetting agent, a catalyst, or a combination thereof.

8. The process of claim 6 , wherein the crosslinking component further comprises a polyisocyanate having two or more free isocyanate functional groups.

9. The process of claim 6 , wherein the weight ratio of alkylated melamine:polyisocyanate is in a range of from about 1:0.1 to about 1:10.

10. The coating composition of claim 1 , wherein the cross-linking component is present in an amount of about 23 parts.

11. The coating composition of claim 10 wherein the melamine crosslinking activator is present in an amount of 20 parts and the cross-linking component further comprises a catalyst present in an amount of about 3 parts, each based on a total weight of the cross-linking component.

12. The coating composition of claim 11 wherein the cross-linking component further comprises a catalyst that comprises 2,4-pentanedione.

13. The process of claim 6 , wherein the cross-linking component is present in an amount of about 23 parts.

14. The process of claim 13 wherein the alkylanted melamine crosslinking activator is present in an amount of 20 parts and the cross-linking component further comprises a catalyst present in an amount of about 3 parts, each based on a total weight of the cross-linking component.

15. The process of claim 14 wherein the cross-linking component further comprises a catalyst that comprises 2,4-pentanedione.

16. The coating composition of claim 1 , wherein the alkylated melamine comprises methyl groups.

17. The coating composition of claim 16 , wherein the alkylated melamine is fully alkylated with methyl groups.

18. The process of claim 6 , wherein the alkylated melamine comprises methyl groups.

19. The process of claim 6 , wherein the alkylated melamine is fully alkylated with methyl groups.

20. A coating composition comprising:

100 parts of a crosslinkable component comprising a film forming acrylate-polyester having a hydroxyl crosslinkable functional group; and

a crosslinking component comprising a methylated melamine crosslinking activator having a crosslinking functional group that reacts with the hydroxyl crosslinkable functional group, the crosslinking activator comprising:

98 wt % of a fully methylated melamine that is essentially unreactive to 1,6-hexamethylene diisocyanate; and

2 wt % of a polyurea sag control agent formed by reacting benzylamine and 1,6-hexamethylene diisocyanate in the presence of the fully methylated melamine,

wherein said coating composition produces a cured sag-free coating layer having a gloss at 60° of 95 measured when the coating layer has a sag-free wet coating thickness of 12 mils.