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A coating composition capable of curing to a high hardness by exposure to sunlight. More particularly, the coating composition comprises a high molecular weight polyurethane (meth)acrylate or methacrylate dissolved in one or more non-alcohol solvent, a visible light photoinitiator, and an alcohol so

A coating composition capable of curing to a high hardness by exposure to sunlight. More particularly, the coating composition comprises a high molecular weight polyurethane (meth)acrylate or methacrylate dissolved in one or more non-alcohol solvent, a visible light photoinitiator, and an alcohol solubilizer.

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1. A liquid, curable coating composition comprising in admixture: (a) one or more polyurethane film-forming polymers having the formula C-(D-[-(R-D)n-(P-D)m-]xE)k-Cwherein:i) D is a diisocyanate group,ii) R is one or more diol or triol groups having a molecular weight less than or equal to 500 Dalto

1. A liquid, curable coating composition comprising in admixture: (a) one or more polyurethane film-forming polymers having the formula C-(D-[-(R-D)n-(P-D)m-]xE)k-Cwherein:i) D is a diisocyanate group,ii) R is one or more diol or triol groups having a molecular weight less than or equal to 500 Daltons;iii) P is one or more oligomeric diol groups having a molecular weight of from about 500 Daltons to about 3000 Daltons;iv) E is a urea group having a molecular weight less than or equal to 500 Daltons;v) C is a monohydroxyl functional acrylate group or methacrylate group;wherein the equivalent ratio of equivalent ratio of (i) to (ii) is less than 1.5:1; and the equivalent ratio of (i) to (iii) is greater than 15:1; n=20 to 450, m=0 to 5, x=1 to 10, and k=1 to 10;b) an alcohol solubilizer;c) a non-alcohol solvent;(d) a photoinitiator in an amount sufficient to polymerize the polyurethane film-forming polymers when exposed to light energy having a wavelength of 395 nm or above at an energy level of about 1 J/cm2 or more. 2. The coating composition according to claim 1 wherein the amount of polyurethane film-forming polymer is from about 15% to about 50% based on the weight of the coating composition. 3. The coating composition according to claim 1 wherein the diisocyanate comprises a residue of one or more of hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate, bis(4-isocyanatocyclohexyl)methane, isophorone diisoycanate, tetramethylxylene diisocyanate, trimethylhexamethylene diisocyanate, toluene diisocyanate, and isophorone diisoycanate. 4. The coating composition according to claim 1 wherein the diol or triol has a molecular weight of about 500 g/mole or less. 5. The coating composition according to claim 1 wherein the oligomeric diol has a molecular weight of from about 1000 Daltons to about 2000 Daltons. 6. The coating composition according to claim 1 wherein the urea group is formed by reaction of ethylenediamine or water with the diisocyanate group (D). 7. The coating composition according to claim 1 wherein the urea group is present in an amount of less than about 0.8% based on the weight of the polyurethane film-forming polymer. 8. The coating composition according to claim 1 wherein the acrylate group or methacrylate group comprises a residue of one or more of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate. N-(2-Hydroxypropyl)methacrylamide and pentaerythritol triacrylate. 9. The coating composition according to claim 1 wherein the polyurethane polymers have a molecular weight of about 100,000 Daltons or less. 10. The coating composition according to claim 1 wherein the polyurethane polymers have a Tg of about 0° C. or greater. 11. The coating composition according to claim 1 wherein the polyurethane polymers have a melting point of about 50° C. or greater. 12. The coating composition according to claim 1 wherein the non-alcohol solvent is organic and has a flash point lower than about 80° C. 13. The coating composition according to claim 1 wherein the non-alcohol solvent is present in an amount of about 20% or more based on the weight of the coating composition. 14. The coating composition according to claim 1 wherein the alcohol solubilizer as a molecular weight of about 500 g/mole or less. 15. The coating composition according to claim 1 wherein the photoinitiator comprises one or more of methanone, 1,1′-(phenylphosphinylidene)bis[1-(2,4,6-trimethylphenyl)-, methanone, (diphenylphosphinyl)(2,4,6-trimethylphenyl)-, phosphinic acid, P-phenyl-P-(2,4,6-trimethylbenzoyl)-, ethyl ester, and bicyclo[2.2.1]heptane-2,3-dione, 1,7,7-trimethyl-, and camphorquinone. 16. The coating composition according to claim 1 wherein the photoinitiator is present in an amount of from about 0.1% to about 10% by weight based on the weight of the coating composition. 17. The coating composition according to claim 1 additionally comprising one or more components selected from the group consisting of film forming polymers, defoamers, pigments and adhesion promoters. 18. A method of forming a substantially tack-free coating which comprises: I) forming a liquid, curable coating composition comprising in admixture:(a) one or more polyurethane film-forming polymers having the formula C-(D-[-(R-D)n-(P-D)m-]xE)k-Cwherein:i) D is a diisocyanate group,ii) R is one or more diol or triol groups having a molecular weight less than or equal to 500 Daltons;iii) P is one or more oligomeric diol groups having a molecular weight of from about 500 Daltons to about 3000 Daltons;iv) E is a urea group having a molecular weight less than or equal to 500 Daltons;v) C is a monohydroxyl functional acrylate group or methacrylate group;wherein the equivalent ratio of equivalent ratio of (i) to (ii) is less than 1.5:1; and the equivalent ratio of (i) to (iii) is greater than 15:1; n=20 to 450, m=0 to 5, x=1 to 10, and k=1 to 10;b) an alcohol solubilizer;c) a non-alcohol solvent;(d) a photoinitiator in an amount sufficient to polymerize the polyurethane film-forming polymers when exposed to light energy having a wavelength of 395 nm or above at an energy level of about 1 J/cm2 or more;II) applying the coating composition onto a substrate following by evaporating the non-alcohol solvent and alcohol solubilizer to form substantially tack-free coating;III) exposing the composition resulting from step II) to light energy having a wavelength of 395 nm or above at an energy level of about 1 J/cm2 or more. 19. The method according to claim 18 wherein the substantially tack-free coating formed after evaporation of non-alcohol solvent and alcohol solubilizer has a pencil hardness of about 2 B or less as measured according to ASTM D3363. 20. The method according to claim 18 wherein the coating resulting from step III) has a pencil hardness of about 2H or more as measured according to ASTM D3363.