Radiation curable polyurethane dispersions

1 . A polyurethane dispersion comprising:

a) 10 to 60 percent by weight of a polymeric polyol;

b) 5 to 40 percent by weight of at least one compound containing both isocyanate reactive groups and meth(acrylate) groups wherein said compound comprises 1 to 30 percent by weight of at least one hydroxyl alkyl acrylate;

c) 1 to 15 percent by weight of at least one compound comprising both isocyanate reactive groups and carboxyl groups; and

d) 10 to 50 percent by weight of at least one isocyanate functional group.

2 . The polyurethane dispersion of claim 1 , further comprising:

a) 0.1 to 10 percent by weight of at least one amine extender compound; and

b) 0.1 to 10 percent by weight of at least one photoinitiator containing at least one isocyanate reactive group.

3 . The polyurethane dispersion of claim 1 , further comprising a diluent.

4 . The polyurethane dispersion of claim 3 , wherein the diluent is a (meth)acrylate of an alkoxylated compound.

5 . The polyurethane dispersion of claim 1 , wherein said dispersion is in the form of an aqueous dispersion.

6 . The polyurethane dispersion of claim 1 , wherein the ratio of isocyanate group equivalents of groups (a), (b) and (c) to equivalents of isocyanate-reactive groups of component (d) is 0.8:1.1.

7 . A coating composition comprising at least one polyurethane dispersion of claim 1 .

8 . A substrate comprising the coating composition of claim 7 .

9 . An aqueous polyurethane dispersion comprising:

a) 10 to 60 percent by weight of a polymeric polyol;

b) 5 to 40 percent by weight of at least one compound containing both isocyanate reactive groups and meth(acrylate) groups wherein said compound comprises 1 to 30 percent by weight of at least one hydroxyl alkyl acrylate;

c) 1 to 15 percent by weight of at least one compound comprising both isocyanate reactive groups and carboxyl groups;

d) 10 to 50 percent by weight of at least one isocyanate functional group; and

e) 0.1 to 10 percent by weight of at least one photoinitiator bonded to the backbone of the at least one isocyanate functional group.

10 . The aqueous polyurethane dispersion according to claim 9 further comprising 0.1 to 10 percent by weight of at least one amine extender compound.

11 . The aqueous polyurethane dispersion of claim 9 , further comprising a diluent.

12 . The aqueous polyurethane dispersion of claim 11 , wherein the diluent is a (meth)acrylate of an alkoxylated compound.

13 . The dispersion of claim 11 , wherein the diluent is the diacrylate of propoxylated neopentyl glycol.

14 . The dispersion of claim 9 , wherein the ratio of isocyanate group equivalents of groups (a), (b) and (c) to equivalents of isocyanate-reactive groups of component (d) is 0.8:1.1.

15 . A method of coating a substrate with a rapidly curing surface comprising:

a) forming a curable coating composition comprising 10 to 60 percent by weight of a polymeric polyol, 5 to 40 percent by weight of at least one compound containing both isocyanate reactive groups and meth(acrylate) groups wherein said compound comprises 1 to 30 percent by weight of at least one hydroxyl alkyl acrylate, 1 to 15 percent by weight of at least one compound comprising both isocyanate reactive groups and carboxyl groups, and 10 to 50 percent by weight of at least one isocyanate functional group,

b) applying the coating composition to a substrate, and

c) curing the coating composition.

16 . The method according to claim 15 , further comprising a diluent.

17 . The method according to claim 18 , wherein the diluent is a (meth)acrylate of an alkoxylated compound.

18 . The method according to claim 15 , wherein said step of curing is done using radiation.