Process for the preparation of low-viscosity, water-dilutable urethane (meth)acrylates

1. A process for preparing a low-viscosity, water-dilutable polyurethane (meth)acrylate comprising reacting components (a), (c), (d), and (e)

(a) at least one oligomeric polyisocyanate having an average of at least three isocyanate groups;

(c) at least one polyoxyalkylene mono-ol;

(d) at least one hydroxyalkyl (meth)acrylate;

(e) at least one polyoxyalkylene polyol based on a starter molecule which has at least three hydroxyl functional groups and is partially reacted by esterification with (meth)acrylic acid such that on average 0.2 to 1.5 hydroxyl functional groups still remain;

to form said low-viscosity, water-dilutable polyurethane (meth)acrylate;

wherein said low-viscosity, water-dilutable polyurethane (meth)acrylate has an NCO content of less than 0.5 weight %.

2. The process of claim 1 , wherein a further component (b), which is at least one further isocyanate with at least two isocyanate functional groups, is reacted with components (a), (c), (d), and (e).

3. The process of claim 1 , wherein a further component (f), which has at least one compound with at least one group which is reactive towards isocyanate and at least one ionic and/or potentially ionic functional group, is reacted with components (a), (c), (d), and (e).

4. The process of claim 1 , wherein (a) is at least one oligomeric polyisocyanate based on 1,6-hexamethylene-diisocyanate.

5. The process of claim 1 , wherein (a) is at least one oligomeric polyisocyanate with isocyanurate groups.

6. The process of claim 1 , wherein the polyoxyalkylene mono-ol (c) contains at least 30 mol % of ethylene oxide units.

7. The process of claim 1 , wherein component (c) is a polyoxyethylene mono-ol with an OH number of from 18 to 238 mg of KOH/g.

8. The process of claim 1 , wherein component (e) contains on average 0.5 to 8.0 ethylene oxide units per OH group of the starter molecule.

9. The process of claim 1 , wherein the process is carried out with 20 to 50 weight % of component (a), 0 to 20 weight % of component (b), 10 to 30 weight % of component (c), 4 to 20 weight % of component (d), 25 to 60 weight % of component (e) and 0 to 10 weight % of component (f), wherein the sum of the weight % of components (a) to (f) is 100; wherein component (b), which is at least one further isocyanate with at least two isocyanate functional groups, is reacted with components (a), (c), (d), and (e); and component (f), which has at least one compound with at least one group which is reactive towards isocyanate and at least one ionic and/or potentially ionic functional group, is reacted with components (a), (c), (d), and (e).

10. A water-dilutable polyurethane (meth)acrylate obtained by the process of claim 1 .

11. A coating comprising the water-dilutable polyurethane (meth)acrylate of claim 10 .

12. The coating of claim 11 , wherein said coating is a lacquer or adhesive.

13. A coating composition comprising the water-dilutable polyurethane (meth)acrylate of claim 10 .

14. A coating composition comprising

A) at least one urethane (meth)acrylate of claim 10 ;

B) optionally a compound which differs from A) and contains groups which react, by polymerization, with ethylenically unsaturated compounds under the action of actinic radiation;

C) optionally an aqueous binder which is not radiation-curable;

D) an initiators;

E) optionally water and/or a solvent;

F) optionally an auxiliary substance and/or additive.

15. A substrate coated with the coating composition of claim 13 .

16. The substrate of claim 15 , wherein said substrate is wood, a ligneous substrate, cork, or a substrate containing cellulose fibres.