RADIATION-CURABLE AQUEOUS POLYURETHANE DISPERSIONS

1 . A radiation-curable aqueous polyurethane dispersion, wherein the dispersion comprises anionically stabilized polyurethane A present in disperse form, and wherein said polyurethane A comprises (meth)acrylamide functional groups in an amount of at least 0.2 mmol per g of the polyurethane A.

2 . The dispersion according to claim 1 , wherein the polyurethane A comprises (meth)acrylamide functional groups in an amount of at least 0.35 mmol per g of the polyurethane A, more preferably in an amount of at least 0.5 mmol per g of the polyurethane A.

3 . The dispersion according to claim 1 , wherein the polyurethane A comprises (meth)acrylamide functional groups in an amount of at most 6 mmol per g of the polyurethane A, more preferably in an amount of at most 4 mmol per g of the polyurethane A and most preferably in an amount of at most 2.5 mmol per g of the polyurethane A.

4 . The dispersion according to claim 1 , wherein the amount of (meth)acrylamide functional groups present in the polyurethane A is chosen such to result in at least 50 mol % of the ethylenically unsaturated bond concentration of the polyurethane A, more preferably at least 75 mol %, even more preferably at least 90 mol % and most preferably 100 mol % of the ethylenically unsaturated bond concentration of the polyurethane A.

5 . The dispersion according to claim 1 , wherein said polyurethane A comprises acrylamide functional groups.

6 . The dispersion according to claim 1 , wherein the amount of (meth)acryloyl ester functional group(s) present in the dispersion is at most 4 meq/g solids content of the dispersion.

7 . The dispersion according to claim 1 , wherein the at least for a part anionically stabilized polyurethane A contains anionic functional groups selected from the group consisting of carboxylate groups, sulfonate groups, phosphonate groups and any combination thereof.

8 . The dispersion according to claim 1 , wherein the polyurethane A contains carboxylic acid groups and/or sulfonic acid groups which become anionic when deprotonated.

9 . The dispersion according to claim 1 , wherein a hydroxy-carboxylic acid(s), preferably a dihydroxy alkanoic acid(s), more preferably α,α-dimethylolpropionic acid, is chemically incorporated into the polyurethane A to provide after deprotonation at least a part of the hydrophilicity required to enable the polyurethane A to be stably dispersed in the aqueous dispersing medium.

10 . The dispersion according to claim 8 , wherein the neutralizing agent used to deprotonate (neutralize) the carboxylic acid groups and/or sulfonic acid groups is an alkali metal hydroxide.

11 . The dispersion according to claim 1 , wherein the polyurethane A is also non-ionically stabilized by chemically incorporating polyethylene oxide and/or polypropylene oxide units into the polyurethane A.

12 . The dispersion according to claim 11 , wherein the amount of (potentially) anionic functional groups present in the polyurethane A is such that the acid value of the polyurethane A is in the range from 10 to 50 mg KOH/g solids of the polyurethane A.

13 . The dispersion according to claim 1 , wherein the number average molecular weight M n of the polyurethane A is in the range from 800 to 50000 Daltons, more preferably in the range of 1000 to 25000 Daltons, most preferably in the range of 1100 to 20000 Daltons, especially preferred in the range of 1200 to 15000 Daltons.

14 . The dispersion according to claim 1 , wherein the polyurethane A comprises as building blocks at least

(a) a polyisocyanate(s),

(b) a component(s) containing or providing a (meth)acrylamide functional group(s),

(c) a component(s) containing an isocyanate-reactive group(s) and an anionic group(s) which is capable to render the polyurethane A dispersible in the aqueous dispersing medium either directly or after reaction with a neutralizing agent to provide a salt, whereby component (c) being different from component (b), and

(d) a component(s) containing at least one isocyanate-reactive group(s), whereby component (d) being different from component (b) and (c).

15 . The dispersion according to claim 14 , wherein component (b) is selected from the group consisting of N-hydroxymethyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, N-hydroxypropyl(meth)acrylamide, N,N-bis(hydroxyethyl)acrylamide, N,N-bis(hydroxypropyl)acrylamide and any mixture thereof, preferably component (b) is N-2-hydroxyethylacrylamide.

16 . The dispersion according to claim 14 , wherein at least one component containing an isocyanate group(s) and a (meth)acrylamide functional group(s) is used as component (b) (component (b2)).

17 . The dispersion according to claim 14 , wherein the polyurethane A is acryloyl amide functional, whereby the acrylamide functional groups are introduced into the polyurethane A by using at least one component containing an isocyanate group(s) and an acrylamide functional group(s) (component (b2)) as building block of the polyurethane A, which component (b2) is obtained in-situ before preparation of the urethane prepolymer by reacting in the presence of a catalyst an isocyanate compound having at least two isocyanate groups with acrylic acid.

18 . The dispersion according to claim 17 , wherein the anionic functionality of the polyurethane A is obtained by incorporating sulfonate groups into the polyurethane A.

19 . The dispersion according to claim 1 , wherein the polyurethane A is free of (meth)acryloyl ester functional groups.

20 . The dispersion according to claim 1 , wherein the dispersed particles have an average particle size of 10 nm or higher and of 200 nm or lower.

21 . The dispersion according to claim 1 , wherein the polyurethane A is present in an amount of from 10 to 50% by solids weight, based on the total solids weight of the dispersion.

22 . Ink composition comprising the dispersion according to claim 1 , wherein the amount of polyurethane A is in the range from 2 to 20 wt. %, relative to the total weight of the ink composition.

23 . Use of an ink composition according to claim 22 for inkjet printing.