Process for producing hard coating systems based on aqueous polyurethane dispersions

1. A process for producing hard, radiation-curable coating systems, based on aqueous polyurethane dispersions, comprising the following steps:

I) reacting by polyaddition:

A) 40% to 80% by weight of a hydroxyl-containing component containing

A1) 10% to 80% by weight, based on the sum of components (A) to (F), of one or more hydroxyl-containing prepolymers selected from the group of polyesters, polyethers, polyepoxy (meth)acrylates and polyurethanes having an OH number in the range from 40 to 300 mg KOH/g and containing groups which, under exposure to high-energy radiation, undergo polymerization reaction with ethylenically unsaturated double bonds,

and optionally

A2) 0% to 50% by weight, based on the sum of components (A) to (F), of one or more alcohols containing (meth)acrylate groups and having an OH number in the range from 35 to 1000 mg KOH/g,

B) 0.1% to 20% by weight of one or more compounds that are reactive towards isocyanate groups and act dispersively for the polyurethane dispersion, and

C) 0% to 30% by weight of hydroxy-functional compounds selected from the group consisting of diols, triols, polyesters, polycarbonates, polyurethanes, C 2 , C 3 , and/or C 4 polyethers, polyether esters and polycarbonate polyesters, the diols and triols having a molecular weight in the range from 62 to 242 g/mol, and the polyesters, polycarbonates, polyurethanes, C 2 , C 3 , and/or C 4 polyethers, polyether esters and polycarbonate polyesters having in each case a molecular weight in the range from 700 to 4000 g/mole,

with

D) 10% to 50% by weight of one or more polyisocyanates to form a polyurethane and thereafter

II) adding:

E) 2% to 40% by weight of oligo(meth)acrylates selected from the group of component (A1) having a double bond density of greater than 2.0 mol of double bonds/kg of substance and through exposure to high-energy radiation undergoing polymerization reaction with ethylenically unsaturated compounds, and/or oligo(meth)acrylates based on (meth)acrylate esters, obtainable by esterification of (meth)acrylic acid with alcohols selected from the group of tetrols and hexols,

III) subsequently dispersing the product obtained according to step II in water to form an aqueous polyurethane dispersion, and

IV) reacting the aqueous polyurethane dispersion obtained from step III) with

F) 0.1% to 10% by weight of one or more mono-, di-, or polyamines and/or amino alcohols,

the fractions of components (A) up to (F) adding up to 100% by weight and the coating systems, after curing, having a König pendulum hardness of greater than 60 sec for an applied film with a wet thickness of 150 μm and a breaking extension of less than 150% for an applied film with a wet thickness of 250 μm.

2. Process according to claim 1 , where components (A), (B) and (C) are introduced as an initial charge to the reactor, optionally in dilution with a solvent which is miscible with water but inert towards isocyanate groups, and this initial charge is heated to temperatures of 30 to 60° C., with isocyanate addition reaction catalysts being optionally added to the mixture of the compounds (A), (B) and (C) before the reaction takes place with the polyisocyanate or polyisocyanates (D); the molar ratios of isocyanate-reactive groups in (A), (B) and (C) to isocyanate groups in (D) being situated in the range from 0.8:1 to 2.5:1, and the polyurethane obtained according to step I) being dissolved with the reactive oligo(meth)acrylate (E) in acetone, to form an oligo(meth)acrylate-acetone solution, and, with vigorous stirring according to step III and IV), either this solution being introduced into the dispersing water comprising the polyamine or polyamines (F) or, conversely, the dispersing water/polyamine mixture being added to the polyurethane-oligo(meth)acrylate-acetone solution, after which, optionally, the acetone is removed by distillation.

3. Hard, radiation-curable coating systems obtained by the process according to claim 1 .

4. Coating system according to claim 3 , wherein the degree of neutralization of the acids and/or bases introduced through component (B) is from 50% to 125%.

5. Coating system according to claim 3 , wherein the reaction V) of the remaining free isocyanate groups of the prepolymer by component (F) takes place to an extent of 35% to 150%.

6. Coating system according to claim 3 , wherein 2% to 40% by weight of oligo(meth)acrylates (E) based on (meth)acrylate esters obtained from the esterification of (meth)acrylic acid with alcohols selected from the group consisting of tetrols and hexyls are present.

7. Coating system according to claim 3 , wherein 2% to 40% by weight of oligo(meth)acrylates (E) based on polyester (meth)acrylates having an OH number in the range from 30 to 300 mg KOH/g are present.

8. Coating system according to any one of claim 3 , wherein 2% to 40% by weight of oligo(meth)acrylates (E) based on polyether (meth)acrylates having an OH number in the range from 5 to 200 mg KOH/g are present.

9. Coating system according to claim 3 , wherein 2% to 40% by weight of oligo(meth)acrylates (E) based on polyepoxy (meth)acrylates having an OH number in the range from 20 to 300 mg KOH/g are present.

10. Coating system according to claim 3 , wherein 2% to 40% by weight of oligo(meth)acrylates (E) based on polyurethane (meth)acrylates having an OH number in the range from 20 to 300 mg KOH/g are present.

11. Coating system obtainable according to claim 3 , wherein 2% to 40% by weight of mixtures of oligo(meth)acrylates (E) selected from the group consisting of polyester, polyether, polyurethane, polyepoxy (meth)acrylates and (meth)acrylate esters obtained by esterification of (meth)acrylic acid with alcohols selected from the group consisting of tetrols and hexyls are present.

12. Coating system according to claim 3 , wherein step IV) is carried out in acetonic solution before or after the addition of component (E).

13. Coating system according to claim 3 , wherein the aqueous polyurethane dispersion obtained according to step III) comprises at least a further initiator and optionally further auxiliaries and additives which allow curing with high-energy radiation.

14. Coating system according to claim 3 , wherein the aqueous polyurethane dispersion obtained according to step III) contains less than 5% by weight of organic solvents.

15. Hard transparent or pigmented coating materials comprising a coating system according to claim 3 .

16. Adhesive comprising a coating system according to claim 3 .

17. Substrate comprising a hard transparent or pigmented coating material according to claim 15 .

18. Substrate according to claim 17 , wherein the substrate is selected from the group consisting of wood, wood-based materials, furniture, wood-block flooring, doors, window frames, metallic articles, plastics, paper, cardboard, cork and leather.

19. Article comprising the adhesive according to claim 16 .

20. Substrate according to claim 19 , wherein the article is selected from at least two alike and/or different materials selected from the group consisting of wood, wood-based materials, furniture, wood-block flooring, doors, window frames, metallic articles, plastics, paper, cardboard, cork and leather.