Low-solvent or solvent-free crosslinker dispersions with pyrazole-blocked isocyanate groups

1. Process for preparing dispersions of blocked polyurethane prepolymers, comprising

I) preparing a blocked polyurethane prepolymer by reacting

(a) 100 equivalent % of at least one polyisocyanate having a functionality of >2, with

b) 50 to 90 equivalent %, based on the isocyanate-reactive groups, of a thermally eliminable blocking agent,

c) 5 to 45 equivalent %, based on the isocyanate-reactive groups, of a monohydroxycarboxylic acid as hydrophilicizing agent

d) 0 to 25 equivalent %, based on the isocyanate-reactive groups, of a polyhydroxycarboxylic acid as hydrophilicizing agent and

(e) greater than 0 to 15 equivalent %, based on the isocyanate-reactive groups, of a chain extender component which is at least, based on isocyanate-reactive groups, trifunctional or higher and has a molecular weight of 32 to 350 g/mol,

wherein

i) step I) takes place using (partly) water-miscible organic solvents which are inert towards NCO groups and have boiling points below 120° C. (at 1013 mbar), and

ii) components a)-e) and the organic solvents are used in an amount such that the polyurethane prepolymer in the reaction solution is present, following complete reaction, in an amount of 70% to 98% by weight,

II) deprotonating, at least partially, the carboxylic acid groups with a base before, during or after step III),

III) dispersing the polyurethane prepolymer solution obtained from step (I) in water, and

IV) distilling the dispersion to completely remove the organic solvent, the distillation occurring during or after step III).

2. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein, the polyisocyanates are polyisocyanates based on compounds selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-diisocyanatodicyclohexylmethane and mixtures thereof.

3. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein the blocking agents are 1H-pyrazoles.

4. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein, the monohydroxycarboxylic acid is hydroxypivalic acid.

5. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 wherein the polyhydroxycarboxylic acid is dimethylolpropionic acid.

6. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 wherein the chain extender is trimethylolpropane.

7. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein the (partly) water-miscible solvents are aliphatic ketones having 3 to 6 carbon atoms.

8. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein the base utilized in step II) is selected from the group consisting of 2-amino-2-methyl-1-propanol, triethylamine, N,N-dimethylethanolamine and mixtures thereof.

9. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein in step IV), the solvent is removed from the dispersion down to a level of less than 3 percent by weight.

10. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein the equivalent ratio of the isocyanate component I)a) to isocyanate reactive groups of components I)b), c), d) and e) is 1:0.5 to 1:1.7.

11. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein step II) is performed prior to step III).

12. Dispersions of blocked polyurethane prepolymers obtained by a process according to claim 1 .

13. Compositions comprising blocked polyurethane prepolymer dispersions according to claim 12 , the compositions selected from the group consisting of coating compositions, adhesives, sealants, and elastomers.

14. Substrates provided with coatings obtained using dispersions according to claim 12 .

15. The process according to claim 1 , wherein there is no N-methylpyrrolidone (NMP) or butyl glycol used.

16. The process according to claim 1 , wherein said chain extender component has a functionality, based on isocyanate-reactive groups, of greater than three.

17. The process according to claim 1 , wherein said chain extender component is, based on isocyanate-reactive groups, trifunctional.

18. Process for preparing dispersions of blocked polyurethane prepolymers according to claim 1 , wherein the equivalent ratio of the isocyanate component I)a) to isocyanate reactive groups of components I)b), c), d) and e) is 1:0.7 to 1:1.3.

19. The compositions according to claim 13 , wherein the compositions are coating compositions which have a pendulum hardness of more than 80 seconds.