Stable polyisocyanates comprising nanoparticles

1. A process for preparing a nanoparticle-modified polyisocyanate having free NCO groups, which comprises

A) reacting

1) nanoparticles having an average particle size, as determined by dynamic light scattering, of smaller than 200 nm with

2) an alkoxysilyl- and an NCO-containing adduct of the formula (I)

OCN—R 1 —NHCO-QR 2 Z—SiX a Y 3-a   (I)

wherein,

R 1 represents a substituent selected from the group consisting of C 1 -C 14 linear groups, C 3 -C 14 cyclic aliphatic groups, C 6 -C 14 araliphatic groups, and C 6 -C 14 aromatic groups;

Q represents a substituent selected from the group consisting of oxygen, sulphur, and nitrogen;

R 2 when Q is nitrogen, represents a substituent selected from the group consisting of hydrogen, C 1 -C 12 alkyl groups, C 6 -C 20 aryl groups, C 6 - C 20 aralkyl groups, and aspartic ester radicals;

X represents a hydrolysable group;

Y independently of one another, represent an alkyl group;

Z represents a C 1 -C 12 alkylene group; and

a represents an integer from 1 to 3;

to form products of the reaction; and

B) blending the products of the reaction with a polyisocyanate having free NCO groups,

wherein the nanoparticle-modified polyisocyanate has an NCO content after 90 days of more than 80% of the initial NCO content measured in accordance with DIN EN ISO 11909.

2. The process according to claim 1 , further comprising mixing the nanoparticles with an organic solvent to form a dispersion.

3. The process according to claim 2 , wherein the organic solvent is selected from the group consisting of butyl acetate, 1-methoxy-2-propyl acetate, ethyl acetate, toluene, xylene, solvent naphtha, methyl ethyl ketone, and mixtures thereof.

4. The process according to claim 1 , wherein the nanoparticles are selected from the group consisting of silicon oxide, aluminium oxide, cerium oxide, zirconium oxide, niobium oxide, titanium oxide, and mixtures thereof.

5. The process according to claim 1 , wherein the nanoparticles have an average particle size, as determined by the Z-average by dynamic light scattering in dispersion, of 5 to 50 nm.

6. The process according to claim 1 , wherein the nanoparticles are surface-modified.

7. The process according to claim 1 , wherein in formula (I)

R 1 represents a substituent selected from the group consisting of a linear aliphatic group, a cycloaliphatic group, an araliphatic C 6 -C 13 group, and an aromatic C 6 -C 13 group;

R 2 applies when Q is nitrogen and represents a C 1 -C 4 alkyl group or an aspartic ester radical of the formula (II)

R 3 OOC—CH 2 —CH(COOR 4 )—  (II)

wherein,

R 3 and R 4 represent, independently of one another, alkyl radicals having 1 to 22 carbon atoms.

Q represents a substituent selected from the group consisting of oxygen, sulphur, and nitrogen;

X represents an alkoxy or hydroxyl group;

Y represents a linear or branched C 1 -C 4 alkyl group;

Z represents a linear or branched C 1 -C 4 alkylene group; and

a represents an integer from 1-2.

8. The process according to claim 7 , wherein at least one of the alkyl radicals represented by R 3 and R 4 in formula (II) is branched.

9. The process according to claim 7 , wherein at least one of the alkyl radicals represented by R 3 and R 4 in formula (II) has 1 to 4 carbon atoms.

10. The process according to claim 7 , wherein R3 and R4 represent, independently of one another, a methyl or an ethyl radical.

11. The process-according to claim 1 , wherein the polyisocyanate is based on IPDI, MDI, TDI, HDI or mixtures thereof.

12. A nanoparticle-modified polyisocyanate having free NCO groups, obtained by the process according to claim 1 .

13. A coating material, adhesive, or sealant comprising the nanoparticle-modified polyisocyanate according to claim 12 .

14. A coated or adhesively bonded substrate comprising the nanoparticle-modified isocyanates having free NCO groups according to claim 12 .

15. The process according to claim 1 , wherein the polyisocyanate in B) has an NCO functionality of 2.3 to 4.5.

16. The process according to claim 2 , further comprising step C), evaporating the solvent.