Polyisocyanate mixtures

1. A solvent-free polyisocyanate mixture A) comprising:

5 to 95 wt.% based on a total wt. of polyisocyanate mixture A) of at least one polyisocyanate a-1), said at least one polyisocyanate a-1) being based on hexamethylene diisocyanate, said at least one polyisocyanate a-1) having an NCO content of from 16 to 24 wt.% based on a total wt. of polyisocyanate a-1), and said at least one polyisocyanate a-1) exhibiting a viscosity at 23° C. of from 70 to 12,000 mPas; and

95 to 5 wt.% based on a total wt. of polyisocyanate mixture A) of at least one polyisocyanate a-2), said at least one polyisocyanate a-2) being based on araliphatic diisocyanate, said at least one polyisocyanate a-2) having an NCO content of from 10 to 22 wt.% based on a total wt. of polyisocyanate a-2), said at least one polyisocyanate a-2) having a monomer araliphatic diisocyanate content of less than 1.0 wt.% based on a total wt. of polyisocyanate a-2), and said at least one polyisocyanate a-2) either being a solid at 23° C. or exhibiting a viscosity at 23° C. of more than 150,000 mPas;

said at least one polyisocyanate a-1) being different from said at least one polyisocyanate a-2); and

said polyisocyanate mixture A) having a total content of isocyanate groups of from 11 to 23 wt.% based on a total wt. of polyisocyanate mixture A), said polyisocyanate mixture A) having a mean isocyanate functionality of at least 2.3, and said polyisocyanate mixture A) having a monomeric diisocyanate content of less than 1 wt. % based on a total wt. of polyisocyanate mixture A).

2. Polyisocyanate mixtures A) according to claim 1 , wherein the polyisocyanates of component a-1) have a viscosity at 23° C. of from 70 to 1600 mPas and a content of isocyanate groups of from 18 to 24 wt.%.

3. Polyisocyanate mixtures A) according to claim 1 , wherein the polyisocyanates of component a-2) are those with a uretdione, allophanate, isocyanurate, iminooxadiazinedione and/or biuret structure.

4. Polyisocyanate mixtures A) according to claim 3 , wherein the polyisocyanates of component a-2) are those based on m-xylylene diisocyanate (m-XDI), p-xylylene diisocyanate (p-XDI) and/or m-tetramethylxylylene diisocyanate (m-TMXDI) having a content of isocyanate groups of from 11 to 21.5 wt.% and a content of monomeric diisocyanates of less than 0.8%.

5. Polyisocyanate mixtures A) according to claim 3 , wherein the polyisocyanates of component a-2) are those based on m-xylylene diisocyanate (m-XDI) having a content of isocyanate groups of from 15 to 21 wt.% and a content of monomeric m-XDI of less than 0.5%.

6. Process for the production of light-fast polyurethane compositions comprising solvent-free reacting of

A) the solvent-free polyisocyanate mixtures according to claim 1 with

B) reactants that are reactive towards isocyanate groups and have a mean functionality of from 2.0 to 6.0, optionally with the concomitant use of

C) further auxiliary substances and additives,

while maintaining an equivalent ratio of isocyanate groups to isocyanate-reactive groups of from 0.5:1 to 2.0:1.

7. Process according to claim 6 , wherein the reactants B) that are reactive towards isocyanate groups are hydroxy-, amino- and/or mercapto-functional compounds having a mean molecular weight of from 60 to 12,000.

8. Process according to claim 6 , wherein there are used as the reactants B) that are reactive towards isocyanate groups polyether polyols, polyester polyols, polycarbonate polyols and/or amino polyethers having a mean molecular weight of from 106 to 12,000, polythioether thiols, polyester thiols, sulfur-containing hydroxy compounds and/or low molecular weight hydroxy- and/or amino-functional components having a mean molecular weight of from 60 to 500.

9. Process according to claim 6 , wherein there are used as auxiliary substances and additives catalysts, UV stabilisers, antioxidants and/or mould release agents.

10. Process according to claim 6 , wherein the reacting of the reactants is carried out at a temperature of up to 180° C. and a pressure of up to 300 bar.