Polyisocyanate mixtures

1. A polyisocyanate mixture which is liquid at temperatures above −5° C. and is based on diphenylmethane 2,4′-diisocyanate, wherein

A) the NCO content of said polyisocyanate mixture is 14.5 to 24% by weight;

B) the content of isocyanate groups bonded in the 2 position of said polyisocyanate mixture is greater than 50%; and

C) the content of allophanate groups (calculated as C 2 HN 2 O 3 having a molecular weight of 101) of said polyisocyanate mixture is 7.7 to 17.6% by weight

wherein said diphenylmethane 2,4′-diisocyanate is pure 2,4′- isomer or a mixture of 2,4′- isomer with up to 2.0% by weight of diphenylmethane 4,4′-diisocyanate and/or up to 1.0% by weight of diphenylmethane 2,2′-diisocyanate, based on the total weight of said polyisocyanate mixture and

wherein said polyisocyanate mixture comprises reaction products prepared with intermediate urethane formation from

A) diphenylmethane 2,4′-diisocyanate with

B) monohydric alcohols having 3 to 18 carbon atoms per molecule while maintaining an NCO/OH ratio of 4:1 to 8.5:1.

2. The polyisocyanate mixture of claim 1 , wherein said polyisocyanate mixture comprises reaction products prepared with intermediate urethane formation from A) diphenylmethane 2,4′-diisocyanate with B) linear, monohydric alcohols having 4 to 10 carbon atoms.

3. A process for preparing a polyisocyanate mixture which is liquid at temperatures between −5 and +5° C. and are based on diphenylmethane 2,4′-diisocyanate, wherein said diphenylmethane 2,4′-diisocyanate is pure 2,4′- isomer or a mixture of 2,4′- isomer with up to 2.0% by weight of diphenylmethane 4,4′-diisocyanate and/or up to 1.0% by weight of diphenylmethane 2,2′-diisocyanate, based on the total weight of said polyisocyanate mixture, comprising reacting said diphenylmethane 2,4′-diisocyanate with monohydric alcohols having 3 to 18 carbon atoms per molecule while maintaining an NCO/OH ratio of 4:1 to 8.5:1 at temperatures up to 160° C. with intermediate urethane formation, wherein said reaction is carried out no later than after completion of urethane formation in the presence of a catalyst which promotes allophanate formation.

4. The process of claim 3 , wherein said catalyst comprises a compound of the third or fourth main group or of transition group 1, 2, 6, 7 or 8 of the Periodic Table of the Elements, and which are soluble in the reaction mixture.

5. The process of claim 4 , wherein said catalyst used comprises tin (II) octoate or zinc acetylacetonate.

6. An isocyanate-functional prepolymer, a polyurethane dispersion, a polyurethane solution, or a silane-terminated prepolymer comprising the polyisocyanate mixture of claim 1 as polyisocyanate component.

7. An isocyanate-functional prepolymer, a polyurethane dispersion, a polyurethane solution, or a silane-terminated prepolymer comprising the polyisocyanate mixture of claim 2 as polyisocyanate component.

8. A single- or two-component polyurethane coating composition comprising the polyisocyanate mixture of claim 1 as polyisocyanate component.

9. A single- or two-component polyurethane coating composition comprising the polyisocyanate mixture of claim 2 as polyisocyanate component.

10. An adhesive comprising a compound obtained from the polyisocyanate mixture of claim 1 .

11. An adhesive comprising a compound obtained from the polyisocyanate mixture of claim 2 .

12. A sealant comprising a compound obtained from the polyisocyanate mixture of claim 1 .

13. A sealant comprising a compound obtained from the polyisocyanate mixture of claim 2 .