Blocked biuretized isocyanates

1. A blocked biuret group-containing polyisocyanate composition having a blocked isocyanate functionality of at least 4 prepared by a process comprising

A) reacting a polyisocyanate adduct which

a) is prepared from an aliphatic and/or cycloaliphatic diisocyanate,

b) has an isocyanate functionality of at least 2.5 and

c) which contains isocyanurate groups,

with a biuretizing agent to incorporate biuret groups into said polyisocyanate, and

B) reacting the biuret-containing polyisocyanate with a blocking agent of the formula:

wherein

R 1 , R 2 , R 3 and R 4 may be the same or different and represent a moiety selected from the group consisting of hydrogen, C 1 -C 6 -alkyl and C 3 -C 6 -cycloalkyl,

R 5 represents a moiety selected from the group consisting of C 1 -C 10 -alkyl and C 3 -C 10 -cycloalkyl, and

B is a group according to one of the following structural formulas

wherein each occurrence of R 6 , R 7 , and R 8 may be the same or different and represent a moiety selected from the group consisting of C 1 -C 6 -alkyl and C 3 -C 6 -cycloalkyl and

R 9 is a moiety selected from the group consisting of hydrogen, C 1 -C 6 -alkyl and C 3 -C 6 -cycloalkyl.

2. The composition of claim 1 , wherein said adduct has an isocyanate functionality of at least 2.8.

3. The composition of claim 2 , wherein said adduct has an isocyanate functionality of at least 3.0 and an isocyanate functionality of no more than 8.

4. The composition of claim 2 , wherein component A)a) is an aliphatic diisocyanate.

5. The composition of claim 2 , wherein said biuretizing agent is selected from the group consisting of water, secondary amines and tertiary alcohols.