Polyisocyanate mixtures, a process for their preparation and their use in coating compositions
The present invention relates to polyacrylate-modified polyisocyanates which are i) prepared from aromatic, araliphatic, cycloaliphatic and/or aliphatic polyisocyanates having an NCO content of 5% to 25% by weight, an NCO functionality ≧2 and a viscosity measured as solvent free resin of 150 to 200,000 mPa·s at 23° C., and ii) contain at least one structural unit of the formula (I) R is hydrogen or a methyl group, R 1 is an optionally heteroatom-containing hydrocarbon radical and R 2 is a hydrocarbon radical having at least one isocyanate group and optionally urethane, allophanate, biuret, uretdione, isocyanurate and/or iminooxadiazinedione groups and n is a number ≧1; and to processes for preparing these polyisocyanates and to binder compositions containing these polyisocyanates, which may be hydrophilically modified and a compound having NCO-reactive groups.
1. A process for preparing a liquid polyacrylate-modified polyisocyanate of the formula (I):
wherein R is hydrogen or a methyl group, R 1 is an optionally heteroatom-containing hydrocarbon radical, R 2 is a hydrocarbon radical having at least one isocyanate group and optionally a urethane, allophanate, biuret, uretdione, isocyanurate or iminooxadiazinedione group, and n is a number ≧1; the process comprising:
(a) providing a starting polyisocyanate selected from the group consisting of aromatic, araliphatic, cycloaliphatic, and aliphatic polyisocyanates and mixtures thereof having an NCO content of 5% to 25% by weight, an NCO functionality ≧2 and a viscosity measured as solvent free resin of 150 to 200,000 mPa·s at 23° C.;
(b) reacting a portion of the isocyanate groups of the starting polyisocyanate with a monoalcohol containing acrylate and/or methacrylate groups to form urethane groups, such that not more than 40 mole % of the isocyanate groups in the starting polyisocyanate are converted to urethane groups; and
(c) subsequently to or simultaneously with the urethanization, reacting the unsaturated groups of the resulting reaction product by free-radically initiated polymerization optionally with other additional unsaturated monomers, to form the liquid polyacrylate-modified polyisocyanate of the formula (I).
2. The process according to claim 1 , wherein the starting polyisocyanate comprises a polyisocyanate containing a urethane, uretdione, allophanate, biuret, isocyanurate or iminooxadiazinedione group and exclusively containing aliphatically and/or cycloaliphatically bound NCO groups.