| abstract |
The present invention relates to a process for the preparation of polyurethane dispersions comprising the steps of: 1) providing an isocyanate-functional prepolymer A) in a liquid phase comprising a water-miscible solvent having a lower boiling point than water, and II) adding the NCO-reactive compound to the isocyanate-functional prepolymer from step I), whereby the reaction with the prepolymer takes place at least partially; wherein the liquid phase in step I) additionally comprises water and/or After step II), water is added to the mixture obtained after step II). Before and/or during carrying out step II), a pressure p1 is applied over the liquid mixture with the isocyanate-functional prepolymer A), wherein p1 is less than the atmospheric pressure locally present at this point in time. The pressure p1 is chosen such that in step II) ≤50 mass % (preferably >0 to ≤40 mass %, more preferably ≥0.1 to ≤30 mass %, further preferably ≥1 to ≤ 10% by mass) of the initially present water-miscible solvent. |