Process for the continuous production of an aqueous polyurethane dispersion
View Patent ↗A process for the continuous production of an aqueous polyurethane dispersion based on at least one aliphatic and/or aromatic polyisocyanate is described, which is characterised by the following steps: a) production of an aqueous pre-emulsion by mixing a polyurethane prepolymer containing hydrophilic and/or potentially hydrophilic groups with water in a mixing nozzle, wherein the polyurethane prepolymer is injected into the water; b) formation of an emulsion by homogenization of the pre-emulsion from step a) in a multi-step homogenizing nozzle. Paint films containing the aqueous polyurethane dispersion produced by the process can be used to coat substrates.
1. A process for the continuous production of an aqueous polyurethane dispersion based on at least one aliphatic and/or aromatic polyisocyanate, comprising the steps of:
a) producing an aqueous pre-emulsion by mixing a polyurethane prepolymer containing hydrophilic and/or potentially hydrophilic groups with water in a mixing nozzle, wherein the polyurethane prepolymer is injected into the water; and
b) forming an emulsion by homogenizing the pre-emulsion from step a) in a multi-step homogenizing nozzle comprising between 2 and 20 nozzles and/or dispersers.
2. The process according to claim 1 further comprising step c), at least a partially reacting the emulsion containing free NCO groups from step b) with at least one amine that is reactive towards isocyanate groups.
3. The process according to claim 2 , wherein the reaction with an amine according to step c) takes place continuously in a mixing nozzle.
4. The process according to claim 1 , wherein the production of the pre-emulsion according to step a) takes place with a pressure difference of 0.1 to 100 bar.
5. The process according to claim 1 , wherein the formation of the emulsion according to step b) takes place with a pressure difference of 1 to 200 bar.
6. The process according to claim 1 , wherein 2 to 20 steps are used for the homogenizing according to step b).
7. The process according to claim 1 , wherein a jet disperser is used as the homogenizing nozzle in step b).
8. The process according to claim 1 , wherein a jet disperser is used as the mixing nozzle in step a).
9. The process according to claim 1 , wherein the temperature of the polyurethane prepolymer in step a) is 10° C. to 100° C.
10. The process according to claim 1 , wherein the temperature of the water in step a) is 5° C. to 95° C.
11. The process according to claim 1 , wherein the formation of the emulsion according to step b) takes place with a pressure difference of 3 to 100 bar.
12. The process according to claim 1 , wherein the formation of the emulsion according to step b) takes place with a pressure difference of 5 to 60 bar.
13. The process according to claim 1 , wherein the production of the pre-emulsion according to step a) takes place with a pressure difference of 0.2 to 50 bar.
14. The process according to claim 1 , wherein the production of the pre-emulsion according to step a) takes place with a pressure difference of 0.5 to 20 bar.
15. The process according to claim 2 , wherein jet dispersers are used in the homogenizing nozzle in step b).
16. The process according to claim 3 , wherein jet dispersers are used in the homogenizing nozzle in step b).
17. The process according to claim 2 , wherein the temperature of the polyurethane prepolymer in step a) is 10° C. to 100° C. and the temperature of the water in step a) is 5° C. to 95° C.
18. The process according to claim 3 , wherein the temperature of the polyurethane prepolymer in step a) is 10° C. to 100° C. and the temperature of the water in step a) is 5° C. to 95° C.