Process for the preparation of aqueous polyurethane dispersions and solutions
First Claim
1. A process for the preparation of aqueous solutions or dispersions of polyurethanes prepared by the reaction of prepolymers which have at least two free isocyanate groups and contain either chemically fixed hydrophilic groups and/or external emulsifiers which are not chemically fixed, with chain lengthening agents in the aqueous phase, characterized in that the isocyanate prepolymer which is hydrophilically modified and/or contains an external emulsifier is mixed with azine chain lengthening agents in the absence of water, and the resulting mixture is then mixed with water before significant increases in viscosity occur.
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Abstract
The present invention relates to a process for the preparation of aqueous solutions or dispersions of polyurethanes, in which process prepolymers which have at least two free isocyanate groups and contain chemically-fixed hydrophilic groups and/or external emulsifiers which are not chemically fixed are reacted with chain lengthening agents in the aqueous phase, characterized in that the isocyanate prepolymer which is hydrophilically modified and/or contains an external emulsifier is mixed with chain lengthening agents selected from the group consisting of azines and hydrazones in the absence of water and the mixture obtained is then mixed with water. The present invention also relates to the dispersions or solutions which can be obtained by this process. Lastly, this invention relates to the use of the dispersions or solutions which can be obtained by this process for coating flexible substrates.
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Citations
18 Claims
- 1. A process for the preparation of aqueous solutions or dispersions of polyurethanes prepared by the reaction of prepolymers which have at least two free isocyanate groups and contain either chemically fixed hydrophilic groups and/or external emulsifiers which are not chemically fixed, with chain lengthening agents in the aqueous phase, characterized in that the isocyanate prepolymer which is hydrophilically modified and/or contains an external emulsifier is mixed with azine chain lengthening agents in the absence of water, and the resulting mixture is then mixed with water before significant increases in viscosity occur.
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7. A process for the preparation of aqueous solutions or dispersions comprising
(A) mixing in the absence of water (i) a hydrophilic isocyanate prepolymer having (a) an average isocyanate functionality of from about 1.8 to 2.2; -
(b) its hydrophilic properties contributed by dispersing centers selected from the group consisting of chemically incorporated cationic or anionic groups present in from about 0 to 100 milliequivalents per 100 g of isocyanate prepolymer, chemically incorporated ethylene oxide units present in the isocyanate prepolymer in from about 0 to 30% by weight, based on the weight of the isocyanate prepolymer, and external emulsifiers present in about 0 to 30% by weight, based on the weight of the isocyanate prepolymer; and (c) an average molecular weight of from about 500 to 10,000 (ii) with an azine chain lengthening agent which forms hydrazine under the hydrolytic influence of water to form a mixture and (B) mixing the mixture of (A), before significant increases in viscosity occur, with water to release the hydrazine and chain lengthen the prepolymer. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15)
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16. A process for the preparation of aqueous solutions or dispersions of polyurethanes prepared by the reaction of prepolymers which have at least two free isocyanate groups and contain either chemically fixed hydrophilic groups and/or external emulsifiers which are not chemically fixed, with chain lengthening agents in the aqueous phase, characterized in that the isocyanate prepolymer which is hydrophilically modified and/or contains an external emulsifier is mixed with hydrazone chain lengthening agents in the absence of water, and the resulting mixture is then mixed with water, before significant increases in viscosity occur.
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17. A process for the preparation of aqueous solutions or dispersions comprising:
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(A) mixing in the absence of water (i) a hydrophilic isocyanate prepolymer having (a) an average isocyanate functionality of from about 1.8 to 2.2; (b) its hydrophilic properties contributed by dispersing centers selected from the group consisting of chemically incorporated cationic or anionic groups present in from about 0 to 100 milliequivalents per 100 g of isocyanate prepolymer, chemically incorporated ethylene oxide units present in the isocyanate prepolymer in from about 0 to 30% by weight, based on the weight of the isocyanate prepolymer, and external emulsifiers present in about 0 to 30% by weight, based on the weight of the isocyanate prepolymers; and (c) an average molecular weight of from about 500 to 10,000 (ii) with an at least partially blocked hydrazone chain lengthening agent which forms hydrazine under the hydrophilic influence of water to form a mixture, and (B) mixing the mixture of (A), before significant increases in viscosity occur, with water to release the hydrazine and chain lengthen the prepolymer. - View Dependent Claims (18)
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Specification