| 摘要 |
The present invention relates to a process for the preparation of aqueous dispersions or solutions of polyurethanes which have urea end groups and contain non-ionic hydrophilic segments and which are capable of being cross-linked with the aid of cross-linking agents which are reactive with urea groups, characterized in that prepolymers which have isocyanurate end groups and which (i) have an average molecular weight of less than about 15,000 and (ii) contain from about 2 to 30%, by weight, of ethylene oxide units corresponding to the following formula: -CH2-CH2-O- within a polyether chain (containing ethylene oxide units) are reacted at from about 10 DEG to 70 DEG C. with an aqueous solution of ammonia or with a primary amine, optionally dissolved in water, the aqueous solution of ammonia or the primary amine, optionally dissolved in water, being added to the prepolymer in the reaction vessel and the quantity of water used for dissolving the ammonia or primary amine being not more than about 10%, by weight, based on the total quantity of reaction mixture, and finally, after termination of the addition reaction between the free isocyanate groups of the prepolymer and the added ammonia or primary amine, the reaction product obtained is stirred with water at from about 10 DEG to 70 DEG C. to form an aqueous dispersion or solution having a concentration of from about 5 to 65%, by weight. The present invention also relates to the use of dispersions or solutions obtainable by the process according to the present invention for the production of cross-linked sheets by application of the dispersion to a substrate and drying, cross-linking of the sheet being ensured by the addition of a cross-linking agent capable of undergoing a cross-linking reaction with the urea groups either before, during or after application of the solution or dispersion to the substrate.
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