| 摘要 |
The present invention relates to a process for preparing aqueous polyurethane dispersions in a multi-step process by forming an NCO prepolymer by a) reacting a cyclic diisocyanate with a compound containing one or two isocyanate-reactive groups and at least one carboxylic acid or carboxylate group at a molar ratio of cyclic diisocyanate to compound containing one isocyanate-reactive group of at least 1:1 or a molar ratio of cyclic diisocyanate to compound containing two isocyanate-reactive groups of at least 1.5:1, b) adding a non-cyclic diisocyanate having 4 to 12 carbon atoms, a high molecular weight polyol having a number average molecular weight of 400 to 6000, optionally an isocyanate-reactive compound containing non-ionic hydrophilic groups and optionally an at least difunctional isocyanate-reactive compound having a number average molecular weight of less than 400 in amounts such that i) the molar ratio of cyclic diisocyanate to non-cyclic diisocyanate is 4:6 to 9:1 and ii) the overall equivalent ratio of isocyanate groups to isocyanate-reactive groups to prepare the NCO prepolymer is 1.1:1 to 2:1, c) dispersing the NCO prepolymer in water, d) neutralizing at least a portion of any carboxylic acid groups either before, during or after step c) and e) optionally adding a polyamine chain extender that contains a maximum of one unblocked primary or secondary amino group to the water either before, during or after the addition of the NCO prepolymer. The present invention is also directed to the aqueous polyurethane dispersions prepared by this process.
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