| abstract |
The present invention relates to aqueous polyurethane dispersions wherein the polyurethanes are reaction products ofA) at least difunctional polyols having a molecular weight of 500 to 6000,B) at least difunctional low molecular weight alcohols,C) di- and/or trifunctional isocyanates andD) compounds with an acid group and one or two hydroxy- and/or primary or secondary amino groups in an amount sufficient to provide an acid number, based on resin solids, of <25 mg KOH/g of substance,whereini) the neutralizing agent is added in an amount sufficient to neutralize 40 to 105% of the acid groups and an amount sufficient to neutralize at least 60% of the acid groups is added prior to the chain extension reaction,ii) at least 1 wt. % of components A) and B), based on the total weight of components A) to D), are tri- or higher-functional compounds andiii) the polyurethane contains 1 to 4 wt. % of the urea groups formed by the reaction of water and isocyanate groups.The present invention also relates to a process for preparing these polyurethane dispersions and to coating compositions containing these polyurethane dispersions. |