Aqueous polyurethane-ureas dispersions and their use for the production of coatings having improved humidity resistance

Claim 1

A stable, aqueous dispersion of polyurethane-ureas in admixture with an epoxy resin which is formed by a process which comprises (a) preparing an isocyanate-terminated prepolymer containing about 5 to 190 milliequivalents per 100 grams of polyurethane-urea of chemically incorporated potential anionic groups and/or anionic groups, and up to about 10% by weight, based on the weight of the polyurethane-urea, of lateral and/or terminal hydrophilic chains containing ethylene oxide units, (b) converting a sufficient amount of said potential anionic groups to anionic groups either before, during or after preparing said prepolymer such that the blend of step (c) can be stably dispersed in water, wherein at least about 50% of the counterions of said anionic groups are derived from volatile organic compounds, (c) blending said prepolymer either before, during or after step (b) with an epoxy resin which is not self-dispersible in water and contains at least one epoxide group, such that the equivalent ratio of potential anionic groups and anionic groups having counterions derived from volatile organic compounds to epoxide groups is about 0.2 to 20.0, (d) dispersing the blend of prepolymer and epoxy resin in water and (e) chain extending said prepolymer with a polyamine having an average functionality of about 2.0 to about 6.0 in an amount sufficient to provide a ratio of amino groups to isocyanate groups of about 0.6:1.0 to 1.0:1.0.