The present invention relates to a radiation-curable, aqueous polyurethane emulsion which is prepared by I) reacting A) 40 to 90 wt. % of an isocyanate-reactive component that contains a polyester acrylate containing hydroxyl groups and having an OH content of 40 to 200 mg KOH/g and optionally other isocyanate-reactive compounds other than B) and B) 0.5 to 20 wt. % of one or more monofunctional and/or difunctional isocyanate-reactive compounds that contain cationic or anionic groups, potential cationic or anionic or hydrophilic ether groups, with C) 10 to 50 wt. % of one or more diisocyanates and/or polyisocyanates, II) optionally converting any potential cationic or anionic groups into cationic or anionic groups by salt formation and III) forming a dispersion of the reaction product of A), B) and C) in water and reacting it with D) 0.1 to 10 wt. % of one or more diamines and/or polyamines, wherein the wt. % percentages of (A) to (D) add up to 100%, and the equivalent ratio of the sum of the isocyanate-reactive groups in (A) and (B) to the isocyanate groups in (C) is 0.8:1 to 1.25:1 and the reaction of components (A) and (B) with (C) is carried out such that 65 to 95% of the isocyanate groups in (C) react with the isocyanate-reactive groups of (A) and (B). The present invention also relates to a process of making these polyurethane emulsions and to substrates coated with the polyurethane emulsions.