A process for the preparation of dual-cure hardeners, coating systems which contain these hardeners, and the use of these coating systems, as well as substrates coated with these coating agents. The dual-cure hardeners are prepared by reacting at least one diisocyanate or polyisocyanate A with the product B of the reaction of B1 acrylic acid, methacrylic acid and/or dimeric acrylic acid with B2 glycidyl methacrylate and/or glycidyl acrylate, wherein B contains less than 0.2 wt. % of epoxide groups.