The present invention is related to a radiation curable binder, comprising the reaction product of a polyisocyanate having 3 free isocyanate moieties with an acrylate having isocyanate-reactive groups and a component selected from the group consisting of a C12-C22 carboxylic acid having one isocyanate-reactive group or a C12-C22 fatty alcohol. The present invention is furthermore related to a radiation curable printing ink, comprising said binder, at least one diluent, at least one pigment, and optionally additives, as well as to a process of preparing said radiation curable binder. Said binder or said printing ink can be used in offset printing or letterpress printing.