Low-viscosity polyurethane acrylate dispersions

A process for preparing a radiation-curable, aqueous dispersion based on a polyurethane acrylate (i) comprising as structural components

• A) one or more polymeric compounds selected from the group consisting of polyester (meth)acrylates, polyether (meth)acrylates, polyether ester (meth)acrylates, unsaturated polyesters having allyl ether structural units, and polyepoxy (meth)acrylates having an OH number in the range from 15 to 300 mg KOH/g of substance;
• B) optionally one or more monomeric compounds other than A) comprising a hydroxy function and at least one (meth)acrylate group;
• C) one or more compounds other than A) or B) comprising at least one group reactive towards isocyanate;
• D) one or more organic polyisocyanates;
• E) one or more compounds comprising at least one hydroxy function and, in addition, at least one carboxylic acid or carboxylate function, wherein said compounds have a dispersing action for the polyurethane dispersion;
• F) compounds other than A) to E) comprising at least one group reactive towards isocyanate;
• wherein components A) through D) are reacted in a first reaction step to form a polyurethane acrylate which comprises neither ionic nor potentially ionic groups and, after determination of the NCO content, an NCO value is reached which can differ from the theoretical NCO content by up to 1.5 wt. % NCO (absolute);
• and
• in a second reaction step, component E) is reacted with any free NCO groups from the reaction product of components A) to D) and, after again determining the NCO content, an NCO value is reached which can differ from the theoretical NCO value by up to 1.5 wt. % NCO (absolute);
• and
• in a third reaction step, component F) is reacted with any free NCO groups.