Cosolvent-free aqueous, anionic polyurethane dispersions and their use as peelable coatings

A process for the preparation of an aqueous, solvent-free coating composition, which is suitable for preparing light fast coatings and contain an anionic polyurethane dispersion which comprises the steps of

• I) preparing an NCO prepolymer a), optionally in the presence of an inert solvent having a boiling range of 50 to 100.degree. C. by reacting
• i) 20 to 60 wt. % of an aliphatic and/or cycloaliphatic diisocyanate,
• ii) 20 to 80 wt. % of a diol having a number average molecular weight of 500 to 10,000 and mixtures thereof,
• iii) 2 to 12 wt. % of a 2,2-bis-(hydroxymethyl)alkane monocarboxylic acid,
• iv) 0 to 15 wt. % of a diol having a molecular weight of 62 to 400, and
• v) 0 to 10 wt. % of a monofunctional alcohol as a chain terminating agent having a molecular weight of 32 to 350
• at a temperature of 50-150.degree. C.,
• II) subsequently reacting the NCO groups of the prepolymer with
• b) 0 to 15 wt. % of a diamine having a molecular weight in the range from 60 to 300 as a chain extender,
• c) 0 to 10 wt. % of a chain terminating agent comprising a member selected from the group consisting of monoamines, alkanolamines and ammonia,
• d) 0 to 30 wt. % of water, based on the solids,
• wherein b), c) and d) are added together or in any desired sequence,
• III) adding 0.1 to 10 wt. % of neutralizing agents and additional water, and
• IV after carrying out the reaction removing any insert solvent by distillation, optionally under reduced pressure, wherein the sum of the preceding percentages is 100% provided that the actual NCO content of prepolymer a) is 65 to 85% of the theoretical NCO content.