Self-crosslinking PU dispersions

A process for preparing self-crosslinking polyurethane polymers comprising:

• i) reacting an isocyanate component (A) having an isocyanate group functionality of 2 or more with (B1) an at least difunctional polyol component of number average molecular weight from 62 to 2500, which contains at least one acid-functional compound (C), to give an isocyanato-containing or hydroxyl-containing prepolymer,
• ii) adding one or more hydroxy-functional components (B2) having an OH functionality of 1 or more to said prepolymer, and, if desired, adding an isocyanate component (A′), which may be identical to or different from (A), with the proviso that the product of step ii) is an NCO-functional product,
• iii) mixing the resultant NCO-functional product with a blocking agent (D), and
• iv) adding a polyol component (B3) having an OH functionality of 2 or more and a number average molecular weight of from 300 to 5000.