| abstract |
The invention relates to a polyurethane with a number average molecular weight Mn of 3,000 to 50,000 and an acid number of 10 to 35. Said polyurethane is produced by reacting (a1) at least one polyesterpolyol with a number average molecular weight Mn of 1,000 to 4,000, preferably 1,200 to 3,000, an acid number of 0 to 15, preferably 0 to 10, and an OH number of 35 to 150, preferably 50 to 120, on the basis of acyclic aliphatic and cycloaliphatic dicarbonic acids, (a2) a mixture of at least one diol and one triol, (a3) at least one compound having at least two functional groups (a31) that are reactive with isocyanate and at least one functional group (a32) that is capable of forming anions, and (a4) a mixture of at least one acyclic aliphatic and at least one cycloaliphatic diisocyanate. The result of said reaction is a prepolymer that contains isocyanate groups. The prepolymer is subjected to a chain extension reaction with a multifunctional amine or amine alcohol and is optionally neutralized. The invention also relates to the use of said polyurethane for producing polyurethane dispersions and coating substances for painting plastic. |