| abstract |
An aqueous polyurethane dispersion comprising A) a polyurethane prepolymer with an NCO content of 1 to 6% by weight, prepared by reacting: a) a mixture of isocyanates comprising i) 5 to 50% by weight of an isocyanate aliphatic and / or cycloaliphatic, and ii) from 50 to 95% by weight of an aromatic diisocyanate, b) a di or polyhydroxy compound with a number average molecular weight of 700 to 16,000, and c) optionally, a dihydroxy and / or polyhydroxy compound with a number average molecular weight of less than 700, with the proviso that 1) at least one of the components a), b) or c) has a functionality greater than 2 and 2) if both components a) and b) are difunctional, the component c) cannot be a trihydroxy component of the formula: R- (OH) 3 in which R is a saturated straight chain or branched chain aliphatic group of 2 to 8 carbon atoms, B) a compound having an anionic group or potentially anionic and two groups that are reactive c on the isocyanate groups and C) a chain extender that has two amine groups that are reactive with the isocyanate groups. |