| abstract |
The disclosure relates to an aqueous dispersion of one or more polyurethane resins with a number average mean molecular weight (Mn) of 2500-1000 000, containing 2-150 mMol of siloxane bridges (-Si-O-Si-) in each 100 g of solid resin, a hydroxyl number of 0-100 and a proportion of ionic groups, groups which can be converted to ionic groups and/or hydrophilic groups of 5-200 milli-Equivalents for 100 g of solid resin, as well as the process for producing the said dispersion by chain extension of a polyurethane prepolymer containing ionic groups, groups which are enabled to form ions and/or hydrophilic groups, the polyurethane prepolymer containing at least one R'OSi-group, in which R' is C1-8 alkyl or C(O)R''' and R''' is C1-10 alkyl. The chain extension is effected by the addition of water. The aqueous dispersion is suitable for use in aqueous coatings, especially those suitable as foundation varnish for multiple-coat varnishes. |