Process for the preparation of stable aqueous dispersions of oligourethanes or polyurethanes and their use as coating compounds for flexible or rigid substrates

A process for the preparation of storage stable, aqueous dispersions of oligo-or polyurethanes containing chemically fixed ionic and/or non-ionic hydrophilic groups in an amount sufficient to ensure dispersibility in water, and auxiliary agents or additives which are neither dispersible nor soluble in water selected from the group consisting of cellulose ethers, cellulose esters of inorganic or organic acids and natural or synthetic waxes, by converting oligourethanes having a molecular weight below about 20,000 which contain chemically fixed potential ionic, ionic, or non-ionic hydrophilic groups and optionally groups enabling a chain lengthening or cross-linking reaction, into an aqueous dispersion by mixing with water, optionally with simultaneous or subsequent chain lengthening of the oligourethanes by a reaction with a chain lengthening agent and optionally with at least partial conversion of any potential ionic groups present into ionic groups, characterized in that before the oligourethanes are dispersed in water, they are intimately mixed in the liquid phase to form a mixture which contains up to 20% by weight solvent based on the weight of the oligourethanes, optionally at an elevated temperature, with said auxiliary agents or additives, or said auxiliary agents or additives are incorporated with one of the starting compounds used for the preparation of the oligourethanes.