Anionically stabilized aqueous polyvinylbutyral dispersions and process for their preparation and use

A process for the preparation of water-dilutable polyvinylbutyral dispersions, which comprises reacting

• A an aliphatic acid having from one to three groups which are reactive toward isocyanate and from one to three acid groups, or a mixture of such acids, with
• B one or more polyfunctional isocyanates whose average functionality is at least two,
• wherein the quantity of the isocyanate component B is chosen such that the ratio of the number of isocyanate groups to the number of groups of component A which are reactive toward isocyanate is between 2.2:1 and 1.7:1;
• continuing the reaction until at least 70% of the isocyanate reactive groups have been consumed;
• thereafter reacting from 25 to 75% of the residual isocyanate groups with
• C at least one monofunctional compound selected from monoalcohols and monoamines to produce an NCO-functional emulsifier resin;
• and
• further reacting this NCO-functional emulsifier resin with
• D a mixture of proportions by mass of
• D1 from 30 to 100% of polyvinylbutyral and
• D2 from 0 to 70% of a plasticizer resin or of a mixture of plasticizer resins, in the presence of an auxiliary solvent, until achievement of substantially complete conversion of all isocyanate groups, with the proviso that the sum of the proportions by mass of D1 and D2 is 100% and the reaction product formed is a resin having a quantity of acid groups which is such that the acid number based on solid resin is between 5 and 50 mg/g.