Aqueously dispersible polyurethane

An aqueous dispersion comprising an aqueously dispersible polyurethane having a specific amount of substance of hydroxyl groups, —OH, of from 1 mol/kg to 4 mol/kg, and a specific amount of tertiary and/or quaternary aliphatic carbon atoms of from 0.01 mol/kg to 0.5 mol/kg, wherein the tertiary and quaternary carbon atoms are derived from tri- and tetravalent alcohols selected from the group consisting of trimethylolethane, trimethylolpropane, trimethylol butane, ditrimethylolethane, ditrimethylolpropane, ditrimethylolbutane, and pentaerythritol, and a specific amount of urea groups >N—CO—N<of from 0.8 mol/kg to 1.7 mol/kg, wherein in each case the specific amount of substance is based on the mass of the polyurethane, said branched aqueously dispersible polyurethane further having a specific amount of substance of acid and/or acid anion groups of from 0.1 mol/kg to 1.8 mol/kg or a specific amount of substance of basic and/or cationic groups of from 0.1 mol/kg to 1.8 mol/kg, and/or a mass fraction of oligo-oxyethylene groups of from 1% to 25%, wherein oligooxyethylene groups obey the formula —O—(—CH2—CH2—O—)n—CH2—CH2—O—, wherein n is from 1 to 100, obtained by a process comprising the steps of

• (1) preparing an aqueously dispersible branched polyurethane by
• (a)—preparing a hydroxy-functional polymer A having a number average molar mass of at least 400 g/mol, and at least two hydroxyl groups per molecule,
• (b)—mixing polymer A with a polyhydric organic compound A′ having at least three hydroxyl groups per molecule, and a molar mass of not more than 500 g/mol, selected from the group consisting of trimethylolethane, trimethylolpropane, trimethylol butane, ditrimethylolethane, ditrimethylolpropane, ditrimethylolbutane, and pentaerythritol, and with either or both of
• an acid B1 which is an hydroxy-functional or amino-functional acid having at least one hydroxyl or primary or secondary amino group and at least one acid group, and
• a polyether B2 which has oligo-oxyethylene groups obeying the formula II
• —O—(—CH2—CH2—O—)n—CH2—CH2—O—, (II)
• wherein n is from 1 to 100, and at least one hydroxyl group,
• or
• with either or both of
• a basic compound B3 which is a hydroxy-functional or amino-functional basic compound having at least one hydroxyl or primary or secondary amino group and at least one basic group which is optionally a tertiary amino group, and
• a polyether B2 which has oligo-oxyethylene groups obeying the formula II
• —O—(—CH2—CH2—O—)n—CH2—CH2—O—, (II)
• wherein n is from 1 to 100, and at least one hydroxyl group,
• (c)—reacting the mixture prepared in step (b) with at least one polyfunctional isocyanate C having at least two isocyanate groups per molecule, wherein the amount of isocyanate C is chosen such that there is a ratio of isocyanate groups in component C to hydroxyl groups present in the mixture prepared in step (b) of from 2:1 to 1.1:1, until at least 90% of the hydroxyl groups of the mixture prepared in step (b) are consumed by reaction with the isocyanate component C,
• (d)—adding to the reaction product of step (c) at least one of a hydroxyamine D having at least one primary or secondary amino group, and at least one hydroxyl group, a polyhydric alcohol E having at least two hydroxyl groups per molecule, and a polyfunctional amine F having at least two amino groups, each of the amino groups being selected from primary and secondary amino groups, in order to obtain an aqueously dispersible branched polyurethane,
• and
• (2)—dispersing the aqueously dispersible branched polyurethane obtained in step (d) in water, and optionally adding a chain extender G.