Aqueous polyester-polyurethane dispersions and their use in coating compositions

An aqueous dispersion of polyester-polyurethanes having an acid number of 5 to 60 mg KOH/g, a hydroxyl group content of 0.25 to 6.5% by weight and a urethane group content (calculated as --NH--CO--O--) of 2 to 25% by weight, wherein these ranges are based on polyester-polyurethane solids and wherein the polyester-polyurethanes are reaction products, optionally at least partly neutralized by bases, of

• a) 15 to 90% by weight of one or more essentially linear, polyester polyols having a molecular weight of 500 to 4000, other than those which satisfy the requirements of component b), in which the polyester polyols are reaction products of
• a1) 30 to 65% by weight of an acid component selected from the group consisting of adipic acid, sebacic acid, azelaic acid, hydrogenated dimeric fatty acids and mixtures thereof,
• a2) 20 to 65% by weight of a diol component selected from the group consisting of ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol and mixtures thereof and
• a3) 0 to 15% by weight of an acid component selected from the group consisting of phthalic anhydride, isophthalic acid, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, dimeric fatty acids containing high proportions of trimeric fatty acids, hydrogenated fatty acids, isononanoic acid, 2-ethylhexanoic acid and mixtures thereof and
• a4) 0 to 7% by weight of a triol component selected from the group consisting of trimethylolpropane, glycerol and mixtures thereof,
• wherein the sum of the percentages of components a1) to a4) is 100,
• b) 4 to 75% by weight of one or more essentially difunctional polyols selected from i) polycarbonates having a molecular weight of 400 to 6000 and ii) dimeric fatty alcohols obtained by the hydrogenation of the carboxyl groups of dimeric fatty acids to hydroxyl groups, the alkoxylation of the carboxyl groups of dimeric fatty acids or the esterification of the carboxyl groups of dimeric fatty acids using low molecular weight diols,
• c) 1 to 10% by weight of one or more acidic components selected from i) hydroxycarboxylic acids, ii) amino acids, iii) aminosulphonic acids and iv) alkali salts of the acids of i), ii) and iii),
• d) 0 to 20% by weight of a low molecular weight component selected from compounds which have a molecular weight of 60 to 300 and contain at least two hydroxyl and/or amino groups,
• e) 0 to 20% by weight of one or more hydrophilic monovalent or divalent alcohols which have a molecular weight of 350 to 3000 and contain lateral and/or terminal ethylene oxide units and
• f) 5 to 50% by weight of a polyisocyanate component selected from organic polyisocyanates having a molecular weight of 168 to 1000, provided that at least 50% by weight of the polyisocyanate component is selected from linear aliphatic diisocyanates having a molecular weight of 168 to 300,
• wherein the sum of the percentages of components a) to f) is 100.