Process for the preparation of water-dilutable air-drying coating binders, and the use thereof

Claim 1

Process for the preparation of water-dilutable air-drying coating binders based on acrylic-modified and vinyl-modified alkyd resin emulsions, characterized in that A) monomer mixture containing a1) from 25 to 50% by weight of unsaturated fatty acids, a2) from 10 to 25% by weight of methacrylic acid, a3) from 1 to 15% by weight of (meth)acrylate monomers containing polyoxyalkylene groups, and a4) from 25 to 50% by weight of other (meth) acrylate and/or vinyl monomers containing no functional groups other than the C--C double bond is polymerized in the presence of a free-radical initiator to a conversion of at least 95% by weight, and B) in a further reaction step b1) from 33 to 44% by weight of copolymer (A), b2) from 20 to 42% by weight of unsaturated fatty acids, b3) from 10 to 25% by weight of polyalcohols having 2 to 6 hydroxyl groups, b4) from 10 to 20% by weight of aromatic and/or aliphatic dicarboxylic acids, b5) from 0 to 15% by weight of cyclic and/or polycyclic carboxylic acids, are reacted to form a modified alkyd resin (B), the sums of the percentages for components a1) to a4) and, respectively, b1) to b5) necessarily being 100 in each case, with the proviso that in stage (B) components b2) to b5) are pre-esterified until a clear melt and an acid number of from 3 to 30 mg of KOH/g are reached, said alkyd resin (B), based on the solids content, having a content of from 30 to 70% by weight, of unsaturated fatty acids, an intrinsic viscosity of from 8 to 15 ml/g (chloroform, 20° C.) and an acid number of from 25 to 70 mg of KOH/g, and at least 80% of the corresponding carboxyl groups deriving from methylacrylic acid units of the copolymer (A), and the modified alkyd resin (B) thus obtained is emulsified in water without the use of organic solvents.