Process for the manufacture of heat-curable synthetic resins which can be diluted with water and are suitable for the electrophoretic coating process

Process for the manufacture of heat-curable synthetic resins, based on reaction products of maleic anhydride with mixtures of polybutadiene, unsaturated hydrocarbon resins and unsaturated fatty acid glyceride esters, which can be diluted with water and are suitable for the electrophoretic coating process, characterized in that a mixture consisting of

• a. 20-60% by weight of a polybutadiene having an average molecular weight of 750-2,000 and an iodine number between 300 and 450,
• b. 10-60% by weight of a hydrocarbon resin of predominantly aliphatic structure, having a viscosity between 30 and 800 cP, measured in 70% strength solution in toluene at 20.degree.C. and an iodine number of between 160 and 400, consisting of
• b.sub.1. 20-80% by weight of polyisoprene,
• b.sub.2. 5-50% by weight of cyclopentadiene and/or dicyclopentadiene, and
• b.sub.3. 5-50% by weight of further mono-unsaturated or poly-unsaturated hydrocarbons with 5-6 C atoms which are of predominantly aliphatic or cycloaliphatic structure, and
• c. 5-40% by weight of a fatty acid glyceride ester, wherein each fatty acid radical contains 16-18 C atoms and the fatty acid glyceride ester has an iodine number between 140 and 220,
• is pre-polymerized by heating to 200.degree.-270.degree.C. until the reaction mixture of components (a), (b) and (c), which has an initial viscosity of about 100 to 300 sec., measured according to DIN 53,211, displays viscosities between 500 and 2,000 sec., measured according to DIN 53,211, the resulting mixture is then reacted with
• d. 10-20% by weight of maleic anhydride at 180.degree. to 190.degree.C., until no further free maleic anhydride is present, the sum of components (a), (b), (c) and (d) employed having to add up to 100 % by weight, and
• e. in the resulting adduct the anhydride groups present are opened by hydrolysis with water or alcoholysis with the amount of monohydric alcohols with 1-4 C atoms required to form the half-ester.