Heat-curable aqueous coating compositions

A binder for a heat-curable aqueous coating composition for metallic surfaces comprising:

• (A) 60-95% by weight of a water-soluble and/or water-dispersible addition compound of
• 10-35% by weight of one or more .alpha.,.beta.-unsaturated dicarboxylic acids have up to 8 carbon atoms and the formula ##STR7## wherein R and R' are an H atom, a halogen atom or an alkyl group;
• X and Y are a hydroxy group, an alkoxy group or an oxygen bond which is formed of X and Y together, assuming that X and Y are not simultaneously an alkoxy group;
• and
• 6- 90% by weight of a butadiene polymer which is liquid at 20.degree. C., contains at least 50 mole% of butadiene units and has a molecular weight of 400 to 6,000,
• the addition compound being at least partially neutralized with a basic compound and partially esterified,
• and
• (B) 5-40% by weight of a water-soluble and/or waterdispersible crosslinking resin having, on the average, at least 2 chemically different reactive groups per mole,
• wherein the addition compound (A) is esterified to 10-70 equivalent percent, based on its acid number, with one or more unsaturated alcohols of the formula ##STR8## and wherein at least one of the reactive groups of the crosslinking resin (B) is of formula II ##STR9## and at least one reactive group is a reactive group of a conventional, crosslinkable, phenolic resin, amino resin or isocyanate resin,
• wherein for both formulae I and II,
• R.sup.1, R.sup.2 and R.sup.3 can be identical or different and each independently is hydrogen or methyl,
• R.sup.4 is hydrogen or C.sub.1-5 -alkyl, and n is 0 or 1.