Aqueous coating composition for corrosion protection

An aqueous resin dispersion D comprising a mixture of a hydrophilically modified epoxy-based resin P and a resole R, and a co-crosslinker E, wherein the hydrophilically modified epoxy-based resin P is made in a reaction or a sequence of reactions which includes at least one step where an advancement reaction is conducted,

• wherein the hydrophilically modified epoxy-based resin P is a non-ionically modified epoxy-based resin Pn,
• wherein the non-ionically modified epoxy-based resin Pn is made by
• synthesizing an emulsifier F which has a nonionic portion which comprises a polyoxyethylene homopolymer or copolymer segment or a sugar alcohol segment, and a non-hydrophilic and compatibilising portion which comprises building blocks derived from epoxide compounds which are at least difunctional, by coupling of the at least difunctional epoxide compounds with hydroxy-functional polyoxyethylene homopolymers or hydroxy-functional polyoxyethylene copolymers or with sugar alcohols catalysed with strong Brønsted acids or Lewis acids, or with epoxide-functional polyoxyethylene homopolymers or epoxide-functional polyoxyethylene copolymers or with epoxide-functional sugar alcohols, and
• incorporation of the emulsifier F into an epoxy resin via an advancement reaction with a diepoxide A1, a dihydric aromatic compound A2, and the emulsifier F, in the presence of a phosphine or amine catalyst, wherein the stoichiometry is chosen such that the advancement reaction product has epoxide end groups, and
• wherein the co-crosslinker E is selected from the group consisting of
• a compound E1 having at least two hydroxyl groups that react with acid compounds present in a coating composition at elevated temperature above 80° C. under ester formation and liberation of water, and
• an ester E2 with at least two ester groups formed by an at least dihydric alcohol E22 and an acid E21 which acid is unstable at elevated temperature above 80° C.