A method for producing a coating system providing corrosion-protective properties when applied to metal surfaces, particularly in the form of a water-based composition, preferably dispersion, wherein the method comprises producing, via emulsion polymerization in a two-stage radical polymerization process, a copolymer comprising moieties (i), (ii) and (iii) according to the following definition and each being different from one another: (i) a first ethylenically unsaturated monomer, the homopolymer of which has a glass transition temperature Tg (i) ranging from 30 °C to 200 °C, especially from 40 °C to 150 °C, (ii) a second ethylenically unsaturated monomer, the homopolymer of which has a glass transition temperature Tg (ii) ranging from -100 °C to -10 °C, especially from -60 °C to -20 °C, and (iii) a phosphate-group containing methacrylic monomer, wherein the phosphate-group containing methacrylic monomer is selected from phosphates and phosphate esters of polyalkylene glycol monomethacrylates and corresponds to the following general formula: in which formula • R 1 and R 2, independently from each other, represent hydrogen or alkyl, preferably C 1 -C 10 -alkyl, preferably wherein both of R 1 and R 2 represent hydrogen at the same time, • "Alk" represents a propylene rest; • "n" is a positive integer in the range of from 2 to 200, especially in the range of from 2 to 100, preferably in the range of from 2 to 50, more preferably in the range of from 2 to 25; wherein: (a) in a first stage (step), an emulsion prepolymerization of at least part of at least one of monomers (i) and (ii) is performed in the absence of monomer (iii), so as to produce an emulsion prepolymerization product to be used as a seed in the subsequent second stage (step) (b); and then (b) in a second stage (step), the emulsion prepolymerization product resulting from stage (a) and the remainder of monomers (i) and (ii), if any, are commonly polymerized together with and in the presence of monomer (iii), so as to yield a composition, preferably a dispersion, which contains a copolymer comprising moieties of (i), (ii) and (iii) with a (i)/(ii)/(iii)-weight ratio of / /, however, with the proviso that the sum of the weight shares results in 100. (i) a first ethylenically unsaturated monomer, the homopolymer of which has a glass transition temperature Tg (i) ranging from 30 °C to 200 °C, especially from 40 °C to 150 °C, (ii) a second ethylenically unsaturated monomer, the homopolymer of which has a glass transition temperature Tg (ii) ranging from -100 °C to -10 °C, especially from -60 °C to -20 °C, and (iii) a phosphate-group containing methacrylic monomer, wherein the phosphate-group containing methacrylic monomer is selected from phosphates and phosphate esters of polyalkylene glycol monomethacrylates and corresponds to the following general formula: in which formula • R 1 and R 2, independently from each other, represent hydrogen or alkyl, preferably C 1 -C 10 -alkyl, preferably wherein both of R 1 and R 2 represent hydrogen at the same time, • "Alk" represents a propylene rest; • "n" is a positive integer in the range of from 2 to 200, especially in the range of from 2 to 100, preferably in the range of from 2 to 50, more preferably in the range of from 2 to 25; • R 1 and R 2, independently from each other, represent hydrogen or alkyl, preferably C 1 -C 10 -alkyl, preferably wherein both of R 1 and R 2 represent hydrogen at the same time, • "Alk" represents a propylene rest; • "n" is a positive integer in the range of from 2 to 200, especially in the range of from 2 to 100, preferably in the range of from 2 to 50, more preferably in the range of from 2 to 25; (a) in a first stage (step), an emulsion prepolymerization of at least part of at least one of monomers (i) and (ii) is performed in the absence of monomer (iii), so as to produce an emulsion prepolymerization product to be used as a seed in the subsequent second stage (step) (b); and then (b) in a second stage (step), the emulsion prepolymerization product resulting from stage (a) and the remainder of monomers (i) and (ii), if any, are commonly polymerized together with and in the presence of monomer (iii), so as to yield a composition, preferably a dispersion, which contains a copolymer comprising moieties of (i), (ii) and (iii) with a (i)/(ii)/(iii)-weight ratio of / /, however, with the proviso that the sum of the weight shares results in 100.