An aqueous multistage polymer dispersion obtainable by free-radically initiated aqueous emulsion polymerization, having a soft phase and a hard phase, and a hard-to-soft stage ratio of 25% to 95% by weight to 75% to 5% by weight, the glass transition temperature (Tg) of the soft phase, as first stage, being -30 to 0°C and that of the hard phase, as second stage, being 20 to 60°C, comprising at least one monomer of the general formula I in which the variables have the following definitions: n = 0 to 2, R1, R2, R3 = independently of one another hydrogen or methyl group, X = 0 or NH, Y = H, alkali metal, NH 4, wherein the polymer of the first stage is a copolymer which (i) is used in an amount of 5% to 50% by weight, based on 100 parts by weight of the total monomers to be polymerized in the first and second stages, and which (ii) is composed to an extent of at least 80% and up to 99% by weight of principal monomers selected from the group consisting of C1 to C10 alkyl (meth)acrylates, amides and hydroxyalkyl esters of α,β-unsaturated C 3 -C 6 carboxylic acids, more preferably acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate or 1,4-butanediol monoacrylate, and mixtures of these monomers, more preferably n-butyl acrylate, methyl methacrylate, and acrylamide, and (iii) comprises to an extent of at least 0.1% and up to 5% by weight, monomers I, which are preferably selected from the group of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), methacrylic acid 3'-sulfopropyl ester, acrylic acid 3'-sulfopropyl ester, methacrylic acid 2'-sulfoethyl ester. n = 0 to 2, R1, R2, R3 = independently of one another hydrogen or methyl group, X = 0 or NH, Y = H, alkali metal, NH 4, wherein the polymer of the first stage is a copolymer which (i) is used in an amount of 5% to 50% by weight, based on 100 parts by weight of the total monomers to be polymerized in the first and second stages, and which (ii) is composed to an extent of at least 80% and up to 99% by weight of principal monomers selected from the group consisting of C1 to C10 alkyl (meth)acrylates, amides and hydroxyalkyl esters of α,β-unsaturated C 3 -C 6 carboxylic acids, more preferably acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate or 1,4-butanediol monoacrylate, and mixtures of these monomers, more preferably n-butyl acrylate, methyl methacrylate, and acrylamide, and (iii) comprises to an extent of at least 0.1% and up to 5% by weight, monomers I, which are preferably selected from the group of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), methacrylic acid 3'-sulfopropyl ester, acrylic acid 3'-sulfopropyl ester, methacrylic acid 2'-sulfoethyl ester. (i) is used in an amount of 5% to 50% by weight, based on 100 parts by weight of the total monomers to be polymerized in the first and second stages, and which (ii) is composed to an extent of at least 80% and up to 99% by weight of principal monomers selected from the group consisting of C1 to C10 alkyl (meth)acrylates, amides and hydroxyalkyl esters of α,β-unsaturated C 3 -C 6 carboxylic acids, more preferably acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl (meth)acrylate or 1,4-butanediol monoacrylate, and mixtures of these monomers, more preferably n-butyl acrylate, methyl methacrylate, and acrylamide, and (iii) comprises to an extent of at least 0.1% and up to 5% by weight, monomers I, which are preferably selected from the group of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), methacrylic acid 3'-sulfopropyl ester, acrylic acid 3'-sulfopropyl ester, methacrylic acid 2'-sulfoethyl ester.