A process for preparing an aqueous binder composition, the process comprising at least the following steps A) and B): A) preparing a carboxylic acid-functional vinyl polymer (polymer A) by emulsion polymerisation of a monomer composition A, whereby monomer composition A comprises the following monomers: Ai) at least one carboxylic acid functional olefinically unsaturated monomer; and Aii) at least one olefinically unsaturated monomer different than Ai); B) preparing a vinyl polymer (polymer B) by emulsion polymerization of a monomer composition B in the presence of Polymer A where the monomer composition B comprises the following monomer(s): Bi) at least one olefinically unsaturated monomer; Bii) optionally carboxylic acid functional olefinically unsaturated monomer different than Bi); where the acid value of polymer B is lower than the acid value of polymer A; where the weight average molecular weight (Mw) of polymer B is higher than the weight average molecular weight (Mw) of polymer A as determined by Size Exclusion Chromatography analysis; where the weight ratio of polymer A to polymer B is in the range of from 5:95 to 95:5; where at least part of the carboxylic acid groups of Polymer A are deprotonated to obtain ionic or potentially ionic water-dispersing groups; whereby the monomer composition A comprises at least two monomer compositions A1 and A2 which differ in chain-transfer agent concentration, whereby the monomer composition A1 comprises at most 1 wt.% of chain-transfer agent (relative to the total monomer composition A1), the monomer composition A2 comprises at least 1 wt.% of chain-transfer agent and at most 3.5 wt.% of chain-transfer agent (relative to the total monomer composition A2) and whereby the difference in amount of chain-transfer agent between monomer composition A1 and monomer composition A2 is at least 0.5 wt.%. A) preparing a carboxylic acid-functional vinyl polymer (polymer A) by emulsion polymerisation of a monomer composition A, whereby monomer composition A comprises the following monomers: Ai) at least one carboxylic acid functional olefinically unsaturated monomer; and Aii) at least one olefinically unsaturated monomer different than Ai); Ai) at least one carboxylic acid functional olefinically unsaturated monomer; and Aii) at least one olefinically unsaturated monomer different than Ai); B) preparing a vinyl polymer (polymer B) by emulsion polymerization of a monomer composition B in the presence of Polymer A where the monomer composition B comprises the following monomer(s): Bi) at least one olefinically unsaturated monomer; Bii) optionally carboxylic acid functional olefinically unsaturated monomer different than Bi); where the acid value of polymer B is lower than the acid value of polymer A; where the weight average molecular weight (Mw) of polymer B is higher than the weight average molecular weight (Mw) of polymer A as determined by Size Exclusion Chromatography analysis; where the weight ratio of polymer A to polymer B is in the range of from 5:95 to 95:5; where at least part of the carboxylic acid groups of Polymer A are deprotonated to obtain ionic or potentially ionic water-dispersing groups; whereby the monomer composition A comprises at least two monomer compositions A1 and A2 which differ in chain-transfer agent concentration, whereby the monomer composition A1 comprises at most 1 wt.% of chain-transfer agent (relative to the total monomer composition A1), the monomer composition A2 comprises at least 1 wt.% of chain-transfer agent and at most 3.5 wt.% of chain-transfer agent (relative to the total monomer composition A2) and whereby the difference in amount of chain-transfer agent between monomer composition A1 and monomer composition A2 is at least 0.5 wt.%. Bi) at least one olefinically unsaturated monomer; Bii) optionally carboxylic acid functional olefinically unsaturated monomer different than Bi); <EOS>