AQUEOUS BINDER COMPOSITION

The current invention relates to aqueous vinyl polymer binder composition comprising (A) dispersed polymer particles comprising at least vinyl polymer A and vinyl polymer B, wherein the vinyl polymer A has an acid value of from 26 to 110 mg KOH/g of vinyl polymer A, wherein the vinyl polymer B has an acid value of below 16.5 mg KOH/g of vinyl polymer B, wherein the weight average molecular weight (Mw) of the vinyl polymer B is higher than the weight average molecular weight (Mw) of the vinyl polymer A, where the vinyl polymer A and the vinyl polymer B are present in a weight ratio of the vinyl polymer A to the vinyl polymer B of from 5:95 to to 95:5, wherein the vinyl polymer A is obtained by heterogeneous radical polymerization of a monomer composition A in an aqueous phase, wherein the monomer composition A comprises i. ethylenically unsaturated monomers bearing crosslinkable functional groups in an amount of from 0.5 to 15 wt.% based on the total weight of the monomer composition A, and ii. at most 2.5 wt.% of dialkyl itaconate ester, based on the total weight of the monomer composition A; and wherein the vinyl polymer B is obtained by emulsion polymerizing a monomer composition B in the presence of the vinyl polymer A, wherein the monomer composition B comprises i. dimethyl itaconate ester, diethyl itaconate ester or dibutyl itaconate ester, respectively, in an amount of from 20 to 60 wt.% based on the total weight of the monomer composition B, and ii. at most 2.5 wt.% of at least one additional dialkyl itaconate ester, based on the total weight of the monomer composition B; and (B) a crosslinking agent.