Aqueous polymer dispersion comprising rubber particles and polymer particles having a reinforcing action

An aqueous polymer dispersion comprising rubber particles and polymer particles having a reinforcing action, wherein the rubber particles are made up of

• x% by weight of an aromatic monovinyl compound and
• y% by weight of an aliphatic conjugated diene having from 4 to 9 carbon atoms
• in copolymerized form, and
• x is from 5 to 35 and
• y is from 65 to 95,
• and the polymer particles having a reinforcing action are made up of
• from 50 to 90% by weight of a first, hard polymer phase A and
• from 10 to 50% by weight of a second, soft polymer phase B, where
• the polymer phase A has a glass transition temperature above 70° C. and comprises from 90 to 100% by weight of an aromatic monovinyl compound and up to 10% by weight of an aliphatic conjugated diene having from 4 to 9 carbon atoms in copolymerized form and
• the polymer phase B comprises
• x±≦3% by weight of the aromatic monovinyl compound used in the rubber particles and
• y±≦3% by weight of the aliphatic conjugated diene having from 4 to 9 carbon atoms used in the rubber particles in copolymerized form.