Method for reducing the quantity of residual monomers in aqueous polymerisate dispersions

A process for reducing the amount of residual monomer in aqueous polymer dispersions by chemical treatment after monomer polymerization with an initiator system, which comprises:

• conducting the chemical treatment of the aqueous polymer dispersion by addition of an initiator system consisting essentially of:
• a) from 0.001 to 5% by weight, based on the total monomer amount required to prepare the polymer dispersion, of:
• a1) at least one oxidizing agent R1OOH in which R1 is hydrogen or an alkyl or aryl group, and/or
• a2) at least one compound which in aqueous media releases hydrogen peroxide;
• and
• b) 0.005 to 5% by weight, based on the total monomer amount required to prepare the polymer dispersion, of a combination of reducing agents b1) and b2) wherein:
• b1) is a carbonyl compound of the formula I
• R2(C═O)R3
• in which R2 is hydrogen or an alkyl, alkenyl, cycloalkyl or aryl group with or without one, two or three substituents which independently of one another are selected from the group consisting of hydroxyl, alkyl, O-alkyl, halogen and trihalomethyl, and R3 is —CO2M, —SO3M, —(C═O)R4 or —CO2R5, where M is hydrogen, ammonium ion, a monovalent metal ion or one equivalent of a divalent metal ion selected from the group consisting of Groups Ia, IIa, IIb, IVa and VIIIb of the Periodic Table, R4 is hydrogen or an alkyl group and R5 is an alkyl group, and
• b2) is an inorganic dithionite.