Patent ID: 7244812

Claim:
A process for reducing the amount of residual monomers in aqueous polymer dispersions by chemical aftertreatmcnt, comprising: treating an aqueous polymer dispersion containing residual monomers with a redox system which consists essentially of a) from 0.005 to 5% by weight based on the total weight of all monomers used for the preparation of the polymer dispersion, of at least one oxidizing agent based on an organic peroxide from the class consisting of the a1) a perester which is tert-butyl perbenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, cumyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxypivalate, tert-butyl peroxyneoheptanoate, tert-amyl peroxypivalate, tert-butyl peroxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxydiethylacetate, tert-butyl peroxyisobutyrate, tert-butyl peroxyacetate or tert-amyl peroxybeuzoate, or a2) a percarbonate which is 1-(2-ethyihexanoylperoxy)-1,3-dimethylbutyl peroxypivalate, di(2-ethylhexyl) peroxydicarbonate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, tert-amylperoxy 2-ethyihexyl carbonate, tert-butylperoxy isopropyl carbonate or tert-butylperoxy 2-ethylhexyl carbonate, or a3) a perketal which is 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,2-di(4,4-di(tert-butylperoxy)cyclohexyl)propane, 1,1-di(tert-butylperoxy)cyclohexane, 2,2-di(tert-butylperoxy)butane, 3,6,9-triethyl-1,4,7-triperoxynonane or 3,6,9-trimethyl-1,4,7-triperoxynonane, and b) from 0.005 to 5% by weight, based on the total weight of all monomers used for the preparation of the polymer dispersion, of at least one reducing agent from the group consisting of the sulfinic acids and the salts thereof having the structure MO—SO—CR 12 R 13 R 14 (2) in which M is hydrogen, NH 4 , a monovalent metal ion or one equivalent of a divalent metal ion of the groups Ia, IIa, lIb, IVa or VIIIb of the Periodic Table of the Elements, in which R 12 =OH, NR 15 R 16 , in which R 15 and R 16 , independently of one another, are hydrogen or C 1 -C 6 -alkyl, in which R 13 =hydrogen or an alkyl, alkenyl, cycloalkyl or aryl group, it being possible for these groups to have 1, 2 or 3 substituents which, independently of one another, are selected from C 1 -C 6 -alkyl, OH, O-C 1 -C 6 -alkyl, halogen and CF 3 , in which R 14 =COOM, SO 3 M, COR 15 , CONR 15 R 16 , COOR 15 , in which M, R 15 and R 16 have the meanings stated above, or, if R 13 is aryl, this may be unsubstituted or substituted as stated above, R 14 is also H, and the salts thereof, and optionally sodium sulfite and/or sulfonic acid derivates which cannot eliminate any formaldehyde.