Finely divided, cationic, aqueous polymer dispersions, method for the production thereof, and the use thereof

A process for the preparation of a finely divided, cationic, aqueous polymer dispersion which is obtainable by emulsion polymerisation of ethylenically unsaturated monomers in an aqueous liquid comprising a cationic prepolymer as a dispersant, wherein

• the cationic prepolymer is prepared in a presence of at least one polymerisation initiator by polymerisation of
• (a) from 15 to 45% by weight of at least one ethylenically unsaturated monomer comprising at least one quaternary ammonium group;
• (b) from 5 to 80% by weight of at least one optionally substituted styrene;
• (c) from 0 to 50% by weight of at least one C1-12 alkyl (meth) acrylate;
• (d) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an acid group;
• (e) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an amine group;
• and
• (f) from 0 to 20% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (b), (c) and (e),
• a sum of (a)+(b)+(c)+(d)+(e)+(0 being 100% by weight,
• in a first emulsion polymerisation in a presence of at least one non-ionic emulsifier, and thereafter, in the aqueous liquid containing the cationic prepolymer, a second emulsion polymerisation is carried out, in a presence of at least one polymerisation initiator, of a monomer mixture comprising
• (i) from 10 to 70% by weight of at least one of an optionally substituted styrene or (meth) acrylonitrile;
• (ii) from 30 to 90% by weight of at least one C1-18 alkyl (meth) acrylate;
• (iii) from 0 to 30% by weight of at least one vinyl ester of linear or branched C1-30 carboxylic acids;
• and
• (iv) from 0 to 30% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (i), (ii) and (iii),
• a sum of (i)+(ii)+(iii)+(iv) being 100% by weight,
• the first emulsion polymerisation and/or the second emulsion polymerisation is optionally carried out in a presence of from 0 to 10% by weight of at least one polymerisation regulator, and
• the aqueous polymer dispersion comprises dispersed particles having a mean particle size of from about 5 to about 250 nm.

A sizing agent for paper, board and cardboard, the sizing agent comprising a finely divided, cationic, aqueous polymer dispersion which is obtainable by emulsion polymerisation of ethylenically unsaturated monomers in an aqueous liquid comprising a cationic prepolymer as a dispersant, wherein

• the cationic prepolymer is prepared in a presence of at least one polymerisation initiator by polymerisation of
• (a) from 15 to 45% by weight of at least one ethylenically unsaturated monomer comprising at least one quaternary ammonium group;
• (b) from 5 to 80% by weight of at least one optionally substituted styrene;
• (c) from 0 to 50% by weight of at least one C1-12 alkyl (meth) acrylate;
• (d) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an acid group;
• (e) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an amine group;
• and
• (f) from 0 to 20% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (b), (c) and (e),
• a sum of (a)+(b)+(c)+(d)+(e)+(f) being 100% by weight,
• in a first emulsion polymerisation in a presence of at least one non-ionic emulsifier, and thereafter, in the aqueous liquid containing the cationic prepolymer, a second emulsion polymerisation is carried out, in the presence of at least one polymerisation initiator, of a monomer mixture comprising
• (i) from 10 to 70% by weight of at least one of an optionally substituted styrene or (meth) acrylonitrile;
• (ii) from 30 to 90% by weight of at least one C1-18 alkyl (meth) acrylate;
• (iii) from 0 to 30% by weight of at least one vinyl ester of linear or branched C1-30 carboxylic acids;
• and
• (iv) from 0 to 30% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (i), (ii) and (iii),
• a sum of (i)+(ii)+(iii)+(iv) being 100% by weight,
• the first emulsion polymerisation and/or the second emulsion polymerisation is optionally carried out in a presence of from 0 to 10% by weight of at least one polymerisation regulator, and
• the aqueous polymer dispersion comprises dispersed particles having a mean particle size of from about 5 to about 250 nm.