CATIONIC SURFACE SIZING AGENT

Provided herein is an aqueous polymer dispersion (A) obtainable by free radical emulsion copolymerizing a first ethylenically unsaturated monomer blend comprising (b) 15 to 100 % by weight of at least one Cl-C4-alkyl (meth)acrylate， in the presence of a water-soluble redox system comprising a first free radical initiator for the free radical emulsion copolymerization and an aqueous prepolymer composition (B) obtainable by free radical emulsion copolymerizing in a polymerization solvent comprising Cl-6-carboxylic acid and Cl-6-carboxylic acid anhydride a second ethylenically unsaturated monomer blend comprising (i) 5 to 50 % by weight of at least one ethylenically unsaturated quaternary amine selected from quaternary salt of N，N，N-tri(Cl-4-alkyl) amino Cl-4-alkyl(meth)acrylate with a mineral acid or an organic acid and/or quaternary salt of N，N，N-tri(Cl-4-alkyl)amino Cl-4-alkyl(meth)acrylamide with a mineral acid or an organic acid， and (iii) 10 to 95 % by weight of at least one optionally substituted styrene， in the presence of a second free radical initiator， and adding water to the obtained polymer dispersion to obtain the aqueous prepolymer composition.