| abstract |
The invention relates to a method for producing paper and cardboard, having the steps of providing an aqueous suspension containing filler, at least one water-soluble amphoteric polymer, and microparticles; adding said aqueous suspension to a paper material, dewatering the obtained paper material, thereby forming sheets in the wire section, until the dry matter content of the paper sheet is at least 18 wt.%; and subsequently pressing and drying the paper sheet. The water-soluble ampoteric polymer can be obtained by copolymerizing a monomer mixture comprising a) at least one N-vinyl carboxylic acid amide of the general formula, in which R 1 and R 2 independently of each other represent H or C 1 - to C 6 -alkyl, b) at least one monoethylenically unsaturated monomer with at least one free acid group or at least one acid group in salt form, c) optionally at least one monoethylenically unsaturated monomer which differs from components (a) and (b), and d) optionally at least one compound which has at least two ethylenically unsaturated double bonds in the molecule, and subsequently partly or completely hydrolyzing the groups -CO-R 1 of the polymerisate, wherein the difference between the contents of the cationic and the anionic monomer units in mol.% absolutely maximally equals 10, in each case based on the total number of moles of all monomer units. |