Patent ID: 7922867

Claim:
A process for the production of paper, board or cardboard, having high dry strength, the process comprising separate addition of a cationic polymer comprising vinylamine units, and of a polymeric anionic compound to a paper stock, draining of the paper stock and drying the product thereof, wherein the polymeric anionic compound comprises (i) ligninsulfonic acid and/or a ligninsulfonate and (ii) at least one copolymer which is obtainable by copolymerization of (a) at least one N-vinylcarboxamide of the formula where R 1 , R 2 is H or C 1 - to C 6 -alkyl, (b) at least one monoethylenically unsaturated monomer comprising acid groups and/or the alkali metal, alkaline earth metal or ammonium salts thereof and, optionally, (c) at least one other monoethylenically unsaturated monomer, and, optionally, (d) at least one compound which has at least two ethylenically unsaturated double bonds in the molecule.