Patent ID: 8382948

Claim:
A process for producing paper, comprising adding 0.01 to 1.00% by weight, based on dry fiber, of water-soluble, amphoteric copolymers to a high-consistency fiber stock, and adding a filler to the high-consistency fiber stock, wherein the water-soluble, amphoteric copolymers are obtained by a polymerization process comprising: (1) copolymerization of a mixture comprising a) at least one N-vinylcarboxamide of the general formula in which R 1 and R 2 , independently of one another, are H or C 1 - to C 6 -alkyl, b) at least one monomer which is selected from the group consisting of (b1) monoethylenically unsaturated sulfonic acids, phosphonic acids, phosphoric acid esters and derivatives thereof, and (b2) monoethylenically unsaturated mono- and dicarboxylic acids, the salts thereof and dicarboxylic anhydrides, c) optionally, at least one monoethylenically unsaturated monomer differing from the components (a) and (b), and d) optionally, at least one compound which has at least two ethylenically unsaturated double bonds in the molecule, wherein the monomer mixture comprises at least one monomer (b) having at least one free acid group and/or an acid group in salt form; and (2) subsequent partial or complete hydrolysis of the groups —CO—R 1 from the monomers (a) incorporated in the form of copolymerized units into the copolymer.