Method for producing paper or cardboard

A method for producing paper or cardboard, comprising the steps of,

• (A) adding a final polymer A to a first aqueous fibrous material suspension, whereby a second aqueous fibrous material suspension comprising final polymer A is created,
• wherein the final polymer A is obtained by
• radical polymerisation of the monomers
• (i) 30 to 90 mol % of a monomer of formula I
• in which R1═H or means C1-C6 alkyl,
• (ii) 3 to 60 mol % of a C1-C4 alkyl ester of acrylic acid or of a C1-C4 alkyl ester of methacrylic acid,
• (iii) 0 to 45 mol % of a monoethylenically unsaturated carboxylic acid, a monoethylenically unsaturated sulfonic acid, or a monoethylenically unsaturated phosphonic acid, or salt forms thereof,
• (iv) 0 to 9 mol % acrylonitrile or methacrylonitrile,
• (v) 0 to 35 mol % of one or more ethylenically unsaturated monomers which are different from a monomer (i), (ii), (iii) and (iv),
• wherein the total amount of all monomers (i), (ii), (iii), (iv) and (v) is 100 mol %, in order to obtain a starting polymer V, and
• hydrolysing the starting polymer V in order to obtain the final polymer A,
• wherein the N—C(═O)R′ groups of formula (I) of the monomers (i) polymerised into the starting polymer V hydrolyse at least in part and in so doing form primary amino groups,
• wherein the ester groups of the monomers (ii) polymerised into the starting polymer V are converted at least in part and at least part of the conversion is the formation of five-membered lactam structural units with the obtained primary amino groups or the formation of carboxylic acid groups or salt forms thereof,
• (B) dewatering the second aqueous fibrous material suspension comprising final polymer A on a water-permeable substrate to form a wet paper structure,
• (C) dewatering the wet paper structure, whereby the paper or the cardboard is formed.