Method for manufacturing paper and cardboard

Abstract

This invention relates to a process for making a paper or cardboard sheet from a fibrous suspension, comprising the following steps: a) injecting a P3 polymer into a suspension of cellulosic fibers, b) forming a paper or cardboard sheet, c) drying the paper or cardboard sheet, the P3 polymer being prepared, prior to step a), from a water-soluble P1 polymer of at least one nonionic monomer selected from acrylamide, methacrylamide, N,N-dimethylacrylamide and acrylonitrile, the P1 polymer being subjected to an Re1 reaction to give a P2 polymer, which is then subjected to an Re2 reaction to give the P3 polymer, which is injected into the fibrous suspension within 24 hours of the start of the Re1 reaction, the Re1 reaction comprises preparing a P2 polymer comprising isocyanate functions by reaction for 10 seconds to 60 minutes between (i) an alkali hydroxide and/or an alkaline earth hydroxide, (ii) an alkali hypohalite and/or an alkaline earth hypohalite and (iii) the P1 polymer, the Re2 reaction comprises preparing a P3 polymer by reaction between (iv) a micro-cellulose compound and (v) the P2 polymer comprising isocyanate functions.

Dependencies are inferred from the claim text.