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.

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.

The present invention concerns a process of making paper, board or paperboard in which a cellulosic thin stock is provided and subjected to one or more shear stages and then drained on a moving screen to form a sheet which is dried, wherein the process employs a treatment system which is applied to the thin stock, said treatment system comprising as components, a) a cationic organic polymer of charge density of at least 3.0 meq/g with a molar mass Mw of up to 3 million Daltons or poly aluminum chloride (PAC), b) a cationic polymer having an average molar mass Mw of at least 500,000 Daltons and a charge density not exceeding 4.0 meq/g; c) a microparticulate material; in which components (b) and (c) are added to the cellulosic thin stock after the last shear stage before the head box and component (a) is added to the cellulosic thin stock before the said last shear stage.

The present invention concerns a process of making paper, board or paperboard in which a cellulosic thin stock is provided and subjected to one or more shear stages and then drained on a moving screen to form a sheet which is dried, wherein the process employs a treatment system which is applied to the thin stock, said treatment system comprising as components, a) a cationic organic polymer of charge density of at least 3.0 meq/g with a molar mass Mw of up to 3 million Daltons or poly aluminum chloride (PAC), b) a cationic polymer having an average molar mass Mw of at least 500,000 Daltons and a charge density not exceeding 4.0 meq/g; c) a microparticulate material; in which components (b) and (c) are added to the cellulosic thin stock after the last shear stage before the head box and component (a) is added to the cellulosic thin stock before the said last shear stage.

The present invention relates to a process for producing paper which comprises: (i) providing an aqueous suspension comprising cellulosic fibers, (ii) adding to the suspension after all points of high shear: a first polymer being a cationic polymer having a charge density above 2.5 meq/g; a second polymer; and a third polymer being an organic or inorganic anionic polymer; and (iii) dewatering the obtained suspension to form paper.