Process for the production of paper

1. 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 polymer P1 being a water-soluble cationic acrylamide-based polymer having an average molecular weight of at least about 1,000,000 prepared by polymerizing a composition comprising a monomer mixture comprising one or more cationic monomers represented by the general structural formula (II)

wherein R 1 is H or CH 3 ; R 2 and R 3 are each H or a hydrocarbon group having from 1 to 2 carbon atoms; A is O; B is an alkyl or alkylene group having from 2 to 8 carbon atoms; R 4 is H or a hydrocarbon group having from 1 to 2 carbon atoms; and X − is an anionic counterion;

a cationic starch having a degree of cationic substitution (DS C ) from 0.01 to 0.5, a charge density of from about 0.05 to about 6.0 meq/g and a weight average molecular weight of above about 1,000,000; and

a polymer P2 being an anionic polymer selected from anionic silica-based polymers comprising anionic silica-based particles having an average particle size in the range of from about 1 to about 10 nm, and a specific surface area within the range of from 50 to 1000 m 2 /g; and

(iii) dewatering the obtained suspension to form paper.

2. The process according to claim 1 , wherein the cationic starch has a degree of cationic substitution (DS C ) within the range of from about 0.025 to about 0.2.

3. The process according to claim 1 , wherein the cationic starch has a cationic charge density within the range of from about 0.1 to about 5.0 meq/g.

4. The process according to claim 1 , wherein the anionic silica-based polymers are prepared by condensation polymerization of siliceous compounds.

5. The process according to claim 1 , wherein the one or more cationic monomers are chosen from dimethylammoniumethyl acrylate methyl chloride, dimethylammoniumethyl methacrylate methyl chloride, diethylammoniumethyl acrylate methyl chloride, diethylammoniumethyl methacrylate methyl chloride, or mixtures thereof.

6. The process according to claim 1 , wherein the one or more cationic monomers are chosen from dimethylaminoethyl acrylate methyl chloride quaternary salt, and dimethylaminoethyl methacrylate methyl chloride quaternary salt, or mixtures thereof.

7. 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 polymer P1 being a water-soluble cationic acrylamide-based polymer having an average molecular weight of at least about 1,000,000 prepared by polymerizing a composition comprising a monomer mixture comprising one or more cationic monomers represented by the general structural formula (II)

wherein R 1 is H or CH 3 , R 2 and R 3 are each H or a hydrocarbon group having from 1 to 2 carbon atoms; A is O; B is an alkyl or alkylene group having from 2 to 8 carbon atoms; R 4 is H or a hydrocarbon group having from 1 to 2 carbon atoms; and X − is an anionic counterion;

a cationic polysaccharide having a degree of substitution (DSc) within the range of from about 0.01 to about 0.5 and a weight average molecular weight of above about 1,000,000; and

a polymer P2 being an anionic polymer selected from anionic silica-based polymers comprising anionic silica-based particles having an average particle size in the range of from about 1 to about 10 nm, and a specific surface area within the range of from 50 to 1000 m 2 /g;

said points of high shear comprising pumping and cleaning stages; the obtained suspension from step (ii) being fed to a headbox which ejects the suspension comprising polymer P1, cationic starch, and polymer P2 onto a forming wire for drainage to form paper, wherein the stages of pumping and cleaning comprise fan pumps, pressure screens and centri-screens.

8. The process according to claim 7 , wherein the last point of high shear occurs at a centri-screen.

9. The process according to claim 7 , wherein the cationic polysaccharide is cationic starch.

10. The process according to claim 7 , wherein the cationic polysaccharide has a degree of substitution (DS C ) within the range of from about 0.02 to about 0.3.

11. The process according to claim 7 , wherein the cationic polysaccharide has a cationic charge density within the range of from about 0.05 to about 6.0 meq/g.

12. The process according to claim 7 , wherein the anionic silica-based polymers are prepared by condensation polymerization of siliceous compounds.

13. The process according to claim 7 , wherein the one or more cationic monomers are chosen from dimethylammoniumethyl acrylate methyl chloride, dimethylammoniumethyl methacrylate methyl chloride, diethylammoniumethyl acrylate methyl chloride, diethylammoniumethyl methacrylate methyl chloride, or mixtures thereof.

14. The process according to claim 7 , wherein the one or more cationic monomers are chosen from dimethylaminoethyl acrylate methyl chloride quaternary salt, and dimethylaminoethyl methacrylate methyl chloride quaternary salt, or mixtures thereof.