Process for the production of paper

1. A process for producing paper which comprises:

(i) providing an aqueous suspension comprising cellulosic fibres,

(ii) adding to the suspension after the last point of high shear and subsequent a centri-screen:

(a) a first anionic component which is a water-soluble anionic polysaccharide;

(b) a second anionic component which is a water-dispersible or branched acrylamide-based polymer;

(c) a third anionic component which is an anionic siliceous material comprising an anionic silica-based polymer comprising anionic silica-based particles having a specific surface area within the range of from 100 to 1700 m2/g;

(iii) dewatering the obtained suspension to form paper;

wherein the anionic polysaccharide is selected from the group consisting of cellulose derivatives.

2. The process of claim 1 , wherein the first anionic component has a weight average molecular weight of at least 10,000.

3. The process of claim 1 , wherein the anionic silica-based particles are present in a sol having an S-value in the range of from 8 to 50%.

4. The process of claim 1 , wherein the anionic silica-based particles have an average particle size in the range of from 1 to 10 nm.

5. The process of claim 1 , wherein the anionic silica-based particles have a specific surface area in the range of from 50 to 1000 m 2 /g.

6. The process claim 1 , wherein the anionic silica-based particles have a specific surface area in the range of from 1000 to 1700 m 2 /g.

7. The process of claim 1 , wherein the second anionic component has an unswollen particle size less than 1500 nm.

8. The process of claim 1 , wherein the second component has an unswollen particle size less than 1000 nm.

9. The process of claim 1 , wherein the second anionic component is a water-dispersible or branched acrylamide-based polymer obtained by polymerization of a monomer mixture comprising polyfunctional crosslinking agents and monomers selected form the group consisting of anionic monomers selected from the group consisting of ethylenically unsaturated carboxylic acids and salts thereof, ethylenically unsaturated sulphonic acids and salts thereof, and mixtures thereof; and non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-isobutyl(meth)acrylamide, N-n-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-dimethyl(meth)acrylamide, dialkylaminoalkyl (meth) acrylamides, and mixtures thereof.

10. The process of claim 1 , wherein the second anionic component is a water-dispersible or branched acrylamide-based polymer obtained by polymerization of a monomer mixture comprising polyfunctional crosslinking agents and monomers selected form the group consisting of non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, and mixtures thereof; and anionic monomers selected from the group consisting of ethylenically unsaturated carboxylic acids and salts thereof.

11. The process of claim 1 , wherein the first, second and third anionic components are present in a weight ratio of 0.1-2:0.1-2:1.

12. The process of claim 1 , wherein the cellulosic suspension after addition of the first, second and third anionic components is fed into a headbox of a paper machine, the headbox ejecting the suspension onto a forming wire for drainage.

13. A process for producing paper which comprises:

(i) providing an aqueous suspension comprising cellulosic fibres,

(ii) adding to the suspension after the last point of high shear and subsequent a centri-screen:

(a) a first anionic component which is a water-soluble anionic polysaccharide;

(b) a second anionic component which is a water-dispersible or branched acrylamide-based polymer;

(c) a third anionic component which is an anionic siliceous material comprising an anionic silica-based polymer comprising anionic silica-based particles having a specific surface area within the range of from 100 to 1700 m2/g;

(iii) dewatering the obtained suspension to form paper;

wherein the anionic polysaccharide is guar gum.

14. The process of claim 13 , wherein the first anionic component has a weight average molecular weight of at least 10,000.

15. The process of claim 13 , wherein the anionic silica-based particles are present in a sol having an S-value in the range of from 8 to 50%.

16. The process of claim 13 , wherein the anionic silica-based particles have an average particle size in the range of from 1 to 10 nm.

17. The process of claim 13 , wherein the anionic silica-based particles have a specific surface area in the range of from 50 to 1000 m 2 /g.

18. The process claim 13 , wherein the anionic silica-based particles have a specific surface area in the range of from 1000 to 1700 m 2 /g.

19. The process of claim 13 , wherein the second anionic component is a water-dispersible or branched acrylamide-based polymer obtained by polymerization of a monomer mixture comprising polyfunctional crosslinking agents and monomers selected form the group consisting of anionic monomers selected from the group consisting of ethylenically unsaturated carboxylic acids and salts thereof, ethylenically unsaturated sulphonic acids and salts thereof, and mixtures thereof; and non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-n-butyl(meth)acrylamide, N-t-butyl(meth)acrylamide, N-isobutyl(meth)acrylamide, N-n-butoxymethyl(meth)acrylamide, N-isobutoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, dialkylaminoalkyl(meth) acrylamides, and mixtures thereof.

20. The process of claim 13 , wherein the second anionic component is a water-dispersible or branched acrylamide-based polymer obtained by polymerization of a monomer mixture comprising polyfunctional crosslinking agents and monomers selected form the group consisting of non-ionic monomers selected from the group consisting of acrylamide, methacrylamide, and mixtures thereof; and anionic monomers selected from the group consisting of ethylenically unsaturated carboxylic acids and salts thereof.