Process for producing paper or board and a product thereof
The present invention provides a process for producing paper or board, comprising slushing a stock of dried fibres in a slushing system comprising a pulper, and/or feeding a stock of never-dried fibres in a fiber line of an integrated paper mill; deflaking and/or refining the stock in a deflaker and/or a refiner, optionally diluting the deflaked and/or refined stock, directing the deflaked and/or refined stock to a headbox, forming a web, and drying the web, wherein a polymeric paper making additive is added to one or more of the stocks of dried fibres and never-dried fibres before deflaking and/or refining of the stock. The present invention further provides paper and board with improved properties.
1. A process for producing paper or board, comprising:
slushing a stock of dried fibres in a slushing system comprising a pulper, and/or feeding a stock of never-dried fibres in a fibre line of an integrated paper mill;
adding a polymeric strength additive comprising at least one polysaccharide to one or more of the stocks of dried fibres and never-dried fibres into the pulper or to the fibre line;
deflaking and/or refining the stock in a deflaker and/or a refiner;
directing a deflaked and/or refined stock from the deflaker and/or refiner into a mixing chest and from the mixing chest to a machine chest;
obtaining a thin stock by diluting the deflaked and/or refined stock with white water from a white water silo;
directing the the thin stock to a headbox;
forming a web; and
drying the web;
wherein the polymeric strength additive has an intrinsic viscosity of at least 200 ml/g, and
wherein consistency of the stock in the slushing system and/or in the fibre lines is 4-20 wt. % at the time and point of the addition of the polymeric strength additive.
2. The process according to claim 1 , wherein the polymeric strength additive is added to the one or more of the stocks as a powder and/or as an aqueous dispersion.
3. The process according to claim 1 , wherein the polymeric strength additive is added to the stock of dried fibres.
4. The process according to claim 1 , wherein the polymeric strength additive has a viscosity of at most 10 000 mPas as measured from 1 weight-% aqueous polymer solution (dry/dry).
5. The process according to claim 1 , wherein the polymeric strength additive comprising at least one polysaccharide comprises at least one cellulose-based polysaccharide, alginate-based polysaccharide, guar-based polysaccharide, starch-based polysaccharide, or any combination thereof.
6. The process according to claim 5 , wherein the at least one polysaccharide comprises at least one cellulose-based polysaccharide comprising at least one anionic cellulose-based polysaccharide comprising at least one oxidized cellulose, phosphorylated cellulose, anionic cellulose ether, or any combination thereof.
7. The process according to claim 5 , wherein the polymeric strength additive comprises at least one cellulose-based polysaccharide comprising microfibrillar cellulose.
8. The process according to claim 1 , wherein the polymeric strength additive comprises at least one natural polymer and at least one synthetic polymer.
9. The process according to claim 1 , wherein the polymeric strength additive has a net anionic or net cationic charge at pH 7.
10. The process according to claim 1 , wherein the polymeric strength additive has a charge density of less than −0.1 meq/g (dry) at pH 7.
11. The process according to claim 1 , wherein the polymeric strength additive contains at most 50 weight-% of water-insoluble material.
12. The process according to claim 1 , wherein temperature of the stock in the slushing system and/or in the fibre lines is at least 40° C.
13. The process according to claim 1 , wherein consistency of the stock in the slushing system and/or in the fibre lines is 4-10 wt. % at the time and point of the addition of the polymeric strength additive.
14. The process according to claim 1 , wherein pH of the stock in the slushing system and/or in the fiber lines is in the range of 5-8 at the time and point of the addition of the polymeric strength additive.
15. The process according to claim 1 , wherein the polymeric strength additive is added to a stock comprising recycled fibre material (RCF), semi-chemical pulp such as chemi-thermomechanical pulp (CTMP), mechanical pulp and/or broke.
16. The process according to claim 1 , wherein at least one cationic agent comprises alum, polyaluminium chloride (PAC), polyvinylamine (PVAM), polyethylene imine (PEI), homopolymer or copolymer of diallyldimethylammonium chloride (DADMAC), polyamine, cationic polyacrylamide-based solution polymer, cationic starch, cationic reactive strength resin, or any combination thereof is added to the stock after deflaking and refining.
17. A paper or board obtainable by the process according to claim 1 , wherein the paper or board is selected from tissues, napkins, towels, graphical papers, coated fine paper, uncoated fine paper, mechanical papers, newsprint, packaging papers, folding boxboard, high performance testliners and media, solid board, multi-layered specialty board, liner, fluting, gypsum board liner, wall paper, core board, carrier board, boxboard (FBB), white lined chipboard (WLC), solid bleached sulphate (SBS) board, solid unbleached sulphate (SUS) board and liquid packaging board (LPB).
18. The process according to claim 1 , wherein the polymeric strength additive is added to the pulper.
19. The process according to claim 1 , wherein the polymeric strength additive has a viscosity of 50-5500 mPas measured from 2 weight-% aqueous polymer solution (dry/dry).