Method for increasing the strength properties of a paper or board product

Patent metadata

Field	Value
Publication number	US-11214927-B2
Application number	US-201816610101-A
Country	US
Kind code	B2
Filing date	Jun 13, 2018
Priority date	Jun 14, 2017
Publication date	Jan 4, 2022
Grant date	Jan 4, 2022

Abstract

A method is disclosed for increasing strength properties, preferably burst strength and SCT strength, of a paper or board product. The paper or board product is manufactured from a fibrous web produced by a multilayer headbox, where an aqueous layer is formed between at least a first and a second fibre layer formed from fibrous stock suspension(s), and where feed water for the aqueous layer includes at least one cationic polymer. The method of the invention includes adding an anionic additive selected from a group comprising anionic synthetic organic polymers, anionic polysaccharides, and any of their combinations to the feed water before formation of the aqueous layer.

First claim

The invention claimed is:

1. A method for increasing strength properties of a paper or board product, manufactured from a fibrous web produced by a multilayer headbox, where an aqueous layer is formed between at least a first and a second fibre layer formed from fibrous stock suspension(s), and where feed water for the aqueous layer comprises at least one cationic polymer, and wherein the method comprises adding an anionic additive selected from the group consisting of copolymers of acrylamide and anionic monomers, a carboxymethyl cellulose having a degree of carboxymethyl substitution in a range of 0.4-1.2, and any of their combinations to the feed water before formation of the aqueous layer.

2. The method according to claim 1 , wherein the feed water further comprises a cellulosic fibre material selected from unrefined cellulosic fibres, refined cellulosic fibres, microfibrillated cellulose fibrils and/or nanocellulose fibrils.

3. The method according to claim 2 , wherein the feed water comprises 1-15 weight % of cellulosic fibre material, based on produced paper or board product.

4. The method according to claim 1 , wherein a consistency of the feed water is lower than a consistency of the fibrous suspension(s) forming the first and the second fibre layer.

5. The method according to claim 1 , wherein the anionic additive has a weight average molecular weight >100 000 g/mol, or a charge density of −0.05-−5 meq/g dry polymer, or both.

6. The method according to claim 1 , wherein the anionic additive is a carboxymethylated cellulose having:
a charge density value below −1.1 meq/g dry polymer, measured at pH 7, or
viscosity in a range of 30-30 000 mPas, measured from 2 weight-% aqueous solution at 25° C. by using Brookfield LV DV1, or both.

7. The method according to claim 1 , wherein the copolymer of acrylamide has a weight average molecular weight <5 000 000 g/mol.

8. The method according to claim 1 , wherein the copolymer of acrylamide has an anionicity in a range of 2-70 mol %.

9. The method according to claim 1 , wherein the anionic additive is added in an amount maintaining a sum of added charges from cationic polymer(s) and anionic additive net cationic.

10. The method according to claim 1 , wherein the anionic additive is added separately from the at least one cationic polymer.

11. The method according to claim 1 , wherein the at least one cationic polymer is cationic starch or cationic synthetic strength polymer.

12. The method according to claim 1 , wherein the at least one cationic polymer is cationic starch added in an amount of 3-20 kg/t.

13. The method according to claim 1 , further comprising adding one or more auxiliary agents to the feed water, the one or more auxiliary agents being selected from alum or anionic microparticles.

14. The method according to claim 13 , wherein the anionic microparticles are anionic silica microparticles or bentonite microparticles.

15. The method according to claim 1 , wherein the at least first and/or the second layer comprises anionic microparticles and cationic synthetic flocculant.

16. The method according to claim 1 , wherein the at least first and/or the second layer comprises recycled cellulosic fibres.

Assignees

• Kemira Oyj

Inventors

• Virtanen Mikko
• Strengell Kimmo
• Cecchini Juan
• Hietaniemi Matti

Classifications

• D21H17/28

  Starch · CPC title

• D21H21/18 Primary

  Reinforcing agents · CPC title

• D21H11/14

  Secondary fibres (working-up waste paper D21C5/02) · CPC title

• D21F9/006

  paper or board consisting of two or more layers · CPC title

• D21H17/42

  anionic · CPC title