Process for the manufacture of paper and paperboard

Abstract

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.

Claims

1. A method of making paper, board or paperboard, said method comprising shearing a cellulosic thin stock in one or more stages to provide a sheared product, draining the sheared product on a moving screen to form a sheet, drying the sheet to produce the paper, board or paperboard, wherein a treatment is applied to the thin stock, said treatment system comprising a) a cationic organic polymer with a charge density of greater than 4 mEq/g and a molar mass Mw of up to 3 million Daltons, b) a cationic polymer with an average molar mass Mw of at least 500,000 Daltons and a charge density not exceeding 3.0 mEq/g, and c) a microparticulate material, and components (b) and (c) are added to the cellulosic thin stock after a last shear stage but before a head box, and component (a) is added to the cellulosic thin stock before said last shear stage.

2. The method according to claim 1 in which the cationic organic polymer of component (a) is selected from the group consisting of polyethylenimines, polyamines, polyvinylamines, partially hydrolysed polyvinyl carboxamides, polymers of diallyl dimethyl ammonium chloride, cationic polyacrylamides and cationic polyacrylates.

3. The method according to claim 1 in which component (b) is selected from the group consisting of cationic polyacrylamides, polymers containing vinyl amines units, cationic polyacrylates and polymers of diallyl dimethyl ammonium chloride.

4. The method according to claim 1 in which the microparticulate material is selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, bentonite, hectorite, somectites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites, sepiolites, anionic cross-linked polymeric microparticles of particle size below 750 nm and nanocellulose.

5. The method according to claim 1 in which the cationic polymer component (b) is added to the thin stock before the microparticulate material.

6. The method according to claim 1 in which the cationic organic polymer of component (a) is added to the thin stock in an amount of from 0.005 to 0.5% by weight based on dry paper stock.

7. The method according to claim 6, in which the cationic organic polymer of component (a) is selected from the group consisting of polyethylenimines, polyamines, polyvinylamines, partially hydrolysed polyvinyl carboxamides, polymers of diallyl dimethyl ammonium chloride, cationic polyacrylamides and cationic polyacrylates.

8. The method according to claim 1 in which the cationic polymer component (b) is added to the thin stock in an amount of from 0.005 to 0.5% by weight based on dry paper stock.

9. The method according to claim 8, in which component (b) is selected from the group consisting of cationic polyacrylamides, polymers containing vinyl amines units, cationic polyacrylates and polymers of diallyl dimethyl ammonium chloride.

10. The method according to claim 1 in which the microparticulate material is added to the thin stock in an amount of from 0.01 to 1.0% by weight based on dry paper stock.

11. The method according to claim 1, in which the cationic organic polymer or poly aluminium chloride of component (a) is added to the thin stock in an amount of from 0.005 to 0.5% by weight based on dry paper stock and the cationic polymer component (b) is added to the thin stock in an amount of from 0.005 to 0.5% by weight based on dry paper stock.

12. The method according to claim 11, in which the cationic organic polymer of component (a) is selected from the group consisting of polyethylenimines, polyamines, polyvinylamines, partially hydrolysed polyvinyl carboxamides, polymers of diallyl dimethyl ammonium chloride, cationic polyacrylamides and cationic polyacrylates; and in which component (b) is selected from the group consisting of cationic polyacrylamides, polymers containing vinyl amines units, cationic polyacrylates and polymers of diallyl dimethyl ammonium chloride.

13. The method according to claim 12, in which the microparticulate material is selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, bentonite, hectorite, somectites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites, sepiolites, anionic cross-linked polymeric microparticles of particle size below 750 nm and nanocellulose.

14. The method according to claim 11, in which the microparticulate material is selected from the group consisting of silica based particles, silica microgels, colloidal silica, silica sols, silica gels, polysilicates, cationic silica, aluminosilicates, polyaluminosilicates, borosilicates, polyborosilicates, zeolites, bentonite, hectorite, somectites, montmorillonites, nontronites, saponite, sauconite, hormites, attapulgites, sepiolites, anionic cross-linked polymeric microparticles of particle size below 750 nm and nanocellulose.

Description

EXAMPLE

(1) A paper stock was prepared comprising a woodfree pulp containing 70% uncoated woodfree paper and 30% coated paper and including 15% ground calcium carbonate filler, 4.6 kg/t cationic starch, and 0.5 kg/t alkyl ketene dimer sizing agent. Calcium chloride was added to paper stock provide a conductivity of 2000 S/cm which is typical for a paper mill furnish. The paper stock had a consistency of 0.99% and a total ash content of 28%.

(2) The following additives were employed in the tests. Product A A polyethylenimine with a molecular weight of 2 million and a cationic charge density of 6.5 meq/g Product B A copolymer of acrylamide with methyl chloride quaternised dimethyl amino ethyl acrylate having an intrinsic viscosity of above 7 dl/g and a cationic charge density of 1.2 meq/g.

(3) Bentonite: sodium activated bentonite prepared at 5% and then diluted at 0.5% for ash retention tests.

(4) The doses of chemical additives employed in the following tests, where employed, are as follows Product A 0.2% Product B 0.025% Bentonite 0.2%

(5) Test 1 is the blank in which there were no chemical additives employed;

(6) Test 2 (comparative) employed Product B followed by high-speed stirring at 1200 rpm for 30 seconds, representing the last shear stage, followed by bentonite;

(7) Test 3 (comparative) employed Product B followed by light mixing followed by bentonite, representing adding both Product B and bentonite after the last shear stage;

(8) Test 4 (comparative) employed Product A followed by high-speed stirring at 1200 rpm for 60 seconds, followed by Product B followed by high-speed stirring at 1200 rpm for 30 seconds, representing the last shear stage, followed by bentonite;

(9) Test 5 (invention) employed Product A followed by high-speed stirring at 1200 rpm for 60 seconds, representing the last shear stage, followed by addition of Product B, followed by light mixing and then addition of bentonite, representing the addition of Product A before the last shear stage and the addition of Product B and bentonite after the last year stage.

(10) The results are shown in Table 1

(11) The ash retention tests are done with a DFR 04 from the company BTG (60 mesh copper screen). The ash retention is evaluated by the measurement of the total ash solids concentration found in a sample of 200 ml of white water (filtration of the white water made with an ash free filter paper type Whatmann 542). The First Pass Ash Retention (FPAR) is then determined by the following ratio:
FPAR (%)=([furnish ash conc. %][white water ash conc.])/[furnish conc.]

(12) TABLE-US-00001 TABLE 1 Test No First Pass Ash Retention 1 (Blank) 24.4 2 (Comparative) 63.6 3 (Comparative) 71.2 4 (Comparative) 61.5 5 (Invention) 74.4