EP2780506A2

EP2780506A2 - A paper product and a method and a system for manufacturing a paper product

Info

Publication number: EP2780506A2
Application number: EP12849476.2A
Authority: EP
Inventors: Mika V. KOSONEN; Isko Kajanto; Kaj Koskinen
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 2011-11-15
Filing date: 2012-11-15
Publication date: 2014-09-24
Also published as: WO2013072550A3; FI20116132A; EP2780506A4; WO2013072550A2; FI124832B

Abstract

The invention relates to a method for manufacturing paper comprising fibril cellulose material, the method comprising introducing raw materials to a system, which raw materials comprise cellulose pulp (2) and fibril cellulose material (4), and conveying the raw materials to a paper machine (20) in order to produce a paper product comprising fibril cellulose material (4), wherein the fibril cellulose content of the produced paper is between 0.1 and 5 % of dry weight, preferably between 1 and 2 % of dry weight. In addition, the invention relates to a system for manufacturing paper and to a paper product.

Description

A PAPER PRODUCT AND A METHOD AND A SYSTEM FOR MANUFACTURING A PAPER PRODUCT

Field of the Invention

This invention relates to a method and a system for manufacturing paper product comprising fibril cellulose material. In addition, this invention relates to a paper product.

Background of the Invention

Cellulose, which is an abundant natural raw material, is a polysaccharide consisting of a linear chain of several hundreds to ten thousand linked D- glucose units. Cellulose is typically used as a raw material for paper products. Papers may also comprise, for example, fillers and chemicals. Typically the produced paper should have, among other things, good strength properties. In addition, the produced paper should typically be manufactured with good production efficiency.

It is an object of the present invention to present a novel solution for manufacturing paper.

Summary of the Invention

The present invention discloses a method and a system for manufacturing paper comprising fibril cellulose. In addition, the invention discloses a paper product comprising fibril cellulose. The invention is based on a usage of fibril cellulose in paper furnish and in papers. Cellulose fibers, preferably chemically pre-treated and/or mechanically pre-treated cellulose fibers, can be reduced to fibril cellulose material that can be used as a strengthening agent in paper. Fibril cellulose as such may provide a paper product with new functional properties. It has been found that if release paper had lower grammage it would be possible to have a longer amount of paper in customer rolls. However, in order to lower the grammage of the paper, the initial wet strength of the paper should be improved to maintain the runnability of the paper and, moreover, to maintain the tensile strength of the paper without sacrificing tear strength of the paper. Fibril cellulose, when used as a paper additive, has surprisingly shown to achieve these needed properties.

The present invention is based on a usage of fibril cellulose in paper furnish. Advantageously in the method according to the present invention, wherein the manufactured paper comprises fibril cellulose material, the method comprises:

introducing raw materials to a system, which raw materials include cellulose pulp and fibril cellulose material, and

- conveying the raw materials to a paper machine in order to produce paper having fibril cellulose content between 0.1 and 5 % of dry weight of furnish.

Advantageously, in the system according to the present invention, wherein the manufactured paper comprises fibril cellulose material, the method comprises:

means for introducing cellulose pulp and fibril cellulose material to the system,

at least one conveyer to convey the introduced raw materials to the paper machine in order to produce paper having fibril cellulose content between 0.1 and 5 % of dry weight.

The fibril cellulose used in this invention may be produced with mechanical treatment from anionized cellulose fibers and/or from cellulose fibers that are not anionized. The anionization of the cellulose fibers may be implemented, for example, by a reaction wherein the primary hydroxyl groups of cellulose are oxidized catalytically by a heterocyclic nitroxyl compound, or by a reaction wherein cellulose fibers are reacted with the carboxymethylating agents to form lightly carboxymethylated cellulose. Therefore, in an embodiment of the invention, cellulose fibers are oxidized by nitroxyl-mediated oxidation of hydroxyl groups of the cellulose in order to achieve anionized cellulose fibers, after which the cellulose fibers are refined into fibril cellulose material, which is added to the paper.

In another embodiment of the invention, cellulose fibers are reacted with carboxymethylating agents in order to achieve anionized cellulose fibers, after which the cellulose fibers are refined into fibril cellulose material, which is added to the paper. In this embodiment, cellulose fibers are reacted with the agents to form lightly carboxymethylated cellulose having such a degree of substitution that it is not soluble in water, i.e. cellulose fibers have a degree of substitution preferably between 0.05 and 0.35 carboxymethyl group per anhydroglucose unit, more preferably between 0.10 and 0.30 carboxymethyl group per anhydroglucose unit.

In another embodiment of the invention, cellulose fibers are refined into fibril cellulose material without anionization stage, which refined fibril cellulose material is added to the paper. Thanks to the present invention, it may be possible to achieve at least some of the below mentioned advantages:

- improved initial wet web strength of the product,

- improved dry paper strength properties, especially internal bond strength,

- low air permeability and absorption properties of the product, and

- decreased coating usage in case of a coated paper, for example decreased silicon usage in the case of a release liner.

In addition, by using fibril cellulose in the paper furnish it may be possible to significantly decrease the basis weight of the paper, especially glassine type paper, without sacrificing the properties of the paper. Therefore, thanks to the present invention, it is possible to maintain strength level of the product and, in addition, to form a denser paper structure if compared to heavier reference papers. Aspects of the invention are characterized by what is stated in the independent claims. Various embodiments of the invention are disclosed in the dependent claims. Description of the Drawings

In the following, the invention will be illustrated by drawings in which

Figs 1a-1e show schematically some example embodiments of the invention, and

Figs 2-4 show results from experimental tests.

Detailed Description of the Invention

In the following disclosure, all percentages are by weight, if not indicated otherwise. Figures 1 to 4 show some advantageous embodiments of the invention. The following reference numbers are used in this application:

1 paper,

2 cellulose pulp,

2a chemical pulp,

3 anionized cellulose material

4 fibril cellulose material,

5 chemical pre-treatment,

8 refiner,

10 refined cellulose pulp, and

20 paper machine.

Cellulose is a renewable natural polymer that can be converted to many chemical derivatives. The derivatization takes place mostly by chemical reactions of the hydroxyl groups in the β-D-glucopyranose units of the polymer. By chemical derivatization the properties of the cellulose can be altered in comparison to the original chemical form while retaining the polymeric structure.

The term "cellulose raw material" refers to any cellulose raw material source that can be used in the production of chemically and/or mechanically treated cellulose fibers. The raw material can be based on any plant material that contains cellulose. The plant material may be wood. The wood can be from softwood trees such as spruce, pine, fir, larch, douglas fir or hemlock, or from hardwood trees such as birch, aspen, poplar, alder, eucalyptus or acasia, or from a mixture of softwood and hardwood. Nonwood material can be from agricultural residues, grasses or other plant substances such as straw, leaves, bark, seeds, hulls, flowers, vegetables or fruits from cotton, corn, wheat, oat, rye, barley, rice, flax, hemp, manila hemp, sisal hemp, jute, ramie, kenaf, bagasse, bamboo or reed.

The term "chemical (cellulose) pulp" 2a refers to cellulose fibers, which are isolated from any cellulose raw material(s) by a chemical pulping process. Therefore, lignin is at least for the most part removed from the cellulose raw material. Chemical cellulose pulp is preferably sulfate wood pulp. The used chemical cellulose pulp may be unbleached or bleached. Typically, the diameter of the fibers varies from 5 to 25 pm and the length exceeds 500 pm, but the present invention is not intended to be limited to these parameters. The term "mechanical (cellulose) pulp" refers to cellulose fibers, which are isolated from any cellulose raw material by a mechanical pulping process. The mechanical pulping process could be preceded by a chemical pretreatment, producing chemimechanical pulp. The cellulose fibers used in this invention preferably comprises mechanically and/or chemically and/or chemimechanically treated cellulose fibers. Herein they are also referred as "raw material pulp".

The term "SEC" refers to specific energy consumption. The term "SR" refers to so-called Schopper-Riegler freeness of pulp. The term "WRV" refers to water retention value. It is possible to use fibril cellulose 4 in mechanical pulp containing papers, such as printing paper. The method according to the present invention may be used, for example, in Light Weight Coated (LWC) or Super Calendered (SC) papers. Advantageously the method according to the present invention is used in paper grades having high chemical pulp share, i.e. in papers comprising more chemical pulp 2a than mechanical pulp. In an embodiment, at least 80 % of dry weight, more preferably at least 90 % of dry weight and most preferably at least 95 % of dry weight of the cellulose fibers used in this invention is from chemical pulp 2a.

The term "fibril cellulose" 4 refers to a collection of isolated cellulose microfibrils or microfibril bundles derived from cellulose raw material. There are several widely used synonyms for fibril cellulose. For example: nanofibrillated cellulose (NFC), nanocellulose, microfibrillar cellulose, nanofibrillar cellulose, cellulose nanofiber, nano-scale fibrillated cellulose, microfibrillated cellulose (MFC), or cellulose microfibrils. Fibril cellulose described in this application is not the same material as the so called cellulose whiskers, which are also known as: cellulose nanowhiskers, cellulose nanocrystals, cellulose nanorods, rod-like cellulose microcrystals or cellulose nanowires. In some cases, similar terminology is used for both materials, for example by Kuthcarlapati et al. (Metals Materials and Processes 20(3):307-314, 2008) where the studied material was called "cellulose nanofiber" although they clearly referred to cellulose nanowhiskers. Typically these materials do not have amorphous segments along the fibrillar structure as fibril cellulose does, which leads to a more rigid structure. Cellulose whiskers are also shorter than fibril cellulose.

Characterizations for the fibril cellulose (advantageous examples) are presented in Tables 1 to 2.

Viscosity of the fibril cellulose: There are several commercial Brookfield viscosimeters available for measuring apparent viscosity, which are all based on the same principle. The vane spindle is preferable because of its vane geometry, which is particularly suitable for testing heterogeneous viscous materials. A low rotation speed (10 rpm) is preferable, because higher rotational speed may give falsely high viscosity values. The viscosity of anionized fibril cellulose is measured at 0.8% concentration. Attention should also be paid to obtaining dilutions of fibril cellulose having constant standard concentration to be able to compare the results correctly. Further, it is preferably that flocking is avoided. Yield Stress of the fibril cellulose can be calculated from the viscosity measurement.

Turbidity of the fibril cellulose: Typically fibril cellulose is substantially transparent in an aqueous medium. More fibrillated cellulose materials have lower turbidity values when compared to less fibrillated ones. The units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU). The measurement is carried out at 0,1 % concentration. Suitably a fibril cellulose sample is diluted with water.

Charge of the fibril cellulose: Charge can be determined by conductometric titration.

Yield Stress of the fibril cellulose: Yield stress can be measured at 0.5% concentration. Characterization for the fibril cellulose manufactured using catalytic oxidation of fibers is presented in Table 1.

Table 1 : Characterization for the fibril cellulose manufactured using TEMPO re-treatment of the cellulose material.

Characterization for the fibril cellulose manufactured using carboxymethylating reaction is presented in Table 2. Table 2: Characterization for the fibril cellulose manufactured carbox meth lation of the cellulose material.

Advantageously, the present invention is used as a solution for manufacturing low basis weight paper comprising fibril cellulose. Preferably the manufactured paper is so-called glassine type paper. The most advantageously the manufactured paper is so called release paper of a label laminate. The label laminate comprises two layers which are laminated together, i.e. a release liner and a face layer, wherein an adhesive layer is provided between the release liner and the face layer. The term "face layer" refers to "the top layer" of the label laminate, also called the face stock. The face layer comprises at least one layer that is attached to another surface with an adhesive layer, when the label laminate is used.

The term "release liner" refers to a structure comprising at least one backing material layer as base material and at least one release coating layer on the backing material layer. In other words, the backing material layer is usually coated with a thin layer of release agent, such as silicone. Therefore, the release liner can be easily removed from the face layer when the label is adhered to a substrate

Low basis weight of release paper may be needed to maximize the number of labels in a reel of manufactured label laminate. Fibril cellulose used as an additive for the paper offers a good combination of properties difficult to obtain otherwise in a cost-efficient way. Therefore, due to the present invention, it may be possible to improve the competitiveness of fibre based release papers. Advantageously the basis weight range of the manufactured paper is between 30 and 90 g/m², more preferably between 40 and 50 g/m². The amount of fibril cellulose in the manufactured paper is preferably between 0.1 and 5.0 w-% of the paper (dry weight), more preferably between 0.5 and 2.5 w-% (dry weight), and most preferably between 1 and 2 w-% of the manufactured paper (dry weight). The produced paper may be, among other things, coated, surface sized and/or calendered. Advantageously the produced paper is coated with at least one silicon coating layer in order to produce a release liner for a label laminate. The pulp from which the handsheet is made is preferably collected from the pulp flow that is going to a headbox of a paper machine. In other words, the pulp preferably comprises every compounds of the base paper to be manufactured, such as fillers, chemicals, pulps etc., but the process parameters of the paper machine cannot have any effect on the results. Typically, fibril cellulose added in small amount in paper has one, two, three or four of the following effects on handsheet, if the handsheet is manufactured from the pulp produced according to the present invention:

- Clearly lower air permeance if compared to a reference handsheets.

- Improved initial wet strength if compared to a reference handsheets. - Improved tensile strength if compared to a reference handsheets.

- Improved Scott Bond if compared to a reference handsheets .

- Higher SR or WRV without adjusting beating if compared to a reference handsheets. Fibril cellulose 4 can be added to the system as already manufactured fibril cellulose material as shown in Figures 1a, 1c and 1e, or it can be added to the system as material to be refined into fibril cellulose material as shown in Figures 1 b and 1d. The fibril cellulose material 4 may be dosed to the short circulation of a paper machine 20. In order to guarantee a proper mixing to basic furnish, the fibril cellulose material 4 is preferably dosed to a place where shear forces are present, such as a refiner 8, a pump, a mixer or a screen. In an embodiment of the invention, fibril cellulose material 4 is dosed to a thick stock and/or to a diluted stock.

Cationic polyelectrolyte, such as starch, is preferably dosed to the cellulose pulp 2 before the dosage of fibril cellulose material 4. Cationic polyelectrolyte should be added before the dosage of fibril cellulose material in case of fibril cellulose addition to short circulation.

Cationic polyelectrolyte can be any retention or strength polymer used in paper manufacturing, e.g. cationic starch, cationic polyacrylamide (CPAM) or polydimethyldiallyl ammonium chloride (PDADMAC). Also, combinations of the different polyelectrolytes can be used. Preferably, the cationic polyelectrolyte is cationic starch (CS). The cationic polyelectrolyte is added in an amount of 0.01 to 5% of dry weight of fibres in the furnish, preferably approximately 0.15 to 1.50% of dry weight.

The solution may comprise a chemical pre-treatment stage 5 (shown in Figure 1 b), wherein at least a part of the cellulose pulp 2 is anionized before it is, at least partly, refined into fibril cellulose to be added to the paper .

The terms "anionized material 3" and "anionized cellulose fibers 3" refer to a material comprising at least 90 w-% (dry weight) cellulose material, in which - cellulose is oxidized by nitroxyl-mediated (such as "TEMPO"- mediated) oxidation of hydroxyl groups of the cellulose,

and/or

- cellulose is reacted with a carboxymethylating agent in order to form lightly carboxymethylated cellulose having such a degree of substitution that it is not soluble in water, i.e. the cellulose fibers have a degree of substitution preferably between 0.05 and 0.35 carboxymethyl group per anhydroglucose unit, more preferably between 0.10 and 0.30 carboxymethyl group per anhydroglucose unit.

If the anionized cellulose fibers comprise the lightly carboxymethylated cellulose, the manufacturing of said lightly carboxymethylated cellulose advantageously comprises a step in which a first chemical, i.e. an alkalizing agent, is dosed and absorbed into the cellulose raw material before or during dosing of a second chemical, i.e. an anionic agent. The first chemical added to the system, i.e. an alkalization agent, may be an alkali metal hydroxide and it is used for activating the pulp. In other words, alkalization agent activates the fibers and contributes to the penetration of the second chemical into the fibers. The alkalization agent can be added to the reaction mixture, for example, in an aqueous solution and/or in a dry state. The most preferably said first chemical (i.e. the alkalization agent) is sodium hydroxide NaOH. The second chemical, i.e. the main chemical added to the system is preferably monochloroacetic acid or a salt thereof, and most preferably sodium monochloroacetic acid. The second chemical can be added to the system in a dry state and/or in an aqueous alkaline solution and/or in a gas form in order to produce ceiiuiosic material. According to this embodiment of the invention, a third chemical, for example H2O2 may be added to the system in order to control (i.e. to decrease) the degree of substitution of the cellulose material.

The anionized cellulose fibers may comprise cellulose material, wherein primary hydroxyl groups of cellulose are oxidized catalytically by a heterocyclic nitroxyl compound, for example 2,2,6,6-tetramethylpiperidinyl-1- oxy free radical, "TEMPO", after which the material is refined at least partly into fibril cellulose. Other heterocyclic nitroxyl compounds known to have selectivity in the oxidation of the hydroxyl groups of C-6 carbon of the glucose units of the cellulose can also be used. The term "oxidation of cellulose" refers to the oxidation of the hydroxyl groups (of cellulose) to aldehydes and/or carboxyl groups. It is preferred that the hydroxyl groups are oxidized to carboxyl groups, i.e. the oxidation is complete, before the refining step in at least one refiner is implemented.

In an advantageous embodiment of the present invention, anionized cellulose material 3 is added to the system as material to be refined into fibril cellulose material 4. In this embodiment shown in Figures 1b and 1d, an addition of the anionized cellulose material 3 is preferably implemented before at least one refiner stage of the cellulose pulp 2a. Most preferably the addition of said anionized cellulose material 3 is done to the unbeaten chemical pulp to be conveyed to at least one refiner 8. The cellulose pulp 2 to be conveyed to at least one refiner 8 may, in addition or instead of, comprise fibers that are pre- refined by at least one refiner. The refiner 8 is preferably a conical refiner, a disc refiner or cylindrical refiner. If the cellulose pulp 2 and the anionized cellulose material 3 are combined with each other before at least one refiner step, anionized cellulose material 3 is fed together with cellulose pulp 2 through beating process in paper machine approach system. In this case, fibrillating of fibril cellulose takes advantageously place at least partly during pulp beating, i.e. fibres get fibrillated due to energy consumed during the beating process. Therefore, advantageously, a separate fibrillating stage to produce fibril cellulose is not needed in order to refine fibril cellulose material from the anionized cellulose material 3. The anionized cellulose material 3 has preferably a high anionic charge and, thus, it is relatively easily fibrillated under shear forces. Thanks to this embodiment of the present invention, it is possible to mix pulp 2 and fibril cellulose efficiently with each other without any separate mixing and fibrillating aggregates.

Due to the present invention it is possible to manufacture a paper product comprising at least some of the following properties:

- high wet strength,

- increased dry tensile strength,

- greatly improved internal bonding,

- lower air permeability, and

- higher transparency.

The invention may cause an effective dispersing of fibril cellulose and a proper mixing with base furnish. In addition, thanks to the present invention, paper properties may be improved without loss of drainage speed. Experimental tests

In the experimental tests, different kind of pulps for paper products were manufactured. Paper sheets were made from the produced pulps and tested afterwards. Example 1

Raw materials and a trial plan

The trial comprised:

- a fourdrinier type former,

- a press section with two nips,

- running speed at 15 m/min,

- bar coating,

- calendering surface temperature ~100°C, pressure setting 140 kN/m, 2 nips

Coating and calendering were done in laboratory and paper was made with a pilot machine.

Trial plan was adjusted to 1 % and 3% fibril cellulose addition. Starch amount was varied from 1 % to 2 %. The trial plan is shown in Table 3. Table 3. Trial plan for example 1.

The paper sample size used was A4. Coated sheets were moisturized over night at RH 80%, +23°C. Air conditioning before measurements was 50 %RH, +23°C. Test Results

Results based on laboratory sheets. Air permeability results are shown in Figure 2a, and tensile strength results are shown in Figure 2b.

It was shown during the experimental tests that basis weight of the produced paper could be decreased 10 g/m² with constant or improved dry paper strength properties if only a small amount of fibril cellulose (between 1 and 1 ,5 %) was added to the pulp. Simultaneously original wet web strength of paper was increased. Air permeability was greatly reduced even in case of lower basis weight paper compared to reference paper. In addition, converting tests have shown a reduction in silicon consumption. Release values of fibril cellulose trial points were comparable to reference samples with lower silicon weight.

Especially good results were shown with an amount of approximately 3% of fibril cellulose. An addition of 2% of CS together with the addition of fibril cellulose showed some good properties.

Example 2

Raw materials and a trial plan The trial was implemented with realistic running conditions:

- glassine type furnish,

- running speed at 600 m/min,

- a head box,

- a hybrid former, and

- a shoe press.

Two kind of anionized cellulose fibers were fibrillated: 1 ) Tempo-treated fibril cellulose (fibril cellulose type 1 in Figures 3a-3b), and 2) lightly carboxymethylated fibril cellulose (fibril cellulose type 2 in Figures 3a-3b). During the trial the two anionized cellulose material were compared with each other. In addition, basis weight and amount of fibril cellulose were studied.

Results

The trial showed very promising results. Thanks to the fibril cellulose used in the paper:

- porosity level decreased by 20%,

- 10 g/m² basis weight reduction potential was shown at constant tensile level,

- 1 %-unit lower brightness but up to 4%-units lower opacity,

- oil absorption decreased by 20%,

- significant increase in wet web strength,

- both tested anionized pulps seemed to give good results, and - no major difference between 1 % and 2% fibril cellulose dosing.

Drainage is an issue with fibril cellulose. However, in pilot scale trials the decrease of dry matter after wire section was only 1 %-unit. Dry matter after wet pressing seems to depend on the press construction. In addition, the reduction of grammage may improve drainage.

In Figure 3a is shown an effect of fibril cellulose on tensile strength of the produced paper. As can be seen, a small amount of fibril cellulose has a strong effect on tensile strength. In Figure 3b is shown an effect of fibril cellulose on air permeability of the produced paper. As can be seen, the addition of fibril cellulose clearly decreased the air permeability properties of the produced paper.

Figures 4a and 4b show results of test runs conducted in mill scale, where Tempo-treated fibril cellulose was supplied to a refiner together with untreated and unbeaten pulp. The energy consumption (SEC) was also lowered by 10% in the test run. The diagram in Fig. 4a shows the tensile index of the manufactured paper in machine direction as Nm/g. The middle column, representing the test made with the mixed pulp, shows how the tensile index of the paper increased compared with reference runs. Fig. 4b shows the effect on air permeability as Bekk air resistance (s/10 ml). The Bekk air resistance of the paper manufactured of the mixed pulp was higher compared with the reference runs, which means lowered air permeability.

Figs. 4c and 4d show some additional laboratory scale test data in terms of Bendtsen air permeance and tensile index. Tempo-treated fibril cellulose was dosed in an amount of 0.5 to 2 wt-% of dry weight of the furnish. In tests no. 12 and 13 fibril cellulose was refined together with unbeaten pulp to achieve 1-2 wt% of the furnish. All papers made of mixed pulp showed lowered air permeance expressed as Bendtsen air permeance (ml/min) and at the same time they showed increased tensile index (Nm/g) compared with reference.

A paper produced from the pulp manufactured according to the present invention may have many advantages. For example, a grammage of the manufactured paper may be decreased. In addition, the amount of a coating may be decreased due to the new properties of the paper. Thus, the competitiveness of renewable fibre based release products against plastic may be improved due to the present invention

One skilled in the art readily understands that the different embodiments of the invention may have applications in environments where optimization of a paper product comprising fibril cellulose is desired. Therefore, it is obvious that the present invention is not limited solely to the above-presented embodiments, but it can be modified within the scope of the appended claims.

Claims

Claims:

1. A method for manufacturing paper comprising fibril cellulose material, the method comprising

- introducing raw materials to a system, which raw materials comprise cellulose pulp (2) and fibril cellulose material (4),

conveying the raw materials to a paper machine (20) in order to produce a paper product comprising fibril cellulose material (4), wherein the fibril cellulose content of the produced paper is between 0.1 and 5 % of dry weight.

2. The method according to claim 1 , characterized in that the paper is a release paper.

3. The method according to claim 1 or 2, characterized in that at least part of the fibril cellulose material is added before at least one refiner (8).

4. The method according to any of the preceding claims, characterized in that the fibril cellulose material (4) comprises material that is made from anionized cellulose material (3).

5. The method according to claim 4, characterized in that at least part of the fibril cellulose material is refined from anionized pulp material into fibril cellulose material in at least one refiner (8).

6. The method according to claim 4 or 5, characterized in that the primary hydroxyl groups of cellulose are oxidized catalytically by a heterocyclic nitroxyl compound before the material is made into fibril cellulose material (4).

7. The method according to claim 4 or 5, characterized in that cellulose fibers are reacted with carboxymethylating agents in order to achieve anionized cellulose fibers having a degree of substitution between 0.05 and 0.35 carboxymethyl group per anhydroglucose unit, after which the cellulose fibers are made into fibril cellulose material.

8. The method according to any of the preceding claims 4 to 7, characterized in that the anionized cellulose pulp is lead to at least one refiner (8) together with chemical pulp that is not anionized, and that the anionized cellulose pulp is at least partly refined into fibril cellulose material in said at least one refiner (8).

9. The method according to any of the preceding claims, characterized in that at least part of the fibril cellulose (4) is added to a short circulation of the paper machine as readymade fibril cellulose.

10. A system for manufacturing paper comprising fibril cellulose material, the system comprising:

means for introducing cellulose pulp (2) and fibril cellulose material (4) to the system,

at least one conveyer to convey the introduced raw materials to the paper machine (20) in order to produce a paper product comprising fibril cellulose material, wherein the fibril cellulose content of the produced paper is between 0.1 and 5 %.

11. A paper comprising fibril cellulose material and cellulose pulp, wherein the paper has at least one of the following:

improved bonding strength properties,

improved wet web tensile index, and

- lowered air permeability properties.

12. The paper according to claim 11 , characterized in that the fibril cellulose content of the manufactured paper is between 0.1 and 5%, preferably between 1 and 2%, of dry weight.

13. The paper according to claim 11 or 12, characterized in that the paper is a release paper.

14. A use of fibril cellulose for manufacturing release paper, wherein fibril cellulose content of the manufactured release paper is between 0.1 and 5 % of dry weight.