Method for producing roll paper containing microfibrillated cellulose and roll paper

Abstract

The present invention relates to a method for producing a roll of paper comprising microfibrillated cellulose, the method comprising the steps of providing a suspension comprising 0.1% to 50% by weight of microfibrillated cellulose based on the total dry weight, forming a fibrous web of the suspension on a wire, the web having a dry content of 1 to 25% by weight, dewatering the fibrous web in at least one dewatering unit, and polishing at least one side of the dewatered fibrous web in a polishing unit to form a roll of paper. The present invention further relates to MG paper produced according to this method.

Description

[Technical Field]

[0001] The present invention relates to a method for producing rolled paper containing microfibrillated cellulose, and to rolled paper containing microfibrillated cellulose produced according to the method. [Background technology]

[0002] Roll (MG) paper is used for label paper, special printing applications, and various food and hygiene packaging applications. Typically, one surface of the paper is glossy, i.e., it is treated to increase the gloss of the surface of the paper. Polishing at least one surface of the paper is performed to provide the paper with improved gloss and increased surface density without losing too much bulk. The glossy surface improves barrier properties, especially improved barrier against grease and oils, and also provides improved printing properties to the surface.

[0003] In addition to having good barrier properties, it is important that MG paper also has good mechanical strength in order for it to cope with the high demands in final packaging applications.

[0004] Microfibrillated cellulose (MFC) is known to be used as a strength or barrier additive when producing paper or paperboard products. However, MFC has a very high water-binding capacity, making it very difficult to reduce the water content of slurries containing microfibrillated cellulose. The dewatering demands of products containing large amounts of MFC are therefore very high. Therefore, it is difficult to dewater products containing large amounts of MFC without reducing their mechanical or barrier properties.

[0005] During the manufacture of web paper it is important that the runnability of the paper is improved. By adding barrier or strength additives to the paper there is a risk of the web lifting or bubbling during drying.

[0006] Therefore, there is a need for new methods to efficiently produce improved MG paper with good strength and barrier properties. Summary of the Invention

[0007] It is an object of the present invention to provide a method for producing rolled paper comprising microfibrillated cellulose in an efficient manner without adversely affecting the strength and barrier properties of the paper, which method further eliminates or mitigates at least some of the disadvantages of prior art methods.

[0008] The present invention is defined by the accompanying independent claims. Embodiments are set out in the accompanying dependent claims and the following description.

[0009] The present invention relates to a method for producing a paper roll comprising microfibrillated cellulose, the method comprising the steps of providing a suspension comprising 0.1% to 50% by weight of microfibrillated cellulose based on the total dry weight, forming a fibrous web of the suspension on a wire, the web having a dry content of 1 to 25% by weight, dewatering the fibrous web in at least one dewatering unit, and polishing at least one surface of the dewatered fibrous web in a polishing unit to form the paper roll.

[0010] It has been found that by using microfibrillated cellulose it is possible to produce rolled paper with good strength and barrier properties. Because MG paper is a very dense paper, it was surprisingly possible to add very large amounts of MFC to the suspension and still produce MG paper with good strength and barrier properties at high production speeds, i.e. the combination of the dewatering and glazing units still allowed the fibrous web to be dewatered and dried in an efficient manner.

[0011] The dewatering unit is preferably a shoe press, belt press or similar extended nip press device having a nip length of at least 150 mm. It has been found that the use of a shoe press, belt press or similar extended nip press device and a polishing unit makes it possible to improve the dewatering of the fibrous web without destroying the barrier properties of the web.

[0012] The polishing unit may be a Yankee cylinder, a glassine calender, or an extended nip calender, such as a shoe calender or a belt calender. The polishing unit is preferably a Yankee cylinder. It has been found that using a Yankee cylinder as the polishing unit and the dewatering unit makes it possible to dry at least one surface of the fibrous web and provide a polished surface in an efficient manner.

[0013] After the fibrous web has been led through a polishing unit, it may be calendered in a calender. Any known calender may be used. It is possible to calender one or both sides of the roll.

[0014] The fibrous web preferably has a dry content of 25-45% by weight after being led through at least one dewatering unit. The fibrous web preferably has a dry content of more than 35% by weight, preferably more than 45% by weight, before being treated in the polishing unit, and the dry content of the fibrous web before being treated in the polishing unit is preferably less than 85% by weight, more preferably 35-85% by weight, or even more preferably 45-85% by weight. By using the above solids content of the fibrous web before being treated in the dewatering and polishing units, roll paper has improved strength, good barrier properties and is produced in an efficient manner.

[0015] The suspension may also contain a hydrophobizing chemical, such as AKD, ASA, or rosin size, in an amount of 0.1 to 10 kg / ton, preferably 0.1 to 5 kg / ton, and more preferably 0.2 to 2 kg / ton, based on dry weight. The addition of a hydrophobizing chemical to the suspension as an internal sizing agent improves the barrier properties of the web. It has also been found that the combination of MFC and a hydrophobizing chemical improves adhesion of the web to the polishing unit and improves process runnability.

[0016] The fibrous web may include two or more layers containing microfibrillated cellulose. In this manner, a multi-layer paper product containing two or more layers containing microfibrillated cellulose is formed. A fibrous web containing two or more layers containing microfibrillated cellulose can be formed by applying at least two suspensions containing microfibrillated cellulose to a wire. The at least two suspensions can be added to the wire in a multi-layer headbox or by using two different headboxes. At least two suspensions, at least one of which contains microfibrillated cellulose, are applied to the wire such that a first suspension is applied onto the wire, i.e., in direct contact with the wire, and the other suspension is applied onto the first suspension. In this manner, a multi-layer fibrous web is formed. It may also be possible to attach two or more fibrous webs together after they are formed on the wire to form a multi-layer paper product, i.e., a first fibrous web is formed on a first wire from a first headbox, and a second fibrous web is formed on a wire support from a second headbox. The first and second fibrous webs then adhere to each other to form a multi-layer fibrous web. Therefore, it is possible to produce multiple fiber webs by using two, three, or more headboxes and wires, then attach the produced fiber webs to each other, and lead the multiple fiber web containing two or more fiber webs through a dewatering unit and a glazing unit to produce rolled paper. It may be preferable to produce three-ply rolled paper in which only the suspension forming the mid-ply of MG paper contains MFC. In this way, the amount of MFC in the mid-ply can be increased, thereby improving the strength and barrier properties of the paper without the disadvantages of peeling or insufficient adhesion to the surface of the glazing unit.

[0017] The resulting roll paper is preferably coated on at least one side with a coating composition. The coating composition preferably comprises a water-soluble polymer, such as cellulose, starch, nanocellulose, a cellulose derivative, e.g., carboxymethylcellulose, a starch derivative, polyvinyl alcohol, or a polyvinyl alcohol derivative, or a combination thereof. The suspension may further comprise performance or functional chemicals, such as a crosslinker, nanofiller, or softener. The coating is preferably applied to the polished side of the MG paper. The coating composition further improves the barrier properties of the paper. Surprisingly, it has been found that adding MFC to paper improves the coating properties of the paper, i.e., significantly improves the coverage of the coating on the paper surface. One theory is that the density of the polished side increases, meaning the coating "sits" on the paper surface, allowing the coating amount to be reduced and still achieve a uniform coating on the surface. The coating is preferably applied in an amount of 0.1 to 5 gsm, preferably 0.2 to 4 gsm, and even more preferably 0.3 to 3 gsm.

[0018] The present invention further relates to a roll of paper produced according to the above method, which contains 0.1 to 50% by weight of microfibrillated cellulose. The roll of paper preferably has a viscosity of 200 cc / m according to ASTM D-3985. 2 / 24h oxygen transmission rate (OTR) value (23°C, 50% RH) of less than 1500 J / m² / 24h, a basis weight of 25 to 160 gsm, a Gurley Hill value of at least 25,000 s / 100 ml as measured according to standard ISO 5636 / 6, more preferably at least 40,000 s / 100 ml, at least one polished side (before the addition of the final coating) having a surface roughness PPS value according to ISO 8791-4 of less than 5 μm, preferably less than 2 μm, a KIT value of at least 6, more preferably more than 8, and a KIT value of 1500 J / m² / 24h as measured according to TAPPI UM-403 on 60 gsm paper. 2 More than 1600 J / m 2 More than 1800 J / m 2It has a Scott Bond value exceeding DETAILED DESCRIPTION OF THE INVENTION

[0019] It has been found that the present invention makes it possible to produce rolls of paper containing MFC with improved strength and good barrier properties, while still achieving high production speeds. Since the dewatering process is often the most difficult process step for the production of large quantities of MFC-containing paper products, improving the dewatering process can also improve the production speed of the entire product line. Surprisingly, it has been found that the combination of a dewatering unit, preferably using an extended nip press such as a shoe press, followed by a polishing unit, preferably a Yankee cylinder, makes it possible to produce rolls of paper containing microfibrillated cellulose in a good and efficient manner.

[0020] The suspension contains 0.1% to 50% by weight of microfibrillated cellulose, preferably 2% to 40% by weight, or even more preferably 5% to 30% by weight, of MFC, based on the total dry weight. In addition to MFC, the suspension also contains cellulosic fibers, preferably chemical pulp fibers such as kraft pulp fibers. The suspension may also contain mechanical pulp fibers or chemothermomechanical pulp (CTMP) fibers. The suspension preferably contains 50% to 99.9% by weight, preferably 60% to 98% by weight, or even more preferably 70% to 95% by weight, of cellulosic fibers, based on the total dry weight. The fibers may be hardwood or softwood fibers. The cellulosic fibers in the suspension, i.e., both the "normal" fibers and the MFC, may be bleached to produce white paper products or left unbleached to produce brown paper products.

[0021] The microfibrillated cellulose of the suspension preferably has a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1, of more than 80, preferably more than 90, even more preferably more than 95, preferably between 90 and 100, or even more preferably between 95 and 100. Consequently, the suspension preferably comprises fine grade MFC quality, which is usually very difficult to dewater.

[0022] The suspension may also contain a hydrophobizing chemical such as AKD, ASA, or rosin size in an amount of 0.1 to 10 kg / ton, preferably 0.1 to 5 kg / ton, and more preferably 0.2 to 2 kg / ton, based on dry weight. Adding a hydrophobizing chemical to the suspension as an internal sizing agent improves the barrier properties of the paper roll. The combination of MFC and a hydrophobizing chemical has also been found to improve the adhesion of the web to the polishing unit, which in turn improves the runnability of the process.

[0023] The suspension may also include additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, fillers, retention and / or drainage chemicals, flocculating additives, deflocculating additives, dry strength additives, softeners, crosslinking aids, dyes and colorants, wet strength resins, fixatives, defoaming aids, microbial and slime control aids, or mixtures thereof.

[0024] The wire is preferably a paper or board machine wire, and dewatering and production of the rolled paper preferably occurs on a paper machine. A paper machine (or papermaking machine) is an industrial machine used in the pulp and paper industry to produce paper in large quantities at high speeds. Modern papermaking machines are typically based on the principle of a Fourdrinier machine, which uses a moving woven mesh, "wire," to create a continuous web by filtering out fibers held in a pulp suspension and producing a continuously moving wet web of fibers. This wet web is dried in the machine to produce a strong paper web.

[0025] A fibrous web of the suspension is formed on a wire, the web having a dry content of 1 to 25% by weight. The fibrous web is then further dewatered or drained on the wire by any known method. Further dewatering typically involves pressing the web to squeeze out as much water as possible. Further dewatering may involve, for example, passing the formed multilayer web through the press section of a papermaking machine, where the web is passed between large rolls loaded under high pressure to squeeze out as much water as possible. The removed water is typically collected by a cloth or felt. The fibrous web is then conducted through at least one dewatering unit. After being conducted through at least one dewatering unit, the fibrous web preferably has a dry content of 25 to 45% by weight. The fibrous web dewatered in the dewatering unit is then conducted through a polishing unit. It is preferred that the fibrous web have a dry content of more than 35% by weight, preferably more than 45% by weight, before being processed in the polishing unit. The dry content of the fibrous web before being treated in the polishing unit is preferably less than 85 wt. %, more preferably 35-85 wt. %, or even more preferably 45-85 wt. By using the above-mentioned solids content of the fibrous web before being treated in the dewatering and polishing units, roll paper has improved strength, good barrier properties and is produced in an efficient manner.

[0026] The dewatering unit is preferably a shoe press, belt press or similar extended nip press device having a nip length of at least 150 mm. It has been found that the use of a shoe press, belt press or similar extended nip press device allows for improved dewatering of the web without increasing the risk of wetting bubbles in the web and without destroying the barrier properties of the fibrous web.

[0027] The extended nip press device preferably has a nip length of at least 150 mm, preferably at least 200 mm, preferably 150-350 mm, even more preferably 200-300 mm.

[0028] The linear load in the extended nip press apparatus is preferably 250 to 1500 kN / m, i.e., the maximum linear load used in the apparatus, e.g., shoe press. The linear load used is preferably changed during processing of the fibrous web. By gradually or stepwise increasing the linear load in the extended nip press apparatus, web dewatering is improved, i.e., a web with a higher dry content can be produced without destroying the barrier properties. It is also possible to increase the linear load in pulses during processing in the nip, i.e., the linear load is increased at least once in at least one pulse during processing of the fibrous web in the shoe press. This can be repeated during processing in the extended nip press apparatus. When two or more extended nip press apparatuses, e.g., shoe presses, are used, it is possible to use the same linear load profile in both apparatuses. However, it is often preferable to design the linear load profile using different linear load profiles so that dewatering is improved without degrading the barrier properties of the dewatered web.

[0029] The shoe press refers to an extended nip press device equipped with a shoe press nip. Any known shoe press can be used. The shoe press nip can be formed using a shoe and roll, or a large-diameter soft roll and roll. The roll preferably has a synthetic belt, but can also have a metal belt. The large-diameter soft roll can have a diameter of 1.5 to 2 meters.

[0030] The position of the shoe relative to the fibrous web can be changed by changing the inclination angle of the shoe press. The inclination angle of at least one shoe press is preferably 7 to 24 degrees. The inclination angle affects the peak linear load, and adjusting the linear load is a way to improve web dewatering efficiency.

[0031] The nip time is preferably at least 30 ms. Depending on the nip length and production speed, the time that the fibrous material is under pressure in the shoe press will vary.

[0032] By belt press is meant an extended nip press device comprising a belt. Any known belt press can be used.

[0033] It may be preferable to use at least two extended nip press devices, preferably at least two shoe presses, and to arrange the two extended nip press devices behind each other. The fibrous web is then first guided through the first shoe press and then through the second shoe press. It has been found that in this way, it is possible to further improve the dewatering of the fibrous web and still produce paper with good barrier properties. The nip pressure used in the first shoe press is preferably lower than the nip pressure used in the second shoe press. The at least two shoe presses are preferably arranged on different sides of the fibrous web. In this way, it is possible to dewater the web from both directions through the fibrous web. When multiple shoe presses are used, the total nip length, i.e., the sum of the nip lengths of the shoe presses, is preferably greater than 350 mm, preferably greater than 400 mm, and even more preferably greater than 450 mm. The geometric designs of the at least two shoe presses are preferably different; for example, one shoe press can have a concave design and one shoe press can have a convex design.

[0034] The polishing unit may be a Yankee cylinder, a glassine calender, or an extended nip calender, such as a shoe calender or a belt calender. The polishing unit is preferably a Yankee cylinder. It has been found that using a Yankee cylinder as a polishing unit allows both drying and providing a polished surface on at least one surface of the fibrous web. Yankee cylinders are typically used to dry tissue paper, which is a very porous material. The use of Yankee cylinders and how drying affects paper have been thoroughly described by Walker in his article "High Temperature Yankee Hoods Save Energy and Improve Quality," P&P, July 2007. When a Yankee cylinder is used to dry a product, the liquid in the product flows through the product toward the Yankee cylinder, i.e., toward the heat and vapor formed during drying. The liquid in our product also contains microfibrils, which results in an increased concentration of microfibrils on the smoothed and polished surface of the paper.

[0035] The temperature of the polishing unit is preferably above 100° C., preferably between 110 and 190° C. The first surface of the fibrous web is in direct contact with the polishing unit, for example, in direct contact with the surface of a Yankee cylinder.

[0036] To control the adhesion of the fibrous web to a polishing unit, such as a Yankee cylinder, it may be preferable to add an adhesion control additive to the surface of the polishing unit. This has been shown to be even more important when microfibrillated cellulose is used, as the microfibrillated cellulose in the fibrous web tends to overtension the fibrous web, which can cause the web to lift or bubble from the surface of the polishing unit. The adhesion control additive ensures sufficient adhesion of the web to the surface of the polishing unit. Suitable adhesion control additives may be water-soluble or partially water-soluble polymers such as polyvinyl alcohol (PVOH), polyamidoamine derivatives, polyethyleneimine, polyacrylamide, and / or polyacrylamide derivatives. The degree of hydrolysis of the PVOH used is preferably less than 99%, even more preferably less than 98%. It is also possible to use modified polymers, such as modified PVOH, preferably ethylene, carboxylated PVOH, cationized PVOH, or siliconized PVOH. The adhesion control additive may also contain nanoparticles such as nanoclay and / or nanocellulose. The adhesion control additive may also contain 0.5 to 20 wt. % nanoparticles based on the total dry weight. The amount of adhesion control additive applied to the surface of the polishing unit is preferably 0.1 to 10 gsm. The adhesion control additive is preferably applied to the surface of the polishing unit by spraying. The adhesion control additive is preferably applied to the surface of the polishing unit as a solution or foam.

[0037] After being led through the polishing unit, the fibrous web may be calendered in at least one calender. Any known calender can be used, such as a mechanical calender, a multi-nip calender, a soft-nip calender, a belt calender, etc. It may be preferable to use a shoe calender or any other extended nip calender. It is possible to calender one or both sides of the paper roll. The calendering is preferably carried out in-line.

[0038] After being calendered, the fibrous web may be treated in a decurling unit, in which way the tendency of the paper to curl can be further reduced.

[0039] The fibrous web preferably comprises two or more layers containing microfibrillated cellulose. In this manner, a multi-layer paper product containing two or more layers containing microfibrillated cellulose is formed. A fibrous web containing two or more layers containing microfibrillated cellulose can be formed by applying at least two suspensions containing microfibrillated cellulose to a wire. The at least two suspensions can be added to the wire in a multi-layer headbox or by using two different headboxes. It may also be possible to create a multi-layer fibrous web using other application methods, such as spray or curtain application using a flexJet headbox. At least two suspensions containing microfibrillated cellulose are applied to the wire, with the first suspension being applied onto the wire, i.e., in direct contact with the wire, and the other suspension being applied onto the first suspension. In this manner, a multi-layer fibrous web is formed. It may also be possible to attach two or more fibrous webs together after they have been formed on the wire to form a multi-layer paper product, i.e., a first fibrous web is formed on a first wire from a first headbox, and a second fibrous web is formed on a wire support from a second headbox. The first and second fibrous webs are then adhered to each other to form a multi-fibrous web. The at least two suspensions containing microfibrillated cellulose may contain the same type, amount, consistency, etc. of microfibrillated cellulose, or different types, amounts, consistencies, etc. of the at least two suspensions may be used. The multi-layer fibrous web may contain two, three, four, five, or more layers. Therefore, it is also possible to produce a multi-fibrous web by using two, three, or more headboxes and wires, and then attach the produced fibrous webs to each other and guide the multi-fibrous web containing two or more fibrous webs through a dewatering unit and a polishing unit to produce roll paper.

[0040] The resulting roll paper is preferably coated on at least one side with a coating composition. The coating composition preferably contains starch, carboxymethyl cellulose, and / or microfibrillated cellulose. The coating is preferably applied to the polished side of the MG paper. The coating composition further improves the paper's barrier properties. Surprisingly, it has been found that adding MFC to paper improves the paper's coating properties, i.e., significantly improves the coverage of the coating on the paper's surface. One theory is that the density of the polished side increases, meaning the coating "sits" on the paper's surface, allowing for a reduced coating weight while still achieving complete coating coverage. The coating is preferably applied in an amount of 0.1 to 5 gsm, preferably 0.2 to 4 gsm, and even more preferably 0.3 to 3 gsm. The coating composition can be applied to the paper's surface using any known coating technique.

[0041] The present invention further relates to MG paper produced according to the methods described herein, which comprises 0.1 to 50 wt. % microfibrillated cellulose, preferably 2 to 40 wt. %, or even more preferably 5 to 30 wt. %.

[0042] The roll paper preferably has a density of 200 cc / m according to ASTM D-3985 2 / 24h less, preferably 150cc / m 2 / 24h or less, even more preferably 100cc / m 2 / 24h oxygen transmission rate (OTR) value (23°C, 50% RH) of less than

[0043] The MG paper preferably has a basis weight of 25 to 160 gsm, preferably 30 to 140 gsm, or even more preferably 40 to 130 gsm.

[0044] The MG paper preferably has a Gurley Hill value, measured according to standard ISO 5636 / 6, of at least 25,000 s / 100 ml, preferably at least 40,000 s / 100 ml, more preferably at least 60,000 s / 100 ml.

[0045] The MG paper preferably has at least one polished side with a surface roughness PPS value according to ISO 8791-4 of less than 5 μm, preferably less than 2 μm (before addition of the final coating).

[0046] MG paper preferably has a thermal resistance of 1500 J / m2 as measured according to TAPPI UM-403 on 60 gsm paper. 2 More than 1600 J / m 2 More than 1800 J / m 2 As a result, the MG paper produced has a very high strength.

[0047] MG paper typically exhibits good resistance to grease and oil. The grease resistance of paper is evaluated by the KIT test according to standard ISO 16532-2. The test uses a series of mixtures of castor oil, toluene, and heptane. As the oil to solvent ratio decreases, the viscosity and surface tension also decrease, making successive mixtures more difficult to tolerate. Performance is evaluated by the highest numbered solution that does not darken the sheet after 15 seconds. The highest numbered solution (most aggressive) that remains on the paper surface without causing failure is reported as the "Kit Rating" (maximum 12). In some embodiments, the KIT value of MG paper is at least 6, preferably at least 8, and even more preferably at least 10, as measured according to standard ISO 16532-2.

[0048] Preferably, the MG paper has high resilience. In some embodiments, the multi-layer MG paper exhibits less than 30%, preferably less than 20%, and more preferably less than 10% failure when tested as a Category II material according to the PTS-RH021 / 97 test method.

[0049] Microfibrillated cellulose (MFC), in the context of patent applications, is intended to mean nanoscale cellulose particle fibers or fibrils having at least one dimension less than 1000 nm. MFC comprises partially or wholly fibrillated cellulose or lignocellulose fibers. While liberated fibrils have diameters less than 1000 nm, the actual fibril diameter or particle size distribution and / or aspect ratio (length / width) depend on the source and production method. The smallest fibrils, called elementary fibrils, have a diameter of about 2 to 4 nm (see, e.g., Chinga-Carrasco, G., Cellulose fibers, nanofibrils, and microfibrils: The morphological sequence of MFC components from a plant physiology and fiber technology point of view, Nanoscale research letters 2011, 6:417), although aggregated forms of elementary fibrils, also defined as microfibrils (Fengel, D., Ultrastructural behavior of cell wall polysaccharides, Tappi J., March 1970, Vol. 53, No. 3), are typically the main product obtained when producing MFCs, for example, by using extended purification or pressure-drop cracking processes. Depending on the source and manufacturing process, the length of the fibrils can vary from about 1 micrometer to more than 10 micrometers. The crude MFC grade contains a significant fraction of fibrillated fibres, i.e. fibrils (cellulose fibres) protruding from the tracheids, and a certain amount of fibrils (cellulose fibres) free from the tracheids.

[0050] MFC has different acronyms, including cellulose microfibrils, fibrillated cellulose, nanocellulose, nanofibrillated cellulose, fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, microfibril cellulose, microfibril aggregates, and cellulose microfibril aggregates. MFC can also be characterized by various physical or physicochemical properties, such as a large surface area or its ability to form a gel-like material at low solids contents (1-5 wt%) when dispersed in water. The cellulose fibers are preferably fibrillated to such an extent that the final specific surface area of ​​the formed MFC is about 1 to about 200 m / g, or more preferably 50-200 m / g, as determined on freeze-dried material using the BET method.

[0051] Various methods exist for producing MFC, such as single-pass or multi-pass purification, prehydrolysis, followed by purification or high-shear disintegration or fibril liberation. To make MFC production both energy-efficient and sustainable, one or more pretreatment steps are usually required. Thus, the cellulose fibers of the pulp feedstock can be enzymatically or chemically pretreated, for example, to hydrolyze or swell the fibers or to reduce the amount of hemicellulose or lignin. Cellulose fibers may also be chemically modified before fibrillation, so that the cellulose molecules contain functional groups other than (or more than) those found in the original cellulose. Such groups include, among others, carboxymethyl (CMC), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, e.g., "TEMPO"), or quaternary ammonium (cationic cellulose). After modification or oxidation by one of the above methods, it is easier to break down the fibers into MFC or nanofibrillar sizes or NFC.

[0052] Nanofibrillar cellulose may contain some hemicellulose, the amount depending on the plant source. Mechanical disintegration of pretreated fibers, such as hydrolyzed, preswollen, or oxidized cellulose feedstock, is carried out using appropriate equipment, such as refiners, grinders, homogenizers, colloidal grinders, friction grinders, ultrasonic sonicators, microfluidizers, macrofluidizers, or fluidizer-type homogenizers. Depending on the MFC production method, the product may also contain fines, nanocrystalline cellulose, or other chemicals present in, for example, wood fiber or papermaking processes. The product may also contain varying amounts of micron-sized fiber particles that are not efficiently fibrillated.

[0053] MFC is made from wood cellulose fibers, both hardwood and softwood. It can also be made from microbial sources, agricultural fibers, such as straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably made from pulp from virgin fibers, including mechanical pulp, chemical pulp, and / or thermomechanical pulp. It can also be made from shredded or recycled paper.

[0054] In view of the above detailed description of the invention, other modifications and variations will become apparent to those skilled in the art, but it is evident that such other modifications and variations can be affected without departing from the spirit and scope of the invention.

Claims

1. 1. A method for producing a roll of paper comprising microfibrillated cellulose, comprising: - providing a suspension comprising 0.1% to 50% by weight of microfibrillated cellulose based on the total dry weight; - forming a fibrous web of said suspension on a wire, said fibrous web having a dry content of 1 to 25% by weight; - dewatering the fibrous web in at least one dewatering unit; - polishing at least one surface of the dewatered fibrous web in a polishing unit to form a paper roll; A method comprising:

2. 10. The method of claim 1, wherein the dewatering unit is a shoe press, belt press or similar extended nip press unit having a nip length of at least 150 mm.

3. 3. The method according to claim 1 or 2, wherein the polishing unit is a Yankee cylinder, an extended nip calender or a glassine calender.

4. 4. The method according to claim 1, wherein the fibrous web is calendered in at least one calender after being led through a polishing unit.

5. 5. The method according to any one of claims 1 to 4, wherein the fibrous web has a dry content of 25 to 45% by weight after being led through at least one dewatering unit.

6. 6. The method according to any one of claims 1 to 5, wherein the fibrous web has a dry content of more than 35% by weight before being treated in the polishing unit.

7. 7. The method according to any one of claims 1 to 6, wherein the suspension further comprises a hydrophobizing chemical in an amount of 0.1 to 10 kg / tonne on a dry weight basis.

8. The method of claim 1, wherein the suspension further comprises a hydrophobizing chemical in an amount of 0.1 to 5 kg / tonne on a dry weight basis.

9. The method of claim 1, wherein the suspension further comprises a hydrophobizing chemical in an amount of 0.2 to 2 kg / tonne on a dry weight basis.

10. 10. The method of any one of claims 7 to 9, wherein the hydrophobizing chemical is AKD, ASA or rosin size.

11. 11. The method of any one of claims 1 to 10, wherein the fibrous web comprises two or more layers comprising microfibrillated cellulose.

12. 12. The method according to any one of claims 1 to 11, wherein the produced roll paper is coated on at least one side with the coating composition.

13. 13. The method of claim 12, wherein the coating composition comprises a water-soluble polymer such as cellulose, starch, nanocellulose, a cellulose derivative, such as carboxymethyl cellulose, a starch derivative, polyvinyl alcohol or a polyvinyl alcohol derivative, or a combination thereof.

14. The method of claim 13, wherein the water-soluble polymer is cellulose.

15. The method of claim 13, wherein the cellulose derivative is carboxymethyl cellulose.