A method for producing a microfibrillated cellulose web

Abstract

The present invention relates to a method for producing a microfibrillated cellulose (MFC) web. An MFC suspension (2) comprising 50-100 weight-% MFC is provided and an MFC web (4) is formed from the MFC suspension by casting on a non-porous support (5). The MFC web is subjected to water removal to obtain a moisture content of 20 weight-% or less. After water removal the MFC web is separated from the non- porous support, conveyed to a reeling device (8).The method further comprises providing water vapor to a vapor chamber device (11) to provide a relative humidity of 50-99% therein and providing the MFC web in the vapor chamber device after the separation from the non-porous support so as to control the moisture content of the MFC web, wherein the MFC web is provided in the vapor chamber device such that the relative humidity is provided around the MFC web.

Description

[0001] A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB

[0002] Technical field

[0003] The present disclosure relates to a method for producing a microfibrillated cellulose (MFC) web, such as an MFC film, involving web formation by casting on a non- porous support.

[0004] Oxygen, grease, water vapor and / or aroma barrier properties are required in many uses of paper and paperboard packaging. However, paper and paperboard substrates do not have these properties inherently. Most commonly barrier characteristics of paper and paperboard substrates are created by adding one or more barrier coatings and / or laminated barrier layers which are based on plastics or other non-renewable materials. The disadvantage with these coatings and barrier layers is their non-renewable raw material basis that can increase the carbon dioxide footprint of the material as well as make the otherwise biodegradable paper or paperboard non-biodegradable and in some cases non-recyclable.

[0005] More recently, microfibrillated cellulose (MFC) webs have been developed, in which cellulosic fibrils, provided by fibrillation of cellulose fibers, have been suspended, e.g., in water and thereafter re-organized and re-bonded together to form a web. For example, MFC webs in the form of MFC films, which are dense films with barrier properties, such as oxygen, aroma, and grease barrier properties, have been developed. MFC webs, such as MFC films, are recyclable and biodegradable as well as based on renewable raw material.

[0006] One approach to produce MFC webs, such as MFC films, is to use a wet laid technique, i.e., to apply a dilute MFC suspension comprising MFC and water as suspension medium on a dewatering wire or membrane in a forming section and dewater it by vacuum, gravitation, capillary dewatering, press dewatering or a combination of these on the wire or membrane followed by drying or liquid evaporation. When this approach is utilized, most of the water of the wet MFC web is removed through the wire or membrane in the forming section. Another approach to produce MFC webs, such as MFC films, is to use a casting method in which a wet MFC web is formed by casting of an MFC suspension comprising MFC on a non-porous support, such as a plastic or metal support, and thereafter dewatering and / or drying to remove water from the wet MFC web. This type of casting method has been shown to produce MFC films with very smooth surfaces and good barrier properties, such as oxygen barrier properties and / or water vapor barrier properties. However, when this type of casting method is utilized, the produced MFC films are dewatered and / or dried to a relatively high dry content in order to facilitate removal of the MFC films from the non-porous support. When dried to a relatively high dry content, this type of casting method has been shown to produce MFC films which are more prone to brittleness, which might impact winding and post-converting of the MFC films. Brittle MFC films have lower elongation at break measured in tensile testing, which is caused by the lower amount of water in the MFC films since water in the MFC films can act as a plasticizer. Too low elongation at break is related to difficulties in reeling or further handling of the MFC films. One known solution is to add plasticizers to the composition of the MFC films. However, plasticizers might also impact barrier properties and mechanical properties negatively and are, thus, not always preferred.

[0007] Thus, there is still room for improvements of methods for producing an MFC web involving formation by casting on a non-porous support.

[0008] Description of the invention

[0009] It is an object of the present invention to provide a method for producing an MFC web involving formation by casting on a non-porous support, which method eliminates or alleviates at least some of the disadvantages of the prior art methods.

[0010] The above-mentioned object, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0011] The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims and in the following description. According to a first aspect illustrated herein, there is provided a method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: providing an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight and a suspension medium, wherein the suspension medium comprises water; forming an MFC web of said MFC suspension by casting on a non-porous support; subjecting said MFC web positioned on said non-porous support to water removal, wherein the water removal comprises dewatering of said MFC web and / or drying of said MFC web to a moisture content of 20 weight-% or less; separating said MFC web from said non-porous support after said water removal; conveying said MFC web after said separation to a reeling device; winding said MFC web onto a core by said reeling device to obtain a reel of said MFC web, wherein the method further comprises the steps of: providing water vapor to a vapor chamber device so as to provide a relative humidity of 50-99% in the vapor chamber device, and providing said MFC web in said vapor chamber device after said separation from said non-porous support so as to control said moisture content of said MFC web, wherein said MFC web is provided in said vapor chamber device such that said relative humidity is provided around said MFC web in said vapor chamber device.

[0012] A too wet MFC web might be difficult or impossible to remove from the non-porous support because it does not have good enough strength. In addition, the adhesion of the MFC web to the surface of the non-porous support is dependent on the dry content of the MFC web and a too wet MFC web adheres to the non-porous support. Thus, a certain dry content level of the MFC web is required to facilitate and enable removal of the MFC web from the non-porous support. However, if the dry content is too high, the MFC web is more prone to brittleness, which might impact winding and post-converting of the MFC web.

[0013] The method according to the first aspect enables production of an MFC web involving casting on a non-porous support, by which method removal of the MFC web from the non-porous support may be facilitated at the same time as the difficulties with the brittleness of the MFC web, having been dewatered and / or dried to a high dry content during water removal when positioned on the non-porous support, may be reduced.

[0014] Furthermore, the drying of the MFC web might be uneven across the width of the MFC web and the edges of the MFC web might be too dry at the same time as a middle part of the MFC web is still adhered to the non-porous support. The possible re-moistening of the MFC web by the method of the first aspect enables compensating the over-drying of the edges. In certain cases, the whole MFC web might dry to a too high dry content, and in that case, the re-moistening is needed. Furthermore, by controlling the moisture content of the MFC web after separation from the non-porous support by providing the MFC web in the vapor chamber device, the elongation at break may be increased which facilitates handling and reeling of the MFC film. Also, by providing the MFC web in the vapor chamber device such that the relative humidity is provided around the MFC web in the vapor chamber device, any unevenness of the moisture profile of the MFC web may be reduced as well as any effects of restrained drying which causes various relaxation when subjected to moisture. Dewatering and / or drying of the MFC web when positioned on the non- porous support may provide an uneven moisture profile in the thickness direction of the MFC web since it is positioned on the non-porous support and / or may provide an uneven moisture profile in the machine direction and / or cross machine direction (e.g., within areas at the longitudinal edges of the MFC web) for different reasons.

[0015] Microfibri Hated cellulose (MFC) shall in the context of this patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm.

[0016] Various methods exist to make MFC, such as single or multiple pass refining, prehydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by oxidation, for example 2, 2', 6,6'- tetramethylpiperidin-N-oxyl (TEMPO) mediated oxidation), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC.

[0017] MFC can be produced from wood cellulose fibers, both from hardwood and / or softwood fibers. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It can be made from pulp, including pulp from virgin fiber, e.g., mechanical, chemical and / or thermomechanical pulps. It can also be made from broke or recycled paper.

[0018] The term film as used herein refers generally to a thin continuous sheet formed material, such as a thin substrate with good gas, aroma and / or grease or oil barrier properties, e.g., oxygen barrier properties and / or water vapor barrier properties. Depending on the composition of the MFC suspension from which it is formed, the MFC film can also be considered as a thin paper (e.g., nanopaper or micropaper) or even as a membrane.

[0019] As mentioned above, the MFC suspension used in the method of the first aspect comprises between 50 weight-% to 100 weight-% MFC based on total dry weight. In some embodiments, the MFC suspension comprises between 60 weight-% to 100 weight-%, preferably between 70 weight-% to 100 weight-%, more preferably between 80 weight-% to 100 weight-%, of MFC based on total dry weight.

[0020] Preferably, the MFC suspension used in the method of the first aspect has a dry content of 1-40 weight-%. In some embodiments, the MFC suspension has a dry content of 1-30 weight-%, such as 1-25 weight-% or 1-20 weight-% or 1-15 weight- %. Preferably, the MFC suspension has a dry content of 2-25 weight-%, such as 2- 20 weight-% or 2-15 weight-% or 3-8 weight-%.

[0021] The MFC suspension used in the method of the first aspect comprises a suspension medium, which is water. Thus, the MFC suspension is an aqueous suspension. The microfibrillated cellulose of the MFC suspension used in the method of the first aspect may comprise one or more fractions of microfibrillated cellulose. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises one fraction of microfibrillated cellulose of a fine grade. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises two or more fractions of microfibrillated cellulose of different fine grades. In some embodiments, the microfibrillated cellulose of the MFC suspension comprises one fraction of a fine grade and one fraction of a coarse grade, wherein the coarse grade for example may be an additive. Coarse MFC in this case has typically a Schopper-Riegler value of 80-100 SR°, such as 80-99 SR° or 90-99 SR° or 95-99 SR°, whereas fine MFC is fibrillated so measurement of the Schopper-Riegler value is not possible (theoretical value about or above 100 SR°) as determined by standard ISO 5267-1 .

[0022] In some embodiments, the MFC suspension used in the method of the first aspect comprises one or more further cellulose pulp fractions in addition to the microfibrillated cellulose, such as e.g., a cellulose pulp fraction having a Schopper- Riegler value of < 70 SR°, such as 15-70 SR° or 25-60 SR°, as determined by standard ISO 5267-1 and / or a further fraction of normal fibers. The MFC suspension may comprise, for example, 1-30 weight-%, more preferably 2-30 weight-%, most preferably 5-30 weight-%, of further cellulose pulp fraction(s), based on the total dry weight of microfibrillated cellulose and further cellulose pulp fraction(s) (i.e., based on the total dry weight of total amount of fibers in the MFC suspension).

[0023] By normal fibers is meant normal pulp fibers of a conventional length and fibrillation for papermaking. Normal fibers may include mechanical pulp, thermochemical pulp, pressure groundwood, chemical pulp such as sulphate (kraft) or sulphite pulp, dissolving pulp, recycled fiber, organosolv pulp or chemi-thermomechanical pulp (CTMP), or combinations thereof. The pulp may be bleached or unbleached. The normal fibers can be vegetable fibers, such as wood derived (e.g., hardwood or softwood) or agricultural sources including straw, bamboo, etc.

[0024] The normal fibers may have a beating degree, i.e., Schopper-Riegler value, in the range of 15 to 50 SR° or more preferably in the range of 18 to 40 SR° as determined by standard ISO 5267-1 . The normal fibers may preferably be chemical pulp, such as kraft pulp. The normal fibers may have a mean length in the MFC suspension of 0.5 to 5 mm, preferably 1 mm to 5 mm, more preferably in the range of 2 mm to 4 mm, as determined using a FS5 fiber analyzer (Valmet). Mean fiber length as used herein refers to the mean length-weighted ISO fiber length measured according to the standard ISO 16065-2 using an FS5 fiber analyzer (Valmet).

[0025] In some embodiments, the MFC suspension used in the method of the first aspect comprises 1-30 weight-%, preferably 2-30 weight-%, most preferably 5-30 weight-%, of reinforcement fibers based on the total dry weight of microfibrillated cellulose and further cellulose pulp fraction(s) (i.e., based on the total dry weight of total amount of fibers in the MFC suspension), wherein the reinforcement fibers have a mean diameter of >10 pm and a mean length of >1 .5 mm, as determined using a FS5 fiber analyzer (Valmet).

[0026] Thus, besides MFC, the prepared MFC suspension may also comprise longer fibers, either hardwood or softwood fibers, preferably kraft pulp softwood fibers.

[0027] The MFC suspension used in the method of the first aspect may in addition to MFC and optional further pulp fraction(s) comprise any conventional paper making additives or chemicals such as film-forming agents, dispersants, fillers, pigments, wet strength chemicals, cross-linkers, plasticizers, softeners, humectants, adhesion primers, wetting agents, biocides, colorants, de-foaming chemicals, hydrophobizing chemicals such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), waxes, rosin resins, mineral additives (fillers) such as bentonite, kaolin, talcum, mica, montmorillonite, organoclays, graphene and graphene oxide, stearate, starch, silica, precipitated calcium carbonate, cationic polysaccharide, rheology modifiers, etc. These additives or chemicals may thus be process chemicals or web performance chemicals added to provide the end product web with specific properties and / or to facilitate production of the web.

[0028] In some embodiments, the MFC suspension is free, or at least essentially free of, cationic flocculation and drainage chemicals. Preferably, the MFC suspension comprises no more than 50 weight-%, more preferably no more than 35 weight-%, most preferably no more than 30 weight-% or no more than 25 weight-%, of additives, based on total dry weight of the MFC suspension. For example, the MFC suspension may comprise 1-50 weight-% or 1-35 weight-% or 1-30 weight-% or 1-25 weight-% of additives, based on total dry weight of the MFC suspension.

[0029] In some embodiments, the MFC suspension comprises a water soluble polymer that can form a network, such as a film, and / or improve binding between cellulose fibrils. Typical examples of such polymers are natural gums or polysaccharides or derivatives thereof such as carboxymethylated cellulose (CMC), hemicellulose, starch, or polyvinyl alcohol (PVOH) or derivatives or analogues thereof. The PVOH may be a single type of PVOH, or it can comprise a mixture of two or more types of PVOH, differing, e.g., in degree of hydrolysis or viscosity. The PVOH may, for example, have a degree of hydrolysis in the range of 80-99 mol%, preferably in the range of 88-99 mol%.

[0030] In some embodiments, the MFC suspension comprises 0-30 weight-% or 0.5-20 weight-% or 3-15 weight-% of one or more humectants and / or plasticizing agents based on total dry weight, such as a sugar alcohol (e.g., sorbitol), glycol, other polyol, or a combination thereof.

[0031] In some embodiments, the MFC suspension comprises up to 20 weight-% of mineral fillers (regular filler or nanofiller) based on total dry weight, such as bentonite, kaolin, talcum, mica, montmorrillonite, organoclays, silica, graphene, graphene oxide or a combination thereof.

[0032] As mentioned above, the method of the first aspect comprises a step of forming a wet MFC web of the MFC suspension by casting on a non-porous support.

[0033] The term “casting”, when utilized in web-forming, such as film-forming, is a known term designating methods wherein a suspension is deposited by means of contact or non-contact deposition and levelling methods on a support to form a wet web. Examples of such a deposition and levelling method are curtain coating / application, slot die casting, or dosing the MFC suspension with spray or similar device and optionally leveling with, for example, a doctor-blade, rod, air knife or roll.

[0034] The non-porous support may be a metal (e.g., steel), rubber, plastic, or polymer (e.g., polyurethane) support (e.g., belt or roll). In some embodiments, the non-porous support is a metal belt (i.e., a belt made of metal) such as a steel belt, a polymer belt, or a coated belt with a permanent or temporary coating such as a polymer coated belt, e.g., a polymer coated steel belt. For example, the belt can be coated with controlled adhesion / releasing agents (e.g., polytetrafluoroethylene). A metal belt may be coated, e.g., with ceramic material. The non-porous support may be a continuous or endless non-porous support, such as a conveyor belt. Thus, in some embodiments the non-porous support is a continuous or endless metal belt.

[0035] In some embodiments, the non-porous support is a metal belt, such as a continuous metal belt, which is heated during the step of web formation and / or the water removal. The metal belt may be heated to a temperature above 30 °C, preferably such that at least the casting surface of the metal belt has a temperature between 30-150 °C, more preferably between 45-150 °C, even more preferred between 60- 100 °C before or immediately after the MFC suspension is applied to the metal belt and the temperature of the metal belt may be kept during parts of the method for producing the MFC web, e.g., during at least some process steps for production of the MFC web, or during the complete method for producing the MFC web. By increasing the temperature of the metal belt and thus on the applied wet MFC web, it is possible to further increase the efficiency of the dewatering and / or drying of the MFC web.

[0036] The MFC web can be a single or multilayer web, or single or multilayer ply. Thus, the formed wet MFC web may comprise a single wet web layer or two or more wet web layers on top of each other.

[0037] As mentioned above, the method of the first aspect comprises a step of subjecting the MFC web positioned on the non-porous support to water removal. Thus, the MFC web is positioned on the non-porous support during the water removal. After the step of water removal is finished, the MFC web has a moisture content of 20 weight-% or less, preferably 15 weight-% or less or 10 weight-% or less, more preferably 7 weight-% or less, most preferably 5 weight-% or less or 4 weight-% or less. In some embodiments, the MFC web has a moisture content of 1-20 weight-%, preferably 1- 15 weight-% or 1-10 weight-%, more preferably 1-7 weight-%, most preferably 1-5 weight-% or 1-4 weight-%, after the step of water removal is finished. The moisture content may be measured under ambient conditions. For example, the moisture content may be measured using spectroscopy methods, such as infra-red (IR) spectroscopy, near infra-red (NIR) spectroscopy or Raman spectroscopy methods, in particular infra-red methods suitable for single side measurement. Alternatively, the dry content may be measured in order to determine the moisture content. For example, the dry content may be measured according to standard ISO 638-2 and the moisture content may be calculated based on the dry content measurement.

[0038] The water removal comprises dewatering and / or drying the MFC web. Thus, in some embodiments the water removal comprises dewatering of the MFC web. In some embodiments the water removal comprises drying of the MFC web. In some embodiments the water removal comprises dewatering and drying of the MFC web. The dewatering and the drying, respectively, may be performed using any method known in the art that are suitable to remove water from the MFC web and obtain a moisture content of the MFC web of 20 weight-% or less. The MFC web is positioned on the non-porous support during the dewatering and / or drying.

[0039] In some embodiments, the water removal comprises dewatering of the MFC web in at least one dewatering step, wherein at least one dewatering step of the at least one dewatering step comprises a mechanical dewatering such as press dewatering, gravitational dewatering or vacuum dewatering. Optionally, mechanical dewatering may be combined with evaporation provided by applying heat.

[0040] In some embodiments, the water removal comprises dewatering of the MFC web in at least one dewatering step, wherein at least one dewatering step of the at least one dewatering step is or comprises a press dewatering step.

[0041] Each press dewatering step may comprise application of a press fabric in direct contact or indirect contact (e.g., via a separate membrane) with the MFC web positioned on the non-porous support and conducting the MFC web, arranged between the press fabric and the non-porous support, through a pressing equipment to remove water from the MFC web by transferring water from the MFC web into the press fabric. With press fabric is meant a fabric that is permeable and allows water to be removed from the MFC web either by absorbing the water or by allowing the water to be removed into and / or through the fabric. The press fabric may be a press felt (dewatering felt). Any known suitable press fabric or press felt may be utilized. With pressing equipment is meant an equipment comprising one or more nip through which the MFC web is conducted and thus pressed and dewatered.

[0042] In some embodiments, the water removal comprises drying of the MFC web in at least one drying step, wherein at least one drying step is or comprises a non-contact drying step and / or at least one drying step is or comprises a contact drying step. Thus, in some embodiments, the drying comprises at least one non-contact drying step and / or at least one contact drying step. Each non-contact drying step may comprise hot gas (or air) impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof. Each contact drying step may comprise contacting the MFC web with at least one heated belt or heated roll.

[0043] As mentioned above, the method of the first aspect comprises a step of separating (such as peeling off) the MFC web from the non-porous support after the step of water removal is finished. After separation from the non-porous support the MFC web is conveyed to a reeling device and the MFC web is wound onto a core by the reeling device to obtain a reel of the MFC web. Thus, a reel of a free-standing continuous MFC web is then formed. The reeling device may be any suitable device for winding the MFC web onto a core to form a reel of the MFC web.

[0044] Furthermore, as mentioned above, the method of the first aspect further comprises the steps of: providing water vapor to a vapor chamber device so as to provide a relative humidity of 50-99% in the vapor chamber device, and providing the MFC web in the vapor chamber device after the separation from the non-porous support so as to control the moisture content of the MFC web, wherein the MFC web is provided in the vapor chamber device such that the relative humidity is provided around the MFC web in the vapor chamber device. The vapor chamber device may be any suitable device in which a relative humidity of 50-99% may be provided and maintained by providing water vapor into the vapor chamber device, in which the MFC web may be provided after separation from the non-porous support, i.e., before and / or during at least parts of the reeling, and in which the relative humidity of 50-99% may be provided around the MFC web. Thus, the vapor chamber device may be a conditioning chamber arranged to adjust and stabilize the moisture profile, and possibly the temperature, in the machine direction, the cross-machine direction and the thickness (z) direction of the MFC web. It may in this context be noted that by the expression that the relative humidity is provided around the MFC web in the vapor chamber device it is herein meant that the MFC web is surrounded by the relative humidity in the vapor chamber device. Thus, the MFC web is in contact with air / gas having the relative humidity on both sides in the vapor chamber device, i.e., both on the side having been in contact with the non- porous support during water removal and on the opposite side.

[0045] The relative humidity in the vapor chamber device may be controlled or set to a predetermined value within the range of 50-99% or to be within a predetermined subrange of the range of 50-99%.

[0046] The temperature in the vapor chamber device may be a temperature within the interval of 20-90 °C, preferably 25-85 °C or 30-80 °C. For example, the delay time of the MFC web in the vapor chamber device is 0.15-30 seconds, preferably 0.5-5 seconds.

[0047] As mentioned above, the MFC web is dewatered and / or dried to a moisture content of 20 weight-% or less before separation from the non-porous support. The relative humidity in the vapor chamber device may be set or controlled such that the moisture content of the MFC web is reduced or increased to a predetermined value or to be within a predetermined range, such as 0.8-12%, preferably 1-8%, most preferably 1.5-6%, during the presence in the vapor chamber device. Thus, in some embodiments, the moisture content of the MFC web is controlled in the vapor chamber device so as to be increased compared to the moisture content of the MFC web obtained by the water removal. In these embodiments, the MFC web is conditioned and remoistened in the vapor chamber device. Alternatively, the relative humidity in the vapor chamber device may be set or controlled such that the moisture content of the MFC web is maintained or controlled to the same, or essentially the same, moisture content as obtained by the water removal. Thus, in some embodiments, the moisture content of the MFC web is controlled in the vapor chamber device so as to be at least essentially maintained compared to the moisture content of the MFC web obtained by the water removal.

[0048] In some embodiments, the moisture content of the MFC web after separation from the non-porous support (but before provision of the MFC web in the vapor chamber device) is measured and / or the relative humidity of air being in contact with the MFC web after separation from the non-porous support (but before provision of the MFC web in the vapor chamber device) is measured. In these embodiments, the relative humidity of the vapor chamber device may be set or controlled based on the measurement of the moisture content of the MFC web after separation from the non- porous support and / or the measurement of the relative humidity of air being in contact with the MFC web after separation from the non-porous support so as to control the moisture content of the MFC web. In some embodiments, the moisture content of the MFC web is controlled to a predetermined value or to be within a predetermined range.

[0049] In some embodiments, the cross-direction moisture profile and / or the machine direction moisture profile of the MFC web after the separation from the non-porous support is measured. In these embodiments the relative humidity in the vapor chamber device may be controlled based on the measurement of the cross-direction moisture profile and / or the machine direction moisture profile of the MFC web after the separation from the non-porous support so as to control the moisture content of the MFC web.

[0050] It is further possible to utilize, for example, an algorithm-based model such as machine learning or artificial intelligence to monitor and predict the required relative humidity in the vapor chamber device, or to control the ambient moisture content in the vapor chamber device by adjusting pressure, temperature, incoming vapor or steam amount, and / or contact time (delay time), in order to provide an MFC web having a certain moisture content after finished treatment in the vapor chamber device, based on one or more incoming process parameters. Examples of such process parameters are moisture content of the MFC web after water removal but before separation from the non-porous support and the relative humidity of air being in contact with the MFC web after water removal but before separation from the non- porous support. The algorithm-based model may be implemented by a control arrangement including a self-learning artificial intelligence unit based on Convolutional Neural Network.

[0051] In some embodiments, the vapor chamber device is arranged such that the MFC web is provided in the vapor chamber device by being conveyed through the vapor chamber device during the conveying to the reeling device. Thus, in these embodiments the vapor chamber device is arranged between the point of separation from the non-porous support and the reeling device, i.e., the MFC web is conveyed through the vapor chamber device after separation from the non-porous support on the way to the reeling device. In these embodiments, the vapor chamber device is arranged to enclose the MFC web during parts of or all of the production line or web path between the point of separation from the non-porous support and the reeling device.

[0052] In some embodiments, the vapor chamber device is arranged such that the MFC web is provided in the vapor chamber device during at least parts of the winding, preferably the complete winding, of the MFC web onto the core. Thus, in these embodiments the vapor chamber device is arranged to enclose at least parts of the reeling device such that the MFC web is provided in the vapor chamber device during at least parts of the winding, preferably the complete winding, of the MFC web onto the core, i.e., at least parts of the reeling device are positioned in the vapor chamber device such that the MFC web is provided in the vapor chamber device during at least parts of the winding, preferably the complete winding, of the MFC web onto the core. In some of these embodiments, the whole reeling device is enclosed by the vapor chamber device, i.e., the whole reeling device is positioned in the vapor chamber device.

[0053] In some embodiments, the vapor chamber device is arranged such that the MFC web is provided in the vapor chamber device by being conveyed through the vapor chamber device during the conveying to the reeling device and such that the MFC web is provided in the vapor chamber device during at least parts of the winding, preferably the complete winding, of the MFC web onto the core. Thus, in these embodiments, the vapor chamber device is arranged to enclose the MFC web during parts of, or all of, the production line or web path between the point of separation from the non-porous support and the reeling device and to enclose at least parts of the reeling device such that the MFC web is provided in the vapor chamber device during at least parts of the winding, preferably the complete winding, of the MFC web onto the core.

[0054] After finished reeling, the reel of the MFC web may be enclosed in a package, such as a plastic package, in order to at least essentially maintain the moisture content of the MFC web, until use.

[0055] The vapor chamber device may comprise one unit or two or more units, wherein water vapor is provided to each unit so as to provide a relative humidity of 50-99% in each unit.

[0056] The water vapor provided to the vapor chamber device may be provided from any suitable source.

[0057] In some embodiments, the method of the first aspect further comprises a step of washing the non-porous support with water in a washing device after the separation of the MFC web from the non-porous support, wherein water vapor is generated during the washing and wherein water vapor generated during the washing is utilized in the step of providing water vapor to the vapor chamber device. Any suitable washing device, which is arranged to wash the non-porous support with water so as to remove remnants on the non-porous support, may be utilized.

[0058] For example, the water vapor generated during the washing may be generated by the non-porous support being heated such that water vapor is generated during the washing, by the relative humidity being elevated at the washing area, by using washing water having such a temperature that water vapor is generated during the washing or by any combination thereof. When the non-porous support is heated it may be actively heated in any suitable way, e.g., by means of active steam heating, or it may be indirectly heated by residual heat from the dewatering and / or drying. In some embodiments, water vapor generated during the washing is utilized in the step of providing water vapor to the vapor chamber device by being provided to the vapor chamber device. Water vapor generated during the washing may be provided to the vapor chamber device by any suitable means. The washing device may be provided in the vicinity of the vapor chamber device, for example so that water vapor created in the washing station contributes to the relative humidity conditions in the vapor chamber device. Optionally, water vapor generated during the washing and provided to the vapor chamber device may be purified in a purification treatment before being provided to the vapor chamber device, e.g., by means of a filter device or any other suitable device.

[0059] In some embodiments, water vapor generated during the washing is utilized in the step of providing water vapor to the vapor chamber device by being provided to a heat exchanger device so as to extract energy from the water vapor generated during the washing, wherein extracted energy is utilized in the step of providing water vapor to the vapor chamber device (i.e., for vaporizing water).

[0060] In some embodiments, the water removal comprises the drying, wherein the drying comprises at least one non-contact drying step removing water vapor from the MFC web, wherein water vapor removed from the MFC web by the drying is utilized in the step of providing water vapor to the vapor chamber device.

[0061] In some embodiments, water vapor removed from the MFC web by the drying is utilized in the step of providing water vapor to the vapor chamber device by being provided to the vapor chamber device. Water vapor removed from the MFC web by the drying may be provided to the vapor chamber device by any suitable means. Optionally, water vapor removed from the MFC web by the drying and provided to the vapor chamber device may be purified in a purification treatment before being provided to the vapor chamber device, e.g., by means of a filter device or any other suitable device.

[0062] In some embodiments, water vapor removed from the MFC web by the drying is utilized in the step of providing water vapor to the vapor chamber device by being provided to a heat exchanger device so as to extract energy from the water vapor removed from the MFC web by the drying, wherein extracted energy is utilized in the step of providing water vapor to the vapor chamber device (i.e., for vaporizing water).

[0063] The MFC web produced in the above-described embodiments of the method of the present disclosure may be an MFC film.

[0064] In some embodiments in which the MFC web is an MFC film, an MFC film having an oxygen transmission rate (OTR), measured according to the standard ASTM F1927- 20 at 50% relative humidity and 23 °C, of less than 10 cc / m2 / 24h, preferably less than 7 cc / m2 / 24h, and more preferably less than 5 cc / m2 / 24h, is produced.

[0065] In some embodiments in which the MFC web is an MFC film, an MFC film having a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of less than 100 g / m2 / 24h, preferably less than 50 g / m2 / 24h, and more preferably less than 20 g / m2 / 24h, is produced.

[0066] In some embodiments in which the MFC web is an MFC film, an MFC film having a dry grammage of 2-120 g / m2, preferably 2-70 g / m2, 5-60 g / m2or 10-50 g / m2, as measured according to ISO 536, is produced.

[0067] In some embodiments in which the MFC web is an MFC film, an MFC film having an average film thickness of 2-1200 pm, preferably 2-60 pm or 5-50 pm or 10-40 pm, is produced. The average film thickness may be defined as an average thickness of the film across the entire width. Thickness of the MFC film may be measured using, as non-limiting examples, white light interferometry, laser profilometry, or optically by cutting a sample in cross-machine directional line (either cast in resin or not) and microscopic imaging (e.g., scanning electron microscopy or other applicable method) of the cut section in thickness direction.

[0068] In some embodiments in which the MFC web is an MFC film, an MFC film having a width of 0.3-4 m, preferably 0.5-4 m, 1-4 m or 2-4 m, is produced. In some embodiments in which the MFC web is an MFC film, an MFC film having a density of 700-1500 kg / m3, preferably 800-1500 kg / m3, most preferably 900-1500 kg / m3, as measured according to ISO 534:2011 , is produced.

[0069] In some embodiments the MFC web produced in the method of the present disclosure is an absorbent layer, a membrane, a separation medium or a prefabricate.

[0070] A free-standing MFC film according to the present disclosure can be used as such. Alternatively, a free-standing MFC film provided by the method of the present disclosure may be applied to the surface of any one of a paper product and a paperboard product so as to form a laminate, such as a paper or paper-based packaging material laminate.

[0071] Paper generally refers to a material manufactured in thin sheets from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paper may be a single ply material, or a multiply material comprised of two or more plies.

[0072] Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for boxes and other types of packaging. Paperboard can either be bleached or unbleached, coated or uncoated, and produced in a variety of thicknesses, depending on the end use requirements. Paperboard may be a single ply material, or a multiply material comprised of two or more plies.

[0073] A free-standing MFC film provided by the method of the present disclosure may be utilized in a laminate together with one or more polymer layers, such as termoplastic polymer layers. For example, the one or more additional polymer layers may be constituted by any suitable polyolefin or polyester. The additional polymer layer(s) can be provided e.g. by extrusion coating, film coating or lamination or dispersion coating. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP) polyethylene terephthalate (PET), polylactic acid (PLA), polyglycolic acid (PGA), polyhydroxyalkanoates (PHA) and polybutylene succinate (PBS).

[0074] A free-standing MFC film provided by the method of the present disclosure may be used as a packaging material or in a packaging material, such as a food or liquid packaging material, and may be incorporated into any type of package, such as a box, bag, a wrapping film, cup, container, tray, bottle etc.

[0075] According to a second aspect illustrated herein, there is provided an MFC web such as an MFC film obtainable by the method of the first aspect. The MFC web according to the second aspect may be further defined as set out above with reference to the method of the first aspect.

[0076] Brief description of the drawings

[0077] In the following, the invention will be further illustrated by description of exemplified embodiments with reference to the accompanying drawings, wherein:

[0078] Fig. 1 shows a schematic overview of a first embodiment of the method according to the present disclosure, and

[0079] Fig. 2 shows a schematic overview of a second embodiment of the method according to the present disclosure.

[0080] Detailed description of the drawings

[0081] Fig. 1 shows a schematic overview of a first embodiment of the method according to the first aspect of the present disclosure performed in a system 1 for MFC web production. In the first embodiment illustrated in Fig. 1 , an MFC suspension 2 is provided to a casting unit 3, such as a slot die applicator. The MFC suspension 2 comprises between 50 weight-% to 100 weight-% MFC based on total dry weight. The MFC suspension 2 comprises water as suspension medium. Optionally, one or more additives (e.g., paper making additives and / or chemicals) and / or one or more other suitable components (e.g., further pulp fraction(s)) may also be comprised in the MFC suspension 2. An MFC web 4 is formed of the MFC suspension 2 by casting a layer of the MFC suspension 2 by the casting unit 3 on a non-porous support in the form of an endless metal belt 5. In the first embodiment illustrated in Fig. 1 , the MFC web 4 positioned on the metal belt 5 is subjected to water removal comprising press dewatering in a press dewatering device 6, and drying in a noncontact drying device 7 to a moisture content of 20 weight-% or less. After noncontact drying, the MFC web 4 is separated from the metal belt 5 and conveyed to a reeling device 8. In the reeling device 8, the MFC web 4 is wound onto a core to form a reel 9 of the MFC web 4. Furthermore, in the first embodiment illustrated in Fig. 1 , the metal belt 5 is washed in a washing device 10 under conditions such that water vapor is generated during the washing. Water vapor generated during the washing in the washing device 10 is provided to a vapor chamber device 11 , by means 12 for providing water vapor to the vapor chamber device 11 , so as to provide a relative humidity of 50-99% in the vapor chamber device 11 . In the first embodiment shown in Fig. 1 , the vapor chamber device 11 is arranged such that the MFC web 4 is provided in the vapor chamber device 11 by being conveyed through the vapor chamber device 11 during the conveying to the reeling device 8. The MFC web 4 is provided in the vapor chamber device 11 such that the relative humidity of the vapor chamber device 11 is provided around the MFC web 4.

[0082] Fig. 2 shows a schematic overview of a second embodiment of the method according to the first aspect of the present disclosure. The second embodiment differs from the first embodiment in the arrangement of the vapor chamber device 11 . In the second embodiment illustrated in Fig. 2, the vapor chamber device 11 is arranged such that the MFC web 4 is provided in the vapor chamber device 11 by being conveyed through the vapor chamber device 11 during the conveying to the reeling device 8 and by being provided in the vapor chamber device 11 during winding of the MFC web 4 onto a core to form the reel 9 in the reeling device 8. Thus, in the second embodiment of Fig. 2, the vapor chamber device 11 is arranged to enclose the MFC web 4 during parts of the production line between the point of separation from the metal belt 5 and the reeling device 8 and to enclose the whole reeling device 8 such that the MFC web 4 is provided in the vapor chamber device 11 during the complete winding of the MFC web 4 onto the core. Also, the second embodiment of Fig. 2 differs from the first embodiment in the fact that water vapor is provided to the vapor chamber device 11 from the non-contact drying device 7 by means 12 for providing water vapor to the vapor chamber device 11.

[0083] Generally, while the products, materials, layers and processes are described in terms of “comprising” various components or steps, the products, materials, layers and processes can also “consist essentially of’ or “consist of’ the various components and steps.

[0084] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims

CLAIMS1 . A method for producing a microfibrillated cellulose (MFC) web (4), wherein the method comprises the steps of: providing an MFC suspension (2) comprising between 50 weight-% to 100 weight-% MFC based on total dry weight and a suspension medium, wherein the suspension medium comprises water; forming an MFC web (4) of said MFC suspension (2) by casting on a non- porous support (5); subjecting said MFC web (4) positioned on said non-porous support (5) to water removal, wherein the water removal comprises dewatering of said MFC web (4) and / or drying of said MFC web (4) to a moisture content of 20 weight- % or less; separating said MFC web (4) from said non-porous support (5) after said water removal; conveying said MFC web (4) after said separation to a reeling device (8); winding said MFC web (4) onto a core by said reeling device (8) to obtain a reel (9) of said MFC web (4), wherein the method further comprises the steps of: providing water vapor to a vapor chamber device (11) so as to provide a relative humidity of 50-99% in the vapor chamber device (11), and providing said MFC web (4) in said vapor chamber device (11) after said separation from said non-porous support (5) so as to control said moisture content of said MFC web (4), wherein said MFC web (4) is provided in said vapor chamber device (11) such that said relative humidity is provided around said MFC web (4) in said vapor chamber device (11).

2. The method according to claim 1 , wherein said moisture content of said MFC web (4) is controlled in said vapor chamber device (11) so as to be increased compared to the moisture content obtained by the water removal.

3. The method according to claim 1 , wherein said moisture content of said MFC web (4) is controlled in said vapor chamber device (11) so as to beessentially maintained compared to the moisture content obtained by the water removal.

4. The method according to any one of the preceding claims, wherein said vapor chamber device (11) is arranged such that said MFC web (4) is provided in said vapor chamber device (11) by being conveyed through said vapor chamber device (11) during said conveying to said reeling device (8).

5. The method according to any one of claims 1 -4, wherein said vapor chamber device (11) is arranged such that said MFC web (4) is provided in said vapor chamber device (11) during at least parts of said winding of said MFC web (4) onto said core.

6. The method according to any one of claims 1-5, wherein the method further comprises a step of washing said non-porous support (5) with water in a washing device (10) after said separation of said MFC web (4) from said non- porous support (5), wherein water vapor is generated during said washing and wherein water vapor generated during said washing is utilized in said step of providing water vapor to said vapor chamber device (11).

7. The method according to claim 6, wherein water vapor generated during said washing is utilized in said step of providing water vapor to said vapor chamber device (11) by being provided to said vapor chamber device (11).

8. The method according to claim 7, wherein said water vapor generated during said washing and provided to said vapor chamber device (11) is purified in a purification treatment before being provided to said vapor chamber device (11).

9. The method according to claim 6, wherein water vapor generated during said washing is utilized in said step of providing water vapor to said vapor chamber device (11) by being provided to a heat exchanger device so as to extract energy from said water vapor generated during said washing, wherein extracted energy is utilized in said step of providing water vapor to said vapor chamber device (11).

10. The method according to any one of the preceding claims, wherein said water removal comprises said drying, wherein said drying comprises at least one non-contact drying step removing water vapor from said MFC web (4), wherein water vapor removed from said MFC web (4) by said drying is utilized in said step of providing water vapor to said vapor chamber device (11).11 . The method according to claim 10, wherein water vapor removed from said MFC web (4) by said drying is utilized in said step of providing water vapor to said vapor chamber device (11) by being provided to said vapor chamber device (11) in said step of providing water vapor to said vapor chamber device (11).

12. The method according to claim 11 , wherein water vapor removed from said MFC web (4) by said drying and provided to said vapor chamber device (11) is purified in a purification treatment before being provided to said vapor chamber device (11).

13. The method according to claim 10, wherein water vapor removed from said MFC web (4) by said drying is utilized in said step of providing water vapor to said vapor chamber device (11) by being provided to a heat exchanger device so as to extract energy from said water vapor removed from said MFC web (4) by said drying, wherein extracted energy is utilized in said step of providing water vapor to said vapor chamber device (11).

14. The method according to any one of claims 10-13, wherein each non-contact drying step comprises hot gas impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof.

15. The method according to any one of the preceding claims, wherein said water removal comprises said dewatering, wherein said dewatering comprises at least one press dewatering step.

16. The method according to claim 15, wherein each press dewatering step comprises: applying a press fabric into direct or indirect contact with saidMFC web (4) formed on said non-porous support (5) and conducting said MFC web (4), arranged between said press fabric and said non-porous support (5), through a pressing equipment to remove water from said MFC web (4) by transferring water from said MFC web (4) into the press fabric.

17. The method according to any one of the preceding claims, wherein said method further comprises the step of measuring the moisture content of said MFC web (4) after said separation from said non-porous support (5) and controlling said relative humidity in said vapor chamber device (11) so as to control the moisture content of said MFC web (4).

18. The method according any one of claims 1-17, wherein said method further comprises the step of measuring the cross-direction moisture profile and / or the machine direction moisture profile of the MFC web (4) after said separation from said non-porous support (5) and controlling said relative humidity in said vapor chamber device (11) so as to control the moisture content of said MFC web (4).

19. The method according to claim 17 or 18, wherein said moisture content is controlled to a predetermined value or to be within a predetermined range.

20. The method according to any one of the preceding claims, wherein said non- porous support is a metal belt (5).21 . The method according to any one of the preceding claims, wherein said formed MFC web (4) comprises a single web layer or two or more web layers formed on top of each other.

22. The method according to any one of the preceding claims, wherein said MFC suspension (2) comprises between 70 weight-% to 100 weight-% of MFC based on total dry weight.

23. The method according to any one of the preceding claims, wherein said MFC web (4) is an MFC film.

24. The method according to claim 23, wherein said MFC film (4) has an average thickness of 2-120 pm and a dry grammage of 2-120 g / m2as measured according to ISO 536.

25. The method according to claim 23 or 24, wherein said MFC film (4) of said obtained reel has an oxygen transmission rate (OTR), measured according to the standard ASTM F1927-20 at 50% relative humidity and 23 °C, of less than 10 cc / m2 / 24h, preferably less than 7 cc / m2 / 24h, and more preferably less than 5 cc / m2 / 24h.

26. The method according to any one of claims 23-24, wherein said MFC film (4) of said obtained reel has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249-20 at 50% relative humidity and 23 °C, of less than 100 g / m2 / 24h, preferably less than 50 g / m2 / 24h, and more preferably less than 20 g / m2 / 24h.

27. An MFC web (4) obtainable by the method as claimed in any one of claims 1- 26.

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