Method for producing microfibrillated cellulose webs

Abstract

The present invention relates to a method for producing a microfibrillated cellulose (MFC) web. The method comprises providing an MFC suspension (2) containing water as a suspension medium. A wet MFC web (4) is formed by casting the MFC suspension onto a non-porous support (5). The wet MFC web (4) positioned on the non-porous support (5) is subjected to dewatering by press dewatering and / or non-contact drying to form a dry MFC web (8). Dewatering further comprises at least one induction heating step, each induction heating step comprising heating the wet MFC web (4) by an induction heating device (10). The dry MFC web (8) is separated from the non-porous support (5).

Description

[Technical Field]

[0001] The present invention relates to a method for producing a microfibrillated cellulose (MFC) web, such as an MFC film, comprising forming a web by casting onto a non-porous support. [Background technology]

[0002] Many applications of paper and cardboard packaging require barrier properties against oxygen, grease, water vapor, and / or odors. However, paper and cardboard substrates inherently lack these properties. Most commonly, barrier properties of paper and cardboard substrates are created by adding one or more barrier coatings and / or laminated barrier layers based on plastics or other non-renewable materials. The drawbacks of these coatings and barrier layers are that they can increase the carbon dioxide emissions of the material due to the use of non-renewable raw materials, and that they can render otherwise biodegradable paper and cardboard non-biodegradable and, in some cases, non-recyclable.

[0003] Recently, microfibrillated cellulose (MFC) webs have been developed, which are formed by suspending cellulose protofibers obtained by fibrillation of cellulose fibers, for example, in water, and then rearranging and recombining them to form a web. For example, MFC webs in the form of MFC films, which are high-density films with barrier properties such as oxygen, fragrance, and grease barriers, have been developed. MFC webs, such as MFC films, are recyclable, biodegradable, and based on renewable raw materials.

[0004] One approach to manufacturing MFC webs, such as MFC films, is to use wet-laid technology. This involves applying a diluted MFC suspension, containing MFC and water as the suspension medium, to a dehydrated wire or membrane in the forming section. The wire or membrane is then dehydrated by vacuum, gravitation, capillary dehydration, press dehydration, or a combination thereof, followed by drying or liquid evaporation. Using this approach, most of the moisture in the wet MFC web is removed through the wire or membrane in the forming section.

[0005] Another approach to manufacturing MFC webs, such as MFC films, involves using a casting method to form a wet MFC web by casting an MFC suspension containing MFCs and water as the suspension medium onto a non-porous support, such as a plastic or metal support, and then removing the water from the wet MFC web by dehydration and / or drying. This type of casting method has been demonstrated to produce MFC films with a very smooth surface and excellent barrier properties, such as oxygen barrier properties and / or water vapor barrier properties. However, when a wet MFC web is positioned on a non-porous support, the removal of moisture from the wet MFC web must be carried out substantially through the surface of the wet MFC web on the opposite side of the non-porous support. Therefore, compared to when wet-laid techniques using dehydration wires or membranes are used, the removal of moisture from the wet MFC web becomes more complex when methods involving casting on a non-porous support are used. In particular, when casting on a non-porous support, a significantly larger amount of moisture needs to be removed in the dehydration section (e.g., press dehydration) and / or drying section (e.g., evaporation) compared to when using wet-laid techniques. To improve the efficiency of moisture removal, when casting onto a non-porous support, it is known to heat the wet MFC web by steaming the non-porous support. However, steam heating of a non-porous support is energy-wasting due to limited heat transfer. Furthermore, steam heating of a non-porous support can present challenges related to controlling the moisture profile in the cross-machine direction and / or machine direction. In addition, direct steam heating of a non-porous substrate is prone to steam leakage and temperature fluctuations. Steam heating of a non-porous substrate also generates condensates on the surface of the non-porous substrate opposite the product, and the condensate layer reduces the efficiency of heat transfer from steam to the substrate. In process configurations where the non-porous substrate supports the product on its downward-facing bottom surface and is heated from its upward-facing top surface, steam heating is not a practical solution due to condensation formation.

[0006] Therefore, there is still room for improvement in methods for fabricating MFC webs, including those formed by casting onto a non-porous support.

[0007] Description of the present invention An object of the present invention is to provide a method for manufacturing an MFC web, which includes forming it by casting onto a non-porous support, thereby eliminating or mitigating at least some of the drawbacks of prior art methods.

[0008] The above-mentioned objectives, and other objectives that can be achieved by those skilled in the art in light of this disclosure, are achieved by various aspects of this disclosure.

[0009] The present invention is defined by the appended independent claims. Embodiments are described in the appended dependent claims and the following description.

[0010] According to a first aspect described herein, a method is provided for producing a microfibrillated cellulose (MFC) web, which is: - A step of providing an MFC suspension comprising an MFC and a suspension medium in an amount between 50% and 100% by weight based on total dry weight, wherein the suspension medium contains water, and the MFC suspension has a dry content of 1 to 30% by weight. - A step of forming a wet MFC web of the MFC suspension by casting it onto a non-porous casting support, - A step of subjecting the wet MFC web, positioned on the non-porous casting support, to dewatering in order to form a dry MFC web, wherein the dewatering includes pressing and dewatering the wet MFC web and / or non-contact drying the wet MFC web, and the dewatering further includes at least one induction heating step, each induction heating step including heating the wet MFC web by an induction heating device, - A step of separating the dried MFC web from the non-porous casting support. Includes.

[0011] A method according to the first embodiment enables the production of an MFC web, which includes casting onto a non-porous support, where moisture removal includes press dewatering and / or non-contact drying, and the efficiency of moisture removal is improved by heating the wet MFC web in at least one induction heating step. Surprisingly, it has been found that by utilizing heating with an induction heating device (e.g., a portion of the non-porous support or an induction-heated roll), efficient heating of the wet MFC web is obtained, i.e., efficient heat transfer to the wet MFC web is obtained. Compared to heating the non-porous support with steam heating, heating with an induction heating device has been found to be more efficient and less energy wasted. Furthermore, when using heating with an induction heating device, the heating and temperature profile of the wet MFC web can be controlled more quickly and accurately than with steam heating.

[0012] In this patent application, microfibrillated cellulose (MFC) means cellulose particles, fibers, or fibrils having a width or diameter of 20 nm to 1000 nm.

[0013] There are various methods for producing MFCs, including single or multi-pass purification, purification after pre-hydrolysis, or high-shear decomposition or liberation of fibrils. To ensure both energy efficiency and sustainability in MFC production, one or more pretreatment steps are usually required. Therefore, the cellulose fibers of the pulp used in producing MFCs may be natural or may be enzymatically or chemically pretreated, for example, to reduce the amount of hemicellulose or lignin. The cellulose fibers may also be chemically modified before fibrillation, and the cellulose molecules may contain functional groups other than (or more than) those found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehydes and / or carboxyl groups (cellulose obtained by oxidation, e.g., 2,2',6,6'-tetramethylpiperidine-N-oxyl (TEMPO)-mediated oxidation), or quaternary ammonium (cationic cellulose). After modification or oxidation by any of the above methods, the decomposition of the fibers into MFCs becomes easier.

[0014] MFCs can be produced from wood cellulose fibers obtained from both hardwood and softwood fibers. MFCs can also be produced from microbial sources, agricultural fibers such as straw pulp, bamboo, and bagasse, or other non-wood fiber sources. For example, they can be produced from pulps containing virgin fiber pulp, such as mechanical pulp, chemical pulp, and / or thermomechanical pulp. They can also be produced from waste paper or recycled paper.

[0015] As used herein, the term "film" generally refers to a thin continuous sheet-forming material, such as a thin substrate, that has good barrier properties against gases, fragrances, greases, or oils, for example, oxygen barrier properties and / or water vapor barrier properties. Depending on the composition of the MFC suspension from which it is formed, an MFC film can also be considered as a thin paper (such as nanopaper or micropaper) or a membrane.

[0016] As described above, the MFC suspension used in the method of the first embodiment contains MFCs between 50% and 100% by weight based on total dry weight. In some embodiments, the MFC suspension contains MFCs between 60% and 100% by weight, preferably between 70% and 100% by weight, and more preferably between 80% and 100% by weight, based on total dry weight.

[0017] The MFC suspension used in the method of the first embodiment has a dry content of 1 to 30% by weight. In some embodiments, the MFC suspension has a dry content of 1 to 25% by weight, for example, 1 to 20% by weight or 1 to 15% by weight. Preferably, the MFC suspension has a dry content of 2 to 25% by weight, for example, 2 to 20% by weight, 2 to 15% by weight or 3 to 8% by weight.

[0018] The MFC suspension used in the method of the first embodiment comprises a suspension medium which is water. Therefore, the MFC suspension is an aqueous suspension.

[0019] The microfibrillated cellulose of the MFC suspension used in the method of the first embodiment may contain one or more microfibrillated cellulose fractions. In some embodiments, the microfibrillated cellulose of the MFC suspension contains one microfibrillated cellulose fraction of fine grade. In some embodiments, the microfibrillated cellulose of the MFC suspension contains two or more microfibrillated cellulose fractions of different fine grades. In some embodiments, the microfibrillated cellulose of the MFC suspension contains one fraction of fine grade and one fraction of coarse grade, the coarse grade being, for example, an additive. In this case, the Schöpper-Leighler value of the coarse MFC is typically 80-100 SR°, for example, 80-99 SR°, 90-99 SR°, or 95-99 SR°, while the Schöpper-Leighler value of fine MFC is not measurable as defined in ISO 5267-1 because it is fibrillated (theoretical value is approximately 100 SR° or higher).

[0020] In some embodiments, the MFC suspension used in the method of the first aspect includes, in addition to microfibrillated cellulose, one or more additional cellulose pulp fractions such as a cellulose pulp fraction having a Schopper - Riegler value of 70 SR° or less, such as 15 - 70 SR° or 25 - 60 SR°, determined by standard ISO 5267 - 1, and / or a further fraction of normal fibers. The MFC suspension may contain, based on the total dry weight of the microfibrillated cellulose and the additional cellulose pulp fraction(s), for example, 1 - 30 wt%, more preferably 2 - 30 wt%, and most preferably 5 - 30 wt% of the additional cellulose pulp fraction(s).

[0021] Normal fibers mean normal length and fibrillated pulp fibers for papermaking. Normal fibers include mechanical pulp, thermochemical pulp, pressure - groundwood pulp, chemical pulps such as kraft (sulfate) pulp and sulfite pulp, dissolving pulp, recycled fibers, organosolv pulp, chemi - thermomechanical pulp (CTMP), or combinations thereof. The pulp may be bleached or unbleached. Normal fibers may be plant fibers such as wood - derived (e.g., hardwood or softwood), or agricultural resources including straw, bamboo, etc.

[0022] Normal fibers can have a Schopper - Riegler value in the range of 15 - 50 SR°, or more preferably in the range of 18 - 40 SR°, according to the ISO 5267 - 1 standard. Chemical pulps such as kraft pulp are preferred as normal fibers.

[0023] When measured using an FS5 fiber analyzer (Valmet), normal fibers have an average length in the range of 0.5 - 5 mm, preferably 1 mm - 5 mm, and more preferably 2 mm - 4 mm in the MFC suspension. The average fiber length used herein refers to the average length - weighted ISO fiber length measured according to ISO 16065 - 2 standard using an FS5 fiber analyzer (Valmet).

[0024] In some embodiments, the MFC suspension used in the method of the first aspect contains reinforcing fibers at 1 to 30% by weight, preferably 2 to 30% by weight, most preferably 5 to 30% by weight, based on the total dry weight of the microfibrillated cellulose and any additional cellulose pulp fraction(s) (i.e., based on the total dry weight of the total amount of fibers in the MFC suspension), and the reinforcing fibers have an average diameter > 10 μm and an average length > 1.5 mm, determined using an FS5 fiber analyzer (Valmet).

[0025] Thus, the prepared MFC suspension may contain, in addition to the MFC, longer fibers, hardwood fibers or softwood fibers, preferably kraft pulp softwood fibers.

[0026] The MFC suspension used in the method of the first aspect may contain, in addition to the MFC and any optional additional pulp fraction, film formers, dispersants, fillers, pigments, wet strength improvers, crosslinking agents, plasticizers, softeners, humectants, adhesion primers, wetting agents, biocides, colorants, defoamers, hydrophobizing agents such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), waxes, rosin resins, bentonite, kaolin, talc, mica, montmorillonite, organic clays and other mineral additives (fillers), graphene and graphene oxide, stearates, starch, silica, precipitated calcium carbonate, cationic polysaccharides, rheology modifiers, etc., conventional papermaking additives or chemicals. Thus, these additives or chemicals may be process chemicals or web performance chemicals added to impart specific properties to the final product web and / or to facilitate the manufacture of the web.

[0027] In some embodiments, the MFC suspension does not contain or at least is essentially free of cationic flocculants and drainage chemicals.

[0028] Preferably, the MFC suspension contains additives in an amount of 50% by weight or less, more preferably 35% by weight or less, most preferably 30% by weight or less, or 25% by weight or less, based on the total dry weight of the MFC suspension. For example, the MFC suspension may contain additives in an amount of 1 to 50% by weight, or 1 to 35% by weight, or 1 to 30% by weight, or 1 to 25% by weight, based on the total dry weight of the MFC film.

[0029] In some embodiments, the MFC suspension includes a water-soluble polymer that can form a network such as a film and / or improve the bonding between cellulose fibers. Typical examples of such polymers are natural gums or polysaccharides or derivatives thereof, such as carboxymethylated cellulose (CMC), hemicellulose, starch, and polyvinyl alcohol (PVOH). The PVOH may be a single type of PVOH, or a mixture of two or more types of PVOH with different degrees of hydrolysis or viscosity, for example. The PVOH has a degree of hydrolysis in the range of 80 to 99 mol%, preferably in the range of 88 to 99 mol%.

[0030] In some embodiments, the MFC suspension contains, based on total dry weight, 0 to 30% by weight, or 0.5 to 20% by weight, or 3 to 15% by weight, one or more humectants and / or plasticizers such as sugar alcohols (e.g., sorbitol), glycols, other polyols, or combinations thereof.

[0031] In some embodiments, the MFC suspension contains up to 20% by weight of mineral fillers (conventional fillers or nanofillers), based on total dry weight, such as bentonite, kaolin, talc, mica, montmorillonite, organic clay, silica, graphene, graphene oxide, or a combination thereof.

[0032] As described above, the method of the first embodiment includes the step of forming a wet MFC web of an MFC suspension by casting it onto a non-porous casting support.

[0033] The term "casting," when used in web formation such as film formation, is a known term referring to a method of forming a wet web by depositing a suspension onto a support by contact or non-contact deposition and leveling methods. Examples of such deposition and leveling methods include curtain coating / coating, slot die casting, or spraying or similar equipment to administer the MFC suspension and, if necessary, planarizing it using, for example, a doctor blade, rod, air knife, or roll.

[0034] The non-porous casting support may be a metal (e.g., steel), rubber, plastic, or polymer (e.g., polyurethane) support (e.g., a belt or roll). The non-porous casting support may or may not be induction-heatable. In some embodiments, the non-porous casting support must be induction-heatable (i.e., embodiments in which at least a portion of the non-porous casting support is induction-heated for induction heating), while in other embodiments, the non-porous casting support does not need to be induction-heatable (i.e., embodiments in which only one or more separate induction heating devices are used for induction heating). In some embodiments, the non-porous casting support is a metal belt (i.e., a metal belt) such as a steel belt, a polymer belt, or a polymer-coated belt, or a coated belt with a permanent or temporary coating such as a polymer-coated steel belt. For example, the belt may be coated with a controlled adhesive / release agent (such as polytetrafluoroethylene). The metal belt may be coated with, for example, a ceramic material. The non-porous casting support may be a continuous or endless non-porous support, such as a conveyor belt. Therefore, in some embodiments, the non-porous casting support is a continuous or endless metal belt.

[0035] An MFC web can consist of a single or multiple layers of web, or a single or multiple layers of ply. Therefore, the formed wet MFC web may consist of a single wet web layer, or two or more wet web layers overlapping each other.

[0036] As described above, the method of the first embodiment includes the step of removing moisture from a wet MFC web positioned on a non-porous casting support to form a dry MFC web. Thus, during moisture removal, the wet MFC web is positioned on the non-porous casting support. The moisture content of the dry MFC web formed by moisture removal is 20% by weight or less, preferably 10% by weight or less, and more preferably 5% by weight or less. In some embodiments, the moisture content of the dry MFC web is 1 to 20% by weight, preferably 1 to 10% by weight, and most preferably 1 to 5% by weight. The moisture content can be measured under ambient conditions. For example, the moisture content can be measured using spectroscopic methods such as infrared (IR) spectroscopy, near-infrared (NIR) spectroscopy, and Raman spectroscopy, particularly infrared methods suitable for single-sided measurement. Alternatively, the dry content can be measured to determine the moisture content. For example, the dry content can be measured according to the ISO 638-2 standard, and the moisture content can be calculated based on the measurement of the dry content.

[0037] Moisture removal consists of press dehydration and / or non-contact drying of the wet MFC web. Press dehydration and non-contact drying can each be performed using any method known in the art that is suitable for removing water from the wet MFC web and providing a dried MFC web. The wet MF web is positioned on a non-porous casting support during press dehydration and / or non-contact drying.

[0038] Press dewatering can be performed in one or more press dewatering steps. Each press dewatering step may include applying a press fabric that is in direct or indirect (e.g., via another membrane) contact with a wet MFC web positioned on a non-porous casting support, and removing water from the wet MFC web by passing the wet MFC web, which is positioned between the press fabric and the non-porous casting support, through a press device to transfer water from the wet MFC web to the press fabric. Press fabric means a permeable fabric that can remove moisture from a wet MFC web by absorbing moisture or removing moisture through the fabric. The press fabric may be press felt (dewatering felt). A known suitable press fabric or press felt can be used. A press device is a device having one or more nips through which a wet MFC web is passed and pressed and dewatered.

[0039] Non-contact drying can be performed in one or more non-contact drying steps. Each non-contact drying step may include high-temperature gas (or air) impact drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near-infrared drying, or a combination thereof.

[0040] Furthermore, moisture removal further includes heating the wet MFC web in at least one induction heating step, i.e., moisture removal includes heating the wet MFC web in at least one induction heating step in addition to press dewatering and / or non-contact drying. Each induction heating step includes heating the wet MFC web by an induction heating device. The induction heating device can be any suitable induction heating device, such as an induction heating belt, an induction heated roll, or a portion of the belt or roll that is induction heated. The temperature of the induction heating device, or the temperature of the surface of the induction heating device positioned to be in direct or indirect contact with the wet MFC web, can be set or controlled to a temperature or temperature range suitable for heating the wet MFC web, for example, 50 to 350°C, preferably 60 to 300°C.

[0041] At least one of the at least one induction heating steps may be performed during at least part of the press dewatering of the wet MFC web, and / or at least one of the at least one induction heating steps may be performed during at least part of the non-contact drying of the wet MFC web.

[0042] In this specification, the phrase "induction heating step performed during at least part of press dewatering" is intended to mean an induction heating step performed when the wet MFC web is press dewatered, that is, when the press equipment used for press dewatering strikes the wet MFC web to remove moisture. The induction heating step may be performed during complete dewatering or during a portion of the dewatering process (such as a step or a part of a step).

[0043] In this specification, the phrase "induction heating step performed during at least part of non-contact drying" is intended to mean an induction heating step performed when the wet MFC web is being dried by non-contact drying, that is, when the non-contact drying equipment used for non-contact drying strikes the wet MFC web to remove moisture. The induction heating step may be performed during the entire non-contact drying process or during a portion of the non-contact drying process (such as a step or a portion of a step).

[0044] In some embodiments, at least one induction heating step is performed during at least part of the press dewatering. In these embodiments, at least one induction heating step may be performed so that the wet MFC web is heated by an induction heating device during or part or more of the complete dewatering.

[0045] In some embodiments, at least one induction heating step is performed during at least a portion of the non-contact drying. In these embodiments, at least one induction heating step may be performed so that the wet MFC web is heated by an induction heating device during the complete non-contact drying, or for part or more of the drying.

[0046] In some embodiments, at least one induction heating step is performed during at least a portion of the press dewatering, and at least one induction heating step is performed during at least a portion of the non-contact drying. In these embodiments, the at least one induction heating step performed during at least a portion of the press dewatering may be performed so that the wet MFC web is heated by an induction heating device during or part of the complete press dewatering. Also in these embodiments, the at least one induction heating step performed during at least a portion of the non-contact drying may be performed so that the wet MFC web is heated by an induction heating device during or part of the complete non-contact drying.

[0047] In some embodiments, at least one of the at least one induction heating steps includes heating a wet MFC web by induction heating at least a portion of a non-porous casting support. Thus, in these embodiments, at least a portion of the non-porous casting support that is induction heated constitutes or forms part of the induction heating device. At least a portion of the non-porous casting support that is induction heated may consist of at least a surface portion of the non-porous casting support that is in contact with the wet MFC web while the wet MFC web is being heated in the induction heating step. Thus, in these embodiments, the non-porous casting support, or at least its surface, is induction heatable. In these embodiments, the non-porous casting support may be a metal casting support, such as a metal casting belt. Preferably, in these embodiments, the non-porous casting support is an endless metal casting belt. The non-porous casting support may be induction heated by any suitable induction heating device, such as one or more induction heating coils and / or one or more induction heated rolls positioned to contact the surface of the non-porous casting support opposite the casting surface and / or one or more induction heated guide rolls (the guide rolls are positioned to guide the movement of the non-porous casting support). Thus, in these embodiments, the wet MFC web is heated by induction heating one or more portions of the non-porous casting support. In these embodiments, the induction heating step, which includes heating the wet MFC web by induction heating at least a portion of the non-porous support, can be performed during at least a portion of press dewatering and / or during at least a portion of non-contact drying. Alternatively or additionally, in these embodiments, the induction heating step, which includes heating the wet MFC web by induction heating at least a portion of the non-porous support, can be performed before press dewatering and / or between press dewatering steps and / or between press dewatering and non-contact drying steps and / or during non-contact drying steps and / or after non-contact drying.One or more portions of the nonporous casting support that are induction heated can be positioned on the production line such that the intended temperature profile of the nonporous casting support, and therefore the wet MFC web, is obtained. In these embodiments, the induction heating of the portions of the nonporous casting support that are induction heated can be controlled to control the temperature profile of the wet MFC web, and therefore the moisture profile of the wet MFC web.

[0048] In some embodiments, at least one of the at least one induction heating steps includes heating the wet MFC web with an induction heated roll provided in indirect or direct contact with the wet MFC web on the opposite side of the non-porous casting support, while heating the wet MFC web with an induction heated roll. Thus, in these embodiments, the induction heated roll constitutes or forms part of the induction heating apparatus. In these embodiments, the induction heating apparatus may be a metal roll. In these embodiments, the induction heating step, which includes heating the wet MFC web with an induction heated roll, can be performed during at least part of the press dewatering and / or at least part of the non-contact drying. Alternatively or additionally, in these embodiments, an induction heating step may be performed before press dewatering and / or during the press dewatering step and / or between press dewatering and non-contact drying (e.g., by induction heating a smoothing roll) and / or during the non-contact drying step and / or after non-contact drying, which includes heating the wet MFC web with an induction heated roll. For example, an induction heating step, which includes heating the wet MFC web with an induction-heated roll positioned in direct contact with the wet MFC web, can be performed during at least part of the non-contact drying process. An induction heating step, which includes heating the wet MFC web with an induction-heated roll positioned in indirect contact with the wet MFC web, can be performed during at least part of the press dewatering process, in which case a press felt may be provided between the induction-heated roll and the wet MFC.

[0049] In some embodiments, at least one induction heating step includes heating the wet MFC web by induction heating at least a portion of a non-porous support, and heating the wet MFC web with an induction heated roll provided in indirect or direct contact with the wet MFC web on the opposite side of the non-porous casting support while the wet MFC web is being heated by the induction heated roll.

[0050] In some embodiments, moisture removal includes press dewatering, at least one of at least one induction heating steps, which is performed during at least a portion of the press dewatering of the wet MFC web, and includes heating the wet MFC web by an induction-heated portion of the non-porous casting support.

[0051] In some embodiments, moisture removal includes press dewatering, where at least one of at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web and includes heating the wet MFC web by an induction heated roll provided in indirect or direct contact with the wet MFC web on the opposite side of the nonporous casting support while heating the wet MFC web by an induction heated roll.

[0052] In some embodiments, moisture removal includes press dewatering, where at least one of at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web and includes heating the wet MFC web by an induction heated roll provided in direct or indirect contact with the wet MFC web on the opposite side of the nonporous casting support, while the wet MFC web is heated by an induction heated portion of the nonporous casting support and by an induction heated roll.

[0053] In some embodiments, moisture removal includes non-contact drying, where at least one of at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web and includes heating the wet MFC web by an induction-heated portion of the non-porous casting support.

[0054] In some embodiments, moisture removal includes non-contact drying, where at least one of at least one induction heating steps is performed during at least a portion of the non-contact drying of the wet MFC web and includes heating the wet MFC web by an induction heated roll provided in indirect or direct contact with the wet MFC web on the opposite side of the non-porous casting support while heating the wet MFC web by an induction heated roll.

[0055] In some embodiments, moisture removal includes non-contact drying, where at least one of at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web and includes heating the wet MFC web by a heated portion of the non-porous casting support and by an induction heated roll provided to be in direct contact with the wet MFC web on the opposite side of the non-porous casting support.

[0056] In some embodiments, moisture removal includes press dewatering, and at least one of at least one induction heating steps is performed after press dewatering. The at least one induction heating step performed after press dewatering may include heating the wet MFC web by an induction heated roll provided in direct contact with the wet MFC web on the opposite side of the nonporous casting support, while heating the wet MFC web by an induction heated portion of the nonporous casting support and / or by an induction heated roll.

[0057] In some embodiments, moisture removal includes non-contact drying, where at least one of at least one induction heating steps is performed before non-contact drying and / or at least one of at least one induction heating steps is performed after non-contact drying. Each of the at least one induction heating step performed before non-contact drying and the at least one induction heating step performed after non-contact drying may include heating the wet MFC web by an induction heated roll provided in direct contact with the wet MFC web on the opposite side of the non-porous casting support, while the wet MFC web is heated by an induction heated portion of the non-porous casting support and / or by an induction heated roll.

[0058] As described above, the method of the first embodiment includes the step of separating (e.g., peeling) the dried MFC web from the non-porous casting support. Typically, after separation from the non-porous support, the dried MFC web is wound onto a core to form a reel of dried MFC web. In this way, a reel of self-supporting continuous dried MFC web is formed. In some cases, further drying of the dried MFC web may be performed after separating the dried MFC web from the non-porous casting support and before or in connection with winding the dried MFC web onto a core to form a reel.

[0059] The MFC web produced in the above embodiments of the method of this disclosure may be an MFC film. In these embodiments, a wet MFC film is formed in the forming step described above, and a dry MFC film is formed in the step of subjecting the wet MFC film to moisture removal.

[0060] In some embodiments where the MFC web is an MFC film, the density was 10 cc / m², measured according to standard ASTM F1927-20 at a relative humidity of 50% and a temperature of 23°C. 2 Less than 24 hours, preferably 7cc / m³ 2 Less than 24 hours, more preferably 5cc / m 2A dry MFC film having an oxygen transmission rate (OTR) of less than 24 hours is formed.

[0061] In some embodiments where the MFC web is an MFC film, 100 g / m measured according to standard ASTM F1249-20 at a relative humidity of 50% and a temperature of 23°C 2 / Less than 24 hours, preferably 50 g / m 2 / Less than 24 hours, more preferably 20 g / m 2 A dry MFC film having a water vapor transmission rate (WVTR) of less than 24 hours is formed.

[0062] In some embodiments where the MFC web is an MFC film, 10 - 70 g / m measured according to ISO 536 2 , preferably 10 - 60 g / m 2 , or 10 - 50 g / m 2 , or 15 - 40 g / m 2 A dry MFC film having a dry basis weight of is formed.

[0063] In some embodiments where the MFC web is an MFC film, a dry MFC film having an average film thickness of 5 - 60 μm, preferably 10 - 50 μm, 15 - 45 μm, or 20 - 40 μm is formed. The average film thickness can be defined as the average thickness across the entire width of the film. The thickness of the MFC film can be measured, by way of non-limiting example, using white light interferometry, laser profilometry, or optically, by cutting the sample with a line in the machine transverse direction (whether or not it is cast in resin) and taking a microscopic image of the thickness direction of the cut cross-section (e.g., scanning electron microscopy or other applicable methods).

[0064] In some embodiments where the MFC web is an MFC film, a dry MFC film having a width of 0.3 - 4 m, preferably 0.5 - 4 m, 1 - 4 m, or 2 - 4 m is formed.

[0065] In some embodiments where the MFC web is an MFC film, the weight is measured according to ISO 534:2011, ranging from 700 to 1500 kg / m². 3 Preferably 800-1500 kg / m 3 Most preferably 900-1500 kg / m 3 A dry MFC film having the density is formed.

[0066] In some embodiments, the MFC web produced by the method of this disclosure is an absorption layer, a membrane, a separation medium, or a prefabricate.

[0067] The self-supporting MFC film provided by the method of this disclosure can be applied to the surface of either a paper product or a cardboard product to form a laminate, such as a paper or paper-based packaging material laminate.

[0068] Paper generally refers to a material manufactured in the form of a thin sheet from wood pulp or other fibrous material containing cellulose fibers, and used for writing, drawing, or printing on packaging materials, or as packaging material itself.

[0069] Paperboard generally refers to strong, thick paper or cardboard containing cellulose fibers, used for boxes and other types of packaging materials. Depending on the requirements of the end use, paperboard can be bleached or unbleached, coated or uncoated, and can be manufactured in various thicknesses.

[0070] The self-supporting MFC film provided by the method of this disclosure can be used as a laminate with one or more polymer layers, such as a thermoplastic polymer layer. For example, one or more additional polymer layers may consist of any suitable polyolefin or polyester. The additional polymer layers can be provided, for example, 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), polyhydroxyalkanoic acid (PHA), and polybutylene succinate (PBS).

[0071] The self-standing MFC film provided by the method of this disclosure can be used as a packaging material, or within a packaging material, such as a food or liquid packaging material, and can be incorporated into any type of packaging, such as boxes, bags, packaging films, cups, containers, trays, and bottles.

[0072] According to a second aspect of this specification, an MFC web, such as an MFC film obtained by the method of the first aspect, is provided. The MFC web according to the second aspect can be further defined as described above with reference to the method of the first aspect.

[0073] The present invention will be further described below with reference to the attached drawings and exemplary embodiments. [Brief explanation of the drawing]

[0074] [Figure 1] A schematic diagram of a first embodiment of the method according to this disclosure is shown. [Figure 2] A schematic diagram of a second embodiment of the method according to this disclosure is shown. [Figure 3] A schematic diagram of a third embodiment of the method according to this disclosure is shown. [Figure 4] A schematic diagram of a fourth embodiment of the method according to this disclosure is shown. [Figure 5] A schematic diagram of a fifth embodiment of the method according to this disclosure is shown. [Figure 6] A schematic diagram of a sixth embodiment of the method according to this disclosure is shown. [Figure 7] A schematic diagram of a seventh embodiment of the method according to this disclosure is shown. [Modes for carrying out the invention]

[0075] Figure 1 shows a schematic diagram of a first embodiment of a method according to a first aspect of the present disclosure, performed in a system 1 for the manufacture of MFC webs. In the first embodiment shown in Figure 1, an MFC suspension 2 is provided to a casting unit 3, such as a slot die applicator. The MFC suspension 2 contains between 50% and 100% by weight of MFCs based on total dry weight, and has a dry content of 1 to 30% by weight. The MFC suspension 2 contains water as the suspension medium. Optionally, one or more additives (e.g., papermaking additives and / or chemicals) and / or one or more other suitable components (e.g., further pulp fractions) may also be included in the MFC suspension 2. A wet MFC web 4 is formed from the MFC suspension 2 by casting layers of the MFC suspension 2 onto a non-porous casting support in the shape of an endless metal belt 5 by the casting unit 3. In the first embodiment shown in Figure 1, a wet MFC web 4 positioned on a metal belt 5 is subjected to moisture removal, including press dewatering in a press dewatering device 6 and drying in a non-contact drying device 7, to form a dried MFC web 8. Furthermore, in the first embodiment shown in Figure 1, moisture removal further includes an induction heating step performed during press dewatering and an induction heating step performed during non-contact drying. The induction heating steps performed between press dewatering and non-contact drying each include heating the wet MFC web 4 by induction heating each portion 10a of the metal belt 5 with an induction heating device 9. The induction heated portion 10a of the metal belt 5 forms an induction heating device 10. After non-contact drying, the dried MFC web 8 is separated from the metal belt 5 and wound onto a core to form a reel 11 of dried MFC web 8.

[0076] Figure 2 shows a schematic diagram of one embodiment of the method according to a second aspect of the present disclosure. The second embodiment differs from the first embodiment in the induction heating step. In the second embodiment shown in Figure 2, moisture removal consists of two induction heating steps performed between each portion of the press dewatering. Each induction heating step includes heating the wet MFC web 4 by induction heating each portion 10a of the metal belt 5 with an induction heating device 9. Each portion 10a of the metal belt 5 to be induction heated forms an induction heating device 10.

[0077] Figure 3 shows a schematic diagram of one embodiment of the method according to a third aspect of the present disclosure. The third embodiment differs from the first embodiment in the induction heating step. In the third embodiment shown in Figure 3, moisture removal consists of one induction heating step performed during non-contact drying. The induction heating step performed during non-contact drying includes heating the wet MFC web 4 by an induction-heated roll 10b which is induction-heated by an induction heating device 9. Thus, the induction-heated roll 10b forms the induction heating device 10. In the embodiment shown in Figure 3, the induction-heated roll 10b is positioned to be in direct contact with the wet MFC web 4.

[0078] Figure 4 shows a schematic diagram of one embodiment of the method according to a fourth aspect of the present disclosure. The fourth embodiment differs from the first embodiment in the induction heating process. In the fourth embodiment shown in Figure 4, moisture removal includes one induction heating step performed during press dewatering and one induction heating step performed during non-contact drying. The induction heating steps performed during press dewatering and non-contact drying each include heating the wet MFC web 4 by induction heating each portion 10a of the metal belt 5 with an induction heating device 9. Each portion 10a of the metal belt 5 that is induction heated forms an induction heating device 10. Furthermore, the induction heating step performed during non-contact drying includes heating the wet MFC web 4 with an induction heated roll 10b that is induction heated by the induction heating device 9. Thus, the induction heated roll 10b forms an induction heating device 10. In the embodiment shown in Figure 4, the induction heated roll 10b is provided to be in direct contact with the wet MFC web 4.

[0079] Figure 5 shows a schematic diagram of one embodiment of the method according to a fifth aspect of the present disclosure. The fifth embodiment differs from the fourth embodiment in the induction heating process. In the fifth embodiment shown in Figure 5, moisture removal includes one induction heating step performed during press dewatering and one induction heating step performed during non-contact drying. Each induction heating step performed between press dewatering and non-contact drying includes heating the wet MFC web 4 by induction heating each portion 10a of the metal belt 5 with an induction heating device 9. Each portion 10a of the metal belt 5 that is induction heated forms an induction heating device 10. Furthermore, each induction heating step performed between press dewatering and non-contact drying includes heating the wet MFC web 4 with an induction heated roll 10b that is induction heated by the induction heating device 9. Thus, the induction heated roll 10b forms an induction heating device 10. In the embodiment shown in Figure 5, the induction-heated roll 10b used during non-contact drying is positioned to be in direct contact with the wet MFC web 4, while the induction-heated roll 10b used during press dewatering is positioned to be in contact with the press felt 12 used during press dewatering, and therefore to be indirectly in contact with the wet MFC web 4.

[0080] Figure 6 shows a schematic diagram of one embodiment of the method according to the sixth aspect of the present disclosure. The sixth embodiment differs from the third embodiment shown in Figure 3 in terms of moisture removal. In the sixth embodiment shown in Figure 6, non-contact drying is omitted. Therefore, moisture removal includes press dewatering in the press dewatering device 6 and one induction heating step performed after press dewatering. The induction heating step performed after press dewatering includes heating the wet MFC web 4 with an induction-heated roll 10b which is induction-heated by an induction heating device 9. Thus, the induction-heated roll 10b forms the induction heating device 10. In the embodiment shown in Figure 6, the induction-heated roll 10b is positioned to be in direct contact with the wet MFC web 4.

[0081] Figure 7 shows a schematic diagram of a seventh embodiment of the method according to the first aspect of this disclosure. The seventh embodiment differs from the first embodiment shown in Figure 1 in the method of removing water. In the seventh embodiment shown in Figure 7, the press dewatering and induction heating steps during non-contact drying are omitted. Therefore, moisture removal includes non-contact drying by the non-contact drying apparatus 7 and one induction heating step performed before non-contact drying. The induction heating step performed before non-contact drying includes heating the wet MFC web 4 by induction heating a portion 10a of the metal belt 5 with the induction heating apparatus 9. The portion 10a of the metal belt 5 that is induction heated forms the induction heating apparatus 10.

[0082] Generally, products, materials, layers, and processes are described in terms of "containing" various components or steps, but products, materials, layers, and processes may also be "essentially composed of" or "composed of" various components and steps.

[0083] Given the above detailed description of the present invention, other modifications and changes will become apparent to those skilled in the art. However, it is clear that such other modifications and changes can be carried out without departing from the spirit and scope of the present invention.

Claims

1. A method for producing a microfibrillated cellulose (MFC) web, - A step of providing an MFC suspension (2) comprising 50% to 100% by weight of MFCs and a suspension medium based on total dry weight, wherein the suspension medium contains water, and the MFC suspension (2) has a dry content of 1 to 30% by weight, - A step of forming a wet MFC web (4) of the MFC suspension (2) by casting it onto a non-porous casting support (5), - A step of subjecting the wet MFC web (4), positioned on the non-porous casting support (5), to dewatering in order to form a dry MFC web (8), wherein the dewatering includes pressing and dewatering the wet MFC web (4) and / or non-contact drying the wet MFC web (4), and the dewatering further includes at least one induction heating step, each induction heating step comprising heating the wet MFC web (4) by induction heating devices (10, 10a, 10b), - A step of separating the dried MFC web (8) from the non-porous casting support (5) Methods that include...

2. The method according to claim 1, wherein at least one of the at least one induction heating steps includes heating the wet MFC web (4) by at least a portion (10a) of the induction heated nonporous casting support (5).

3. The method according to claim 1 or 2, wherein at least one of the at least one induction heating steps includes heating the wet MFC web (4) with an induction heated roll (10b) while heating the wet MFC web (4) with an induction heated roll (10b) provided in indirect or direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5).

4. The method according to any one of claims 1 to 3, wherein at least one of the at least one induction heating steps includes heating the wet MFC web (4) by at least a portion of the induction heated nonporous casting support (5) and heating the wet MFC web (4) by an induction heated roll (10b), between these two steps, heating the wet MFC web (4) by an induction heated roll (10b) provided on the opposite side of the nonporous casting support (5) in indirect or direct contact with the wet MFC web (4).

5. The method according to any one of claims 1 to 4, wherein at least one of the at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web (4) and / or at least one of the at least one induction heating steps is performed during at least a portion of the non-contact drying of the wet MFC web (4).

6. The method according to any one of claims 1 to 5, wherein the moisture removal includes press dewatering, and at least one of the at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web (4) and includes heating the wet MFC web (4) by the induction heated portion (10a) of the nonporous casting support (5).

7. The method according to any one of claims 1 to 6, wherein the moisture removal includes press dewatering, and at least one of the at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web (4), and includes heating the wet MFC web (4) by an induction heated roll (10b) provided in indirect or direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5).

8. The method according to any one of claims 1 to 7, wherein the moisture removal includes press dewatering, and at least one of the at least one induction heating steps is performed during at least a portion of the press dewatering of the wet MFC web (4), and includes heating the wet MFC web (4) by the induction heated portion (10a) of the nonporous casting support (5) and by the induction heated roll (10b), with the induction heated roll (10b) being in indirect or direct contact with the wet MFC web (4) on the opposite side of the nonporous casting support (5).

9. The method according to any one of claims 1 to 8, wherein the moisture removal includes non-contact drying, and at least one of the at least one induction heating steps is performed during at least a portion of the non-contact drying of the wet MFC web (4), and includes heating the wet MFC web (4) by the induction heated portion (10a) of the non-porous casting support (5).

10. The method according to any one of claims 1 to 6, wherein the moisture removal includes the non-contact drying, and at least one of the at least one induction heating steps is performed during at least a portion of the non-contact drying of the wet MFC web (4), and includes heating the wet MFC web (4) by an induction heated roll (10b) while heating the wet MFC web (4) by an induction heated roll (10) provided in direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5).

11. The method according to any one of claims 1 to 10, wherein the moisture removal includes non-contact drying, and at least one of the at least one induction heating steps is performed during at least a portion of the non-contact drying of the wet MFC web (4), and includes heating the wet MFC web (4) by an induction heated portion of the non-porous casting support (5) and by an induction heated roll (10b) provided in direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5).

12. The method according to any one of claims 1 to 11, wherein the moisture removal includes press dehydration, and at least one of the at least one induction heating steps is performed after the press dehydration.

13. The method according to claim 12, wherein the at least one induction heating step performed after the press dewatering step includes heating the wet MFC web (4) by the induction heated roll (10b) which is provided to be in direct contact with the wet MFC web (4) on the opposite side of the nonporous casting support (5), while heating the wet MFC web (4) by the induction heated portion of the nonporous casting support (5) and / or by the induction heated roll (10b).

14. The method according to any one of claims 1 to 13, wherein the moisture removal includes non-contact drying, and at least one of the at least one induction heating steps is performed before the non-contact drying and / or at least one of the at least one induction heating steps is performed after the non-contact drying.

15. The method according to claim 14, wherein each of the at least one induction heating step performed before the non-contact drying and the at least one induction heating step performed after the non-contact drying is heating the wet MFC web (4) by the induction heated roll (10b) which is in direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5), while the wet MFC web (4) is heated by the induction heated roll (10b) which is provided in direct contact with the wet MFC web (4) on the opposite side of the non-porous casting support (5).

16. The method according to any one of claims 1 to 15, wherein the non-porous casting support (5) is a metal belt.

17. The method according to any one of claims 1 to 16, wherein the press dewatering comprises at least one press dewatering step, each press dewatering step comprising: applying a press fabric (12) so as to be in direct or indirect contact with the wet MFC web (4) positioned on the non-porous casting support (5); and removing water from the wet MFC web (4) by passing the wet MFC web (4), positioned between the press fabric (12) and the non-porous casting support (5), through a press device (6) to transfer water from the wet MFC web (4) to the press fabric (12).

18. The method according to any one of claims 1 to 17, wherein the non-contact drying comprises at least one non-contact drying step, each non-contact drying step comprising high-temperature gas impact drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near-infrared drying, or a combination thereof.

19. The method according to any one of claims 1 to 18, wherein the formed wet MFC web (4) includes a single web layer or two or more web layers formed to overlap each other.

20. The method according to any one of claims 1 to 19, wherein the MFC web is an MFC film.

21. The dried MFC film (8) has an average thickness of 5 to 60 μm and a density of 2 to 70 g / m² as measured according to ISO 536. ２ The method according to claim 20, having a dry basis weight.

22. An MFC web obtainable by the method described in any one of claims 1 to 21.

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