A method for producing a laminate

Abstract

548 428The present invention relates to a method for producing a laminate comprising a multiply paperboard provided with a microfibrillated cellulose (MFC) film. The method comprises a step of applying a wet MFC film having a dry content of 2-50 weight-% to a wet multiply paperboard web having a dry content of 20-58 weight-% to form a wet laminate, wherein the step of applying comprises wet pressing the wet MFC film and the wet multiply paperboard web together in at least one press dewatering step. The wet laminate is then dried to a dry content of at least 85 weight-% to form the laminate comprising a multiply paperboard provided with an MFC film. The invention relates also to a laminate comprising a multiply paperboard provided with a microfibrillated cellulose (MFC) film.

Description

The present disclosure relates to a method for producing a laminate comprising a multiply paperboard provided with a barrier film, wherein the barrier film is a micro fibrillated cellulose (MFC) film.BackgroundOxygen, 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.More recently, microfibrillated cellulose (MFC) films 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 dense film with barrier properties, such as oxygen, aroma and grease barrier properties. MFC films are recyclable and biodegradable as well as based on renewable raw material. For example, MFC films can be used in packaging applications, such as food or liquid packaging applications, as a barrier layer, as a stand-alone film or as a coating on paper or paperboard.One approach to produce MFC films is to use a casting method in which a wet MFC web is formed by casting of an MFC suspension comprising MFC and a suspension medium 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 film. Casting methods have been shown to produce MFC films with very smooth surfaces with good barrier properties, such as oxygen barrier properties and / or water vapor barrier properties.Another approach to produce MFC films is to use a wet laid technique, i.e., to apply a dilute MFC suspension comprising MFC and a suspension medium on a dewatering wire, membrane or dewatering fabric, such as a press felt, in a forming section and dewater it by vacuum, gravitation, capillary dewatering, press dewatering or a combination of these on the wire, membrane or dewatering fabric followed by drying or liquid evaporation.MFC films can be laminated to paperboard in different ways for providing a barrier layer or coating on the paperboard for improvement of the barrier properties of the paperboard.One way of lamination of MFC films to paperboard proposed in the prior art is lamination of a dry MFC film to dry paperboard by means of an adhesive. However, lamination of a dry MFC film to dry paperboard by means of an adhesive is associated with challenges, e.g., since the MFC films are sensitive to re-wetting.Another way of lamination of MFC films to paperboard proposed in the prior art is lamination of a wet MFC film to dry paperboard. However, lamination of a wet MFC film to dry paperboard is also associated with challenges, e.g., since re-wetting of the paperboard may imply impact on curl and shrinkage upon drying of the wet MFC film and since lamination of a wet MFC film to dry paperboard may imply difficulties with adhesion / delamination.Thus, there is still room for improvements of methods for producing a laminate comprising a multiply paperboard substrate provided with a barrier film, which barrier film is an MFC film.Description of the inventionIt is an object of the present invention to provide an improved method for producing a laminate comprising a multiply paperboard provided with an MFC film, which method eliminates or alleviates at least some of the disadvantages with the prior art methods.The above-mentioned object, as well as other objects as will be realized by the skilled person in the light of the present disclosure, is achieved by the various aspects of the present disclosure.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 laminate comprising a multiply paperboard provided with a microfibrillated cellulose (MFC) film, wherein the method comprises the steps of:- providing a wet multiply paperboard web;- wet pressing the wet multiply paperboard web so as to obtain a dry content of 20-58 weight-% of the wet multiply paperboard web, wherein the wet pressing comprises at least one wet pressing step;- providing a wet MFC film having a dry content of 2-50 weight-% and comprising between 70 weight-% to 100 weight-% of MFC based on total dry weight, wherein the wet MFC film is provided on a support; - applying the wet MFC film having a dry content of 2-50 weight-% to the wet multiply paperboard web having a dry content of 20-58 weight-% to form a wet laminate, wherein the step of applying the wet MFC film to the wet multiply paperboard web comprises wet pressing the wet MFC film and the wet multiply paperboard web together in at least one press dewatering step, and- drying the wet laminate to a dry content of at least 85 weight-% to form the laminate comprising a multiply paperboard provided with an MFC film.Thus, the method of the first aspect provides a laminate comprising a multiply paperboard substrate provided with an MFC film, which is a barrier film. Accordingly, the laminate is a barrier laminate.With the method according to the first aspect, it is possible to essentially reduce or mitigate challenges with re-wetting of a dry MFC film and a dry multiply paperboard associated with use of an adhesive for adhesion of the dry MFC film to the dry multiply paperboard according to prior art. It has surprisingly been found that a good adhesion of the MFC film to the multiply paperboard is obtained when the wet MFC film has a dry content of 2-50 weight-% and the wet multiply paperboard web has a dry content of 20-58 weight-% when applied to each other, since both the MFC film and the multiply paperboard web then are sufficiently wet to ensure good deformability during wet pressing. Also, the dry content of 2-50 weight-% of the MFC film enables the MFC film to provide good contact with the rough counter surface of the multiply paperboard. Also, the challenges with impact on curl and shrinkage when a wet MFC film is applied to a dry multiply paperboard according to prior art are possible to essentially reduce or mitigate with the method according to the first aspect, since the MFC film and the multiply paperboard are laminated to each other in a wet state. The moisture distribution throughout the board will be more even which hence impacts the dimensional stability. Furthermore, the lamination of the MFC film and the multiply paperboard in wet state to each other and additional dewatering and / or drying together of the MFC film and the multiply paperboard imply a positive effect on delamination issues. Without being bound to any theories, it is believed that better interfacial contact is obtained when pressing the layers together in the presence of more water. Also, more water and pressing of non-dried substrate allows for some re-distribution of fines, and optionally co-binders, in the boundary layer, hence better layer-layer contact.As mentioned above, the method of the first aspect comprises a step of providing a wet multiply paperboard web.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. In the method according to the first aspect, a multiply paperboard is utilized.The multiply paperboard used as a substrate in accordance with the present disclosure can be made from pulp, including pulp from virgin fiber, e.g., mechanical, semi-chemical, chemical and / or thermomechanical pulps. It can also be made from broke or recycled paperboard. The multiply paperboard used as a substrate in accordance with the present disclosure is prepared using methods known in the art.In some embodiments, the multiply paperboard comprises at least 10% recycled material, such as at least 20% or at least 30% or at least 40% or at least 50% or at least 60% or at least 70% recycled material, which can be either pre- or postconsumer grade.The multiply paperboard of the method of the first aspect has preferably a grammage in the range of 100-600 g / m2 or 120-450 g / m2, more preferably in the range of 200-500 g / m2 or 180-380 g / m2. Unless otherwise stated herein, the grammage is determined according to the standard ISO 536.The multiply paperboard of the method of the first aspect comprises two or more plies. In some embodiments, the multiply paperboard comprises three or more plies. In some embodiments, the multiply paperboard comprises at least one lower density mid-ply sandwiched between two higher density outer plies. In some embodiments, the multiply paperboard comprises two or more plies, wherein the outer ply provided with the MFC film is a lower density ply.In some embodiments, the multiply paperboard comprises at least one lower density mid-ply (also sometimes referred to as “bulk ply”) sandwiched between two higher density outer plies. The lower density mid-ply may typically have a density below 750 kg / m3, preferably below 700, below 650, below 600, below 550, below 500, below 450, below 400 or below 350 kg / m3, as determined according to standard ISO 534. The higher density outer plies typically have a density at least 100 kg / m3 higher than the mid-ply, preferably at least 200 kg / m3 higher than the mid-ply, as determined according to standard ISO 534.In some embodiments, the multiply paperboard is a foam formed paperboard. In some embodiments, at least one of the plies, preferably a mid-ply, is foam formed. In some embodiments, at least one of the plies, preferably a mid-ply, is a bulky ply.The method of the first aspect comprises a step of wet pressing the wet multiply paperboard web so as to obtain a dry content of 20-58 weight-% of the wet multiply paperboard web. Preferably, the wet pressing of the wet multiply paperboard web is performed so as to obtain a dry content of 20-55 weight-%, more preferably 25-55 weight-%, most preferably 35-55 weight-% such as 40-55 weight-% or 35-50 weight%, of the wet multiply paperboard web. The wet pressing comprises at least one wet pressing step. The wet pressing can be performed in any suitable way with any suitable means known in the art. The wet pressing may be performed in a press section, which may comprise one or more sub-sections.According to the method of the first aspect, a wet MFC film having a dry content of 2-50 weight-% and comprising between 70 weight-% to 100 weight-% of MFC based on total dry weight is provided on a support.The term film as used herein refers generally to a thin continuous sheet or layer formed material, such as a thin substrate with good gas, aroma 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.In some embodiments, the step of providing a wet MFC film comprises providing an MFC suspension comprising between 70 weight-% to 100 weight-% of MFC based on total dry weight and forming the MFC film from the provided MFC suspension on the support. In some embodiments, the provided MFC suspension comprises between 75 weight-% to 100 weight-%, or 80 weight-% to 100 weight-%, or between 85 weight-% to 100 weight-%, or between 90 weight-% to 100 weight-%, of MFC based on total dry weight. Optionally, the wet MFC film is subjected to water removal on the support to obtain the dry content of 2-50 weight-%.The MFC suspension comprises a suspension medium in which a mixture of cellulose-based material and optionally additives are suspended. Preferably, the MFC suspension is an aqueous suspension comprising a water-suspended mixture of cellulose-based material and optionally additives.The provided MFC suspension may have a dry content of 1-30 weight-%. In some embodiments, the MFC suspension has a dry content of 1-25 weight-%, such as 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-%.Microfibrillated cellulose (MFC) shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm.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.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.The MFC of the MFC suspension may comprise one or more fractions of MFC. In some embodiments, the MFC of the MFC suspension comprises one fraction of MFC of a fine grade. In some embodiments, the MFC of the MFC suspension comprises two or more fractions of MFC of different fine grades. In some embodiments, the MFC 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 BO-99 SR° or 90-99 SR° or 95-99 SR°, whereas fine MFC is fibrillated to a Schopper-Riegler value above the measurement range (theoretical value about or above 100 SR°) as determined by standard ISO 5267-1. In some embodiments, the fine grade MFC is chemically derivatized, such as carboxymethylated MFC.The MFC suspension may in addition to MFC comprise any conventional paper making additives or chemicals such as film-forming agents, dispersants, 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 film performance chemicals added to provide the end product film with specific properties and / or to facilitate production of the film. In some embodiments, the MFC film comprises at least one further polymer that can form 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. In some embodiments, the MFC film comprises at least one additive selected from the group of: PVOH and derivatives or analogues thereof, polysaccharides such as starch and CMC, sorbitol and polyethylene glycol. 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%.The MFC suspension may comprise no more than 30 weight-%, such as no more than 25 weight-% or no more than 20 weight-% or no more than 15 weight-% of additives.In some embodiments, the MFC suspension comprises no fixatives or retention aids to avoid or essentially reduce flocculation. If the MFC film is formed on a non-porous support, no fixatives or retention aids are needed.In some embodiments, the MFC suspension comprises no wet strength chemicals.In some embodiments, the MFC suspension comprises less than 30 weight-%, preferably less than 25 weight-% or less than 20 weight-% such as 1-10 weight-%, inorganic fillers.As mentioned above, the provided wet MFC film has a dry content of 2-50 weight-%. Preferably, the provided wet MFC film has a dry content of 2-40 weight-%, more preferably 4-40 weight-%, most preferably 5-35 weight-%.In some embodiments, the wet MFC film is formed from an amount of an MFC suspension comprising between 70 weight-% to 100 weight-% MFC based on total dry weight such that the MFC film of the produced laminate has a grammage of 1-25 g / m2 (dry), preferably 1-15 g / m2, more preferably 2-9 g / m2 (dry).In some embodiments, the support on which the wet MFC film is provided, is a nonporous support.In some embodiments, the step of providing a wet MFC film comprises providing an MFC suspension comprising between 70 weight-% to 100 weight-% of MFC based on total dry weight and forming the MFC film from the provided MFC suspension on the support by casting on the support, which preferably is a non-porous support.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 levelling with, for example, a doctor-blade, rod, air knife or roll.The non-porous support may be a metal (e.g., steel), rubber or elastomer, plastic, polymer (e.g., polyurethane) or composite 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. Preferably, the non-porous support is coated with an adhesion / releasing controlling agent. Examples of agents of such a coating are poly(aminoamide)-epihalohydrin polymer (PAE) resins, polyvinyl alcohol resins (PVOH), polyvinyl alcohol copolymers, starches, ethylene glycol, vegetable oils, fatty acids and sugar alcohols. The nonporous 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, preferably coated with an adhesion / releasing controlling agent.In some embodiments, the non-porous support is a metal belt, such as a continuous metal belt, which is at least partly heated. For example, the metal belt may be heated during the step of MFC film formation and / or the optional 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. Preferably, the metal belt is heated by steam.In some embodiments, the support on which the wet MFC film is provided, is a porous support, such as a dewatering wire, dewatering fabric or membrane.In some embodiments, the step of providing a wet MFC film comprises providing an MFC suspension comprising between 70 weight-% to 100 weight-% of MFC based on total dry weight and forming the MFC film from the provided MFC suspension on the support by wet-laying, i.e., applying the MFC suspension on a porous support such as a dewatering wire, dewatering fabric or membrane.In some embodiments, the wet MFC film is provided in the form of a foam and has a density of 50-800 kg / m3, such as 50-500 kg / m3.The provided wet MFC film may be a single or multilayer film. Thus, the provided wet MFC film may comprise a single wet layer or two or more wet layers on top of each other, which may be made with one or several headboxes or with curtain or spray application in multilayer coating mode.As mentioned above, the formed wet MFC film is optionally subjected to water removal to obtain the dry content of 2-50 weight-%. The water removal may comprise dewatering and / or drying the wet MFC film to obtain the dry content of 2-50 weight-%. The dewatering and the drying, respectively, may be performed using any method known in the art that is suitable to remove water from the wet MFC film and obtain the dry content of 2-50 weight-%.As mentioned above, the method of the first aspect comprises a step of applying the wet MFC film having a dry content of 2-50 weight-% to the wet multiply paperboard web having a dry content of 20-58 weight-% to form a wet laminate. The step of applying the wet MFC film to the wet multiply paperboard web comprises wet pressing the wet MFC film and the wet multiply paperboard web together in at least one press dewatering step. The press dewatering may be performed in any suitable way by any suitable means, such as in a press section.In some embodiments, the step of applying the wet MFC film to the wet multiply paperboard web comprises wet pressing the wet MFC film and the wet multiply paperboard web together in an extended nip of a pressing equipment, e.g., in a press section. The extended nip may be comprised in a shoe press. The shoe press can be a single or double felted shoe press. The line load in the shoe press is preferably less than 800 kN / m, more preferably less than 600 kN / m.In some embodiments, the speed at lamination (i.e. , during the step of applying the wet MFC film to the wet multiply paperboard web, is above 100 m / min, such as above 150 m / min, or 200-1000 m / min.In some embodiments, the wet pressing of the wet multiply paperboard is performed in a press section and the support, on which the wet MFC film is provided, is partly integrated in the press section such that the step of applying the wet MFC film to the wet multiply paperboard web is performed by transferring the wet MFC film from the support to the wet multiply paperboard web in the press section. In some of these embodiments, the support is partly integrated in the press section such that also the optional step of water removal of the wet MFC film is performed in the press section.In some embodiments, the wet pressing of the wet multiply paperboard is performed in a press section and the step of applying the wet MFC film to the wet multiply paperboard web is performed by transferring the wet MFC film from the support to a transfer support and from the transfer support to the wet multiply paperboard web with no free draw between the support and the transfer support. In some of these embodiments, the support is partly integrated in the press section such that the optional step of water removal of the wet MFC film is performed in the press section.In some embodiments involving providing the wet MFC film on a non-porous support, e.g., involving formation by casting, and wet pressing of the wet multiply paperboard in a press section, the non-porous support is partly integrated in the press section. In these embodiments the wet MFC film may be transferred from the non-porous support to the wet multiply paperboard web, or may be transferred from the nonporous support to a transfer support and from the transfer support to the wet multiply paperboard web with no free draw between the support and the transfer support, in the press section in the step of applying the wet MFC film to the wet multiply paperboard web to form a wet laminate. In some of these embodiments, the nonporous support is partly integrated in the press section such that also the optional step of water removal of the wet MFC film is performed in the press section. In some of these embodiments, the non-porous support is a metal belt. The metal belt may be at least partly heated, such as heated to a temperature above 30 °C, at least during at least parts of the step of applying the wet MFC film to the wet multiply paperboard. The heating of the metal belt improves dewatering during the transfer process.Preferably, the metal belt is heated by steam.The method of the first aspect further comprises, after application of the wet MFC film to the wet multiply paperboard web to form a wet laminate, a step of drying the wet laminate to a dry content of at least 85 weight-% to form the laminate comprising a multiply paperboard provided with an MFC film. Thus, after the application of the wet MFC film to the wet multiply paperboard web to form a wet laminate, the wet laminate is dried to obtain a dry content of at least 85 weight-% of the formed laminate. Drying of the wet laminate may be performed in any suitable way by any suitable means.In some embodiments, the wet MFC film and the wet multiply paperboard web is wet pressed in the at least one press dewatering step such that the formed wet laminate has a dry content of 55-75 weight-%. Thereby, the wet MFC film may be subjected to gentle dewatering in order to ensure a high dry content of the wet laminate before the drying section.In some embodiments, the method further comprises smoothing of the wet MFC film of the wet laminate by applying at least one smoothing press to the wet MFC film of the wet laminate to smoothen the surface of the MFC film. The smoothing is performed after the wet pressing comprising at least one press dewatering step, but before drying of the wet laminate. Alternatively, a counch press or counch roll could be utilized. A smoothing press applies rather low pressures such as less than 100 kN / m, more preferably less than 80 kN / m such as 5-55 kN / m. The smoothing press can also be such that one of the rolls, preferably in contact with base web (multiply paperboard) is a vacuum suction roll. Hence, pressing and smoothing is made during dewatering of the web.In some embodiments, the method further comprises a step of calendaring the laminate after the drying step. Gentle calendaring may improve the adhesion.In some embodiments, the method further comprises a step of surface sizing or film press coating or blade coating of said laminate on at least one side with a water based barrier dispersion or solution, for example a solution comprising a water soluble polymer such as polysaccharide (e.g., starch), CMC or a dispersion barrier comprising e.g., PVOH or latex.In some embodiments, the wet MFC film is applied to a back ply of the wet multiply paperboard web. In some of these embodiments, the back ply comprises 50%, preferably 60%, by dry weight of bleached or unbleached kraft pulp, as calculated on the total weight of the back ply, and has a grammage of 10-60 g / m2, such as 15-45 g / m2. The kraft pulp can be of hardwood or softwood or a mixture thereof. It was surprisingly found that a lower thickness back ply in combination with the wet MFC film provide a more efficient dewatering.In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has an oil resistance determined with Cobb-Unger (30 s) of less than 10 g / m2, preferably less than 5 g / m2, according to the SCAN-P 37:77 when determined for the smooth side, i.e. the side provided with the MFC film. In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has an oil and grease resistance (KIT test) above 10, preferably above 11, according to the ISO 16532-2 standard. In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has a Water Vapor Transmission Rate (WVTR) below 100 g / m2 / day, preferably below 50 g / m2 / day, when determined at 23° C and 50% RH according to standard ASTM F1249-20. In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has a Z-tensile strength above 200 kPa, preferably above 250 kPa, according to SCAN-P 80:98. In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has a Scott Bond value higher than 120 J / m2, preferably higher than 150 J / m2, according to the TAPPI 569 standard.In some embodiments, the obtained laminate comprising a multiply paperboard provided with an MFC film has a wet tensile strength (machine direction, MD) of more than 0.4 kN / m, preferably more than 0.6 kN / m, and most preferably more than 0.8 kN / m, as measured according to standard ISO 3781:2011.There is a demand for improved solutions to replace aluminum foils and barrier plastic layers, such as polyolefin films, as barrier layers and substrates in packaging materials with alternatives that facilitate re-pulping and recycling of the used packaging materials. The laminate according to the present disclosure can advantageously be manufactured almost entirely from biobased materials, and preferably from cellulose based materials, thereby facilitating re-pulping and recycling of used packaging materials comprising the laminate according to the present disclosure.The laminate according to the present disclosure can provide an alternative to conventional materials using barrier plastic layers, such as polyolefin films, and / or aluminum foil layers, which can more readily be repulped and recycled. In some embodiments, the laminate has a reject rate according to PTS RH 021 / 97 of less than 30%, preferably less than 20%, more preferably less than 10%, most preferably less than 5%. The laminate according to the present disclosure may provide at least a reduction of the use of barrier plastic layers and / or aluminum foil layers as used in conventional materials.However, the laminate of the present disclosure may further be provided with an outermost polymer layer on one side or on both sides. The outermost polymer layers preferably provide liquid barrier properties and mechanical protection, such as print protection, for the laminate surface(s). The outermost polymer layer is preferably also heat-sealable.In some embodiments, the method of the first aspect further comprises a step of providing the laminate with an outermost first polymer layer on the MFC film. In some embodiments, the outermost first polymer layer comprises a thermoplastic polymer. In some embodiments, the outermost first polymer layer comprises a polymer selected from the group consisting of polyolefins and polyesters. In some embodiments, the outermost first polymer layer comprises a polymer selected from the group consisting of thermoplastic polyolefins and thermoplastic polyesters. In some embodiments, the outermost first polymer layer comprises polypropylene or polyethylene. In some embodiments, the outermost first polymer layer comprises polyethylene, more preferably LDPE or HDPE.In some embodiments, the method of the first aspect further comprises a step of providing the laminate with an outermost second polymer layer on the paperboard. In some embodiments, the outermost second polymer layer comprises a thermoplastic polymer. In some embodiments, the outermost second polymer layer comprises a polymer selected from the group consisting of polyolefins and polyesters. In some embodiments, the outermost second polymer layer comprises a polymer selected from the group consisting of thermoplastic polyolefins and thermoplastic polyesters. In some embodiments, the outermost second polymer layer comprises polypropylene or polyethylene. In some embodiments, the outermost second polymer layer comprises polyethylene, more preferably LDPE or HDPE.The outermost polymer layers may comprise any of the thermoplastic polymers commonly used in protective and / or heat-sealable layers in paper or paperboard based packaging laminates in general or polymers used in liquid or food packaging board in particular. Examples include polyethylene (PE), polyethylene terephthalate (PET), polyethylene furanoate (PEF), polypropylene (PP), polyhydroxyalkanoates (PHA), polylactic acid (PLA), polyglycolic acid (PGA), starch and cellulose.Polyethylenes, especially low density polyethylene (LDPE) and high density polyethylene (HDPE), are the most common and versatile polymers used in liquid or food packaging board. The polymers used are preferably manufactured from renewable materials. The outermost first polymer layer and the outermost second polymer layer may comprise the same or different polymers.The outermost polymer layers may of course interfere with repulpability but may still be required or desired in some applications. The additional polymer layers may, for example, be applied by extrusion coating, film lamination or dispersion coating after the laminate is formed. Thermoplastic polymers are useful since they can be conveniently processed by extrusion coating techniques to form very thin and homogenous films with good liquid barrier properties.In some embodiments, the outermost polymer layers are formed by extrusion coating of the polymer onto the laminate. Extrusion coating is a process by which a molten plastic material is applied to a substrate to form a very thin, smooth uniform layer. The coating can be formed by the extruded plastic itself, or the molten plastic can be used as an adhesive to laminate a solid plastic film onto the substrate. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).The basis weight of each of the outermost polymer layers is preferably less than 50 g / m2. In order to achieve a continuous and substantially defect free film, a basis weight of each of the outermost polymer layers of at least 6 g / m2, preferably at least 8 g / m2 or at least 12 g / m2 is typically required if provided by extrusion coating. In some embodiments, the basis weight of each of the outermost polymer layers is in the range of 6-50 g / m2, preferably in the range of 8-50 g / m2 or 10-25 g / m2 or 10-20 g / m2, wherein the outermost polymer layers are provided by extrusion coating. In some embodiments, the basis weight of the outermost polymer layers are in the range of 2-10 g / m2, wherein the outermost polymer layers are provided by foamed film.According to a second aspect of the present disclosure there is provided a laminate comprising a multiply paperboard provided with an MFC film, which laminate is obtainable by the method of the first aspect.The laminate obtainable by the method of the first aspect can be used as such. Alternatively, it can be combined with one or more further layers, such as one or more further paper or paperboard layers and / or other layers, into a laminated material. When the laminate is combined with one or more further layers, such as one or more paper or paperboard layers, into a laminated material, the laminated material may optionally be provided with an outermost polymer layer (corresponding to the outermost polymer layer described above) on one side or on both sides. Other examples of further layers that may be combined with the laminate obtainable by the method of the first aspect are further polymer layers such that there are multiple polymer layers of same or different polymers on each side, a protective varnish layer, a décor layer on top of the laminate, and a sealing layer that can be activated (molten) with heat.For example, the laminate or laminated material can be used as a packaging material or in a packaging material, such as a food or liquid packaging material. For example, the laminate or laminated material can be part of a flexible packaging material, such as a free-standing pouch or bag, which may be opaque or translucent. Thus, the laminate or laminated material may be used as bag material in boxes when packaging dry food such as cereals. Furthermore, the laminate or laminated material may be used as a wrapping substrate, such as a flow wrap material, as a laminate material in paper, paperboard or plastics and / or as a substrate for disposable electronics. The laminate or laminated material may also be included in for example a closure, a lid or a label. The laminate or laminated material can be incorporated into any type of package, such as a box, bag, wrap, wrapping film, cup, container, tray, bottle, etc. The present disclosure also relates to a packaging product comprising the laminate or laminated material obtainable by the method of the first aspect.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.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

1. Method for producing a laminate comprising a multilayer cardboard provided with a film of microfibrillated cellulose (MFC), said method comprising the steps of:- providing a wet web of multi-layer cardboard,- wet pressing said wet web of multi-ply board to obtain a dry content of 20-58% by weight of said wet web of multi-ply board, said wet pressing comprising at least one wet pressing step, - providing a wet MFC film having a dry content of 2-50% by weight and comprising between 70% by weight and 100% by weight of MFC based on total dry weight, said wet MFC film being provided on a substrate, - applying said MFC film having a dry content of 2-50% by weight to said wet web of multi-ply board having a dry content of 20-58% by weight to form a wet laminate, said step of applying said wet MFC film to said wet web of multi-ply board comprising wet pressing said wet MFC film and said wet web of multi-ply board together in at least one press dewatering step, and- drying said wet laminate to a dry content of at least 85% by weight to form said laminate comprising a multi-layer board provided with an MFC film.

2. The method of claim 1, wherein said step of applying said wet MFC film to said wet web of multi-ply paperboard comprises wet pressing said wet MFC film and said wet web of multi-ply paperboard together in an extended nip of a press equipment.

3. Method according to claim 2, wherein said extended nip is included in a shoe press.

4. A method according to any one of claims 1-3, wherein said wet MFC film and said wet web of multi-ply paperboard are wet-pressed in said at least one press dewatering step such that said formed wet laminate has a dry content of 55-75% by weight.

5. Method according to any one of claims 1-4, wherein said method further comprises smoothing said wet MFC film of said wet laminate by applying at least one smoothing press to said wet MFC film of said wet laminate, after said wet pressing comprising at least one press dewatering step but before said drying step.

6. A method according to any one of the preceding claims, wherein said method further comprises a step of calendering said laminate after said drying step.

7. Method according to any one of the preceding claims, wherein said substrate is a non-porous substrate such as a metal strip, a rubber strip or a plastic strip.

8. The method of claim 7, wherein said non-porous substrate is a strip of metal heated to a temperature greater than 30°C during at least portions of said step of applying said wet MFC film to said wet multi-ply board.

9. Method according to any one of claims 1-6, wherein said substrate is a porous substrate, such as a dewatering screen, a dewatering felt or a membrane.

10. Method according to any one of the preceding claims, wherein said wet pressing of said wet multi-layer board is carried out in a press section and wherein said substrate is partially integrated in said press section so that said step of applying said wet MFC film to said wet web of multi-layer board is carried out by transferring said wet MFC film from said substrate to said wet web of multi-layer board in said press section.

11. Method according to any one of claims 1-9, wherein said wet pressing of said wet multi-layer board is carried out in a press section and wherein said step of applying said wet MFC film to said wet web of multi-layer board is carried out by transferring said wet MFC film from said substrate to a transfer substrate and from saidtransfer substrate to said wet web of multi-ply paperboard without any free draft between said substrate and said transfer substrate.

12. Method according to claim 10 or 11, wherein said substrate is partially integrated in said press section and wherein said method further comprises a step of removing water from said wet MFC film, to obtain said dry content of 2-50% by weight, which is carried out in said press section.

13. A method according to any one of the preceding claims, wherein said provided wet MFC film comprises a single web layer or two or more web layers formed on top of each other.

14. A method according to any one of the preceding claims, wherein said wet MFC film is formed from an amount of an MFC suspension comprising between 70 wt% to 100 wt% MFC based on total dry weight such that said MFC film of said produced laminate has a basis weight of 1-25 g / m2 (dry).

15. Method according to any one of the preceding claims, wherein said MFC suspension comprises at most 30% by weight of additives.

16. Method according to any one of the preceding claims, wherein said MFC suspension comprises no fixatives and no retention agents.

17. A method according to any one of the preceding claims, wherein said MFC suspension comprises less than 30% by weight of inorganic fillers.

18. A method according to any one of the preceding claims, wherein said wet MFC film is provided in the form of a foam and has a density of 50-800 kg / m3.

19. Method according to any one of the preceding claims, wherein said multilayer cardboard has a basis weight of 100-600 g / m2 determined according to standard ISO 536.

20. Method according to any one of the preceding claims, wherein said multi-layer cardboard comprises at least one lower density middle layer which is placed between two higher density outer layers, wherein said lower density middle layer has a density which is lower than 750 kg / m3 and wherein said higher density outer layer has a density which is at least 100 kg / m3 higher than that of said lower density middle layer determined according to standard ISO 534.

21. A method according to any one of the preceding claims, wherein said wet MFC film is applied to a backing layer of said wet web of multi-ply paperboard.

22. A method according to claim 21, wherein said backing layer comprises at least 60% dry weight of bleached or unbleached kraft pulp and has a basis weight of 10-60 g / m2.

23. A method according to any one of the preceding claims, wherein said method further comprises a step of surface sizing or film press coating or sheet coating said laminate on at least one side with an aqueous barrier dispersion or solution.

24. Method according to any one of the preceding claims, wherein said laminate comprising said multi-layer cardboard provided with said MFC film has an oil absorption determined by Cobb-Unger (30 s) which is lower than 10 g / m2 according to SCAN-P 37:77 when determined for said side provided with said MFC film.

25. Method according to any one of the preceding claims, wherein said laminate comprising said multilayer cardboard provided with said MFC film has an oil and grease resistance (KIT test) higher than 10 according to the ISO 16532-2 standard.

26. Method according to any one of the preceding claims, wherein said laminate comprising said multilayer board provided with said MFC film has a water vapor transmission rate (WVTR) lower than 100 g / m2 / day when determined at 23° C and 50% RH according to standard ASTM F1249-20.

27. Method according to any one of the preceding claims, wherein said laminate comprising said multilayer cardboard provided with said MFC film has a Z-tensile strength higher than 200 kPa according to SCAN-P 80:98.

28. Method according to any one of the preceding claims, wherein said laminate comprising said multilayer board provided with said MFC film has a Scott Bond value higher than 120 J / m2 according to the TAPPI 569 standard.

29. Laminate comprising a multilayer cardboard provided with an MFC film, obtainable by the method according to any one of claims 1-28.