Method for producing a cellulosic laminate including a mineral-based layer - Patent Application 20070122997

Abstract

The present invention provides a method for producing a cellulosic laminate including a mineral-based layer on a papermaking machine, comprising the steps of: a) forming a first web layer on a first wire; b) forming a second web layer on the second wire, the second web layer comprising 60-95% by dry weight of particulate mineral and 5-40% by dry weight of binder; c) laminating the second web layer and the first web layer to obtain a laminated web; d) dewatering and optionally drying the formed laminate web to obtain a cellulosic laminate including a mineral-based layer; The present invention relates to a method, including:

Description

[Technical Field]

[0001] The present disclosure relates to methods for producing paper and paperboard that include a mineral-based layer. [Background technology]

[0002] Many paper or paperboard products have a mineral coating applied to their surface to impart desirable properties such as whiteness, brightness, gloss, and / or high-quality printing. Typical coating ingredients include pigments, binders, additives, and water. Commonly used pigments include calcium carbonate, talc, titanium dioxide, and / or kaolin clay. Binders may include styrene-butadiene latex, styrene-acrylate latex, vinyl acetate latex, vinyl acetate-acrylate latex, carboxymethyl cellulose, and / or starch. Examples of other additives include insolubilizers, lubricants, defoamers, thickeners, co-binders, stabilizers, and optical brighteners (OBAs).

[0003] Mineral-coated paper or paperboard, also commonly referred to as whitetop liner or whitetop paper or paperboard, is typically produced either by adding particulate mineral to the top ply of a multi-layer paper or paperboard via a headbox, or by coating the paper or paperboard product with a coating composition comprising particulate mineral and a binder.

[0004] Applying particulate mineral to the top ply of multi-layer paper or paperboard via a headbox severely limits the amount of particulate mineral that can be added. The amount of particulate mineral that can be applied by this method is typically limited to less than 10% by dry weight of the top ply because the addition of particulate mineral also affects stiffness, strength, and retention.

[0005] Application of particulate minerals to paper or paperboard products by coating with a coating composition comprising the particulate mineral and a binder often limits the coating weight to a relatively narrow range, as low coating weights (typically <5 g / m 2 ), the coating coverage becomes too sensitive to the properties of the base substrate, the coating formulation, and the coating conditions. When other types of additives such as fibrils and fiber fragments are used, they cause problems in the flow behavior and often cause feasibility problems when leveling the coating dispersion. At high coating weights (typically >10 g / m), 2 ), the amount of water applied is also higher, leading to problems with dewatering, drying and rewetting of the paper or paperboard substrate.

[0006] From a technical and economic standpoint, it would be desirable to find a solution that would allow for the production of cellulosic laminates containing mineral-based layers without the drawbacks and limitations inherent in existing coating methods. Summary of the Invention

[0007] It is an object of the present disclosure to provide a method for producing paper and paperboard comprising a mineral-based layer, which method alleviates at least some of the above-mentioned problems associated with prior art methods.

[0008] It is a further object of the present disclosure to provide an improved method for producing paper and paperboard containing a mineral-based layer in a paper machine or board machine type process.

[0009] It is a further object of the present disclosure to provide an improved method for producing paper and paperboard comprising a mineral-based layer in a paper machine or board machine type process, wherein the grammage and composition of the mineral-based layer can be selected independently of the cellulosic layer.

[0010] The above objectives, as well as other objectives which will be realized by those skilled in the art in light of this disclosure, are achieved by various aspects of the present disclosure.

[0011] The method of the present invention allows for efficient production of paper and paperboard containing a mineral-based layer, also known as a whitetop liner or whitetop paper or paperboard, in a paper machine-type process. This method can replace traditional mineral coating methods. This method allows for good mineral coverage to be achieved even with particulate minerals having smaller particle sizes at relatively low mineral-based layer gram weights, such as in the range of 10 to 30 gsm, or even 10 to 15 gsm. DETAILED DESCRIPTION OF THE INVENTION

[0012] According to a first aspect exemplified herein, there is provided a method for producing a cellulosic laminate including a mineral-based layer on a papermaking machine, the method comprising: a) forming a first web layer by applying a first suspension onto a first wire, the first suspension comprising at least 50% by dry weight of a cellulosic fibrous material having a Shopper-Rigler (SR) value in the range of 18 to 50, and partially dewatering the first web layer on the first wire; b) forming a second web layer by applying a second suspension onto a second wire, the second suspension comprising 60-95% by dry weight of particulate mineral and 5-40% by dry weight of binder, the binder being highly refined cellulose (HRC) having an SR value in the range of 75-100, and partially dewatering the second web layer on the second wire, wherein the second suspension has a dry solids content of at least 0.5 wt % and is applied directly onto the second wire using a curtain applicator; and partially dewatering the second web layer on the second wire; c) laminating the partially dewatered second web layer and the partially dewatered first web layer to obtain a laminated web; d) dewatering and optionally drying the formed laminate web to obtain a cellulosic laminate including a mineral-based layer; Includes.

[0013] As used herein, the term "web" or "web layer" refers to a sheet-shaped material obtained by applying a suspension containing dispersed solid material (e.g., cellulosic fibrous material, highly refined cellulose, or particulate minerals) onto a surface, preferably a porous surface, and at least partially dewatering the applied suspension to increase the dry solids content of the suspension until a web layer is formed on the surface.

[0014] The term cellulosic laminate as used herein generally refers to a multi-layer sheet-form material obtained by laminating a cellulosic web layer with one or more other layers. Depending on the thickness and composition of the cellulosic laminate, it may be considered multi-layer paper or paperboard.

[0015] The term mineral-based layer refers to a layer formed from a second suspension.

[0016] The cellulosic laminate may be used as is or may be combined with one or more other layers. The cellulosic laminate may be useful, for example, as a paper or paperboard based packaging material.

[0017] Although different arrangements for carrying out the steps of the method of the present invention can be envisaged by those skilled in the art, the method of the present invention can advantageously be carried out on a paper machine, more preferably on a Fourdrinier machine, i.e. a paper machine based on the principle of a Fourdrinier machine.

[0018] An advantage of the method of the present invention is that it can be easily implemented on an existing paper or board machine by simply adding a second wire section. The added wire section does not require a headbox or extensive water circulation system. Alternatively, the method of the present invention can be implemented on an existing multi-ply machine with two or more wires by simply shutting down the headbox and adding or running an existing curtain applicator on one of the wires.

[0019] Conventional headboxes are limited in their use to high dry solids concentrations when processing suspensions rich in particulate minerals and highly refined pulp. Typical headboxes can handle such suspensions up to about 0.5 wt. %, depending on the suspension viscosity and flow behavior. When using curtain applicators, the consistency and / or viscosity of the applied suspension can and should be significantly higher. Higher consistency of the applied suspension means that less water must be removed during dewatering, allowing for significantly smaller short cycle times. A further advantage of the method of the present invention, in which web layers are formed on different wires, is that different additives can be utilized in different suspensions; chemicals and other additives that are not normally suitable for use with one type of suspension can be used only with the other suspension.

[0020] A paper machine (or papermaking machine) is an industrial machine used in the pulp and paper industry to create paper or fiber-based substrates in large quantities at high speeds. Modern papermaking machines are based on the Fourdrinier principle, which uses a moving dewatering cloth or woven mesh, commonly called a "wire," to filter fibers held in a pulp suspension, producing a continuously moving wet web of fibers. This wet web is then dried in the machine and turned into paper or film.

[0021] The forming and dewatering steps of the method of the present invention are preferably carried out in the forming section of a paper machine, also commonly referred to as the wet end.

[0022] The wet-laid web layers are formed on different wires in the forming section of a paper machine. A preferred type of forming section for use in the present invention includes at least two wires. The wires are preferably endless wires. The dewatering fabrics on the wires can be single- or multi-layer fabrics made of plastic, nonwoven, composite, or metal. The first wire can be any known to those skilled in the art for use in paper or paperboard production. The second wire can be selected to provide a combination of acceptable dewatering rates and retention of particulate minerals and highly refined cellulose. The second wire used in the process of the present invention is preferably 2000 to 7000 m at 100 Pa. 3 / m 2 / h, preferably 2500-5500 m at 100 Pa 3 / m 2 The second wire used in the process of the present invention preferably has a relatively high porosity to allow for fast dewatering and high drainage capacity. The second wire has a high fiber support index (FSI), typically greater than 190, so that fine materials do not penetrate the structure, resulting in fewer wire marks and a rough, open backside. The wire section of the paper machine can have a variety of dewatering devices, such as blades, table and / or foil elements, suction boxes, low-friction dewatering, ultrasonically assisted dewatering, couch rolls, or dandy rolls.

[0023] In the method of the present invention, the first and second web layers are separately formed by applying a first suspension onto a first wire, the first suspension comprising at least 50% by dry weight of cellulosic fibrous material having a Shopper-Rigler (SR) value in the range of 18 to 50, and partially dewatering the first web layer on the first wire; and applying a second suspension onto a second wire, the second suspension comprising 60 to 95% by dry weight of particulate mineral and 5 to 40% by dry weight of binder, the binder having an SR value in the range of 75 to 100, and partially dewatering the second web layer on the second wire.

[0024] The partially dewatered second web layer and the partially dewatered first web layer are then laminated to obtain a laminate web, which is then dewatered and optionally dried to obtain a cellulosic laminate including a mineral-based layer.

[0025] The first web layer, comprising a relatively easy-to-drain cellulosic fibrous material having a Shopper-Rigler (SR) value in the range of 18 to 50, can be prepared by any suitable method, the most common being to apply a first suspension onto a first wire using a so-called headbox, at a dry solids content of less than 1.5 wt%, typically less than 0.5 wt%.

[0026] A second suspension containing at least 50% by dry weight of particulate minerals and highly refined cellulose (HRC), which are extremely difficult to dewater, is applied to the wire at a dry solids content of at least 0.5 wt %. Suspensions with such high dry solids content, together with a high content of particulate minerals and HRC, are not suitable for application using a headbox due to their high viscosity and the tendency of the HRC to form a gel, and therefore the second suspension is applied instead using a so-called curtain applicator.

[0027] Curtain applicators, sometimes called curtain coaters or wet-end applicators, transfer a thin film of liquid ("curtain") falling from an applicator die onto a moving surface. The die is typically a slot-type die. The second suspension is supplied to the curtain applicator using one or more supply lines. The applicator can be open-ended, i.e., with return circulation from the applicator, or closed-ended, i.e., without return circulation from the applicator. The slot opening preferably does not vary over the length of the slot by more than 1 mm, more preferably more than 500 μm, and even more preferably more than 250 μm. In some embodiments, the slot is a layered slot, allowing multiple layers to be deposited without intermixing. The second suspension is applied onto the second wire at a jet / wire speed ratio preferably in the range of 0.8 to 2.5, more preferably in the range of 0.85 to 2.0. Jet speed refers to the speed at which the second suspension exits the slot of the curtain applicator. Wire speed refers to the speed of the wire in the machine direction. The jet / wire speed ratio refers to the ratio of the jet speed to the wire speed. A jet / wire speed ratio in the range of 0.8 to 2.5, and more preferably in the range of 0.85 to 2.0, has been found to provide optimal formation of the second web layer. The jet / wire speed ratio prevents turbulence, air entrapment, and pinhole formation in the formed web layer. It also results in uniform curtain settling and improved curtain stability.

[0028] Before the second suspension is fed to the curtain applicator, it may preferably be subjected to mechanical deagglomeration, for example in a hydrocyclone, pressure screen, static or rotary screener, high shear rotor-stator mixer, or high shear mixer. The purpose of mechanical deagglomeration is to homogenize the thick suspension and to break down fiber-fibril bundles, hard gel particles, or coarse, long fibers (>4 mm in length). The screening is preferably oscillation-free screening. The mechanical deagglomeration preferably includes pressure screening.

[0029] The second suspension is applied directly onto the second wire. This means that there should be no fibers or fibrous webs on the wire when the second suspension is applied. The curtain can be positioned so that it hangs directly from the curtain applicator onto the wire, or it can be positioned so that it hangs via a curtain guide. The distance between the slot of the curtain applicator or curtain guide and the dewatering fabric on the second wire is preferably within the range of 0.8 to 30 mm. The curtain guide can be, for example, a roll or an inclined metal plane that helps guide the curtain onto the second wire and / or evenly distribute the second suspension on the second wire. The advantage of this is that thickness and shear can be more precisely controlled. The transfer from the curtain guide to the wire can be non-contact or soft-contact.

[0030] The thickness and composition of each applied layer must be consistent across the entire surface, which can be particularly difficult to achieve on large webs.

[0031] The application of the second suspension may be performed in a single deposition step or using multiple deposition steps, and may be accomplished, for example, using at least two successive curtain applicator units applying the same or different suspensions.

[0032] The curtain application of the second suspension may also be performed using two or more curtain applicators arranged side by side. This arrangement can improve cross-direction (CD) profile control. This can be particularly useful in forming wide webs, where application using a single curtain applicator across the entire width of the web can lead to problems with variations in the web's thickness profile in the cross direction. The two or more curtain applicators arranged side by side may be positioned directly next to each other or may be offset relative to each other in the machine direction (MD).

[0033] The water content of the first and second suspensions can be removed by draining through the first and second wires, respectively, or by drying, or a combination thereof. Dewatering of the web layer on the wires can be performed using methods and devices known in the art. Dewatering can occur on one side, i.e., through only the first and second wires, respectively, or on both sides, e.g., through an auxiliary wire arranged in a twin-wire configuration with the first and / or second wires, respectively. Examples include blades, tables and / or foil elements, suction boxes, low-friction dewatering, ultrasonically assisted dewatering, couch rolls, or dandy rolls. The drainage and / or drying of the first and second suspensions forms a partially dewatered web layer on the wires.

[0034] The second wire may be provided with suction, such as a suction box, preferably below the wire at the point where the curtain meets the wire, and optionally just before and / or just after this point in the machine direction, which helps to prevent air from becoming trapped in the web or wire and stabilize the curtain.

[0035] Partial dewatering means that the dry solids content of the web is increased relative to the dry solids content of the suspension, but the dewatered web still contains a significant amount of water. In some embodiments, partial dewatering of a wet web means that the dry solids content of the partially dewatered web is greater than 1 wt% and less than 25 wt%. In some embodiments, partial dewatering of a wet web means that the dry solids content of the partially dewatered web is greater than 1.5 wt% and less than 15 wt%. Dry solids content of a partially dewatered web layer within this range has been found to be particularly suitable for joining the partially dewatered web layer to a multilayer web.

[0036] Because the first and second suspensions are different and the partial dewatering of the suspensions is performed separately, the solids contents of the partially dewatered first and second web layers may also be different. In some embodiments, the dry solids content of the partially dewatered first web layer is in the range of 1.5 to 15 wt%, preferably 2.5 to 15 wt%, and more preferably 6 to 15 wt%. In some embodiments, the dry solids content of the partially dewatered second web layer is in the range of 1.2 to 25 wt%, preferably 2.5 to 20 wt%, and more preferably 5 to 15 wt%.

[0037] The partially dewatered web layers are preferably laminated by wet lamination. As the first suspension dewaters on the wire, a visible boundary line appears where the web changes from a reflective water layer to a point where the reflective layer disappears. This boundary line between the reflective and non-reflective webs is called the waterline. The waterline indicates the solids content, or wetness, of the web. The web layers are preferably laminated after the waterline. Laminating the web layers while at least one, preferably both, of the web layers is still wet ensures good adhesion between the layers. The lamination in step c) can be accomplished by stacking one of the partially dewatered web layers on top of the other. The web surface facing the wire is called the wire side, and the web surface facing away from the wire is called the non-wire side. Bonding can be done non-wire-side to non-wire-side, or wire-side to non-wire-side. In some embodiments, the lamination in step c) includes laminating a partially dewatered second web layer to the non-wire side of a partially dewatered first web layer. The lamination and further dewatering of the formed multi-layer web can be improved by various additional treatments. In some embodiments, the lamination further comprises pressing the partially dewatered web layers together. In some embodiments, the lamination further comprises applying suction to the laminated partially dewatered web layers. Applying pressure and / or suction to the formed multi-layer web improves adhesion between the web layers.

[0038] Laminating the web layers while they are still wet ensures good adhesion between the layers and also increases production speed. The method of the present invention provides an alternative method for increasing dewatering rates that is less dependent on the addition of retention and drainage chemicals.

[0039] Adhesion between web layers can be further improved by applying a binder between the joined web layers prior to lamination. In some embodiments, the lamination in step c) further comprises applying a binder to one or both of the joined surfaces. The binder can also improve the ply strength and mechanical properties (such as burst strength, compressive strength, stiffness, and puncture resistance) of the cellulosic laminate. Additionally, the applied binder can improve workability, for example, reducing dusting. In some embodiments, the binder is selected from starch, microfibrillated cellulose (MFC), nanocrystalline cellulose, or a combination thereof. In some embodiments, the binder comprises a combination of a polysaccharide, preferably starch, with microfibrillated cellulose (MFC) or nanocrystalline cellulose. In some embodiments, the binder application amount is 0.2 to 10 gsm on a dry weight basis. The binder can be applied using any suitable coating technique, preferably by spray coating or curtain coating, at a concentration in the range of 0.2 to 20 wt %.

[0040] The dry solids content of the multilayer web typically increases further when the partially dewatered first and second web layers are laminated. The increase in dry solids content can be due to dewatering of the multilayer web on the wire by any pressure and / or suction applied to the laminate, or due to a drying process, such as impingement drying, air drying, or steam drying, performed during or immediately after lamination. The dry solids content of the multilayer web after lamination, or after any optional further increase in dry solids on the wire, if applicable, is typically greater than 8 wt% and less than 28 wt%. In some embodiments, the dry solids content of the multilayer web before further dewatering and any optional drying steps is in the range of 8 to 25 wt%, preferably in the range of 10 to 20 wt%, and more preferably in the range of 12 to 18 wt%.

[0041] This type of wet lamination allows multiple webs, including web layers formed from suspensions with very different compositions, to be combined without (or with reduced) mixing of the process water of the suspensions. Dewatering of the first suspension on the first wire and the second suspension on the second wire allows the white water and waste from the different wires to be recovered and recycled or reused independently of each other. This allows the use of additives in the second suspension that are not typically used in conventional papermaking and that could inhibit wet-end chemistry during the short circulation of the first suspension.

[0042] In some embodiments, the water obtained by dewatering the second web layer on the second wire is not mixed with the water obtained by dewatering the first web layer on the first wire.

[0043] Another advantage of the method of the present invention is that the temperatures of the different suspensions and the web can be controlled and adjusted independently. The temperature at the time of injection of the second suspension is preferably in the range of 40 to 100°C, preferably in the range of 50 to 100°C, more preferably in the range of 60 to 100°C, for example in the range of 62 to 95°C. The temperature at the time of injection of the second suspension is preferably at least 5°C higher, more preferably at least 10°C higher, or at least 15°C higher than the temperature at the time of injection of the first suspension. Maintaining a high temperature of the second suspension can keep microbial activity low and / or reduce the viscosity of the suspension.

[0044] The formed multi-layer web is then further dewatered and optionally dried to obtain a cellulosic laminate including a mineral-based layer. The dewatering and optional drying step d) further increases the dry solids content of the multi-layer web. The resulting cellulosic laminate preferably has a dry solids content of greater than 90 wt%.

[0045] Further dewatering typically involves pressing the multi-layer web to squeeze out as much water as possible. Further dewatering can include, for example, passing the formed multi-layer web through the press section of a papermaking machine, where the web passes between large rolls loaded under high pressure to squeeze out as much water as possible. In some embodiments, further dewatering involves passing the web through one or more shoe presses. The removed water is typically captured by a cloth or felt. In some embodiments, the dry solids content of the cellulosic laminate after further dewatering is in the range of 15 to 65 wt%, preferably in the range of 18 to 60 wt%, and more preferably in the range of 22 to 55 wt%.

[0046] Optional drying can include drying the multi-layer web, for example, by passing the multi-layer web around a series of heated drying cylinders. Drying can typically reduce the moisture content to a level of about 1 to 15 wt %, preferably about 2 to 10 wt %. In some embodiments, drying includes drying the web on a Yankee cylinder. Yankee cylinders can also be used to create a glossy surface on the finished laminate.

[0047] In some embodiments, the multi-layer web or laminate is further subjected to smoothing by hard calendering, soft calendering, or super calendering.

[0048] The dry solids content of the final cellulosic laminate may vary depending on the intended use of the laminate, for example a laminate for use as a stand-alone product may have a dry solids content in the range of 85-99 wt%, preferably in the range of 90-98 wt%, while a laminate for use in further laminations to form paper or paperboard based packaging materials may have a dry solids content in the range of less than 90 wt%, preferably less than 85 wt%, for example in the range of 30-85 wt%.

[0049] The first suspension is an aqueous suspension containing a water-suspended mixture of cellulosic fibrous material and optional non-fibrous additives. The cellulosic fibrous material of the first suspension may also be referred to as "pulp." Thus, the first suspension is preferably a pulp suspension. The cellulosic fibrous material or pulp of the first suspension may be made from different raw materials selected from the group consisting of bleached or unbleached softwood or hardwood pulp, bleached or unbleached kraft pulp, pressure groundwood (PGW), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), neutral sulfite semi-chemical pulp (NSSC), shredded or recycled fibers, or a combination thereof.

[0050] The cellulosic fibrous material of the first suspension can be unrefined or refined. Refining (beating) cellulosic fibrous material refers to mechanical treatment and modification to provide desired properties to the cellulose fibers. The cellulosic fibrous material of the first suspension is preferably unrefined or only slightly refined, so that the cellulosic fibrous material has a relatively high drainage rate and low water retention. The drainage rate is expressed as the Shopper-Rigler (SR) value according to ISO Standard 5267-1. The cellulosic fibrous material of the first suspension has an SR (Shopper-Rigler) value in the range of 18 to 50. In some embodiments, the cellulosic fibrous material of the first suspension has an SR value in the range of 20 to 35. The water retention rate of the cellulosic fibrous material is expressed as a Water Retention Value (WRV) as determined by ISO Standard 23714:2014. In some embodiments, the cellulosic fibrous material of the first suspension has a water retention value (WRV) in the range of 100-220%, preferably in the range of 120-190%.

[0051] The dry solids content of the first suspension when applied to the first wire is typically in the range of 0.1 to 1.5 wt%, preferably in the range of 0.1 to 1 wt%, more preferably in the range of 0.1 to 0.5 wt%.

[0052] The dry solids content of the first suspension may consist solely of cellulosic fibrous material, or may include a mixture of cellulosic fibrous material with other ingredients or additives.

[0053] The first suspension preferably comprises cellulosic fibrous material as its major component, based on the total dry weight of the suspension, hi some embodiments, the first suspension comprises at least 50% by dry weight, preferably at least 70% by dry weight, more preferably at least 80% by dry weight, or at least 90% by dry weight of cellulosic fibrous material, based on the total dry weight of the suspension.

[0054] In some embodiments, the first suspension is a kraft pulp suspension. Refined kraft pulp typically contains at least 10% hemicellulose by dry weight. Thus, in some embodiments, the first suspension contains at least 10% hemicellulose by dry weight, e.g., in the range of 10-25% hemicellulose by dry weight, based on the amount of cellulosic fibrous material.

[0055] The first suspension may further comprise additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, fillers, retention and / or drainage chemicals, flocculating additives, deflocculating additives, dry strength additives, softeners, crosslinking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, defoaming aids, microbial and slime control aids, or mixtures thereof.

[0056] The first suspension preferably comprises no more than 10% by dry weight of particulate mineral, preferably no more than 7% by dry weight, more preferably no more than 5% by dry weight. The particulate mineral present in the first suspension may be obtained, for example, from recycled fibers or broke used as a raw material for cellulosic fibrous material.

[0057] In some embodiments, the first suspension comprises a hydrophobizing chemical, such as alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), or rosin size, in an amount of 0 to 10 kg / ton, preferably 0.1 to 5 kg / ton, and more preferably 0.2 to 2 kg / ton, based on the total dry weight of the suspension.

[0058] In some embodiments, the first suspension includes unbleached pulp to give the laminate a natural appearance.

[0059] The first web layer typically has a kappa number greater than 30, preferably greater than 50, as measured in accordance with ISO 3260.

[0060] The dry basis weight of the first web layer can generally be in the range of 10 to 500 gsm, hi some embodiments, the dry basis weight of the first web layer is in the range of 20 to 400 gsm, more preferably in the range of 40 to 200 gsm.

[0061] The second suspension is an aqueous suspension comprising a water-suspended mixture of mineral particles (referred to herein as particulate mineral), highly refined cellulosic fibrous material (referred to herein as highly refined cellulose (HRC)), and any additional additives.

[0062] The second suspension comprises, on a dry weight basis, a particulate mineral as a major component. In some embodiments, the second suspension comprises 60-95% particulate mineral by dry weight. In some embodiments, the second suspension comprises 65-95% particulate mineral by dry weight, preferably 70-90% particulate mineral by dry weight.

[0063] The particulate mineral can be any particulate mineral useful in the manufacture of paper or paperboard. Such particulate minerals are typically used in paper or paperboard as fillers or pigments, or both. In some embodiments, the particulate mineral of the second suspension is a mineral filler or a mineral pigment.

[0064] In some embodiments, the particulate minerals of the second suspension are selected from phyllosilicates (such as clays, montmorillonite, and bentonite), artificial clays (such as calcined clays), ground calcium carbonate (GCC), kaolin, precipitated calcium carbonate (PCC), talc, titanium dioxide (TiO), aluminum trihydrate, amorphous silica and silicates, satin white (ettringite), zinc oxide (ZnO), and barium sulfate (BaSO), or combinations thereof.

[0065] In some embodiments, the particulate mineral of the second suspension is a mineral filler, hi some embodiments, the mineral filler is selected from ground calcium carbonate (GCC), kaolin, precipitated calcium carbonate (PCC), talc, titanium dioxide (TiO), or a combination thereof.

[0066] In some embodiments, the particulate mineral of the second suspension is a mineral pigment, hi some embodiments, the mineral pigment is selected from ground calcium carbonate (GCC), kaolin, precipitated calcium carbonate (PCC), talc, titanium dioxide (TiO), aluminum trihydrate, amorphous silica and silicates, satin white (ettringite), zinc oxide (ZnO), and barium sulfate (BaSO), or combinations thereof.

[0067] The particulate mineral is preferably a plate-like mineral. In some embodiments, the particulate mineral has a shape factor greater than 20, preferably greater than 30, and more preferably greater than 40. As used herein, "shape factor" is a measure of the average ratio (weight average basis) of the average particle diameter to particle thickness of a population of particles of various sizes and shapes, as measured using, for example, the electrical conductivity methods and apparatus described in U.S. Patent Publications Nos. 5,128,606 and 5,576,617.

[0068] The combination of particulate mineral with highly refined cellulose (HRC) improves the retention of the particulate mineral on the wire. The method of the present invention allows for good mineral coverage to be achieved using particulate minerals with smaller particle sizes at relatively low mineral-based layer grams, such as in the range of 10-30 gsm, or even 10-15 gsm.

[0069] The second suspension further comprises highly refined cellulose (HRC) as a binder having an SR in the range of 75 to 100. In some embodiments, the second suspension comprises 5 to 40% HRC by dry weight. In some embodiments, the second suspension comprises 10 to 40% HRC by dry weight, preferably 15 to 35% HRC by dry weight. In other words, the dry content of the second suspension may consist solely of particulate mineral and HRC, or may consist of particulate mineral, HRC, and one or more additional components.

[0070] The HRC of the second suspension can be produced from wood cellulose fibers, both hardwood and softwood fibers, or a combination thereof. The HRC can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. The HRC is preferably made from pulp from virgin fibers, including mechanical pulp, chemical pulp, and / or thermomechanical pulp. It can also be made from shredded or recycled paper.

[0071] The HRC of the second suspension is more refined than that of the cellulosic fibrous material of the first suspension. The drainage rate is expressed as the Shopper-Rigler (SR) value according to ISO Standard 5267-1. As used herein, the term highly refined cellulose preferably refers to a refined cellulosic material having a Shopper-Rigler (SR) value within the range of 75 to 100 as determined by ISO Standard 5267-1.

[0072] The HRC of the second suspension has an SR value in the range of 75 to 100. In some embodiments, the second HRC has an SR value in the range of 80 to 98. In some embodiments, the second HRC has an SR value in the range of 85 to 98. The water retention of the HRC is expressed as a Water Retention Value (WRV) as determined by ISO Standard 23714:2014. In some embodiments, the HRC of the second suspension has a Water Retention Value (WRV) of >200%, preferably >250%.

[0073] The HRC of the second suspension is significantly more refined than that of the cellulosic fibrous material of the first suspension, more specifically, the SR value of the HRC is preferably at least 10 SR degrees higher, more preferably at least 20 or at least 30 SR degrees higher than that of the cellulosic fibrous material of the first suspension.

[0074] In some embodiments, highly purified cellulose is formed from fractionated cellulosic fibrous material in which a fraction of the finest particulate material has been removed. This fractionated cellulosic fibrous material provides highly purified cellulose enriched in long fibrils and fibrillated fibers, while removing most of the fine fibrils. This can significantly improve both the rheology of the suspension and its retention on the wire. The long fiber and fibrillated fiber content of a sample can be measured using an L&W Fiber tester Plus instrument (L&W / ABB). The L&W Fiber tester Plus determines the content of fibers with a length >0.2 mm (including long fibrils and fibrillated fibers with a length >0.2 mm). Using a known sample weight of 0.100 g for each sample, calculate the content of fibers with a length >0.2 mm (million fibers per gram) using the following formula: Fibers per gram = (Number of fibers in sample) / (Sample weight) / 1000000 = (Property ID 3141) / Property ID 3141) / 1000000.

[0075] In some embodiments, the HRC of the second suspension has a content of at least 8 million fibers per gram based on dry weight having a length >0.2 mm. In some embodiments, the HRC of the second suspension has a content of at least 10 million fibers per gram based on dry weight, preferably at least 12 million fibers per gram based on dry weight, and more preferably at least 14 million fibers per gram based on dry weight having a length >0.2 mm, as determined using an L&W Fiber tester Plus instrument (L&W / ABB).

[0076] The inventors have found that it is desirable for the second suspension applied to the second wire to have a relatively high dry solids content. More specifically, the dry solids content of the second suspension when applied to the second wire should be at least 0.5 wt%. Preferably, the dry solids content of the second suspension when applied to the second wire should be significantly higher than 0.5 wt%. Without being bound by any theory, it is believed that suspensions comprising a mixture of particulate mineral and HRC and having a high dry solids content of at least 0.5 wt% in accordance with the present invention reach the immobilization point more quickly, likely due to a relatively higher amount of particles and fibrils per gram, and therefore more particle-fiber, particle-particle, and / or fiber-fiber contact, which affects flow behavior and / or percolation network threshold. Thus, highly concentrated suspensions exhibit better wire retention than less concentrated suspensions.

[0077] In some embodiments, the second suspension has a dry solids content of at least 0.75 wt%, preferably at least 1 wt%, and more preferably at least 2 wt%.

[0078] In some embodiments, the second suspension has a dry solids content in the range of 0.75 to 40 wt%, preferably in the range of 1 to 20 wt%, and more preferably in the range of 2 to 15 wt%.

[0079] One advantage of the high dry solids content of the second suspension of the method of the present invention is that it may reduce or even eliminate the need for retention or flocculation chemicals or fixatives commonly used to improve wire retention of particulate minerals and highly refined cellulose.

[0080] Another advantage of the high dry solids content of the second suspension of the process of the present invention is that the paper machine can be run at a higher speed and the wire can be shorter because the higher solids content means less water needs to be removed. In some embodiments, the wire is processed at a speed greater than 100 m / min, preferably greater than 200 m / min, and more preferably greater than 250 m / min. The wire speed typically does not exceed 1500 m / min.

[0081] Such a high dry solids suspension is not suitable for direct application to a wire in the conventional manner using a headbox. The inventors have found that the second suspension can be applied using a so-called curtain applicator.

[0082] The second suspension is applied directly onto the second wire, which means that there should be no fibers or fibrous webs on the wire when the second suspension is applied.

[0083] The inventors have discovered that it is preferable for the second wire to be wet when the second suspension is applied. Wetting the wire before applying the second suspension initially improves drainage and can prevent the wire material from adhering to the formed web. Another advantage of adding water or a chemical solution immediately before the wet-end applicator is that it can reduce wear on the wire material as well as eliminate or reduce air entrapment. Thus, in some embodiments, the second wire is treated with steam, water, or an aqueous solution so that the wire surface is wet when the second suspension is applied to the wire. The aqueous solution preferably contains a wetting agent, lubricant, or humectant, or a combination thereof. Examples of wetting agents, lubricants, and humectants useful in the aqueous solution include, but are not limited to, polymeric or non-polymeric surfactants, calcium stearate, sorbitol, polyethylene glycol, polyvinyl alcohol, and proteins. The amount of water or aqueous solution applied to the wire is preferably 1 to 10 g / m. 2 The range is.

[0084] As previously mentioned, the dry content of the second suspension may consist solely of particulate mineral and HRC, or may consist of particulate mineral, HRC and one or more additional components.

[0085] The second suspension comprises at least 65% by dry weight of the particulate mineral and HRC combined. In some embodiments, the second suspension comprises at least 70% by dry weight, more preferably at least 80% by dry weight, or at least 90% by dry weight of the particulate mineral and HRC combined, based on the total dry weight of the suspension. In some embodiments, the second suspension comprises in the range of 50-99% by dry weight, preferably in the range of 70-99% by dry weight, more preferably in the range of 80-99% by dry weight, and more preferably in the range of 90-99% by dry weight of the particulate mineral and HRC combined, based on the total dry weight of the suspension.

[0086] In some embodiments, the particulate mineral and HRC are co-refined, co-precipitated, and / or pre-agglomerated before being applied to the second wire.

[0087] The HRC acts as a binder for the particulate mineral. In some embodiments, the second suspension can further include a co-binder. In some embodiments, the second suspension further includes a co-binder in a range of 1-10% by dry weight, preferably in a range of 3-8% by dry weight.

[0088] In some embodiments, the co-binder comprises starch, latex, polyhydroxyalkanoate (PHA), polyvinyl alcohol (PVOH), or modified cellulose.

[0089] In some embodiments, the second suspension further comprises a viscosity modifier that acts to increase the viscosity of the suspension, making it more suitable for application to the wire. In some embodiments, the second suspension further comprises a viscosity modifier in the range of 0.1-5% by dry weight, preferably in the range of 0.5-4% by dry weight.

[0090] The viscosity modifier can be any compound that can increase the viscosity of the aqueous composition. Typically, the viscosity modifier is a water-soluble or water-swellable anionic, amphoteric, branched or nonionic polymer. Examples of useful viscosity modifiers include, but are not limited to, polysaccharides or chemically modified polysaccharides, polyvinyl alcohol (PVOH), proteins, alginates, SA or SB latex, and polyhydroxyalkanoate (PHA) emulsions.

[0091] In some embodiments, the viscosity modifier comprises a polysaccharide or a chemically modified polysaccharide, the chemical modification preferably comprising at least one of cross-linking, oxidation, carboxymethylation, and acetylation.

[0092] In some embodiments, the viscosity modifier comprises natural rubber or chemically modified natural rubber, the chemical modification preferably comprising at least one of crosslinking, oxidation, carboxymethylation, and acetylation.

[0093] In some embodiments, the viscosity modifier is selected from the group consisting of carboxymethyl cellulose (CMC), hemicellulose, modified starch, chitosan, pectin, alginate, hydroxyethyl cellulose, and ethyl hydroxyethyl cellulose (EHEC). In some embodiments, the viscosity modifier is selected from the group consisting of carboxymethyl cellulose (CMC), modified starch, and ethyl hydroxyethyl cellulose (EHEC).

[0094] In some embodiments, the second suspension has a viscosity (also called Brookfield viscosity) in the range of 100 to 100,000 mPas, preferably in the range of 200 to 75,000 mPas, and more preferably in the range of 250 to 10,000 mPas, measured according to standard SCAN-P 50:84 at 23°C.

[0095] In some embodiments, the second suspension has a viscosity of 50 g / m as determined according to Tappi T701 pm-01. 2 More than 75 g / m 2 It has an Åbo Akademi Gravimetric Water Retention (ÅAGWR) value of over 10 ...

[0096] In some embodiments, the second suspension comprises hemicellulose in an amount of at least 10% by dry weight of the amount of HRC, such as in the range of 10-25% by dry weight.

[0097] The second suspension may further include additives such as flocculating or de-flocculating additives, dry strength additives, latex, softeners, crosslinking aids, sizing chemicals, dyes and colorants, wet strength resins, defoaming or foaming aids, microbial and slime control aids or mixtures thereof.

[0098] The second suspension may further include additives to improve different properties of the mixture and / or the produced mineral layer, such as latex and / or polyvinyl alcohol (PVOH) to increase the ductility of the mineral layer. The method of the present invention provides another way to improve the dewatering rate, which is less dependent on the addition of retention and drainage chemicals, yet still allows for the use of smaller amounts of retention and drainage chemicals, preferably less than 150 g / tn, more preferably less than 50 g / tn, based on the total dry weight of the second suspension. In some embodiments, the second suspension does not include added retention and drainage chemicals.

[0099] In some embodiments, the second suspension is applied to the second wire in the form of a foam. Applying the second suspension in the form of a foam has the advantage over applying it in the form of a liquid suspension because it allows for a higher dry solids content in the suspension. The foamed second suspension preferably has a foam density of 350 kg / m 3 less than 250 kg / m 3 Applying the second suspension in the form of a foam is advantageous, as this also allows for the use of long fibrils or fibers, which helps to ensure good formation and controlled fiber orientation.

[0100] The pH value of the second suspension may typically be in the range of 4 to 10, preferably in the range of 5 to 8, and more preferably in the range of 5.5 to 7.5.

[0101] The temperature of the second suspension may typically be in the range of 40 to 100°C, preferably in the range of 50 to 100°C, and more preferably in the range of 60 to 100°C.

[0102] In some embodiments, the highly purified cellulose in the second suspension comprises or consists of microfibrillated cellulose (MFC).

[0103] Microfibrillated cellulose (MFC), in the context of patent applications, refers to cellulose particles, fibers, or fibrils with a width or diameter between 20 nm and 1000 nm. Various methods exist for the production of MFC, including single-pass or multi-pass purification, prehydrolysis followed by purification, or high-shear degradation or fibril release. To ensure that MFC production is both energy-efficient and sustainable, one or several pretreatment steps are typically required. The cellulose fibers of the pulp used in MFC production may be natural or may have been enzymatically or chemically pretreated, for example, to reduce the amount of hemicellulose or lignin. Cellulose fibers may be chemically modified before fibrillation, so that the cellulose molecules contain functional groups other than (or more than) those found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and / or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, e.g., "TEMPO"), or quaternary ammonium (cationic cellulose). After being modified or oxidized by any of the above methods, the degradation of the fibers into MFC becomes easier.

[0104] MFC is made from wood cellulose fibers, both hardwood and softwood. HRC can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. HRC is preferably made from pulp from virgin fibers, including mechanical pulp, chemical pulp, and / or thermomechanical pulp. It can also be made from shredded or recycled paper.

[0105] The second web layer preferably has a lower dry basis weight than the first web layer. In some embodiments, the dry basis weight of the second web layer is in the range of 5 to 50 gsm, preferably in the range of 8 to 40 gsm, and more preferably in the range of 10 to 35 gsm. The method of the present invention allows for the use of particulate minerals having smaller particle sizes at relatively low mineral-based layer weights, such as in the range of 10 to 30 gsm, or even 10 to 15 gsm, to achieve good mineral coverage. The density of the second web layer in the formed multilayer webs and laminates is typically significantly higher than the density of the corresponding first web layer. In some embodiments, the density of the second web layer in the formed multilayer webs and laminates is in the range of 800 to 2500 kg / m 3 within the range of 1000 to 2500 kg / m 3 within the range of 1500 to 2500 kg / m 3 is within the range.

[0106] In some embodiments, the dry basis weight of the formed multi-layer webs and laminates is in the range of 25 to 500 gsm, preferably in the range of 50 to 400 gsm, and more preferably in the range of 50 to 300 gsm.

[0107] In some embodiments, the density of the formed multilayer webs and laminates is between 800 and 2500 kg / m 3 within the range of 1000 to 2500 kg / m 3 within the range of 1000 to 2000 kg / m 3 is within the range.

[0108] The present invention is described herein primarily with reference to embodiments in which the laminate is formed from two web layers. However, it is understood that the laminate may include additional web layers. Thus, it is also possible for the laminate to be formed from more than two web layers, such as three, four, five, six, or seven web layers.

[0109] In some embodiments, the method comprises: e) coating the second web layer of the resulting cellulosic laminate with a water-soluble polymer layer. Further includes:

[0110] In some embodiments, the mineral-based layer of the resulting cellulosic laminate is cellulose-based according to ISO standard 2471 (C / 2 o ) of at least 80%, preferably at least 85%.

[0111] The resulting cellulosic laminate preferably has a Cobb-Unger value (30s) of 20 g / m 2 The Cobb-Unger value is a measure of oil absorption as determined according to SCAN-P standard 37:77 (30 seconds). In some embodiments, the mineral-based layer of the resulting cellulosic laminate has an oil absorption of 0.5 to 25 g / m2 as determined according to SCAN-P standard 37:77 (30 seconds). 2 in the range of 1 to 20 g / m 2 in the range of 5 to 15 g / m 2 The Cobb-Unger value is in the range of

[0112] The cellulosic laminate may be provided with a polymer layer on one or both sides. The polymer layer may, of course, hinder repulpability, but may still be necessary or desirable in some applications. The polymer layer may be applied, for example, by extrusion coating, film lamination, or dispersion coating.

[0113] The polymer layer may generally comprise any of the thermoplastic polymers typically used in paper or paperboard-based packaging materials, or polymers specifically used in liquid packaging boards. Examples include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyhydroxyalkanoates (PHAs), polylactic acid (PLA), polyglycolic acid (PGA), starch, and cellulose. Polyethylene, particularly low-density polyethylene (LDPE) and high-density polyethylene (HDPE), is the most common and versatile polymer used in liquid packaging boards.

[0114] Thermoplastic polymers are useful because they can be easily processed by extrusion coating techniques to form very thin, uniform films with excellent liquid barrier properties. In some embodiments, the polymer layer comprises polypropylene or polyethylene. In preferred embodiments, the polymer layer comprises polyethylene, more preferably LDPE or HDPE.

[0115] The polymer layer can include one or more layers formed of the same or different polymer resins. In some embodiments, the polymer layer includes a mixture of two or more different polymer resins. In some embodiments, the polymer layer is a multilayer structure comprising two or more layers, where a first layer is comprised of a first polymer resin and a second layer is comprised of a second polymer resin different from the first polymer resin.

[0116] In some embodiments, the polymer layer is formed by extrusion coating a polymer onto the surface of the laminate. Extrusion coating is a process in which molten plastic material is applied to a substrate to form a very thin, smooth, and uniform layer. The coating can be formed from 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).

[0117] The basis weight of each polymer layer of the laminate is preferably 50 g / m 2 To achieve a continuous, substantially defect-free film, a film thickness of at least 8 g / m is typically required. 2 , preferably at least 12 g / m 2 In some embodiments, the polymer layer has a basis weight of 8 to 50 g / m 2 within the range of 12 to 50 g / m 2 is within the range.

[0118] Generally, products, polymers, materials, layers, and processes are described in terms of "comprising" various components or steps, but products, polymers, materials, layers, and processes may also "consist essentially of" or "consist of" various components and steps.

[0119] While the present invention has been described with reference to various exemplary embodiments, it will be apparent to those skilled in the art that various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended that the invention be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but the invention is intended to include all embodiments falling within the scope of the appended claims.

Claims

1. 1. A method for producing a cellulosic laminate including a mineral-based layer on a papermaking machine, comprising: a) forming a first web layer by applying onto a first wire a first suspension comprising at least 50% by dry weight of a cellulosic fibrous material having a Shopper-Rigler (SR) value in the range of 18 to 50, and partially dewatering the first web layer on the first wire; b) forming a second web layer by applying onto a second wire a second suspension comprising 60-95% by dry weight of particulate mineral and 5-40% by dry weight of binder which is highly refined cellulose (HRC) having an SR value in the range of 75-100, and partially dewatering the second web layer on the second wire, wherein the second suspension has a dry solids content of at least 0.5 wt % and is applied directly onto the second wire using a curtain applicator; and partially dewatering the second web layer on the second wire; c) laminating the partially dewatered second web layer and the partially dewatered first web layer to obtain a laminated web; d) dewatering and optionally drying the formed laminate web to obtain a cellulosic laminate including a mineral-based layer; A method comprising:

2. 10. The method of claim 1, wherein the cellulosic fibrous material of the first suspension has an SR value in the range of 20 to 35.

3. 3. The method of claim 1 or 2, wherein the cellulosic fibrous material of the first suspension has a water retention value (WRV) in the range of 100 to 220%, preferably in the range of 120 to 190%, determined in accordance with ISO standard 23714:2014.

4. A method according to any one of claims 1 to 3, wherein the second suspension comprises 65 to 95% by dry weight of said particulate mineral, preferably 70 to 90% by dry weight.

5. 5. The method of claim 1, wherein the particulate mineral of the second suspension is a mineral filler or a mineral pigment.

6. The particulate minerals of the second suspension may be ground calcium carbonate (GCC), kaolin, precipitated calcium carbonate (PCC), talc, titanium dioxide (TiO ２ 6. The method of claim 1, wherein the mineral filler is selected from the group consisting of methyl methyl acrylate, methyl meth ...

7. The particulate minerals of the second suspension are ground calcium carbonate (GCC), kaolin, precipitated calcium carbonate (PCC), talc, titanium dioxide (TiO ２ ), aluminum trihydrate, amorphous silica and silicates, satin white (ettringite), zinc oxide (ZnO) and barium sulfate (BaSO ４ 7. The method of claim 1, wherein the mineral pigment is selected from the group consisting of methyl methacrylate, ...

8. 8. The method according to any one of claims 1 to 7, wherein the second suspension comprises 10 to 40% by dry weight of the HRC, preferably 15 to 35% by dry weight.

9. 9. The method according to any one of claims 1 to 8, wherein the HRC of the second suspension has an SR value in the range of 80 to 98, preferably in the range of 85 to 98.

10. 10. The method according to any one of claims 1 to 9, wherein the HRC of the second suspension has a water retention value (WRV) of >200%, preferably >250%, determined in accordance with ISO standard 23714:2014.

11. 11. The method of claim 1, wherein the HRC of the second suspension is formed from fractionated cellulosic fibrous material from which a fraction of the finest particulate material has been removed.

12. 12. The method of any one of claims 1 to 11, wherein the HRC of the second suspension, when determined using an L&W Fiber tester Plus instrument, has a content of fibers with a length of >0.2 mm of at least 10 million fibers per gram on a dry weight basis, preferably at least 12 million fibers per gram on a dry weight basis, more preferably at least 14 million fibers per gram on a dry weight basis.

13. 13. The method of any one of claims 1 to 12, wherein the particulate mineral and the HRC are co-refined, co-precipitated, and / or pre-agglomerated before being applied to the second wire.

14. 14. The method according to any one of claims 1 to 13, wherein the second suspension further comprises a co-binder in the range of 1 to 10% by dry weight, preferably in the range of 3 to 8% by dry weight.

15. 15. The method of any one of claims 1 to 14, wherein the co-binder comprises starch, latex, polyhydroxyalkanoate (PHA), polyvinyl alcohol (PVOH), or modified cellulose.

16. 16. The method of any one of claims 1 or 15, wherein the second suspension further comprises a viscosity modifier in the range of 0.1 to 5% by dry weight, preferably in the range of 0.5 to 4% by dry weight.

17. 17. The method of claim 16, wherein the viscosity modifier comprises a polysaccharide or a chemically modified polysaccharide.

18. 17. The method of claim 16, wherein the viscosity modifier is selected from the group consisting of carboxymethyl cellulose (CMC), modified starch, and ethylhydroxyethyl cellulose (EHEC).

19. 19. A method according to any one of the preceding claims, wherein the second suspension has a dry solids content of at least 0.75 wt%, preferably at least 1 wt%, more preferably at least 2 wt%.

20. 20. The method of any one of claims 1 to 19, wherein the second suspension has a dry solids content in the range of 0.75 to 40 wt%, preferably in the range of 1 to 20 wt%, more preferably in the range of 2 to 15 wt%.

21. 21. The method according to any one of claims 1 to 20, wherein the second suspension has a viscosity in the range of 100 to 100,000 mPas, preferably in the range of 200 to 75,000 mPas, more preferably in the range of 250 to 10,000 mPas, measured according to standard SCAN-P 50:84 at 23°C.

22. The second suspension has a viscosity of 50 g / m as determined in accordance with Tappi T701 pm-01. ２ More than 75 g / m ２ 22. The method of claim 1, having an Åbo Akademi Gravimetric Water Retention (ÅAGWR) value of greater than 2.

23. 23. The method of any one of claims 1 to 22, wherein the second suspension is applied onto the second wire in the form of a foam.

24. 24. The method of any one of claims 1 to 23, wherein the second suspension has a temperature in the range of 40 to 100°C, preferably in the range of 50 to 100°C, more preferably in the range of 60 to 100°C.

25. The second wire has a length of 2000 to 7000 m at 100 Pa. ３ / m ２ / hour, more preferably in the range of 2500 to 5500 m at 100 Pa ３ / m ２ 25. The method of claim 1, wherein the air permeability is in the range of 1 / hour.

26. 26. The method of any one of claims 1 to 25, wherein the second suspension is applied onto the second wire at a jet / wire speed ratio in the range of 0.8 to 2.5, more preferably in the range of 0.85 to 2.

0.

27. 27. The method according to any one of claims 1 to 26, wherein the second wire is subjected to a treatment with steam, water or an aqueous solution, preferably an aqueous solution comprising a wetting agent, a lubricant or a moisturizing agent or a combination thereof, so that the surface of the wire is wet when the second suspension is applied onto the wire.

28. 28. The method according to any one of the preceding claims, wherein the dry basis weight of the first web layer is in the range of 10 to 500 gsm, preferably in the range of 20 to 400 gsm, more preferably in the range of 40 to 200 gsm.

29. 29. The method of any one of the preceding claims, wherein the dry basis weight of the second web layer is in the range of 5 to 50 gsm, preferably in the range of 8 to 40 gsm, more preferably in the range of 10 to 35 gsm.

30. 30. The method of any one of claims 1 to 29, wherein the dry solids content of the partially dewatered first web layer is in the range of 1.5 to 15 wt%, preferably in the range of 2.5 to 15 wt%, more preferably in the range of 6 to 15 wt%.

31. 31. The method of any one of claims 1 to 30, wherein the dry solids content of the partially dewatered second web layer is in the range of 1.2 to 25 wt%, preferably in the range of 2.5 to 20 wt%, more preferably in the range of 5 to 15 wt%.

32. 32. The method of any one of claims 1 to 31, wherein the water obtained by dewatering the second web layer on the second wire is not mixed with the water obtained by dewatering the first web layer on the first wire.

33. 33. The method of any one of claims 1 to 32, wherein the laminating of step c) comprises laminating the partially dewatered second web layer to the non-wire side of the partially dewatered first web layer.

34. 34. The method of any one of claims 1 to 33, wherein the laminating of step c) further comprises applying a bonding agent to one or both of the surfaces to be joined.

35. 35. The method of claim 34, wherein the binder is selected from starch or microfibrillated cellulose (MFC), nanocrystalline cellulose, or a combination thereof.

36. e) coating the second web layer of the resulting cellulosic laminate with a water-soluble polymer layer.

36. The method of any one of claims 1 to 35, further comprising:

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