A method, a paperboard product, and the use of a foam applicator and a subsequent high-consistency metering size press

Abstract

According to an example aspect of the present application, there is provided a method comprising: providing a paper web comprising fibrous material; coating a first adhesive composition in the form of a foamed composition on the paper web; subsequently coating a second adhesive composition on the paper web; wherein the second adhesive composition has a higher solids content than the first adhesive composition.

Description

TECHNICAL FIELD

[0001] The present invention relates to the manufacture of paper and paperboard, in particular to a method of applying a binder during the manufacturing process. BACKGROUND

[0002] In paper and paperboard production, surface sizing material, typically a starch solution, is added to the surface of the substantially dried paper web before final drying, the purpose of sizing being to increase the surface strength, internal bond strength, stiffness and absorption properties, to bind filler and fibres to the surface and to reduce dusting.

[0003] Surface sizing is performed by a size press consisting of two rolls. The paper web is passed through the nip of the rolls and a solution containing the sizing agent is applied to the surface of the paper web.

[0004] In paperboard production, internal bond strength is an important parameter and in known sizing methods, the use of surface starch is limited to low solids methods and low molecular weight and degree of branching to maintain a sufficiently low viscosity to enable penetration into the layer zone in the paperboard product and achieve a sufficiently high internal bond strength.

[0005] Thus, surface sizing adds more moisture to the paper web, increasing the drying requirement after the size press and increasing the energy cost of the process. For example, in a papermaking process, the rewetting caused by surface sizing can reduce the dryness of the sheet by tens of percentage points, which can limit the machine production capacity if drying energy is a bottleneck of the process.

[0006] Furthermore, in known methods, a relatively large amount of size solution is required to achieve an effective concentration of the size in the layer zone.

[0007] Furthermore, in known methods such as spraying, wet-end binder application is limited to low viscosity (e.g. less than 50 cP) solutions of particulate material.

[0008] The present invention can at least partially overcome these disadvantages. SUMMARY

[0009] The present invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a method comprising: providing a paper web comprising fibrous material; applying a first binder composition in the form of a foamed composition to the paper web; subsequently applying a second binder composition to the paper web; wherein the solids content of the second binder composition is higher than the first binder composition.

[0011] Various embodiments of the first aspect can include at least one feature from the following list:

[0012] • said providing a paper web comprises forming a fibrous slurry on a wire to obtain a wet paper web.

[0013] • between the coating of the first binder and the coating of the second binder, the moisture is removed, for example by suction, pressing and / or heating, thereby increasing the solids content of the paper web.

[0014] • the first binder composition is coated on the paper web, the solids content of the paper web being in the range of 4 to 45 wt-%, such as 8 to 15 wt-%, calculated on the total weight of the paper web.

[0015] • the solids content of the first binder composition is less than 20 wt-%, such as 0.1 to 15 wt-%, such as 0.5 to 10 wt-%.

[0016] • the first binder composition comprises a binder in at least partly particulate form.

[0017] • the first binder composition comprises nanostructured cellulose or microstructured cellulose, such as cellulose fibres, having an average fibre diameter of preferably less than 1 μm.

[0018] • the first binder composition comprises a binder in at least partly aqueous dispersion form.

[0019] • at least a portion of the first binder composition is retained in the surface portion of the wet paper web.

[0020] • at least a portion of the first binder composition penetrates into the wet paper web, the penetration depth preferably being at least 10 %, preferably at least 20 %, such as at least 30 % of the total thickness of the wet paper web.

[0021] • the first binder composition comprises starch, preferably at least a portion of the starch being in gelatinized form, and optionally further comprises a dry-strength resin.

[0022] • the first binder composition comprises a polyvinyl amine.

[0023] • the first binder composition comprises starch.

[0024] • the first binder composition contains less than 0.5 g / m 2 of filler.

[0025] • the coating of the first binder composition is performed in the form of a foamed composition, preferably using a foam applicator or a foam applicator.

[0026] • the coating of the first binder composition is performed in the wire section of the paperboard production process.

[0027] • The first adhesive composition is applied in one or more separate coating doses.

[0028] • The first adhesive composition is applied in one or more separate coating doses.

[0029] • The first adhesive composition is applied in one or more separate coating doses.

[0030] • The first adhesive composition is applied in one or more separate coating doses.

[0031] • The first adhesive composition is applied in one or more separate coating doses.

[0032] • The first adhesive composition is applied in one or more separate coating doses.

[0033] • The first adhesive composition is applied in one or more separate coating doses.

[0034] • The first adhesive composition is applied in one or more separate coating doses.

[0035] • The first adhesive composition is applied in one or more separate coating doses.

[0036] • The first adhesive composition is applied in one or more separate coating doses.

[0037] • The first adhesive composition is applied in one or more separate coating doses.

[0038] • The first adhesive composition is applied in one or more separate coating doses.

[0039] • The first adhesive composition is applied in one or more separate coating doses.

[0040] • The first adhesive composition is applied in one or more separate coating doses.

[0041] • The first adhesive composition is applied in one or more separate coating doses. 2

[0042] • The first adhesive composition is applied in one or more separate coating doses.

[0043] • The first adhesive composition is applied in one or more separate coating doses.​

[0044] • The coating of the second adhesive composition is performed by means of a size press suitable for high consistency surface sizing, such as a high consistency metering size press.

[0045] • The method is performed during a paper or paperboard manufacturing process.

[0046] • The coating of the first adhesive composition and the coating of the second adhesive composition are performed in a first step and a subsequent or later second step, respectively, of a paper or paperboard manufacturing process.

[0047] • The paper or paperboard manufacturing process does not comprise any step of spraying starch in non-foamed form on the paper web.

[0048] According to a second aspect of the invention, there is provided a paperboard product obtained by the method of the first aspect.

[0049] Various embodiments of the second aspect can comprise at least one feature from the following list:

[0050] • The tensile strength index of the paperboard product is at least 43 kNm / kg in the machine direction and at least 22 kNm / kg in the cross direction.

[0051] • The tensile stiffness index of the paperboard product is at least 5.5 kN / m in the machine direction and at least 2.4 kN / m in the cross direction.

[0052] • The internal bond strength (Scott bond) of the paperboard product is at least 130 J / m 2 .

[0053] • The bending stiffness index of the paperboard product is at least 0.34 Nm 7 / kg 3 in the cross direction and at least 0.68 Nm7 / kg 3 in the machine direction, according to Taber 15° ISO 2493 and gram determination ISO 536.

[0054] • The paperboard product is a folding boxboard.

[0055] • The paperboard product is a linerboard.

[0056] According to a third aspect of the invention, there is provided the use of a foaming coater and a subsequent high consistency metering size press in a paperboard manufacturing process, respectively for coating an adhesive composition onto a paper web in a first step and a subsequent second step.

[0057] Advantages of the invention

[0058] The invention can improve the interlayer strength and the intralayer strength of a multilayer paperboard product.

[0059] The present invention enables more effective optimization of adhesive properties.

[0060] The present invention helps to control the penetration depth of the sizing agent.

[0061] The present invention can increase the range of surface adhesive penetration that can be achieved to optimize product quality.

[0062] The present invention can reduce drying costs in paper and board manufacturing processes.

[0063] In some embodiments, the addition of adhesive at the interface between adjacent layers on the wet end of a paperboard manufacturing process can improve the internal bond strength and delamination resistance during printing and processing of the paperboard product. BRIEF DESCRIPTION OF DRAWINGS

[0064] FIG. 1A A micrograph of a two layer structure is shown in which a starch containing adhesive composition is applied to one of the layers by a foam applicator on the wet end of a paperboard manufacturing process and then the two layers are brought together.

[0065] FIG. 1B A micrograph of a control sample is shown. In this case, the foam composition is identical except that it does not contain starch or other adhesive.

[0066] FIG. 2A A micrograph of a three layer structure is shown in which a 15 wt-% starch adhesive composition is applied by a high consistency metered size press.

[0067] FIG. 2B A micrograph of a three layer structure is shown in which a 25 wt-% starch adhesive composition is applied by a high consistency metered size press.

[0068] FIG. 2C A micrograph of a three layer structure is shown in which a 30 wt-% starch adhesive composition is applied by a high consistency metered size press.

[0069] FIG. 3A to FIG. 3C A micrograph of a three layer structure is shown in which a lower solids content foam adhesive is used between the top and middle layers and a higher solids content adhesive is used on the surface of the combined multi-layer structure. DETAILED DESCRIPTION

[0070] DEFINITIONS

[0071] Unless otherwise indicated herein, or in the context in which it is used, all percentages referred to herein are based on weight percent of the total weight of the respective composition.

[0072] The term "average particle size" as used herein refers to the average number particle size based on the largest linear dimension (also referred to as "diameter") of the particles determined using techniques known to those skilled in the art, such as scanning electron microscopy, transmission electron microscopy and / or light scattering techniques.

[0073] In the present context, the term "paperboard" is to be understood to mean a fibrous web which can be used as paperboard, typically having a grammage in the range indicated below, or as part of a paperboard or reconstituted paperboard. The paperboard or reconstituted paperboard can be uncoated or coated.

[0074] The present application can be used for manufacturing paper or paperboard from single layer to multi-layered structures, thus comprising one or more layers, preferably 1 to 3 layers.

[0075] "Grammage" means grams per square meter. The grammage of paperboard is typically in the range of 90 to 600 g / m 2 .

[0076] "Bulk" means the specific volume of a material. Bulk is the inverse of density.

[0077] In the present context, the term "filler" generally refers to any conventional filler or combination of fillers, such as precipitated calcium carbonate, kaolin, talc, ground calcium carbonate, kaolin, calcinated clay, synthetic silicates, titanium dioxide, plastic pigments or any other mineral or organic filler or pigment.

[0078] In the production of paper or paperboard, an improved method of applying a binder composition to the paper web has been found. In this method, advantageously, at least two stages of binder composition are applied. A first binder composition is preferably applied to the wet paper web by a foaming process at the wire section or similar in the paper or paperboard manufacturing process. A second binder composition, preferably a high concentration binder, is applied to the dry paper web at a later stage in the paper or paperboard manufacturing process.

[0079] In the present application, the application of the binders is divided into two separate steps and carried out in two separate units, which brings unexpected benefits. The properties of each binder can be better optimized, taking into account the required functionality of the final product and taking into account the limitations and opportunities offered by the unit or process stage at which the binder is applied.

[0080] In some embodiments, the amount of binder or surface size (e.g. starch) can be reduced compared to conventional methods. In addition, the strength and stiffness of the binder can be maximized. For example, the amount of binder added can be reduced without compromising quality. In addition, the need for drying the paper web after the sizing step can be reduced.

[0081] In some embodiments, the strength of the paperboard can be improved by applying the adhesive in two stages. The first stage can enhance the web strength more deeply. The second stage is a high concentration surface sizing, where more adhesive can be applied on the surface. The combination of these two stages can reduce the amount of water that needs to be dried.

[0082] Some embodiments can alleviate the problem of reduced production due to the bottleneck of drying requirements.

[0083] Some embodiments can improve the running speed and production.

[0084] In some embodiments, applying functional agents (such as adhesives in foamed form) at the wet end of the paper or paperboard manufacturing process also enables the addition of materials that improve the delamination resistance in the final product.

[0085] We note that the combination of particulate adhesives and dispersion adhesives can be beneficial for improving the delamination resistance, strength, stiffness, and other functional properties, such as sizing and wet strength.

[0086] A typical process for producing paperboard using a paperboard machine line is described below. The process can be broken down into the steps of pulping, preparing the pulp, forming (wire section), wet pressing, drying, surface sizing, drying, pre-calendering, coating, drying, calendering, and rewinding.

[0087] Mechanical pulping is used to produce fibrous products such as printing and writing papers, paperboard, newsprint, or toilet paper. Mechanical pulp has a high bulk and good opacity. Mechanical pulp can be used in combination with chemical pulp to produce mixed properties and characteristics. Chemical pulp is made from cooked wood chips. Mixed pulping methods, such as chemi-mechanical pulping (CTMP), combine chemical treatment and heat treatment. Chemi-mechanical pulp is the preferred raw material for the processes and products of the present invention, especially CTMP with a low degree of refining. In multi-layer products, one or more layers can use this CTMP, while other layers can use other types of pulp.

[0088] The pulp raw material is processed to form a slurry, i.e., a fibrous mud. The slurry preparation system modifies the raw material so that the slurry supplied to the paperboard machine line meets the requirements of the paperboard machine line. The quality of the slurry supplied to the paperboard machine line affects the quality of the paperboard. Various additives can be added to the slurry.

[0089] The fibrous mud is transported from one or more headboxes to a moving wire section. In the wire section, the fibrous mud is drained, typically using foils, foil boxes, vacuum boxes, or vacuum rolls. This results in a web. After the wire section, the dry content of the web is typically between 18% and 30%, calculated on the total weight of the web.

[0090] The paper web is guided from the wire section to a press section, where dewatering and consolidation takes place in a nip. After the press section, the dry content is increased to 40-50%.

[0091] After the press section, the paper web is guided to a drying section. In the drying section, the moisture on the paper web is evaporated, typically using hot cylinders.

[0092] After the drying section, the board machine has a surface sizing unit, followed by drying, coating and calendering units, which finally form the surface of the board.

[0093] The present invention relates to the application of a sizing agent or binder in the production of paper or board. By the present invention, it is possible to dispense with the traditional size press, such as a pond size press, which is suitable for the application of low concentrations of binder.

[0094] In a preferred embodiment, the method comprises the steps of providing a paper web comprising fibrous material; applying a first binder composition in foamed form on the paper web; subsequently applying a second binder composition on the paper web; wherein the second binder composition has a higher solids content than the solids content of the first binder composition, so that the amount of water that needs to be removed in a post-dryer is reduced. Advantageously, the first binder composition is applied in the forming section of the board machine, and the second binder composition is applied in the surface sizing section of the board machine.

[0095] In the present invention, the initial material used for making the paper web comprising fibrous material can comprise any suitable lignocellulosic fibrous material, such as wood pulp, e.g. mechanical pulp and / or chemical pulp. Various additives can be added to the pulp, such as binders, hydrophobic sizing agents, retention aids or combinations thereof.

[0096] In some embodiments, the first binder composition in foamed form can be applied on the paper web at a solids content of the paper web of not more than 45 wt-% and not less than 4 wt-%, more preferably in the range of 6 to 30 wt-%, most effectively in the range of 8 to 15 wt-%.

[0097] The paper web forming technique can be any suitable technique and can also comprise any paper web forming method where a wet paper web is part of the process. By "wet paper web" is meant a paper web having a solids content of not more than 50 wt-%.

[0098] In one embodiment, the forming is carried out by a Fourdrinier, gap former or hybrid former.

[0099] In one embodiment, the forming is carried out by air-laying or other nonwoven forming technique.

[0100] Preferably, the first adhesive composition is applied to the wet paper web during the forming stage. The wet paper web can be on a moving wire and the first adhesive composition is applied to the exposed surface of the wet paper web from above the wire.

[0101] In some embodiments, the final product is a multi-ply paperboard product. During its production, the paper web used to produce the multi-ply board of the final product is formed separately. At least one of the paper webs can be treated with the first adhesive composition. Preferably, the first adhesive composition is applied before the paper webs are combined into the multi-ply board. Preferably, the layer where the treated paper web forms a junction point is treated with the first adhesive. After the treated paper web is combined with the other ply or plies, the board will enter the pressing and pre-drying stages.

[0102] In one embodiment, the first adhesive composition comprises an adhesive in at least partially particulate form. The adhesive composition can comprise particles having an average particle size of greater than 20 μm. One advantage of including particulate adhesive is that the particles can be retained on the surface of the wet paper web to which the adhesive composition is applied. Thus, the treated wet paper web is well suited for combining with other paper webs to form a multi-ply paperboard. The adhesive particles on the surface of the paper web can increase the adhesion between the paper webs, thereby improving the ply-to-ply adhesion of the multi-ply board product.

[0103] Advantageously, applying the first adhesive composition to at least one ply of a multi-ply product and then combining the plies with each other can improve the ply-to-ply strength.

[0104] In one embodiment, at least a portion of the first adhesive composition penetrates into the wet paper web, preferably to a depth of at least 10%, preferably at least 20%, for example at least 30% of the total thickness of the wet paper web.

[0105] In one embodiment, substantially, for example, a majority of the first adhesive composition is retained in the surface portion of the wet paper web, for example, the portion that is closest to the surface of the wet paper web and that is at most 15%, for example, at most 10%, for example, at most 5% of the total thickness of the wet paper web. The surface portion described above will become the ply interface after the multi-ply paper webs are combined with each other.

[0106] In one embodiment, the concentration profile of the first adhesive exhibits a gradient away from the surface, i.e., the concentration is highest at the surface and decreases as one moves away from the surface into the paper web.

[0107] With the present method, the concentration profile of one or more adhesives within a single ply or a multi-ply can be better controlled.

[0108] Advantageously, the first adhesive can eventually pass through the layer interface and be distributed to the second layer, since the first adhesive, which preferably moves towards the direction of the second layer, has a gradient. In this way, the adhesive can continue to move after the layers have been joined, and the forces during pressing and drying will move the liquid in the web towards the surfaces in both directions, thereby carrying and depositing part of the adhesive.

[0109] In a preferred embodiment, the first adhesive is applied as a foam layer on one surface of the wet paper web. By using vacuum and / or pressure, the foam and water components in the paper web can be moved, thereby redistributing the adhesive from the surface. The advantage of this process is that by controlling the method and direction of water removal, the final distribution of the adhesive can be controlled.

[0110] Another advantage or alternative advantage of the method is that the amount of water used (by using a higher solids content) can be reduced in the step of applying the second adhesive, and also the drying energy required is less.

[0111] Advantageously, the first adhesive composition is applied on one or more surfaces of the single paper web that is to face the surface of another layer in the multilayer structure. In an embodiment, the first adhesive composition is applied on each surface of the single paper web that is to face the surface of another layer in the multilayer structure. Each surface to be treated can be treated with a corresponding first adhesive composition and amount. In this way, the interlayer bonding at each interface between adjacent layers in the multilayer structure can be optimized.

[0112] The first adhesive composition can be any suitable adhesive composition, as long as it can be used at the wet end of a paper or board machine.

[0113] In an embodiment, the solids content of the first adhesive composition is 0.1 to 20 wt-%, such as 1 to 10 wt-%, for example 1 to 5 wt-%, of the total weight of the composition.

[0114] In an embodiment, the solids content of the first adhesive composition to be foamed is less than 5 wt-%.

[0115] The advantage of using the first adhesive in foamed form is that a wider range of adhesives, additives and solids contents can be used more conveniently in the composition to be foamed.

[0116] In an embodiment, the viscosity of the first adhesive composition before foaming is in the range of 1 to 1500 cP, such as 50 to 1500 cP.

[0117] The first adhesive composition can include native starch (solubilized and / or unsolubilized / immature granules), modified starch (solubilized and / or unsolubilized / immature granules), carboxymethylcellulose (CMC), polyvinyl alcohol (PVOH) (solubilized and unsolubilized forms), polyacrylamide (PAM), polyvinyl amine (PVAm), polyimide, latex adhesives (such as SBR and acrylic combinations), synthetic starches, and combinations thereof.

[0118] In addition to the adhesive, the first adhesive composition can also include functional additives such as internal sizing agents, wet strength resins, barrier materials, and combinations thereof.

[0119] In a preferred embodiment, the first adhesive composition includes at least one adhesive capable of increasing the interlayer bond strength.

[0120] In one embodiment, the first adhesive composition includes one or more of the following: unripened native starch, ripened native starch, unripened cationic starch, ripened cationic starch, and combinations of ripened cationic starch and unripened cationic starch.

[0121] In one embodiment, the first adhesive composition includes a mixture of dry strength resins (such as cationic polyvinyl amine) and natural adhesives (such as unripened or ripened cationic starch).

[0122] In one embodiment, the first adhesive composition includes a polyvinyl amine-based polymer.

[0123] In one embodiment, the first adhesive composition includes a cationic starch.

[0124] In one embodiment, the first adhesive composition includes a polyacrylamide-based polymer.

[0125] In one embodiment, the first adhesive composition includes a mixture of polyvinyl amine and starch.

[0126] In one embodiment, the first adhesive composition includes a latex adhesive based on styrene-acrylic copolymer.

[0127] In one embodiment, the first adhesive composition includes cellulose fibers. Cellulose fibers can also be referred to as nanocellulose, nanofibrillated cellulose, or microfibrillated cellulose. Cellulose fibers have a diameter < 1 μm, typically 0.02 to 0.04 μm, but the cellulose fibers can not be uniform and can contain some material with diameters up to 5 μm. The length of the cellulose fibers also varies widely, from 0.1 to > 1000 μm, with more typical fiber lengths of 0.5 to 200 μm. The cellulose fibers can come from a variety of sources, such as wood pulp or bacteria. Wood-based feedstocks are preferred.

[0128] Advantages of using cellulose fibers in the first binder composition include higher potential for bonding within and between layers, increased stiffness, improved tensile strength and compression resistance. The use of cellulose fibers in the first binder composition can avoid a reduction in drainage rate and reduce alignment in the machine direction, which can improve cross-machine performance more than adding cellulose fibers to the stock before the paper web is formed.

[0129] In one embodiment, the first binder composition includes starch, preferably at least a portion of the starch is in a gelatinized form. The first binder composition preferably forms a particulate binder.

[0130] In a preferred embodiment, the first binder composition includes a particulate binder and a suspended and / or dissolved polymeric binder in a weight / weight ratio of 4: 1 to 1 :4, preferably 2: 1 to 1 :2. The particulate binder can be selected from the group consisting of unripened starch, cellulose fibers, un-dissolved PVOH, and combinations thereof, preferably unripened natural starch or modified starch.

[0131] The dissolved and / or suspended polymeric binder can be selected from the group consisting of natural binders and synthetic binders, such as including natural starch (dissolved and / or un-dissolved / unripened particulate), modified starch (dissolved and / or un-dissolved / unripened particulate), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVOH) (dissolved and un-dissolved forms), polyacrylamide (PAM), polyvinyl amine (PVAm), polyimide, latex binders (such as SBR and acrylic combinations), synthetic starch, and combinations thereof, preferably a cationic polymer based on polyvinyl amine.

[0132] The combination of a particulate binder and a suspended and / or dissolved polymeric binder has the advantages of both the particulate binder, which can provide interlayer strength due to its size, which can be kept in or very close to the layer zone, and the suspended and / or dissolved polymeric binder, which can travel with the foam and liquid phase into adjacent layer zones to provide intra-layer strength to the layers surrounding the layer zone.

[0133] In some embodiments, the first binder composition is substantially free of filler.

[0134] In one embodiment, the amount of filler (i.e., basis weight) in the first binder composition is less than 5 g / m 2 , such as less than 3 g / m 2 , such as less than 1 g / m 2 , such as less than 0.5 g / m 2 .

[0135] In the present context, the term "foam" can refer to a gas suspended or dispersed in a liquid medium. The gas component can be any gas or mixture of gases capable of producing a foam with the liquid medium. For example, the gas can be air, nitrogen, oxygen, carbon dioxide, an inert gas or the like, or any combination or mixture thereof. The liquid medium can be any liquid medium, provided that it is capable of producing a foam composition and is applied to the paper web, and is compatible with the desired final additives or functional agents. For example, the liquid medium can be water, ethanol, an organic solvent or the like, or a mixture thereof. Examples of suitable foam components are given in US 4571360.

[0136] The properties of the foam, such as density, bubble size and stability (half-life), can be referred to as described in US 4099913 and US 4023526.

[0137] In one embodiment, the density of the foam is in the range of 80 to 600 g / L, preferably 100 to 450 g / L, such as 125 to 200 g / L.

[0138] In one embodiment, the half-life of the foam is in the range of 60 to 7200 s, such as at least 300 s, preferably at least 600 s.

[0139] In one embodiment, the bubble size of the foam (expressed as the average diameter of the bubbles at atmospheric pressure) is in the range of 10 to 500 μm, preferably in the range of 20 to 200 μm, more preferably in the range of 70 to 150 μm.

[0140] In a preferred embodiment, the first adhesive composition is applied on the wet paper web in the forming section or the wire section of the paperboard manufacturing process.

[0141] In one embodiment, the first adhesive composition is applied on the wet paper web in the form of a foamed composition. Preferably, the solid content of the wet paper web is not more than 45 wt-% and not less than 4 wt-%, more preferably in the range of 6-30 wt-%, most effectively in the range of 8-15 wt-%.

[0142] In one embodiment, the first adhesive composition is applied on the paper web in the form of a foamed composition after the wet-dry line, before the couch point, which is the point where the individual layers are joined together to form a multi-ply board.

[0143] The foam can be used in all layers, or only in some of the layers, such as in at least one layer of the final product, but still achieving effective delamination resistance. The order of the dewatering direction can be used to determine in which layer or layers the adhesive composition will be located, and to influence the properties of that layer or layers.

[0144] In a preferred embodiment, the first adhesive composition is in the form of a foamed composition.

[0145] The general steps of producing and applying the foam can be referred to the description in US 4435965.

[0146] In some embodiments, the first adhesive composition is applied by a foam applicator or a foam coater.

[0147] After or during the application of the foam, suction and / or pressure can be used to control the distribution and limitation of the first adhesive composition.

[0148] The directional application can be effective to control the distribution of the first adhesive composition. By "directional application" is meant a method in which, in a first step, a vacuum or pressure is applied to the web to which the foam is applied, causing the foam to penetrate deeper away from the surface of the web. In a second step, a vacuum or pressure is applied to the web to cause the foam to move in the opposite direction. This method has the advantage that it can ensure that the foamed composition is distributed throughout the thickness of the web, for example on both sides or surfaces of the web, so as to improve the interlayer adhesion of the two sides of the treated web or ply when the treated web is subsequently combined with other webs.

[0149] In some embodiments, applying the first adhesive composition comprises applying the first adhesive composition to one side of the wet web and providing suction from the other side of the wet web to cause the adhesive composition to penetrate deeper into the wet web.

[0150] In some embodiments, after applying the first adhesive composition on the surface of the wet web, the web is combined with other wet webs to form a multi-ply structure, and then water is removed from the obtained multi-ply structure by providing suction from both sides of the multi-ply structure. One or more of the webs to be combined can have been treated with a corresponding first adhesive composition on one or both sides of the web.

[0151] In one embodiment, the application of the first adhesive composition is carried out in one or more separate application doses. The amount of each dose can be different.

[0152] In some embodiments, the method is used to manufacture a multi-ply paperboard product, the first adhesive composition being applied on one or more wet webs, which are combined with each other and / or with other wet webs to form a multi-ply paperboard.

[0153] Advantageously, the method of the present application comprises the use of two different adhesive compositions, namely a first and a second adhesive composition, in separate steps. The composition and / or concentration of the first and second adhesive compositions are preferably different from each other.

[0154] The role of the first adhesive composition can be to provide adhesion strength in the layer region, so that a second adhesive composition with a higher solids content can be used in a later stage without reducing the product quality, such as the peel strength.

[0155] In a preferred embodiment, the first adhesive composition is applied in the form of a foamed composition, and the second adhesive composition is applied in the form of a non-foamed composition, such as a suspension or dispersion.

[0156] Preferably, the first adhesive composition is applied at the wire section, and the second adhesive composition is applied after the wire section.

[0157] In some embodiments, both the first adhesive composition and the second adhesive composition comprise one or more of the same adhesive compounds, such as starch, which can be a cooked starch or an uncooked starch. For example, the first adhesive composition can comprise starch, water, and a foaming agent, while the second adhesive composition can comprise starch and water, and does not contain any foaming agent.

[0158] Preferably, the second adhesive composition is applied on a paper web on which the first adhesive composition has been applied and has dried or has had moisture removed, so that a paper web with a higher solids content is obtained.

[0159] The second adhesive solution preferably comprises a surface size, the application of which typically results in a surface size layer on or in the paper web.

[0160] The surface size typically comprises a synthetic water-soluble polymer or a natural polymer or a derivative thereof.

[0161] Surface sizes suitable for use in some embodiments of the present application can be divided into several groups, of which the main groups are cationic and anionic surface sizes. In addition or optionally, some reactive sizing agents, such as alkyl ketene dimer (AKD), can also be used as surface sizes.

[0162] Cationic surface sizes include cationic starches and starch derivatives and corresponding carbohydrate-based natural polymers. Synthetic polymers can use styrene / acrylate copolymers (SA), polyvinyl alcohol, polyurethane and alkyl polyurethane, among others.

[0163] Anionic surface sizes include anionic starches and starch derivatives and corresponding carbohydrate-based natural polymers, such as carboxymethylcellulose and its salts, alkylcelluloses, such as methylcellulose and ethylcellulose. Synthetic polymers include: styrene / maleic acid copolymers (SMA), diisobutylene / maleic anhydride, styrene acrylate copolymers, acrylonitrile / acrylate copolymers, and polyurethanes and similar latex products containing the same chemical functions.

[0164] Many of the above surface sizes are provided in the form of a viscous solution of the sodium or ammonium salt of the corresponding polycarboxylic acid.

[0165] The concentration of the surface size in the second adhesive solution is typically about 0.01 to 25% by weight, usually about 15% by weight.

[0166] The amount of surface size (i.e. basis weight) in the second adhesive composition is typically about 0.1 to 10 g / m 2 , in particular about 0.2 to 5 g / m 2 , for example about 0.3 to 3 g / m 2 .

[0167] The amount of surface size (i.e. basis weight) in the second adhesive composition can be at least 0.1 g / m 2 , in particular at least 0.3 g / m 2 , for example at least 0.5 g / m 2 .

[0168] In some embodiments, the second adhesive can be starch, wherein it can be modified or unmodified starch, preferably starch derived from wheat, potato, rice, corn or tapioca.

[0169] In one embodiment, the second adhesive composition comprises cooked starch, preferably completely free of uncooked starch.

[0170] In one embodiment, the second adhesive composition has a solids content of at least 5 wt-%, for example at least 10 wt-%, for example at least 20 wt-%, for example at least 30 wt-%.

[0171] In one embodiment, the second adhesive composition comprises or consists of a high solids content adhesive composition, preferably having a solids content of at least 30 wt-%.

[0172] In some embodiments, the second adhesive composition is essentially free of filler.

[0173] In one embodiment, the amount of filler (i.e. basis weight) in the second adhesive composition is less than 5 g / m 2 , for example less than 3 g / m 2 , for example less than 1 g / m 2 , for example less than 0.5 g / m 2 .

[0174] Preferably, the method is used for manufacturing a multi-ply paperboard product, the second adhesive composition is applied on at least one surface of the multi-ply paperboard, the multi-ply paperboard being composed of a plurality of plies, wherein at least one of the plies has been treated with a first adhesive composition.

[0175] Typically, the multi-ply board has been at least partially dried before the second adhesive composition is applied. The partial drying can be performed by wet pressing and a pre-drying stage.

[0176] Preferably, the dryness of the paper web is in the range of 85 to 100% before or immediately after the application of the second adhesive composition.

[0177] In some embodiments, the application of the second adhesive composition is performed by a size press suitable for high consistency surface sizing, such as a high consistency metering size press. Preferably, a conventional size press, such as a pond press, is not used.

[0178] In some embodiments, the application of the second adhesive composition is performed by a metering press, preferably a high consistency metering size press.

[0179] Preferably, the dryness of the paper web is maximized after the application of the second adhesive composition to reduce the energy needed to remove the water added when surface sizing.

[0180] The method can be performed in a paperboard manufacturing process.

[0181] In one embodiment, in a paperboard manufacturing process, no other adhesive composition than the first and second adhesive composition is applied on the paper web.

[0182] The present invention also relates to a multi-ply paperboard product obtained by the method of the present invention.

[0183] In one embodiment, the tensile strength index of the paperboard product is at least 43 kNm / kg in the machine direction and at least 22 kNm / kg in the cross direction.

[0184] In one embodiment, the tensile stiffness index of the paperboard product is at least 5.5 kN / m in the machine direction and at least 2.4 kN / m in the cross direction.

[0185] In one embodiment, the internal bond strength (Scott bond) of the paperboard product is at least 130 J / m 2 .

[0186] In one embodiment, the bending stiffness index of the paperboard product is at least 0.34 Nm 7 / kg3 in the cross direction and at least 0.68 Nm 7 / kg3 in the machine direction, measured according to Taber 15° ISO 2493 and grammage determination ISO 536.

[0187] In one preferred embodiment, the paperboard product is or comprises a folding boxboard or a linerboard.

[0188] "Folding box board" (FBB or DIN standard 19303 GC or UC code) is a paperboard grade consisting of multiple layers of chemical pulp and mechanical pulp. Typically, this paperboard grade consists of mechanical pulp sandwiched between two layers of chemical pulp. The top layer is typically bleached chemical pulp, optionally with a pigment coating.

[0189] "Liner board" generally refers to a strong, stiff paperboard used as a flat cover for corrugated fiberboard in the corrugation process. Corrugated fiberboard is a material consisting of fluted corrugated board (corrugated core) and one or two flat liner boards.

[0190] In one embodiment, the paperboard product has a grammage in the range of 90 to 600 g / m2 2 , such as 90 to 450 g / m2 2 , such as 150 to 500 g / m2 2 .

[0191] In one embodiment, the paperboard product is a coated or uncoated folding box board, wherein the pulp of the middle layer comprises or consists of mechanical pulp, and the pulp of the top and bottom layers comprises or consists of chemical pulp.

[0192] The mechanical pulp of the middle layer can be selected from the group of groundwood pulp (GW), pressure groundwood pulp (PGW), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), bleached chemi-thermomechanical pulp (BCTMP), semi-chemical pulp and combinations thereof, preferably BCTMP.

[0193] The chemical pulp of the top and bottom layers can be bleached chemical pulp, in particular bleached kraft pulp, which can comprise softwood, such as spruce or pine or mixtures thereof, or hardwood, such as birch, poplar, aspen, alder, maple, eucalyptus tropical hardwood or mixtures thereof, or a mixture of softwood and hardwood chemical pulp.

[0194] In one embodiment, a double-layered linerboard is manufactured. Each of the two layers is shaped independently. The face layer is shaped by a Fourdrinier former, and the base layer is shaped by a hybrid former. The two layers are coupled together on a bonding roll with the top face of the face layer in contact with the top face of the base layer. Foam can be applied to the top face of the base layer, preferably after the hybrid unit and before the bonding roll. Alternatively, foam can also be applied to the top face of the face layer paperboard, preferably after the dry end wet line and before the bonding roll. In either case, the foam is applied before the bonding point. Preferably, at least one vacuum box is placed below the foam application point.

[0195] Reference is now made to the drawings, wherein the exemplary embodiments of the present application are described.

[0196] FIG. 1A and FIG. 1BFigure illustrates the case where starch is used as a first binder and how the first binder is positioned between two layers and directed towards the interface. The sample is dyed with an iodine solution which makes the starch binder appear dark blue to purple. The areas with the darkest color are located at the interface of the layer where starch was applied. The purple color (dark areas) extending in both directions shows the distribution of the starch in the finished paperboard.

[0197] FIG. 1A Figure shows a micrograph of a multi-layer structure according to one embodiment of the application. The binder composition comprising starch (first binder) is applied on the top surface of the bottom layer alone before combining the layers. The starch is applied using a foam applicator at the wet end of the paperboard manufacturing process.

[0198] FIG. 1B Figure shows a micrograph of a control sample. In this case, the foam composition is the same as in the case of the sample, but does not contain starch or any other binder.

[0199] It can be seen from FIG. 1A that most of the applied starch remains on the layer interface. A small portion of the starch has penetrated into both layers. The amount of starch is indicated by the darkness of the color. It can be observed that the starch extends in a gradient towards the bottom layer, approximately 50% of the thickness of the bottom layer, and the gradient of the binder extends further towards the top layer, almost to the surface.

[0200] FIG. 2A , FIG. 2B and FIG. 2C Figure shows the case where starch is used as a high solids binder (second binder) and how this binder remains in the surface part of the multi-layer structure (three-layer paperboard). The solids content of the binder composition varies from 15 wt-% to 30 wt-%.

[0201] FIG. 2A Figure shows a cross-sectional view of a structure where a binder composition comprising 15 wt-% starch is applied.

[0202] FIG. 2B Figure shows a cross-sectional view of a structure where a binder composition comprising 25 wt-% starch is applied.

[0203] FIG. 2C Figure shows a cross-sectional view of a structure where a binder composition comprising 30 wt-% starch is applied.

[0204] The advantage of a high solids content of the second binder is that the binder does not penetrate deep into the structure, thus reducing the amount of binder and also the amount of water. The drying requirements can thus be reduced, lowering the drying energy consumption.

[0205] By using a lower solids content adhesive composition in the wire section, good interlayer adhesion between adjacent layers can be achieved. Therefore, a higher solids content adhesive composition is not required to penetrate to the layer interface in the subsequent layers. Instead, the higher solids content adhesive composition can be located only in the surface portion of the structure and perform, for example, it can reduce dusting and increase the surface abrasion resistance.

[0206] FIG. 3A to FIG. 3C For the purpose of demonstrating the use of a lower solids content foamed adhesive (first adhesive) between the top ply and the middle ply to achieve good interlayer adhesion, while using a higher solids content adhesive (second adhesive) on the surface of the combined multi-ply board, the amount of second adhesive applied to the top surface was reduced by 33% to 36% to reduce penetration and moisture that needs to be removed by drying. This is described in Example 1 below FIG. 3A to FIG. 3C The process of creating the samples shown.

[0207] FIG. 3A A cross-section of a three-coated three-ply paperboard is shown without the addition of the first adhesive. FIG. 3A A reference example of a typical three-ply folding boxboard is shown. The cross-section has been stained with an iodine solution, which turns the starch a deep blue to purple color, the intensity of which is related to the concentration of starch. Other components will not stain blue-purple. Note the deep blue color near the top surface extends through the top ply to the interface with the middle ply.

[0208] FIG. 3B A cross-section of a three-coated three-ply paperboard is shown with the same fiber and surface coating composition as in FIG. 3A except that no sprayed particulate starch is included, and a dry-strength resin DS#2 is added to the surface of the middle ply by means of a foamed coating at the wet end before the middle ply is combined with the top ply paperboard, the amount of surface starch is reduced by 33%. By comparison with FIG. 3A it can be seen that the surface starch does not penetrate as deeply into the structure as in FIG. 3A

[0209] FIG. 3C A cross-section of a three-coated three-ply paperboard is shown with the same fiber and surface coating composition as in FIG. 3B except that the first adhesive composition, which is foamed coated at the wet end, includes a dry-strength resin DS#2 and starch. By comparison with FIG. 3B it is apparent that the starch extends through the top ply from the fiber surface to the top surface of the middle ply. By further comparison with FIG. 3A it can be seen that in FIG. 3A the starch penetration stops abruptly near the top of the middle ply; but in FIG. 3C the starch extends into the middle ply in a gradient fashion (color intensity decreases gradually) to about 30% of the middle ply thickness. ​

[0210] Example 1: Adding reinforcement to the surface in the wet end and reducing the surface size amount

[0211] A test scale wet end chemical application was set up on a typical three-ply paperboard machine.

[0212] The three plies were formed separately and then joined in the wet state prior to wet pressing. The surface plies (ply 1 and 3, or top and bottom plies, respectively) were formed using typical fourdrinier forming technology. The middle ply (ply 2) was formed using a hybrid system of typical fourdrinier and top dewatering device, placed after the initial dewatering. The plies were joined such that the top surface of the middle ply was joined with the top surface of the top ply, with both forming wires supporting the joined plies. Vacuum was used to draw the joined web toward the top ply forming wire. The middle ply forming wire was directed away from the bottom surface of the middle ply. The exposed bottom surface of the middle ply was brought into contact with the top surface of the bottom ply, forming a second joining point. The two sides of the three joined plies were supported by the top and back plies forming wires. As with the first joining point, vacuum was used to draw the joined web toward the bottom ply, with the top ply forming wire directed away, exposing the bottom or "mesh" side of the top ply. The web was picked from the bottom ply forming wire using a felt, and then a second felt was used to support the bottom surface to move the three-ply joined web out of the forming section and into the press section. The wet web had a solids content measurement of 15.0% to 15.3% prior to transfer to the press section.

[0213] The three-ply web was consolidated by pressing in two nip pressings with felt support and a third nip pressing without support. The solids content leaving the press section was estimated to be in the range of 45% to 48%.

[0214] The consolidated web was then dried on steam heated cylinders to a moisture content in the range of 8.5 to 11.0 wt-%. The drying cylinders were divided into five sections, and the steam load was monitored to determine if the use of chemicals would have an impact on drying requirements.

[0215] After the fifth drying section, surface size was applied to the top and back surfaces by a metering size press. In this test, a #4 bar was used to meter the surface size, and enough surface size was applied to ensure that the surface size penetrated to both ply interfaces, resulting in good delamination resistance. The top surface size was reduced by 1 / 3 to create a test point. The reduction in size was accomplished by changing the size of the bar to a #2 bar.

[0216] The sized web was then dried to a target moisture content of 9 wt-% using an infrared preheater and steam heated cylinders. The steam pressure was again monitored to evaluate the impact of the reduced press size on drying capacity.

[0217] The dried web is calendered, then three-coated on the top surface, re-calendered, and wound onto a jumbo reel. Samples of the finished paperboard are taken from the outer ply of the jumbo reel to test the major performance properties. Further, after slitting and rewinding, small rolls are made, then slit into sheets, and then printed via four-color offset. The printed samples are evaluated for delamination defects.

[0218] The steps for applying the foamed adhesive solution are described below.

[0219] Chemical coating is achieved by applying a foamed solution of an adhesive (first adhesive) to the top surface of the middle layer. The point of application is after the top dewatering, before the point of joining with the top layer, and is in the middle of one vacuum box, with another vacuum box before the point of joining. The solids content of the middle layer web ranges from 12.2 to 12.5 wt-% before the application of the chemical, and ranges from 13.0 to 13.5 wt-% at the point of joining. The test foaming coating system includes a chemical feed system, a foam generator, and a narrow applicator.

[0220] The adhesive, foaming agent, and water are formulated and stored separately in different containers. Each container is connected to a metering pump. By controlling the pump rate of each container, different chemical blends can be obtained.

[0221] Foaming is done in a rotor-stator foam mixer. The chemicals from the metering pumps are fed into the foam mixer along with pressurized air to produce a foam with a density of 150 g / L. During the tests, the foam generation variables are kept constant, allowing only minor adjustments to the foaming agent concentration and rotor speed.

[0222] The pressurized foam flows from the foam generator to the applicator, which is mounted above the moving middle layer wet web. The foam is emitted from a fixed gap slot at a fixed distance above the web, thus applying a uniform foam layer of 65 g / m 2 on the moving web.

[0223] The reference material includes 0.5 g / m 2 of uncooked starch, which is sprayed on the middle layer web before the point of joining with the top layer web (the foam applicator is located about 0.5 m upstream of the sprayer).

[0224] The materials applied by the foam applicator (DS#1, DS#2, and DS#3) are composed of three different adhesives targeted for dry strength, which can be used individually or in combination:

[0225] DS#1 dry strength agent is a cationic polyvinyl amine polymer

[0226] DS#2 dry strength agent is a polyacrylamide polymer

[0227] DS #3 cationic starch of medium degree of substitution

[0228] The solids content of the applied foamed adhesive was 0.3 to 3 wt-%.

[0229] The surface size (second adhesive) was a low degree of substitution cationic starch with a solids content of 12.6 wt-%.

[0230] Paperboard: 290 g / m2three-coat top side

[0231] Quality evaluation: Each test point was sampled at two locations on the same cross-directional strip taken from the outside of the jumbo roll. The two locations were chosen with one location in the area where the test applicator passed through the foamed coating chemical. The chosen location should be close to the center of the area of chemical application to avoid the effects of uneven application or edge reactions. The second point was chosen outside the area of chemical application. A peel test (average vertical force required to separate plies) was used to demonstrate resistance to delamination. Finally, the paper in the coated area was four-color offset printed and visually inspected for delamination defects.

[0232] Table 1

[0233]

[0234] * The TP8 paper was printed both in the area of chemical application and outside the area of chemical application.

[0235] ** The steam pressure required to maintain the first 5 zones was kept constant within normal variation throughout the test.

[0236] *** "Outside" refers to the area of the web outside the area of chemical application with foamed coating, "Inside" refers to the area within the area of chemical application with foamed coating

[0237] The results of Table 1 show that adhesive application that could not be achieved with conventional wet end surface sizing methods (e.g. sprayers) can be achieved with the foamed application method of the present invention and still provide good print delamination resistance with no starch sprayed and 1 / 3 less surface size adhesive. Further, even with the addition of 60 g / m 2 of water in the wet end foam, the reduced water amount on the size press was only 7 g / m 2 and the drying requirement after surface sizing was reduced by 25%. Thus, energy can be saved or the machine production capacity can be increased for drying limited production.

[0238] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein but are extended to equivalents thereof as would be recognized by those skilled in the relevant arts. It will also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0239] Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0240] As used herein, a list of items prefaced by "comprising" or "containing" indicates that the list is inclusive of other items not expressly identified. As used herein, "one" or "a" means "at least one" or "one or more" unless otherwise indicated. As used herein, "another" means "at least one" or "one or more" unless otherwise indicated.

[0241] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the application. One skilled in the relevant art will recognize, however, that the application can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the application.

[0242] While the forgoing examples are illustrative of the principles of the application in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications, including the use of alternative methods, components, materials, etc., can be made without departing from the principles of the application. Accordingly, the application is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0243] The verbs "comprise" and "include" used in the text are open-ended, both in the conjunctive and disjunctive sense, that is, they mean "including, but not limited to," or "comprising, but not limited to," and also consist of, encompass, contain, and so forth. Unless otherwise specified, "a" or "an" means "one or more." Further, unless otherwise specified, "or" means "and / or." Unless otherwise specified, the use of "an" or "a" means "one or more" rather than "one and only one." Furthermore, unless otherwise specified, the use of "comprises" or "comprising" means "consisting of, in addition to, or "including, or "including but not limited to" rather than "consisting only of."

[0244] Industrial applicability

[0245] The method of the present invention is at least applicable to the production of folding boxboard and linerboard.

[0246] List of citations

[0247] Patent literature

[0248] US4571360

[0249] US4099913

[0250] US4435965

[0251] US4023526

[0252] Non-patent literature

[0253] Eklund, R. W. and Hobbs, O. J., High Speed Application of Foamed Starch “Foamcote”, to a paper web, Proceedings TAPPI Coating Conference, pp. 83-89, 1986.

[0254] Skelton, J., Foam assisted dewatering - a new technology emerges. PTI March 1987, pp. 431-436.

[0255] Kinnunen-Raudaskoski, K. et. al., Novel thin functional coatings for paper by foam coating, Tappi Journal, Vol. 16, No. 4, April 2017, pp. 179-186.

Claims

1. A method, comprising: - providing a paper web comprising fibrous material, wherein, providing a paper web comprising forming a fibrous slurry on a wire to obtain a wet paper web; - applying a first binder composition in the form of a foamed composition on the paper web; followed by - applying a second binder composition on the paper web; wherein the solids content of the paper web is increased between the application of the first binder composition and the application of the second binder composition; wherein the application of the first binder composition comprises applying the first binder composition on one side of the wet paper web and providing a suction from the other side of the wet paper web to allow the first binder composition to penetrate into the wet paper web; and the second binder composition is applied in a non-foamed form and has a higher solids content than the first binder composition.

2. The method according to claim 1, characterized in that: - the solids content of the paper web is increased between the application of the first binder and the application of the second binder by removing water by suction, pressing and / or heating.

3. The method of claim 1, wherein, the solids content of the paper web is in the range of 4 to 45 wt-%, calculated on the total weight of the paper web, when the first binder composition is applied on the paper web.

4. The method of claim 3, wherein, the solids content of the paper web is in the range of 8 to 15 wt-%, calculated on the total weight of the paper web.

5. The method of claim 1, wherein, the solids content of the first binder composition is less than 20 wt-%.

6. The method of claim 5, wherein, the solids content of the first binder composition is in the range of 0.1 to 15 wt-%.

7. The method of claim 5, wherein, the solids content of the first binder composition is in the range of 0.5 to 10 wt-%.

8. The method of claim 1, wherein, the first binder composition comprises a binder in at least partially particulate form.

9. The method of claim 1, wherein, the first binder composition comprises nanostructured cellulose or microstructured cellulose having an average fiber diameter of less than 1 pm.

10. The method of claim 1, wherein, the first binder composition comprises cellulose fibers.

11. The method of claim 1, wherein, the first binder composition comprises a binder in at least partially aqueous dispersion form.

12. The method of claim 1, wherein, at least a portion of the first binder composition is retained in a surface portion of the wet paper web.

13. The method of claim 1, wherein, at least a portion of the first binder composition penetrates into the wet paper web to a penetration depth of at least 10% of the total thickness of the wet paper web.

14. The method of claim 13, wherein, at least a portion of the first binder composition penetrates into the wet paper web to a penetration depth of at least 20% of the total thickness of the wet paper web.

15. The method of claim 13, wherein, at least a portion of the first binder composition penetrates into the wet paper web to a penetration depth of at least 30% of the total thickness of the wet paper web.

16. The method of claim 1, wherein, the first binder composition comprises starch, at least a portion of which is in gelatinized form.

17. The method of claim 16, wherein, the first binder composition further comprises a dry strength resin.

18. The method of claim 1, wherein, the first binder composition comprises polyvinyl amine and / or starch.

19. The method of claim 1, wherein, The first adhesive composition comprises less than 0.5 g / m 2 of filler.

20. The method of claim 1, wherein, the first binder composition is applied in the form of a foamed composition.

21. The method of claim 20, wherein, the first binder composition is applied in the form of a foamed composition using a foam applicator or a foam applicator.

22. The method of claim 1, wherein, the application of the first binder composition is performed in the wire section of a paperboard making process.

23. The method of claim 1, wherein, After the surface of the paper web has been coated with the first adhesive composition, the paper web is combined with other paper webs to form a multi-layered structure, wherein one or more of the other paper webs are also treated with the first adhesive composition, and subsequently, water is removed from the multi-layered structure by providing suction from either side of the multi-layered structure.

24. The method of claim 1, wherein, Coating the first adhesive composition is performed in one or more separate coating doses.

25. The method according to claim 1, characterized in that: - the method is used for manufacturing a multi-layered paperboard product; and - the first adhesive composition is coated on one or more wet paper webs separately, followed by combining the one or more wet paper webs with each other and / or with additional wet paper webs to form a multi-layered board; and - coating the adhesive in any foamed form is performed prior to the combining.

26. The method according to claim 1, characterized in that, - coating the first adhesive composition is performed in the form of a foamed composition by means of a foam applicator or a foam coater; - coating the first adhesive composition is performed at the wire section in the paperboard manufacturing process; and - the first adhesive composition is coated on a paper web having a solids content in the range of 8 to 15 wt-%.

27. The method of claim 1, wherein, The second adhesive composition comprises one or more different adhesives and / or a different solids content than the first adhesive composition.

28. The method of claim 1, wherein, The solids content of the second adhesive composition is at least 5 wt-%.

29. The method of claim 1, wherein, The second adhesive composition comprises a surface size.

30. The method of claim 1, wherein, The second adhesive composition comprises a cationic starch.

31. The method of claim 1, wherein, The second adhesive composition comprises less than 0.5 g / m 2 of filler.

32. The method of claim 1, wherein, The method is used for manufacturing a multi-layered paperboard product, and the second adhesive composition is coated on the surface of a dried multi-layered board comprising one or more layers treated with the first adhesive composition.

33. The method of claim 1, wherein, Coating the second adhesive composition is performed by means of a size press suitable for high consistency surface sizing.

34. The method of claim 33, wherein, Coating the second adhesive composition is performed by means of a high consistency metering size press.

35. The method according to claim 1, characterized in that: - the solids content of the second adhesive composition is at least 10 wt-%; - coating the second adhesive composition is performed by means of a high consistency metering size press; and - coating the second adhesive composition is performed on a paper web having a dryness in the range of 85 to 100%.

36. The method according to claim 1, characterized in that: - coating the first adhesive composition is performed in the form of a foamed composition by means of a foam applicator or a foam coater; - coating the first adhesive composition is performed at the wire section in the paperboard manufacturing process; - the first adhesive composition is coated on a paper web having a solids content in the range of 8 to 15 wt-%; - the solids content of the second adhesive composition is at least 10 wt-%; - coating the second adhesive composition is performed by means of a high consistency metering size press; and - coating the second adhesive composition is performed on a paper web having a dryness in the range of 85 to 100%.

37. The method of claim 1, wherein, The method is performed during a paper or paperboard manufacturing process, the coating of the first adhesive composition and the coating of the second adhesive composition being performed in a first step and a subsequent or later second step, respectively, of the paper or paperboard manufacturing process.

38. The method of claim 37, wherein, The paper or paperboard manufacturing process does not comprise any step of spraying starch in non-foamed form on the paper web.

39. A paperboard product manufactured by the method according to any one of the preceding claims.

40. The paperboard product of claim 39, wherein, The tensile strength index of the paperboard product is at least 43 kNm / kg in the machine direction and at least 22 kNm / kg in the cross direction.

41. The paperboard product of claim 39, wherein, The tensile stiffness index of the paperboard product is at least 5.5 kN / m in the machine direction and at least 2.4 kN / m in the cross direction.

42. The paperboard product of any one of claims 39-41, wherein, The inner bond strength of the paperboard product is at least 130 J / m 2 .

43. The paperboard product according to any one of claims 39-41, characterized in that, According to measurements in Taber 15° ISO2493 and grammage determination ISO 536, the flexural stiffness index of the paperboard product is at least 0.34 Nm in the transverse direction. 7 / kg 3 In the mechanical direction, it is at least 0.68 Nm. 7 / kg 3 .

44. The paperboard product of any one of claims 39-41, wherein, The paperboard product is a folding boxboard or a linerboard.

45. Use of a foaming coater and a subsequent high-consistency metering press in a paperboard manufacturing process, wherein an adhesive composition is coated onto a paper web in a first step and a subsequent second step, respectively, wherein, The use comprises forming a fibrous pulp on a wire to obtain a wet paper web, applying a first adhesive composition in the form of a foam composition to one side of the wet paper web by means of a foam applicator, providing a suction from the other side of the wet paper web, allowing the first adhesive composition to penetrate into the wet paper web, and coating a second adhesive composition in non-foamed form, wherein the solids content of the second adhesive composition is higher than the first adhesive composition.

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