阅读说明：本技术 生产包含第一片层的产品的方法 (Method for producing a product comprising a first sheet layer ) 是由 K.巴克福尔克 I.海斯卡南 E.索科南 于 2019-02-25 设计创作，主要内容包括：本发明涉及生产包含第一片层的产品的方法,该方法包括以下步骤：提供包含纤维的纤维悬浮体；向多孔介质提供所述纤维悬浮体以形成包含纤维的基材；提供包含第一增强剂的第一添加剂悬浮体,其中第一增强剂为微原纤化纤维素；提供包含至少一种留着剂和/或至少一种排水剂的第二添加剂悬浮体；使在所述多孔介质上的所述基材脱水；在所述多孔介质上的所述基材的所述脱水期间向所述基材进行添加剂添加,其中当基材的干含量小于20重量％、优选小于10重量％、最优选小于7重量％时,进行添加剂添加,并且其中添加剂添加包括利用多层帘式涂覆向所述基材添加至少所述第一添加剂悬浮体的层和所述第二添加剂悬浮体的层,以及在所述多孔介质上进行所述脱水之后进一步脱水和干燥所述基材以提供所述第一片层。本发明还涉及能够通过该方法获得的纸、板或非织造的产品。(The present invention relates to a process for producing a product comprising a first sheet layer, the process comprising the steps of: providing a fiber suspension comprising fibers; providing the fiber suspension to a porous media to form a substrate comprising fibers; providing a first additive suspension comprising a first reinforcing agent, wherein the first reinforcing agent is microfibrillated cellulose; providing a second additive suspension comprising at least one retention agent and/or at least one drainage agent; dehydrating the substrate on the porous medium; performing additive addition to said substrate during said dewatering of said substrate on said porous media, wherein additive addition is performed when the dry content of substrate is less than 20 wt%, preferably less than 10 wt%, most preferably less than 7 wt%, and wherein additive addition comprises adding at least a layer of said first additive suspension and a layer of said second additive suspension to said substrate using multi-layer curtain coating, and further dewatering and drying said substrate after said dewatering is performed on said porous media to provide said first sheet layer. The invention also relates to a paper, board or nonwoven product obtainable by the method.)

1. A method of producing a product comprising a first sheet layer, the method comprising the steps of:

-providing a fiber suspension comprising fibers;

-providing the fibrous suspension to a porous medium to form a substrate comprising fibers;

-providing a first additive suspension comprising a first reinforcing agent, wherein the first reinforcing agent is microfibrillated cellulose;

-providing a second additive suspension comprising at least one retention agent and/or at least one drainage agent;

-dewatering the substrate on the porous medium;

-performing additive addition to the substrate during the dewatering of the substrate on the porous medium, wherein additive addition is performed when the dry content of the substrate is less than 20 wt. -%, preferably less than 10 wt. -%, most preferably less than 7 wt. -%, and wherein additive addition comprises adding at least a layer of the first additive suspension and a layer of the second additive suspension to the substrate with multi-layer curtain coating, and

-further dewatering and drying the substrate after the dewatering is performed on the porous medium to provide the first sheet.

2. The method of claim 1, wherein the layers added to the substrate using multi-layer curtain coating are added simultaneously.

3. The method of claim 1, wherein the layers added to the substrate using multi-layer curtain coating are added non-simultaneously.

4. The method according to any one of claims 1-3, wherein the first additive suspension comprises at least one additional component selected from the group consisting of: retention agents, drainage agents, fillers, debonders, defoamers, colorants, optical agents, internal sizing agents, fixatives, and reinforcing agents.

5. The method according to any one of the preceding claims, wherein the first additive suspension comprises at least one second enhancing agent selected from the group consisting of: starch, such as starch granules, granules or dissolved starch, synthetic binders, such as latex, modified biopolymers, such as modified starch, proteins, and other natural polysaccharides, such as sodium carboxymethylcellulose, guar gum, hemicellulose or lignin.

6. The method according to any one of the preceding claims, wherein the second additive suspension comprises at least one additional component selected from the group consisting of: reinforcing agents, fillers, debonders, defoamers, colorants, optical agents, internal sizing agents, and fixatives.

7. The method of claim 6, wherein the second additive suspension comprises at least one enhancing agent selected from the group consisting of: microfibrillated cellulose, starch, such as starch granules, pellets or dissolved starch, synthetic binders, such as latex, modified biopolymers, such as modified starch, proteins, and other natural polysaccharides, such as sodium carboxymethylcellulose, guar gum, hemicellulose or lignin.

8. The method according to any preceding claims, wherein the total amount of microfibrillated cellulose added to the substrate by the additive addition is 0.1-30kg on a dry basis per ton of the provided first ply.

9. The method of any preceding claim, wherein the total amount of retention and/or drainage agent added to the substrate by the additive addition is from 10g to 5kg on a dry basis per ton of the provided first sheet layer.

10. The method of any one of the preceding claims, wherein at least one retention agent in the second additive suspension comprises nanoparticles or microparticles.

11. The method of any one of the preceding claims, wherein the second additive suspension comprises at least two retention agents, wherein one of the at least two retention agents comprises microparticles or nanoparticles and one of the at least two retention agents comprises a cationic, anionic or amphoteric polymer.

12. The method of claim 10 or 11, wherein the microparticles or nanoparticles are cationic or anionic at neutral, acidic or basic pH.

13. The method according to any one of claims 10-12, wherein the micro-or nanoparticles comprise silica, such as colloidal silica, micro-or sol-silica, or bentonite, such as micro-or nano-bentonite, or clay particles.

14. The method according to any of the preceding claims, wherein the fibers of the fiber suspension comprise cellulose fibers, preferably cellulose fibers from the group consisting of: chemical pulp, chemical thermomechanical pulp (CTMP), thermomechanical pulp (TMP), mechanical pulp, nanopaste or recycled pulp or mixtures thereof.

15. The process according to claim 14, wherein the cellulose fibres have a Schopper Riegler value of from 12 to 50 °, preferably from 15 to 30 °.

16. A method according to any of claims 1-13, wherein the fibres in the suspension are fibres made from regenerated cellulose and/or synthetic fibres such as polymer fibres.

17. The method according to any one of the preceding claims, wherein the fiber suspension further comprises microfibrillated cellulose.

18. The method according to any one of claims 1-15 or 17, wherein the product is a multi-ply paper or board product and wherein the method further comprises the step of attaching said provided first ply to at least a second ply.

19. Product obtainable by the process according to any one of claims 1-15, 17-18, wherein the product is a paper or board product.

20. Product obtainable by the process according to any one of claims 1-17, wherein the product is a non-woven product.

Technical Field

The present invention relates to a method of producing a product comprising a first sheet layer, wherein microfibrillated cellulose (MFC) is used as an additive to improve at least the strength properties of the first sheet layer. Furthermore, the invention relates to a paper, board or nonwoven product obtainable by the method.

Background

It is known to use different chemicals or reagents as additives in the production of paper and board products to provide paper and board products with desired properties, functions or to improve the runnability of the production and process. One additive that has attracted increasing attention in recent years is microfibrillated cellulose (MFC).

The use of MFC as a surface sizing agent or surface coating chemical has previously been described, for example to improve barrier properties, enhance printability or to improve adhesion between different layers of paper or board products. The characteristic particle shape and size distribution of MFC can give MFC a strong tendency to remain on or near the surface. However, since MFC has a high water binding capacity, gelling behaviour, and due to immobilization at the surface of the layer, MFC located at the surface may have a surface densification or blocking effect, negatively affecting the dewatering.

The use of MFC as a wet end additive has also been described previously for the purpose of acting as a performance or process chemical in the production of paper and board products. For example, it has been described to add MFC to the stock (stock) in the production of paper and board products to provide strength properties, to provide bending stiffness, to provide creep resistance, to provide retention of materials and chemicals used during production and to reduce the porosity of the formed paper or board product.

The unique property of using MFC as a wet-end additive to provide i.a. strength properties is based on the fact that MFC has a high surface area (i.e. preferably in wet, unconsolidated (compacted) or non-cornified form) and a large number of available sites to promote, for example, hydrogen bonding between materials such as fibres, fines, fillers, plastics or water soluble polymers such as starch.

However, MFC tends to self-associate (self-associate) or recombine (re-organize), thereby requiring efficient mixing devices when feeding MFC into a feedstock as a wet end additive. Furthermore, for many feedstock compositions, after providing a feedstock comprising MFC to a porous medium for dewatering, retention of the MFC itself has been shown to be poor and limited. This in turn suggests that the improvement of desired properties, such as improved mechanical properties, provided by using MFC as an additive included in the feedstock, is also poor or limited. In addition, poor or limited retention of MFC has negative effects, such as changing chemical retention and/or material retention.

AU2016203734 describes that nanoparticles, which may include MFC, can be incorporated into a paper sheet by adding the nanoparticles to a pulp slurry fed to the headbox of a paper machine, thereby distributing the nanoparticles throughout the ply (ply) of the headbox, either by spraying the nanoparticles onto the face of one or more plies on a wire at the wet end of the paper machine and applying another ply thereon, or by applying the nanoparticles to the plies after they have been bonded together (e.g. in a size press or by a metering press roll).

However, there is still room for improvement of the method of producing a product, such as a paper, board or nonwoven product comprising a first sheet, which method involves the use of MFC as an additive for improving at least the strength properties of the first sheet and the product provided thereby.

Disclosure of Invention

It is an object of the present disclosure to provide an improved method of producing a product comprising a first sheet, such as for example a paper, board or non-woven product, which method involves the use of MFC as an additive for improving at least the strength properties of the first sheet and the product provided thereby, and which method obviates or mitigates at least some of the disadvantages of prior art methods.

As a first aspect of the present disclosure, there is provided a process for producing a product comprising a first sheet layer, the process comprising the steps of:

-providing a fiber suspension comprising fibers;

-providing the fibrous suspension to a porous medium to form a substrate comprising fibers;

-providing a first additive suspension comprising a first reinforcing agent, wherein the first reinforcing agent is microfibrillated cellulose;

-providing a second additive suspension comprising at least one retention agent and/or at least one drainage agent;

-dewatering the substrate on the porous medium;

-performing additive addition to the substrate during the dewatering of the substrate on the porous medium, wherein additive addition is performed when the dry content of the substrate is less than 20 wt. -%, preferably less than 10 wt. -%, most preferably less than 7 wt. -%, and wherein additive addition comprises adding at least a layer of the first additive suspension and a layer of the second additive suspension to the substrate with multi-layer curtain coating, and

-further dewatering and drying the substrate after the dewatering is performed on the porous medium to provide the first sheet.

It has surprisingly been found that the retention of MFC in a wet substrate is improved by adding MFC to the wet substrate at a location (position) where the wet substrate has a low dry content, i.e. a dry content of less than 20 wt%, during dewatering on a porous medium during production of the first sheet according to the method of the first aspect, when compared to the situation where MFC is added as an additive of the raw material. As the retention of MFC in the wet substrate is improved, the strength enhancing effect of MFC is also improved. Thus, the addition of MFC to a wet substrate according to the method of the first aspect is advantageous for the strength enhancing effect of MFC.

Further, the retention of MFC in the wet substrate is further improved by additionally adding at least one retention agent and/or at least one drainage agent to the wet substrate at locations where the wet substrate has a low dry content, i.e. a dry content of less than 20 wt%, during dewatering on the porous medium during production of the first sheet according to the method of the first aspect.

As mentioned above, MFC has a high water binding capacity. However, the additional addition of at least one retention agent and/or at least one drainage agent also implies that the dewatering is also improved.

Furthermore, by adding MFC to the wet substrate at a location where the wet substrate has a low dry content during dewatering on the porous medium during production of the first sheet layer according to the method of the first aspect, the penetration/penetration of MFC and retention/drainage agent into the wet substrate is improved compared to the case where MFC and retention/drainage agent are added at a location where the wet substrate has a high dry content, e.g. above 20 wt%.

The improved penetration/penetration of the MFC and the retention/drainage agent into the wet substrate implies that the distribution of the MFC and retention/drainage agent in the z-direction of the wet substrate is improved. A good distribution of MFC and retention/drainage agent in the z-direction of the wet substrate is advantageous for the strength enhancing effect of MFC.

Also, if MFC addition to the substrate is to be applied when the substrate has a high dry content, e.g. above 20 wt.%, the dehydrating properties may be negatively affected, i.e. the densification or blocking effect of the MFC, due to the high water binding capacity of MFC.

It has also surprisingly been found that the strength enhancing effect of MFC is further improved by adding MFC (i.e. a first additive suspension comprising MFC) to a wet substrate in one layer and at least one retention agent and/or at least one drainage agent (i.e. a second additive suspension comprising at least one retention agent and/or at least one drainage agent) to a wet substrate in another layer using the multi-layer curtain coating technique according to the method of the first aspect at locations where the wet substrate has a low dry content. By using the method according to the first aspect for multilayer curtain coating the layers for adding the first and second additive suspensions at locations where the wet substrate has a low dry content, the penetration/penetration of the MFC and the retention/drainage agent into the wet substrate is facilitated/improved. This is due to the fact that the multilayer curtain coating enables simultaneous metering or non-simultaneous metering of two or more chemical layers (preferably of low consistency) on the web by curtain coating. Low consistency and curtain application provide further improved penetration, especially in cases where dewatering occurs and continues on the wire (wet end).

Also, the method of the first aspect is advantageous in that it is associated with the possibility of influencing/controlling/adjusting the dewatering properties. This is due to the fact that the addition of MFC in one layer and the addition of at least one retention agent and/or at least one drainage agent in one layer with a multi-layer curtain coating implies the possibility to influence/control/adjust the amount of MFC added to the wet substrate and the amount and type of retention/drainage chemicals and thus the dewatering. This in turn means that there is a possibility to influence/control/adjust the strength enhancing effect of the MFC. Thus, by means of the method of the first aspect, products, such as paper, board or non-woven products, having an improved or tailored structure may be produced, in order to optimize the bending stiffness, the modulus of elasticity, the dimensional stability (e.g. curl), the moldability, the crease properties, the compression strength of the product.

Further, the method of the first aspect is advantageous in that the need for efficient mixing means, which may be necessary when dosing MFC as an additive to a feedstock, can be reduced or eliminated.

The process of the first aspect may be a process for producing a paper, board or nonwoven product comprising a first sheet layer.

The method of the first aspect may be carried out in a papermaking machine. The paper machine that can be used in the method of the first aspect may be any conventional type of paper machine for producing paper, board, tissue, nonwoven or similar products known to the person skilled in the art, but which has been equipped with equipment for performing additive addition (i.e. equipment comprising means for performing multi-layer curtain coating).

As used herein, the term "board" refers not only to board, but also to cardboard, chipboard and paperboard, respectively.

As used herein, the term "sheet" means any or all of a topsheet, a middle sheet, or a backsheet or a multi-sheet structure (body). The sheet layer may thus be a single sheet layer or a multi-sheet substrate. The invention disclosed herein may be used with one sheet or several sheets.

In addition to the various end substrates described above, the sheet is preferably part of corrugated board, Liquid Packaging Board (LPB), Folding Box Board (FBB), multi-ply paper such as flexible paper products, multi-ply grease-proof paper, Solid Unbleached Board (SUB), Solid Bleached Board (SBB), white lined chipboard (WCB), and the like.

The provided fibrous suspension may comprise cellulosic fibres and the cellulosic fibres preferably have a Schopper Riegler value of from 12 to 50 °, preferably from 15 to 30 °. The fibrous suspension thus comprises cellulosic fibres suitable for use in the production of a ply of porous paper or board. The Schopper Riegler value can be determined by the standard method defined in EN ISO 5267-1.

The fibrous suspension may comprise one type of cellulose fiber. Alternatively, however, the fibrous suspension may comprise a mixture of different types of cellulose fibers. For example, the cellulosic fibers of the fibrous suspension may comprise fibers from unbleached and/or bleached pulp. Unbleached and bleached pulps may be chemical pulps such as kraft, soda, sulfate or sulfite, mechanical, Chemithermomechanical (CTMP), Thermomechanical (TMP), nano-or regenerated pulps or mixtures thereof. The raw material may be based on softwood, hardwood, recycled fibre or non-wood based pulp suitable for use in papermaking or board making.

In addition to the fibers, the fiber suspension may also contain one or more other process or functional additives, for example additives selected from the group consisting of: fillers, pigments, dry and wet strength agents, retention agents, crosslinking agents, softeners or plasticizers, adhesion primers, fixatives, debonders (debonders), wetting agents, optical dyes/agents, optical brighteners, defoamers, and hydrophobicizing agents such as AKD, ASA, waxes, resins, and the like.

The fibrous suspension may comprise fibers made from regenerated cellulose, for example viscose or lyocell fibers and/or synthetic fibers such as polymer fibers. The polymer fibers are preferably fibers from polyolefins or polyesters such as polyethylene terephthalate.

In one embodiment, the fiber suspension further comprises microfibrillated cellulose.

The porous medium to which the fibrous suspension is provided may for example be a wire mesh or a membrane.

By "substrate comprising fibers" is meant herein a base web or sheet comprising fibers, such as cellulose or synthetic fibers.

The term "dewatering" as used herein encompasses any form of dewatering including, for example, evaporation, pressure dewatering, dewatering using radiation, ultrasound, vacuum or suction boxes, and the like. The dehydration may be carried out in one or more steps and may involve one form of dehydration or a combination of forms of dehydration.

In embodiments that include the use of a porous wire, dewatering on the porous wire may be performed using known techniques with single or double wire systems, frictionless dewatering, membrane assisted dewatering, vacuum or ultrasound assisted dewatering, or the like. Further, after the wire section, the substrate in these embodiments is further dewatered and dried, such as by mechanical dewatering, hot air, radiation drying, convection drying, and the like. "mechanical dewatering" means dewatering by mechanical force, for example by mechanical pressing (compression) including a shoe press.

In the context of the present disclosure, microfibrillated cellulose (MFC) shall mean cellulose particle fibres or fibrils of nanometer scale having at least one dimension smaller than 100 nm. MFC comprises partially or fully fibrillated cellulose or lignocellulose fibers. The diameter of the released fibrils is less than 100nm, while the actual fibril diameter or particle size distribution and/or aspect ratio (length/width) depends on the source and manufacturing method.

The smallest fibrils are called base fibrils (primary fibrils) and have a diameter of about 2-4nm (see, e.g., Chinga-Carrasco, G., Cellulose fibers, nanofibers and microfibers: the morphology sequence of MFC components from a plant physiology and fiber technology point of view, Nanoscale research letters 2011,6:417), whereas it is common to have base fibrils in aggregated form (which are also defined as microfibrils) (Fengel, D., Ultratual fibers of cell research polysaccharides, Tappi J., Mar1970, Vol 53, No.3.) be the main product obtained when manufacturing MFCs, e.g., by using an extended process or a pressure drop decomposition process. The length of the fibrils may vary from about 1 to greater than 10 microns depending on the source and method of manufacture. The coarse MFC grade may contain a substantial part of fibrillated fibres, i.e. protruding fibrils from the tracheids (cellulose fibres), and a certain amount of fibrils released from the tracheids (cellulose fibres).

MFC has different acronyms, such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose, fibril aggregates, nano-sized cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, microfibrillar cellulose, microfibrillar aggregates and cellulose microfibril aggregates. MFC may also be characterized by various physical or physicochemical properties, such as a large surface area or its ability to form a gel-like material at low solids (1-5 wt%) when dispersed in water. The cellulose fibres are preferably fibrillated to such an extent that the resulting specific surface area of the MFC formed is from about 1 to about 300m²G, e.g. 1 to 200m²In g, or more preferably in the range from 50 to 200m²The freeze-dried material was measured by the BET method.

There are various methods of manufacturing MFC, such as single or multiple refining, prehydrolysis followed by refining or high shear disintegration or fibril release. One or several pre-treatment steps are usually required to make MFC manufacture both energy efficient and sustainable. Thus, the cellulose fibers of the pulp to be supplied may be subjected to enzymatic or chemical pretreatment, for example to reduce the amount of hemicellulose or lignin. The cellulose fibers may be chemically modified prior to fibrillation, wherein the cellulose molecules contain functional groups other than (or more than) those found in the original cellulose. These groups include, in particular, Carboxymethyl (CM), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl-mediated oxidation, for example "TEMPO"), or quaternary ammonium (cationic cellulose). After modification or oxidation in one of the above methods, the fiber is more easily broken down into MFC or nano-fibril sized fibrils.

The nanofibrillar cellulose may contain some hemicellulose; the amount depends on the plant source and the cooking process of the pulp. The mechanical disintegration of the pretreated fibers, for example hydrolyzed, preswollen or oxidized cellulose raw materials, is carried out using suitable equipment, for example refiners, grinders, homogenizers, colloid discharge devices (colloiders), friction grinders, ultrasonic sonicators, fluidizers, such as microfluidizers, macrofluidizers or fluidizer-type homogenizers. Depending on the MFC manufacturing process, the product may also contain fine particles or nanocrystalline cellulose or other chemicals present e.g. in wood fibre or paper making processes. The product may also contain various amounts of micron-sized fiber particles that are not effectively fibrillated.

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

The above definition of MFC includes, but is not limited to, the newly proposed TAPPI standard W13021 on cellulose nanofibrils (CMF), which defines a cellulose nanofibril material containing a plurality of base fibrils, which have both crystalline and amorphous regions.

According to the above, the first additive suspension comprises MFC. However, in an embodiment of the process of the first aspect, the first additive suspension comprises, in addition to MFC, at least one further component selected from: retention agents, drainage agents, fillers, debonders, defoamers, colorants, optical agents, internal sizing agents, fixatives, and reinforcing agents.

In an embodiment of the process of the first aspect, the first additive suspension comprises, in addition to MFC, at least one second enhancing agent selected from the group consisting of: starch, such as starch granules, granules or dissolved starch, synthetic binders, such as latex, modified biopolymers, such as modified starch, proteins, and other natural polysaccharides, such as sodium carboxymethylcellulose, guar gum, hemicellulose or lignin. The second reinforcing agent may act as a co- (co) reinforcing agent together with the first reinforcing agent, i.e. the microfibrillated cellulose. In an embodiment of the process of the first aspect, the first additive suspension comprises starch, such as starch granules, pellets or dissolved starch, in addition to MFC.

According to the above, the second additive suspension comprises at least one retention agent and/or at least one drainage agent. The at least one retention agent may for example be selected from nano-or micro-particles such as nano-silica or colloidal anionic or cationic silica, bentonite, nanoclay, nanocellulose, and/or polymers, preferably PAM, CPAM, APAM, PDADMAC, PVAm, cationic or anionic starch, polyethyleneimine, poly (poly) amine amide, polyethylene oxide, phenolic (phenolic) resins, and the like. It is generally preferred that the retention agent comprises two or three different components, such as a two-component retention system. The retention system may also comprise one or more microparticles and one or two retention polymers. The at least one drainage agent may, for example, be selected from polyethyleneimine, PAC, alum, and other low molecular weight charged polymers. Drainage can be optimized by using a variety of microparticles and polymers, as known to those skilled in the art, but performance is typically dependent on pulp type, machine speed, conductivity, dewatering section, pH, load (charge) and/or cationic demand, white water consistency, temperature, and other chemicals or additives.

In an embodiment of the method of the first aspect, the at least one retention agent in the second additive suspension comprises nanoparticles or microparticles.

In an embodiment of the method of the first aspect, the second additive suspension comprises at least two retention agents, wherein one of the at least two retention agents comprises micro-or nanoparticles and one of the at least two retention agents comprises a cationic, anionic or amphoteric polymer.

The microparticles or nanoparticles in the second additive suspension may be cationic or anionic microparticles or nanoparticles at neutral, acidic or basic pH.

The micro-or nanoparticles in the second additive suspension may comprise silica such as colloidal silica, micro-or sol-silica, or bentonite such as micro-or nano-bentonite, or clay particles.

In an embodiment of the process of the first aspect, the second additive suspension comprises, in addition to the at least one retention agent and/or the at least one drainage agent, at least one further component selected from: reinforcing agents, fillers, debonders, defoamers, colorants, optical agents, internal sizing agents, and fixatives.

In an embodiment of the process of the first aspect, the second additive suspension comprises, in addition to the at least one retention agent and/or the at least one drainage agent, at least one reinforcing agent selected from: microfibrillated cellulose, starch, such as starch granules, pellets or dissolved starch, synthetic binders, such as latex, modified biopolymers, such as modified starch, proteins, and other natural polysaccharides, such as sodium carboxymethylcellulose, guar gum, hemicellulose or lignin.

The term "multilayer curtain coating" means herein that two or more coating layers are added to a substrate using any suitable curtain coating apparatus/device, such as a slot die, a slip die, a drop die or similar metered addition system based on one or more slots.

In an embodiment of the method of the first aspect, the layers added to the substrate by means of multilayer curtain coating are added simultaneously, i.e. two or more coating layers added by means of multilayer curtain coating are added simultaneously to the substrate in one curtain coating station by means of any suitable curtain coating apparatus/device (e.g. multilayer curtain coater) at the same or substantially the same dry content of the substrate. Thus, coatings that are simultaneously added to a substrate using multilayer curtain coating are added on top of each other at the location of addition to the substrate.

In an embodiment of the method of the first aspect, the layers added to the substrate by means of multilayer curtain coating are added non-simultaneously, i.e. the two or more coating layers added by means of multilayer curtain coating are added to the substrate by means of any suitable curtain coating apparatus/device (which may be located in a single separate curtain coating station for each layer) rather than simultaneously.

The position of the layer added to the substrate may vary. On the substrate, the first additive suspension preferably forms a first layer and the second additive suspension preferably forms a second layer. The first layer may be located between the substrate and the second layer. The second layer may also be positioned between the substrate and the first layer.

In an embodiment of the method of the first aspect, three or more layers are added to the substrate using multi-layer curtain coating and the layers are added using a combination of simultaneous and non-simultaneous additions.

For example, with multilayer curtain coating, two or more layers may be added to the substrate at the same time and one or more additional layers may be added to the substrate non-simultaneously with the two or more layers mentioned with multilayer curtain coating. The two or more simultaneously added layers may be added in one curtain coating station and one or more further layers may be added in a single separate curtain coating station for each layer.

As another example, two or more layers of the first set of layers can be added to the substrate simultaneously with the multilayer curtain coating and two or more layers of the second set of layers can be added to the substrate simultaneously (but not simultaneously with the layers of the first set) with the multilayer curtain coating.

The layers applied to the substrate by multilayer curtain coating, rather than being added simultaneously, may be added in any suitable order. For example, when the substrate has a first dry content, a layer of the first additive suspension may be added to the substrate and when the substrate has a second dry content, a layer of the second additive suspension may be added to the substrate, wherein the first dry content is lower than the second dry content, or vice versa.

When comparing the widths of any two layers of layers added using multi-layer curtain coating, the widths of the two layers compared may be the same or different.

In accordance with the above, the multi-layer curtain coating is performed during a dewatering step of the substrate on the porous medium, wherein the dry content of the substrate at (the point of coating with) the multi-layer coating apparatus (i.e. additive addition) is less than 20 wt. -%, preferably less than 10 wt. -%, most preferably less than 7 wt. -%. Thus, all layers added using multilayer curtain coating are added when the substrate has a specified dry content during dewatering on the porous media.

Thus, in embodiments where two or more coating layers are added simultaneously to the substrate by multilayer curtain coating, the curtain coating apparatus is positioned such that the two or more coating layers are added simultaneously to the substrate at a location having a specified dry content during dewatering of the substrate on the porous media. In embodiments where the coatings are added to the substrate non-simultaneously by multilayer curtain coating, the curtain coating apparatus is positioned such that each of the two or more coatings is added to the substrate at a location having a specified dry content during dewatering of the substrate on the porous medium.

In one embodiment, when additive addition is performed (i.e., when coating with a multilayer coating apparatus (at)), the dry content of the substrate is less than 20 wt.%, such as greater than 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, or 2 wt.% but less than 20 wt.%. In one embodiment, the dry content of the substrate is less than 10 wt%, such as more than 0.5 wt%, 1.0 wt%, 1.5 wt% or 2 wt% but less than 10 wt% when (where) coated with the multilayer coating apparatus. In one embodiment, the dry content of the substrate is less than 7 wt%, such as more than 0.5 wt%, 1.0 wt%, 1.5 wt% or 2 wt% but less than 7 wt% when (where) coated with the multilayer coating apparatus. In one embodiment, the dry content of the substrate is less than 5 wt%, such as more than 0.5 wt%, 1.0 wt%, 1.5 wt% or 2 wt% but less than 5 wt% when (where) coated with the multilayer coating apparatus.

"dry content" means the content of dry matter in a slurry, suspension or solution. That is to say, for example, a dry content of 50% means that the weight of dry matter is 50% based on the total weight of the solution, suspension or slurry. Similarly, "dry weight" means the weight of dry matter.

In accordance with the above, the method of the first aspect may comprise adding a layer of the first additive suspension and a layer of the second additive suspension using multi-layer curtain coating. Alternatively, however, the method of the first aspect may comprise adding more than one layer of the first additive suspension and/or more than one layer of the second additive suspension.

In an embodiment of the method of the first aspect, the method further comprises adding one or more additional additive suspensions to the substrate (i.e. in addition to the layers of the first and second additive suspension layers) using the multi-layer curtain coating. The one or more additional additive suspensions may comprise at least one component selected from the group consisting of: reinforcing agents, retention agents, drainage agents, fillers, debonders, defoamers, colorants, optical agents, internal sizing agents, and fixing agents. Thus, one or more enhancing agents may be included in one or more additional additive suspensions. The one or more enhancing agents in the additional additive suspension may be selected from: microfibrillated cellulose, starch, such as starch granules, pellets or dissolved starch, synthetic binders, such as latex, modified biopolymers, such as modified starch, proteins, and other natural polysaccharides, such as sodium carboxymethylcellulose, guar gum, hemicellulose or lignin.

In an embodiment of the method of the first aspect, the total amount of microfibrillated cellulose added to the substrate by additive addition is 0.1-30kg on a dry basis per tonne of said provided first ply.

In an embodiment of the method of the first aspect, the total amount of retention and/or drainage agent added to the substrate by additive addition is from 10g to 5kg on a dry basis per tonne of said provided first sheet layer.

According to the above, after dewatering on the porous medium, the substrate is further dewatered and dried to provide the first sheet layer. Further dewatering and drying is carried out by any suitable means after the section of porous media (which may be a wire section according to above).

The product produced by the method of the present disclosure may be a paper or board product, which may be a single ply paper or board product or a multi ply paper or board product.

The basis weight of the paper or board product produced by the process of the present disclosure may be from 20 to 600g/m²Or more preferably 30 to 500g/m². The first sheet may have a basis weight of 20 to 200g/m²Or more preferably 30 to 150g/m²。

In an embodiment of the method of the first aspect, the product produced is a multi-ply paper or board product, wherein the method further comprises the step of attaching said provided first ply to at least one additional ply. Each respective additional ply may be provided by the same method steps as the first ply, i.e., each respective additional ply may be similar to the first ply or may be different.

The present disclosure also relates to a paper or board product obtainable according to the method of the present disclosure.

The present disclosure also relates to nonwoven products obtainable according to the process of the present disclosure.

Other modifications and variations will become apparent to those skilled in the art in view of the foregoing detailed description of the invention. However, it should be apparent that such other modifications and variations can be made without departing from the spirit and scope of the invention as defined in the appended claims.