Recyclable bonded air-laid blanks

Abstract

A method of producing a bonded air-laid blank (10) comprises defibrating pulp into a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight. The partly defibrated cellulose and / or lignocellulose fiber material and a polymer binder are introduced into a forming head (110) and captured as an unbonded air-laid web (20) on a conveyor (120) arranged in connection 5 with an outlet (113) of the forming head (110). The unbonded air-laid web (20) is heated to at least partly melt the polymer binder and bind the partly defibrated cellulose and / or lignocellulose fiber material to form a bonded air-laid blank (10) comprising less than 10 % by weight of the polymer binder and at least 80 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material. The produced bonded air-laid blank (10) can more easily be recycled due to the low polymer binder content and further 0 has low linting.

Description

[0001] RECYCLABLE BONDED AIR-LAID BLANKS

[0002] TECHNICAL FIELD

[0003] The present invention generally relates to bonded air-laid blanks, and to recyclable bonded air-laid blanks and to a method for producing such bonded air-laid blanks.

[0004] BACKGROUND

[0005] With growing awareness for the environment and humanly induced climate change, the use of plastic insulation and / or cushioning products has come more and more into question. However, despite this concern the use of these products has grown vastly with new trends in lifestyles and consumer habits of the last decade. One reason for this is that more and more goods are transported around the globe and these goods need protection against impact or shock and / or extreme temperatures. A common way of protecting the goods is to include cushioning and / or insulating products, such as inserts of suitable form into the packaging. These can be made from different materials but are typically made from a foamed polymer, of which expanded polystyrene (EPS) is by far cheapest and most common. In some cases, the entire packaging can be made out of EPS. EPS is, however, one of the most questioned plastic materials and many brand owners are looking for more sustainable solutions for these packaging applications.

[0006] There is therefore a need for alternative materials that could replace the plastic insulation and / or cushioning products. A bonded air-laid blank, sometimes also referred to as bonded dry-laid blank, dry- formed blank, air-laid batt, dry-laid batt, air-laid mat, or dry-laid mat, is formed by a process known as airlaying, in which cellulose and / or lignocellulose fibers and a polymer binder are mixed with air to form a porous fiber mixture deposited onto a support and consolidated or bonded by heating. During the heating the cellulose and / or lignocellulose fibers are bonded by the polymer binder. The bonded air-laid blank is characterized by being porous, having the character of an open cell foam. Bonded air-laid blanks are produced in a so-called dry forming method, i.e., generally without addition of water. The air-laying process is described in, for instance, U.S. patent no. 6,233,787. The characteristics of bonded air-laid blanks make them suitable for the production of insulation and / or cushioning products.

[0007] Commonly, defibrated paper and / or pulp material is used as a source for the cellulose and / or lignocellulose fibers in the air-laying process. These materials, however, demand a comparatively high ratio of polymer binder to keep the cellulose and / or lignocellulose fibers together in the bonded air-laid blank. The high amount of polymer binder in the bonded air-laid blank may make recycling of the products produced from the bonded air-laid blank difficult. There is therefore a need for bonded air-laid blanks that can be more easily recycled.

[0008] US 11 ,834,785 B2 discloses a method of transforming a pulp fibrous into a pre-dispersed semi-dry or dry fibrous material. The method opens, de-entangles and fibrillates the fibrous material of the input pulp. The method mixes the input fibrous with chemicals while evaporating moisture in a mechanical disc refiner process. The refiner operates to set three process variables: 1) applied refining specific energy; 2) refiner gap opening and 3) refiner output consistency. Depending on the feed pulp type and consistency, the refiner's output is a pre-dispersed semi-dry fibrous material of 30 to 99% solids with 70 to 100% of separated fibers that depending on chemical treatment are loosely entangled fibrous that disperse in water using common techniques. The pre-dispersed semi-dry output is further processed inline or by batch process air agitation at velocities sufficient to further separate fibers and loosen fibrous entanglements.

[0009] SUMMARY

[0010] It is a general objective to provide recyclable bonded air-laid blanks.

[0011] It is another general objective to provide non- or low-linting bonded air-laid blanks.

[0012] These and other objectives are met by embodiments disclosed herein.

[0013] The present invention is defined in the independent claims. Further embodiments of the invention are defined in the dependent claims.

[0014] An aspect of the invention relates to a method of producing a bonded air-laid blank. The method comprises defibrating pulp into a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight. The method also comprises introducing the partly defibrated cellulose and / or lignocellulose fiber material and a polymer binder into a forming head and capturing the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder as an unbonded air-laid web on a conveyor arranged in connection with an outlet of the forming head. The method further comprises heating the unbonded air-laid web to at least partly melt the polymer binder and bind the partly defibrated cellulose and / or lignocellulose fiber material to form a bonded air-laid blank comprising less than 10 % by weight of the polymer binder and at least 80 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material. Another aspect of the invention relates to a bonded air-laid blank comprising at least 80 % by weight of a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight, and less than 10 % by weight of a polymer binder binding together the partly defibrated cellulose and / or lignocellulose fiber material.

[0015] The present invention produces bonded air-laid blanks with a comparatively low amount of polymer binder by using a cellulose and / or lignocellulose fiber material that is merely partly defibrated and thereby comprises a significant amount of knots, i.e., cellulose and / or lignocellulose fiber aggregates. These aggregates thereby maintain the cellulose and / or lignocellulose fibers within the bonded air-laid blank even with a low amount of polymer binder. This means that the bonded air-laid blank and products produced therefrom can be more easily recycled, such as in paper recycling streams, due to the low content of polymer binder. Another advantage of using the partly defibrated cellulose and / or lignocellulose fiber material in the air-laying process is that the partly defibrated cellulose and / or lignocellulose fiber material comprises less non-fibrous cellulose and / or lignocellulose particles, or fines, that otherwise may cause linting or dusting during production and handling of the bonded air-laid blank, and products produced therefrom.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The embodiments, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:

[0018] Fig. 1 is a perspective view of a bonded air-laid blank according to an embodiment;

[0019] Fig. 2 is a flow chart illustrating a method of producing an air-laid blank according to an embodiment;

[0020] Fig. 3 is a flow chart illustrating additional, optional steps of the method in Fig. 2 according to various embodiments;

[0021] Fig. 4 is a flow chart illustrating an additional, optional step of the method in Fig. 2 according to an embodiment;

[0022] Fig. 5 is a schematic illustration of a system for producing an air-laid blank according to various embodiments; Fig. 6 illustrates knots remaining after air-jet sieving (6A) disc milled Stora Enso Nova (disc milled unbleached Kraft pulp (UKP) from Enocell, Stora Enso and (6B) disc milled Supreme (disc milled UKP) from Varkaus, Stora Enso;

[0023] Fig. 7 illustrates the measuring apparatus used in Example 2;

[0024] Fig. 8 illustrates (8A) knots remaining and (8B) fibers after sieving disc milled Stora Enso Nova using the SGS analysis operating protocol; and

[0025] Fig. 9 illustrates (9A) knots remaining and (9B) fibers after sieving disc milled Supreme using the SGS analysis operating protocol.

[0026] DETAILED DESCRIPTION

[0027] The present invention generally relates to bonded air-laid blanks, and to recyclable bonded air-laid blanks and to a method for producing such bonded air-laid blanks.

[0028] Bonded air-laid blanks are characterized by being porous, having the character of an open cell foam. They are resilient and have great damping and insulation capacity. These characteristics of bonded airlaid blanks make the material suitable to replace polymer foams and formed in-place fossil-based materials in packaging solutions. A common way of protecting the goods is to include cushioning or insulation elements or products, such as inserts of suitable form into the packaging. These cushioning or insulation elements or products are typically made from a foamed petroleum-based polymer, of which expanded polystyrene (EPS) is by far cheapest and most common. EPS is, however, one of the most questioned plastic materials and many brand owners are looking for more sustainable solutions for these packaging applications. Bonded air-laid blanks are useful for production of more environmentally friendly replacements to corresponding cushioning inserts made of or from foamed polymers, for instance EPS or foamed polyurethane (PU). Bonded air-laid blanks also find uses where there is a need for providing insulation, such as thermal or sound insulation. Illustrative, but non-limiting examples, of such applications include thermal insulation of heated or cold food products or other articles that need to be kept within defined temperature ranges. Furthermore, sound absorbing panels or elements could be produced from the bonded air-laid blanks. In the production of bonded air-laid blanks, non-bonded cellulose and / or lignocellulose fibers present on or in the bonded air-laid blanks or detached therefrom during production are perceived as lint or dust. This lint, to a major part, consists of cellulose and / or lignocellulose fibers, fiber fragments or smaller particles commonly referred to as "fines” in the art that have not been sufficiently bound by the polymer binder either on the surfaces or within the bonded air-laid blanks. The lint or dust may constitute aesthetic problems for products formed from the bonded air-laid blanks. Furthermore, in larger quantities, such dust can cause inconvenience and irritations for persons handling the bonded air-laid blanks during and following production. The lint or dust may also cause problems for electronics and electronic equipment if these are packaged using cushioning or insulation elements or inserts made by the bonded air-laid blanks. In such a case, non-bonded cellulose and / or lignocellulose fibers may cause short circuits if reaching the electronic circuitry within the electronics or electronic equipment. Such non-bonded cellulose and / or lignocellulose fibers might also be a risk during operation of the electronics or electronic equipment causing heat development that might ignite the non-bonded cellulose and / or lignocellulose fibers.

[0029] A solution to such a linting problem in the art has been to use a comparatively high amount of polymer binder to bind and thereby capture such fines in the bonded air-laid blank. However, if the amount of the polymer binder used to bind the cellulose and / or lignocellulose fibers is high then it is not straightforward to recycle the products produced from the bonded air-laid blanks. Thus, in order to promote repulpability of the bonded air-laid blanks and products produced therefrom in, for instance, board mills and thereby to increase the environmental friendliness of the bonded air-laid blanks and the products produced therefrom, then the linting tendency of the bonded air-laid blanks is generally increased significantly. In other words, there is a trade-off between recyclability and linting for the prior art bonded air-laid blanks.

[0030] The present invention has taken a radically different approach as compared to prior art bonded air-laid blanks and methods of producing such bonded air-laid blanks that reduces linting problem but without the need for high amounts of polymer binder. This is possible by merely partly defibrating pulp into partly defibrated cellulose and / or lignocellulose fiber material. This partly defibrated cellulose and / or lignocellulose fiber material thereby contain loose aggregates of cellulose and / or lignocellulose fiber, referred to as knots in the art, that have not been defibrated into free fibers. In clear contrast, the cellulose and / or lignocellulose fibers are held together by maintained hydrogen bonds between the fibers in the aggregates. One of the advantages of merely partly defibrating the pulp into the partly defibrated cellulose and / or lignocellulose fiber material is that hydrogen bonds between cellulose and / or lignocellulose fibers in the partly defibrated cellulose and / or lignocellulose fiber material are maintained after the defibration. This means that cellulose and / or lignocellulose fibers in bonded air-laid blanks produced from such partly defibrated cellulose and / or lignocellulose fiber material are bonded together not only by the polymer binder but also by hydrogen bonds in the cellulose and / or lignocellulose fiber aggregates. The bonded air-laid blanks of the invention thereby have less linting problems as compared to prior art bonded airlaid blanks and additionally require less polymer binder to keep the cellulose and / or lignocellulose fibers together in the bonded air-laid blanks as compared to prior art bonded air-laid blanks.

[0031] The approach taken by the present invention is fundamentally different from prior art air-laying methods. Generally, the cellulose and / or lignocellulose fiber material input into the forming head of an air-laying apparatus should be in the form of fluffed cellulose and / or lignocellulose fibers. In such prior art production, cellulose and / or lignocellulose fiber aggregates are regarded as an undesirable by-product after the defibration process. Accordingly, in the art the content of such cellulose and / or lignocellulose fiber aggregates are kept as low as possible and typically at most 5 % by weight. For instance, US, 11 ,834,785 B1 discloses that fluffed fibers may contain some levels of aggregates or knots of fibers. They are fiber clumps that remain as undesirable by-products after the defibration process. However, the fluffed fibers should be highly individualized and contain as little as possible of knots and fines.

[0032] This means that the prior art has not realized that it is possible to produce recyclable bonded air-laid blanks with low linting by using a partly defibrated cellulose and / or lignocellulose fiber material comprising a significant amount of such cellulose and / or lignocellulose fiber aggregates.

[0033] The present invention therefore relates to a method of producing a bonded air-laid blank 10, see Figs. 1 , 2, and 5. The method comprises defibrating, in step S1, pulp into a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight. The method also comprises introducing, in step S2, the partly defibrated cellulose and / or lignocellulose fiber material and a polymer binder into a forming head 110. The partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder are captured in step S3 as an unbonded air-laid web 20 on a conveyor 120 arranged in connection with an outlet 113 of the forming head 110. The method also comprises heating, in step S4, the unbonded air-laid web 20 to at least partly melt the polymer binder and bind the partly defibrated cellulose and / or lignocellulose fiber material to form a bonded air-laid blank 10 comprising less than 10 % by weight of the polymer binder and at least 80 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material.

[0034] The heating as applied in step S4 will partly melt the polymer binder to become tacky and adhere to the partly defibrated cellulose and / or lignocellulose fiber material in the unbonded air-laid web 20 to thereby form the bonded air-laid blank 10. Most of free cellulose and / or lignocellulose fibers and fines in the unbonded air-laid web 20 that are not already bonded or aggregated together in the knots will thereby be bonded together by the polymer binder forming the porous, open cell foam like structure of the bonded air-laid blank 10.

[0035] Partly defibrated cellulose and / or lignocellulose fiber material as used herein include a cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight. Accordingly, at least 20 % by weight of the cellulose and / or lignocellulose fiber material obtained by defibrating the pulp in step S1 is present in aggregates or knots. Figs. 6A, 6B, 8A and 9A are photographs showing such knots remaining on a sieve following sieving, whereas Figs. 8B and 9B illustrate "free” cellulose and / or lignocellulose fibers having passed through the sieve.

[0036] Generally, some cellulose and / or lignocellulose fibers will not be bonded by the polymer binder. Further, there is generally a distribution in the dimensions of the cellulose and / or lignocellulose fibers especially if the cellulose and / or lignocellulose fibers are produced by mechanical pulping processes or heavily defibrated to a high defibration degree. Some cellulose and / or lignocellulose fibers may be broken into smaller parts during the production of the bonded air-laid blank 10. Such shorter fibers or indeed fiber particles or debris, also referred to as fines in the art, may then, if not bonded by the polymer binder following step S4, escape through the fiber structure of the bonded air-laid blank 10. Additionally, cellulose and / or lignocellulose fibers may be at least partly bonded by the polymer binder, but the bond might be far from sufficient so that such cellulose and / or lignocellulose fibers become detached from the fiber structure of the bonded air-laid blank 10.

[0037] The present invention solves or at least reduces the above-mentioned problems by conducting a "mild” defibration of the pulp in step S1 to produce a partly defibrated cellulose and / or lignocellulose fiber material with a significant amount of knots, i.e., a knots content of at least 20 % by weight. This mild defibration means that the produced cellulose and / or lignocellulose fiber material contains a mixture of fully defibrated cellulose and / or lignocellulose fibers and non-defibrated cellulose and / or lignocellulose fibers, i.e., cellulose and / or lignocellulose fiber aggregates or knots, also referred to as nits, nodules, bundles, non-defibrated pulp in the art. These knots thereby maintain the cellulose and / or lignocellulose fibers together in aggregates, such as by maintaining hydrogen bonds between cellulose and / or lignocellulose fibers. This means that polymer binder can bind and thereby capture any loose cellulose and / or lignocellulose fibers and fines in the unbonded air-laid web 20. This means that the amount of loose fibers and fines in the bonded air-laid blank 10 is reduced, thereby resulting in less linting. Another advantage of the mild defibration of the pulp in step S1 is that the amount of fines produced in the defibration is comparatively lower when producing the partly defibrated cellulose and / or lignocellulose fiber material as compared to producing defibrated cellulose and / or lignocellulose fiber material with a much higher defibration degree. This is shown in Example 2 where the amount of fines in "fully” defibrated cellulose and / or lignocellulose fiber material obtained by heavily defibrating pulp (Comparative material 1-6) typically has twice as much fines as the partly defibrated cellulose and / or lignocellulose fiber material of the invention (Test material 1 and 2). Example 2 further shows that the "fully” defibrated cellulose and / or lignocellulose fiber material has a high fraction of "free” cellulose and / or lignocellulose fibers, typically 80-90 % by weight, and a low fraction of knots, typically less than 5 % by weight, whereas the partly defibrated cellulose and / or lignocellulose fiber material used in the invention has a significant amount of the cellulose and / or lignocellulose fiber material in the form of knots.

[0038] Fig. 1 schematically shows a bonded air-laid blank 10 produced by the method as shown in Fig. 2. As is shown in Fig. 1 , a bonded air-laid blank 10 is typically in the form of a sheet having a length L, a width W and a thickness T. Generally, lint and dust are present on and released from the surfaces 1 1, 12, 13, 14 of the bonded air-blank 10. Fig. 1 illustrates main surfaces 12, 14 of the bonded air-laid blank 10 that are the two surfaces defined by the length L and the width W. The main surfaces 12, 14 are substantially parallel with the upper surface of the conveyor 120 (Fig. 5) with one of the main surfaces 14 facing the conveyor 120 (Fig. 5) and being positioned thereon during production of the bonded air-laid blank 10 and with the other main surface 12 facing in a direction opposite to the conveyor 120 (Fig. 5). The main surfaces 12, 14 of the bonded air-laid blank 10 have a respective surface area that is typically substantially larger than the surface area of the longitudinal sides 11 or end sides 13 of the bonded airlaid blank 10.

[0039] In an embodiment, step S1 in Fig. 2 is performed as shown in Fig. 3. In an embodiment, step S1 comprises disc milling the pulp in step S11 into the partly defibrated cellulose and / or lignocellulose fiber material. The method then continues to step S2 in Fig. 2.

[0040] Disc milling is an illustrative, but preferred, embodiment of defibrating the pulp since such a disc milling maintains a high amount of hydrogen bonds between the cellulose and / or lignocellulose fibers during defibration and at the same time make the resulting partly defibrated cellulose and / or lignocellulose fiber material fluffy. Such disc milling thereby produces a low-density cellulose and / or lignocellulose fiber material that binds together in loose knots and have a low content or fraction of small non-agglomerating particles, i.e., fines.

[0041] In the art, hammer milling has been extensively used to produce defibrated cellulose and / or lignocellulose fibers for air-laying. Such a hammer milling achieves an efficient defibration of the pulp into individual, i.e., free, cellulose and / or lignocellulose fibers and a low amount of knots. However, hammer milling has the disadvantage of a significant amount of fines in the defibrated cellulose and / or lignocellulose fiber material.

[0042] In an embodiment, the method comprises an additional step S10 as shown in Fig. 3. This step S10 comprises selecting at least one operational parameter of a disc mill based on the type. The at least one operational parameter of the disc mill is preferably selected from the group consisting of a disc gap of the disc mill, rotational speed or speeds of the discs of the disc mill and a flow-rate of an air-flow transporting the pulp into the disc mill. In such an embodiment, step S11 comprises disc milling the pulp with the disc mill operated according to the selected at least one operation parameter to form the partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight.

[0043] Generally, the above-mentioned operational parameters of a disc mill, i.e., disc gap, rotational speed and flow rate can be used to control the defibration of the pulp. Generally, a smaller disc gap between the two discs of the disc mill increases the defibration degree of the pulp and a larger disc gap reduces the defibration degree of the pulp. Correspondingly, a higher rotational speed or speeds of the discs increases the defibration degree of the pulp and a lower rotational speed or speeds of the discs reduces the defibration degree of the pulp. Further, a higher flow rate of the air-flow transporting the pulp means that the pulp is transported faster through the disc mill and thereby exposed to a shorter disc milling operation, i.e., shorter dwell time, as compared to when using a lower flow rate of the air-flow.

[0044] This means that one or more of these operational parameters of the disc mill can be used to control the disc milling performed in step S11 to achieve a partly defibrillated cellulose and / or lignocellulose fiber material with a desired defibration degree and thereby a desired knots content. In an embodiment, step S10 comprises selecting one operational parameter, such as selecting the disc gap, selecting the rotation speed or selecting the flow rate. In another embodiment, step S10 comprises selecting two operational parameters, such as selecting the disc gap and the rotational speed, selecting the disc gap and the flow rate, or selecting the rotational speed and the flow rate. In a further embodiment, step S10 comprises the three operational parameters, i.e., selecting the disc gap, the rotational speed and the flow rate. The at least one operational parameter of the disc mill is selected in step S10 based on the type of pulp to be disc milled in order to obtain the desired (minimum) knots content.

[0045] In an embodiment, step S1 of Fig. 2 comprises defibrating the pulp into the partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 30 % by weight. In a preferred embodiment, the partly defibrated cellulose and / or lignocellulose fiber material has a knots content of at least 40 % by weight, and more preferably at least 50 % by weight.

[0046] In an embodiment, the knot content of the partly defibrated cellulose and / or lignocellulose fiber is determined by air-jet sieving with a sieve size of 1400 pm (14 mesh, American Society for Testing and Materials (ASTM) no. 14), a sieving pressure of 4000 Pa and a sieving time of 10 min.

[0047] Air-jet sieving is a standard operating procedure for particle size analysis and in particular analysis of the knots content of cellulose and / or lignocellulose fiber material.

[0048] An example of an air-jet sieving apparatus, also referred to as air-jet sieve in the art, that could be used to determine the knots content is Air Jet Sieve e200 LS by Hosokawa Alpine. In such a sieving operation, the 14 mesh sieve is inserted in the air-jet sieve, the cellulose and / or lignocellulose fiber material to analyze is spread on the sieve and the air-jet sieve is set to manual sieving with a sieving pressure of 4000 Pa and a sieving duration of 10 min. When the sieving is finished the knots remain on the sieve. The knot content can then be calculated as: 100 wherein represents the initial weight of the cellulose and / or lignocellulose fiber material and w2represents the amount of remaining knots after sieving.

[0049] In an embodiment, the method comprises mixing the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder to form a mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder. In such an embodiment, step S2 of Fig. 2 comprises introducing the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder into the forming head 1 10. In an embodiment, the method comprises an additional step S20 as shown in Fig. 4. The method continues from step S1 in Fig. 2. A next step S20 comprises transporting a mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder by an air flow in a conduit 170 to the forming head 110. The method then continues to step S2. Hence, in a preferred embodiment, the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder are preferably introduced into the forming head 110 in the form of a mixture as transported by an air flow in a conduit 170 in fluid connection with an inlet 111 of the forming head 110.

[0050] In an embodiment, the system 100 for producing a bonded air-laid blank 10 as shown in Fig. 5 comprises a single conduit 170 arranged to convey the airflow of the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder into the inlet 1 11 of the forming head 110. In another embodiment, the system 100 comprises multiple conduits 170 arranged to convey the air flow of the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder into separate inlets 111 of the forming head 110. In a further embodiment, the system 100 comprises at least one conduit 170 arranged to convey an air flow of the partly defibrated cellulose and / or lignocellulose fiber material and at least one conduit arranged to convey an air flow of the polymer binder. In this embodiment, the polymer binder is conveyed by at least one other conduit into the forming head 110 and the mixing of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder is taking place within the forming head 110.

[0051] The conduit 170 in Fig. 5 is illustrated as a vertical conduit 170 connected to the forming head 110. The embodiments are, however, not limited thereto. The conduit 170 could be a horizontal conduit connected to the forming head 110 or being angled with an angle from 0° (vertical conduit) up to 90° (horizontal conduit) relative to the forming head 110. In these various embodiments, the air flow flowing through the conduit 170 will incident into the forming head 1 10 with an angle of incidence from 0° (vertical conduit) up to 90° (horizontal conduit). The conduit 170 can also comprise multiple conduit sections separated by a turn. As an example, an upstream section of the conduit 170 could be an upstream vertical conduit section, which is followed by a turn and then a downstream horizontal conduit section that is in fluid communication with the inlet 111 of the forming head 110. Another example is a conduit 170 with an upstream horizontal section followed by a turn and then a downstream vertical conduit section. The partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder are introduced in step S2 into the forming head 110, also referred to as forming chamber in the art, as discrete input streams and / or as one or more mixed input streams at one or more inlets 111. The partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder are mixed and blended during the passage through the forming head 110 ultimately forming an unbonded air-laid web 20 on the conveyor 120. The forming head 110 may include equipment arranged inside the forming head 110 to promote separation and mixing of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder during the passage through the forming head 110. Such equipment may comprise, for instance, rolls with interlocking spikes, one or more drums, such as slit drums, and / or one or more strainers.

[0052] The partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder or the mixture thereof pass(es) through the forming head 110 to the outlet 113, such as arranged in connection with a lower end 114 of the forming head 110 and is further mixed through this passage. The mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder is then captured on the conveyor 120. In an embodiment, the conveyor 120 is an air-permeable conveyor 120 and the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder is captured at least partly by a vacuum, i.e., an air suction or under-pressure, applied across the air-permeable conveyor 120 that is disposed in connection with the outlet 113 of the forming head 110. Hence, in an embodiment, the method of Fig. 2 preferably comprises an additional step of passing the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder to the outlet 113 of the forming head 110 while applying a gas suction through the air-permeable conveyor 120 in connection with the outlet 113 of the forming head 110.

[0053] Such a gas suction or vacuum is applied through the air-permeable conveyor 120. The gas suction or vacuum applied across the air-permeable conveyor 120, thus, draws the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder down onto the air-permeable conveyor 120. For instance, the air-permeable conveyor 120 could comprise a plurality of openings, through holes or channels allowing air to be sucked or drawn through the air-permeable conveyor 120. As an illustrative, but non-limiting, example, the air-permeable conveyor 120 could be a mesh conveyor, a wire conveyor or a belt conveyor with a belt comprising a plurality of minute through holes. However, any such openings are preferably small enough to prevent the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder from passing through the air-permeable conveyor 120. Hence, the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder are instead deposited as a mixture onto the air-permeable conveyor 120 in the form of an unbonded air-laid web 20.

[0054] In an embodiment, the conveyor 120 is an endless air-permeable conveyor. As an example, the conveyor 120 could comprise an endless conveyor belt 122 running along driver rollers 124, 126 as shown in Fig. 5. An endless conveyor belt 122 is a conveyor belt 122 that has been made into an endless belt 122 without joints. Such an endless conveyor belt 122 is also referred to as jointless conveyor belt in the art.

[0055] In an embodiment, step S4 comprises heat treating the unbonded air-laid web 20 to at least partly melt, i.e., tackify, the polymer binder and form the bonded air-laid blank 10. The heat treatment applied in step S4 performs a bonding operation, in which the unbonded air-laid web 20 is introduced into or otherwise passes a heating device 140, also referred to as a bonding oven or heater, see Fig. 5, where heat, such as in the form of heated or hot air, is blown into, sucked into and / or circulated through the unbonded airlaid web 20 to melt or partially melt the polymer binder. The polymer binder thereby becomes tacky and adheres to the partly defibrated cellulose and / or lignocellulose fiber material and, thus, holds the fiber material together and thereby results in a bonded air-laid blank 10.

[0056] In a particular embodiment, the heating device 140 is arranged to heat the unbonded air-laid web 20 to a temperature selected within an interval of from 100°C up to 210°C, preferably within an interval of from 100°C up to 190°C, and more preferably within an interval of from 100°C up to 165°C. A too high temperature may damage and deteriorate the partly defibrated cellulose and / or lignocellulose fiber material in the unbonded air-laid web 20.

[0057] The heating or bonding operation in step S4 may also comprise, and / or be accompanied by, a densification to create a larger number of binding points in the fiber structure and, thus, a stronger and denser bonded air-laid blank 10. Such a densification operation could be applied either before the bonded air-laid blank 10 has been allowed to cool after the heating device 140 or upon renewed heating, such as in a heated calender. It is also possible to perform the densification operation in the heating device 140, e.g., as a combined heating and densification operation. In this latter case, step S4 comprises heat treating the unbonded air-laid web 20 to at least partly melt the polymer binder and simultaneously applying pressure onto the unbonded air-laid web 20 to form the bonded air-laid blank 10. The densification can include various types of operations including, but not limited to, calendering and / or pressing operations. In an embodiment, the method also comprises cooling the bonded air-laid blank 10 by blowing a gas or gas mixture through the bonded air-laid blank 10.

[0058] In this embodiment, the system 100 comprises a cooling device 150 arranged downstream of the heating device 140. Such a cooling device 150 is then arranged to blow a gas or a gas mixture, typically air, through the bonded air-laid blank 10 to cool the bonded air-laid blank 10 as output from the heating device 140. The cooling device 150 could then cool the air-laid blank 10 to a temperature at or slightly above ambient temperature or to a temperature above ambient temperature but below the temperature inside the heating device 140, such as to a temperature at which the polymer binder solidifies sufficiently.

[0059] In an embodiment, the method also comprises cutting the bonded air-laid blank 10 following heating in step S4 in Fig. 2 or the optional cooling step. The cutting operation could be performed using any suitable cutter or cutting device 160. Illustrative, but non-limiting examples, of such cutting device 160 include a saw, a punch, a knife, etc. The cutting device 160 is preferably in the form of a cross-cutting device 160 that cuts through the whole thickness of the bonded air-laid blank 10.

[0060] The cutting step divides the (continuous) bonded air-laid blank 10 into suitable sizes for downstream handling and processing, see Fig. 1. The cutting could be across the width of the bonded air-laid blank 10 to get, for instance, rectangular or quadratic bonded air-laid blank pieces.

[0061] The cutting is preferably performed while the bonded air-laid blank 10 is transported on the conveyor 120. Hence, it is generally preferred if the cutting device 160 is moved in synchrony with the bonded airlaid blank 10 during the cutting step. For instance, the cutting device 160 is starting the cutting from a start position and then moves in synchrony with the bonded air-laid blank 10 in the longitudinal direction of the bonded air-laid blank 10 until the cutting is completed at a stop position. The cutting device 160 is then preferably transported back to the start position to be ready for a next cutting operation.

[0062] As shown in Fig. 5, the conveyor 120 could include bend rollers 121 and at least one take-up roller 123 arranged to divert the conveyor belt 122 away from the cutting device 160. This means that the conveyor belt 122 turns away from the cutting device 160 to enable the cutting device 160 to cut through the complete thickness of the bonded air-laid blank 10 without the risk of engaging and damaging the conveyor belt 122. The bend rollers 121 could be in the form of bend pulleys or bend idlers and the takeup roller(s) 123 could be in the form of take-up pulley (s) or take-up idler(s). In an embodiment, the cutting device 160 and the bend rollers 121 and take-up roller(s) 123 are preferably movable relative to the conveyor 120 to be moved, preferably in synchrony, with the bonded air-laid blank 10 transported by the conveyor 120. This is schematically illustrated by the hatched arrow in Fig. 5.

[0063] Another aspect of the invention relates to a bonded air-laid blank 10 comprising at least 80 % by weight of a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight, and less than 10 % by weight of a polymer binder binding together the partly defibrated cellulose and / or lignocellulose fiber material.

[0064] In an embodiment, the partly defibrated cellulose and / or lignocellulose fiber material has a knots content of at least 30 % by weight, preferably at least 40 % by weight, and more preferably at least 50 % by weight.

[0065] Percentage by weight (% by weight) as used herein is preferably determined using standard atmosphere for testing pulp, paper and board as defined in ISO 187:2022 Paper, board and pulps — Standard atmosphere for conditioning and testing and procedure for monitoring the atmosphere and conditioning of samples, i.e., temperature 23 ± 1 °C and relative humidity (RH) 50 ± 2 %.

[0066] In an embodiment, the partly defibrated cellulose and / or lignocellulose fiber material comprises disc milled pulp.

[0067] In an embodiment, the pulp defibrillated, such as disc milled, to produce the partly defibrated cellulose and / or lignocellulose fiber material is selected from the group consisting of sulfate pulp, sulfite pulp, thermomechanical pulp (TMP), high temperature thermomechanical pulp (HTMP), mechanical fiber intended for medium density fiberboard (MDF-fiber), chemi-thermomechanical pulp (CTMP), high temperature chemi-thermomechanical pulp (HTCTMP), and a combination thereof.

[0068] The pulp could be bleached pulp, unbleached pulp, or a combination of bleached and unbleached pulp.

[0069] The partly defibrated cellulose and / or lignocellulose fiber material is preferably a partly defibrated cellulose fiber material. The cellulose fiber may, though, also contain lignin, such as in the form of lignocellulose. The fiber material may also be a mixture of cellulose fiber material and lignocellulose fiber material. In an embodiment, the bonded air-laid blank 10 comprises at least 85 % by weight of partly defibrated cellulose and / or lignocellulose fiber material. In a preferred embodiment, the bonded air-laid blank 10 comprises at least 90 % by weight, preferably at least 92.5 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material.

[0070] In an embodiment, the bonded air-laid blank 10 comprises the polymer binder at a concentration selected within an interval of from 0.1 up to 10 % by weight. In a preferred embodiment, the bonded air-laid blank 10 comprises the polymer binder at a concentration selected within an interval of from 0.5 up to 9 % by weight, more preferably selected within an interval of from 0.5 up to 5 % by weight.

[0071] Reference to an interval of from X up to Y herein includes the range of values between X and Y including the end points of the interval, i.e., X and Y.

[0072] As discussed herein and further shown in Example 2, the partly defibrated cellulose and / or lignocellulose fiber material has a low fraction and amount of non-fibrous cellulose and / or lignocellulose particles, i.e., so called fines. Hence, in an embodiment, the partly defibrated cellulose and / or lignocellulose fiber material comprises no more than 15 % by weight of non-fibrous cellulose and / or lignocellulose particles (fines). In a preferred embodiment, the partly defibrated cellulose and / or lignocellulose fiber material comprises no more than 12.5 % by weight of non-fibrous cellulose and / or lignocellulose particles, preferably no more than 10 % by weight of non-fibrous cellulose and / or lignocellulose particles.

[0073] The polymer binder is included to bind the bonded air-laid blank 10 together and preserve its form and structure during use, handling, and storage. In an embodiment, the polymer binder may also assist in building up the foam-like structure of the bonded air-laid blank 10. The polymer binder is, in such an embodiment, intermingled with the partly defibrated cellulose and / or lignocellulose fiber material during the air-laying process forming a fiber mixture. The polymer binder may be added in the form of a powder but is more often added in the form of fibers that are intermingled with the partly defibrated cellulose and / or lignocellulose fiber material in the air-laying process.

[0074] In a particular embodiment, the polymer binder is selected from the group consisting of a polymer powder, polymer fibers and a combination thereof. The polymer binder could be a natural or synthetic polymer binder, or a mixture of natural polymer binders, a mixture of synthetic polymer binders, or a mixture of natural and synthetic polymer binders, but is preferably a thermoplastic polymer binder.

[0075] In an embodiment, the polymer binder is selected from the group consisting of a thermoplastic polymer powder, thermoplastic polymer fibers, and a combination thereof. In a preferred embodiment, the polymer binder is in the form of thermoplastic polymer fibers.

[0076] In an embodiment, the polymer binder is made from i) a material selected from the group consisting of polyvinyl alcohol (PVOH), thermoplastic starch (TPS), polyethylene (PE), ethylene acrylic acid copolymer (EAA), ethylene-vinyl acetate (EVA), polypropylene (PP), polystyrene (PS), such as styrene-butadiene rubber (SBR) or styrene acrylate copolymer, polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyethylene terephthalate (PET), polycaprolactone (PCL), polyvinyl alcohol (PVA), polyethylene glycol (PEG), poly (2-ethyl-2-oxazoline) (PEOX), polyvinyl ether (PVE), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyvinyl acetate (PVAc), polyurethane (PU), copolymers thereof and mixtures thereof, and II) optionally one or more additives.

[0077] Hence, in an embodiment, the polymer binder is made of a material selected from the above-mentioned group. In another embodiment, the polymer binder is made of a material selected from the above- mentioned group and one or more additives.

[0078] In an embodiment, the polymer binder is or comprises, such as consists of, mono-component and / or bicomponent polymer fibers. Bi-component polymer fibers, also known as bico fibers, comprise a first polymer, copolymer and / or polymer mixture and a second, different polymer, copolymer and / or polymer mixture. Most often the bi-component polymer fiber comprises a core made of the first polymer, copolymer and / or polymer mixture and a sheath made of the second polymer, copolymer and / or polymer mixture, although other combinations of two or even more polymers, copolymers and / or polymer mixtures are possible.

[0079] In an embodiment, the polymer binder is a thermoplastic polymer binder and the thermoplastic polymer binder is or comprises, such as consists of, mono-component thermoplastic polymer fibers made of I) a material selected from the group consisting of PVOH, TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives. In another particular embodiment, the thermoplastic polymer binder is or comprises, such as consists of, bi-component thermoplastic polymer fibers having a first material, such as a core made of i) a first material, selected from the group consisting of PVOH, TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives, and a second material, such as a sheath made of i) a second material, typically a different material, selected from the group consisting of TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives. In a further embodiment, the thermoplastic polymer binder is or comprises, such as consists of, a combination or mixture of mono-component thermoplastic polymer fibers made of i) a material selected from the group consisting of PVOH, TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives, and bi-component thermoplastic polymer fibers having i) materials, such as of the core and / or sheath, selected from the group consisting of PVOH, TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives.

[0080] The thermoplastic polymer binder could be made of a single type of thermoplastic polymer fibers, i.e., made of a same material in the case of mono-component thermoplastic polymer fibers or made of the same materials in the case of bi-component thermoplastic polymer fibers. However, it is also possible to use a thermoplastic polymer binder made of one or multiple, i.e., two or more, different mono-component thermoplastic polymer fibers made of different materials and / or one or multiple different bi-component thermoplastic polymer fibers made of different materials.

[0081] An advantage of using bi-component thermoplastic polymer fibers is that they can have a core with a higher melting point that keeps its fiber form during the binding operation, whereas the sheath melts and becomes tacky. The intact core will support the three-dimensional structure of the bonded air-laid blank 10 and, thus, promote porosity while the melted or tackified sheath will attach to the partly defibrated cellulose and / or lignocellulose fiber material and preserve the strength of the bonded air-laid blank 10.

[0082] In an embodiment, the polymer binder is a polymer powder, preferably a thermoplastic polymer powder, made of i) a material selected from the group consisting of PVOH, TPS, PE, EAA, EVA, PP, PS, PBAT, PBS, PLA, PET, PCL, PVA, PEG, PEOX, PVE, PVP, PAA, PMAA, PVAc, PU, copolymers thereof and mixtures thereof, and ii) optionally one or more additives. It is also, as mentioned in the foregoing, possible to use a thermoplastic polymer binder that is a combination of thermoplastic polymer fibers and thermoplastic polymer powder.

[0083] The bonded air-laid blank 10 may comprise one or more additives in addition to the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder. One or more additives could be added to the polymer binder and / or added when producing the polymer binder. Alternatively, or in addition, one or more additives could be added to the partly defibrated cellulose and / or lignocellulose fiber material. Alternatively, or in addition, one or more additives could be added to the mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder, such as during the air-laying process or prior to the air-laying process.

[0084] Illustrative, but non-limiting, examples of such additives include electrically conducting or semiconducting fillers, coupling agents, flame retardants, dyes, impact modifiers, hydrophobization agents, etc.

[0085] The bonded air-laid blank 10 produced according to the invention has preferably an average thickness W, see Fig. 1 , of at least 5 mm, and preferably an average thickness of at least 5 mm and at most 200 mm.

[0086] In an embodiment, the bonded air-laid blank 10 has an average density selected within an interval of from 10 up to 200 kg / m3, such as from 18 up to 190 kg / m3.

[0087] In an embodiment, the bonded air-laid blank 10 has an average grammage selected within an interval of from 300 up to 10000 g / m2.

[0088] The bonded air-laid blank 10 as produced according to the method and by the system 100 of the present invention comprises significantly less non-bonded cellulose and / or lignocellulose fiber material as compared to bonded air-laid blanks 10 produced according to prior art technologies. This means that the bonded air-laid blank 10 produce less linting. Furthermore, the low amount of polymer binder present in the bonded air-laid blank 10 means that the bonded air-laid blank 10 can be recycled in the paper or board recycling streams, preferably in the paper recycling stream. EXAMPLES

[0089] EXAMPLE 1 - Air-jet sieving

[0090] This Example determined the knot content in samples by air-jet sieving.

[0091] An Air Jet Sieve e200 LS (Hosokawa Alpine) equipped with a vacuum cleaner and a sieve with an opening of mesh of 1400 pm (14 mesh) was used to determine the knot content of two partly defibrated cellulose and / or lignocellulose fiber materials by separating the knots (non-defibrated pulp) from the materials.

[0092] Test material 1 : disc milled Stora Enso Nova from Enocell, Stora Enso (disc milled unbleached Kraft pulp (UKP))

[0093] Test material 2: disc milled Supreme from Varkaus, Stora Enso (disc milled UKP)

[0094] 5.00 g of the sample was spread on the sieve followed by placing the plastic lid of the Alpine Air Jet Sieve e200 LS on the sieve. Manual sieving was selected on the control panel with the following settings: pressure 4000 Pa and duration 10.00 min. Sieving was conducted and the knots remaining on the sieve following sieving were collected and weighed. The weight was entered in the Retained field of the Alpine Air Jet Sieve e200 LS and the knot content was calculated as: 100 wherein represents the initial weight of the sample and w2represents the amount of remaining knots after sieving. The results are presented in Table 1 below.

[0095] Table 1 - knots content

[0096] Figs. 6A and 6B illustrate the knots remaining following air-jet sieving of test material 1 in Fig. 6A and test material 2 in Fig. 6B. As a comparison, the knots content of fluff pulp, i.e., fully defibrated cellulose and / or lignocellulose fiber materials, measured by Alpline Air Jet Sieve e200 LS is 8 % for NaturaFluff Absorb (softwood (pine and spruce) elemental chlorine free fluff pulp) and 3 % NaturaFluff Soft (softwood (pine and spruce) elemental chlorine free fluff pulp).

[0097] EXAMPLE 2 - Fiber separation

[0098] This Example separated fibers from materials into knots, fibers and fines and powder by creation of an air turbulence and depression via sieves with different mesh according to an analysis operating protocol from SGS.

[0099] The measuring apparatus, see Fig. 7, comprises a reactor with an opening on one side for the air flow entrance (18 mm diameter, taping over 1 / 3 of the entrance) and a set of two stainless steel sieves of diameter 200 mm, a first sieve with an opening of mesh of 1700 mm corresponding to 12 mesh and a second sieve with an opening of mesh of 150 m corresponding to 100 mesh. The measuring apparatus also comprises a bottom tank with an inner diameter 202 mm and height 300 mm having a perforated bottom with opening of 50 mm. The bottom tank is connected by a pipe to a vacuum cleaner. A transparent Plexiglas cover closes the reactor.

[0100] Test material 1 : disc milled Stora Enso Nova from Enocell, Stora Enso (disc milled UKP)

[0101] Test material 2: disc milled Supreme from Varkaus, Stora Enso (disc milled UKP)

[0102] Comparative material 1 : hammer milled, bleached (ISO brightness 70) chemical thermomechanical pulp (CTMP)

[0103] Comparative material 2: hammer and disc milled, bleached (ISO brightness 70) CTMP

[0104] Comparative material 3: hammer milled, bleached (ISO brightness 78) CTMP

[0105] Comparative material 4: hammer and disc milled, bleached (ISO brightness 78) CTMP

[0106] Comparative material 5: hammer milled, unbleached CTMP

[0107] Comparative material 6: hammer and disc milled, unbleached CTMP

[0108] Comparative material 7: NaturaFluff Absorb (softwood (pine and spruce) elemental chlorine free fluff pulp)

[0109] Comparative material 8: NaturaFluff Soft (softwood (pine and spruce) elemental chlorine free fluff pulp)

[0110] The samples were conditioned 1 hour before measurements at ambient conditions (temperature 23±1 °C, RH 50±2 %). 3.00 g of the sample was placed on the grid of the sieve no. 12 and the measuring apparatus was closed by the cover. The vacuum cleaner was started for 3 minutes (85 mbar) and the sample was set into motion on the sieve no. 12. The vacuum cleaner was stopped after 3 minutes. Sieve no. 12 was removed and the vacuum cleaner was started for 90 s (110 mbar). The vacuum cleaner was stopped after 90 s. The different fractions were measured with knots remaining on sieve no. 12, fibers remaining on sieve no. 100 and remaining fractions are regarded as fines and loss. The amount of the different fractions were calculated as: knot content (%) = yjx100 100 fines and loss content (%) = 100 — knot content — fiber content wherein w12represents the weight of the fraction remaining on sieve no. 12 and w100represents the weight of the fraction remaining on sieve no. 100. The results are presented in Table 2 below.

[0111] Table 2 - knots, fiber and fines content Fig. 8A illustrates the knots remaining on sieve no. 12 and Fig. 8B illustrates the fibers remaining on sieve no. 100 for test material 1 and Fig. 9A illustrates the knots remaining on sieve no. 12 and Fig. 9B illustrates the fibers remaining on sieve no. 100 for test material 2. The results as presented in Table 2 shows that the test material of the invention has a significantly higher knots content than the comparative materials. Furthermore, the test material of the invention had a significantly lower fines content than the comparative materials (Comparative materials 1-6) previously used for air-laying. The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

CLAIMS1 . A method of producing a bonded air-laid blank (10), the method comprising: defibrating (S1) pulp into a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight; introducing (S2) the partly defibrated cellulose and / or lignocellulose fiber material and a polymer binder into a forming head (110); capturing (S3) the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder as an unbonded air-laid web (20) on a conveyor (120) arranged in connection with an outlet (113) of the forming head (110); and heating (S4) the unbonded air-laid web (20) to at least partly melt the polymer binder and bind the partly defibrated cellulose and / or lignocellulose fiber material to form a bonded air-laid blank (10) comprising less than 10 % by weight of the polymer binder and at least 80 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material.

2. The method according to claim 1 , wherein defibrating (S1) the pulp comprises disc milling (S1 1) the pulp into the partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight.

3. The method according to claim 2, further comprising selecting (S10) at least one operational parameter of a disc mill based on the type of pulp, wherein the at least one operational parameter is selected from the group consisting of a disc gap of the disc mill, rotational speed(s) of the discs of the disc mill, and flow rate of an air-flow transporting the pulp into the disc mill; and disc milling (S1 1) the pulp comprises disc milling (S11) the pulp with the disc mill operated according to the selected at least one operational parameter to form the partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight.

4. The method according to any one of claims 1 to 3, wherein defibrating (S1) the pulp comprises defibrating (S1) the pulp into the partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 30 % by weight, preferably at least 40 % by weight and more preferably at least 50 % by weight.

5. The method according to any one of claims 1 to 4, further comprising transporting (S20) a mixture of the partly defibrated cellulose and / or lignocellulose fiber material and the polymer binder by an air flow in a conduit (170) to the forming head (110).

6. The method according to any one of claims 1 to 5, wherein the bonded air-laid blank (10) comprises at least 85 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material, preferably at least 90 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material, and more preferably at least 92.5 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material.

7. The method according to any one of claims 1 to 6, wherein the bonded air-laid blank (10) comprises the polymer binder at a concentration selected within an interval of from 0.1 up to 10 % by weight, preferably selected within an interval of from 0.5 up to 9 % by weight, and more preferably selected within an interval of from 0.5 up to 5 % by weight.

8. The method according to any one of claims 1 to 7, wherein the pulp is selected from the group consisting of sulfate pulp, sulfite pulp, thermomechanical pulp (TMP), high temperature thermomechanical pulp (HTMP), mechanical fiber intended for medium density fiberboard (MDF-fiber), chemi-thermomechanical pulp (CTMP), high temperature chemi-thermomechanical pulp (HTCTMP), and a combination thereof.

9. The method according to any one of claims 1 to 8, wherein the partly defibrated cellulose and / or lignocellulose fiber material comprises no more than 15 % by weight of non-fibrous cellulose and / or lignocellulose particles, preferably no more than 12.5 % by weight of non-fibrous cellulose and / or lignocellulose particles, and more preferably no more than 10 % by weight of non-fibrous cellulose and / or lignocellulose particles.

10. The method according to any one of claims 1 to 9, wherein the knot content of the partly defibrated cellulose and / or lignocellulose fiber material is determined by air-jet sieving with a sieve size of 1400 m, a sieving pressure of 4000 Pa and a sieving time of 10 min.11 . The method according to any one of claims 1 to 10, wherein the bonded air-laid blank (10) has an average density selected within an interval of from 10 up to 200 kg / m3, preferably selected within an interval of from 18 up to 190 kg / m3.

12. The method according to any one of claims 1 to 11, wherein the polymer binder is selected from the group consisting of a polymer powder, polymer fibers, and a combination thereof, preferably selected from the group consisting of a thermoplastic polymer powder, thermoplastic polymer fibers and a combination thereof, and more preferably thermoplastic polymer fibers.

13. The method according to claim 12, wherein the thermoplastic polymer fibers are selected from the group consisting of mono-component thermoplastic polymer fibers, bi-component thermoplastic polymer fibers and a mixture thereof, preferably bi-component thermoplastic polymer fibers.

14. The method according to any one of claims 1 to 13, wherein the polymer binder is made from I) a material selected from the group consisting of polyvinyl alcohol (PVOH), thermoplastic starch (TPS), polyethylene (PE), ethylene acrylic acid copolymer (EAA), ethylene-vinyl acetate (EVA), polypropylene (PP), polystyrene (PS), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyethylene terephthalate (PET), polycaprolactone (PCL), polyvinyl alcohol (PVA), polyethylene glycol (PEG), poly (2-ethyl-2-oxazoline) (PEOX), polyvinyl ether (PVE), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyvinyl acetate (PVAc), polyurethane (PU), copolymers thereof and mixtures thereof, and ii) optionally one or more additives.

15. A bonded air-laid blank (10) comprising: at least 80 % by weight of a partly defibrated cellulose and / or lignocellulose fiber material having a knots content of at least 20 % by weight; and less than 10 % by weight of a polymer binder binding together the partly defibrated cellulose and / or lignocellulose fiber material.

16. The bonded air-laid blank according to claim 15, wherein the partly defibrated cellulose and / or lignocellulose fiber material has a knots content of at least 30 % by weight, preferably at least 40 % by weight and more preferably at least 50 % by weight.

17. The bonded air-laid blank according to claim 15 or 16, wherein the bonded air-laid blank (10) comprises the polymer binder at a concentration selected within an interval of from 0.1 up to 10 % by weight, preferably selected within an interval of from 0.5 up to 9 % by weight, and more preferably selected within an interval of from 0.5 up to 5 % by weight.

18. The bonded air-laid blank according to any one of claims 15 to 17, wherein the bonded air-laid blank (10) comprises at least 85 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material, preferably at least 90 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material, and more preferably at least 92.5 % by weight of the partly defibrated cellulose and / or lignocellulose fiber material.

19. The bonded air-laid blank according to any one of claims 15 to 18, wherein the partly defibrated cellulose and / or lignocellulose fiber material comprises disc milled pulp.

20. The bonded air-laid blank according to claim 19, wherein the pulp is selected from the group consisting of sulfate pulp, sulfite pulp, thermomechanical pulp (TMP), high temperature thermomechanical pulp (HTMP), mechanical fiber intended for medium density fiberboard (MDF-fiber), chemi-thermomechanical pulp (CTMP), high temperature chemi-thermomechanical pulp (HTCTMP), and a combination thereof.

21. The bonded air-laid blank according to any one of claims 15 to 20, wherein the partly defibrated cellulose and / or lignocellulose fiber material comprises no more than 15 % by weight of non-fibrous cellulose and / or lignocellulose particles, preferably no more than 12.5 % by weight of non-fibrous cellulose and / or lignocellulose particles, and more preferably no more than 10 % by weight of non-fibrous cellulose and / or lignocellulose particles.

22. The bonded air-laid blank according to any one of claims 15 to 21, wherein the knot content of the partly defibrated cellulose and / or lignocellulose fiber material is determined by air-jet sieving with a sieve size of 1400 m, a sieving pressure of 4000 Pa and a sieving time of 10 min.

23. The bonded air-laid blank according to any one of claims 15 to 22, wherein the bonded air-laid blank (10) has an average density selected within an interval of from 10 up to 200 kg / m3, preferably selected within an interval of from 18 up to 190 kg / m3.

24. The bonded air-laid blank according to any one of claims 15 to 23, wherein the polymer binder is selected from the group consisting of a polymer powder, polymer fibers, and a combination thereof, preferably selected from the group consisting of a thermoplastic polymer powder, thermoplastic polymer fibers and a combination thereof, and more preferably thermoplastic polymer fibers.

25. The bonded air-laid blank according to claim 24, wherein the thermoplastic polymer fibers are selected from the group consisting of mono-component thermoplastic polymer fibers, bi-component thermoplastic polymer fibers and a mixture thereof, preferably bi-component thermoplastic polymer fibers.

26. The bonded air-laid blank according to any one of claims 15 to 25, wherein the polymer binder is made from I) a material selected from the group consisting of polyvinyl alcohol (PVOH), thermoplastic starch (TPS), polyethylene (PE), ethylene acrylic acid copolymer (EAA), ethylene-vinyl acetate (EVA), polypropylene (PP), polystyrene (PS), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polylactic acid (PLA), polyethylene terephthalate (PET), polycaprolactone (PCL), polyvinyl alcohol (PVA), polyethylene glycol (PEG), poly (2-ethyl-2-oxazoline) (PEOX), polyvinyl ether (PVE), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyvinyl acetate (PVAc), polyurethane (PU), copolymers thereof and mixtures thereof, and ii) optionally one or more additives.

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