Method and system for producing a web from reconstituted material

Abstract

A method for producing a continuous layer of reconstituted material comprises: a step of dry shredding solid components of a starting material until a dry product having a first particle size is obtained; a subsequent step of mixing the dry product with water to obtain a mixture; a subsequent step of refining applied to the mixture to obtain a refined mixture (C) having a second particle size smaller than the first particle size; a subsequent step of supplementing the refined mixture by adding at least one binder and / or an aerosol-forming material thereto, thereby obtaining a supplemented mixture; a subsequent step of forming a continuous web from the supplemented mixture; and a subsequent step of drying the continuous web.

Description

Technical area

[0001] This invention relates to a method and a plant for producing a web of reconstituted material, preferably but not necessarily tobacco, in particular for producing traditional or HNB smoking articles. Background state of the art

[0002] It is known in the prior art to produce a tobacco sheet from a mixture of tobacco particles and water, the particles having a very small size and a water content that is lower than in the slurry technology as described in the introductory section of patent application WO2020 / 058814 in the name of the present applicant.

[0003] The applicant has determined that, although this technology is satisfactorily practical, it can still be improved, particularly with regard to simplifying the plant. Indeed, it has been identified that a particularly critical aspect concerns the complexity of the plant required for the initial comminution of the tobacco into extremely fine particles, as well as the aspect of dividing the mixture into portions and then subjecting it to multiple lamination processes. Furthermore, the process and machine are optimized for a specific web format (particle size, thickness, etc.), and adapting to different formats involves complex procedures. Furthermore, the process requires the use of several comminution mills installed at the beginning of the plant to finely shred the material. Shredding is carried out with the material in a dry state and generates large amounts of dust.This not only creates the need to contain and / or remove the dust, but also creates a fire hazard, which in turn requires the provision of flame retardant systems in compliance with the strict fire regulations currently in force. Aim of the invention

[0004] In this context, it is therefore the technical purpose of this invention to provide a method and a plant for producing a web of reconstituted material which are free from the disadvantages of the prior art.

[0005] The aim of this invention is therefore to provide a method and a plant for producing a web from reconstituted material, which represent a technically simpler solution compared to prior art solutions.

[0006] A further object of the invention is to provide a method and a plant for producing a web from reconstituted material in order to increase the operational reliability of the plant.

[0007] Another object of the invention is to provide a method and a plant for producing a web of reconstituted material which have a high operational flexibility and which can be used in particular to obtain webs in different formats and different specifications.

[0008] The objects are essentially achieved by a method and a plant in accordance with the features set out in the appended claims 1 and 12 and / or in one or more of the dependent claims. Short description of the drawings

[0009] Further features and advantages of this invention will become apparent from the description given by way of example and not by way of limitation of a preferred but not exclusive embodiment of a method and a plant for producing a web of reconstituted material, as shown in the accompanying drawing, in which: - Fig. Figure 1 is a schematic view of a first part of the plant according to the invention; - Fig. Figure 2 is a schematic view of a second part of the plant according to the invention in a first embodiment thereof; - Fig. 3 a detail of the first section of the part of the plant of Fig. 2 shows; - Fig. 3A an enlargement of a detail from the view in Fig. 3 in an operating state; - Fig. 4 a detail of the second section of the part of the plant of Fig. 2 shows; - Fig. 4A-4C enlarged views of respective details from the view of Fig. 4 show in an operating state; - Fig. 5 is a schematic view of the second part of the plant according to the invention in a second embodiment thereof. Detailed description of preferred embodiments of the invention

[0010] The accompanying drawings illustrate various parts of a plant for producing a web of reconstituted tobacco or a material based on reconstituted tobacco according to this invention. Therefore, an embodiment of the method for producing a continuous web of reconstituted material will now be described with reference to the plant used to implement the method.

[0011] “Reconstituted tobacco” refers to a type of tobacco that, at the raw material level, is made from the solid waste remaining after the processing of tobacco leaves, such as stems and leaf veins, as well as very small pieces of leaves and tobacco dust.

[0012] It is noted, however, that the same plant may be used to produce layers or sheets of generic reconstituted material (in particular of plant origin), which is not necessarily tobacco, in accordance with the generic nature of the invention (for example, hemp, aromatic leaves or others).

[0013] For this purpose, the system comprises a shredder unit 100 designed to shred the solid tobacco components, and comprising, for example, a silo and one or more lower shredder wheels, in particular for shredding bales (which are parallelepiped in shape) of the solid components. The shredder unit 100 is designed to achieve a maximum particle size between 5 and 25 mm, preferably between 10 and 15 mm. In other words, the tobacco solid particles leaving the shredder unit 100, although they have a wide range of sizes, comprise particles having a maximum size of up to 25 mm, preferably up to 15 mm.Alternatively, the shredding may be characterized in that the predominant weight fraction of the material leaving the shredding unit 100 (i.e. essentially exclusively the powder component) has a particle size between 0.5 and 25 mm, preferably between 0.8 mm and 15 mm.

[0014] For this purpose, the shredding unit 100 may be specifically provided with screens or other screening means designed to allow only particles smaller than the predetermined size to pass through them.

[0015] Preferably, the shredding unit is defined by a single stage, in particular of the silo or mill type.

[0016] As in Fig. As shown in Figure 1, downstream of the shredder unit 100, there is a first mixing machine 200 configured to combine and mix the tobacco solid particles leaving the shredder unit 100 with water supplied by at least one feeder, designated in its entirety by reference numeral 210. In particular, according to the invention, the first mixing machine 200 does not supply binding agents and / or aerosol-forming materials, but preferably only water.

[0017] The resulting mixture has a liquid content (by weight) between 10% and 60%, preferably between 15% and 50%. In other words, the mixture has a liquid content that is lower than that of a slurry, but nevertheless sufficient to make the mixture compact enough to be suitable for subsequent processes that give it its shape.

[0018] The first mixing machine 200 has a structure of a known type and can, for example, be designed to deliver discontinuous amounts of mixture, each resulting from a cycle of loading components and mixing them.

[0019] This solution for the shredder unit 100 and the first mixing machine 200 is common to both embodiments of the invention. Fig. 2-4 represent a different part of the plant downstream of the first mixing machine 200 according to the first embodiment of the invention.

[0020] As in Fig. As shown in Figure 2, the mixture is collected from the first mixing machine 200 and transported by an endless conveyor, for example a first screw feeder 220 and a conveyor belt 230, to be processed in a subsequent pre-refining unit 300 (optional).

[0021] The pre-refinement unit 300, which is described in detail in Fig. 3 is of the two-roller type, i.e., it comprises a container 310 provided at its bottom with two rollers 320 arranged mutually opposite one another in a preferably horizontal direction to define a narrow gap or passage through which the mixture material can pass. The mixture material in the container 310, after being conveyed into a niche defined by the side surfaces of the two rollers 320, for example, via converging walls 330, accumulates in the niche itself and is drawn into the gap between the rollers, forming two thin layers, each adhering to a respective roller 320. This mode of operation results in a "flattening" of the material, i.e., in its accumulation (and optionally mixing) in the niche and then in its compression by the rollers 320.

[0022] The two thin layers are then removed from the rollers 320 by respective scraping elements 340, each associated with a respective roller.

[0023] Preferably and as in Fig. As shown in Figure 3A below, the two layers thus detached are arranged on respective conveyor belts, the speed of which is selected such that the layers are set in a wave-like movement forming a sequence of ridges and depressions along the feed direction.

[0024] The layers thus formed are transferred for further processing by suitable conveyors 350 (e.g., a screw feeder and / or a conveyor belt). One or more of the conveyors 350 can act as a device for homogenizing the material and remixing the two layers separated by the rollers 320.

[0025] In particular, as in Fig. 3 and Fig. As shown in Figure 4, downstream of the pre-refining unit 300 there is a distribution device 400 which is designed to deliver a continuous mixture flow F. Preferably, the distribution device 400 is designed as a laminating device to deliver a continuous layer of mixture.

[0026] Preferably, the continuous mixture flow F is released onto a feed conveyor 410, preferably a belt conveyor, designed to carry and move the flow F along a feed direction. Preferably, the continuous flow F arranged on the feed conveyor 300 has a layered configuration with a substantially uniform thickness.

[0027] Also preferably, the continuous mixture flow F arranged on the feed conveyor 410 has a thickness between 1 mm and 10 mm, and more preferably between 2 and 5 mm.

[0028] Downstream of the feed conveyor 410 is a refinement unit 500, which receives the continuous mixture flow F of preferably constant thickness. Although the refinement unit 500 is preferably a multi-stage unit, in a possible embodiment, which is not shown but falls within the scope of the same inventive concept, it may have only one stage. In particular, the refinement unit 500 (detailed in Fig. 4) comprises a plurality of refinement stages 510, 520, 530, specifically three in the illustrated embodiment, although the number may vary from two to more than three, depending on operating requirements. The refinement stages 510, 520, 530 each act on the continuous mixture (layer) flow F to remix and compress it, thereby reducing the particle size of the mixture in each stage.

[0029] Each refinement stage 510, 520, 530 comprises a pair of counter-rotating rollers 540, 550 arranged one above the other and defining between them a calibrated passage for compressing and forming the mixture material into a continuous layer C of constant thickness. Preferably, the rollers 540, 550 of each pair are of substantially identical diameter.

[0030] The two rollers 540, 550 of each stage define, just upstream of them, a niche for accumulating the mixture material, which tends to form a mass with the shape of the niche itself and is therefore deformed and / or premixed compared to the continuous flow or layer arriving at the rollers 540, 550. The mixture material is then gradually "pulled" and compressed under the action of the rotating rollers 540, 550 until the aforementioned continuous layer C is obtained.

[0031] Thus, each stage 510, 520, 530 processes the mixture material by flattening it. In the context of this invention, the term "flattening" is used to refer to a process comprising the steps of accumulating the material in the niche defined between the surfaces of the two rollers ( Fig. 4A-4C) and compressing it between the two rollers to form the continuous layer of constant thickness. Thanks to this process, the mixture material undergoes a mixing step in the accumulation zone (niche), which, in combination with the subsequent step of compressing the material between the two rollers and with the specific liquid content of the material, further grinds the particles of the mixture, thereby reducing the particle size. Therefore, the greater the number of stages, the more the particle size can be reduced. The rollers 540, 550 of each flattening stage 510, 520, 530 thus form the actual continuous layer C from the non-planar, shapeless mixture material that has been accumulated in the niche.

[0032] Preferably, both rollers 540, 550 of each flattening stage 510, 520, 530 are motor-driven.

[0033] Preferably, the rotation speed at which one of the rollers 540, 550 of each pair of rollers is driven is different from that of the other roller. In particular, the lower roller 550 is driven in rotation at a higher speed than the upper roller 540. Thanks to the higher rotation speed of the roller 550, the continuous layer C leaving the pair of rollers 540, 550 is held adhering to the roller 550, and for this reason, a scraping element 551 is provided to scrape the continuous layer C from the roller 550. The continuous layer C, which moves away from the pair of rollers 540, 550 and adheres to the roller 550 rotating faster, preferably has a thickness between 30 µm and 90 µm, preferably a thickness between 40 µm and 75 µm, and more preferably a thickness between 50 µm and 60 µm.

[0034] According to a preferred aspect, the speed of at least one of the two rollers 540, 550, in particular the (lower) faster roller 550, can be adjusted so that the optimal speed difference between the two rollers 540, 550 can be selected each time as needed.

[0035] Preferably, each refinement stage 510, 520, 530 also comprises, just downstream of the pair of rollers 540, 550, a belt conveyor 560 onto which the continuous layer C leaving the pair of rollers 540, 550 is laid after being scraped by the scraping element 551. Preferably, the continuous layer C is laid onto the conveyor with a wave-like movement (giving it a "bellows-like" shape) defining an alternating sequence of lands and recesses along the feed direction of the continuous layer C ( Fig. 4A-4C). This wave-like movement optimizes the process of mixing the material in the accumulation niche of the next pair of rollers 540, 550.

[0036] The wave-like motion is achieved by driving the belt conveyor 560 downstream of the pair of rollers 540, 550 at a feed speed lower than the speed of the rollers 540, 550 (and in particular lower than the tangential speed of the faster roller 550), so that the continuous layer C is gradually accumulated. Preferably, the feed speed of the belt conveyor 560 is adjustable so that the refining unit 500 can be adapted to different operating modes.

[0037] Preferably, the wave-like motion is also maintained downstream of all stages, but not downstream of the last stage, where the motion of the continuous layer C is preferably planar. Alternatively, only some of the intermediate refinement stages may provide the wave-like motion, while the others produce a planar continuous layer that lies flat on the next belt conveyor 560.

[0038] The refining unit 500 is also configured such that the belt conveyor 560, located downstream of a pair of rollers 540, 550, also defines the conveyor that feeds the continuous layer C to the next pair of rollers 540, 550 of the next stage. In other words, two consecutive pairs of rollers 540, 550 are connected by a belt conveyor 560 located between them. The first pair of rollers 540, 550, on the other hand, is fed by the feed conveyor 410, which carries the continuous flow F to the first stage 510 of the refining unit 1. Preferably, the feed conveyor 410 directly connects the distribution device 400 to the pair of rollers 540, 550 of the first refining stage 510.

[0039] Preferably, each belt conveyor 560 is inclined upwards along the feed direction of the continuous layer C, thereby defining an increasing feed stretch for the continuous layer C. In this way, the belt conveyor 560 compensates for the height difference between its infeed section, which is located at a height below the cutting edge of the scraping element 551 (which, as mentioned above, preferably acts on the lower roller 550) and its outfeed section, which directly faces the infeed niche of the next pair of rollers 540, 550.

[0040] Preferably, the individual refinement stages 510, 520, 530 are modular and / or identical, so that the refinement unit 500 can be configured with any desired number of stages. Alternatively, each pair of rollers 540, 550 is part of a respective separate module, and, in the same way, each belt conveyor 560 is also part of a respective separate module, so that any desired combination of stages can be produced.

[0041] For example, each refinement stage 510, 520, 530 comprises a box-shaped frame 80 containing the two rollers 540, 550 and the respective auxiliary parts (motors, supports, etc.) and provided with inlet and outlet openings that can be engaged by the preceding belt conveyor 560 and the next belt conveyor 560, respectively (which can be partially inserted into the respective inlet or outlet opening of the box-shaped frame 580). These openings can be arranged at different heights, taking into account the above-described inclination of the belt conveyors 60.

[0042] Likewise, the second particle size of the material moving out of the refinement unit 500 is preferably between 0.1 mm and 0.7 mm, more preferably between 0.2 mm and 0.5 mm, and even more preferably between 0.3 mm and 0.4 mm, in particular approximately 0.35 mm. In an exemplary embodiment, starting from a maximum particle size between 0.15 mm and 0.5 mm, the first refinement stage 510 brings the maximum particle size to a range of 0.1 to 0.42 mm, the second refinement stage 510 brings the maximum particle size to a range of 0.085 - 0.39 mm, and the third refinement stage 530 brings the maximum particle size to a range of 0.06 - 0.35 mm.

[0043] According to a further aspect of the invention, the refining unit 500 also comprises adjustment means 570 acting on one of the rollers of each pair of rollers 540, 550, in particular on the faster, lower roller 550, to adjust the position and / or thrust of the roller 550 relative to the other roller 540, so as to vary the compression and / or thickness of the continuous layer C emerging from the refining stage 510, 520, 530. This is preferably accomplished by supporting the roller 550 with an adjustable support element, preferably a linear actuator 571. Preferably, each belt conveyor 560 is also associated with a respective inspection device 590 configured to detect at least one property—for example, the density and / or thickness—of the continuous layer C arranged thereon.The inspection device 590 may be connected to a control unit that acts by feedback on one or more of the preceding stages 510, 520, 530 to perform a controlled adjustment of the compression action exerted by the rollers 540, 550.

[0044] Fig. Figure 5 shows a different embodiment which is identical to the previous one in the first section of the plant, ie up to the (optional) pre-refinement unit 300.

[0045] Downstream of the pre-refining unit 300, the mixture material (in the form of a preferably continuous flow) is sent to a cylinder refining machine 600, in particular with five cylinders, and thus of the type comprising a train of tangential cylinders for continuously processing a layer of material. Preferably, the cylinder refining machine 600 operates along a substantially vertical direction, specifically from bottom to top, and is optionally provided with means for scraping the layer of material from the last cylinder. The cylinder refining machine will not be described in detail, as it is essentially of a known type. Preferably, the second particle size of the material emerging from the cylinder refining unit 600 preferably has a maximum value between 0.01 mm and 0.08 mm, preferably between 0.025 and 0.055 mm.

[0046] Regardless of the structure of the refinement unit 500, 600 itself, the process comprises, downstream of the refinement unit 500, 600, a subsequent step of supplementing the refined mixture by adding at least one binder and / or an aerosol-forming material thereto, in particular by a further step of mixing, whereby a supplemented mixture is obtained.

[0047] For this purpose, the system comprises a second mixing machine 700, which is different and separate from the first mixing machine 200, and to which the refined mixture and the at least one binder and / or aerosol-forming material are fed to obtain a supplemented mixture. Flavorings can also be added during this step.

[0048] In particular, the second mixing machine 700 is connected to a feed tank 710 for supplying the at least one binder (e.g., based on cellulose) and / or the aerosol-forming material and / or flavorings, as well as to the refined mixture from the multi-stage refining unit 500 or from the cylinder refining machine 600.

[0049] According to one aspect of this invention, the step of supplementing the refined mixture is performed by adding the at least one binder and / or the aerosol-forming material while keeping the liquid content of the mixture substantially unchanged. Therefore, the refined mixture and the supplemented mixture have a substantially constant percentage of moisture.

[0050] In other words, the step of supplementing the refined mixture with the at least one binder and / or with the aerosol-forming material does not significantly increase the liquid content of the mixture. Consequently, the mechanical properties of the mixture remain essentially unchanged.

[0051] Downstream of the second mixing machine 700, the method may comprise a further step of refining the supplemented mixture so as to obtain a supplemented mixture having a third particle size that is smaller than the second particle size (optional).

[0052] For this purpose, the plant may comprise a further refining unit (not shown in the attached drawing), as described above with reference to the refining unit 500, 600. Regardless of whether the further refining unit is provided or not, the method comprises a subsequent step of forming a continuous web from the supplemented mixture. For this purpose, the plant comprises a forming unit 800 for forming the continuous web from the supplemented mixture. Preferably, the step of forming the continuous web is accomplished by laminating the supplemented mixture by at least one pair of rolls. For this purpose, the forming unit for forming a continuous web comprises at least one pair of laminating rolls 810.

[0053] Alternatively, the mixture could be divided into portions and a layered web formed, as described in patent application WO2020 / 058814.

[0054] The continuous web thus obtained can be subjected to a further step of multi-stage lamination (optional). For this purpose, the plant may comprise a laminator (not shown in the attached drawing) arranged downstream of the forming unit for forming the continuous web and comprising a succession of roller pairs designed to progressively reduce the thickness of the continuous web, as described in patent application WO2020 / 058814.

[0055] Finally, the method comprises a subsequent step of drying the continuous web. For this purpose, the system comprises a dryer 900 of a known type for drying the continuous web as it leaves the forming unit or the laminating device 800. The dryer 900 performs a final drying process on the continuous web to bring the liquid content of the continuous web to the desired level, for example, below 10%.

[0056] The plant described above thus produces a continuous web by refining in two stages: a first, "dry" refining stage in which the material has a very low liquid content, and a second, "wet" refining stage in which the material, already mixed with one or more liquids, has such a moisture content that it can be subjected to refining without emitting powder.

[0057] The present invention achieves the stated objectives and overcomes the disadvantages of the prior art.

[0058] Indeed, the method and the plant according to the invention allow a reduced labor input in terms of dry comminution followed by a multi-stage refining process capable of gradually reducing the particle size of the mixture material, processing the mixture in a wet state and greatly reducing the risk of fire due to powder circulation. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2020 / 058814 [0002, 0053, 0054]

Claims

[1] A method for producing a continuous web of reconstituted material comprising the following steps: - a step of dry shredding solid components of a starting material until a dry product having a first particle size is obtained; - a subsequent step of mixing the dry product with water to obtain a mixture; - a subsequent refining step applied to the mixture to obtain a refined mixture (C) having a second particle size smaller than the first particle size; - a subsequent step of supplementing the refined mixture by adding thereto at least one binder and / or an aerosol-forming material, in particular by a further step of mixing, whereby a supplemented mixture is obtained; - a subsequent step of forming a continuous web from the supplemented mixture; - a subsequent step of drying the continuous web. [2] The method of claim 1, wherein the step of mixing and the step of supplementing are carried out by respective different mixing machines. [3] A method according to claim 1 or 2, wherein the step of forming the continuous web is accomplished by laminating the supplemented mixture by at least one pair of rolls. [4] A method according to any one of the preceding claims, wherein the step of replenishing the mixture leaves the liquid content of the mixture substantially unchanged. [5] A method according to any one of the preceding claims, wherein the step of refining is carried out continuously by compression exerted by rollers. [6] A method according to claim 5, wherein the refining step is carried out by a cylinder refining machine (600) operating in particular along a substantially vertical direction; wherein the second particle size preferably has a maximum value between 0.01 and 0.08 mm, preferably between 0.025 and 0.055 mm. [7] Method according to claim 5, wherein the refining step is carried out by a multi-stage refining unit (500) operating in particular along a substantially horizontal direction; wherein the second particle size preferably has a maximum value between 0.04 and 0.50 mm, preferably between 0.06 and 0.035 mm. [8] A method according to claim 7, wherein the multi-stage refining unit comprises two or more stages (510, 520, 530), each comprising a pair of rollers (540, 550) arranged one above the other, and in each stage (510, 520, 530) is arranged to carry out a step of mixing the mixture in a niche defined between the two rollers (540, 550), followed by a step of compressing the mixture in the passage slot between the two rollers (540, 550), each stage (510, 520, 530) carrying out a respective step of reducing the particle size of the mixture. [9] A method according to claim 8, wherein each stage (510, 520, 530) produces a continuous layer of mixture (C) which adheres to one of the two rollers (550), and wherein said roller is associated with a scraping element (551) for removing the layer of mixture (C) from the roller (550). [10] A method according to any one of the preceding claims, further comprising a pre-refining step performed between the mixing step and the refining step so as to bring the mixture to a particle size intermediate between the first and second particle sizes; wherein the pre-refining step is preferably performed by a two-roll pre-refiner (300). [11] A method according to any one of the preceding claims, further comprising a refining step performed on the supplemented mixture between the step of supplementing and the step of forming so as to obtain a supplemented mixture having a third particle size smaller than the second particle size. [12] Plant for producing a continuous web of reconstituted material, comprising: - a shredding unit (100) for shredding solid components of the material and designed to obtain a dry product having a first particle size; - a first mixing machine (200) to which measured amounts of shredded solid components from the shredding unit (100) and water are fed, and which is designed to obtain a mixture; - a refining unit (500, 600) arranged downstream of the mixing machine (200) for performing at least one refining process on the mixture to obtain a refined mixture having a second particle size smaller than the first particle size; - a second mixing machine (700) to which the refined mixture and at least one binder and / or an aerosol-forming material are fed and which is designed to obtain a supplemented mixture; - a forming unit (800) for forming a continuous web from the supplemented mixture; - a dryer (900) for drying the continuous web emerging from the forming unit. [13] Plant according to claim 12, wherein the second mixer (700) is connected to a feed tank (710) for feeding the at least one binder and / or aerosol-forming material. [14] Plant according to claim 12 or 13, wherein the forming unit (800) for forming a continuous web comprises at least one pair of laminating rollers (810). [15] Plant according to one of claims 12 to 14, wherein the refining unit (500, 600) is designed to operate continuously by compression exerted by rollers. [16] Plant according to one of claims 12 to 15, wherein the refining unit (500, 600) comprises a cylinder refining machine (600), in particular operating along a substantially vertical direction. [17] Plant according to one of claims 12 to 16, wherein the refinement unit (500, 600) is designed as a multi-stage refinement unit (500), in particular operating along a substantially horizontal direction, and wherein the multi-stage refinement unit (500) comprises two or more stages (510, 520, 530), each comprising a pair of rollers (540, 550) arranged one above the other, and in each stage (510, 520, 530) is designed to carry out a step of mixing the mixture in a niche defined between the two rollers (540, 550), followed by a step of compressing the mixture in the passage slot between the two rollers (540, 550), wherein each stage (510, 520, 530) comprises a respective step of reducing the particle size of the mixture carries out. [18] Plant according to claim 17, wherein each stage (510, 520, 530) comprises a scraping element (551) associated with one of the two rollers (540, 550), in particular the lower roller (550), in order to remove the mixture layer from the roller (550). [19] Plant according to one of claims 12 to 18, further comprising a pre-refining unit (300) arranged between the first mixing unit (200) and the refining unit (500, 600) so as to bring the mixture to a particle size intermediate between the first and the second particle size; wherein the pre-refining unit (300) preferably comprises a two-roll pre-refiner (300). [20] Plant according to one of claims 12 to 19, further comprising a laminating device (800) arranged between the forming unit (800) for forming the continuous web and the dryer (900) and comprising a succession of pairs of rollers designed to gradually reduce the thickness of the continuous web; wherein the continuous web subjected to lamination is preferably obtained by layering the continuous web emerging from the second mixing machine (700).

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