Technical field

This invention relates to a method and a plant for making a web of reconstituted material, preferably but not necessarily, tobacco, in particular for making traditional or HNB smoking articles.

Background art

Known in the prior art is the production of a web of tobacco from a highly fluid mixture (or "slurry"), hence having a high water content, as described in the introductory section of patent application W02020/058814 in the name of the present Applicant. The method, as described in that document, has the disadvantage of requiring large installations involving high energy consumption, in particular at the oven drying stage. Moreover, the need to start with material having a very small particle size also means complex machinery and large factory floor spaces to accommodate the necessary machinery and equipment.

The same patent application also describes a method and a plant for the production of a tobacco web, characterized by the preparation of a mixture of tobacco particles and water, with extremely fine particles and a lower water content than in slurry technology, and wherein the mixture is divided into predetermined portions and then subjected to a succession of distinct laminating steps to obtain the web of tobacco which is then dried.

The Applicant has noticed that although this technology is satisfactorily practicable, it can be further improved, in particular in terms of simplifying the plant. In effect, it was noticed that a particularly critical aspect regarded the complexity of the plant needed for initially comminuting the tobacco into extremely fine particles, as well as the aspect of dividing the mixture into portions and then subjecting it to multiple laminating processes. Further, the method and the machine are optimized for a specific web format (particle size, thickness, etc.) and adapting to different formats involves onerous procedures.

Moreover, the method requires the use of a plurality of comminuting mills installed at the beginning of the plant to finely shred the material. Shredding is performed with the material in a dry state and creates large quantities of dust. This not only gives rise to the need to contain and/or remove the dust but also creates a fire hazard which in turn means providing flame prevention systems in accordance with the stringent fire regulations currently in force.

Aim of the invention

The aim of this invention is, therefore, to provide a method and a plant for making a web of reconstituted material and constituting a technically simpler solution compared to prior art solutions.

A further aim of the invention is to provide a method and a plant for making a web of reconstituted material to allow increasing the operational safety of the plant.

A further aim of the invention is to provide a method and a plant for making a web of reconstituted material, having high operational flexibility and which, in particular, can be used to obtain webs in different formats and to different specifications.

The aims are substantially achieved by a method and a plant in accordance with the features set out in the accompanying claims 1 and 13, respectively, and/or in one or more of the claims dependent thereon.

Brief description of the drawings

Further features and advantages of this invention are more apparent in the exemplary, hence non-limiting description of a preferred, but non-exclusive, embodiment of a method and a plant for making a web of reconstituted material, as illustrated in the accompanying drawings, in which: - Figure 1 is a schematic view of a first part of the plant according to the invention;

- Figure 2 is a schematic view of a second part of the plant according to the invention in a first embodiment thereof;

- Figure 3 shows a detail of the first section of the part of the plant of Figure 2;

- Figure 3A shows an enlargement of a detail from the view of Figure 3, in an operating condition;

- Figure 4 shows a detail of the second section of the part of the plant of Figure 2;

- Figures 4A-4C show enlarged views of respective details from the view of Figure 4, in an operating condition;

- Figure 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

The accompanying drawings illustrate different parts of a plant for making reconstituted tobacco or a material based on reconstituted tobacco according to this invention. By "reconstituted tobacco" is meant a type of tobacco which, at raw material level, is made from the solid waste remaining after the processing of tobacco leaves, and such as, for example, stems and leaf ribs, as well as very small parts of lamina and tobacco dust.

It is, however, specified that the same plant can be used to make layers or webs of generic reconstituted material (in particular of plant origin), not necessarily tobacco, in line with the generic nature of the invention (for example, hemp, aromatic leaves or others still).

For this purpose, the plant comprises a shredding unit 100 configured for shredding the solid components of tobacco and, for example, comprising a silo and one or more lower shredding wheels, in particular for comminuting bales (which are parallelepipedal in shape) of the solid components. The shredding unit 100 is configured for obtaining a maximum particle size of between 5 and 25 mm, preferably between 10 and 15 mm. In other words, the solid particles of tobacco leaving the shredding unit 100, although they have a wide range of sizes, include particles having a maximum size of up to 25 mm, preferably up to 15 mm. Alternatively, shredding may be characterized in that the predominant share by weight of the material leaving the shedding unit 100 (hence substantially excluding the powder component) has a particle size of between 0.5 and 25 mm, preferably between 0.8 mm and 15 mm.

For this purpose, the shredding unit 100 may be specifically provided with screens or other sifting means configured to allow only particles that are smaller than the predetermined size to pass through them.

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

As shown in Figure 1 , downstream of the shredding unit 100, there is a mixing machine 200, configured to combine and mix the solid tobacco particles leaving the shredding unit 100 with one or more liquids fed by at least one feeder denoted in its entirety by the numeral 210. The liquids may be, for example, water and/or at least one binding agent (for example, cellulose based) and an aerosol forming material and/or aromatizers.

The mixture thus obtained has a liquid content (by weight) of 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 such as to make the mixture compact enough to make it suitable for subsequent processes that give it its shape.

The mixing machine 200 has a structure of known type and, for example, may be configured to deliver discontinuous quantities of mixture, each deriving from a cycle of loading components and mixing them together.

This solution for the shredding unit 100 and the mixing machine 200 is common to both of the embodiments of the invention.

Figures 2-4 represent a different part of the plant, downstream of the mixing machine 200, according to the first embodiment of the invention. As shown in Figure 2, the mixture is collected by the 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 pre-refining unit 300 that follows (optional).

The pre-refining unit 300, shown in detail in Figure 3, is of the type with two rollers, that is to say, comprising a container 310 provided, at the bottom of it, with two rollers 320 that are mutually juxtaposed 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 lateral 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 "flattening" the material, that is to say, accumulating it (and, where necessary mixing it) in the niche and then compressing it through the rollers 320.

The two thin layers are then detached from the rollers 320 by respective scraping members 340, each associated with a respective roller.

Preferably, as shown at the bottom of Figure 3A, the two layers thus detached are placed on respective conveyor belts whose speed is selected in such way as to impart an undulatory motion to the layers, forming a succession of ridges and depressions along the feed direction.

The layers thus formed are transferred by suitable conveyors 350 (for example, a screw feeder and/or a conveyor belt) for further processing. One or more of the conveyors 350 may act as a device for homogenizing the material and blending together again the two layers detached from the rollers 320.

In particular, as shown in Figures 3 and 4, downstream of the pre-refining unit 300, there is a distributing device 400 configured to deliver a continuous flow F of mixture. Preferably, the distributing device 400 is configured as a laminating device to deliver a continuous layer of mixture. Preferably, the continuous flow F of mixture is released onto a feed conveyor 410, preferably a belt conveyor, intended to support and move the flow F along a feed direction. Preferably, the continuous flow F placed on the feed conveyor 300 has a layer configuration with substantially uniform thickness.

Preferably, also, the continuous flow F of mixture placed on the feed conveyor 410 has a thickness of between 1 and 10 mm and, more preferably, between 2 and 5 mm.

Downstream of the feed conveyor 410, there is a refining unit 500, which receives the continuous flow F of mixture, preferably constant in thickness. Although the refining unit 500 is preferably a multi-stage unit, in a possible embodiment, not illustrated but falling within the scope of the same inventive concept, it may comprise one stage only.

In particular, the refining unit 500 (shown in detail in Figure 4) comprises a plurality of refining stages 510, 520, 530, specifically three in the embodiment illustrated but whose number may vary from two to more than three, depending on operational requirements. The refining stages 510, 520, 530 each operate on the continuous flow (layer) F of mixture to remix it and compress it in such a way as to reduce the particle size of the mixture at each stage.

Each refining stage 510, 520, 5530 comprises a pair of counter-rotating rollers 540, 550, superposed on each other and defining between them a calibrated passage for compressing and forming the mixture material into a continuous layer C with constant thickness. Preferably, the rollers 540, 550 of each pair are substantially identical in diameter.

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 having the shape of the niche itself, hence deformed and/or pre-mixed compared to the continuous flow or layer arriving at the rollers 540, 550. The mixture material is then progressively "drawn" under the action of the rotating rollers 540, 550 and compressed until obtaining the aforementioned continuous layer C.

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 denote a process that includes steps of accumulating the material in the niche defined between the surfaces of the two rollers (Figures A-4C) and compressing it between the two rollers to form the continuous, constant-thickness layer. Thanks to this process, the mixture material is subjected to a step of mixing 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. The higher the number stages, therefore, the more the size of the particles 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 which has been accumulated in the niche.

Preferably, the rollers 540, 550 of each flattening stage 510, 520, 530 are both motor driven.

Preferably, the speed of rotation at which one of the rollers 540 550 of each pair of rollers is driven is different from that of the other roller. More particularly, 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 kept adherent to the roller 550, and for this reason, a scraping member 551 is provided to scrape the continuous layer C off the roller 550. The continuous layer C moving away from the pair of rollers 540, 550 and remaining adherent to the roller 550 which is rotating faster, preferably has a thickness of between 30 pm and 90 pm, more preferably a thickness of between 40 pm and 75 pm and, still more preferably, a thickness of between 50 pm and 60 pm.

According to a preferable aspect, the speed of at least one of the two rollers 540, 550, in particular the (lower) faster roller 550 can be set in such a way that the optimal speed difference between the two rollers 540, 550 is selected each time, as required.

Preferably, just downstream of the pair of rollers 540, 550, each refining stage 510, 520, 530 also comprises a belt conveyor 560 onto which the continuous layer C leaving the pair of rollers 540, 550 is laid after being scraped off by the scraping member 551. Preferably, the continuous layer C is laid on the conveyor with an undulatory motion (giving it a "bellows-like" shape) defining an alternating succession of ridges and recesses along the feed direction of the continuous layer C (Figures 4A-4C). This undulatory motion optimizes the process of mixing the material in the accumulation niche of the next pair of rollers 540, 550.

The undulatory motion is obtained 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 progressively 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.

Preferably, also, the undulatory motion is obtained downstream of all the 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 refining stages may provide the undulatory motion, while the others produce a planar continuous layer that lies flat on the next belt conveyor 560.

The refining unit 500 is also configured in such a way 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 successive pairs of rollers 540, 550 are connected by a belt conveyor 560 interposed between them. The first pair of rollers 540, 50, 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 connects the distributing device 400 directly to the pair of rollers 540, 550 of the first refining stage 510.

Preferably, each belt conveyor 560 is inclined upwards along the feed direction of the continuous layer C, thus defining an ascending feed stretch for the continuous layer C. That way, the belt conveyor 560 makes up for the difference in height between its infeed section, located at a height below the blade of the scraping member 551 (which, as mentioned above, preferably operates on the lower roller 550) and its outfeed section, which directly faces the infeed niche of the next pair of rollers 540, 550.

Preferably, the individual refining stages 510, 520, 530 are modular and/or identical so that the refining unit 500 can be made in a configuration with a desired number of stages. Alternatively, each pair of rollers 540, 550 forms part of a respective, distinct module and, in the same way, each belt conveyor 560 also forms part of a respective, distinct module so that a desired combination of stages can be made.

For example, each refining 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 infeed and outfeed openings which are engageable, respectively, by the preceding belt conveyor 560 and the next belt conveyor 560 (which can be partly inserted into the respective infeed or outfeed opening of the box-shaped frame 580). These openings may be disposed at different heights on account of the inclination of the belt conveyors 60 described above.

Preferably, also, the second particle size of the material moving out from the refining unit 500 is between 0.1 mm and 0.7 mm, more preferably between 0.2 mm and 0.5 mm and, still more preferably, between 0.3 mm and 0.4 mm, in particular around 0.35 mm.

In an example embodiment, starting from a maximum particle size of between 0.15 mm and 0.5 mm, the first refining stage 510 brings the maximum particle size to a 0.1 -0.42 mm range, the second refining stage 510 brings the maximum particle size to a 0.085-0.39 mm range and the third refining stage 530 brings the maximum particle size to a 0.06-0.35 mm range.

According to another aspect of the invention, the refining unit 500 also comprises adjusting 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 the thrust pressure of the roller 550 relative to the other roller 540 so as to vary the compression and/or the thickness of the continuous layer C feeding out from the refining stage 510, 520, 530. This is preferably accomplished by supporting the roller 550 with an adjustable supporting member, preferably a linear actuator 571 .

Preferably, also, each belt conveyor 560 is associated with a respective inspection device 590 configured to detect at least one property - for example, the density and/or the thickness - of the continuous layer C placed on it. The inspection device 590 may be connected to a control unit operating by feedback on one or more of the preceding stages 510, 520, 530 to perform a closed-loop adjustment of the compressive action applied by the rollers 540, 550.

Preferably, downstream of the refining unit 500, there is a laminating line (not illustrated), for example, described in patent application W02020/058814 (reference number 116), comprising a succession of roller pairs, each successively reducing the thickness of the continuous web.

Preferably, the continuous web subjected to lamination is preferably obtained by transversely layering the continuous web 2 feeding out from the refining unit 500. In other words, the refining unit 500 and the feed line extend perpendicularly to each other and the continuous web 2 feeding out from the refining unit 500 is released in layers onto the feed line to obtain a multiple thickness to be subjected to lamination.

Figure 5 shows a different embodiment, identical to the previous one in the first section of the plant, that is to say, up to the (optional) pre-refining unit 300. 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, hence of the type having a train of tangent cylinders for continuously processing a layer of material. Preferably, the cylinder refining machine 600 operates along a substantially vertical direction, specifically from the bottom up, provided, if necessary, with means for scraping the layer of material off the last cylinder. The cylinder refining machine is not described in detail in that it is of substantially known type. Preferably, the second particle size of the material feeding out from the cylinder refining unit 600 preferably has a maximum value of between 0.01 and 0.08 mm, preferably between 0.025 and 0.055 mm.

In this embodiment, the cylinder refining unit 600 is followed by a further mixing machine 700, which adds at least one or more liquids, and a laminating device (not illustrated) for forming a continuous web from the mixture released by the further mixing machine 700. Preferably, the mixture produced by the further mixing machine 700 has a liquid content of between 15% and 50%. In other words, the further mixing machine 700 may restore the mixture to the moisture content it has when it leaves the first mixing machine 200 or, alternatively, it may increase the moisture content.

In this case too, the web obtained from the laminating device may be subjected to lamination in a laminating line like the one described in patent application W02020/058814.

Alternatively, the five-cylinder refining machine 600 may have a slurry processing line downstream of it. For this purpose, downstream of the five- cylinder refining machine 600, there may be a further mixing machine 700 for adding at least one further liquid to the mixture of the continuous web 2 feeding out from the five-cylinder refining machine 600, thereby forming a slurry-like mixture, with a liquid content greater than 50% by weight, preferably greater than 60% or 70%), followed by a device for pouring this mixture onto a conveyor belt to form a continuous layer and by a dryer for drying the continuous layer (neither of these being illustrated). The plant described above thus produces a continuous web by refining in two stages: a first, "dry" refining stage, where the material has a very low liquid content, and a second, "wet" refining stage, where the material, already mixed with one or more liquids, has a moisture content such that it can be subjected to refining without emitting powders.

Moreover, in both embodiments, the plant comprises a dryer of known type (not illustrated) to perform a final drying operation on the continuous web so as to bring the liquid content of the continuous web to the desired level, for example, below 10%. The present invention achieves the preset aims, overcoming the disadvantages of the prior art.

In effect, the method and the plant according to the invention allow a reduced operating requirement in terms of dry comminution followed by a multi-stage refining process capable of progressively reducing the particle size of the mixture material, working the mixture in a wet state and thereby greatly reducing the risk of fire due to the circulation of powder.