Method and apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article

Abstract

The present disclosure relates to an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article, comprising a mixer (1a) for mixing ingredients of a recipe and water to form a slurry mixture (55) and a slot die (6) in fluid communication with the mixer (1a) for depositing the slurry mixture on a surface (22) located under the slot die (6) and moving with respect to the slot die (6) along a conveying direction (24). The apparatus further includes a stirrer (7) upstream a manifold (12) of the slot die for stirring the slurry mixture entering said manifold. The disclosure further concerns a method for producing a sheet of aerosol-generating substrate for an aerosol-generating article.

Description

[0001] METHOD AND APPARATUS FOR PRODUCING A SHEET OF AEROSOL-GENERATING

[0002] SUBSTRATE FOR AN AEROSOL-GENERATING ARTICLE

[0003] The present disclosure relates to a method and to an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article.

[0004] Aerosol-generating articles or heat-not-burn cigarettes, in which an aerosol-generating substrate is heated rather than combusted, are known in the art. Typically, in such heated aerosolgenerating articles, an aerosol is generated by the transfer of heat from a heat source to the physically separate aerosol-generating substrate or material, which may be located in contact with, within, around, or downstream of the heat source. During use of the aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by heat transfer from the heat source and are entrained in air drawn through the aerosol-generating article. As the released compounds cool, they condense to form an aerosol.

[0005] An aerosol-generating article is an assembly of different kinds of components which are rodshaped elements (small cylinders) enclosed in one or more wrapping materials. One of the rodshaped elements is usually made of a substrate which generates aerosol when heated (Heat Not Burn consumable). The aerosol-generating substrate is usually made from a continuous sheet which is gathered, wrapped in a wrapper and cut in a plurality of rod-shaped elements.

[0006] Currently, a sheet of aerosol-generating substrate is prepared by casting a slurry on a moving belt through a casting box. For instance, a tobacco slurry is transformed into tobacco cast leaf by the following operations: the tobacco slurry (tobacco powder, water, glycerine, fibres and binders) is manufactured in a tank, the tobacco slurry is then poured into an open-air casting box having an exit at its bottom, an exit height is controlled by a knife which cast the exiting tobacco slurry at a determined thickness on a moving conveyor (e.g. a metal belt). The tobacco slurry is subsequently dried to become tobacco cast leaf to be cut and shaped into cylindrical plugs. WO2016096963A1 , WO2016050471 and WO2017089589 disclose methods for the preparation of tobacco slurries and casting of the slurries through casting boxes to form sheets.

[0007] Document US2023025967A1 discloses a method for the production of a sheet of a material containing alkaloids, comprising the steps of: providing a slurry including a material containing alkaloids, an aerosol former and water, extruding the slurry, collecting the extruded slurry in a tank having a plurality of outlets, providing substrate sheets including fibres; supplying slurry from the plurality of outlets so as to form a plurality of strips of slurry on the substrate sheets, to form sheets of material containing alkaloids.

[0008] Document CN116746700B discloses a casting device, comprising a conveying mechanism, on which a material discharge box body matched with a steel belt is arranged, the bottom of the material discharge box body is arc-shaped toward the conveying direction of the steel belt, and a material discharge port is opened. A stirring unit is arranged in the material discharge box body. In this technical field, it would be desirable to have a method and an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article able to improve the quality of the manufactured aerosol-generating substrates and thus of the resulting aerosol-generating articles.

[0009] It would be desirable to have an apparatus and a method capable of manufacturing sheets of aerosol-generating substrate such as to guarantee an optimal and consistent experience to the final user.

[0010] It would be particularly desirable to have an apparatus and a method capable of providing an accurate and constant thickness of the sheets of aerosol-generating substrate.

[0011] It would be also desirable to have an apparatus and a method capable of manufacturing homogeneous sheets of aerosol-generating substrate.

[0012] Indeed, constant thickness and homogeneity of the sheet allow to provide an accurate and replicable amount of substance in each consumable and in each aerosol-generating article, thus assuring a consistency of smoking experiences to the user.

[0013] It would be further desirable to have an apparatus and a method capable of manufacturing sheets of aerosol-generating substrate from slurries with high viscosity, i.e. viscosity of 10-300 Pa*S considering shear rate 10 sec-1 , or with viscosity that varies during casting.

[0014] Particularly, it would be further desirable to have an apparatus and a method allowing to control thickness and grammage of the cast sheet obtained from slurries with high viscosity and / or varying viscosity.

[0015] The present disclosure relates to an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article. The apparatus comprises: a mixer for mixing ingredients of a recipe and water to form a slurry mixture, a slot die in fluid communication with the mixer for deposition of the slurry mixture on a surface located under the slot die and moving with respect to it along a conveying direction to form a cast sheet. The slot die includes a head that internally delimits: a distribution channel having a slot inlet for receiving the slurry mixture, a manifold in fluid communication with the distribution channel, and a narrow section in fluid communication with the manifold and terminating in a slot outlet facing the surface. The apparatus further comprises a stirrer located upstream the manifold of the slot die for stirring the slurry mixture entering said manifold.

[0016] The present disclosure also relates to a method for producing a sheet of aerosol-generating substrate for an aerosol-generating article, comprising the steps of mixing a recipe with water to form a slurry mixture, feeding the slurry mixture to a slot die and depositing the slurry mixture on a surface to form a cast sheet, and stirring the slurry mixture entering a manifold of the slot die. The slot die may comprise a head that internally delimits: at least one distribution channel having a slot inlet for receiving the slurry mixture, a manifold (in fluid communication with the distribution channel, a narrow section in fluid communication with the manifold and terminating in a slot outlet, wherein the apparatus further comprises a stirrer upstream of the manifold of the slot die, wherein the method further comprises a step of stirring, via the stirrer, the slurry mixture entering the manifold of the slot die.

[0017] The present disclosure relates to a process for manufacturing an aerosol-generating article component. The process comprises: manufacturing a sheet of aerosol-generating substrate for an aerosol-generating article in an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article or through the method for producing a sheet of aerosol-generating substrate for an aerosol-generating article; gathering the sheet of aerosol-generating substrate and wrapping the gathered sheet of aerosol-generating substrate in a wrapper to form a continuous rod; cutting the continuous rod into a plurality of aerosol-generating article components each having a rod shape, each aerosol-generating article component comprising a gathered sheet formed from a cut portion of the sheet of aerosol-generating substrate. Optionally, before gathering, the process comprises: weakening the sheet of aerosol-generating substrate by making weakened lines in said sheet of aerosol-generating substrate, optionally through a crimping step generating a plurality of substantially parallel ridges or corrugations.

[0018] The apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article comprises: a mixer for mixing ingredients of a recipe and water to form a slurry mixture, a slot die in fluid communication with the mixer for deposition of the slurry mixture on a surface located under the slot die and moving with respect to it along a conveying direction to form a cast sheet. The slot die includes a head that internally delimits: a distribution channel having a slot inlet for receiving the slurry mixture, a manifold in fluid communication with the distribution channel, and a narrow section in fluid communication with the manifold and terminating in a slot outlet facing the surface. The apparatus further comprises a stirrer located upstream the manifold of the slot die for stirring the slurry mixture entering said manifold.

[0019] The method for producing a sheet of aerosol-generating substrate for an aerosol-generating article, comprises the steps of mixing a recipe with water to form a slurry mixture, feeding the slurry mixture to a slot die and depositing the slurry mixture on a surface to form a cast sheet, and stirring the slurry mixture entering a manifold of the slot die. The slot die may comprise a head that internally delimits: at least one distribution channel having a slot inlet for receiving the slurry mixture, a manifold (in fluid communication with the distribution channel, a narrow section in fluid communication with the manifold and terminating in a slot outlet, wherein the apparatus further comprises a stirrer upstream of the manifold of the slot die, wherein the method further comprises a step of stirring, via the stirrer, the slurry mixture entering the manifold of the slot die.

[0020] The present disclosure also relates to an aerosol-generating article comprising at least one aerosol-generating article component made through said process for manufacturing an aerosolgenerating article component.

[0021] The inventor found that the disclosed apparatus and method create a shearing stress in the slurry mixture via the stirrer, causing temperature increase which impacts locally on viscosity of the slurry mixture. Specifically, the inventor found that the disclosed device and method decrease locally the viscosity of the slurry mixture by controlling the rotational speed of the stirrer in contact with the slurry, or locally increasing the temperature of the slurry via a heater.

[0022] The inventor found that a decrease in the viscosity of the slurry mixture leads to improved homogeneity and increased stability of the deposition by the slot die. Additionally, the disclosed apparatus and method allow for proper tuning of various properties of the aerosol-generating article components, such as the consistency and quality of the tobacco cast sheet, as well as flavor and aroma.

[0023] The inventor also found positioning the stirrer at or near the manifold of the slot die reduces the travel time of the slurry mixture, thereby improving the homogeneity of the cast sheet.

[0024] Additionally, the inventor found that the disclosed apparatus and method increase material yield and reduce costs.

[0025] Furthermore, the inventor found that the apparatus is structurally simple and cost-effective.

[0026] In some embodiments, the stirrer operates within a loading pipe external to the slot die. The loading pipe may be in fluid communication with the slot inlet of the distribution channel.

[0027] In some embodiments, the stirrer operates within a loading pipe defining a section of a distribution channel of the slot die.

[0028] In some embodiments, the stirrer operates within a loading pipe internal the at least one distribution channel of the slot die.

[0029] In some embodiments, the the loading pipe surrounds entirely the stirrer defining a closed chamber.

[0030] In some embodiments, the apparatus comprises a delivery pipe placing the mixer or the slurry tank in fluid communication with the slot die. The loading pipe may define a section of the delivery pipe. The delivery pipe and the loading pipe may have respective inner surfaces contacting the slurry mixture with equal transversal cross-sectional areas.

[0031] The inventor found that a closed loading pipe improves the homogeneity of the slurry mixture casted via the slot die, as opposed to the traditional deposition process using an open casting box where air is incorporated in the slurry, thereby increasing its heterogeneity.

[0032] The loading pipe may be sloped with respect to a horizontal plane, optionally by an inner angle comprised between 5° and 60°, optionally comprised between 10° and 45°.

[0033] The loading pipe may extend between a first end in proximity of the manifold of the slot die and a second end, located superiorly to the first end.

[0034] In some embodiments, the stirrer is movable with respect to the manifold of the slot die for stirring the slurry mixture. The stirrer may be movable by rotation.

[0035] In some embodiments, it is provided for controlling, as a function of one or more detected properties of the slurry mixture, a movement of the stirrer. A control unit may be connected to the stirrer for controlling thereof as a function of a detected property of the slurry mixture. A motor may be connected to the stirrer for rotation.

[0036] In some embodiments, the control unit regulates the stirrer, or optionally the motor operating the stirrer, to match a specified speed or power threshold value.

[0037] The inventor found that controlling the rotation of the stirrer allows for adjusting the viscosity of the slurry mixture in contact with the stirrer. Specifically, the control unit evaluates the actual viscosity of the slurry and adjusts the motor speed to ensure the slurry in the slot die matches an optimal viscosity range.

[0038] In some embodiments, feeding the slurry mixture to the slot die comprises: pumping the slurry mixture to the slot die. The apparatus may include a pump, for instance a volumetric pump or a cavity pump, operating between the mixer or the slurry tank and the stirrer. The pump may operate on the delivery pipe.

[0039] A control unit may be connected to the pump for controlling thereof as a function of a detected property of the slurry mixture. In some embodiments, the control unit regulates the flow rate of a pump channeling the slurry mixture toward the slot die. Optionally, it is provided for pumping the slurry mixture to the slot die with a flow rate between 0.5 dm3 / s and 1 dm3 / s, optionally of 0.8 dm3 / s.

[0040] The inventor found that regulating the pump's flow rate improves the homogeneity of slurry deposition and allows the slurry mixture to be cast at a constant thickness, thereby enhancing the overall quality of the cast sheet.

[0041] The detected property may comprise a viscosity value of the slurry. The detected property may comprise a resistance torque value of the slurry to the movements of the stirrer. The detected property may comprise a measured thickness value of the slurry mixture deposited on the surface. The detected property may comprise a measured flow rate of the slurry mixture.

[0042] At least one viscometer may be configured for generating a signal representative of a viscosity of the slurry mixture processed by the stirrer. The control unit may be connected to the viscometer and configured for determining the viscosity value based on the signal generated by the viscometer. The viscometer may be located within the loading pipe. The control unit may be configured for controlling the motor as a function of the viscosity value.

[0043] In some embodiments, the control unit is further configured for: comparing the determined viscosity value with a viscosity threshold value, increasing or decreasing an angular speed of the motor so that the viscosity value matches the viscosity threshold value.

[0044] In some embodiments, the control unit is connected to the motor and is configured for estimating, based on a current value absorbed by the motor, the resistance torque value applied from the slurry mixture to the stirrer, controlling the motor as a function of the estimated resistance torque.

[0045] In some embodiments, the control unit is further configured for comparing the estimated resistance torque with a torque threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor, to locally increase or decrease temperature of the slurry mixture, so that the estimated resistance torque value matches the torque threshold value.

[0046] The control unit may be configured for regulating the angular speed of the motor between 1000 rpm and 10000 rpm.

[0047] At least one speed sensor may be coupled with the stirrer, optionally a projection, and may be configured for generating a signal representative of a rotational speed of the stirrer. The control unit may be connected to the speed sensor and may be configured for determining a measured angular speed value of the stirrer based on the signal generated by the speed sensor, controlling the stirrer as a function of the measured angular speed value.

[0048] In some embodiments, the control unit is further configured for comparing the measured angular speed value with a speed or power threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor so that the measured angular speed value matches the speed or power threshold value.

[0049] In some embodiments, at least one height sensor may be configured for generating a signal representative of a thickness of the slurry mixture deposited by the slot die on the surface, optionally a thickness of the cast sheet. The control unit may be connected to the height sensor and may be configured for determining a measured thickness value based on the signal generated by the height sensor. The height sensor may be located at or close to the slot outlet of the slot die.

[0050] In some embodiments, the control unit is configured for controlling the motor or the pump as a function of the thickness value. The control unit may be further configured for: comparing the measured thickness value with a thickness threshold value, increasing or decreasing an angular speed of the motor so that the measured thickness value matches the thickness threshold value.

[0051] At least one flow meter may be configured for generating a signal representative of a flow rate of the slurry mixture processed by the stirrer. The control unit may be connected to the flow meter and may be configured for determining the measured flow rate based on the signal generated by the flow meter. The flow meter may be located close to the stirrer. The control unit may be configured for controlling the pump as a function of the measured flow rate.

[0052] In some embodiments, the control unit is further configured for comparing the measured flow rate with a flow rate threshold value, regulating the pump so that the measured flow rate value matches the flow rate threshold value.

[0053] The control unit may be configured to control the motor to subject the stirrer to full rotations or the control unit may be configured to control the motor to subject the stirrer to an oscillating movement between two end positions for creating a vibrating motion.

[0054] In some embodiments, the stirrer includes one or more projections, e.g., conformed as elongated pins or having a cylindrical shape, contacting the slurry mixture for stirring. Said one or more projections have constant cross section, optionally comprised between 1 mm and 5 mm. Each of said one or more projections may be made of abrasion resistance metal. Said one or more projections may include a frictionless coating on an external surface in direct contact with the slurry mixture.

[0055] Optionally, the stirrer includes a plurality of projections contacting the slurry mixture for stirring. The plurality of projections may range from 2 to 50, optionally from 3 to 32. The plurality of projections may extend radially from a junction area. The projections may rotate about a rotational axis passing through the junction area.

[0056] In some embodiments, the projections of the stirrer are fixed with the loading pipe which rotates about the rotational axis.

[0057] In some embodiments, the projections of the stirrer are decoupled to the loading pipe, resulting rotativity movable with respect to the loading pipe about the rotational axis.

[0058] A radial pattern may be defined by the projections of said plurality lying on an ideal plane transversal, optionally orthogonal, to the rotational axis of the stirrer.

[0059] In some embodiments, the projections extend radially from a junction area coincident with a rotational axis of the stirrer, for defining a radial pattern.

[0060] In some embodiments, the projections of a radial pattern are angularly offset to each other, optionally by an angle comprised between 70° and 110°, optionally comprised between 80° and 100°.

[0061] The stirrer may include a plurality of radial patterns, each distinct and spaced apart from the others, resulting axially offset along a direction parallel to the rotational axis of the stirrer. Each projection of a radial pattern is angularly offset relative to a respective projection of an adjacent radial pattern, optionally by an angle comprised between 10° and 80°, even more optionally comprised between 25° and 65°. The plurality of radial patterns may cover a preponderant part of the loading pipe. The plurality of radial patterns may cover between 10% and 90%, optionally between 30% and 70%, of a length of the loading pipe.

[0062] In some embodiments, a transmission member, optionally a belt or a timing belt, couples the motor with the loading pipe for rotating the stirrer.

[0063] In some embodiments, a supporting structure within the loading pipe has: a shaft radially attached inside the loading pipe, said shaft being integral with the loading pipe, an arm movable by rotation about the shaft.

[0064] In some embodiments, a supporting structure includes projections extending transversally, optionally orthogonally, to a flow direction of the slurry mixture.

[0065] The plurality of projections may be transversally engaged to the arm. The plurality of projections may be integral with the rotational movement of the arm.

[0066] An internal magnet may be embedded in the arm with poles located at respective ends of the arm. An external magnet may be located outside the loading pipe and coupled to the motor, such that rotation of the external magnet induces, optionally through the internal magnet, rotation of the arm via magnetic interaction, optionally causing the projections to rotate and stir the slurry mixture for increasing temperature locally and reducing locally its viscosity.

[0067] In some embodiments, the supporting structure is magnetically rotated by means of external permanent magnets, which are magnetically coupled with internal permanent magnets attached to the supporting structure.

[0068] The inventor found that using external permanent magnets to induce the rotation of the supporting structure via internal permanent magnets eliminates the need for sealing members on the openings of the loading pipe, thereby improving the sealing performance of the stirrer.

[0069] In some embodiments, the supporting structure further includes an auxiliary shaft radially attached inside the loading pipe, an auxiliary arm movable by rotation about the auxiliary shaft.

[0070] An auxiliary internal magnet may be embedded in the auxiliary arm with poles located at respective ends of the auxiliary arm. An auxiliary external magnet may be located outside the loading pipe and coupled to the motor, such that rotation of the auxiliary external magnet induces rotation of the auxiliary arm. The shaft or the auxiliary shaft may have an elongated body extending in alignment with a flow direction of the slurry mixture to prevent the slurry mixture from depositing on the shaft or on the auxiliary shaft.

[0071] In some embodiments, the supporting structure pivots about one or more opposing shafts with a symmetric biconvex airfoil profile.

[0072] The inventor found that shafts with a symmetric biconvex airfoil profile prevent the slurry mixture from depositing on the shafts.

[0073] In some embodiments, an elongated body of each shaft in the supporting structure has a symmetrical cross-sectional shape with respect to an ideal plane parallel to the flow direction of the slurry mixture.

[0074] In some embodiments, an elongated body of each shaft includes a first and a second surface of convex shape with concavities facing each other. The first surface may join the second surface at opposite ends forming sharp or tapered edges of the elongated body.

[0075] The elongated body may have a maximum thickness at a central section of the elongated body itself, gradually decreasing towards each end.

[0076] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0077] EX1. Apparatus for producing a sheet of aerosol-generating substrate for an aerosolgenerating article, the apparatus comprising: a mixer configured for mixing ingredients of a recipe and water to form a slurry mixture, a slot die in fluid communication with the mixer or with a slurry tank for the slurry mixture, said slurry tank being interposed between the mixer and the slot die, a surface located under the slot die and moving with respect to the slot die along a conveying direction for receiving the slurry mixture from said slot die to form a cast sheet, wherein the slot die comprises a head that internally delimits: at least one distribution channel having a slot inlet for receiving the slurry mixture, a manifold in fluid communication with the distribution channel, a narrow section in fluid communication with the manifold and terminating in a slot outlet, wherein the apparatus further comprises a stirrer interposed between the manifold of the slot die and either the mixer or the slurry tank, for stirring the slurry mixture entering the manifold of the slot die.

[0078] EX2. The apparatus according to EX1 , wherein the stirrer operates within a loading pipe external to the slot die and in fluid communication with the slot inlet of the distribution channel.

[0079] EX3. The apparatus according to EX1 , wherein the stirrer operates within a loading pipe internal the at least one distribution channel of the slot die.

[0080] EX4. The apparatus according to EX3, wherein the loading pipe defines a section of the at least one distribution channel of the slot die.

[0081] EX5. The apparatus according to any of EX1 to EX4, wherein the apparatus comprises a delivery pipe placing the mixer or the slurry tank in fluid communication with the slot die.

[0082] EX6. The apparatus according to EX5 when depending on EX2, wherein the loading pipe defines a section of the delivery pipe.

[0083] EX7. The apparatus according to EX6, wherein the delivery pipe and the loading pipe have respective inner surfaces contacting the slurry mixture with equal transversal cross-sectional areas.

[0084] EX8. The apparatus according to EX2 or EX3, wherein the loading pipe surrounds entirely the stirrer defining a closed chamber.

[0085] EX9. The apparatus according to EX2 or EX3, wherein the loading pipe is sloped with respect to a horizontal plane.

[0086] EX10. The apparatus according to EX2 or EX3, wherein the loading pipe is sloped by an inner angle comprised between 5° and 60°, optionally comprised between 10° and 45°.

[0087] EX11 . The apparatus according to EX2 or EX3, wherein the loading pipe extends between a first end in proximity of the manifold of the slot die and a second end, located superiorly to the first end.

[0088] EX12. The apparatus according to any of EX1 to EX11 , wherein the stirrer is movable with respect to the manifold of the slot die for stirring the slurry mixture.

[0089] EX13. The apparatus according to EX12, wherein the stirrer is movable by rotation.

[0090] EX14. The apparatus according to any of EX1 to EX13, wherein the apparatus includes a pump operating between the mixer or the slurry tank and the stirrer.

[0091] EX15. The apparatus according to EX14 when depending on EX5, wherein the pump operates on the delivery pipe. EX16. The apparatus according to EX14 or EX15, wherein the pump is a volumetric pump, optionally a cavity pump.

[0092] EX17. The apparatus according to any of EX14 to EX16 comprising a control unit connected to the pump for controlling thereof as a function of a detected property of the slurry mixture.

[0093] EX18. The apparatus according to any of EX1 to EX17 comprising a control unit connected to the stirrer for controlling thereof as a function of a detected property of the slurry mixture.

[0094] EX19. The apparatus according to EX17 or EX18, wherein the detected property comprises a viscosity value of the slurry.

[0095] EX20. The apparatus according to EX17 or EX18, wherein the detected property comprises a resistance torque value of the slurry to the movements of the stirrer.

[0096] EX21. The apparatus according to EX17 or EX18, wherein the detected property comprises a measured thickness value of the slurry mixture deposited on the surface.

[0097] EX22. The apparatus according to EX17, wherein the detected property comprises a measured flow rate of the slurry mixture.

[0098] EX23. The apparatus according to any of EX1 to EX22, comprising at least one viscometer configured for generating a signal representative of a viscosity of the slurry mixture processed by the stirrer.

[0099] EX24. The apparatus according to EX23 when depending on EX19, wherein the control unit is connected to the viscometer and configured for determining the viscosity value based on the signal generated by the viscometer.

[0100] EX25. The apparatus according to EX23 or EX24, wherein the viscometer is located within the loading pipe.

[0101] EX26. The apparatus according to any of EX1 to EX25 comprising a motor connected to the stirrer for rotation.

[0102] EX27. The apparatus according to EX26 when depending on EX24, wherein the control unit is configured for controlling the motor as a function of the viscosity value.

[0103] EX28. The apparatus according to EX27, wherein the control unit is further configured for: comparing the determined viscosity value with a viscosity threshold value, increasing or decreasing an angular speed of the motor so that the viscosity value matches the viscosity threshold value.

[0104] EX29. The apparatus according to EX26 when depending on EX20, wherein the control unit is connected to the motor and is configured for: estimating, based on a current value absorbed by the motor, the resistance torque value applied from the slurry mixture to the stirrer, controlling the motor as a function of the estimated resistance torque.

[0105] EX30. The apparatus according to EX29, wherein the control unit is further configured for: comparing the estimated resistance torque with a torque threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor so that the estimated resistance torque value matches the torque threshold value.

[0106] EX31. The apparatus according to EX26 when depending on EX18, wherein the control unit is configured to regulate the angular speed of the motor between 1000 rpm and 10000 rpm.

[0107] EX32. The apparatus according to any of EX1 to EX31 comprising at least one speed sensor coupled with the stirrer, optionally a projection, and configured for generating a signal representative of a rotational speed of the stirrer.

[0108] EX33. The apparatus according to EX32 when depending on EX18, wherein the control unit is connected to the speed sensor and configured for: determining a measured angular speed value of the stirrer based on the signal generated by the speed sensor, controlling the stirrer as a function of the measured angular speed value.

[0109] EX34 The apparatus according to EX33 in combination with EX26, wherein the control unit is further configured for: comparing the measured angular speed value with a speed or power threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor so that the measured angular speed value matches the speed or power threshold value.

[0110] EX35. The apparatus according to any of EX1 to EX34, comprising at least one height sensor configured for generating a signal representative of a thickness of the slurry mixture deposited by the slot die on the surface, optionally a thickness of the cast sheet.

[0111] EX36. The apparatus according to EX35 when depending on EX21 , wherein the control unit is connected to the height sensor and configured for determining a measured thickness value based on the signal generated by the height sensor.

[0112] EX37. The apparatus according to EX35 or EX36, wherein the height sensor is located at or close to the slot outlet of the slot die.

[0113] EX38. The apparatus according to EX36 in combination with EX26, wherein the control unit is configured for controlling the motor or the pump as a function of the thickness value.

[0114] EX39. The apparatus according to EX38, wherein the control unit is further configured for: comparing the measured thickness value with a thickness threshold value, increasing or decreasing an angular speed of the motor so that the measured thickness value matches the thickness threshold value.

[0115] EX40. The apparatus according to any of EX1 to EX39, comprising at least one flow meter configured for generating a signal representative of a flow rate of the slurry mixture processed by the stirrer. EX41 . The apparatus according to EX40 when depending on EX22 wherein the control unit is connected to the flow meter and configured for determining the measured flow rate based on the signal generated by the flow meter.

[0116] EX42. The apparatus according to EX40 or EX41 , wherein the flow meter is located close to the stirrer.

[0117] EX43. The apparatus according to EX41 , wherein the control unit is configured for controlling the pump as a function of the measured flow rate.

[0118] EX44. The apparatus according to EX43, wherein the control unit is further configured for: comparing the measured flow rate with a flow rate threshold value, regulating the pump so that the measured flow rate value matches the flow rate threshold value.

[0119] EX45. The apparatus according to EX26 when depending on EX18, wherein the control unit is configured to control the motor to subject the stirrer to full rotations.

[0120] EX46. The apparatus according to EX26 when depending on EX18, wherein the control unit is configured to control the motor to subject the stirrer to an oscillating movement between two end positions for creating a vibrating motion.

[0121] EX47. The apparatus according to any of EX1 to EX46, wherein the stirrer includes one or more projections contacting the slurry mixture for stirring.

[0122] EX48. The apparatus according to EX47, wherein said one or more projections are conformed as elongated pins.

[0123] EX49. The apparatus according to EX47 or EX48, wherein said one or more projections have cylindrical shape.

[0124] EX50. The apparatus according to any of EX47 to EX49, wherein said one or more projections have constant cross section, optionally comprised between 1 mm and 5 mm.

[0125] EX51 . The apparatus according to any of EX47 to EX50, wherein each of said one or more projections is made of abrasion resistance metal.

[0126] EX52. The apparatus according to any of EX47 to EX51 , wherein said one or more projections include a frictionless coating on an external surface in direct contact with the slurry mixture.

[0127] EX53. The apparatus according to any of EX1 to EX52, wherein the stirrer includes a plurality of projections contacting the slurry mixture for stirring.

[0128] EX54. The apparatus according to EX53, wherein the plurality of projections ranges from 2 to 50, optionally from 3 to 32.

[0129] EX55. The apparatus according to EX53 or EX54, wherein said plurality of projections extend radially from a junction area.

[0130] EX56. The apparatus according to EX55, wherein the projections rotate about a rotational axis passing through the junction area. EX57. The apparatus according to EX56 in combination with EX2 or EX3, wherein the projections of the stirrer are fixed with the loading pipe which rotates about the rotational axis.

[0131] EX58. The apparatus according to EX56 in combination with EX2 or EX3, wherein the projections of the stirrer are decoupled to the loading pipe, resulting rotativity movable with respect to the loading pipe about the rotational axis.

[0132] EX59. The apparatus according to any of EX56 to EX58 comprising a radial pattern defined by the projections of said plurality lying on an ideal plane transversal, optionally orthogonal, to the rotational axis of the stirrer.

[0133] EX60. The apparatus according to EX59, wherein the projections of said radial pattern are angularly offset to each other.

[0134] EX61 . The apparatus according to EX59 or EX60, wherein the projections of said radial pattern are angularly offset to each other by an angle comprised between 70° and 110°, optionally comprised between 80° and 100°.

[0135] EX62. The apparatus according to any of EX56 to EX61 , wherein the stirrer includes a plurality of radial patterns, each distinct and spaced apart from the others, resulting axially offset along a direction parallel to the rotational axis of the stirrer.

[0136] EX63. The apparatus according to EX62, wherein each projection of a radial pattern is angularly offset relative to a respective projection of an adjacent radial pattern, optionally by an angle comprised between 10° and 80°, even more optionally comprised between 25° and 65°.

[0137] EX64. The apparatus according to EX62 or EX63 in combination with EX2 or EX3, wherein the plurality of radial patterns covers a preponderant part of the loading pipe.

[0138] EX65. The apparatus according to EX62 or EX63 in combination with EX2 or EX3, wherein the plurality of radial patterns covers between 10% and 90%, optionally between 30% and 70%, of a length of the loading pipe.

[0139] EX66. The apparatus according to EX26 when depending on EX2 or EX3, comprising a transmission member, optionally a belt or a timing belt, coupling the motor with the loading pipe for rotating the stirrer.

[0140] EX67. The apparatus according to any of EX1 to EX54 when depending on EX2 or EX3 comprising a supporting structure within the loading pipe; the supporting structure optionally pivoting about one or more opposing shafts with a symmetric biconvex airfoil profile; the supporting structure optionally having: a shaft radially attached inside the loading pipe, said shaft being integral with the loading Pipe, an arm movable by rotation about the shaft.

[0141] EX68. The apparatus according to EX67 in combination with EX53, wherein the plurality of projections is transversally engaged to the arm. EX69. The apparatus according to EX68, wherein the plurality of projections is integral with the rotational movement of the arm.

[0142] EX70. The apparatus according to any of EX67 to EX69, comprising an internal magnet embedded in the arm with poles located at respective ends of the arm.

[0143] EX71. The apparatus according to any of EX67 to EX70 in combination with EX26, comprising an external magnet located outside the loading pipe and coupled to the motor, such that rotation of the external magnet induces, optionally through the internal magnet, rotation of the arm via magnetic interaction, optionally causing the projections to rotate and stir the slurry mixture for locally increasing a temperature of the slurry mixture and locally reducing its viscosity.

[0144] EX72. The apparatus according to any of EX67 to EX71 , wherein the supporting structure further includes: an auxiliary shaft radially attached inside the loading pipe, an auxiliary arm movable by rotation about the auxiliary shaft.

[0145] EX73. The apparatus according to EX72, comprising an auxiliary internal magnet embedded in the auxiliary arm with poles located at respective ends of the auxiliary arm.

[0146] EX74. The apparatus according to EX72 or EX73 in combination with EX26, comprising an auxiliary external magnet located outside the loading pipe and coupled to the motor, such that rotation of the auxiliary external magnet induces rotation of the auxiliary arm.

[0147] EX75. The apparatus according to EX67 or EX74, wherein the shaft or the auxiliary shaft has an elongated body extending in alignment with a flow direction of the slurry mixture to prevent the slurry mixture from depositing on the shaft or on the auxiliary shaft.

[0148] EX76. The apparatus according to EX75, wherein the elongated body has a symmetrical cross-sectional shape with respect to an ideal plane parallel to the flow direction of the slurry mixture.

[0149] EX77. The apparatus according to EX75 or EX76, wherein the elongated body includes a first and a second surface of convex shape.

[0150] EX78. The apparatus according to EX77, wherein the first and second surfaces have concavities facing to each other.

[0151] EX79. The apparatus according to EX77 or EX78, wherein the first surface joins the second surface at opposite ends forming sharp or tapered edges of the elongated body.

[0152] EX80. The apparatus according to EX79, wherein the elongated body has a maximum thickness at a central section of the elongated body itself, gradually decreasing towards each end.

[0153] EX81. A method for producing a sheet of aerosol-generating substrate for an aerosolgenerating article, the method comprising: mixing a recipe with water to form a slurry mixture, the recipe comprising as ingredients vegetable and / or alkaloid particles, a binder and an aerosol forming agent, feeding the slurry mixture to a slot die and depositing the slurry mixture on a surface via said slot die to form a cast sheet, wherein the slot die comprises a head that internally delimits: at least one distribution channel having a slot inlet for receiving the slurry mixture, a manifold in fluid communication with the distribution channel, a narrow section in fluid communication with the manifold and terminating in a slot outlet, wherein the apparatus further comprises a stirrer upstream of the manifold of the slot die, wherein the method further comprises a step of stirring, via the stirrer, the slurry mixture entering the manifold of the slot die.

[0154] EX82. The method according to EX81 , wherein said method is performed through the apparatus of any of EX1 to EX80.

[0155] EX83. The method according to EX81 or EX82, further comprising controlling, as a function of one or more detected properties of the slurry mixture, a movement of the stirrer.

[0156] EX84. The method according to EX83, wherein the detected property comprises a viscosity value of the slurry mixture.

[0157] EX85. The method according to EX83 or EX84, wherein the detected property comprises a resistance torque value of the slurry mixture to the movements of the stirrer.

[0158] EX86. The method according to any of EX83 to EX85, wherein the detected property comprises a measured thickness value of the slurry mixture deposited on the surface.

[0159] EX87. The method according to any of EX81 to EX86, wherein feeding the slurry mixture to the slot die comprises: pumping the slurry mixture to the slot die, optionally with a flow rate between 0.5 dm3 / s and 1 dm3 / s, optionally of 0.8 dm3 / s.

[0160] EX88. A process for manufacturing an aerosol-generating article component, comprising: manufacturing a sheet of aerosol-generating substrate for an aerosol-generating article in the apparatus according to any of EX1 to EX80 or through the method according to any of EX81 to EX87, gathering the sheet of aerosol-generating substrate and wrapping the gathered sheet of aerosol-generating substrate in a wrapper to form a continuous rod, cutting the continuous rod into a plurality of aerosol-generating article components each having a rod shape, each aerosol-generating article component comprising a gathered sheet formed from a cut portion of the sheet of aerosol-generating substrate.

[0161] EX89. The process according to EX88, wherein, before gathering, the process comprises: weakening the sheet of aerosol-generating substrate by making weakened lines in said sheet of aerosol-generating substrate, optionally through a crimping step generating a plurality of substantially parallel ridges or corrugations.

[0162] EX90. An aerosol-generating article comprising at least one aerosol-generating article component made according to the process of EX88 or EX89.

[0163] Examples will now be further described with reference to the figures:

[0164] Figure 1 shows an apparatus for manufacturing aerosol-generating article components; Figures 2 shows apparatus for producing a sheet of aerosol-generating substrate according to the present disclosure;

[0165] Figure 3 shows an enlarged portion of a delivery pipe of the apparatus of Figure 2;

[0166] Figure 4 is a broken view of a portion of the delivery pipe of Figure 3;

[0167] Figure 5 is an additional view of the delivery pipe of Figure 2;

[0168] Figure 6 is a longitudinal cross-sectional view of a variant of the delivery pipe of Figure 2;

[0169] Figure 7 is an enlarged view of a supporting structure of the delivery pipe of Figure 6.

[0170] Figure 8 is a flowchart of a method for producing a sheet of aerosol-generating substrate for an aerosol-generating article.

[0171] Figure 1 shows an apparatus 100 for manufacturing aerosol-generating article components for aerosol-generating articles and may be part of a plant, not shown, for manufacturing aerosolgenerating articles. An overview of the components and general operation of apparatus 100 is provided below, demonstrating the use of a cast sheet 21 of aerosol-generating substrate for making aerosol-generating article components, such as plugs 114. Subsequently, a detailed description of the apparatus 60 (shown in Figure 2) and the method for producing the cast sheet 21 used by the apparatus 100 to create the plugs 114 will be provided.

[0172] Referring to Figure 1 , the apparatus 100 includes a reel holder 101 where the cast sheet 21 of aerosol-generating substrate is coiled in a reel 103. The cast sheet 21 can be composed of paperboard, tobacco cast leaf, or a porous fibrous substrate incorporating cellulose fibers, cellulose acetate, or polylactic acid, depending on the component to be manufactured. It may also contain graphite or be made from botanical substrate.

[0173] An extraction device (not shown) is configured to uncoil a strip of cast sheet 21 from the reel 103, and a conveyor guides the sheet along a conveying direction “C,” parallel to its longitudinal direction. For instance, the conveyor comprises a plurality of motorized rollers and / or one or more motorized belt conveyors located along the conveying direction "C".

[0174] Downstream of the reel holder 101 , in the conveying direction “C,” the apparatus 100 includes a weakening device 104 comprising counterrotating rollers 102 and 105 for weakening the cast sheet 21. Each counterrotating roller is operatively connected to a motor (not shown) for rotation.

[0175] Further downstream, the apparatus 100 includes a gathering device 106, a wrapping device 111 , and a cutter 113. The gathering device 106 includes a converging tool shaped like a tapered funnel 110, which transitions the cast sheet 21 from a flat configuration (upstream of the gathering device) to a gathered rod-shaped configuration (downstream of the gathering device) as it is conveyed and pulled through the tool. In another example (not shown), the cast sheet 21 is pulled through devices and / or conveyors from downstream of the converging tool.

[0176] The wrapping device 111 is designed to wrap the rod-shaped cast sheet 21 in a wrapper 109 to form a continuous rod 112. The wrapping device 111 comprises a guide cooperating with a feeder of the wrapper 109. The guide, not shown in figure, may comprise a U-shaped channel with additional folding elements configured to close the wrapper 109 around the gathered cast sheet 21. The feeder of the wrapper 109 is represented as an auxiliary reel holder 107 on which the wrapper 109 is wound in an auxiliary reel 108.

[0177] The cutter 113, such as a rotating blade, is positioned downstream of the wrapping device 111 and is designed to cut the continuous rod 112 into multiple rod-shaped elements, such as the aerosol-generating plugs 114.

[0178] The apparatus 100 may also include a controller (not shown in the figures) configured to synchronize the operations of the reel holder 101 , the weakening device 104, the auxiliary reel holder 107, the conveyor, and the cutter 113.

[0179] An apparatus 60 for making a sheet of aerosol-generating substrate is further described with reference to Figures 2-7. As previously mentioned, the apparatus 60 is responsible for producing the tobacco cast sheet 21 , which is subsequently reeled and used by apparatus 100 for making the plugs 114.

[0180] Referring to Figure 2, the apparatus 60 comprises a slurry tank 1 equipped with a mixer 1a for blending the recipe ingredients and water to form a slurry mixture 55. For example, the slurry mixture may be created from a blend of tobacco powder, water, glycerine, fibers, binders, or a combination of HPMC, botanical, and graphite products.

[0181] The apparatus 60 may also include a pump 2, such as a volumetric pump or a cavity pump, located downstream of the slurry tank 1 . This pump channels the slurry mixture 55 from the slurry tank 1 towards a slot die 6 for deposition onto a surface 22. Additionally, the apparatus 60 may include a pulsation dampener 3 connected to the slurry tank to minimize flow pulsations or fluctuations caused by pump 2. Particularly, the pulsation dampener 3, positioned downstream of the slurry tank and pump 2, absorbs the pulsations generated by pump 2, ensuring a steady and continuous flow of the slurry mixture towards the slot die 6 for a more uniform deposition on the surface 22.

[0182] Furthermore, the apparatus 60 may also include a degasification tank 4 for removing dissolved gases and air bubbles from the slurry mixture 55. In an example, the degasification tank 4 is located downstream the slurry tank 1 and optionally downstream the pulsation dampener 3, allows the slurry mixture 55 to settle and release trapped air or gas. Consequently, the degasification tank 4 ensures that the slurry mixture 55 entering the slot die 6 is bubble-free, improving the quality of the cast slurry mixture on surface 22.

[0183] The apparatus further includes one or more delivery pipes 5 for channelling the slurry mixture 55 from the slurry tank 1 , optionally through the pulsation dampener 2 and the degasification tank 4, towards the slot die 6. In an example, each delivery pipe 5 has a sloped tubular body, with an end facing the slot die 6 being lower than an opposite end facing the slurry tank 1.

[0184] The tubular body of each delivery pipe 5 may have adjacent tubular sections 5', 5" that can be removably coupled to each other or removably coupled to a loading pipe 30 subsequently described, forming a single channel. In this regard, a section 5' of the delivery pipe 5 may have a terminal annular rib 31 that fits into a cavity of the adjacent section 5" to engage and seal the sections. Alternatively, when adjacent sections 5', 5" are coupled via a loading pipe 30, the loading pipe 30 may include terminal annular ribs 31 on both ends, fitting into the cavities of the adjacent sections 5', 5", as shown in Figure 3. Notably, the loading pipe 30, when coupled to the adjacent sections 5', 5" of the delivery pipe 5 via the terminal annular ribs 31 , is rotationally movable relative to the adjacent sections 5', 5" of the delivery pipe, which remain fixed with respect to the slot die 6.

[0185] As previously mentioned, the apparatus 60 includes a slot die 6 that receives the slurry mixture 55 from the delivery pipe 5, depositing a uniform layer onto a surface 22 located beneath the slot die 6 to form the cast sheet 21. In one example, surface 22 is a conveyor belt moving with respect to the slot die 6 along a conveying direction 24 while receiving the slurry mixture from the slot die 6.

[0186] Referring to Figure 2, the slot die 6 comprises a head divided transversely into two halves, forming the slots through which the slurry mixture is deposited. The head internally delimits a distribution channel 10 that receives the slurry mixture through a slot inlet 11 and directing the slurry into a manifold 12. The slot die 6 may have multiple slot inlets 11 to ensure even deposition of the slurry mixture across the entire width of the die 6.

[0187] The head of the slot die 6 further delimits the manifold 12, which has a tubular body extending along an entire width of the slot die 6, transversely distributing the slurry mixture 55 received from each distribution channel 10 across the desired deposition width. The slot die 6 may include manifolds 12 of various shapes, such as T-Shaped, Coat-Hanger, and Constant Shear designs. In one example, the slot die 6 includes a Constant Shear manifold to provide an even flow rate and distribution of the slurry mixture 55.

[0188] Furthermore, the head of the slot die 6 also delimits a narrow section 16 shaped as a tubular channel, connecting the manifold with a slot outlet 15 where the slurry mixture 55 exits the die to reach the surface 22.

[0189] It should be noted that the viscosity of the slurry mixture 55 may vary as it travels from the slurry tank 1 towards the slot die 6 or within the slot die 6, expositing to the formation of slurry agglomerates that can clog the slot die 6, thus interfering with the homogeneous deposition of the cast sheet 21 on surface 22. The stirrer 7 addresses this issue by regulating the viscosity of the slurry mixture 55 traveling towards or within the slot die 6. Notably, the stirrer 7 locally decreases the viscosity of the slurry mixture 55 by increasing the temperature locally wherever stirring occurs.

[0190] In an embodiment shown for example in figures 3-6, the stirrer 7 operates within a loading pipe 30 external to the slot die 6 and in fluid communication with the slot inlet 11 of the distribution channel 10. In this scenario, the loading pipe 30 may be rotatably coupled between the adjacent sections 5', 5" of the delivery pipe 5. Notably, the loading pipe 30 may entirely surround the stirrer 7, forming a closed chamber in cooperation with the adjacent sections 5', 5" to which it is coupled. The loading pipe 30 may also be sloped according to the angle of the delivery pipe 5, forming a single channel of uniform slope.

[0191] In a further variant not shown in the accompanying figures, the stirrer 7 may operate within a loading pipe 30 internal to the distribution channel 10 of the slot die 6, defining a section the distribution channel 10 located just before the manifold 12.

[0192] Referring to figures 4, 6 and 7, the stirrer 7 may include one or more projections 8, for example elongated pins, to create shear stress in the slurry mixture 55, thus locally increasing temperature of the slurry mixture and reducing locally its viscosity before deposition through the slot die 6. The slurry mixture 55, being a shear-thinning substrate, benefits from the induced shear stress, which lowers its viscosity and enhances the stability of the deposition process.

[0193] The projections 8, they may have a cylindrical shape with a constant cross-section of diameter between 1mm and 5mm and length between 10mm and 100mm, depending on the size of the loading pipe where the stirrer 7 operates. Furthermore, the projections 8 may be made from abrasion-resistant metal such as AR200, AR400, AR500, or AR600, for durability and resistant to wear. Moreover, the projections 8 are covered in a frictionless coating to prevent the slurry mixture 55 from sticking and causing travel time discrepancies, thus ensuring uniform shear stress distribution.

[0194] To create shear stress in the slurry mixture 55, the projections 8 of the stirrer 7 rotate about a rotational axis "A" parallel to a flow direction "F" of the slurry mixture 55 along the delivery pipe 5. In an example, the projections 8 may be fixed with the loading pipe 30, which rotates about the rotational axis "A" (figure 4). Alternatively, in a variant of the stirrer 7 shown in figure 6, the projections 8 are decoupled to the loading pipe 30, resulting rotatably movable with respect to the loading pipe 30 about the rotational axis "A". Further structural details about variations of the stirrer 7 with projections fixed or decoupled with the loading pipe 30 will be further provided below.

[0195] In the first embodiment, shown in Figure 4, a stirrer 7 with projections 8 fixed to the loading pipe 30 is depicted. The stirrer includes a plurality of projections 8 extending radially from a central junction area 9 until they contact the inner surface 20 of the loading pipe 30, forming a radial pattern "S". The radial pattern "S" is created by projections 8 radiating from the junction area 9 and lying on an ideal plane transverse, optionally orthogonal, to the flow direction "F" of the slurry mixture 55. Notably, the projections 8 in a radial pattern "S" may be angularly offset from each other, for example, by an angle between 70° and 110°, optionally between 80° and 100°.

[0196] The stirrer 7 may also include multiple radial patterns "S", each distinct and axially offset along the flow direction "F" of the slurry mixture 55. These radial patterns "S" may cover a significant portion of the loading pipe 30, for example, between 10% and 90%, optionally between 30% and 70%, of a length of the loading pipe 30 measured parallel to the rotational axis "A". Referring again to Figure 4, each projection 8 in a radial pattern "S" may be angularly offset relative to a corresponding projection 8 in an adjacent radial pattern "S" to enhance the manipulation of the slurry mixture. In an example, projections in adjacent radial patterns "S" may be offset by an angle between 10° and 80°, optionally between 25° and 65°.

[0197] As shown in Figure 5, the rotation of the stirrer 7 may be indirectly achieved by rotating the loading pipe 30. In this scenario, the apparatus 30 includes a motor 34 coupled with the loading pipe 30 via a transmission member 33, such as a belt or timing belt. The transmission member 33 connects an outer surface of the loading pipe 30 to a rotating shaft driven by the motor 34. When the motor 34 rotates the shaft, the belt 33 transmits rotational motion to the loading pipe 30, causing it to rotate. As the loading pipe 30 rotates, the incoming slurry mixture 55 from the slurry tank 1 passes through the rotating projections 8, generating shearing stress within the slurry mixture. This process increases locally a temperature of the slurry mixture and reduces locally the viscosity of the slurry mixture before it enters the manifold 12 of the slot die 6.

[0198] In a further embodiment shown in Figure 6, a stirrer with projections decoupled from the inner surface of the loading pipe 30 is depicted. In this embodiment, the stirrer 7 includes a supporting structure 40 bearing the projections 8, which rotate relative to the loading pipe 30 about a rotational axis "A" transverse, optionally orthogonal, to the flow direction "F" of the slurry mixture 55.

[0199] In this example, the supporting structure 40 includes a shaft 41 radially attached inside the loading pipe 30, thus being fixed with the pipe itself, and an arm 42 pivotally coupled to the shaft 41. The projections 8 of the supporting structure 40 are terminally coupled to the arm 42, allowing pivotal movement about the shaft 41 via the arm 42. The rotation of the arm 42 may be magnetically driven by a pair of permanent magnets generating an electromagnetic field sufficient to rotate the arm 42 and the projections 8. In this setup, the apparatus includes an internal magnet 43, 44 embedded in the arm 42, with poles located at the respective ends of the arm 42, and an external magnet 46 located outside the loading pipe 30 and coupled to a motor 34 for rotation. The rotation of the external magnet 46 induces the rotation of the arm 42 via magnetic interaction, causing the projections 8 to rotate and stir the slurry mixture, thereby increasing locally the temperature and reducing its viscosity.

[0200] Notably, rotating the supporting structure using magnetic interaction between internal and external permanent magnets eliminates the need for openings around the shaft 41 to the outside of the loading pipe, sealing the stirrer and preventing slurry leakages.

[0201] In one example, the supporting structure 40 in Figure 6 may be shaped like a cylindrical cage, where the projections 8 define longitudinal ribs joining two opposite arms 42, 42'. In this scenario, the supporting structure 40 may also include an auxiliary shaft 4T radially attached inside the loading pipe 30, aligned with the primary shaft 41 along a direction parallel to the rotational axis "A" of the projections 8. Additionally, the supporting structure 40 may include an auxiliary arm 42' pivotally coupled to the auxiliary shaft 4T. An auxiliary internal magnet 43', 44' is embedded in the auxiliary arm 42', interacting with an auxiliary external magnet 46' outside the loading pipe 30, which is coupled to a motor for rotation. Referring now to Figure 7, the shaft 41 and / or the auxiliary shaft 4T may be designed to facilitate the flow of the slurry mixture 55 along the flow direction "F". Specifically, the shaft 41 (and / or the auxiliary shaft 4T) may have an elongated body 51 aligned with the flow direction "F" to prevent the slurry mixture from depositing on the shafts. The elongated body 51 features a first and a second surface 47a, 47b of convex shape, symmetrical with respect to an ideal plane parallel to the flow direction "F", forming a symmetric biconvex airfoil profile. Thus, the first and second surfaces 47a, 47b have concavities facing each other, with opposite ends joined together forming sharp or tapered edges. The elongated body 51 may also have a maximum thickness at a central section 48c, which gradually decreases towards each end 48a, 48b.

[0202] To further improve the overall homogeneity of the slurry mixture 55 forming the cast sheet 21 , various control schemes may be implemented by a control unit 50, either simultaneously or as alternatives to each other, as described below. These control strategies may, for example, enhance the overall quality and homogeneity of the slurry mixture 55 by regulating the flow rate of the slurry traveling through the apparatus. They may also focus on regulating the viscosity of the slurry through mechanical interaction, such as with the stirrer 7 that locally increases temperature, or by controlling the slurry's temperature via a heater.

[0203] Examples of control schemes performed by controlling the pump 2 are firstly discussed below, followed by a description of control schemes performed by controlling the stirrer 7. Both the pump 2 and the stirrer 7 may be controlled based on one or more detected properties of the slurry mixture 55 among a viscosity value of the slurry mixture, a measured flow rate of the slurry mixture 55, a resistance torque value of the slurry to the movements of a stirrer 7 and a measured thickness value of the slurry mixture 55 deposited on the surface 22.

[0204] In an example, a control scheme may regulate the flow rate of the slurry mixture through the delivery pipe 5 using the pump 2. Particularly, the pump 2 generates low shear stress on the slurry mixture, so that the local temperature and viscosity of the slurry is addressed only in an area close to the stirrer. In other words, the action of the pump 2 does not interfere with the action of the stirrer for adjusting the local temperature and viscosity of the slurry. On the other hand, adjusting the pump’s flow rate enhances the homogeneity of the slurry cast via the slot die and maintains a consistent height of the cast slurry, thereby improving the cast sheet’s quality.

[0205] This control scheme may utilize a flow meter 23 located downstream of the pump 2 in the slurry flow direction "F". As shown in Figure 4, the flow meter 23 may be placed near the stirrer 7 or between adjacent radial patterns "S". Alternatively, the flow meter may also be located at the slot outlet 15 of the slot die 6. The flow meter 23 may be configured for generating a signal representative of a flow rate of the slurry mixture processed by the stirrer 7. The control unit 50, connected to the flow meter 23, determines the measured flow rate from the signal and controls the pump 2 accordingly. Specifically, the control unit compares the measured flow rate with a flow rate threshold value and adjusts the pump 2 so that the measured flow rate value matches the flow rate threshold value, ensuring optimal slurry mixture homogeneity for deposition on the surface 22. Optionally, the flow rate threshold value may range between 0.5 dm3 / s and 1 dm3 / s, preferably around 0.8 dm3 / s.

[0206] Further examples involve control schemes for regulating the stirrer 7, specifically the motor

[0207] 34 coupled to the stirrer 7, to maintain locally the slurry mixture 55 within a temperature providing an optimal viscosity range of 16 Pa s to 85 Pa s. This optimal range is measured with a Brookfield viscometer for a slurry deposition 2-3m wide, with a thickness of 350-600 pm, and a flow rate of 27-

[0208] 35 m / min.

[0209] In such a scenario, the apparatus 60 may include a viscometer 19 located in proximity of the stirrer or between adjacent radial pattern "S" of the stirrer 7, for example being inside the loading pipe 30. The viscometer 19 may be configured for generating a signal representative of a viscosity of the slurry mixture locally heated by the stirrer 7. The control unit 50 is connected to the viscometer 19 and it is configured for determining a viscosity value based on the signal generated by the viscometer 19 for controlling the motor 34 accordingly. The control unit 50 is further configured for comparing the determined viscosity value with a viscosity threshold value, and subsequently increasing or decreasing an angular speed of the motor 34 so that the viscosity value matches the viscosity threshold value. The control unit 50, leveraging the measure performed by the viscometer 19, maintains a viscosity value of the slurry mixture 55 within the optimal viscosity range, improving the overall homogeneity of the cast sheet 21 .

[0210] The viscosity of the slurry mixture may also be regulated by controlling the motor 34, leveraging data representative of a resistance torque value applied from the slurry mixture to the stirrer 7 or data representative of a rotational speed of the stirrer 7. In the first case, the control unit 50 is connected to the motor 34 and estimates the resistance torque applied by the slurry mixture to the stirrer 7 based on the current value absorbed by the motor. The control unit then compares the estimated resistance torque with a torque threshold value and adjusts the angular speed of the motor 34 to match the torque threshold value. Notably, the torque threshold value may be predefined or adjusted by a user so that the torque threshold value is representative of a viscosity value of the slurry mixture falling within the optimal viscosity range.

[0211] In the second case, the apparatus includes a speed sensor (identified as reference number 18 in figure 4) coupled with one or more projections 8 of the stirrer 7 and configured for generating a signal representative of a rotational speed of the stirrer 7. The control unit 50 is connected to the speed sensor 18 and it is configured for determining a measured angular speed value of the stirrer 7 based on the signal generated by the speed sensor 18 for controlling the stirrer accordingly. The control unit 50 may be further configured for comparing the measured angular speed value with a speed or power threshold value, and subsequently increasing or decreasing an angular speed of the motor 34 so that the measured angular speed value matches the speed or power threshold value. Notably, the speed or power threshold value is representative of a viscosity value falling within the optimal viscosity range. Therefore, the control unit 50 adjusts, typically decreases, the slurry mixture's viscosity by regulating the motor 34's angular speed based on the measured speed.

[0212] The homogeneity of the slurry mixture 55 may also be regulated by sensing a height of the mixture deposited on the surface 22 via the slot die 6. In such a scenario, the apparatus includes a height sensor 17 located at or close to the slot outlet 15 of the slot die 6 and configured for generating a signal representative of a thickness of the slurry mixture deposited by the slot die 6 on the surface 22. The control unit 50 is connected to the height sensor 17 and configured for determining a measured thickness value of the slurry mixture based on the signal generated by the height sensor 17. The control unit 50 may be further configured for comparing the measured thickness value with a thickness threshold value, and subsequently increasing or decreasing an angular speed of the motor 34 so that the measured thickness value matches the thickness threshold value.

[0213] Notably, in any implementation of the aforementioned control schemes involving a feedback control loop on the motor 34 to regulate the viscosity of the slurry mixture 55, the control unit 50 may be configured to control the motor 34 to subject the stirrer 7 to full rotations or to an oscillating movement between two end positions, creating a vibrating motion.

[0214] In a further example, the apparatus may include a heater and a temperature sensor (not shown in the accompanying figures) for regulating the temperature of the slurry mixture 55 and locally adjusting its viscosity near the heater. In this scenario, the temperature sensor can be fitted within the delivery pipe 5, in contact with or in proximity to the slurry entering the slot die 6, to generate a signal representing the temperature of the slurry mixture 55. The control unit 50 may be connected to the temperature sensor and configured for determining a measured temperature value of the slurry mixture to be used as a feedback measure for controlling the heater. The control unit 50 may be configured for comparing the measured temperature value with a temperature threshold value representative of a viscosity value of the slurry falling within the optimal viscosity range. Subsequently, the control unit 50 may be configured for regulating the heater for increasing or decreasing the temperature of the slurry to match the temperature threshold value.

[0215] A flow chart of a method 130 performed by the apparatus 60 for producing a cast sheet 21 of aerosol-generating substrate is disclosed with reference to figure 8. In an example, the method 130 includes a first step 131 of mixing a recipe of vegetable and / or alkaloid particles with a binder, an aerosol forming agent and water to form a slurry mixture. Subsequently the method includes a step 132 of feeding the slurry mixture towards a slot die 6 and stirring such a slurry mixture 55, e.g., via the stirrer 7, before it enters the manifold 12 of the slot die 6 (step 133). A further step 134 may involve controlling the stirring action based on one or more detected properties of the slurry mixture. Notably, the step 134 of controlling the stirring action may be performed by implementing one or more of the previously described control systems regulating the stirrer 7, optionally the motor 34, the pump 2 and the heater, as described earlier. The method may further include a step 135 of depositing the slurry mixture on a surface 22 to form the cast sheet 21.

Claims

CLAIMS1 . Apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article, the apparatus comprising: a mixer (1a) configured for mixing ingredients of a recipe and water to form a slurry mixture (55), a slot die (6) in fluid communication with the mixer (1a) or with a slurry tank (1) for the slurry mixture (55), said slurry tank (1) being interposed between the mixer (1a) and the slot die (6), a surface (22) located under the slot die (6) and moving with respect to the slot die (6) along a conveying direction (24) for receiving the slurry mixture from said slot die (6) to form a cast sheet (21), wherein the slot die (6) comprises a head that internally delimits: at least one distribution channel (10) having a slot inlet (11) for receiving the slurry mixture, a manifold (12) in fluid communication with the distribution channel (10), a narrow section (16) in fluid communication with the manifold (12) and terminating in a slot outlet (15), wherein the apparatus further comprises a stirrer (7) interposed between the manifold (12) of the slot die (6) and either the mixer (1a) or the slurry tank (1), for stirring the slurry mixture entering the manifold (12) of the slot die (6).

2. Apparatus according to claim 1 , wherein the stirrer (7) operates within a loading pipe (30), which is either: external to the slot die (6) and in fluid communication with the slot inlet (11) of the distribution channel (10), or internal the at least one distribution channel (10) of the slot die (6), wherein the apparatus comprises a delivery pipe (5) placing the mixer (1a) or the slurry tank (1) in fluid communication with the slot die (6), the loading pipe (30) defining a section of the delivery pipe (5) or a section of the at least one distribution channel (10) of the slot die (6).

3. Apparatus according to claim 2, wherein the loading pipe (30) is sloped and extends between a first end (30a) in proximity of the manifold (12) of the slot die (6) and a second end (30b), located superiorly to the first end (30a).

4. Apparatus according to any of claims 1 to 3, wherein the stirrer (7) is movable by rotation with respect to the manifold (12) of the slot die (6) for stirring the slurry mixture,wherein the apparatus further includes a control unit (50) connected to the stirrer (7) for controlling thereof as a function of a detected property of the slurry mixture, said detected property comprising at least one of: a viscosity value of the slurry, a resistance torque value of the slurry to the movements of the stirrer (7), a measured thickness value of the slurry mixture deposited on the surface (22), a measured flow rate of the slurry mixture.

5. Apparatus according to claim 4 comprising a motor (34) connected to the stirrer (7) for rotation, wherein the control unit (50) is connected to the motor (34) and configured for: estimating, based on a current value absorbed by the motor (34), the resistance torque applied from the slurry mixture to the stirrer (7), controlling the motor (34) as a function of the estimated resistance torque, wherein the control unit (50) is further configured for: comparing the estimated resistance torque with a torque threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor (34) so that the estimated resistance torque value matches the torque threshold value.

6. Apparatus according to the claim 5 comprising at least one viscometer (19) located within the loading pipe (30) and configured for generating a signal representative of a viscosity of the slurry mixture processed by the stirrer (7), wherein the control unit (50) is connected to the viscometer (19) and configured for: determining the viscosity value based on the signal generated by the viscometer (19), controlling the motor (34) as a function of the viscosity value, wherein the control unit (50) is further configured for: comparing the determined viscosity value with a viscosity threshold value, increasing or decreasing an angular speed of the motor (34) so that the viscosity value matches the viscosity threshold value.

7. Apparatus according to claim 5 or 6 comprising at least one speed sensor (18) configured for generating a signal representative of a rotational speed of the stirrer (7), wherein the control unit (50) is connected to the speed sensor (18) and configured for: determining a measured angular speed value of the stirrer (7) based on the signal generated by the speed sensor (18), controlling the motor (34) connected to the stirrer (7) as a function of the measured angular speed value,wherein the control unit (50) is further configured for: comparing the measured angular speed value with a speed or power threshold value representative of an optimal viscosity value of the slurry mixture, increasing or decreasing an angular speed of the motor (34) so that the measured angular speed value matches the speed or power threshold value.

8. Apparatus according to any of claims 5 to 7 comprising at least one height sensor (17) located at or close to the slot outlet (15) of the slot die (6) and configured for generating a signal representative of a thickness of the slurry mixture deposited by the slot die (6) on the surface (22), wherein the control unit (50) is connected to the height sensor (17) and configured for: determining the measured thickness value based on the signal generated by the height sensor (17), controlling the motor (34) connected to the stirrer (7) as a function of the thickness value, wherein the control unit (50) is further configured for: comparing the measured thickness value with a thickness threshold value, increasing or decreasing an angular speed of the motor (34) so that the thickness value matches the thickness threshold value.

9. Apparatus according to any of claims 1 to 8, wherein the stirrer (7) includes one or more projections (8) contacting the slurry mixture for stirring, wherein said one or more projections (8) are conformed as elongated pins.

10. Apparatus according to the claim 9, wherein said plurality of projections (8) extend radially from a junction area (9) for defining a radial pattern (S), wherein the projections (8) rotate about a rotational axis (A) passing through the junction area (9), wherein the projections (8) of said radial pattern (S) are angularly offset to each other, wherein the projections (8) of said radial pattern (S) lie on an ideal plane transversal to the rotational axis (A) of the stirrer (7).

11. Apparatus according to claim 10 in combination with claim 2, wherein the projections (8) of the stirrer (7) are fixed with the loading pipe (30), said loading pipe (30) being integral to the movement of the stirrer (7) about the rotational axis (A).

12. Apparatus according to claim 10 in combination with claim 2, wherein the projections (8) of the stirrer (7) are decoupled to the loading pipe (30), resulting rotativity movable with respect to the loading pipe (30) about the rotational axis (A) transversal to a flow direction (F) of the slurry mixture, wherein the apparatus comprises a supporting structure (40) within the loading pipe (30) having:a shaft (41) radially attached inside the loading pipe (30), said shaft (41) being integral with the loading pipe (30), an arm (42) movable by rotation about the shaft (41), wherein the plurality of projections (8) is transversally engaged to the arm (42), said projections (8) being integral with the rotational movement of the arm (42), wherein the apparatus further comprises: an internal magnet (43, 44) embedded in the arm (42) with poles located at respective ends of the arm (42), an external magnet (46) located outside the loading pipe (30), such that rotation of the external magnet (46) induces, through the internal magnet, rotation of the arm (42) within the loading pipe (30) via magnetic interaction, thereby causing the projections (8) to rotate and stir the slurry mixture for locally increasing temperature and reducing its viscosity.

13. Apparatus according to claim 12, wherein the shaft (41) has an elongated body (51) extending in alignment with the flow direction (F) of the slurry mixture to prevent the slurry mixture from depositing on the shaft itself, wherein the elongated body (51) of the shaft (41) includes a first and a second surface (47a, 47b) of convex shape, with said first and second surfaces (47a, 47b) having concavities facing to each other, wherein the first surface (47a) joins the second surface (47b) at opposite ends (48a, 48b) forming sharp or tapered edges of the elongated body (51).

14. Method for producing a sheet of aerosol-generating substrate for an aerosol-generating article, the method comprising: mixing a recipe with water to form a slurry mixture, the recipe comprising as ingredients vegetable and / or alkaloid particles, a binder and an aerosol forming agent, feeding the slurry mixture to a slot die (6) and depositing the slurry mixture on a surface (22) via said slot die (6) to form a cast sheet (21), wherein the slot die (6) comprises a head that internally delimits: at least one distribution channel (10) having a slot inlet (11) for receiving the slurry mixture, a manifold (12) in fluid communication with the distribution channel (10), a narrow section (16) in fluid communication with the manifold (12) and terminating in a slot outlet (15), wherein the apparatus further comprises a stirrer (7) upstream of the manifold (12) of the slot die (6), wherein the method further comprises a step of stirring, via the stirrer (7), the slurry mixture entering the manifold (12) of the slot die (6).

15. Method according to claim 14, further comprising:controlling, as a function of one or more detected properties of the slurry mixture, a movement of the stirrer (7) to match a torque threshold value, and / or regulating, as a function of said one or more detected properties of the slurry mixture a flow rate of the slurry entering the manifold (12) of the slot die (6) to match a predetermined flow rate of the slurry mixture, wherein the detected property comprises at least one of: a viscosity value of the slurry, a resistance torque value of the slurry to the movements of the stirrer (7), a measured thickness value of the slurry mixture deposited on the surface (22).

Images