Apparatus and method for producing a cast sheet for a smoking article

Abstract

An apparatus (1) for producing a cast sheet for a smoking article, comprises a continuous mixer (13) delimiting a mixing path and configured to mix ingredients and water while advancing said ingredients and water in the mixing path towards an outlet (39). A degassing device (40) is connected to the mixing path and is configured to generate a negative relative pressure (ΔP) in the mixing path for removing air from the slurry mixture. A casting device (45) in fluid communication with the outlet (39) receives the slurry mixture. A surface located under the casting device (45) receives the slurry mixture from the casting device (45) to form a cast sheet (2).

Description

[0001] PMP1P36WO FTR3938PCT

[0002] - 1 -

[0003] APPARATUS AND METHOD FOR PRODUCING A CAST SHEET FOR A SMOKING ARTICLE

[0004] The present disclosure relates to an apparatus and a method for producing a cast sheet for a smoking article. The present disclosure also relates to the cast sheet manufactured in said apparatus and / or through said method.

[0005] Cast sheets for smoking articles are known in the art and may be employed in the manufacturing of traditional smoking articles, which are ignited at one end causing them to smolder, and of aerosol-generating articles or heat-not-burn cigarettes, in which an aerosolgenerating substrate is heated rather than combusted. In the traditional smoking articles, the cast sheet may be a reconstituted tobacco leaf which may be used in tobacco blends in combination with other tobacco leaves. For instance, the reconstituted tobacco leaf may be shredded and mixed with other leaves to obtain a resulting tobacco blend intended to be ignited and smoked. In the aerosol-generating articles, the cast sheet may be a sheet of the abovementioned aerosol-generating substrate. For instance, the aerosol-generating substrate sheet is crimped, gathered, wrapped in a rod and cut in aerosol-generating substrate plugs intended to release volatile compounds by heat transfer from a heat source of an aerosol-generating system.

[0006] The cast sheet is prepared by casting a slurry with a high content of water on a movable support. Currently, the slurry preparation takes place in batch mode. Current slurry preparation process is performed mixing different ingredients inside a slurry preparation tank at a certain mixing speed to achieve proper homogeneity. After the preparation, the slurry is transferred into a slurry storage tank, where it is stored for a maximum four hours before the following casting process.

[0007] For instance, document US5724998 discloses a process for producing reconstituted tobacco sheets manufactured from tobacco dust. The process comprises mixing tobacco with dust particles, the binder and other agents in an aqueous media to form a slurry, casting the slurry on a continuous stainless-steel belt, drying the cast slurry to form a reconstituted tobacco sheet. Prior to casting, entrained air may be removed from the slurry.

[0008] Document KR2020 / 0017762A discloses an apparatus for making a slurry for homogenized tobacco material. The formed slurry is transferred to a vacuum tank, where the pressure is maintained below 750 mmHg to facilitate removal of air bubbles and creating a slurry with uniform density and viscosity. Subsequently, the slurry is cast and dried onto a support, forming a web.

[0009] Also documents US2013263870A1 and CN117281283A disclose methods of making a tobacco product including a step of deaerating the slurry. PMP1P36WO FTR3938PCT

[0010] - 2 -

[0011] Document EP4183268A1 discloses a manufacturing device for a reconstituted tobacco sheet comprising a die that discharges reconstituted tobacco raw material and an extruder that press-feeds the reconstituted tobacco raw material to the die by rotation of a screw that is rotatably disposed inside the extruder. The extruder is connected to a deaeration chamber.

[0012] Document CN117598515A discloses a preparation system and method of a viscous auxiliary agent for reconstituted tobacco production, comprising containers with agitators connected through ducts and pumps.

[0013] Document US2024 / 268443A1 discloses a method for making an aerosol-forming substrate from a cast slurry. The slurry is mixed in lab disperser in which pressure is reduced to remove air bubbles. The slurry is cast on a flat support and dried.

[0014] Document CN109619650A discloses preparation of heat-not-burn tobacco sheet in which the slurry is prepared, then degassed in a vacuum device and then cast on a stainless-steel belt.

[0015] It would be desirable to have an apparatus and a method for producing a cast sheet for a smoking article allowing to improve the quality of the cast sheets and therefore also the quality of the smoking articles comprising said cast sheets.

[0016] It would be particularly desirable to have an apparatus and a method for producing a cast sheet for a smoking article allowing to prevent formation of or at least decrease the amount of air bubbles appearing and remaining in the slurry due to the mixing process.

[0017] It would be particularly desirable to have an apparatus and a method for producing a cast sheet for a smoking article capable to control the amount of air in the slurry, i.e. to ensure that the slurry has the right amount of air by removing the excess of it.

[0018] It would be also desirable to increase the productivity of the apparatuses and methods for producing a cast sheet for a smoking article.

[0019] Particularly but not exclusively, it would be desirable to achieve the above objectives when the cast sheet is made through a continuous slurry preparation and from ingredients other than tobacco, for instance comprising: cellulose fibers, carboxymethylcellulose (CMC) and / or hydroxypropylmethylcellulose (HPMC), triethylene glycol or 1 ,3-butanediol or glycerine, nicotine and / or fumaric acid.

[0020] The present disclosure relates to an apparatus for producing a cast sheet for a smoking article. The apparatus comprises a continuous mixer configured for mixing ingredients of a recipe and water to form a slurry mixture. The continuous mixer delimits a mixing path and has at least one inlet communicating with the mixing path. The at least one inlet is configured to feed the ingredients and the water into the mixing path. The continuous mixer has an outlet located at an end of the mixing path. The outlet is configured to PMP1P36WO FTR3938PCT

[0021] - 3 - discharge the slurry mixture from the continuous mixer. The continuous mixer is configured to mix the ingredients and the water while advancing said ingredients and water in the mixing path towards the outlet. A degassing device is connected to the mixing path and is configured to generate a negative relative pressure in at least part of the mixing path for removing air from the slurry mixture. The degassing device may be a vacuum pump, optionally a vane pump. A casting device may be in fluid communication with the outlet to receive the slurry mixture from the continuous mixer or may be in fluid communication with a storage tank receiving the slurry mixture from said outlet. A surface may be located under the casting device and may be configured to receive the slurry mixture from said casting device and to form a cast sheet. The casting device and the surface may be a plurality (two or more), all in fluid communication with the outlet or with the storage tank. The apparatus may also comprise heating devices, like an oven, to dry the cast sheet.

[0022] The present disclosure relates also to a method for producing a cast sheet for a smoking article. The method comprises: feeding ingredients of a recipe and water through at least one inlet and into a mixing path of a continuous mixer; advancing said ingredients and water along the mixing path towards an outlet of the continuous mixer while mixing the ingredients and the water to form a slurry mixture and discharging the slurry mixture from the outlet. The method may also comprise: casting the slurry mixture coming from the outlet on a surface to form a cast sheet. The method may comprise: drying the cast sheet. At least during part of advancing and mixing said ingredients and water, a negative relative pressure is applied in at least part of the mixing path for removing air from the slurry mixture.

[0023] Said method may be carried out through said apparatus and / or said apparatus may be configured to perform said method.

[0024] The inventor found that the disclosed apparatus and method (based on continuous feeding of water and ingredients, continuous mixing of the same ingredients and of the slurry being formed and discharging of said slurry, coupled to a continuous vacuum action to remove air) produce a fresh and homogeneous slurry, avoid slurry degradation and prevent unwanted air bubbles inclusions.

[0025] The inventor found that this allows to accurately meet the specifications of the resulting slurry and cast sheet, such as viscosity and density of the slurry, grammage, density and thickness of the cast sheet. For instance, an excessive amount of air bubbles in the slurry results in a high porosity of the cast sheet, thus for a same grammage, the thickness of the cast sheet will be larger than expected.

[0026] The inventor found that the proper specifications of the cast sheet positively affect the aerosol-generating substrate plugs manufactured by gathering and cutting said cast sheet. Indeed, a thicker cast sheet will have a higher filling power (solid to void ratio in a cross PMP1P36WO FTR3938PCT

[0027] - 4 - section of the aerosol-generating substrate plug) in the aerosol-generating substrate plug which will also influences the aerosol deliveries. Therefore, the apparatus and method of the present disclosure allow also to control and tune the filling power of the cast sheet inside the aerosol-generating substrate plugs and thus the properties of the delivered aerosol.

[0028] Particularly, the inventor found that the disclosed apparatus and method allow to actively control the density of the slurry - i.e. by controlling the incorporated air - in a continuous way and to produce a slurry with a controlled density according to the specifications. By using a same slurry formulation, a thicker or thinner cast sheet with desired level of density may be obtained and therefore the properties of the cast sheet may be adjusted according to any dimensions of the aerosol-generating substrate plugs.

[0029] The inventor found that the disclosed apparatus and method are particularly useful and effective for slurry mixtures that contain a film forming agent, like hydroxypropylmethylcellulose (HPMC), that creates a sort of matrix that holds the air in the slurry mixture.

[0030] The inventor also found that the disclosed apparatus and method allow to limit the footprint of the equipment, since large tanks for deaeration are no longer required.

[0031] The inventor also found that the disclosed apparatus and method allow to quickly start production.

[0032] The negative relative pressure, optionally generated by the degassing device, may be equal to or lower than -0.3 bar, optionally between -0.8 bar and -0.3 bar, optionally between -0.5 bar and -0.6 bar.

[0033] The inventor found that these optional ranges of negative pressure allow to control the density and viscosity of the slurry and the thickness of the cast sheet to remain in the specification ranges.

[0034] The at least one inlet may be placed at a proximal end of the continuous mixer opposite the outlet. The at least one inlet may comprise a plurality of inlet ports. The at least one inlet may comprise a liquid port and a powder port.

[0035] In some embodiments, the continuous mixer comprises at least one mixing tool located in the mixing path and configured to mix the ingredients and the water and to advance the ingredients and the water and the slurry mixture along the mixing path.

[0036] The mixing tool of the continuous mixer performs two functions: mixing and advancing, i.e. the ingredients and the water and the slurry mixture travel towards the outlet while being mixed.

[0037] The at least one mixing tool may be configured to rotate about an axis parallel to the mixing path. The mixing path and the axis may be horizontal. The continuous mixer may be a horizontal mixer. PMP1P36WO FTR3938PCT

[0038] - 5 -

[0039] The inventor found that the horizontal mixing tool or horizontal continuous mixer are configured to hold the ingredients and the water and the slurry mixture in the continuous mixer (while they travel towards the outlet) for a holding time that may be from 1 min to 20 min, optionally from 5 min to 15 min, optionally from 8 min to 10 min.

[0040] In some embodiments, the at least one mixing tool is a mixing screw. In some embodiments, the at least one mixing tool comprises at least two mixing tools rotating about parallel axes.

[0041] According to some embodiments, the mixing path comprises a first part and a second part placed downstream of the first part. The degassing device may be connected at least to the second part.

[0042] According to some embodiments, advancing and mixing comprises: performing a main mixing action along a first part of the mixing path; performing an auxiliary mixing action along a second part of the mixing path placed downstream of the first part. The negative relative pressure may be applied during the auxiliary mixing action in the second part. Air higher than an optimum may be added to the slurry mixture during the main mixing action, by controlling a speed of the main mixing action, and the negative relative pressure may be applied during the auxiliary mixing action to remove excess air from the slurry mixture.

[0043] According to some other embodiments, the continuous mixer comprises a first mixer delimiting a first part of the mixing path and a second mixer placed downstream of the first mixer, operatively connected to the first mixer and delimiting a second part of the mixing path. The degassing device may be connected at least to the second mixer. The main mixing action may be carried out in the first mixer and the auxiliary mixing action may be carried out in the second mixer.

[0044] The inventor found that the first mixer produces the slurry mixture in a continuous process and while advancing the mixture towards the second mixer and the downstream second mixer removes air from the slurry mixture while still continuously advancing the slurry mixture towards the outlet.

[0045] The first mixer may comprise at least one first mixing tool, optionally contra-rotating first mixing tools. The second mixer may be a vacuum mixer. The second mixer may comprise at least one second mixing tool, optionally a high shear mixing tool, optionally contra-rotating second mixing tools.

[0046] In some embodiments, a transfer pump is operatively placed between the first mixer and the second mixer and is configured to pump the slurry mixture from the first part to the second part of the mixing path.

[0047] A control unit may be operatively connected to the degassing device. The control unit may be configured to execute the following procedure: controlling the degassing device to PMP1P36WO FTR3938PCT

[0048] - 6 - adjust the negative relative pressure and thus at least one between a density of the slurry mixture received by the casting device, a density of the cast sheet and a thickness of the cast sheet. According to the method, at least one between a density of the slurry mixture, a density of the cast sheet, a grammage of the cast sheet and a thickness of the cast sheet may be adjusted by controlling the negative relative pressure.

[0049] The negative relative pressure may be controlled such that the density of the slurry mixture is between 0.95 g / cm3and 1 g / cm3. The negative relative pressure may be controlled such that the density of the cast sheet is between 0.6 g / cm3and 0.8 g / cm3. The negative relative pressure may be controlled such that the thickness of the cast sheet is between 170 pm and 220 pm. The negative relative pressure may be controlled such that the grammage of the cast sheet is between 120 g / m2and 150 g / m2.

[0050] The inventor found that the above values allow to guarantee a proper filling power of the aerosol-generating substrate plugs.

[0051] In some embodiments, the control unit is operatively connected to the continuous mixer. The control unit is configured to execute the following procedure: controlling a rotational speed of the at least one mixing tool. The rotational speed may be between 50 rpm and 200 rpm, optionally between 120 rpm and 190 rpm. The control unit may be operatively connected to the first mixer and to the second mixer. The control unit may be configured to execute the following procedure: controlling a rotational speed of the at least one first mixing tool and of the at least one second mixing tool. The rotational speed of the at least one first mixing tool may be between 50 rpm and 200 rpm, optionally between 120 rpm and 190 rpm. The rotational speed of the at least one second mixing tool may be between 50 rpm and 200 rpm, optionally between 100 rpm and 150 rpm.

[0052] The inventor found that the control unit performs an automatic control of the apparatus and allows to obtain a slurry and a cast sheet provided with the desired specifications.

[0053] In some embodiments, at a start of production, the main mixing action is started and carried out in the first mixer by diverting the slurry mixture from the second mixer until the slurry mixture at an exit of the said first mixer reaches stability. In some embodiments, when stability is reached, the slurry mixture is directed from the first mixer to the second mixer and the second mixer is filled at atmospheric pressure. In some embodiments, when a flow rate of the slurry mixture entering the second mixer and a flow rate of the slurry mixture exiting the second mixer are equalized, vacuum is progressively applied in the second mixer until reaching said relative negative pressure.

[0054] In some embodiments, the second mixer is filled at atmospheric pressure until the slurry mixture reaches the discharge pump, then the discharge pump is started and adjusted PMP1P36WO FTR3938PCT

[0055] - 7 - such that a flow rate of the slurry mixture through the second mixer is the same as a flow of the slurry mixture rate through the first mixer.

[0056] In some embodiments, a flow rate of the discharge pump is increased while progressively applying vacuum in the second mixer to compensate for a pressure difference at a discharge pump inlet resulting from a vacuum increase inside the second mixer.

[0057] In some embodiments, once said relative negative pressure is reached in the second mixer, the flow rate of the discharge pump is adjusted to achieve a target filling level inside the second mixer.

[0058] In some embodiments, the casting device is a casting box or a slot die.

[0059] In some embodiments, a discharge pump is operatively placed downstream of the outlet of the continuous mixer. The discharge pump may be placed between the continuous mixer and the storage tank. The discharge pump may be an additional vacuum pump, optionally a progressive cavity pump. A further pump may be operatively placed between the storage tank and the casting device.

[0060] In some embodiments, a pulping mixer is connected to the at least one inlet port, optionally through a pulp buffer tank, optionally through a pulp pump. A fiber source (optionally a fiber tank) and a water source (optionally a water tank) may be connected to the pulping mixer. The fiber source contains cellulose fibers. The water source contains water. The pulping mixer is configured to prepare a pulp with the fibers and the water.

[0061] In some embodiments, a binder source (optionally a binder tank) contains a binder, optionally carboxymethylcellulose (CMC), and is connected to the at least one inlet port, optionally through a gravimetric feeder. The binder source may contain a first premix of the binder, optionally comprising a derivative of cellulose such as carboxymethylcellulose (CMC) and a film forming agent as hydroxypropylmethylcellulose (HPMC). In other embodiments, carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) are dosed independently from respective sources (tanks) and feeders.

[0062] In some embodiments, an aerosol forming agent source (optionally an aerosol forming agent tank) contains an aerosol forming agent and is connected to the at least one inlet port, optionally through an aerosol forming agent pump. The aerosol forming agent source may contain a second premix with the aerosol forming agent and at least one between nicotine and organic acids, like fumaric acid. The aerosol forming agent may comprise a polyhydric alcohol, for instance triethylene glycol or 1 ,3-butanediol or glycerine. In other embodiments, the organic acid is dosed independently from a respective source (tank) and feeder.

[0063] The ingredients of the recipe may comprise: fibers, for instance cellulose fibers, a binder, for instance a derivative of cellulose such as carboxymethylcellulose (CMC), a film PMP1P36WO FTR3938PCT

[0064] - 8 - forming agent as hydroxypropylmethylcellulose (HPMC), and an aerosol forming agent, such as a polyhydric alcohol, for instance triethylene glycol or 1 ,3-butanediol or glycerine; optionally the ingredients further comprise nicotine and / or organic acids like fumaric acid.

[0065] In some embodiments, a pulp with the fibers and the water is prepared, a first premix of the binder is prepared, a second premix of the aerosol forming agent is prepared. Feeding the ingredients of the recipe and the water may comprise: feeding the pulp, the first premix and the second premix through the at least one inlet. In other embodiments, carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) are dosed independently.

[0066] The water in the slurry may be from 65 to 90 percent by weight. The fibers in the slurry may be from 13 to 21 percent by weight (in dry basis). The aerosol forming agent in the slurry may be from 35 to 58 percent by weight (in dry basis). The film forming agent in the slurry may be from 15 to 30 percent (in dry basis). The optional nicotine in the slurry may be from 0.5 to 2.5... percent by weight (in dry basis). The optional organic acid (like fumaric acid) in the slurry may be from 0.5 to 3 percent by weight (in dry basis).

[0067] The inventor found that the apparatus and method of the disclosure may be used also for the continuous productions of a tobacco slurry. However, the production of the slurry identified above from ingredients other than tobacco (fibers, binder, aerosol forming agent) requires higher mixing speeds to provide the proper dispersion of the binder and this involves higher air inclusion, bubbles formation and uncontrolled density. Therefore, the air removal provided by the method and apparatus of the disclosure is particularly relevant and effective when processing this kind of slurry.

[0068] The present disclosure also relates to cast sheet manufactured in an apparatus for producing a cast sheet for a smoking article. The apparatus for producing a cast sheet for a smoking article comprises a continuous mixer configured for mixing ingredients of a recipe and water to form a slurry mixture. The continuous mixer delimits a mixing path and has at least one inlet communicating with the mixing path. The at least one inlet is configured to feed the ingredients and the water into the mixing path. The continuous mixer has an outlet located at an end of the mixing path. The outlet is configured to discharge the slurry mixture from the continuous mixer. The continuous mixer is configured to mix the ingredients and the water while advancing said ingredients and water in the mixing path towards the outlet. A degassing device is connected to the mixing path and is configured to generate a negative relative pressure in at least part of the mixing path for removing air from the slurry mixture. The degassing device may be a vacuum pump, optionally a vane pump. A casting device may be in fluid communication with the outlet to receive the slurry mixture from the continuous mixer or may be in fluid communication with a storage tank receiving the slurry PMP1P36WO FTR3938PCT

[0069] - 9 - mixture from said outlet. A surface may be located under the casting device and may be configured to receive the slurry mixture from said casting device and to form a cast sheet. The casting device and the surface may be a plurality (two or more), all in fluid communication with the outlet or with the storage tank. The apparatus may also comprise heating devices, like an oven, to dry the cast sheet.

[0070] The present disclosure also relates to a cast sheet manufactured through a method for producing a cast sheet for a smoking article. The method comprises: feeding ingredients of a recipe and water through at least one inlet and into a mixing path of a continuous mixer; advancing said ingredients and water along the mixing path towards an outlet of the continuous mixer while mixing the ingredients and the water to form a slurry mixture and discharging the slurry mixture from the outlet. The method may also comprise: casting the slurry mixture coming from the outlet on a surface to form a cast sheet. The method may comprise: drying the cast sheet. At least during part of advancing and mixing said ingredients and water, a negative relative pressure is applied in at least part of the mixing path for removing air from the slurry mixture.

[0071] The present disclosure also relates to a smoking article comprising said cast sheet. The smoking article may be an aerosol-generating article.

[0072] The present disclosure also relates to a plant for manufacturing smoking articles comprising an apparatus for producing a cast sheet for a smoking article. The apparatus for producing a cast sheet for a smoking article comprises a continuous mixer configured for mixing ingredients of a recipe and water to form a slurry mixture. The continuous mixer delimits a mixing path and has at least one inlet communicating with the mixing path. The at least one inlet is configured to feed the ingredients and the water into the mixing path. The continuous mixer has an outlet located at an end of the mixing path. The outlet is configured to discharge the slurry mixture from the continuous mixer. The continuous mixer is configured to mix the ingredients and the water while advancing said ingredients and water in the mixing path towards the outlet. A degassing device is connected to the mixing path and is configured to generate a negative relative pressure in at least part of the mixing path for removing air from the slurry mixture. The degassing device may be a vacuum pump, optionally a vane pump. A casting device may be in fluid communication with the outlet to receive the slurry mixture from the continuous mixer or may be in fluid communication with a storage tank receiving the slurry mixture from said outlet. A surface may be located under the casting device and may be configured to receive the slurry mixture from said casting device and to form a cast sheet. The casting device and the surface may be a plurality (two or more), all in fluid communication with the outlet or with the storage tank. The apparatus may also comprise heating devices, like an oven, to dry the cast sheet. PMP1P36WO FTR3938PCT

[0073] - 10 -

[0074] According to some embodiments, the plant comprises a reel holder carrying a bobbin of the cast sheet; two optional rotating cylindrical crimping rollers configured to crimp the cast sheet unrolled from the bobbin; a folding device placed downstream of the reel holder or of the two optional rotating cylindrical rollers and configured to move the cast sheet from a flat configuration (upstream of the folding device) to a gathered rod-shaped configuration (downstream of the folding device); a wrapping device placed downstream of the folding device and configured to wrap a wrapper from an auxiliary bobbin on an auxiliary reel holder around the gathered cast sheet to obtain a continuous rod; a cutter placed downstream of the wrapping device and configured to cut the continuous rod in a plurality of aerosolgenerating substrate plugs. The plant may also comprise a combiner configured to combine the aerosol-generating substrate plugs at least with filters to form the smoking articles.

[0075] The present disclosure also relates to a process for manufacturing smoking articles comprising a method for producing a cast sheet for a smoking article. The method comprises: feeding ingredients of a recipe and water through at least one inlet and into a mixing path of a continuous mixer; advancing said ingredients and water along the mixing path towards an outlet of the continuous mixer while mixing the ingredients and the water to form a slurry mixture and discharging the slurry mixture from the outlet. The method may also comprise: casting the slurry mixture coming from the outlet on a surface to form a cast sheet. The method may comprise: drying the cast sheet. At least during part of advancing and mixing said ingredients and water, a negative relative pressure is applied in at least part of the mixing path for removing air from the slurry mixture.

[0076] According to said process, the cast sheet may be gathered, wrapped in a rod and cut in a plurality of aerosol-generating substrate plugs intended to release volatile compounds by heat transfer from a heat source of an aerosol-generating system.

[0077] The process may also comprise: combining the plurality of aerosol-generating substrate plugs at least with filters to form the smoking articles.

[0078] The inventor found that, for a given plug diameter and a given cast sheet width, a filling power (solid to void ratio in a cross section of the aerosol-generating substrate plug) of the cast sheet inside the plug, once that the cast sheet is gathered and wrapped, is function of the thickness of the cast sheet. Therefore, the disclosed apparatus and method for producing a cast sheet for a smoking article are also capable of controlling the filling power of the cast sheet in the aerosol-generating substrate plugs.

[0079] As used in the present description, the term “continuous mixer” means a device capable of mixing ingredients while transporting said ingredients from one or more inlets to an outlet. The continuous mixer receives a continuous input of ingredients through the one or more inlets and provides a continuous output through the outlet, as opposed to “batch PMP1P36WO FTR3938PCT

[0080] - 11 - mixer” which is loaded with given quantities of ingredients and, after mixing, must be stopped to discharge a given output.

[0081] As used in the present description, the term “smoking article” means both the traditional smoking articles which are ignited at one end causing them to smolder, like cigars and cigarettes, and the aerosol-generating articles or heat-not-burn cigarettes, in which an aerosol-generating substrate is heated rather than combusted.

[0082] As used in the present description, the term “slurry” means a watery mixture of insoluble matter with a water content so high (e.g. 65 percent - 90 percent by weight) that cannot be kneaded or rolled out, as opposed to “dough” which is a mixture that is stiff enough to be kneaded or rolled out.

[0083] As used in the present description, the “holding time” is the average time a particle of the slurry mixture is inside the continuous mixer during the continuous process.

[0084] As used in the present description, the term “recipe” means a group of ingredients without any limitation concerning the order and the timing in which they are combined with each other and / or with water.

[0085] As used in the present description, the terms “upstream” and “downstream” are used to describe the relative positions of components, or portions of components, of the apparatus in relation to the direction in which a material or materials passes through the apparatus along a given path.

[0086] 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.

[0087] EX1. An apparatus for producing a cast sheet for a smoking article, comprises: a continuous mixer configured for mixing ingredients of a recipe and water to form a slurry mixture; the continuous mixer delimiting a mixing path and having at least one inlet communicating with the mixing path, the at least one inlet being configured to feed the ingredients and the water into the mixing path, and an outlet located at an end of the mixing path, the outlet being configured to discharge the slurry mixture from the continuous mixer; the continuous mixer being configured to mix the ingredients and the water while advancing said ingredients and water in the mixing path towards the outlet; a degassing device connected to the mixing path and configured to generate a negative relative pressure in at least part of the mixing path for removing air from the slurry mixture; optionally the degassing device is a vacuum pump, optionally a vane pump; PMP1P36WO FTR3938PCT

[0088] - 12 - a casting device in fluid communication with the outlet to receive the slurry mixture from the continuous mixer or in fluid communication with a storage tank receiving the slurry mixture from said outlet; a surface located under the casting device and configured to receive the slurry mixture from said casting device and to form a cast sheet; optionally the casting device and the surface are a plurality (two or more) and all in fluid communication with the outlet or with the storage tank; optionally heating devices, like an oven, are provided to dry the cast sheet.

[0089] EX2. The apparatus according to EX1 , wherein the negative relative pressure generated by the degassing device is equal to or lower than -0.3 bar.

[0090] EX3. The apparatus according to EX1 or EX2, wherein the negative relative pressure is between -0.8 bar and -0.3 bar, optionally between -0.5 bar and -0.6 bar.

[0091] EX4. The apparatus according to any of EX1 to EX3, wherein the continuous mixer comprises at least one mixing tool located in the mixing path and configured to mix the ingredients and the water and to advance the ingredients and the water and the slurry mixture along the mixing path; optionally the at least one inlet is placed at a proximal end of the continuous mixer opposite the outlet.

[0092] EX5. The apparatus according to EX4, wherein the at least one mixing tool is configured to rotate about an axis parallel to the mixing path.

[0093] EX6. The apparatus according to EX5, wherein the mixing path and the axis are horizontal.

[0094] EX7. The apparatus according to EX5 or EX6, wherein the continuous mixer is a horizontal mixer.

[0095] EX8. The apparatus according to any of EX4 to EX7, wherein the at least one mixing tool is a mixing screw.

[0096] EX9. The apparatus according to any of EX4 to EX8, wherein the at least one mixing tool comprises at least two mixing tools rotating about parallel axes.

[0097] EX10. The apparatus according to any of EX1 to EX9, wherein the mixing path comprises a first part and a second part placed downstream of the first part.

[0098] EX11. The apparatus according to EX10, wherein the degassing device is connected at least to the second part.

[0099] EX12. The apparatus according to any of EX1 to EX9, wherein the continuous mixer comprises a first mixer delimiting a first part of the mixing path and a second mixer placed downstream of the first mixer, operatively connected to the first mixer and delimiting a second part of the mixing path. PMP1P36WO FTR3938PCT

[0100] - 13 -

[0101] EX13. The apparatus according to EX12, wherein the degassing device is connected at least to the second mixer.

[0102] EX14. The apparatus according to EX12 or EX13, wherein the first mixer comprises at least one first mixing tool, optionally contra-rotating first mixing tools.

[0103] EX15. The apparatus according to any of EX12 to EX14, wherein the second mixer is a vacuum mixer.

[0104] EX16. The apparatus according to any of EX12 to EX15, wherein the second mixer comprises at least one second mixing tool, optionally a high shear mixing tool, optionally contra-rotating second mixing tools.

[0105] EX17. The apparatus according to any of EX12 to EX16, comprising a transfer pump operatively placed between the first mixer and the second mixer and configured to pump the slurry mixture from the first part to the second part of the mixing path.

[0106] EX18. The apparatus according to any of EX1 to EX17, comprising a control unit operatively connected to the degassing device.

[0107] EX19. The apparatus according to EX18, wherein the control unit is configured to execute the following procedure: controlling the degassing device to adjust the negative relative pressure and thus at least one between a density of the slurry mixture received by the casting device, a density of the cast sheet, a grammage of the cast sheet and a thickness of the cast sheet.

[0108] EX20. The apparatus according to EX18 or EX19, wherein the control unit is operatively connected to the continuous mixer and is configured to execute the following procedure: controlling a rotational speed of the at least one mixing tool.

[0109] EX21. The apparatus according to EX20, wherein the rotational speed is between 50 rpm and 200 rpm, optionally between 120 rpm and 190 rpm.

[0110] EX22. The apparatus according to EX18 or EX19 when EX18 is according to EX14 and to EX16, wherein the control unit is operatively connected to the first mixer and to the second mixer and is configured to execute the following procedure: controlling a rotational speed of the at least one first mixing tool and of the at least one second mixing tool.

[0111] EX23. The apparatus according to EX22, wherein the rotational speed of the at least one first mixing tool is between 50 rpm and 200 rpm, optionally between 120 rpm and 190 rpm, and the rotational speed of the at least one second mixing tool is between 50 rpm and 200 rpm, optionally between 100 rpm and 150 rpm.

[0112] EX24. The apparatus according to any of EX1 to EX23, wherein the casting device is a casting box or a slot die.

[0113] EX25. The apparatus according to any of EX1 to EX24, comprising a discharge pump operatively placed downstream of the outlet of the continuous mixer; optionally the PMP1P36WO FTR3938PCT

[0114] - 14 - discharge pump is placed between the continuous mixer and the storage tank; optionally the discharge pump is an additional vacuum pump, optionally a progressive cavity pump; optionally a further pump is operatively placed between the storage tank and the casting device.

[0115] EX26. The apparatus according to any of EX1 to EX25, wherein the at least one inlet comprises a plurality of inlet ports, optionally a liquid port and a powder port.

[0116] EX27. The apparatus according to any of EX1 to EX26, comprising: a pulping mixer connected to the at least one inlet port, optionally through a pulp buffer tank, optionally through a pulp pump; a fiber source (optionally a fiber tank) and a water source (optionally a water tank) connected to the pulping mixer; optionally the fiber source containing cellulose fibers and the water source containing water; the pulping mixer being configured to prepare a pulp with the fibers and the water.

[0117] EX28. The apparatus according to any of EX1 to EX28, comprising a binder source (optionally a binder tank) containing a binder, optionally carboxymethylcellulose (CMC), and connected to the at least one inlet port, optionally through a gravimetric feeder; optionally the binder source containing a first premix of the binder, optionally comprising a derivative of cellulose such as carboxymethylcellulose (CMC), a film forming agent as hydroxypropylmethylcellulose (HPMC); optionally carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) are dosed independently from respective sources (tanks) and feeders.

[0118] EX29. The apparatus according to any of EX1 to EX28, comprising an aerosol forming agent source (optionally an aerosol forming agent tank) containing an aerosol forming agent and connected to the at least one inlet port, optionally through an aerosol forming agent pump; optionally the aerosol forming agent source containing a second premix with the aerosol forming agent and at least one between nicotine and organic acid like fumaric acid, optionally the aerosol forming agent comprises a polyhydric alcohol, for instance triethylene glycol or 1 ,3-butanediol or glycerine; optionally the organic acid is dosed independently from a respective source (tank) and feeder.

[0119] EX30. A method for producing a cast sheet for a smoking article, comprising: feeding ingredients of a recipe and water through at least one inlet and into a mixing path of a continuous mixer; advancing said ingredients and water along the mixing path towards an outlet of the continuous mixer while mixing the ingredients and the water to form a slurry mixture and discharging the slurry mixture from the outlet; casting the slurry mixture coming from the outlet on a surface to form a cast sheet, optionally drying the cast sheet; PMP1P36WO FTR3938PCT

[0120] - 15 - wherein, at least during part of advancing and mixing said ingredients and water, a negative relative pressure is applied in at least part of the mixing path for removing air from the slurry mixture.

[0121] EX31 . The method according to EX30 carried out through the apparatus according to any of EX1 to EX29.

[0122] EX32. The method according to EX30 or EX31 , wherein advancing and mixing comprises: performing a main mixing action along a first part of the mixing path; performing an auxiliary mixing action along a second part of the mixing path placed downstream of the first part; wherein the negative relative pressure is applied during the auxiliary mixing action in the second part; optionally wherein air higher than an optimum is added to the slurry mixture during the main mixing action and wherein the negative relative pressure applied during the auxiliary mixing action removes excess air from the slurry mixture.

[0123] EX33. The method according to EX32 when according to EX31 and when the apparatus is according to any of EX12 to EX17, wherein the main mixing action is carried out in the first mixer and the auxiliary mixing action is carried out in the second mixer.

[0124] EX34. The method according to EX33, wherein at a start of production said method comprises: starting and carrying out the main mixing action in the first mixer by diverting the slurry mixture from the second mixer until the slurry mixture at an exit of the said first mixer reaches stability; when stability is reached, directing the slurry mixture from the first mixer to the second mixer and filling the second mixer at atmospheric pressure; when a flow rate of the slurry mixture entering the second mixer and a flow rate of the slurry mixture exiting the second mixer are equalized, progressively applying vacuum in the second mixer until reaching said relative negative pressure.

[0125] EX35. The method according to EX34 when the apparatus is also according to EX25, wherein the second mixer is filled at atmospheric pressure until the slurry mixture reaches the discharge pump, then the method comprises: starting and adjusting the discharge pump such that a flow rate of the slurry mixture through the second mixer is the same as a flow of the slurry mixture rate through the first mixer.

[0126] EX36. The method according to EX35, further comprising: increasing a flow rate of the discharge pump while progressively applying vacuum in the second mixer to compensate for a pressure difference at a discharge pump inlet resulting from a vacuum increase inside the second mixer. PMP1P36WO FTR3938PCT

[0127] - 16 -

[0128] EX37. The method according to EX36, further comprising: once said relative negative pressure is reached in the second mixer, adjusting the flow rate of the discharge pump to achieve a target filling level inside the second mixer.

[0129] EX38. The method according to any of EX30 to EX37, wherein the negative relative pressure is equal to or lower than -0.3 bar.

[0130] EX39. The method according to any of EX30 to EX38, wherein the negative relative pressure is between -0.8 bar and -0.3 bar, optionally between -0.5 bar and -0.6 bar.

[0131] EX40. The method according to any of EX30 to EX39, comprising: adjusting at least one between a density of the slurry mixture, a density of the cast sheet, a grammage of the cast sheet and a thickness of the cast sheet by controlling the negative relative pressure.

[0132] EX41 . The method according to EX40, comprising: controlling the negative relative pressure such that the density of the slurry mixture is between 0.95 g / cm3and 1 g / cm3.

[0133] EX42. The method according to EX40 or EX41 , comprising: controlling the negative relative pressure such that the density of the cast sheet is between 0.6 g / cm3and 0.8 g / cm3.

[0134] EX43. The method according to any of EX40 to EX42, comprising: controlling the negative relative pressure such that the thickness of the cast sheet is between 170 pm and 220 pm and / or the grammage of the cast sheet is between 120 g / m2and 150 g / m2.

[0135] EX44. The method according to any of EX30 to EX43, wherein the ingredients of the recipe comprise: fibers, for instance cellulose fibers, a binder, for instance a derivative of cellulose such as carboxymethylcellulose (CMC), a film forming agent as hydroxypropylmethylcellulose (HPMC), and an aerosol forming agent, such as a polyhydric alcohol, for instance triethylene glycol or 1 ,3-butanediol or glycerine; optionally the ingredients further comprise nicotine and / or organic acid like fumaric acid.

[0136] EX45. The method according to EX44, further comprising: preparing a pulp with the fibers and the water, preparing a first premix of the binder, preparing a second premix of the aerosol forming agent; wherein feeding the ingredients of the recipe and the water comprises: feeding the pulp, the first premix and the second premix through the at least one inlet; optionally, carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) are dosed independently.

[0137] EX46. The method according to EX44 or EX45, wherein the water in the slurry is from 65 to 90 percent by weight; the fibers in the slurry are from 13 to 21 percent by weight (in dry basis); the aerosol forming agent in the slurry is from 35 to 58 percent by weight (in dry basis); the film forming agent in the slurry is from 15 to 30 percent (in dry basis); the optional nicotine in the slurry is from 0.5 to 2.5 percent by weight (in dry basis), the optional organic acid in the slurry is from 0.5 to 3 percent by weight (in dry basis). PMP1P36WO FTR3938PCT

[0138] - 17 -

[0139] EX47. The apparatus of EX1 to EX29 which is configured to perform the method according to any of EX30 to EX46.

[0140] EX48. A cast sheet manufactured in the apparatus according to any of EX1 to EX29 and / or through the method according to any of EX30 to EX46.

[0141] EX49. A smoking article comprising a cast sheet according to EX48, wherein the smoking article is an aerosol-generating article.

[0142] EX50. A plant for manufacturing smoking articles comprising the apparatus of any of EX1 to EX29.

[0143] EX51. The plant according to EX50, comprising: a reel holder carrying a bobbin of the cast sheet; two optional rotating cylindrical crimping rollers configured to crimp the cast sheet unrolled from the bobbin; a folding device placed downstream of the reel holder or of the two optional rotating cylindrical rollers and configured to move the cast sheet from a flat configuration (upstream of the folding device) to a gathered rod-shaped configuration (downstream of the folding device); a wrapping device placed downstream of the folding device and configured to wrap a wrapper from an auxiliary bobbin on an auxiliary reel holder around the gathered cast sheet to obtain a continuous rod; a cutter placed downstream of the wrapping device and configured to cut the continuous rod in a plurality of aerosolgenerating substrate plugs.

[0144] EX52. The plant according to EX51 , comprising a combiner configured to combine the aerosol-generating substrate plugs at least with filters to form the smoking articles.

[0145] EX53. A process for manufacturing smoking articles comprising the method of any of EX30 to EX46.

[0146] EX54. The process according to EX53, wherein the cast sheet is gathered, wrapped in a continuous rod and cut in a plurality of aerosol-generating substrate plugs intended to release volatile compounds by heat transfer from a heat source of an aerosol-generating system.

[0147] EX55. The process according to EX54, further comprising: combining the plurality of aerosol-generating substrate plugs least with filters to form the smoking articles.

[0148] Examples will now be further described with reference to the figures in which:

[0149] Figure 1 shows an apparatus for producing a cast sheet for a smoking article;

[0150] Figures 2A and 2B are schematic enlarged views of a continuous mixer of the apparatus of Figure 1 ;

[0151] Figure 3 shows a detailed view of a casting device of the apparatus of Figure 1 ;

[0152] Figure 4 shows part of a plant for manufacturing smoking articles;

[0153] Figures 5 and 6 show respectively a longitudinal section and a cross section of an aerosol-generating substrate plug manufactured through the part of the plant of Figure 4; PMP1P36WO FTR3938PCT

[0154] - 18 -

[0155] Figure 7 is an exploded view of an aerosol-generating article comprising the aerosolgenerating substrate plug of Figures 5 and 6;

[0156] Figure 8 is a flowchart of a method for producing a cast sheet for a smoking article.

[0157] The apparatus 1 depicted in Figures 1 , 2A, 2B and 3 is structured and configured for producing a cast sheet 2 for a smoking article 3. Figure 3 shows the cast sheet 2 coiled in a bobbin 4.

[0158] An exemplary smoking article 3 is shown in the exploded view of Figure 7 and is an aerosol-generating article. The aerosol-generating article 3 comprises (from left to right in Figure 7): a front plug 5 (solid plug), an aerosol-generating substate plug 6, a tubular plug 7 (hollow plug, for instance of cellulose acetate), a fine tubular plug 8 (like the tubular plug 7 but with a thinner wall) and a filter plug 9 (mouthpiece filter, usually made of tow). Each plug has a wrapping of its own helping to contain properly their content. A tipping paper 10 connects the filter plug 9 to the rest of the plugs, and the front plug 5, aerosol-generating substate plug 6, tubular plug 7 and fine tubular plug 8 are wrapped together into a wrapping paper 11. The tubular plug 7 and fine tubular plug 8 are cooling plugs configured to cool down the aerosol formed by heating the aerosol-generating substate plug 6. The aerosolgenerating substrate plugs 6 are intended to release volatile compounds by heat transfer from a heat source of an aerosol-generating system, not shown in Figures.

[0159] The aerosol-generating substate plug 6 is better depicted in Figures 5 and 6 and comprises a section of the cast sheet 2 gathered and wrapped in a wrapper 12 according to the steps described below.

[0160] The apparatus 1 comprises a continuous mixer 13 configured for mixing ingredients of a recipe and water to form a slurry mixture. In the embodiment of Figure 1 , the continuous mixer 13 comprises a first mixer 14 and a second mixer 15 connected in series through pipelines.

[0161] The first mixer 14 comprises an external casing housing a couple of contra-rotating first mixing tools, not shown, each rotating about a respective horizontal axis. The first mixer 14 is a continuous horizontal mixer. The mixing tools are lodged in a chamber delimiting a first part 17 of a mixing path. The first part 17 of the mixing path is parallel to the horizontal axis.

[0162] The first part 17 of the mixing path extends from a plurality of inlet ports 18, 19, 20 to an outlet port 21. The plurality of inlet ports 18, 19, 20 are placed at a proximal end of the first part 17 of the mixing path and comprise a first liquid port 18 connected to a pulp buffer tank 22, a second liquid port 19 connected to an aerosol forming agent tank 23 and a powder port 20 connected to a binder tank 24. The outlet port 21 is placed at a distal end of the first part 17 of the mixing path. PMP1P36WO FTR3938PCT

[0163] - 19 -

[0164] A pulping mixer 25 receives cellulose fibers from a fiber tank 26 and water from a water tank 28 placed upstream of the pulp buffer tank 22 and connected to said pulp buffer tank 22. The pulping mixer 25 is configured to prepare a pulp with the fibers and the water. The pulp buffer tank 22 is connected to the first liquid port 18 through a hopper 28 and a pulp pump 29.

[0165] The binder tank 24 contains a first premix with a binder comprising carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) and is connected to the second inlet port 20 through a gravimetric feeder 31. The carboxymethylcellulose (CMC) and the hydroxypropylmethylcellulose (HPMC) may also be dosed independently from respective tanks and feeders.

[0166] The aerosol forming agent tank 23 contains a second premix with an aerosol forming agent comprising a polyhydric alcohol (e.g. triethylene glycol or 1 ,3-butanediol or glycerine) and is connected to the second liquid port 19 through an aerosol forming agent pump 30. The second premix may also contain nicotine or organic acid like fumaric acid. The organic acid may also be dosed independently from a respective tank and feeder.

[0167] The outlet port 21 of the first mixer 14 is connected to an inlet port 32 of the second mixer 15 through a transfer pump 33 and a first three-way valve 34. The first three-way valve 34 connects the outlet port 21 of the first mixer 14 to the inlet port 32 of the second mixer 15 and to a first drain 35. The transfer pump 33 is configured to pump the slurry mixture from the first mixer 14 to the second mixer 15.

[0168] The second mixer 15 comprises (Figures 2A and 2B) an external casing 36 housing a couple of contra-rotating high shear second mixing tools 37 shaped like mixing screws engaged in each other each and each rotating about a respective horizontal axis “X-X”, as shown in Figure 2B. The second mixer 15 is a continuous horizontal mixer. The second mixing tools 37 are lodged in a chamber inside the second mixer 15 that delimits a second part 38 of the mixing path. The second part 38 of the mixing path extends from the inlet port 32 to an outlet 39. The inlet port 32 is placed at a proximal end of the second part 38 of the mixing path and the outlet 39 is placed at a distal end of the second part 38 of the mixing path. The mixing path therefore comprises the first part 17 in the first mixer 14 and the second part 38 in the second mixer 15. The second part 38 is placed downstream of the first part 17.

[0169] The second mixer 15 is a vacuum mixer. Indeed, the second mixer 15 comprises a degassing device 40 connected to the second part 38 of the mixing path. The degassing device 40 is for instance a vane vacuum pump. The degassing device 40 is configured to generate a negative relative pressure AP inside the second part 38 of the mixing path and to remove air from the slurry mixture flowing through the second mixer 15. PMP1P36WO FTR3938PCT

[0170] - 20 -

[0171] The outlet 39 is connected to a storage tank 41 through a discharge pump 42 and a second three-way valve 43. The discharge pump 42 is an additional vacuum pump, for instance a progressive cavity pump. The second three-way valve 43 connects the outlet 39 of the second mixer 15 to the storage tank 41 and to a second drain 44.

[0172] The storage tank 41 is connected to one or more casting device / s 45. In the example embodiment of Figure 1 three casting devices 45 are schematically depicted, each connected to an exit of the storage tank 41 through a respective further pump 46.

[0173] Each casting device 45 may be structured as shown in Figure 3. In this example embodiment, the casting device 45 comprises a casting box 47. A belt conveyor 48 is located under the casting box 47. The belt conveyor 48 comprises a first drum 49, a second drum 50 and a belt 51 forming a closed loop around the first drum 49 and the second drum 50. A conveyor motor, not shown, is connected to the first drum 49 or to the second drum 50 to move an upper branch of the belt 51 along a conveying direction “F”.

[0174] The casting box 47 has a top opening 52 and a bottom opening 53. The top opening 52 receives the slurry mixture from the further pump 46. The bottom opening 53 is close to and faces a portion of the upper branch of the belt 51 located at the first drum 49. The casting box 47 comprises a casting blade, not shown in detail, delimiting a slot 54 together with the upper branch of the belt 51. The casting blade is an element having one edge that is intended to come into contact with the slurry mixture. The upper branch of the belt 54 is a movable surface located under the casting box 47 moving along the conveying direction “F” and configured to receive the slurry mixture from said casting box 47 and to form a cast sheet 2.

[0175] The apparatus 1 further comprises heating devices 55 configured to heat the upper branch of the belt 51 and the cast sheet 2 supported by the upper branch and to dry the cast sheet 2. In the example embodiment of Figure 1 , the heating devices 55 are schematically represented as an oven crossed by the upper branch.

[0176] A control unit 56 is operatively connected to the apparatus 1 to control and manage process steps of the apparatus 1. Particularly, the control unit 56 is operatively connected to the first mixer 14 and to the second mixer 15 and is configured to control a rotational speed of the first and second mixing tools. The control unit 56 is also operatively connected to the degassing device 40 and is configured to control and adjust the negative relative pressure AP inside the second part 38 of the mixing path. The control unit 56 is also operatively connected to the pulp pump 29, the aerosol forming agent pump 30, the gravimetric feeder 31 , the transfer pump 33, the first three-way valve 34, the discharge pump 42, the second three-way valve 43, the further pumps 46, the conveyor motor and the heating devices 55. PMP1P36WO FTR3938PCT

[0177] - 21 -

[0178] In use and according to the method of the present disclosure (Figure 8), the pulp with the fibers and the water is prepared in the pulping mixer 25 and stored in the pulp buffer tank 22, the first premix is prepared and stored in the binder tank 24, the second premix is prepared and stored in the aerosol forming agent tank 23. According to variants of the method, the binder (CMC), the film forming agent (HPMC) and the organic acid (fumaric acid) are prepared and dosed independently through respective feeders.

[0179] At a start of production, the control unit 56 controls the pulp pump 29, the aerosol forming agent pump 30 and the gravimetric feeder 31 to feed the pulp, the first premix and the second premix to the first mixer 14 and to start a main mixing action in the first part 17 of the mixing path. The combination of the pulp with the first premix and the second premix forms a slurry mixture comprising ingredients of a recipe and water.

[0180] An exemplary slurry composition is shown in the following Table 1.

[0181] Table 1

[0182] All the ingredients and the water are advanced along the first part 17 of the mixing path towards the outlet port 21 of the first mixer while the first mixer 14 mixes said ingredients and the water to form the slurry mixture. The slurry mixture at the outlet port 21 is diverted to the first drain 35 through the first three-way valve 34 until the slurry mixture reaches stability.

[0183] When the stability is reached, the control unit 56 controls the first three-way valve 34 to direct the slurry mixture from the first mixer 14 to the second mixer 15 and fill the second mixer 15 at atmospheric pressure until a flow rate of the slurry mixture entering the second mixer 15 and a flow rate of the slurry mixture exiting the second mixer 15 are equalized. The second mixer 15 is filled at atmospheric pressure until the slurry mixture reaches the discharge pump 42. Then, the discharge pump 42 is started and adjusted such that a flow rate of the slurry mixture through the second mixer 15 is the same as a flow of the slurry mixture rate through the first mixer 14.

[0184] Then, the control unit 56 controls the degassing device 40 to apply progressively vacuum in the second mixer 15 until reaching a predetermined relative negative pressure AP. Meanwhile, a flow rate of the discharge pump 42 is increased by progressively applying PMP1P36WO FTR3938PCT

[0185] - 22 - vacuum in the second mixer 15 to compensate for a pressure difference at an inlet of the discharge pump 42 resulting from a vacuum increase inside the second mixer 15. Meanwhile, the slurry mixture from the outlet 39 is diverted to the second drain 44 through the second three-way valve 34.

[0186] Once said relative negative pressure AP is reached in the second mixer 15, the flow rate of the discharge pump 42 is adjusted to achieve a target filling level inside the second mixer 15 and production of the slurry mixture continues at a steady state. The discharge pump 42 pumps the slurry mixture to the storage tank 41 and the further pumps 46 pump the slurry mixture to the casting boxes 47 of the casting devices 45.

[0187] The cast sheet 2 manufactured by each casting device 45 is wound in a respective bobbin 4, as shown in Figure 3.

[0188] In steady state production, the degassing device 40 is controlled by the control unit 56 to keep the predetermined relative negative pressure AP in the second mixer 15, where a vacuum auxiliary mixing action is carried out, for removing excess air included in the slurry mixture during the main mixing action in the first mixer 14. For instance, air higher than an optimum is added to the slurry mixture during the main mixing action in the first mixer 14 and the negative relative pressure applied during the auxiliary mixing action in the second mixer 15 removes excess air from the slurry mixture (excess with respect to the optimum).

[0189] Adjusting the relative negative pressure AP inside the second mixer 15 allows to control a density of the slurry mixture received by the casting device or devices 45, a density of the cast sheet 2, a grammage of the cast sheet 2 and a thickness of the cast sheet 2.

[0190] In other embodiments, not shown in the Figures, the continuous mixer is only one horizontal mixer (in place of the first mixer 14 and second mixer 15) and delimits internally both the first part 17 and the second part 18 of the mixing path. For instance, the mixing tool or tools may have certain features in the first part 17 and other features in the second part 38. The degassing device 40 is operatively connected to the second part 38.

[0191] In other embodiments, not shown in the Figures, the storage tank 41 is not provided and the outlet 39 of the second mixer 15 is directly connected, through pipelines, to the casting device or devices 45.

[0192] In other embodiments, not shown in the Figures, the casting device or each casting device 45 comprises a slot die, per se known for other applications, in place of the casting box 47 to cast the slurry mixture on the upper branch of the belt 51 .

[0193] Exemplary target parameters of the cast sheet 2 after drying are shown in the following Table 2.

[0194] Table 2 PMP1P36WO FTR3938PCT

[0195] - 23 -

[0196] In order to achieve these ranges, a density of the slurry mixture at the outlet 39 of the second mixer 15 should be from 0.95 g / cm3to 1 g / cm3.

[0197] The degassing device 40 and also the discharge pump 42 are controlled and adjusted to reach this density of the slurry mixture. Exemplary working parameters of the degassing device 40 and of the discharge pump 42 set to obtain said density of the slurry mixture are shown in the following Table 3.

[0198] Table 3

[0199] Figure 4 shows a part 100 of a plant for manufacturing the smoking articles. Said part 100 is configured to manufacture the aerosol-generating substrate plugs 6 of Figures 5, 6 and 7. This part 100 of the plant comprises a reel holder 101 carrying the bobbin 4 of the cast sheet 2 previously manufactured. Proper devices, not shown, are positioned and configured to unroll the cast sheet 2 from the bobbin 4 and to feed the same in a travel direction “C” and along a travel path. Two rotating cylindrical crimping rollers 104 are positioned along the travel path and are configured to crimp (to form weakened lines in the cast sheet 2) the cast sheet 2 unrolled from the bobbin 4 and passing between lateral faces with relieves and recesses of the two crimping rollers 104.

[0200] A folding device 105, shaped like a tapered funnel 106, is placed downstream of the two rotating cylindrical rollers 104 and is configured to move the cast sheet 2 from a flat configuration (upstream of the folding device 105) to a gathered rod-shaped configuration (downstream of the folding device 105). The gathered shape of the cast sheet 2 is shown in Figure 6.

[0201] A wrapping device 107 placed downstream of the folding device 105 is configured to wrap the wrapper 12, uncoiled from an auxiliary bobbin 108 placed on an auxiliary reel holder 109, around the gathered cast sheet 2 to obtain a continuous rod 110.

[0202] A cutter 111 placed downstream of the wrapping device 107 is configured to cut the continuous rod 110 in a plurality of aerosol-generating substrate plugs 6. The wrapping device 107 comprises a guide 112 cooperating with the auxiliary reel holder 110. The guide 112, not shown in detail, may comprise a U-shaped channel with additional folding elements configured to close the wrapper 12 around the gathered cast sheet 2. PMP1P36WO FTR3938PCT

[0203] - 24 -

[0204] The plant comprises other manufacturing stations, not shown in Figures, configured to manufacture the front plugs 5, the tubular plugs 7, the fine tubular plugs 8 and the filter plugs 9. The plant further comprises a combiner or combining machine, not shown in Figures, configured to combine the aerosol-generating substrate plugs 6 with these other components to form a plurality of smoking articles 3.

[0205] The grammage / thickness of the cast sheet 2 after drying disclosed above allows to reach a target filling power of the cast sheet inside the plug 6 (solid to void ratio in a cross section of the aerosol-generating substrate plug 6) and thus to accurately tune the aerosol delivery.

Claims

PMP1P36WO FTR3938PCT- 25 -CLAIMS1. Apparatus (1) for producing a cast sheet for a smoking article, comprising: a continuous mixer (13) configured for mixing ingredients of a recipe and water to form a slurry mixture; the continuous mixer (13) delimiting a mixing path and having at least one inlet communicating with the mixing path, the at least one inlet being configured to feed the ingredients and the water into the mixing path, and an outlet (39) located at an end of the mixing path, the outlet (39) being configured to discharge the slurry mixture from the continuous mixer (13); the continuous mixer (13) being configured to mix the ingredients and the water while advancing said ingredients and water in the mixing path towards the outlet (39); a degassing device (40) connected to the mixing path and configured to generate a negative relative pressure (AP) in at least part of the mixing path for removing air from the slurry mixture; a casting device (45) in fluid communication with the outlet (39) to receive the slurry mixture from the continuous mixer (13) or in fluid communication with a storage tank (41) receiving the slurry mixture from said outlet (13); a surface located under the casting device (45) and configured to receive the slurry mixture from said casting device (45) and to form a cast sheet (2).

2. The apparatus according to claim 1 , wherein the negative relative pressure (AP) generated by the degassing device (40) is equal to or lower than -0.3 bar.

3. The apparatus of according to claims 1 or 2, wherein the continuous mixer (13) comprises at least one mixing tool located in the mixing path and configured to mix the ingredients and the water and to advance the ingredients and the water and the slurry mixture along the mixing path; wherein the at least one mixing tool is configured to rotate about an axis parallel to the mixing path; wherein the mixing path and the axis are horizontal; wherein the continuous mixer (13) is a horizontal mixer.

4. The apparatus of according to any of claims 1 to 3, wherein the mixing path comprises a first part (17) and a second part (38) placed downstream of the first part (17); wherein the degassing device (40) is connected at least to the second part (38).

5. The apparatus of according to any of claims 1 to 3, wherein the continuous mixer (13) comprises a first mixer (14) delimiting a first part (17) of the mixing path and a secondPMP1P36WO FTR3938PCT- 26 - mixer (15) placed downstream of the first mixer (14), operatively connected to the first mixer (14) and delimiting a second part (38) of the mixing path; wherein the degassing device (40) is connected at least to the second mixer (15).

6. The apparatus according to claim 5, comprising: a transfer pump (33) operatively placed between the first mixer (14) and the second mixer (15) and configured to pump the slurry mixture from the first part (17) to the second part (38) of the mixing path; a discharge pump (42) operatively placed downstream of the outlet (39) of the continuous mixer (13).

7. The apparatus according to any of claims 1 to 6, comprising a control unit (56) operatively connected to the degassing device (40), wherein the control unit (56) is configured to execute the following procedure: controlling the degassing device (40) to adjust the negative relative pressure (AP) and thus at least one between a density of the slurry mixture received by the casting device (45), a density of the cast sheet (2) and a thickness of the cast sheet (2).

8. A method for producing a cast sheet for a smoking article, comprising: feeding ingredients of a recipe and water through at least one inlet and into a mixing path of a continuous mixer (13); advancing said ingredients and water along the mixing path towards an outlet (39) of the continuous mixer (13) while mixing the ingredients and the water to form a slurry mixture and discharging the slurry mixture from the outlet (39); casting the slurry mixture coming from the outlet (39) on a surface to form a cast sheet (2); wherein, at least during part of advancing and mixing said ingredients and water, a negative relative pressure (AP) is applied in at least part of the mixing path for removing air from the slurry mixture.

9. The method according to claim 8, wherein advancing and mixing comprises: performing a main mixing action along a first part (17) of the mixing path; performing an auxiliary mixing action along a second part (38) of the mixing path placed downstream of the first part (17); wherein the negative relative pressure (AP) is applied during the auxiliary mixing action in the second part (38).PMP1P36WO FTR3938PCT- 27 -10. The method according to claim 8 or 9, wherein air higher than an optimum is added to the slurry mixture during the main mixing action and wherein the negative relative pressure applied during the auxiliary mixing action removes excess air from the slurry mixture.

11. The method according to claim 8, 9 or 10, wherein the negative relative pressure (AP) is between -0.8 bar and -0.3 bar.

12. The method according to any of claims 8 to 11 , comprising: adjusting at least one between a density of the slurry mixture, a density of the cast sheet (2) and a thickness of the cast sheet (2) by controlling the negative relative pressure (AP).

13. The method according to claim 12, comprising: controlling the negative relative pressure (AP) such that the density of the slurry mixture is between 0.95 g / cm3and 1 g / cm3.

14. The method according to claim 12 or 13, comprising: controlling the negative relative pressure (AP) such that the density of the cast sheet (2) is between 0.6 g / cm3and 0.8 g / cm3.

15. The method according to any of claims 8 to 14, wherein the ingredients comprise: fibers, a binder, a film forming agent and an aerosol forming agent.

Images