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

Abstract

A method for producing a sheet of aerosol-generating substrate for an aerosol-generating article, comprises: kneading a mixture with a recipe and water to form a dough (D); making a continuous dough sheet (7) from the dough (D) and advancing the continuous dough sheet (7) along a conveying path; flattening the continuous dough sheet (7) by running the continuous dough sheet (7) through a couple of motorised stretching rollers (10, 11) placed along the conveying path to form the sheet of aerosol-generating substrate (S). The method further comprises: tuning a porosity and a roughness of the sheet of aerosol-generating substrate (S) by stretching the continuous dough sheet (7) while running between the couple of motorised stretching rollers (10, 11) and setting or adjusting a magnitude of stretching as a function of a target density to be provided to the sheet of aerosol-generating substrate (S).

Description

[0001] METHOD AND APPARATUS FOR PRODUCING A SHEET OF AEROSOLGENERATING SUBSTRATE FOR AN AEROSOL-GENERATING ARTICLE

[0002] The present disclosure relates to a method and an apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article.

[0003] Aerosol-generating articles or heat-not-burn cigarettes, in which an aerosolgenerating substrate is heated rather than combusted, are known in the art. The aerosolgenerating substrate is for instance a sheet of reconstituted tobacco, a tobacco-free herbaceous or plant-based sheet or a plastic fibre-based sheet or a biodegradable fibrebased sheet. The sheet is gathered and enclosed in a wrapping to form a rod of aerosol generating substrate.

[0004] Typically, in such heated aerosol-generating articles, an aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-generating substrate or material, which may be 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] A sheet of aerosol-generating substrate may be prepared by casting methods (cast leaf production) or rolling methods (dough sheet production), depending on the amount of water used in the process. The manufacturing of tobacco cast leaf requires about 70-80% water in the mass, and the final sheet has only 6-11 %water in the mass meaning that a lot of water evaporates and is lost in the atmosphere during drying of the cast leaf. If the amount of water is low in the starting mixture, the sheet is usually obtained by rolling steps, because the mixture is like pasta or dough. Sheet material from a dough may require less than 15% of the water consumption needed for the production of cast leaf. In order to flatten the dough material to a constant thickness, the dough is processed through multiple sequential rolling steps until the desired thickness of the material is obtained.

[0006] For instance, document WO2023161784 discloses a unit for refining a continuous layer of reconstituted material, comprising feed means for feeding a continuous flow of a mixture containing the reconstituted material, and a refining unit located downstream of the feed means for receiving and processing the continuous flow by a continuous process. The refining unit comprises at least one refining stage equipped with a pair of rollers that delimit a niche for accumulating and mixing the mixture fed to it by the feed means, the niche terminating in a through slot defined between the two rollers to produce a continuous layer of predetermined thickness so that the mixture, by passing through the rollers, undergoes a continuous mixing and compressing process such as to reduce the particle size of the mixture.

[0007] Document AU622360B2 is also known disclosing an apparatus and a method for controlling the quality of dough or other similar viscoelastic materials for foodstuff, like bread or confectionary products. The apparatus comprises a hopper and vertical conveyor with rollers for vertically conveying dough, followed by a first stretching system and a second stretching system. Conveying speeds of the first stretching system and second stretching system are adjusted through a control unit to stretch the dough strip coming from the rollers. The weight density of the strip of dough is adjusted by adjusting the thickness of the strip through stretching.

[0008] Document US4056346A discloses a method and apparatus for the shaping and cutting of bread dough which forms the dough into a bar or belt shaped strip, stretches the dough, cuts and overlaps the dough.

[0009] Document JP3206857B2 discloses a method and a machine for producing sheet tobacco shreds comprising a molding machine comprising a pair of rolling. Moist powder material fed to the molding machine is rolled into a sheet and discharged as a tobacco sheet. The tobacco sheet is then cut in many strings parallel to the longitudinal direction through the slitter.

[0010] Document US3709232A discloses machine and a method in the manufacture of lengthy tobacco webs of a pasty mass as a starting material which contains finely disintegrated tobacco. The machine comprises a container for the tobacco mass, a first roll and a second roll delimiting a nip, a belt conveyor and a drying oven.

[0011] In this technical field, it would be desirable to improve the quality of sheets of aerosolgenerating substrate and of the aerosol-generating articles including these aerosolgenerating substrates.

[0012] It would be particularly desirable to accurately control a thickness of the sheet of aerosol-generating substrate manufactured form a dough and thus to control the filling amount of said aerosol-generating substrate once gathered in an aerosol-generating article component part of an aerosol-generating article.

[0013] The present disclosure relates to a method for producing a sheet of aerosolgenerating substrate for an aerosol-generating article. The method comprises: kneading a mixture with a recipe and water to form a dough; making a continuous dough sheet from said dough and advancing the continuous dough sheet along a conveying path; flattening the continuous dough sheet by running the continuous dough sheet through at least one couple of motorised stretching rollers placed along the conveying path to form the sheet of aerosol-generating substrate. The method further comprises: tuning a porosity and a roughness of the sheet of aerosol-generating substrate by stretching the continuous dough sheet while running between the at least one couple of motorised stretching rollers and setting or adjusting a magnitude of stretching as a function of a target density to be provided to the sheet of aerosol-generating substrate. The method may also further comprise: drying the sheet of aerosol-generating substrate. The at least one couple of motorised stretching rollers may comprise: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened.

[0014] The present disclosure also relates to an apparatus for producing a sheet of aerosolgenerating substrate for an aerosol-generating article. The apparatus comprises: a dough mixer configured for kneading a mixture with a recipe and water to form a dough; a dough sheeter configured to make a continuous dough sheet from said dough. The dough sheeter may comprise calendering rollers. The apparatus comprises: at least one couple of motorised stretching rollers placed downstream of the dough sheeter with respect to a conveying direction of the continuous dough sheet and configured to flatten and stretch the continuous dough sheet and to form the sheet of aerosol-generating substrate. The at least one couple of motorised stretching rollers comprises: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened. The apparatus comprises: a driving unit operatively connected to the first stretching roller and to the second stretching roller to impart a first peripheral speed W1 to the first stretching roller rotating about a respective first main axis and a second peripheral speed W2 to the second stretching roller rotating about a respective second main axis. The driving unit is configured for setting or controlling a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1.

[0015] Said method may be carried out through said apparatus and / or said apparatus may be configured to carry out said method.

[0016] The inventor found that the disclosed method and apparatus allow to control and adjust a density and a thickness of the manufactured sheet of aerosol-generating substrate by adjusting the porosity and the roughness of the continuous dough sheet while keeping the grammage constant. Indeed, the thickness is the ratio of the grammage of the sheet to the density of said sheet.

[0017] Changes in the density are achieved through porosity changes due to stretching and to roughness changes due to shearing. Stretching and shearing are determined by the passage of the continuous dough sheet between the at least one couple of motorised stretching rollers. Stretching causes a porosity increase and shearing causes a roughness increase. The thickness may be finetuned to be in a desired range. Porosity increase and roughness increase determine a density reduction and a thickness increase for a given grammage. Therefore, for instance, the thickness of the sheet can be modified while maintaining its grammage.

[0018] In order to correlate the densities to the required magnitudes of stretching, formulas and / or correlation tables may be obtained through testing. These formulas and / or correlation tables are then used in production to set the first peripheral speed W1 and the second peripheral speed W2 to achieve the desired target density for a given grammage.

[0019] The present disclosure also relates to a process for manufacturing an aerosolgenerating article component, comprising: producing a sheet of aerosol-generating substrate for an aerosol-generating article through a method for producing a sheet of aerosol-generating substrate for an aerosol-generating article and / or using an apparatus 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; wherein the method comprises: kneading a mixture with a recipe and water to form a dough; making a continuous dough sheet from said dough and advancing the continuous dough sheet along a conveying path; flattening the continuous dough sheet by running the continuous dough sheet through at least one couple of motorised stretching rollers placed along the conveying path to form the sheet of aerosol-generating substrate; tuning a porosity and a roughness of the sheet of aerosol-generating substrate by stretching the continuous dough sheet while running between the at least one couple of motorised stretching rollers and setting or adjusting a magnitude of stretching as a function of a target density to be provided to the sheet of aerosol-generating substrate. The method may also further comprise: drying the sheet of aerosol-generating substrate. The at least one couple of motorised stretching rollers may comprise: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened; and / or wherein the apparatus comprises: a dough mixer configured for kneading a mixture with a recipe and water to form a dough; a dough sheeter configured to make a continuous dough sheet from said dough. The dough sheeter may comprise calendering rollers. The apparatus comprises: at least one couple of motorised stretching rollers placed downstream of the dough sheeter with respect to a conveying direction of the continuous dough sheet and configured to flatten and stretch the continuous dough sheet and to form the sheet of aerosol-generating substrate. The at least one couple of motorised stretching rollers comprises: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened. The apparatus comprises: a driving unit operatively connected to the first stretching roller and to the second stretching roller to impart a first peripheral speed W1 to the first stretching roller rotating about a respective first main axis and a second peripheral speed W2 to the second stretching roller rotating about a respective second main axis. The driving unit is configured for setting or controlling a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1.

[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 aerosol-generating article component.

[0021] Stretching the continuous dough sheet may comprise: imparting a first peripheral speed W1 to the first stretching roller rotating about a respective first main axis and a second peripheral speed W2 to the second stretching roller rotating about a respective second main axis, setting or controlling a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1. The first peripheral speed W1 and second peripheral speed W2 may be set before starting production and kept constant during production or may be adjusted during production.

[0022] The inventor found that the different speeds of the first and second stretching rollers cause stretching and shearing of the continuous dough sheet and an amount of stretching and shearing may be controlled by adjusting said speeds.

[0023] The inventor also found that, by keeping the ratio W2 / W1 steady through the manufacturing process, the density of the resulting sheet of aerosol-generating substrate is kept substantially constant.

[0024] The first peripheral speed W1 may be from 1.0 m / min to 5.0 m / min. The second peripheral speed W2 may be from 1.0 m / min to 2.0 m / min. According to embodiments, the ratio W2 / W1 is set or controlled as a function of a target density to be provided to the sheet of aerosol-generating substrate. The target density may be between 0.75 g / cm3and 1 .25 g / cm3, optionally between 0.85 g / cm3and 0.95 g / cm3.

[0025] The ratio W2 / W1 may be lower than 1.0. The driving unit may set or may control the ratio W2 / W1 to be lower than 1.0 to stretch the continuous dough sheet. The ratio W2 / W1 may be from 0.30 to 0.90, optionally from 0.40 to 0.85. The driving unit may set or may control the ratio W1 / W2 to be from 0.30 to 0.90, optionally from 0.40 to 0.85.

[0026] The inventor found that by keeping the ratio W2 / W1 in the disclosed range, a desired density and a desired thickness of the sheet are obtained.

[0027] The inventor found that, when the continuous dough sheet is made in the dough sheeter, the porosity may decrease severely and the disclosed ranges of the ratio W2 / W1 allow to adjust the porosity and roughness such as to obtain the desired density and thickness of the sheet.

[0028] According to embodiments, the first stretching roller is placed below the second stretching roller. While running between the motorised stretching rollers and through the gap, the continuous dough sheet lies in contact with an upper portion of the first lateral surface and with a lower portion of the second lateral surface.

[0029] According to embodiments, the driving unit comprises a first motor connected to the first stretching roller and a second motor connected to the second stretching roller. According to embodiments, the driving unit comprises a single motor and a gearbox connecting the single motor to the first stretching roller and to the second stretching roller.

[0030] According to embodiments, the driving unit comprises a control unit operatively connected to the first motor and to the second motor or to the single motor and the gearbox to adjust the ratio W2 / W1 as a function of the target density.

[0031] According to embodiments, a first conveying surface is placed upstream of the at least one couple of motorised stretching rollers and moves towards the gap. The first conveying surface may be an upper branch of a first belt conveyor moved by a respective motor or connected to the first motor or to the second motor.

[0032] According to embodiments, a second conveying surface is placed downstream of the at least one couple of motorised stretching rollers and moves away from the gap. The second conveying surface may be an upper branch of a second belt conveyor moved by a respective motor or connected to the first motor or to the second motor.

[0033] The continuous dough sheet may be conveyed to the gap upstream of the at least one couple of motorised stretching rollers with a first linear speed V1 . The first linear speed V1 may be from 0.2 m / min to 4.0 m / min. The sheet of aerosol-generating substrate may be moved away from the gap downstream of at least one couple of motorised stretching rollers with a second linear speed V2. The second linear speed V2 may be from 1.0 m / min to 5.0 m / min. The driving unit or an auxiliary driving unit may be operatively connected to the first conveying surface and to the second conveying surface to impart a first linear speed V1 to the first conveying surface and a second linear speed V2 to the second conveying surface.

[0034] According to embodiments, the driving unit or the auxiliary driving unit is configured for setting or controlling a ratio V2 / V1 of the second linear speed V2 to the first linear speed V1 . A ratio V2A / 1 of the second linear speed V2 to the first linear speed V1 may be greater than 1.0. The driving unit or the auxiliary driving unit may set or control the ratio V2 / V1 to be greater than 1. The ratio V2 / V1 of the second linear speed V2 to the first linear speed V1 may be from 1.3 to 6.5. The driving unit or the auxiliary driving unit may set or control the ratio V2 / V1 to be from 1.3 to 6.5. The second linear speed V2 may also be the same as the first peripheral speed W1 . The driving unit or the auxiliary driving unit may set or control the second linear speed V2 to be the same as the first peripheral speed W1.

[0035] The first peripheral speed W1 , second peripheral speed W2, first linear speed V1 , second linear speed V2, in addition to the gap between the rollers, are such that the continuous dough sheet does not accumulate just before the gap between the at least one couple of motorised stretching rollers.

[0036] According to embodiments, a ratio t / H (spring factor) of a thickness of the continuous dough sheet downstream of the at least one couple of motorised stretching rollers to a height of the gap is from 1 .20 to 4, optionally to 2.50. Indeed, just downstream of the couple of rollers, the sheet is more likely to recover some of its original thickness the greater its porosity.

[0037] According to embodiments, the at least one couple of motorised stretching rollers comprises a plurality of couples of motorised stretching rollers. The couples of motorised stretching rollers may be arranged one after the other along the conveying path. The continuous dough sheet may be stretched while running sequentially between each couple of motorised stretching rollers.

[0038] According to embodiments, the ratio W2 / W1 of one couple of motorised stretching rollers is smaller than the ratio W2 / W1 of a different couple of motorised stretching rollers placed upstream. According to embodiments, the ratio W2 / W1 of one couple of motorised stretching rollers is greater than the ratio W2 / W1 of a different couple of motorised stretching rollers placed downstream. The driving unit may be configured such that the ratio W2 / W1 of one couple of motorised stretching rollers is smaller than the ratio W2 / W1 of a different couple of motorised stretching rollers placed upstream. The driving unit may be configured such that the ratio W2 / W1 of one couple of motorised stretching rollers is greater than the ratio W2 / W1 of a different couple of motorised stretching rollers placed downstream. The ratios W2 / W1 of the couples of motorized stretching rollers may decrease moving downstream along the conveying path.

[0039] The ratio W2 / W1 of a first couple of motorised stretching rollers may be from 0.7 to 0.9. The ratio W2 / W1 of a second couple of motorised stretching rollers placed downstream of the first couple may be from 0.5 to 0.8. The ratio W2 / W1 of a third couple of motorised stretching rollers placed downstream of the second couple may be from 0.3 to 0.6. The driving unit may be configured such that the ratio W2 / W1 of a first couple of motorised stretching rollers is from 0.7 to 0.9. The driving unit may be configured such that the ratio W2 / W1 of a second couple of motorised stretching rollers placed downstream of the first couple is from 0.5 to 0.8. The driving unit may be configured such that the ratio W2 / W1 of a third couple of motorised stretching rollers placed downstream of the second couple is from 0.3 to 0.6.

[0040] The ratio V2 / V1 pertaining to the first couple of motorised stretching rollers may be from 4 to 6.5. The ratio V2 / V1 pertaining to the second couple of motorised stretching rollers may be from 1 .3 to 2.5. The ratio V2 / V1 pertaining to the third couple of motorised stretching rollers may be from 2.0 to 3. The driving unit may be configured such that the ratio V2 / V1 pertaining to the first couple of motorised stretching rollers is from 4 to 6.5. The driving unit may be configured such that the ratio V2 / V1 pertaining to the second couple of motorised stretching rollers is from 1.3 to 2.5. The driving unit may be configured such that the ratio V2 / V1 pertaining to the third couple of motorised stretching rollers is from 2 to 3.

[0041] According to embodiments, a height of the gap of one couple of motorised stretching rollers is smaller than a height of the gap of a different couple of motorised stretching rollers placed upstream. According to embodiments, a height of the gap of one couple of motorised stretching rollers is greater than a height of the gap of a different couple of motorised stretching rollers placed downstream.

[0042] According to embodiments, the height of the gap of the first couple of motorised stretching rollers is from 400 pm to 600 pm. According to embodiments, the height of the gap of the second couple of motorised stretching rollers is from 200 pm to 300 pm. According to embodiments, the height of the gap of the third couple of motorised stretching rollers is from 50 pm to 100 pm.

[0043] According to embodiments, the ratio t / H (spring factor) of the first couple of motorised stretching rollers is from 1 .4 to 2. According to embodiments, the ratio t / H (spring factor) of the second couple of motorised stretching rollers is from 1.5 to 3. According to embodiments, the ratio t / H (spring factor) of the third couple of motorised stretching rollers is from 2.0 to 4. The porosity (volume fraction of air in a sample measured with a sample dried to a -10% moisture) of the dough after kneading and before making the continuous dough sheet may be greater than 14%, optionally from 14% to 16%. The porosity of the continuous dough sheet before flattening and stretching may be less than 5%, optionally from 4% to 5%. The porosity of the sheet of aerosol-generating substrate after flattening and stretching may be greater than 10%, optionally from 10% to 20%.

[0044] According to embodiments, the first lateral surface and the second lateral surface are made of steel, optionally of stainless-steel or cast iron.

[0045] The apparatus may further comprise a drier, such as an oven, placed downstream of the at least one couple of motorised stretching rollers along the conveying path.

[0046] According to embodiments, the recipe comprises as ingredients: vegetable and / or alkaloid particles, a binder and an aerosol forming agent. The vegetable and / or alkaloid particles may comprise tobacco and / or cellulose fibers and / or cellulose powder and / or nicotine and / or botanicals. The binder may comprise a derivative of cellulose such as carboxymethylcellulose (CMC). The aerosol forming agent may comprise polyhydric alcohol such as glycerine. An amount of water in the dough may be from 25 percent to 35 percent on wet weight basis.

[0047] As used in the present description, the “porosity” is the volume fraction of air in the sample expressed as percentage.

[0048] As used in the present description, the “roughness” takes into account irregularities present on surfaces of the sheet.

[0049] As used in the present description, the “density” is estimated by dividing a grammage (g / m2) by a thickness (pm) of the sheet.

[0050] As used in the present description, the “dough” means a watery mixture of insoluble matter with a water content so low (e.g. 25 percent to 35 percent on wet weight basis) that can be kneaded or rolled out, as opposed to “slurry” which is a mixture that is almost liquid.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] EX1. A method for producing a sheet of aerosol-generating substrate for an aerosol-generating article, the method comprising: kneading a mixture with a recipe and water to form a dough; making a continuous dough sheet from said dough and advancing the continuous dough sheet along a conveying path; flattening the continuous dough sheet by running the continuous dough sheet through at least one couple of motorised stretching rollers placed along the conveying path to form the sheet of aerosol-generating substrate; wherein the method further comprises: tuning a porosity and a roughness of the sheet of aerosol-generating substrate by stretching the continuous dough sheet while running between the at least one couple of motorised stretching rollers and setting or adjusting a magnitude of stretching as a function of a target density to be provided to the sheet of aerosol-generating substrate; wherein optionally the method further comprises: drying the sheet of aerosolgenerating substrate.

[0055] EX2. The method according to EX1 , wherein the at least one couple of motorised stretching rollers comprises: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened.

[0056] EX3. The method according to EX2, wherein stretching the continuous dough sheet comprises: imparting a first peripheral speed W1 to the first stretching roller rotating about a respective first main axis and a second peripheral speed W2 to the second stretching roller rotating about a respective second main axis, setting or controlling a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1 ; optionally the first peripheral speed W1 is from 1.0 m / min to 5.0 m / min; optionally the second peripheral speed W2 is from 1.0 m / min to 2.0 m / min; optionally the first peripheral speed W1 and second peripheral speed W2 are set before starting production and kept constant or are adjusted during production.

[0057] EX4. The method according to EX3, wherein the ratio W2 / W1 is controlled as a function of the target density; optionally wherein the target density is between 0.75 g / cm3and 1.25 g / cm3, optionally between 0.85 g / cm3and 0.95 g / cm3.

[0058] EX5. The method according to EX3 or EX4, wherein the ratio W2 / W1 is lower than

[0059] 1.0. EX6. The method according to any of EX3 to EX5, wherein the ratio W2 / W1 is from 0.30 to 0.90, optionally from 0.40 to 0.85.

[0060] EX7. The method according to any of EX3 to EX6, wherein the first stretching roller is placed below the second stretching roller.

[0061] EX8. The method according to EX7, wherein, while running between the motorised stretching rollers and through the gap, the continuous dough sheet lies in contact with an upper portion of the first lateral surface and with a lower portion of the second lateral surface.

[0062] EX9. The method according to any of EX3 to EX8, comprising: conveying the continuous dough sheet to the gap upstream of the at least one couple of motorised stretching rollers with a first linear speed V1 ; optionally the first linear speed V1 is from 0.2 m / min to 4.0 m / min.

[0063] EX10. The method according to any of EX3 to EX9, comprising: moving away the sheet of aerosol-generating substrate from the gap downstream of at least one couple of motorised stretching rollers with a second linear speed V2; optionally the second linear speed V2 is from 1.0 m / min to 5.0 m / min.

[0064] EX11 . The method according to EX9 and EX10, wherein a ratio V2 / V1 of the second linear speed V2 to the first linear speed V1 is greater than 1 .0.

[0065] EX12. The method according to EX11 , wherein the ratio V2 / V1 of the second linear speed V2 to the first linear speed V1 is from 1 .3 to 6.5.

[0066] EX13. The method according to EX11 or EX12, wherein the second linear speed V2 is the same as the first peripheral speed W1 .

[0067] EX14. The method according to any of EX3 to EX13, wherein a ratio t / H (spring factor) of a thickness of the continuous dough sheet downstream of the at least one couple of motorised stretching rollers to a height of the gap is from 1.20 to 4, optionally to 2.50.

[0068] EX15. The method according to any of EX3 to EX14, wherein the at least one couple of motorised stretching rollers comprises a plurality of couples of motorised stretching rollers, the couples of motorised stretching rollers being arranged one after the other along the conveying path, the continuous dough sheet being stretched while running sequentially between each couple of motorised stretching rollers.

[0069] EX16. The method according to EX15, wherein the ratio W2 / W1 of one couple of motorised stretching rollers is smaller than the ratio W2 / W1 of a different couple of motorised stretching rollers placed upstream and / or greater than the ratio W2 / W1 of a different couple of motorised stretching rollers placed downstream.

[0070] EX17. The method according to EX16, wherein the ratios W2 / W1 of the couples of motorised stretching rollers decrease moving downstream along the conveying path. EX18. The method according to EX16 or EX17, wherein the ratio W2 / W1 of a first couple of motorised stretching rollers is from 0.7 to 0.9, the ratio W2 / W1 of a second couple of motorised stretching rollers placed downstream of the first couple is from 0.5 to 0.8, the ratio W2 / W1 of a third couple of motorised stretching rollers placed downstream of the second couple is from 0.3 to 0.6.

[0071] EX19. The method according to EX18 and according to EX11 or EX12 or EX13, wherein the ratio V2 / V1 pertaining to the first couple of motorised stretching rollers is from 4 to 6.5, the ratio V2 / V1 pertaining to the second couple of motorised stretching rollers is from 1.3 to 2.5, the ratio V2 / V1 pertaining to the third couple of motorised stretching rollers is from 2.0 to 3.

[0072] EX20. The method according to any of EX16 to EX19, wherein a height of the gap of one couple of motorised stretching rollers is smaller than a height of the gap of a different couple of motorised stretching rollers placed upstream and / or greater than a height of the gap of a different couple of motorised stretching rollers placed downstream.

[0073] EX21. The method according to EX20 when according to EX18 or EX19, wherein the height of the gap of the first couple of motorised stretching rollers is from 400 pm to 600 pm, the height of the gap of the second couple of motorised stretching rollers is from 200 pm to 300 pm, the height of the gap of the third couple of motorised stretching rollers is from 50 pm to 100 pm.

[0074] EX22. The method according to EX20 or EX21 and EX14, wherein the ratio t / H of the first couple of motorised stretching rollers is from 1.4 to 2, the ratio t / H of the second couple of motorised stretching rollers is from 1.5 to 3, the ratio t / H of the third couple of motorised stretching rollers is from 2.0 to 4.

[0075] EX23. The method according to any of EX1 to EX22, wherein the recipe comprises as ingredients: vegetable and / or alkaloid particles, a binder and an aerosol forming agent.

[0076] EX24. The method according to EX23, wherein the vegetable and / or alkaloid particles comprises tobacco and / or cellulose fibers and / or cellulose powder and / or nicotine and / or botanicals, the binder comprises a derivative of cellulose such as carboxymethylcellulose (CMC), the aerosol forming agent comprises polyhydric alcohol such as glycerine.

[0077] EX25. The method according to any of EX1 to EX24, wherein an amount of water in the dough is from 25 percent to 35 percent on wet weight basis.

[0078] EX26. The method according to any of EX1 to EX25, wherein the porosity (volume fraction of air in a sample) of the dough after kneading and before making the continuous dough sheet is greater than 14%, optionally from 14% to 16%. EX27. The method according to any of EX1 to EX26, wherein the porosity of the continuous dough sheet before flattening and stretching is less than 5%, optionally from 4% to 5%.

[0079] EX28. The method according to any of EX1 to EX27, wherein the porosity of the sheet of aerosol-generating substrate after flattening and stretching is greater than 10%, optionally from 10% to 20%.

[0080] EX29. An apparatus for producing a sheet of aerosol-generating substrate for an aerosol-generating article, the apparatus comprising: a dough mixer configured for kneading a mixture with a recipe and water to form a dough; a dough sheeter configured to make a continuous dough sheet from said dough, optionally the dough sheeter comprising calendering rollers; at least one couple of motorised stretching rollers placed downstream of the dough sheeter with respect to a conveying direction of the continuous dough sheet and configured to flatten and stretch the continuous dough sheet and to form the sheet of aerosolgenerating substrate; the at least one couple of motorised stretching rollers comprising: a first stretching roller having a first lateral surface and a second stretching roller having a second lateral surface, the first lateral surface and the second lateral surface facing each other and delimiting a gap for the passage of the continuous dough sheet to be flattened; a driving unit operatively connected to the first stretching roller and to the second stretching roller to impart a first peripheral speed W1 to the first stretching roller rotating about a respective first main axis and a second peripheral speed W2 to the second stretching roller rotating about a respective second main axis wherein the driving unit is configured for setting or controlling a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1.

[0081] EX30. The apparatus according to EX29, wherein the ratio W2 / W1 is set or controlled as a function of a target density to be provided to the sheet of aerosol-generating substrate.

[0082] EX31 . The apparatus according to EX29 or EX30, wherein the first stretching roller is placed below the second stretching roller.

[0083] EX32. The apparatus according to EX29 or EX30 or EX31 , wherein the driving unit sets or controls the ratio W2 / W1 to be lower than 1.0 to stretch the continuous dough sheet.

[0084] EX33. The apparatus according to any of EX29 to EX32, wherein the driving unit sets or controls the ratio W2 / W1 to be from 0.30 to 0.90, optionally from 0.40 to 0.85.

[0085] EX34. The apparatus according to any of EX29 to EX33, wherein the driving unit comprises a first motor connected to the first stretching roller and a second motor connected to the second stretching roller; or the driving unit comprises a single motor and a gearbox connecting the single motor to the first stretching roller and to the second stretching roller.

[0086] EX35. The apparatus according to EX34, wherein the driving unit comprises a control unit operatively connected to the first motor and to the second motor or to the single motor and the gearbox to adjust the ratio W2 / W1 as a function of the target density.

[0087] EX36. The apparatus according to any of EX29 to EX35, comprising a first conveying surface placed upstream of the at least one couple of motorised stretching rollers and moving towards the gap; optionally the first conveying surface is an upper branch of a first belt conveyor moved by a respective motor or connected to the first motor or to the second motor.

[0088] EX37. The apparatus according to EX36, comprising a second conveying surface placed downstream of the at least one couple of motorised stretching rollers and moving away from the gap; optionally the second conveying surface is an upper branch of a second belt conveyor moved by a respective motor or connected to the first motor or to the second motor.

[0089] EX38. The apparatus according to EX36 and EX37, wherein the driving unit or an auxiliary driving unit is operatively connected to the first conveying surface and to the second conveying surface to impart a first linear speed V1 to the first conveying surface and a second linear speed V2 to the second conveying surface.

[0090] EX39. The apparatus according to EX38, wherein the driving unit or the auxiliary driving unit is configured for setting or controlling a ratio V2 / V1 of the second linear speed V2 to the first linear speed V1 .

[0091] EX40. The apparatus according to EX39, wherein the driving unit or the auxiliary driving unit sets or controls the ratio V2 / V1 to be greater than 1.

[0092] EX41 . The apparatus according to EX40, wherein the driving unit or the auxiliary driving unit sets or controls the ratio V2 / V1 to be from 1.3 to 6.5.

[0093] EX42. The apparatus according to any of EX39 to EX41 , wherein the driving unit or the auxiliary driving unit sets or controls the second linear speed V2 to be the same as the first peripheral speed W1.

[0094] EX43. The apparatus according to any of EX29 to EX42, wherein the first lateral surface and the second lateral surface are made of steel, optionally of stainless-steel or cast iron.

[0095] EX44. The apparatus according to any of EX29 to EX43, wherein the at least one couple of motorised stretching rollers comprises a plurality of couples of motorised stretching rollers, the couples of motorised stretching rollers being arranged one after the other along the conveying path. EX45. The apparatus according to EX44, wherein the driving unit is configured such that the ratio W2 / W1 of one couple of motorised stretching rollers is smaller than the ratio W2 / W1 of a different couple of motorised stretching rollers placed upstream and / or greater than the ratio W2 / W1 of a different couple of motorised stretching rollers placed downstream.

[0096] EX46. The apparatus according to EX45, wherein the driving unit is configured such that the ratio W2 / W1 of a first couple of motorised stretching rollers is from 0.7 to 0.9, the ratio W2 / W1 of a second couple of motorised stretching rollers placed downstream of the first couple is from 0.5 to 0.8, the ratio W2 / W1 of a third couple of motorised stretching rollers placed downstream of the second couple is from 0.3 to 0.6.

[0097] EX47. The apparatus according to EX46, wherein the driving unit is configured such that the ratio V2 / V1 pertaining to the first couple of motorised stretching rollers is from 4 to 6.5, the ratio V2 / V1 pertaining to the second couple of motorised stretching rollers is from 1.3 to 2.5, the ratio V2 / V1 pertaining to the third couple of motorised stretching rollers is from 2 to 3.

[0098] EX48. The apparatus according to any of EX29 or EX47, wherein a height of the gap of one couple of motorised stretching rollers is smaller than a height of the gap of a different couple of motorised stretching rollers placed upstream and / or greater than a height of the gap of a different couple of motorised stretching rollers placed downstream.

[0099] EX49. The apparatus according to EX48 when according to EX46 or EX47, wherein the height of the gap of the first couple of motorised stretching rollers is from 400 pm to 600 pm, the height of the gap of the second couple of motorised stretching rollers is from 200 pm to 300 pm, the height of the gap of the third couple of motorised stretching rollers is from 50 pm to 100 pm.

[0100] EX50. The apparatus according to any of EX29 to EX49, further comprising a drier, such as an oven, placed downstream of the at least one couple of motorised stretching rollers along the conveying path.

[0101] EX51 . The apparatus according to any of EX29 to EX50 which is configured to carry out the method according to any of EX1 to EX28.

[0102] EX52. A process for manufacturing an aerosol-generating article component, comprising: producing the sheet of aerosol-generating substrate for an aerosol-generating article through the method according to any of EX1 to EX28 and / or using the apparatus according to any of EX29 to EX51 ; 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.

[0103] EX53. An aerosol-generating article comprising at least one aerosol-generating article component made through the process according to EX52.

[0104] Examples will now be further described with reference to the figures in which:

[0105] Figure 1 shows schematically an apparatus for producing a sheet of aerosolgenerating substrate for aerosol-generating articles;

[0106] Figure 2 is an enlarged part of the apparatus of figure 1 ;

[0107] Figure 3 shows an apparatus for manufacturing aerosol-generating article components;

[0108] Figures 4 and 5 show respectively a longitudinal section and a cross section of aerosol-generating article component manufactured through the apparatus of Figure 3;

[0109] Figure 6 is an exploded view of an aerosol-generating article comprising the aerosolgenerating article component of Figures 4 and 5;

[0110] Figure 7 is a flowchart of a method for producing a sheet of aerosol-generating substrate for aerosol-generating articles according to the invention.

[0111] Figure 3 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 aerosol-generating articles. The apparatus 100 is configured for actuating a process for manufacturing aerosol-generating article components. An overview of the components and general operation of apparatus 100 is provided below, demonstrating the use of a sheet of aerosol-generating substrate “S” for making aerosol-generating article components 114.

[0112] Subsequently, a detailed description of an apparatus 1 (shown in Figures 1 and 2) and a method for producing the sheet of aerosol-generating substrate “S” used by the apparatus 100 to create the aerosol-generating article component 114 will be provided.

[0113] Referring to Figure 3, the apparatus 100 for manufacturing aerosol-generating article components includes a reel holder 101 where the sheet of aerosol-generating substrate “S” is coiled in a reel 103. The sheet of aerosol-generating substrate “S” may be composed of vegetable and / or alkaloid particles (e.g. tobacco or tobacco free), a binder and an aerosol forming agent (e.g. glycerine). An extraction device (not shown) is configured to uncoil the sheet of aerosol-generating substrate “S” from the reel 103, and a conveyor guides the sheet “S” 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". 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 sheet of aerosol-generating substrate “S”. Each counterrotating crimping roller 102, 105 is operatively connected to a motor (not shown) for rotation to generate a plurality of substantially parallel ridges or corrugations on the sheet of aerosol-generating substrate “S”. 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 sheet of aerosol-generating substrate “S” 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 sheet of aerosol-generating substrate “S” is pulled through devices and / or conveyors from downstream of the converging tool. The wrapping device 111 is designed to wrap the rodshaped sheet of aerosol-generating substrate “S” 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 sheet of aerosolgenerating substrate “S”. 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. 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 aerosol-generating article components 114. 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.

[0114] One aerosol-generating article component 114 comprising the gathered sheet of aerosol-generating substrate “S” in the wrapper 109 is shown in figures 4 and 5. An aerosolgenerating article 200 comprising one aerosol-generating article component 114 is shown in in the exploded view of figure 6. The aerosol-generating article 200 comprises (from left to right in figure 6): a front plug 203 (solid plug), the aerosol-generating article component 114, a tubular plug 205 (hollow plug, for instance of cellulose acetate), a fine tubular plug 206 (like the tubular plug 205 but with a thinner wall) and a filter plug 207 (mouthpiece filter, usually made of tow). Each plug has a wrapping of its own helping to contain properly their content. A tipping paper 208 connects the filter plug 207 to the rest of the plugs, and the front plug 203, aerosol-generating article component 114, tubular plug 205 and fine tubular plug 206 are wrapped together into a wrapping paper 209. The tubular plug 205 and fine tubular plug 206 are cooling plugs configured to cool down the aerosol formed by heating the aerosol-generating article component 114.

[0115] The apparatus 1 for producing the sheet of aerosol-generating substrate “S” is described with reference to figures 1 and 2. As previously mentioned, the apparatus 1 is responsible for producing the sheet of aerosol-generating substrate “S”, which is subsequently reeled and used by apparatus 100 for making the aerosol-generating article component 114.

[0116] Referring to figure 1 , the apparatus 1 comprises a dough mixer 2 configured for kneading a mixture with a recipe and water to form a dough “D”. The dough mixer 2 may be per se known and may comprise or may be connected to an extruder having an outlet 3 for the dough “D”.

[0117] The recipe comprises as ingredients: vegetable and / or alkaloid particles, for instance tobacco and / or cellulose fibers and / or cellulose powder and / or nicotine and / or botanicals, a binder, for instance a derivative of cellulose such as carboxymethylcellulose (CMC), and an aerosol forming agent, for instance a polyhydric alcohol such as glycerine. An amount of water in the dough is from 25 percent to 35 percent on wet weight basis.

[0118] While kneading in the mixer 2, air is incorporated in the mixture and a porosity (volume fraction of air in a sample) of the dough after kneading may be from 14% to 16%.

[0119] A dough sheeter 4, embodied as calendering rollers 5, 6, is placed just downstream the outlet 3 and is configured to make a continuous dough sheet 7 from said dough “D”. Through calendering, the porosity of the dough may be reduced to less than 5%.

[0120] A first belt conveyor 8 is placed downstream of the calendering rollers 5, 6. The first belt conveyor 8 is schematically shown in figures 1 and 2 and comprises a belt coupled to a pair of motorised rollers according to a closed path. An upper branch of the closed path defines a first conveying surface 9 which is configured to support and transport the continuous dough sheet 7 along a conveying path and in a conveying direction with a first conveying speed “V1” and towards a first couple of motorised stretching rollers 10, 11.

[0121] A second belt conveyor 12 is placed downstream of first couple of motorised stretching rollers 10, 11 and comprises a belt coupled to a pair of motorised rollers according to a closed path. An upper branch of the closed path defines a second conveying surface 13 which is configured to support and transport the continuous dough sheet 7 in a conveying direction with a second conveying speed “V2” and towards a second couple of motorised stretching rollers 14, 15.

[0122] A third belt conveyor 16 is placed downstream of second couple of motorised stretching rollers 14, 15 and comprises a belt coupled to a pair of motorised rollers according to a closed path. An upper branch of the closed path defines a third conveying surface 17 which is configured to support and transport the continuous dough sheet 7 in a conveying direction with a third conveying speed “V3” and towards a third couple of motorised stretching rollers 18, 19.

[0123] A fourth belt conveyor 20 is placed downstream of third couple of motorised stretching rollers 18, 19 and comprises a belt coupled to a pair of motorised rollers according to a closed path. An upper branch of the closed path defines a fourth conveying surface 21 which is configured to support and transport the continuous dough sheet 7 in a conveying direction with a fourth conveying speed “V4” and towards and through an oven 22 where the dough sheet 7 is dried. The sheet of aerosol-generating substrate “S” coming out of the oven 22 is wound in the bobbin 103.

[0124] The first couple of motorised stretching rollers 10, 11 comprises (figure 2) a first stretching roller 10 placed below a second stretching roller 11. The first stretching roller 10 has a first lateral surface 23 and rotates about a first main axis thereof. The second stretching roller 11 has a second lateral surface 24 and rotates about a second main axis thereof. The main axes of the first and second stretching rollers 10, 11 are parallel to each other and the first lateral surface 23 and the second lateral surface 24 face each other. The first lateral surface 23 and the second lateral surface 24 delimit a gap therebetween for the passage of the continuous dough sheet 7 coming from the calendering rollers 5, 6. While running between the motorised stretching rollers and through the gap, the continuous dough sheet 7 lies in contact with an upper portion of the first lateral surface 23 and with a lower portion of the second lateral surface 24.

[0125] The first stretching roller 10 and the second stretching roller 11 are made, for instance, of stainless-steel or cast iron.

[0126] The first stretching roller 10 and the second stretching roller 11 are configured to flatten and stretch the continuous dough sheet 7 and to form the sheet of aerosol-generating substrate “S”.

[0127] A driving unit 25 (schematically represented in figure 2) is operatively connected to the first stretching roller 10 and / or to the second stretching roller 11 to impart a first peripheral speed W1 to the first stretching roller 10 and a second peripheral speed W2 to the second stretching roller 11. The first stretching roller 10 and the second stretching roller 11 are rotated in opposite direction such that the first and second peripheral speeds W1 , W2 at the gap are directed towards the second belt conveyor 12.

[0128] For instance, the driving unit 25 comprises a first motor connected to the first stretching roller 10 and a second motor connected to the second stretching roller 11. Otherwise, the driving unit 25 may comprise a single motor and a gearbox connecting the single motor to the first stretching roller 10 and / or to the second stretching roller 11. The driving unit 25 comprises an electronic control unit 26 operatively connected to the first motor and to the second motor or to the single motor and the gearbox to adjust the first and second peripheral speeds W1 , W2 and / or a ratio W2 / W1 of the second peripheral speed W2 to the first peripheral speed W1.

[0129] The driving unit 25, or an auxiliary driving unit, is operatively connected to the first belt conveyor 8 and to the second belt conveyor 12 to impart the first linear speed “V1” to the first conveying surface 9, which moves towards the gap, and the second linear speed “V2” to the second conveying surface 13, which moves away from the gap. The electronic control unit 26 is also configured to set or control the first linear speed “V1” and the second linear speed “V2” and / or a ratio V2 / V1 of the second linear speed “V2” to the first linear speed “V1”.

[0130] The first peripheral speed “W1” is greater than the second peripheral speed W2. Therefore, the ratio W2 / W1 is lower than 1 .0. The first peripheral speed “W1” is equal to the second linear speed “V2”. The first peripheral speed “W1” and the second linear speed “V2” are greater than the first linear speed “V1”. For instance, the second peripheral speed “W2” is greater than the first linear speed “V1”. The continuous dough sheet 7 is flattened and stretched while running through the first couple of motorised stretching rollers 10, 11 and does not accumulate just before the gap between said first couple of motorised stretching rollers 10, 11. The first couple of motorised stretching rollers 10, 11 causes also a shearing effect on the continuous dough sheet 7.

[0131] Stretching causes a porosity increase and shearing causes a roughness increase. Porosity increase and roughness increase determine a density reduction and a thickness increase of the sheet of aerosol-generating substrate “S” for a given grammage.

[0132] A magnitude of stretching may be set or adjusted by setting or adjusting the first and second peripheral speeds W1 , W2 as a function of a target density to be provided to the sheet of aerosol-generating substrate “S”. For instance, the first and second peripheral speeds W1 , W2 are set before starting production and may kept constant or may be adjusted during production. The target density is usually between 0.75 g / cm3and 1.25 g / cm3, preferably between 0.85 g / cm3and 0.95 g / cm3.

[0133] Possible parameter ranges are listed in the following Table 1.

[0134] Table 1

[0135] The second couple of motorised stretching rollers 14, 15 and the third couple of motorised stretching rollers 18, 19 are structurally similar to the first couple of motorised stretching rollers 10, 11 and the second, third and fourth belt conveyors 12, 16, 20 are structurally similar to the first belt conveyor 8. Therefore, said elements will not be described in detail here.

[0136] The driving unit 25 is configured to impart to the second couple of motorised stretching rollers 14, 15 and to the third couple of motorised stretching rollers 18, 19 first and second peripheral speeds different from the first and second peripheral speeds W1 , W2 of the first couple of motorised stretching rollers 10, 11 and to control the third and fourth linear speeds “V3, “V4”. The first and second peripheral speeds W1 , W2 of the first couple of motorised stretching rollers 10, 11 are lower than the first and second peripheral speeds W1 , W2 of the second couple of motorised stretching rollers 14, 15, which are lower than the first and second peripheral speeds W1 , W2 of the third couple of motorised stretching rollers 18, 19. The linear speeds increase from the first linear speed “V1” to the fourth linear speed “V4”.

[0137] Furthermore, a height “H” of the gap of the first couple of motorised stretching rollers 10, 11 is greater than a height “H” of the gap of the second couple of motorised stretching rollers 14, 15 which is greater that a height “H” of the gap of the third couple of motorised stretching rollers 18, 19.

[0138] The following table 2 contains one example of parameter values.

[0139] Table 2

[0140] The height “H” of the gap decreases from the first to the third couple of motorised stretching rollers to progressively flatten the sheet of aerosol-generating substrate “S”. Indeed, the thickness “t” progressively decreases. The ratio W2 / W1 decreases from the first to the third couple of motorised stretching rollers. The linear speeds “V1”, “V2”, “V3”, “V4” increases from the first to the fourth belt conveyor 8, 12, 16, 20.

[0141] Each of the second and third couple of motorized stretching rollers 14, 15 and 18, 19 affects the porosity, roughness, density and thickness of the sheet of aerosol-generating substrate “S”. The thickness “t” is determined by the density and by the height “H” of the gaps. Just downstream of each couple of motorised stretching rollers, the sheet is more likely to recover some of its original thickness the greater its porosity. Indeed, downstream of each couple of motorised stretching rollers, a ratio t / H (spring factor) ranges from 1.4 to 4.

[0142] The porosity of the sheet of aerosol-generating substrate after flattening and stretching is greater than 10%, for instance from 10% to 20.

[0143] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5 percent of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

CLAIMS1. Method for producing a sheet of aerosol-generating substrate for an aerosolgenerating article, the method comprising: kneading a mixture with a recipe and water to form a dough (D); making a continuous dough sheet (7) from said dough (D) and advancing the continuous dough sheet (7) along a conveying path; flattening the continuous dough sheet (7) by running the continuous dough sheet (7) through at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) placed along the conveying path to form the sheet of aerosol-generating substrate (S); wherein the method further comprises: tuning a porosity and a roughness of the sheet of aerosol-generating substrate (S) by stretching the continuous dough sheet (7) while running between the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) and setting or adjusting a magnitude of stretching as a function of a target density to be provided to the sheet of aerosol-generating substrate (S).

2. Method according to claim 1 , wherein the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) comprises: a first stretching roller (10) having a first lateral surface (23) and a second stretching roller (11) having a second lateral surface (24), the first lateral surface (23) and the second lateral surface (24) facing each other and delimiting a gap for the passage of the continuous dough sheet (7) to be flattened; and wherein stretching the continuous dough sheet (7) comprises: imparting a first peripheral speed (W1) to the first stretching roller (10) rotating about a respective first main axis and a second peripheral speed (W2) to the second stretching roller (11) rotating about a respective second main axis, setting or controlling a ratio W2 / W1 of the second peripheral speed (W2) to the first peripheral speed (W1) as a function of the target density.

3. Method according to claim 2, wherein the first stretching roller (10) is placed below the second stretching roller (11) and the ratio W2 / W1 is lower than 1 .0.

4. Method according to claim 3, wherein the ratio W2 / W1 is from 0.30 to 0.90.

5. Method according to any of claims 2 to 4, comprising: conveying the continuous dough sheet (7) to the gap upstream of the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) with a first linear speed (V1) and moving away the sheet of aerosol-generating substrate (7) from the gap downstream of at least one couple ofmotorised stretching rollers (10, 11 , 14, 15, 18, 19) with a second linear speed (V2); wherein a ratio V2 / V1 of the second linear speed (V2) to the first linear speed (V1) is greater than 1.0.

6. Method according to claim 5, wherein the ratio V2 / V1 of the second linear speed (V2) to the first linear speed (V1) is from 1.3 to 6.5.

7. Method according to any of claims 5 or 6, wherein the second linear speed (V2) is the same as the first peripheral speed (W1).

8. Method according to any of claims 1 to 7, wherein the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) comprises a plurality of couples of motorised stretching rollers, the couples of motorised stretching rollers being arranged one after the other along the conveying path, the continuous dough sheet (7) being stretched while running sequentially between each couple of motorised stretching rollers .

9. Method according to any of claims 1 to 8, wherein the recipe comprises as ingredients vegetable and / or alkaloid particles, a binder and an aerosol forming agent and wherein an amount of water in the dough is from 25 percent to 35 percent on wet weight basis.

10. Apparatus for producing a sheet of aerosol-generating substrate for an aerosolgenerating article, the apparatus comprising: a dough mixer (2) configured for kneading a mixture with a recipe and water to form a dough (D); a dough sheeter (4) configured to make a continuous dough sheet (7) from said dough (D); at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) placed downstream of the dough sheeter (4) with respect to a conveying direction of the continuous dough sheet (7) and configured to flatten and stretch the continuous dough sheet (7) and to form the sheet of aerosol-generating substrate (S); the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) comprising: a first stretching roller (10) having a first lateral surface (23) and a second stretching roller (11) having a second lateral surface (24), the first lateral surface (23) and the second lateral surface (24) facing each other and delimiting a gap for the passage of the continuous dough sheet (7) to be flattened;a driving unit (25) operatively connected to the first stretching roller (10) and to the second stretching roller (11) to impart a first peripheral speed (W1) to the first stretching roller (10) rotating about a respective first main axis and a second peripheral speed (W2) to the second stretching roller (11) rotating about a respective second main axis; wherein the driving unit (25) is configured for setting or controlling a ratio W2 / W1 of the second peripheral speed (W2) to the first peripheral speed (W1) as a function of a target density to be provided to the sheet of aerosol-generating substrate (S).

11. Apparatus according to claim 10, wherein the first stretching roller (10) is placed below the second stretching roller (11) and the driving unit (25) sets or controls the ratio W2 / W1 to be lower than 1.0 to stretch the continuous dough sheet (7).

12. Apparatus according to claim 11 , wherein the driving unit (25) sets or controls the ratio W2 / W1 to be from 0.30 to 0.90.

13. Apparatus according to any of claims 10 to 12, comprising a first conveying surface (9) placed upstream of the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) and moving towards the gap and a second conveying surface (13) placed downstream of the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) and moving away from the gap; the driving unit (25) or an auxiliary driving unit being operatively connected to the first conveying surface (9) and to the second conveying surface (13) to impart a first linear speed (V1) to the first conveying surface (9) and a second linear speed (V2) to the second conveying surface (13); wherein the driving unit (25) or the auxiliary driving unit is configured for setting or controlling a ratio V2 / V1 of the second linear speed (V2) to the first linear speed (V1).

14. Apparatus according to any of claims 10 to 13, wherein the at least one couple of motorised stretching rollers (10, 11 , 14, 15, 18, 19) comprises a plurality of couples of motorised stretching rollers, the couples of motorised stretching rollers being arranged one after the other along the conveying path.

15. Apparatus according to claim 14, wherein the driving unit (25) is configured such that the ratio W2 / W1 of one couple of motorised stretching rollers (14, 15) is smaller than the ratio W2 / W1 of a different couple of motorised stretching rollers (10, 11) placed upstream and / or greater than the ratio W2 / W1 of a different couple of motorised stretching rollers (18, 19) placed downstream.

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