IMPROVED AEROSOL-FORMING SUBTRATE

Abstract

There is provided an aerosol-forming substrate comprising, on a dry weight basis: between 10 and 90 wt % carbon particles; between 7 and 60 wt % of an aerosol former; between 2 and 20 wt % of fibres; and between 2 and 10 wt % of a binder. Each of the carbon particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond. There is also provided an aerosol-generating article comprising the aerosol-forming substrate and a method of forming the aerosol-forming substrate.

Claims

1. An aerosol-forming substrate comprising, on a dry weight basis: between 70 and 90 wt % carbon particles; between 7 and 26 wt % of an aerosol former; between 2 and 20 wt % of fibres; and between 2 and 10 wt % of a binder, wherein each of the carbon particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond.

2. An aerosol-forming substrate according to claim 1, wherein the carbon particles have a particle size distribution having a volume D10 particle size between 1 and 20 microns.

3. An aerosol-forming substrate according to claim 1, wherein the carbon particles have a particle size distribution having a volume D90 particle size between 50 and 300 microns.

4. An aerosol-forming substrate according to claim 1, wherein the carbon particles have a particle size distribution having a volume D10 particle size and a number D90 particle size, wherein the volume D90 particle size is no more than 50 times the number D10 particle size.

5. An aerosol-forming substrate according to claim 1, wherein some or all of the carbon particles are substantially spherical.

6. An aerosol-forming substrate according to claim 1, wherein each of the carbon particles consists of one or more of expanded graphite, graphene, and diamond.

7. An aerosol-forming substrate according to claim 1, wherein the substrate comprises, on a dry weight basis, at least 75 wt % of the carbon particles.

8. An aerosol-forming substrate according to claim 1, wherein the substrate comprises, on a dry weight basis, at least 80 wt % of the carbon particles.

9. An aerosol-forming substrate according to claim 1, wherein the carbon particles are substantially homogeneously distributed throughout the aerosol-forming substrate.

10. An aerosol-forming substrate according to claim 1, wherein the aerosol-forming substrate is a tobacco-free aerosol-forming substrate.

11. An aerosol-forming substrate according to claim 1, wherein the aerosol-forming substrate comprises between 1 and 20 wt % water.

12. A combined aerosol-forming substrate comprising: a first material and a second material, the first material being comprised in the combined aerosol-forming substrate as a first plurality of discrete elements and the second material being comprised in the combined aerosol-forming substrate as a second plurality of discrete elements, in which the first material comprises an aerosol former and has a first thermal conductivity, and in which the second material comprises, or is, an aerosol-forming substrate according to claim 1 and has a second thermal conductivity that is greater than the first thermal conductivity.

13. An aerosol-generating article comprising an aerosol-forming substrate according to claim 1.

14. An aerosol-generating system comprising an aerosol-generating article according to claim 13 and an electrical aerosol-generating device for heating the aerosol-forming substrate.

15. A method of forming an aerosol-forming substrate according to claim 1, the method comprising: forming a slurry comprising the carbon particles, the aerosol former, the fibres, and the binder; and casting and drying the slurry to form the aerosol-forming substrate or a precursor for forming into the aerosol-forming substrate.

16. An aerosol-generating article comprising an aerosol-forming substrate according to the combined aerosol-forming substrate according to claim 12.

17. An aerosol-generating system comprising an aerosol-generating article according to claim 16 and an electrical aerosol-generating device for heating the combined aerosol-forming substrate of the aerosol-generating article.

18. A method of forming a combined aerosol-forming substrate according to claim 12, the method comprising: forming a slurry comprising the carbon particles, the aerosol former, the fibres, and the binder; and casting and drying the slurry to form the aerosol-forming substrate or a precursor for forming into the aerosol-forming substrate.

Description

[0200] Examples will now be further described with reference to the figures in which:

[0201] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article;

[0202] FIG. 2 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article;

[0203] FIG. 3 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system;

[0204] FIG. 4 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system; and

[0205] FIG. 5 shows a schematic cross-sectional view of a third embodiment of an aerosol-generating article.

[0206] FIG. 1 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating article 10. The aerosol-generating article 10 extends from an upstream or distal end 18 to a downstream or proximal or mouth end 20 and has an overall length of about 45 millimetres.

[0207] The aerosol-generating article 10 comprises a rod 12 of aerosol-forming substrate and a downstream section 14 at a location downstream of the rod 12 of aerosol-forming substrate. Further, the aerosol-generating article 10 comprises an upstream section 16 at a location upstream of the rod 12 of aerosol-forming substrate.

[0208] The downstream section 14 comprises a support element 22 located immediately downstream of the rod 12 of aerosol-forming substrate, the support element 22 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the upstream end of the support element 22 abuts the downstream end of the rod 12 of aerosol-generating substrate. In addition, the downstream section 14 comprises an aerosol-cooling element 24 located immediately downstream of the support element 22, the aerosol-cooling element 24 being in longitudinal alignment with the rod 12 and the support element 22. In the embodiment of FIG. 1, the upstream end of the aerosol-cooling element 24 abuts the downstream end of the support element 22.

[0209] As will become apparent from the following description, the support element 22 and the aerosol-cooling element 24 together define an intermediate hollow section 50 of the aerosol-generating article 10. As a whole, the intermediate hollow section 50 does not substantially contribute to the overall RTD of the aerosol-generating article. An RTD of the intermediate hollow section 26 as a whole is substantially 0 millimetres H.sub.2O.

[0210] The support element 22 comprises a first hollow tubular segment 26. The first hollow tubular segment 26 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 26 defines an internal cavity 28 that extends all the way from an upstream end 30 of the first hollow tubular segment 26 to a downstream end 32 of the first hollow tubular segment 26. The internal cavity 28 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 28. As such, the first hollow tubular segment 26and, as a consequence, the support element 22does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the first hollow tubular segment 26 (which is essentially the RTD of the support element 22) is substantially 0 millimetres H.sub.2O.

[0211] The first hollow tubular segment 26 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (D.sub.FTS) of about 1.9 millimetres. Thus, a thickness of a peripheral wall of the first hollow tubular segment 26 is about 2.67 millimetres.

[0212] The aerosol-cooling element 24 comprises a second hollow tubular segment 34. The second hollow tubular segment 34 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 34 defines an internal cavity 36 that extends all the way from an upstream end 38 of the second hollow tubular segment to a downstream end 40 of the second hollow tubular segment 34. The internal cavity 36 is substantially empty, and so substantially unrestricted airflow is enabled along the internal cavity 36. The second hollow tubular segment 28and, as a consequence, the aerosol-cooling element 24does not substantially contribute to the overall RTD of the aerosol-generating article 10. In more detail, the RTD of the second hollow tubular segment 34 (which is essentially the RTD of the aerosol-cooling element 24) is substantially 0 millimetres H.sub.2O.

[0213] The second hollow tubular segment 34 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter (D.sub.STS) of about 3.25 millimetres. Thus, a thickness of a peripheral wall of the second hollow tubular segment 34 is about 2 millimetres. Thus, a ratio between the internal diameter (D.sub.FTS) of the first hollow tubular segment 26 and the internal diameter (D.sub.STS) of the second hollow tubular segment 34 is about 0.75.

[0214] The aerosol-generating article 10 comprises a ventilation zone 60 provided at a location along the second hollow tubular segment 34. In more detail, the ventilation zone is provided at about 2 millimetres from the upstream end of the second hollow tubular segment 34. In this embodiment, the ventilation zone 60 comprises a circumferential row of perforations through a paper wrapper 70 and a ventilation level of the aerosol-generating article 10 is about 25 percent.

[0215] In the embodiment of FIG. 1, the downstream section 14 further comprises a mouthpiece element 42, also referred to as a mouth plug filter, at a location downstream of the intermediate hollow section 50. In more detail, the mouthpiece element 42 is positioned immediately downstream of the aerosol-cooling element 24. As shown in the drawing of FIG. 1, an upstream end of the mouthpiece element 42 abuts the downstream end 40 of the aerosol-cooling element 24.

[0216] The mouthpiece element 42 is provided in the form of a cylindrical plug of low-density cellulose acetate.

[0217] The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.25 millimetres. The RTD of the mouthpiece element 42 is about 12 millimetres H.sub.2O. The ratio of the length of the mouthpiece element 42 to the length of the intermediate hollow section 50 is approximately 0.6.

[0218] The rod 12 of aerosol-forming substrate has an external diameter of about 7.25 millimetres and a length of about 12 millimetres.

[0219] The upstream section 16 comprises an upstream element 46, also referred to as a front plug, located immediately upstream of the rod 12 of aerosol-forming substrate, the upstream element 46 being in longitudinal alignment with the rod 12. In the embodiment of FIG. 1, the downstream end of the upstream element 46 abuts the upstream end of the rod 12 of aerosol-forming substrate. The upstream element 46 is provided in the form of a cylindrical plug of cellulose acetate. The upstream element 46 has a length of about 5 millimetres. The RTD of the upstream element 46 is about 30 millimetres H.sub.2O.

[0220] The upstream element 46, rod 12 of aerosol-forming substrate, support element 22, aerosol-cooling element 24, and mouthpiece element 42 are circumscribed by a paper wrapper 70.

[0221] The rod 12 of aerosol-forming substrate comprises, on a dry weight basis, around 76.1 wt % thermally conductive particles 44. In this embodiment, the thermally conductive particles 44 are graphite particles, specifically FP 99.5 (>99.5% purity) graphite particles from Graphit Kropfml GmbH, AMG Graphite GK, though other particles or mixtures of particles could be used. Each thermally conductive particle has a thermal conductivity of around 6 W/(mK) in at least one direction at 25 degrees Celsius.

[0222] The rod 12 of aerosol-forming substrate comprises, on a dry weight basis, around 17.7 wt % of an aerosol former. In this embodiment, the aerosol former is glycerol, specifically ICOF Europe fodd grade (>99.5% purity) glycerol.

[0223] The rod 12 of aerosol-forming substrate comprises, on a dry weight basis, around 3.9 wt % of fibres. In this embodiment, the fibres are cellulose fibres, specifically Birch cellulose fibers from Stora Enso OYJ.

[0224] The rod 12 of aerosol-forming substrate comprises, on a dry weight basis, around 2.3 wt % of a binder. In this embodiment, the binder is a guar gum, specifically guar gum from Gumix International Inc.

[0225] The rod 12 of aerosol-forming substrate comprises about 10 wt % water, when measured at 25 degrees Celsius.

[0226] In other embodiments, the rod 12 of aerosol-forming substrate further comprises one or more of nicotine, an acid such as fumaric acid, a botanical such as clove or rosmarinus, and a flavourant.

[0227] The aerosol-forming substrate has a thermal conductivity of at least 0.1 W/(mK) in at least one direction at 25 degrees Celsius. The aerosol-forming substrate may have a thermal conductivity of 0.2, 0.5, 1, 1.5 or greater W/(mK) in at least one direction at 25 degrees Celsius

[0228] Each of the thermally conductive particles 44 is substantially spherical in shape. The thermally conductive particles 44 are substantially homogeneously distributed throughout the aerosol-forming substrate. The particle size distribution has a volume D10 particle size of around 6 microns, a volume D50 particle size of around 20 microns, and a volume D90 particle size of around 56 microns. Each of the thermally conductive particles 44 has a particle size greater than around 1 microns and less than around 300 microns.

[0229] The thermally conductive particles 44 have a density of around 2200 kilograms per metre cubed. The aerosol-forming substrate has a density of around 800 kilograms per metre cubed.

[0230] The rod 12 of aerosol-forming substrate is formed by the process set out below.

[0231] A slurry is formed using a lab disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (for example by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available lab disperser from PC Laborsystem was used.

[0232] To form the slurry, a first mixture is formed by adding to the lap disperser around 7.11 grams of the aerosol former, then around 157.5 grams of water, then around 1.57 grams of the fibres. Then, these first ingredients are mixed at 25 degrees Celsius for 5 minutes at 600-700 rpm to ensure a homogeneous mixture and to hydrate the fibers. Then, a second mixture is formed by manually mixing around 32.95 grams of the thermally conductive particles and around 0.92 grams of the binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. Then, the second mixture is added to the first mixture to form a combined mixture. Then, the combined mixture is mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of around 200 mbar. The reduced pressure may help to ensure that the thermally conductive particles are homogeneously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. Then, the combined mixture is mixed at 5000 rpm for 20 second minutes at 25 degrees Celsius and a second reduced pressure of around 100 mbar. This second reduced pressure may help to remove any remaining air bubbles. This forms a slurry for casting.

[0233] The slurry is then casted and dried using a suitable apparatus. In this embodiment, a commercially available Labcoater Mathis apparatus is used. This apparatus includes a stainless steel, flat support, and a coma blade for adjusting a thickness of slurry cast onto the flat support.

[0234] The slurry is cast onto the flat support and a gap between the coma blade and the flat support is set at 0.6 millimetres. This ensures that a thickness of the slurry is no more than 0.6 millimetres at any given point.

[0235] The slurry is then dried with hot air between 120 and 140 degrees Celsius for between 2 and 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet has a thickness of around 159 microns, a grammage of around 125.7 grams per metre squared, and a density of around 0.79 kilograms per metre cubed.

[0236] The sheet is then gathered and cut to form the rod 12 of aerosol-forming substrate. In other embodiments, the sheet is also crimped.

[0237] After forming the rod 12 of aerosol-forming substrate, the aerosol-generating article 10 is assembled by positioning the various components of the article 10 and wrapping the components in the wrapper 70.

[0238] FIG. 2 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating article 11. This second embodiment is identical to the first embodiment of FIG. 1 except that the rod 12 of aerosol-forming substrate has been replaced by an alternative rod 13 of a combined aerosol-forming substrate. Identical reference numerals have been used for identical components in the embodiments of FIGS. 1 and 2.

[0239] In the rod 13 of the second embodiment, the combined aerosol-forming substrate comprises a first material and a second material. The first material is comprised in the combined aerosol-forming substrate as a first plurality of discrete elements and the second material is comprised in the combined aerosol-forming substrate as a second plurality of discrete elements. In this embodiment, the first material and the second material are equally abundant by weight in the combined aerosol-forming substrate. In other embodiments, however, more or less of the first material may be present in the combined aerosol-forming substrate than the second material.

[0240] In this embodiment, the elements of both the first and second plurality of discrete elements have an average thickness of between 150 microns and 300 microns, an average width of between 600 microns and 1000 microns, and an average length of between 1000 microns and 10000 microns.

[0241] The first material may be a conventional tobacco cut-filler. As such, the first material may be formed by a conventional tobacco cut-filler manufacturing process and may comprise an aerosol former, fibres and a binder, but does not comprise any thermally conductive particles. As an example, the first material may be made using a similar method to that set out above for the rod 12 of aerosol-forming substrate of the first embodiment of FIG. 1, except that no thermally conductive particles are included and, rather than gathering and cutting the sheet to form the rod 12, the sheet is shredded to form reconstituted cut-filler.

[0242] The second material is formed from a similar aerosol-forming substrate to that of the rod 12 in the first embodiment of FIG. 1. The second material comprises on a dry weight basis, around 76.1 wt % thermally conductive particles 45, around 17.7 wt % of an aerosol former, around 3.9 wt % of fibres, and around 2.3 wt % of a binder. In the second material, the thermally conductive particles are all either graphite particles or expanded graphite particles, though other particles or mixtures of particles could be used.

[0243] The first material has a first thermal conductivity and the second material has a second thermal conductivity at least 10% greater than the first thermal conductivity. Thus, the second material helps to increase the thermal conductivity of the combined aerosol-forming substrate.

[0244] The rod 13 of combined aerosol-forming substrate is formed by the process set out below. A slurry is formed using a lab disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (for example by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available lab disperser from PC Laborsystem was used.

[0245] To form the slurry, a first mixture is formed by adding to the lap disperser around 7.11 grams of the aerosol former, then around 157.5 grams of water, then around 1.57 grams of the fibres. Then, these first ingredients are mixed at 25 degrees Celsius for 5 minutes at 600-700 rpm to ensure a homogeneous mixture and to hydrate the fibers. Then, a second mixture is formed by manually mixing around 32.95 grams of the thermally conductive particles and around 0.92 grams of the binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. Then, the second mixture is added to the first mixture to form a combined mixture. Then, the combined mixture is mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of around 200 mbar. The reduced pressure may help to ensure that the thermally conductive particles are homogeneously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. Then, the combined mixture is mixed at 5000 rpm for 20 second minutes at 25 degrees Celsius and a second reduced pressure of around 100 mbar. This second reduced pressure may help to remove any remaining air bubbles. This forms a slurry for casting.

[0246] The slurry is then casted and dried using a suitable apparatus. In this embodiment, a commercially available Labcoater Mathis apparatus is used. This apparatus includes a stainless steel, flat support, and a coma blade for adjusting a thickness of slurry cast onto the flat support.

[0247] The slurry is cast onto the flat support and a gap between the coma blade and the flat support is set at 0.6 millimetres. This ensures that a thickness of the slurry is no more than 0.6 millimetres at any given point.

[0248] The slurry is then dried with hot air between 120 and 140 degrees Celsius for between 2 and 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet has a thickness of around 159 microns, a grammage of around 125.7 grams per metre squared, and a density of around 0.79 kilograms per metre cubed.

[0249] The sheet is then shredded to form a plurality of discrete elements of the aerosol-forming substrate. In other words, the sheet is then cut to form the second material present in the combined aerosol-forming substrate as a second plurality of discrete elements.

[0250] This second material is then mixed with the first material, which is a first plurality of discrete elements. As set out above, the first material may be formed using a conventional tobacco cut-filler manufacturing process. This is therefore not explained in detail here.

[0251] The mixed first and second materials present as pluralities of discrete elements are then formed into the rod 13 of combined aerosol-forming substrate, for example by circumscribing in a wrapper.

[0252] Then, after forming the rod 13 of combined aerosol-forming substrate, the aerosol-generating article 11 is assembled by positioning the various components of the article 11 and wrapping the components in the wrapper 70.

[0253] FIG. 3 shows a schematic cross-sectional view of a first embodiment of an aerosol-generating system 100. The system 100 comprises an aerosol-generating device 102 and the aerosol-generating article 10 of FIG. 1, though the device 102 could equally be used with the aerosol-generating article 11 of FIG. 2.

[0254] The aerosol-generating device 102 comprises a battery 104, a controller 106, a heating blade 108 coupled to the battery, and a puff-detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating blade 108 and the puff-detection mechanism.

[0255] The aerosol-generating device 102 further comprises a housing 110 defining a substantially cylindrical cavity for receiving a portion of the article 10. The heating blade 108 is positioned centrally within the cavity and extends longitudinally from a base of the cavity.

[0256] In this embodiment, the heating blade 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating blade 108 so as to be able to pass a current through the electrically resistive track and heat the electrically resistive track and heating blade 108 to an operational temperature.

[0257] In use, a user inserts the article 10 into the cavity, causing the heating blade 108 to penetrate the upstream element 46 and rod 12 of aerosol-forming substrate of the article 10. FIG. 3 shows the article 10 inserted into the cavity of the device 102.

[0258] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 102, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0259] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to pass a current through the electrically resistive track and heat up the heating blade 108. This heats up the rod 12 of aerosol-forming substrate, which is in contact with the heating blade 108.

[0260] The thermally conductive particles 44 have a significantly higher thermal conductivity than the surrounding aerosol-forming material. As such, these particles may act as local hot-spots and provide a more even temperature throughout the aerosol-forming substrate, particularly in a radial direction from the heating blade 108 where, with prior art substrates, there would be a significant temperature gradient. This may result in a greater proportion of the aerosol-forming substrate reaching a sufficiently high temperature to release volatile compounds, and thus a higher usage efficiency of the aerosol-forming substrate.

[0261] Heating of the aerosol-forming substrate cause the aerosol-forming substrate to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element 22 and the aerosol-cooling element 24. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0262] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to reduce the current being passed through the electrically resistive track to zero.

[0263] After a number of puffs on the article 10, the user may choose to replace the article 10 with a fresh article.

[0264] FIG. 4 shows a schematic cross-sectional view of a second embodiment of an aerosol-generating system 200. The system 200 comprises an aerosol-generating device 202 and the aerosol-generating article 11 of FIG. 2, though the device 202 could equally be used with the aerosol-generating article 10 of FIG. 1.

[0265] The aerosol-generating device 202 comprises a battery 204, a controller 206, an inductor coil 208, and a puff-detection mechanism (not shown). The controller 206 is coupled to the battery 204, the inductor coil 208 and the puff-detection mechanism.

[0266] The aerosol-generating device 202 further comprises a housing 210 defining a substantially cylindrical cavity for receiving a portion of the article 11. The inductor coil 208 spirals around the cavity.

[0267] The battery 204 is coupled to the inductor coil 208 so as to be able to pass an alternating current through the inductor coil 208.

[0268] In use, a user inserts the article 11 into the cavity. FIG. 4 shows the article 11 inserted into the cavity of the device 202.

[0269] Then, the user puffs on the downstream end of the article 11. This causes air to flow through an air inlet (not shown) of the device 202, then through the article 11, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0270] The user puffing on the article 11 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to pass an alternating current through the inductor coil 208. This causes the inductor coil 208 to generate a fluctuating electromagnetic field. The rod 13 of combined aerosol-forming substrate is located within this fluctuating electromagnetic field. The materials of the particles 45, graphite and expanded graphite, are susceptor materials. Thus, the fluctuating electromagnetic field causes eddy currents in the particles 45. This causes the particles 45 to heat up, thereby also heating nearby aerosol-forming material.

[0271] Heating of the aerosol-forming material cause the aerosol-forming material to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 11 towards the downstream end 20 of the article 11. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0272] When the user stops inhaling on the article 11, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puff-detection mechanism. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to reduce the current being passed through the electrically resistive track to zero.

[0273] After a number of puffs on the article 11, the user may choose to replace the article 11 with a fresh article.

[0274] FIG. 5 shows a schematic cross-sectional view of a third embodiment of an aerosol-generating article 510. This third embodiment is identical to the first embodiment of FIG. 1 except that the rod 12 of aerosol-forming substrate has been replaced by an alternative rod 512 of aerosol-forming substrate. Identical reference numerals have been used for identical components in the embodiments of FIGS. 1 and 5.

[0275] The rod 512 of aerosol-forming substrate of the third embodiment of FIG. 5 includes an elongate susceptor element 580.

[0276] The susceptor element 580 is arranged substantially longitudinally within the rod 512 of aerosol-forming substrate so as to be approximately parallel with a longitudinal axis of the rod 512 of aerosol-forming substrate. As shown in the drawing of FIG. 5, the susceptor element 580 is positioned in a radially central position within the rod and extends along the longitudinal axis of the rod 12.

[0277] The susceptor element 580 extends all the way from an upstream end to a downstream end of the rod 512 of aerosol-forming substrate. As such, the susceptor element 580 has substantially the same length as the rod 512 of aerosol-forming substrate.

[0278] In the embodiment of FIG. 5, the susceptor element 580 is provided in the form of a strip of a ferromagnetic steel and has a length of about 12 millimetres, a thickness of about 60 micrometres, and a width of about 4 millimetres.

[0279] The aerosol-generating article 510 of FIG. 5 may be used with the aerosol-generating device 202 of FIG. 4 in the same way as the aerosol-generating article 11 of FIG. 2. Notably, the inclusion of the susceptor element 580 means that the article 510 may be inductively heated regardless of whether the thermally conductive particles comprise a suitable susceptor material for inductive heating.

[0280] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 66 wt % thermally conductive particles 44. In this embodiment, the thermally conductive particles 44 are graphite particles, specifically commercially available FP 99.5 (>99.5% purity) graphite particles from Graphit Kropfml GmbH, AMG Graphite GK, though other particles or mixtures of particles could be used. Each thermally conductive particle has a thermal conductivity of around 6 W/(mK) in at least one direction at 25 degrees Celsius.

[0281] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 20 wt % of an aerosol former. In this embodiment, the aerosol former is glycerol, specifically commercially available ICOF Europe fodd grade (>99.5% purity) glycerol.

[0282] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 7 wt % of fibres. In this embodiment, the fibres are cellulose fibres, specifically commercially available Birch cellulose fibers from Stora Enso OYJ.

[0283] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 4 wt % of a binder. In this embodiment, the binder is a Sodium Carboxymethyl cellulose, specifically commercially available Sodium Carboxymethyl cellulose (CMC) Type K-700 from GumixInternational Inc.

[0284] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 1 wt % nicotine.

[0285] The rod 512 of aerosol-forming substrate comprises, on a dry weight basis, around 2 wt % of an acid. In this embodiment, the acid is fumaric acid, specifically a commercially available fumaric acid from Sigma-Aldrich (>99% purity).

[0286] In other embodiments, the substrate further includes at least one botanical, for example clove or Rosmarinus.

[0287] The rod 12 of aerosol-forming substrate comprises about 10 wt % water, when measured at 25 degrees Celsius.

[0288] The aerosol-forming substrate has a thermal conductivity of at least 0.1 W/(mK) in at least one direction at 25 degrees Celsius. The aerosol-forming substrate may have a thermal conductivity of 0.2, 0.5, 1, 1.5 or greater W/(mK) in at least one direction at 25 degrees Celsius

[0289] The thermally conductive particles 44 are identical to those in the rod 12 of the first embodiment of FIG. 1.

[0290] The rod 512 of aerosol-forming substrate is formed by the process set out below.

[0291] A slurry is formed using a lab disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (for example by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available lab disperser from PC Laborsystem was used.

[0292] To form the slurry, a first mixture is formed by adding to the lap disperser around 12 grams of a solution of nicotine in glycerine (the aerosol former) at a concentration of 10%, then around 13.2 grams of glycerine, then around 2.4 grams of fumaric acid, then around 280 grams of water, then around 8.4 grams of the fibres. Then, these first ingredients are mixed at 25 degrees Celsius for 5 minutes at 600-700 rpm to ensure a homogeneous mixture and to hydrate the fibers. Then, a second mixture is formed by manually mixing around 79.2 grams of the thermally conductive particles and around 4.8 grams of the binder. This mixing of the second mixture avoids the formation of lumps in the lab dispersion. Then, the second mixture is added to the first mixture to form a combined mixture. Then, the combined mixture is mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of around 200 mbar. The reduced pressure may help to ensure that the thermally conductive particles are homogeneously dispersed in the mixture and that there is little trapped air and few lumps in the combined mixture. Then, the combined mixture is mixed at 5000 rpm for 20 second minutes at 25 degrees Celsius and a second reduced pressure of around 100 mbar. This second reduced pressure may help to remove any remaining air bubbles. This forms a slurry for casting.

[0293] The slurry is then casted and dried using a suitable apparatus. In this embodiment, a commercially available Labcoater Mathis apparatus is used. This apparatus includes a stainless steel, flat support, and a coma blade for adjusting a thickness of slurry cast onto the flat support.

[0294] The slurry is cast onto the flat support and a gap between the coma blade and the flat support is set at 0.6 millimetres. This ensures that a thickness of the slurry is no more than 0.6 millimetres at any given point.

[0295] The slurry is then dried with hot air between 120 and 140 degrees Celsius for between 2 and 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet has a thickness of around 230 microns, and a grammage of around 200 grams per metre squared.

[0296] The sheet is then gathered and cut to form a substantially rod-shaped precursor. Then the susceptor element inserted into the precursor to form the rod 512 of aerosol-forming substrate.

[0297] After forming the rod 512 of aerosol-forming substrate, the aerosol-generating article 510 is assembled by positioning the various components of the article 510 and wrapping the components in the wrapper 70.

[0298] 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 A10% 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.