ES3055709T3 - Improved aerosol-forming substrate - Google Patents

Abstract

An aerosol-forming substrate is provided comprising, on a dry weight basis, between 10% and 90% by weight of carbon particles; between 7% and 60% by weight of an aerosol former; between 2% and 20% by weight of fibers; and between 2% and 10% by weight of a binder. Each carbon particle is composed of one or more of the following materials: graphite, expanded graphite, graphene, carbon nanotubes, charcoal, and diamond. An aerosol-generating article is also provided, comprising the aerosol-forming substrate and a method for its formation.

Description

[0001] DESCRIPTION

[0002] Improved aerosol-forming substrate

[0003] This description relates to an aerosol-forming substrate. This description also relates to a method for manufacturing an aerosol-forming substrate, an aerosol-generating article, and an aerosol-generating system.

[0004] A typical aerosol generating system comprises an aerosol generating device and an aerosol generating article comprising an aerosol forming substrate. During use, the aerosol generating device interacts with the aerosol generating article to heat the aerosol forming substrate and cause the aerosol forming substrate to release volatile compounds. These compounds are then cooled to form an aerosol that is inhaled by a user.

[0005] Known aerosol-forming substrates have relatively low thermal conductivities. This can be inconvenient, particularly in aerosol-generating systems where a foil is inserted into the aerosol-forming substrate and heated to warm the substrate. This is because the low thermal conductivity of the aerosol-forming substrate can lead to a relatively large temperature gradient within the substrate during use. This can mean that portions of the aerosol-forming substrate farther from the foil do not reach high temperatures and therefore do not release as many volatile compounds as they would if the substrate had a higher thermal conductivity. In other words, the low thermal conductivity of the aerosol-forming substrate can undesirably result in low utilization efficiency of the aerosol-forming substrate.

[0006] Furthermore, known aerosol-forming substrates typically cannot be heated to operating temperatures by induction. This means that a separate susceptor element is typically required for inductive heating. This can increase costs. Moreover, this can lead to the same problems discussed earlier. For example, when an inductively heated susceptor element is placed in a central position on the substrate, the portions of the aerosol-forming substrate farther from the susceptor element may not reach a high enough temperature and, therefore, may not release many volatile compounds.

[0007] Attempts have been made to increase the thermal conductivity of aerosol-forming substrates. However, to date, these attempts have been inadequate in one or more respects.

[0008] US Patent 2021/112860 relates to a conductive substrate useful for Joule heating, such as in an electronic smoking device. The conductive substrate comprises an electrically conductive material and a carbonaceous additive, such as a binder. The conductive substrate is carbonized because it is subjected to calcination conditions to effectively reduce the carbonaceous additive to its carbon skeleton.

[0009] It is an objective of the present invention to provide an improved aerosol-forming substrate, for example, an aerosol-forming substrate having increased thermal conductivity.

[0010] The invention is defined in the appended independent claims, to which reference shall now be made. Optional features of the invention are defined in the dependent claims. Aspects, embodiments, or examples that fall outside the scope of the appended independent claims do not form part of the invention and are included for illustrative or explanatory purposes only.

[0011] Therefore, according to a first aspect of the present description, an aerosol-forming substrate is provided comprising, on a dry weight basis: between 70 and 90 wt% of thermally conductive particles; between 7 and 26 wt% of an aerosol former; between 2 and 20 wt% of fibers; and between 2 and 10 wt% of a binder, wherein each of the thermally conductive particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, carbon, and diamond.

[0012] When the term “thermally conductive particles” is used to refer to particles comprising carbon, for example particles comprising or consisting of one or more of graphite, expanded graphite, graphene, carbon nanotubes, coal, and diamond, the thermally conductive particles may be referred to as carbon particles or carbon-containing particles.

[0013] Advantageously, thermally conductive particles can increase the thermal conductivity of the aerosol-forming substrate. The increased thermal conductivity of the substrate can provide a more uniform temperature distribution throughout the substrate during use. This can result in a greater proportion of the aerosol-forming substrate reaching a temperature high enough to release volatile compounds, and therefore greater efficiency in the use of the aerosol-forming substrate. In addition, the increased thermal conductivity of the substrate can allow a heater, for example, a heating sheet configured to heat the substrate, to operate at a lower temperature and thus require less energy. Furthermore, the increased thermal conductivity of the substrate can allow a heater to heat the substrate to a temperature at which volatile compounds are released in less time. Therefore, the increased thermal conductivity can reduce the time required to form an inhalable aerosol for a user.

[0014] Advantageously, one or both fibers and the binder can increase the tensile strength of the aerosol-forming substrate. The increased tensile strength can enable the production of a sheet of the aerosol-forming substrate that does not tear easily. The increased tensile strength can enable the production of a sheet of the aerosol-forming substrate using existing production machinery.

[0015] The aerosol-forming substrate may have a thermal conductivity of at least 0.05, 0.1, 0.15, 0.2, 0.22, 0.3, 0.4, or 0.5 W/(mK) in at least one direction, or in all directions, at 25 degrees Celsius. This thermal conductivity may be measured when the moisture content of the substrate is between 0 and 20, or 5 and 15, for example, around 10%. The moisture or water content of the substrate may be measured using a titration method.

[0016] Optionally, some or all of the thermally conductive particles comprise at least 10, 30, 50, 70, 90, 95, 98 or 99% by weight of carbon.

[0017] Optionally, some or all of the thermally conductive particles are graphite particles. Optionally, some or all of the thermally conductive particles are expanded graphite particles. Optionally, some or all of the thermally conductive particles are graphene particles. Optionally, some or all of the thermally conductive particles are carbon nanotubes or carbon nanotube particles. Optionally, some or all of the thermally conductive particles are carbon particles. Optionally, some or all of the thermally conductive particles are diamond particles, for example, artificial diamond particles. Advantageously, such materials can have relatively high thermal conductivities.

[0018] Expanded graphite may have a density less than 2, 1.8, 1.5, 1.2, 1, 0.8, or 0.5, 0.2, 0.1, 0.05, 0.02 grams per cubic centimeter (g/cm³). Expanded graphite may have a density greater than 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5 or 1.8 grams per cubic centimeter (g/cm³). Expanded graphite can have a density between 0.01 and 3, 0.01 and 2, 0.01 and 1.8, 0.01 and 1.5, 0.01 and 1.2, 0.01 and 1, 0.01 and 0.8, 0.01 and 0.5, 0.02 and 3, 0.02 and 2, 0.02 and 1.8, 0.02 and 1.5, 0.02 and 1.2, 0.02 and 1, 0.02 and 0.8, 0.02 and 0.5, 0.01 and 3, 0.05 and 2, 0.05 and 1.8, 0.05 and 1.5, 0.05 and 1.2, 0.05 and 1, 0.05 and 0.8. 0.05 and 0.5 g/cm³, 0.1 and 3, 0.1 and 2, 0.1 and 1.8, 0.1 and 1.5, 0.1 and 1.2, 0.1 and 1, 0.1 and 0.8, 0.1 and 0.5, 0.2 and 3, 0.2 and 2, 0.2 and 1.8, 0.2 and 1.5, 0.2 and 1.2, 0.2 and 1, 0.2 and 0.8, 0.2 and 0.5, 0.5 and 3, 0.5 and 2, 0.5 and 1.8, 0.5 and 1.5, 0.5 and 1.2, 0.5 and 1, 0.5 and 0.8, 0.8 and 3, 0.8 and 2 0.8 and 1.8, 0.8 and 1.5, 0.8 and 1.2, 0.8 and 1 grams per cubic centimeter (g/cm³).

[0019] The following aspects where each of the thermally conductive particles does not necessarily consist of one or more of graphite, expanded graphite, graphene, carbon nanotubes, coal, and diamond are not in accordance with the invention but are present for illustrative purposes.

[0020] Optionally, in accordance with aspects where each of the thermally conductive particles does not necessarily consist of one or more of graphite, expanded graphite, graphene, carbon nanotubes, carbon, and diamond, some or all of the thermally conductive particles comprise a metal. Alternatively, or furthermore, some or all of the thermally conductive particles comprise an alloy. Alternatively or further, some or all of the thermally conductive particles comprise an intermetallic material. Advantageously, such materials can have relatively high thermal conductivities.

[0021] Optionally, in accordance with alternative aspects where each of the thermally conductive particles does not necessarily consist of one or more of graphite, expanded graphite, graphene, carbon nanotubes, carbon, and diamond, some or all of the thermally conductive particles comprise one or more of silicon carbide, silver, copper, gold, aluminum nitride, aluminum, tungsten, and boron nitride. Optionally, some or all of the thermally conductive particles are silicon carbide particles. Optionally, some or all of the thermally conductive particles are silver particles. Optionally, some or all of the thermally conductive particles are copper particles. Optionally, some or all of the thermally conductive particles are gold particles. Optionally, some or all of the thermally conductive particles are aluminum nitride particles. Optionally, some or all of the thermally conductive particles are aluminum particles. Optionally, some or all of the thermally conductive particles are tungsten particles. Optionally, some or all of the thermally conductive particles may be boron nitride particles. Advantageously, such materials can have relatively high thermal conductivities.

[0022] Thermally conductive particles can each have a “particle size.” The meaning of the term “particle size” and a method for measuring particle size are set out below.

[0023] Thermally conductive particles can be characterized by a particle size distribution. The particle size distribution can have D10, D50, and D90 particle sizes. The D10 particle size is defined such that 10% of the particles have a particle size less than or equal to the D10 particle size. Similarly, the D50 particle size is defined such that 50% of the particles have a particle size less than or equal to the D50 particle size. Therefore, the D50 particle size can be referred to as the median particle size. The D90 particle size is defined such that 90% of the particles have a particle size less than or equal to the D90 particle size. Therefore, if there were 1000 particles in the distribution and the particles were ordered by ascending particle size, the D10 particle size number would be expected to be approximately equal to the particle size of the 100th particle, the D50 particle size number should be approximately equal to the particle size of the 500th particle, and the D90 particle size number to be approximately equal to the particle size of the 900th particle.

[0024] The particle size distribution can have particle sizes of volume D10, D50, and D90. The D10 particle size volume is defined such that 10% of the sum of the volumes of all particles is accounted for by summing the volumes of particles that have a particle size less than or equal to the D10 particle size volume. Similarly, the D50 particle size volume is defined such that 50% of the sum of the volumes of all particles is accounted for by summing the volumes of particles that have a particle size less than or equal to the D50 particle size volume. And the D90 particle size volume is defined such that 90% of the sum of the volumes of all particles is accounted for by summing the volumes of particles that have a particle size less than or equal to the D90 particle size volume.

[0025] Optionally, the thermally conductive particles have a particle size distribution having a numerical particle size D10, wherein the numerical particle size D10 is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0026] Optionally, the thermally conductive particles have a particle size distribution having a numerical particle size D10, wherein the numerical particle size D10 is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0027] A compromise must be reached when deciding on particle sizes. Larger thermally conductive particles can advantageously increase the thermal conductivity of the aerosol-forming substrate more than smaller thermally conductive particles. However, larger thermally conductive particles can reduce the space available for the aerosol-forming material on the substrate.

[0028] Optionally, the thermally conductive particles have a particle size distribution having a numerical D50 particle size, wherein the numerical D50 particle size is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0029] Optionally, the thermally conductive particles have a particle size distribution having a numerical D50 particle size, wherein the numerical D50 particle size is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0030] Optionally, the thermally conductive particles have a particle size distribution having a numerical D90 particle size, wherein the numerical D90 particle size is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0031] Optionally, the thermally conductive particles have a particle size distribution having a numerical D90 particle size, wherein the numerical D90 particle size is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0032] Optionally, the thermally conductive particles have a particle size distribution having a numerical particle size D10 and a numerical particle size D90, wherein the numerical particle size D90 is no more than 50, 40, 30, 20, 10 or 5 times the numerical particle size D10.

[0033] Optionally, the thermally conductive particles have a particle size distribution having a numerical particle size D10 and a numerical particle size D90, wherein the numerical particle size D90 is at least 1.5, 2, 3, 5, 10 or 20 times the numerical particle size D10.

[0034] A compromise must be reached regarding the particle size distribution. A tighter particle size distribution, for example characterized by a smaller ratio between the D90 and D10 particle sizes, can advantageously provide more uniform thermal conductivity throughout the aerosol-forming substrate. This is because there will be less variation in particle size at different locations on the substrate. This can advantageously allow for more efficient use of the aerosol-forming material along the aerosol-forming substrate. However, a tighter particle size distribution can be disadvantageously more difficult and costly to achieve. The inventors have found that the particle size distributions described above can provide an optimal compromise between these two factors.

[0035] Optionally, the thermally conductive particles have a particle size distribution having a volume D10 particle size, wherein the volume D10 particle size is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0036] Optionally, the thermally conductive particles have a particle size distribution having a volume D10 particle size, wherein the volume D10 particle size is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns

[0037] Optionally, the thermally conductive particles have a particle size distribution having a volume D50 particle size, wherein the volume D50 particle size is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0038] Optionally, the thermally conductive particles have a particle size distribution having a volume D50 particle size, wherein the volume D50 particle size is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0039] Optionally, the thermally conductive particles have a particle size distribution having a volume D90 particle size, wherein the volume D90 particle size is at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200 or 500 microns.

[0040] Optionally, the thermally conductive particles have a particle size distribution having a volume D90 particle size, wherein the volume D90 particle size is no more than 1000, 500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns.

[0041] It may be particularly preferable that the thermally conductive particles have a particle size distribution having a volume D10 particle size between 1 and 20 microns. Alternatively or additionally, it may be particularly preferable that the thermally conductive particles have a particle size distribution having a volume D90 particle size between 50 and 300 microns, or between 50 and 200 microns.

[0042] Optionally, the thermally conductive particles have a particle size distribution having a volume D10 particle size and a volume D90 particle size, wherein the volume D90 particle size is no more than 50, 40, 30, 20, 10 or 5 times the volume D10 particle size.

[0043] Optionally, the thermally conductive particles have a particle size distribution having a volume D10 particle size and a volume D90 particle size, wherein the volume D90 particle size is at least 1.5, 2, 3, 5, 10 or 20 times the volume D10 particle size.

[0044] As explained above, a compromise must be made regarding the particle size distribution, and the inventors have found that the above particle size distributions can provide an optimal compromise.

[0045] Optionally, each of the thermally conductive particles has a particle size of at least 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 microns. Optionally, each of the thermally conductive particles has a particle size of no more than 1000, 500, 300, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, or 0.2 microns. It may be particularly preferable that each of the thermally conductive particles has a particle size of at least 1 micron. Alternatively or additionally, it may be particularly preferable that each of the thermally conductive particles has a particle size of no more than 300 microns. Particles smaller than 1 micron can be difficult to handle during manufacturing. Furthermore, particles smaller than 1 micron are more likely to pass through a filter in an aerosol-generating article comprising the aerosol-forming substrate. Particles larger than 300 microns can occupy a significant amount of space on the substrate that could be used for aerosol-forming material. Therefore, it can be particularly advantageous for each of the thermally conductive particles to have a particle size of at least 1 micron, or a particle size of no more than 300 microns, or both.

[0046] Optionally, each of the thermally conductive particles has three mutually perpendicular dimensions, the largest of which is no more than 10, 8, 5, 3, or 2 times larger than the smallest of which dimensions. Alternatively, each of the thermally conductive particles is essentially spherical. Advantageously, the orientation of essentially spherical particles may not affect the thermal conductivity of the substrate as much as the orientation of non-spherical particles. Therefore, the use of more spherical particles may result in less variability between different substrates where particle orientations are not controlled. Furthermore, essentially spherical particles may be easier to characterize.

[0047] Optionally, the thermally conductive particles comprise at least 10, 20, 50, 100, 200, 500, or 1000 particles. Advantageously, a higher number of particles in the aerosol-forming substrate can allow the thermal conductivity of the substrate to be more uniform.

[0048] Optionally, the substrate comprises, on a dry weight basis, at least 75, 80, or 85% by weight of the thermally conductive particles. Optionally, the substrate comprises, on a dry weight basis, no more than 85, 80, or 75% by weight of the thermally conductive particles. Optionally, the substrate comprises, on a dry weight basis, between 80 and 90 or 70 and 80% by weight of the thermally conductive particles.

[0049] An understanding must be made regarding the weight percent of thermally conductive particles in the substrate. Increasing the weight percent of particles in the aerosol-forming substrate can advantageously increase the substrate's thermal conductivity. However, increasing the weight percent of particles in the aerosol-forming substrate can also reduce the space available for one or more of the aerosol former, binder, and fibers, which could result in a substrate that forms less aerosol or has lower tensile strength.

[0050] Optionally, the substrate comprises, on a dry weight basis, at least 10, 15, 20, or 25% by weight of the aerosol former. Optionally, the substrate comprises, on a dry weight basis, no more than 25, 20, or 15% by weight of the aerosol former. Optionally, the substrate comprises, on a dry weight basis, between 7 and 20, 10 and 20, or 7 and 10% by weight of the aerosol former. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 15 and 25% by weight of the aerosol former.

[0051] Optionally, the aerosol former comprises or consists of one or more of: polyhydric alcohols, such as propylene glycol, polyethylene glycol, triethylene glycol, 1,3-butanediol, and glycerin; esters of polyhydric alcohols, such as mono-, di-, or tri-glycerol acetate; and aliphatic esters of mono-, di-, or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Optionally, the aerosol-forming substrate comprises one or both of glycerin and glycerol.

[0052] Optionally, the substrate comprises, on a dry weight basis, at least 2, 4, 6, 8, 10, 12, 14, 16 or 18% by weight of fibers. Optionally, the substrate comprises, on a dry weight basis, not more than 20, 18, 16, 14, 12, 10, 8, 6 or 4% by weight of fibers. Optionally, the substrate comprises, on a dry weight basis, between 4 and 20, 6 and 20, 8 and 20, 10 and 20, 12 and 20, 14 and 20, 16 and 20, 18 and 20, 2 and 18, 4 and 18, 6 and 18, 8 and 18, 10 and 18, 12 and 18, 14 and 18, 16 and 18, 2 and 16, 4 and 16, 6 and 16, 8 and 16, 10 and 16, 12 and 16, 14 and 16, 2 and 14, 4 and 14, 6 and 14, 8 and 14, 10 and 14, 12 and 14, 2 and 12, 4 and 12, 6 and 12, 8 and 12, 10 and 12, 2 and 10, 4 and 10, 6 and 10, 8 and 10, 2 and 8, 4 and 8, 6 and 8, 2 and 6, 4 and 6, or 2 and 4% by weight of the fibers. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 2 and 10% by weight of the fibers.

[0053] Optionally, the fibers are cellulosic fibers. Advantageously, cellulosic fibers are not excessively expensive and can increase the tensile strength of the substrate.

[0054] Optionally, each fiber has three mutually perpendicular dimensions, the largest of which is at least 1.5, 2, 3, 5, 10, or 20 times larger than the smallest of which.

[0055] Optionally, the substrate comprises, on a dry weight basis, at least 4, 6, or 8% by weight of the binder. Optionally, the substrate comprises, on a dry weight basis, no more than 8, 6, or 4% by weight of the binder. Optionally, the substrate comprises, on a dry weight basis, between 4 and 10, 6 and 10, 8 and 10, 2 and 8, 4 and 8, 6 and 8, 2 and 6, 4 and 6, 2 and 4% by weight of the binder. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 2 and 10% by weight of the binder.

[0056] Suitable binders are well known in the art and include, but are not limited to, natural pectins, such as fruit, citrus, or tobacco pectins; guar gums, such as hydroxyethyl guar and hydroxypropyl guar; locust bean gums, such as hydroxyethyl and hydroxypropyl locust bean gum; alginate; starches, such as modified or derivatized starches; celluloses, such as methyl, ethyl, ethylhydroxymethyl, and carboxymethylcellulose; tamarind gum; dextran; pullaloon; konjac flour; xanthan gum, and the like. It may be particularly preferable that the binder be or comprise guar. It may be particularly preferable that the binder comprise or consist of one or more of carboxymethylcellulose or hydroxypropylcellulose or a gum such as guar gum. Optionally, the thermally conductive particles are distributed essentially homogeneously throughout the aerosol-forming substrate. Optionally, the aerosol former is distributed essentially homogeneously throughout the aerosol-forming substrate. Optionally, the fibers are distributed essentially homogeneously throughout the aerosol-forming substrate. Optionally, the binder is distributed essentially homogeneously throughout the aerosol-forming substrate. Advantageously, a homogeneous distribution of the substrate components can result in the substrate having more spatially uniform properties. For example, essentially homogeneously distributed thermally conductive particles can result in the substrate having essentially uniform thermal conductivity. As another example, essentially homogeneously distributed binder or fibers can result in the substrate having essentially uniform tensile strength.

[0057] Optionally, the substrate comprises nicotine. Optionally, the substrate comprises, on a dry weight basis, at least 0.01, 1, 2, 3, or 4% by weight of nicotine. Optionally, the substrate comprises, on a dry weight basis, not more than 5, 4, 3, 2, or 1% by weight of nicotine. Optionally, the substrate comprises, on a dry weight basis, between 0.01 and 5, 1 and 5, 2 and 5, 3 and 5, 4 and 5, 0.01 and 4, 1 and 4, 2 and 4, 3 and 4, 0.01 and 3, 1 and 3, 2 and 3, 0.01 and 2, 1 and 2, 0.01 and 1% by weight of nicotine. It may be particularly preferable that the substrate comprise, on a dry weight basis, between 0.5 and 4% by weight of nicotine.

[0058] Optionally, nicotine is distributed essentially homogeneously throughout the aerosol-forming substrate.

[0059] Optionally, the substrate comprises an acid. Optionally, the substrate comprises, on a dry weight basis, at least 0.01, 1, 2, 3, or 4% by weight of the acid. Optionally, the substrate comprises, on a dry weight basis, not more than 5, 4, 3, 2, or 1% by weight of the acid. Optionally, the substrate comprises, on a dry weight basis, between 0.01 and 5, 1 and 5, 2 and 5, 3 and 5, 4 and 5, 0.01 and 4, 1 and 4, 2 and 4, 3 and 4, 0.01 and 3, 1 and 3, 2 and 3, 0.01 and 2, 1 and 2, 0.01 and 1% by weight of the acid. It may be particularly preferable that the substrate comprise, on a dry weight basis, between 0.5 and 5% by weight of acid.

[0060] Optionally, the acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid.

[0061] Optionally, the acid is distributed essentially homogeneously throughout the aerosol-forming substrate.

[0062] Optionally, the substrate comprises at least one botanical. Optionally, the substrate comprises, on a dry weight basis, at least 0.01, 1, 2, 5, 10 or 15% by weight of at least one botanical plant. Optionally, the substrate comprises, on a dry weight basis, no more than 20, 15, 10, 5, 2 or 1% by weight of at least one botanical plant. Optionally, the substrate comprises, on a dry weight basis, between 0.01 and 20, 1 and 20, 2 and 20, 5 and 20, 10 and 20, 15 and 20, 0.01 and 15, 1 and 15, 2 and 15, 5 and 15, 10 and 15, 0.01 and 10, 1 and 10, 2 and 10, 5 and 10, 0.01 and 5, 1 and 5, 2 and 5, 0.01 and 2, 1 and 2, 0.01 and 1% by weight of at least one botanical. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 1 and 15% by weight of at least one botanical.

[0063] Optionally, the at least one botanical comprises or consists of one or both of clove and rosemary.

[0064] Optionally, at least one botanical is distributed essentially homogeneously throughout the aerosol-forming substrate.

[0065] Optionally, the substrate comprises at least one flavoring. Optionally, the substrate comprises, on a dry weight basis, at least 0.1, 1, 2, or 5% by weight of the at least one flavoring. Optionally, the substrate comprises, on a dry weight basis, no more than 10, 5, 2, or 1% by weight of the at least one flavoring. Optionally, the substrate comprises, on a dry weight basis, between 0.1 and 10, 1 and 10, 2 and 10, 5 and 10, 0.1 and 5, 1 and 5, 2 and 5, 0.1 and 2, 1 and 2, 0.1 and 1% by weight of the at least one flavoring. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 0.1 and 5% by weight of the at least one flavoring.

[0066] Optionally, at least one flavoring is present as a coating, for example, a coating on one or more components of the aerosol-forming substrate. Alternatively, or in addition, the at least one flavoring is distributed essentially homogeneously throughout the aerosol-forming substrate.

[0067] Optionally, the aerosol-forming substrate comprises at least one organic material such as tobacco. Optionally, the at least one organic material comprises one or more of the following: grass leaf, tobacco leaf, tobacco midrib fragments, reconstituted tobacco, homogenized tobacco, extruded tobacco, and expanded tobacco. Optionally, the at least one organic material is distributed essentially homogeneously throughout the aerosol-forming substrate.

[0068] The substrate may comprise, on a dry weight basis, less than 10, 5, 3, 2 or 1% by weight of tobacco. Optionally, the aerosol-forming substrate is a tobacco-free aerosol-forming substrate.

[0069] The aerosol-forming substrate may be in the form of a rod. As such, a rod of aerosol-forming substrate may be provided.

[0070] A susceptor element may be located within the aerosol-forming substrate bar. The susceptor element may be an elongated susceptor element. The susceptor element may extend longitudinally within the aerosol-forming substrate bar. The bar may be essentially cylindrical, e.g., right-hand cylindrical. The susceptor element may be positioned radially centrally within the aerosol-forming substrate bar. The susceptor element may extend along a central, longitudinal axis of the aerosol-forming substrate bar. The susceptor element may extend to a downstream end of the aerosol-forming substrate bar. The susceptor element may extend to an upstream end of the aerosol-forming substrate bar. The susceptor element may be essentially the same length as the aerosol-forming substrate bar. The susceptor element may extend from the upstream end to the downstream end of the aerosol-forming substrate bar. The susceptor element can be in the form of a pin, a rod, a strip, or a sheet. The susceptor element can have a length of between 5 and 15, 6 and 12, or 8 and 10 millimeters. The susceptor element can have a width of between 1 and 5 millimeters. The susceptor element can have a thickness of between 0.01 and 2, 0.5 and 2, or 0.5 and 1 millimeter.

[0071] Alternatively, there may be no susceptor materials present in the aerosol-forming substrate or in the aerosol-forming substrate rod.

[0072] Optionally, some or all of the thermally conductive particles may be inductively heatable, for example, to a temperature of at least 100, 150, or 200 degrees Celsius. Optionally, some or all of the thermally conductive particles may comprise or consist of one or more susceptor materials. Advantageously, this may allow the thermally conductive particles to be inductively heated. The thermally conductive particles may comprise or be the only susceptor material(s) present in the aerosol-forming substrate or in the aerosol-forming substrate rod. That is, there may be no susceptor elements present in the aerosol-forming substrate or in the aerosol-forming substrate rod except for the thermally conductive or carbon particles.

[0073] Suitable susceptor materials include, but are not limited to: carbon, carbon-based materials, graphene, graphite, expanded graphite, molybdenum, silicon carbide, stainless steels, niobium, aluminum, nickel, nickel-containing compounds, titanium, and compounds of metallic materials. Suitable susceptor materials may comprise a ferromagnetic material, for example, ferritic iron, a ferromagnetic alloy, such as ferromagnetic steel or stainless steel, ferromagnetic particles, and ferrite. A suitable susceptor material may be, or comprise, aluminum. A susceptor material preferably comprises more than 5 percent, preferably more than 20 percent, and more preferably more than 50 percent or more than 90 percent of ferromagnetic or paramagnetic materials. Preferred susceptor materials may comprise a metal, metal alloy, or carbon.

[0074] Particularly preferred susceptor materials may be, or comprise, carbon, carbon-based materials, graphene, graphite, or expanded graphite. Advantageously, such materials have relatively high thermal conductivities, relatively low densities, and can be inductively heated.

[0075] Optionally, the aerosol-forming substrate has a thermal conductivity of more than 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.25, 1.5, 2, 5, 10, 20, 50, 100, 200, or 500 W/(mK) in at least one direction at 25 degrees Celsius.

[0076] Optionally, the aerosol-forming substrate has a density of no more than 1500, 1450, 1400, 1350, 1300, 1250, 1200, 1100, 1050, 1000, 950, 900, 850, 800, 850, 800, 750, 700, 650, or 600 kg/m³. Alternatively, the aerosol-forming substrate has a density between 600 and 1400, 800 and 1200, or 900 and 1100 kg/m³. Advantageously, reducing the substrate density can reduce substrate transportation costs.

[0077] Optionally, the aerosol-forming substrate has a moisture content of between 1 and 20, or 3 and 15% by weight. This moisture content can be measured after 48 hours of equilibration at 50% relative humidity at 20 degrees Celsius. The moisture or water content of the substrate can be measured using a titration method.

[0078] Optionally, the aerosol-forming substrate comprises, or is in the form of, one or more of: chopped particles, powder particles, granules, pellets, fragments, spaghetti, strips, threads, tapes, or sheets. Optionally, the aerosol-forming substrate comprises, or is in the form of, one or more sheets or strips.

[0079] Optionally, the aerosol-forming substrate comprises, or is in the form of, one or more sheets, for example, crinkled sheets. Optionally, the aerosol-forming substrate comprises, or is in the form of, a plurality of strips.

[0080] Optionally, the sheet or strip may have a thickness of at least 5, 10, 20, 50, 100, 150, or 200 microns. Optionally, the sheet or strip may have a thickness of no more than 2000, 1000, 500, 400, 300, or 250 microns. Optionally, the sheet or strip may have a thickness between 100 and 350, or 150 and 300 microns.

[0081] Optionally, the sheet or strip may have a width of at least 100, 200, 500, or 1000 microns. Optionally, the sheet or strip may have a width of no more than 2000, 1000, 500, 400, 300, 250, or 200 microns. Optionally, the sheet or strip may have a width between 100 and 2000, or 500 and 1000, or 600 and 1000 microns.

[0082] Optionally, the sheet or strip may have a length of at least 100, 200, 500, 1000, 2000, or 3000 microns. Optionally, the sheet or strip may have a length of no more than 6000, 5000, 3000, 2000, 1000, 500, or 200 microns. Optionally, the sheet or strip may have a length of between 100 and 6000, or 500 and 5000, or 1000 and 4000 microns.

[0083] Optionally, the sheet or strip may have a basis weight of at least 20, 50 or 100 g/m². Optionally, the sheet or strip may have a basis weight of no more than 300 g/m². Optionally, the sheet or strip may have a basis weight of between 20 and 300, 50 and 250, or 100 and 250 g/m².

[0084] Optionally, the sheet or strip may have a density of at least 0.1, 0.2, 0.3, or 0.5 g/m³. Optionally, the sheet or strip may have a density of no more than 2, 1.5, 1.2, or 1 g/m³. Optionally, the sheet or strip may have a density of between 0.1 and 2, 0.2 and 2, 0.3 and 2, 0.3 and 1.5, or 0.3 and 1.2 g/m³.

[0085] When the substrate comprises one or more crinkled sheets, the crinkled sheet or each crinkled sheet may have a width of at least approximately 1, 2, 5, 10, 25, 50 or 100 mm.

[0086] In accordance with the present description, a combined aerosol-forming substrate is also provided. The combined aerosol-forming substrate may comprise a first material and a second material, the first material comprising the combined aerosol-forming substrate as a first plurality of discrete elements and the second material comprising the combined aerosol-forming substrate as a second plurality of discrete elements. The first material may comprise an aerosol former. The first material may have a first thermal conductivity. The second material may have a second thermal conductivity that is greater than the first thermal conductivity.

[0087] Therefore, in accordance with a second aspect of the present description, a combined aerosol-forming substrate comprising:

[0088] a first material and a second material, the first material comprising the combined aerosol-forming substrate as a first plurality of discrete elements and the second material comprising the combined aerosol-forming substrate as a second plurality of discrete elements,

[0089] wherein the first material comprises an aerosol former and has a first thermal conductivity, wherein the second material has a second thermal conductivity that is greater than the first thermal conductivity.

[0090] Advantageously, the second material can increase the thermal conductivity of the substrate. As explained above in relation to the first aspect, this can provide one or more of the following advantages: a lower temperature gradient is present in the substrate during use, the efficiency of substrate use increases, a heater in an aerosol-generating device can operate at a lower temperature, and the time required to produce an aerosol is reduced.

[0091] The first material may be described as having a different material composition than the second material. Optionally, the second material comprises, or is, an aerosol-forming substrate as described above, e.g., the aerosol-forming substrate of the first aspect.

[0092] Optionally, the second thermal conductivity is at least 5% greater than the first thermal conductivity, for example at least 7, 10, 12, 15, 30, 50, 100, 200 or 500% greater. Optionally, the thermal conductivity of the second material is at least 10% greater than the thermal conductivity of the first material, for example at least 12, 15, 20, 30, 50, 100, 200 or 500% greater.

[0093] Optionally, the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements, are elongated elements, each of which has a length dimension that is greater than a width dimension and a thickness dimension. Optionally, the elongated elements are in the form of strips, fragments, threads, or ribbons.

[0094] Optionally, the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements, are formed by a casting process, for example by a casting process followed by a cutting process.

[0095] Optionally, the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements, are formed by an extrusion process.

[0096] Optionally, at least a portion of the first plurality of discrete elements, or at least a portion of the second plurality of discrete elements, or at least a portion of both the first and second plurality of discrete elements, are curled elements. For example, each curled element may have one or more twists or directional changes defined in a length dimension of the curled element.

[0097] Optionally, one or both of the first material and the second material are comprised in the combined stippled aerosol-forming substrate.

[0098] Optionally, the discrete elements of the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements have an average thickness of between 5 microns and 2000 microns, for example between 50 microns and 500 microns, for example between 150 microns and 300 microns.

[0099] Optionally, the discrete elements of the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements have an average width of between 100 microns and 2000 microns, for example between 500 microns and 1,500 microns, for example between 600 microns and 1000 microns.

[0100] Optionally, the discrete elements of the first plurality of discrete elements, or the second plurality of discrete elements, or both the first and second plurality of discrete elements have an average length of between 100 microns and 60 millimeters, for example between 500 microns and 30 millimeters, for example between 1000 microns and 10000 microns.

[0101] Advantageously, it has been found that the thicknesses, widths, and lengths established above facilitate the production of an adequate quantity of an aerosol with convenient properties when heated by a heating element of an aerosol generating device.

[0102] Optionally, the second material comprises thermally conductive particles. Optionally, the second material comprises at least 1, 2, 5, 10, 20, 30, 40, 50, 60, 70 or 80% by weight of thermally conductive particles. Optionally, the second material comprises no more than 90, 80, 70, 60, 50, 40, 30, 20, 10 or 5% by weight of thermally conductive particles. Optionally, the second material comprises, on a dry weight basis, between 1 and 90, 2 and 90, 5 and 90, 10 and 90, 20 and 90, 30 and 90, 40 and 90, 50 and 90, 60 and 90, 70 and 90, 80 and 90, 10 and 80, 20 and 80, 30 and 80, 40 and 80, 50 and 80, 60 and 80, 70 and 80, 10 and 70, 20 and 70, 30 and 70, 40 and 70, 50 and 70, 60 and 70, 10 and 60, 20 and 60, 30 and 60, 40 and 60, 50 and 60, 10 and 50, 20 and 50, 30 and 50, 40 and 50, 10 and 40, 20 and 40, 30 and 40, 10 and 30, 20 and 30, or 10 and 20% by weight of the thermally conductive particles.

[0103] Optionally, the second material comprises thermally conductive particles formed from a thermally conductive material selected from the list consisting of carbon, graphite, expanded graphite, graphene, and metal. Alternatively, the second material is a thermally conductive material selected from the list consisting of carbon, graphite, expanded graphite, graphene, and metal, for example, wherein each discrete element of the second material is a strip of metal foil or carbon foil, for example, copper foil, aluminum foil, stainless steel foil, or graphite foil. Advantageously, such materials have relatively high thermal conductivities.

[0104] Optionally, the first material has a thermal conductivity of less than 10, 5, 2, 1, 0.5, or 0.2 W/(mK) in at least one direction at 25 degrees Celsius. Optionally, the second material has a thermal conductivity of more than 0.1, 0.22, 0.3, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 1500, or 1700 W/(mK) in at least one direction at 25 degrees Celsius.

[0105] Optionally, the first material is configured to generate an aerosol when heated, for example, when heated to a temperature between 120 degrees Celsius and 395 degrees Celsius, and the second material is not configured to generate an aerosol when heated, for example, when heated to a temperature between 120 degrees Celsius and 350 degrees Celsius. Optionally, both the first and second materials are configured to generate an aerosol when heated, for example, when heated to a temperature between 120 degrees Celsius and 395 degrees Celsius.

[0106] Optionally, the first material comprises tobacco, for example, wherein the first material is formed from homogenized tobacco. Optionally, the first material comprises tobacco and an aerosol former, and is configured to generate an aerosol when heated to a temperature between 120 degrees Celsius and 395 degrees Celsius. Optionally, the first material is a homogenized tobacco material, and further comprises one or both fibers and a binder.

[0107] Optionally, the second material comprises an aerosol former and thermally conductive particles constituting between 3% and 90% by weight of the second material on a dry weight basis. The second material is configured to generate an aerosol when heated to a temperature between 120°C and 395°C. Optionally, the second material comprises tobacco and an aerosol former and conductive particles constituting between 3% and 90% by weight of the second material on a dry weight basis. The second material is configured to generate an aerosol when heated to a temperature between 120°C and 395°C. Optionally, the second material is a thermally conductive, homogenized tobacco material and further comprises fibers and a binder.

[0108] Optionally, the second material does not comprise tobacco, for example wherein the second material is a tobacco-free, thermally conductive material, and further comprises fibers and a binder.

[0109] Optionally, discrete elements of the first material and discrete elements of the second material are formed separately and mixed together in a predetermined ratio to form the combined aerosol-forming substrate.

[0110] Optionally, the ratio of the first material to the second material in the combined aerosol forming substrate is between 1:10 and 10:1, for example between 1:5 and 8:1, for example between 1:1 and 5:1.

[0111] Optionally, the second material comprises, on a dry weight basis: between 40 and 80% by weight of particulate carbon material; between 10 and 40% by weight of an aerosol former; between 4 and 20% by weight of fibers; and between 2 and 10% by weight of a binder, wherein the particulate carbon material consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, and carbon.

[0112] Optionally, the first material comprises, on a dry weight basis: between 40 and 80% by weight of particulate carbon material; between 10 and 40% by weight of an aerosol former; between 4 and 20% by weight of fibers; and between 2 and 10% by weight of a binder, wherein the particulate carbon material consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes and carbon, the first material having a lower thermal conductivity than the second material.

[0113] Optionally, the particulate carbon material consists of graphite.

[0114] Optionally, the second material and the first material are distributed homogeneously within the combined aerosol forming substrate.

[0115] According to the present description, a method is provided for forming a combined aerosol-forming substrate, for example, a combined aerosol-forming substrate as described above, such as the combined aerosol-forming substrate of the second aspect. The method may comprise steps of forming a first plurality of discrete elements from a first material. The method may comprise forming a second plurality of discrete elements from a second material. The method may comprise combining the first plurality of discrete elements with the second plurality of discrete elements, for example, to form the combined aerosol-forming substrate. The second material may have a higher thermal conductivity than the first material.

[0116] Therefore, in accordance with a third aspect of the present description, a method is provided for forming a combined aerosol-forming substrate, e.g., a combined aerosol-forming substrate as described above, such as the combined aerosol-forming substrate of the second aspect, comprising the steps of forming a first plurality of discrete elements from a first material; forming a second plurality of discrete elements from a second material; and combining the first plurality of discrete elements with the second plurality of discrete elements to form the combined aerosol-forming substrate, wherein the second material has a higher thermal conductivity than the first material. Optionally, the method comprises steps of providing a first plurality of discrete elements of a first material; providing a second plurality of discrete elements of a second material; and combining the first plurality of discrete elements with the second plurality of discrete elements to form the combined aerosol-forming substrate, wherein the second material has a higher thermal conductivity than the first material.

[0117] Optionally, the first plurality of discrete elements is formed by cutting a sheet of the first material into strips, and wherein the second plurality of discrete elements is formed by cutting a sheet of the second material into strips.

[0118] Optionally, the first plurality of discrete elements and the second plurality of discrete elements are cut so that they are essentially the same size.

[0119] Optionally, the step of forming at least one of the first plurality of discrete elements and the second plurality of discrete elements involves a curling step, for example such that the first plurality of discrete elements, the second plurality of discrete elements, or both the first and second plurality of discrete elements are curled elements.

[0120] Optionally, the method comprises the steps of forming the first material, forming the second material, or forming both the first and second material.

[0121] Optionally, the combined aerosol forming substrate is a combined aerosol forming substrate in accordance with the second aspect.

[0122] In accordance with a fourth aspect of the present description, an aerosol generating article is also provided.

[0123] The article may comprise an aerosol-forming substrate as described above, e.g., the aerosol-forming substrate according to the first aspect.

[0124] The article may comprise a combined aerosol-forming substrate as described above, e.g., the combined aerosol-forming substrate according to the second aspect.

[0125] The article can be manufactured by any method described above.

[0126] Optionally, the article is in the form of a bar and comprises a plurality of components, including the aerosol forming substrate or the combined aerosol forming substrate, assembled within a wrapper or housing.

[0127] Optionally, the aerosol-generating article comprises a front cap. Optionally, the aerosol-generating article comprises a first hollow tube, for example, a first hollow acetate tube. Optionally, the aerosol-generating article comprises a second hollow tube, for example, a second hollow acetate tube. Optionally, the second hollow tube comprises one or more vent holes. Optionally, the aerosol-generating article comprises a mouth-plug filter. Optionally, the aerosol-generating article comprises a wrapper, for example, a paper wrapper.

[0128] Optionally, the front cap is disposed at the upstream end of the article. Optionally, the aerosol-forming substrate is disposed downstream of the front cap. Optionally, the first hollow tube is disposed downstream of the aerosol-forming substrate. Optionally, the second hollow tube is disposed downstream of the first hollow tube. Optionally, the mouth-cap filter is disposed downstream of one or both of the first and second hollow tubes. Optionally, the mouth-cap filter is disposed at the downstream end of the article. Optionally, the downstream end of the article, which may be referred to as the mouth end of the article, may be configured for insertion into a user's mouth. A user may be able to inhale, for example, directly into the mouth end of the article.

[0129] Optionally, the front plug, the aerosol-forming substrate, one or both of the first hollow tube and the second hollow tube, and the mouth-plug filter are enclosed by a wrapper, for example, a paper wrapper. Optionally, the front plug has a length of between 2 and 10, 3 and 8, or 4 and 6 mm, for example, about 5 mm. Optionally, the aerosol-forming substrate has a length of between 5 and 20, 8 and 15, or 10 and 15 mm, for example, about 12 mm. Optionally, the first hollow tube has a length of between 2 and 20, 5 and 15, or 5 and 10 mm, for example, about 8 mm. Optionally, the second hollow tube has a length of between 2 and 20, 5 and 15, or 5 and 10 mm, for example, about 8 mm. Optionally, the mouthpiece filter has a length of between 5 and 20, 8 and 15, or 10 and 15 mm, for example around 12 mm. The lengths of one or more of the front plug, the aerosol-forming substrate, the first hollow tube, the second hollow tube, and the mouthpiece filter can be extended in a longitudinal direction.

[0130] One or more of the front plug, aerosol-forming substrate, first hollow tube, second hollow tube, and mouth plug filter may be essentially cylindrical in shape, e.g., right-hand cylindrical.

[0131] Pursuant to a fourth aspect of this description, an aerosol generating system is provided. The system may comprise an aerosol generating article and an electric aerosol generating device. The article may be an article as described above, e.g., an article pursuant to the third aspect.

[0132] Optionally, the electric aerosol generating device is configured to resistively heat the aerosol generating item in use.

[0133] Optionally, the electric aerosol generating device is configured to inductively heat the aerosol generating article, e.g., the aerosol forming substrate of the aerosol generating article, during use. According to the present description, a method is provided for forming an aerosol forming substrate, e.g., a substrate as described above, such as the substrate according to the first aspect. The method may comprise forming a suspension comprising one or more or all of the thermally conductive particles, the aerosol former, the fibers, and the binder. The method may comprise melting and drying the suspension to form the aerosol forming substrate or a precursor to forming the aerosol forming substrate. Therefore, according to a fifth aspect of the present description, a method is provided for forming an aerosol forming substrate, e.g., a substrate as described above, such as the substrate according to the first aspect. The method comprises forming a suspension comprising the thermally conductive particles, the aerosol former, the fibers, and the binder. and melt and dry the suspension to form the aerosol-forming substrate or a precursor to form the aerosol-forming substrate.

[0134] Optionally, the suspension contains water. Optionally, the suspension comprises between 20 and 90, 30 and 90, 40 and 90, 40 and 85, 50 and 80, 60 and 80 or 60 and 75% by weight of water.

[0135] Optionally, the suspension comprises an acid. Optionally, the acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid.

[0136] Optionally, the suspension comprises nicotine.

[0137] Optionally, forming the suspension comprises forming a first mixture. The first mixture may comprise the aerosol former. The first mixture may comprise the fibers. The first mixture may comprise water. The first mixture may comprise the acid. The first mixture may comprise nicotine. Forming the suspension may comprise forming a second mixture. The second mixture may comprise the thermally conductive particles. The second mixture may comprise the binder. Forming the suspension may comprise adding the second mixture to the first mixture to form a combined mixture.

[0138] Therefore, the formation of the suspension may comprise:

[0139] form a first mixture comprising the aerosol former, the fibers, water, optionally, the acid and, optionally, the nicotine;

[0140] form a second mixture comprising the thermally conductive particles and the binder;

[0141] and add the second mixture to the first mixture to form a combined mixture.

[0142] The combined mixture can subsequently form in the suspension, for example by mixing.

[0143] Optionally, forming the first mixture comprises providing the aerosol former or a solution comprising the aerosol former and nicotine.

[0144] Optionally, forming the first mixture comprises adding the acid to the aerosol former or the solution comprising the aerosol former and nicotine to form a first premix.

[0145] Optionally, forming the first mixture comprises adding water to the aerosol former or the solution comprising the aerosol former and nicotine, or to the first premix, to form a second premix. Optionally, forming the first mixture comprises adding the fibers to the second premix.

[0146] Optionally, forming the second mixture comprises mixing the thermally conductive particles and the binder. Optionally, the method, for example, the suspension-forming step, comprises a first mixing of the combined mixture. Optionally, the first mixing occurs under a first pressure of no more than 500, 400, 300, 250, or 200 mbar. Optionally, the first mixing occurs for between 1 and 10, 2 and 8, or 3 and 6 minutes, for example, for about 4 minutes.

[0147] Optionally, the method, for example the suspension formation step, comprises, after the first mixing, a second mixing. Optionally, the second mixing occurs under a second pressure that is lower than the first pressure. Optionally, the second pressure is no more than 500, 400, 300, 200, 150, or 100 mbar. Optionally, the second mixing occurs for between 5 and 120, 5 and 80, 5 and 40, or 10 and 30 seconds, for example, about 20 seconds.

[0148] Optionally, the casting of the suspension comprises casting the suspension onto a flat support, for example, a flat steel support.

[0149] Optionally, after melting the suspension and before drying the suspension, the method comprises establishing a thickness of the suspension, for example establishing a thickness of the suspension between 100 and 1200, 200 and 1000, 300 and 900, 500 and 700 microns, for example around 600 microns.

[0150] Optionally, drying the suspension comprises providing a flow of a gas such as air over or past the suspension. Optionally, the gas flow is heated. Optionally, the gas flow is heated to a temperature between 100 and 160, or 120 and 140 degrees Celsius. Optionally, the gas flow is provided for between 1 and 10 or 2 and 5 minutes. Optionally, drying the suspension comprises drying the suspension until the suspension has a moisture content of between 1 and 20, 2 and 15, 2 and 10, or 3 and 7% by weight.

[0151] Optionally, drying the suspension forms the precursor for forming the aerosol-forming substrate, the precursor being a sheet of aerosol-forming material. Optionally, the method comprises cutting the sheet of aerosol-forming material.

[0152] As will be understood by the expert who has read this description, the characteristics described herein in relation to one aspect may apply to any other aspect. For example, the characteristics described in relation to the combined aerosol-forming substrate of the second aspect, or in relation to the first second material of the combined aerosol-forming substrate of the second aspect, may be applicable to the aerosol-forming substrate of the first aspect, and vice versa.

[0153] As used herein, the term “aerosol-forming substrate” may refer to a substrate capable of releasing an aerosol or volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may comprise an aerosol-forming material. An aerosol-forming substrate may be adsorbed, coated, impregnated, or otherwise loaded onto a carrier or support. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or a smoking article.

[0154] As used herein, the term “thermally conductive particles” may refer to particles having a thermal conductivity greater than 0.3, preferably 0.5, or more preferably 1 W/(mK) in at least one direction at 25 degrees Celsius, for example in all directions at 25 degrees Celsius. The particles may exhibit anisotropic or isotropic thermal conductivity.

[0155] As used herein, the term “expanded graphite” may refer to a graphite-based material, or a material having a graphite-like structure. Expanded graphite may have carbon layers (similar to graphite, for example) with a greater separation between the carbon layers than the separation found between carbon layers in regular graphite. Expanded graphite may have carbon layers with elements or compounds intercalated in the spaces between the carbon layers.

[0156] As used herein, the term “particle size” can refer to a single dimension and can be used to characterize the size of a given particle. The dimension can be the diameter of a spherical particle that occupies the same volume as the given particle. All particle sizes and particle size distributions in herein can be obtained using a standard laser diffraction technique. The particle sizes and particle size distributions as stated herein can be obtained using a commercially available sensor, for example, a Sympatec HELOS laser diffraction sensor.

[0157] As used herein, unless otherwise specified, the term “density” may be used to refer to true density. Therefore, unless otherwise specified, the density of a powder or plurality of particles may refer to the true density of the powder or plurality of particles (rather than the apparent density of the powder or plurality of particles, which can vary greatly depending on how the powder or plurality of particles is handled). True density can be measured using several standard methods, often based on Archimedes' principle. The most common method for measuring the true density of a powder involves placing the powder inside a container (a pycnometer) of known volume and weighing it. The pycnometer is then filled with a fluid of known density in which the powder is insoluble. The volume of the powder is determined by the difference between the volume shown by the pycnometer and the volume of liquid added (i.e., the volume of air displaced).

[0158] As used in the present description, the term “aerosol generating article” may refer to an article capable of generating, or releasing, an aerosol, for example when heated.

[0159] As used herein, the term “longitudinal” may refer to a direction that extends between a downstream or proximal end and an upstream or distal end of a component such as an aerosol-forming substrate or an aerosol-generating article.

[0160] As used in the present description, the term “transverse” may refer to a direction perpendicular to the longitudinal direction.

[0161] As used herein, the term “aerosol generating device” may refer to a device for use with an aerosol generating article to enable the generation, or release, of an aerosol.

[0162] As used herein, the term “creased sheet” may refer to a sheet of an aerosol-forming substrate or aerosol-generating article that is convoluted, folded, or otherwise compressed or constricted essentially transversely to a longitudinal axis of the aerosol-forming substrate, or aerosol-generating article.

[0163] As used in the present description, the term “sheet” may refer to a generally flat sheet element having a width and length that are essentially greater than, for example, at least 2, 3, 5, 10, 20 or 50 times its thickness.

[0164] As used herein, the term “strip” may refer to a generally flat, sheet-like element having a width and length that are substantially greater than its thickness. The width of a strip may be greater than its thickness, for example, at least 2, 3, 5, or 10 times its thickness. The length of a strip may be greater than its width, for example, at least 2, 3, 5, or 10 times its width.

[0165] As used herein, the term “aerosol former” may refer to any suitable known compound or mixture of compounds that, during use, facilitates the formation of an aerosol. The aerosol may be a dense and stable aerosol. The aerosol may be essentially resistant to thermal degradation at the operating temperature of the aerosol-forming substrate or aerosol-generating article.

[0166] As used herein, the term “aerosol cooling element” may refer to a component of an aerosol-generating article located downstream of the aerosol-forming substrate such that, during use, an aerosol formed by the substrate or by volatile compounds released from the aerosol-forming substrate passes through it and is cooled by the aerosol cooling element before being inhaled by a user.

[0167] As used in the present description, the term “bar” may refer to a generally cylindrical element, e.g., a right-handed cylinder, with an essentially circular, oval, or elliptical cross-section.

[0168] As used herein, the term “ribbed” may refer to a sheet having one or more ridges or corrugations. The ridges or corrugations may be essentially parallel. When present on a component of an aerosol-generating article, the ridges or corrugations may extend in a longitudinal direction with respect to the aerosol-generating article.

[0169] As used in this description, the term “vent level” may refer to a volume ratio between the airflow admitted into an aerosol-generating article through the vent zone (vent airflow) and the sum of the aerosol airflow and the vent airflow. The higher the vent level, the greater the dilution of the aerosol flow delivered to the consumer.

[0170] The examples will now be described in more detail with reference to the figures in which:

[0171] Figure 1 shows a schematic cross-sectional view of a first modality of an aerosol generating article;

[0172] Figure 2 shows a schematic cross-sectional view of a second modality of an aerosol generating article;

[0173] Figure 3 shows a schematic cross-sectional view of a first modality of an aerosol generating system;

[0174] Figure 4 shows a schematic cross-sectional view of a second modality of an aerosol generating system; and

[0175] Figure 5 shows a schematic cross-sectional view of a third modality of an aerosol generating article.

[0176] Figure 1 shows a schematic cross-sectional view of a first modality of an aerosol generating article 10. The aerosol generating article 10 extends from an upstream or distal end 18 to a downstream or proximal end or mouth end 20 and has a total length of approximately 45 millimeters.

[0177] The aerosol-generating article 10 comprises an aerosol-forming substrate bar 12 and a downstream section 14 located downstream of the aerosol-forming substrate bar 12. In addition, the aerosol-generating article 10 comprises an upstream section 16 located upstream of the aerosol-forming substrate bar 12.

[0178] The downstream section 14 comprises a support element 22 located immediately downstream of the aerosol-forming substrate bar 12, the support element 22 being longitudinally aligned with the bar 12. In the embodiment of Figure 1, the upstream end of the support element 22 abuts the downstream end of the aerosol-generating substrate bar 12. Furthermore, the downstream section 14 comprises an aerosol cooling element 24 located immediately downstream of the support element 22, the aerosol cooling element 24 being longitudinally aligned with the bar 12 and the support element 22. In the embodiment of Figure 1, the upstream end of the aerosol cooling element 24 abuts the downstream end of the support element 22.

[0179] As will be evident 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 total RTD of the aerosol generating article. An RTD of the intermediate hollow section 26 as a whole is essentially 0 millimeters of H<2>O.

[0180] 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 extending 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 essentially empty, and therefore an essentially unrestricted airflow is enabled along the internal cavity 28. As such, the first hollow tubular segment 26 – and, consequently, the support element 22 – does not essentially 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 essentially 0 mm H₂O.

[0181] The first hollow tubular segment 26 has a length of approximately 8 millimeters, an outer diameter of approximately 7.25 millimeters, and an inner diameter (D<FTS>) of approximately 1.9 millimeters. Therefore, the thickness of a peripheral wall of the first hollow tubular segment 26 is approximately 2.67 millimeters. 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 extending 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 essentially empty, and therefore an essentially unrestricted airflow is enabled along the internal cavity 36. The second hollow tubular segment 28 – and, consequently, the aerosol cooling element 24 – does not essentially 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 essentially 0 millimeters of H₂O.

[0182] The second hollow tubular segment 34 has a length of approximately 8 millimeters, an outer diameter of approximately 7.25 millimeters, and an inner diameter (D<STS>) of approximately 3.25 millimeters. Therefore, the thickness of a peripheral wall of the second hollow tubular segment 34 is approximately 2 millimeters. Therefore, the ratio between the inner diameter (D<FTS>) of the first hollow tubular segment 26 and the inner diameter (D<STS>) of the second hollow tubular segment 34 is approximately 0.75.

[0183] The aerosol generating article 10 comprises a ventilation zone 60 provided at a location along the second hollow tubular segment 34. More specifically, the ventilation zone is provided approximately 2 millimeters 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 wrapping 70 and a ventilation level of the aerosol generating article 10 is approximately 25 percent.

[0184] In the embodiment of Figure 1, the downstream section 14 further comprises a nozzle element 42, also referred to as a mouth-plug filter, in a location downstream of the intermediate hollow section 50. In more detail, the nozzle element 42 is positioned immediately downstream of the aerosol cooling element 24. As shown in the drawing of Figure 1, an upstream end of the nozzle element 42 abuts the downstream end 40 of the aerosol cooling element 24.

[0185] Nozzle element 42 is provided in the form of a cylindrical plug made of low-density cellulose acetate. Nozzle element 42 has a length of approximately 12 millimeters and an outside diameter of approximately 7.25 millimeters. The RTD of nozzle element 42 is approximately 12 millimeters of H₂O. The ratio of the length of nozzle element 42 to the length of the intermediate hollow section 50 is approximately 0.6.

[0186] The aerosol forming substrate rod 12 has an outer diameter of approximately 7.25 millimeters and a length of approximately 12 millimeters.

[0187] The upstream section 16 comprises an upstream element 46, also called a front plug, located immediately upstream of the aerosol-forming substrate bar 12. The upstream element 46 is in longitudinal alignment with the bar 12. In the embodiment of Figure 1, the downstream end of the upstream element 46 abuts the upstream end of the aerosol-forming substrate bar 12. The upstream element 46 is provided in the form of a cylindrical plug made of cellulose acetate. The upstream element 46 has a length of approximately 5 millimeters. The RTD of the upstream element 46 is approximately 30 millimeters of H₂O.

[0188] The upstream element 46, the aerosol-forming substrate bar 12, the support element 22, the aerosol cooling element 24, and the nozzle element 42 are enclosed by a paper wrapper 70.

[0189] The aerosol-forming substrate rod 12 comprises, on a dry weight basis, about 76.1 wt% of thermally conductive particles 44. In this embodiment, the thermally conductive particles 44 are graphite particles, specifically FP 99.5 graphite particles (>99.5% purity) from Graphit Kropfmül GmbH, AMG Graphite GK, although other particles or mixtures of particles could be used. Each thermally conductive particle has a thermal conductivity of about 6 W/(mK) in at least one direction at 25 degrees Celsius.

[0190] Bar 12 of the aerosol-forming substrate comprises, on a dry weight basis, about 17.7% by weight of an aerosol former. In this embodiment, the aerosol former is glycerol, specifically ICOF Europe food grade glycerol (>99.5% purity).

[0191] Bar 12 of the aerosol-forming substrate comprises, on a dry weight basis, about 3.9% by weight of fibers. In this embodiment, the fibers are cellulosic fibers, specifically birch cellulosic fibers from Stora Enso OYJ.

[0192] Bar 12 of the aerosol-forming substrate comprises, on a dry weight basis, about 2.3% by weight of a binder. In this embodiment, the binder is guar gum, specifically guar gum from Gumix International Inc.

[0193] Bar 12 of the aerosol-forming substrate comprises approximately 10% by weight of water, when measured at 25 degrees Celsius.

[0194] In other embodiments, bar 12 of the aerosol forming substrate further comprises one or more nicotine, an acid such as fumaric acid, a plant such as clove or rosemary, and a flavoring.

[0195] 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.

[0196] Each of the thermally conductive particles 44 has an essentially spherical shape. The thermally conductive particles 44 are distributed essentially homogeneously throughout the aerosol-forming substrate. The particle size distribution has a volumetric D10 particle size of about 6 microns, a volumetric D50 particle size of about 20 microns, and a volumetric D90 particle size of about 56 microns. Each of the thermally conductive particles 44 has a particle size greater than about 1 micron and smaller than about 300 microns.

[0197] The thermally conductive particles 44 have a density of about 2200 kilograms per cubic meter. The aerosol-forming substrate has a density of about 800 kilograms per cubic meter.

[0198] Bar 12 of the aerosol forming substrate is formed by the process described below.

[0199] A suspension is formed by using a laboratory disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (e.g., by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available laboratory disperser from PC Laborsystem was used.

[0200] To form the suspension, a first mixture is prepared by adding approximately 7.11 grams of the aerosol former to the foil disperser, followed by approximately 157.5 grams of water, and then approximately 1.57 grams of fibers. These first ingredients are then mixed at 25 degrees Celsius for 5 minutes at 600–700 rpm to ensure a homogeneous mixture and to hydrate the fibers. A second mixture is then prepared by manually mixing approximately 32.95 grams of the thermally conductive particles and approximately 0.92 grams of the binder. This second mixture prevents clumping in the laboratory dispersion. The second mixture is then added to the first mixture to form a combined mixture. The combined mixture is then mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a reduced initial pressure of approximately 200 mbar. The reduced pressure helps ensure that the thermally conductive particles are evenly dispersed in the mixture, minimizing trapped air and lumps in the combined mixture. The combined mixture is then blended at 5000 rpm for 20 seconds at 25 degrees Celsius under a second reduced pressure of approximately 100 mbar. This second reduced pressure helps eliminate any remaining air bubbles, resulting in a suspension suitable for molding.

[0201] Next, the suspension is melted and dried using a suitable apparatus. In this modality, a commercially available Mathis Labcoater apparatus is used. This apparatus includes a flat stainless steel support and a comma blade for adjusting the thickness of the melted suspension on the flat support.

[0202] The suspension is poured onto the flat support, and a gap between the comma blade and the flat support is set at 0.6 millimeters. This ensures that the thickness of the suspension does not exceed 0.6 millimeters at any given point.

[0203] The suspension is then dried with hot air at 120–140 degrees Celsius for 2–5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet is approximately 159 microns thick, has a basis weight of approximately 125.7 grams per square meter, and a density of approximately 0.79 kilograms per cubic meter.

[0204] Next, the sheet is collected and cut to form bar 12 of the aerosol forming substrate. In other embodiments, the sheet is also curled.

[0205] After forming the aerosol-forming substrate bar 12, the aerosol-generating article 10 is assembled by placing the various components of article 10 and wrapping the components in the wrapper 70.

[0206] Figure 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 Figure 1 except that the aerosol-forming substrate bar 12 has been replaced by an alternative bar 13 of a combined aerosol-forming substrate. Identical part numbers have been used for identical components in the embodiments of Figures 1 and 2.

[0207] In bar 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.

[0208] In this mode, the elements of 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.

[0209] The first material may be conventional tobacco shred. As such, the first material may be formed by a conventional tobacco shred manufacturing process and may comprise an aerosol former, fibers, and a binder, but does not comprise thermally conductive particles. As an example, the first material may be manufactured using a method similar to that set out above for the aerosol-forming substrate bar 12 of the first embodiment of Figure 1, except that thermally conductive particles are not included and, instead of collecting and cutting the foil to form the bar 12, the foil is shredded to form reconstituted shred.

[0210] The second material is formed from an aerosol-forming substrate similar to that of bar 12 in the first embodiment of Figure 1. The second material comprises, on a dry weight basis, about 76.1 wt% of thermally conductive particles 45, about 17.7 wt% of an aerosol former, about 3.9 wt% of fibers, and about 2.3 wt% of a binder. In the second material, the thermally conductive particles are all graphite particles or expanded graphite particles, although other particles or mixtures of particles could be used.

[0211] The first material has a first thermal conductivity, and the second material has a second thermal conductivity at least 10% higher than the first thermal conductivity. Therefore, the second material helps to increase the thermal conductivity of the combined aerosol-forming substrate.

[0212] Bar 13 of the combined aerosol-forming substrate is formed by the process described below. A suspension is formed using a laboratory disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (e.g., by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available laboratory disperser from PC Laborsystem was used.

[0213] To form the suspension, a first mixture is prepared by adding approximately 7.11 grams of the aerosol former to the foil disperser, followed by approximately 157.5 grams of water, and then approximately 1.57 grams of fibers. These first ingredients are then mixed at 25 degrees Celsius for 5 minutes at 600–700 rpm to ensure a homogeneous mixture and to hydrate the fibers. A second mixture is then prepared by manually mixing approximately 32.95 grams of the thermally conductive particles and approximately 0.92 grams of the binder. This second mixture prevents clumping in the laboratory dispersion. The second mixture is then added to the first mixture to form a combined mixture. The combined mixture is then mixed at 5000 rpm for 4 minutes at 25 degrees Celsius and a reduced initial pressure of approximately 200 mbar. The reduced pressure helps ensure that the thermally conductive particles are evenly dispersed in the mixture, minimizing trapped air and lumps in the combined mixture. The combined mixture is then blended at 5000 rpm for 20 seconds at 25 degrees Celsius under a second reduced pressure of approximately 100 mbar. This second reduced pressure helps eliminate any remaining air bubbles, resulting in a suspension suitable for molding.

[0214] Next, the suspension is melted and dried using a suitable apparatus. In this modality, a commercially available Mathis Labcoater apparatus is used. This apparatus includes a flat stainless steel support and a comma blade for adjusting the thickness of the melted suspension on the flat support.

[0215] The suspension is poured onto the flat support, and a gap between the comma blade and the flat support is set at 0.6 millimeters. This ensures that the thickness of the suspension does not exceed 0.6 millimeters at any given point.

[0216] The suspension is then dried with hot air at 120–140 degrees Celsius for 2–5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet is approximately 159 microns thick, has a basis weight of approximately 125.7 grams per square meter, and a density of approximately 0.79 kilograms per cubic meter.

[0217] 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.

[0218] This second material is then mixed with the first material, which is a first plurality of discrete elements. As explained above, the first material can be formed using a conventional tobacco shredding manufacturing process. Therefore, this is not explained in detail here.

[0219] The first and second mixed materials that are presented as pluralities of discrete elements are then formed in the combined aerosol-forming substrate bar 13, for example by circumscribing it in an envelope.

[0220] Next, after forming the combined aerosol forming substrate bar 13, the aerosol generating article 11 is assembled by placing the various components of article 11 and wrapping the components in the wrapper 70.

[0221] Figure 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 Figure 1, although the device 102 could equally be used with the aerosol generating article 11 of Figure 2.

[0222] The aerosol generating device 102 comprises a battery 104, a controller 106, a heating plate 108 coupled to the battery, and a puff detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating plate 108, and the puff detection mechanism.

[0223] The aerosol generating device 102 further comprises a housing 110 defining an essentially cylindrical cavity for receiving a portion of article 10. The heating sheet 108 is positioned centrally within the cavity and extends longitudinally from a base of the cavity.

[0224] In this embodiment, the heating sheet 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating sheet 108 to allow a current to pass through the electrically resistive track and heat the electrically resistive track and the heating sheet 108 to an operating temperature.

[0225] During use, a user inserts item 10 into the cavity, causing the heating foil 108 to penetrate the upstream element 46 and the bar 12 of the aerosol-forming substrate of item 10. Figure 3 shows item 10 inserted into the cavity of device 102.

[0226] Next, the user takes a puff on the downstream end of article 10. This causes air to flow through an air inlet (not shown) of device 102, then through article 10, from the upstream end 18 to the downstream end 20, and into the user's mouth.

[0227] The user taking a puff of item 10 causes air to flow through the device's air inlet. The puff detection mechanism senses that the airflow velocity through the air inlet has increased to a threshold flow velocity greater than zero. The puff detection mechanism sends a signal to controller 106 accordingly. Controller 106 then controls battery 104 to pass a current through the electrically resistive track and heat the heating foil 108. This heats the aerosol-forming substrate rod 12, which is in contact with the heating foil 108.

[0228] The thermally conductive particles 44 have a significantly higher thermal conductivity than the surrounding aerosol-forming material. As such, these particles can act as local hot spots and provide a more uniform temperature throughout the aerosol-forming substrate, particularly in a radial direction from the heating sheet 108 where, with prior art substrates, there would be a significant temperature gradient. This can result in a greater proportion of the aerosol-forming substrate reaching a sufficiently high temperature to release volatile compounds, and thus greater utilization efficiency of the aerosol-forming substrate.

[0229] Heating the aerosol-forming substrate causes it to release volatile compounds. These compounds are carried by the air flowing from the upstream end 18 of Article 10 to the downstream end 20 of 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 nozzle element 42, which can filter out unwanted particles carried in the airflow, and into the user's mouth.

[0230] When the user stops inhaling through item 10, the airflow velocity through the device's air inlet decreases unless the non-zero flow threshold is reached. This is detected by the puff detection mechanism. The puff detection mechanism sends a signal to controller 106 accordingly. Controller 106 then controls battery 104 to reduce the current passing through the electrically resistive track to zero.

[0231] After several puffs of item 10, the user may choose to replace item 10 with a new item.

[0232] Figure 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 Figure 2, although the device 202 could equally be used with the aerosol generating article 10 of Figure 1.

[0233] 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.

[0234] The aerosol generating device 202 further comprises a housing 210 defining an essentially cylindrical cavity for receiving a portion of article 11. The inductor coil 208 is wound around the cavity.

[0235] The battery 204 is coupled to the inductor coil 208 in order to pass an alternating current through the inductor coil 208.

[0236] During use, a user inserts item 11 into the cavity. Figure 4 shows item 11 inserted into the cavity of device 202.

[0237] Next, the user takes a puff on the downstream end of article 11. This causes air to flow through an air inlet (not shown) of device 202, then through article 11, from the upstream end 18 to the downstream end 20, and into the user's mouth.

[0238] The user taking a puff of item 11 causes air to flow through the device's air inlet. The puff detection mechanism detects that the airflow velocity through the air inlet has increased to a threshold flow velocity greater than zero. The puff detection mechanism sends a signal to controller 206 accordingly. Controller 206 then controls battery 204 to pass an alternating current through inductor coil 208. This causes inductor coil 208 to generate a fluctuating electromagnetic field. Bar 13 of the combined aerosol-forming substrate is located within this fluctuating electromagnetic field. The particle materials 45, graphite and expanded graphite, are susceptor materials. Therefore, the fluctuating electromagnetic field causes eddy currents in the 45 particles. This causes the 45 particles to heat up, which also heats the nearby aerosol-forming material.

[0239] Heating the aerosol-forming material causes it to release volatile compounds. These compounds are carried by the air flowing from the upstream end 18 of Article 11 to the downstream end 20 of 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 nozzle element 42, which can filter out unwanted particles carried in the airflow, and into the user's mouth.

[0240] When the user stops inhaling through item 11, the airflow velocity through the device's air inlet decreases unless the non-zero flow threshold is reached. This is detected by the puff detection mechanism. The puff detection mechanism sends a signal to controller 206 accordingly. Controller 206 then controls battery 204 to reduce the current passing through the electrically resistive track to zero.

[0241] After several puffs of item 11, the user may choose to replace item 11 with a new item.

[0242] Figure 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 in Figure 1 except that the aerosol-forming substrate bar 12 has been replaced by an alternative aerosol-forming substrate bar 512. Identical part numbers have been used for identical components in the embodiments of Figures 1 and 5.

[0243] The aerosol-forming substrate bar 512 of the third modality of Figure 5 includes an elongated susceptor element 580.

[0244] The susceptor element 580 is arranged essentially longitudinally within the aerosol-forming substrate bar 512 so that it is approximately parallel to a longitudinal axis of the aerosol-forming substrate bar 512. As shown in the drawing in Figure 5, the susceptor element 580 is positioned radially centrally within the bar and extends along the longitudinal axis of the bar 12.

[0245] Susceptor element 580 extends from an upstream end to a downstream end of aerosol-forming substrate rod 512. As such, susceptor element 580 is essentially the same length as aerosol-forming substrate rod 512.

[0246] In the modality of Figure 5, the susceptor element 580 is provided in the form of a strip of ferromagnetic steel and has a length of approximately 12 millimeters, a thickness of approximately 60 micrometers, and a width of approximately 4 millimeters.

[0247] The aerosol generating article 510 of Figure 5 can be used with the aerosol generating device 202 of Figure 4 in the same manner as the aerosol generating article 11 of Figure 2. In particular, the inclusion of the susceptor element 580 means that article 510 can be inductively heated regardless of whether the thermally conductive particles comprise a susceptor material suitable for inductive heating. The aerosol-forming substrate rod 512 comprises, on a dry weight basis, about 66 wt% of thermally conductive particles 44. In this embodiment, the thermally conductive particles 44 are graphite particles, specifically commercially available FP 99.5 graphite particles (>99.5% purity) from Graphit Kropfmül GmbH, AMG Graphite GK, although other particles or particle mixtures could be used. Each thermally conductive particle has a thermal conductivity of about 6 W/(mK) in at least one direction at 25 degrees Celsius.

[0248] The aerosol-forming substrate rod 512 comprises, on a dry weight basis, about 20% by weight of an aerosol former. In this embodiment, the aerosol former is glycerol, specifically commercially available ICOF Europe food grade glycerol (>99.5% purity).

[0249] The aerosol-forming substrate rod 512 comprises, on a dry weight basis, about 7% by weight of fibers. In this embodiment, the fibers are cellulosic fibers, specifically commercially available spruce cellulosic fibers from Stora Enso OYJ.

[0250] The aerosol-forming substrate 512 rod comprises, on a dry weight basis, about 4% by weight of a binder. In this embodiment, the binder is sodium carboxymethylcellulose, specifically sodium carboxymethylcellulose (CMC) Type K-700 commercially available from Gumix International Inc.

[0251] The aerosol-forming substrate bar 512 comprises, on a dry weight basis, about 1% by weight of nicotine.

[0252] The aerosol-forming substrate rod 512 comprises, on a dry weight basis, about 2% by weight of an acid. In this embodiment, the acid is fumaric acid, specifically a commercially available fumaric acid from Sigma-Aldrich (>99% purity).

[0253] In other forms, the substrate also includes at least one botanical plant, for example, clove or Rosmarinus. Bar 12 of the aerosol-forming substrate comprises approximately 10% water by weight, when measured at 25 degrees Celsius.

[0254] 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.

[0255] The thermally conductive particles 44 are identical to those of bar 12 of the first modality of Figure 1. The aerosol-forming substrate bar 512 is formed by the process described below.

[0256] A suspension is formed by using a laboratory disperser capable of mixing viscous liquids, dispersing powders through liquids, and removing gas from a mixture (e.g., by applying a vacuum or other suitably low pressure). In this embodiment, a commercially available laboratory disperser from PC Laborsystem was used.

[0257] To form the suspension, a first mixture is prepared by adding approximately 12 grams of a 10% nicotine solution in glycerin (the aerosol former) to the foil disperser, followed by approximately 13.2 grams of glycerin, then approximately 2.4 grams of fumaric acid, then approximately 280 grams of water, and finally approximately 8.4 grams of fibers. These first ingredients are then mixed at 25 degrees Celsius for 5 minutes at 600–700 rpm to ensure a homogeneous mixture and to hydrate the fibers. A second mixture is then prepared by manually mixing approximately 79.2 grams of the thermally conductive particles and approximately 4.8 grams of the binder. This second mixture prevents clumping in the laboratory dispersion. The second mixture is then added to the first mixture to form a combined mixture. The combined mixture is then blended at 5000 rpm for 4 minutes at 25 degrees Celsius and a first reduced pressure of approximately 200 mbar. This reduced pressure helps ensure that the thermally conductive particles are evenly dispersed in the mixture, minimizing trapped air and lumps. The mixture is then blended again at 5000 rpm for 20 seconds at 25 degrees Celsius and a second reduced pressure of approximately 100 mbar. This second reduced pressure helps eliminate any remaining air bubbles, resulting in a suspension suitable for molding.

[0258] Next, the suspension is melted and dried using a suitable apparatus. In this modality, a commercially available Mathis Labcoater apparatus is used. This apparatus includes a flat stainless steel support and a comma blade for adjusting the thickness of the melted suspension on the flat support.

[0259] The suspension is poured onto the flat support, and a gap between the comma blade and the flat support is set at 0.6 millimeters. This ensures that the thickness of the suspension does not exceed 0.6 millimeters at any given point.

[0260] The suspension is then dried with hot air between 120 and 140 degrees Celsius for 2 to 5 minutes. After this drying, a sheet of the aerosol-forming substrate is formed. This sheet is approximately 230 microns thick and has a basis weight of approximately 200 grams per square meter.

[0261] Next, the sheet is crumpled and cut to form an essentially rod-shaped precursor. The susceptor element is then inserted into the precursor to form the 512 rod of the aerosol-forming substrate.

[0262] After forming the aerosol-forming substrate bar 512, the aerosol-generating article 510 is assembled by placing the various components of article 510 and wrapping the components in wrapper 70.

[0263] For the purposes of this description and the appended claims, except where otherwise indicated, all numbers expressing quantities, figures, percentages, etc., shall be understood to be modified in all cases by the term "approximately". Furthermore, all intervals include the maximum and minimum points described and include any intermediate intervals therein, which may or may not be specifically enumerated in this description. In this context, therefore, a number A is understood to be A ± 10% of A. Within this context, a number A may be considered to include numerical values that are within the general standard error for the measurement of the property that the number A modifies. The number A, in some cases as used in the appended claims, may deviate by the percentages enumerated above, provided that the amount by which A deviates does not materially impair the basic and novel feature(s) of the claimed invention. Furthermore, all intervals include the maximum and minimum points described and include any intermediate intervals within them, which may or may not be specifically listed in this description.

Claims (15)

1. CLAIMS 1. An aerosol-forming substrate comprising, on a dry weight basis: between 70 and 90% by weight of carbon particles (44, 45); between 7 and 26% by weight of an aerosol former; between 2 and 20% by weight of fibers; and between 2 and 10% by weight of a binder, where each of the carbon particles consists of one or more of graphite, expanded graphite, graphene, carbon nanotubes, carbon, and diamond. 2. An aerosol-forming substrate according to claim 1, wherein the carbon particles (44, 45) 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 or 2, wherein the carbon particles (44, 45) have a particle size distribution having a volume D90 particle size between 50 and 300 microns. 4. An aerosol-forming substrate according to any preceding claim, wherein the carbon particles (44, 45) have a particle size distribution having a particle size D10 by volume and a particle size D90 by number, wherein the particle size D90 by volume is no more than 50 times the particle size D10 by number. 5. An aerosol-forming substrate according to any of the preceding claims, wherein some or all of the carbon particles (44, 45) are essentially spherical. 6. An aerosol-forming substrate according to any of the preceding claims, wherein each of the carbon particles (44, 45) consists of one or more expanded graphite, graphene, and diamond. 7. An aerosol-forming substrate according to any of the preceding claims, wherein the substrate comprises, on a dry weight basis, at least 75% by weight of carbon particles. 8. An aerosol-forming substrate according to any of the preceding claims, wherein the substrate comprises, on a dry weight basis, at least 80% by weight of carbon particles. 9. An aerosol-forming substrate according to any of the preceding claims, wherein the carbon particles (44, 45) are distributed essentially homogeneously throughout the aerosol-forming substrate. 10. An aerosol-forming substrate according to any of the preceding claims, wherein the aerosol-forming substrate is a tobacco-free aerosol-forming substrate. 11. An aerosol-forming substrate according to any of the preceding claims, wherein the aerosol-forming substrate comprises between 1 and 20% by weight of water. 12. A combined aerosol-forming substrate comprising: a first material and a second material, the first material comprising the combined aerosol-forming substrate as a first plurality of discrete elements and the second material comprising the combined aerosol-forming substrate as a second plurality of discrete elements, wherein the first material comprises an aerosol former and has a first thermal conductivity, and wherein the second material comprises, or is, an aerosol-forming substrate according to any preceding claim and has a second thermal conductivity that is greater than the first thermal conductivity. 13. An aerosol generating article (10) comprising an aerosol forming substrate according to any of claims 1 to 11 or a combined aerosol forming substrate according to claim 12. 14. An aerosol generating system comprising an aerosol generating article according to claim 13 and an electric aerosol generating device (102) for heating the aerosol forming substrate or the combined aerosol forming substrate of the aerosol generating article (10). 15. A method for forming an aerosol-forming substrate according to any one of claims 1 to 11 or a combined aerosol-forming substrate according to claim 12, the method comprising: forming a suspension comprising the carbon particles (44, 45), the aerosol former, the fibers, and the binder; and melt and dry the suspension to form the aerosol-forming substrate or a precursor to form the aerosol-forming substrate.