Aerosol-forming substrate

Abstract

There is provided an aerosol-forming substrate (12, 512, 1020) comprising, on a dry weight basis: X weight percent non-expanded graphite; and Y weight percent expanded graphite. X divided by Y is at least 0.5. There is also provided an aerosol-generating article (10, 510, 1000), an aerosol- generating system (100, 200, 2000), and a method of making an aerosol-forming substrate.

Description

[0001] AEROSOL-FORMING SUBSTRATE

[0002] The present disclosure relates to an aerosol-forming substrate. The present disclosure also relates to an aerosol-generating article, an aerosol-generating system, and a method of making an aerosol-forming substrate.

[0003] A typical aerosol-generating system comprises an aerosol-generating device and an aerosol-generating article comprising an aerosol-forming substrate. In use, the aerosolgenerating 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 then cool to form an aerosol which is inhaled by a user.

[0004] Known aerosol-forming substrates typically have relatively low thermal conductivities. This may be undesirable, particularly in aerosol-generating systems in which a blade is inserted into the aerosol-forming substrate and heated in order to heat the aerosol-forming substrate. This is because the low thermal conductivity of the aerosol-forming substrate may lead to a relatively large temperature gradient in the aerosol-forming substrate during use. This may mean that portions of the aerosol-forming substrate which are located furthest from the blade do not reach a high temperature and so do not release as many volatile compounds as they would if the aerosol-forming substrate had a higher thermal conductivity. In other words, the low thermal conductivity of the aerosol-forming substrate may undesirably result in a low usage efficiency of the aerosol-forming substrate. This low usage efficiency may lead to one or both of an insufficient extraction of flavours and nicotine and a waste of material of the aerosol-forming substrate.

[0005] Further, known aerosol-forming substrates are typically not heatable to operating temperatures by induction. This means that, for inductive heating, a separate susceptor element is typically required. This can increase costs. In addition, this can lead to the same issues as discussed above. For example, where an inductively heated susceptor element is placed in a central position in the aerosol-forming substrate, portions of the aerosol-forming substrate which are located furthest from the susceptor element may not reach a high temperature and therefore may not release many volatile compounds.

[0006] 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.

[0007] It is an aim of the present invention to provide an improved aerosol-forming substrate, for example an aerosol-forming substrate having an increased thermal conductivity, ideally an aerosol-forming substrate that can be manufactured using existing machinery.

[0008] There is provided an aerosol-forming substrate. The aerosol-forming substrate may comprise, on a dry weight basis, X weight percent non-expanded graphite. The aerosol-forming substrate may comprise, on a dry weight basis, Y weight percent expanded graphite. X divided by Y may be at least 0.5. Thus, according to a first aspect of this disclosure, there is provided an aerosol-forming substrate comprising, on a dry weight basis, X weight percent non-expanded graphite. The aerosol-forming substrate also comprises, on a dry weight basis, Y weight percent expanded graphite. And X divided by Y is at least 0.5.

[0009] Surprisingly, including expanded graphite in an aerosol-forming substrate may improve the performance of the aerosol-forming substrate more than including the same amount of nonexpanded graphite in the aerosol-forming substrate. In this context, performance may refer to nicotine and glycerine yield from an aerosol-generating article comprising the aerosol-forming substrate over a course of 12 puffs. This improvement is shown by the data in Table 1 below. To collect the data in Table 1 , three different plugs of aerosol-forming substrate were made by hand and then tested under the Health Canada Intense (HCI) smoking regime for 12 puffs using FTIR spectroscopy. However, as the skilled person would understand, the plugs of aerosol-forming substrates could have been made using other techniques, for example with machinery, and the data could have been collected using other tests.

[0010] Table 1 :

[0011] Without wishing to be bound by theory, it is believed that at least some of this improvement in performance is a result of the fact that expanded graphite has a lower bulk density than nonexpanded graphite. This means that, for a sheet of aerosol-forming substrate having a particular grammage, an aerosol-forming substrate comprising expanded graphite is thicker than an aerosol-forming substrate comprising non-expanded graphite. This may advantageously result in one or both of fewer air gaps and smaller air gaps in the aerosol-forming substrate itself, or between surfaces of the aerosol-forming substrate, for example when the aerosol-forming substrate is in the form of a gathered sheet. These air gaps may act as thermal insulators in the aerosol-forming substrate so reducing one or both of the number and the average size of these air gaps may advantageously improve the thermal conductivity of the aerosol-forming substrate, and thus increase nicotine and glycerine yield when the aerosol-forming substrate is heated. However, using too much expanded graphite can make manufacturing the aerosol-forming substrate more difficult, particularly if trying to use existing machinery. For example, an aerosolforming substrate may be manufactured by a method involving making a slurry comprising expanded graphite, then mixing the slurry, then casting and drying the slurry. However, in this case, as the proportion of expanded graphite in the slurry increases, the viscosity of the slurry also increases. And if the viscosity of the slurry is too high, it may be difficult to mix or cast the slurry, particularly if trying to use existing machinery. Any references to a viscosity of a slurry herein are references to dynamic viscosity and may be measured at room temperature unless otherwise specified, and may be measured using the commercially available Anton Paar MCR302 rheometer device.

[0012] The inventors have creatively overcome this potential problem by including non-expanded graphite, as well as expanded graphite, in the substrate. Referring back to the method mentioned in the previous paragraph, the inventors have surprisingly found that adding non-expanded graphite to the slurry may reduce the viscosity of the slurry. Thus, the non-expanded graphite reducing the viscosity of the slurry may be used to counteract the expanded graphite increasing the viscosity of the slurry. By maintaining a ratio of non-expanded graphite to expanded graphite in the slurry at or above a threshold, the viscosity of the slurry can be maintained at an acceptable level whilst still obtaining the improvements in performance offered by the expanded graphite.

[0013] Optionally, X divided by Y is at least 0.65, 0.8, 1 , 1.2, or 1 .4. Advantageously, as X divided by Y increases, the aerosol-forming substrate may become easier to make, particularly with existing machinery. As explained above, this may be because, as the ratio of non-expanded graphite to expanded graphite increases in a slurry for making the aerosol-forming substrate, the viscosity of the slurry decreases.

[0014] Optionally, X divided by Y is no more than 10, 8, 6, 4 or 2. Advantageously, as X divided by Y decreases, the performance of the aerosol-forming substrate may improve, approaching the performance of an aerosol-forming substrate with expanded graphite and without non-expanded graphite. As explained above, this may be at least partly because of the reduction in air gaps in the aerosol-forming substrate when proportionally more expanded graphite is present.

[0015] Optionally, X divided by Y is between 0.5 and 10, 0.5 and 8, 0.5 and 6, 0.5 and 4, or 0.5 and 2. Optionally, X divided by Y is between 0.65 and 10, 0.65 and 8, 0.65 and 6, 0.65 and 4, or 0.65 and 2. Optionally, X divided by Y is between 0.8 and 10, 0.8 and 8, 0.8 and 6, 0.8 and 4, or 0.8 and 2. Optionally, X divided by Y is between 1 and 10, 1 and 8, 1 and 6, 1 and 4, or 1 and 2. Optionally, X divided by Y is between 1.2 and 10, 1.2 and 8, 1 .2 and 6, 1 .2 and 4, or 1 .2 and 2. Optionally, X divided by Y is between 1.4 and 10, 1.4 and 8, 1 .4 and 6, 1 .4 and 4, or 1 .4 and 2. Advantageously, these ranges may provide an optimal compromise between manufacturability, which may improve as X divided by Y increases, and aerosol-forming substrate performance, which may improve as X divided by Y decreases. As discussed above, the aerosol-forming substrate may comprise, on a dry weight basis, X weight percent non-expanded graphite. Optionally, X is at least 1 , 2, 3, 4, or 5. It may be particularly preferable for X to be at least 4. Advantageously, increasing X may improve manufacturability of the aerosol-forming substrate, as explained above.

[0016] Optionally, X is no more than 50, 30, 20, 15, 12 or 10. It may be particularly preferable for X to be no more than 20. Advantageously, limiting how much non-expanded graphite is in the aerosol-forming substrate may leave more room for other constituents, such as expanded graphite, tobacco, fibres, binder, flavourings, and so on.

[0017] Optionally, X is between 1 and 50, 1 and 30, 1 and 20, 1 and 15, 1 and 12, or 1 and 10. Optionally, X is between 2 and 50, 2 and 30, 2 and 20, 2 and 15, 2 and 12, or2 and 10. Optionally, X is between 2 and 30, 2 and 20, 2 and 15, 2 and 12, or 2 and 10. Optionally, X is between 3 and 50, 3 and 30, 3 and 20, 3 and 15, 3 and 12, or 3 and 10. Optionally, X is between 4 and 50, 4 and 30, 4 and 20, 4 and 15, 4 and 12, or 4 and 10. Optionally, X is between 5 and 50, 5 and 30, 5 and 20, 5 and 15, 5 and 12, or 5 and 10. It may be particularly preferable for X to be between 4 and 20. Advantageously, these ranges may provide an optimal compromise between manufacturability of the aerosol-forming substrate, which may improve as X increases, and allowing greater amounts of other constituents of the aerosol-forming substrate, which may improve as X decreases.

[0018] As discussed above, the aerosol-forming substrate may comprise, on a dry weight basis, Y weight percent expanded graphite. Optionally, Y is at least 1 , 2, 3, or 4. It may be particularly preferable for Y to be at least 2. Advantageously, increasing Y may improve performance of the aerosol-forming substrate, as explained above.

[0019] Optionally, Y is no more than 40, 20, 15, 10, 8, or 6. It may be particularly preferable for Y to be no more than 10. Advantageously, limiting how much expanded graphite is in the aerosolforming substrate may improve manufacturability of the aerosol-forming substrate and allow greater amounts of other constituents, such as tobacco, fibres, binder, flavourings, and so on.

[0020] Optionally, Y is between 1 and 40, 1 and 20, 1 and 15, 1 and 10, 1 and 8, or 1 and 6. Optionally, Y is between 2 and 40, 2 and 20, 2 and 15, 2 and 10, 2 and 8, or 2 and 6. Optionally,

[0021] Y is between 3 and 40, 3 and 20, 3 and 15, 3 and 10, 3 and 8, or 3 and 6. Optionally, Y is between 4 and 40, 4 and 20, 4 and 15, 4 and 10, 4 and 8, or 4 and 6. It may be particularly preferable for

[0022] Y to be between 2 and 10. Advantageously, these ranges may provide an optimal compromise between performance of the aerosol-forming substrate, which may improve as Y increases, and manufacturability and allowing greater amounts of other constituents of the aerosol-forming substrate, which may both improve as Y decreases.

[0023] It may be preferable for X to be between 2 and 50 and Y to be between 2 and 40. It may be more preferable for X to be between 2 and 30 and Y to be between 2 and 20. It may be even more preferable for X to be between 2 and 20 and Y to be between 2 and 20. It may be even more preferable still for X to be between 4 and 20 and Y to be between 2 and 10. It may be most preferable for X to be between 4 and 15 and Y to be between 2 and 8.

[0024] Optionally, the X weight percent non-expanded graphite comprises or consists of a plurality of non-expanded graphite particles. The term "non-expanded graphite particles" may refer to particles comprising non-expanded graphite, for example at least 50, 75, 90, 95, or 98 weight percent non-expanded graphite, or to particles consisting of non-expanded graphite, or to particles consisting of non-expanded graphite except for trace impurities.

[0025] Optionally, the Y weight percent expanded graphite comprises or consists of a plurality of expanded graphite particles. The term "expanded graphite particles" may refer to particles comprising expanded graphite, for example at least 50, 75, 90, 95, or 98 weight percent expanded graphite, or to particles consisting of expanded graphite, or to particles consisting of expanded graphite except for trace impurities.

[0026] The particles may be spherical but, for the avoidance of doubt, the term "particles" does not imply spherical particles. The non-expanded graphite particles may include one or more of nonexpanded graphite flakes, non-expanded graphite sheets, and non-expanded graphite fibres. The expanded graphite particles may include one or both of expanded graphite flakes, expanded graphite sheets, and expanded graphite fibres.

[0027] Optionally, one or both of the plurality of non-expanded graphite particles and the plurality of expanded graphite particles may have a particle size distribution. A particle size distribution may be characterised by volume D10, D50 and D90 particle sizes. The volume D10 particle size is defined such that 10% of the sum of the volumes of all of the particles is accounted for by the sum of the volumes of the particles having a particles size less than or equal to the volume D10 particle size. Similarly, the volume D50 particle size is defined such that 50% of the sum of the volumes of all of the particles is accounted for by the sum of the volumes of the particles having a particles size less than or equal to the volume D50 particle size. And the volume D90 particle size is defined such that 90% of the sum of the volumes of all of the particles is accounted for by the sum of the volumes of the particles having a particles size less than or equal to the volume D90 particle size.

[0028] Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D90 diameter of at least 0.1 , 0.5, 1 , 5 or 10 microns. Optionally, the plurality of nonexpanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 500, 200, 100, 75 50 or 35 microns. Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D90 diameter between 1 and 200 microns, preferably between 5 and 100 microns, particularly preferably between 10 and 75 microns, most preferably between 35 and 75 microns.

[0029] Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D50 diameter of at least 0.1 , 0.5, 1 , 5 or 10 microns. Optionally, the plurality of non- expanded graphite particles has a particle size distribution with a volume D50 diameter no greater than 500, 200, 100, 75 50 or 35 microns. Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D50 diameter between 0.5 and 200 microns, preferably between 1 and 100 microns, particularly preferably between 2 and 75 microns, most preferably between 5 and 50 microns.

[0030] Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D10 diameter of at least 0.1 , 0.5, 1 , or 5 microns. Optionally, the plurality of nonexpanded graphite particles has a particle size distribution with a volume D10 diameter no greater than 500, 200, 100, 75, 50 or 35 microns. Optionally, the plurality of non-expanded graphite particles has a particle size distribution with a volume D10 diameter between 0.1 and 100 microns, preferably between 0.1 and 75 microns, particularly preferably between 0.5 and 50 microns, most preferably between 1 and 35 microns.

[0031] Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D90 diameter of at least 0.1 , 0.5, 1 , 5 or 10 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 500, 200, 100, 75 50 or 35 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D90 diameter between 1 and 200 microns, preferably between 5 and 100 microns, particularly preferably between 10 and 75 microns, most preferably between 35 and 75 microns.

[0032] Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D50 diameter of at least 0.1 , 0.5, 1 , 5 or 10 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D50 diameter no greater than 500, 200, 100, 75 50 or 35 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D50 diameter between 0.5 and 200 microns, preferably between 1 and 100 microns, particularly preferably between 2 and 75 microns, most preferably between 5 and 50 microns.

[0033] Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D10 diameter of at least 0.1 , 0.5, 1 , or 5 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D10 diameter no greater than 500, 200, 100, 75, 50 or 35 microns. Optionally, the plurality of expanded graphite particles has a particle size distribution with a volume D10 diameter between 0.1 and 100 microns, preferably between 0.1 and 75 microns, particularly preferably between 0.5 and 50 microns, most preferably between 1 and 35 microns.

[0034] Advantageously, the above ranges may provide an optimal compromise between larger particles increasing the thermal conductivity of the aerosol-forming substrate more than smaller particles but also reducing the space available for other constituents in the aerosol-forming substrate. Optionally, the plurality of non-expanded graphite particles has a particle size distribution where the volume D90 particle size is no more than 50, 40, 30, 20, 10, or 5 times the volume D10 particle size. Optionally, the plurality of non-expanded graphite particles has a particle size distribution where the volume D90 particle size is at least 1.5, 2, 3, 5, 10, or 20 times the volume D10 particle size.

[0035] Optionally, the plurality of expanded graphite particles has a particle size distribution where the volume D90 particle size is no more than 50, 40, 30, 20, 10, or 5 times the volume D10 particle size. Optionally, the plurality of expanded graphite particles has a particle size distribution where the volume D90 particle size is at least 1.5, 2, 3, 5, 10, or 20 times the volume D10 particle size.

[0036] A compromise must be made in relation to the particle size distribution. A tighter particle size distribution, for example characterised by a smaller ratio between the D90 and D10 particle sizes, may advantageously provide a more uniform thermal conductivity throughout the aerosolforming substrate. This is because there will be less variation in particle size in different locations in the substrate. This may advantageously allow for more efficient usage of the aerosol-forming material throughout the aerosol-forming substrate. However, a tighter particle size distribution may disadvantageously be more difficult and expensive to achieve. The particle size distributions above may provide an optimal compromise between these two factors.

[0037] Optionally, each of the plurality of non-expanded graphite particles has three mutually perpendicular dimensions, a largest dimension of the three dimensions being one or both of: no more than 10, 8, 5, 3, or 2 times larger than a smallest dimension of the three dimensions; and no more than 10, 8, 5, 3, or 2 times larger than a second largest dimension of the three dimensions. Optionally, each of the plurality of non-expanded graphite particles is substantially spherical.

[0038] Optionally, each of the plurality of expanded graphite particles has three mutually perpendicular dimensions, a largest dimension of the three dimensions being one or both of: no more than 10, 8, 5, 3, or 2 times larger than a smallest dimension of the three dimensions; and no more than 10, 8, 5, 3, or 2 times larger than a second largest dimension of the three dimensions. Optionally, each of the plurality of expanded graphite particles is substantially spherical.

[0039] Optionally, the plurality of non-expanded graphite particles comprises at least 10, 20, 50, 100, 200, 500, or 1000 particles. Optionally, the plurality of expanded graphite particles comprises at least 10, 20, 50, 100, 200, 500, or 1000 particles. Advantageously, a greater number of particles may allow the thermal conductivity of the aerosol-forming substrate to be more uniform.

[0040] The expanded graphite may have a density of less than 0.2, 0.1 , 0.05, or 0.01 times the density of the non-expanded graphite.

[0041] The 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 centimetre cubed (g / cm3). The 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 centimetre cubed (g I cm3). The expanded graphite may 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

[0042] 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

[0043] 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 centimetre cubed (g I cm3).

[0044] Optionally, the substrate comprises at least one aerosol former. Optionally, the substrate comprises, on a dry weight basis, at least 5, 10, 20, 30 or 50 weight percent of the at least one aerosol former. Optionally, the substrate comprises, on a dry weight basis, no more than 95, 80, 50, or 30 weight percent of the at least one aerosol former. Optionally, the substrate comprises, on a dry weight basis, between 5 and 80, 5 and 50, 5 and 30, 10 and 80, 10 and 50, 10 and 30, 20 and 80, 20 and 50, 20 and 30, or 30 and 80 weight percent of the at least one aerosol former. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 10 and 80, more preferably between 10 and 50, of the at least one aerosol former.

[0045] Optionally, the at least one aerosol-former comprises or consists of one or more of: polyhydric alcohols, such as propylene glycol, polyethylene glycol, triethylene glycol, 1 , 3- butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or tri-acetate; and aliphatic esters of mono-, di- or poly-carboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Optionally, the aerosol-forming substrate comprises one or both of glycerine and propylene glycol.

[0046] Optionally, the substrate comprises fibres. Optionally, the substrate comprises, on a dry weight basis, at least 2, 5 or 10 weight percent of fibres. Optionally, the substrate comprises, on a dry weight basis, no more than 20 or 10 weight percent of the fibres. Optionally, the substrate comprises, on a dry weight basis, between 2 and 20, 2 and 10, 5 and 20, 5 and 10, or 10 and 20 weight percent of the fibres. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 2 and 10 weight percent of the fibres.

[0047] Optionally, the fibres are cellulose fibres. Advantageously, cellulose fibres are not overly costly and can increase the tensile strength of the substrate.

[0048] Optionally, each of the fibres has three mutually perpendicular dimensions, a largest dimension of the three dimensions being at least 1 .5, 2, 3, 5, 10, or 20 times larger than a smallest dimension of the three dimensions. Optionally, each of the fibres has three mutually perpendicular dimensions, a largest dimension of the three dimensions being at least 1.5, 2, 3, 5, 10, or 20 times larger than a second largest dimension of the three dimensions. Optionally, the substrate comprises at least one binder. Optionally, the substrate comprises, on a dry weight basis, at least 1 , 2 or 5 weight percent of at least one binder. Optionally, the substrate comprises, on a dry weight basis, no more than 20, 15, 10 or 5 weight percent of the at least one binder. Optionally, the substrate comprises, on a dry weight basis, between 1 and 20, 2 and 20, 5 and 20, 1 and 15, 2 and 15, 5 and 15, 1 and 10, 2 and 10, 5 and 10, 1 and 5, or 2 and 5 weight percent of the at least one binder. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 1 and 20, more preferably between 2 and 20, most preferably between 2 and 15, weight percent of the at least one binder.

[0049] 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 carboxymethyl cellulose; tamarind gum; dextran; pullalon; konjac flour; xanthan gum and the like. It may be particularly preferable for the binder to be or comprise any one or more of: carboxymethyl cellulose, hydroxypropyl cellulose, gum or guar such as guar gum. It may be more particularly preferable for the at least one binder to comprise or consist of one or both of carboxymethyl cellulose and guar gum.

[0050] Advantageously, carboxymethyl cellulose may have an added benefit of reducing crusting of the aerosol-forming substrate when used in an aerosol-generating article.

[0051] Optionally, the carboxymethyl cellulose comprises sodium carboxymethyl cellulose. Advantageously, sodium carboxymethyl cellulose is a carboxymethyl cellulose that may be particularly effective at preventing the above-mentioned problem of crusting.

[0052] Optionally, the substrate comprises nicotine. Where the substrate comprises tobacco, and that tobacco comprises nicotine, the substrate may comprise additional nicotine in addition to the nicotine of the tobacco.

[0053] Optionally, the substrate comprises, on a dry weight basis, at least 0.01 , 0.1 , 1 , or 2 weight percent nicotine. Optionally, the substrate comprises, on a dry weight basis, no more than 5, 2 or 1 weight percent nicotine. Optionally, the substrate comprises, on a dry weight basis, between 0.01 and 5, 0.01 and 2, 0.01 and 1 , 0.1 and 5, 0.1 and 2, 0.1 and 1 , 1 and 5, 1 and 2, or 2 and 5 weight percent nicotine. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 0.1 and 2 weight percent nicotine. These weight percents of nicotine may refer to a weight percent of nicotine in the substrate in its entirety. Alternatively, where the substrate comprises tobacco, and that tobacco comprises nicotine, these weight percents may refer to weight percents of additional nicotine in addition to the nicotine of the tobacco.

[0054] Optionally, the substrate comprises at least one acid. Optionally, the substrate comprises, on a dry weight basis, at least 0.01 , 1 , 2, 3, or 4 weight percent of the at least one acid. Optionally, the substrate comprises, on a dry weight basis, no more than 5, 4, 3, 2 or 1 weight percent of the at least one 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 weight percent of the at least one acid. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 0.5 and 3 weight percent of the at least one acid.

[0055] Optionally, the at least one acid comprises or consists of one or more carboxylic acids. Optionally, the at least one acid comprises or consists of one or more of fumaric acid, lactic acid, benzoic acid, and levulinic acid.

[0056] Optionally, the substrate comprises at least one botanical. The at least one botanical may be an at least one non-tobacco botanical. Optionally, the substrate comprises, on a dry weight basis, at least 0.01 , 1 , 2, 5 or 10 weight percent of the at least one botanical. Optionally, the substrate comprises, on a dry weight basis, no more than 50, 20, 10, or 5 weight percent of the at least one botanical. Optionally, the substrate comprises, on a dry weight basis, between 0.01 and 50, 1 and 50, 2 and 50, 5 and 50, 10 and 50, 0.01 and 20, 1 and 20, 2 and 20, 5 and 20, 10 and 20, 0.01 and 10, 1 and 10, 2 and 10, 5 and 10, 0.01 and 5, 1 and 5, or 2 and 5 weight percent of the at least one botanical. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 2 and 20 weight percent of the at least one botanical.

[0057] The at least non-tobacco botanical may comprise or consist of any one or more of: peppermint, star anise, lavender, clove, common sage, chamomile, rosemary, eucalyptus, ginger, dill seed, thyme, oregano and cumin. Preferably, at least non-tobacco botanical may comprise or consist of any one or more of: peppermint, star anise, lavender, clove, common sage, chamomile and rosemary. Advantageously, the at least one botanical may impart desirable flavour characteristics to the substrate.

[0058] Optionally, at least a portion of the at least one botanical may be present in the substrate in the form of particles. These particles may be dispersed, for example substantially homogeneously dispersed, through the aerosol-forming substrate.

[0059] Optionally, the substrate comprises at least one flavourant. Optionally, the substrate comprises, on a dry weight basis, at least 0.1 , 1 , 2, or 5 weight percent of the at least one flavourant. Optionally, the substrate comprises, on a dry weight basis, no more than 10, 5, 2 or 1 weight percent of the at least one flavourant. 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 weight percent of the at least one flavourant. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 0.1 and 5 weight percent of the at least one flavourant.

[0060] 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 herb leaf, tobacco leaf, fragments of tobacco ribs, reconstituted tobacco, homogenised tobacco, tobacco powder, extruded tobacco and expanded tobacco.

[0061] Optionally, the aerosol-forming substrate comprises, on a dry weight basis, at least 20, 30, 40, 50, or 60 weight percent of the at least one organic material such as tobacco. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, no more than 90, 80 or 70 weight percent of the at least one organic material such as tobacco. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, between 20 and 90, 20 and 80, 20 and 70, 30 and 90, 30 and 80, 30 and 70, 40 and 90, 40 and 80, 40 and 70, 50 and 90, 50 and 80, or 50 and 70 weight percent of the at least one organic material such as tobacco. It may be particularly preferable for the substrate to comprise, on a dry weight basis, between 40 and 90, more preferably between 50 and 80, most preferably between 60 and 70, weight percent of the at least one organic material such as tobacco.

[0062] Alternatively, the aerosol-forming substrate may be a low- or no-tobacco aerosol-forming substrate. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, less than 10 or 5 weight percent tobacco. Optionally, the aerosol-forming substrate is a substantially tobacco-free aerosol-forming substrate.

[0063] Optionally, the aerosol-forming substrate has a moisture content of between 1 and 20, or 3 and 15 weight percent This moisture content may be measured after 48 hours equilibration at 50 % relative humidity at 20 degrees Celsius. Optionally, the aerosol-forming substrate comprises between 1 and 20, or 3 and 15 weight percent water. The moisture or water content of the substrate may be measured using a titration method. The moisture or water content of the substrate may be measured using the Karl Fisher method.

[0064] In view of the foregoing, in a first set of particularly preferred embodiments of this disclosure, such as a first set of particularly preferred embodiments of the first aspect of this disclosure, the substrate comprises: non-expanded graphite; expanded graphite; at least one organic material, which preferably comprises or consists of tobacco; at least one binder, which preferably comprises or consists of guar gum; at least one aerosol former, which preferably comprises or consists of glycerine; and fibres, which preferably comprise or consist of cellulose fibres.

[0065] In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 3 weight percent, and no more than 20 weight percent, of the non-expanded graphite. The substrate preferably comprises, on a dry weight basis, between 4 and 12 weight percent of the non-expanded graphite.

[0066] In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 15 weight percent, of the expanded graphite. The substrate preferably comprises, on a dry weight basis, between 3 and 10 weight percent of the expanded graphite. In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 40 weight percent, and no more than 90 weight percent, of the at least one organic material. The substrate preferably comprises, on a dry weight basis, between 50 and 80 weight percent of the at least one organic material.

[0067] In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 0.5 weight percent, and no more than 10 weight percent, of the at least one binder. The substrate preferably comprises, on a dry weight basis, between 1 and 5 weight percent of the at least one binder.

[0068] In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 5 weight percent, and no more than 50 weight percent, of the at least one aerosol former. The substrate preferably comprises, on a dry weight basis, between 10 and 30 weight percent of the at least one aerosol former.

[0069] In the first set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 1 weight percent, and no more than 15 weight percent, of the fibres. The substrate preferably comprises, on a dry weight basis, between 2 and 10 weight percent of the fibres. Thus, according to the first set of particularly preferred embodiments, the substrate may comprise, on a dry weight basis: between 3 and 20, preferably between 4 and 12, weight percent non-expanded graphite; between 2 and 15, preferably between 3 and 10, weight percent expanded graphite; between 40 and 90, preferably between 50 and 80, weight percent of at least one organic material, which preferably comprises or consists of tobacco; between 0.5 and 10, preferably between 1 and 5, weight percent of at least one binder, which preferably comprises or consists of guar gum; between 5 and 50, preferably between 10 and 30, weight percent of at least one aerosol former, which preferably comprises or consists of glycerine; and between 1 and 15, preferably between 2 and 10, weight percent fibres, which preferably comprise or consist of cellulose fibres.

[0070] As the skilled person would understand after reading this disclosure, other features described herein may be applicable to the first set of particularly preferred embodiments. The method of making an aerosol-forming substrate described later may be a method of making an aerosol-forming substrate of the first set of particularly preferred embodiments.

[0071] Optionally, the aerosol-forming substrate comprises hydroxypropylmethyl cellulose. Optionally, the aerosol-forming substrate comprises one or more cellulose-based strengthening agents. Optionally, the aerosol-forming substrate comprises hydroxypropylmethyl cellulose and one or more cellulose-based strengthening agents. Optionally, the aerosol-forming substrate comprises hydroxypropylmethyl cellulose and one or more cellulose-based strengthening agents, and preferably also one or both of: is tobacco-free; and comprises one or more aerosol formers. Thus, optionally, the aerosol-forming substrate comprises hydroxypropylmethyl cellulose and one or more cellulose-based strengthening agents, is tobacco-free, and also comprises one or more aerosol formers.

[0072] An aerosol-forming substrate that includes hydroxypropylmethyl cellulose and one or more cellulose-based strengthening agent may have a number of advantages.

[0073] The inclusion of hydroxypropylmethyl cellulose in the aerosol-forming substrate may improve the manufacturing process of the aerosol-forming substrate. For example, hydroxypropylmethyl cellulose may reduce the viscosity of the slurry that is mixed when making the aerosol-forming substrate. A lower viscosity slurry may flow more easily compared to conventional slurries, and a lower viscosity slurry is easier to mix, transfer and handle during the manufacturing process.

[0074] The inclusion of a cellulose-based strengthening agent in the aerosol-forming substrate may increase the tensile strength of the aerosol-forming substrate. This may be particularly beneficial if hydroxypropylmethyl cellulose is present because hydroxypropylmethyl cellulose can reduce the tensile strength of the substrate. An aerosol-forming substrate with a higher tensile strength may be less likely to deteriorate or break, for example during transit or during the manufacturing process.

[0075] Optionally, the aerosol-forming substrate comprises, on a dry weight basis, at least 0.5, 1 , 5, 10, 15 or 20 weight percent hydroxypropylmethyl cellulose. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, no more than 50, 45, 40, 35, 30, 25 or 20 weight percent hydroxypropylmethyl cellulose. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, between 0.1 and 50, 1 and 50, 5 and 50, 10 and 50, 20 and 50, 0.1 and 40, 1 and 40, 5 and 40, 10 and 40, 20 and 40, 0.1 and 30, 1 and 30, 5 and 30, 10 and 30, 20 and 30, 0.1 and 20, 1 and 20, 5 and 20, 10 and 20, 0.1 and 10, 1 and 10, or 5 and 10 weight percent hydroxypropylmethyl cellulose. It may be preferable for the aerosol-forming substrate to comprise, on a dry weight basis, between 5 and 50, more preferably between 10 and 50, most preferably between 20 and 50 weight percent hydroxypropylmethyl cellulose.

[0076] Optionally, the aerosol-forming substrate comprises, on a dry weight basis, at least 0.5, 1 , 5, 10, 15 or 20 weight percent of the one or more cellulose-based strengthening agents. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, no more than 50, 45, 40, 35, 30, 25 or 20 weight percent of the one or more cellulose-based strengthening agents. Optionally, the aerosol-forming substrate comprises, on a dry weight basis, between 0.1 and 50, 1 and 50, 5 and 50, 10 and 50, 20 and 50, 0.1 and 40, 1 and 40, 5 and 40, 10 and 40, 20 and 40, 0.1 and 30, 1 and 30, 5 and 30, 10 and 30, 20 and 30, 0.1 and 20, 1 and 20, 5 and 20, or 10 and 20, weight percent of the one or more cellulose-based strengthening agents. It may be preferable for the aerosol-forming substrate to comprise, on a dry weight basis, between 5 and 50, more preferably between 10 and 50, most preferably between 20 and 50 weight percent of the one or more cellulose-based strengthening agents.

[0077] The one or more cellulose-based strengthening agents may comprise or consist of one or more of: cellulose fibres, microcrystalline cellulose, and cellulose powder. Advantageously, such cellulose-based strengthening agents may be particularly effective at increasing the tensile strength of an aerosol-forming substrate.

[0078] In view of the foregoing, in a second set of particularly preferred embodiments of this disclosure, such as a second set of particularly preferred embodiments of the first aspect of this disclosure, the substrate comprises: non-expanded graphite; expanded graphite; hydroxypropylmethyl cellulose; and at least one aerosol-former, preferably glycerine.

[0079] The second set of particularly preferred embodiments may preferably comprise less than 10 or 5 weight percent tobacco on a dry weight basis. It may be particularly preferable that the substrate is tobacco-free.

[0080] This second set of particularly preferred embodiments may comprise any one or more or all of: fibres, preferably cellulose fibres; microcrystalline cellulose; cellulose powder; sodium carboxymethyl cellulose; at least one binder or gelling agent, preferably agar; nicotine; and at least one acid such as a carboxylic acid, for example lactic acid.

[0081] In the second set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 3 weight percent, and no more than 20 weight percent, of the non-expanded graphite. The substrate preferably comprises, on a dry weight basis, between 4 and 12 weight percent of the non-expanded graphite.

[0082] In the second set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 15 weight percent, of the expanded graphite. The substrate preferably comprises, on a dry weight basis, between 3 and 10 weight percent of the expanded graphite.

[0083] In the second set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 5 weight percent, and no more than 50 weight percent, of the hydroxypropylmethyl cellulose. The substrate preferably comprises, on a dry weight basis, between 5 and 40 weight percent of the hydroxypropylmethyl cellulose.

[0084] In the second set of particularly preferred embodiments, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 30 weight percent, and no more than 80 weight percent, of the at least one aerosol former. The substrate preferably comprises, on a dry weight basis, between 40 and 70 weight percent of the at least one aerosol former.

[0085] In the second set of particularly preferred embodiments, where the substrate comprises the at least one binder or gelling agent, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 20 weight percent, of the at least one binder or gelling agent. The substrate preferably comprises, on a dry weight basis, between 2 and 10 weight percent of at least one binder or gelling agent.

[0086] In the second set of particularly preferred embodiments, where the substrate comprises the fibres, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 50 weight percent, of the fibres. The substrate preferably comprises, on a dry weight basis, between 2 and 40 weight percent of the fibres.

[0087] In the second set of particularly preferred embodiments, where the substrate comprises the microcrystalline cellulose, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 20 weight percent, of the microcrystalline cellulose. The substrate preferably comprises, on a dry weight basis, between 2 and 10 weight percent of the microcrystalline cellulose.

[0088] In the second set of particularly preferred embodiments, where the substrate comprises the sodium carboxymethyl cellulose, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 20 weight percent, of the sodium carboxymethyl cellulose. The substrate preferably comprises, on a dry weight basis, between 2 and 10 weight percent of the sodium carboxymethyl cellulose.

[0089] In the second set of particularly preferred embodiments, where the substrate comprises the cellulose powder, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 2 weight percent, and no more than 40 weight percent, of the cellulose powder. The substrate preferably comprises, on a dry weight basis, between 5 and 30 weight percent of the cellulose powder.

[0090] In the second set of particularly preferred embodiments, where the substrate comprises the nicotine, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 0.5 weight percent, and no more than 5 weight percent, of the nicotine. The substrate preferably comprises, on a dry weight basis, between 1 and 4 weight percent of the nicotine.

[0091] In the second set of particularly preferred embodiments, where the substrate comprises the at least one acid, it is preferable that the substrate comprises, on a dry weight basis, one or both of: at least 1 weight percent, and no more than 20 weight percent, of the at least one acid. The substrate preferably comprises, on a dry weight basis, between 1 and 10 weight percent of the at least one acid.

[0092] Thus, according to the second set of particularly preferred embodiments, the substrate may comprise, on a dry weight basis: between 3 and 20, preferably between 4 and 12, weight percent non-expanded graphite; between 2 and 15, preferably between 3 and 10, weight percent expanded graphite; between 5 and 50, preferably between 5 and 40, weight percent hydroxypropylmethyl cellulose; and between 30 and 80, preferably between 40 and 70 weight percent of the at least one aerosol former.

[0093] In addition, also according to the second set of particularly preferred embodiments, the substrate may comprise, on a dry weight basis any one or more or all of: between 2 and 20, preferably between 2 and 10 weight percent of at least one binder or gelling agent; between 20 and 50, preferably between 2 and 40 weight percent of fibres; between 20 and 20, preferably between 2 and 10 weight percent microcrystalline cellulose; between 2 and 20, preferably between 2 and 10 weight percent of the sodium carboxymethyl cellulose; between 2 and 40, preferably between 5 and 30 weight percent cellulose powder between 0.5 and 5, preferably between 1 and 4 weight percent of the nicotine; and between 1 and 20, preferably between 1 and 10 weight percent of the at least one acid.

[0094] As the skilled person would understand after reading this disclosure, other features described herein may be applicable to the second set of particularly preferred embodiments.

[0095] Optionally, in any of the substrates described herein, the non-expanded graphite is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the expanded graphite is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one aerosol former is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the fibres are substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one binder is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the nicotine is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one acid is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one botanical is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one flavourant is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the at least one organic material is substantially homogeneously distributed throughout the aerosolforming substrate. Optionally, the hydroxypropylmethyl cellulose is substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the one or more cellulose-based strengthening agents are substantially homogeneously distributed throughout the aerosol-forming substrate. Optionally, the carboxymethyl cellulose is substantially homogeneously distributed throughout the aerosol-forming substrate.

[0096] Advantageously, a homogenous distribution of components of the substrate may result in the substrate have more spatially uniform properties. For example, substantially homogeneously distributed non-expanded and expanded graphite particles may result in the substrate having a substantially uniform thermal conductivity. As another example, substantially homogeneously distributed binder or fibres may result in the substrate having a substantially uniform tensile strength.

[0097] Optionally, the aerosol-forming substrate comprises, or is in the form of, one or more of: cut-filler, powder particles, granules, pellets, shreds, spaghettis, strips, threads, ribbons, or sheets.

[0098] Optionally, the aerosol-forming substrate comprises, or is in the form of, one or more sheets, for example gathered sheets or rolled sheets. Optionally, the aerosol-forming substrate comprises, or is in the form of, a plurality of strips. Optionally the aerosol-forming substrate is in the form of a tube.

[0099] Optionally, the or each sheet is crimped. Optionally, the or each sheet is crimped and gathered. The or each sheet may be crimped and then gathered to form the or each crimped and gathered sheet.

[0100] Optionally, the or each sheet or strip has a thickness of at least 5, 10, 20, 50, 100, 150, or 200 microns. Optionally, the or each sheet or strip has a thickness of no more than 2000, 1000, 500, 400, 300, or 250 microns. Optionally, the or each sheet or strip has a thickness of between 100 and 350, or 150 and 300 microns.

[0101] Optionally, the or each sheet or strip has a width of at least 100, 200, 500, or 1000 microns. Optionally, the or each sheet or strip has a width of no more than 2000, 1000, 500, 400, 300, 250, or 200 microns. Optionally, the or each sheet or strip has a width of between 100 and 2000, or 500 and 1000, or 600 and 1000 microns.

[0102] Optionally, the or each sheet or strip has a length of at least 100, 200, 500, 1000, 2000, or 3000 microns. Optionally, the or each sheet or strip has a length of no more than 6000, 5000, 3000, 2000, 1000, 500, or 200 microns. Optionally, the or each sheet or strip has a length of between 100 and 6000, or 500 and 5000, or 1000 and 4000 microns.

[0103] Optionally, the or each sheet or strip has a grammage of at least 20, 50, or 100 g / m2. Optionally, the or each sheet or strip has a grammage of no more than 300 g / m2. Optionally, the or each sheet or strip has a grammage of between 20 and 300, 50 and 250, or 100 and 250 g / m2.

[0104] Optionally, the or each sheet or strip has a density of at least 0.1 , 0.2, 0.3, or 0.5 g / m3. Optionally, the or each sheet or strip has a density of no more than 2, 1.5, 1.2, or 1 g / m3. Optionally, the or each sheet or strip has 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.

[0105] Where the substrate comprises one or more gathered sheets, the or each gathered sheet may have a width of at least about 1 , 2, 5, 10, 25, 50, or 100 mm.

[0106] The aerosol-forming substrate may be in the form of a rod. As such, there may be provided a rod of aerosol-forming substrate. The rod may be substantially cylindrical, for example right cylindrical, in shape. The aerosol-forming substrate may comprise a susceptor element. The susceptor element may be distinct from the expanded graphite and the non-expanded graphite. The susceptor element may be located in contact with, or within, the aerosol-forming substrate. The susceptor element may be an elongate susceptor element. The susceptor element may extend longitudinally within the rod of aerosol-forming substrate. The susceptor element may be positioned in a radially central position within the rod of aerosol-forming substrate. The susceptor element may extend along a central, longitudinal axis of the rod of aerosol-forming substrate. The susceptor element may extend all the way to a downstream end of the rod of aerosol-forming substrate. The susceptor element may extend all the way to an upstream end of the rod of aerosol-forming substrate. The susceptor element may have substantially the same length as the rod of aerosolforming substrate. The susceptor element may extend from the upstream end to the downstream end of the rod of aerosol-forming substrate. The susceptor element may be in the form of a pin, rod, strip or blade. The susceptor element may have a length of between 5 and 15, 6 and 12, or 8 and 10 millimetres. The susceptor element may have a width of between 1 and 5 millimetres. The susceptor element may have a thickness of between 0.01 and 2, 0.5 and 2, or 0.5 and 1 millimetres.

[0107] Alternatively, there may be no such susceptor element present in the aerosol-forming substrate or in the rod of aerosol-forming substrate.

[0108] Optionally, the aerosol-forming substrate comprises or is in the form of a gel, for example a stable gel. The non-expanded graphite may be dispersed in the gel. The expanded graphite may be dispersed in the gel.

[0109] Optionally, the gel comprises a gelling agent, for example a gelling agent forming a solid medium. Optionally, the gel comprises an aerosol former such as glycerine. Optionally, the gel comprises nicotine. Optionally, the gel comprises a gelling agent forming a solid medium, glycerine dispersed in the solid medium, and nicotine dispersed in the glycerine.

[0110] The gelling agent may comprise one or more of agar, xanthan gum, and low acyl gellan. Optionally, the gel comprises between 2.5 and 5 weight percent of the gelling agent on a dry weight basis. Optionally, the gel comprises between 1 and 3, or between 1.5 and 2.5, weight percent nicotine on a dry weight basis. Optionally, the gel comprises between 35 and 95, preferably between 50 and 95, more preferably between 70 and 95, weight percent aerosol former such as glycerine on a dry weight basis. Optionally, the gel comprises less than 22 weight percent water. Optionally, the gel comprises an acid such as a carboxylic acid, for example levulinic acid. Optionally, the gel comprises divalent cations such as calcium ions.

[0111] There is also provided an aerosol-generating article comprising an aerosol-forming substrate. The aerosol-forming substrate may be an aerosol-forming substrate according to the first aspect. Thus, according to a second aspect of this disclosure, there is provided an aerosolgenerating article comprising an aerosol-forming substrate according to the first aspect.

[0112] Optionally, the article is in the form of a rod. Optionally, the article comprises a plurality of components, including the aerosol-forming substrate, assembled within a wrapper or casing.

[0113] Optionally, the aerosol-generating article comprises a front plug. Optionally, the aerosolgenerating 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 ventilation holes. Optionally, the aerosol-generating article comprises a mouth plug filter. Optionally, the aerosolgenerating article comprises wrapper, for example a paper wrapper.

[0114] Optionally, the front plug is arranged a most upstream end of the article. Optionally, the aerosol-forming substrate is arranged downstream of the front plug. Optionally, the first hollow tube is arranged downstream of the aerosol-forming substrate. Optionally, the second hollow tube is arranged downstream of the first hollow tube. Optionally, the mouth plug filter is arranged downstream of one or both of the first hollow tube and the second hollow tube. Optionally, the mouth plug filter is arranged at a most downstream end of the article. Optionally, the most downstream end of the article, which may be referred to as a mouth end of the article, may be configured for insertion into a mouth of a user. A user may be able to inhale on, for example directly on, the mouth end of the article.

[0115] 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 circumscribed by a wrapper, for example a paper wrapper.

[0116] One or more of the front plug, the aerosol-forming substrate, the first hollow tube, the second hollow tube, and the mouth plug filter may be substantially cylindrical, for example right cylindrical, in shape.

[0117] There is also provided an aerosol-generating system comprising an aerosol-generating article. The aerosol- generating article may be an aerosol- generating article according to the second aspect.

[0118] Thus, according to a third aspect of this disclosure, there is provided an aerosol-generating system comprising an aerosol-generating device and an aerosol-generating article. The aerosolgenerating article is an aerosol-generating article according to the second aspect.

[0119] Optionally, the device comprises an inductor configured to inductively heat the article, for example one or both of the non-expanded graphite and the expanded graphite of the substrate of the article, during use.

[0120] Optionally, the device comprises an electrically resistive heating element configured to heat the article, for example the substrate of the article, during use. There is also provided a method of forming an aerosol-forming substrate. The aerosolforming substrate may be an aerosol-forming substrate according to the first aspect. The aerosolforming substrate may be an aerosol-forming substrate of the first set of particularly preferred embodiments described earlier. The method may comprise forming a slurry. The method may comprise casting the slurry. The method may comprise drying the slurry. The method may comprise casting then drying the slurry. The method may comprise casting then drying the slurry to form the aerosol-forming substrate ora precursor for forming into the aerosol-forming substrate.

[0121] Thus, according to a fourth aspect of this disclosure, there is provided a method of forming an aerosol-forming substrate according to the first aspect. The method comprises forming a slurry. The method comprises casting and drying the slurry to form the aerosol-forming substrate or a precursor for forming into the aerosol-forming substrate.

[0122] The aerosol-forming substrate may be an aerosol-forming substrate of the first set of particularly preferred embodiments described earlier.

[0123] The slurry may comprise non-expanded graphite. The slurry may comprise expanded graphite.

[0124] Optionally, the method comprises forming a slurry comprising any one or more of: water, tobacco, acid, nicotine, aerosol former, fibres, binder, hydroxypropylmethyl cellulose, one or more cellulose based strengthening agents, carboxymethyl cellulose, non-expanded graphite optionally in the form of non-expanded graphite particles, and expanded graphite optionally in the form of expanded graphite particles.

[0125] Optionally, the slurry comprises water. Optionally, the slurry comprises between 20 and 90, 30 and 90, 40 and 90, 40 and 85, 50 and 80, 60 and 80, or 60 and 75 weight percent water.

[0126] Optionally, the slurry comprises, on a dry weight basis, between 0.5 X and 1.5 X weight percent non-expanded graphite, for example around X weight percent expanded graphite. Optionally, the slurry comprises, on a dry weight basis, between 0.5 Y and 1.5 Y weight percent expanded graphite, for example around Y weight percent expanded graphite.

[0127] Optionally, forming the slurry comprises forming a first mixture. The first mixture may comprise aerosol former. The first mixture may comprise fibres. The first mixture may comprise water. The first mixture may comprise acid. The first mixture may comprise nicotine.

[0128] Forming the slurring may comprise forming a second mixture. The second mixture may comprise the non-expanded graphite particles. The second mixture may comprise the expanded graphite particles. The second mixture may comprise binder.

[0129] Forming the slurry may comprise adding the second mixture to the first mixture to form a combined mixture.

[0130] Thus, forming the slurry may comprise forming the first mixture; forming the second mixture; and adding the second mixture to the first mixture to form a combined mixture. The combined mixture may subsequently be formed into the slurry, for example by mixing the combined mixture. Optionally, casting the slurry comprises casting the slurry onto a flat support, for example a steel flat support.

[0131] Optionally, after casting the slurry and before drying the slurry, the method comprises setting a thickness of the slurry, for example setting a thickness of the slurry to between 100 and 1200, 200 and 1000, 300 and 900, 500 and 700 microns, for example around 600 microns.

[0132] Optionally, drying the slurry comprises providing a flow of a gas such as air over or past the slurry. Optionally, the flow of gas is heated. Optionally, the flow of gas is heated to a temperature of between 50 and 200, 100 and 160, or 120 and 140 degrees Celsius. Optionally, the flow of gas is provided for between 1 and 10 or 2 and 5 minutes. Optionally, drying the slurry comprises drying the slurry until the slurry has a moisture content of between 1 and 20, 2 and 15, 2 and 10, or 3 and 7 weight percent.

[0133] Optionally, drying the slurry forms the precursor for forming into the aerosol-forming substrate, the precursor being a sheet of aerosol-forming material. Optionally, the method comprises cutting the sheet of aerosol-forming material.

[0134] As would be understood by the skilled person having read this disclosure, the features described herein in relation to one aspect may be applicable to any other aspect. For example, features 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.

[0135] 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 smoking article.

[0136] As used herein, the term “nicotine” may refer to nicotine and nicotine derivatives such as free-base nicotine, nicotine salts and the like.

[0137] As used herein, the term “non-expanded graphite” may refer to natural graphite or synthetic graphite. The non-expanded graphite may have carbon layers without any elements or compounds intercalated into spaces between the carbon layers.

[0138] Suitable non-expanded graphite particles for use as described herein are commercially available. For example, suitable non-expanded graphite particles include the FP 99,5 L (>99.5% purity) natural graphite particles from Graphit Kropfmuhl GmbH, AMG Graphite GK. These particles typically have a carbon content of 99.7%, and, measured using laser diffraction with a Sympatec HELOS laser diffraction sensor, a volume D10 particle size of 7 microns, a volume D50 particle size of 21 microns and a volume D90 particle size of 55 microns. As used herein, the term “expanded graphite” may refer to a modified graphite material, or a material having a graphite-like structure. Expanded graphite may have carbon layers (similar to graphite, for example) with average, for example mean, spacing between the carbon layers greater, for example at least 2, 5 or 10 times greater, than the average, for example mean, spacing found between carbon layers in the non-expanded graphite. Expanded graphite may have carbon layers (similar to graphite, for example) with average, for example mean, spacing between the carbon layers greater, for example at least 2, 5 or 10 times greater, than the average, for example mean, spacing found between carbon layers in natural graphite. In some circumstances, nonexpanded graphite can be heated to form expanded graphite. Expanded graphite may have carbon layers with elements or compounds intercalated into spaces between the carbon layers.

[0139] Suitable expanded graphite particles for use as described herein are commercially available. For example, suitable expanded graphite particles include the SC 20 OS (>99% purity) expanded graphite particles from Graphit Kropfmuhl GmbH, AMG Graphite GK. These particles typically have a carbon content of 99.1 %, and, measured using laser diffraction with a Sympatec HELOS laser diffraction sensor, a volume D10 particle size of 6.5 microns, a volume D50 particle size of 20 microns and a volume D90 particle size of 56 microns.

[0140] As used herein, the term “particle size” may refer to a single dimension and may be used to characterise the size of a given particle. The dimension may be the diameter of a spherical particle occupying the same volume as the given particle at the same density as the given particle. All particle sizes and particle size distributions herein can be obtained using a standard laser diffraction technique. Particle sizes and particle size distributions as stated herein may be obtained using a commercially available sensor, for example a Sympatec HELOS laser diffraction sensor.

[0141] As used herein, where not otherwise specified, the term “density” may be used to refer to true density. Thus, where not otherwise specified, the density of a powder or a plurality of particles may refer to the true density of the powder or plurality of particles (rather than a bulk density of the powder or plurality of particles, which can vary greatly depending on how the powder or plurality of particles are handled). The measurement of true density can be done using a number of standard methods, these methods often being based on Archimedes’ principle. The most widely used method, when used to measure the true density of a powder, entails the powder being placed inside a container (a pycnometer) of known volume, and weighed. The pycnometer is then filled with a fluid of known density, in which the powder is not soluble. The volume of the powder is determined by the difference between the volume as shown by the pycnometer, and the volume of liquid added (i.e. the volume of air displaced).

[0142] As used herein, the term “aerosol-generating article” may refer to an article able to generate, or release, an aerosol, for example when heated. As used herein, the term “longitudinal” may refer to a direction extending between a downstream or proximal end and an upstream or distal end of a component such as an aerosolforming substrate or aerosol-generating article.

[0143] As used herein, the term “transverse” may refer to a direction perpendicular to the longitudinal direction.

[0144] 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 from the aerosolgenerating article.

[0145] As used herein, the term “gathered sheet” may refer to a sheet, for example of an aerosolforming substrate or aerosol-generating article, that is convoluted, folded, or otherwise compressed or constricted substantially transversely to a longitudinal axis of the aerosol-forming substrate or of the aerosol-generating article.

[0146] As used herein, the term “sheet” may refer to a generally planar, laminar element having a width and a length which are substantially greater than, for example at least 2, 3, 5, 10, 20 or 50 times, its thickness.

[0147] As used herein, the term “strip” may refer to a generally planar, laminar element having one or both of a width substantially greater than its thickness and a length 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.

[0148] As used herein, the term “aerosol former” may refer to any suitable known compound or mixture of compounds that, in use, facilitates formation of an aerosol. The aerosol may be a dense and stable aerosol. The aerosol may be substantially resistant to thermal degradation at the operating temperature of the aerosol-forming substrate or aerosol-generating article.

[0149] 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, in use, an aerosol formed by the substrate or by volatile compounds released from the aerosol-forming substrate passes through and is cooled by the aerosol-cooling element before being inhaled by a user.

[0150] As used herein, the term “rod” may refer to a generally cylindrical, for example right cylindrical, element of substantially circular, oval or elliptical cross-section.

[0151] As used herein, the term “crimped” may refer to a sheet having one or more ridges or corrugations. The ridges or corrugations may be substantially parallel. When present in a component of an aerosol-generating article, the ridges or corrugations may extend in a longitudinal direction with respect to the aerosol-generating article.

[0152] As used herein, the term “stable gel phase” or “stable gel” may refer to gel that substantially maintains its shape and mass when exposed to a variety of environmental conditions. The stable gel may not substantially release (sweat) or absorb water when exposed to a standard temperature and pressure while varying relative humidity from about 10% to about 60%. For example, the stable gel may substantially maintain its shape and mass when exposed to a standard temperature and pressure while varying relative humidity from about 10% to about 60%.

[0153] The invention is defined in the claims. However, below there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein. Ex1 . An aerosol-forming substrate comprising, on a dry weight basis:

[0154] X weight percent non-expanded graphite; and

[0155] Y weight percent expanded graphite, wherein X divided by Y is at least 0.5.

[0156] Ex2. An aerosol-forming substrate according to Example Ex1 , wherein X divided by Y is at least 0.65, 0.8, 1 , 1.2, or 1.4.

[0157] Ex3. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0158] Y is no more than 10, 8, 6, 4 or 2.

[0159] Ex4. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0160] Y is between 0.5 and 10, 0.5 and 8, 0.5 and 6, 0.5 and 4, or 0.5 and 2.

[0161] Ex5. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0162] Y is between 0.65 and 10, 0.65 and 8, 0.65 and 6, 0.65 and 4, or 0.65 and 2.

[0163] Ex6. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0164] Y is between 0.8 and 10, 0.8 and 8, 0.8 and 6, 0.8 and 4, or 0.8 and 2.

[0165] Ex7. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0166] Y is between 1 and 10, 1 and 8, 1 and 6, 1 and 4, or 1 and 2.

[0167] Ex8. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0168] Y is between 1.2 and 10, 1.2 and 8, 1.2 and 6, 1.2 and 4, or 1.2 and 2.

[0169] Ex9. An aerosol-forming substrate according to any preceding Example, wherein X divided by

[0170] Y is between 1.4 and 10, 1.4 and 8, 1.4 and 6, 1.4 and 4, or 1.4 and 2.

[0171] Ex10. An aerosol-forming substrate according to any preceding Example, wherein X is at least 1 , 2, 3, 4, or 5.

[0172] Ex11 . An aerosol-forming substrate according to any preceding Example, wherein X is no more than 30, 20, 15, 12 or 10.

[0173] Ex12. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0174] 1 and 30, 1 and 20, 1 and 15, 1 and 12, or 1 and 10.

[0175] Ex13. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0176] 2 and 30, 2 and 20, 2 and 15, 2 and 12, or 2 and 10. Ex14. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0177] 2 and 30, 2 and 20, 2 and 15, 2 and 12, or 2 and 10.

[0178] Ex15. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0179] 3 and 30, 3 and 20, 3 and 15, 3 and 12, or 3 and 10.

[0180] Ex16. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0181] 4 and 30, 4 and 20, 4 and 15, 4 and 12, or 4 and 10.

[0182] Ex17. An aerosol-forming substrate according to any preceding Example, wherein X is between

[0183] 5 and 30, 5 and 20, 5 and 15, 5 and 12, or 5 and 10.

[0184] Ex18. An aerosol-forming substrate according to any preceding Example, wherein Y is at least 1 , 2, 3, or 4.

[0185] Ex19. An aerosol-forming substrate according to any preceding Example, wherein Y is no more than 20, 15, 10, 8, or 6.

[0186] Ex20. An aerosol-forming substrate according to any preceding Example, wherein Y is between

[0187] 1 and 20, 1 and 15, 1 and 10, 1 and 8, or 1 and 6.

[0188] Ex21. An aerosol-forming substrate according to any preceding Example, wherein Y is between

[0189] 2 and 20, 2 and 15, 2 and 10, 2 and 8, or 2 and 6.

[0190] Ex22. An aerosol-forming substrate according to any preceding Example, wherein Y is between

[0191] 3 and 20, 3 and 15, 3 and 10, 3 and 8, or 3 and 6.

[0192] Ex23. An aerosol-forming substrate according to any preceding Example, wherein Y is between

[0193] 4 and 20, 4 and 15, 4 and 10, 4 and 8, or 4 and 6.

[0194] Ex24. An aerosol-forming substrate according to any preceding Example, wherein:

[0195] X is between 2 and 50 and Y is between 2 and 40; or

[0196] X is between 2 and 30 and Y is between 2 and 20; or

[0197] X is between 2 and 20 and Y is between 2 and 20; or

[0198] X is between 4 and 20 and Y is between 2 and 10; or

[0199] X is between 4 and 15 and Y is between 2 and 8.

[0200] Ex25. An aerosol-forming substrate according to any preceding Example, wherein one or both of: the X weight percent non-expanded graphite comprises or consists of a plurality of nonexpanded graphite particles; and the Y weight percent expanded graphite comprises or consists of a plurality of expanded graphite particles.

[0201] Ex26. An aerosol-forming substrate according to any preceding Example, wherein: the X weight percent non-expanded graphite comprises or consists of a plurality of nonexpanded graphite particles; and the Y weight percent expanded graphite comprises or consists of a plurality of expanded graphite particles.

[0202] Ex27. An aerosol-forming substrate according to Example Ex25 or Ex26, wherein the plurality of non-expanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 100 or 75 microns, preferably wherein the volume D90 diameter is between 10 and 100 microns, or between 35 and 75 microns, for example wherein the volume D90 diameter is around 55 microns.

[0203] Ex28. An aerosol-forming substrate according to Example Ex25 or Ex26, wherein the plurality of expanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 100 or 75 microns, preferably wherein the volume D90 diameter is between 10 and 100 microns, or between 35 and 75 microns, for example wherein the volume D90 diameter is around 55 microns.

[0204] Ex29. An aerosol-generating article comprising an aerosol-forming substrate according to any preceding example.

[0205] Ex30. An aerosol-generating article according to Example Ex29, wherein the aerosol-forming substrate is in the form of a gathered sheet.

[0206] Ex31. An aerosol-generating system comprising an aerosol-generating device and an aerosolgenerating article according to Example Ex29 or Ex30.

[0207] Ex32. An aerosol-generating system according to Example Ex31 , wherein the device comprises an inductor configured to inductively heat the article, for example one or both of the nonexpanded graphite and the expanded graphite of the substrate of the article, during use.

[0208] Ex33. A method of forming an aerosol-forming substrate according to any of Examples Ex1 to Ex28, the method comprising: forming a slurry comprising the non-expanded graphite and the expanded graphite; casting and drying the slurry to form the aerosol-forming substrate or a precursor for forming into the aerosol-forming substrate.

[0209] Examples will now be further described with reference to the figures in which:

[0210] Figure 1 shows a schematic cross-sectional view of a first embodiment of an aerosolgenerating article;

[0211] Figure 2 shows a schematic cross-sectional view of a first embodiment of an aerosolgenerating system comprising a first aerosol-generating device;

[0212] Figure 3 shows a schematic cross-sectional view of a second embodiment of an aerosolgenerating system comprising a second aerosol-generating device;

[0213] Figure 4 shows a schematic cross-sectional view of a second embodiment of an aerosolgenerating article;

[0214] Figure 5 illustrates an example of an aerosol-generating article containing the aerosolforming substrate as described herein; and

[0215] Figure 6 illustrates an example of an aerosol-generating system comprising an aerosolgenerating device and the aerosol-generating article shown in Figure 5.

[0216] Figure 1 shows a schematic cross-sectional view of a first embodiment of an aerosolgenerating article 10. The aerosol-generating article 10 comprises a rod 12 of aerosol-forming substrate, a downstream section 14 downstream of the rod 12, and an upstream section 16 upstream of the rod 12. The aerosol-generating article 10 extends from an upstream or distal end 18 to a downstream or proximal or mouth end 20. The aerosol-generating article has an overall length of about 45 millimetres.

[0217] The downstream section 14 comprises a support element 22 located immediately downstream of the rod 12 of aerosol-forming substrate, the support element 22 being in longitudinal alignment with the rod 12. The upstream end of the support element 22 abuts the downstream end of the rod 12. The downstream section 14 further comprises an aerosol-cooling element 24 located immediately downstream of the support element 22, the aerosol-cooling element 24 being in longitudinal alignment with the rod 12 and the support element 22. The upstream end of the aerosol-cooling element 24 abuts the downstream end of the support element 22. The support element 22 and the aerosol-cooling element 24 together define an intermediate hollow section 50 of the aerosol-generating article 10.

[0218] The support element 22 comprises a first hollow tubular segment 26. The first hollow tubular segment 26 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The first hollow tubular segment 26 defines an internal cavity 28 that extends all the way from an upstream end 30 of the first hollow tubular segment to a downstream end 32 of the first hollow tubular segment 20. The first hollow tubular segment 26 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter of about 1.9 millimetres. Thus, a thickness of a peripheral wall of the first hollow tubular segment 26 is about 2.67 millimetres.

[0219] The aerosol-cooling element 24 comprises a second hollow tubular segment 34. The second hollow tubular segment 34 is provided in the form of a hollow cylindrical tube made of cellulose acetate. The second hollow tubular segment 34 defines an internal cavity 36 that extends all the way from an upstream end 38 of the second hollow tubular segment to a downstream end 40 of the second hollow tubular segment 34. The second hollow tubular segment 34 has a length of about 8 millimetres, an external diameter of about 7.25 millimetres, and an internal diameter of about 3.25 millimetres. Thus, a thickness of a peripheral wall of the second hollow tubular segment 34 is about 2 millimetres.

[0220] The aerosol-generating article 10 comprises a ventilation zone 60 provided at a location about 2 millimetres from the upstream end of the second hollow tubular segment 34. The ventilation zone 60 comprises a circumferential row of perforations through a paper wrapper 70.

[0221] The downstream section 14 further comprises a mouthpiece element 42 positioned immediately downstream of the aerosol-cooling element 24. An upstream end of the mouthpiece element 42 abuts the downstream end 40 of the aerosol-cooling element 24. The mouthpiece element 42 is provided in the form of a cylindrical plug of low-density cellulose acetate. The mouthpiece element 42 has a length of about 12 millimetres and an external diameter of about 7.25 millimetres.

[0222] The upstream section 16 comprises an upstream element 46 located immediately upstream of the rod 12 of aerosol-forming substrate, the upstream element 46 being in longitudinal alignment with the rod 12. The downstream end of the upstream element 46 abuts the upstream end of the rod 12. The upstream element 46 is provided in the form of a cylindrical plug of cellulose acetate. The upstream element 46 has a length of about 5 millimetres.

[0223] The rod 12 of aerosol-forming substrate has an external diameter of about 7.25 millimetres and a length of about 12 millimetres.

[0224] The upstream element 46, rod 12 of aerosol-forming substrate, support element 22, aerosol-cooling element 24, and mouthpiece element 42 are circumscribed by the paper wrapper 70.

[0225] The rod 12 of aerosol-forming substrate comprises an aerosol-forming material, nonexpanded graphite particles 44, and expanded graphite particles 45. The aerosol-forming material comprises a reconstituted and gathered sheet comprising tobacco material, glycerine, cellulose fibres and guar gum.

[0226] The non-expanded graphite particles 44 are FP 99,5 L (>99.5% purity) natural graphite particles from Graphit Kropfmuhl GmbH, AMG Graphite GK, although any suitable non-expanded graphite could be used. These non-expanded graphite particles are natural graphite particles with a carbon content of 99.7%, an ash content of 0.3% and, measured using laser diffraction with a Sympatec HELOS laser diffraction sensor, a volume D10 particle size of 7 microns, a volume D50 particle size of 21 microns and a volume D90 particle size of 55 microns.

[0227] The expanded graphite particles 45 are SC 20 OS (>99% purity) expanded graphite particles from Graphit Kropfmuhl GmbH, AMG Graphite GK, though any suitable expanded graphite could be used. These expanded graphite particles have a carbon content of 99.1 %, an ash content of 0.9% and, measured using laser diffraction with a Sympatec HELOS laser diffraction sensor, a volume D10 particle size of 6.5 microns, a volume D50 particle size of 20 microns and a volume D90 particle size of 56 microns.

[0228] Each of the particles 44, 45 is substantially spherical in shape.

[0229] The aerosol-forming substrate has the following composition, on a dry weight basis:

[0230] • 64 weight percent tobacco;

[0231] • 18 weight percent glycerine;

[0232] • 7.4 weight percent non-expanded graphite;

[0233] • 4.6 weight percent expanded graphite;

[0234] • 4 weight percent fibres, specifically cellulose fibres; and

[0235] • 2 weight percent binder, specifically guar gum. However, as the skilled person would understand after reading this disclosure, other compositions, including compositions with much greater levels of non-expanded graphite and expanded graphite, are also possible.

[0236] The rod 12 of aerosol-forming substrate is formed by a process including the following steps:

[0237] • pre-mixing the binder, guar gum, with an aerosol-former, glycerine, to form a first pre-mixture;

[0238] • pre-mixing cellulose fibres, finely shredded tobacco material and a powder consisting of the particles 44, 45 to form a second pre-mixture;

[0239] • mixing the first and second pre-mixtures with water to form a slurry;

[0240] • homogenising the slurry using a high-shear mixer;

[0241] • casting the slurry onto a conveyor belt;

[0242] • controlling a thickness of the slurry and drying the slurry to form a large sheet of aerosolforming substrate;

[0243] • crimping the large sheet using crimping rollers to form a large, crimped sheet; and

[0244] • gathering and cutting the large, crimped sheet of aerosol-forming substrate to form the rod 12 of aerosol-forming substrate.

[0245] Advantageously, the presence of the graphite, particularly the expanded graphite, means the resulting aerosol-forming substrate has a high thermal conductivity, and the presence of the nonexpanded graphite makes the substrate easily manufacturable with existing machinery because the non-expanded graphite counteracts the effect that the expanded graphite has of increasing a viscosity of the slurry.

[0246] After forming the rod 12 of aerosol-forming substrate, the aerosol-generating article 10 is assembled by positioning the various components of the article 10 and wrapping the components in the wrapper 70.

[0247] Figure 2 shows a schematic cross-sectional view of a first embodiment of an aerosolgenerating system 100. The system 100 comprises an aerosol-generating device 102 and the aerosol-generating article 10 of Figure 1.

[0248] The aerosol-generating device 102 comprises a battery 104, a controller 106, a heating blade 108 coupled to the battery, and a puff-detection mechanism (not shown). The controller 106 is coupled to the battery 104, the heating blade 108 and the puff-detection mechanism.

[0249] The aerosol-generating device 102 further comprises a housing 110 defining a substantially cylindrical cavity for receiving a portion of the article 10. The heating blade 108 is positioned centrally within the cavity and extends longitudinally from a base of the cavity.

[0250] In this embodiment, the heating blade 108 comprises a substrate and an electrically resistive track located on the substrate. The battery 104 is coupled to the heating blade 108 so as to be able to pass a current through the electrically resistive track and heat the electrically resistive track and heating blade 108 to an operational temperature of around 400 degrees Celsius. In use, a user inserts the article 10 into the cavity, causing the heating blade 108 to penetrate the upstream element 46 and rod 12 of aerosol-forming substrate of the article 10. Figure 2 shows the article 10 inserted into the cavity of the device 102.

[0251] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 102, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0252] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to pass a current through the electrically resistive track and heat up the heating blade 108. This heats up the rod 12 of aerosol-forming substrate, which is in contact with the heating blade 108.

[0253] The particles 44, 45 have a significantly higher thermal conductivity than the surrounding aerosol-forming material. As such, these particles 44, 45 may act as local hot-spots and provide a more even temperature throughout the aerosol-forming substrate, particularly in a radial direction from the heating blade 108 where, with prior art substrates, there would be a significant temperature gradient. This may result in a greater proportion of the aerosol-forming substrate reaching a sufficiently high temperature to release volatile compounds, and thus a higher usage efficiency of the aerosol-forming substrate.

[0254] Heating of the aerosol-forming substrate cause the aerosol-forming substrate to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0255] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puffdetection mechanism. The puff-detection mechanism sends a signal to the controller 106 accordingly. The controller 106 then controls the battery 104 so as to reduce the current being passed through the electrically resistive track to zero.

[0256] After a number of puffs on the article 10, the user may choose to replace the article 10 with a fresh article.

[0257] Figure 3 shows a schematic cross-sectional view of a second embodiment of an aerosolgenerating system 200. The system 200 comprises an aerosol-generating device 202 and the aerosol-generating article 10 of Figure 1. 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.

[0258] The aerosol-generating device 202 further comprises a housing 210 defining a substantially cylindrical cavity for receiving a portion of the article 10. The inductor coil 208 spirals around the cavity.

[0259] The battery 204 is coupled to the inductor coil 208 so as to be able to pass an alternating current through the inductor coil 208.

[0260] In use, a user inserts the article 11 into the cavity. Figure 3 shows the article 10 inserted into the cavity of the device 202.

[0261] Then, the user puffs on the downstream end of the article 10. This causes air to flow through an air inlet (not shown) of the device 202, then through the article 10, from the upstream end 18 to the downstream end 20, and into the mouth of the user.

[0262] The user puffing on the article 10 causes air to flow through the air inlet of the device. The puff-detection mechanism detects that the air flow rate through the air inlet has increased to greater than a non-zero threshold flow rate. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to pass an alternating current through the inductor coil 208. This causes the inductor coil 208 to generate a fluctuating electromagnetic field. The rod 13 of aerosol-forming substrate is located within this fluctuating electromagnetic field and the non-expanded graphite and the expanded graphite, the materials of the particles 44, 45, are susceptor materials. Thus, the fluctuating electromagnetic field causes eddy currents in the particles 44, 45. This causes the particles 44, 45 to heat up, thereby also heating nearby aerosol-forming material.

[0263] Heating of the aerosol-forming material cause the aerosol-forming material to release volatile compounds. These compounds are entrained by the air flowing from the upstream end 18 of the article 10 towards the downstream end 20 of the article 10. The compounds cool and condense to form an aerosol as they pass through the internal cavities 28, 36 of the support element and the aerosol-cooling element. The aerosol then passes through the mouthpiece element 42, which may filter out unwanted particles entrained in the air flow, and into the mouth of the user.

[0264] When the user stops inhaling on the article 10, the air flow rate through the air inlet of the device decreases to less than the non-zero threshold flow rate. This is detected by the puffdetection mechanism. The puff-detection mechanism sends a signal to the controller 206 accordingly. The controller 206 then controls the battery 204 so as to reduce the current being passed through the electrically resistive track to zero.

[0265] After a number of puffs on the article 10, the user may choose to replace the article 10 with a fresh article. The aerosol-forming substrate of the article 10 shown in Figures 1 , 2 and 3 has been found by the inventors to have an improved performance compared with alternative substrates during experiments. In this context, performance refers to nicotine and glycerine yield from an aerosolgenerating article comprising the aerosol-forming substrate. This improvement is shown by the data in Table 2 below. To collect the data in Table 2, three different plugs of aerosol-forming substrates were made using standard, existing machinery, including a development crimper in this case, and then tested under the Health Canada Intense (HCI) smoking regime for 12 puffs using FTIR spectroscopy. However, as the skilled person would understand, the plugs of aerosolforming substrates could have been made using other techniques, for example by hand, and the data could have been collected using other tests.

[0266] Table 2: generating article 510. This second embodiment is identical to the first embodiment of Figure 1 except that the rod 12 of aerosol-forming substrate has been replaced by an alternative rod 512 of aerosol-forming substrate. Identical reference numerals have been used for identical components in the embodiments of Figures 1 and 3.

[0267] The rod 512 of aerosol-forming substrate of the second embodiment of Figure 4 is identical to the rod 12 of aerosol-forming substrate of the first embodiment of Figure 1 except that the rod 512 of aerosol-forming substrate of the third embodiment of Figure 4 additionally includes an elongate susceptor element 580.

[0268] The susceptor element 580 is arranged substantially longitudinally within the rod 512 of aerosol-forming substrate so as to be approximately parallel with a longitudinal axis of the rod 512 of aerosol-forming substrate. As shown in the drawing of Figure 4, the susceptor element 580 is positioned in a radially central position within the rod and extends along the longitudinal axis of the rod 12.

[0269] The susceptor element 580 extends all the way from an upstream end to a downstream end of the rod 512 of aerosol-forming substrate. As such, the susceptor element 580 has substantially the same length as the rod 512 of aerosol-forming substrate.

[0270] In the embodiment of Figure 4, the susceptor element 580 is provided in the form of a strip of a ferromagnetic steel and has a length of about 12 millimetres, a thickness of about 60 micrometres, and a width of about 4 millimetres.

[0271] The aerosol-generating article 510 of Figure 4 may be used with the aerosol-generating device 202 of Figure 3 in the same way as the aerosol-generating article 10 of Figure 1 . Notably, the inclusion of the susceptor element 580 means that the article 510 may be inductively heated. In the example shown in Figure 4, both the particles 44, 45 and the susceptor element 580 are inductively heatable. So, both the susceptor element 580 and the particles 44, 45 contribute to heating during use.

[0272] Figure 5 illustrates an example of an aerosol-generating article 1000 containing a tobacco- free aerosol-forming substrate.

[0273] The aerosol-generating article 1000 includes four elements: the aerosol-forming substrate 1020, a hollow cellulose acetate tube 1030, a spacer element 1040, and a mouthpiece filter 1050. The four elements 1020, 1030, 1040, 1050 are arranged sequentially and in a coaxial alignment. The four elements 1020, 1030, 1040, 1050 are assembled by a cigarette paper 1060 to form the aerosol-generating article 1000.

[0274] The aerosol-generating article 1000 has a mouth-end 1012 and a distal end 1013. A user may insert the mouth-end 1012 into his or her mouth during use. The distal end 1013 is located at the opposite end of the aerosol-generating article 1000 to the mouth end 1012. The example of an aerosol-generating article 1000 illustrated in Figure 5 is particularly suitable for use with an electrically operated aerosol-generating device comprising a heater for heating the aerosolgenerating substrate.

[0275] When assembled, the aerosol-generating article 1000 is about 45 millimetres in length and has an outer diameter of about 7.2 millimetres and an inner diameter of about 6.9 millimetres.

[0276] The aerosol-forming substrate 1020 is provided in the form of a plug made by crimping a sheet of aerosol-forming substrate. A number of example compositions of aerosol-forming substrate 1020 are shown in the table below. The sheet is crimped, gathered, and wrapped in a filter paper (not shown) to form the plug.

[0277] An aerosol-generating article 1000 as illustrated in Figure 5 is designed to engage with an aerosol-generating device in order to be consumed. Such an aerosol-generating device includes means for heating the aerosol-forming substrate 1020 to a sufficient temperature to form an aerosol. Typically, the aerosol-generating device may comprise a heating element that surrounds the aerosol-generating article 1000 adjacent to the aerosol-forming substrate 1020, or a heating element that is inserted into the aerosol-forming substrate 1020.

[0278] Once engaged with an aerosol-generating device, a user draws on the mouth-end 1012 of the smoking article 1000 and the aerosol-forming substrate 1020 is heated to a temperature of about 375 degrees Celsius. At this temperature, volatile compounds, including nicotine and glycerine in Examples A to E discussed below, are evolved from the aerosol-forming substrate 1020. These compounds condense to form an aerosol. The aerosol is drawn through the filter 1050 and into the user’s mouth.

[0279] Figure 6 illustrates a portion of an electrically operated aerosol-generating system 2000. The aerosol-generating system utilises a heating blade 2100 to heat an aerosol-generating substrate 1020 of an aerosol-generating article 1000. In the example of Figure 6, the heating blade 2100 is mounted within an aerosol article receiving chamber of an electrically operated aerosol-generating device 2010. The aerosol-generating device 2010 defines a plurality of air holes 2050 for allowing air to flow to the aerosol-generating article 1000. Air flow is indicated by the arrows in Figure 6. The aerosol-generating device 2010 comprises a power supply and electronics, which are not illustrated in Figure 6. The aerosol-generating article 1000 of Figure 6 is as described in relation to Figure 5.

[0280] Example compositions of the aerosol-forming substrate shown in Figures 5 and 6 (Examples A, B, C, D and E) are shown Table 3 below. All % by weight values are measured on a dry weight basis.

[0281] Table 3:

[0282] In all of Examples A, B, C, D, and E, the substrate comprises, on a dry weight basis, 7.4 weight percent non-expanded graphite and 4.6 weight percent expanded graphite. This non- expanded graphite and expanded graphite could be present in the form of particles, as for the substrates shown and described with reference to Figures 1 to 4, or in any other suitable manner.

[0283] Advantageously, the presence of the non-expanded graphite and expanded graphite, particularly the expanded graphite, means the resulting aerosol-forming substrate has a high thermal conductivity. And the presence of the non-expanded graphite makes the substrate easily manufacturable with existing machinery because the non-expanded graphite counteracts the effect that the expanded graphite has of increasing a viscosity of the slurry.

[0284] The aerosol-forming substrates of Examples A, B, C, D and E are prepared by:

[0285] (1) mixing the components together with water using heat and agitation to form a slurry;

[0286] (2) casting a layer of the slurry onto a plane surface to form a film having a thickness of about 210 micrometres;

[0287] (3) leaving the film on the plane surface to solidify; and

[0288] (3) drying the film by heating the film to about 140 degrees Celsius for about 8 minutes to form a solid aerosol-forming substrate.

[0289] For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 10% of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic(s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

CLAIMS1. An aerosol-forming substrate comprising, on a dry weight basis:X weight percent non-expanded graphite; andY weight percent expanded graphite, wherein X divided by Y is at least 0.5.

2. An aerosol-forming substrate according to any preceding claim, wherein X divided by Y is between 0.65 and 8.

3. An aerosol-forming substrate according to any preceding claim, wherein X divided by Y is between 0.8 and 4.

4. An aerosol-forming substrate according to any preceding claim, wherein X divided by Y is between 1.0 and 2.

5. An aerosol-forming substrate according to any preceding claim, wherein X is at least 4.

6. An aerosol-forming substrate according to claim 5, wherein X is between 4 and 12.

7. An aerosol-forming substrate according to any preceding claim, wherein Y is at least 3.

8. An aerosol-forming substrate according to claim 7, wherein Y is between 3 and 10.

9. An aerosol-forming substrate according to any preceding claim, wherein: the X weight percent non-expanded graphite comprises or consists of a plurality of non-expanded graphite particles; and the Y weight percent expanded graphite comprises or consists of a plurality of expanded graphite particles.

10. An aerosol-forming substrate according to claim 9, wherein the plurality of non-expanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 75 microns.

11. An aerosol-forming substrate according to claim 9 or 10, wherein the plurality of expanded graphite particles has a particle size distribution with a volume D90 diameter no greater than 75 microns.

12. An aerosol-generating article comprising an aerosol-forming substrate according to any preceding claim.

13. An aerosol-generating article according to claim 12, wherein the aerosol-forming substrate is in the form of a crimped and gathered sheet.

14. An aerosol-generating system comprising an aerosol-generating device and an aerosolgenerating article according to claim 12 or 13.

15. A method of forming an aerosol-forming substrate according to any of claims 1 to 11, the method comprising: forming a slurry comprising the non-expanded graphite and the expanded graphite; casting and drying the slurry to form the aerosol-forming substrate or a precursor for forming into the aerosol-forming substrate.

Images