AEROSOL GENERATING SUBSTRATE COMPRISING AN AEROSOL GENERATING FILM

Abstract

An aerosol-generating article (10)(70) comprising an aerosol-generating substrate rod (14), wherein the aerosol-generating substrate rod (14) comprises: an aerosol-generating film (24)(76) comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulose-based film-forming agent, wherein the aerosol-generating film (24)(76) is configured such that the exposed surface area of ​​the aerosol-generating film within the aerosol-generating substrate (14) is at least 5 square millimeters per mg of the aerosol-generating film (24)(76). The aerosol-generating film (24)(76) is essentially tobacco-free.

Description

AEROSOL GENERATING SUBSTRATE COMPRISING AN AEROSOL GENERATING FILM The present invention relates to an aerosol generating substrate formed with an aerosol generating film, and to an aerosol generating article incorporating such an aerosol generating substrate. Aerosol-generating articles in which an aerosol-generating substrate, such as a nicotine-containing or tobacco-containing substrate, is heated rather than burned, are known in the art. Typically, in such heated smoking articles, an aerosol is generated by the transfer of heat from a heat source to a physically separate aerosol-generating material or substrate, which may be located in contact with, within, around, or downstream of the heat source. During use of the aerosol-generating article, volatile compounds are released from the aerosol-generating substrate by the heat transfer from the heat source and are carried in the air drawn through the article. As the released compounds cool, they condense to form an aerosol. A number of prior art documents describe aerosol-generating devices for the consumption of aerosol-generating articles. Such devices include, for example, electrically heated aerosol-generating devices in which an aerosol is generated by the transfer of heat from one or more electrical heating elements of the aerosol-generating device to the aerosol-generating substrate of a heated aerosol-generating article. In the past, substrates for heated aerosol-generating articles have often been produced using randomly oriented fragments, strands, or strips of tobacco material. Alternatively, bars for heated aerosol-generating articles formed from crinkled sheets of tobacco material have been described, by way of example, in International Patent Application WO-A-2012 / 164009. International patent application WO-A-2011 / 101164 describes alternative bars for heated aerosol-generating articles formed from strands of homogenized tobacco material, which can be formed by casting, rolling, calendering, or extruding a mixture comprising particulate tobacco and at least one aerosol former to form a sheet of homogenized tobacco material. In alternative embodiments, the bars of WO-A-2011 / 101164 can be formed from strands of homogenized tobacco material obtained by extruding a mixture comprising particulate tobacco and at least one aerosol former to form continuous lengths of homogenized tobacco material. Alternative forms of nicotine-comprising substrates have also been described. For example, liquid nicotine compositions, often referred to as e-liquids, have been proposed. These liquid compositions can be heated, for instance, by means of an electrically resistive filament wound around an aerosol-generating device. Substrates of this type may require particular care in the manufacture of the containers holding the liquid composition to prevent unwanted leakage. To address this problem and simplify the overall manufacturing process, it has also been proposed to provide a gel composition comprising nicotine that generates a nicotine-containing aerosol when heated. As an example, WO-A-2018 / 019543 describes a thermoreversible gel composition, i.e., a gel that will become fluid when heated to a melting temperature and solidify again into a gel at a freezing temperature. The gel is provided within a cartridge housing, and the cartridge can be discarded and replaced when the gel has been consumed. It would be advantageous to provide an aerosol-generating article that incorporates a novel aerosol-generating film with improved stability. Furthermore, it would be advantageous to provide such an aerosol-generating article with an aerosol-generating film that has a high aerosol former content, enabling its successful use as an aerosol-generating substrate. It would be particularly advantageous to provide such an aerosol-generating article that is easier to dispose of after use or has a reduced environmental impact. It would also be advantageous to provide such an aerosol-generating article that optimizes aerosol generation from the aerosol-generating substrate during use. The present invention relates to an aerosol generating article comprising a rod and an aerosol generating substrate comprising an aerosol generating film. The aerosol generating film may comprise at least approximately 25 percent by weight of a polyhydric alcohol. The aerosol generating film may comprise at least approximately 10 percent by weight of a cellulose-based film-forming agent. The aerosol generating film may be configured such that the exposed surface area of ​​the aerosol generating film within the aerosol generating substrate is at least approximately 5 square millimeters per milligram of aerosol generating film. Alternatively or additionally, the aerosol generating film may be configured such that the bulk density of the aerosol generating film is at least approximately 100 mg per cubic centimeter of aerosol generating substrate. According to a first aspect of the present invention, an aerosol-generating article is provided comprising an aerosol-generating substrate rod, wherein the aerosol-generating substrate rod comprises: an aerosol-generating film comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulose-based film-forming agent. The aerosol-generating film is configured such that the exposed surface area of ​​the aerosol-generating film within the aerosol-generating substrate rod is at least approximately 5 square millimeters per milligram of aerosol-generating film. The aerosol-generating film is preferably essentially tobacco-free. According to a second aspect of the present invention, an aerosol-generating article is provided comprising an aerosol-generating substrate rod, wherein the aerosol-generating substrate rod comprises: an aerosol-generating film comprising at least approximately 25 percent by weight of a polyhydric alcohol and at least approximately 10 percent by weight of a cellulose-based film-forming agent. The aerosol-generating film is configured such that the bulk density of the aerosol-generating film is at least approximately 100 mg per cubic centimeter of the aerosol-generating substrate rod. The aerosol-generating film is preferably essentially tobacco-free. According to a third aspect of the present invention, a rod is provided for use as an aerosol-generating substrate in an aerosol-generating article, the rod comprising: an aerosol-generating film comprising at least approximately 25 percent by weight of an alcohol and at least approximately 10 percent by weight of a cellulose film-forming agent, wherein the aerosol-generating film is configured such that the exposed surface area of ​​the aerosol-generating film within the aerosol-generating substrate rod is at least approximately 5 square millimeters per milligram of aerosol-generating film. The aerosol-generating film is preferably essentially tobacco-free. According to a fourth aspect of the present invention, a rod is provided for use as an aerosol-generating substrate in an aerosol-generating article, the rod comprising: an aerosol-generating film comprising at least approximately 25 percent by weight of an alcohol and at least approximately 10 percent by weight of a cellulose-based film-forming agent, wherein the aerosol-generating film is configured such that the apparent density of the aerosol-generating film is at least approximately 100 mg per cubic centimeter of the aerosol-generating substrate rod. The aerosol-generating film is preferably essentially tobacco-free. Pursuant to a fifth aspect of the present invention, an aerosol generating system is provided comprising an aerosol generating article and an electrically operated aerosol generating device comprising a heating element configured to heat an aerosol generating substrate of the aerosol generating article, wherein: the aerosol generating article comprises an aerosol generating substrate bar according to the present invention, as defined above in relation to the third and fourth aspects of the invention. The heating element of the aerosol generating device is a heating sheet or a heating pin configured to be inserted into the aerosol generating substrate bar in order to heat the aerosol generating film. Any reference in this description to features of the aerosol generating article or aerosol generating substrate according to the present invention should be assumed to apply to all aspects of the present invention, unless otherwise stated. As used in the present description, the term “aerosol generating article” refers to an aerosol generating article for producing an aerosol comprising an aerosol generating substrate that is intended to be heated rather than burned in order to release volatile compounds that can form an aerosol. As used herein, the term “aerosol-generating substrate” refers to a substrate capable of releasing volatile compounds upon heating, which can form an aerosol. The aerosol generated from the aerosol-forming substrates of the aerosol-generating articles described herein may be visible or invisible and may include vapors (e.g., fine particles of substances, which are in a gaseous state, that are normally liquid or solid at room temperature) as well as gases and liquid droplets of condensed vapors. Substrates for heated aerosol-generating articles typically comprise an “aerosol former,” that is, a compound or mixture of compounds that, during use, facilitates aerosol formation and is preferably essentially resistant to thermal degradation at the operating temperature of the aerosol-generating article. Examples of suitable aerosol formers include: polyhydric alcohols, such as propylene glycol, 1,3-butanediol, and glycerin; esters of polyhydric alcohols, such as glycerol monoacetate, dicetate, or triacetate; and aliphatic esters of monocarboxylic, dicarboxylic, or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. The polyhydric alcohol in the aerosol-generating film of the aerosol-generating articles of the invention is also an aerosol former within the above-expressed sense. As used in the present description, the term “bar” refers to a generally cylindrical element with an essentially polygonal cross-section and preferably with a circular, oval, or elliptical cross-section. As used in the present description, the term “film” describes a solid sheet element that has a thickness that is less than its width or length. The film can be self-supporting. In other words, a film can have mechanical and cohesive properties such that the film, even if obtained by melting a film-forming formulation onto a support surface, can be separated from the support surface. Alternatively, the film can be placed on a support or sandwiched between other materials. This can improve the film's mechanical stability. The “thickness” of the aerosol generating film of the aerosol generating articles according to the invention corresponds to the minimum distance measured between the essentially parallel opposite surfaces of a film. The thickness of the aerosol-generating film can essentially correspond to the thickness at which a corresponding film-forming composition is melted or extruded, since the melted or extruded film-forming composition does not essentially shrink during drying, despite the loss of water. The “weight” of the aerosol-generating film of aerosol-generating articles according to the invention will generally correspond to the weight of the components of the film composition less the weight of the water evaporated during the drying stage. If a film is self-supporting, the film can be weighed on its own. If a film is placed on a support, the film and the support can be weighed, and the weight of the support, measured before the film is applied, is subtracted from the combined weight of the film and the support. Unless otherwise stated, the weight percentages of the aerosol generating film components mentioned in this description are based on the total weight of the aerosol generating film. As used in this description, the term “longitudinal” refers to the direction corresponding to the main longitudinal axis of the aerosol-generating article, which extends between the upstream and downstream ends of the aerosol-generating article. During use, air is drawn through the aerosol-generating article in the longitudinal direction. The term “transverse” refers to the direction that is perpendicular to the longitudinal axis. Any reference to the “cross-section” of the aerosol-generating article or a component of the aerosol-generating article refers to the cross-section, unless otherwise stated. As used herein, the term “length” refers to the dimension of a component in the longitudinal direction and the term “width” refers to the dimension of a component in the transverse direction. As used in this description, “upstream” and “downstream” describe the relative positions of elements, or portions of elements, of the aerosol-generating article with respect to the direction in which the aerosol is carried through the aerosol-generating article during use. As described above, the present invention provides an aerosol-generating article having a novel aerosol-generating substrate formed with an aerosol-generating film. Upon heating, an aerosol is generated from the aerosol-generating film, released within the aerosol-generating article, and can be inhaled through the article into the consumer's mouth. The aerosol-generating film can be provided in place of, or in addition to, any other aerosol-generating substrate within the aerosol-generating article. In many embodiments of the present invention, the aerosol-generating film can be configured to form a self-supporting rod, and no additional support structures are required within the aerosol-generating substrate. In many cases, the aerosol-generating substrate rod can be formed from the aerosol-generating film using existing apparatus and methods. The aerosol-generating substrate bar incorporating the aerosol-generating film can be easily incorporated into existing aerosol-generating article constructions without the need for significant modification, and the aerosol-generating articles according to the invention can therefore potentially be manufactured at high speed using existing manufacturing apparatus and methods. The composition of the aerosol-generating film can be selected so that most of the film's components evaporate upon heating during use of the aerosol-generating item, leaving minimal residue. This can advantageously provide an aerosol-generating item that is easier to dispose of and has a reduced environmental impact. The properties and composition of the aerosol-generating film can be easily adapted to control the resulting aerosol produced after heating the film. Using the aerosol-generating film also allows for the delivery of a highly consistent aerosol to the consumer. The aerosol generating articles according to the present invention are particularly suitable for use in an aerosol generating system comprising an electrically heated aerosol generating device having an internal heating element for heating the aerosol generating substrate bar, as described in more detail below. For example, the aerosol generating articles according to the invention find particular application in aerosol generating systems comprising an electrically heated aerosol generating device having an internal heating sheet adapted for insertion within the aerosol generating article near the aerosol generating substrate bar. Aerosol generating articles of this type are described in the prior art, for example, in European patent application EP-A-0 822 670. The aerosol-generating films as described herein are particularly suitable for heating from within the aerosol-generating article. When heated by an internal heating element, the aerosol-generating film on the inner surface of the tubular carrier element can contract, which can advantageously bring the aerosol-generating film closer to the surfaces of the heating element, thereby optimizing the heating of the aerosol-generating film. As used in the present description, the term “aerosol generating device” refers to a device comprising a heating element that interacts with the aerosol generating substrate of the aerosol generating article to generate an aerosol. Alternatively, the aerosol-generating article according to the invention may comprise a combustible coal heat source for heating the aerosol-generating substrate during use. Aerosol-generating articles of this type are described in the prior art, for example, in International Patent Application WO-A-2009 / 022232. According to the invention, the aerosol-generating film is configured to maximize its total exposed surface area within the aerosol-generating substrate bar. By maximizing the exposed surface area, the aerosol release efficiency of a given volume of aerosol-generating substrate can be improved. The "exposed" surface area of ​​the aerosol-generating film corresponds to the cumulative area of ​​unobstructed surfaces within the aerosol-generating substrate bar, from which volatile components can be freely released upon heating of the aerosol-generating film. During use, the exposed surfaces of the aerosol-generating film may be exposed to the flow of gaseous air through the aerosol-generating article. According to the invention, the total exposed surface area of ​​the aerosol-generating film within the aerosol-generating substrate rod can be maximized by increasing the exposed surface area per unit weight of the aerosol-generating film. In this way, the aerosol release efficiency from a given weight of aerosol-generating film can be improved. Therefore, it may be possible to reduce the total weight of aerosol-generating film required to produce a desired quantity of aerosol from the aerosol-generating substrate rod during a heating cycle within an aerosol-generating device. The exposed surface area of ​​the aerosol-generating film is preferably at least approximately 5 square millimeters per mg of aerosol-generating film, with a higher preference of at least approximately 10 square millimeters per mg of aerosol-generating film, and with a maximum preference of at least approximately 20 square millimeters per mg of aerosol-generating film. The exposed surface area of ​​the aerosol-generating film is preferably no more than approximately 40 square millimeters per millimeter of aerosol-generating film, more preferably no more than approximately 30 square millimeters per millimeter of aerosol-generating film. For example, the exposed surface area of ​​the aerosol-generating film may be between approximately 5 square millimeters and approximately 40 square millimeters per millimeter of aerosol-generating film, or between approximately 10 square millimeters and approximately 30 square millimeters per millimeter of aerosol-generating film, or between approximately 20 square millimeters and approximately 30 square millimeters. Alternatively, or additionally, the total exposed surface area of ​​the aerosol-generating film can be maximized by increasing the bulk density of the aerosol-generating film within the aerosol-generating substrate rod. This allows for a greater amount of film, and therefore potentially a larger exposed surface area, to be provided per unit volume of the aerosol-generating substrate rod. The aerosol release efficiency of a given volume of aerosol-generating substrate can thus be improved. Therefore, it may be possible to produce a desired quantity of aerosol with a reduced size of aerosol-generating substrate. The apparent density of the aerosol-generating film within the aerosol-generating substrate bar is preferably at least approximately 100 mg per cubic centimeter of the aerosol-generating substrate bar, more preferably at least approximately 200 mg per cubic centimeter of the aerosol-generating substrate bar, more preferably at least approximately 300 mg per cubic centimeter of the aerosol-generating substrate bar, with the highest preference at least approximately 400 mg per cubic centimeter. The bulk density of the aerosol-generating film within the aerosol-generating substrate rod is preferably no more than approximately 1,000 mg per cubic centimeter of the aerosol-generating substrate rod, more preferably no more than approximately 850 mg per cubic centimeter, more preferably no more than approximately 750 mg per cubic centimeter, and most preferably no more than approximately 600 mg per cubic centimeter. For example, the bulk density of the aerosol-generating film within the aerosol-generating substrate rod may be between approximately 100 mg and approximately 1,000 mg per cubic centimeter, or between approximately 200 mg and approximately 8,500 mg per cubic centimeter, or between approximately 300 mg and approximately 750 mg per cubic centimeter, or between approximately 400 mg per cubic centimeter and approximately 600 mg per cubic centimeter. The apparent density of the aerosol generating film corresponds to the total weight of the film provided on the aerosol generating substrate rod (in mg), not including the weight of any carrier material, divided by the total volume of the rod (in cubic centimeters). The present invention encompasses a variety of different configurations of the aerosol-generating film to provide an increased total exposed surface area. In certain preferred embodiments, the aerosol-generating substrate bar comprises a plurality of stacked layers of the aerosol-generating film. As used herein, the term “stacked” refers to the arrangement of a plurality of aerosol-generating film layers one on top of the other. In the present invention, the “stacked” layers may be arranged one on top of the other with spacing between adjacent layers. Alternatively, adjacent layers may be at least partially in contact with each other, such that the layers are separated in some areas while in other areas the spacing between adjacent layers may approach zero. The term “stacked” is used herein regardless of the orientation of the stacked layers. Providing multiple stacked layers of the aerosol-generating film advantageously offers a relatively high exposed surface area, as the surface of the film on both sides of each layer can be exposed. The exposed surface area can be easily increased by increasing the number of layers within the stack. The regular arrangement of the multiple layers advantageously provides the stick with a uniform distribution of the aerosol-generating film and consistent suction resistance. The stick's suction resistance can be easily controlled by adjusting the layer spacing and thickness. This regular layer arrangement also optimizes heat transfer from a heating element in contact with the stick during use. The multiple layers of the aerosol-generating film can be stacked such that each layer extends in the longitudinal direction of the aerosol-generating article. Preferably, the layers are separated from each other in the transverse direction to allow airflow through the bar during use. This arrangement of layers with transverse spacing between adjacent layers can facilitate the insertion of a heating element, such as a heating sheet, into the bar. In such embodiments having a plurality of longitudinally extending layers, preferably at least approximately 80 percent of the plurality of layers extends essentially the entire length of the boom, more preferably at least approximately 90 percent of the plurality of layers, and more preferably at least approximately 95 percent of the plurality of layers. Preferably, in particular, each of the plurality of layers extends essentially the entire length of the boom. A layer that extends essentially the entire length of the boom extends essentially the entire way between the upstream and downstream ends of the boom. Such an arrangement provides better control over the boom's suction resistance and, therefore, over the aerosol delivery.The relative widths of the multiple layers can be varied to provide different arrangements of stacked layers. For example, at least two layers can have different widths. Alternatively, the multiple layers can have an essentially constant width. In such embodiments having a plurality of longitudinally extending layers, the plurality of layers are preferably arranged essentially parallel to each other to provide an essentially constant transverse spacing of the layers along the length of the bar. The transverse spacing between the layers can be adapted to provide the desired level of airflow and, therefore, the desired suction resistance of the bar. Preferably, the layers are separated from each other in a transverse direction by at least approximately 10 micrometers, more preferably at least approximately 20 micrometers, and most preferably at least approximately 50 micrometers. Preferably, the layers are separated from each other in a transverse direction by no more than approximately 300 micrometers, more preferably no more than approximately 200 micrometers, and most preferably no more than approximately 150 micrometers. Alternatively, the multiple layers of aerosol-generating film can be stacked such that each layer extends in the transverse direction of the aerosol-generating article. The stack of layers thus extends along the length of the rod. Preferably, the transverse layers of aerosol-generating film are adapted to allow airflow in a longitudinal direction through the rod during use. For example, each layer can be provided with one or more holes or slits through the layer. In such embodiments having a plurality of transverse layers of aerosol-generating film, the layers are preferably separated from each other in a longitudinal direction in order to maximize the exposed surface areas of the layers. In this case, the layers are preferably separated from each other by at least approximately 50 micrometers, more preferably by at least approximately 100 micrometers, and most preferably by at least approximately 150 micrometers. Preferably, the layers are separated from each other in a longitudinal direction by no more than approximately 1,500 micrometers, more preferably by no more than approximately 800 micrometers, and most preferably by no more than approximately 600 micrometers. Alternatively, the layers may be stacked such that adjacent layers are at least partially in contact with each other, with essentially no longitudinal spacing between them. The following further discussion of embodiments of the invention comprising a plurality of stacked layers of the aerosol-generating film applies to all layer arrangements as described above. The number of layers of aerosol-generating film stacked within the stick can be varied depending on the thickness of the layers and the length of the stick. The number of layers can be increased to increase the total exposed surface area of ​​the aerosol-generating film. Preferably, the stick comprises between approximately 2 and approximately 50 stacked layers of aerosol-generating film. The multiple layers of the aerosol-generating film may be essentially the same thickness. Alternatively, the multiple layers may include layers of at least two different thicknesses. In certain preferred embodiments of the present invention, the plurality of stacked layers of the aerosol-generating film is mounted within a tubular carrier element, such as a paper or cardboard tube. In alternative embodiments, the plurality of stacked layers is enclosed by a wrapper. By providing the stacked layers within a tubular carrier or a wrapper, the aerosol-generating film can be more conveniently combined with other components to form the aerosol-generating article. In alternative embodiments of the present invention, the aerosol-generating substrate rod comprises one or more crinkled layers of the aerosol-generating film. As used herein with reference to the invention, the term “crinkled” describes a layer that is convoluted, folded, or otherwise compressed or contracted essentially transversely to the longitudinal axis of the aerosol-generating article. Using one or more crinkled layers of aerosol-generating film is an alternative way to provide a relatively high exposed surface area within the aerosol-generating substrate rod. The exposed surface area of ​​the aerosol-generating film, as well as its apparent density within the rod, can be easily controlled by adjusting the degree of convolution or folding of the layers. Preferably, the one or more gathered layers of aerosol-generating film are enclosed by a wrapper. Preferably, the one or more gathered layers of aerosol-generating film extend along essentially the entire length of the rod and across essentially the entire cross-sectional area of ​​the rod. In further alternative embodiments of the present invention, the aerosol-generating substrate rod comprises a plurality of strips or fragments of the aerosol-generating film. For example, the rod may be formed from a plurality of strips of aerosol-generating film that are aligned in the longitudinal direction and have been assembled and wrapped to form an aerosol-generating substrate rod. Alternatively, the strips of aerosol-generating film may be randomly oriented within the rod. The use of a plurality of strips or fragments is an additional way in which the total exposed surface area of ​​the aerosol-generating film can be increased. The exposed surface area of ​​the aerosol-generating film and also the bulk density of the aerosol-generating film within the rod can be easily controlled by adjusting the number of strips within the volume of the rod. In such embodiments, the aerosol-generating film strips preferably have a length of between approximately 10 millimeters and approximately 20 millimeters, more preferably between approximately 12 millimeters and approximately 18 millimeters, more preferably between approximately 14 millimeters and approximately 16 millimeters, and more preferably approximately 15 millimeters. Alternatively or additionally, the aerosol-generating film strips preferably have a width of between approximately 0.4 millimeters and approximately 0.8 millimeters. In further embodiments of the present invention, the aerosol-generating substrate rod may comprise a plurality of hollow beads formed from the aerosol-generating film, for example, a plurality of spherical beads. The use of a plurality of beads is an additional way in which the total exposed surface area of ​​the aerosol-generating film can be increased. The exposed surface area of ​​the aerosol-generating film and also the apparent density of the aerosol-generating film within the rod can be easily controlled by adjusting the number of beads within the rod and the packing density of the beads. The aerosol-generating substrate rod may comprise from approximately 2 to approximately 30 beads of the aerosol-generating film. The plurality of beads is preferably provided within a cavity of a tubular carrier element so that they can be contained within the aerosol-generating substrate. In any embodiment of the present invention, the aerosol-generating film can be advantageously textured over at least part of its surface. As used herein, the term “textured” refers to a film that has been curled, embossed, stamped, perforated, or otherwise locally deformed. For example, the film may comprise a plurality of indentations, protrusions, separate perforations, or combinations thereof. The texture can be provided on one side of the film or on both sides. When a plurality of stacked layers of the aerosol-generating film are provided, some or all of the layers can be textured. Providing texture over at least part of the surface of the aerosol-generating film is an alternative or additional way in which the exposed surface area of ​​the aerosol-generating film can be maximized. In certain preferred embodiments, the aerosol-generating film is crimped over at least a portion of its surface. As used herein, the term “crimped” denotes a film having a plurality of essentially parallel ridges or corrugations. Preferably, when the aerosol-generating article has been assembled, the essentially parallel ridges or corrugations extend along, or are parallel to, the longitudinal axis of the aerosol-generating article. A single crimped layer of aerosol-generating film can be provided on the aerosol-generating substrate bar. In such embodiments, the single crimped layer is preferably crinkled as described above. Alternatively, a plurality of crimped layers of aerosol-generating film can be provided. For example, a plurality of crimped layers of aerosol-generating film can be stacked to form the aerosol-generating substrate bar, as described above. The thickness of the aerosol-generating film in aerosol-generating articles according to the present invention is preferably at least approximately 0.05 millimeters, more preferably at least approximately 0.1 millimeters, and most preferably at least approximately 0.15 millimeters. The thickness of the aerosol-generating film is preferably no more than approximately 1.0 millimeter, more preferably no more than approximately 0.5 millimeters, and most preferably no more than approximately 0.3 millimeters. For example, the film thickness may be between approximately 0.05 millimeters and approximately 10 millimeters, or between approximately 0.1 millimeters and approximately 0.5 millimeters, or between approximately 0.15 millimeters and approximately 0.3 millimeters.The present invention therefore provides a relatively thin layer of the aerosol-generating film so as to maximize the surface area-to-weight ratio of the film. This improves the release efficiency of the volatile components of the aerosol-generating film upon heating. The use of a relatively thin layer of the aerosol-generating film also allows the film weight to be kept low while retaining sufficient surface area. This advantageously decreases the thermal inertia of the aerosol-generating film, further improving aerosol generation efficiency. The weight of the aerosol-generating film on the aerosol-generating substrate bar can also be adjusted depending on the desired level of aerosol delivery during use. Preferably, the weight of the aerosol-generating film is selected so that essentially all the volatile components of the film are released during a typical heating cycle of the aerosol-generating item, in order to minimize waste and maximize the degradability of the aerosol-generating substrate bar. Preferably, the tubular carrier element provides at least approximately 20 milligrams of the aerosol-generating film, more preferably at least approximately 50 milligrams, and more preferably at least approximately 100 milligrams. Preferably, the tubular carrier element provides no more than approximately 300 milligrams of the aerosol-generating film, more preferably no more than approximately 200 milligrams. For example, the tubular carrier element may provide between approximately 20 milligrams and approximately 300 milligrams of the aerosol-generating film, or between approximately 50 milligrams and approximately 200 milligrams of the aerosol-generating film, or between approximately 100 milligrams and approximately 200 milligrams of the aerosol-generating film. The aerosol-generating film preferably has a basis weight of at least approximately 100 grams per square meter, more preferably at least approximately 120 grams per square meter, and most preferably at least approximately 140 grams per square meter. Preferably, the aerosol-generating film has a basis weight of no more than 300 grams per square meter, more preferably no more than 280 grams per square meter, and most preferably no more than 260 grams per square meter. For example, the aerosol-generating film may have a basis weight of between approximately 100 grams per square meter and approximately 300 grams per square meter, or between approximately 120 grams per square meter and approximately 280 grams per square meter, or between approximately 140 grams per square meter and approximately 260 grams per square meter. The aerosol-generating substrate bar preferably has an outer diameter that is approximately equal to the outer diameter of the aerosol-generating article. Preferably, the aerosol-generating substrate rod has an outer diameter of at least 5 millimeters. The aerosol-generating substrate rod may have an outer diameter of between approximately 5 millimeters and approximately 12 millimeters, for example, between approximately 5 millimeters and approximately 10 millimeters or between approximately 6 millimeters and approximately 8 millimeters. In a preferred embodiment, the aerosol-generating substrate rod has an outer diameter of approximately 7 millimeters. The aerosol-generating substrate rod can be between approximately 5 mm and approximately 15 mm long. In one embodiment, the aerosol-generating substrate rod can be approximately 10 mm long. In a preferred embodiment, the aerosol-generating substrate rod is approximately 12 mm long. Preferably, the aerosol-generating substrate bar has an essentially uniform cross-section along its length. More specifically, the aerosol-generating substrate bar has an essentially circular cross-section. The aerosol-generating film can be incorporated directly into the aerosol-generating substrate bar as a single-layer substrate. The single-layer aerosol-generating film can be textured as described above. Alternatively, the aerosol-generating film can be coated or infiltrated onto a carrier layer, such as a layer of porous or fibrous sheet-like material, before being incorporated into the aerosol-generating substrate bar. Suitable sheet-like materials for the carrier layer include, but are not limited to, paper, cardboard, and homogenized plant material. The carrier layer with the applied aerosol-generating film can be textured as described above. The aerosol generating film of the aerosol generating articles according to the present invention has a composition comprising at least approximately 25 percent by weight of a polyhydric alcohol, more preferably at least approximately 30 percent by weight of a polyhydric alcohol, more preferably at least approximately 35 percent by weight of a polyhydric alcohol, more preferably at least approximately 40 percent by weight of a polyhydric alcohol. Preferably, the aerosol generating film preferably comprises less than approximately 90 percent by weight of a polyhydric alcohol, more preferably less than approximately 80 percent by weight of a polyhydric alcohol, more preferably less than approximately 70 percent by weight of a polyhydric alcohol, more preferably less than approximately 60 percent by weight of a polyhydric alcohol. For example, the aerosol-generating film may comprise from approximately 25 percent by weight to approximately 90 percent by weight of polyhydric alcohol, or from approximately 30 percent by weight to approximately 80 percent by weight of polyhydric alcohol, or from approximately 35 percent by weight to approximately 70 percent by weight of polyhydric alcohol, or from approximately 40 percent by weight to approximately 60 percent by weight of polyhydric alcohol. Suitable polyhydric alcohols for use in the aerosol-generating film include, but are not limited to, propylene glycol, triethylene glycol, 1,3-butanediol, and glycerin. Preferably, in an aerosol-generating film according to the invention, the polyhydric alcohol is selected from the group consisting of glycerin, propylene glycol, and combinations thereof. In particularly preferred embodiments, the polyhydric alcohol is glycerin. Therefore, the invention advantageously provides a film having a significant polyhydric alcohol content that can be easily melted or extruded and solidified from a composition having a gel-like texture. Since significant percentages of the polyhydric alcohol, particularly glycerin, can be provided in film form, while at the same time the film geometry can be precisely controlled, the invention advantageously provides a film that is particularly suitable for use as an aerosol-generating substrate in an aerosol-generating article designed to be heated to release the aerosol. Preferably, the aerosol-generating film further comprises at least approximately 3 percent by weight of a cellulose-based film-forming agent, more preferably at least approximately 6 percent by weight of a cellulose-based film-forming agent, more preferably at least approximately 10 percent by weight of a cellulose-based film-forming agent, more preferably at least approximately 14 percent by weight of a cellulose-based film-forming agent, more preferably at least approximately 16 percent by weight of a cellulose-based film-forming agent, more preferably at least approximately 18 percent by weight of a cellulose-based film-forming agent. The aerosol-generating film may comprise up to approximately 70 percent by weight of a cellulose-based film-forming agent. Preferably, the aerosol-generating film comprises no more than approximately 26 percent by weight of the cellulose-based film-forming agent, more preferably no more than approximately 24 percent by weight of the cellulose-based film-forming agent, and more preferably no more than approximately 22 percent by weight of the cellulose-based film-forming agent. For example, the aerosol-generating film may comprise from approximately 3 percent by weight to approximately 70 percent by weight of a cellulose-based film-forming agent, or from approximately 6 percent by weight to approximately 26 percent by weight of a cellulose-based film-forming agent, or from approximately 10 percent by weight to approximately 24 percent by weight of a cellulose-based film-forming agent, or from approximately 14 percent by weight to approximately 24 percent by weight of a cellulose-based film-forming agent, or from approximately 16 percent by weight to approximately 22 percent by weight of a cellulose-based film-forming agent, or from approximately 18 percent by weight to approximately 22 percent by weight of a cellulose-based film-forming agent. In the context of the present invention, the term “cellulose-based film-forming agent” is used to describe a cellulosic polymer capable, by itself or in the presence of an auxiliary thickening agent, of forming a continuous film. Preferably, the cellulose-based film-forming agent is selected from the group consisting of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), ethylcellulose (EC), hydroxyethyl methylcellulose (EIEMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (EIPC), and combinations thereof. In a particularly preferred embodiment, the cellulose-based film-forming agent is ECPMC. Preferably, in the aerosol-generating film, the ratio of the weight of the cellulose-based film-forming agent to the weight of the polyhydric alcohol is at least approximately 0.1, more preferably at least approximately 0.2, and even more preferably approximately 0.3. Alternatively, in the aerosol-generating film, the ratio of the weight of the cellulose-based film-forming agent to the weight of the polyhydric alcohol is preferably less than or equal to approximately 1. In preferred embodiments, in the aerosol-generating film, the ratio of the weight of the cellulose-based film-forming agent to the weight of the polyhydric alcohol is approximately 0.1 to approximately 1. The inventors have surprisingly discovered that aerosol-generating films comprising at least 6 percent by weight of a cellulose-based film-forming agent, preferably HPMC, are particularly stable. They essentially maintain their shape when exposed to a variety of environmental conditions, such as a change in relative humidity from 10 percent to 60 percent. Consequently, the aerosol-generating films as described above do not advantageously release a liquid phase during storage or transportation. Preferably, the aerosol-generating film further comprises at least approximately 1 percent by weight of a non-cellulose-based thickening agent, more preferably at least approximately 2 percent by weight of the non-cellulose-based thickening agent, more preferably at least approximately 3 percent by weight of the non-cellulose-based thickening agent. Preferably, the aerosol-generating film comprises no more than approximately 10 percent by weight of the non-cellulose-based thickening agent, more preferably no more than approximately 8 percent by weight of the non-cellulose-based thickening agent, more preferably no more than approximately 6 percent by weight of the non-cellulose-based thickening agent.For example, the aerosol-generating film may comprise from approximately 1 percent by weight to approximately 10 percent by weight of the non-cellulose-based thickening agent, or from approximately 2 percent by weight to approximately 8 percent by weight of the non-cellulose-based thickening agent, or from approximately 3 percent by weight to approximately 6 percent by weight of the non-cellulose-based thickening agent. As used herein with reference to the invention, the term “non-cellulose-based thickening agent” is used to describe a non-cellulosic substance that, when added to an aqueous or non-aqueous liquid composition, increases the viscosity of the liquid composition without substantially altering its other properties. The thickening agent may increase the stability and improve the suspension of the components in the liquid composition. A thickening agent may also be referred to as a “thickener” or a “rheology modifier.” Preferably, in an aerosol-generating film according to the invention, the non-cellulose-based thickening agent is selected from the group consisting of agar, xanthan gum, gum arabic, guar gum, locust bean gum, pectin, carrageenan, starch, alginate, and combinations thereof. In preferred embodiments, the non-cellulose-based thickening agent is agar. Preferably, in the aerosol-generating film, the weight ratio of the non-cellulose-based thickening agent to the weight ratio of the polyhydric alcohol is at least approximately 0.05, more preferably at least 0.1, and even more preferably at least 0.2. Alternatively, in the aerosol-generating film, the weight ratio of the non-cellulose-based thickening agent to the weight ratio of the polyhydric alcohol is preferably less than or equal to approximately 0.5. In preferred embodiments, in the aerosol-generating film, the ratio of the weight of the non-cellulose-based thickening agent to the weight of the polyhydric alcohol is approximately 0.1 to approximately 0.5. The inventors have surprisingly discovered that incorporating a combination of a cellulose-based film-forming agent and a non-cellulose-based thickening agent into the film along with polyhydric alcohol can provide a film that has improved stability that can be produced with high accuracy and repeatability. Preferably, the aerosol-generating film comprises less than approximately 30 percent water by weight. More preferably, the aerosol-generating film comprises between approximately 10 percent and approximately 20 percent water by weight. In some embodiments, the aerosol-generating film also comprises an alkaloid compound or a cannabinoid compound or both. As used herein with reference to the invention, the term “alkaloid compound” describes any of a class of naturally occurring organic compounds containing one or more basic nitrogen atoms. Generally, an alkaloid contains at least one nitrogen atom in an amine-type structure. This or another nitrogen atom in the alkaloid compound molecule may be active as a base in acid-base reactions. Most alkaloid compounds have one or more of their nitrogen atoms as part of a cyclic system, such as a heterocyclic ring. In nature, alkaloid compounds are found primarily in plants and are especially common in certain families of flowering plants. However, some alkaloid compounds are found in animal species and fungi.In the context of the present invention, the term “alkaloid compounds” is used to describe both naturally occurring alkaloid compounds and synthetically manufactured alkaloid compounds. Preferably, the alkaloid compound is selected from the group consisting of nicotine, anatabine, and combinations thereof. As used herein with reference to the invention, the term “cannabinoid compound” describes any of a class of naturally occurring compounds found in parts of the cannabis plant—specifically, the species Cannabis sativa, Cannabis indica, and Cannabis ruderalis. Cannabinoid compounds are particularly concentrated in the flower heads of the female plants. Naturally occurring cannabinoid compounds in the cannabis plant include tetrahydrocannabinol (THC) and cannabidiol (CBD). In the context of the present invention, the term “cannabinoid compounds” is used to describe both naturally occurring and synthetically produced cannabinoid compounds. Preferably, the cannabinoid compound is selected from the group consisting of: tetrahydrocannabinol (THC), tetrahydrocannabinolic acid (THCA), cannabidiol (CBD), cannabidiolic acid (CBDA), cannabinol (CBN), cannabigerol (CBG), cannabigerol monomethyl ether (CBGM), cannabivarin (CBV), cannabidivarin (CBDV), tetrahydrocannabivarin (THCV), cannabichromene (CBC), cannabicyclol (CBL), cannabichromevarin (CBCV), cannabigerovarin (CBGV), cannabielsoin (CBE), cannabicitran (CBT) and combinations thereof. In general, the aerosol-generating film can comprise up to approximately 10 percent by weight of an alkaloid compound, a cannabinoid compound, or both. The content of the alkaloid compound, cannabinoid compound, or both in the film can be increased and adjusted to optimize the delivery of the alkaloid compound, cannabinoid compound, or both in aerosol form to the consumer. Compared to existing aerosol-generating substrates based on the use of plant material, this can advantageously allow for higher contents of the alkaloid compound, cannabinoid compound, or both per volume of substrate (film) or per weight of substrate (film), which can be convenient from a manufacturing standpoint. Preferably, the aerosol-generating film comprises at least approximately 0.5 percent by weight of an alkaloid compound or a cannabinoid compound, or both. Therefore, the aerosol-generating film preferably comprises at least approximately 0.5 percent by weight of an alkaloid compound, or at least 0.5 percent by weight of a cannabinoid compound, or at least approximately 0.5 percent by weight of a combination of an alkaloid compound and a cannabinoid compound. More preferably, the aerosol-generating film comprises at least approximately 1 percent by weight of an alkaloid compound or a cannabinoid compound or both, and more preferably at least approximately 2 percent by weight of an alkaloid compound or a cannabinoid compound or both. The aerosol-generating film preferably comprises less than approximately 6 percent by weight of an alkaloid compound or a cannabinoid compound or both, and more preferably less than approximately 5 percent by weight of an alkaloid compound or a cannabinoid compound or both, and more preferably less than approximately 4 percent by weight of an alkaloid compound or a cannabinoid compound or both. For example, the aerosol-generating film may comprise from approximately 0.5 percent by weight to approximately 10 percent by weight of an alkaloid compound or a cannabinoid compound or both, or from approximately 1 percent by weight to approximately 6 percent by weight of an alkaloid compound or a cannabinoid compound or both, or from approximately 2 percent by weight to approximately 5 percent by weight of an alkaloid compound or a cannabinoid compound or both. In some embodiments, the aerosol-generating film comprises one or more cannabinoids and an alkaloid compound comprising nicotine or anatabine. In some preferred embodiments, the aerosol-generating film comprises nicotine. As used herein with reference to the invention, the term “nicotine” is used to describe nicotine, a nicotine base, or a nicotine salt. In embodiments where the aerosol-generating film comprises a nicotine base or a nicotine salt, the amounts of nicotine referred to herein are the amount of freebase nicotine or the amount of protonated nicotine, respectively. The aerosol-generating film may comprise natural nicotine or synthetic nicotine. The aerosol-generating film may comprise one or more monoprotic nicotine salts. As used in the present description, with reference to the invention, the term “monoprotic nicotine salt” is used to describe a nicotine salt of a monoprotic acid. Preferably, the aerosol-generating film comprises at least approximately 0.5 percent by weight of nicotine. More preferably, the aerosol-generating film comprises at least approximately 1 percent by weight of nicotine. Even more preferably, the aerosol-generating film comprises at least approximately 2 percent by weight of nicotine. Alternatively, the aerosol-generating film preferably comprises less than approximately 10 percent by weight of nicotine. More preferably, the aerosol-generating film comprises less than approximately 6 percent by weight of nicotine. Even more preferably, the aerosol-generating film comprises less than approximately 5 percent by weight of nicotine. For example, the aerosol-generating film may comprise between approximately 0.5 percent by weight and approximately 10 percent by weight of nicotine, or between approximately 1 percent by weight and approximately 6 percent by weight of nicotine or between approximately 2 percent by weight and approximately 5 percent by weight of nicotine. In some preferred embodiments, the aerosol-generating film comprises a cannabinoid compound. Preferably, the cannabinoid compound is selected from CBD and THC. More preferably, the cannabinoid compound is CBD. The aerosol-generating film may comprise up to approximately 10 percent by weight of CBD. Preferably, the aerosol-generating film comprises at least approximately 0.5 percent by weight of CBD, more preferably at least approximately 1 percent by weight of CBD, more preferably at least approximately 2 percent by weight of CBD. Preferably, the aerosol-generating film comprises less than approximately 6 percent by weight of CBD, more preferably less than approximately 5 percent by weight of CBD, more preferably less than approximately 4 percent by weight of CBD. For example, the aerosol-generating film may comprise from approximately 0.5 percent by weight to approximately 10 percent by weight of CBD, with a greater preference for approximately 1 percent by weight to approximately 6 percent by weight of CBD, and even more preferentially from approximately 2 percent by weight to approximately 5 percent by weight of CBD. The aerosol generating film can be an essentially tobacco-free aerosol generating film. As used herein with reference to the invention, the term “essentially tobacco-free aerosol-generating film” describes an aerosol-generating film having a tobacco content of less than 1 percent by weight. For example, the aerosol-generating film may have a tobacco content of less than approximately 0.75 percent by weight, less than approximately 0.5 percent by weight, or less than approximately 0.25 percent by weight. The aerosol generating film can be a tobacco-free aerosol generating film. As used herein with reference to the invention, the term “tobacco-free aerosol generating film” describes an aerosol generating film having a tobacco content of 0 percent by weight. In some embodiments, the aerosol-generating film comprises tobacco material, non-tobacco plant material, or a plant extract. By way of example, the aerosol-generating film may comprise tobacco particles, such as tobacco leaf particles, as well as particles of other botanical products, such as clove and eucalyptus. When the aerosol-generating film comprises tobacco, the tobacco content is preferably no more than approximately 70 percent by weight, more preferably no more than approximately 50 percent by weight, more preferably no more than approximately 30 percent by weight, and most preferably no more than approximately 10 percent by weight. In preferred embodiments, the aerosol-generating film comprises an acid. More preferably, the aerosol-generating film comprises one or more organic acids. Even more preferably, the aerosol-generating film comprises one or more carboxylic acids. In particularly preferred embodiments, the acid is lactic acid or levulinic acid. The inclusion of an acid is particularly preferred in aerosol film formulations containing nicotine, as the presence of an acid has been observed to stabilize the dissolved species in the film-forming composition, such as with nicotine and other plant extracts. Without wishing to be bound by theory, it is understood that the acid can interact with the nicotine molecule, especially when the nicotine is provided in salt form, essentially preventing the nicotine from evaporating during the drying process. As such, nicotine loss during film manufacturing can be minimized, and a higher and more controlled nicotine delivery to the consumer can be advantageously ensured. Preferably, the aerosol-generating film comprises at least approximately 0.25 percent by weight of the acid. More preferably, the aerosol-generating film comprises at least approximately 0.5 percent by weight of the acid. Even more preferably, the aerosol-generating film comprises at least approximately 1 percent by weight of the acid. Alternatively, the aerosol-generating film preferably comprises less than approximately 3.5 percent by weight of the acid. More preferably, the aerosol-generating film comprises less than approximately 3 percent by weight of the acid. Even more preferably, the aerosol-generating film comprises less than approximately 2.5 percent by weight of the acid. For example, the aerosol-generating film may comprise from approximately 0.25 percent by weight to approximately 3.5 percent by weight of the acid, or from approximately 0.5 percent by weight to approximately 3 percent by weight of the acid, or from approximately 1 percent by weight to approximately 2.5 percent by weight of the acid. The aerosol-generating film may optionally include a flavoring agent. In some embodiments, the aerosol-generating film may include up to approximately 2 percent by weight of a flavoring agent. By way of example, the aerosol-generating film may include one or more of the following: menthol, terpenes, terpenoids, eugenol, and eucalyptol. The aerosol-generating film can be produced by forming a film-forming composition from the film components, preferably an aqueous film-forming composition, melting or extruding the film-forming composition onto a support surface, allowing the film-forming composition to gel, and then drying the film-forming composition to obtain an aerosol-generating film. The film can then be peeled off the support surface and incorporated into an aerosol-generating substrate for an aerosol-generating article. Alternatively, the film can be incorporated into an aerosol-generating substrate together with the support surface. Upon heating, most of the components of the aerosol-generating film are found to evaporate. In fact, it has been observed that only some residue of the cellulose-based film-forming agent, when present, typically remains after use. As such, aerosol-generating articles incorporating substrates comprising an aerosol-generating film as described may be easier to dispose of and may have an improved environmental impact. During use, the aerosol-generating film can be heated to a temperature between approximately 180 degrees Celsius and approximately 250 degrees Celsius in order to generate an aerosol. The inventors have surprisingly discovered that when the aerosol-generating film is heated in an aerosol-generating device, it can release polyhydric alcohol without essentially releasing a liquid phase. The aerosol generating articles according to the invention preferably comprise one or more elements in addition to the aerosol generating substrate bar, wherein the bar and the one or more elements are assembled within a substrate wrap or within a tubular carrier element. Preferably, the aerosol-generating article further comprises a flow-restricting element downstream of the aerosol-generating substrate bar. The flow-restricting element can be advantageously incorporated to provide the aerosol-generating article with an acceptable level of resistance to suction (RTD). Those skilled in the art would be aware of suitable flow-restricting elements to provide a desired level of RTD. In some embodiments, the flow-restricting element can be a constriction, such as one or more holes having a diameter smaller than the diameter of the internal cavity. In preferred embodiments, the flow-restricting element comprises one or more plugs of fibrous filter material, such as one or more cellulose acetate plugs. The resistance to suction (RTD) of the aerosol generating article after the insertion of a heating element is preferably between approximately 40 mm WG and approximately 140 mm WG, with greater preference between approximately 80 mm WG and approximately 120 mm WG. As used in the present description, suction resistance is expressed in pressure units “mm WG” or “mm of water column” and is measured in accordance with ISO 6565:2002. The flow restriction element can extend to the downstream end of the aerosol-generating item. Alternatively, an end cavity can be provided on the hollow mouth side downstream of the flow restriction element. The flow restriction element preferably extends longitudinally between approximately 15 millimeters and approximately 25 millimeters along the aerosol generating article. Preferably, the flow-restricting element is separated from the aerosol-generating substrate bar in a longitudinal direction such that the flow-restricting element and the aerosol-generating substrate bar are separated by a hollow space or cavity. This separation of the components advantageously provides space for aerosol formation within the aerosol-generating article. Preferably, the longitudinal spacing between the flow-restricting element and the aerosol-generating film is at least approximately 10 percent of the length of the aerosol-generating article, more preferably at least approximately 20 percent of the length. Preferably, the length of the space between the aerosol-generating film and the flow-restricting element is at least 50 percent of the length of the aerosol-generating substrate bar. Preferably, the aerosol generating article further comprises an upstream sealing element that covers the upstream end of the aerosol generating substrate bar. Sealing the upstream end advantageously reduces the ingress of air and water into the aerosol generating substrate bar prior to use. This helps retain the freshness of the aerosol generating film during storage in order to optimize aerosol delivery after heating. Furthermore, sealing the upstream end of the aerosol generating substrate bar can reduce the loss of volatile components from the aerosol generating film during storage, thereby maximizing the delivery of these components to the consumer. The upstream sealing element may take any suitable form but is preferably a sheet of material covering the upstream face of the aerosol-generating substrate bar. Preferably, the sheet of material is essentially impermeable. The upstream sealing element may be formed from any suitable sheet-like material, including, but not limited to, paper, aluminum, polymer, or combinations thereof. Preferably, a frangible upstream sealing element is provided. The sealing element is frangible so that it can be punctured by a heating element or other puncture-making means after the aerosol-generating article is inserted into an aerosol-generating device. If desired, a support element, such as a plug of fibrous filter material, may be provided directly downstream of the frangible upstream sealing element to facilitate puncture of the frangible upstream sealing element by the heating element or other puncture-making means. Alternatively or in addition to an upstream sealing element, the aerosol-generating article may further comprise a downstream sealing element at its downstream end. The downstream sealing element may have the same or a different shape as the upstream sealing element. When a downstream sealing element is provided, it may be removable so that it can be taken out of the aerosol-generating article prior to use. Alternatively or in addition to providing an upstream sealing element, a tubular support element may be provided at the upstream end of the aerosol-generating article, upstream of the aerosol-generating substrate bar. For example, a hollow acetate tube may be provided upstream of the aerosol-generating substrate bar, at the upstream end of the aerosol-generating article. The tubular support element can advantageously minimize the risk of loss of any of the aerosol-generating films from the aerosol-generating article before use. Furthermore, the tubular support element can facilitate the insertion and removal of an internal heating element in the aerosol-generating article during its use in an aerosol-generating device.Additionally, the tubular support element can be used to direct or control the airflow through the aerosol-generating item. As defined above, aspects three and four of the present invention provide bars for use as an aerosol-generating substrate for an aerosol-generating article, wherein the bar comprises an aerosol-generating film. The aerosol-generating substrate bar and the aerosol-generating film may have any of the features or properties described above in relation to aspects one and two of the invention. The aerosol-generating substrate sticks according to the third aspect of the invention, as described above, can be produced using a method according to the invention, as defined below. The method according to the invention comprises a first step of providing an aqueous film-forming composition comprising polyhydric alcohol and a cellulose-based film-forming agent, and a second step of providing a sheet-like material. In a third step, the aqueous film-forming composition is applied onto the surface of the sheet-like material to form a film layer, and in a fourth step, the film layer is dried to form an aerosol-generating film having at least 25 percent by weight of polyhydric alcohol and at least 10 percent by weight of cellulose-based film-forming agent.In a fifth stage, the film layer is configured to form an aerosol-generating substrate bar such that the exposed surface area of ​​the aerosol-generating film is at least approximately 5 square millimeters per mg of aerosol-generating film. The aerosol-generating substrate sticks according to the fourth aspect of the invention, as described above, can be produced using a method according to the invention, as defined below. The method according to the invention comprises a first step of providing an aqueous film-forming composition comprising polyhydric alcohol and a cellulose-based film-forming agent, and a second step of providing a sheet-like material. In a third step, the aqueous film-forming composition is applied onto the surface of the sheet-like material to form a film layer, and in a fourth step, the film layer is dried to form an aerosol-generating film having at least approximately 40 percent by weight of polyhydric alcohol and at least approximately 10 percent by weight of cellulose-based film-forming agent.In a fifth stage, the film layer is configured to form an aerosol-generating substrate rod such that the apparent density of the aerosol-generating film is at least approximately 100 mg per cubic centimeter of the aerosol-generating substrate rod. In any of the methods according to the present invention, the configuration step will depend on the desired configuration of the aerosol-generating film within the aerosol-generating substrate rod. For example, when it is desired to form an aerosol-generating substrate rod comprising a plurality of stacked layers of the aerosol-generating film, as described above, the configuration step of the aerosol-generating film may comprise the step of forming a plurality of layers of the aerosol-generating film and stacking the plurality of layers to form the rod. Alternatively, the configuration step of the aerosol-generating film may comprise joining the aerosol-generating film to form a rod. Alternatively, the configuration step of the aerosol-generating film may comprise cutting a plurality of strips from the film layer and forming the plurality of strips into a rod. As described above, the present invention further provides an aerosol generating system comprising an aerosol generating article including an aerosol generating substrate bar according to the invention, in combination with an electrically operated aerosol generating device adapted to receive the aerosol generating article and having a heating element configured to heat the aerosol generating film of the aerosol generating substrate bar. The aerosol generating article comprises an aerosol generating substrate according to the third or fourth aspect of the invention, as described in detail above. Preferably, the heating element is configured to heat the aerosol generating film to a temperature between approximately 120 degrees Celsius and approximately 350 degrees Celsius, with greater preference to a temperature between approximately 200 degrees Celsius and approximately 220 degrees Celsius. The electrically operated aerosol generating device can be configured to heat the aerosol generating item externally. An elongated heating chamber is provided, which is adapted to receive the aerosol generating item, and the heating element is provided circumferentially around the heating chamber to partially or totally surround the aerosol generating item within the chamber so that the aerosol generating substrate bar is heated. Alternatively, the electrically operated aerosol generating device can be configured to heat the aerosol generating article internally, from within the tubular carrier element. A heating element in the form of an elongated heating sheet or pin is provided, which is adapted to be inserted into the aerosol generating substrate bar in order to heat the aerosol generating film. In any of the aerosol generating systems according to the invention, the heating element may have any shape suitable for conducting heat. The aerosol generating system may be an electrically operated aerosol generating system comprising an inductive heating device. Inductive heating devices typically comprise an induction source configured to couple to a susceptor. The induction source generates an alternating electromagnetic field that induces an eddy current or magnetizing current in the susceptor. The susceptor may be heated as a result of hysteresis losses or the induced eddy current heating the susceptor through ohmic or resistive heating. Electrically operated aerosol generating systems comprising an inductive heating device may also comprise the aerosol generating article having the aerosol generating film and a susceptor in thermal proximity to the aerosol generating film. The susceptor is heated through hysteresis losses or induced eddy current, which in turn heats the aerosol generating film. Typically, the susceptor is in direct contact with the aerosol generating film, and heat is transferred from the susceptor to the generating film primarily by conduction. Examples of electrically operated aerosol generating systems having inductive heating devices and aerosol generating articles having susceptors are described in WO-A1-95 / 27411 and WO-A1-2015 / 177255. The invention will now be described further with reference to the figures in which: Figure 1 shows a schematic longitudinal cross-sectional view of an aerosol generating article according to a first embodiment of the invention; Figure 2 shows a schematic longitudinal cross-sectional view of the aerosol generating article of Figure 1 in combination with an internal heating element of an aerosol generating device; Figure 3 shows a schematic longitudinal cross-sectional view of the aerosol generating article of Figure 1 in combination with an external heating element of an aerosol generating device; and Figure 4 shows a schematic longitudinal cross-sectional view of an aerosol generating article according to a second embodiment of the invention. The aerosol generating article 10 shown in Figure 1 comprises a tubular carrier element 12, an aerosol generating substrate bar 14, and a flow restriction element 16. The tubular carrier element 12 is in the form of a paper tube that has a length of approximately 12 millimeters and an external diameter of approximately 7 millimeters. The tubular carrier element 12 is cylindrical in shape and defines an internal cavity that extends longitudinally 18 from an upstream end 20 of the tubular carrier element 12 to a downstream end 22. The aerosol-generating substrate rod 14 comprises a plurality of 24 layers of an aerosol-generating film. As shown in Figure 1, each of the plurality of layers 24 extends longitudinally along the entire length of the rod 14. Although not shown in Figure 1, the layers 24 are separated from each other transversely. Each of the layers 24 is approximately 0.25 millimeters thick and approximately 10 millimeters long. The rod contains approximately 30 layers. The total amount of aerosol-generating film within the rod 14 is approximately 200 mg. The exposed surface area of ​​the 24 layers of aerosol-generating film is greater than 5 square millimeters per mg of aerosol-generating film. The apparent density of the aerosol-generating film inside bar 14 is greater than 100 mg per cubic centimeter of bar 14. The aerosol generating film 14 has the following composition: Aerosol-generating film composition (w / w) 19.3% HPMC 4.8% agar 1.4% nicotine 48% glycerin 2.1% levulinic acid 24.4% water «oz i η / ι ζπζ / ε / υιλι The flow restriction element 16 comprises a single segment of cellulose acetate tow which is provided within the internal cavity 18 of the tubular carrier element 12, at the downstream end 22. The flow restriction element 16 has a length of approximately 20 millimeters and an external diameter corresponding to the diameter of the internal cavity 18 of the tubular carrier element 12. The flow restriction element 16 is downstream of the aerosol generating film 14 and separated from the aerosol generating film 14 so as to define a void space within the tubular carrier element 12, between the downstream end of the aerosol generating film 14 and the upstream end of the flow restriction element 16. The upstream end 20 of the tubular carrier element 12 is sealed by means of the upstream sealing element 26 which comprises an aluminum sheet provided over the end of the tubular carrier element 12 to seal the upstream end of the internal cavity 18. The aerosol generating article 10 shown in Figure 1 is suitable for use with an electrically operated aerosol generating device comprising a heater for heating the aerosol generating substrate film 14. Figure 2 shows a schematic view of the aerosol generating article 10 being heated in an aerosol generating device 50 having a heating sheet 52. The aerosol generating article is inserted into the aerosol generating device 50 such that the heating sheet 52 passes through the upstream sealing element 24 and is inserted into the aerosol generating substrate bar 14 between the aerosol generating film layers 24. During use, the heating foil 52 heats the 24 layers of the aerosol-generating film to a temperature sufficient to generate an aerosol from the film. The aerosol is drawn in through the flow-restricting element 16 and exits through the downstream end 22 of the tubular carrier element. Figure 3 shows a schematic view of the aerosol-generating article 10 being heated in an alternative aerosol-generating device 60 having a heating chamber 62 into which the upstream end of the aerosol-generating article is inserted such that an external heating element 64 surrounds the upstream portion of the tubular carrier element 12 incorporating the aerosol-generating substrate bar 14. The heating element 64 heats the aerosol-generating film layers 24 on the aerosol-generating substrate bar 14 circumferentially from the outside of the tubular carrier element 12. The aerosol generating device 60 further comprises a piercing element 66 which pierces the upstream sealing element 24 when the aerosol generating article 10 is inserted into the heating chamber 62. Figure 4 shows an aerosol generating article 70 according to a second embodiment of the present invention, which is similar in construction to the aerosol generating article 10 shown in Figure 1 but comprises an aerosol generating substrate rod 74 having a different aerosol generating film configuration. The bar 74 comprises a plurality of aerosol-generating film layers 76. As shown in Figure 4, each of the aerosol-generating film layers 76 extends in a transverse direction. The layers 76 are parallel to each other and stacked so that adjacent layers are in contact with each other, with no longitudinal spacing between them. The layers 76 are circular in shape and have a diameter essentially corresponding to the diameter of the internal cavity 18 of the tubular carrier element 12. Each of the layers 76 is approximately 0.25 millimeters thick, and the bar contains approximately 45 layers. The length of the bar 74 is approximately 5 millimeters. The total amount of aerosol-generating film within the bar 74 is approximately 200 mg. The exposed surface area of ​​the 76 layers of aerosol-generating film is greater than 5 square millimeters per mg of aerosol-generating film. The apparent density of the aerosol-generating film inside bar 74 is greater than 100 mg per cubic centimeter of bar 74. Each of the layers 76 comprises a plurality of airflow holes (not shown) arranged on the surface, which provide the layers 76 with sufficient porosity to allow airflow through the bar 74 during use. The aerosol generating article 70 can be heated in an aerosol generating device as described above with reference to aerosol generating article 10. It will be appreciated that the aerosol generating articles 10 shown in Figure 1 may also be suitable for use with other types of aerosol generating devices.

Claims

1. An aerosol generating article comprising an aerosol generating substrate rod, wherein the aerosol generating substrate rod comprises: an aerosol generating film comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulose-based film-forming agent, wherein the aerosol generating film is configured such that the exposed surface area of ​​the aerosol generating film within the aerosol generating substrate is at least 5 square millimeters per mg of aerosol generating film and wherein the aerosol generating film is essentially tobacco-free.

2. An aerosol generating article comprising an aerosol generating substrate rod, wherein the aerosol generating substrate rod comprises: an aerosol generating film comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulose-based film-forming agent, wherein the aerosol generating film is configured such that the bulk density of the aerosol generating film is at least 100 mg per cubic centimeter of the aerosol generating substrate rod and wherein the aerosol generating film is essentially tobacco-free.

3. An aerosol generating article according to claim 1 or 2, wherein the aerosol generating substrate bar comprises a plurality of stacked layers of the aerosol generating film.

4. An aerosol generating article according to claim 3, wherein the plurality of layers of the aerosol generating film are stacked such that each layer extends in the transverse direction of the aerosol generating article.

5. An aerosol generating article according to claim 3, wherein the plurality of layers of the aerosol generating film are stacked such that each layer extends in the longitudinal direction of the aerosol generating article.

6. An aerosol generating article according to any of claims 3 to 5, wherein the aerosol generating substrate comprises a tubular carrier element defining a longitudinally extending internal channel and wherein the plurality of stacked layers is provided within the internal channel.

7. An aerosol generating article according to any of claims 3 to 6, wherein the plurality of stacked layers of the aerosol generating film comprises between 2 and 50 stacked layers.

8. An aerosol generating article according to claim 1 or 2, wherein the aerosol generating substrate bar comprises one or more crinkled layers of aerosol generating film.

9. An aerosol generating article according to claim 1 or 2, wherein the aerosol generating substrate bar comprises a plurality of strips of aerosol generating film.

10. An aerosol generating article according to any of the preceding claims, wherein the thickness of the aerosol generating film is between 0.1 millimeters and 0.5 millimeters.

11. An aerosol generating article according to any of the preceding claims, wherein the aerosol generating film is textured, preferably curled.

12. An aerosol generating article according to any of the preceding claims, wherein the aerosol generating film is provided on at least one surface of a carrier layer, preferably a paper layer.

13. A bar for use as an aerosol-generating substrate in an aerosol-generating article, the bar comprising: an aerosol-generating film comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulosic film-forming agent, wherein the aerosol-generating film is configured such that the exposed surface area of ​​the aerosol-generating film within the aerosol-generating substrate is at least 5 square millimeters per mg of the aerosol-generating film and wherein the aerosol-generating film is essentially tobacco-free.

14. A rod for use as an aerosol-generating substrate in an aerosol-generating article, the rod comprising: an aerosol-generating film comprising at least 25 percent by weight of a polyhydric alcohol and at least 10 percent by weight of a cellulose-based film-forming agent, wherein the aerosol-generating film is configured such that the apparent density of the aerosol-generating film is at least 100 mg per cubic centimeter of the aerosol-generating substrate rod and wherein the aerosol-generating film is essentially tobacco-free.

15. An aerosol generating system comprising an aerosol generating article and an electrically operated aerosol generating device comprising a heating element configured to heat an aerosol generating substrate of the aerosol generating article, wherein: the aerosol generating article comprises an aerosol generating substrate bar according to claim 13 or 14; and wherein the heating element is a heating sheet or heating pin configured to be inserted into the aerosol generating substrate bar for the purpose of heating the aerosol generating film.