Method for producing an aerosol-forming substrate and an aerosol-forming substrate

Abstract

The present invention relates to providing a cellulosic reinforcing agent; providing a binder; mixing hydroxypropyl methylcellulose, water, and an aerosol former to form a first slurry, the first slurry having a viscosity of 0.9 Pa·s to 5 Pa·s; - combining the cellulosic reinforcement agent, the binder, and the first slurry to obtain a final slurry; - drying the final slurry to obtain the aerosol-forming substrate. This method provides a first slurry having a reduced viscosity and lower water content.

Description

[Technical field]

[0001] The present invention relates to a method for producing an aerosol-forming substrate The present invention further relates to an aerosol-forming substrate produced by the method. [Background technology]

[0002] Aerosol-forming substrates often contain cellulose, such as hydroxypropylmethylcellulose. In addition, aerosol formers, such as polypropylene glycol or glycerin, may be present. Furthermore, the aerosol-forming substrate may contain a binder. These aerosol-forming substrates are prepared from slurries that also contain water to wet and disperse these components. Mixing different components often leads to agglomeration and high viscosity solutions due to low solubility of some of the components in either water or the aerosol former. These dispersions are often difficult to handle during the manufacture of the aerosol-forming substrate. Mixing slurries may also lead to excessive foaming. This may further complicate slurry handling. Summary of the Invention [Problem to be solved by the invention]

[0003] It would be desirable to provide a method for producing an aerosol-forming substrate that provides a solution that is easy to handle. It would further be desirable to provide a method for producing an aerosol-forming substrate that allows for easy and rapid drying of the slurry to produce the aerosol-forming substrate. It would further be desirable to provide an aerosol-forming substrate that is simple to produce and can be stored stably.

[0004] One embodiment of the present invention provides a method of making an aerosol-forming substrate, comprising providing a cellulosic reinforcing agent. The method may also comprise providing a binder. The method may also comprise mixing hydroxypropyl methylcellulose, water, and an aerosol former to form a first slurry, the first slurry having a viscosity of 0.9 Pa·s to 5 Pa·s, preferably 0.9 Pa·s to 4 Pa·s. The method also comprises combining some of the cellulosic reinforcing agent, the binder, and the first slurry to obtain a final slurry. The final slurry may be dried to obtain the aerosol-forming substrate.

[0005] Another embodiment of the present invention provides a method of making an aerosol-forming substrate, comprising providing a cellulosic reinforcing agent. The method further comprises providing a binder. Additionally, the method comprises the method step of mixing hydroxypropyl methylcellulose, water, and an aerosol former to form a first slurry, the first slurry having a viscosity of 0.9 Pa·s to 5 Pa·s, preferably 0.9 Pa·s to 4 Pa·s. The cellulosic reinforcing agent, binder, and first slurry are combined to obtain a final slurry. The final slurry is dried to obtain the aerosol-forming substrate.

[0006] In particular, a rheometer such as the modular compact rheometer MCR 302 marketed by Anton Paar GmbH may be employed. The initial shear rate for the rheological measurements may be 0.1 l / s and may increase to a final value of 500 l / s. The number of points per analysis may be set to 150. The duration may be set to "slope logarithmic" and the gap will be 1 mm. The temperature for the rheological measurements may be set to 23.5° C. and the number of replicates per sample may be 3.

[0007] One advantage of the method of the present invention may be that the hydroxypropyl methylcellulose and the binder are not mixed directly with each other, which may avoid the formation of a lump-like mixture with a very high viscosity, which may be difficult to handle and difficult to transfer from one tank to another via pump.

[0008] In addition, the mixing of the hydroxypropyl methylcellulose, water, and aerosol former forms a first slurry having a sufficient viscosity of 0.9 Pa·s to 5 Pa·s. This may allow mixing of the components of the first slurry employing a liquid mixer having at least one of an impeller or a dispersion disk. This may not require a soft mass mixer device. The first slurry may have a sufficiently high viscosity. This may avoid the formation of foam during mixing.

[0009] Hydroxypropyl methylcellulose may function as a film former. Hydroxypropyl methylcellulose may enable the formation of a film including the aerosol-forming substrate, for example, via casting. Cellulosic reinforcing agents may increase the cohesiveness and gel properties of the substrate of the aerosol-forming substrate. Binders may function as thickeners for the aerosol-forming substrate.

[0010] The different components of the aerosol-forming substrate may be added in different sequential orders. For example, it may be possible to add the binder, the cellulosic reinforcing agent, and then mix the first slurry with the resulting slurry. Alternatively, it may be possible to mix one or both of the cellulosic reinforcing agent and the binder with the first slurry.

[0011] The viscosity of the first slurry may depend on the shear rate introduced into the first slurry when mixing the slurry. The first slurry may behave as a non-Newtonian fluid, and its viscosity depends on the shear force introduced into the first slurry. A viscosity between 0.9 Pa·s and 5 Pa·s may behave as a non-Newtonian fluid, and its viscosity depends on the shear force introduced into the first slurry. A viscosity between 0.1 s and 0.9 Pa·s may behave as a non-Newtonian fluid, and its viscosity depends on the shear force introduced into the first slurry. -1 ~500s -1 , preferably 100s -1 The viscosity may be measured at a shear rate of 0.9 Pa·s to 3 Pa·s. The shear rate can be determined, for example, using the spindle of a PP25 measuring system of an Anton Paar rheometer. The viscosity may preferably be 0.9 Pa·s to 3 Pa·s.

[0012] The weight ratio of water:aerosol former:hydroxypropyl methylcellulose in the first slurry may be 1:2-10:2-3.5. This may result in an amount of water of 10-25 weight percent in the first slurry, based on the total weight of the first slurry. This low amount of water may reduce the viscosity of the first slurry. This amount of water may also allow for easy drying of the final slurry to produce the aerosol-forming substrate.

[0013] This amount of water may improve the dispersion of hydroxypropyl methylcellulose. Furthermore, these weight ratios may reduce the formation of foam. The low viscosity may allow the first slurry to be easily handled. This allows the first slurry to be pumped between different containers during handling. The low amount of water relative to hydroxypropyl methylcellulose may also reduce the formation of agglomerates of hydroxypropyl methylcellulose.

[0014] Preferably, the first water and aerosol former may be mixed in a weight ratio of water:aerosol former of 1:2-10. Hydroxypropyl methylcellulose may then be added in a weight ratio of hydroxypropyl methylcellulose:aerosol former of 1:1-3. This procedure may be particularly suitable for obtaining a first slurry that can be easily processed. It may also avoid the formation of agglomerates. Such a first slurry may also be easy to mix, which may also reduce the amount of time to prepare the first slurry.

[0015] The cellulose-based reinforcing agent may be selected from the group consisting of cellulose fibers, microcrystalline cellulose, and cellulose powder. It is preferred that cellulose fibers are employed as the cellulose-based reinforcing agent. The cellulose fibers may have a diameter of less than 0.03 mm, preferably a length of 0.02 mm. The fibers may have a length of 0.7 to 1.6 mm, preferably a length of 0.9 mm.

[0016] These cellulosic reinforcing agents may be particularly well suited to provide cohesiveness to the aerosol-forming substrate.

[0017] The aerosol former may be selected from the group consisting of polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, and glycerin), esters of polyhydric alcohols (such as glycerol monoacetate, glycerol diacetate, or glycerol triacetate), and aliphatic esters of mono-, di-, or polycarboxylic acids.

[0018] The aerosol former may facilitate the formation of a dense and stable aerosol below the combustion temperature of the aerosol-forming substrate. The aerosol may be substantially resistant to thermal decomposition at the temperature at which the aerosol-forming substrate is heated. Suitable aerosol formers are well known in the art and include, but are not limited to, polyhydric alcohols (such as triethylene glycol, 1,3-butanediol, glycerin, etc.), esters of polyhydric alcohols (such as glycerol monoacetate, glycerol diacetate, or glycerol triacetate, etc.), and aliphatic esters of mono-, di-, or polycarboxylic acids (such as dimethyl dodecanedioate, dimethyl tetradecanedioate, etc.). The aerosol former may be a polyhydric alcohol or a mixture thereof (such as triethylene glycol, 1,3-butanediol, and glycerin). The aerosol former may be propylene glycol. The aerosol former may include both glycerin and propylene glycol, preferably glycerin.

[0019] The binder may be selected from the group consisting of methylcellulose and carboxymethylcellulose. Preferably, carboxymethylcellulose may be employed as the binder.

[0020] The cellulosic reinforcement agent may be mixed with water in a weight ratio of cellulosic reinforcement agent:water of 1:20 to 40. This may form a second slurry. This second slurry may be combined with one or both of the first slurry or the binder.

[0021] Dispersing the cellulosic strengthening agent and water may reduce some of the problems associated with clumping and viscosity. It may also avoid the cellulosic strengthening agent competing for water already combined with other components of the final slurry, such as the binder or hydroxypropyl methylcellulose.

[0022] The weight ratio of the second slurry:the first slurry may be 1:4-8, preferably 1:5-7, more preferably 1:6-6.5.

[0023] The binder may be mixed with water to provide a third slurry, which may also reduce any issues of cohesion and viscosity associated with the binder. The weight ratio of binder:water may be 1:3-200, preferably 1:4-150.

[0024] The first slurry, the second slurry, and the third slurry may be formed and then combined, for example by mixing, for example by employing a slurry mixing tank having one or both of an anchor stirrer or a dispersing disk, preferably one or several dispersing disks and an anchor stirrer.

[0025] The weight ratio of the first slurry:the second slurry:the third slurry may be 1:0.1-10:3-20, preferably 1:0.5-8:4-15.

[0026] Within these weight ratios, a final slurry may be formed that may be easily processed due to sufficient viscosity. In particular, these weight ratios may allow different slurries to be easily mixed and transferred to different tanks.

[0027] In the sense of the present invention, naming different slurries as "first slurry", "second slurry" or "third slurry" does not indicate a sequence of adding different slurries in a particular order to form a final slurry. For example, the second slurry containing the cellulosic reinforcing agent can be combined with the third slurry containing the binder. The first slurry containing hydroxypropyl methylcellulose, water and an aerosol former can then be added to the mixture of the second and third slurries. This preferred sequence may avoid foaming during mixing. Other sequences of combining the first, second and third slurries are also possible. One or both of the cellulosic reinforcing agent and the binder can be combined with the first slurry without forming the second and third slurries.

[0028] Nicotine may be included in at least one of the first slurry, the second slurry, the third slurry, or the final slurry. The amount of nicotine in the final slurry may be 0-5 weight percent, preferably 0.1-3 weight percent, more preferably 0.3-2 weight percent.

[0029] An organic acid may be included in at least one of the first slurry, the second slurry, the third slurry, or the final slurry. The organic acid may function to protonate nicotine. This may provide a nicotine salt with higher solubility in the slurry. Preferably, the organic acid may be selected from the group consisting of lactic acid, citric acid, pyruvic acid, tartaric acid, benzoic acid, pectic acid, alginic acid, maleic acid, fumaric acid, malic acid, levulinic acid, and salicylic acid. These organic acids may be particularly suitable for forming salts with nicotine. Preferably, lactic acid may be used as the organic acid.

[0030] The final slurry may be prepared by mixing under reduced pressure compared to standard pressure. Mixing may be carried out at reduced pressure of 500 to 50 mbar absolute. In particular, mixing may be carried out under vacuum. This may avoid the formation of bubbles during mixing.

[0031] The aerosol-forming substrate may comprise a plant-derived material. The aerosol-forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavor compounds that are released from the aerosol-forming substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco-containing material. The aerosol-forming substrate may comprise a homogenized plant-derived material. The final slurry may contain a minor amount of tobacco. In particular, the final slurry may contain up to 5 weight percent, based on the total weight of the aerosol-forming substrate. Preferably, the final slurry contains tobacco extract. This may produce an aerosol-forming substrate containing tobacco extract.

[0032] Additionally, the final slurry may contain flavorings, which may impart flavors such as menthol, apple, mint, grapefruit, or vanilla.

[0033] The final slurry was -1 ~500s -1 , preferably 1s -1 ~150s -1 The final slurry may be prepared by mixing at a shear rate of 100 / min. Similarly, the first slurry may be prepared at the same shear rate, which may allow for thorough mixing of the components of either the final slurry or the first slurry.

[0034] The mixing and combining of the different slurries may be performed by employing one or more of a pulper, a high shear mixer with a dispersion disk, a Rushton impeller, an anchor stirrer, and a liquid mixer with a dispersion disk, and a helical agitator. These mixing tools are particularly suitable for mixing hydroxypropyl methylcellulose, water, and an aerosol former for the first slurry. These mixing tools may also be suitable for producing the second and third slurries.

[0035] During mixing of the components of the first slurry, the temperature may be kept between 15 degrees Celsius and 30 degrees Celsius. Preferably, the temperature may be kept at room temperature. Therefore, providing the first slurry by mixing hydroxypropyl methylcellulose, water, and aerosol former may be performed without heating. Heating may require more complicated equipment, such as jacketed tanks and preheating of the components via heat exchangers. Therefore, avoiding heating may be advantageous. In addition, heating may result in undesirable release of aerosol formers, nicotine, or any flavorings during production.

[0036] After mixing of the final slurry, the slurry may be cast to produce sheets of the aerosol-forming substrate.

[0037] The final slurry may be cast on a belt dryer to provide a sheet. Drying of the final slurry may be performed employing one or both of a steam pan dryer and a belt dryer. The speed of the belt dryer may be 8 meters per minute to 9 meters per minute. A doctor blade may be used to cast the final slurry on the belt dryer. Due to the low amount of water in the final slurry, the speed of the belt dryer may be increased compared to other slurries containing a higher amount of water. The final slurry may be dried to contain residual water at a temperature of 80 degrees Celsius to 150 degrees Celsius. The cast final slurry may be dried under standard pressure. The final slurry may be dried to a target residual water content of 5 percent to 15 percent water by weight based on the total weight of the aerosol-forming substrate.

[0038] Before casting the slurry, the final slurry may be transferred to a buffer tank. This may be particularly simple due to the low viscosity of the final slurry, which may allow pumping the final slurry between different tanks. The final slurry may be stored in the buffer tank before drying. This may also make the mixing tank available for preparation of the next batch of first and final slurries.

[0039] Another embodiment of the present invention provides a solid aerosol-forming substrate for use in an aerosol generating system. The aerosol-forming substrate may comprise an aerosol former. The aerosol-forming substrate may comprise hydroxypropyl methylcellulose. The solid aerosol-forming substrate may comprise a binder. In addition, a cellulose-based reinforcing agent may be present. The aerosol-forming substrate may also comprise water.

[0040] In a further embodiment of the present invention, a solid aerosol-forming substrate for use in an aerosol generating system is provided. The aerosol-forming substrate comprises an aerosol former. In addition, hydroxypropyl methylcellulose is present. The aerosol-forming substrate also comprises a binder and a cellulose-based reinforcing agent. In addition, water, particularly residual water, is present in the solid aerosol-forming substrate.

[0041] Such solid aerosol-forming substrates may be easily produced by the method according to the invention. In particular, due to the simple drying procedure, residual water content may be present within the aerosol-forming substrate.

[0042] The residual water content may be between 5 percent and 15 percent by weight based on the total weight of the aerosol-forming substrate. Preferably, the residual water content may be between 8 percent and 11 percent by weight based on the total weight of the aerosol-forming substrate.

[0043] The aerosol-forming substrate may contain 12 to 25 percent by weight of hydroxypropyl methylcellulose, preferably 16 to 23 percent by weight of hydroxypropyl methylcellulose, based on the total weight of the aerosol-forming substrate.

[0044] The aerosol-forming substrate may contain from 3 percent to 10 percent by weight of the binder, based on the total weight of the aerosol-forming substrate. Preferably, from 4 percent to 7 percent by weight of the binder may be present in the aerosol-forming substrate.

[0045] The aerosol-forming substrate may contain 40 percent to 60 percent by weight of the aerosol-forming material, based on the total weight of the aerosol-forming substrate.

[0046] A cellulosic reinforcing agent may also be present in the aerosol-forming substrate in an amount of from 4 percent to 25 percent by weight based on the total weight of the aerosol-forming substrate. Preferably, a cellulosic reinforcing agent may be present in the aerosol-forming substrate in an amount of from 5 percent to 20 percent by weight based on the total weight of the aerosol-forming substrate.

[0047] The invention also provides a solid aerosol-forming substrate for use in an aerosol-generating system, manufactured according to any of the methods described herein.

[0048] The solid aerosol-forming substrate, in particular a sheet of aerosol-forming substrate, may be part of an aerosol-generating article. The aerosol-generating article may comprise a substrate section comprising the solid aerosol-forming substrate. The aerosol-generating article may have a tubular shape. As a result, the substrate section of the aerosol-generating article may also comprise a tubular shape. In addition to the substrate section, the aerosol-generating article may comprise one or both of a filter section or a hollow tubular section. The aerosol-generating article may comprise a wrapping material, in particular a paper, surrounding the substrate section and other optional sections.

[0049] The present invention also provides an aerosol generating system comprising an aerosol-generating article comprising the aerosol-forming substrate of the present invention and an aerosol generating device. The aerosol generating device may comprise a cavity configured to receive the aerosol-generating article. The cavity may be a heating chamber. The aerosol generating device may comprise a heating element for heating the aerosol-generating article received in the cavity. Heating of the aerosol-generating article may be performed by heating below the combustion temperature of the aerosol-forming substrate. This may produce an aerosol comprising the aerosol former and optionally nicotine, other tobacco flavors, and additional flavorants added to the aerosol-forming substrate.

[0050] The aerosol generating device may include a heating element. The heating element may take the form of one or more flexible heating foils on a dielectric substrate such as polyimide. The flexible heating foils may be shaped to fit the periphery of the cavity that receives the substrate. Alternatively, the external heating element may take the form of a metal grid(s), flexible printed circuit board, molded circuit components (MIDs), ceramic heaters, flexible carbon fiber heaters, or may be formed using coating techniques such as plasma deposition on a substrate of suitable shape. The heating element may also be formed using a metal that has a well-defined relationship between temperature and resistivity. In such an exemplary device, the metal may be formed as a track between two layers of suitable insulating material. The heating element thus formed may be used to both heat the external heating element and monitor its temperature during operation. The heating element may be configured as a resistive heating element.

[0051] Alternatively, the heating element may be configured as an induction heating element. The induction heating element may comprise an induction coil disposed at least partially surrounding the cavity of the aerosol generating device. The induction coil may be a helical induction coil. The induction coil may have a tubular shape coaxially surrounding the cavity. The induction heating element may further comprise a susceptor.

[0052] Generally, a susceptor is a material that can absorb electromagnetic energy and convert it into heat. When located in an alternating electromagnetic field, eddy currents are typically induced in the susceptor and hysteresis losses occur, causing the susceptor to heat up. The changing electromagnetic field generated by one or several induction coils heats the susceptor, which then transfers the heat to the aerosol-generating article, thereby forming the aerosol. The heat transfer may be primarily by conduction. Such heat transfer is best when the susceptor is in intimate thermal contact with the aerosol-generating article. The susceptor may have a tubular shape. The outer diameter of the susceptor may be smaller than the inner diameter of the induction coil. The susceptor may be disposed within the induction coil. The susceptor may form a sidewall of a cavity.

[0053] The susceptor may be formed from any material that can be inductively heated to a temperature sufficient to generate an aerosol from the aerosol-forming substrate. Preferred susceptors may include or consist of a ferromagnetic material (e.g., ferromagnetic alloys, ferritic iron, or ferromagnetic steel or stainless steel). Suitable susceptors may be or include aluminum. Preferred susceptors may be heated to temperatures in excess of 250 degrees Celsius.

[0054] Below 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 the other examples, embodiments, or aspects described herein.

[0055] Example A: A method for producing an aerosol-forming substrate comprising: providing a cellulosic reinforcing agent; providing a binder; mixing hydroxypropyl methylcellulose, water, and an aerosol former to form a first slurry, the first slurry having a viscosity of 0.9 Pa·s to 5 Pa·s; - combining the cellulosic reinforcement agent, the binder, and the first slurry to obtain a final slurry; - drying the final slurry to obtain an aerosol-forming substrate.

[0056] Example B: The method according to example A, wherein the weight ratio of water:aerosol former:hydroxypropyl methylcellulose in the first slurry is 1:2-10:2-3.5, preferably the first water and aerosol former are mixed in a weight ratio of water:aerosol former of 1:2-10, and then hydroxypropyl methylcellulose is added in a weight ratio of hydroxypropyl methylcellulose:aerosol former of 1:1-3.

[0057] Example C: The method according to any of the preceding examples, wherein the cellulosic reinforcing agent is selected from the group consisting of cellulose fibers, microcrystalline cellulose, and cellulose powder, preferably cellulose fibers.

[0058] Example D: The method according to any of the preceding examples, wherein the aerosol former is selected from the group consisting of polyhydric alcohols such as triethylene glycol, 1,3-butanediol, and glycerin; esters of polyhydric alcohols such as glycerol monoacetate, glycerol diacetate, or glycerol triacetate; and aliphatic esters of mono-, di-, or polycarboxylic acids, preferably the aerosol former is selected from the group consisting of propylene glycol and glycerin, more preferably the aerosol former is glycerin.

[0059] Example E: The method according to any of the preceding examples, wherein said binder is selected from the group consisting of methylcellulose and carboxymethylcellulose, preferably carboxymethylcellulose.

[0060] Example F: The method according to any of the preceding examples, wherein the cellulosic reinforcing agent and water are mixed in a weight ratio of 1:20-40 cellulose fiber:water to form a second slurry, and the second slurry is combined with one or both of the first slurry or the binder.

[0061] Example G: The process according to the preceding Example F, wherein the weight ratio of the second slurry:first slurry is 1:4-8, preferably 1:5-7, more preferably 1:6-6.5.

[0062] Example H: The method according to any of the preceding examples, wherein a binder is mixed with water to provide a third slurry, preferably in a binder:water weight ratio of 1:30-200.

[0063] Example I: The method according to any of the preceding examples, wherein a first slurry, a second slurry, and a third slurry are formed, and then the slurries are mixed in a weight ratio of first slurry:second slurry:third slurry of preferably 1:0.1-10:3-20, preferably 1:0.5-8:4-15.

[0064] Example J: The method according to any of the preceding examples, wherein nicotine is included in at least one of the first slurry, the second slurry, the third slurry, or the final slurry.

[0065] Example K: The method of the preceding Example J, wherein an organic acid is included in at least one of the first slurry, the second slurry, the third slurry, or the final slurry, preferably the organic acid is selected from the group consisting of lactic acid, citric acid, pyruvic acid, tartaric acid, benzoic acid, pectinic acid, alginic acid, maleic acid, fumaric acid, malic acid, levulinic acid, and salicylic acid.

[0066] Example L: The method according to any of the preceding examples, wherein at least one of the first slurry, the second slurry, the third slurry, or the final slurry is prepared by mixing under vacuum. Example M: ​​One or both of the first and final slurries are mixed for 0.1 s -1 ~500s -1 , preferably 1s -1 ~150s -1 The method according to any of the preceding Examples, wherein the mixture is prepared by mixing at a shear rate of

[0067] Example N: The method according to any of the preceding examples, wherein the mixing is performed by employing one or more of a pulper, a high shear mixer with a dispersion disc, a Rushton impeller, an anchor stirrer, and a liquid mixer with a dispersion disc, and a helical agitator.

[0068] Example O: A method according to any of the preceding examples, wherein after mixing of the final slurry, the slurry is cast to produce a sheet of the aerosol-forming substrate.

[0069] Example P: The method according to any of the preceding examples, wherein drying the final slurry is performed employing one or both of a steam pan dryer and a belt dryer.

[0070] Example Q: The method according to any of the preceding examples, wherein the aerosol-forming substrate is dried to a residual water content of between 5 percent by weight and 15 percent by weight, based on the total weight of the aerosol-forming substrate.

[0071] Example R: A solid aerosol-forming substrate for use in an aerosol generating system comprising: The aerosol-forming substrate is an aerosol former, -hydroxypropyl methylcellulose, a binder; - a cellulose-based reinforcing agent; and water.

[0072] Example S: The aerosol-forming substrate according to the preceding Example R, wherein the water has a residual water content of 5 weight percent to 15 weight percent based on the total weight of the aerosol-forming substrate, preferably a residual water content of 8 weight percent to 11 weight percent based on the total weight of the aerosol-forming substrate.

[0073] Example T: An aerosol-forming substrate according to any of the preceding examples R or S, comprising from 12 weight percent to 25 weight percent, preferably from 16 weight percent to 23 weight percent, of hydroxypropyl methylcellulose based on the total weight of the aerosol-forming substrate.

[0074] Example U: An aerosol-forming substrate according to any of the preceding Examples R to T, comprising from 3 weight percent to 10 weight percent, preferably from 4 weight percent to 7 weight percent, of a binder based on the total weight of the aerosol-forming substrate.

[0075] Example V: An aerosol-forming substrate according to any of the preceding Examples R-U, comprising 40 weight percent to 60 weight percent of the aerosol former, based on the total weight of the aerosol-forming substrate.

[0076] Example W: An aerosol-forming substrate according to any of the preceding Examples R to V, comprising from 4 weight percent to 25 weight percent, preferably from 5 weight percent to 20 weight percent, of a cellulosic reinforcing agent based on the total weight of the aerosol-forming substrate.

[0077] Example X: A solid aerosol-forming substrate for use in an aerosol-generating system prepared according to the method of any of Examples A-Q. Features described with respect to one embodiment may equally be applied to other embodiments of the invention.

[0078] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0079] [Figure 1] The figure shows a graph illustrating the viscosity of the first slurry versus the weight percentage of water. [Diagram 2] FIG. 2 illustrates a flow chart of a method for producing an aerosol-forming substrate according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] FIG. 1 shows a graph 10, which plots the weight percent content of water based on the total weight of the first slurry on the x-axis versus 100s on the y-axis. -1The viscosity of the first slurry at shear rates of 10-25 weight percent water is plotted in mPas·s. The graph shows that the optimum is between 10 and 25 weight percent water, with the viscosity of the first slurry being the lowest. Partly, the viscosity is in the range of 900 mPa·s and 2800 mPa·s, indicated by reference number 12. The graph shows that at higher water contents, greater than 25 weight percent and up to about 50 weight percent, the viscosity of the first slurry is surprisingly very high (area of ​​high viscosity indicated by reference number 14), which additionally also results in foaming when mixing the first slurry (area labeled "foaming" indicated by reference number 16). On the other hand, a higher water percentage of 55 weight percent to 68 weight percent again reduces the viscosity, but leads to the generation of agglomerates (area labeled "lump generation" indicated by reference number 18). The dashed line indicated by 20 shows the viscosity of the guar glycerin reference mixture. This may be the reference mixture for which the mixing equipment was designed. The guar glycerin standard mixture contains 5 parts by weight guar gum and 27 parts by weight glycerin.

[0081] Thus, Figure 1 shows that the inventors were able to identify a low amount of water contained in the first slurry, which on the one hand provides a low viscosity and on the other hand also avoids foaming and clumping problems. This is somewhat surprising since a person skilled in the art would expect a decrease in viscosity with increasing water content. The low water content of 10-25 weight percent water also allows for faster and easier drying of the final slurry to produce the aerosol-forming substrate.

[0082] FIG. 2 illustrates a flow chart of the method of the present invention for producing an aerosol-forming substrate. Water and a cellulose-based strengthening agent, designated "SA", can be mixed in a first step to provide a second slurry. Cellulosic fibers are preferably employed as the cellulose-based strengthening agent. In a further step, a binder, water, and an aerosol former, designated "AF", and optionally nicotine, designated "N", and an organic acid, designated "OA", are mixed to provide a third slurry. Carboxymethylcellulose is preferably employed as the binder and lactic acid as the organic acid. In a further step, hydroxypropylmethylcellulose is added to the mixture of water and aerosol former and mixed to provide the first slurry.

[0083] All the slurries, the first slurry, the second slurry, and the third slurry, are combined and mixed (see boxes labeled "Transfer" and "Mix"), after which the final slurry is transferred to a buffer tank and finally cast, for example, on a belt dryer, to provide a dry sheet of the aerosol-forming substrate. EXAMPLES

[0084] A first slurry was prepared with a weight ratio of water:glycerin:hydroxypropylmethylcellulose of 3:10:5. A second slurry was then prepared with a weight ratio of cellulose fiber:water of 3.5:111. A third slurry containing carboxymethylcellulose was prepared and added to the second slurry in a weight ratio of third slurry:second slurry of 1:114.5. The first slurry was then added to a mixture of the third and second slurries to prepare the final slurry.

Claims

1. 1. A method for producing an aerosol-forming substrate, comprising the steps of: providing a cellulose-based reinforcing agent, the cellulose-based reinforcing agent being selected from the group consisting of cellulose fibers, microcrystalline cellulose, and cellulose powder; providing a binder selected from the group consisting of methyl cellulose and carboxymethyl cellulose; mixing hydroxypropyl methylcellulose, water, and an aerosol former to form a first slurry, the first slurry having a viscosity of 0.9 Pa·s to 5 Pa·s; combining the cellulosic reinforcing agent, the binder, and the first slurry to obtain a final slurry; and drying said final slurry to obtain said aerosol-forming substrate.

2. 2. The method of claim 1, wherein the weight ratio of water:aerosol former:hydroxypropyl methylcellulose in the first slurry is 1:2-10:2-3.

5.

3. The method of claim 1 , wherein the cellulosic reinforcing agent is a cellulose fiber.

4. 10. The method of claim 1, wherein the aerosol former is selected from the group consisting of polyhydric alcohols, such as triethylene glycol, 1,3-butanediol, and glycerin; esters of polyhydric alcohols, such as glycerol monoacetate, glycerol diacetate, or glycerol triacetate; and aliphatic esters of mono-, di-, or polycarboxylic acids.

5. The method of claim 1 , wherein the binder is carboxymethyl cellulose.

6. 10. The method of claim 1, wherein the cellulosic reinforcing agent and water are mixed in a weight ratio of 1:20 to 40 cellulose fibers:water to form a second slurry, and the second slurry is combined with one or both of the first slurry or the binder.

7. The method of claim 6, wherein the weight ratio of the second slurry to the first slurry is 1:4-8.

8. The method of claim 1 , wherein the binder is mixed with water to provide a third slurry.

9. The method of claim 1, further comprising forming a second slurry, which is a mixture of the cellulose-based reinforcing agent and the water, and a third slurry, which is a mixture of the binder and the water, and then mixing the first slurry, the second slurry, and the third slurry in a predetermined weight ratio.

10. 2. The method of claim 1, wherein nicotine is included in at least one of the first slurry, the second slurry which is a mixture of the cellulosic fortifier and the water, the third slurry which is a mixture of the binder and the water, or the final slurry.

11. 10. The method of claim 1, wherein the aerosol-forming substrate is dried to a residual water content of from 5 percent to 15 percent by weight, based on the total weight of the aerosol-forming substrate.

12. 1. A solid aerosol-forming substrate for use in an aerosol generation system, comprising: The aerosol-forming substrate is 40 weight percent to 60 weight percent of an aerosol former based on the total weight of the aerosol-forming substrate; 12 weight percent to 25 weight percent hydroxypropyl methylcellulose based on the total weight of the aerosol-forming substrate; from 3 weight percent to 10 weight percent of a binder based on the total weight of the aerosol-forming substrate, the binder being selected from the group consisting of methylcellulose and carboxymethylcellulose; from 4 weight percent to 25 weight percent of a cellulosic reinforcing agent based on the total weight of the aerosol-forming substrate, the cellulosic reinforcing agent being selected from the group consisting of cellulose fibers, microcrystalline cellulose, and cellulose powder; Water, 1. A solid aerosol-forming substrate comprising:

13. 13. The aerosol-forming substrate of claim 12, comprising 16 percent to 23 percent by weight of hydroxypropyl methylcellulose.

14. 13. The aerosol-forming substrate according to claim 12, comprising from 4 weight percent to 7 weight percent of a binder, based on the total weight of the aerosol-forming substrate.

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