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

Abstract

The present invention relates to a method for producing an aerosol-forming substrate comprising: providing a cellulose-based reinforcing agent, providing a binder, mixing hydroxypropyl methylcellulose, water and an aerosol former to form a first slurry, the first slurry having a viscosity between 0.9 Pa-s and 5 Pa-s, and combining the cellulose-based reinforcing agent, the binder and the first slurry so as to obtain a final slurry, and drying the final slurry to obtain the aerosol-forming substrate. The method provides a first slurry having a reduced viscosity and a lower water content.

Description

[0001] The present invention relates to a method for producing an aerosol-forming substrate. The present invention also relates to an aerosol-forming substrate produced according to the method.

[0002] Aerosol-forming substrates often contain cellulose, such as hydroxypropyl methylcellulose. In addition, aerosol formers, such as polypropylene glycol or glycerol, can be present. Furthermore, the aerosol-forming substrate can comprise a binder. These aerosol-forming substrates are prepared from a slurry which also comprises water in order to wet and disperse the components. Mixing the different components often leads to agglomeration and high viscosity solutions due to the low solubility of some components in water or in the aerosol former. These dispersions are often difficult to handle during the production of the aerosol-forming substrate. Mixing the slurry can also lead to excessive foaming. This can further complicate the handling of the slurry.

[0003] It is desirable to provide a method for producing an aerosol-forming substrate which provides an easy-to-handle solution. Furthermore, it is desirable to provide a method for producing an aerosol-forming substrate which allows easy and fast drying of the slurry in order to produce the aerosol-forming substrate. Furthermore, it is desirable to provide an aerosol-forming substrate which is easy to produce and which can be stably stored.

[0004] One embodiment of the present invention provides a method for producing an aerosol-forming substrate comprising providing a cellulose-based reinforcing agent. The method can further comprise providing a binder. The method can further comprise mixing hydroxypropyl methylcellulose, water and an aerosol former to form a first slurry, the first slurry having a viscosity between 0.9 Pa s and 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The method can further comprise combining the cellulose-based reinforcing agent, the binder and the first slurry in order to obtain a final slurry. The final slurry can be dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate.

[0005] One embodiment of the present invention provides a method for producing an aerosol-forming substrate comprising providing a cellulose-based reinforcing agent. The method can further comprise providing a binder. The method can further comprise mixing hydroxypropyl methylcellulose, water and an aerosol former to form a first slurry, the first slurry having a viscosity between 0.9 Pa s and 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The method can further comprise combining the cellulose-based reinforcing agent, the binder and the first slurry in order to obtain a final slurry. The final slurry can be dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate. s to 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose-based reinforcing agent, the binder and the first slurry are combined in order to obtain a final slurry. The final slurry is dried in order to obtain the aerosol-forming substrate.

[0006] In particular, a rheometer, such as a modular compact rheometer MCR 302 sold by the company Anton Paar GmbH, can be employed. The initial shear rate for the rheology measurement can be 0.1 l / s and can be raised to a final value of 500 l / s. The number of points per analysis can be set to 150. The duration can be set to "Ramp Logarithmic" and the gap will be 1 mm. The temperature for the rheology measurement can be set to 23.5 °C and the number of replicates per sample can be 3.

[0007] One advantage of the method of the present application can be that the hydroxypropyl methylcellulose and the binder are not mixed directly with each other. This can avoid the formation of a dough-like mixture having a very high viscosity. Such a dough-like mixture can be difficult to handle and can be difficult to transfer from one tank to another via pumping.

[0008] Further, the mixing of the hydroxypropyl methylcellulose, the water and the aerosol- forming agent forms a first slurry having a sufficient viscosity between 0.9 Pa s and 5 Pa s. This can allow employing a liquid mixer having at least one of an impeller or a disperser disc to mix the components of the first slurry. This can not require a dough mixer device. The first slurry can have a sufficiently high viscosity. This can avoid the formation of a foam during mixing.

[0009] The hydroxypropyl methylcellulose can act as a film former. The hydroxypropyl methylcellulose can enable forming a film comprising the aerosol-forming substrate, e.g. via casting. The cellulose-based reinforcing agent can increase the matrix cohesion and gel properties of the aerosol-forming substrate. The binder can act as a thickening agent of the aerosol-forming substrate.

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

[0011] The viscosity of the first slurry can depend on the shear rate introduced to the first slurry when mixing the slurry. The first slurry can behave as a non-Newtonian fluid, whose viscosity depends on the shear force introduced to the first slurry. The viscosity between 0.9 Pa s and 5 Pa s can be measured at a shear rate of 0.1 s -1 to 500 s -1 , preferably 100 s -1 or above. The shear rate can be determined, for example, with the spindle of the PP25 measurement system of the Anton Paar Rheometer. The viscosity can preferably be measured at a shear rate of 0.1 l / s to 500 l / s, preferably 100 l / s or above. s to 3 Pa s between.

[0012] The weight ratio of water: aerosol forming agent: hydroxypropyl methylcellulose in the first slurry can be 1 :2 to 10:2 to 3.5. This can correspond to between 10 and 25 weight % water in the first slurry, based on the total weight of the first slurry. This low amount of water can reduce the viscosity of the first slurry. This amount of water can also enable easy drying of the final slurry in order to produce an aerosol forming substrate.

[0013] This amount of water can improve the dispersion of the hydroxypropyl methylcellulose. Furthermore, these weight ratios can reduce the formation of foam. The low viscosity can allow easy handling of the first slurry. This can allow pumping of the first slurry between different containers during processing. The low amount of water relative to the hydroxypropyl methylcellulose can also reduce the formation of agglomerates of the hydroxypropyl methylcellulose.

[0014] Preferably, the water and the aerosol forming agent can first be mixed in a weight ratio of water: aerosol forming agent of 1 :2 to 10. Subsequently, the hydroxypropyl methylcellulose can be added in a weight ratio of hydroxypropyl methylcellulose: aerosol forming agent of 1 : 1 to 3. This procedure can be particularly suitable in order to obtain a first slurry that can be easily processed. This can also avoid the formation of agglomerates. Such a first slurry can also be easily mixed, which can also reduce the amount of time to prepare the first slurry.

[0015] The cellulose-based reinforcing agent can be selected from the group consisting of cellulose fibres, microcrystalline cellulose and cellulose powder. Preferably, cellulose fibres are employed as the cellulose-based reinforcing agent. The cellulose fibres can have a diameter of less than 0.03 mm, preferably a length of 0.02 mm. The fibres can have a length of between 0.7 and 1.6 mm, preferably a length of 0.9 mm.

[0016] These cellulose-based reinforcing agents can be particularly suitable to provide cohesion to the aerosol forming substrate.

[0017] The aerosol forming agent can be selected from the group consisting of polyols, such as triethylene glycol, 1,3-butanediol and glycerol; esters of polyols, such as glycerol monoacetate, glycerol diacetate or glycerol triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids.

[0018] The aerosol forming agent can facilitate the formation of a dense and stable aerosol below the combustion temperature of the aerosol forming substrate. The aerosol can be substantially resistant to thermal degradation at the temperature at which the aerosol forming substrate is heated. Suitable aerosol forming agents are well known in the art and include, but are not limited to: polyhydric alcohols such as triethylene glycol, 1,3-butanediol and glycerol; esters of polyhydric alcohols such as glycerol monoacetate, glycerol diacetate or glycerol triacetate; and aliphatic esters of mono-, di- or polybasic carboxylic acids such as dimethyl dodecanedioate and dimethyl tetradecanedioate. The aerosol forming agent can be a polyhydric alcohol or a mixture thereof such as triethylene glycol, 1,3-butanediol and glycerol. The aerosol forming agent can be propylene glycol. The aerosol forming agent can comprise both glycerol and propylene glycol, preferably glycerol.

[0019] The binder can be selected from: methyl cellulose and carboxymethyl cellulose. Preferably, carboxymethyl cellulose can be employed as the binder.

[0020] The cellulose-based reinforcing agent can be mixed with water in a weight ratio of cellulose-based reinforcing agent: water of 1 :20 to 40. This can form a second slurry. This second slurry can be combined with one or both of the first slurry or the binder.

[0021] Dispersing the cellulose-based reinforcing agent and water can reduce any issues relating to agglomeration and viscosity. This can also avoid the cellulose-based reinforcing agent competing for water that has already been bound to other components of the final slurry such as the binder or hydroxypropyl methyl cellulose.

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

[0023] The binder can be mixed with water to provide a third slurry. This can also reduce any agglomeration and viscosity issues relating to the binder. The weight ratio of binder: water can be 1 :3 to 200, preferably 1 :4 to 150.

[0024] The first, second and third slurries can be formed and subsequently combined. This can be done by mixing, for example by employing a slurry mixing tank with one or both of an anchor stirrer or a disperser disc, preferably with one or several disperser discs and an anchor stirrer.

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

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

[0027] In the sense of the present invention, the different slurries are named "first slurry", "second slurry" or "third slurry" does not indicate the order in which the different slurries are added to form the final slurry. For example, the second slurry comprising the cellulose-based reinforcing agent can be combined with the third slurry comprising the binder. Subsequently, the first slurry comprising the hydroxypropyl methylcellulose, the water and the aerosol former can be added to the mixture of the second and third slurry. This preferred order can avoid foaming during mixing. Other orders of combining the first, second and third slurry are possible. One or both of the cellulose-based reinforcing agent and the binder can be combined with the first slurry without forming a second and third slurry.

[0028] Nicotine can be comprised 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 can be between 0 and 5 wt%, preferably between 0.1 and 3 wt%, more preferably between 0.3 and 2 wt%.

[0029] An organic acid can be comprised in at least one of the first slurry, the second slurry, the third slurry or the final slurry. The organic acid can be used to protonate the nicotine. This can provide a nicotine salt having a higher solubility in the slurry. Preferably, the organic acid can be selected from 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 can be particularly suitable for forming a salt with nicotine. Preferably, lactic acid can be used as the organic acid.

[0030] The final slurry can be prepared by mixing under reduced pressure compared to standard pressure. The mixing can be performed at a reduced absolute pressure between 500 and 50 mbar. In particular, the mixing can be performed under vacuum. This can avoid the formation of air bubbles during mixing.

[0031] The aerosol-forming substrate can comprise a plant-based material. The aerosol-forming substrate can comprise tobacco. The aerosol-forming substrate can comprise a tobacco- containing material containing volatile tobacco flavour compounds which are released from the aerosol-forming substrate upon heating. Alternatively, the aerosol-forming substrate can comprise a tobacco-free material. The aerosol-forming substrate can comprise a homogenized plant-based material. The final slurry can contain a small amount of tobacco. In particular, the final slurry can contain at most 5 wt% based on the total weight of the aerosol-forming substrate. Preferably, the final slurry contains a tobacco extract. This can result in an aerosol-forming substrate containing a tobacco extract.

[0032] In addition, the final slurry can contain a flavourant. These flavourants can impart a flavour such as menthol, apple, mint, grapefruit or vanilla.

[0033] The final slurry can be prepared by mixing the first slurry, the second slurry and the third slurry for a time period of at most 0.1 s-1 between 500s and 1500s -1 between 1 s and 10 s, preferably at 1 s -1 between 500s and 1500s -1 between 500s and 1500s Similarly, the first slurry can be prepared at the same shear rate. This can allow for sufficient mixing of the components of the final slurry or the first slurry.

[0034] Mixing and combining of the different slurries can be carried out by employing one or more of the following: a pulper, a high shear mixer with disperser discs, a liquid mixer with Rushton impellers, anchor stirrers and disperser discs, and a screw agitator. These mixing tools are particularly suitable for mixing the hydroxypropyl methylcellulose, water and aerosol former to form the first slurry. These mixing tools can also be suitable for producing the second slurry and the third slurry.

[0035] During mixing of the components of the first slurry, the temperature can be kept between 15 degrees Celsius and 30 degrees Celsius. Preferably, the temperature can be kept at room temperature. Thus, providing the first slurry by mixing the hydroxypropyl methylcellulose, water and aerosol former can be carried out without heating. Heating can require more complex equipment, such as a jacketed tank and pre-heating of parts via a heat exchanger. Thus, avoiding heating can be advantageous. Additionally, heating can cause an undesirable release of aerosol former, nicotine or any flavouring during production.

[0036] After mixing of the final slurry, the slurry can be cast to produce a sheet of the aerosol-forming substrate.

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

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

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

[0040] In yet another embodiment of the present application, 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 further comprises a binder and a cellulose-based reinforcing agent. In addition, water, in particular residual water, is present in the solid aerosol-forming substrate.

[0041] Such a solid aerosol-forming substrate can be easily produced by the method according to the present application. In particular, due to the easy drying procedure, a residual water content can be present in the aerosol-forming substrate.

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

[0043] The aerosol-forming substrate can contain between 12 wt.% and 25 wt.% hydroxypropyl methylcellulose based on the total weight of the aerosol-forming substrate. Preferably, the aerosol-forming substrate can contain between 16 wt.% and 23 wt.% hydroxypropyl methylcellulose.

[0044] The aerosol-forming substrate can contain between 3 wt.% and 10 wt.% binder based on the total weight of the aerosol-forming substrate. Preferably, between 4 wt.% and 7 wt.% of the binder can be present in the aerosol-forming substrate.

[0045] The aerosol-forming substrate can contain between 40 wt.% and 60 wt.% aerosol-former based on the total weight of the aerosol-forming substrate.

[0046] Between 4 wt.% and 25 wt.% cellulose-based reinforcing agent can also be present in the aerosol-forming substrate based on the total weight of the aerosol-forming substrate. Preferably, between 5 wt.% and 20 wt.% of the cellulose-based reinforcing agent can be present in the aerosol-forming substrate.

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

[0048] A solid aerosol-forming substrate, in particular a sheet of aerosol-forming substrate, can be part of an aerosol-generating article. The aerosol-generating article can comprise a substrate portion comprising the solid aerosol-forming substrate. The aerosol-generating article can have a tubular shape. Accordingly, the substrate portion of the aerosol-generating article can also comprise a tubular shape. In addition to the substrate portion, the aerosol-generating article can comprise one or both of a filter portion or a hollow tubular portion. The aerosol-generating article can comprise a wrapper, in particular paper, surrounding the substrate portion and other optional portions.

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

[0050] The aerosol-generating device can comprise a heating element. The heating element can be in the form of one or more flexible heating foils on a dielectric substrate such as polyimide. The flexible heating foils can be shaped to conform to the periphery of the substrate receiving cavity. Alternatively, the external heating element can take the form of a metal mesh, a flexible printed circuit board, a molded interconnect device (MID), a ceramic heater, a flexible carbon fibre heater, or can be formed on a suitable shaped substrate using a coating technique (e.g. plasma vapour deposition). The heating element can also be formed using a metal having a defined relationship between temperature and resistivity. In such an exemplary device, the metal can be formed as a trace between two layers of suitable insulating material. A heating element formed in this way can be used to heat and monitor the temperature of the external heating element during operation. The heating element can be configured as a resistive heating element.

[0051] Alternatively, the heating element can be configured as an inductive heating element. The inductive heating element can comprise an induction coil arranged at least partially around the cavity of the aerosol-generating device. The induction coil can be a spiral induction coil. The induction coil can have a tubular shape coaxially surrounding the cavity. The inductive heating element can further comprise a susceptor.

[0052] Generally, a susceptor is a material that is capable of absorbing electromagnetic energy and converting it into heat. When located in an alternating electromagnetic field, eddy currents are typically induced and hysteresis losses occur in the susceptor, causing heating of the susceptor. The electromagnetic field generated by one or more induction coils heats the susceptor, which then transfers heat to the aerosol-generating article, thereby forming an aerosol. Heat transfer can be primarily through thermal conduction. Such heat transfer is optimal if the susceptor is in intimate thermal contact with the aerosol-generating substrate. The susceptor can have a tubular shape. The outer diameter of the susceptor can be smaller than the inner diameter of the induction coil. The susceptor can be arranged within the induction coil. The susceptor can form a side wall of the cavity.

[0053] The susceptor can be formed of any material that is capable of being inductively heated to a temperature sufficient to generate an aerosol from an aerosol-forming substrate. Preferred susceptors can comprise or consist of a ferromagnetic material, such as a ferromagnetic alloy, ferritic iron, or a ferromagnetic steel or stainless steel. Suitable susceptors can be of aluminium or comprise aluminium. Preferred susceptors can be heated to a temperature in excess of 250 degrees Celsius.

[0054] A non-exhaustive list of non-limiting examples is provided below. Any one or more features of these examples can be combined with any one or more features of another example, embodiment, or aspect described herein.

[0055] Example A: A method for producing an aerosol-forming substrate, the method comprising:

[0056] - providing a cellulose-based reinforcing agent,

[0057] - providing a binder,

[0058] - mixing hydroxypropyl methylcellulose, water and an aerosol-forming agent to form a first slurry, the first slurry having a viscosity between 0.9 Pa s and 5 Pa s,

[0059] - combining the cellulose-based reinforcing agent, the binder and the first slurry so as to obtain a final slurry, and

[0060] - drying the final slurry to obtain an aerosol-forming substrate.

[0061] Example B: The method according to example A, wherein the weight ratio of water: aerosol-forming agent: hydroxypropyl methylcellulose in the first slurry is 1 :2 to 10:2 to 3.5, preferably wherein the first water and the aerosol-forming agent are mixed in a weight ratio of water: aerosol-forming agent of 1 :2 to 10, and subsequently the hydroxypropyl methylcellulose is added in a weight ratio of hydroxypropyl methylcellulose: aerosol-forming agent of 1 :1 to 3.

[0062] Example C: The method according to any one of the preceding examples, wherein the cellulose-based reinforcing agent is selected from: cellulose fibres and microcrystalline cellulose and cellulose powder, preferably cellulose fibres.

[0063] Example D: The method according to any one of the preceding examples, wherein the aerosol former is selected from: polyols, such as triethylene glycol, 1,3-butanediol and glycerol; esters of polyols, such as glycerol monoacetate, glycerol diacetate or glycerol triacetate; and aliphatic esters of mono-, di- or poly-carboxylic acids; preferably wherein the aerosol former is selected from: propylene glycol and, more preferably wherein the aerosol former is glycerol.

[0064] Example E: The method according to any one of the preceding examples, wherein the binder is selected from: methylcellulose and carboxymethylcellulose, preferably carboxymethylcellulose.

[0065] Example F: The method according to any one of the preceding examples, wherein the cellulose-based reinforcing agent and water are mixed in a weight ratio of cellulose fibres: water of 1 :20 to 40 to form a second slurry, and wherein the second slurry is combined with one or both of the first slurry or the binder.

[0066] Example G: The method according to the preceding example F, wherein the weight ratio of the second slurry: first slurry is 1 :4 to 8, preferably 1 :5 to 7, more preferably 1 :6 to 6.5.

[0067] Example H: The method according to any one of the preceding examples, wherein the binder is mixed with water to provide a third slurry, preferably wherein the weight ratio of binder: water is 1 :30 to 200.

[0068] Example I: The method according to any one of the preceding examples, wherein a first slurry, a second slurry and a third slurry are formed, and wherein the slurries are subsequently mixed, preferably in a weight ratio of first slurry: second slurry: third slurry of 1 :0.1 to 10:3 to 20, preferably 1 :0.5 to 8:4 to 15.

[0069] Example J: The method according to any one of the preceding examples, wherein the nicotine is comprised in at least one of: the first slurry, the second slurry, the third slurry or the final slurry.

[0070] Example K: The method according to the preceding example J, wherein the organic acid is comprised in at least one of: the first slurry, the second slurry, the third slurry or the final slurry, preferably wherein the organic acid is selected from 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.

[0071] Example L: The method according to any one 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.

[0072] Example M: The method according to any one of the preceding examples, wherein one or both of the first slurry and the final slurry is prepared by mixing at a shear rate between 0.1 s -1 to 500 s -1 , preferably between 1 s -1 to 150 s -1 .

[0073] Example N: The method according to any one of the preceding examples, wherein mixing is carried out using one or more of the following: a pulper, a high shear mixer with disperser discs, a liquid mixer with Rushton impellers, anchor stirrers and disperser discs, and a screw agitator.

[0074] Example O: The method according to any one of the preceding examples, wherein after mixing the final slurry, the cast slurry is subjected to produce a sheet of aerosol-forming substrate.

[0075] Example P: The method according to any one of the preceding examples, wherein drying the final slurry is carried out using one or both of the following: a steam pan dryer and a belt dryer.

[0076] Example Q: The method according to any one of the preceding examples, wherein the aerosol-forming substrate is dried to a residual water content of between 5 wt% to 15 wt% based on the total weight of the aerosol-forming substrate.

[0077] Example R: A solid aerosol-forming substrate for use in an aerosol-generating system, the aerosol-forming substrate comprising:

[0078] - an aerosol former;

[0079] - hydroxypropyl methylcellulose;

[0080] - a binder,

[0081] - a cellulose-based reinforcing agent, and

[0082] - water.

[0083] Example S: The aerosol-forming substrate according to the preceding example R, wherein the water is a residual water content of between 5 wt% to 15 wt% based on the total weight of the aerosol-forming substrate, preferably a residual water content of between 8 wt% to 11 wt% based on the total weight of the aerosol-forming substrate.

[0084] Example T: An aerosol-forming substrate according to any one of the preceding Examples R or S, comprising between 12 and 25 weight% of hydroxypropyl methylcellulose, preferably between 16 and 23 weight%, based on the total weight of the aerosol-forming substrate.

[0085] Example U: An aerosol-forming substrate according to any one of the preceding Examples R to T, comprising between 3 and 10 weight% of a binder, preferably between 4 and 7 weight%, based on the total weight of the aerosol-forming substrate.

[0086] Example V: An aerosol-forming substrate according to any one of the preceding Examples R to U, comprising between 40 and 60 weight% of an aerosol former, based on the total weight of the aerosol-forming substrate.

[0087] Example W: An aerosol-forming substrate according to any one of the preceding Examples R to V, comprising between 4 and 25 weight% of a cellulose-based reinforcing agent, preferably between 5 and 20 weight%, based on the total weight of the aerosol-forming substrate.

[0088] Example X: A solid aerosol-forming substrate for use in an aerosol-generating system produced according to the method of any one of Examples A to Q.

[0089] Features described in relation to one embodiment can equally apply to other embodiments of the application.

[0090] The application will be further described, by way of example only, with reference to the accompanying drawings in which:

[0091] Figure 1 A graph depicting the viscosity of the first slurry against the weight percentage of water is shown;

[0092] Figure 2 A flow chart of a method for producing an aerosol-forming substrate according to the application is depicted.

[0093] Figure 1 A graph 10 is shown in which the viscosity of the first slurry at a shear rate of 100 s -1 is plotted on the y-axis in mPas s, and the weight percentage content of water, based on the total weight of the first slurry, is plotted on the x-axis. This graph shows that between 10 and 25 weight% of water is optimal, where the viscosity of the first slurry is lowest. In part, the viscosity is between 900 mPa s and 2800 mPa The curve shows that at higher water contents, greater than 25 wt% to about 50 wt%, the viscosity of the first slurry is surprisingly very high (high viscosity area denoted with reference 14), which additionally leads to foaming upon mixing the first slurry (area denoted with reference 16 named "foaming"). At higher percentages of water between 55 wt% to 68 wt%, the viscosity is again reduced on the one hand, but on the other hand leads to the production of agglomerates (area denoted with reference 18 named "agglomerate production"). The dotted line denoted with 20 shows the viscosity of the guar gum glycerol reference mixture. This can be the reference mixture for which the mixing equipment is designed. The guar gum glycerol reference mixture contains 5 parts by weight of guar gum and 27 parts by weight of glycerol.

[0094] Thus, Figure 1 It appears that the inventors were able to determine that a small amount of water contained in the first slurry provides on the one hand a low viscosity and on the other hand also avoids the problems of foaming and agglomeration. This is somewhat surprising because the skilled person would expect that with increasing water content the viscosity would decrease. The low water content of water between 10 and 25 wt% also enables faster and easier drying of the final slurry in order to produce the aerosol-forming substrate.

[0095] Figure 2 A flow chart of the method for producing an aerosol-forming substrate according to the present application is depicted. Water and a cellulose-based reinforcing agent (denoted with "SA") can be mixed in a first step in order to provide a second slurry. Preferably, cellulose fibers are employed as cellulose-based reinforcing agent. In a further step, a binder, water and an aerosol-forming agent (denoted with "AF") and optionally nicotine (denoted with "N") and an organic acid (denoted with "OA") are mixed in order to provide a third slurry. Preferably, carboxymethyl cellulose is employed as binder and lactic acid is employed as organic acid. In a further step, hydroxypropyl methyl cellulose is added to the mixture of water and aerosol-forming agent and mixed in order to provide the first slurry.

[0096] All slurries: the first slurry, the second slurry and the third slurry are combined and mixed (see blocks denoted with "transfer" and "mixing"). The final slurry is subsequently transferred to a buffer tank and finally cast on e.g. a belt dryer to provide a dried sheet of aerosol-forming substrate. Example:

[0097] A first slurry is prepared with a weight ratio of 3:10:5 water: glycerol: hydroxypropyl methylcellulose. A second slurry is then prepared with a weight ratio of 3.5:111 cellulose fiber: water. A third slurry containing carboxymethyl cellulose is prepared and added to the second slurry in a weight ratio of 1:114.5 third slurry: second slurry. The first slurry is then added to the mixture of the third slurry and the second slurry to produce a final slurry.

Claims

1. A method for producing an aerosol-forming substrate, the method comprising: - providing a cellulose-based reinforcing agent, wherein the cellulose-based reinforcing agent is selected from the group consisting of cellulose fibres and microcrystalline cellulose, - providing a binding agent, wherein the binding agent is selected from the group consisting of methylcellulose and carboxymethylcellulose, - mixing hydroxypropyl methylcellulose, water and aerosol former to form a first slurry, the first slurry having a viscosity between 0.9 Pa s and 5 Pa s, and - combining the cellulose-based reinforcing agent, the binding agent and the first slurry so as to obtain a final slurry, and - drying the final slurry to obtain the aerosol-forming substrate.

2. A method for producing an aerosol-forming substrate, the method comprising: - providing a cellulose-based reinforcing agent, wherein the cellulose-based reinforcing agent is selected from the group consisting of cellulose powder, - providing a binding agent, wherein the binding agent is selected from the group consisting of methylcellulose and carboxymethylcellulose, - mixing hydroxypropyl methylcellulose, water and aerosol former to form a first slurry, the first slurry having a viscosity between 0.9 Pa s and 5 Pa s, and - combining the cellulose-based reinforcing agent, the binding agent and the first slurry so as to obtain a final slurry, and - drying the final slurry to obtain the aerosol-forming substrate.

3. The method according to claim 1 or 2, wherein the weight ratio of water:aerosol- forming agent:hydroxypropylmethylcellulose in the first slurry is 1 :2 to 10:2 to 3.

5.

4. The method according to claim 1 or 2, wherein water and aerosol-forming agent are first mixed in a weight ratio of water:aerosol-forming agent of 1 :2 to 10, and hydroxypropylmethylcellulose is subsequently added in a weight ratio of hydroxypropylmethylcellulose:aerosol-forming agent of 1 :1 to 3.

5. The method according to claim 1, wherein the cellulose-based reinforcing agent is cellulose fibres.

6. The method according to claim 1 or 2, wherein the aerosol-forming agent is selected from the group consisting of a polyol; an ester of a polyol; and an aliphatic ester of a mono-, di- or poly-carboxylic acid.

7. The method according to claim 6, wherein the polyol is at least one selected from the group consisting of triethylene glycol, 1,3-butanediol and glycerol.

8. The method according to claim 6, wherein the ester of a polyol is at least one selected from the group consisting of glycerol monoacetate, glycerol diacetate or glycerol triacetate.

9. The method according to claim 6, wherein the aerosol-forming agent is selected from the group consisting of propylene glycol and glycerol.

10. The method according to claim 9, wherein the aerosol-forming agent is glycerol.

11. The method according to claim 1 or 2, wherein the binding agent is carboxymethylcellulose.

12. The method according to claim 1 or 2, wherein the cellulose-based reinforcing agent and water are mixed in a weight ratio of cellulose-based reinforcing agent:water of 1 :20 to 40 to form a second slurry, and wherein the second slurry is combined with one or both of the first slurry or the binding agent.

13. The method according to claim 12, wherein the weight ratio of the second slurry:first slurry is 1 :4 to 8.

14. The method according to claim 13, wherein the weight ratio of the second slurry:first slurry is 1 :5 to 7.

15. The method according to claim 14, wherein the weight ratio of the second slurry:first slurry is 1 :6 to 6.

5.

16. The method of claim 12, wherein the binder is mixed with water to provide a third slurry.

17. The method of claim 16, wherein the weight ratio of binder:water is 1 :30 to 200.

18. The method of claim 16, wherein the first, second, and third slurries are formed, and wherein the slurries are subsequently mixed.

19. The method of claim 18, wherein the slurries are mixed in a weight ratio of first slurry:second slurry:third slurry of 1 :0.1 to 10:3 to 20.

20. The method of claim 19, wherein the slurries are mixed in a weight ratio of first slurry:second slurry:third slurry of 1 :0.5 to 8:4 to 15.

21. The method of claim 18, wherein nicotine is included in at least one of: the first slurry, the second slurry, the third slurry, or the final slurry.

22. The method of claim 1 or 2, wherein the aerosol-forming substrate is dried to a residual water content of between 5% to 15% by weight based on the total weight of the aerosol-forming substrate.

23. A solid aerosol-forming substrate for use in an aerosol-generating system produced by the method of any one of claims 1-22, the aerosol-forming substrate comprising: - between 40% to 60% by weight of an aerosol former based on the total weight of the aerosol-forming substrate; - between 12% to 25% by weight of hydroxypropyl methylcellulose based on the total weight of the aerosol-forming substrate; - between 3% to 10% by weight of a binder based on the total weight of the aerosol-forming substrate, wherein the binder is selected from the group consisting of: methylcellulose and carboxymethylcellulose, - between 4% to 25% by weight of a cellulose-based reinforcing agent based on the total weight of the aerosol-forming substrate, and - water.

24. The aerosol-forming substrate of claim 23, comprising between 16% to 23% by weight of hydroxypropyl methylcellulose.

25. The aerosol-forming substrate of claim 23 or 24, comprising between 4% to 7% by weight of a binder.

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