The present invention relates to a method for producing an aerosol-forming substrate. The present invention further relates to an aerosol-forming substrate produced according to the method.

Aerosol-forming substrates often contain cellulose, such as hydroxypropylmethyl cellulose. Additionally, aerosol-formers, such as polypropylene glycol or glycerin may be present. Furthermore, the aerosol-forming substrates may comprise binders. These aerosol forming substrates are prepared from slurries which also include water in order to wet and disperse these components. Mixing the different components often leads to agglomeration and to high viscosity solutions due to the low solubilities of some of the components either in water or in the aerosol-formers. These dispersions are often difficult to handle during the production of the aerosol-forming substrate. Mixing the slurries also may lead to excessive foaming. This may further complicate handling slurries.

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

One embodiment of the invention provides a method for producing aerosol-forming substrate comprising providing a cellulose based strengthening agent. The method may comprise also providing a binder. The method may also comprise mixing of hydroxypropylmethyl cellulose, water and an aerosol-former to form a first slurry, the first slurry having a viscosity of between 0.9 Pa s and 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The method may also include combining the several cellulose based strengthening agent, the binder and the first slurry in order to obtain a final slurry. The final slurry may be dried to obtain the aerosol-forming substrate.

Another embodiment of the invention provides a method for producing an aerosol forming substrate comprising providing a cellulose based strengthening agent. The method furthermore comprises providing a binder. Additionally, the method includes the method step of mixing of hydroxypropylmethyl cellulose, water and an aerosol-former to form a first slurry, the first slurry having a viscosity of between 0.9 Pa s and 5 Pa s, preferably between 0.9 Pa s and 4 Pa s. The cellulose based strengthening 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. In particular, a rheometer, such as a Modular Compact Rheometer MCR 302 marketed by the company Anton Paar GmbH could be employed. The initial shear rate for the rheology measurements might be 0.1 I/s and could be raised to the final value of 500 I/s. The number of points per analysis could be set to 150. The duration could be set to “Ramp Logarithmic” and the gap would be 1 mm. The temperature for the rheology measurements could be set to 23.5°C and the number of replicates per sample could be 3.

One advantage of the method of the present invention may be that hydroxypropylmethyl cellulose and the binder are not directly mixed which each other. This may avoid the formation of a dough-like mixture having very high viscosity. Such a dough-like mixture may be difficult to handle and may be difficult to transfer from one tank to another tank via pumping.

Additionally, mixing of hydroxypropylmethyl cellulose, water and an aerosol-former forms a first slurry having a sufficient viscosity of between 0.9 Pa s and 5 Pa s. This may allow the mixing of the components of the first slurry employing liquid mixers with at least one of impellers or dispersion discs. This may not require dough mixer equipment. The first slurry may have a sufficient high viscosity. This may avoid the formation of foam during mixing.

The hydroxypropylmethyl cellulose may serve as a film forming agent. The hydroxypropylmethyl cellulose may enable the formation of a film comprising the aerosol forming substrate for example via casting. The cellulose based strengthening agent may increase the substrate cohesion and the gel properties of the aerosol-forming substrate. The binder may serve as a thickening agent for the aerosol-forming substrate.

The different components of the aerosol-forming substrate may be added in different sequences of orders. For example, it may be possible to add the binder, the cellulose based strengthening agent and then mix the resulting slurry with the first slurry. Otherwise, it may be possible to mix one or both of the cellulose based strengthening agent and the binder with the first slurry.

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

The weight proportions of water: aerosol-former: hydroxypropylmethyl cellulose in the first slurry may be 1 : 2 to 10 : 2 to 3.5. This may amount to between 10 to 25 weight percent of water 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 also may enable an easy drying of the final slurry in order to produce the aerosol-forming substrate.

This amount of water may improve the dispersion of the hydroxypropylmethyl cellulose. Furthermore, these weight proportions may reduce the formation of foam. The low viscosity may allow an easy handling of the first slurry. This may allow the first slurry to the pumped between different containers during handling. The low amount of water in relation to hydroxypropylmethyl cellulose also may reduce the formation of agglomerates of hydroxypropylmethyl cellulose.

Preferably first water and the aerosol-former may be mixed in a weight proportion of water: aerosol-former of 1 :2 to 10. Subsequently hydroxypropylmethyl cellulose may be added in a weight proportion of hydroxypropylmethyl cellulose : aerosol-former of 1 :1 to 3. This procedure may be particularly appropriate in order to obtain a first slurry which can easily be processed. This also may avoid the formation of agglomerates. Such a first slurry also may be easy to mix, which also may reduce the amount of time for preparing the first slurry.

The cellulose based strengthening agent may be selected from a group consisting of: cellulose fibers, microcrystalline cellulose and cellulose powder. Preferably cellulose fibers are employed as cellulose based strengthening agent. The cellulose fibers may have a diameter of smaller than 0.03 mm, preferably a length of 0.02 mm. The fibers may have a length of between 0.7 to 1 .6 mm, pereferably a length of 0.9 mm.

These cellulose based strengthening agents may be particularly well suited in order to provide cohesion to the aerosol-forming substrate.

The aerosol former may be selected from a group consisting of: polyhydric alcohols, such as triethylene glycol, 1 ,3-butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids.

An aerosol-former may facilitate formation of a dense and stable aerosol below the combustion temperature of the aerosol-forming substrate. The aerosol may be substantially resistant to thermal degradation at the temperature of heating the aerosol-forming substrate. 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 and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Aerosol-formers may be polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1 ,3-butanediol and glycerine. The aerosol-former may be propylene glycol. The aerosol-former may comprise both glycerine and propylene glycol, preferably glycerin.

The binder may be selected from a group consisting of: methyl cellulose and carboxymethyl cellulose. Preferably carboxymethyl cellulose may be employed as a binder. The cellulose based strengthening agent may be mixed with water in weight proportions of the cellulose based strengthening 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.

Dispersing the cellulose based strengthening agent and water may reduce any problems related to agglomeration and viscosity. This also may avoid competition of the cellulose based strengthening agent for the water already bound to the other components of the final slurry, such as the binder or the hydroxypropylmethyl cellulose.

A weight proportion of the second slurry: first slurry may be 1 :4 to 8, preferably 1 :5 to 7, more preferably 1 :6 to 6.5.

Binder may be mixed with water to provide a third slurry. This also may reduce any problems of agglomeration and viscosity related to the binder. The weight proportion of binder: water may be 1 : 3 to 200, preferably 1 :4 to 150.

The first slurry, second slurry and third slurry may be formed and subsequently may be combined. This may be done by mixing, for example by employing slurry mixing tanks with one or both of an anchor stirrer or dispersion discs, preferably with one or several dispersion discs and an anchor stirrer.

The weight proportion of first slurry: second slurry: third slurry may be 1 : 0.1 to 10 : 3 to 20, preferably 1 : 0.5 to 8 : 4 to 15.

Within these weight proportions a final slurry may be formed which may easily be processed due to sufficient viscosity. In particular, these weight proportions may allow the different slurries to be mixed easily and transferred into different tanks.

In the sense of the present invention the denomination of the different slurries as “first slurrf, “second slurry’ or “third slurry’ does not indicate a sequence of adding the different slurries in a certain order to form the final slurry. For example, it is possible that the second slurry including the cellulose based strengthening agent is combined with the third slurry including the binder. Subsequently, the first slurry including the hydroxypropylmethyl cellulose, the water and the aerosol-former may be added to the mixture of the second and third slurry. This preferred sequence may avoid foaming during the mixing. Other sequences of combining the first slurry, second slurry and third slurry are also possible. One or both of the cellulose based strengthening agent and the binder may be combined with the first slurry without forming the second and third slurry.

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 between 0 to 5 weight percent, preferably between 0.1 to 3 weight percent, more preferably between 0.3 to 2 weight percent. 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 serve to protonate the nicotine. This may provide a nicotine salt with a higher solubility in the slurry. Preferably the organic acid may be selected from a 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 suited in order to form salts with the nicotine. Preferably, lactic acid may be used as an organic acid.

The final slurry may be prepared by mixing under a reduced pressure in comparison to standard pressure. The mixing may be done at a reduced absolute pressure of between 500 to 50 mbar. Particularly, the mixing may be performed under vacuum. This may avoid the formation of bubbles during mixing.

The aerosol-forming substrate may comprise plant-based material. The aerosol forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may alternatively comprise a non-tobacco-containing material. The aerosol-forming substrate may comprise homogenised plant-based material. The final slurry may contain low amounts 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 a tobacco extract. This may produce an aerosol-forming substrate containing a tobacco extract.

Additionally, the final slurry may contain flavorants. These flavorants may impart a flavor, such as menthol, apple, mint, grapefruit, or vanilla.

The final slurry may be prepared by mixing at shear rates of between 0.1 s ^_1 to 500 s ^_1 , preferably 1 s ^_1 to 150 s ^_1 . Similarly, the first slurry may be prepared at the same shear rates. This may allow for a sufficient mixing of the components of either the final slurry or the first slurry.

The mixing and the combining of the different slurries may be done by employing one or more of: a pulper, a high shear mixer with dispersion discs, a liquid mixer with Rushton impeller, an anchor stirrer and dispersion discs and a helicoidal agitator. These mixing tools are particularly suited in order to mix the hydroxypropylmethyl cellulose, the water and the aerosol-former for the first slurry. These mixing tools also may be suited in order to produce the second slurry and the third slurry.

During the mixing of the components of the first slurry the temperature may be kept between 15 degrees Celsius to 30 degrees Celsius. Preferably the temperature may be kept at room temperature. Thus, providing the first slurry by mixing the hydroxypropylmethyl cellulose, the water and the aerosol-former may be performed without heating. Heating may require more complex equipment, such as jacketed tanks and preheating of the components via heat exchangers. Therefore, it may be advantageous to avoid heating. Additionally, heating may result in an undesired release of the aerosol-former, the nicotine or any flavorants during production.

After mixing of the final slurry, the slurry may be cast for producing a sheet of aerosol forming substrate.

The final slurry may be cast on a belt dryer in order to provide the sheet. Drying the final slurry may be done employing one or both of: a steam pan dryer and a belt dryer. The velocity of the belt dryer may be between 8 meter per minute and 9 meter per minute. A doctor blade may be used in order to cast the final slurry on the belt dryer. Owing to the low amount of water in the final slurry, the velocity of the belt dryer may be increased in comparison to other slurries containing a higher amount of water. The final slurry may be dried to include residual water at temperatures of between 80 degrees Celsius and 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 between 5 weight percent to 15 weight percent water based on the total weight of the aerosol-forming substrate.

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

Another embodiment of the 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 hydroxypropylmethyl cellulose. The solid aerosol-forming substrate may comprise a binder. Additionally, a cellulose based strengthening agent may be present. The aerosol-forming substrate also may comprise water.

In a further embodiment of the invention a solid aerosol-forming substrate for use in an aerosol-generating system is provided. The aerosol-forming substrate comprises an aerosol- former. Additionally, hydroxypropylmethyl cellulose is present. The aerosol-forming substrate also comprises a binder and a cellulose based strengthening agent. Additionally, water, in particular residual water is present in the solid aerosol-forming substrate.

Such a solid aerosol-forming substrate may easily be produced by method according to the present invention. In particular, owing to the easy drying procedure residual water content may be present in the aerosol-forming substrate.

The residual water content may be between 5 weight percent and 15 weight percent based on the total weight of the aerosol-forming substrate. Preferably, the residual water content may be between 8 weight percent to 11 weight percent based on the total weight of the aerosol-forming substrate. The aerosol-forming substrate may contain between 12 weight percent to 25 weight percent of hydroxypropylmethyl cellulose based on the total weight of the aerosol-forming substrate. Preferably the aerosol-forming substrate may contain between 16 weight percent to 23 weight percent of hydroxypropylmethyl cellulose.

The aerosol-forming substrate may contain between 3 weight percent to 10 weight percent of binder based on the total weight of the aerosol-forming substrate. Preferably, between 4 weight percent and 7 weight percent of binder may be present in the aerosol-forming substrate.

The aerosol-forming substrate may contain between 40 weight percent to 60 weight percent of the aerosol-former based on the total weight of the aerosol-forming substrate.

Between 4 weight percent to 25 weight percent of cellulose based strengthening agent based on the total weight of the aerosol-forming substrate also may be present in the aerosol forming substrate. Preferably between 5 weight percent to 20 weight percent of cellulose based strengthening agent may be present in the aerosol-forming substrate.

The invention also provides a solid aerosol-forming substrate for use in an aerosol generating system which is produced according to any of the methods described herein.

The solid aerosol-forming substrate, in particular the sheets of aerosol-forming substrate may be part of an aerosol-generating article. The aerosol-generating article may comprise a substrate section including the solid aerosol-forming substrate. The aerosol generating article may have a tubular shape. Consequently, 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.

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

The aerosol-generating device may comprise 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 can be shaped to conform to the perimeter of the substrate receiving cavity. Alternatively, an external heating element may take the form of a metallic grid or grids, a flexible printed circuit board, a molded interconnect device (MID), ceramic heater, flexible carbon fibre heater or may be formed using a coating technique, such as plasma vapour deposition, on a suitable shaped substrate. A heating element may also be formed using a metal having a 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 materials. A heating element formed in this manner may be used to both heat and monitor the temperature of the external heating element during operation. The heating element may be configured as a resistive heating element.

Alternatively, the heating element may be configured as an induction heating element. The induction heating element may comprise an induction coil arranged at least partly 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.

In general, the susceptor is a material that is capable of absorbing electromagnetic energy and converting it to heat. When located in an alternating electromagnetic field, typically eddy currents are induced and hysteresis losses occur in the susceptor causing heating of the susceptor. Changing electromagnetic fields generated by one or several induction coils heat the susceptor, which then transfers the heat to the aerosol-generating article, such that an aerosol is formed. The heat transfer may be mainly by conduction of heat. Such a transfer of heat is best, if the susceptor is in close 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 arranged within the induction coil. The susceptor may form the sidewall of the cavity.

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. A preferred susceptor may comprise or consist of a ferromagnetic material, for example a ferromagnetic alloy, ferritic iron, or a ferromagnetic steel or stainless steel. A suitable susceptor may be, or comprise, aluminium. Preferred susceptors may be heated to a temperature in excess of 250 degrees Celsius.

Below, there is provided a non-exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

Example A: Method for producing an aerosol-forming substrate comprising: providing a cellulose based strengthening agent, providing a binder, mixing of hydroxypropylmethyl cellulose, water and an aerosol-former to form a first slurry, the first slurry having a viscosity of between 0.9 Pa s and 5 Pa s, and combining the cellulose based strengthening agent, the binder and the first slurry in order to obtain a final slurry, and drying the final slurry to obtain the aerosol-forming substrate.

Example B: Method according to Example A, wherein the weight proportions of water: aerosol-former: hydroxypropylmethyl cellulose in the first slurry are 1 : 2 to 10 : 2 to 3.5, preferably wherein first water and aerosol-former are mixed in a weight proportion of water : aerosol-former of 1 : 2 to 10 and subsequently hydroxypropylmethyl cellulose is added in a weight proportion of hydroxypropylmethyl cellulose : aerosol-former of 1 : 1 to 3 .

Example C: Method according to any of the preceding examples, wherein the cellulose based strengthening agent is selected from a group consisting of: cellulose fibers and microcrystalline cellulose and cellulose powder, preferably cellulose fibers.

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

Example E: Method according to any of the preceding examples, wherein the binder is selected from a group consisting of: methyl cellulose and carboxymethyl cellulose, preferably carboxymethyl cellulose.

Example F: Method according to any of the preceding examples, wherein the cellulose based strengthening agent and water are mixed in weight proportions of cellulose fibers : 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.

Example G: Method according to the preceding example F, wherein the weight proportion of the second slurry : first slurry is 1 : 4 to 8, preferably 1 : 5 to 7, more preferably 1 : 6 to 6.5.

Example FI: Method according to any of the preceding examples, wherein the binder is mixed with water to provide a third slurry, preferably wherein the weight proportion of binder : water is 1 : 30 to 200.

Example I: Method according to any of the preceding examples, wherein the first slurry, second slurry and third slurry are formed and wherein subsequently the slurries are mixed, preferably at a weight proportion 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.

Example J: 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. Example K: Method according to 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 wherein the organic acid is 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.

Example L: 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: Method according to any of the preceding examples, wherein the one or both of the first slurry and the final slurry is prepared by mixing at shear rates of between 0.1 s ¹ to 500 s ¹ , preferably 1 s ^-1 to 150 s ^-1 .

Example N: Method according to any of the preceding examples, wherein mixing is done employing one or more of: a pulper, a high shear mixer with dispersion discs, a liquid mixer with Rushton impeller, an anchor stirrer and dispersion discs, and a helicoidal agitator.

Example O: Method according to any of the preceding examples, wherein after mixing of the final slurry, the slurry is cast for producing a sheet of aerosol-forming substrate.

Example P: Method according to any of the preceding examples, wherein drying the final slurry is done employing one or both of: a steam pan dryer and a belt dryer.

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

Example R: A solid aerosol-forming substrate for use in an aerosol-generating system, the aerosol-forming substrate comprising: an aerosol-former; hydroxypropylmethyl cellulose; a binder, a cellulose based strengthening agent, and water.

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

Example T : The aerosol-forming substrate according to any of the preceding examples R or S, comprising between 12 weight percent to 25 weight percent based on the total weight of the aerosol-forming substrate of hydroxypropylmethyl cellulose, preferably between 16 weight percent to 23 weight percent.

Example U: The aerosol-forming substrate according to any of the preceding examples R to T, comprising between 3 weight percent to 10 weight percent based on the total weight of the aerosol-forming substrate of binder, preferably between 4 weight percent to 7 weight percent.

Example V: The aerosol-forming substrate according to any of the preceding examples R to U, comprising between 40 weight percent to 60 weight percent based on the total weight of the aerosol-forming substrate of aerosol-former.

Example W: The aerosol-forming substrate according to any of the preceding examples R to V, comprising between 4 weight percent to 25 weight percent based on the total weight of the aerosol-forming substrate of cellulose based strengthening agent, preferably between 5 weight percent to 20 weight percent.

Example X: A solid aerosol-forming substrate for use in an aerosol-generating system, produced according to a method of any of the examples A to Q.

Features described in relation to one embodiment may equally be applied to other embodiments of the invention.

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

Fig. 1 shows a graph depicting the viscosity of the first slurry in relation to the weight percentage of water;

Fig. 2 depicts a flow chart of the method for producing an aerosol-forming substrate in accordance with the present invention.

Figure 1 shows a graph 10, wherein on the y-axis the viscosity of the first slurry in mPas-s at a shear rate of 100 s ^_1 is plotted against the weight percent content of the water based on the total weight of the first slurry on the x-axis. The graph shows an optimum of between 10 to 25 weight percent of water, wherein the viscosity of the first slurry is the lowest. In part, the viscosity is in the range of 900 mPa-s and 2800 mPa-s, which is denoted with the reference numeral 12. The graph shows that at higher water contents of larger than 25 weight percent to around 50 weight percent the viscosity of the first slurry is surprisingly very high (area of high viscosity denoted with the reference numeral 14) which additionally also results in foaming when mixing the first slurry (area named “foaming” denoted with the reference numeral 16). Higher percentages of water of between 55 weight percent to 68 weight percent on the one hand decreases the viscosity again, but leads to the creation of agglomerates (area named “lump creation” denoted with the reference numeral 18). The dashed line denoted with 20 shows the viscosity of the guar glycerin reference mixture. This may be the reference mixture for which the mixing equipment was designed for. The guar glycerin reference mixture contains 5 weight parts of guar gum and 27 weight parts of glycerin.

Fig. 1 therefore shows that the inventors were able to identify a low amount of water included in the first slurry which on the one hand provides low viscosity and the other hand also avoids the problems of foaming and agglomeration. This is somehow surprising as a skilled person would expect that with increasing water content viscosity would be reduced. The low water content of between 10 to 25 weight percent of water also enables a quicker and easier drying of the final slurry in order to produce the aerosol-forming substrate.

Fig. 2 depicts a flow chart of the method of the present invention for producing the aerosol-forming substrate. Water and cellulose based strengthening agent, denoted with “SA” can be mixed in a first step in order to provide the second slurry. Preferably, cellulose fibers are employed as cellulose based strengthening agent. In a further step the binder, water and the aerosol-former, denoted with “AF’ and optionally nicotine denoted with “N” and organic acid, denoted with “OA” are mixed in order to provide a third slurry. Preferably, carboxy methyl cellulose is employed as a binder and lactic acid as organic acid. In a further step, the hydroxypropylmethyl cellulose is added to a mixture of water and aerosol-former and mixed in order to provide the first slurry.

All the slurries, the first slurry, the second slurry and the third slurry are combined and mixed (see boxes denoted with “transfer” and “mixing”). Subsequently the final slurry is transferred to a buffer tank and finally casted, for example on a belt dryer for providing dried sheets of aerosol-forming substrate.

Example:

A first slurry was prepared with a weight proportion of water : glycerin: hydroxypropylmethyl cellulose of 3 : 10 : 5. Subsequently a second slurry was prepared with a weight proportion of cellulose fibers: water of 3.5 : 111 . A third slurry containing carboxy methyl cellulose is prepared and added to the second slurry in a weight proportion of third slurry: second slurry of 1 : 114.5. The first slurry is subsequently added to the mixture of the third and second slurry for preparing the final slurry.