EP4176128B1 - Heat-resistant wrapping paper for aerosol-generating articles - Google Patents

Description

FIELD OF INVENTION

The invention relates to a wrapping paper for an aerosol-generating article which is comparatively heat-resistant and therefore still has sufficient mechanical strength after the article has been used to ensure that the article can be handled without any problems and also has a fire-retardant effect so that the aerosol-generating article made from it cannot be smoked like a smoking article. This is achieved by a high content of certain carbon formers in the wrapping paper.

BACKGROUND AND STATE OF THE ART

Aerosol-generating articles are known in the prior art that comprise an aerosol-generating material and a paper that envelops the aerosol-generating material, thus forming a typically cylindrical rod. The aerosol-generating material is a material that releases an aerosol when exposed to heat, whereby the aerosol-generating material is only heated but not burned. In many cases, the aerosol-generating article also comprises a filter that can filter components of the aerosol and that is enveloping a filter wrapping paper and another wrapping paper that connects the filter and the enveloping rod with aerosol-generating material.

When an aerosol-generating article is used as intended, it is common for the aerosol-generating material to be heated but not burned. This heating can be done, for example, by an external device into which the aerosol-generating article is inserted, or by a heat source attached to one end of the aerosol-generating article which is activated to use the article, for example by lighting it. When the aerosol-generating material is heated, the wrapping paper is also heated and thermally degraded. This can cause the wrapping paper to lose so much strength that it tears when the aerosol-generating article is removed from the heating device. This requires increased cleaning effort from the consumer and is therefore undesirable. Even with aerosol-generating articles with an integrated heat source, the wrapping paper can lose its strength when heated, causing the heat source to fall off and pose a fire risk.

In addition, it is desirable to prevent the consumer from inadvertently using aerosol-generating articles in the same way as a cigarette and attempting to light one end of the aerosol-generating article, thereby starting a combustion or smoldering process of the aerosol-generating material. To this end, it is necessary that the wrapping material of the aerosol-generating article has flame-retardant properties.

Attempts to make wrapping papers for such aerosol-generating articles heat-resistant or fire-retardant have only been partially successful.

In WO 2015/082648 For example, a wrapping paper is described that consists of relatively few cellulose fibers and is coated with a composition of lime and a binding agent, so that at least 50% of the wrapping paper is made up of lime. The disadvantage of this wrapping material is that the thick coating makes it relatively brittle and creates a lot of dust when the wrapping paper is processed into an aerosol-generating article. In addition, the strength is not particularly high due to the low proportion of cellulose fibers.

In WO 2011/117750 describes a wrapping material that consists of a laminate of aluminum foil and paper. The aluminum foil faces the aerosol-generating material and partially protects the paper from the effects of heat. The disadvantages of this wrapping material are the complex manufacturing process and the lack of biodegradability, because experience shows that many aerosol-generating articles are simply disposed of in the environment after use.

EP 1 084 629 A1 discloses methods for improving the ash properties of a wrapping paper for a smoking article and for improving the ash properties of the smoking article as a whole. In particular, it is disclosed that the ash cohesion of a wrapping paper is significantly improved when carbon fibers having an average length of less than about 1.9 cm are incorporated into the paper in an amount of up to about 60% by weight. Wrapping papers made with carbon fibers exhibit superior ash properties compared to wrapping papers containing only flax or other cellulosic fibers. In addition, the ash cohesion of the paper is improved without compromising the quality of other ash properties.

US$4,998,543 discloses a cigarette comprising a tobacco rod surrounded by an inner and an outer paper layer designed to reduce the amount of sidestream smoke produced by the cigarette, the outer paper layer having a basis weight of about 30-70 g/m ² , an initial porosity of about 2-10 cm ³ /min by the Coresta process, a calcium carbonate loading of about 30-40 wt.% using calcium carbonate having a surface area of about 20-80 m ² /g by the BET process, about 2-10 wt.% of a combustion chemical, about 0-1 wt.% monoammonium phosphate, and about 0-1 wt.% sodium carboxymethyl cellulose. The outer paper is perforated to increase its porosity to about 50-100 cm ³ /min by the Coresta process. The inner paper layer has a basis weight of about 15-25 g/m ² , a porosity of about 20-40 cm ³ /min by the Coresta process, a calcium carbonate loading of about 2-15 wt.%, and has about 0-2 wt.% of a caustic chemical. There is therefore an interest in having a wrapping paper available that is still sufficiently strong after heating, has a fire-retardant effect and is still biodegradable. In addition, when designing wrapping paper for aerosol-generating articles, legal regulations, toxicology and the influence of the wrapping paper on the taste of the aerosol-generating article must be taken into account.

SUMMARY OF THE INVENTION

The invention is based on the object of providing an aerosol-generating article with a wrapping paper that is largely heat-resistant or fire-retardant and has favorable properties with regard to strength, processability, biodegradability and taste influence. A wrapping paper that can be a component of the aerosol-generating article according to the invention is referred to below as "wrapping paper according to the invention".

Aerosol-generating articles within the meaning of this invention are rod-shaped articles that comprise an aerosol-generating material and a wrapping paper that envelops the aerosol-generating material, whereby the aerosol-generating material is only heated and not burned when used as intended. Heating without burning occurs for typical aerosol-generating materials, such as tobacco, in any case when the aerosol-generating material is heated to a temperature of at most 400°C.

This object is achieved by an aerosol generating article according to claim 1. Advantageous further developments are specified in the dependent claims.

The inventors have found that this object can be achieved by a wrapping paper which is suitable for use on aerosol-generating articles according to the invention and which comprises cellulose fibres and a carbon former, wherein the cellulose fibres make up at least 70% and at most 95% of the mass of the wrapping paper and the carbon former in a concentration of not less than 5% and not more than 20% by mass of the wrapping paper and is present in the wrapping paper in such a concentration that the quotient r = R _T /R _o of the tensile strength R _o measured according to ISO 1924-2:2008 under the conditions of ISO 187:1990 and the tensile strength R _T measured according to ISO 1924-2:2008 under the conditions of ISO 187:1990 after the wrapping paper has been exposed to a temperature of 230 °C for one minute is not less than 0,20 and not more than 0,90.

According to the inventors' findings, the high proportion of cellulose fibers is necessary to achieve a high initial strength of the wrapping paper. It is known that many carbon formers that could potentially be used in paper damage the cellulose fibers in the paper and thus quickly lead to a significant loss of strength when heated. However, they partially protect the cellulose fibers further in the paper structure from thermal degradation. Since paper is generally highly flammable, it is generally believed that carbon formers would have to be used in paper in very high concentrations to achieve an effective fire-retardant effect. However, according to general opinion and also according to experiments by the inventors, at this concentration the cellulose fibers are so severely damaged and the strength of the paper is so greatly reduced that their use is not sensible.

In contrast, the inventors have recognized that for a few carbon formers there is actually a suitable narrow concentration range in which both a good fire-retardant effect is present and the reduction in the strength of the paper is not too high.

Only the combination of the high content of cellulose fibers and the appropriately selected concentration of the carbon former makes it possible to produce a wrapping paper that, thanks to its initially high strength and despite the loss of strength due to the carbon former, has such a high tensile strength even after heating that an aerosol-generating article made from it can be easily removed from the heating device and there is no risk that a heat source integrated into the aerosol-generating article could fall off. The fire-retardant effect is also sufficient that the aerosol-generating article cannot be smoked like a cigarette.

The components of the wrapping paper also allow for excellent biodegradability and very good processability in the production of the aerosol-generating article.

The wrapping paper requires cellulose fibers for its strength, with the cellulose fibers making up at least 70% and at most 95% of the mass of the wrapping paper. To achieve an even more favorable ratio between cellulose fibers and carbon former, the proportion of cellulose fibers can preferably be at least 75% and at most 90% and very particularly preferably at least 80% and at most 90%, in each case based on the mass of the wrapping paper.

The cellulose fibers are preferably obtained from one or more plants selected from the group consisting of conifers, deciduous trees, spruce, pine, fir, beech, birch, eucalyptus, flax, hemp, jute, ramie, abaca, sisal, kenaf and cotton. The cellulose fibers can also be wholly or partly fibers made from regenerated cellulose, such as Tencel ^™ fibers, Lyocell ^™ fibers, viscose fibers or Modal ^™ fibers.

Preferably, the pulp fibers are formed from pulp fibers from coniferous trees to a proportion of at least 40% and at most 100% based on the mass of the pulp fibers, because these pulp fibers impart a high level of strength to the wrapping paper.

The wrapping paper contains a carbon former, whereby the carbon former makes up at least 5% and at most 20% of the mass of the wrapping paper. According to the inventors' findings, the carbon former protects the cellulose fibers inside the paper structure from excessive oxidation, but also damages the cellulose fibers itself, so the concentration of the carbon former must be within a narrow range and depends on the type of carbon former. As the concentration of the carbon former increases, the fire-retardant effect increases, but the strength of the wrapping paper decreases again after heating due to increasing damage to the cellulose fibers. The proportion of carbon formers in the wrapping paper is therefore preferably at least 9% and at most 16% of the mass of the wrapping paper.

The carbon former is preferably an ammonium phosphate and particularly preferably a monoammonium phosphate, a diammonium phosphate, a triammonium phosphate, an ammonium polyphosphate or a mixture thereof. The carbon former is less preferably a guanylurea phosphate, guanidine phosphate, phosphoric acid, a phosphonate, melamine phosphate, dicyandiamide, boric acid or borax. These less preferred compounds are more difficult to process or are not entirely toxicologically unthinkable. Sodium polyphosphate is also a carbon former, but not according to the invention.

The choice of the concentration of the carbon former is not free within the specified range, but depends on the type of carbon former and must be made in such a way that the reduction in the strength of the wrapping paper after heating is not too high.

For this purpose, the tensile strength of the wrapping paper in the longitudinal direction is determined as a characteristic of the strength and is determined first under the conditions of ISO 187:1990 and then after heating the wrapping paper. More precisely, the loss of strength can be determined by the following method.

First, a paper sample of appropriate geometry, typically a 15 mm wide strip, is conditioned according to ISO 187:1990 and tested in a tensile test according to ISO 1924-2:2008. The tensile strength depends on the direction in which the paper sample was taken. Tensile strength here always means the tensile strength in the running direction of the wrapping paper during paper production, the so-called longitudinal direction. The initial tensile strength, designated R _o , is determined according to the invention by conditioning the paper sample without prior thermal stress according to ISO 187:1990 and testing it according to ISO 1924-2:2008. The tensile strength after thermal stress, R _T , is determined by exposing the sample to a temperature of 230 °C in an air atmosphere for 1 minute, whereby the air can reach essentially all sides of the paper sample and there is little air flow. The paper sample is then conditioned in accordance with ISO 187:1990 and the tensile strength is also determined in accordance with ISO 1924-2:2008. The quotient r = R _T /R _o describes which proportion of the tensile strength is retained after thermal stress on the wrapping paper and thus characterizes the thermal resistance of the wrapping paper. High values of the quotient r describe high thermal resistance. According to the invention, the concentration of the carbon former in the wrapping paper should be selected such that the quotient r of the tensile strength R _T after thermal stress (230°C for 1 minute) and the initial tensile strength R _o is at least 0.20 and at most 0.90 and particularly preferably at least 0.25 and at most 0.80. This means that the tensile strength is not reduced by more than 80%.

The quotient can be influenced by the amount of cellulose fibers and the type and concentration of the carbon former, with more cellulose fibers leading to a higher initial tensile strength R _o and an increasing concentration of the carbon former generally leading to a falling tensile strength after thermal stress R _T. The negative effect of the carbon former on the tensile strength R _T must be weighed against the increasingly better fire-retardant effect with increasing concentration depending on the type of use on the aerosol-generating article. It has been shown that in the inventive and preferred interval A very good compromise can be found for the concentration of the carbon former for aerosol generating articles.

Preferably, the tensile strength R _T after thermal stress should not fall below a certain value so that the aerosol-generating article can be handled without problems during and after use. Preferably, therefore, the tensile strength of the wrapping paper R _T in the longitudinal direction after thermal stress is at least 8 N/15 mm and at most 50 N/15 mm and particularly preferably at least 10 N/15 mm and at most 40 N/15 mm.

According to the inventors' findings, it is important how the carbon former is distributed over the thickness of the wrapping paper. In general, a good fire-retardant effect can be achieved if the carbon former is distributed essentially homogeneously in the wrapping paper. In a preferred embodiment, however, the wrapping paper is designed such that the side of the wrapping paper facing the aerosol-generating material contains a higher proportion of carbon former than the other side of the wrapping paper. The side facing the aerosol-generating material is typically exposed to higher thermal stress. A higher content of carbon former on this side of the wrapping paper can therefore contribute particularly well to the fire-retardant effect. This allows the proportion of carbon former in the wrapping paper to be reduced without compromising the fire-retardant effect and thus the proportion of cellulose fibers in the wrapping paper to be increased with the same basis weight, thereby increasing the overall strength of the wrapping paper. Alternatively, with this preferred distribution of the carbon former in the wrapping paper, the basis weight can also be reduced without compromising the fire-retardant effect, which reduces the material requirement.

The distribution of the carbon former in the wrapping paper can be influenced by the manufacturing process, as explained below.

Preferably, the carbon former is distributed substantially uniformly over at least 70% of the surface area of the wrapping paper, particularly preferably over at least 95% of the surface area, wherein fluctuations in the proportion of carbon former within these surfaces are only due to the manufacturing process and are not intended.

A disadvantage of the carbon former may be that it darkens the wrapping paper when exposed to heat. This disadvantage can be overcome by connecting the wrapping paper according to the invention to another paper layer, for example by gluing it, so that the wrapping paper according to the invention is exposed to the aerosol-generating material and the other paper layer is attached to the side facing away from the aerosol-generating material. When thermally stressed, this additional paper layer covers the wrapping paper so that the color visible from the outside is not changed or only slightly changed.

The wrapping paper is therefore preferably connected to a paper layer. This paper layer particularly preferably comprises cellulose fibers and lime particles, with the lime particles making up at least 15% and at most 40% of the mass of the paper layer. The lime particles ensure that the paper layer is white in color and has a high opacity, so that the discoloration of the wrapping paper according to the invention underneath is not or only slightly visible. It should be noted that the wrapping paper with the additional paper layer as a whole could in principle also be referred to as "two-layer wrapping paper", but this nomenclature is avoided here. Instead, in the language used in the present disclosure, such a two-layer structure is referred to as "wrapping paper with an additional paper layer", because only the portion of the two-layer structure referred to as "wrapping paper" has to meet the above requirements with regard to the proportion of cellulose fibers, carbon formers and the quotient of the tensile strengths.

In addition to the cellulose fibers and the carbon former, the wrapping paper according to the invention can contain other components. These include, for example, fillers, sizing agents, wet strength agents, additives, processing aids, humectants and flavorings. The expert can choose these components according to his experience. Wet strength agents in particular can be helpful for use on aerosol-generating articles because the aerosol formed when the aerosol-generating article is used has a high moisture content. The wrapping paper can partially absorb the water from the aerosol, which reduces its strength. This can be prevented by using wet strength agents.

The fillers in the wrapping paper according to the invention can help to ensure that the wrapping paper discolors less. However, the fillers also reduce the tensile strength of the wrapping paper, so their proportion should not be too high. The proportion of fillers in the wrapping paper is therefore preferably at least 0% and at most 20%, particularly preferably at least 0% and at most 10%, and very particularly preferably at least 0% and at most 5%, in each case based on the mass of the wrapping paper.

The filler is preferably selected from the group consisting of calcium carbonate, magnesium carbonate, titanium dioxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, kaolin, talc and mixtures thereof. Less preferably, the filler is a carbonate.

In a preferred embodiment, the wrapping paper additionally contains starch or a starch derivative or is coated with starch or a starch derivative. In this preferred embodiment, the proportion of starch or starch derivative is at least 2% and at most 10% of the mass of the wrapping paper. This preferred embodiment offers the additional advantage of resistance to the penetration of oils. The aerosol-generating material can contain oils, for example flavorings, which penetrate the wrapping paper during storage or use of the aerosol-generating article and lead to stains. The resistance to the penetration of oils can be determined according to TAPPI T559 cm-12 and is given as the KIT level. In this preferred embodiment, the KIT level is at least 4 and at most 8.

The basis weight of the wrapping paper can vary, with a higher basis weight generally also meaning a higher tensile strength. However, with a higher basis weight, the wrapping paper also becomes stiffer and more difficult to process and the material requirement increases. The basis weight of the wrapping paper according to the invention is therefore preferably at least 15 g/m ² and at most 80 g/m ² , particularly preferably at least 20 g/m ² and at most 60 g/m ² . The basis weight of the wrapping paper can be determined according to ISO 536:2019.

The thickness of the wrapping paper primarily influences the flexural rigidity and the heat transport within the wrapping paper. A high flexural rigidity is advantageous because the aerosol-generating article made from the wrapping paper then deforms less; on the other hand, a high flexural rigidity can cause problems due to the restoring forces if the aerosol-generating material is to be wrapped with the wrapping paper. A high thickness slows down the heat transport through the wrapping paper and is also advantageous for this reason. The thickness of the wrapping paper according to the invention is preferably at least 25 µm and at most 100 µm and particularly preferably at least 40 µm and at most 80 µm. The thickness can be determined on a single layer according to ISO 534:2011.

The initial tensile strength R _o of the wrapping paper, measured in the longitudinal direction, is preferably at least 10 N/15 mm and at most 100 N/15 mm, particularly preferably at least 20 N/15 mm and at most 80 N/15 mm. A high tensile strength can be achieved by a high proportion of cellulose fibres. However, this also means a higher material expenditure, which is why it is not sensible to try to achieve a particularly high tensile strength. The preferred intervals allow a particularly favourable combination of problem-free Processability and material consumption. The tensile strength can be determined according to ISO 1924-2:2008.

The aerosol-generating material often contains humectants, so that when heated, the resulting aerosol has a comparatively high moisture content. This moisture can reduce the strength of the wrapping paper, which is why it is advantageous if the wrapping paper also has a corresponding strength when wet. The wet breaking strength in the longitudinal direction is therefore preferably at least 1 N/15 mm and at most 10 N/15 mm and particularly preferably at least 2 N/15 mm and at most 8 N/15 mm. The wet breaking strength in the longitudinal direction can be determined according to ISO 12625-5:2016.

The air permeability of the wrapping paper can be low. Low air permeability is often achieved by more intensively refining the pulp fibres. This also contributes to increasing strength, so that the air permeability is preferably at least 0 cm ³ /(cm ² min kPa) and at most 50 cm ³ /(cm ² min kPa) and particularly preferably at least 0 cm ³ /(cm ² min kPa) and at most 20 cm ³ /(cm ² min kPa). The air permeability can be measured according to ISO 2965:2019.

If the wrapping paper according to the invention is visible from the outside on the aerosol-generating article, the optical properties can be important. In general, high opacity and high whiteness are desirable. Both properties can be significantly influenced by the type and amount of filler in the wrapping paper. The opacity is preferably at least 40% and at most 90%, particularly preferably at least 45% and at most 80%. The whiteness is preferably at least 80% and at most 95%, particularly preferably at least 83% and at most 90%.

Aerosol-generating articles can be manufactured from the wrapping material according to the invention using methods known from the prior art. An aerosol-generating article according to the invention therefore comprises an aerosol-generating material and a wrapping paper according to one of the embodiments described above, wherein the wrapping paper envelops the aerosol-generating material.

In a preferred embodiment of the aerosol generating article, the proportion of said carbon former is higher on one side of the wrapping paper than on the other side and the side with the higher proportion of carbon former faces the aerosol generating material.

The wrapping paper according to the invention can be advantageously used in aerosol-generating articles, which is why the use of the wrapping paper according to the invention in aerosol-generating articles is also disclosed.

1. A - Suspendieren von Zellstofffasern in einer wässrigen Suspension,
2. B - Mahlen der suspendierten Zellstofffasern in einem Mahlaggregat,
3. C - Aufbringen der Suspension auf ein umlaufendes Sieb,
4. D - Bilden einer Faserbahn durch Entwässern der Suspension,
5. E - Pressen der Faserbahn,
6. F - Trocknen der Faserbahn,
7. G - Aufrollen des Umhüllungspapiers, wobei

• zwischen den Schritten F und G mindestens eine Kohlebildner enthaltende Zusammensetzung auf die Faserbahn aufgetragen wird und die Faserbahn getrocknet wird, um das Umhüllungspapier zu bilden,
• und wobei das Umhüllungspapier aus Schritt G Zellstofffasern und Kohlebildner umfasst und die Zellstofffasern mindestens 70% und höchstens 95% der Masse des Umhüllungspapiers ausmachen und der Kohlebildner mindestens 5% und höchstens 20% der Masse des Umhüllungspapiers ausmacht, und wobei der Kohlebildner in einer solchen Konzentration im Umhüllungspapier vorhanden ist, dass der Quotient r = R_T/R_o aus der Zugfestigkeit R_o gemessen nach ISO 1924-2:2008 unter den Bedingungen von ISO 187:1990 und aus der Zugfestigkeit R_T gemessen nach ISO 1924-2:2008 unter den Bedingungen von ISO 187:1990, nachdem das Umhüllungspapier eine Minute lang einer Temperatur von 230°C ausgesetzt war, mindestens 0,20 und höchstens 0,90 beträgt.

The wrapping paper according to the invention can be produced by the following process according to the invention, comprising steps A to G.

1. A - Suspending pulp fibres in an aqueous suspension,
2. B - Grinding the suspended pulp fibres in a grinding unit,
3. C - Applying the suspension to a rotating sieve,
4. D - Forming a fibrous web by dewatering the suspension,
5. E - Pressing the fibre web,
6. F - Drying of the fibre web,
7. G - Rolling up the wrapping paper, whereby

• between steps F and G, at least one carbon-forming composition is applied to the fibrous web and the fibrous web is dried to form the wrapping paper,
• and wherein the wrapping paper from step G comprises pulp fibers and carbon former, and the pulp fibers make up at least 70% and at most 95% of the mass of the wrapping paper and the carbon former makes up at least 5% and at most 20% of the mass of the wrapping paper, and wherein the carbon former is present in the wrapping paper in such a concentration that the quotient r = R _T /R _o of the tensile strength R _o measured according to ISO 1924-2:2008 under the conditions of ISO 187:1990 and of the tensile strength R _T measured according to ISO 1924-2:2008 under the conditions of ISO 187:1990 after the wrapping paper has been exposed to a temperature of 230°C for one minute is at least 0.20 and at most 0.90.

Preferably, the step of applying the carbon-forming composition to the fibrous web is carried out by one or a combination of two or more of the following steps: F.1 Application of a composition containing carbon formers to the fibre web in a size press of a paper machine, F.2 one-sided application of a composition containing carbon formers to the fibre web in a film press or in a coating unit of a paper machine, and F.3 one-sided application of a composition containing carbon formers to the fibre web by printing, in particular gravure printing or spraying.

Step F.1 is carried out in a size press and the fiber web is saturated with a composition containing carbon formers. This variant offers the advantage that that it is easy to carry out. It generally leads to a largely homogeneous distribution of the carbon former across the thickness of the wrapping paper, so that comparatively more carbon former is needed to achieve the desired effect. However, it is also possible to adjust the settings of the size press in this step so that the carbon former is unevenly distributed across the thickness of the fiber web, and therefore of the wrapping paper.

According to step F.2, the composition containing carbon former is applied to one side of the fiber web in a film press or in a coating unit. This results in an uneven distribution of the carbon former over the thickness of the wrapping paper and the high flame retardant effect can be achieved by a lower proportion of carbon former in the wrapping paper.

According to step F.3, the composition containing carbon formers is applied to one side of the fibrous web by printing or spraying, wherein in particularly preferred embodiments the composition is printed onto one side of the fibrous web by a gravure printing unit. The fibrous web is preferably dried, rolled up and unrolled again before step F.3. In the rolled state, the fibrous web can then be transported to another device on which the composition is applied by printing or spraying. While steps F.1 and F.2 are generally carried out on the same paper machine on which the wrapping paper is produced, the application according to step F.3 typically takes place in a separate device.

In a particularly preferred embodiment, steps F.1 and F.3 are combined, so that in a step F.1 the fiber web is first impregnated with a composition containing carbon formers in a size press and in step F.3 a further composition containing carbon formers is printed onto one side of the fiber web in a gravure printing unit. In this particularly preferred embodiment, the carbon former is distributed both in the wrapping paper and in a higher concentration on one side of the wrapping paper, whereby the fire-retardant effect can be significantly increased again.

In another particularly preferred embodiment, steps F.1 and F.2 are combined, with step F.1 being carried out in a size press and step F.2 in a coating unit. In this particularly preferred embodiment, the wrapping paper can be produced particularly efficiently because, for example, all application devices can be integrated into a paper machine.

Irrespective of which of steps F.1, F.2 or F.3 is/are used, the composition containing carbon formers is preferably applied to at least 70% of the surface area of the wrapping paper, particularly preferably to at least 95% of the surface area of the wrapping paper.

The composition used in steps F.1, F.2 or F.3 contains the carbon former and a solvent, the solvent preferably being water. The amount of carbon former in the composition can vary and depends on the type of application method, the application amount and the desired amount of carbon former in the wrapping paper. The person skilled in the art is able to determine a suitable composition from these perspectives and to design the application method accordingly.

In the most preferred embodiment, one of steps F.1 and F.2 is carried out, the fibrous web is then dried, rolled up and unrolled again, and then step F.3 is carried out, wherein the fibrous web in the dried, rolled up state before step F.3 preferably contains the carbon former in an amount of at least 5% and at most 10% of the mass of the fibrous web in this dried, rolled up state.

If steps F.1, F.2 and/or F.3 are combined in any form, the carbon former-containing compositions applied in steps F.1, F.2 and/or F.3 may be different.

In the wrapping paper according to step G, the cellulose fibers make up at least 70% and at most 95% of the mass of the wrapping paper. To achieve an even more favorable ratio between cellulose fibers and carbon former, the proportion of cellulose fibers can preferably be at least 75% and at most 90% and very particularly preferably at least 80% and at most 90%, in each case based on the mass of the wrapping paper according to step G.

The cellulose fibers in step A are preferably obtained from one or more plants selected from the group consisting of conifers, deciduous trees, spruce, pine, fir, beech, birch, eucalyptus, flax, hemp, jute, ramie, abaca, sisal, kenaf and cotton. The cellulose fibers can also be wholly or partly fibers made from regenerated cellulose, such as Tencel ^™ fibers, Lyocell ^™ fibers, viscose fibers or Modal ^™ fibers.

Preferably, the pulp fibres in step A are made from pulp fibres from conifers in a proportion of at least 40% and at most 100% based on the mass of the pulp fibres formed because these pulp fibers impart a high initial strength to the wrapping paper in step G.

The wrapping paper according to step G contains carbon formers, the carbon former making up at least 5% and at most 20% of the mass of the wrapping paper. Preferably, the proportion of carbon formers in the wrapping paper according to step G is at least 9% and at most 16% of the mass of the wrapping paper.

The carbon former is preferably an ammonium phosphate and particularly preferably a monoammonium phosphate, a diammonium phosphate, a triammonium phosphate, an ammonium polyphosphate or a mixture thereof. The carbon former is less preferably a guanylurea phosphate, guanidine phosphate, phosphoric acid, a phosphonate, melamine phosphate, dicyandiamide, boric acid or borax. These less preferred compounds are more difficult to process or are not entirely toxicologically unthinkable. Sodium polyphosphate is also a carbon former, but not according to the invention.

In a preferred embodiment, the wrapping paper according to step G is a wrapping paper according to one of the embodiments described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, some preferred embodiments of wrapping papers are described which can be part of an aerosol generating article according to the invention and are referred to in the present disclosure for short as "wrapping paper according to the invention".

A wrapping paper P1 according to the invention was produced on a fourdrinier paper machine. For this purpose, pulp fibers were suspended in water (step A) and ground in a grinding unit (step B). The suspension was then applied to a rotating screen (step C) and dewatered there to form a fiber web (step D). The fiber web was pressed (step E) to further dewater it and dried by contact with heated drying cylinders (step F). In the size press of the paper machine, the fiber web was completely impregnated on both sides with a composition comprising water and monoammonium phosphate (step F.1) and the fiber web was then dried by contact with heated drying cylinders. Finally, the fiber web was rolled up (step G) to obtain a wrapping paper P1 according to the invention.

The amount of pulp fibers was chosen so that the wrapping paper P1 contained about 87% of the mass of pulp fibers. The composition in step F.1 comprised water and monoammonium phosphate and was chosen together with the settings of the size press so that the amount of monoammonium phosphate in the wrapping paper after step G was about 7%. It can be assumed that the distribution of the monoammonium phosphate in the wrapping paper P1 was largely homogeneous across the thickness.

A wrapping paper P2 according to the invention was produced from the wrapping paper P1 according to the invention by unrolling the roll of wrapping paper P1 and printing a composition comprising water and monoammonium phosphate over the entire surface of one side of the wrapping paper in a gravure printing unit (step F.3). The wrapping paper was then dried in a hot air dryer and rolled up again (step G). The composition in step F.3, together with the settings of the gravure printing unit and in particular the geometry of the printing cylinder, was selected such that in the finished wrapping paper P2 a total of 12.5% of the mass of the wrapping paper was made up of monoammonium phosphate. This resulted in an inhomogeneous distribution of the monoammonium phosphate in the wrapping paper, so that the content of monoammonium phosphate on the printed side was higher than on the other side.

In the wrapping paper P2, 82% of the mass was made up of pulp fibres.

A wrapping paper Z1 not according to the invention comprising 70% cellulose fibres and 29% precipitated lime, but without carbon formers, was used as a comparative example.

Likewise, a wrapping paper Z2 not according to the invention comprising 90% cellulose fibers and 10% sodium polyphosphate, (NaPO ₃ ) _n , as carbon former was used as a comparative example.

In order to obtain a further wrapping paper P3, the non-inventive wrapping paper Z1 was bonded to the inventive wrapping paper P2 to form a two-layer structure in such a way that the side of the wrapping paper P2 with the higher monoammonium phosphate content faced away from the wrapping paper Z1.

The data of the wrapping papers P1 and P2 according to the invention, the two-layer structure P3 and the comparative examples Z1 and Z2 not according to the invention were determined according to the usual standards.

To determine the tensile strength after thermal stress R _T, the wrapping papers P1, P2, P3 and Z1, Z2 were stored for 1 minute in a drying cabinet heated to 230°C. They were then conditioned according to ISO 187:1990 and the tensile strength was measured according to ISO 1924-2:2008.

The quotient r = R _T /R _o was determined from the initial tensile strength R _o and the tensile strength R _T after thermal stress to characterize the thermal resistance.

All data of the wrapping papers P1, P2, P3 and Z1, Z2 can be found in Table 1. Table 1 P1 P2 P3 Z1 Z2 Basis weight g/ ^m2 28.8 31.9 72.2 29 30.3 thickness µm 46.4 46.4 79.2 45.3 47.3 Tensile strength R _o N/15mm 30.4 36.0 65.7 15.2 32.7 Tensile strength R _T N/15mm 16.7 12.1 27.2 14.3 6.3 r = R _T /R _o 0.55 0.34 0.41 o,94 0.19 Wet breaking strength N/15mm 3.0 3.0 10.1 2.5 3.1 Air permeability cm ³ /(cm ² ·min·kPa) < 20 < 20 < 20 60 <20 opacity % 44.8 41.8 41.2 white % 87.4 88.6 88.6

Table 1 shows that in the wrapping papers P1 and P2 according to the invention, as well as in the two-layer structure P3 containing the wrapping paper P2 according to the invention, the tensile strength is reduced by thermal stress to 34% to 55%. In the non-inventive comparative example Z1, which does not contain a carbon former, the tensile strength is hardly reduced by thermal stress and is still about 94% of the initial tensile strength. In the non-inventive comparative example Z2, which contains sodium polyphosphate as a carbon former, the tensile strength after thermal stress is only 19% of the initial tensile strength and even the absolute value of 6.3 N/15 mm is too low to be able to easily remove an aerosol-generating article made from it from the heater after use.

The wrapping papers P1 and P2 according to the invention and the two-layer structure P3 all show an acceptable reduction in tensile strength. However, when comparing the wrapping papers P1 and P2 according to the invention, it is clear that the higher content of monoammonium phosphate in the wrapping paper P2 the fibres are more damaged and the tensile strength is reduced more after thermal stress.

In addition to a not too strong reduction in tensile strength, the fire-retardant effect is also important. In order to test the fire-retardant effect, aerosol-generating articles intended for use with a heating device were produced from the wrapping papers P1/P2 according to the invention, the two-layer structure P3 and the non-inventive comparative examples Z1 and Z2. The production of the aerosol-generating articles was problem-free with all wrapping papers. When attempting to light the aerosol-generating article like a cigarette with a lighter, it immediately became clear that the non-inventive comparative example Z1 had no fire-retardant effect. The aerosol-generating article made from it could be lit without any problem. The aerosol-generating articles with the wrapping papers P1/P2 according to the invention, the two-layer structure P3 and the non-inventive comparative example Z2 could not be lit in such a way that combustion or a stable smoldering process began, despite prolonged exposure to the flame of the lighter. It was also not possible to smoke these aerosol-generating articles in a standardized process. With regard to the fire-retardant effect, the wrapping paper P2 according to the invention proved to be somewhat better than P1, which shows that an uneven distribution of the carbon former over the thickness of the wrapping paper can contribute to increasing the fire-retardant effect.

The two-layer structure P3 was a laminate of the wrapping paper P2 according to the invention and the non-inventive comparative example Z1 and showed significantly less discoloration after use of the aerosol-generating article made therefrom than the aerosol-generating articles with P1 and P2. The wrapping paper Z1 therefore fulfilled its function of covering the discoloration of the wrapping paper P2.

No influences on the taste of the aerosol-generating articles could be detected.

The wrapping papers according to the invention are therefore very well suited for use in aerosol-generating articles and, with good biodegradability after heating, have a strength and a fire-retardant effect in a better combination than comparable wrapping papers from the prior art.

Claims (15)

1. Aerosol-generating article which comprises a wrapper paper and an aerosol-generating material, which, in its intended use, is only heated, but not burned, wherein the wrapper paper wraps the aerosol-generating material,
   wherein the wrapper paper comprises pulp fibers and a char-former, wherein the pulp fibers make up at least 70% and at most 95% of the mass of the wrapper paper and the char-former is contained in a concentration of at least 5% and at most 20% with respect to the mass of the wrapper paper and is present in a concentration in the wrapper paper such that the quotient r = R_T/R_o of the tensile strength R_o, measured in accordance with ISO 1924-2:2008 under the conditions of ISO 187:1990, and of the tensile strength R_T, measured in accordance with ISO 1924-2:2008 under the conditions of ISO 187:1990 after the wrapper paper has been exposed to a temperature of 230°C for one minute, is at least 0.20 and at most 0.90.
2. Aerosol-generating article according to claim 1, in which the proportion of pulp fibers in the wrapper paper is at least 75% and at most 90%, preferably at least 80% and at most 90%, each with respect to the mass of the wrapper paper.
3. Aerosol-generating article according to claim 1 or 2, in which the pulp fibers are entirely or partially sourced from one or more plants selected from the group consisting of coniferous trees, deciduous trees, spruce, pine, fir, beech, birch, eucalyptus, flax, hemp, jute, ramie, abaca, sisal, kenaf and cotton.
4. Aerosol-generating article according to one of the preceding claims, in which the pulp fibers are entirely or partially formed by fibers from regenerated cellulose, in particular by Tencel^™ fibers, Lyocell^™ fibers, viscose fibers or Modal^™ fibers, and/or
   in which the pulp fibers are sourced from coniferous trees to a proportion of at least 40% and at most 100% with respect to the mass of the pulp fibers.
5. Aerosol-generating article according to one of the preceding claims, in which the proportion of char-formers in the wrapper paper makes up at least 9% and at most 16% of the mass of the wrapper paper.
6. Aerosol-generating article according to one of the preceding claims, wherein the char-former is an ammonium phosphate, preferably a monoammonium phosphate, a diammonium phosphate, a triammonium phosphate, an ammonium polyphosphate or a mixture thereof, or wherein the char-former is at least partially formed by a guanyl urea phosphate, guanidine phosphate, phosphoric acid, a phosphonate, melamine phosphate, dicyandiamide, boric acid or borax.
7. Aerosol-generating article according to one of the preceding claims, wherein the tensile strength R_T of the wrapper paper, after the wrapper paper has been exposed to a temperature of 230°C for one minute is at least 8 N/ 15 mm and at most 50 N/15 mm, preferably at least 10 N/15 mm and at most 40 N/15 mm.
8. Aerosol-generating article according to one of the preceding claims, in which a side of the wrapper paper facing the aerosol-generating material during the intended use contains a higher proportion of char-former than the other side of the wrapper paper, and/or
   in which the char-former is at least substantially uniformly distributed over at least 70%, preferably over at least 90% of the surface area of the wrapper paper.
9. Aerosol-generating article according to one of the preceding claims, wherein the wrapper paper is combined with a further paper layer, in particular by gluing, so that the wrapper paper according to the invention faces the aerosol-generating material during the intended use and the further paper layer is disposed on the side facing away from the aerosol-generating material,
   wherein the further paper layer comprises pulp fibers and calcium carbonate particles, wherein the calcium carbonate particles make up at least 15% and at most 40% of the mass of the further paper layer.
10. Aerosol-generating article according to one of the preceding claims, in which the wrapper paper further comprises at least one further component which is selected from the group consisting of filler materials, sizing agents, wet strength agents, additives, processing aids, humectants and flavors,

    wherein the proportion of filler materials preferably is at least 0% and at most 20%, particularly preferably at least 0% and at most 10% and most preferably at least 0% and at most 5%, each with respect to the mass of the wrapper paper, and/or

    wherein the filler material preferably is selected from the group consisting of calcium carbonate, magnesium carbonate, titanium dioxide, magnesium dioxide, magnesium hydroxide, aluminum hydroxide, kaolin, talcum and mixtures thereof.
11. Aerosol-generating article according to one of the preceding claims, wherein the wrapper paper contains starch or a starch derivative or is coated with starch or a starch derivative, wherein the proportion of the starch or the starch derivative is preferably at least 2% and at most 10% of the mass of the wrapper paper, and/or
    in which the wrapper paper has a KIT level determined in accordance with TAPP T559 cm-12, which is at least 4 and at most 8.
12. Aerosol-generating article according to one of the preceding claims, in which the wrapper paper has a basis weight of at least 15 g/m² and at most 80 g/m², preferably at least 20 g/m² and at most 60 g/m², and/or
    in which the wrapper paper has a thickness of at least 25 µm and at most 100 µm, preferably at least 40 µm and at most 80 µm.
13. Aerosol-generating article according to one of the preceding claims in which the wrapper paper has a tensile strength R_o before a thermal load measured in the machine direction of at least 10 N/15 mm and at most 100 N/15 mm, preferably at least 20 N/15 mm and at most 80 N/15 mm, and/or
    in which the wrapper paper has a wet strength in accordance with ISO 12625-5:2016 in the machine direction thereof of at least 1 N/15 mm and at most 10 N/15 mm, preferably at least 2 N/15 mm and at most 8 N/15 mm.
14. Aerosol-generating article according to one of the preceding claims, in which the wrapper paper has a air permeability of at least 0 cm³/(cm²·min·kPa) and at most 50 cm³/(cm²·min·kPa), preferably at least 0 cm³/(cm²·min·kPa) and at most 20 cm³/(cm²·min·kPa), and/or
    in which the wrapper paper has an opacity of at least 40% and at most 80%, preferably at least 45% and at most 80% and/or the brightness of at least 80% and at most 95%, preferably at least 83% and at most 90%.
15. Aerosol-generating article according to one of the preceding claims, wherein the proportion of said char-former is higher on one side of the wrapper paper than on the other side and the side with the higher proportion of char-former faces the aerosol-generating material.