Multi-layer susceptor device for inductively heating aerosol-forming substrate

Abstract

The invention relates to a multi-layer susceptor device (120) for inductively heating an aerosol-forming substrate (130), the susceptor device (120) comprising or consisting of: a first layer (121) comprising or consisting of a first susceptor material; a second layer (122) comprising or consisting of a second susceptor material; and a third layer (123) comprising or consisting of a third material. A second layer (122) is sandwiched between the first layer and the third layer. The second susceptor material comprises or consists of a Ni-Fe-alloy, the Ni-Fe-alloy having a Ni content of equal to or less than 65% by weight. The third layer has a layer thickness equal to or less than 8 microns. The invention also relates to an aerosol-generating article (100) and an aerosol-generating system comprising an aerosol-generating article and an induction-heated aerosol-generating device for use with the article.

Description

[0001] The present invention relates to a multi-layer susceptor device for inductively heating an aerosol-forming substrate and an inductively heatable aerosol-generating article comprising an aerosol-forming substrate and such a multi-layer susceptor device for heating said substrate. The present invention also relates to an aerosol-generating article and an aerosol-generating system comprising an aerosol-generating article and an inductively heated aerosol-generating device for use with the article.

[0002] Generating an aerosol by inductively heating an aerosol-forming substrate capable of forming an inhalable aerosol when heated is generally known from the prior art. To heat the substrate, the substrate may be part of an aerosol-generating article received in an aerosol-generating device. The device may comprise an induction source for generating an alternating magnetic field for inductively heating the susceptor device by inducing at least one of eddy currents and hysteresis losses in the material of the susceptor device. The susceptor device may be an integral part of the article and arranged so as to be in thermal proximity or direct physical contact with the substrate to be heated. Alternatively, the susceptor device may be part of the device and in thermal proximity or direct physical contact with the substrate when the article is engaged with the device.

[0003] In order to control the temperature of a substrate, a multilayer susceptor device has been proposed, comprising a first layer and a second layer firmly bonded together. While the first layer comprises a first susceptor material optimized in terms of heat loss and therefore in terms of heating efficiency, the second layer comprises a second susceptor material used as a temperature marker. To this end, the second susceptor material is a magnetic (ferromagnetic or ferrimagnetic) material and is selected so as to have a Curie temperature corresponding to a predefined temperature point of the heated substrate. At its Curie temperature, the magnetic permeability of the second susceptor material drops to unity, causing its magnetic properties to change from ferromagnetic or ferrimagnetic to paramagnetic. The change in magnetic properties is accompanied by a temporary change in the resistance of the susceptor device. Thus, by monitoring the corresponding change in the current through the induction source, it is possible to detect when the second susceptor material has reached its Curie temperature and therefore when the predefined temperature point has been reached.

[0004] Depending on the specific composition of the first and second susceptors, such susceptor arrangements may be subject to material diffusion from the susceptor material into the aerosol-forming substrate, as well as material aging, in particular corrosion. Additionally, depending on the material pairing resulting from the specific materials of the first and second layers, such susceptor arrangements may be subject to changes in the magnetic properties of the susceptor material and thermal bending due to differences in thermal expansion between the layers.

[0005] It would therefore be desirable to have a susceptor device for inductively heating an aerosol-forming substrate that has the advantages of prior art solutions while alleviating their limitations. In particular, it would be desirable to have a susceptor device and an aerosol-generating article comprising such a susceptor device that have improved properties at least in terms of material diffusion from the susceptor material into the aerosol-forming substrate and material aging.

[0006] According to the present invention, there is provided a multilayer susceptor device for inductively heating an aerosol-forming substrate, the susceptor device comprising or consisting of a first layer, a second layer and a third layer, the first layer comprising or consisting of a first susceptor material, the second layer comprising or consisting of a second susceptor material, the third layer comprising or consisting of a third material. The second layer is sandwiched between the first layer and the third layer. The second susceptor material comprises or consists of a Ni-Fe-alloy having a Ni content equal to or less than 65 wt.%. The layer thickness of the third layer is equal to or less than 8 micrometers.

[0007] According to the present invention, it has been found that the properties of the susceptor device can already be easily improved by adding a third layer on the second layer opposite the first layer such that the second layer is sandwiched between the first and third layers. Thus, the third layer may act as a protective layer configured to at least one of: avoid material diffusion (e.g. metal migration) from the second susceptor material into the aerosol-forming substrate, or to protect the other layers (in particular the second layer) from ageing, e.g. from corrosion. Both aspects are particularly important when the susceptor device is intended to be embedded in an aerosol-forming substrate of an aerosol-generating article, i.e. when the susceptor device is intended to be arranged in direct physical contact with the aerosol-forming substrate.

[0008] In particular, the third layer allows the composition of the second susceptor material to be more selective and freely chosen in terms of its magnetic properties, in particular in terms of the desired Curie temperature, while being less constrained by limitations related to material aging and material diffusion. For example, the third layer allows deliberately selecting as the temperature marker material in the second layer a material that is less corrosion resistant but has a desired Curie temperature close to or equal to a predefined temperature point for heating the substrate.

[0009] According to the invention, it has also been found that the layer thickness of the third layer can be relatively small, i.e. equal to or less than 8 micrometers. A smaller third layer thickness has proven to be beneficial not only in terms of material saving, but also in terms of less shielding of the second layer from the alternating magnetic field of the induction source used for inductive heating of the susceptor arrangement. As a result, when the second susceptor material is used as a temperature maker, the above-mentioned changes in the magnetic properties of the second susceptor material in the vicinity of its Curie temperature will have a more pronounced effect on the current through the induction source. Advantageously, this will enable a more reliable determination of when the second susceptor material has reached its Curie temperature and therefore when a predefined temperature point has been reached.

[0010] As used herein, the term "thickness" refers to any dimension extending between a top side and a bottom side, such as between the top side and the bottom side of a layer or between the top side and the bottom side of a multilayer susceptor device.

[0011] Basically, the lower the layer thickness of the third layer, the greater the material saving and the more reliable the temperature monitoring. Therefore, the layer thickness of the third layer can be equal to or less than 7 micrometers, in particular equal to or less than 6 micrometers, more in particular equal to or less than 5 micrometers, preferably equal to or less than 4 micrometers, or equal to or less than 3 micrometers.

[0012] Relatively speaking, the layer thickness of the third layer can be equal to or less than 50% of the layer thickness of the first layer, in particular equal to or less than 40%, more in particular equal to or less than 30%, preferably equal to or less than 25%, more preferably equal to or less than 20%, even more preferably equal to or less than 15%, most preferably equal to or less than 10%.

[0013] Conversely, the third layer should not be too thin in order to properly perform its protective function. In particular, if the third layer is too thin, it may be brittle and tend to break. Therefore, the layer thickness of the third layer can be at least 0.75 micrometers, in particular at least 1 micrometer.

[0014] In view of the above upper and lower limits, it may be advantageous if the layer thickness of the third layer is preferably in the range between 0.75 μm and 8 μm, in particular between 1 μm and 5 μm, more particularly between 2 μm and 4 μm, for example 3.5 μm.

[0015] As used herein, the term "susceptor material" refers to a material that is capable of converting field energy into heat when subjected to an alternating magnetic field. Depending on its electrical and magnetic properties, this may be the result of at least one of hysteresis losses or eddy currents induced in the susceptor material. In ferromagnetic or ferrimagnetic susceptor materials, hysteresis losses occur due to the transformation of magnetic domains within the material under the influence of the alternating magnetic field. If the susceptor material is electrically conductive, eddy currents may be induced. In the case of a conductive ferromagnetic susceptor or a conductive ferrimagnetic susceptor, heat may be generated due to both eddy currents and hysteresis losses.

[0016] As mentioned above, the first layer comprising the first susceptor material preferably acts as the primary susceptor for heating the aerosol-forming substrate.To this end, the first susceptor material may be optimized with respect to heat losses and thus with respect to heating efficiency.

[0017] At least a portion of the outer surface of the first layer may be unprotected, i.e., bare, exposed to the environment or in direct contact with the environment. In particular, in the case where the susceptor device is embedded in the aerosol-forming substrate, at least a portion of the outer surface of the first layer may be exposed to the aerosol-forming substrate and in direct physical contact with the aerosol-forming substrate. Advantageously, this allows good heat transfer to the aerosol-forming substrate, which is preferably and mainly to be heated by the first layer. Preferably, all parts of the outer surface of the first layer are unprotected, but bare or exposed to the environment, unless in close physical contact with other layers (particularly the second layer). Advantageously, this will ensure maximum heat transfer to the aerosol-forming substrate.

[0018] The first susceptor material may be at least one of electrically conductive or magnetic (i.e. either ferromagnetic or ferrimagnetic). If the first susceptor material is electrically conductive, it may also be paramagnetic. In case the first susceptor material is magnetic (ferromagnetic or ferrimagnetic), it is preferably selected so as to have a Curie temperature that is different from, and in particular higher than, the Curie temperature of the second susceptor material. In this particular configuration, the first susceptor material may have a first Curie temperature and the second susceptor material may have a second Curie temperature.

[0019] Preferably, the first susceptor material is made of a corrosion resistant material. Thus, the first susceptor material itself is advantageously resistant to any corrosive influences.

[0020] Preferably, the first susceptor material comprises or consists of a metal, such as ferritic iron or stainless steel, in particular ferromagnetic stainless steel, such as ferritic stainless steel. It may be particularly preferred that the first susceptor material comprises or consists of 400 series stainless steel, such as 410 grade stainless steel, or 420 grade stainless steel, or 430 grade stainless steel or similar grades of stainless steel.

[0021] The first susceptor material may alternatively comprise or consist of a suitable non-magnetic, in particular paramagnetic, electrically conductive material, such as aluminium (Al). In paramagnetic electrically conductive materials, inductive heating occurs exclusively by resistive heating due to eddy currents.

[0022] Alternatively, the first susceptor material may comprise or consist of a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic. In such a case, heat is generated only by hysteresis losses.

[0023] As also described above, the second susceptor material is preferably used as a temperature marker. That is, the second susceptor material is preferably configured for monitoring the temperature of the susceptor device. To this end, the second susceptor material may be selected to have a Curie temperature that substantially corresponds to a predefined temperature point of the heating process. In particular, the second susceptor material may be selected to have a Curie temperature that substantially corresponds to a predefined maximum heating temperature of the susceptor device. The maximum expected heating temperature may be defined as the approximate temperature to which the susceptor device should be heated in order to generate an aerosol from the aerosol-forming substrate. However, the maximum expected heating temperature should be low enough to avoid local overheating or even combustion of the aerosol-forming substrate. Preferably, the Curie temperature of the second susceptor material should be below the ignition point of the aerosol-forming substrate to be heated. The second susceptor material, in particular a Ni-Fe-alloy of the second susceptor material, may have a Curie temperature below 500° C., preferably equal to or below 400° C., in particular equal to or below 390° C. For example, the second susceptor, in particular a Ni-Fe-alloy of the second susceptor material, may have a Curie temperature in the range of between 180° C. and 420° C., in particular between 210° C. and 380° C., preferably between 250° C. and 380° C. Although the second layer may be primarily a functional layer providing a temperature signature by the Curie temperature of the second susceptor material, it may also contribute to the inductive heating of the susceptor arrangement. Preferably, however, the first layer comprising the first susceptor material is configured primarily for heating the aerosol-forming substrate.

[0024] As defined above, the second susceptor material comprises or consists of a Ni-Fe-alloy having a Ni content equal to or less than 65 wt. %. As used herein, the unit "wt % (weight %)" stands for "weight per cent" or "percentage by weight". That is, it indicates the mass fraction of an element within an alloy, which is the ratio of the mass of the respective element to the total mass of a sample of the alloy.

[0025] Advantageously, most Ni-Fe-alloys having a Ni content equal to or less than 65 wt. % have a Curie temperature in the range below 600° C. and are therefore very suitable as temperature markers for a wide range of heat-not-burn substrates, most of which have a flash point above 600° C. In addition, most Ni-Fe-alloys having a Ni content of 65 wt. % or less still have a sufficiently large magnetic permeability that the magnetic permeability shows a clearly detectable drop when the temperature of the material reaches the Curie point.

[0026] The Ni content can also be much lower than 65 wt. %. Thus, the Ni-Fe alloy of the second susceptor material can have a Ni content equal to or less than 50 wt. %, in particular equal to or less than 44 wt. %, more particularly in the range between 36 wt. % and 44 wt. %, preferably in the range between 36 wt. % and 40 wt. %, for example 36.1 wt. % or 36.4 wt. % or 40 wt. %; the remainder is preferably Fe.

[0027] The Ni—Fe alloy of the second susceptor material may be a binary Ni—Fe alloy, ie a Ni—Fe alloy consisting of Ni and Fe only.

[0028] Alternatively, the Ni—Fe alloy may contain one or more of the following elements: Co, Cr, Cu, Mn, Mo, Nb, Si, Ti, and V.

[0029] As used herein, the symbol Ni represents the chemical element nickel, the symbol Fe represents the chemical element iron, the symbol Co represents the chemical element cobalt, the symbol Cr represents the chemical element chromium, the symbol Cu represents the chemical element copper, the symbol Mn represents the chemical element manganese, the symbol Mo represents the chemical element molybdenum, the symbol Nb represents the chemical element niobium, the symbol Si represents the chemical element silicon, the symbol Ti represents the chemical element titanium, and the symbol V represents the chemical element vanadium.

[0030] Advantageously, the Curie temperature of the Ni-Fe alloy can be selectively adjusted by adding chromium. Therefore, the Ni-Fe alloy of the second susceptor material may additionally contain chromium. In particular, the second susceptor material may contain or consist of a Ni-Fe-Cr alloy. The higher the chromium content, the lower the Curie temperature of the alloy. In addition, the addition of chromium has an effect on the corrosion resistance of the Ni-Fe alloy. In general, the corrosion resistance can be enhanced by increasing the chromium content. As a specific example, the Ni-Fe alloy of the second susceptor material may also contain 8 wt.%-12 wt.% Cr, in particular 9 wt.%-11 wt.% Cr. Depending on the actual Ni content, the Curie temperature of the Ni-Fe alloy additionally containing 8 wt.%-12 wt.% Cr, in particular 9 wt.%-11 wt.% Cr, can be advantageously adjusted to a range between 200°C and 300°C.

[0031] According to one example, a Ni-Fe alloy may contain or consist of 50% by weight of Ni, 9% by weight of Cr, and the remainder is Fe. Such an alloy is commercially available, for example, under the trade name Phytherm 260, and has a Curie temperature of 260°C. According to another example, a Ni-Fe alloy may contain or consist of 50% by weight of Ni, 10% by weight of Cr, and the remainder is Fe. Such an alloy is also commercially available, for example, under the trade name Phytherm 220, and has a Curie temperature of 230°C. According to yet another example, a Ni-Fe alloy may contain or consist of 50% by weight of Ni, 11% by weight of Cr, and the remainder is Fe. Such an alloy is also commercially available, for example, under the trade name Phytherm 210, and has a Curie temperature of 210°C. Advantageously, all of the aforementioned alloys (Phytherm alloys) are corrosion-resistant materials.

[0032] Besides chromium, the Ni—Fe alloy may also contain one or more further elements.

[0033] According to one example, the Ni—Fe-alloy of the second susceptor material may comprise or consist of 50 wt% Ni, 9 wt% Cr, up to 1 wt% Si and up to 1 wt% Mn, the remainder being Fe. According to another example, the Ni—Fe-alloy of the second susceptor material may comprise or consist of 50 wt% Ni, 10 wt% Cr, up to 1 wt% Si and up to 1 wt% Mn, the remainder being Fe. According to yet another example, the Ni—Fe-alloy of the second susceptor material may comprise or consist of 50 wt% Ni, 11 wt% Cr, up to 1 wt% Si and up to 1 wt% Mn, the remainder being Fe.

[0034] As mentioned above, the Ni-Fe-alloy of the second susceptor material may have a Ni content even less than 50 wt.-%. In particular, the Ni-Fe-alloy of the second susceptor material may have a Ni content equal to or less than 44 wt.-%, more particularly in the range between 36 wt.-% and 44 wt.-%, preferably in the range between 36 wt.-% and 40 wt.-%, for example 36.1 wt.-% or 36.4 wt.-% or 40 wt.-% Ni content; the remainder is preferably Fe. As an example, the Ni-Fe-alloy may be an alloy available from Hitachi under the designation "MS-10" having a Ni content of 36.1 wt.-% and a Curie temperature of 213°C. Likewise, the Ni-Fe-alloy may be an alloy available from Hitachi under the designation "MS-16" having a Ni content of 36.4 wt.-% and a Curie temperature of 221.5°C.

[0035] As used herein, the term "third layer" refers to a layer other than the first layer and the second layer that is different from the first layer and the second layer. In particular, any possible oxide layer on the surface of the first layer or the second layer resulting from oxidation of the first susceptor material or the second susceptor material is not considered to be a third layer, and in particular is not considered to be a third layer comprising or consisting of an anti-corrosion material.

[0036] Preferably, the third material comprises or consists of an anti-corrosion material. Advantageously, the anti-corrosion material will improve the aging characteristics of those parts of the outer surface of the second layer that are covered by the third layer and are therefore not directly exposed to the environment.

[0037] The third layer may comprise or consist of the same material as the first susceptor material of the first layer. That is, the third material may be the same as the first susceptor material. Thus, the multilayer susceptor device comprises at least two layers having the same thermal expansion coefficient, which results in reduced deformation of the susceptor device within the temperature operating range. This is particularly applicable when the susceptor device comprises only the first layer, the second layer and the third layer such that the second layer is symmetrically sandwiched between the first layer and the third layer.

[0038] Alternatively, the third material may be different from the first susceptor material.In this way, the properties of the first and third layers may be independently selected to achieve optimal effect for their respective purposes.

[0039] In particular, where the third material is the same as the first susceptor material, the third material may comprise or consist of a metal, for example ferritic iron or stainless steel, for example ferritic stainless steel, in particular 400 series stainless steel, such as 410 grade stainless steel, or 420 grade stainless steel, or 430 grade stainless steel or a similar grade of stainless steel.

[0040] Alternatively, the third material may contain or consist of a suitable non-magnetic, in particular paramagnetic, electrically conductive material, such as aluminum (Al). Likewise, the third material may contain or consist of a non-conductive ferrimagnetic material, such as a non-conductive ferrimagnetic ceramic.

[0041] The third material may also comprise or consist of austenitic stainless steel. Advantageously, due to its paramagnetic properties and high electrical resistance, austenitic stainless steel only weakly shields the second layer from the magnetic field applied to the first susceptor material and the second susceptor material. By way of example, the third material may comprise or consist of X5CrNi18-10 (material number 1.4301 according to EN (European Standard) nomenclature, also known as V2A steel) or X2CrNiMo17-12-2 (material number 1.4571 or 1.4404 according to EN (European Standard) nomenclature, also known as V4A steel). In particular, the third material may comprise or consist of one or more of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel or 316L stainless steel (according to the nomenclature of SAE steel grades [Society of Automotive Engineers]).

[0042] The layer thickness of the first layer can be in the range between 20 μm and 60 μm, in particular between 30 μm and 50 μm, for example 40 μm or 42.5 μm.

[0043] Likewise, the layer thickness of the second layer can be in the range between 4 μm and 20 μm, in particular between 8 μm and 18 μm, preferably between 10 μm and 16 μm, for example 10 μm or 14 μm.

[0044] In terms of relative values, the layer thickness of the first layer may be in the range of between 1.5 and 5 times, in particular between 2 and 4 times, preferably between 2.5 and 3.5 times, more preferably about 3 times the layer thickness of the second layer. In this regard, it has been found that the layer thickness of the second layer does not need to be very large as compared to the first layer, i.e. the temperature marking layer does not need to be very large as compared to the main heating layer.

[0045] Likewise, the third layer may be equal to or less than 70% of the second layer, particularly equal to or less than 60%, more particularly equal to or less than 50%, even more particularly equal to or less than 45%, preferably equal to or less than 40%, more preferably equal to or less than 35%, even more preferably equal to or less than 30%, and most preferably equal to or less than 25%.

[0046] As defined above, the second layer is sandwiched between the first layer and the third layer. This does not necessarily mean that the first layer, the second layer and the third layer are adjacent layers. That is, there may be one or more additional layers between the first layer and the second layer and / or between the second layer and the third layer and / or on top of the third layer opposite the second layer and / or below the first layer opposite the second layer.

[0047] However, it is preferred that the first layer, the second layer and the third layer are directly adjacent layers of the multi-layer susceptor device, in particular are in direct physical contact with each other.

[0048] At least one of the first layer or the third layer may be an edge layer of the multi-layer susceptor device.

[0049] More particularly, the multi-layer susceptor device may consist of only the first layer, the second layer and the third layer. That is, the multi-layer susceptor device is preferably a three-layer susceptor device.

[0050] In the case where the first and second layers are directly adjacent layers, the second layer can be closely coupled to the first layer, especially on top of the first layer. Similarly, in the case where the second and third layers are directly adjacent layers, the third layer can be closely coupled to the second layer, especially on top of the second layer.

[0051] With regard to the processing of the susceptor device, in particular with regard to the assembly of the various layers, each of the layers may be plated, deposited, coated, clad or welded to the respective adjacent layer. In particular, each of these layers may be applied to the respective adjacent layer by spraying, dipping, rolling, electroplating or cladding. This applies in particular to the first layer, the second layer and the third layer and, if present, at least one further layer. In any case, any of the above-described configurations or layer structures fall within the term "closely coupled" as used herein.

[0052] Generally, the multilayer susceptor device may have various shapes. In particular, the susceptor device has the form of a blade or a strip or a sheet. Preferably, the multilayer susceptor device may be an elongated, in particular a strip-shaped susceptor device.

[0053] The overall thickness of the susceptor device may be in the range of 24 to 88 microns, in particular 50 to 65 microns, preferably 54 to 62 microns, such as 56 or 60 microns.

[0054] The width of the susceptor device in a direction perpendicular to the overall thickness of the susceptor device may be in the range between 3 mm and 7 mm, in particular between 4 mm and 6 mm, for example 5 mm.

[0055] The length of the susceptor device in a direction perpendicular to the overall thickness of the susceptor device may be in the range between 10 mm and 15 mm, in particular between 11 mm and 13 mm, for example 12 mm.

[0056] As used herein, the term "thickness" refers to any dimension extending between the top side and the bottom side (e.g., between the top side and the bottom side of a layer or between the top side and the bottom side of a multilayer susceptor device). Likewise, the term "width" is used herein to refer to any dimension extending between two opposing sides of a layer or susceptor device. The term "length" is used herein to refer to any dimension extending between the front and back or between two other opposing sides orthogonal to the two opposing sides forming the width. Preferably, the width extension is greater than the thickness extension. Likewise, the width extension may be less than the length extension. The thickness, width and length may be orthogonal to each other.

[0057] According to another aspect of the present invention, there is provided a double-layer susceptor device for inductively heating an aerosol-forming substrate, the susceptor device consisting of a first layer comprising or consisting of a first susceptor material and a second layer comprising or consisting of a second susceptor material, wherein the first layer and the second layer are tightly coupled to each other, wherein the second susceptor material comprises or consists of a Ni-Fe-alloy having a Ni content equal to or less than 65 wt.-% and a Cr content equal to or greater than 13 wt.-%, and wherein the layer thickness of the second layer is in the range between 1 μm and 22 μm.

[0058] According to this aspect of the invention, it has been found that a Ni-Fe-alloy having a Ni content equal to or less than 65 wt.-% and a Cr content equal to or greater than 13 wt.-% provides sufficient corrosion resistance due to its chemical composition (mainly due to the chromium content) so that a protective layer on top of the second layer (opposite to the first layer) can be omitted. This has proven to be beneficial in terms of material saving. The corrosion resistance results from the relatively high chromium content, which is passivated by reaction with oxygen to form a passive, microscopically thin surface film of inert chromium oxide. This passivating film prevents further corrosion by blocking the diffusion of oxygen to the surface of the second layer and thus prevents the corrosion from propagating into the metal body. The passivating film is self-healing, even when scratched or temporarily disturbed by abnormal conditions in the environment. Preferably, the layer thickness of the second layer of the double-layer susceptor device can be in the range of between 1 micrometer and 15 micrometers, in particular between 4 micrometers and 15 micrometers, or between 1 micrometer and 11 micrometers, more in particular between 4 micrometers and 11 micrometers. The layer thickness of the first layer of the double-layer susceptor device may be in the range of 20 to 60 μm, in particular in the range of 30 to 50 μm, for example 40 μm or 42.5 μm. The overall thickness of the double-layer susceptor device may be in the range of 21 to 75 μm or 21 to 82 μm, in particular in the range of 24 to 71 μm, more particularly in the range of 44 to 55 μm.

[0059] According to the present invention, there is also provided an inductively heatable aerosol-generating article comprising at least one aerosol-forming substrate and a multi-layer susceptor arrangement according to the present invention and as described herein.

[0060] As used herein, the term "aerosol generating article" refers to an article comprising at least one aerosol-forming substrate capable of releasing volatile compounds that can form an aerosol when heated. Preferably, the aerosol generating article is a heated aerosol generating article, that is, an aerosol generating article comprising at least one aerosol-forming substrate intended to be heated rather than burned. Such an article may be represented as a heat-not-burn aerosol generating article, and the substrate may be represented as a heat-not-burn aerosol-forming substrate. The aerosol generating article may be a consumable, in particular a consumable that is discarded after a single use. The aerosol generating article may be a tobacco product. For example, the article may be a cartridge comprising a liquid aerosol-forming substrate to be heated. As another example, the article may be an elongated article or a strip-shaped article. The elongated or strip-shaped article may have a shape similar to that of a conventional cigarette. In particular, such an article may have a circular or elliptical or oval or square or rectangular or triangular or polygonal cross-section.

[0061] As used herein, the term "aerosol forming substrate" means a substrate formed by or comprising an aerosol forming material, which can release volatile compounds when heated to generate an aerosol. Preferably, the aerosol forming substrate is intended to be heated rather than burned to release the volatile compounds that form an aerosol. The aerosol forming substrate can be a solid aerosol forming substrate, a liquid aerosol forming substrate, a gel-like aerosol forming substrate, or any combination thereof. For example, the aerosol forming substrate can include both solid components and liquid components. The aerosol forming substrate can include a tobacco-containing material, which contains volatile tobacco flavor compounds released from the substrate when heated. Alternatively or in addition, the aerosol forming substrate can include non-tobacco materials. The aerosol forming substrate can also include an aerosol forming agent. The example of a suitable aerosol forming agent is glycerol and propylene glycol. The aerosol forming substrate can also include other additives and ingredients, such as nicotine or spices. The aerosol-forming substrate may also be a paste-like material, a pouch of porous material comprising an aerosol-forming substrate, or for example loose tobacco mixed with a gelling agent or binder, which may include common aerosol formers such as glycerol, and compressed or moulded into a rod.

[0062] Preferably, the multi-layer susceptor device is embedded in the aerosol-forming substrate.

[0063] For example, the aerosol-generating article may be a rod-shaped article. In particular, the cylindrical article comprises one or more of the following elements: a distal front-rod element, a matrix element, a first tube element, a second tube element and a filter element.

[0064] The substrate element preferably comprises at least one aerosol-forming substrate to be heated and a susceptor device in thermal contact or thermal proximity with the aerosol-forming substrate. The substrate element may have a length of 10 mm to 14 mm (e.g. 12 mm). The susceptor device may extend along the entire length of the substrate element, or may have a length extension that is shorter than the length of the substrate element.

[0065] The first tube element is more distal than the second tube element. Preferably, the first tube element is proximal to the matrix element, while the second tube element is proximal to the first tube element and distal to the filter element, i.e., between the first tube element and the filter element. At least one of the first tube element and the second tube element may include a central air passage. The cross-section of the central air passage of the second tube element may be greater than the cross-section of the central air passage of the first tube element. Preferably, at least one of the first tube element and the second tube element may include a hollow cellulose acetate tube. At least one of the first tube element and the second tube element may have a length of 6 mm to 10 mm (e.g., 8 mm).

[0066] The filter element is preferably used as a mouthpiece, or is part of a mouthpiece together with the second tube element. As used herein, the term "mouthpiece" refers to the part of the article through which the aerosol leaves the aerosol generating article. The filter element may have a length of 10 mm to 14 mm, for example 12 mm.

[0067] The distal front rod element can be used to cover and protect the distal front end of the matrix element. The distal front rod element can have a length of 3 mm to 6 mm (e.g., 5 mm). The distal front rod element can be made of the same material as the filter element.

[0068] All the aforementioned elements can be arranged in sequence along the length axis of the article in the above order, wherein the distal front rod element is preferably arranged at the distal end of the article, and the filter element is preferably arranged at the proximal end of the article. Each of the aforementioned elements can be substantially cylindrical. In particular, all elements can have the same outer cross-sectional shape and / or size.

[0069] In addition, these elements can be limited by one or more outer packagings, so that these elements are kept together and maintain the cross-sectional shape of the expectation of strip-shaped product.Preferably, packaging is made of paper.Packing can also include the adhesive that the overlapping free ends of packaging are adhered to each other.For example, far-front rod element, matrix element and the first tube element can be limited by the first packaging, and the second tube element and filter element can be limited by the second packaging.The second packaging can also limit (after being wrapped by the first packaging, namely on the top of the first packaging) at least a portion of the first tube element to be connected to the second tube element and filter element far-front rod element, matrix element and the first tube element limited by the first packaging.The second packaging can include the perforation around its circumference.

[0070] Other features and advantages of aerosol-generating articles according to the present invention have been described above in relation to susceptor devices according to the present invention, and apply equally.

[0071] According to one aspect of the present invention, there is also provided an aerosol generating system comprising an inductively heatable aerosol generating article according to the present invention and as described herein and an inductively heated aerosol generating device for use with the aerosol generating article.

[0072] According to another aspect of the present invention, there is provided an aerosol generating system comprising an induction heating aerosol generating device and an aerosol generating article for use with the aerosol generating device, wherein the aerosol generating device comprises a multi-layer susceptor device according to the present invention and as described herein, and wherein the aerosol generating article comprises an aerosol-forming substrate to be heated by the multi-layer susceptor device.

[0073] That is, according to one aspect of the invention (first configuration of the system), the susceptor means is part of the aerosol-generating article, whereas according to another aspect of the invention (second configuration of the system), the susceptor means is part of the aerosol-generating device.

[0074] As used herein, in either configuration, the term "aerosol generating device" describes an electrically operated device for interacting with an aerosol generating article so as to generate an aerosol by heating an aerosol-forming substrate via interaction of a susceptor device with an alternating magnetic field provided by the aerosol generating device. Preferably, the aerosol generating device is a suction device for generating an aerosol that can be inhaled directly by a user through the user's mouth. In particular, the aerosol generating device is a handheld aerosol generating device.

[0075] In either configuration of the system, the device may comprise a receiving cavity for removably receiving at least a portion of a respective aerosol-generating article.

[0076] In either configuration of the system, the aerosol generating device may comprise an induction heating device configured and arranged to generate an alternating magnetic field in the receiving cavity so as to inductively heat the susceptor device.

[0077] In order to generate the alternating magnetic field, the induction heating device may comprise at least one induction coil which surrounds at least a portion of the susceptor device when the system is in use. The at least one induction coil may be a spiral coil or a planar coil, in particular a pancake coil or a curved planar coil. In a first configuration, the aerosol generating device and the aerosol generating article are preferably configured such that the susceptor device is arranged in a cavity of the aerosol generating device, in particular in an inner space of the at least one induction coil, so as to experience the alternating magnetic field when the article is received in the aerosol generating device. Likewise, in a second configuration, the susceptor device is preferably fixedly arranged in the cavity of the aerosol generating device, in particular in an inner space of the at least one induction coil, so as to experience the alternating magnetic field.

[0078] The induction heating device may further comprise an alternating current (AC) generator. The AC generator may be powered by a power supply of the aerosol generating device. The AC generator may be operably coupled to at least one induction coil. In particular, at least one induction coil may be an integral part of the AC generator. The AC generator is configured to generate a high frequency oscillating current through at least one induction coil for generating an alternating magnetic field. The AC current may be supplied to the at least one induction coil continuously after activation of the system, or may be supplied intermittently, for example on a puff-by-puff basis. Preferably, the induction heating device comprises a DC / AC converter comprising an LC network, wherein the LC network comprises a series connection of a capacitor and an inductor. The DC / AC converter may be connected to a DC power supply.

[0079] The induction heating device is preferably configured to generate a high-frequency magnetic field. As mentioned herein, the frequency of the high-frequency magnetic field may be between 500kHz (kilohertz) and 30MHz (megahertz), in particular between 5MHz (megahertz) and 15MHz (megahertz), preferably between 5MHz (megahertz) and 10MHz (megahertz).

[0080] In any configuration of the system, the aerosol generating device may further comprise a controller configured to control the operation of the heating process. The controller may be an overall controller of the aerosol generating device, or may be part of the overall controller. The controller may comprise a microprocessor, such as a programmable microprocessor, a microcontroller or an application specific integrated chip (ASIC), or other electronic circuitry capable of providing control. The controller may comprise other electronic components, such as at least one DC / AC inverter and / or a power amplifier, such as a class C power amplifier or a class D power amplifier or a class E power amplifier. In particular, the inductive source may be part of the controller.

[0081] In any configuration of the system, the aerosol generating device may further comprise a power source, in particular a DC power source, configured to provide a DC power supply voltage and a DC power supply current to the induction source. Preferably, the power source is a battery, such as a lithium iron phosphate battery. The power source may be rechargeable. The power source may have a capacity that allows sufficient energy to be stored for one or more user experiences. For example, the power source may have sufficient capacity to allow continuous generation of aerosol for a time of about six minutes or a multiple of six minutes. In another example, the power source may have sufficient capacity to allow a predetermined number of puffs or discontinuous activation of the induction source.

[0082] Other features and advantages of the aerosol generating system according to any aspect of the invention have been described in relation to the susceptor device and the aerosol generating article and therefore apply equally.

[0083] The invention is defined in the claims. However, a non-exhaustive list of non-limiting examples is provided below. Any one or more features of these examples may be combined with any one or more features of another example, embodiment or aspect described herein.

[0084] Example Ex1: A multi-layer susceptor device for inductively heating an aerosol-forming substrate, the susceptor device comprising or consisting of

[0085] - a first layer comprising or consisting of a first susceptor material,

[0086] - a second layer, said second layer comprising or consisting of a second susceptor material, and

[0087] - a third layer, said third layer comprising or consisting of a third material,

[0088] wherein the second layer is sandwiched between the first layer and the third layer, wherein the second susceptor material comprises or consists of a Ni-Fe alloy having a Ni content equal to or less than 65 wt.-%, and wherein the layer thickness of the third layer is equal to or less than 8 micrometers.

[0089] Example Ex2: A multilayer susceptor device according to example Ex1, wherein the layer thickness of the third layer is equal to or less than 7 μm, in particular equal to or less than 6 μm, more in particular equal to or less than 5 μm, preferably equal to or less than 4 μm, or equal to or less than 3 μm.

[0090] Example Ex3: The multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the third layer is in the range of between 0.75 μm and 8 μm, in particular between 1 μm and 5 μm, preferably between 2 μm and 4 μm, for example 3.5 μm.

[0091] Example Ex4: The multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the first layer is in the range between 1.5 and 5 times, in particular between 2 and 4 times, preferably between 2.5 and 3.5 times, more preferably about 3 times the layer thickness of the second layer.

[0092] Example Ex5: The multilayer susceptor device according to any of the preceding examples, wherein the first susceptor material comprises or consists of a metal, such as ferritic iron or stainless steel, in particular 410 grade, 420 grade or 430 grade stainless steel.

[0093] Example Ex6: The multilayer susceptor device according to any of the preceding examples, wherein the Ni—Fe-alloy of the second susceptor material further comprises 8-12 wt. % Cr, in particular 9-11 wt. % Cr.

[0094] Example Ex7: A multilayer susceptor device according to any of Examples Ex1 to Ex6, wherein the Ni-Fe alloy of the second susceptor material has a Ni content equal to or less than 50 wt.-%, in particular equal to or less than 44 wt.-%, more particularly in a specific range between 36 wt.-% and 44 wt.-%, preferably in a range between 36 wt.-% and 40 wt.-%, for example 36.1 wt.-% or 36.4 wt.-% or 40 wt.-%, the remainder preferably being Fe.

[0095] Example Ex8: The multilayer susceptor device according to any one of Examples Ex1 to Ex6, wherein the Ni—Fe-alloy of the second susceptor material comprises or consists of one of the following:

[0096] - 50 wt% Ni, 9 wt% Cr, the remainder Fe;

[0097] - 50 wt% Ni, 10 wt% Cr, and the rest Fe;

[0098] - 50 wt% Ni, 11 wt% Cr, the remainder Fe;

[0099] - 50 wt.-% Ni, 9 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe;

[0100] - 50 wt.-% Ni, 10 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe;

[0101] - 50 wt.-% Ni, 11 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe.

[0102] Example Ex9: The multilayer susceptor device according to any of the preceding examples, wherein the Ni-Fe-alloy of the second susceptor material has a Curie temperature in the range between 180°C and 420°C, in particular between 210°C and 380°C, preferably between 250°C and 380°C.

[0103] Example Ex10: The multilayer susceptor device according to any of the preceding examples, wherein the third material comprises or consists of a corrosion-resistant material.

[0104] Example Ex11: The multilayer susceptor device according to any one of Examples Ex1 to Ex10, wherein the third material is the same as the first susceptor material.

[0105] Example Ex12: The multilayer susceptor device according to any one of Examples Ex1 to Ex10, wherein the third material is different from the first susceptor material.

[0106] Example Ex13: The multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the first layer is in the range between 20 and 60 micrometers, in particular between 30 and 50 micrometers, such as 40 micrometers or 42.5 micrometers.

[0107] Example Ex14: The multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the second layer is in the range of between 4 and 20 μm, in particular between 8 and 18 μm, preferably between 10 and 16 μm, such as 10 or 14 μm.

[0108] Example Ex15: A multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the third layer is equal to or less than 50% of the layer thickness of the first layer, in particular equal to or less than 40%, more in particular equal to or less than 30%, preferably equal to or less than 25%, more preferably equal to or less than 20%, even more preferably equal to or less than 15%, most preferably equal to or less than 10%.

[0109] Example Ex16: The multilayer susceptor device according to any of the preceding examples, wherein the layer thickness of the third layer is at least 0.75 micrometers, in particular at least 1 micrometer.

[0110] Example Ex 17: The multi-layered susceptor device according to any of the preceding examples, wherein the second layer is tightly coupled to the first layer, in particular on top of the first layer.

[0111] Example Ex18: The multi-layered susceptor device according to any of the preceding examples, wherein the third layer is tightly coupled to the second layer, in particular on top of the second layer.

[0112] Example Ex 19: The multi-layer susceptor device according to any of the preceding examples, wherein the first layer, the second layer, and the third layer are directly adjacent layers of the multi-layer susceptor device.

[0113] Example Ex20: The multilayer susceptor device according to any one of the preceding examples, wherein the susceptor device has the form of a blade or a strip or a sheet.

[0114] Example Ex21: The multilayer susceptor device according to any of the preceding examples, wherein the overall thickness of the susceptor device is in the range of 24 to 88 μm, in particular 50 to 65 μm, preferably 54 to 62 μm, such as 56 or 60 μm.

[0115] Example Ex22: The multilayer susceptor device according to any of the preceding examples, wherein the width of the susceptor device in a direction perpendicular to the overall thickness of the susceptor device is in the range of 3 mm to 7 mm, in particular 4 mm to 6 mm, such as 5 mm.

[0116] Example Ex23: The multilayer susceptor device according to any of the preceding examples, wherein the length of the susceptor device in a direction perpendicular to the overall thickness of the susceptor device is in the range of 10 mm to 15 mm, in particular 11 mm to 13 mm, such as 12 mm.

[0117] Example Ex24: An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor device according to any of the preceding examples.

[0118] Example Ex25: An aerosol-generating article according to example Ex24, wherein the multi-layer susceptor device is embedded in the aerosol-forming substrate.

[0119] Example Ex26: An aerosol generating system, comprising an inductively heatable aerosol generating article according to any one of Examples Ex24 to Ex25, and an inductively heated aerosol generating device for use with the aerosol generating article.

[0120] Example Ex27: An aerosol generating system, comprising an induction heating aerosol generating device and an aerosol generating article for use with the aerosol generating device, wherein the aerosol generating device comprises a multi-layer susceptor device according to any one of Examples Ex1 to Ex23, and wherein the aerosol generating article comprises an aerosol-forming substrate to be heated by the multi-layer susceptor device.

[0121] Several examples will now be further described with reference to the accompanying drawings, in which:

[0122] Figure 1 schematically illustrates an exemplary embodiment of an inductively heatable aerosol-generating article comprising a multi-layer susceptor device according to the present invention;

[0123] Figure 2 Schematically shows the Figure 1 Exemplary embodiments of an aerosol generating system for an aerosol generating article;

[0124] Figure 3 The perspective diagram shows the Figure 1 details of a multi-layer susceptor device of an aerosol-generating article; and

[0125] Figure 4 The cross-sectional view shows the Figure 1 Details of the multi-layer susceptor device of the aerosol-generating article.

[0126] Figure 1 An exemplary embodiment of an inductively heatable aerosol-generating article 100 according to the present invention is schematically shown (not shown to scale). The aerosol-generating article 100 is a substantially strip-shaped consumable comprising five elements arranged in sequence in coaxial alignment: a distal front rod element 150, a matrix element 110, a first tube element 140, a second tube element 145 and a filter element 160. The distal front rod element 150 is arranged at the distal end 102 of the article 100 to cover and protect the distal front end of the matrix element 110, while the filter element 160 is arranged at the proximal end 103 of the article 100. Both the distal front rod element 150 and the filter element 160 may be made of the same filter material. The filter element 160 is preferably used as a mouthpiece, preferably as a part of a mouthpiece together with the second tube element 145. The filter element 160 may have a length of 10 mm to 14 mm (e.g. 12 mm), while the distal front rod element 150 may have a length of 3 mm to 6 mm (e.g. 5 mm). The substrate element 110 comprises an aerosol-forming substrate 130 to be heated and a multilayer susceptor device 120 for heating the substrate 130 according to an exemplary embodiment of the present invention. Conveniently, the susceptor device 120 has the form of a blade or strip which is fully embedded in the substrate 130 so as to be in direct thermal contact with the substrate 130. The substrate element 110 may have a length of 10 mm to 14 mm, for example 12 mm. Figure 1As shown in the figure, the susceptor device 120 extends along the entire length of the matrix element 110, but may alternatively have a length extension that is shorter than the length of the matrix element 110. Each of the first tube element 140 and the second tube element 145 is a hollow cellulose acetate tube having a central air passage 141, 146, wherein the cross-section of the central air passage 146 of the second tube element 145 is larger than the cross-section of the central air passage 141 of the first tube element 140. The first tube element 140 and the second tube element 145 may have a length of 6 mm to 10 mm (e.g., 8 mm). Each of the aforementioned elements 150, 110, 140, 145, 160 may be substantially cylindrical. In particular, all elements 150, 110, 140, 145, 160 may have the same outer cross-sectional shape and size.

[0127] In addition, element 150,110,140,145,160 can be limited by one or more outer packagings, so that these elements are kept together and maintain the desired cross-sectional shape of strip-shaped products.In the present embodiment, far-front rod element 150, matrix element 110 and first tube element 140 are limited by first packaging 171, and second tube element 145 and filter element 160 are limited by second packaging 172.Second packaging 172 also limits at least a portion of first tube element 140 (after being wrapped by first packaging 171) so that far-front rod element 150, matrix element 110 and first tube element 140 limited by first packaging 171 are connected to second tube element 145 and filter element 160.Preferably, first packaging 171 and second packaging 172 are made of paper.In addition, second packaging 172 can comprise the perforation (not shown) around its circumference. The wrappers 171 , 172 may further include an adhesive that adheres the overlapping free ends of the wrappers 171 , 172 to each other.

[0128] like Figure 2As shown in , an aerosol generating article 100 is configured for use with an induction heated aerosol generating device 10. The device 10 and the article 100 together form an aerosol generating system 1 according to the present invention. The aerosol generating device 10 comprises a cylindrical receiving cavity 20, which is defined in a proximal portion 12 of the device 10, for receiving at least a distal portion of the article 100 therein. The device 10 further comprises an induction heating device, which comprises an induction coil 30 for generating a high frequency alternating magnetic field in the cavity 20. In the present embodiment, the induction coil 30 is a spiral coil circumferentially surrounding the cylindrical receiving cavity 20. The coil 30 is arranged so that the susceptor device 120 of the aerosol generating article 100 is exposed to the alternating magnetic field when the article 100 is inserted into the cavity 20 of the device 10. Therefore, when the induction heating device is activated, the susceptor device 120 heats up due to eddy currents and / or hysteresis losses induced by the alternating magnetic field, which depends on the magnetic and electrical properties of the susceptor material of the susceptor device 120. The susceptor device 120 is heated until an operating temperature is reached that is sufficient to vaporize the aerosol-forming substrate 130 surrounding the susceptor device 120 within the article 100. In use, an aerosol formed by volatile compounds released from the heated substrate 130 is drawn through the first tube element 140 and the second tube element 145 and further through the filter element 160 towards the proximal end 103 of the article 100.

[0129] Within the distal portion 13, the aerosol generating device 10 also includes a DC power supply 40 and a controller 50 (only in Figure 2 Schematically shown in FIG), for powering and controlling the heating process. In addition to the induction coil 30, the induction heating device is preferably at least partially an integrated part of the controller 50.

[0130] Figure 3 and Figure 4 Shows Figure 1 Detailed view (not to scale) of a susceptor device 120 for use in an aerosol-generating article shown in . According to the present invention, the susceptor device 120 is a multi-layer susceptor device 120 comprising a first layer 121, a second layer 122 and a third layer 123, the layers being arranged such that the second layer 122 is sandwiched between the first layer 121 and the third layer 123. In the present invention, the multi-layer susceptor device 120 is a three-layer susceptor device 120 consisting of only these three layers 121, 122, 123. Thus, the first layer 121 and the third layer 123 each form an edge layer of the susceptor device 120.

[0131] As from Figure 3 and Figure 4It can be seen that the second layer 122 is closely coupled to the first layer 121, while the third layer 123 is closely coupled to the second layer 121, opposite the first layer 121. In terms of manufacturing, the susceptor device 120 can be formed, for example, as follows: the material of the second layer 122 is first coated onto the material of the first layer 121. Thereafter, the material of the third layer 123 can be coated on top of the second layer 122.

[0132] The first layer 121 is primarily used for heating purposes. For this reason, the first layer consists of a first susceptor material that is optimized in terms of heat loss and therefore heating efficiency. Conveniently, the first susceptor material is a 400 series stainless steel, such as 410 grade stainless steel, or 420 grade stainless steel, or 430 grade stainless steel or similar grade stainless steel. The use of stainless steel has proven to be advantageous in terms of the aging characteristics of the first layer 121 that is in direct contact with the aerosol-forming substrate 130 in the substrate element 110.

[0133] While the first layer 121 is primarily used to heat the substrate 130, the second layer 122 is primarily a functional layer used as a temperature marker. To this end, the second layer 122 comprises a ferromagnetic second susceptor material, which is selected so as to have a Curie temperature corresponding to the predefined temperature point of the heated substrate 130. At its Curie temperature, the magnetic permeability of the second susceptor material drops to a unit that changes its magnetic properties from ferromagnetic to paramagnetic. The change in magnetic properties is accompanied by a temporary change in the resistance of the susceptor device 120. Thus, by monitoring the corresponding change in the current absorbed by the induction heating device of the device 10, it is possible to detect when the second susceptor material has reached its Curie temperature, and therefore when the predefined temperature point has been reached.

[0134] As defined above, the second susceptor material comprises or consists of a Ni-Fe-alloy having a Ni content equal to or less than 65% by weight. Conveniently, the Ni-Fe-alloy comprises 50% by weight of Ni, 9% by weight of Cr, the remainder being Fe. Such an alloy is commercially available, for example, under the trade name Phytherm 260 and has a Curie temperature of 260°C. If a lower Curie temperature is required, the Ni-Fe-alloy may alternatively comprise or consist of 50% by weight of Ni, 10% by weight of Cr, the remainder being Fe. Such an alloy has a Curie temperature of 230°C and is also commercially available, for example, under the trade name Phytherm 220. According to yet another alternative, the Ni-Fe-alloy may comprise or consist of 50% by weight of Ni, 11% by weight of Cr, the remainder being Fe. Such an alloy is also commercially available, for example, under the trade name Phytherm 210 and has a Curie temperature of 210°C. Advantageously, all of the aforementioned alloys (Phytherm alloys) are corrosion-resistant materials.

[0135] Although Phytherm alloy is already a corrosion resistant material, it is preferred that the second layer 122 is protected not only from one side by the first layer 121, but also from the opposite side. This is achieved by the third layer 123, which comprises or consists of a third material. In particular, the third layer 123 may reduce diffusion of materials, such as metals, from the second susceptor material into the surrounding aerosol-forming substrate 130. Furthermore, the third layer 123 may help avoid or reduce thermal bending due to differences in thermal expansion between the various layers 121, 122, 123.

[0136] Preferably, the third layer 123 comprises or consists of the same material as the first layer 121. Thus, the multilayer susceptor device 120 comprises at least two layers 121, 123 having the same coefficient of thermal expansion, which results in reduced deformation of the susceptor device 120 within its temperature operating range. Therefore, in this embodiment, the third material of the third layer 123 is preferably also 400 series stainless steel, such as 410 grade stainless steel, or 420 grade stainless steel, or 430 grade stainless steel or similar grades of stainless steel.

[0137] Alternatively, the third material of the third layer 123 may be austenitic stainless steel. As an example, the third material of the third layer 123 may be X5CrNi18-10 or X2CrNiMo17-12-2 (according to EN (European Standard) nomenclature). In particular, the third material of the third layer 123 may be one of 301 stainless steel, 304 stainless steel, 304L stainless steel, 316 stainless steel or 316L stainless steel (according to the nomenclature of SAE steel grades [Society of Automotive Engineers]). Advantageously, due to its paramagnetic properties and high electrical resistance, austenitic stainless steel only weakly shields the second susceptor material of the second layer 222 from the magnetic field applied thereto.

[0138] As further described above, it has been found that the layer thickness of the third layer 123 can be relatively small, i.e. equal to or less than 8 micrometers. A smaller third layer thickness has proven to be beneficial not only in terms of material saving, but also in terms of making the second layer 122 less shielded from the alternating magnetic field of the induction source used for inductive heating of the susceptor device 120. As a result, when the second susceptor material is used as a temperature maker, the effect of the above-mentioned change in the magnetic properties of the second susceptor material on the current through the induction source will be more obvious. Advantageously, this will enable a more reliable determination of when the second susceptor material has reached its Curie temperature and therefore when a predefined temperature point has been reached. In the present embodiment, the first layer 121 has a layer thickness in the range between 42 micrometers and 43 micrometers, while the third layer 123 has a layer thickness in the range between 3 micrometers and 4 micrometers. Therefore, the layer thickness of the third layer 123 is in the range between about 7% and 9% of the layer thickness of the first layer 121.

[0139] The layer thickness of the second layer 122 can be between the layer thicknesses of the first layer 121 and the third layer 123. Conveniently, the second layer 122 has a layer thickness in the range between 10 μm and 16 μm or between 13 μm and 15 μm, preferably about 10 μm or about 14 μm.

[0140] like Figure 3 As can be particularly seen in the figure, the multilayer susceptor device 120 according to the present embodiment is in the form of an elongated strip. The strip-shaped susceptor device 120 has a length L of 10 to 12 mm and a width W of 4 to 5 mm. That is, all three layers 121, 122, 123 have a length L of 10 to 12 mm and a width W of 4 to 5 mm, but have different layer thicknesses. In view of the above values ​​of the corresponding layer thicknesses, the overall thickness T of the susceptor device 120 is in the range between 55 μm and 63 μm, for example, about 56 μm or about 60 μm.

[0141] For the purpose of this specification and the appended claims, unless otherwise indicated, all numbers representing amounts, quantities, percentages, etc. should be understood to be modified by the term "about" in all cases. Moreover, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein that may or may not be specifically listed herein. Therefore, in this context, the number A is understood to be A±5%A. In this context, the number A can be regarded as including a value within the general standard error for the measurement of the attribute modified by the number A. In certain cases used in the appended claims, the number A may deviate from the percentages listed above, provided that the amount of A deviation does not substantially affect the basic features and novel features of the invention claimed for protection. Moreover, all ranges include the disclosed maximum and minimum points, and include any intermediate ranges therein that may or may not be specifically listed herein.

Claims

1. A multilayer susceptor device for inductively heating an aerosol-forming substrate, the susceptor device comprising or consisting of - a first layer comprising or consisting of a first susceptor material, - a second layer, said second layer comprising or consisting of a second susceptor material, and - a third layer, said third layer comprising or consisting of a third material, wherein the second layer is sandwiched between the first layer and the third layer, wherein the second susceptor material comprises or consists of a Ni-Fe alloy having a Ni content equal to or less than 65 wt.-%, and wherein the layer thickness of the third layer is equal to or less than 8 micrometers.

2. The multilayer susceptor device according to claim 1, wherein the third layer has a layer thickness of 7 μm or less, in particular 6 μm or less, more in particular 5 μm or less, preferably 4 μm or less, or 3 μm or less.

3. The multilayer susceptor device according to claim 1 , wherein the layer thickness of the first layer is in the range between 1.5 and 5 times, in particular between 2 and 4 times, preferably between 2.5 and 3.5 times, more preferably about 3 times, the layer thickness of the second layer.

4. The multilayer susceptor device according to any of the preceding claims, wherein the first susceptor material comprises or consists of a metal, such as ferritic iron or stainless steel, in particular 410 grade, 420 grade or 430 grade stainless steel.

5. The multilayer susceptor arrangement according to any of the preceding claims, wherein the Ni-Fe alloy of the second susceptor material further comprises 8-12 wt.-% Cr, in particular 9-11 wt.-% Cr.

6. The multilayer susceptor device according to any of claims 1 to 5, wherein the Ni-Fe alloy of the second susceptor material has a Ni content equal to or less than 50 wt.-%, in particular equal to or less than 44 wt.-%, more in particular in a specific range between 36 wt.-% and 44 wt.-%, preferably in a range between 36 wt.-% and 40 wt.-%, for example 36.1 wt.-% or 36.4 wt.-% or 40 wt.-%, the remainder preferably being Fe.

7. The multilayer susceptor device according to any one of claims 1 to 5, wherein the Ni-Fe-alloy of the second susceptor material comprises or consists of one of the following: - 50 wt% Ni, 9 wt% Cr, the remainder Fe; - 50 wt% Ni, 10 wt% Cr, and the rest Fe; - 50 wt% Ni, 11 wt% Cr, the remainder Fe; - 50 wt.-% Ni, 9 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe; - 50 wt.-% Ni, 10 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe; - 50 wt.-% Ni, 11 wt.-% Cr, up to 1 wt.-% Si and up to 1 wt.-% Mn, the remainder being Fe.

8. The multilayer susceptor arrangement according to any of the preceding claims, wherein the Ni-Fe alloy of the second susceptor material has a Curie temperature in the range between 180°C and 420°C, in particular between 210°C and 380°C, preferably between 250°C and 380°C.

9. The multilayer susceptor device of any one of the preceding claims, wherein the third material comprises or consists of a corrosion resistant material.

10. The multilayer susceptor device of any one of the preceding claims, wherein the third material is the same as the first susceptor material, or wherein the third material is different from the first susceptor material.

11. The multilayer susceptor device according to any of the preceding claims, wherein the first layer has a layer thickness in the range between 20 and 60 micrometers, in particular between 30 and 50 micrometers, for example 40 micrometers or 42.5 micrometers.

12. The multilayer susceptor device according to any of the preceding claims, wherein the layer thickness of the second layer is in the range between 4 and 20 μm, in particular between 8 and 18 μm, preferably between 10 and 16 μm, for example 10 or 14 μm.

13. The multilayer susceptor device according to any of the preceding claims, wherein the layer thickness of the third layer is equal to or less than 50%, in particular equal to or less than 40%, more in particular equal to or less than 30%, preferably equal to or less than 25%, more preferably equal to or less than 20%, even more preferably equal to or less than 15%, most preferably equal to or less than 10% of the layer thickness of the first layer.

14. The multilayer susceptor device according to any of the preceding claims, wherein the third layer has a layer thickness of at least 0.75 micrometers, in particular at least 1 micrometer.

15. An inductively heatable aerosol-generating article comprising an aerosol-forming substrate and a multi-layer susceptor device according to any preceding claim.

Images