Abstract
The present invention relates to a susceptor assembly (1) for inductively heating an aerosol-forming substrate and to a method for producing such an assembly. The susceptor assembly comprises a first susceptor (10) and a second susceptor (20). A Curie temperature of the second susceptor is lower than 500° C. At least a portion of an outer surface of the second susceptor comprises an anti-corrosion covering (30) and at least a portion of an outer surface of the first susceptor is exposed. The invention further relates to aerosol-generating article comprising an aerosol-forming substrate and a susceptor assembly.
Claims
1. A susceptor assembly for inductively heating an aerosol-forming substrate, comprising a first susceptor and a second susceptor, the second susceptor having a Curie temperature lower than 500° C., wherein the first susceptor and the second susceptor are in intimate physical contact with each other, wherein at least a portion of an outer surface of the second susceptor comprises an anti-corrosion covering and wherein at least a portion of an outer surface of the first susceptor is exposed.
2. The susceptor assembly according to claim 1, wherein the anti-corrosion covering comprises at least one of a corrosion-proof metal, an inert metal, a corrosion-proof alloy, a corrosion-proof organic coating, a glass, a ceramic, a polymer, an anti-corrosion paint, a wax or a grease.
3. The susceptor assembly according to claim 1, wherein the first susceptor comprises ferromagnetic stainless steel and wherein the second susceptor comprises nickel or a nickel alloy.
4. The susceptor assembly according to claim 1, wherein the first susceptor or the second susceptor or both, the first and the second susceptor, have a planar or blade-like shape.
5. The susceptor assembly according to claim 1, wherein the susceptor assembly is a multilayer susceptor assembly, and wherein the first susceptor, the second susceptor and the anti-corrosion covering form adjacent layers of the multilayer susceptor assembly.
6. The susceptor assembly according to claim 5, wherein the anti-corrosion covering is an edge layer of the multilayer susceptor assembly.
7. The susceptor assembly according to claim 1, wherein all portions of the outer surface of the second susceptor, unless in intimate physical contact with the first susceptor, comprise an anti-corrosion covering.
8. The susceptor assembly according to claim 1, wherein all portions of an outer surface of the first susceptor, unless in intimate physical contact with the second susceptor, are exposed.
9. The susceptor assembly according to claim 1, wherein the second susceptor comprises one or more second susceptor elements, each being in intimate physical contact with the first susceptor, wherein at least a portion of an outer surface of each second susceptor element comprises an anti-corrosion covering.
10. An aerosol-generating article comprising an aerosol-forming substrate and a susceptor assembly according to claim 1.
11. The aerosol-generating article according to claim 10, wherein the susceptor assembly is embedded in the aerosol-forming substrate.
12. A method for producing a susceptor assembly for inductively heating an aerosol-forming substrate, the method comprising the following steps: providing a first susceptor, wherein at least a portion of an outer surface of the first susceptor is exposed; providing a second susceptor, wherein a Curie temperature of the second susceptor is lower than 500° C.; assembling the first and the second susceptor to be in intimate physical contact with each other; and applying an anti-corrosion covering to at least a portion of an outer surface of the second susceptor.
13. The method according to claim 12, wherein the anti-corrosion covering is plated, deposited coated, cladded or welded onto at least the portion of the outer surface of the second susceptor.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:
(2) FIG. 1 shows a schematic perspective illustration of a first embodiment of a multilayer susceptor assembly according to the invention;
(3) FIG. 2 shows a schematic side-view illustration of the susceptor assembly according to FIG. 1;
(4) FIG. 3 shows a schematic cross-sectional illustration of second embodiment of a multilayer susceptor assembly according to the invention;
(5) FIG. 4 shows a schematic cross-sectional illustration of third embodiment of a multilayer susceptor assembly according to the invention;
(6) FIG. 5 shows a schematic cross-sectional illustration of fourth embodiment of a multilayer susceptor assembly according to the invention;
(7) FIG. 6 shows a schematic perspective illustration of fifth embodiment of a multilayer susceptor assembly according to the invention;
(8) FIG. 7 shows a schematic cross-sectional illustration of the susceptor assembly according to FIG. 6;
(9) FIG. 8 shows a schematic cross-sectional illustration of first embodiment of an aerosol-generating article according to the invention; and
(10) FIG. 9 shows a schematic cross-sectional illustration of second embodiment of an aerosol-generating article according to the invention.
DETAILED DESCRIPTION
(11) FIG. 1 and FIG. 2 schematically illustrate a first embodiment of a susceptor assembly 1 according to the present invention that is configured for inductively heating an aerosol-forming substrate. As will be explained below in more detail with regard to FIG. 8 and FIG. 9, the susceptor assembly 1 is preferably configured to be embedded in an aerosol-generating article, in direct contact with the aerosol-forming substrate to be heated. The article itself is adapted to be received within an aerosol-generating device which comprises an induction source configured for generating an alternating, in particular high-frequency electromagnetic field. The fluctuating field generates eddy currents and/or hysteresis losses within the susceptor assembly causing the assembly to heat up. The arrangement of the susceptor assembly in the aerosol-generating article and the arrangement of the aerosol-generating article in the aerosol-generating device are such that the susceptor assembly is accurately positioned within the fluctuating electromagnetic field generated by the induction source.
(12) The susceptor assembly 1 according to the first embodiment shown in FIG. 1 and FIG. 2 is a three-layer susceptor assembly 1. The assembly comprises a first susceptor 10 as base layer. The first susceptor 10 is optimized with regard to heat loss and thus heating efficiency. For this, the first susceptor 10 comprises ferromagnetic stainless steel having a Curie temperature in excess of 400° C. For controlling the heating temperature, the susceptor assembly 1 comprises a second susceptor 20 as intermediate or functional layer being arranged upon and intimately coupled to the base layer. The second susceptor 20 comprises nickel having a Curie temperature of in the range of about 354° C. to 360° C. or 627 K to 633 K, respectively (depending on the nature of impurities), which proves advantageous with regard to both, temperature control and controlled heating of aerosol-forming substrate. Once the susceptor assembly reaches the Curie temperature of nickel during heating, the magnetic properties of the second susceptor 20 change as a whole. This change can be detected as reduced power dissipation, whereupon heat generation may be decreased or interrupted, for example by a controller of an aerosol-generating device the susceptor assembly is to be used with. When the assembly has cooled down below the Curie temperature and the second susceptor 20 has regained its ferromagnetic properties, heat generation can be increased or resumed.
(13) Nickel, however, is susceptible to corrosion. Therefore, the susceptor assembly comprises a top layer of an anti-corrosion covering 30 arranged upon and intimately coupled to the intermediate layer. This top layer protects the second susceptor 20 from corrosion, in particular when the susceptor assembly 1 is embedded in an aerosol-forming substrate.
(14) With regard to the first embodiment shown in FIG. 1 and FIG. 2, the susceptor assembly 1 is in the form of an elongate strip having a length L of 12 mm and a width W of 4 mm. All layers have a length L of 12 mm and a width W of 4 mm. The first susceptor 10 is a strip of grade 430 stainless steel having a thickness T10 of 35 μm. The second susceptor 20 is a strip of nickel having a thickness T20 of 10 μm. The anti-corrosion material 30 is a strip of austenitic stainless steel having a thickness T30 of 10 μm. The total thickness T of the susceptor assembly 1 is 55 μm. The susceptor assembly 1 is formed by cladding the strip of nickel 20 to the strip of stainless steel 10. After that, the austenitic stainless steel strip 30 is cladded on top of the nickel strip 20 such that the entire top surface of the second susceptor 20—opposite to its bottom surface being in intimate contact with the first susceptor 10—is covered by the anti-corrosion material. In contrast, a circumferential outer surface 21 of the second susceptor 20 is not covered by the anti-corrosion covering 30, but exposed to the environment of the susceptor assembly 1. Due to the small thickness T20 of the second susceptor 20, its unprotected circumferential outer surface 21 is negligible as compared to its top and bottom surface being in contact with and protected by the first susceptor 10 and the anti-corrosion covering 30, respectively. Therefore, the susceptor assembly 1 according to this first embodiment has significant improved aging characteristics as compared to a susceptor assembly without any anti-corrosion covering.
(15) As the first susceptor 10 is made of stainless steel, it is resistant to corrosion and does not require any anti-corrosion covering. The entire outer surface of the first susceptor 10—unless in intimate contact with the second susceptor 20—is deliberately chosen to be bare or exposed to the environment of the susceptor assembly 1. Advantageously, this ensures maximum heat transfer to the aerosol-forming substrate.
(16) FIG. 3 illustrates a second embodiment of the susceptor assembly 1, which is very similar to the first embodiment shown in FIG. 1 and FIG. 2. Therefore, identical features are denoted with identical reference numbers. In contrast to the first embodiment, the anti-corrosion covering 30 in this second embodiment covers not only the top surface of the second susceptor 20, but also its lateral circumferential surface 21. This configuration advantageously allows for maximum protection of the second susceptor 20. The second susceptor 20 has the same width and length extension than the first susceptor 10. Therefore, the anti-corrosion covering 30 laterally projects above the width and length extension of the first and second susceptor 10, 20. The covering 30 may be attached to the bonded first and second susceptor by applying a strip of austenitic stainless steel on top of the second susceptor 20, beading over the rim portions of the covering strip to the circumferential surface 21 of the second susceptor 20, and subsequently cladding the covering strip to the covered circumferential and top surface of the second susceptor 20.
(17) FIG. 4 illustrates a third embodiment of the susceptor assembly 1, which differs from the second embodiment according to FIG. 3 in that the anti-corrosion covering 30 covers in addition at least partially a lateral circumferential surface of the first susceptor 10. This configuration may result from applying the covering material by dip-coating or spraying onto the bonded first and second susceptor and may thus have advantages with regard to a simple manufacture. Apart from that, the susceptor assembly 1 according to this third embodiment advantageously has a regular outer surface without any recessed and protruding portions.
(18) FIG. 5 illustrates a fourth embodiment of the susceptor assembly 1, which is also similar to the afore-mentioned embodiments. In contrast to these, the width and length extension of the second susceptor 20 of the fourth embodiment is slightly smaller than the width and length extension of the first susceptor 10. Thus, when attached to each other, there is a circumferential lateral offset between the first and the second susceptor. The volume of this circumferential offset is—in addition to the top surface of the second susceptor also filled with anti-corrosion covering material. This results in a susceptor assembly 1 having a regular outer shape and a maximum anti-corrosion protection of the second susceptor 20.
(19) FIG. 6 and FIG. 7 illustrate a fifth embodiment of a susceptor assembly 1 which is also in the form of an elongate strip having for example a length L of 12 mm and a width W of 4 mm. The susceptor assembly is formed from a first susceptor 10 that is intimately coupled to a second susceptor 20. The first susceptor 10 is a strip of grade 430 stainless steel having dimensions of 12 mm by 4 mm by 35 μm and thus defines the basic shape of the susceptor assembly 1. The second susceptor 20 is a patch of nickel of dimensions 3 mm by 2 mm by 10 μm. The patch of nickel has been electroplated onto the strip of stainless steel. Though the patch of nickel is significantly smaller than the strip of stainless steel, it is still sufficient to allow for accurate control of the heating temperature. Advantageously, the susceptor assembly 1 according to this fifth embodiment provides significant savings in second susceptor material. As can be seen from FIG. 6 and FIG. 7, the entire outer surface of the patch—unless in intimate contact with the first susceptor 10—is capped by an anti-corrosion covering 30. In contrast, the entire outer surface of the first susceptor 10—unless in intimate contact with the second susceptor 20—is uncovered to allow for maximum heat transfer. Alternatively, at least those portions of the top surface of the first susceptor 10 being not in contact with the second susceptor 20 may also be covered by the anti-corrosion covering. In further embodiments (not shown), there may be more than one patch of the second susceptor 20 located in intimate contact with the first susceptor 10.
(20) As mentioned above, the susceptor assembly accordingly to the present invention is preferably configured to be part of an aerosol-generating article including an aerosol-forming substrate to be heated.
(21) FIG. 8 schematically illustrates a first embodiment of such an aerosol-generating article 100 according to the present invention. The aerosol-generating article 100 comprises four elements arranged in coaxial alignment: an aerosol-forming substrate 102, a support element 103, an aerosol-cooling element 104, and a mouthpiece 105. Each of these four elements is a substantially cylindrical element, each having substantially the same diameter. These four elements are arranged sequentially and are circumscribed by an outer wrapper 106 to form a cylindrical rod. Further details of this specific aerosol-generating article, in particular of the four elements, are disclosed in WO 2015/176898 A1.
(22) An elongate susceptor assembly 1 is located within the aerosol-forming substrate 102, in contact with the aerosol-forming substrate 102. The susceptor assembly 1 as shown in FIG. 8 corresponds to the susceptor assembly 1 according to the first embodiment described above in relation to FIGS. 1 and 2. The layer structure of the susceptor assembly as shown in FIG. 8 is illustrated oversized, but not true to scale with regard to the other elements of the aerosol-generating article. The susceptor assembly 1 has a length that is approximately the same as the length of the aerosol-forming substrate 102, and is located along a radially central axis of the aerosol-forming substrate 102. The aerosol-forming substrate 102 comprises a gathered sheet of crimped homogenized tobacco material circumscribed by a wrapper. The crimped sheet of homogenized tobacco material comprises glycerin as an aerosol-former.
(23) The susceptor assembly 1 may be inserted into the aerosol-forming substrate 102 during the process used to form the aerosol-forming substrate, prior to the assembly of the plurality of elements to form the aerosol-generating article.
(24) The aerosol-generating article 100 illustrated in FIG. 8 is designed to engage with an electrically-operated aerosol-generating device. The aerosol-generating device may comprise an induction source having an induction coil or inductor for generating an alternating, in particular high-frequency electromagnetic field in which the susceptor assembly of the aerosol-generating article is located in upon engaging the aerosol-generating article with the aerosol-generating device.
(25) FIG. 9 shows another embodiment of an aerosol-generating article 100 according to the present invention. The embodiment of FIG. 9 differs from the embodiment shown in FIG. 8 only with regard to the susceptor assembly 1. Instead of a multilayer susceptor assembly having a first and second susceptor layer as well as an anti-corrosion layer in intimate physical contact with each other, the susceptor assembly according to FIG. 9 comprises a first and second susceptor being separate from each other and having different geometrical configurations. The first susceptor 10 which is responsible for heating the aerosol-forming substrate 102 is a blade made of ferromagnetic stainless steel. The blade has a length that is approximately the same as the length of the aerosol-forming substrate 102. The blade is located along a radially central axis of the aerosol-forming substrate 102. The second susceptor 20 is of particulate configuration comprising a plurality of nickel particles. The particles may have an equivalent spherical diameter of 10 μm to 100 μm. The entire outer surface of each of the nickel particles 20 comprises an anti-corrosion covering 30, for example a ceramic covering. The thickness of the covering 30 may be about 10 μm. The anti-corrosion covering is applied to the nickel particles prior to embedding the covered particles into the aerosol-forming substrate 102.
(26) The particles are distributed throughout the aerosol-forming substrate 102. Preferably, the particle distribution has local concentration maximum in proximity to the first susceptor 10 to ensure an accurate control of the heating temperate.
(27) Instead of a blade configuration, the first susceptor 10 may alternatively be of one of a filament, or mesh-like, or wire-like configuration.
(28) The first and second susceptor 10, 20 may be inserted into the aerosol-forming substrate 102 during the process used to form the aerosol-forming substrate, prior to the assembly of the plurality of elements to form the aerosol-generating article.
(29) It should be noted though, that as need may be, the geometrical configuration of the first and second susceptor may be interchanged. Thus, the second susceptor may be one of a filament, or mesh-like, or wire-like or a blade configuration comprising an anti-corrosion covering, and the first susceptor material may be of particulate configuration.
