Aerosol-generating article with multi-material susceptor

Abstract

An aerosol-generating article is provided, including an aerosol-forming substrate and a susceptor configured to heat the aerosol-forming substrate. The susceptor includes a first susceptor material and a second susceptor material having a Curie temperature, the first susceptor material being disposed in intimate physical contact with the second susceptor material. The first susceptor material may also have a Curie temperature, the second Curie temperature being lower than 500 C., and lower than the Curie temperature of the first susceptor material, if the first susceptor material has a Curie temperature. The use of such a multi-material susceptor allows heating to be optimised and the temperature of the susceptor to be controlled to approximate the second Curie temperature without need for direct temperature monitoring.

Claims

1. An aerosol-generating article, comprising: an aerosol-forming substrate; and a susceptor configured to heat the aerosol-forming substrate, the susceptor comprising a first susceptor material and a second susceptor material, the second susceptor material being different from the first susceptor material, the second susceptor material being plated, deposited, or welded onto the first material, wherein the first susceptor material has a first Curie temperature, wherein the second susceptor material has a second Curie temperature that is lower than 500 C., wherein the second Curie temperature is lower than the first Curie temperature, wherein the first susceptor material is configured to heat the aerosol-forming substrate and the second susceptor material is configured to determine when the susceptor reaches a temperature corresponding to the second Curie temperature of the second susceptor material, and wherein, upon reaching the second Curie temperature, the second susceptor material reversibly changes from a ferromagnetic phase to a paramagnetic phase thereby causing a change in the apparent resistance of the susceptor.

2. The aerosol-generating article according to claim 1, wherein the first susceptor material is iron or an iron alloy, and the second susceptor material is nickel or a nickel alloy.

3. The aerosol-generating article according to claim 1, wherein the first susceptor material is a grade 410, 420, or 430 stainless steel, and the second susceptor material is nickel or a nickel alloy.

4. The aerosol-generating article according to claim 1, wherein the Curie temperature of the second susceptor material is lower than 400 C.

5. The aerosol-generating article according to claim 1, further comprising: a plurality of elements assembled within a wrapper in the form of a rod having a mouth end and a distal end upstream from the mouth end, the plurality of elements including the aerosol-forming substrate disposed at or towards the distal end of the rod, wherein the aerosol-forming substrate is a solid aerosol-forming substrate, and wherein the susceptor is an elongate susceptor having a width of between 3 mm and 6 mm and a thickness of between 10 m and 200 m, the susceptor being disposed within the aerosol-forming substrate.

6. The aerosol-generating article according to claim 5, wherein the elongate susceptor is disposed in a radially central position within the aerosol-forming substrate and extends along a longitudinal axis of the aerosol-forming substrate.

7. The aerosol-generating article according to claim 1, wherein the first susceptor material is in the form of an elongate strip having a width of between 3 mm and 6 mm and a thickness of between 10 m and 200 m, and wherein the second susceptor material is in the form of discrete patches that are plated, deposited, or welded onto the first susceptor material.

8. The aerosol-generating article according to claim 1, wherein the first susceptor material and the second susceptor material are co laminated in the form of an elongate strip having a width of between 3 mm and 6 mm and a thickness of between 10 m and 200 m, and wherein the first susceptor material has a thickness that is greater than a thickness of the second susceptor material.

9. The aerosol-generating article according to claim 1, wherein the susceptor is an elongate susceptor having a width of between 3 mm and 6 mm and a thickness of between 10 m and 200 m, the susceptor further comprising a core of the first susceptor material encapsulated by the second susceptor material.

10. The aerosol-generating article according to claim 1, wherein the aerosol forming substrate is in the form of a rod comprising a gathered sheet of aerosol forming material, the gathered sheet comprising a gathered sheet of homogenised tobacco, or comprising a nicotine salt and an aerosol former.

11. The aerosol-generating article according to claim 1, further comprising a plurality of susceptors.

12. An aerosol-generating system, comprising: an electrically-operated aerosol-generating device comprising an inductor configured to produce a fluctuating electromagnetic field; and an aerosol-generating article comprising an aerosol-forming substrate; and a susceptor configured to heat the aerosol-forming substrate, the susceptor comprising a first susceptor material and a second susceptor material, the second susceptor material being different from the first susceptor material, the second susceptor material being plated, deposited, or welded onto the first material, wherein the first susceptor material has a first Curie temperature, wherein the second susceptor material has a second Curie temperature that is lower than 500 C., wherein the second Curie temperature is lower than the first Curie temperature, wherein the first susceptor material is configured to heat the aerosol-forming substrate and the second susceptor material is configured to determine when the susceptor reaches a temperature corresponding to the second Curie temperature of the second susceptor material, and wherein, upon reaching the second Curie temperature, the second susceptor material reversibly changes from a ferromagnetic phase to a paramagnetic phase thereby causing a change in the apparent resistance of the susceptor, wherein the aerosol-generating article is configured to engage with the aerosol generating device such that the fluctuating magnetic field produced by the inductor induces a current in the susceptor, causing heating of the susceptor, and wherein the electrically-operated aerosol-generating device further comprises electronic circuitry configured to detect the Curie transition of the second susceptor material.

13. The aerosol-generating system according to claim 12, wherein the electronic circuitry is configured for closed loop control of the heating of the aerosol-forming substrate.

14. The aerosol-generating system according to claim 12, wherein the electrically-operated aerosol-generating device is configured to induce a fluctuating magnetic field having a frequency of between 1 MHz and 30 MHz and an H-field strength of between 1 kA/m and 5 kA/m, and wherein the susceptor in the aerosol-generating article is configured to dissipate power of between 1.5 W and 8 W when positioned within the fluctuating magnetic field.

15. A method of using an aerosol-generating article comprising an aerosol forming substrate and a susceptor configured to heat the aerosol-forming substrate, the susceptor comprising a first susceptor material and a second susceptor material the second susceptor material being different from the first susceptor material, the second susceptor material being plated, deposited, or welded onto the first material, wherein the first susceptor material has a first Curie temperature, wherein the second susceptor material has a second Curie temperature that is lower than 500 C., wherein the second Curie temperature is lower than the first Curie temperature, wherein the first susceptor material is configured to heat the aerosol-forming substrate and the second susceptor material is configured to determine when the susceptor reaches a temperature corresponding to the second Curie temperature of the second susceptor material, and wherein, upon reaching the second Curie temperature, the second susceptor material reversibly changes from a ferromagnetic phase to a paramagnetic phase thereby causing a chance in the apparent resistance of the susceptor, and the method comprising: positioning the aerosol-generating article relative to an electrically-operated aerosol generating device such that the susceptor of the aerosol-generating article is within a fluctuating electromagnetic field generated by the electrically-operated aerosol generating device, the fluctuating electromagnetic field causing heating of the susceptor; and monitoring at least one parameter of the electrically-operated aerosol-generating device to detect the Curie transition of the second susceptor material.

16. The method according to claim 15, further comprising: controlling, using electronic circuitry within the electrically-operated aerosol generating device, the fluctuating electromagnetic field such that a temperature of the susceptor is maintained at the Curie temperature of the second susceptor material plus or minus 20 C.

Description

(1) Features described in relation to one aspect or embodiment may also be applicable to other aspects and embodiments. Specific embodiments will now be described with reference to the figures, in which:

(2) FIG. 1A is a plan view of a susceptor for use in an aerosol-generating article according to an embodiment of the invention;

(3) FIG. 1B is a side view of the susceptor of FIG. 1A;

(4) FIG. 2A is a plan view of a second susceptor for use in an aerosol-generating article according to an embodiment of the invention;

(5) FIG. 2B is a side view of the susceptor of FIG. 2A;

(6) FIG. 3 is a schematic cross-sectional illustration of a specific embodiment of an aerosol-generating article incorporating a susceptor as illustrated in FIGS. 2A and 2B;

(7) FIG. 4 is a schematic cross-sectional illustration of a specific embodiment of an electrically-operated aerosol-generating device for use with the aerosol-generating article illustrated in FIG. 3,

(8) FIG. 5 is a schematic cross-sectional illustration of the aerosol-generating article of FIG. 3 in engagement with the electrically-operated aerosol-generating device of FIG. 4;

(9) FIG. 6 is a block diagram showing electronic components of the aerosol-generating device described in relation to FIG. 4;

(10) and

(11) FIG. 7 is a graph of DC current vs. time illustrating the remotely detectable current changes that occur when a susceptor material undergoes a phase transition associated with its Curie point.

(12) Inductive heating is a known phenomenon described by Faraday's law of induction and Ohm's law. More specifically, Faraday's law of induction states that if the magnetic induction in a conductor is changing, a changing electric field is produced in the conductor. Since this electric field is produced in a conductor, a current, known as an eddy current, will flow in the conductor according to Ohm's, law. The eddy current will generate heat proportional to the current density and the conductor resistivity. A conductor which is capable of being inductively heated is known as a susceptor material. The present invention employs an inductive heating device equipped with an inductive heating source, such as, e.g., an induction coil, which is capable of generating an alternating electromagnetic field from an AC source such as an LC circuit. Heat generating eddy currents are produced in the susceptor material which is in thermal proximity to an aerosol-forming substrate which is capable of releasing volatile compounds that can form an aerosol upon heating. The primary heat transfer mechanisms from the susceptor material to the solid material are conduction, radiation and possibly convection.

(13) FIG. 1A and FIG. 1B illustrate a specific example of a unitary multi-material susceptor for use in an aerosol-generating article according to an embodiment of the invention. The susceptor 1 is in the form of an elongate strip having a length of 12 mm and a width of 4 mm. The susceptor is formed from a first susceptor material 2 that is intimately coupled to a second susceptor material 3. The first susceptor material 2 is in the form of a strip of grade 430 stainless steel having dimensions of 12 mm by 4 mm by 35 micrometres. The second susceptor material 3 is a patch of nickel of dimensions 3 mm by 2 mm by 10 micrometres. The patch of nickel has been electroplated onto the strip of stainless steel. Grade 430 stainless steel is a ferromagnetic material having a Curie temperature in excess of 400 C. Nickel is a ferromagnetic material having a Curie temperature of about 354 C.

(14) In further embodiments the material forming the first and second susceptor materials may be varied. In further embodiments there may be more than one patch of the second susceptor material located in intimate contact with the first susceptor material.

(15) FIG. 2A and FIG. 2B illustrate a second specific example of a unitary multi-material susceptor for use in an aerosol-generating article according to an embodiment of the invention. The susceptor 4 is in the form of an elongate strip having a length of 12 mm and a width of 4 mm. The susceptor is formed from a first susceptor material 5 that is intimately coupled to a second susceptor material 6. The first susceptor material 5 is in the form of a strip of grade 430 stainless steel having dimensions of 12 mm by 4 mm by 25 micrometres. The second susceptor material 6 is in the form of a strip of nickel having dimensions of 12 mm by 4 mm by 10 micrometres. The susceptor is formed by cladding the strip of nickel 6 to the strip of stainless steel 5. The total thickness of the susceptor is 35 micrometres. The susceptor 4 of FIG. 2 may be termed a bi-layer or multilayer susceptor.

(16) FIG. 3 illustrates an aerosol-generating article 10 according to a preferred embodiment. The aerosol-generating article 10 comprises four elements arranged in coaxial alignment: an aerosol-forming substrate 20, a support element 30, an aerosol-cooling element 40, and a mouthpiece 50. 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 60 to form a cylindrical rod. An elongate bi-layer susceptor 4 is located within the aerosol-forming substrate, in contact with the aerosol-forming substrate. The susceptor 4 is the susceptor described above in relation to FIG. 2. The susceptor 4 has a length (12 mm) that is approximately the same as the length of the aerosol-forming substrate, and is located along a radially central axis of the aerosol-forming substrate.

(17) The aerosol-generating article 10 has a proximal or mouth end 70, which a user inserts into his or her mouth during use, and a distal end 80 located at the opposite end of the aerosol-generating article 10 to the mouth end 70. Once assembled, the total length of the aerosol-generating article 10 is about 45 mm and the diameter is about 7.2 mm.

(18) In use air is drawn through the aerosol-generating article by a user from the distal end 80 to the mouth end 70. The distal end 80 of the aerosol-generating article may also be described as the upstream end of the aerosol-generating article 10 and the mouth end 70 of the aerosol-generating article 10 may also be described as the downstream end of the aerosol-generating article 10. Elements of the aerosol-generating article 10 located between the mouth end 70 and the distal end 80 can be described as being upstream of the mouth end 70 or, alternatively, downstream of the distal end 80.

(19) The aerosol-forming substrate 20 is located at the extreme distal or upstream end 80 of the aerosol-generating article 10. In the embodiment illustrated in FIG. 3, the aerosol-forming substrate 20 comprises a gathered sheet of crimped homogenised tobacco material circumscribed by a wrapper. The crimped sheet of homogenised tobacco material comprises glycerine as an aerosol-former.

(20) The support element 30 is located immediately downstream of the aerosol-forming substrate 20 and abuts the aerosol-forming substrate 20. In the embodiment shown in FIG. 3, the support element is a hollow cellulose acetate tube. The support element 30 locates the aerosol-forming substrate 20 at the extreme distal end 80 of the aerosol-generating article. The support element 30 also acts as a spacer to space the aerosol-cooling element 40 of the aerosol-generating article 10 from the aerosol-forming substrate 20.

(21) The aerosol-cooling element 40 is located immediately downstream of the support element 30 and abuts the support element 30. In use, volatile substances released from the aerosol-forming substrate 20 pass along the aerosol-cooling element 40 towards the mouth end 70 of the aerosol-generating article 10. The volatile substances may cool within the aerosol-cooling element 40 to form an aerosol that is inhaled by the user. In the embodiment illustrated in FIG. 3, the aerosol-cooling element comprises a crimped and gathered sheet of polylactic acid circumscribed by a wrapper 90. The crimped and gathered sheet of polylactic acid defines a plurality of longitudinal channels that extend along the length of the aerosol-cooling element 40.

(22) The mouthpiece 50 is located immediately downstream of the aerosol-cooling element 40 and abuts the aerosol-cooling element 40. In the embodiment illustrated in FIG. 3, the mouthpiece 50 comprises a conventional cellulose acetate tow filter of low filtration efficiency.

(23) To assemble the aerosol-generating article 10, the four cylindrical elements described above are aligned and tightly wrapped within the outer wrapper 60. In the embodiment illustrated in FIG. 3, the outer wrapper is a conventional cigarette paper. The susceptor 4 may be inserted into the aerosol-forming substrate 20 during the process used to form the aerosol-forming substrate, prior to the assembly of the plurality of elements to form a rod.

(24) The aerosol-generating article 10 illustrated in FIG. 3 is designed to engage with an electrically-operated aerosol-generating device comprising an induction coil, or inductor, in order to be smoked or consumed by a user.

(25) A schematic cross-sectional illustration of an electrically-operated aerosol-generating device 200 is shown in FIG. 4. The aerosol-generating device 200 comprises an inductor 210. As shown in FIG. 4, the inductor 210 is located adjacent a distal portion 231 of a substrate receiving chamber 230 of the aerosol-generating device 200. In use, the user inserts an aerosol-generating article 10 into the substrate receiving chamber 230 of the aerosol-generating device 200 such that the aerosol-forming substrate 20 of the aerosol-generating article 10 is located adjacent to the inductor 210.

(26) The aerosol-generating device 200 comprises a battery 250 and electronics 260 that allow the inductor 210 to be actuated. Such actuation may be manually operated or may occur automatically in response to a user drawing on an aerosol-generating article 10 inserted into the substrate receiving chamber 230 of the aerosol-generating device 200. The battery 250 supplies a DC current. The electronics include a DC/AC inverter for supplying the inductor with a high frequency AC current.

(27) When the device is actuated, a high-frequency alternating current is passed through coils of wire that form part of the inductor. This causes the inductor 210 to generate a fluctuating electromagnetic field within the distal portion 231 of the substrate receiving cavity 230 of the device. The electromagnetic field preferably fluctuates with a frequency of between 1 and 30 MHz, preferably between 2 and 10 MHz, for example between 5 and 7 MHz. When an aerosol-generating article 10 is correctly located in the substrate receiving cavity 230, the susceptor 4 of the article 10 is located within this fluctuating electromagnetic field. The fluctuating field generates eddy currents within the susceptor, which is heated as a result. Further heating is provided by magnetic hysteresis losses within the susceptor. The heated susceptor heats the aerosol-forming substrate 20 of the aerosol-generating article 10 to a sufficient temperature to form an aerosol. The aerosol is drawn downstream through the aerosol-generating article 10 and inhaled by the user. FIG. 5 illustrates an aerosol-generating article in engagement with an electrically-operated aerosol-generating device.

(28) FIG. 6 is a block diagram showing electronic components of the aerosol-generating device 200 described in relation to FIG. 4. The aerosol-generating device 200 comprises a DC power source 250 (the battery), a microcontroller (microprocessor control unit) 3131, a DC/AC inverter 3132, a matching network 3133 for adaptation to the load, and an inductor 210. The microprocessor control unit 3131, DC/AC inverter 3132 and matching network 3133 are all part of the power supply electronics 260. The DC supply voltage VDC and the DC current IDC drawn from the DC power source 250 are provided by feed-back channels to the microprocessor control unit 3131, preferably by measurement of both the DC supply voltage VDC and the DC current IDC drawn from the DC power source 250 to control the further supply of AC power PAC to the inductor 3134. A matching network 3133 may be provided for optimum adaptation to the load but is not essential.

(29) As the susceptor 4 of an aerosol-generating article 10 is heated during operation its apparent resistance (Ra) increases. This increase in resistance can be remotely detected by monitoring the DC current drawn from the DC power source 250, which at constant voltage decreases as the temperature of the susceptor increases. The high frequency alternating magnetic field provided by the inductor 210 induces eddy currents in close proximity to the susceptor surface, an effect that is known as the skin effect. The resistance in the susceptor depends in part on the electrical resistivities of the first and second susceptor materials and in part on the depth of the skin layer in each material available for induced eddy currents. As the second susceptor material 6 (Nickel) reaches its Curie temperature it loses its magnetic properties. This causes an increase in the skin layer available for eddy currents in the second susceptor material, which causes a decrease in the apparent resistance of the susceptor. The result is a temporary increase in the detected DC current when the second susceptor material reaches its Curie point. This can be seen in the graph of FIG. 7.

(30) By remote detection of the change in resistance in the susceptor, the moment at which the susceptor 4 reaches the second Curie temperature can be determined. At this point the susceptor is at a known temperature (354 C. in the case of a Nickel susceptor). At this point the electronics in the device operate to vary the power supplied and thereby reduce or stop the heating of the susceptor. The temperature of the susceptor then decreases to below the Curie temperature of the second susceptor material. The power supply may be increased again, or resumed, either after a period of time or after it has been detected that the second susceptor material has cooled below its Curie temperature. By use of such a feedback loop the temperature of the susceptor may be maintain to be approximately that of the second Curie temperature.

(31) The specific embodiment described in relation to FIG. 3 comprises an aerosol-forming substrate formed from homogenised tobacco. In other embodiments the aerosol-forming substrate may be formed from different material. For example, a second specific embodiment of an aerosol-generating article has elements that are identical to those described above in relation to the embodiment of FIG. 3, with the exception that the aerosol-forming substrate 20 is formed from a non-tobacco sheet of cigarette paper that has been soaked in a liquid formulation comprising nicotine pyruvate, glycerine, and water. The cigarette paper absorbs the liquid formulation and the non-tobacco sheet thus comprises nicotine pyruvate, glycerine and water. The ratio of glycerine to nicotine is 5:1. In use, the aerosol-forming substrate 20 is heated to a temperature of about 220 degrees Celsius. At this temperature an aerosol comprising nicotine pyruvate, glycerine, and water is evolved and may be drawn through the filter 50 and into the user's mouth. It is noted that the temperature that the substrate 20 is heated to is considerably lower than the temperature that would be required to evolve an aerosol from a tobacco substrate. As such it is preferred that the second susceptor material is a material having a lower Curie temperature than Nickel. An appropriate Nickel alloy may, for example, be selected.

(32) The exemplary embodiments described above are not intended to limit the scope of the claims. Other embodiments consistent with the exemplary embodiments described above will be apparent to those skilled in the art.