Cartridge with a heater assembly for an aerosol-generating system

Abstract

An aerosol-generating system including a cartridge is provided, the cartridge including a liquid storage portion including a housing configured to hold a liquid aerosol-forming substrate, the housing having an opening; and a heater assembly including at least one heater element fixed to the housing and extending across an opening of the housing, wherein a width of the at least one heater element of the heater assembly is smaller than a width of the opening of the housing. The heater element may be spaced from a periphery of the opening, leading to more efficient heating and aerosol production.

Claims

1. A cartridge for use in an aerosol-generating system, comprising: a liquid storage portion comprising a housing configured to hold a liquid aerosol-forming substrate, the housing having an opening; and a heater assembly comprising at least one heater element fixed to the housing and extending across the opening of the housing, wherein the heater assembly is substantially flat and formed in a single plane, wherein the at least one heater element of the heater assembly has a width that is smaller than a width of the opening of the housing, wherein the at least one heater element is fluid-permeable and comprises a plurality of electrically conductive filaments, and a mesh having interstices between the electrically conductive filaments, wherein the housing of the liquid storage portion contains a capillary material, and wherein the capillary material extends into the interstices between the filaments.

2. The cartridge according to claim 1, wherein the width of the at least one heater element is less than 90% of the width of the opening of the housing.

3. The cartridge according to claim 1, wherein an area of the heater elements of the heater assembly is less than 90% of an area of the opening of the housing.

4. The cartridge according to claim 1, wherein the heater assembly has a total resistance of over 1 Ohm.

5. The cartridge according to claim 1, wherein the heater assembly comprises a plurality of heater elements connected in series.

6. The cartridge according to claim 5, wherein the heater elements of the heater assembly are arranged substantially in parallel to each other.

7. The cartridge according to claim 1, wherein at least a portion of the at least one heater element is spaced apart from a periphery of the opening by a distance that is greater than a dimension of the interstices of said portion of the heater element.

8. The cartridge according to claim 1, wherein the width of the at least one heater element is less than 50% of the width of the opening of the housing.

9. The cartridge according to claim 1, wherein the width of the at least one heater element is less than 25% of the width of the opening of the housing.

10. The cartridge according to claim 1, wherein an area of the heater elements of the heater assembly is between 10% and 50% of an area of the opening of the housing.

11. The cartridge according to claim 1, wherein an area of the heater elements of the heater assembly is between 15% and 25% of an area of the opening of the housing.

12. The cartridge according to claim 1, wherein the heater assembly has a total resistance of between 1 Ohm and 4 Ohm.

13. The cartridge according to claim 1, wherein the heater assembly has a total resistance of about 1.5 Ohm.

14. A method of manufacture of a cartridge for use in an aerosol-generating system, comprising: providing a liquid storage: portion comprising a housing having an opening; filling the liquid storage portion with liquid aerosol-forming substrate; and providing a heater assembly comprising at least one heater element extending across the opening of the housing, wherein the heater assembly is substantially flat and formed in a single plane, wherein the at least one heater element of the heater assembly is smaller than the opening of the housing, wherein the at least one heater element is fluid-permeable and comprises a plurality of electrically conductive filaments, and a mesh having interstices between the electrically conductive filaments, wherein the housing of the liquid storage portion contains a capillary material, and wherein the capillary material extends into the interstices between the filaments.

15. An aerosol-generating system, comprising a main unit; and a cartridge for use in an aerosol-generating system, the cartridge being removably coupled to the main unit and comprising: a liquid storage portion comprising a housing configured to hold a liquid aerosol-forming substrate, the housing having an opening, and a heater assembly comprising at least one heater element fixed to the housing and extending across the opening of the housing, wherein the heater assembly is substantially flat and formed in a single plane, wherein the at least one heater element of the heater assembly has a width that is smaller than a width of the opening of the housing, wherein the at least one heater element is fluid-permeable and comprises a plurality of electrically conductive filaments, and a mesh having interstices between the electrically conductive filaments, wherein the housing of the liquid storage portion contains a capillary material, wherein the capillary material extends into the interstices between the filaments, and wherein the liquid storage portion and heater assembly are provided in the cartridge and the main unit comprises a power supply.

16. The aerosol-generating system according to claim 15, further comprising electric circuitry connected to the heater assembly and to an electrical power source, the electric circuitry configured to monitor an electrical resistance of the heater assembly or of one or more filaments of the plurality of filaments, and to control a supply of power from the electrical power source to the heater assembly dependent on the electrical resistance of the heater assembly or the one or more filaments.

17. An aerosol-generating system comprising a cartridge, the cartridge comprising: a liquid storage portion comprising a housing configured to hold a liquid aerosol-forming substrate, the housing having an opening; and a heater assembly comprising at least one heater element fixed to the housing and extending across the opening of the housing, wherein the heater assembly is substantially flat and formed in a single plane, wherein the at least one heater element of the heater assembly has a width that is smaller than a width of the opening of the housing, wherein the at least one heater element is fluid-permeable and comprises a plurality of electrically conductive filaments, and a mesh having interstices between the electrically conductive filaments, wherein the housing of the liquid storage portion contains a capillary material, wherein the capillary material extends into the interstices between the filaments, and wherein the system is an electrically operated smoking system.

Description

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIGS. 1a to 1d are schematic illustrations of a system, incorporating a cartridge, in accordance with an embodiment of the invention;

(3) FIG. 2 is an exploded view of an example cartridge of a system shown in FIG. 1;

(4) FIG. 3 shows a heater assembly with three heater elements;

(5) FIG. 4 shows a heater assembly with four heater elements; and

(6) FIG. 5 is a diagram showing the TPM yield of different heater geometries;

(7) FIGS. 1a to 1d are schematic illustrations of an aerosol-generating system, including a cartridge in accordance with an embodiment of the invention. FIG. 1a is a schematic view of an aerosol-generating device 10 and a separate cartridge 20, which together form the aerosol-generating system. In this example, the aerosol-generating system is an electrically operated smoking system.

(8) The cartridge 20 contains an aerosol-forming substrate and is configured to be received in a cavity 18 within the device. Cartridge 20 should be replaceable by a user when the aerosol-forming substrate provided in the cartridge is depleted. FIG. 1a shows the cartridge 20 just prior to insertion into the device, with the arrow 1 in FIG. 1a indicating the direction of insertion of the cartridge.

(9) The aerosol-generating device 10 is portable and has a size comparable to a conventional cigar or cigarette. The device 10 comprises a main body 11 and a mouthpiece portion 12. The main body 11 contains a battery 14, such as a lithium iron phosphate battery, control electronics 16 and a cavity 18. The mouthpiece portion 12 is connected to the main body 11 by a hinged connection 21 and can move between an open position as shown in FIG. 1 and a closed position as shown in FIG. 1d. The mouthpiece portion 12 is placed in the open position to allow for insertion and removal of cartridges 20 and is placed in the closed position when the system is to be used to generate aerosol, as will be described. The mouthpiece portion comprises a plurality of air inlets 13 and an outlet 15. In use, a user sucks or puffs on the outlet to draw air from the air inlets 13, through the mouthpiece portion to the outlet 15, and thereafter into the mouth or lungs of the user. Internal baffles 17 are provided to force the air flowing through the mouthpiece portion 12 past the cartridge, as will be described.

(10) The cavity 18 has a circular cross-section and is sized to receive a housing 24 of the cartridge 20. Electrical connectors 19 are provided at the sides of the cavity 18 to provide an electrical connection between the control electronics 16 and battery 14 and corresponding electrical contacts on the cartridge 20.

(11) FIG. 1b shows the system of FIG. 1a with the cartridge inserted into the cavity 18, and the cover 26 being removed. In this position, the electrical connectors rest against the electrical contacts on the cartridge, as will be described.

(12) FIG. 1c shows the system of FIG. 1b with the cover 26 fully removed and the mouthpiece portion 12 being moved to a closed position.

(13) FIG. 1d shows the system of FIG. 1c with the mouthpiece portion 12 in the closed position. The mouthpiece portion 12 is retained in the closed position by a clasp mechanism, as is schematically illustrated in FIG. 2. FIG. 2 illustrates the main body 11 and mouthpiece portion 12 connected by hinged connection 21. The mouthpiece portion 12 comprises an inwardly extending tooth 8. When the mouthpiece portion is in a closed position, the tooth 8 engages a clasp 6 on the main body of the device. The clasp 6 is biased by biasing spring 5 to engage the tooth 8. A button 4 is fixed to the clasp 6. Button 4 can be depressed by a user against the action of the biasing spring 5 to release the tooth 8 from the clasp 6, allowing the mouthpiece portion to move to an open position. It will now be apparent to a person of ordinary skill in the art that other suitable mechanisms for retaining the mouthpiece in a closed position may be used, such as a snap fitting or a magnetic closure.

(14) The mouthpiece portion 12 in a closed position retains the cartridge in electrical contact with the electrical connectors 19 so that a good electrical connection is maintained in use, whatever the orientation of the system is. The mouthpiece portion 12 may include an annular elastomeric element that engages a surface of the cartridge and is compressed between a rigid mouthpiece housing element and the cartridge when the mouthpiece portion 12 is in the closed position. This ensures that a good electrical connection is maintained despite manufacturing tolerances.

(15) Of course other mechanisms for maintaining a good electrical connection between the cartridge and the device may, alternatively or in addition, be employed. For example, the housing 24 of the cartridge 20 may be provided with a thread or groove (not illustrated) that engages a corresponding groove or thread (not illustrated) formed in the wall of the cavity 18. A threaded engagement between the cartridge and device can be used to ensure the correct rotational alignment as well as retaining the cartridge in the cavity and ensuring a good electrical connection. The threaded connection may extend for only half a turn or less of the cartridge, or may extend for several turns. Alternatively, or in addition, the electrical connectors 19 may be biased into contact with the contacts on the cartridge.

(16) FIG. 2 is an exploded view of a cartridge 20 suitable for use in an aerosol-generating system, for example an aerosol-generating system of the type of FIG. 1. The cartridge 20 comprises a generally circular cylindrical housing 24 that has a size and shape selected to be received into a corresponding cavity of, or mounted in an appropriate way with other elements of the aerosol-generating system, for example cavity 18 of the system of FIG. 1. The housing 22 contains a capillary material 22 that is soaked in a liquid aerosol-forming substrate. In this example the aerosol-forming substrate comprises 39% by weight glycerine, 39% by weight propylene glycol, 20% by weight water and flavourings, and 2% by weight nicotine. A capillary material is a material that actively conveys liquid from one end to another, and may be made from any suitable material. In this example the capillary material is formed from polyester.

(17) The housing 22 has an open end to which a heater assembly 30 is fixed. The heater assembly 30 comprises a substrate 34 having an aperture 35 formed in it, a pair of electrical contacts 32 fixed to the substrate and separated from each other by a gap 33, and a heater element 36 formed from a mesh of electrically conductive heater filaments, spanning the aperture 35 and fixed to the electrical contacts 32 on opposite sides of the aperture 35.

(18) The heater assembly 30 is covered by a removable cover 26. The cover 26 comprises a liquid impermeable plastic sheet that is glued to the heater assembly but which can be easily peeled off. A tab is provided on the side of the cover 26 to allow a user to grasp the cover when peeling it off. It will now be apparent to one of ordinary skill in the art that although gluing is described as the method to a secure the impermeable plastic sheet to the heater assembly 30, other methods familiar to those in the art may also be used including heat sealing or ultrasonic welding, so long as the cover 26 may easily be removed by a consumer.

(19) It will be understood that other cartridge designs are possible. For example, the capillary material with the cartridge may comprise two or more separate capillary materials, or the cartridge may comprise a tank for holding a reservoir of free liquid.

(20) The heater filaments 36 are exposed through the aperture in the substrate 34 so that vapourised aerosol-forming substrate can escape into the airflow past the heater assembly.

(21) In use, the cartridge 20 is placed in the aerosol-generating system, and the heater assembly 30 is contacted to a power source comprised in the aerosol-generating system. An electronic circuitry is provided to power the heater element 36 and to volatilize the aerosol-generating substrate.

(22) In FIG. 3 an example of the heater assembly 30 of the present invention is depicted, in which three substantially parallel heater elements 36a, 36b, 36c are electrically connected in series. The heater assembly 30 comprises an electrically insulating substrate 34 having a square aperture 35 formed in it. The size of the aperture is 5 mm5 mm in this example, although it will be appreciated that other shapes and sizes of aperture could be used as appropriate for the particular application of the heater. A first and a second electrical contact 32a, 32b are provided at opposite sides of the aperture 35 and extend substantially parallel to the side edges 35a, 35b of the aperture 35. Two additional contacts 32c, 32d are provided adjacent parts of opposing side edges 35c, 35d of the aperture 35. The first heater element is connected between the first contact portion 32a and the additional contact portion 32c. The second heater element 36b is connected between additional contact portion 32c and additional contact portion 32d. The third heater element 36c is connected between additional contact portion 32c and the second contact portion 32b. In this embodiment the heater assembly 30 comprises an odd number of heater elements 36, namely three heater elements and the first and second contact portions 32a, 32b are located on opposite sides of the aperture 35 of the substrate 34. Heater elements 36a and 36c are spaced from the side edges 35a, 35c of the aperture such that there is no direct physical contact between these heater elements 36a, 36c and the insulating substrate 34. Without wishing to be bound by any particular theory, it is thought that this arrangement can reduces heat transfer to the insulating substrate 34 and can allow for effective volatilization of the liquid aerosol-generating substrate.

(23) In FIG. 4 a further example of the heater assembly 30 of the present invention is depicted, in which four heater elements 36a, 36b, 36c, 36d are electrically connected in series. The heater assembly 30 comprises an electrically insulating substrate 34 having a square aperture 35 formed in it. The size of the aperture is 5 mm5 mm. A first and a second contact portion 32a, 32b is provided adjacent an upper and lower portion, respectively, of the same side edge 35b of the aperture 35. Three additional contact portions 32c, 32d, 32e are provided, wherein two contact portions are provided adjacent parts of opposing side edge 35a, and one contact portion is provided parallel to side edge 35b between the first and second contact portions 32a, 32b. The four heater elements 36a, 36b, 36c, 36d are connected in series between the these five contact portions 32a, 32c, 32d, 32e, 32b as illustrated in FIG. 4. Again none of the long side edges of the heater elements is in direct physical contact with any of the side edges of the aperture such that again heat transfer to the insulating substrate is reduced.

(24) In this embodiment the heater assembly 30 comprises an even number of heater elements 36, namely four heater elements 36a, 36b, 36c, 36d and the first and second contact portions 32a, 32b are located on the same side of the aperture 35 of the substrate 34.

(25) In arrangements such as that shown in FIGS. 3 and 4, the arrangement of the heater elements may be such that the gap between adjacent heater elements is substantially the same. For example, the heater elements may be regularly spaced across the width of the aperture 35. In other arrangements, different spacings between the heater elements may be used, for example to obtain a desired heating profile. Other shapes of aperture or of the heater elements may be used.

(26) The heater assembly may comprise a mesh formed from 304L stainless steel, with a mesh size of about 400 Mesh US (about 400 filaments per inch). The filaments have a diameter of around 16 m. The mesh is connected to electrical contacts 32 that are separated from each other by a gap and are formed from a copper foil having a thickness of around 30 m. The electrical contacts 32 are provided on a polyimide substrate 34 having a thickness of about 120 m. The filaments forming the mesh define interstices between the filaments. The interstices in this example have a width of around 37 m, although larger or smaller interstices may be used. Using a mesh of these approximate dimensions allows a meniscus of aerosol-forming substrate to be formed in the interstices, and for the mesh of the heater assembly to draw aerosol-forming substrate by capillary action. The open area of the mesh, i.e. the ratio of the area of interstices to the total area of the mesh is advantageously between 25 and 56%. The total resistance of the heater assembly is around 1 Ohm. The mesh provides the vast majority of this resistance so that the majority of the heat is produced by the mesh. In this example the mesh has an electrical resistance more than 100 times higher than the electrical contacts 32.

(27) The substrate 34 is electrically insulating and, in this example, is formed from a polyimide sheet having a thickness of about 120 m. The substrate is circular and has a diameter of 8 mm. The mesh is rectangular and in some examples has side lengths of 5 mm and 2 mm. These dimensions allow for a complete system having a size and shape similar to a convention cigarette or cigar to be made. Another example of dimensions that have been found to be effective is a circular substrate of diameter 5 mm and a rectangular mesh of 1 mm4 mm.

(28) In an alternative, heater assembly in accordance with the disclosure, the mesh 36 can be replaced by an array of parallel electrically conductive filaments. The array of filaments are formed from 304L stainless steel and have a diameter of around 16 m.

(29) The filaments may be bonded directly to the substrate 34, the contacts 32 then being bonded onto the filaments. The contacts 32 are separated from each other by an insulating gap, and are formed from copper foil of a thickness of around 30 m. The same arrangement of substrate filaments and contacts can be used for a mesh type heater. Having the contacts as an outermost layer can be beneficial for providing reliable electrical contact with a power supply.

(30) The heater assembly may comprise a plurality of heater filaments that are integrally formed with electrical contacts. Both the filaments and the electrical contacts are formed from a stainless steel foil that is etched to define filaments. The contacts are separated by a gap except when joined by the filaments. The stainless steel foil is provided on a polyimide substrate 34. Again the filaments provide the vast majority of this resistance, so that the majority of the heat is produced by the filaments. In this example the filaments have an electrical resistance more than 100 times higher than the electrical contacts.

(31) In the cartridge shown in FIG. 3, the contacts 32 and filaments 36, 38 are located between the substrate layer 34 and the housing 24. However, it is possible to mount the heater assembly to the cartridge housing the other way up, so that the polyimide substrate is directly adjacent to the housing 24.

(32) Although the embodiments described have cartridges with housings having a substantially circular cross section, it is of course possible to form cartridge housings with other shapes, such as rectangular cross section or triangular cross section. These housing shapes would ensure a desired orientation within the corresponding shaped cavity, to ensure the electrical connection between the device and the cartridge.

(33) The capillary material 22 is advantageously oriented in the housing 24 to convey liquid to the heater assembly 30. When the cartridge is assembled, the heater filaments 36 may be in contact with the capillary material 22 and so aerosol-forming substrate can be conveyed directly to the heater. In examples of the invention, aerosol-forming substrate contacts most of the surface of each filament so that most of the heat generated by the heater assembly passes directly into the aerosol-forming substrate. In contrast, in conventional wick and coil heater assemblies only a small fraction of the heater wire is in contact with the aerosol-forming substrate. The capillary material 27 may extend into the interstices between the filaments 36.

(34) In use the heater assembly operates by resistive heating. Current is passed through the filaments 36 under the control of control electronics 16, to heat the filaments to within a desired temperature range. The mesh or array of filaments has a significantly higher electrical resistance than the electrical contacts 32 and electrical connectors 19 so that the high temperatures are localised to the filaments. The system may be configured to generate heat by providing electrical current to the heater assembly in response to a user puff or may be configured to generate heat continuously while the device is in an on state. Different materials for the filaments may be suitable for different systems. For example, in a continuously heated system, graphite filaments are suitable as they have a relatively low specific heat capacity and are compatible with low current heating. In a puff actuated system, in which heat is generated in short bursts using high current pulses, stainless steel filaments, having a high specific heat capacity may be more suitable.

(35) In a puff actuated system, the device may include a puff sensor configured to detect when a user is drawing air through the mouthpiece portion. The puff sensor (not illustrated) is connected to the control electronics 16 and the control electronics 16 are configured to supply current to the heater assembly 30 only when it is determined that the user is puffing on the device. Any suitable air flow sensor may be used as a puff sensor, such as a microphone.

(36) In a possible embodiment, changes in the resistivity of one or more of the filaments 36 or of the heater element as a whole may be used to detect a change in the temperature of the heater element. This can be used to regulate the power supplied to the heater element to ensure that it remains within a desired temperature range. Sudden changes in temperature may also be used as a means to detect changes in air flow past the heater element resulting from a user puffing on the system. One or more of the filaments may be dedicated temperature sensors and may be formed from a material having a suitable temperature coefficient of resistance for that purpose, such as an iron aluminium alloy, NiCr, platinum, tungsten or alloy wire.

(37) The air flow through the mouthpiece portion when the system is used is illustrated in FIG. 1d. The mouthpiece portion includes internal baffles 17, which are integrally moulded with the external walls of the mouthpiece portion and ensure that, as air is drawn from the inlets 13 to the outlet 15, it flows over the heater assembly 30 on the cartridge where aerosol-forming substrate is being vapourised. As the air passes the heater assembly, vapourised substrate is entrained in the airflow and cools to form an aerosol before exiting the outlet 15. Accordingly, in use, the aerosol-forming substrate passes through the heater assembly by passing through the interstices between the filaments 36, 37, 38 as it is vapourised.

(38) Other cartridge designs incorporating a heater assembly in accordance with this disclosure can now be conceived by one of ordinary skill in the art. For example, the cartridge may include a mouthpiece portion, may include more than one heater assembly and may have any desired shape. Furthermore, a heater assembly in accordance with the disclosure may be used in systems of other types to those already described, such as humidifiers, air fresheners, and other aerosol-generating systems.

(39) FIG. 5 shows a diagram indicating the performance of three different configurations of heater elements in a test to measure the total particulate matter (TPM) deliveries provided by the example heating elements.

(40) The heating elements tested were as follows:

(41) Heater AAperture 5 mm5 mm. Three heater elements arranged as for FIG. 3each having a width of 1 mm. Approximate heater area 15 mm.sup.2.

(42) Resistance approximately 1.2 Ohms. Power consumption 6 W.

(43) Heater BAperture approximately 3 mm3 mm. One heater element covering whole aperture. Approximate heater area 10 mm.sup.2 Resistance approximately 0.5 Ohms. Power consumption 6 W

(44) Heater CAperture 5 mm5 mm. One heater element arranged as for FIG. 2, having a width of 2 mm. Approximate heater area 10 mm.sup.2. Resistance approximately 0.8 Ohms. Power consumption 4 W.

(45) A liquid-containing capillary material was mounted adjacent the heater. The liquid comprised by weight, 39% propylene glycol, 39% glycerine, 20% water, 2% nicotine.

(46) A puff comprising an air flow of 55 ml per 3 seconds was passed over the heater during heating and the resulting aerosol entrained in the airflow is trapped on a fiberglass filter disc (Cambridge Pad). After the test run of 45 puffs, the aerosol components are extracted from the fiberglass filter disc using an alcohol solution in a known way to determine the total particulate matter (TPM) for that test run. The TPM per puff was calculated and is shown in FIG. 5.

(47) Heater B including the heater element covering the whole aperture proved to have the lowest TPM yield (Total Particulate Matter) of only 1.1 milligramm per puff. The heater assembly had a power consumption of 6 Watts.

(48) A higher TPM was observed with the heater C including only one 10 mm.sup.2 heater element. With this heater assembly a TPM yield of about 2.2 milligramm per puff was achieved, while at the same time the power consumption only amounted to 4 Watts. Thus, a higher TPM was seen for a heater element of similar size to that of Heater B, even at lower power.

(49) Without wishing to be bound by any particular theory, it is thought that for Heater C, where the edges of the heater are spaced from the aperture edge, there is less heat transfer to the substrate element. Also, it is thought that for heater B, some of the heat heats liquid underneath the substrate element and that that liquid is unable to be released through the aperture, thus leading to less efficient use of heat from the heater elements.

(50) For Heater A including three heater strips, the TPM is also greater than for Heater B. Without wishing to be bound by any particular theory, TPM for Heater A may be lower than that for Heater C because the three 1 mm strips have a greater contact length with the edge of the aperture compared with the single 2 mm strip of Heater C which may lead to more heat transfer to the substrate or more ineffective heating of liquid underneath the substrate.

(51) The exemplary embodiments described above illustrate but are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.