WO2021116354A1

WO2021116354A1 - Heater assembly

Info

Publication number: WO2021116354A1
Application number: PCT/EP2020/085644
Authority: WO
Inventors: Tony Reevell
Original assignee: Jt International Sa
Priority date: 2019-12-13
Filing date: 2020-12-10
Publication date: 2021-06-17
Also published as: JP2023505331A; EP4074140A1; CN114788406A; KR20220113432A

Abstract

The invention relates to a heater assembly for an aerosol generating device. The heater assembly includes a flexible electrically insulating backing film, a flexible heating element supported on a surface of the electrically insulating backing film and a cover film positioned on the surface of the electrically insulating backing film so as to at least partially enclose the heating element between the cover film and the backing film. Together the backing film, heating element and cover film form a thin film heater assembly and a layer of graphite is arranged against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping with the heating element. The heater assembly further includes a tubular heating chamber arranged to receive an aerosol generating consumable; wherein the thin film heater assembly is wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film toward the heating chamber. In this way, the graphite layer acts to spread the heat generated by the heating element uniformly within the plane of the thin film heater assembly during use. In particular, the high thermal conductivity of graphite means that heat is spread rapidly laterally within the thin film heater assembly to prevent localised hot spots, for example is regions close to the heating element.

Description

HEATER ASSEMBLY

TECHNICAL FIELD

The present invention relates to a method of fabricating a heater assembly, more particularly a heater assembly for an aerosol generating device.

BACKGROUND

Thin film heaters are used for a wide range of applications which generally require a flexible, low profile heater which can conform to a surface or object to be heated. One such application is within the field of aerosol generating devices such as reduced risk nicotine delivery products, including e-cigarettes and tobacco vapour products. Such devices heat an aerosol generating substance within a heating chamber to produce a vapour. One means to heat the consumable is to use a heater assembly comprising a thin film heater which conforms to a surface of a heating chamber to ensure efficient heating of an aerosol-generating substance within the chamber.

Thin film heaters generally comprise a resistance heating element enclosed in a sealed envelope of flexible electrically insulating thin film with contact points to the heating element for connection to a power source, the contact points usually soldered on to exposed parts of the heating element.

Such thin film heaters are generally manufactured by depositing a layer of metal onto the electrically insulating thin film support, etching the metal layer supported on the thin film into the required shape of the heating element, applying a second layer of electrically insulating thin film onto the etched heating element and heat pressing to seal the heating element with the electrically insulating thin film envelope. The electrically insulating thin film is then die cut to create openings for contacts which are soldered on to the portions of the heating element exposed by the openings

These conventional thin film heaters, formed of a planar heating element sealed within an insulating thin film envelope, must then be attached to a surface to be heated. In the context of aerosol generating devices, this involves attaching the thin film heater to the outer surface of a heating chamber to form a heater assembly so as to transfer heat to an aerosol generating consumable placed within the chamber.

Such conventional thin film heaters and heater assemblies suffer from a number of disadvantages. One known issue is that often heating is not uniform across the thin film heater. In particular, hot spots can often occur in the region of the heating track causing a non-uniform heater temperature across the heating area of the thin film heater. The electrical resistance of the heater tracks increases when the metal gets hotter and this compounds the effect, resulting in existing hot spots getting hotter due to the greater resistance in these areas and an associated increase in localised resistive heating. In some cases this can lead to burning of the electrically insulating sealing layers and reduced performance when the thin film heater is applied in a device.

The present invention aims to make progress in addressing these issues to provide an improved heater assembly and method of fabricating a heater assembly

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a heater assembly for an aerosol generating device, the heater assembly comprising: a flexible electrically insulating backing film; a flexible heating element supported on a surface of the electrically insulating backing film; a cover film positioned on the surface of the electrically insulating backing film so as to at least partially enclose the heating element between the cover film and the backing film; wherein together the backing film, heating element and cover film form a thin film heater assembly; a layer of graphite arranged against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping with the heating element; and a tubular heating chamber arranged to receive an aerosol generating consumable; wherein the thin film heater assembly is wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film toward the heating chamber. In this way, the graphite layer acts to spread the heat generated by the heating element uniformly within the plane of the thin film heater assembly during use. In particular, the high thermal conductivity of graphite means that heat is spread rapidly laterally within the thin film heater assembly to prevent localised hot spots, for example in regions close to the heating element. By overlapping the graphite layer with the heating element heat is rapidly conducted to the graphite layer and subsequently spread over an area corresponding to the graphite layer. This prevents localised areas of the consumable exceeding the optimal temperature for aerosolisation and possibly burning, releasing unwanted compounds into the vapour to be inhaled by the user. The graphite layer also ensures that the consumable is uniformly heated so as to efficiently aerosolise the complete volume of the consumable, overcoming a known problem in prior art devices of waste associated with incomplete heating of aerosol-generating consumables. Uniform heating at a fine length scale is necessary in the heating of aerosol generating consumables to avoid the above issues with waste and hot spots so the use of the heating assembly for these applications is particularly preferable.

The thin film heater assembly comprises a number of film layers which are overlaid to provide a multilayer planar assembly. The term “overlapping” is intended to describe how the surface areas of the layers overlap in the plane of the thin film heater assembly, even if they are separated by one or more layers. “Partially overlapping” is intended to mean that the layer of graphite and the heating element are positioned such that they are overlaid in the plane of the thin film heater assembly. In other words, the heating element and the graphite sheet cover corresponding portions of the surface area of the thin film heater assembly (within their respective layers). Preferably the layer of graphite covers a heating area of the heating element, where the heating area is the surface area defined by a heater track of the heating element. These definitions hold whether the thin film heater assembly is in a planar configuration, i.e. lying flat, or whether it is wrapped around a curved heating chamber.

The layer of graphite may be positioned against the flexible electrically insulating backing film (i.e. against a first side of the thin film heater assembly) and/or against the cover film (i.e. against a second side of the thin film heater assembly which is on the opposite side to the first side). Preferably the layer of graphite is attached to the outer surface of the thin film heater assembly, i.e. it is attached to the electrically insulating backing film or cover film, for example with an adhesive.

The backing film may comprise polyimide such as a polyimide film with a layer of Si adhesive. The backing film may alternatively or additionally comprise a fluoropolymer such as PTFE. When the backing film comprises a fluoropolymer it may comprise an at least partially defluorinated surface layer, formed for example by a surface treatment such as plasma and/or chemical etching. This allows for an adhesive to be applied to the treated surface which otherwise would not adhere given the extremely low friction surfaces provided by fluoropolymers. The backing film may additionally or alternatively comprise PEEK. Preferably the flexible electrically insulating backing film has a thickness of less than 80pm preferably less than 50pm, and preferably a thickness of greater than 20 pm.

The cover film preferably comprises a heat shrink film. In this way, the heat shrink film acts to both seal the heating element between the heat shrink film and backing film and also acts to provide an attachment mechanism such that the thin film heater assembly can be attached to a heating chamber by heat shrinking. The heat shrink film may comprise one or more of polyimide, a fluoropolymer such as PTFE and PEEK. The heat shrink film is preferably a preferential heat shrink film arranged to shrink preferentially in one direction. For example the heat shrink film may be polyimide 208x tape manufactured by Dunstone. The heat shrink film may be in the form of an initially planar layer, i.e. a piece of heat tape arranged to be wrapped around the heating chamber or it may be in the form of a tube arranged to be passed around (i.e. sleeved on) a heating chamber and heated to shrink it to the surface of a heating chamber.

Preferably the cover film is attached using an adhesive provided on the surface of the flexible electrically insulating backing film which supports the heating element. The adhesive may be for example a silicon adhesive. The adhesive provides a straightforward means of reliably securing both the heating element and the cover film to the backing film. The flexible electrically insulating backing film may comprise a layer of adhesive, for example it may be polyimide film with a layer of Si adhesive. The heating element may be attached by subsequent heating of the flexible electrically insulating backing film, adhesive layer and positioned heating element to bond the heating element to the surface using the adhesive. The subsequent heating may be a heating step used to shrink the heat shrink film to attach the thin film heater to a heating chamber.

The heating element is preferably a flexible planar heating element. Preferably the heating element is a planar heating element comprising a heater track which follows a circuitous path over a heating area within the plane of the heating element; and two contact legs for connection to a power source, the contact legs extending away from the heater track in the plane of the heating element. Preferably the heater track is configured to provide substantially uniform heating over the heating area. The heater track path may be a serpentine or meandering path over the heating area and the heater track may have a substantially uniform width and thickness. Preferably cover film is attached so as to enclose the heater track between the backing film and the cover film, leaving the contact legs exposed. In this way the heater track is electrically insulated between the electrically insulating backing film and the heat shrink film whilst the contact legs are exposed such that they can be connected to a power source. The contact legs may be sufficiently long to allow direct connection to a power source when the thin film heater is employed in the device. For example the length of the contact legs may be substantially equal or greater than one or both of the dimensions defining the heating area. The circuitous path may be configured to leave a vacant region within the heating area.

The heater assembly comprises a tubular heating chamber; wherein the thin film heater assembly is wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film toward the heating chamber. In this way, the thin film heater assembly may be applied to heat the contents of a heating chamber, where the graphite layer acts to spread the heat from the heating element uniformly to provide improved heating of the heating chamber.

Preferably the heating chamber comprises one or more indentations in an outer surface and the thin film heater assembly is positioned relative to the heating chamber such that a temperature sensor, attached to the flexible electrically insulating backing film, is positioned within an indentation. Preferably the method further comprises wrapping a further electrically insulating film around the attached thin film heater assembly. In some examples, the further electrically insulating film may have lower thermal conduction than the backing film.

Preferably the layer of graphite is arranged between the electrically insulating backing film of the thin film heater assembly and the outer surface of the heating chamber. The graphite layer may be attached to the heating chamber or to the backing film of the thin film heater assembly, prior to wrapping the thin film heater assembly around the heating chamber. This provides a straightforward method to accurately align the graphite layer such that it overlaps with the heating area during assembly.

Alternatively, the layer of graphite may be arranged against the outer surface of the cover film of the thin film heater assembly. This step can be carried out after heat shrinking to attach to the thin film heater assembly to the heating chamber.

Preferably the heater assembly comprises a second layer of graphite; wherein a first layer of graphite is arranged between the electrically insulating backing film and the outer surface of the heating chamber; and the second layer of graphite is arranged against the outer surface of the cover film. This provides further optimised heat distribution as the heating element is positioned between two layers of graphite, which act together to spread the heat through the thin film heater assembly, without requiring significant extra work during assembly.

Preferably the heater assembly further comprises an electrically insulating sealing layer arranged around an outer surface of the wrapped thin film heater assembly and one or more graphite layers. This provides enhanced heat insulation such that heat is more efficiently directed to the heating chamber. Furthermore, the thin film heater may be sealed to prevent the release of one or more by-products during heating. In some examples, the layers of the thin film heater are configured to provide increased heat transfer from the heating element in one direction. For example the thickness and/or material properties of one or more of: the flexible electrically insulating backing film, the second flexible electrically insulating film and the one or more sealing layers are selected to provide an increased heat transfer in a direction corresponding to towards the heating chamber during use. For example the insulating backing film may have an increased thermal conductivity relative to the cover film layer and/or a sealing layer. In this way the transfer of heat to the heating chamber is promoted and transfer of heat away from the heating chamber is reduced to mitigate heat loss. Preferably the side of the thin film heater arranged to contact the heating chamber is configured to have a higher thermal conductivity than the opposite, outer side. Preferably the sealing layer has a lower thermal conductivity than the backing film.

Preferably the heating element is a planar heating element comprising a heater track which follows a circuitous path over a heating area within the plane of the heating element; wherein the layer of graphite covers an area of the surface of the thin film heater assembly which corresponds with the heating area of the heating element. This ensures that heat is distributed uniformly over the heating area of the thin film heater assembly.

Preferably the layer of graphite is provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer. For example the layer of graphite may comprise an adhesive graphite tape. This provides a straightforward means to secure the graphite layer in position by using the adhesive layer.

Preferably the adhesive graphite sheet comprises a graphite layer having a thickness between 5 and 30 pm and an adhesive layer having a thickness between 0 and 35 pm, wherein preferably the graphite layer has a thickness between 10 and 12 pm and the adhesive layer has a thickness between 5 and 10 pm. In other examples a graphite tape may be used with a graphite layer thickness of 10, 17 or 25 pm and a respective adhesive layer thickness of 6, 10 or 30 pm. This minimises the thermal mass of the thin film heater assembly, such that heat transfer to the heating chamber is maximised. The thermal conductivity of the graphite layer is preferably between 700 and 2000 W/m.K. This helps in effectively distributing the heat generated by the heater track across the heating area. The graphite layer preferably comprises a graphite polymer film.

The heater assembly preferably further comprises a temperature sensor including a sensing part (also referred to in the following description as a sensor head) and wherein the sensing part is positioned in an area of the thin film heater assembly which is covered by the layer of graphite. In other words, the graphite layer covers the sensor part of the temperature sensor in the plane of the thin film heater. In this way the temperature sensor can be used to monitor the heating temperature in order to accurately control the heater. In particular, this means that the graphite film overlaps both the heating element and the sensing part of the temperature sensor such that heat from the heating element is distributed effectively to the sensing part such that the temperature sensor provides an accurate measurement of the temperature of the heating element. This prevents the heating element from overheating as an accurate temperature of the heating element can be monitored.

In another aspect of the present invention there is provided a method of fabricating a heater assembly comprising: providing a heating element supported on a surface of a flexible dielectric backing film; and attaching a layer of cover film onto the surface of the dielectric backing film so as to at least partially enclose the heating element between the cover film and the dielectric backing film, wherein together the attached backing film, heating element and cover film form a thin film heater assembly; positioning a layer of graphite arranged against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping with the heating element. This provides a straightforward assembly method of providing a heater assembly with improved thermal properties and reduced risk of hot spots due to preferential heating at areas near a heating track of the heating element. It also allows for the graphite heater to be added at various stages of the assembly process to improve the efficiency of assembly, for example it can be added to an outer surface of the heating chamber during manufacture of the heating chamber, it can be added to a surface of the thin film heater assembly during its assembly or it can be added as a final step after the thin film heater has been attached to a heating chamber.

Preferably the layer of graphite is provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer and the step of positioning the layer of graphite comprises: sticking the adhesive graphite sheet to the dielectric backing film; and/or sticking the adhesive graphite sheet to the cover film. In an alternative step the adhesive graphite sheet can be stick directly to the outer surface of a heating chamber.

Preferably the method further comprises: wrapping the thin film heater assembly around the outer surface of a tubular heating chamber with the dielectric backing film toward the outer surface of the heating chamber; and providing a cover film constituted of heat shrink layer and heating the thin film heater assembly to shrink the heat shrink layer, securing the thin film heater assembly against the tubular heating chamber.

Preferably the method further comprises: sticking an adhesive graphite sheet to the outer surface of the tubular heater chamber before wrapping the thin film heater assembly around the outer surface of a tubular heating chamber.

In a further aspect of the invention there is provided an aerosol generating device a heater assembly as set out in the claims. In this way the aerosol generating device can provide improved heating by providing a more uniform heating temperature across the heating chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figures 1A and 1 B schematically illustrate a heater assembly according to the present invention from two opposing views; Figure 2A illustrates a heater assembly including a thin film heater assembly wrapped around a heating chamber;

Figure 2B illustrates a cross-section view of a heater assembly including a thin film heater assembly wrapped around a heating chamber;

Figure 3A illustrates a heater assembly including a thin film heater assembly wrapped around a heating chamber;

Figure 3B and 3B respectively illustrates cross-section views of two examples of heater assemblies according to the present invention;

Figures 4 schematically illustrates a graphite layer for use in a heater assembly according to the present invention;

Figures 5A to 5E illustrate a method of assembling a heater assembly according to the present invention;

Figure 6 illustrates an alternative assembly step in a method of assembling a heater assembly according to the present invention.

DETAILED DESCRIPTION

Figures 1A and 1 B schematically illustrate a heater assembly 10 for an aerosol generating device according to the present invention. The heater assembly 10 includes a flexible electrically insulating backing film 30 and a flexible heating element 20 supported on a surface of the electrically insulating backing film 30. The heater assembly 10 further includes a cover film 50 which is positioned on the surface of the electrically insulating backing film 30 so as to at least partially enclose the heating element 20 between the cover film 50 and the backing film 30. Together, the assembled backing film 30, heating element 20 and cover film 50 are referred to as a thin film heater assembly 100. The heater assembly 10 further includes a layer of graphite 40 arranged against an outer surface of the thin film heater assembly 100, the layer of graphite 40 at least partially overlapping with the heating element 20. In other words, the layer of graphite 40 is applied to one of the two sides of the thin film heater assembly 100, where the thin film heater assembly 100 comprises the flexible heating element 20 enclosed between the opposing backing film 30 and the heat shrink film 50.

The layer of graphite 40 acts to spread the generated heat quickly around the heating area such that heat is dispersed away from any potential hot spots resulting in a much more uniform heating temperature across the heating area. Since graphite has a high thermal conductivity, typically between about 700 and 2000 W/m.K, heat is rapidly dispersed laterally in the plane of the thin film heater assembly 100 such that no hot spots are formed and the heater assembly 10 provides a better performance when employed in a device such as an aerosol generating device. This is achieved even though the graphite layer 40 is separated from the heating element 20 by one or more thin film layers.

In the exemplary embodiment illustrated in the figures, the cover film comprises a layer of heat shrink film 50. This provides a number of advantages. In particular, the heat shrink film both seals (at least a portion of) the heating element 20 between the backing film 30 and the opposing heat shrink film but also acts as an attachment means for attaching the thin film heater assembly 100 to the surface of a heating chamber. It therefore provides an effective way of attaching the heating element while minimising the amount of additional material and associated thermal mass in the layers of the thin film heater assembly. Further details of this attachment mechanism are provided below.

In the example of Figure 1 , the layer of graphite 40 is applied to the surface of the flexible electrically insulating backing film 30. That is, the thin film heater assembly 100 is first formed by positioning the planar heating element between the backing film and the heat shrink 50. This thin film heater assembly may be attached using an adhesive positioned between the layers, in particular the backing film may comprise a layer of adhesive which serves to both attach the heating element 20 and the cover film 50. A layer of graphite 30 is then positioned against the backing film 30, on the opposite surface to the heating element 20, such that it at least partially overlaps with the heating element 20. In other examples of the invention, the layer of graphite 40 may be applied on the opposing side of the thin film heater assembly 100, namely against the layer of heat shrink film 50, as will be described in more detail below.

Preferably, as illustrated in Figure 1 , the size and shape of the layer of graphite 40 substantially corresponds with the size and shape of a heating area 22 defined by the heating track 21 of the heating element 20, as best seen in Figure 1 B. In particular the graphite layer 40 preferably covers an area on the outer surface of the thin film heater assembly 100 which substantially corresponds with the heating area 22 of the heating element. In this way, heat is distributed uniformly across the intended heating area.

In the example of Figure 1A and 1 B the thin film heater assembly additionally comprises a temperature sensor 70 in the form of a thermistor 70 with a temperature sensing part 71 (the “sensor head”) and the sensor connections 72. Importantly, the sensor head 71 is positioned in an area of the thin film heater assembly 100 which is covered by the graphite layer 40. In particular, the thermistor may be positioned with the sensing part positioned adjacent to the heater track 21 of the heating element 20 between the backing film 30 and the cover film 50. The graphite layer 40 is then positioned so that it covers both the heating area 22 and the sensor head 71 . In this way, heat is distributed effectively to the temperature sensor head 71 such that the temperature sensor provides an accurate measurement of the actual heating temperature of the heating element 20. When employed in a device, this allows the heater to be accurately controlled using the measured temperature of the heating element to provide a precise heating temperature and ensure that the heating element 20 does not overheat, which could happen in examples where the temperature sensor is not positioned to provide an accurate reading of the heating element 20 itself.

As shown in Figure 2A, the thin film heater assembly 100 is wrapped around the outer surface of a tubular heating chamber 60 in order to provide uniform heating of the heating chamber 60 over the heating area 22. Figure 2A shows the assembled heater assembly 10 comprising the flexible electrically insulated backing film 30, the flexible heating element 20, the layer of heat shrink film 50 and the layer of graphite 40, together wrapped around the outer surface of the tubular heating chamber 40, such that heat may be transferred to the chamber 60 when a power source is connected to the contacts 24 on the extended contact legs 23 of the heating element 20. The example of Figure 2 uses the heater assembly 10 of Figure 1 , in which the layer of graphite 40 is applied against the surface of the backing film.

The thin film heater assembly 100 is then wrapped around the heating chamber 60 such that the layer of graphite 40 and the flexible electrically insulating backing film 30 are adjacent to the outer surface of the heating chamber 60. This is illustrated in the cross section shown in Figure 2B. In particular, the heater assembly 10 is arranged with the layer of graphite 40 positioned against the outer surface of the heating chamber 60, the flexible electrically insulating backing film 30 positioned around the layer of graphite 40, the heating element 20 positioned against the backing film 30 and finally the layer of heat shrink film 50 wrapping around the outer surface of each of the layers to secure the thin film heater assembly to the heating chamber 60. The assembly 10 shown in Figure 2 may then be initially heated in order to contract the heat shrink film 50, sealing the thin film heater assembly 100 against the outer surface of the heating chamber 60.

Although in the examples of Figure 1 and 2 the layer of graphite 40 is applied to the surface of the backing film 30 of the thin film heater assembly 100 before it is wrapped around the heating chamber 60, in other examples of the invention the layer of graphite 40 may be applied to the outer surface of the heating chamber directly, with the thin film heater assembly 100 (comprising the backing film 30, the heating element 20 and heat shrink film 50) subsequently wrapped around the layer of graphite 20 and the heating chamber 60 such that the layer of graphite 20 at least partially overlaps with the heating element 20.

Figure 3A to 3C illustrate an alternative example of the present invention in which the layer of graphite 40 is arranged against the outer surface of the heat shrink film 50 of the thin film heater assembly 100, instead of against the backing film 30. In particular, rather than applying the layer of graphite 40 against the backing film 30 as shown in Figures 1A and 1 B, the layer of graphite 40 is instead applied to the opposing side of the thin film heater assembly 100 such that it lies against the cover film 50 (in this case the heat shrink 50) but still overlaps with the heating area 22 in the same way as that shown in Figure 1 . The thin film heater assembly 100, with the layer of graphite 40 attached to the heat shrink film 50, is then wrapped around the tubular heating chamber 60 as shown in Figure 3A. In particular, the thin film heater assembly 100 is still wrapped around the heating chamber 60 such that the electrically insulating backing film 30 is toward the outer surface of the heating chamber 60 but the layer of graphite 40 is arranged around the outer surface of the heat shrink 50.

Figure 3B shows a cross section through the arrangement of Figure 3A, illustrating the sequence of layers in the heater assembly 10. In particular, the backing film 30 lies against the outer surface of the heating chamber 60; the heating element 20 is supported on the outer surface of the backing film 30; the heat shrink film 50 is wrapped around the outer surface of the heating element 20 to seal the thin film heating element 20 against the outer surface of the chamber 60; and the layer of graphite 40 is applied to the outer surface of the wrapped heater assembly 10, as shown in Figure 3B. In this arrangement, the graphite 40 still provides the same effect of spreading the heat generated in the heating element 20 laterally through the planar layers to disperse the heat and prevent any hot spots forming.

An alternative example of the heater assembly 10 is illustrated in cross section in Figure 3C. This example incorporates a first layer of graphite 41 arranged against the flexible electrically insulating backing film 30 (as shown in Figure 1) and a second layer of graphite 42 arranged against the surface of the heat shrink 50, as shown in Figure 3A and 3B. Preferably, both graphite layers 41 , 42 are arranged so as to overlap with the heating area 22 of the heating element 20 in order to disperse the heat throughout the layers of the heater assembly 10, in particular spreading the heat laterally to prevent the build-up of any hot spots. In particular, the alternative example of Figure 3C includes a first layer of graphite 41 , either applied directly to the outer surface of the heating chamber 60 or applied directly to the backing film 30 such that it lies between the heating chamber 60 and the backing film 30 when the thin film heater assembly 100 is wrapped around the heating chamber 60. The flexible heating element 20 is supported on the backing film 30, as with all examples, and the heat shrink 50 wraps around the outer surface of the heating element 20 to seal the heating element 20 between the backing film 30 and the heat shrink 50. The second layer of graphite 42 is arranged on the outer surface of the heat shrink 50. In this way, the heating element 20 lies between the first and second graphite layers 41 , 42 which further optimises the dispersion of heat generated at the heating element 20 throughout the layers to prevent the build-up of hot spots.

Each of the examples shown may additionally include an electrically insulating sealing layer (not pictured) which can be wrapped around the outer most surface of the arrangements shown in Figures 2B, 3B and 3C. The electrically insulating sealing layer, such as polyimide thin film, may be applied to the thin film heater assembly 100 before it is wrapped around the heating chamber 60, i.e. applied to the planar assembly shown in Figures 1 A and 1 B. Alternatively, it may be applied after attaching each of the layers of the heater assembly 10 such that it is wrapped around the outer most surface of the assembled heater assembly 10, such as the arrangement shown in Figure 2B, 3B and 3C.

Figure 4 shows a layer of graphite film 40 which can be applied as the graphite layer 40 in the examples of the present invention described. In particular, the layer of graphite 40 may be provided by an adhesive graphite sheet comprising a graphite layer 43 and at least one adhesive layer 44. The example of Figure 4 shows a graphite sheet or tape which has a graphite layer 43 and a single adhesive layer 44 but in other examples the graphite tape 40 may comprise multiple adhesive layers, in particular an adhesive layer 44 on each opposing side of the graphite layer 43. The adhesive layer 44 may comprise an acrylic or silicon adhesive where the thickness 43t of the graphite layer may be between 5 and 30 microns, preferably between 10 and 12 microns and the adhesive layer may have a thickness 44t between 0 and 35 microns, preferably between 5 and 10 microns. Examples of commercially available graphite tapes which may be used for this application include EYGA121801 F sold by Panasonic™ and DSN5012-05DC sold by DSN Thermal Solutions™. Such graphite tapes have a graphite layer of about 10 microns and an adhesive layer of around 6 microns. Graphite tapes 40 with a graphite layer of about 10 to 12 microns with an adhesive layer with a thickness 44t of between 5 and 10 microns optically preferred, particularly the graphite tape is positioned between the heating chamber 60 and the heating element 20. The thermal conductivity of the graphite tape 40 may be within the range 700 to 2000 W/m.K. The graphite tape may have a specific gravity between about 0.85 and 0.213 g/cm³. The graphite layer 43 of the tape may be a pyrolytic graphite sheet, in particular formed of a highly oriented graphite polymer film. Such graphite layers can withstand a temperature of up to 400°C making them highly suited for application in a heating chamber 60 where elevated temperatures are required. Such graphite tapes may be protected by a PTE release liner which protects the adhesive film 44 and can be removed before attachment of the graphite sheet 40 to the thin film heater assembly 100 or the heating chamber 60.

Further details of the heater assembly 10 according to the present invention and a method of fabricating such a heater assembly 10 will now be described with reference to Figures 5 and 6.

As shown in Figure 5A, the first step involves providing a heating element 20 supported on a surface of a flexible electrically insulating backing film 30. This may be achieved in a number of different ways. In particular, the heating element

20 may be etched from a thin metal sheet of around 50 pm, for example a sheet of stainless steel such as 18SR or SUS304, although other materials and heater thicknesses may be selected depending on the application. The specific metal and thickness of the metal sheet are selected such that the resulting heating element 20 is flexible so that it can deform with the supporting flexible thin film 30 in order to conform to the shape of a surface to be heated. The metal sheet may be deposited initially on the surface of the flexible electrically insulating backing film 30, before being etched whilst supported on the film to form the heater track

21 pattern. Alternatively, and preferably, the heating element 20 may be etched from a metal sheet independently of the flexible electrically insulating backing film. For example a free standing metal foil may be chemically etched from both sides in order to provide one or more connected heating elements 20 which are subsequently detached and positioned on the surface of an electrically insulating backing film 30. The heating element 20 of the examples illustrated in the figures is a planar heating element 20 including a heater track 21 which follows a circuitous path over a heating area 22 within the plane of the heating element 20. The heating element has two contact legs 23 allowing connection to a power source, the contact legs 23 extending away from the heater track 21 in the plane of the heating element 20. The contact legs may also extend in a plane inclined relative to the heating element. The heater track 21 is preferably shaped so as to provide substantially uniform heating over the heating area 22. In particular, the heater track is shaped such that it contains no sharp corners and has a uniform thickness and width, with the gaps between neighbouring parts of the heater track 22 being substantially constant to minimise increased heating at specific points within the heating area 22. The heater track 21 in the example of Figure 5A follows a serpentine path over the heater area 22 and is split into two parallel track paths 21a and 21 b, each connected to both contact legs 23. The heater layer 23 may be soldered at connection point 24 on each contact leg 23 to allow for the connection of the heater to a PCB and power source.

The flexible electrically insulating backing film 30 must have suitable properties provide a flexible substrate to support and electrically insulate the heating element 20. Appropriate materials include polyimide, PEEK and fluoropolymers such as PTFE. In this case the heating element comprises a heater track pattern 21 etched from a layer of 50 pm stainless steel 18SR which is supported on a single sided polyimide/Si adhesive film comprising a 25 pm polyimide film with a 37 pm silicon adhesive layer. The heating element 20 is supported on the adhesive to allow the heating element to be attached to the backing film. The thin film heater assembly 100 of Figure 5A may be prepared in advance and stored with a release layer which is attached to the adhesive surface supporting the heating element 20 to preserve the adhesive layer until it is ready for use. The release layer may be provided for example by polyester or similar material. The release layer can then be peeled off to uncover the sticky adhesive layers supporting the heating element in order to proceed to the next assembly steps shown in Figure 5B. The next step in this exemplary method of fabricating a heater assembly 100 is the application of a layer of heat shrink film 50 directly onto the surface of the electrically insulating backing film 30 so as to at least partially enclose the heating element 20 between the heat shrink film 50 and the backing film 30. The heat shrink film 50 can be attached with the adhesive directly onto the surface of the heater element 20 so as to enclose the heating area 20 between the backing film 30 and the heat shrink 50. In particular, the heater track 21 is insulated within a sealed envelope formed by the flexible backing film 30 and the heat shrink 50, while the contact legs 23 remain exposed to allow connection to a power source.

The heat shrink 50 is larger than the backing film 30 and heating element 20 such that it extends beyond the heating element 20 by predetermined distance in two orthogonal directions 51 , 52. This alignment of the heat shrink 50 relative to the heating element 20 allows for the later alignment of the heating area 22 relative to the heating chamber 60. Therefore, careful control of the size of these extending portions of the heat shrink 51 , 52 at this stage allows for the heater assembly 100 to be attached to a heating chamber 60 in a straightforward manner to provide precise alignment. The relative alignment of the heat shrink and thin film heater 10 can be achieved in a number of different ways. The heat shrink 50 may be pre-cut to correct size and then aligned to an edge of the flexible electrically insulating backing film 30 to provide the correct predetermined distances 51 , 52 of the extending portions. Alternatively, an alignment apparatus may be used to achieve this precise alignment.

In particular, a series of corresponding alignment holes (not pictured) may be provided in both the backing film 30 and heat shrink 50 which can be used for the relative alignment of the backing film 30 and heat shrink 50. The alignment holes are arranged such that when the holes of the backing film 30 are brought into alignment with the alignment holes of the heat shrink 50, the heat shrink 50 is positioned at precisely the correct position relative to the thin film heater 10 such that the heat shrink 50 extends beyond the heating area 22 by the correct lengths 51 , 52 to allow for precise alignment of the heating element 20 relative to the heating chamber 60 when attached. The heat shrink 50 is then aligned relative to the thin film heater 10 using a positioning fixture comprising a supporting surface with upstanding alignment pins which correspond in their relative displacement to the positions of the alignment holes on the backing film 30 and the heat shrink 50. The heating element 20 on the backing film 30 and the heat shrink 50 can then be positioned on the surface of the alignment fixture such that the alignment pins extend through the backing film alignment holes, ensuring that the heat shrink is aligned precisely relative to the heating element 20 and backing film 30.

The heat shrink 50 extends beyond the heating area 20 in a direction opposite to the contact legs 23 to provide an alignment region 52 of the heat shrink 50. This alignment region 52 can be aligned with the top edge of a heating chamber 60 such that the heating area 20 is positioned at a position along the length of the heating chamber corresponding to the predetermined length 52 of the alignment region from the top edge of the heater track 21 . In this way, the heater element

20 can be provided at a correct position along the heating chamber 60. The heat shrink 50 also has an attachment region 51 which extends past the heater track

21 and backing film 30 in a direction perpendicular to the direction of extension of the contact legs 23 to provide an attachment region 51 . The direction of extension of the attachment region 51 from the heating element 20 to the edge of the heat shrink 50 may be referred to as the “wrapping direction” since this portion of the heat shrink 50 allows for it to be wrapped around a tubular heating chamber 60 and subsequently heat shrunk to provide the required tight connection. Similarly, the direction opposite to the heater legs 23 in the direction that the alignment region 52 extends from the heating element 20 may be referred to as the upward or alignment direction which corresponds with the elongate axis of the heating chamber 60, directed towards the top open end. These extension distances 51 , 52 may be configured by cutting the heat shrink 50 to the correct dimensions either before or after attaching to the surface of the electrically insulating backing film 30.

As shown in Figure 5B, a temperature sensor 70 is attached to the thin film heater assembly 100 between the flexible backing film 30 and the heat shrink 50. The temperature sensor 70 in this case is a thermistor with a sensor head 71 configured to detect the local temperature and temperature sensor connections 72 configured to carry the sensed signal from the sensor head 71 to the PCB. The heater track 22 is preferably shaped so as to leave a vacant region 22v within the heating area 22, as most clearly shown in Figure 5A. The sensor head 71 is positioned in this vacant area 22v between the backing film 30 and the heat shrink 50 such that it is in close proximity with the heater track 21. By positioning the sensor head 71 in close proximity to the heating element 20 between the heat shrink 50 and the backing film 30 the temperature sensor 70 is sealed in close proximity to the heating element to provide accurate temperature readings of the heating area 22. This is further improved by the provision of the graphite sheet 40 covering both the heating element 20 and the sensor head 71 .

As shown in Figures 5B the heat shrink 50 is preferably positioned so as to leave a free edge region 32 of the backing film 30 exposed. This free edge region 32 is folded over onto the heat shrink film 50 to seal an edge of the backing film 30 and heat shrink 50 and fold over the temperature sensor head 71 to secure it within the fold.

Once the thin film heater assembly 100 has been assembled, as shown in Figure 5B, a layer of graphite film 40 in the form of an adhesive graphite tape is attached to an outer surface of the thin film heater assembly 100 such that it is at least partially overlapping with the heating area 22 defined by the heater track 21 . In this example the graphite tape 40 is attached to the exposed surface of the backing film 30, as shown in Figure 5C (and Figure 1A). The size and shape of the graphite tape closely corresponds to that of the heating area 22 such that it covers an area on the backing film 30 corresponding with the heating area 22. The graphite tape 40 also extends over the temperature sensing part 71 of the temperature sensor such that the heat generated by the heating element 20 is distributed effectively to the temperature sensor 70 and it provides an accurate reading of the heating element 20 temperature.

The graphite tape 10 is attached by applying the tape 40 with the adhesive layer against the backing film 30. As described above, although it this example it is applied to surface of the backing film, it could equally be applied to the outer surface of the heating chamber 60 using the adhesive layer 44 against the surface of the heating chamber to attach the graphite layer 43 so it will be overlap with the heating element 20 when the thin film heater assembly 100 is wrapped around the heating chamber 60. Similarly, alternatively or in addition, a graphite layer 40 can be applied to the surface of the heat shrink layer 50 (the surface opposite to that which is against the heating element 20) such that, when the thin film heater assembly 100 is wrapped around the heating chamber, a graphite layer is outside the heating element (i.e. radially further from the heating chamber 60).

Once the graphite layer 40 is attached to the thin film heater assembly 100 (or alternatively to the outer surface of the heating chamber 60) so as to overlap with the heating area 22 of the heating element 20, the thin film heater assembly is then attached to the heater chamber 60. This can be achieved by attaching two pieces of adhesive tape 55a, 55b to the thin film heater assembly 100 to allow the thin film heater assembly to be initially attached to the heating chamber 60 at the correct position before heating the assembly to shrink the heat shrink 60.

The sticky tape 55a, 55b may be provided by pieces of polyimide adhesive tape, for example commercially available 0.5 inch polyimide tape with 12.7 micrometre polyimide and 12.7 micrometre silicon adhesive. The sticky attachment tape 55a, 55b is positioned along each edge of the heat shrink 50 at the extremities in the wrapping direction as shown in Figure 5D. As shown in Figure 5E, the thin film heater assembly 100 may then be attached to the heating chamber 60 by aligning the top edge 53 of the heat shrink 50 with the top edge 62 of the heating chamber 60. Given the distance 52 of the alignment region has been carefully selected this alignment step allows for the heating area 22 and corresponding graphite layer 40 to be placed at the correct position along the heating chamber 60. Certain consumables will contain a charge of aerosol generating substance at a particular position so it is important that the correct portion of the heater chamber 60 is heated to efficiently release the vapour from the consumable.

The thin film heater assembly 100 is initially attached to the heating chamber using the adhesive tape 55a. The heating chamber 60 is a tubular heating chamber 60 arranged to accept a consumable to be heated in order to generate a vapour to be inhaled by a user. The heating chamber 60 preferably has one or more indentations 61 on an outer surface which provide internal protrusions which assist with the positioning and heat transfer to a consumable received within the chamber 60. The circumference of the heating chamber 60 preferably closely matches the width of the heating element 20 (the length in a direction perpendicular to the direction of extension of the contact legs) such that the heating element provides one complete circumferential loop around the chamber 60. In other examples the heater element 20 might be sized to wrap more than once around the circumference of the heating chamber, i.e. the heating element may be sized so as to provide an integral number of circumferential loops around the heating chamber so as not to produce any variation in the heating temperature around the circumference of the heating chamber. The thin film heater assembly 100 is positioned and attached such that the temperature sensor head 71 lies within an indentation 61 on the outer surface on the heating chamber 60 to provide a more accurate reading of the internal temperature of the heating chamber 60. In an alternative of the embodiment of Fig. 3C, the temperature sensor may also be positioned between graphite layer 50 and the heat shrink 50.

As described above, in an alternative method, the graphite layer 40 is attached directly to the heater chamber 60, as shown in Figure 6. In particular the graphite layer 40 is positioned over a portion of the length of the heating chamber 60 which corresponds to the heating area 22 of the thin film heater assembly 100 when wrapped around the heating chamber 60, such that it overlaps with heating area and acts to uniformly spread the generated heat over the heating area 22.

Once attached with first adhesive tape portion 55a, the thin film heater assembly 100 is then rolled around the heating chamber 60 with the extended attachment portion 51 of the heat shrink 50 wrapping circumferentially around the chamber 60 to cover the heating element 20 with the heat shrink 50 before being attached by the second piece of attachment tape 55b to provide the heater assembly 10 (including the heater element 20, backing film 30, graphite layer 40, heat shrink film 50, thermistor 70 and heater chamber 60) shown in Figure 2A. Since the length of the attachment region 51 is approximately the same as the length of the heating area 22 (and the circumference of the heating chamber 60), the attachment portion 51 wraps around to cover the heating area 22 once, such that the heater element is insulated by two layers of heat shrink film in the attached heater assembly 10 shown in Figure 5E and 6. The attachment region 51 may be sized to provide more than one additional covering of the heating element 20. For example the attachment region 51 may extend beyond the heating element by a distance corresponding to an integer multiple of the outer circumference of the heating chamber 60.

As can be seen in the Figure 2A, once assembled the temperature sensor connections 72 and the heater legs 23 are positioned such that they are aligned following this rapid step for ease of connection to the PCB. The attached heater assembly 10 is then heated to shrink the heat shrink 50 tight against the heating chamber 60 as shown in Figure 2A. For example, the assembly 10 can be heated in an oven at around 210°C for ten minutes to shrink the film, although the time and temperature can be adapted for other varieties of heat shrink. This process allows large numbers of units to be heat treated in a small oven at the same time. This is the only heating step which can both simultaneously seal the thin film heater to the heating chamber and bond the backing film to the heat shrink.

Finally, although not essential, a final sealing layer of electrically insulating film may be added around the outside of the heating element to complete the heating assembly. This final insulating layer may be for example a further layer of adhesive polyimide such as 1 inch polyimide tape with 25 micrometre polyimide and 37 micrometres silicon adhesive. This outer layer of electrically insulating film provides a further layer of insulation and further secures the attachment of the thin film heater assembly 100 to the heating chamber 60.

The thickness and/or material of the backing film 30, heat shrink 50 and final insulating layer may be selected to enhance heat transfer to the heating chamber, for example with lower thermal conductivity layers provided outside the heating element (i.e. for the heat shrink 50 and insulating layer in this example) and a higher thermal conductivity layer provided as the backing film.

Once the outer insulating layer of electrically insulating film has been applied, the assembly 10 may again be heated. This second heating step allows for further outgassing of the outer layer of electrically insulating film, as well as the other layers. For example, in the second heating stage, the heating temperature may be taken up to a higher temperature than the heat shrinking stage, closer to the operating temperature of the device. This allows for further outgassing, for example of the adhesive layers that may not have taken place during the heat shrinking step at the lower temperatures. It is also beneficial to expose the heat shrink to a temperature closer to the operating temperature prior to heating during first use of the device. Once assembled, the graphite layer 40 is positioned such that it is aligned with the heating area 22 of the heating element and positioned either between the heating element 20 and the heating chamber 60, around the heating element 20 such that the heating element 20 is positioned between the graphite layer 40 and the heating chamber 60 or both. Due to the thermal conductivity of graphite, the graphite layer spreads the heat generated by the heating element 20 rapidly in the planar direction to provide homogenous heating temperature over the area covered by the graphite layer 40, thereby reducing hotspots and reducing the risk of damage to the film layers due to local overheating and providing a more uniform transfer of heat to a consumable received in the heating chamber 60.

Claims

1 . A heater assembly for an aerosol generating device, the heater assembly comprising: a flexible electrically insulating backing film; a flexible heating element supported on a surface of the electrically insulating backing film; a cover film positioned on the surface of the electrically insulating backing film so as to at least partially enclose the heating element between the cover film and the backing film; wherein together the backing film, heating element and cover film form a thin film heater assembly; a layer of graphite arranged against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping with the heating element; and a tubular heating chamber arranged to receive an aerosol generating consumable; wherein the thin film heater assembly is wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film toward the heating chamber.

2. The heater assembly of claim 1 wherein the layer of graphite is arranged between the electrically insulating backing film of the thin film heater assembly and the outer surface of the heating chamber.

3. The heater assembly of claim 1 wherein the layer of graphite is arranged against the outer surface of the cover film of the thin film heater assembly.

4. The heater assembly of claim 1 further comprising a second layer of graphite; wherein a first layer of graphite is arranged between the electrically insulating backing film and the outer surface of the heating chamber; and the second layer of graphite is arranged against the outer surface of the cover film.

5. The heater assembly of any of claims 1 to 4 further comprising an electrically insulating sealing layer arranged around an outer surface of the wrapped thin film heater assembly and one or more graphite layers.

6. The heater assembly of any preceding claim wherein the heating element is a planar heating element comprising a heater track which follows a circuitous path over a heating area within the plane of the heating element; wherein the layer of graphite covers an area of the surface of the thin film heater assembly which corresponds with the heating area of the heating element.

7. The heater assembly of any preceding claim wherein the layer of graphite is provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer.

8. The heater assembly of claim 7 wherein the adhesive graphite sheet comprises a graphite layer having a thickness between 5 and 30 microns and an adhesive layer having a thickness between 0 and 35 microns, wherein preferably the graphite layer has a thickness between 10 and 12 microns and the adhesive layer has a thickness between 5 and 10 microns.

9. The heater assembly of any preceding claim wherein the thermal conductivity of the graphite layer is between 700 and 2000 W/m.K.

10. The heater assembly of any preceding claim wherein the graphite layer comprises a graphite polymer film.

11. The heater assembly of any preceding claim further comprising a temperature sensor comprising a sensing part; wherein the sensing part is positioned in an area of the thin film heater assembly which is covered by the layer of graphite.

12. A method of fabricating a heater assembly comprising: providing a heating element supported on a surface of a flexible dielectric backing film; and attaching a layer of cover film onto the surface of the dielectric backing film so as to at least partially enclose the heating element between the cover film and the dielectric backing film, wherein together the attached backing film, heating element and cover film form a thin film heater assembly; positioning a layer of graphite arranged against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping with the heating element; and wrapping the thin film heater assembly around the outer surface of a tubular heating chamber, arranged to receive an aerosol generating consumable, with the dielectric backing film toward the outer surface of the heating chamber.

13. The method of claim 12 wherein the layer of graphite is provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer and the step of positioning the layer of graphite comprises: sticking the adhesive graphite sheet to the dielectric backing film; and/or sticking the adhesive graphite sheet to the cover film.

14. The method of claim 12 or 13 further comprising: providing a cover film comprising a heat shrink layer and heating the thin film heater assembly to shrink the heat shrink layer, securing the thin film heater assembly against the tubular heating chamber.

15. The method of claim 14 further comprising sticking an adhesive graphite sheet to the outer surface of the tubular heater chamber before wrapping the thin film heater assembly around the outer surface of a tubular heating chamber.