JP7638283B2 - Heater Assembly - Google Patents

Description

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

Thin film heaters are commonly used in a wide range of applications that require a flexible, low-profile heater that can conform to the surface or object to be heated. One such application is in the field of aerosol generating devices, such as low-risk nicotine delivery products, including e-cigarettes and tobacco vapor products. Such devices heat an aerosol generating material in a heating chamber to generate vapor. One means of heating the consumable is to use a heater assembly that includes a thin film heater that conforms to the surface of the heating chamber to ensure efficient heating of the aerosol generating material in the chamber.

Thin film heaters generally comprise a resistive heating element encased in a sealed enclosure of flexible, electrically insulating thin film, with contacts to the heating element for connection to a power source, the contacts usually being soldered to the exposed portion of the heating element.

Such thin film heaters are typically manufactured by depositing a metal layer on an electrically insulating thin film support, etching the metal layer supported on the thin film into the shape of the required heating element, placing a second layer of electrically insulating thin film over the etched heating element, and heat pressing to encapsulate the heating element with an electrically insulating thin film encapsulation. The electrically insulating thin film is then die cut to create openings for contacts that are soldered to the portions of the heating element exposed by the openings.

These conventional thin film heaters, formed of planar heating elements sealed within an insulating thin film encapsulation, must then be attached to the surface to be heated. In the context of an aerosol generating device, this attachment involves attaching the thin film heater to the exterior surface of a heating chamber to form a heater assembly so as to transfer heat to an aerosol generating consumable disposed within the chamber.

Such conventional thin film heaters and heater assemblies have many drawbacks. One known problem is that heating is often not uniform throughout the thin film heater. In particular, hot spots often occur within the area of the heating track, which can result in non-uniform heater temperature throughout the heating area of the thin film heater. As the metal heats up, the electrical resistance of the heater track increases, which exacerbates the effect, causing existing hot spots to heat up even more due to the increased resistance in these areas and the associated increased localized resistive heating. In some cases, this can lead to burnout of the electrically insulating sealing layer and reduced performance when the thin film heater is applied to a device.

The present invention aims to make progress in addressing these problems and provide an improved heater assembly and method for manufacturing the heater assembly.

According to a first aspect of the present invention, there is provided a heater assembly for an aerosol generating device, the heater assembly including: a flexible electrically insulating backing film; a flexible heating element supported on a surface of the electrically insulating backing film; a cover film disposed on the surface of the electrically insulating backing film so as to at least partially encapsulate the heating element between the cover film and the backing film, the backing film, the heating element, and the cover film together forming a thin film heater assembly; a layer of graphite disposed on an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping the heating element; and a tubular heating chamber configured to house an aerosol generating consumable, the thin film heater assembly being wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film facing the heating chamber.

In this way, the graphite layer serves to distribute 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 diffuses quickly laterally within the thin film heater assembly, preventing, for example, localized hot spots in areas close to the heating element. By overlapping the graphite layer with the heating element, heat is rapidly conducted to the graphite layer and then diffused to the area corresponding to the graphite layer. This prevents localized areas of the consumable from exceeding the optimal temperature for aerosolization and possibly burning, releasing undesirable compounds in the vapor to be inhaled by the user. The graphite layer also ensures that the consumable is heated uniformly so that the entire amount of the consumable is efficiently aerosolized, overcoming known problems in prior art devices with respect to debris associated with incomplete heating of the aerosol generating consumable. To avoid the above problems with debris and hot spots, uniform heating on fine length scales is required for heating of the aerosol generating consumable, and therefore the use of a heating assembly for these applications is particularly preferred.

The thin film heater assembly includes multiple film layers that are superimposed to provide a multi-layer planar assembly. The term "overlapping" is intended to describe how the surface areas of multiple 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 graphite layer and the heating element are arranged to overlap 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). The graphite layer preferably covers the heating area of the heating element, which is the surface area defined by the heater track of the heating element. These definitions hold whether the thin film heater assembly is in a planar configuration, i.e., flat, or wrapped around a curved heating chamber.

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

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

The cover film preferably comprises a heat shrink film. In this manner, the heat shrink film functions to seal the heating element between the heat shrink film and the backing film and to provide an attachment mechanism by which the thin film heater assembly can be attached to the 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 selective heat shrink film configured to selectively shrink in one direction. For example, the heat shrink film may be a 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 configured to be wrapped around the heating chamber, or in the form of a tube configured to be passed around the heating chamber (i.e., sleeved) and heated to shrink to the surface of the heating chamber.

The cover film is preferably attached using an adhesive provided on the surface of the flexible, electrically insulating backing film that supports the heating element. The adhesive may be, for example, a silicone adhesive. The adhesive provides a simple and straightforward means of securely fixing the heating element and cover film to the backing film. The flexible, electrically insulating backing film may include an adhesive layer, and may be, for example, a polyimide film with a Si adhesive layer. The heating element may be attached by subsequently heating the flexible, electrically insulating backing film, adhesive layer, and positioned heating element, and using the adhesive to bond the heating element to the surface. The subsequent heating may be a heating step used to shrink the heat shrink film to attach the thin film heater to the heating chamber.

The heating element is preferably a flexible planar heating element. The heating element is preferably a planar heating element including a heater track that follows a serpentine path across the heating area in the plane of the heating element, and two contact legs for connection to a power source, the contact legs extending outwardly from the heater track in the plane of the heating element. The heater track is preferably configured to provide substantially uniform heating across the heating area. The heater track path may be a serpentine or serpentine path across the heating area, and the heater track may have a substantially uniform width and thickness. The cover film is preferably attached to encapsulate 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, while the contact legs are exposed so as to be connectable to a power source. If a thin film heater is used in the device, the contact legs may be long enough to be directly connectable to a power source. For example, the length of the contact legs may be substantially equal to or greater than one or both of the dimensions that define the heated region. The serpentine path may be configured to leave an empty area within the heated region.

The heater assembly includes a tubular heating chamber. A thin film heater assembly is wrapped around the outer surface of the tubular heating chamber with an electrically insulating backing film facing the heating chamber. In this manner, the contents of the heating chamber can be heated over the thin film heater assembly, with the graphite layer functioning to evenly spread heat from the heating element resulting in improved heating of the heating chamber.

Preferably, the heating chamber includes one or more recesses in an outer surface, and the thin film heater assembly is positioned relative to the heating chamber such that the temperature sensors mounted on the flexible, electrically insulating backing film are positioned within the recesses. The method preferably further includes wrapping a further electrically insulating film around the mounted thin film heater assembly. In some examples, the further electrically insulating film may be less thermally conductive than the backing film.

The graphite layer is preferably disposed between an 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 simple and straightforward method of precisely aligning the graphite layer so that it overlaps the heating area during assembly.

Alternatively, the graphite layer may be placed against the outer surface of the cover film of the thin film heater assembly. This step may be performed after heat shrinking and mounting the thin film heater assembly in a heating chamber.

The heater assembly preferably includes a second graphite layer, where the first graphite layer is disposed between the electrically insulating backing film and the outer surface of the heating chamber, and the second graphite layer is disposed against the outer surface of the cover film. This provides a more optimized heat distribution because the heating element is disposed between two graphite layers, which work together to spread heat through the thin film heater assembly without requiring significant additional labor during assembly.

The heater assembly preferably further includes an electrically insulating sealing layer disposed around the outer surface of the wrapped thin film heater assembly and the one or more graphite layers. This provides increased insulation so that heat is more efficiently directed to the heating chamber. Additionally, the thin film heater may be sealed to prevent one or more by-products from being released during heating. In some examples, the layers of the thin film heater are configured to provide increased heat transfer in one direction from the heating element. 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 increased heat transfer in a direction consistent with toward the heating chamber during use. For example, the insulating backing film may have an increased thermal conductivity compared to the cover film layer and/or the sealing layer. In this way, heat transfer to the heating chamber is enhanced and heat transfer lost from the heating chamber is reduced to mitigate heat loss. The side of the thin film heater that is disposed to contact the heating chamber is preferably configured to have a higher thermal conductivity than the opposite outside. The sealing layer preferably has a lower thermal conductivity than the backing film.

The heating element is preferably a planar heating element including a heater track that follows a serpentine path across a heating area in the plane of the heating element, where the layer of graphite covers an area of the surface of the thin film heater assembly that corresponds to the heating area of the heating element. This ensures that heat is distributed evenly across the heating area of the thin film heater assembly.

The graphite layer is preferably provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer. For example, the graphite layer may comprise an adhesive graphite tape. This provides a simple and straightforward means of fixing the graphite layer in place by using an adhesive layer.

The adhesive graphite sheet preferably includes a graphite layer having a thickness between 5-30 μm and an adhesive layer having a thickness between 0-35 μm, with the graphite layer having a thickness between 10-12 μm and the adhesive layer having a thickness between 5-10 μm. Other examples may use graphite tapes with graphite layer thicknesses of 10, 17, or 25 μm and adhesive layer thicknesses of 6, 10, or 30 μm, respectively. This minimizes the thermal mass of the thin film heater assembly, thereby maximizing heat transfer to the heating chamber.

The thermal conductivity of the graphite layer is preferably between 700 and 2000 W/m.K. This helps to effectively distribute the heat generated by the heater track throughout the heated area. The graphite layer preferably comprises a graphite polymer film.

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

In another aspect of the invention, a method of manufacturing a heater assembly is provided, the method including providing a heating element supported on a surface of a flexible dielectric backing film, attaching a layer of cover film to the surface of the dielectric backing film to at least partially encapsulate the heating element between the cover film and the dielectric backing film, the attached backing film, heating element, and cover film together forming a thin film heater assembly, and disposing a layer of graphite disposed against an outer surface of the thin film heater assembly, the layer of graphite at least partially overlapping the heating element. This results in a straightforward assembly method that provides a heater assembly with improved thermal performance and reduced risk of hot spots due to selective heating in areas near the heating track of the heating element. This also allows the graphite heater to be added at various stages of the assembly process to improve the efficiency of the assembly. For example, it can be added to the outer surface of the heating chamber during manufacture of the heating chamber, or it can be added to the surface of the thin film heater assembly during assembly of the thin film heater assembly, or it can be added as a final step after the thin film heater is attached to the heating chamber.

The layer of graphite is preferably provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer, and the step of disposing the layer of graphite comprises attaching the adhesive graphite sheet to a dielectric backing film and/or attaching the adhesive graphite sheet to a cover film. In an alternative step, the adhesive graphite sheet may be attached directly to the outer surface of the heating chamber.

The method preferably further includes wrapping the thin film heater assembly around an outer surface of the tubular heating chamber with the dielectric backing film facing the outer surface of the heating chamber, providing a cover film comprised of a heat shrink layer, and heating the thin film heater assembly to shrink the heat shrink layer and secure the thin film heater assembly to the tubular heating chamber.

The method preferably further includes attaching an adhesive graphite sheet to the outer surface of the tubular heater chamber prior to wrapping the thin film heater assembly around the outer surface of the tubular heater chamber.

In a further aspect of the present invention, there is provided an aerosol generating device heater assembly as claimed. In this way, the aerosol generating device can provide improved heating by providing a more uniform heating temperature throughout the heating chamber.

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

1 shows a schematic representation of a heater assembly according to the present invention from two opposite views; 1 shows a schematic representation of a heater assembly according to the present invention from two opposite views; 1 shows a heater assembly including a thin film heater assembly wrapped around a heating chamber. FIG. 1 shows a cross-sectional view of a heater assembly including a thin film heater assembly wrapped around a heating chamber. 1 shows a heater assembly including a thin film heater assembly wrapped around a heating chamber. 1A-1D show cross-sectional views of two examples of heater assemblies according to the present invention, respectively. 1A-1D show cross-sectional views of two examples of heater assemblies according to the present invention, respectively. 2 illustrates diagrammatically a graphite layer for use in a heater assembly according to the present invention; 4 illustrates a method of assembling a heater assembly according to the present invention. 4 illustrates a method of assembling a heater assembly according to the present invention. 4 illustrates a method of assembling a heater assembly according to the present invention. 4 illustrates a method of assembling a heater assembly according to the present invention. 4 illustrates a method of assembling a heater assembly according to the present invention. 4 illustrates an alternative assembly step in a method of assembling a heater assembly according to the present invention.

1A and 1B are schematic diagrams of 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 disposed on a surface of the electrically insulating backing film 30 so as to at least partially encapsulate the heating element 20 between the cover film 50 and the backing film 30. The assembled backing film 30, heating element 20, and cover film 50 are collectively referred to as a thin film heater assembly 100. The heater assembly 10 further includes a layer of graphite 40 disposed against an outer surface of the thin film heater assembly 100, the layer of graphite 40 at least partially overlapping 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 includes a flexible heating element 20 encapsulated between opposing backing films 30 and heat shrink films 50.

The graphite layer 40 functions to rapidly diffuse the generated heat around the heating area, so that the heat is dispersed outward from any potential hot spots, resulting in a much more uniform heating temperature throughout the heating area. Because graphite has a high thermal conductivity, typically between about 700-2000 W/m.K, heat is rapidly dispersed laterally within the plane of the thin film heater assembly 100, so that hot spots do not form and the heater assembly 10 provides better performance when used in devices such as aerosol generating devices. This is accomplished even when the graphite layer 40 is separated from the heating element 20 by one or more thin film layers.

In the exemplary embodiment shown in the figures, the cover film includes a layer 50 of heat shrink film. This has many advantages. In particular, the heat shrink film not only seals (at least a portion of) the heating element 20 between the backing film 30 and the opposing heat shrink film, but also serves as an attachment means for attaching the thin film heater assembly 100 to the surface of the heating chamber. Thus, it minimizes the amount of additional material and associated thermal mass in the layers of the thin film heater assembly while providing an effective method of attaching the heating element. Further details of this attachment mechanism are provided below.

In the example of FIG. 1, the graphite layer 40 is applied to a surface of the flexible, electrically insulating backing film 30. That is, the thin film heater assembly 100 is formed by first placing a planar heating element between the backing film and the heat shrink 50. The thin film heater assembly may be attached using an adhesive disposed between the layers, and in particular, the backing film may include a layer of adhesive that serves to attach both the heating element 20 and the cover film 50. The graphite layer 30 is then disposed on the surface opposite the heating element 20 and in contact with the backing film 30 such that the graphite layer 30 at least partially overlaps the heating element 20. In other examples of the invention, the graphite layer 40 may be applied to the opposite side of the thin film heater assembly 100, i.e., in contact with the heat shrink film layer 50, as described in more detail below.

As shown in FIG. 1, the size and shape of the graphite layer 40 preferably substantially matches the size and shape of the heating area 22 defined by the heating track 21 of the heating element 20, as best seen in FIG. 1B. In particular, the graphite layer 40 preferably covers an area on the outer surface of the thin film heater assembly 100 that substantially matches the heating area 22 of the heating element. In this manner, heat is distributed evenly throughout the intended heating area.

1A and 1B, the thin film heater assembly further includes a temperature sensor 70 in the form of a thermistor 70 with a temperature sensing portion 71 ("sensor head") and a sensor connection 72. Importantly, the sensor head 71 is located within the area of the thin film heater assembly 100 covered by the graphite layer 40. In particular, the thermistor may be located with the sensing portion located 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 to cover both the heating area 22 and the sensor head 71. In this way, heat is effectively distributed 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 used in a device, this allows the measured temperature of the heating element to be used to accurately control the heater to provide an accurate heating temperature, and also ensures that the heating element 20 does not overheat, which can occur in instances where the temperature sensor is not positioned to provide an accurate reading of the heating element 20 itself.

As shown in FIG. 2A, the thin film heater assembly 100 is wrapped around the outer surface of the tubular heating chamber 60 to provide uniform heating of the heating chamber 60 throughout the heating area 22. FIG. 2A shows an assembled heater assembly 10 including a flexible electrically insulating backing film 30, a flexible heating element 20, a layer of heat shrink film 50, and a layer of graphite 40 wrapped together around the outer surface of the tubular heating chamber 40, capable of transferring heat to the chamber 60 when a power source is connected to the contacts 24 on the extending contact legs 23 of the heating element 20. The example of FIG. 2 uses the heater assembly 10 of FIG. 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 shown in cross section in FIG. 2B. In particular, the heater assembly 10 is arranged such that the layer of graphite 40 is placed against the outer surface of the heating chamber 60, the flexible electrically insulating backing film 30 is placed around the layer of graphite 40, the heating element 20 is placed against the backing film 30, and finally the layer of heat shrink film 50 is wrapped around the outer surface of each of these layers to secure the thin film heater assembly to the heating chamber 60. The assembly 10 shown in FIG. 2 may then be first heated to shrink the heat shrink film 50, and the thin film heater assembly 100 is sealed against the outer surface of the heating chamber 60.

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

3A-3C show an alternative embodiment of the present invention in which the layer of graphite 40 is disposed 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 FIGS. 1A and 1B, the layer of graphite 40 is instead applied to the opposite side of the thin film heater assembly 100 such that the layer of graphite 40 is positioned against the cover film 50 (heat shrink 50 in this case) but still overlaps the heating region 22 in the same manner as shown in FIG. 1. The thin film heater assembly 100 with the layer of graphite 40 attached to the heat shrink film 50 is then wrapped around a tubular heating chamber 60 as shown in FIG. 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 oriented toward the outer surface of the heating chamber 60, but the layer of graphite 40 is disposed about the outer surface of the heat shrink 50.

3B shows a cross-section through the arrangement of FIG. 3A, illustrating the order of layers within the heater assembly 10. In particular, as shown in FIG. 3B, the backing film 30 is positioned against the outer surface of the heating chamber 60, the heating element 20 is supported on the outer surface of the backing film 30, a 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 a layer of graphite 40 is applied to the outer surface of the wrapped heater assembly 10. In this arrangement, the graphite 40 still provides the same effect of spreading the heat generated by the heating element 20 laterally through a planar layer to disperse the heat and prevent the formation of hot spots.

An alternative embodiment of the heater assembly 10 is shown in the cross-sectional view of FIG. 3C. This embodiment incorporates a first graphite layer 41 disposed against the flexible, electrically insulating backing film 30 (as shown in FIG. 1) and a second graphite layer 42 disposed against the surface of the heat shrink 50 as shown in FIGS. 3A and 3B. Both graphite layers 41, 42 are preferably disposed to overlap the heating area 22 of the heating element 20 to distribute heat throughout the layers of the heater assembly 10, and in particular to spread heat laterally to prevent hot spots. In particular, the alternative embodiment of FIG. 3C includes a first graphite layer 41 applied directly to the outer surface of the heating chamber 60 or directly to the backing film 30, such that the first graphite layer 41 is located between the heating chamber 60 and the backing film 30 when the thin film heater assembly 100 is wrapped around the heating chamber 60. As in all examples, the flexible heating element 20 is supported on a backing film 30 and the heat shrink 50 is wrapped 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. A second layer of graphite 42 is disposed on the outer surface of the heat shrink 50. In this manner, the heating element 20 is located between the first graphite layer 41 and the second graphite layer 42, which further optimizes the spreading of heat generated by the heating element 20 throughout the layers and prevents the development of hot spots.

Each of the illustrated examples may further include an electrically insulating sealing layer (not shown) that may be wrapped around the outermost surface in the arrangements shown in Figures 2B, 3B, and 3C. An electrically insulating sealing layer, such as a polyimide thin film, may be applied to the thin film heater assembly 100 before the thin film heater assembly 100 is wrapped around the heating chamber 60, i.e., in the planar assembly shown in Figures 1A and 1B. Alternatively, the electrically insulating sealing layer may be applied after the layers of the heater assembly 10 are attached, such that it is wrapped around the outermost surface of the assembled heater assembly 10, such as in the arrangements shown in Figures 2B, 3B, and 3C.

4 shows a layer of graphite film 40 that can be applied as graphite layer 40 in the described examples of the invention. In particular, layer of graphite 40 may be provided by an adhesive graphite sheet comprising graphite layer 43 and at least one adhesive layer 44. While the example of FIG. 4 shows a graphite sheet or tape having graphite layer 43 and a single adhesive layer 44, in other examples graphite tape 40 may comprise multiple adhesive layers, in particular adhesive layers 44 on both sides of graphite layer 43. Adhesive layer 44 may comprise an acrylic or silicone adhesive, and graphite layer thickness 43t may be between 5-30 microns, preferably between 10-12 microns, and adhesive layer may have a thickness 44t between 0-35 microns, preferably between 5-10 microns. Examples of commercially available graphite tapes that can be used for this application include EYGA121801F 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 about 6 microns. A graphite tape 40, particularly a graphite tape having a graphite layer of about 10-12 microns with an adhesive layer having an optically preferred thickness 44t between 5-10 microns, is placed between the heating chamber 60 and the heating element 20. The thermal conductivity of the graphite tape 40 may be in the range of 700-2000 W/m.K. The graphite tape may have a specific gravity between about 0.85-0.213 g/ ^cm3 . The graphite layer 43 of the tape may be a pyrolytic graphite sheet, particularly formed from a highly oriented graphite polymer film. Such graphite layers can withstand temperatures up to 400° C. and are well suited for applications in the heating chamber 60 where high temperatures are required. Such graphite tapes may be protected by a PTE release liner that protects the adhesive film 44 and that can be removed prior to attachment of the graphite sheet 40 to the thin film heater assembly 100 or heating chamber 60.

Now, with reference to Figures 5 and 6, further details of the heater assembly 10 according to the present invention and a method of manufacturing such a heater assembly 10 will be described.

As shown in FIG. 5A, the first step involves providing a heating element 20 supported on the surface of a flexible, electrically insulating backing film 30. This may be accomplished in a number of different ways. In particular, the heating element 20 may be etched from a thin metal plate of about 50 μm, for example a stainless steel plate such as 18SR or SUS304, although other materials and heater thicknesses may be selected depending on the application. The particular metal and thickness of the metal plate are selected so that the resulting heating element 20 is flexible so that it can deform together with the supporting flexible thin film 30 to conform to the shape of the surface to be heated. The metal plate may first be placed on the surface of the flexible, electrically insulating backing film 30 before being etched while supported on the film to form the heater track 21 pattern. Alternatively, and preferably, the heating element 20 may be etched from the metal plate separately from the flexible, electrically insulating backing film. For example, a free-standing metal foil may be chemically etched from both sides to provide one or more connected heating elements 20 that are then pulled apart and disposed on the surface of the electrically insulating backing film 30.

The heating element 20 in the illustrated example is a planar heating element 20 including a heater track 21 that follows a serpentine path across a heating area 22 in the plane of the heating element 20. The heating element has two contact legs 23 that allow connection to a power source, the contact legs 23 extending outwardly from the heater track 21 in the plane of the heating element 20. The contact legs may also extend in a plane that is inclined relative to the heating element. The heater track 21 is preferably shaped to provide substantially uniform heating across the heating area 22. In particular, the heater track is shaped to have a uniform thickness and width without sharp corners, and the gap between adjacent portions of the heater track 22 is substantially constant to minimize excessive heating at a particular point in the heating area 22. The heater track 21 in the example of FIG. 5A follows a serpentine path across the heater area 22 and is divided into two parallel track paths 21a and 21b, each of which is connected to both contact legs 23. The heater layer 23 may be soldered at connection points 24 on each contact leg 23 to allow connection of the heater to a PCB and a power source.

The flexible electrically insulating backing film 30 must have suitable properties and provide a flexible substrate for supporting and electrically insulating the heating element 20. Suitable materials include polyimide, PEEK, and fluoropolymers such as PTFE. In this case, the heating element includes a heater track pattern 21 etched from a layer of 50 μm stainless steel 18SR supported on a single-sided polyimide/Si adhesive film that includes a 25 μm polyimide film with a 37 μm silicone adhesive layer. The heating element 20 is supported on the adhesive to allow attachment of the heating element to the backing film. The thin film heater assembly 100 of FIG. 5A may be prepared in advance and stored with a release layer that protects the adhesive layer until it is attached to the adhesive surface that supports the heating element 20 and is ready for use. The release layer may be provided, for example, by polyester or a similar material. The release layer may then be peeled off to uncover the tacky adhesive layer that supports the heating element in order to proceed to the next assembly step shown in FIG. 5B.

The next step in this exemplary method of manufacturing the heater assembly 100 is to apply a layer of heat shrink film 50 directly to the surface of the electrically insulating backing film 30 so as to at least partially encapsulate the heating element 20 between the heat shrink film 50 and the backing film 30. The heat shrink film 50 can be attached with an adhesive directly onto the surface of the heater element 20 so as to encapsulate the heating area 20 between the backing film 30 and the heat shrink 50. In particular, the heater track 21 is insulated within the hermetic encapsulation 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 the heating element 20 so that it extends beyond the heating element 20 a predetermined distance in two orthogonal directions 51, 52. This alignment of the heat shrink 50 to the heating element 20 allows for the subsequent alignment of the heating area 22 to the heating chamber 60. Careful control of the size of these extensions 51, 52 of the heat shrink at this stage therefore allows for the attachment of the heater assembly 100 to the heating chamber 60 in a straightforward manner that provides precise alignment. The alignment of the heat shrink relative to the thin film heater 10 can be achieved in many different ways. The heat shrink 50 may be pre-cut to the correct size and then aligned to the edge of the flexible electrically insulating backing film 30 to provide the correct extensions of the predetermined distances 51, 52. Alternatively, an alignment device may be used to achieve this precise alignment.

In particular, both the backing film 30 and the heat shrink 50 may be provided with a series of corresponding alignment holes (not shown) that can be used to align the backing film 30 and the heat shrink 50 relative to one another. The alignment holes are positioned such that when the holes in the backing film 30 are aligned with the alignment holes in the heat shrink 50, the heat shrink 50 will extend beyond the heating area 22 by the correct length 51, 52 to position the heat shrink 50 in a precisely correct location relative to the thin film heater 10, allowing precise alignment of the heating element 20 relative to the heating chamber 60 when installed. The heat shrink 50 is then aligned relative to the thin film heater 10 using a positioning fixture that includes a support surface with upstanding alignment pins that correspond to the relative displacements of the alignment holes in the backing film 30 and the heat shrink 50 relative to the location of the alignment holes. The heating element 20 and heat shrink 50 on the backing film 30 may then be placed on the surface of the alignment fixture such that the alignment pins extend through the backing film alignment holes to ensure that the heat shrink is precisely aligned with the heating element 20 and backing film 30.

The heat shrink 50 extends beyond the heating area 20 in a direction opposite the contact legs 23 to provide an alignment area 52 of the heat shrink 50. This alignment area 52 can be aligned with the top of the heating chamber 60 such that the heating area 20 is located at a position along the length of the heating chamber corresponding to the predetermined length 52 of the alignment area from the top of the heater track 21. In this manner, the heater element 20 can be provided at the correct position along the heating chamber 60. The heat shrink 50 also has an attachment area 51 that extends beyond the heater track 21 and backing film 30 in a direction perpendicular to the extension of the contact legs 23 to provide an attachment area 51. The extension direction of the attachment area 51 from the heating element 20 to the edge of the heat shrink 50 is sometimes referred to as the "wrap direction" because this portion of the heat shrink 50 can be wrapped around the tubular heating chamber 60 and then heat shrunk to provide the required tight connection. Similarly, the direction in which the alignment region 52 extends from the heating element 20 opposite the heater legs 23 may be referred to as the upward or alignment direction toward the top open end and aligned with the long axis of the heating chamber 60. These extension distances 51, 52 may be configured by cutting the heat shrink 50 to the correct size before or after application of the heat shrink 50 to the surface of the electrically insulating backing film 30.

As shown in FIG. 5B, the temperature sensor 70 is attached to the thin film heater assembly 100 between the flexible backing film 30 and the heat shrink 50. In this case, the temperature sensor 70 is a thermistor with a sensor head 71 configured to detect the local temperature and a temperature sensor connection 72 configured to carry a sensed signal from the sensor head 71 to the PCB. The heater track 22 is preferably shaped to leave an open area 22v in the heating area 22, as shown most clearly in FIG. 5A. The sensor head 71 is placed in this open area 22v between the backing film 30 and the heat shrink 50 in close proximity to the heater track 21. By placing 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 an accurate temperature measurement of the heating area 22. This is further improved by providing a graphite sheet 40 that covers both the heating element 20 and the sensor head 71.

As shown in FIG. 5B, the heat shrink 50 is preferably positioned such that the free end region 32 of the backing film 30 remains exposed. This free end region 32 is folded back over the heat shrink film 50 to seal the edges of the backing film 30 and the heat shrink 50, and then folded over and secured within the fold the temperature sensor 71.

5B, once the thin film heater assembly 100 is assembled, a layer 40 of graphite film in the form of adhesive graphite tape is attached to the outer surface of the thin film heater assembly 100 so that the layer 40 of graphite film at least partially overlaps 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 FIG. 5C (and FIG. 1A). The dimensions and shape of the graphite tape closely match those of the heating area 22 so that the graphite tape covers the area of the backing film 30 corresponding to the heating area 22. The graphite tape 40 also extends over the temperature sensing portion 71 of the temperature sensor so that heat generated by the heating element 20 is effectively distributed to the temperature sensor 70, providing an accurate reading of the temperature of the heating element 20.

Graphite tape 10 is attached by attaching tape 40 having an adhesive layer to backing film 30. As mentioned above, in this example, the graphite tape is attached to the surface of the backing film, but the graphite tape can also be attached to the outer surface of the heating chamber 60 using adhesive layer 44 to attach graphite layer 43 to the surface of the heating chamber, so that the graphite tape overlaps heating element 20 when thin film heater assembly 100 is wrapped around heating chamber 60. Similarly, instead or in addition, graphite layer 40 can be attached to the surface of heat shrink layer 50 (opposite the surface in contact with heating element 20) so that the graphite layer is on the outside of the heating element (i.e., radially away from heating chamber 60) when thin film heater assembly 100 is wrapped around heating chamber.

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 the heating area 22 of the heating element 20, the thin film heater assembly is attached to the heating chamber 60. This can be accomplished by attaching two pieces of adhesive tape 55a, 55b to the thin film heater assembly 100 so that the thin film heater assembly is first attached to the heating chamber 60 in the correct location before heating the assembly to shrink the heat shrink 60.

The adhesive tape 55a, 55b may be provided by a piece of polyimide adhesive tape, such as a commercially available 0.5 inch polyimide tape having 12.7 micrometer polyimide and 12.7 micrometer silicone adhesive. The adhesive mounting tape 55a, 55b is placed along each edge of the heat shrink 50 at the leading edge in the wrapping direction, as shown in FIG. 5D. 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, as shown in FIG. 5E. This alignment step allows the heating region 22 and corresponding graphite layer 40 to be placed in the correct location along the heating chamber 60, provided that the alignment region distance 52 is carefully selected. Because certain consumables contain a charge of aerosol generating material in specific locations, it is important to heat the correct portion of the heater chamber 60 to efficiently release vapor from the consumable.

The thin film heater assembly 100 is first attached to the heating chamber 60 using adhesive tape 55a. The heating chamber 60 is a tubular heating chamber 60 configured to house a consumable that is to be heated to produce a vapor that is to be inhaled by a user. The heating chamber 60 preferably has one or more recesses 61 on its outer surface that provide internal protrusions that aid in positioning and heat transfer to the consumable contained within the chamber 60. The circumference of the heating chamber 60 preferably closely matches the width (length in a direction perpendicular to the extension direction of the contact legs) of the heating element 20 so that the heating element provides one complete circumferential loop around the chamber 60. In other examples, the heater element 20 may be sized to wrap around the circumference of the heating chamber more than once, i.e., the heating element may be sized to provide an integer number of circumferential loops around the circumference of the heating chamber so as to avoid variations in the heating temperature around the circumference of the heating chamber. The thin film heater assembly 100 is positioned and mounted so that the temperature sensor head 71 is located within a recess 61 in the outer surface of the heating chamber 60 to provide a more accurate measurement of the interior temperature of the heating chamber 60. In an alternative to the embodiment of FIG. 3C, the temperature sensor may be located between the graphite layer 50 and the heat shrink 50.

As mentioned above, in an alternative method, the graphite layer 40 is attached directly to the heater chamber 60, as shown in FIG. 6. In particular, the graphite layer 40 is disposed over the length of the heating chamber 60 that corresponds to the heating region 22 of the thin film heater assembly 100 when wrapped around the heating chamber 60, such that the graphite layer 40 overlaps the heating region and serves to spread the heat generated evenly across the heating region 22.

Once attached with the first adhesive tape portion 55a, the thin film heater assembly 100 is then wrapped 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 with a second piece of attachment tape 55b to provide the heater assembly 10 shown in FIG. 2A (including the heater element 20, the backing film 30, the graphite layer 40, the heat shrink film 50, the thermistor 70, and the heater chamber 60). Since the length of the attachment area 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 and covers the heating area 22 once, so that the heater element is insulated by two layers of heat shrink film in the attached heater assembly 10 shown in FIGS. 5E and 6. The attachment area 51 may be sized to provide two or more additional coverings of the heating element 20. For example, the attachment region 51 may extend beyond the heating element a distance corresponding to an integer multiple of the circumference of the heating chamber 60.

As can be seen in FIG. 2A, once assembled, the temperature sensor connections 72 and heater legs 23 are positioned to be aligned after this quick step to facilitate connection to the PCB. The attached heater assembly 10 is then heated to shrink the heat shrink 50 tightly against the heating chamber 60 as shown in FIG. 2A. For example, the assembly 10 can be heated in an oven at about 210° C. for 10 minutes to shrink the film, although the time and temperature can be adapted for other types of heat shrink. This process allows multiple units to be heat treated simultaneously in a small oven. This is the only heating step that can simultaneously both seal the thin film heater to the heating chamber and adhere the backing film to the heat shrink.

Finally, although not required, 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, an additional layer of adhesive polyimide, such as 1 inch polyimide tape with 25 micrometers of polyimide and 37 micrometers of silicone adhesive. This outer layer of electrically insulating film provides an additional layer of insulation to further secure attachment of the thin film heater assembly 100 to the heating chamber 60.

The thickness and/or materials 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, by providing a low thermal conductivity layer on the outside of the heating element (i.e., in this example, for the heat shrink 50 and insulating layer) and a high thermal conductivity layer as the backing film.

Once the outer insulating layer of the electrically insulating film has been applied, the assembly 10 may be heated again. This second heating step may allow for further outgassing of the outer layer of the electrically insulating film as well as other layers. For example, in the second heating stage, the heating temperature may be increased to a higher temperature than the heat shrink stage that is closer to the operating temperature of the device. This may allow for further outgassing of the adhesive layer that would not have occurred during the heat shrink step at a lower temperature, for example. It may also be beneficial to expose the heat shrink to a temperature closer to the operating temperature prior to heating during initial use of the device.

Once assembled, the graphite layer 40 is positioned to align with the heating area 22 of the heating element and is positioned 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 rapidly diffuses the heat generated by the heating element 20 in a planar direction, resulting in a uniform heating temperature over the entire area covered by the graphite layer 40, thereby reducing hot spots, reducing the risk of damage to the film layer due to localized overheating, and providing a more uniform heat transfer to the consumables contained in the heating chamber 60.

Claims (14)

1. A heater assembly for an aerosol generating device, comprising:
a flexible, electrically insulating backing film;
a flexible heating element supported on a surface of the electrically insulating backing film;
a cover film disposed on the surface of the electrically insulating backing film so as to at least partially encapsulate the heating element between the cover film and the backing film, the backing film, the heating element, and the cover film together forming a thin film heater assembly;
a layer of graphite disposed on an exterior surface of the thin film heater assembly, the layer of graphite at least partially overlapping the heating element;
a tubular heating chamber configured to house an aerosol generating consumable, the thin film heater assembly being wrapped around the outer surface of the tubular heating chamber with the electrically insulating backing film facing the heating chamber;
an electrically insulating sealing layer disposed about an outer surface of the wrapped thin film heater assembly and the one or more graphite layers . The heater assembly of claim 1, wherein the layer of graphite is disposed between the electrically insulating backing film of the thin film heater assembly and the outer surface of the heating chamber. The heater assembly of claim 1, wherein the layer of graphite is disposed in contact with the outer surface of the cover film of the thin film heater assembly. further comprising a second layer of graphite;
a first graphite layer disposed between the electrically insulating backing film and the exterior surface of the heating chamber;
The heater assembly of claim 1 , wherein the second layer of graphite is disposed against the outer surface of the cover film. the heating element is a planar heating element including a heater track that follows a serpentine path across a heating area in a plane of the heating element;
5. The heater assembly of claim 1 , wherein the layer of graphite covers an area of the surface of the thin film heater assembly corresponding to the heating area of the heating element. 6. The heater assembly of claim 1 , wherein the layer of graphite is provided by an adhesive graphite sheet comprising a graphite layer and at least one adhesive layer. 7. The heater assembly of claim 6, wherein the adhesive graphite sheet comprises a graphite layer having a thickness between 5-30 microns and an adhesive layer having a thickness between 0-35 microns, preferably the graphite layer has a thickness between 10-12 microns and the adhesive layer has a thickness between 5-10 microns. 8. The heater assembly of claim 1 , wherein the thermal conductivity of the graphite layer is between 700 and 2000 W/m.K. The heater assembly of claim 1 , wherein the graphite layer comprises a graphite polymer film. The heater assembly of claim 1 , further comprising a temperature sensor having a sensing portion, the sensing portion being disposed within an area of the thin film heater assembly covered by the layer of graphite. 1. A method of manufacturing a heater assembly, comprising:
providing a heating element supported on a surface of a flexible dielectric backing film;
attaching a layer of cover film to the surface of the dielectric backing film so as to at least partially encapsulate the heating element between the cover film and the dielectric backing film, the attached backing film, heating element, and cover film together forming a thin film heater assembly;
disposing a layer of graphite disposed on an exterior surface of the thin film heater assembly, the layer of graphite at least partially overlapping the heating element;
wrapping the thin film heater assembly around an exterior surface of a tubular heating chamber configured to house an aerosol generating consumable, with the dielectric backing film facing the exterior surface of the heating chamber;
and disposing an electrically insulating sealing layer about an outer surface of the wrapped thin film heater assembly and the one or more graphite layers . The layer of graphite is provided by an adhesive graphite sheet including a graphite layer and at least one adhesive layer, and the step of disposing the layer of graphite includes:
The method of claim 11 , comprising: attaching the adhesive graphite sheet to the dielectric backing film; and/or attaching the adhesive graphite sheet to the cover film. 13. The method of claim 11 or 12, further comprising providing a cover film including a heat shrink layer, and heating the thin film heater assembly to shrink the heat shrink layer and secure the thin film heater assembly to the tubular heating chamber. 14. The method of claim 13 , further comprising attaching an adhesive graphite sheet to the exterior surface of the tubular heating chamber prior to wrapping the thin film heater assembly about the exterior surface of the tubular heating chamber.

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