Thin Film Heater

Abstract

A thin film heater and a method for fabricating the thin film heater are described. The thin film heater includes a flexible heating element and a flexible, electrically insulating backing film supporting the heating element, the backing film including one or both of a fluoropolymer or polyetheretherketone. The use of a fluoropolymer or polyetheretherketone provides improved dielectric and mechanical properties that are particularly suitable for use in aerosol generating devices.

Description

[Technical field]

[0001] The present invention relates to a thin film heater and a method for fabricating a thin film heater. [Background technology]

[0002] Thin film heaters are used in a wide range of applications that require a generally 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 reduced risk nicotine delivery products, including electronic cigarettes and tobacco vapor products. Such devices heat an aerosol generating material in a heating chamber to produce a vapor, and thus may employ 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.

[0003] Thin film heaters generally include a resistive heating element encapsulated in a sealed envelope of flexible dielectric thin film with contact points to the heating element for connection to a power source, the contact points typically being soldered onto the exposed portion of the heating element.

[0004] Such thin film heaters are generally manufactured by depositing a metal layer on a dielectric 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 dielectric thin film over the etched heating element, and heat pressing to encapsulate the heating element with a dielectric thin film envelope. The dielectric thin film is then die cut to create openings for contacts that are soldered over the portions of the heating element exposed by the openings. Sheets of polyimide thin film with a silicone adhesive layer are readily available and are often used to form the dielectric envelope.

[0005] Etching of the metal layer is typically accomplished by screen printing a resist onto the surface of the metal foil, applying a resist pattern, which may be designed in CAD, and transferring the resist to the foil by selectively exposing it, and then spraying the exposed surfaces of the metal layer with an appropriate etching chemistry to preferentially etch the metal layer to leave the desired heating element pattern supported on the polyimide film.

[0006] Such conventional thin film heaters suffer from several drawbacks. In particular, existing materials used for the dielectric layer, such as polyimide, do not have optimal dielectric and mechanical properties, meaning that a thicker dielectric layer is required. This results in an increase in thermal mass and correspondingly less than optimal heat transfer to the heating chamber. Furthermore, polyimide is relatively expensive, increasing the manufacturing costs of devices incorporating thin film polyimide heaters. There is also a need to identify alternative materials to polyimide to provide increased flexibility and increased material selection options in the manufacture of thin film devices. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to go some way towards addressing these problems to provide improved thin film heaters for use and methods of fabricating thin film heaters. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a thin film heater for wrapping around a heating chamber of an aerosol generation device, the thin film heater comprising a flexible heating element and a flexible electrically insulating backing film supporting the heating element, the backing film comprising one or both of a fluoropolymer or a polyetheretherketone.

[0009] Fluoropolymers and / or polyetheretherketones (PEEK) provide a low-cost alternative to polyimide-based thin film heaters while offering improved dielectric properties and good mechanical properties over a wide temperature range, and thus may be employed in thin film heaters. Thus, the present invention provides an alternative to polyimide thin film heaters with improved properties.

[0010] Preferably, the backing film comprises one or more of polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE or PTFCE), and polyetheretherketone. Such materials have suitable properties over a wide temperature range to allow application in thin film heaters. In particular, each of these materials has a high melting point to maintain their mechanical properties at elevated temperatures, allowing them to be used as an insulating support for the heating element. The specific melting points of these materials are different, which dictate the maximum usable heating temperature when applied to thin film heaters and therefore also the specific applications for which they may be used. However, all are suitable for application in controlled temperature aerosol generating devices (or "heated" devices) in a certain temperature range.

[0011] Fluoropolymers have several additional properties that make them particularly suitable for application in flexible heating films, offering several advantages over conventional materials used in such devices. For example, fluoropolymers, and especially PTFE, are very soft compared to polyimides, allowing them to be stretched and compressed, which may enable them to fit snugly around the heating element when used as a sealing layer. This property also allows them to conform more closely to the surface of the object to be heated, such as a heating chamber, allowing for improved heat transfer. Fluoropolymers have much lower surface friction (unless surface treated), which may be advantageous when employed in multi-layer heater assemblies where sliding of the layers may result in better heater compression and formation. Fluoropolymers, and especially PTFE, are more resistant to tearing, which is beneficial in the assembly process, meaning that thin film heaters based on these materials have a reduced risk of damage.

[0012] Preferably, the thin film heater is a thin film heater for an aerosol generating device. Fluoropolymers and polyetheretherketones provide suitable temperature characteristics such that they can be employed in thin film heaters used in aerosol generating devices to, for example, heat a heating chamber.

[0013] Preferably, the thin film heater is configured such that it can conform to the outer surface of a tubular heating chamber, i.e., the thin film heater has sufficient flexibility to allow it to be rolled into a closed loop. Preferably, the thin film heater is configured such that it can be rolled into a tubular configuration, e.g., a cylindrical configuration. In this way, the thin film heater can be attached to the outer surface of the heating chamber of the aerosol generation device to provide efficient heat transfer to the heating chamber.

[0014] Preferably, the thin film heater is a thin film heater for a heated aerosol generating device. Such devices heat substances at a controlled temperature to release vapor without burning the material, thus limiting the maximum heating temperature. The melting points of fluoropolymers and polyetheretherketones, and their corresponding processing temperature ranges accordingly, mean that they are very suitable for use in controlled temperature aerosol generating devices (or "heated" devices).

[0015] Preferably, the flexible electrically insulating backing film comprises one or more of polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE or PTFCE). Such fluoropolymers have advantageous electrical insulating and mechanical properties over a wide temperature range. PTFE has a dielectric constant of 2.1 and a dielectric constant of typically 10 18 It is particularly preferred because it has a volume resistivity of over Ω·cm. PTFE also has good mechanical properties over a wide temperature range, and with a melting point of 327°C, it can be used in a wide range of heater applications. The improved electrical insulating properties of such materials over commonly used dielectric thin films improve the insulation of the heating element, further enhancing the performance of thin film heaters.

[0016] Preferably, the flexible electrically insulating backing film comprises polyetheretherketone (PEEK). PEEK has a dielectric constant of 3.2 and a dielectric constant of 10 16 It provides a further preferred option due to its volume resistivity exceeding Ω·cm, thus providing good electrical insulation properties.

[0017] When the flexible electrically insulating backing film comprises a fluoropolymer, preferably one side of the flexible electrically insulating backing film comprises an at least partially defluorinated surface layer. The defluorinated surface layer is preferably provided by etching one surface of the fluoropolymer backing film. The backing film may be etched using one or both of plasma etching or chemical etching. Plasma etching may be applied using gas mixtures such as Ar, CF4, CO2, H2, H2O, He, N2, Ne, NH3, and O2, or Ar+O2, He+H2O, He+O2, and N2+H2. Chemical etching may include the use of sodium-containing solutions such as sodium ammonia. Fluoropolymers generally have an extremely low coefficient of friction and are chemically inert, which means that the fluoropolymer film must be treated to allow the film to adhere to a surface. By treating the film to provide a defluorinated surface layer, the surface may be functionalized so that it can be adhered to another surface. In this way, a flexible heating element and possibly further thin film layers can be attached to the defluorinated side of the fluoropolymer film.

[0018] Preferably, the defluorinated surface layer is provided by a sodium ammonia etch, using a mixture of sodium and ammonia, which provides a fast and efficient low-cost method for producing a bondable surface.

[0019] Preferably, an adhesive layer is provided on the surface of the backing film to hold the flexible heating element.

[0020] The membrane may thus include an adhesive layer provided on the surface of the PEEK backing film that contacts the heating element.

[0021] For the fluoropolymer layer, an adhesive layer is provided on the etched surface layer, the adhesive being preferably a silicone adhesive. Preferably, the heating element is supported on the defluorinated surface of the backing film and is adhesively attached to the defluorinated surface layer. In this way, the heater can be reliably fixed to the etched surface of the electrically insulating backing film in a low-cost and simple manner. In some embodiments of the present invention, the heating element can be attached by subsequent heating of the flexible electrically insulating backing film, the adhesive layer, and the positioned heating element to bond the heating element to the surface using the adhesive.

[0022] The thin film heater preferably further comprises a second flexible electrically insulating film facing the flexible electrically insulating backing film so as to at least partially encapsulate the heating element between the flexible electrically insulating backing film and the second flexible electrically insulating film. In this manner, the heating element can be insulated within a dielectric envelope to allow the heating element to be applied to a device. Preferably, the thin film heater comprises two contact points that allow connection of a power source to the heating element, for example, the contact points can be soldered to the exposed portion of the heating element through one of the electrically insulating films.

[0023] In one mode, the second flexible film overlaps the first flexible film and extends beyond the first flexible film in the rolling direction.

[0024] Preferably, the flexible heating element is a flat heating element including a heater track that follows a circuitous path covering the heating area in the plane of the heating element, and two extended contact legs for connection to a power source. The contact legs may be long enough to allow direct connection to a power source when the thin film heater is employed in a device. 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 heating area. The circuitous path may be configured to leave an open area in the heating area. The thin film heater may further include a temperature sensor that is disposed in the open area or in contact with the heating element. Preferably, the thin film heater includes a second flexible electrically insulating film that faces the flexible electrically insulating backing film to encapsulate the heater track between the flexible electrically insulating backing film and the second flexible electrically insulating film. Preferably, the heater track is encapsulated between the backing film and the second flexible film layer while leaving the contact legs exposed to allow connection to a power source. This also allows for extending a portion of the second flexible film used to attach the heating element and support the backing film against the surface. It may also allow for aligning the heating element with respect to the heating chamber by using one of the extensions, where they extend a predetermined distance beyond the heating element.

[0025] Preferably, the second flexible film is attached directly to the heating element. In this way, the heating element is sealed directly between the flexible dielectric backing film and the second flexible film such that no additional sealing layer is required. In other words, the heat shrink provides both the sealing layer and the attachment means.

[0026] Preferably, the second flexible film is attached using an adhesive provided on the surface of the flexible dielectric layer supporting the heating element. The adhesive may be, for example, a silicone adhesive. The adhesive provides a simple means of securely fixing the heating element to the backing film. The flexible dielectric backing film may include a layer of adhesive, for example it may be a polyimide film with a layer of silicone adhesive. The heating element may be attached by subsequent heating of the flexible dielectric backing film, the adhesive layer and the 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 the heating chamber.

[0027] The second flexible film overlaps the first flexible film and preferably extends beyond the first flexible film in the winding direction As a result, a thin film heater can be wound onto a heating chamber with high efficiency and high electrical insulation.

[0028] Preferably, the second flexible film is at least about twice as long as the first flexible film in the rolling direction. As a result, the thickness of the second flexible film may be kept small enough, thus facilitating the rolling action while ensuring high dielectric strength and mechanical properties.

[0029] Preferably, the second flexible film includes an alignment region that extends beyond the heating element by a predetermined distance in a direction opposite to the direction of the extended contact legs of the heater, i.e. perpendicular to the winding direction, i.e. along the length of the tubular heating chamber to which the thin film heater is attached. In particular, the second flexible film extends beyond the top edge of the heating element. In particular in an upward direction, i.e. in a direction corresponding to the upper, open end of the heating chamber as attached. By providing an alignment region that extends beyond the heating element and / or backing film by a selected distance, the alignment region can be used to position the heating region of the heater in a required location. For example, the method can further include aligning a peripheral edge of the top of the alignment region with an edge of the heating chamber, and attaching the thin film heater to the chamber with the second flexible film. In this way, the heating region is positioned at a known location along the length of the heating chamber from the edge of the chamber without having to carefully measure or adjust the heating element to precisely align the heating element. Preferably, the predetermined distance is measured from the side of the heating region opposite the contact legs to the periphery of the alignment region.

[0030] Preferably, the second flexible film includes an attachment area that extends beyond the flexible backing film. Preferably, the attachment area extends beyond the backing film in a direction that is approximately perpendicular to the direction of the rolling, i.e., the direction of the extended contact legs. In particular, the second flexible film may have a width such that the second flexible film extends beyond the heating element and the flexible dielectric backing film in one or both directions perpendicular to the direction of extension of the heater contact legs. This direction may be referred to as the rolling direction, which is the direction that is approximately perpendicular to the elongated axis of the heating chamber when the thin film heater is attached to the heating chamber. The attachment portion of the second flexible film is preferably arranged to extend around the heating chamber when attached to secure the heating element to the heating chamber.

[0031] Preferably, the attachment area of ​​the second flexible film is sufficiently expandable so that it may be wrapped circumferentially around the outer surface of the heating chamber, for example, the attachment area may extend at least a distance corresponding to the width of the heating region (i.e., the dimension perpendicular to the direction of extension of the contact legs).

[0032] The second flexible film may include a heat shrink material. By using a heat shrink material, the second flexible film may be used to attach the thin film heater to a surface of the heating chamber. More specifically, the attached layer of heat shrink film may include an attachment area that extends in a wrapping direction beyond the flexible backing film, and the attachment area may be wrapped around the outer surface of the heating chamber to hold the thin film heater against the surface. The assembly may then be heated to shrink the heat shrink film that secures the thin film heater to the surface of the heating chamber. The heat shrink film may be a tubular heat shrink film configured to sleeve over the heating chamber before being heated to shrink the tubular heat shrink film to the outer surface of the heating chamber.

[0033] In particular, the heat shrink film may preferably comprise a heat shrink tape that preferentially shrinks in one direction, such as a heat shrink polyimide tape or tube (e.g., 208x manufactured by Dunstone). The winding direction is preferably aligned with the preferential shrink direction. Alternatively, the heat shrink may comprise a heat shrink PTFE film or tube, or a PEEK film or tube. When heat shrink tubing is used, the preferential shrink direction may be at least approximately aligned with the circumference of the heat shrink tubing.

[0034] In other embodiments of the invention, the second flexible film is not a heat shrink film, but another electrically insulating film. For example, the second flexible film may include a fluoropolymer such as PTFE or PEEK. The second flexible film may be attached to a flexible backing film having the heating element therebetween. The flexible backing film and the second flexible film may form a sealed envelope that encapsulates all or a portion of the heating element.

[0035] The thin film heater may further include a third flexible film, preferably a heat shrink film, disposed on the second flexible electrically insulating film so as to at least partially overlap the second flexible electrically insulating film. For example, the backing film and the second flexible film may be disposed on either side of the heating element with the third flexible film disposed on the second flexible film. In this way, the third flexible film, preferably a heat shrink film, does not contact the heating element.

[0036] In some examples, a flexible electrically insulating backing film and a second flexible electrically insulating film may encapsulate at least a portion of the heating element, and a heat shrink film may be disposed on the backing film or the second film such that heat shrinking may be used to attach the thin film heater to a heating chamber. Both the backing film and the second film may comprise a fluoropolymer such as PTFE or PEEK, and in some examples, the backing film and the second film form a sealed electrically insulating envelope that encapsulates the heating element, and a layer of heat shrink film is attached to the electrically insulating envelope to allow the thin film heater to be attached to the heating chamber by heat shrinking.

[0037] The thin film heater may include one or more sealing layers disposed around the flexible backing film and the heating element to seal the flexible backing film and the heating element. In this manner, the backing film may be sealed to prevent emission or one or more by-products when the temperature of the film exceeds a temperature at which the material undergoes a chemical change. In some embodiments, the sealing layer may be provided by a heat shrink layer. The seal may be particularly useful when the flexible backing film is a fluoropolymer to prevent the emission of fluorine once the temperature of the fluoropolymer film exceeds a temperature at which fluorine is released.

[0038] In some examples, the layers of the thin film heater are configured to provide increased heat transfer in one direction away 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 corresponding direction toward the heating chamber during use. For example, the insulating backing film may have an increased thermal conductivity compared to the second flexible electrically insulating 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. Preferably, the side of the thin film heater configured to contact the heating chamber is configured to have a higher thermal conductivity than the opposite outside. Preferably, the sealing layer has a lower thermal conductivity than the backing film.

[0039] Preferably, the flexible electrically insulating backing film has a thickness of less than 80 μm, preferably less than 50 μm, and preferably greater than 20 μm. In this way, the fluoropolymer or PEEK film has a reduced thermal mass to allow efficient heat transfer to a heated object, such as a heating chamber, while remaining mechanically stable.

[0040] In a further aspect of the invention, there is provided an aerosol generating device comprising a thin film heater as defined in the claims and a tubular heating chamber, the thin film heater being attached to an outer surface of the heating chamber and configured to supply heat to the heating chamber. In this way, an aerosol generating device with improved properties is provided with reduced manufacturing costs compared to those using conventional thin film heaters. In particular, the heater may have improved dielectric properties and a reduced thickness and associated thermal mass to enable efficient heat transfer to the heating chamber.

[0041] Preferably, the thin film heater includes a heat shrink film facing the backing film to at least partially encapsulate the heating element between the flexible electrically insulating backing film and the heat shrink film, the heat shrink film expanding around the thin film heater and the heating chamber to attach the flexible electrically insulating backing film of the thin film heater to the outer surface of the heating chamber. By using a heat shrink material, a second flexible film can be used to attach the thin film heater to the surface of the heating chamber. More specifically, the attached layer of heat shrink film includes an attachment area that extends beyond the flexible backing film in a wrapping direction, the attachment area can be wrapped around the outer surface of the heating chamber to hold the thin film heater against the surface. The assembly can then be heated to shrink the heat shrink film that secures the thin film heater to the surface of the heating chamber. Preferably, the heat shrink film has a lower thermal conductivity than the flexible electrically insulating backing film.

[0042] In particular, the heat shrink film may include a heat shrink tape that preferentially shrinks in one direction, such as a heat shrink polyimide tape (e.g., 208x manufactured by Dunstone). By wrapping a layer of the preferential heat shrink tape around the thin film heater and securing the thin film heater to the heat chamber with the direction of the preferential heat shrink aligned with the direction of the wrap, the heat shrink layer shrinks upon heating to hold the thin film heater firmly against the heat chamber. The heat shrink film may include a heat shrink tube that is sleeved over the heat chamber and heated to shrink the heat shrink tube to secure the thin film heater to the heat chamber.

[0043] Preferably, the heating chamber includes a tubular sidewall having a sealed end and an open end, and the device is configured to allow air to flow in and out of the open end of the heating chamber such that airflow through the device is restricted to within the heating chamber. In this way, the thin film heater does not come into contact with the air entering the heating chamber such that by-products, even if released by the fluoropolymer film, cannot reach the airflow path into or out of the device if the heating temperature exceeds a maximum temperature. That is, the thin film heater is sealed within the device and separated from the airflow path.

[0044] Preferably, the aerosol generating device further comprises a power source connected to the heating element of the thin film heater and a control circuit configured to control the supply of power from the power source to the thin film heater, the power source and / or the control circuit configured to limit the maximum temperature of the thin film heater to a predefined temperature value, the predefined temperature value being preferably below the melting temperature of the electrically insulating backing film. In this way, the heating temperature is limited to the processable range of the fluoropolymer or PEEK material. Preferably, the predefined maximum temperature value is within the range of 150°C to 270°C.

[0045] For example, the maximum temperature values ​​for a particular fluoropolymer may be as shown in the table below.

[0046] [Table 1]

[0047] Preferably, the aerosol generating device further includes a sealing layer disposed around an outer surface of the thin film heater so as to seal the thin film heater between the sealing layer and the heating chamber, the sealing layer having a lower thermal conductivity than the flexible electrically insulating backing film.

[0048] In a further aspect of the invention, a method of manufacturing a thin film heater for an aerosol generating device is provided, the method comprising: providing a flexible thin film backing layer comprising a fluoropolymer; etching one side of the backing layer to provide a defluorinated surface layer; applying an adhesive to the defluorinated surface layer; and adhering a flexible heating element to the etched side of the backing layer using the adhesive.

[0049] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0050] [Figure 1] 1 shows a thin film heater according to the present invention. [Diagram 2] 1 shows a thin film heater according to the present invention including a second electrically insulating film that forms a sealed envelope that encapsulates the heating element. [Figure 3A] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 3B] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 3C] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 3D] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 3E] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 3F] 1 illustrates the assembly of a heater assembly using a thin film heater according to the present invention. [Figure 4A] 1 shows a thin film heater according to the present invention incorporating a second flexible film layer and an additional heat shrink layer. [Figure 4B] 1 shows a thin film heater according to the present invention incorporating a second flexible film layer and an additional heat shrink layer. [Figure 4C] 1 shows a thin film heater according to the present invention incorporating a second flexible film layer and an additional heat shrink layer. [Figure 4D] 1 shows a thin film heater according to the present invention incorporating a second flexible film layer and an additional heat shrink layer. [Diagram 5] 1 shows an aerosol generating device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] 1 shows a schematic of a thin film 100 including a flexible heating element 20 and a flexible electrically insulating backing film 30 supporting the heating element 20, the backing film 30 comprising a fluoropolymer or PEEK. Fluoropolymer and PEEK have a range of advantageous properties that are maintained over a wide processing temperature range, thereby allowing them to be applied as the dielectric layer in the thin film heater 100. In particular, these materials have improved electrical insulating properties over conventional materials, meaning that the thickness of the film can be reduced, reducing thermal mass and enhancing heat transfer from the heating element to the structure to be heated, such as the heating chamber of an aerosol generating device.

[0052] Fluoropolymers and PEEK are characterized by high resistance to solvents, acids and radicals, are materials with good dielectric properties and their mechanical properties are maintained over a wide temperature range. They are therefore able to handle the required elevated temperature conditions of thin film heaters, particularly when employed in aerosol generating devices where the heater is used to heat a heating chamber. Specific examples of fluoropolymers that can be employed in the flexible electrically insulating backing film of the thin film heater according to the invention are given in the table below with approximate values ​​for their associated melting points and the maximum temperature that the heater can reach. Values ​​for PEEK are also given.

[0053] [Table 2]

[0054] These values ​​mean that both these embodiments of PEEK and fluoropolymers can be used in a wide variety of applications. In particular, the materials may be employed in aerosol generating devices, such as heated devices that heat an aerosol generating substance, such as tobacco, to an elevated temperature at which the substance releases vapor without exceeding the temperature at which the substance burns. In this way, vapors can be released for inhalation that do not contain the wide range of unwanted by-products of combustion, which are known to be harmful to health. Such controlled heating devices generally have maximum operating temperatures around 150-260°C, as can be seen from the values ​​given in the table above, making these ideal materials to provide the electrically insulating backing film in such thin film heaters for these applications.

[0055] The thin film heater 100 shown in Figure 1 uses PTFE as an electrically insulating backing film, which has particularly optimal properties considering that it has a high melting point of about 327°C and can therefore be operated up to a maximum heating temperature of around 260°C. The optimum temperature for the release of vapour from tobacco is 200-260°C, therefore making the above materials ideal candidates for such applications, with PTFE and PEEK being particularly usable up to the upper end of this range where vapour release is extended.

[0056] 1, the planar heating elements 20 are provided on one surface 31 of a flexible, electrically insulating backing film 30. The flexible heating elements 20 may be etched from a layer of metal, such as stainless steel, that is first deposited on the flexible backing film 30, or alternatively, the heating elements 20 may be etched from both sides of a free-standing metal sheet to provide individual heating elements 30 (or an array of connected heating elements 30) that can then be subsequently attached to the backing film 30.

[0057] One property of fluoropolymers is that they have a very low coefficient of friction and are not as susceptible to van der Waals forces as most materials. This property, which is utilized in a wide range of applications, gives fluoropolymers non-stick and friction-reducing properties that prevent the flexible heating element in the thin film heater of the present invention from being attached to an untreated surface. Thus, one side of the flexible electrically insulating fluoropolymer backing film 30 is etched to provide a defluorinated surface layer. By treating the surface of the flexible electrically insulating backing film 30 in this manner, the surface is functionalized to allow the thin film heater to be attached, for example, by application of an adhesive (which sticks to the etched defluorinated surface layer, but not to the untreated surface of the fluoropolymer film). Etching the surface of the fluoropolymer film may be performed by a wide range of known processes, such as plasma etching or chemical etching. A particularly advantageous method is by chemical etching with sodium ammonia, which quickly and efficiently creates an adhesive surface layer.

[0058] The chemical etching process induces a reaction between fluorine molecules at the surface of the material and a sodium solution. The fluorine molecules are removed from the carbon backbone of the fluoropolymer, which leaves the carbon atoms electron deficient. Once exposed to air, hydrogen, oxygen molecules, and water vapor restore the electrons around the carbon atoms. This results in groups of organic molecules that allow adhesion to occur. An alternative is plasma treatment, where hydrogen is used as the process gas in a low pressure plasma. The hydrogen ions and radicals react with the fluorine atoms to form hydrofluoric acid, leaving unsaturated carbon bonds that provide complete links to the organic molecules of the coating material.

[0059] After the surface treatment resulting in an at least partially defluorinated surface layer, an adhesive may be applied to the surface layer and the heating element 20 may be attached with the adhesive so as to remain fixed to the etched surface layer. The adhesive is preferably a silicone adhesive and the heating element may be applied to the silicone adhesive layer that adheres the heating element to the etched defluorinated surface layer and subsequently heated.

[0060] As shown in Fig. 2, the heating element 20 comprises a heater track 21 that follows a circuitous path substantially covering a heating area 22 in the plane of the heating element 20, and two extended contact legs 23 for connecting the heating element 20 to a power source. The heating element 20 is a resistive heating element, i.e. it is configured such that when the contact legs 23 are connected to a power source and a current is passed through the heating element 20, the heating element 20 is heated by a resistance in the heater track 21. The heater track 21 is preferably formed to provide substantially uniform heating over the heating area 22. In particular, the heater track 21 is formed such that it does not include corners, has a uniform thickness and width, and the gap between adjacent portions of the heater track 21 is substantially constant in order to minimize heating rises in certain areas on the heating area 22. The heater track 21 follows a serpentine path over the heating area 22 while complying with the above criteria. The heater track 21 in the embodiment of Figure 2 splits into two parallel heater track paths 21a and 21b, each following a serpentine path over the heating area 22. The heater legs 23 may be soldered at connection points 24 allowing wiring connections to attach the heater to a PCB and power supply. Alternatively, the heating element may be fabricated with extended contact legs that may be directly connected to a PCB or power supply within the device.

[0061] As shown in FIG. 2, the heating element 20 is sealed between the flexible backing film 30 and the second flexible electrically insulating film 50 such that the heating element is sealed in an electrically insulating envelope. A portion of the legs 23 remains exposed at the solder points 24 to allow connection of the heating element to a power source. The sealing of the heating element 20 with the second flexible electrically insulating film 50 can be achieved in several different ways. In the embodiment of FIG. 2, the second flexible electrically insulating film 50 is another layer of fluoropolymer or PEEK film, and both of the opposing sides of the corresponding film are etched to allow for adhesion of the intermediate silicone adhesive and the heating element. In particular, the sealed heating element of FIG. 2 can be formed from two fluoropolymer backing films (or two PEEK backing films or one fluoropolymer and one PEEK backing film), each having a defluorinated side coated with an adhesive. The heating element 20 is then placed between opposing films and heat sealed to form the sealed thin film heater 100 shown in Figure 2. The thin film heater 100 of Figure 2 may then be attached to the outer surface of the heating chamber 60 with an additional adhesive film to hold the heating region 22 of the heating element 20 against the outer surface of the heating chamber in the appropriate location along the length of the chamber where heat is applied during use.

[0062] An alternative to the second flexible electrically insulating film 50 is shown in the attachment method of Figure 3. Here, the thin film heater 100 is not encapsulated and die cut into two layers of fluoropolymer or PEEK film to provide the heating element as shown in Figure 2, but instead a piece of heat shrink film 50 provides the second electrically insulating film, which is applied directly to the surface of the thin film heater with the heating element exposed, as shown in Figure 1. This reduces the number of layers of film between the heating element and the heating chamber, reducing thermal mass and enhancing heat transfer to the heating chamber.

[0063] FIG. 3 illustrates a method for attaching the thin film heater 100 of FIG. 1 to the heating chamber 60 using a heat shrink film 50, which allows the thin film heater 100 to be firmly and securely attached to the outer surface of the heating chamber 60. First, a second flexible film 50 is placed to encapsulate the heating area 22 of the heating element between the backing film 30 and the heat shrink film 50, while leaving the heater legs 23 exposed for later connection to a power source. In this embodiment, the heat shrink film 50 comprises a heat shrink tape that preferentially shrinks in one direction, such as a heat shrink polyimide tape (e.g., 208x manufactured by Dunstone) or, more preferably, a PEEK tape. By wrapping a layer of the preferential heat shrink tape around the thin film heater 100 with the direction of preferential heat shrink aligned with the winding direction to secure the thin film heater 100 to the heating chamber, the heat shrink layer shrinks upon heating to hold the thin film heater 100 firmly against the heating chamber 60.

[0064] The heat shrink film 50 is placed over the heating area 22 of the heating element 20 on the surface of the thin film heater 100 as shown in FIG. 3A. The heat shrink 50 is sized and positioned to extend beyond the area of ​​the flexible electrically insulating backing film 30 by a predetermined distance in directions 51 and 52. The attachment portion 51 extends beyond the heating element in a direction corresponding to the direction in which the heater assembly 100 is wrapped around the heater cup 60 (and also the preferred shrink direction of the heat shrink film 50). In particular, the heat shrink film 50 extends beyond the backing film 30 and the supported heating element 20 in a direction 51 that is approximately perpendicular to the direction in which the heating element contact legs 23 extend from the heating area 22. When wrapped around the heating chamber 60, the heating area is appropriately aligned to extend around the circumference of the heating chamber, and the extended attachment portion 51 of the heat shrink film 50 is wrapped once more around the circumference of the chamber 60 to cover the heating area 22 and secure the thin film heater to the chamber 60.

[0065] The heat shrink film 50 preferably expands sufficiently in the wrapping direction such that when the thin film heater 100 is wrapped around the heating chamber 60, the attached portion 51 expands around the circumference of the heating chamber. The adhesive on the fluoropolymer or PEEK backing film 30 may affect the shrinkage of the heat shrink film in the area where it contacts the adhesive. Thus, a sufficient expansion area 51 free of an adhesive layer should be provided that the heat shrink 50 may be wrapped around the heating chamber to ensure that it shrinks properly during heating to reliably attach the thin film heater 100 to the heating chamber 60.

[0066] The heat shrink film 50 also preferably extends upward (in a direction corresponding to the elongated axis of the heat chamber 60) beyond the heating element 20 and backing film 30 in a direction 52 opposite the extension direction of the heater contact legs to form an alignment region 52. By measuring this distance in direction 52 from the heating element to an edge of the alignment region, the alignment region can be used as a reference to properly place the heating region 22 in the correct location along the length of the heat chamber 60, if necessary. In particular, by aligning this top edge of the alignment region 52 of the heat shrink 50 with the top edge 62 of the heat chamber, the heating region 22 can be assuredly placed at the correct point along the length of the heat chamber 60 during assembly.

[0067] As shown in FIG. 3B, the thermistor 70 may be introduced between the fluoropolymer backing film 30 and the heat shrink layer 50. The thermistor 70 may be attached adjacent to the heater track 21 on the silicone adhesive layer of the backing film 30 or may be disposed on the surface of the heater track 21. The heater track 21 may be etched in a pattern such that the path followed by the heater track 21 leaves a free area 22v of the heating area 22. The thermistor 70 may be attached with its temperature sensing head disposed in this free area 22v in close proximity to the adjacent heater track 21. In this embodiment of the assembly method, the heat shrink film 50 may be disposed to leave a free end area 32 of the backing film 30 adjacent to the heating area 20. This free end area 32 is disposed on the opposite side of the heating element 20 relative to the extended attachment portion 51 of the heat shrink material 50. This adhesive end portion 32 may then be folded to secure the heat shrink layer 50 and the encapsulated thermistor 70 to the backing film 30.

[0068] Attachment of the thin film heater assembly 100 to the outer surface of the heating chamber 60 can be accomplished in several different ways. In the method shown in FIG. 3, adhesive tape 55a, 55b is attached to each side of the thin film heater assembly 100 (at each opposing peripheral edge of the heat shrink 50 in the winding direction), as shown in FIG. 3C. The thin film heater assembly 100 is then attached to the heating chamber 60 with the adhesive tape 55a adjacent to the thermistor 70, and the electrically insulating backing film 30 contacts the outer surface of the heating chamber 60 and the outwardly facing heat shrink film 50, as shown in FIG. 3D. The heating region 20 can be positioned by aligning the top side of the alignment region 52 of the electrically insulating film with the upper edge of the heating chamber 60. The thermistor 70, held between the heat shrink 60 and the backing film 30, can be aligned so that it fits within a recess 61 provided on the outer surface of the heating chamber 60. These elongated recesses 61 are provided around the circumference of the heating chamber 60 and protrude into the internal volume to enhance heat transfer to consumer goods inserted into the chamber 60 during use. By providing a thermistor 70 within such recesses 61, a more accurate indication of the internal temperature of the heating chamber 60 can be obtained.

[0069] The thin film heater assembly 100 is then wrapped around the circumference of the heating chamber 60 such that the heating area 20 is around the complete circumference of the heating chamber 60. The extended portion 51 of the heat shrink film 50 is wrapped around the heating chamber 60 to cover the heating element 20 with an additional layer on its outer surface. The extended wrapped portion 51 of the heat shrink material 50 is then attached using a second attached portion of the adhesive tape 55b. The wrapped heater assembly 110 shown in FIG. 3E is then heated to heat shrink the thin film heater 100 to the outer surface of the heating chamber 60. Finally, an additional layer of thin film 56, such as an additional fluoropolymer film or PEEK film or polyimide thin film 56, can be applied around the outer surface of the heater assembly 110. The additional layer of thin film 56 further secures the thin film heater assembly to the heating chamber and provides additional strength. It can provide several additional benefits such as sealing the backing film and providing improved insulation, as described below.

[0070] This additional film layer 56 may be a material other than a fluoropolymer, such as a polyimide, and may be used to seal the fluoropolymer film against the heating chamber. Fluoropolymers undergo chemical changes at certain elevated temperatures and may release unwanted by-products of this chemical change process that should be sealed within the device to prevent them from entering the resulting vapor to be inhaled by the user. Thus, one or more sealing layers 56 may be wrapped around the heater either before the heater is attached to the heating chamber as shown in Figures 1 and 2, or after attachment to the heating chamber to seal all of the fluoropolymer film within the sealing layer. It may be useful to select a material for the sealing layer that has a reduced thermal conductivity compared to the backing film to further insulate the heater and to facilitate heat transfer from the heating element 20 to the chamber 60. Once the outer insulating layer 56 has been applied, the assembly 110 may be heated again. This second heating step allows for further outgassing of the outer layer of the dielectric film 56 as well as the other layers. For example, in the second heating stage, the heating temperature can be increased to a higher temperature than the heat shrink stage, closer to the device operating temperature. This allows for further outgassing of, for example, silicone adhesive, which may not occur during the lower temperature heat shrink step. It may also be beneficial to expose the heat shrink to a temperature closer to the operating temperature prior to heating during the initial use of the device.

[0071] Further embodiments of a thin film heater 100 according to the present invention are shown in Figures 4A and 4B. In both of these embodiments, the heating element 20 is encapsulated between a flexible electrically insulating backing film 30 and an opposing second electrically insulating film 50. Both of these layers 30, 50 comprise either fluoropolymer or PEEK. In this case, both films 30, 50 are films with an adhesive layer on one side, and the adhesive side is adhered to the periphery of the heating element 20 to form a sealed insulating envelope around the heating element 20. In some embodiments, the second flexible film 50 and the backing film 30 may cover different amounts of the heating element 20, for example, the backing film may extend to completely cover the heating element, while the second opposing film 50 may only cover the heating area 22. In this case, however, both films cover the entire heating element 20 to completely encapsulate and insulate the heating element, and the backing film is cut to about the periphery of the heating element to provide a sealed thin film heater.

[0072] Both thin film heaters 100 of Figures 4A and 4B also include an additional third thin film 90 in the form of an additional heat shrink film 90. These embodiments therefore differ from those of Figure 3 in that the heat shrink is not applied directly to the heating element and the adhesive side of the backing film 30, but instead is attached to a sealed envelope formed by the backing film and a second PTFE or PEEK film formed around the heater such that the heat shrink 90 does not come into contact with the heating element 20.

[0073] In the case of FIG. 4A, a heat shrink film 90 is placed over the sealed thin film heater so that it extends beyond the area of ​​the second film layer 50. Heat shrink can then be used to attach the thin film to the outer surface of the heating chamber. In particular, the outer surface of the backing film 30 can be wrapped around the heating chamber 60 with the heat shrink layer 90 wrapped over the outer surface of the second thin film layer 50 and attached around the outer surface of the heating chamber 60. The thin film heater formed by the heat shrink film 90 and / or the heating element sealed between the backing film 30 and the second film 50 can first be attached with adhesive tape before the assembly is heated to shrink the heat shrink to secure the thin film heater.

[0074] In Fig. 4A, the heat shrink extends in multiple directions beyond the backing film 30 and second film 50, in other embodiments of the invention the heat shrink 90 may be placed in other ways. For example, in Fig. 4B, the heat shrink 90 is first attached with adhesive tape 35 to the edge regions of the sealed thin film heater so that it extends away from the sealed heating element 20. The sealing dielectric envelope 30, 50 sealing the heating element 20 is then attached to the heating chamber on one side (next to the thermistor 70) so that the thermistor is within an indentation as described above. The heating element and then the heat shrink 90 are then wrapped around the heating chamber 60 so that the heat shrink overlaps the sealed heating element 20 forming a circumferential layer around the thin films 30, 50 and heating element 90 before the heat shrink is applied to adhere the thin film heater 100 to the chamber 60.

[0075] The heat shrink may be arranged in any manner to attach the heating element to the chamber 60. For example, the heat shrink 90 may overlap only the top of the heating region 22 or may be spirally wrapped around the heating chamber 60. In other embodiments, multiple heat shrinks 90 are used to attach the thin film heater 100 to the heating chamber 60, such as a perimeter strip on the top of the heating element 20 and a perimeter strip on the bottom of the heating element, leaving the heater legs 23 exposed for connection to a PCB.

[0076] Once the thin film heater is attached with a layer of heat shrink 90, the heater is heated to bond the thin film heater, as shown in Figure 4C. A cross section through the prepared heater assembly is shown in Figure 4D. It can be seen that the outer heat shrink 90 does not contact the heating element 20, since the heating element 20 is encapsulated between the backing film 30 and the second facing film 50.

[0077] The additional heat shrink 90 may support the encapsulated heating element 20, with the backing film 30 and the opposing second film layer being provided by a fluoropolymer such as PTFE or PEEK, provided by a preferential heat shrink polyimide tape 90. The thickness and / or specific material may be configured to optimize heat transfer to the heating chamber 60. For example, the backing film 30 may be thinner as shown in FIG. 4D to promote heat transfer to the heating chamber, and the second film layer 50 and heat shrink 90 may be thicker to insulate the heating element 20.

[0078] The heater assembly 110, including the thin film heater 100 according to the invention wrapped around the outer surface of the heating chamber 60, can be used in several different applications. FIG. 5 shows the application of the thin film heater 100, assembled according to the method of the invention, applied in a heated aerosol generating device 200. Such a device 200 controllably heats an aerosol generating consumable 210 in the heating chamber 60 to generate vapor for inhalation without burning the consumable material. FIG. 5 shows the consumable 210 housed in the heating chamber 60 of the device 200. The heater assembly 110 of the device 200 includes a substantially cylindrical heat conducting chamber 60 having the thin film heater 100 according to the invention wrapped around its outer surface. The device further includes an outer sealing layer wrapped around the outer surface of the thin film heater, having a reduced thermal conductivity compared to the backing film to insulate the thin film heater. As mentioned above, once the outer sealing layer is attached, the assembly can be heated again closer to the operating temperature to ensure efficient outgassing takes place.

[0079] The aerosol generating device 200 of FIG. 5 also includes a power source 201 and a control circuit 202 configured to control the power supply from the power source 201 to the thin film heater 100. The power source 201 and the control circuit 202 are configured to limit the maximum temperature of the thin film heater 100 to a predefined temperature value. This predefined temperature value may be selected according to the material used and may be selected from the values ​​shown in Table 1 above. In this way, the heating temperature can be limited to an optimal temperature for releasing steam from the consumable 210 and for maintaining the backing film 30 within its processing temperature range to prevent chemical changes in the backing film 30. The aerosol generating device 200 is further preferably configured such that the airflow route F flows into the open end of the chamber and is sucked through the consumable 210 from the mouth end of the consumable. In particular, the heating chamber 60 has a closed proximal end 63 such that air must flow into and out of the open end of the heating chamber 60. In this way, even if the backing film 30 exceeds its processing temperature and potentially releases unwanted by-products of the chemical reaction process, the airflow route does not pass near the housing of the device 200 and / or the fluoropolymer backing film 30, so that these by-products do not reach the airflow route F into or out of the aerosol generating device.

[0080] The thin film 100 according to the invention provides further alternatives for backing films for thin film heaters, particularly suitable for application in aerosol generating devices. In particular, fluoropolymers and PEEK provide good mechanical and thermal properties over a wide temperature range, and provide enhanced electrical insulation properties that may reduce the thickness of the electrically insulating backing film required to ensure that the heating element 20 is insulated, thereby reducing the amount of material required to enhance heat transfer from the heating element to the consumable 210. These materials are also more resistant to tearing than conventional materials such as polyimide, thereby reducing the risk of damage during the assembly process.

[0081] As a matter of example, the PEEK film for the backing layer may be a Vitrex™ PEEK film having the following properties: Density (ISO1183): 1.3 Dielectric strength for a thickness of 50 microns (IEC60243-1): 200 kV mm -1 .

Claims

1. A thin film heater configured to be wrapped around a heating chamber of an aerosol generating device, a flexible heating element; a first flexible, electrically insulating backing film supporting the heating element, the first flexible, electrically insulating backing film comprising one or both of a fluoropolymer or polyetheretherketone (PEEK); a second flexible electrically insulating film facing the first flexible electrically insulating backing film to at least partially encapsulate the heating element between the first flexible electrically insulating backing film and the second flexible electrically insulating film; a thin film heater, wherein the second flexible electrically insulating film overlaps the first flexible electrically insulating backing film and extends beyond the first flexible electrically insulating backing film in a rolled direction.

2. The thin film heater of claim 1 , wherein the thin film heater is sufficiently flexible to allow it to be wrapped into a tubular configuration.

3. 3. The thin film heater of claim 1 or claim 2, wherein the first flexible electrically insulating backing film comprises one or more of polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE or PTFCE).

4. The thin film heater of claim 3 , wherein one side of the first flexible electrically insulating backing film includes an at least partially defluorinated surface layer.

5. 5. The thin film heater of claim 4, further comprising an adhesive layer provided on said defluorinated surface layer, said adhesive being preferably a silicone adhesive.

6. 3. The thin film heater of claim 1 or claim 2, wherein the first flexible, electrically insulating backing film comprises PEEK, and the thin film heater further comprises an adhesive layer provided on a surface of the first flexible, electrically insulating backing film comprising PEEK that contacts the heating element.

7. 6. The thin film heater of claim 5, wherein the heating element is supported on the defluorinated surface of the first flexible electrically insulating backing film and is attached to the defluorinated surface layer with the adhesive.

8. The thin film heater of any one of claims 1 to 7, wherein the second flexible electrically insulating film comprises one or both of a fluoropolymer and polyetheretherketone (PEEK).

9. The thin film heater of any one of claims 1 to 8, wherein the second flexible electrically insulating film is at least about twice the length of the first flexible electrically insulating backing film in a rolling direction.

10. The thin film heater of any one of claims 1 to 9, wherein the second flexible electrically insulating film comprises a heat shrink material.

11. 11. The thin film heater of claim 10, wherein the second flexible, electrically insulating film includes a heat shrink film disposed over the first flexible, electrically insulating backing film such that the second flexible, electrically insulating film covers the heating element and extends beyond the area of ​​the first flexible, electrically insulating backing film.

12. 10. The thin film heater of claim 1, further comprising a heat shrink film disposed on the second flexible electrically insulating film so as to at least partially overlap the second flexible electrically insulating film.

13. 13. The thin film heater of claim 1, further comprising one or more sealing layers disposed around the first flexible electrically insulating backing film and the heating element so as to seal the first flexible electrically insulating backing film and the heating element.

14. A thin film heater according to any one of the preceding claims, wherein the first flexible electrically insulating backing film has a thickness of less than 80 μm, preferably less than 50 μm.

15. 1. An aerosol generating device comprising: A thin film heater according to any one of claims 1 to 14, a tubular heating chamber, the thin film heater being wrapped around an outer surface of the heating chamber and configured to supply heat to the heating chamber; An aerosol generating device comprising:

16. the thin film heater includes a heat shrink film opposing the first flexible, electrically insulating backing film to at least partially encapsulate the heating element between the first flexible, electrically insulating backing film and the heat shrink film; 16. The aerosol generating device of claim 15, wherein the heat shrink film extends around the thin film heater and the heating chamber to adhere the first flexible electrically insulating backing film of the thin film heater to the outer surface of the heating chamber.

17. a power source connected to the heating element of the thin film heater; and a control circuit configured to control a supply of power from the power source to the thin film heater; 17. The aerosol generating device of claim 15 or 16, wherein the power supply and / or control circuit is configured to limit the maximum temperature of the thin film heater to a predefined temperature value below the melting temperature of the first flexible electrically insulating backing film.

18. 18. The aerosol generating device according to any one of claims 15 to 17, further comprising a sealing layer disposed around an outer surface of the thin film heater so as to seal the thin film heater between the sealing layer and the heating chamber, the sealing layer having a lower thermal conductivity than the first flexible electrically insulating backing film.

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