Patent Application
20220322498
The present invention relates to a heater assembly, more particularly a heater assembly incorporating a thin film heater for an aerosol generating device.
Thin film heaters are used for a wide range of applications which generally require a flexible, low profile heater which can conform to a surface or object to be heated. One such application is within the field of aerosol generating devices such as reduced risk nicotine delivery products, including e-cigarettes and tobacco vapour products. Such devices heat an aerosol generating substance within a heating chamber to produce a vapour. One means to heat the consumable is to use a heater assembly comprising a thin film heater which conforms to a surface of a heating chamber to ensure efficient heating of an aerosol-generating substance within the chamber.
Thin film heaters generally comprise a resistance heating element enclosed in a sealed envelope of flexible dielectric thin film with contact points to the heating element for connection to a power source. These conventional thin film heaters, formed of a planar heating element sealed within an insulating thin film envelope, must then be attached to a surface to be heated. In the context of aerosol generating devices, this involves attaching the thin film heater to the outer surface of a heating chamber to form a heater assembly so as to transfer heat to an aerosol generating consumable placed within the chamber. This is generally achieved by attaching the thin film heater with an adhesive or other fastening means to hold the thin film heater against the heating chamber during use. Other techniques use additional pieces of thin film to wrap around the heater assembly to hold the thin film heater against the heating chamber. The thin film heater must then be connected to a power source when assembled in the device.
Often the temperature of such thin film heaters needs to be carefully monitored when employed in a device, for example to provide feedback to control circuitry to adjust the heater to a required heating temperature or to prevent the heating temperature exceeding a selected maximum temperature. For example, in the case of a controlled temperature aerosol generating device, the temperature must be carefully monitored and controlled to maintain the temperature of the heating chamber within a prescribed operating window to deliver efficient vapour delivery, without exceeding a temperature at which a consumable might burn.
One issue with known thin film heaters and heater assemblies is that conventional means for detecting the heating temperature lack the required level of accuracy and reliability. Known methods include mounting a temperature sensor within the device in proximity to the sealed dielectric envelope of the thin film heater or using monitored parameters of the heating element such as current, voltage and resistance to infer the heating temperature. These known methods are limited in the precision and accuracy with which they can measure the true temperature within a heating chamber. Furthermore the attaching of a heat sensor through known methods adds additional complexity to the assembly procedure, it is difficult to reproducibly position the temperature sensor in the same position across devices and the sensor can come loose or move during use of the device. Inferring the heating temperature using measured properties of the heater lacks precision due to inconsistencies in heater geometry and properties and the method requires more complex configuration of the hardware and software components.
The present invention aims to make progress in addressing these issues to provide an improved heater assembly for an aerosol generating device.
According to a first aspect of the invention, there is provided a heater assembly for an aerosol generating device comprising: a flexible heating element; a temperature sensor; and a flexible dielectric backing film with an adhesive on a surface of the flexible dielectric backing film, wherein the temperature sensor and the flexible heating element are supported adjacent to each other on the adhesive on the surface of the flexible backing film. With the heater assembly according to the present invention, the temperature sensor is incorporated into the thin film heater and positioned close to the heating element to provide a more precise measure of the heating temperature. The assembly process is also simplified by using the adhesive surface of the dielectric backing film to secure both the temperature sensor and the heating element.
The term “dielectric” used to define the backing film is intended to be interpreted broadly as meaning “electrically insulating”. Preferably the flexible dielectric backing film has a thickness of less than 80 μm preferably less than 50 μm, and preferably a thickness of greater than 20 μm. The flexible dielectric backing film may comprise one or more of a fluoropolymer (such as PTFE), PEEK or polyimide.
The temperature sensor may be any known type of temperature sensor configured to sense the local temperature, where the sensed temperature can be provided as a signal to a PCB to monitor and/or control the heater. For example the temperature sensor may incorporate one or more of: a thermistor, a thermocouple, a resistance thermometer, a silicon bandgap temperature sensor, an integrated circuit sensor.
The adhesive may be for example a silicon adhesive. The adhesive provides a straightforward means of reliably securing the heating element and temperature sensor to the backing film. The flexible dielectric backing film may comprise a layer of adhesive, for example the film may comprise a fluoropolymer such as PTFE, PEEK or polyimide film with a layer of Si adhesive.
The assembled dielectric backing film, heating element and temperature sensor may be referred to as a thin film heater assembly or subassembly. When the thin film heater subassembly is attached to a heating chamber, this subassembly is referred to as a heating chamber subassembly. The term heater assembly applies to both of these subassemblies.
Preferably the heater assembly further comprises a second flexible dielectric film which opposes the flexible dielectric backing film to at least partially enclose the heating element; wherein at least a portion of the temperature sensor is positioned between the flexible dielectric backing film and the second flexible film. In this way, the temperature sensor is held within the dielectric envelope next to the heating element to provide an improved temperature reading. This simplifies the manufacturing process as the thin film heater subassembly (including the flexible heating element, temperature sensor, flexible dielectric backing film and second flexible dielectric film) may be handled as a complete integral subassembly in which the relative position of the heating element and temperature sensor is fixed, rather than requiring independent installation of the thin film heater and temperature sensor.
Preferably the second flexible film comprises a layer of heat shrink material which opposes the flexible backing film. In this way, the number of thin film heater layers is reduced, since the layer of heat shrink film provides both the function of sealing the heating element and temperature sensor with the flexible backing film and also the means of attaching the heating element to a heating chamber. Therefore the thermal mass of the heater assembly is reduced and the efficiency of heat transfer is enhanced. Furthermore, a secure attachment is provided by the heat shrink film in a simplified method in which sealing of the heating element and attachment may be carried out simultaneously. Heat shrinking provides a reliable close contact between the thin film heater and heating chamber to ensure effective heat transfer. The method further allows the heater to be placed accurately at the desired position on a heating chamber before heating to shrink the film and attach the heater at that position.
Preferably the layer of heat shrink film is attached directly against the heating element. In this way, the heating element is sealed directly between the flexible dielectric backing film and the layer of heat shrink such that an additional sealing layer is not required. In other words the heat shrink provides both a sealing layer and means of attachment. Preferably the layer of attached heat shrink film comprises an alignment region which extends beyond the heating element by a predetermined distance in a direction opposite to the direction of the extending contact legs. The alignment region can be used to position the heating area of the heater at the required position by aligning a top, marginal edge of the alignment region with an end of the heating chamber and attaching the thin film heater to the chamber using the heat shrink film. In this way, the heating area and temperature sensor are positioned at a known location along the length of the heating chamber from the end of the chamber.
Preferably the layer of attached heat shrink film comprises an attachment region which extends beyond the flexible backing film a direction approximately perpendicular to the direction of the extending contact legs. The attachment portion of the heat shrink is preferably arranged to extend around the heating chamber when attached to secure the heating element to the heating chamber. Preferably the attachment region of the heat shrink may extend sufficiently such that it can circumferentially wrap around an outer surface of the heating chamber. The attachment region may be in the form of a tubular portion of heat shrink which is sleeved around the heating chamber. For example, the heating element and supporting backing film may be wrapped into a tube and sleeved within the heat shrink. The tubular heat shrink and tubular thin film heater within may then be sleeved onto a heating chamber.
The heat shrink film may comprise one or more of polyimide, a fluoropolymer such as PTFE and PEEK. The heat shrink film is preferably a preferential heat shrink film arranged to shrink preferentially in one direction. For example the heat shrink film may be polyimide 208x tape manufactured by Dunstone. The heat shrink film may be in the form of an initially planar layer, i.e. a piece of heat tape arranged to be wrapped around the heating chamber or it may be in the form of a tube arranged to be passed around (i.e. sleeved on) a heating chamber and heated to shrink it to the surface of a heating chamber.
Preferably the flexible backing film comprises an edge region which is folded over on itself or over the second flexible film to at least partially enclose the temperature sensor within the fold. In this way, the temperature sensor is secured in position next to the heating element within the fold. The second flexible dielectric film may be attached first, with the edge region subsequently folded over to seal a peripheral edge of the dielectric backing film and second dielectric film and/or attach the second dielectric film to the flexible backing film. The edge region may be folded without the second dielectric film layer present to directly contact the temperature sensor and secure it within the fold. The edge region of the backing film may comprise a hole arranged to expose a portion of the temperature sensor when folded over onto the temperature sensor.
Preferably the temperature sensor comprises a temperature sensor head and electrical connections arranged to transport signals from the sensor head. Preferably the temperature sensor head is enclosed between flexible backing film and the second flexible film. In this way the sensor head is secured in a desired fixed position relative to the heating element while the temperature sensor connections remain free for connection to a PCB.
In some examples, the temperature sensor comprises a temperature sensor head and electrical connections arranged to transport signals from the sensor head; wherein the flexible backing film comprises an opening or a through-hole in the flexible backing film and temperature sensor is positioned such that the temperature sensor head lies on the opening or through-hole and is exposed through the flexible dielectric backing film. In this way, when the thin film heater assembly is wrapped around a heating chamber, the temperature sensor head may directly contact the surface of the heating chamber through the hole, thereby providing a direct measurement of the heating chamber, without any intervening insulating layers.
Preferably the heating element is a planar heating element comprising a heater track which follows a circuitous path over a heating area within the plane of the heating element and two contact legs for connection to a power source, the contact legs extending away from the heater track in the plane of the heating element; wherein at least the heating area of the heating element is enclosed between the flexible dielectric backing film and the second flexible thin film. Preferably the heater track is configured to provide substantially uniform heating over the heating area. The heater track path may be a serpentine or meandering path over the heating area and the heater track may have a substantially uniform width and thickness. Preferably the second opposing dielectric film, for example the layer of heat shrink film, encloses the heater track between the backing film and the opposing film layer, leaving the contact legs exposed. In this way the heater track is electrically insulated between the dielectric backing film and the heat shrink film whilst the contact legs are exposed such that they can be connected to a power source.
The contact legs may be sufficiently long to allow direct connection to a power source when the thin film heater is employed in the device. For example the length of the contact legs may be substantially equal or greater than one or both of the dimensions defining the heating area.
Preferably, the circuitous heater track path is shaped so as to leave a vacant region on the flexible dielectric backing film, unoccupied by the heating element; wherein the temperature sensor is held by the adhesive in the vacant region of the flexible backing film. This allows the temperature sensor to be fixed in close proximity to the heating element, within the heating area, so as to provide a more accurate measurement of the heating temperature.
Preferably the temperature sensor comprises a temperature sensor head and elongated electrical connections, the elongated electrical connections oriented substantially in the same direction as the contact legs of the heating element. This simplifies the process of connecting the heater legs and sensor connections to a PCB. In particular, the temperature sensor may be arranged such that the connection wires lie adjacent to the extended contact legs of the heater element when assembled in a device to allow for mutual support and/or ease of connection to a PCB.
In a further example, the flexible dielectric backing film comprises a first piece of film which supports the flexible heating element and a second piece of film which supports the temperature sensor, the first piece of film attached to the second piece of film. In particular the first piece of dielectric film and second piece of dielectric film may together be considered the flexible dielectric backing film. The first piece of flexible dielectric backing film may form a sealed dielectric envelop with an opposing second dielectric film which together seals the heating element. The second piece of dielectric film may be connected, for example by an adhesive surface, and support the temperature sensor. In this example, the heating element is sealed within an envelope of insulating thin film whereas the temperature sensor remains exposed such that it may be directly in contact with the heating chamber when assembled in a device. The second piece of flexible dielectric film may be provided by a piece of adhesive tape which is attached to a peripheral edge of the sealed dielectric envelop enclosing the heating element.
Preferably the flexible dielectric backing film comprises one or more of polyimide, a fluoropolymer such as PTFE and PEEK. The backing film may comprise a polyimide film with a layer of Si adhesive. When the backing film comprises a fluoropolymer it may comprise an at least partially defluorinated surface layer, formed for example by a surface treatment such as plasma and/or chemical etching. This allows for an adhesive to be applied to the treated surface which otherwise would not adhere given the extremely low friction surfaces provided by fluoropolymers.
The flexible heating element, the temperature sensor and the flexible dielectric backing film may together be referred to as a thin film heater subassembly, wherein the heater assembly further comprises: a heating chamber; and the thin film heater subassembly is wrapped around a surface of the tubular chamber with the temperature sensor held adjacent to the heating chamber. Preferably the thin film heater subassembly is wrapped around the heating chamber with the backing film against the outer surface of the hating chamber.
The heating chamber is preferably a tubular heating chamber, open at one or both ends to accept a consumable. The circumference of the heating chamber preferably closely matches the width of the heating element (the length in a direction perpendicular to the contact legs) such that the heating element provides one complete circumferential loop around the chamber. The heating chamber preferably comprises one or more indentations on an outer surface of the heating chamber where the indentations are preferably a plurality of elongate indentations running along a portion of the length of the heating chamber, periodically arranged around the circumference. The indentations therefore may provide longitudinal ridges running along a portion of the length of the internal surface of the heating chamber, configured to engage a consumable when inserted into the chamber to enhance heat transfer to the consumable.
Preferably thin film heater is wrapped around the heating chamber such that at least part of the temperature sensor is positioned within an indentation. In this way, a more accurate reading of the temperature within the heating chamber may be obtained.
In a further aspect of the invention there is provided an aerosol generating device comprising a heater assembly as set out in the claims. Preferably the aerosol generating device comprises control circuitry configured to receive a temperature measurement from the temperature sensor and control the power provided to the heating element.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Since the thin film heater subassembly 10 includes a temperature sensor 70 positioned directly adjacent to the flexible heating element 20 on the same surface of the flexible dielectric backing film, the temperature sensor 70 provides a highly accurate reading of the heating temperature provided by the heating element 20 and therefore can allow for accurate temperature control when the thin film heater subassembly is employed in an aerosol generating device or other heating device. This makes improvements over known devices in which the temperature sensor is generally separate from the heating element rather than being directly incorporated in the heater assembly 10.
The heating element is a planar heating element 20 including a heater track 21 which follows a circuitous path over a heating area 22 within the plane of the heating element 20. The heating element has two contact legs 23 allowing for connection to a power source, the contact legs 23 extending away from the heater track 21 in the plane of the heating element 20. The heater track is preferably shaped so as to provide substantially uniform heating over the heating area 22. In particular, the heater track is shaped such that it contains no sharp corners and has a uniform thickness and width, with the gaps between neighbouring parts of the heater track 22 being substantially constant to minimise increased heating at specific points within the heating area 22. The heater track 21 in the example of
The heating element 20 may be etched from a thin metal sheet of around 50 μm, for example a sheet of stainless steel such as 18SR or SUS304, although other materials and heater thicknesses may be selected depending on the application. The specific metal and thickness of the metal sheet are selected such that the resulting heating element 20 is flexible so that it can deform with the supporting flexible thin film 30 in order to conform to the shape of a surface to be heated. The metal sheet may be deposited initially on the surface flexible dielectric backing film 30, before being etched whilst supported on the film to form the heater track 21 pattern. Alternatively, the heating element 20 may be etched from a metal sheet independently of the flexible dielectric backing film 30. For example a free standing metal foil may be chemically etched from both sides in order to provide one or more connected heating elements 20 which are subsequently detached and positioned on the surface of a dielectric backing film 30.
The heater track 22 is preferably shaped so as to leave a vacant region 22v within the heating area 22, as most clearly shown in
The flexible dielectric backing film 30 must have suitable properties to provide a flexible substrate to support and electrically insulate the heating element 20. Appropriate materials include polyimide, PEEK and fluoropolymers such as PTFE. In this example the heating element comprises a heater track pattern 21 etched from a layer of 50 μm stainless steel 18SR which is supported on a single sided polyimide/Si adhesive film comprising a 25 μm polyimide film with a 37 μm silicon adhesive layer. The heating element 20 is supported on the adhesive to allow the heating element to be attached to the backing film 30. The heater assembly 10 of
In the example of
The thin film heater subassembly 10 as shown in
The thin film heater subassembly 10 may take a number of different forms, with the positioning of the temperature sensor 70 and the attaching of the heater subassembly 10 to the heating chamber 60 achieved in a number of different ways within the scope of the present invention.
As with conventional thin film heaters, the dielectric layers may be heat sealed to form a sealed insulating envelope, enclosing the heating element 20. The difference in the present case being that the sensor head 71 and a portion of the temperature sensor connections 72 are sealed within the dielectric envelope together with the heating element 20. The sealed dielectric envelope may be cut to trim the dielectric films closer to the parameter of the heating element 20 to provide a thin film heater 10 as shown in
The second part of the flexible dielectric backing film 30′ may be attached to an edge portion so as to extend the first backing film part 30 into the vacant region 22v provided by the curved path of the heater track 21. The sensor head 71 is therefore positioned in close proximity to the heating element 20 to read the heating temperature with increased accuracy. Furthermore, since the temperature sensor 70 is not sealed within the dielectric envelope 30, 31 but exposed on a surface of the dielectric backing film 30′, when the thin film heater 10 is attached to the outer surface of a heating chamber 60 the temperature sensor head 71 may be held in direct contact with the surface of the heater chamber 60 to provide a more accurate reading of the heater chamber temperature.
The thin film heaters 10 shown in
The heating chamber 60 is a tubular heating chamber arranged to accept a consumable to be heated in order to generate a vapour to be inhaled by a user. The heating chamber 60 preferably has one or more indentations 61 on an outer surface which provide internal protrusions which assist with the positioning and heat transfer to a consumable received within the chamber 60. The circumference of the heating chamber 60 preferably closely matches the width of the heating element 20 (the length in a direction perpendicular to the direction of extension of the contact legs) such that the heating element provides one complete circumferential loop around the chamber 60. In other examples the heater element might be sized to wrap more than once around the circumference of the heating chamber, i.e. the heating element may be sized so as to provide an integral number of circumferential loops around the heating chamber so as not to produce any variation in the heating temperature around the circumference of the heating chamber. The thin film heater assembly 100 is positioned and attached such that the temperature sensor head 71 lies within an indentation 61 on the outer surface on the heating chamber 60 to provide a more accurate reading of the internal temperature of the heating chamber 60.
After attaching the first edge of the thin film heater subassembly 10 to the surface of the heating chamber, the thin film heater is wrapped around the outer surface of the heating chamber 60 with the extending piece of heat shrink film 50 wrapping around the heating chamber and over the flexible dielectric backing film 30 and heating element 20 before being secured with adhesive tape 35 to the outer surface of the heating chamber 60. In this way, a heating chamber subassembly 100 is provided as shown in
As described above, using a strip of heat shrink tape 50 provides an efficient means of securely fastening the thin film heater 10 to a heating chamber 60.
In
The heat shrink 50 is larger than the backing film 30 and heating element 20 such that it extends beyond the heating element 20 by predetermined distance in two orthogonal directions 51, 52. This alignment of the heat shrink 50 relative to the heating element 20 allows for the later alignment of the heating area 20 relative to the heating chamber 60. Therefore, careful control of the size of these extending portions of the heat shrink 51, 52 at this stage allows for the heater assembly 100 to be attached to a heating chamber 60 in a straightforward manner to provide precise alignment. The heat shrink 50 extends beyond the heating area 20 in a direction opposite to the contact legs 23 to provide an alignment region 52 of the heat shrink 50. This alignment region 52 can be aligned with the top edge of a heating chamber 60 such that the heating area 20 is positioned at a position along the length of the heating chamber corresponding to the predetermined length 52 of the alignment region from the top edge of the heater track 21. In this way, the heater element 20 can be provided at a correct position along the heating chamber 60.
The heat shrink 50 also has an attachment region 51 which extends past the heater track 21 and backing film 30 in a direction perpendicular to the direction of extension of the contact legs 23 to provide an attachment region 51. The direction of extension of the attachment region 51 may be referred to as the “wrapping direction” since this portion of the heat shrink 50 allows for it to be wrapped around a tubular heating chamber 60 and subsequently heat shrunk to provide the required tight connection. Similarly, the direction opposite to the heater legs 23 in the direction that the alignment region 52 extends from the heating element 20 may be referred to as the upward or alignment direction which corresponds with the elongate axis of the heating chamber 60, directed towards the top open end. These extension distances 51, 52 may be configured by cutting the heat shrink 50 to the correct dimensions either before or after attaching to the surface of the dielectric backing film 30.
As shown in
In the method of
The thin film heater assembly 10 is initially attached to the heating chamber using the adhesive tape 35a neighbouring the thermistor 70. The heating chamber 60 is as described above, having one or more indentations 61 on an outer surface which provide internal protrusions which assist with the positioning and heat transfer to a consumable received within the chamber 60. The thin film heater assembly 10 is positioned and attached such that the temperature sensor head 71 lies within an indentation 61 on the outer surface on the heating chamber 60. In this way the temperature sensor 70 provides a more accurate reading of the internal temperature of the heating chamber 60.
Once attached with first adhesive tape portion 35a, the thin film heater assembly 100 is then rolled around the heating chamber 60 with the extended attachment portion 51 of the heat shrink 50 wrapping circumferentially around the chamber 60 to cover the heating element 20 again before being attached by the second piece of attachment tape 35b to provide the heater chamber subassembly 100 shown in
As can be seen in
Finally, although not essential, a final layer of dielectric film 36 may be added around the outside of the heating element to complete the heater chamber subassembly. This final dielectric layer may be for example a further layer of adhesive polyimide such as 1 inch polyimide tape with 25 micrometre polyimide and 37 micrometres silicon adhesive. This outer layer of dielectric film 36 provides a further layer of insulation and further secures the attachment of the thin film heater 10 to the heating chamber 60. The thickness and/or material of the backing film 30, heat shrink 50 and final insulating layer 36 may be selected to enhance heat transfer to the heating chamber, for example with lower thermal conductivity layers provided outside the heating element (i.e. for the heat shrink 50 and insulating layer 36 in this example) and a higher thermal conductivity layer provided as the backing film 30. The thermistor 70 of this example is only separated from the heating chamber 60 by the thin backing film, which has high thermal conductivity, allowing an accurate reading of the temperature of the chamber.
As discussed above, one of the advantages of using an exposed temperature sensor (such as in
In
As with the thin film heater subassembly 10 of
As clear from
The thin film heater subassembly 10 of
The heat shrink 50 may then aligned relative to the thin film heater 10 using a positioning fixture, as shown in
Once the heat shrink 50 is correctly positioned, the remaining peripheral edge region 32 of the backing film 30 which is left free by the positioning of the heat shrink 50 is folded over on top of the heat shrink as shown in
Once the thin film heater subassembly 10 is attached to the heating chamber 60, the resulting heater chamber subassembly 100 can then be employed in a heating device, such as an aerosol generating device, by connecting the thermistor connections 72 and the heated contact legs 23 to a PCB and power source. An aerosol generating device incorporating the thin film heater 10 and heater assembly 100 of the present invention has significant advantages in performance compared to known devices. In particular, because the temperature sensor 70 is positioned in close proximity to the heating element 20 and the heating chamber 60, the heating temperature may be measured with increased precision. In turn this allows for a more precise control of the heating temperature of the device, which is particularly beneficial in the context of controlled temperature aerosol generating devices where a specific heating temperature must be maintained to provide efficient aerosol generation without burning the aerosol generating substance or exceeding the working temperature range of the device components. The heater assembly according to the present invention is also easier to assemble, requires fewer parts and, since the temperature sensor is incorporated within the thin film heater, ensures the temperature sensor is maintained at the correct position throughout the lifetime of the device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19196025.1 | Sep 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/074149 | 8/28/2020 | WO |
