WO2023070255A1

WO2023070255A1 - Method of forming a tubular heater

Info

Publication number: WO2023070255A1
Application number: PCT/CN2021/126042
Authority: WO
Inventors: Qian Wang
Original assignee: Philip Morris Products S.A.
Priority date: 2021-10-25
Filing date: 2021-10-25
Publication date: 2023-05-04

Abstract

A method of forming a tubular heater (6) for an aerosol-generating system, the method comprising: providing a thermally conductive tube (61); providing a flexible heating element (62); at least partially circumscribing the thermally conductive tube (61) with the flexible heating element (62); clamping the flexible heating element (61) to the thermally conductive tube (61) with a clamp fixture (300); and heating the clamped thermally conductive tube (61) and flexible heating element (62).

Description

METHOD OF FORMING A TUBULAR HEATER

The present disclosure relates to a method of forming a tubular heater for an aerosol-generating system. More particularly, the present disclosure relates to a method of forming a tubular heater for an aerosol-generating system.

It is known to provide an aerosol-generating device for generating an inhalable aerosol. Such devices may heat an aerosol-forming substrate to a temperature at which one or more components of the aerosol-forming substrate are volatilised without burning the aerosol-forming substrate. The vapour generated from the heated aerosol-forming substrate forms an aerosol when being cooled down before reaching the mouth of a user. The aerosol-forming substrate may be provided as part of an aerosol-forming article. The aerosol-forming article may have a rod shape for insertion of the aerosol-generating article into a cavity of the aerosol-generating device. A tubular heater may be arranged around the cavity for heating the aerosol-forming substrate once the aerosol-forming article has been inserted into the cavity of the aerosol-generating device. The tubular heater may comprise a resistive heating element or an induction heating element, such as a susceptor.

It would be desirable to provide a tubular heater for an aerosol-generating device that is robust and straightforward to manufacture.

According to the present disclosure, there is provided a method of forming a tubular heater for an aerosol-generating system. The method may comprise providing a thermally conductive tube. The method may further comprise providing a flexible heating element. The method may further comprise at least partially circumscribing the thermally conductive tube with the flexible heating element. The method may further comprise clamping the flexible heating element to the thermally conductive tube with a clamp fixture. The method may further comprise heating the thermally conductive tube, flexible heating element, and clamp fixture.

Advantageously, heating the thermally conductive tube and flexible heating element while the thermally conductive tube and the flexible heating element are clamped together by the clamp fixture may secure the flexible heating element to the thermally conductive tube. In some preferred embodiments, heating the thermally conductive tube and flexible heating element while the thermally conductive tube and the flexible heating element are clamped together by the clamp fixture may secure the flexible heating element to the thermally conductive tube by thermocompression. In preferred embodiments, an adhesive is provided between the thermally conductive tube and the flexible heating element, and heating the thermally conductive tube and flexible heating element while the thermally conductive tube and the flexible heating element are clamped together by the clamp fixture activates the adhesive to secure the flexible heating element to the thermally conductive tube.

Advantageously, a tubular heater formed by this method is compact and efficient, as the flexible heating element is in close proximity to the thermally conductive tube. Advantageously, a tubular heater formed by this method is robust, as the flexible heating element is strongly bonded to the thermally conductive tube. Advantageously, a tubular heater formed by this method facilitates homogeneous heating of the aerosol-forming substrate received in the tubular heater, as the thermally conductive tube distributes heat from the flexible heater evenly around an aerosol-forming substrate received in the tubular heater.

The tubular heater comprises a thermally conductive tube. The thermally conductive tube may be formed from any suitable thermally conductive material. As used herein, the term “thermally conductive” refers to a material having a bulk thermal conductivity of greater than about 10 Watts per metre Kelvin (W/ (m·K) ) at 23 degrees Celsius and a relative humidity of 50 percent as measured using the modified transient plane source (MTPS) method. Preferably, the thermally conductive tube comprises a metal. In some preferred embodiments, the thermally conductive tube comprises a stainless steel, such as SAE 304.

The thermally conductive tube may be open at one end for receiving an aerosol-forming substrate. Preferably, the thermally conductive tube is open at both ends. The thermally conductive tube may have any suitable cross-sectional shape. For example, the thermally conductive tube may have a circular, elliptical, triangular or rectangular cross-sectional shape. Preferably, the thermally conductive tube has a circular cross-sectional shape. Preferably, the thermally conductive tube is sized to receive an aerosol-forming substrate, such as an end of a rod shaped aerosol-generating article. The thermally conductive tube may have any suitable thickness. For example, the thermally conductive tube may have a thickness of between about 50 micrometres and about 200 millimetres, and preferably has a thickness of about 100 micrometres.

The tubular heater further comprises a flexible heating element. As used herein, the term “flexible” is used to mean that the heating element may, at 23 degrees Celsius, be bent or rolled to conform substantially to the shape of the tubular heating element. For example, the flexible heating element may be rolled into a tube.

The flexible heating element at least partially circumscribes the thermally conductive tube. In some preferred embodiments, the flexible heating element circumscribes the thermally conductive tube. The thermally conductive tube and the flexible heating element may form coaxially aligned tubes. The thermally conductive tube may be received inside the flexible heating element when the flexible heating element is rolled into a tube.

In some preferred embodiments, the flexible heating element comprises an electrically insulative substrate. As used herein, the term “electrically insulative” refers to a material having a volume resistivity at 20 degrees Celsius (℃) of greater than about 1 x10^6 Ohm meters (Ωm) , typically between about 1 x 10^9 Ohm meters (Ωm) and about 1 x 10^21 Ohm meters (Ωm) .

The electrically insulative substrate may be formed from any suitable electrically insulative material. The electrically insulative substrate may be formed from any suitable material that is able to tolerate high temperatures, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. The electrically insulative material may be a dielectric material. The electrically insulative substrate may comprise a polymer. In some preferred embodiments, the electrically insulative substrate comprises polyimide. The electrically insulative substrate may consist of polyimide. The electrically insulative substrate may comprise a polyimide film, such as

Preferably, the electrically insulative substrate is flexible. The flexible electrically insulative substrate may, at 23 degrees Celsius, be bent or rolled to conform substantially to the shape of the tubular heating element.

Preferably, the electrically insulative substrate is thermally insulative. As used herein, the term “thermally insulative” refers to a material having a bulk thermal conductivity of less than about 6 Watts per metre Kelvin (W/ (m·K) ) at 23 degrees Celsius and a relative humidity of 50%as measured using the modified transient plane source (MTPS) method.

The electrically insulative substrate may have any suitable thickness. For example, the electrically insulative substrate may have a thickness of between about 15 micrometres and 50 micrometres, or between about 20 micrometres and about 30 micrometres. Preferably, the electrically insulative substrate has a thickness of about 25 micrometres.

In some preferred embodiments, the flexible heating element comprises an electrically conductive track. As used herein, the term “electrically conductive” refers to a material having a volume resistivity at 20℃ of less than about 1 x 10^-5 Ohm meters (Ωm) , typically between about 1 x 10^-5 Ohm meters (Ωm) and about 1 x 10^-9 Ohm meters (Ωm) .

The electrically conductive track may be formed from any suitable electrically conductive material. For example, the electrically conductive track may comprise at least one of copper, gold, platinum and stainless steel, such as SAE 304. The electrically conductive track may comprise conductive inks. Where the electrically conductive track comprises an electrically conductive ink, the electrically conductive track may be printed on the electrically insulative substrate. Suitable conductive inks may include silver to provide electrical conductivity.

In some preferred embodiments, the electrically insulative substrate comprises a first electrically insulative substrate and a second electrically insulative substrate. In these preferred embodiments, the electrically conductive track may be arranged between the first electrically insulative substrate and the second electrically insulative substrate.

The electrically conductive track may form a resistive heating track. The resistive heating track may act as an electrically resistive heater.

In some embodiments, the electrically conductive track comprises a single track. In other embodiments, the electrically conductive track comprises at least two electrically conductive tracks.

The electrically conductive track may have any suitable thickness. For example, the electrically conductive track may have a thickness of between about 20 micrometres and about 60 micrometres, or between about 30 micrometres and about 50 micrometres. Preferably, the electrically conductive track has a thickness of about 40 micrometres.

In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated to a temperature sufficient to directly bond the thermally conductive tube and the flexible heating element. Such bonding may result from the simultaneous application of pressure and heat, resulting in thermocompression bonding.

In some preferred embodiments, an adhesive is provided between the thermally conductive tube and the flexible heating element. Heating the thermally conductive tube and flexible heating element while the thermally conductive tube and the flexible heating element are clamped together by the clamp fixture may activate the adhesive. Any suitable adhesive may be used. The adhesive may be any suitable adhesive that is able to tolerate high temperatures once cured, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. The adhesive may be a thermoset adhesive. As used herein, a thermoset adhesive is an adhesive that irreversibly hardens after an application of heat and pressure. The adhesive may comprise an epoxy resin. The adhesive may comprise an acrylic resin. The adhesive may comprise polyimide.

The adhesive may have any suitable thickness. For example, the adhesive may have a thickness of between about 3 micrometres and about 10 micrometres. Preferably the adhesive has a thickness of about 5 micrometres.

In some embodiments, the adhesive may be applied to the thermally conductive tube. In some embodiments, the adhesive may be applied to the flexible heating element.

In some preferred embodiments, in which the flexible heating element comprises an electrically insulative substrate comprising a first electrically insulative substrate, a second electrically insulative substrate, and an electrically conductive track arranged between the first electrically insulative substrate and the second electrically insulative substrate, an adhesive may be provided between the first electrically insulative substrate and the second electrically insulative substrate. The adhesive may be any suitable adhesive that is able to tolerate high temperatures once cured, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. The adhesive may be a thermoset adhesive. The adhesive may comprise an epoxy resin. The adhesive may comprise an acrylic resin. The adhesive may comprise polyimide.

In some embodiments, the adhesive between the thermally conductive tube and the flexible heating element may be the same as the adhesive between the first electrically insulative substrate and the second electrically insulative substrate. In some embodiments, the adhesive between the thermally conductive tube and the flexible heating element may be different to the adhesive between the first electrically insulative substrate and the second electrically insulative substrate.

The thermally conductive tube, flexible heating element, and optional adhesive, are clamped together by a clamp fixture. In some embodiments, the clamping force is no greater than 50 Newtons, 100 Newtons, 150 Newtons, 200 Newtons or 250 Newtons. Preferably, the clamping force is no greater than 200 Newtons. Advantageously, limiting the clamping force reduces the likelihood of the clamping damaging the thermally conductive tube. Advantageously, limiting the clamping force may reduce the likelihood of pressing adhesive out from between the thermally conductive tube and flexible heating element during clamping.

Preferably, the clamping fixture is configured to provide a uniform clamping force around the surface of the thermally conductive tube and the flexible heating element.

Preferably, the clamp fixture comprises a nonstick coating. The clamp fixture may comprise a friction reducing coating. For example, the clamp fixture may comprises a coating of polytetrafluoroethylene (PTFE) . Providing a nonstick, or friction reducing coating on the clamp fixture may reduce the likelihood of the flexible heating element being damaged during heating.

The method comprises heating the clamped thermally conductive tube and flexible heating element. The heating may be performed at any suitable temperature, and for any suitable duration of time, to enable the flexible heating element to bond with the thermally conductive tube.

In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of at least 250 degrees Celsius, at least 300 degrees Celsius or at least 360 degrees Celsius. In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of between about 250 degrees Celsius and about 400 degrees Celsius. In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of 380 degrees Celsius or within five degrees Celsius of 380 degrees Celsius.

In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of at least 250 degrees Celsius, at least 300 degrees Celsius or at least 360 degrees Celsius for at least 5 minutes. In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of between about 250 degrees Celsius and about 400 degrees Celsius for between about 5 minutes and about 20 minutes. In some embodiments, the clamped thermally conductive tube and flexible heating element may be heated at a temperature of 380 degrees Celsius or within five degrees Celsius of 380 degrees Celsius for between 10 and 15 minutes.

After heating, the clamped thermally conductive tube and flexible heating element may be cooled before the clamp fixture is removed. the clamped thermally conductive tube and flexible heating element may be cooled at any suitable temperature and for any suitable duration of time.

In some embodiments, after heating the clamped thermally conductive tube and flexible heating element, the clamped thermally conductive tube and flexible heating element are cooled at room temperature.

In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of at least about 160 degrees Celsius. In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of between about 160 degrees Celsius and about 240 degrees Celsius. In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of 200 degrees Celsius or within five degrees Celsius of 200 degrees Celsius.

In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of at least about 160 degrees Celsius for at least 1 minute. In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of between about 160 degrees Celsius and about 240 degrees Celsius for between about 1 minute and about 5 minutes. In some preferred embodiments, the clamped thermally conductive tube and flexible heating element are cooled at a temperature of 200 degrees Celsius or within five degrees Celsius of 200 degrees Celsius for about 3 minutes.

After heating the clamped thermally conductive tube and flexible heating element, the clamp fixture may be removed from the thermally conductive tube and flexible heating element, and a temperature sensor provided. The method may comprise, after heating the clamped thermally conductive tube and flexible heating element: removing the clamp fixture from the thermally conductive tube and flexible heating element; providing a temperature sensor; positioning the temperature sensor on one of the thermally conductive tube and the flexible heating element with a positioning fixture; and securing the temperature sensor to at least one of the thermally conductive tube and the flexible heating element. Advantageously, providing a temperature sensor on the thermally conductive tube or the flexible heating element may enable the tubular heater to provide accurate feedback to an aerosol-generating device of the temperature of the tubular heater during use.

The temperature sensor may be secured to at least one of the thermally conductive tube and the flexible heating element by any suitable means. In some preferred embodiments, the temperature sensor is welded to at least one of the thermally conductive tube and the flexible heating element. In some particularly preferred embodiments, the temperature sensor is welded to at least one of the thermally conductive tube and the flexible heating element by resistance welding.

The temperature sensor may be any suitable temperature sensor that is able to tolerate high temperatures, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. In some preferred embodiments, the temperature sensor is a resistance thermometer. In some particularly preferred embodiments, the temperature sensor is a platinum resistance temperature detector, such as a PT100 or a PT1000.

In some embodiments, an electrically conductive track is provided for electrical connection to the temperature sensor. In some preferred embodiments, an electrically conductive track is provided on the flexible heating element for electrical connection to the temperature sensor.

Where the flexible heating element comprises an electrically insulative substrate and an electrically conductive track, the flexible heating element may comprise a first electrically conductive track and a second electrically conductive track. The first electrically conductive track may be arranged on a first side of the electrically insulative substrate, and the second electrically conductive track may be arranged on a second side of the electrically insulative substrate, opposite the first side. The first electrically conductive track may act as a resistive heating element and the second electrically conductive track may be for electrical connection to the temperature sensor.

Where the flexible heating element comprises a first electrically insulative substrate, a second electrically insulative substrate, and an electrically conductive track arranged between the first and second electrically insulative substrates, the electrically conductive track arranged between the first and second electrically insulative substrates may be a first electrically conductive track, and the flexible heater may comprise a second electrically conductive track arranged on an outer surface of the second electrically insulative substrate. The first electrically conductive track may act as a resistive heating element and the second electrically conductive track may be for electrical connection to the temperature sensor.

In some embodiments, an electrically insulative substrate may be arranged at least partially over the electrically conductive track for electrical connection to the temperature sensor. Advantageously, positioning an electrically insulative substrate at least partially over the electrically conductive track for electrical connection to the temperature sensor may help to protect the electrically conductive track from being damaged during heating of the clamped thermally conductive tube and flexible heating element.

The electrically insulative substrate arranged at least partially over the electrically conductive track for electrical connection to the temperature sensor may be formed from any suitable electrically insulative material. The electrically insulative substrate may be formed from any suitable material that is able to tolerate high temperatures, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. The electrically insulative material may be a dielectric material. The electrically insulative substrate may comprise a polymer. In some preferred embodiments, the electrically insulative substrate comprises polyimide. The electrically insulative substrate may consist of polyimide. The electrically insulative substrate may comprise a polyimide film, such as

In some embodiments, an adhesive may be arranged between the electrically conductive track for electrical connection to the temperature sensor and the electrically insulative substrate arranged at least partially over the electrically conductive track for electrical connection to the temperature sensor. The adhesive may be any suitable adhesive that is able to tolerate high temperatures once cured, such as temperatures in the range of between 150 degrees Celsius to 250 degrees Celsius, or in the range of between 250 degrees Celsius to 350 degrees Celsius. The adhesive may be a thermoset adhesive. The adhesive may comprise an epoxy resin. The adhesive may comprise an acrylic resin. The adhesive may comprise polyimide.

In some embodiments, the adhesive between the electrically conductive track for electrical connection to the temperature sensor and the electrically insulative substrate arranged at least partially over the electrically conductive track for electrical connection to the temperature sensor may be the same as the adhesive between the first electrically insulative substrate and the second electrically insulative substrate. In some embodiments, the adhesive between the electrically conductive track for electrical connection to the temperature sensor and the electrically insulative substrate arranged at least partially over the electrically conductive track for electrical connection to the temperature sensor may be different to the adhesive between the first electrically insulative substrate and the second electrically insulative substrate.

In some embodiments, the flexible heating element may comprise one or more electrical contacts. The electrical contacts may be arranged at the periphery of the flexible heating element. The electrical contacts may extend away from the thermally conductive tube. The electrical contacts may provide contact points for wires to electrically connect the tubular heater to other electrical components of an aerosol-generating device. In these embodiments, the method may further comprise: providing one or more wires; positioning the one or more wires on each of the one or more electrical contacts of the flexible heating element; and securing the one or more wires to the one or more electrical contacts of the flexible heating element.

The one or more wires may be secured to the one or more electrical contacts of the flexible heating element by welding. In particular, the one or more wires may be secured to the one or more electrical contacts of the flexible heating element by resistance welding or laser welding.

The one or more wires may be secured to the one or more contact points of the flexible heating element at any suitable point in the method of forming the tubular heater. For example, the one or more wires may be secured to the one or more contact points before the temperature sensor is secured to at least one of the thermally conductive tube and the flexible heating element. In preferred embodiments, the one or more wires are secured to the one or more contact points of the flexible heating element after the temperature sensor is secured to at least one of the thermally conductive tube and the flexible heating element.

After securing the temperature sensor to at least one of the thermally conductive tube and the flexible heating element, the method may further comprise: providing a heat-shrinkable sleeve configured to reduce in size when heated; inserting the thermally conductive tube, the flexible heating element and the temperature sensor into the heat-shrinkable sleeve; and heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve.

The heat-shrinkable sleeve may be formed from any suitable material that enables the sleeve to reduce in size when heated. In some embodiments, the heat-shrinkable sleeve comprises a polymer. In some particularly preferred embodiments, the heat-shrinkable sleeve comprises polyether ether ketone (PEEK) .

Preferably, the heat-shrinkable sleeve is heated to a suitable temperature and for a suitable duration of time for the heat-shrinkable sleeve to reduce in size. Providing the heat-shrinkable sleeve over the thermally conductive tube, the flexible heating element and the temperature sensor, and heating so that the heat-shrinkable sleeve reduces in size, may cause the heat-shrinkable sleeve to compress the temperature sensor against at least one of the thermally conductive tube and the flexible heating element. Advantageously, this may improve the accuracy of the temperature readings from the temperature sensor, and ensure that the temperature sensor is robustly held against at least one of the thermally conductive tube and the flexible heating element.

In some preferred embodiments, the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve are heated at a temperature of at least 300 degrees Celsius. In some preferred embodiments, the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve are heated at a temperature of between about 300 degrees Celsius and 400 degrees Celsius. 340 degrees Celsius or within 5 degrees Celsius of 340 degrees Celsius.

In some preferred embodiments, the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve are heated at a temperature of at least 300 degrees Celsius for at least 5 seconds. In some preferred embodiments, the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve are heated at a temperature of between about 300 degrees Celsius and 400 degrees Celsius for between about 5 seconds and about 15 seconds. In some preferred embodiments, the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve are heated at a temperature of 340 degrees Celsius or within 5 degrees Celsius of 340 degrees Celsius for between 8 seconds and 10 seconds.

According to the present disclosure, there is also provided a tubular heater formed by the method described above.

In particularly preferred embodiments, a tubular heater according to the disclosure comprises a thermally conductive tube; a flexible heating element at least partially circumscribing the thermally conductive tube; a temperature sensor secured to at least one of the thermally conductive tube and the flexible heating element; and a heat-shrinkable tube circumscribing the thermally conductive tube, the flexible heating element and the temperature sensor.

Examples in accordance with the aspects of the disclosure will be now be described with reference to the accompany drawings, in which:

Figure 1 is a schematic cross-sectional view showing the interior of an aerosol-generating device 100 and an aerosol-generating article 200 received within the aerosol-generating device 100;

Figure 2 is a schematic exploded view of a tubular heater according to the present disclosure for use in a system as shown in Figure 1;

Figure 3 is a side view of the tubular heater of Figure 2;

Figure 4 is a cross-sectional view showing the interior layers of the tubular heater of Figure 1;

Figure 5 is a diagrammatic representation of the interior layers of the tubular heater of Figure 1;

Figure 6 is a diagrammatic representation of the interior layers of an alternative tubular heater according to the present disclosure;

Figure 7 is a diagrammatic representation of the interior layers of an alternative tubular heater according to the present disclosure;

Figure 8 is a schematic view of a clamp fixture for use in a method according to the present disclosure in an open position; and

Figure 9 is a schematic view of the clamp fixture of Figure 8 in a closed position.

Figure 1 is a schematic cross-sectional view showing the interior of an aerosol-generating device 100 and an aerosol-generating article 200 received within the aerosol-generating device 100. Together, the aerosol-generating device 100 and aerosol-generating article 200 form an aerosol-generating system. In Figure 1, the aerosol-generating device 100 is shown in a simplified manner. In particular, the elements of the aerosol-generating device 100 are not drawn to scale. Furthermore, elements that are not relevant for the understanding of the aerosol-generating device 100 have been omitted.

The aerosol-generating device 100 comprises a housing 102 containing a tubular heater 6, a power supply 103 and control circuitry 105. In Figure 1, the bottom heater casing part 2, heater mount 8 and top heater casing part 4 are shown. The power supply 103 is a battery and, in this example, it is a rechargeable lithium ion battery. The control circuitry 105 is connected to both the power supply 103 and the heating element and controls the supply of electrical energy from the power supply 103 to the heater to regulate the temperature of the heater.

The housing 102 comprises an opening 104 at a proximal or mouth end of the aerosol-generating device 100 through which an aerosol-generating article 200 is received. The opening 104 is connected to the opening 12 in the heater module 1, through which aerosol exits the heater module 1. However, it will be appreciated that aerosol largely exits the heater module 1 and the aerosol-generating device 100 via the aerosol-generating article 200. The housing 102 further comprises an air inlet 106 at a distal end of the aerosol-generating device 100. The air inlet 106 is connected to the air inlet arranged at a distal end of the first tubular section 2b of the bottom casing part 2. The first tubular section 2b delivers air from the air inlet 106 to the aerosol-generating article.

The aerosol-generating article 200 comprises an end plug 202, an aerosol-forming substrate 204, a hollow tube 206, and a mouthpiece filter 208. Each of the aforementioned components of the aerosol-generating article 100 is a substantially cylindrical element, each having substantially the same diameter. The components are arranged sequentially in abutting coaxial alignment and are circumscribed by an outer paper wrapper 210 to form a cylindrical rod. The aerosol-forming substrate 204 is a tobacco rod or plug comprising a gathered sheet of crimped homogenised tobacco material circumscribed by a wrapper (not shown) . The crimped sheet of homogenised tobacco material comprises glycerine as an aerosol-former. The end plug 202 and mouthpiece filter 208 are formed from cellulose acetate fibres.

A distal end of the aerosol-generating article 200 is inserted into the aerosol-generating device 100 via the opening 104 in the housing 102 and pushed into the aerosol-generating device 100 until it engages a stop (not shown in Figure 1) arranged on the heater mount 8, at which point it is fully inserted. The stop helps to correctly locate the aerosol-forming substrate 204 within the heater so that the heater can heat the aerosol-forming substrate 204 to form an aerosol.

The aerosol-generating device 100 may further comprise: a sensor (not shown) for detecting the presence of the aerosol-generating article 200; a user interface (not shown) such as a button for activating the heater; and a display or indicator (not shown) for presenting information to a user, for example, remaining battery power, heating status and error messages.

In use, a user inserts an aerosol-generating article 200 into the aerosol-generating device 100, as shown in Figure 1. The user then starts a heating cycle by activating the aerosol-generating device 100, for example, by pressing a switch to turn the device on. In response, the control circuitry 105 controls a supply of electrical power from the power supply 103 to the heater to heat the heater. During a heating cycle, the heater is heated to a predefined temperature, or to a range of predefined temperatures according to a temperature profile. A heating cycle may last for around 6 minutes. The heat from the heater 6 is transferred to the aerosol-forming substrate 204 which releases volatile compounds from the aerosol-forming substrate 204. The volatile compounds form an aerosol within an aerosolisation chamber formed by the hollow tube 206. During a heating cycle, the user places the mouthpiece filter 208 of the aerosol-generating article 200 between the lips of their mouth and takes a puff or inhales on the mouthpiece filter 208. The generated aerosol is then drawn through the mouthpiece filter 102 into the mouth of the user.

Figure 2 shows an exploded view of a tubular heater 6 that is suitable for use in the aerosol-generating device 100 of Figure 1. The tubular heater 6 comprises a thermally conductive tube 61 having a circular cross-section and two open ends. The thermally conductive tube 61 is formed from a 100 micrometre thick sheet of SAE 304 stainless steel. The tubular heater 6 further comprises a flexible heating element 62, which comprises a serpentine electrically conductive track 63 arranged between a first electrically insulative substrate 64 and a second electrically insulative substrate 64. The electrically conductive track 63 is formed from 40 micrometre thick SAE 304 stainless steel. The first and second electrically

insulative substrates

64, 65 are formed from 25 micrometre thick polyimide

film. A further broken electrically conductive track 66 is provided on an outer surface of the second electrically insulative substrate 65, on the opposite side to the electrically conductive track 63. The further broken electrically conductive track 66 is for electrical connection of a temperature sensor 67, which in this embodiment is a PT1000 platinum resistance detector. Four electrical contacts 68 extend from the flexible heating element 62 for electrical connection of the tubular heater to other electrical components of an aerosol-generating device. Two of the electrical contacts 68 are electrically connected to the electrically conductive track 66 for powering the flexible heating element 62. The other two electrical contacts 68 are connected to opposite ends of the broken electrically conductive track 66, for electrical connection to the temperature sensor 67. The tubular heater further comprises a heat-shrinkable sleeve 69, which fits over the thermally conductive tube 61 and flexible heater 62. The heat-shrinkable sleeve 69 reduces in size when heated, and compresses the temperature sensor 67 against the second electrically insulative substrate 65 of the flexible heating element 62 to ensure that the temperature sensor 67 is held closely against the flexible heating element 62, and in a robust way that is unlikely to dislodge in normal use. In this embodiment, the heat-shrinkable sleeve is formed from PEEK, and is configured to reduce in diameter from about 10 millimetres before heating to about 8.5 millimetres after heating.

A layer of adhesive (not shown in Figure 2) is provided between the thermally conductive tube 61 and the first electrically insulative substrate 64. In this embodiment, the adhesive is a thermoset adhesive that requires heat and pressure to form a strong bond.

Another layer of adhesive (also not shown in Figure 2) is provided between the electrically conductive track 63 and the second electrically insulative substrate 65. In this embodiment, both adhesive layers are formed from the same adhesive, and have a thickness of about 5 micrometres. It will be appreciated that in other embodiments different adhesives may be used.

Figure 3 shows the tubular heater 6 of Figure 2 in an assembled form, ready for connection to an aerosol-generating device.

Figure 4 shows a cross-sectional view of the tubular heater of Figure 1, taken though the temperature sensor 68, showing the interior layers forming the tubular heater 6. Figure 5 shows a diagrammatic representation of the interior layers of the tubular heater of Figure 1. As shown in Figures 4 and 5, the tubular heater 6 of Figures 2 and 3 comprises the following layers, starting from the inner layer and moving to the outer layer: the thermally conductive tube 61, a layer of adhesive 70, the first electrically insulative substrate 64, the electrically conductive track 63, a further layer of adhesive 70, the second electrically insulative substrate 65, the temperature sensor 67 and broken electrically conductive track 66, and the heat-shrinkable sleeve 69.

Figure 6 shows a diagrammatic representation of the interior layers of an alternative tubular heater to that shown in Figures 2 to 5. The tubular heater 6 of Figure 6 is substantially similar to the tubular heater 6 of Figures 2 to 5, and like reference numerals represent like features. The only difference between the tubular heater 6 of Figure 6 compared to the tubular heater 6 of Figures 2 to 5 is that the tubular heater 6 of Figure 6 comprises an additional layer of adhesive 70 between the second electrically insulating substrate 64 and the broken electrical track 66.

Figure 7 shows a diagrammatic representation of the interior layers of an alternative tubular heater to that shown in Figures 2 to 5, and the tubular heater 6 of Figure 6. The tubular heater 6 of Figure 7 is substantially similar to the tubular heater 6 of Figures 2 to 5, and the tubular heater 6 of Figure 6, and like reference numerals represent like features. The only difference between the tubular heater 6 of Figure 7 compared to the tubular heater 6 of Figure 6 is that the tubular heater 6 of Figure 7comprises a third electrically insulative substrate 71 over the broken electrically conductive track 66, and the third electrically insulative substrate comprises apertures or holes for receiving the temperature sensor 67.

The tubular heaters 6 described above with references to Figures 2 to 5 was formed by the following method:

1. providing the thermally conductive tube 61;

2. providing the flexible heating element 62;

3. fully circumscribing the thermally conductive tube 61 with the flexible heating element 62;

4. clamping the flexible heating element 62 to the thermally conductive tube 61 with a clamp fixture 300, as shown in Figures 8 and 9;

5. heating the clamped thermally conductive tube 61 and flexible heating element 62 at a temperature of 380 degrees Celsius (±5 degrees Celsius) for 12 minutes in a tunnel over with a conveyor configured to move the clamped thermally conductive tube 61 and flexible heating element 62 from one end of the tunnel oven to the other;

6. cooling the clamped thermally conductive tube 61 and flexible heating element 62 at a temperature of 200 degrees Celsius (±5 degrees Celsius) for about 3 in another tunnel over with a conveyor configured to move the clamped thermally conductive tube 61 and flexible heating element 62 from one end of the tunnel oven to the other;

7. cooling the clamped thermally conductive tube 61 and flexible heating element 62 to room temperature (around 23 degrees Celsius) ;

8. removing the thermally conductive tube 61 and flexible heating element 62 from the clamp fixture 300;

9. inspecting the thermally conductive tube 61 and flexible heating element 62 and testing the resistance of the electrically conductive track 63, which in this embodiment should be about 1 Ohm (±2 percent) ;

10. providing the temperature sensor 67;

11. positioning the temperature sensor 67 on the flexible heating element 62 with a positioning fixture (not shown) and aligning the broken electrical track 66 with the temperature sensor 67 such that the temperature sensor 67 electrically connects to the broken electrical track 66;

12. securing the temperature sensor 67 to the flexible heating element 62 by resistance welding or laser welding;

13. remove the thermally conductive tube 61, flexible heating element 62, and temperature sensor 67 from the positioning fixture;

14. test the resistance of the temperature sensor 67;

15. providing one or more wires;

16. positioning the one or more wires (not shown) on each of the one or more electrical contacts 68 of the flexible heating element 62 with another positioning fixture;

17. securing the one or more wires to the one or more electrical contacts 68 of the flexible heating element 62 by resistance welding or laser welding;

18. remove the thermally conductive tube 61, flexible heating element 62, temperature sensor 67, and wires from the positioning fixture;

19. inspect the thermally conductive tube 61, flexible heating element 62, temperature sensor 67, and wires;

20. providing the heat-shrinkable sleeve 69;

21. inserting the thermally conductive tube 61, the flexible heating element 62 and the temperature sensor 67 into the heat-shrinkable sleeve 69;

22. heating the thermally conductive tube 61, the flexible heating element 62, the temperature sensor 67, and the heat-shrinkable sleeve 69 at a temperature of 340 degrees Celsius (±5 degrees Celsius) for between 8 seconds and 10 seconds; and

23. inspect the completed tubular heater 6.

It will be appreciated that some steps in this method are not essential for forming the tubular heater 6, and some additional or alternative steps may be required to provide a tubular heater according to a different embodiment of the disclosure. It will also be appreciated that some of the steps in this method may be conducted in a different order, or simultaneously. For example, in some embodiments some of the inspection steps may be combined.

Regarding the step of clamping the flexible heating element 62 to the thermally conductive tube 61 with a clamp fixture 300, as shown in Figures 8 and 9, the clamp fixture 300 comprises a spindle 301, onto which the thermally conductive tube 61 is received, and a pair of

jaws

302, 303. The

jaws

302, 303, are arrangeable together in a closed position, as shown in Figure 9, in which the

jaws

302, 303 define a cavity with a shape that is complementary to the thermally conductive tube 61, but with a slightly larger diameter. Each

jaw

302, 303 defines half of the cavity. The

jaws

302, 303 are separable from each other, as shown in Figure 8, into an open position. In the open position, the flexible heating element 62 may be arranged across the half of the cavity defined by the jaw 301. The spindle 301 and thermally conductive tube 61 may then be pressed into the half of the cavity defined by the jaw 301, deforming a portion of the flexible heating element 62 around a portion of the thermally conductive tube 61. The remaining portions of the flexible heating element 62 may then be bend around the remaining portion of the thermally conductive tube 61, and the jaw 302 placed over the jaw 303 to move the clamp fixture 300 into the closed position, and clamp the flexible heating element 62 to the thermally conductive tube 61. The

jaws

302, 303 may be secured in the closed position by various means, including torque screws which may be used to vary the clamping force on the flexible heating element 62 to the thermally conductive tube 61. The clamping force on the flexible heating element 62 to the thermally conductive tube 61 is maintained at 200 Newtons or less to reduce the likelihood of the clamp damaging the thermally conductive tube.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about" . Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In this context, therefore, a number A is understood as A ± 5 percent (5%) of A. Within this context, a number A may be considered to include numerical values that are within general standard error for the measurement of the property that the number A modifies. The number A, in some instances as used in the appended claims, may deviate by the percentages enumerated above provided that the amount by which A deviates does not materially affect the basic and novel characteristic (s) of the claimed invention. Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

Claims

A method of forming a tubular heater for an aerosol-generating system, the method comprising:

providing a thermally conductive tube;

providing a flexible heating element;

at least partially circumscribing the thermally conductive tube with the flexible heating element;

clamping the flexible heating element to the thermally conductive tube with a clamp fixture; and

heating the clamped thermally conductive tube and flexible heating element.
A method according to claim 1, wherein the flexible heating element comprises an electrically insulative substrate and an electrically conductive track.
A method according to claim 2, wherein the electrically insulative substrate comprises a first electrically insulative substrate and a second electrically insulative substrate, and wherein the electrically conductive track is arranged between the first electrically insulative substrate and the second electrically insulative substrate.
A method according to claim 2 or claim 3, wherein the electrically insulative substrate comprises a polymer, and optionally the electrically insulative substrate comprises polyimide.
A method according to any one of claims 1 to 4, further comprising providing an adhesive between the thermally conductive tube and the flexible heating element.
A method according to claim 5, wherein the method further comprises applying the adhesive to the thermally conductive tube.
A method according to claim 5, wherein the method further comprises applying the adhesive to the flexible heating element.
A method according to any one of claims 1 to 7, wherein the thermally conductive tube comprises stainless steel, such as SAE 304.
A method according to any one of claims 1 to 8, wherein the clamping comprises clamping the flexible heating element to the thermally conductive tube with a force no greater than 200 Newtons.
A method according to any one of claims 1 to 9, wherein the clamp fixture comprises a coating of polytetrafluoroethylene (PTFE) .
A method according to any one of claims 1 to 10, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature of at least 360 degrees Celsius.
A method according to any one of claims 1 to 11, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature between about 360 degrees Celsius and about 400 degrees Celsius.
A method according to any one of claims 1 to 12, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature of 380 degrees Celsius or within five degrees Celsius of 380 degrees Celsius.
A method according to any one of claims 1 to 13, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature of at least 360 degrees Celsius for at least 5 minutes.
A method according to any one of claims 1 to 14, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature between about 360 degrees Celsius and about 400 degrees Celsius for between about 5 minutes and about 20 minutes.
A method according to any one of claims 1 to 15, wherein the heating comprises heating the clamped thermally conductive tube and flexible heating element at a temperature of 380 degrees Celsius or within five degrees Celsius of 380 degrees Celsius for between 10 and 15 minutes.
A method according to any one of claims 1 to 16, further comprising, after heating the clamped thermally conductive tube and flexible heating element, cooling the clamped thermally conductive tube and flexible heating element.
A method according to claim 17, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of at least about 160 degrees Celsius.
A method according to claim 17 or claim 18, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of between about 160 degrees Celsius and about 240 degrees Celsius.
A method according to any one of claims 17 to 19, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of 200 degrees Celsius or within five degrees Celsius of 200 degrees Celsius.
A method according to any one of claims 17 to 20, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of at least about 160 degrees Celsius for at least 1 minute.
A method according to claim 17 or claim 21, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of between about 160 degrees Celsius and about 240 degrees Celsius for between about 1 minute and about 5 minutes.
A method according to any one of claims 17 to 22, wherein the cooling comprises cooling the clamped thermally conductive tube and flexible heating element at a temperature of 200 degrees Celsius or within five degrees Celsius of 200 degrees Celsius for about 3 minutes.
A method according to any one of claims 1 to 23, further comprising, after heating the clamped thermally conductive tube and flexible heating element:

removing the clamp fixture from the thermally conductive tube and flexible heating element; providing a temperature sensor;

positioning the temperature sensor on one of the thermally conductive tube and the flexible heating element with a positioning fixture; and

securing the temperature sensor to at least one of the thermally conductive tube and the flexible heating element.
A method according to claim 24, wherein the securing comprises welding the temperature sensor to at least one of the thermally conductive tube and the flexible heating element.
A method according to claim 25, wherein the securing comprises resistance welding or laser welding the temperature sensor to at least one of the thermally conductive tube and the flexible heating element.
A method according to any one of claims 24 to 26, wherein the temperature sensor is a resistance thermometer.
A method according to any one of claims 24 to 27, wherein:

the flexible heating element comprises one or more electrical contacts; and

the method further comprises, after securing the temperature sensor to at least one of the thermally conductive tube and the flexible heating element:

providing one or more wires;

positioning the one or more wires on each of the one or more electrical contacts of the flexible heating element; and

securing the one or more wires to the one or more electrical contacts of the flexible heating element.
A method according to claim 28, wherein the securing the one or more wires to the one or more electrical contacts of the flexible heating element comprises welding the one or more wires to the one or more electrical contacts of the flexible heating element.
A method according to claim 28, wherein the securing the one or more wires to the one or more electrical contacts of the flexible heating element comprises resistance welding the one or more wires to the one or more electrical contacts of the flexible heating element.
A method according to any one of claims 24 to 30, further comprising, after securing the temperature sensor to at least one of the thermally conductive tube and the flexible heating element:

providing a heat-shrinkable sleeve configured to reduce in size when heated;

inserting the thermally conductive tube, the flexible heating element and the temperature sensor into the heat-shrinkable sleeve; and

heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve.
A method according to claim 31, wherein the heat-shrinkable sleeve comprises a polymer, such as polyether ether ketone (PEEK) .
A method according to claim 31 or claim 32, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of at least 300 degrees Celsius.
A method according to any one of claims 31 to 33, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of between about 300 degrees Celsius and 400 degrees Celsius.
A method according to any one of claims 31 to 34, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of 340 degrees Celsius or within 5 degrees Celsius of 340 degrees Celsius.
A method according to any one of claims 31 to 35, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of at least 300 degrees Celsius for at least 5 seconds.
A method according to any one of claims 31 to 36, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of between about 300 degrees Celsius and 400 degrees Celsius for between about 5 seconds and about 15 seconds.
A method according to any one of claims 31 to 37, wherein the heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve comprises heating the thermally conductive tube, the flexible heating element, the temperature sensor, and the heat-shrinkable sleeve at a temperature of 340 degrees Celsius or within 5 degrees Celsius of 340 degrees Celsius for between 8 seconds and 10 seconds.
A tubular heater formed by the method of any one of claims 1 to 38.
A tubular heater comprising:

a thermally conductive tube;

a flexible heating element at least partially circumscribing the thermally conductive tube;

a temperature sensor secured to at least one of the thermally conductive tube and the flexible heating element; and

a heat-shrinkable tube circumscribing the thermally conductive tube, the flexible heating element and the temperature sensor.