FIELD OF THE INVENTION

The invention relates to an aerosol generating article for producing an aerosol for inhalation by a user.

BACKGROUND

Aerosol generating devices have become popular as alternatives to traditional combustible tobacco products. Heated tobacco products, also referred to as heat- not-burn products, are one class of aerosol generating device that are configured to heat a tobacco substrate to a temperature that is sufficient to produce an aerosol from the substrate but is not so high that the tobacco combusts. Although this specification makes reference to heated tobacco products in particular, it will be appreciated that the discussion that follows applies equally to aerosol generating systems that incorporate other kinds of heatable substrate.

In some heated tobacco products, the tobacco substrate is provided as a separate article that is loaded into the aerosol generating device, which contains apparatus for heating the article. For example, the aerosol generating device may have an oven compartment into which the article is loaded, or could include an electromagnetic coil that inductively heats one or more susceptors inside the article. This arrangement provides advantages over, for example, disposable devices, since it minimises waste (as the only waste is the spent articles) and only requires the user to carry a single, reusable device. However, safety concerns arise when a user attempts to ignite the separate aerosol generating article (using a lighter, for example) rather than using the article in its intended manner in a heated tobacco device.

Another limitation associated with current heated tobacco systems is that the user may begin drawing on the device before the substrate reaches its intended operating temperature. This can diminish the user’s experience since it may result in the user receiving the aerosol at an insufficient rate or with unsatisfactory qualities, for example composition and temperature.

There is a need for an aerosol generating system that overcomes these problems.

SUMMARY OF THE INVENTION

A first aspect of the invention provides an aerosol generating article comprising: an airflow channel; a substrate for generating an aerosol, wherein the substrate is disposed inside the airflow channel; a valve disposed inside the airflow channel, the valve having an open state and a closed state, wherein the valve is configured to restrict air flow through the airflow channel when in the closed state relative to when in the open state, and wherein the valve comprises a shape memory alloy arranged such that the valve changes from the closed state to the open state when heated to a transition temperature of the shape memory alloy.

Shape memory alloys are a class of alloy that can be plastically deformed at low temperatures, but revert to their original form when heated to a transition temperature, which is particular to each material. Nickel-titanium and copper- aluminium-nickel are examples of shape memory alloys.

As the article is heated, the temperature of both the substrate and the valve increases. Until the shape memory alloy material reaches the transition temperature, the valve remains in the closed state and prevents airflow through the article; and when the shape memory allow material reaches the transition temperature, the valve opens, allowing the user to consume the aerosol by drawing air through the airflow channel. This arrangement prevents the user from igniting the article, since while the valve is in the closed state, air cannot flow through the airflow channel that contains the substrate, preventing sustained combustion of the substrate. It also prevents the generated aerosol being released from inside the airflow channel until the article reaches the transition temperature, so the valve can be configured to prevent the user from extracting the aerosol until the article is near or at its optimum operating temperature. The choice of a shape memory alloy as the material of the valve is particularly advantageous due to the fact that the shape of the valve transitions sharply at the transition temperature. This ensures that the airflow chamber remains closed while the article is being heated and then rapidly opens once the valve reaches its transition temperature. By contrast, valves whose operation relies on thermal expansion (for example bimetal valves) change form much more gradually as the temperature varies. This is a result of the fact that the rate of thermal expansion of most materials suitable for this purpose (for example copper and aluminium) is relatively constant across the range of temperatures at which articles of this kind are typically used. Valves that rely on thermal expansion thus have a tendency to open gradually, which can result in the valve permitting airflow through the channel before the substrate is at the required temperature. This can reduce the quality of the generated vapour that the user receives and diminish the user’s experience by restricting airflow through the channel while the valve is in the partially open state. The provision of a shape memory alloy valve in accordance with the present invention overcomes these limitations thanks to the fact that the shape memory alloy valve does not begin to open until it is at the transition temperature, but once at this temperature rapidly switches to its fully open position, which quickly allows the maximum rate of airflow through the channel to be achieved.

The aerosol-generating article may be a single-use aerosol generating article. In other words, the aerosol-generating article may be disposable. This means that once the substrate has been consumed (e.g. by use in an aerosol generating device, examples of which will be described below), the article is intended to be discarded and replaced.

The substrate is preferably a solid substrate. For example, the substrate could have the form of a solid stick or pellet comprising tobacco.

The airflow channel is preferably defined by a shell. In general, the shell may be any structure capable of defining an airflow channel and containing the substrate and valve in the manner defined above. The shell could be made of paper, card, or a suitable polymer material, for example. The airflow channel is preferably linear in shape, for example cylindrical. This allows the substrate, valve and any other components inside the airflow channel to be arranged in a linear manner. The cylindrical shape could be defined by the shape of the shell described above, if provided.

Preferably the shape memory alloy is configured to be in a first form when the valve is in the closed state and to be in a second form when the valve is in the open state, and the shape memory alloy is arranged such that when heated to the transition temperature while in the first form, the shape memory alloy transitions from the first form to the second form so as to change the valve from the closed state to the open state. The operation of the valve is thus controlled by the action of the shape memory alloy as it changes from one form to the other.

In preferred implementations, the valve comprises: a flap arranged to substantially close the airflow channel when the valve is in the closed state; and an actuating portion that comprises the shape memory alloy material and is mechanically connected to the flap, wherein the actuating portion is arranged such that when the valve is heated to the transition temperature while the valve is in the closed state, the actuating portion moves the flap so as to open the airflow channel. In these embodiments, the flap obstructs the airflow channel when the valve is in the closed state. This impedes the flow of air through the channel. When the valve is in the open state, the flap should impede the flow of air through the channel to a lesser degree than when in the closed state (and preferably substantially not at all). The actuating portion may have the first form referred to above when the valve is in the closed state the second form referred to above when the valve is in the open state.

In particularly preferred implementations, the actuating portion and the flap are integral with one another. The valve can easily be manufactured with this configuration, for example by cutting or stamping a sheet of the shape memory alloy material. However, the flap could be formed of a different material, for example a metal or polymer, and attached to valve. In some preferred embodiments, the valve is inductively heatable. The temperature of the valve (and hence that of the shape memory alloy) will increase when the valve is placed in a time-varying magnetic field, which could be used to heat the substrate, as will be described later. This ensures that the valve reaches the transition temperature and opens correctly. This characteristic can be achieved simply by forming the entire valve of a shape memory alloy, since shape memory alloys are conductive (and hence susceptible to the formation of eddy currents that result in inductive heating). Moreover, shape memory alloys are typically capable of capable of being permanently magnetised. In this case, the shape memory alloy will heat produce heat when placed in an oscillating magnetic field due to the repeated changes in its magnetisation caused by the changing magnetic field. These two mechanisms each contribute to the heating of the valve. As was noted above, the valve could simply be a single integral unit formed of the shape memory alloy. The valve could, however, incorporate several different materials as noted above, provided that at least one is inductively heatable.

The shape memory alloy material will experience inductive heating when placed in a time-varying magnetic field (for example when the substrate is heated inductively, as will be described later). Over-heating of the shape memory alloy material can cause various problems, for example scorching the substrate and/or the material that defines the airflow channel. Hence, in particularly preferred embodiments, the shape memory alloy material is configured to be substantially planar when the valve is in the open state. The shape memory alloy material can be oriented so as to lie in a plane parallel to the magnetic field when in the open state, thereby minimising the magnetic flux intercepted by it and hence reducing the rate at which it is inductively heated. The shape memory alloy could be arranged to lie parallel to a wall of the airflow channel when in the open state, for example. This provides a further advantage in that it minimises the obstruction of the airflow channel by the shape memory alloy when the valve is in the open state.

The shape memory alloy material preferably has a Curie temperature of less than 200°C, more preferably less than 100° C. When in a time-varying magnetic field, the shape memory alloy material experiences heating that is in part due to the changes in the permanent magnetisation caused by the changing strength and direction of the magnetic field. Above the Curie temperature, no permanent magnetisation can exist, so this feature reduces the likelihood of the shape memory alloy material over-heating in use.

In preferred implementations, the aerosol generating article comprises one or more inductively heatable susceptors for heating the substrate, the one or more inductively heatable susceptors being disposed inside the airflow channel. The aerosol generating article can be placed in a time-varying magnetic field (which could be provide by an aerosol generating device into which the article is loaded), which will heat the susceptors and, consequently, the substrate. This improves the uniformity with which the substrate is heated. In particularly preferred embodiments, the inductively heatable susceptors are embedded in the substrate. This further improves the uniformity with which the substrate is heated.

The aerosol generating article preferably comprises a filter for filtering the aerosol generated by the material part. The filter may be disposed inside the airflow channel, for example. The filter may be configured to cool the aerosol passing through it.

A second aspect of the invention provides an aerosol generating system comprising: an aerosol generating article accordance with the first aspect of the invention; and a heating device arranged to heat the substrate in use. The heating device could be a hand-held device that facilitates consumption of the generated vapour by inhalation, and could include additional features such as an electrical power source for powering the heating device and a mouthpiece in fluid communication with the chamber whereby the aerosol can be drawn from the article by a user.

The heating device preferably comprises a chamber adapted to hold the aerosol generating article while being heated by the heating device and from which the aerosol generating article can be removed. This enables the aerosol generating article to be removed and replaced once consumed, which is particularly convenient where the aerosol generating article provided is of the single-use kind. For example, the chamber could comprise an opening via which the aerosol generating article can be received and removed.

In a system in accordance with the second aspect of the invention, the aerosol generating article preferably comprises one or more inductively heatable susceptors for heating the substrate, the one or more inductively heatable susceptors being disposed inside the airflow channel. The discussion of these features given above with reference to the first aspect of the invention applies equally here.

Where the aerosol generating article comprises one or more inductively heatable susceptors, the heating device preferably comprises an inductor that is configured to produce, in use, an oscillating magnetic field suitable for heating one or more inductively heatable susceptors. Advantageously, the inductor may comprise an electrically-powered coil, for example a helical coil. The magnetic field produced inside such a coil as a current is passed through it can be strong and highly uniform, since the field lines run parallel to one another along the axis about which the coil is wound. As such, the coil can be adapted such that the aerosol generating article can be disposed inside of it, preferably such that the airflow channel is concentric with the coil. In particularly preferred embodiments, the coil may be arranged to surround a chamber of the kind described above, which enables the aerosol generating article to be easily placed inside and removed from the inside of the coil.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of an aerosol generating device in accordance with the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 shows a valve suitable for use in embodiments of the invention in (a) an open state and (b) a closed state;

Figure 2 is a cross-sectional view of an aerosol generating article in accordance with an embodiment of the invention; and Figure 3 shows an example of an aerosol generating system in accordance with the second aspect of the invention.

DETAILED DESCRIPTION

Figures 1 (a) and (b) show an example of a valve 101 suitable for use in aerosol generating articles in accordance with the invention. The valve includes an elliptically-shaped flap 103, which is attached to an actuating portion 105.

The actuating portion 105 is formed of a shape memory alloy material. When the shape memory alloy is below its transition temperature, it has a first form, and when heated to the transition temperature, transitions to a second form. When in the first form, as shown in Figure 1 (a), the actuating portion 105 has a curved shape. When the actuating portion 105 is heated to the transition temperature, it transitions to the second form, shown in Figure 1(b), which is planar in shape. As the actuating portion 105 transitions from the first form to the second form, it moves the flap 103. As will be shown later, the first and second forms of the actuating portion 105 can define closed and open states of the valve 101.

The flap 103 may be formed of the same shape memory alloy as the actuating portion 105, in which case the valve 101 may be formed as a single integral unit. This is not essential, however, since the flap 103 itself is not required to change form in the manner that is enabled by the shape memory alloy. The flap 103 could, therefore, be manufactured separately, for example from a metal or polymer, and attached to the actuating portion 105.

Figure 2(a) shows a cross-sectional view of an aerosol generating article 201 in accordance with an embodiment of the invention. The aerosol generating article 201 includes a shell 203, which defines an airflow channel 211 inside of which components of the aerosol generating article 201 are disposed. The shell 203 is cylindrical in shape and can be made of paper, cardboard or a suitable polymer- based material, for example. A material part 213 is disposed inside the airflow channel 211 at one end of the article 201. The material part includes a substrate 205, which, when heated, produces an aerosol suitable for consumption by inhalation. The substrate may comprise tobacco, for example in the form of reconstituted tobacco, or any other substrate which, when heated, produces a vapour suitable for consumption by inhalation. It may also include additives such as humectants, fragrances and flavourings. In this example, the material part 213 also includes a plurality of inductively heatable susceptors 207 embedded in the substrate 205. When placed in a time-varying magnetic field, the susceptors 207 convert the electromagnetic energy received from the electromagnetic field to heat and in turn heat the substrate 205. The susceptors 207 could be made of aluminium, iron, nickel, stainless steel, or an alloy (e.g. nickel chromium or nickel copper) for example. In this example, each susceptor 207 has the form of an elongate strip or rod that extends along the direction of the airflow channel 211.

At the other end of the airflow channel 211 is a filter 209. The filter 209 allows the aerosol produced by the substrate 205 to be drawn through it by a user and cools the aerosol passing through it. The filter 209 may be adapted to mimic the appearance and touch sensation of a conventional cigarette filter.

A valve 101 as described above with reference to Figures 1(a) and 1 (b) is disposed inside the airflow channel 211 between the substrate 205 and the filter 209. The actuating portion 105 is attached to an interior surface of the shell 203 (by an adhesive, for example). In Figure 2(a), the valve 101 is below the transition temperature and the actuating portion has the first form described above. The flap 103 projects away from the surface of the shell 203 in such a way that it closes the airflow channel 211 , preventing airflow through the article 201. In this example, the flap 103 projects away from the interior surface of the airflow channel 211 at a non-perpendicular angle, and the elliptical shape of the flap 103 cooperates with the cylindrical shape of the airflow channel 211 such that the airflow channel 211 is almost or completely closed when the flap 103 is in this position. Because air cannot be drawn through the article 201 while the valve 101 is in the closed state, it is very difficult to achieve sustained combustion of the substrate 205. This prevents a user from lighting the article 201 in the manner of a conventional cigarette and ensures that the article 201 can only be consumed by use with a suitable device that is capable of heating the article 201 in such a way that causes the valve 101 to open.

As was explained above, the actuating portion 105 transitions to the second form when heated to the transition temperature of the shape memory alloy. As this happens, the actuating portion 105 moves the flap 103 such that it lies flat against the interior surface of the shell 203. The second form of the actuating portion 105 thus defines an open state of the valve 101 , in which the flap substantially does not obstruct the airflow channel 211 and air can be drawn through the article 201 by the user. Figure 2(b) shows the article 201 when the valve 101 is in the open state.

The speed with which the valve 101 reaches the transition temperature of the shape memory alloy relative to the rate at which the substrate heats can be controlled by varying the properties of the valve 101. The total heat capacity of the valve 101 depends on the material of which the flap 103 and actuating portion 105 are formed, and also on the dimensions of these components (since, as the amount of any given material in the valve 101 increases, so also does the heat capacity of the valve 101). If the heat capacity of the valve 101 is increased, it must absorb and retain a greater amount of heat before it reaches the transition temperature. Thus, by selecting the material and dimensions of the valve 101 to provide a suitable heat capacity, the time at which the valve 101 opens (relative to the commencement of heating of the article 201) can be varied such that a greater or lesser amount of heat will have been supplied to the article 201 , and hence the substrate 205, by the time the valve 101 opens.

The processes that contribute to the heating of the valve 101 during the use of the article 101 will now be discussed. In this example, the substrate 205 is contains a plurality of inductively heatable susceptors 207, which, as explained above, produce heat when placed in a time-varying magnetic field that is aligned with (or has a substantial component aligned along) the direction along which the airflow channel 211 extends. The susceptors 207 heat the surrounding substrate 205, which causes an aerosol to be released. The aerosol fills the section of the airflow channel 211 in which the valve 101 is located and thus heats the valve 101. In some embodiments, the valve 101 can be configured such that heating by the aerosol alone is sufficient to cause the actuating portion 105 to transition to the second form such that the valve 101 changes to the open state.

The valve 101 , and in particular the shape memory alloy (which forms the actuating portion 105, and, in some embodiments, also the flap 103), may also be configured to produce heat when placed in a time varying magnetic field. This heating occurs by two main modes. The first is resistive heating due to eddy currents induced in the conductive materials in the valve (including but not necessarily limited to the shape memory alloy) by the time-varying electromagnetic field. The second is the production of heat by changes in the magnetisation of the shape memory alloy (and any other magnetisable materials in the valve) caused by the changing electromagnetic field. This second mode of heat generating can only occur when the shape memory alloy is below its Curie temperature, above which no permanent magnetisation exists. As was explained above, it is preferably that the Curie temperature of the material(s) of which the valve 101 is formed is sufficiently low that this mode of heat production ceases when the valve 101 is in the open state.

As can be seen in Figure 2(b), the flap 103 and the actuating portion 105 assume a substantially planar configuration when the valve 101 is in the open state. Firstly, this minimises obstruction of the airflow channel 211 by the valve 101 when open. It also minimises the magnetic flux intercepted by the valve 101 when the article is placed inside an oscillating magnetic field of the kind that is suitable for heating the susceptors 207, i.e. one that is aligned substantially along the direction along which the airflow channel 211 extends. As a result, the rate at which the valve 101 is inductively heated by such a magnetic field is greatly reduced when the valve 101 is in the open state. This prevents the valve 101 reaching excessively high temperatures, which in turn prevents the shell 203, filter 209 and substrate 205 being scorched by the valve 101 . So far, modes of heat production by the interaction of components of the article 101 with an oscillating magnetic field have been described. It is not essential, however, that the article 201 includes inductively heatable susceptors 207 as described above. If the susceptors 207 are omitted, then the article 201 can simply be placed in an oven that heats the materials part 213 (or indeed the entire article 201) substantially uniformly in order to achieve a sufficient temperature for producing the aerosol. In that case, the valve 101 would be heated as a result of the overall heating of the article 101 and the presence of the hot aerosol released by the substrate 205. As in the example above, the properties of the valve 101 (for example the material and the shape and thickness of the valve and actuating portion) can be controlled such that the transition to the open state occurs when the article 101 has reached a particular desired temperature.

Figure 3 is a cross-sectional view of part of an aerosol generating system in accordance with the second aspect of the invention. The system includes an inductor in the form of a helical coil 301. The system also includes an aerosol generating article 201 as described above with reference to Figure 2. The article 201 is positioned inside the coil 301 such that the coil 301 and the airflow channel 211 are concentric with one another. When an alternating electrical current is passed through the coil 301 , an oscillating magnetic field is produced which, inside the coil, is aligned along the direction of the airflow channel 211. This heats the susceptors 207 in the manner described above, and can also cause the valve 101 to heat by induction and/or magnetic heat losses.

The system can include other components that are not shown here. The coil 301 could be arranged inside, or to surround, a chamber suitable for holding the article 101. The chamber could be in fluid communication with an inlet and a mouthpiece that together allow air to be drawn through the article (whereby the air enters through the inlet and exits via the mouthpiece) such that the user can consume the aerosol by drawing on the mouthpiece. The chamber can be adapted to hold the aerosol generating article 201 while being heated by the coil 301 and such that the aerosol generating article 201 can be removed from the chamber after use, for example through an opening in the chamber. The device that incorporates the coil could also include a power source (for example a rechargeable battery) that powers the coil 301 in use. Once the article 101 is spent, it can be ejected from the device for disposal and replaced with a fresh article.