Note: Descriptions are shown in the official language in which they were submitted.
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SMOKING ARTICLE WITH SINGLE RADIALLY-SEPARATED HEAT-CONDUCTING
ELEMENT
The present invention relates to a smoking article comprising a combustible
heat source
having opposed front and rear faces, an aerosol-forming substrate downstream
of the rear face
of the combustible heat source and a single heat-conducting element overlying
a rear portion of
the combustible heat source and at least a front portion of the aerosol-
forming substrate.
A number of smoking articles in which tobacco is heated rather than combusted
have
been proposed in the art. One aim of such 'heated' smoking articles is to
reduce known harmful
smoke constituents of the type produced by the combustion and pyrolytic
degradation of
tobacco in conventional cigarettes. In one known type of heated smoking
article, an aerosol is
generated by the transfer of heat from a combustible heat source to an aerosol-
forming
substrate. The aerosol-forming substrate may be located within, around or
downstream of the
combustible heat source. During smoking, volatile compounds are released from
the aerosol-
forming substrate by heat transfer from the combustible heat source and
entrained in air drawn
through the smoking article. As the released compounds cool, they condense to
form an
aerosol that is inhaled by the user. Typically, air is drawn into such known
heated smoking
articles through one or more airflow channels provided through the combustible
heat source and
heat transfer from the combustible heat source to the aerosol-forming
substrate occurs by
forced convection and conduction.
For example, WO-A2-2009/022232 discloses a smoking article comprising a
combustible heat source, an aerosol-forming substrate downstream of the
combustible heat
source, and a heat-conducting element around and in direct contact with a rear
portion of the
combustible heat source and an adjacent front portion of the aerosol-forming
substrate.
The heat-conducting element in the smoking article of WO-A2-2009/022232
transfers
heat generated during combustion of the combustible heat source to the aerosol-
forming
substrate by conduction. In smoking articles in which tobacco is heated rather
than combusted,
the temperature attained in the aerosol-forming substrate has a significant
impact on the ability
to generate a sensorially acceptable aerosol.
It is typically desirable to maintain the
temperature of the aerosol-forming substrate within a certain range in order
to optimise the
aerosol delivery to a user. In some cases, radiative heat losses from the
outer surface of a
heat-conducting element around and in direct contact with the combustible heat
source and the
aerosol-forming substrate may cause the temperature of the combustible heat
source and the
aerosol-forming substrate to drop outside of a desired range, thereby
impacting the
performance of the smoking article. If the temperature of the aerosol-forming
substrate drops
too low, for instance, it may adversely impact the consistency and the amount
of aerosol
delivered to a user.
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EP-A1-2 550 879 discloses a smoking article comprises a multilayered tube
member 9
including at least one metal layer and one paper layer, a carbon heat source 4
arranged in an
end portion of the tube member 9 to be at least partly in direct close contact
with an inner
surface of the tube member 9 and a smoking flavor releasing source 8 arranged
in the tube
member 9 to adjoin the carbon heat source 4, and a holder part 14 keeping the
carbon heat
source 4 in direct contact with said end portion and holding the carbon heat
source 4 against
said end portion.
In the embodiment shown in Fig. 1 the non-combustible wrapping material 9 is
formed
by bonding a three-layer composite sheet 16 to the outer side of a two-layer
composite sheet
15. The part of the three-layer composite sheet 16 projecting from the two
layer composite
sheet 15 forms the holder part 14. As shown in Fig. 2, the two-layer composite
sheet 15
comprises an inner aluminum layer 17 and an outer paper layer 18 and the three-
layer
composite sheet 16 comprises an inner paper layer 18, a central aluminum layer
17 and an
outer paper layer 18. The innermost layer of the non-combustible wrapper 9 is
the aluminum
layer 17 of the two-layer composite sheet 15 and the outermost layer of the
non-combustible
wrapper 9 is the outer paper layer 18 of the three-layer composite sheet 16.
In some heated smoking articles, forced convective heat transfer from a
combustible
heat source to the aerosol-forming substrate is provided in addition to
conductive heat transfer
via a heat-conducting element. For example, in some known heated smoking
articles one or
more airflow channels are provided along the combustible heat source in order
to provide forced
convective heating of the aerosol-forming substrate. In such smoking articles,
the aerosol-
forming substrate is heated by a combination of conductive heating and forced
convective
heating.
For example, WO-A2-2009/022232 discloses providing at least one longitudinal
airflow
channel through the combustible heat source to provide a controlled amount of
forced
convective heating of the aerosol-forming substrate.
In known heated smoking articles in which heat transfer from the combustible
heat
source to the aerosol-forming substrate occurs primarily by forced convection,
the forced
convective heat transfer and hence the temperature in the aerosol-forming
substrate can vary
considerably depending upon the puffing behaviour of a user. As a result, the
composition and
hence the sensory properties of the mainstream aerosol generated by such known
heated
smoking articles may disadvantageously be highly sensitive to a user's puffing
regime.
In particular, in known heated smoking articles comprising one or more airflow
channels
along the combustible heat source, direct contact between air drawn through
the one or more
airflow channels and the combustible heat source during puffing by a user
results in activation
of combustion of the combustible heat source. Intense puffing regimes may
therefore lead to
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sufficiently high forced convective heat transfer to cause spikes in the
temperature of the
aerosol-forming substrate, disadvantageously leading to pyrolysis and
potentially even localised
combustion of the aerosol-forming substrate. As used herein, the term 'spike'
is used to
describe a short-lived increase in the temperature of the aerosol-forming
substrate. As a result,
the levels of undesirable pyrolytic and combustion by-products in the
mainstream aerosols
generated by such known heated smoking articles may also disadvantageously
vary
significantly depending upon the particular puffing regime adopted by a user.
In other heated smoking articles no airflow channels are provided through the
combustible heat source. In such heated smoking articles heating of the
aerosol-forming
substrate is achieved primarily by conductive heat transfer via a heat-
conducting element. In
heated smoking articles where the aerosol-forming substrate is heated
primarily by conductive
heat transfer, the temperature of the aerosol-forming substrate can become
more sensitive to
changes in the temperature of the heat-conducting element. This means that any
cooling of a
heat-conducting element around and in direct contact with the combustible heat
source and the
aerosol-forming substrate due to radiative heat loss in such heated smoking
articles may have a
greater impact on the aerosol generation than in heated smoking articles where
the aerosol-
forming substrate is also heated by forced convective heat transfer.
It would be desirable to provide a heated smoking article including a
combustible heat
source having opposed front and rear faces and an aerosol-forming substrate
downstream of
the rear face of the combustible heat source which provides improved smoking
performance. In
particular, it would be desirable to provide a heated smoking article in which
there is improved
control of the heating of the aerosol-forming substrate in order to help
maintain the temperature
of the aerosol-forming substrate within a desired temperature range during
smoking.
According to the invention there is provided a smoking article comprising: a
combustible
heat source having opposed front and rear faces; an aerosol-forming substrate
downstream of
the rear face of the combustible heat source; and a single heat-conducting
element overlying a
rear portion of the combustible heat source and at least a front portion of
the aerosol-forming
substrate. The single heat-conducting element comprises one or more layers of
heat
conductive material and the one or more layers of heat conductive material are
radially
separated from the combustible heat source and the aerosol-forming substrate.
The
combustible heat source is either a blind combustible heat source or the
combustible heat
source is a non-blind combustible heat source and the smoking article further
comprises a non-
combustible substantially air impermeable barrier between the non-blind
combustible heat
source and one or more airflow channels extending from the front face to the
rear face of the
non-blind combustible heat source. The single heat-conducting element
comprises an outer
layer of heat conductive material that is visible on the exterior of the
smoking article
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As used herein, the terms 'distal', 'upstream' and 'front', and 'proximal',
'downstream'
and 'rear', are used to describe the relative positions of components, or
portions of components,
of the smoking article in relation to the direction in which a user draws on
the smoking article
during use thereof. Smoking articles according to the invention comprise a
proximal end
through which, in use, an aerosol exits the smoking article for delivery to a
user. The proximal
end of the smoking article may also be referred to as the mouth end. In use, a
user draws on
the proximal end of the smoking article in order to inhale an aerosol
generated by the smoking
article.
The combustible heat source is located at or proximate to the distal end. The
mouth end
is downstream of the distal end. The proximal end may also be referred to as
the downstream
end of the smoking article and the distal end may also be referred to as
upstream end of the
smoking article. Components, or portions of components, of smoking articles
according to the
invention may be described as being upstream or downstream of one another
based on their
relative positions between the proximal end and the distal end of the smoking
article.
The front face of the combustible heat source is at the upstream end of the
combustible
heat source. The upstream end of the combustible heat source is the end of the
combustible
heat source furthest from the proximal end of the smoking article. The rear
face of the
combustible heat source is at the downstream end of the combustible heat
source. The
downstream end of the combustible heat source is the end of the combustible
heat source
closest to the proximal end of the smoking article.
As used herein, the term 'length' is used to describe the maximum dimension in
the
longitudinal direction of the smoking article. That is, the maximum dimension
in the direction
between the proximal end and the opposed distal end of the smoking article.
As used herein, the term 'aerosol-forming substrate' is used to describe a
substrate
capable of releasing upon heating volatile compounds, which can form an
aerosol. The
aerosols generated from aerosol-forming substrates of smoking articles
according to the
invention may be visible or invisible and may include vapours (for example,
fine particles of
substances, which are in a gaseous state, that are ordinarily liquid or solid
at room temperature)
as well as gases and liquid droplets of condensed vapours.
As used herein, the term "radially separated" is used to indicate that the one
or more
layers of heat conductive material of the single heat-conducting element are
spaced apart from
both the combustible heat source and the aerosol-forming substrate in a radial
direction, such
that there is no direct contact between the one or more layers of heat
conductive material of the
single heat-conducting element and the combustible heat source or the aerosol-
forming
substrate.
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As used herein, the term 'radial' is used to describe the direction
perpendicular to the
direction between the proximal end and the opposed distal end of the smoking
article.
As used herein, the term 'direct contact' is used to mean contact between two
components without any intermediate material, such that the surfaces of the
components are
touching each other.
The aerosol-forming substrate may be in the form of a plug or segment
comprising a
material capable of releasing upon heating volatile compounds, which can form
an aerosol,
circumscribed by a wrapper. Where an aerosol-forming substrate is in the form
of such a plug
or segment, the entire plug or segment including the wrapper is considered to
be the aerosol-
forming substrate.
In such embodiments, the one or more layers of heat conductive material of the
single
heat-conducting element are radially separated from the wrapper of the aerosol-
forming
substrate.
Smoking articles according to the invention comprise a single heat-conducting
element
overlying a rear portion of the combustible heat source and at least a front
portion of the
aerosol-forming substrate. The single heat-conducting element comprises one or
more layers
of heat conductive material and the one or more layers of heat conductive
material are radially
separated from the combustible heat source and the aerosol-forming substrate.
Smoking articles according to the invention do not comprise any additional
heat-
conducting elements underlying or overlying the single heat-conducting
element. In particular,
smoking articles according to the invention do not comprise any heat-
conducting elements
around and in direct contact with one or both of the combustible heat source
and the aerosol-
forming substrate.
Smoking articles according to the invention may comprise a blind combustible
heat
source or a non-blind combustible heat source.
As used herein, the term 'blind' is used to describe a combustible heat source
wherein
there are no airflow channels extending from the front face to the rear face
of the combustible
heat source.
In use, the air drawn through smoking articles according to the invention
comprising a
blind combustible heat source for inhalation by a user does not pass through
any airflow
channels along the blind combustible heat source. In smoking articles
according to the
invention comprising a blind combustible heat source, heating of the aerosol-
forming substrate
occurs primarily by conduction and heating of the aerosol-forming substrate by
forced
convection is minimised or reduced.
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As used herein, the term 'airflow channel' is used to describe a channel
extending along
the length of a combustible heat source through which air may be drawn
downstream for
inhalation by a user.
As used herein, the term 'non-blind' is used to describe a combustible heat
source
wherein there are one or more airflow channels extending from the front face
to the rear face of
the combustible heat source.
In use, the air drawn through smoking articles according to the invention
comprising a
non-blind combustible heat source for inhalation by a user passes through one
or more airflow
channels along the non-blind combustible heat source. In smoking articles
according to the
invention comprising a non-blind combustible heat source, heating of the
aerosol-forming
substrate occurs by conduction and forced convection.
Smoking articles according to the invention comprising a non-blind combustible
heat
source further comprise a non-combustible substantially air impermeable
barrier between the
non-blind combustible heat source and the one or more airflow channels
extending from the
front face to the rear face of the non-blind combustible heat source.
As used herein, the term 'non-combustible' is used to describe a barrier that
is
substantially non-combustible at temperatures reached by the non-blind
combustible heat
source during combustion and ignition thereof.
Where smoking articles according to the invention comprise a non-blind
combustible
heat source, the lack of any airflow channels through the blind combustible
heat source
advantageously substantially prevents or inhibits activation of combustion of
the blind
combustible heat source during puffing by a user.
Similarly, where smoking articles according to the invention comprise a non-
blind
combustible heat source inclusion of a non-combustible substantially air
impermeable barrier
between the non-blind combustible heat source and the one or more airflow
channels extending
from the front face to the rear face of the non-blind combustible heat source
advantageously
substantially prevents or inhibit activation of combustion of the non-blind
combustible heat
source during puffing by a user.
Preventing or inhibiting activation of combustion of the combustible heat
source during
puffing by a user, advantageously substantially prevents or inhibits spikes in
the temperature of
the aerosol-forming substrate of smoking articles according to the invention
during puffing by a
user.
By preventing or inhibiting activation of combustion of the combustible heat
source, and
so preventing or inhibiting excess temperature increases in the aerosol-
forming substrate,
combustion or pyrolysis of the aerosol-forming substrate of smoking articles
according to the
invention under intense puffing regimes may be advantageously avoided. In
addition, the
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impact of a user's puffing regime on the composition of the mainstream aerosol
of smoking
articles according to the invention may be advantageously minimised or
reduced.
The single heat-conducting element overlies a rear portion of the combustible
heat
source and at least a front portion of the aerosol-forming substrate.
The one or more layers of heat conductive material of the single heat-
conducting
element are radially separated from the combustible heat source and the
aerosol-forming
substrate. This limits conductive heat transfer from the combustible heat
source to the single
heat-conducting element and conductive heat transfer from the single heat-
conducting element
to the aerosol-forming substrate. In use, this advantageously helps to
maintain the temperature
attained in the aerosol-forming substrate of smoking articles according to the
invention below
that at which combustion or pyrolysis of the aerosol-forming substrate may
occur.
Preferably, heat transfer by conduction from the combustible heat source to
the single
heat-conducting element is substantially reduced. This results in the single
heat-conducting
element of smoking articles according to the invention retaining a lower
temperature than the
heat-conducting element of known heated smoking articles in which the heat-
conducting
element is around and in direct contact with a rear portion of the combustible
heat source and at
least a front portion of the aerosol-forming substrate.
In heated smoking articles in which the heat-conducting element is around and
in direct
contact with a rear portion of the combustible heat source and at least a
front portion of the
aerosol-forming substrate, the heat drain exerted by conductive heat transfer
via the heat-
conducting element significantly lowers the temperature of the rear portion of
the combustible
heat source. This can shorten the burning lifetime of the combustible heat
source and may lead
to non-acceptable aerosol delivery.
The radial separation between the one or more layers of heat conductive
material of the
single heat-conducting element and the combustible heat source and the aerosol-
forming
substrate of smoking articles according to the invention advantageously
reduces the heat drain
exerted by conductive heat transfer via the single heat-conducting element.
The single heat-conducting element advantageously reduces heat losses from the
combustible heat source. The one or more layers of heat conductive material of
the single heat-
conducting element increase in temperature during smoking of the smoking
article, as heat is
generated by the combustible heat source. The increased temperature of the one
or more
layers of heat conductive material of the single heat-conducting element
reduce the temperature
differential between the combustible heat source and overlying components of
the smoking
article, such that heat losses from the combustible heat source can be
reduced.
By reducing heat losses from the combustible heat source, the single heat-
conducting
element advantageously helps to maintain the temperature of the aerosol-
forming substrate
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within a desired temperature range. This improves the generation of aerosol
from the aerosol-
forming substrate.
The one or more layers of heat conductive material of the single heat-
conducting
element conduct heat along the smoking article. This improves the efficiency
of conductive heat
transfer from the combustible heat source to the aerosol-forming substrate and
therefore the
heating of the aerosol-forming substrate. The improvement in conductive heat
transfer
achieved through the inclusion of the single heat-conducting element is
particularly beneficial for
smoking articles according to the invention comprising a blind combustible
heat source in which
there is substantially no forced convective heat transfer.
The radial separation between the one or more layers of heat conductive
material of the
single heat-conducting element and the combustible heat source and the aerosol-
forming
substrate is preferably achieved through the inclusion of one or more
intermediate layers of
material between the one or more layers of heat conductive material of the
single heat-
conducting element and the combustible heat source and the aerosol-forming
substrate. The
one or more intermediate layers of material may be provided over the entire
area in which the
single heat-conducting element overlies the combustible heat source and the
aerosol-forming
substrate. Alternatively, the one or more intermediate layers of material may
be provided in
only part or parts of this area. In some embodiments, the one or more
intermediate layers of
material may extend beyond the one or more layers of heat conductive material
of the single
heat-conducting element in one or both of the upstream direction and the
downstream direction.
Preferably, the one or more layers of heat conductive material of the single
heat-
conducting element are radially separated from the combustible heat source and
the aerosol-
forming substrate by one or more layers of heat insulative material. Suitable
heat insulative
materials include, but are not limited to, paper, ceramics and metal oxides.
For example, in certain preferred embodiments of the invention, the rear
portion of the
combustible heat source and the at least a front portion of the aerosol-
forming substrate
overlain by the single heat-conducting element are covered by a paper wrapper
that
circumscribes the smoking article along at least a portion of its length. In
such embodiments,
the paper wrapper radially separates the single heat-conducting element from
the combustible
heat source and the aerosol-forming substrate such that there is no direct
contact between the
single heat-conducting element and the combustible heat source or the aerosol-
forming
substrate.
The single heat-conducting element comprises an outer layer of heat conductive
material provided on the outside of the smoking article, such that the outer
layer of heat
conductive material of the single heat-conducting element is visible on the
exterior of the
smoking article.
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In certain embodiments, the one or more layers of heat conductive material of
the single
heat-conducting element are radially separated from the combustible heat
source and the
aerosol-forming substrate by a wrapper that extends along all or just a part
of the smoking
article. In such embodiments, the wrapper is wrapped around the smoking
article over the
combustible heat source and the aerosol-forming substrate and the single heat-
conducting
element is then provided over at least a portion of the wrapper.
Provision of the single heat-conducting element over a wrapper of the smoking
article
may provide benefits in relation to the appearance of smoking articles
according to the
invention, in particular during and after smoking thereof. In certain cases,
some discolouration
of the wrapper in the region of the combustible heat source may be observed
when the wrapper
is exposed to heat from the combustible heat source. The wrapper may
additionally be
discoloured as a result of the migration of volatile compounds from the
aerosol-forming
substrate into the wrapper around and downstream of the aerosol-forming
substrate. In certain
embodiments, the single heat-conducting element of smoking articles according
to the invention
may be provided over the wrapper around at least a rear part of the
combustible heat source
and at least a front part of the aerosol-forming substrate so that
discolouration of the wrapper is
covered and no longer or less visible. In certain embodiments, the single heat-
conducting
element may extend around the entire length of the aerosol-forming substrate.
In certain
preferred embodiments, the single heat-conducting element may extend
downstream beyond
the aerosol-forming substrate. The initial appearance of the smoking article
can therefore be
retained during smoking.
Alternatively or in addition to one or more layers of heat insulative material
between the
one or more layers of heat conductive material of the single heat-conducting
element and the
combustible heat source and the aerosol-forming substrate, at least part of
the single heat-
conducting element may be radially separated from the combustible heat source
and the
aerosol-forming substrate by an air gap. An air gap may be provided through
the inclusion of
one or more spacer elements between the one or more layers of heat conductive
material of the
single heat-conducting element and the combustible heat source and the aerosol-
forming
substrate to maintain a defined separation between the single heat-conducting
element and the
combustible heat source and the aerosol-forming substrate. The one or more
spacer elements
may be, for example, one or more strips of paper wrapped radially around the
combustible heat
source and the aerosol-forming substrate.
Preferably, the one or more layers of heat conductive material of the single
heat-
conducting element are radially separated from the combustible heat source and
the aerosol-
forming substrate by at least 20 microns, more preferably by at least 50
microns. In certain
embodiments, the one or more layers of heat conductive material of the single
heat-conducting
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element are radially separated from the combustible heat source and the
aerosol-forming
substrate by at least 75 microns or more or by at least 100 microns or more.
Where one or more layers of heat insulative material are provided between the
one or
more layers of heat conductive material of the single heat-conducting element
and the
combustible heat source and the aerosol-forming substrate, as described above,
the radial
separation between the one or more layers of heat conductive material of the
single heat-
conducting element and the combustible heat source and the aerosol-forming
substrate will be
determined by the thickness of the one or more layers of heat insulative
material.
The one or more layers of heat conductive material of the single heat-
conducting
element may comprise any suitable heat conductive material or combination of
materials with
an appropriate thermal conductivity.
Preferably, the one or more layers of heat conductive material of the single
heat-
conducting element comprise heat conductive materials having a bulk thermal
conductivity of
between about 10 W per metre Kelvin (W/(m=K)) and about 500 W per metre Kelvin
(W/(m=K)),
more preferably between about 15 W per metre Kelvin (W/(m=K)) and about 400 W
per metre
Kelvin (W/(m=K)), at 23 C and a relative humidity of 50% as measured using the
modified
transient plane source (MTPS) method. Suitable heat conductive materials
include, but are not
limited to: metal foil wrappers such as, for example, aluminium foil wrappers,
steel wrappers,
iron foil wrappers and copper foil wrappers; and metal alloy foil wrappers.
In certain preferred embodiments, the single heat-conducting element comprises
one or
more layers of aluminium.
Preferably, the one or more layers of heat conductive material of the single
heat-
conducting element comprise a heat reflective material, such as aluminium or
steel. In such
embodiments, in use, the single heat-conducting element advantageously
reflects heat radiating
from the combustible heat source and the aerosol-forming substrate back
towards the
combustible heat source and the aerosol-forming substrate.
As used herein the term 'heat reflective material' refers to a material that
has a relatively
high heat reflectivity and a relatively low heat emissivity such that the
material reflects a greater
proportion of incident radiation from its surface than it emits. Preferably,
the heat reflective
material reflects more than 50% of incident radiation, more preferably more
than 70% of
incident radiation and most preferably more than 75% of incident radiation.
In such embodiments, the relatively high heat reflectivity and relatively low
heat
emissivity of the single heat-conducting element reduces heat losses from the
combustible heat
source and the aerosol-forming substrate.
The reflectivity of the one or more layers of heat conductive material of the
single heat-
conducting element may be improved by providing the one or more layers of heat
conductive
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material of the single heat-conducting element with a shiny inner surface,
wherein the inner
surface is the surface that faces the combustible heat source and the aerosol-
forming substrate.
The single heat-conducting element may be formed of a single layer of heat
conductive
material. Alternatively, the single heat-conducting element may be formed of a
multilayer or
laminate material comprising at least one layer of heat conductive material in
combination with
one or more other heat-conducting layers or non-heat-conducting layers. In
such embodiments,
the at least one layer of heat conductive material may comprise any of the
heat conductive
materials listed above.
In certain preferred embodiments, the single heat-conducting element may be
formed of
a laminate material comprising at least one layer of heat conductive material
and at least one
layer of heat insulative material. In such embodiments, the inner layer of the
single heat-
conducting element facing the combustible heat source and the aerosol-forming
substrate may
be a layer of heat insulative material. In this way, the inner layer of heat
insulative material
provides the required radial separation between the at least one layer of heat
conductive
material of the single heat-conducting element and the combustible heat source
and the
aerosol-forming substrate.
In certain preferred embodiments, the single heat-conducting element comprises
a
single layer of heat conductive material.
In certain preferred embodiments, the single heat-conducting element is a
laminate
material comprising a single layer of heat conductive material and one or more
layers of heat
insulative material. In certain particularly preferred embodiments, the single
heat-conducting
element is a laminate material comprising a single layer of heat conductive
material and a single
layer of heat insulative material. Preferably, the single heat-conducting
element is a laminate
material comprising a single outer layer of heat conductive material and a
single inner layer of
heat insulative material.
One example of a particularly suitable laminate material for forming the
single heat-
conducting element is a double layer laminate material comprising an outer
layer of aluminium
and an inner layer of paper.
The use of a single heat-conducting element comprising a laminate material may
additionally be beneficial during the production of the smoking articles
according to the
invention, since the at least one heat-insulating layer may provide added
strength and rigidity.
This enables the laminate material to be processed more easily, with a reduced
risk of collapse
or breakage of the at least one heat-conducting layer, which may be relatively
thin and fragile.
Preferably the thickness of the single heat-conducting element is between
about
5 microns and about 100 microns, more preferably between about 5 microns and
about
80 microns.
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Preferably the single heat-conducting element comprises one or more layers of
heat
conductive material having a thickness of between about 2 microns and about 50
microns, more
preferably between about 4 microns and about 30 microns.
In certain embodiments, the single heat-conducting element may comprise
aluminium
foil having a thickness of about 20 microns.
In certain preferred embodiments, the single heat-conducting element may
comprise a
laminate material comprising an outer layer of aluminium having a thickness of
between about 5
microns and about 6 microns and an inner layer of paper.
As described above, the single heat-conducting element of smoking articles
according to
the invention overlies a rear portion of the combustible heat source and at
least a front portion
of the aerosol-forming substrate.
The position and extent of the single heat-conducting element relative to the
combustible
heat source and the aerosol-forming substrate may be adjusted in order to
control heating of the
aerosol-forming substrate during smoking. In particular, the extent of the
single heat-conducting
element relative to the combustible heat source and the aerosol-forming
substrate in the
upstream direction and the downstream direction may be adjusted in order to
adjust the aerosol
delivery profile of the smoking article.
The single heat-conducting element may extend around all or a part of the
circumference of the smoking article. Preferably, the single heat-conducting
element forms a
continuous sleeve that circumscribes the smoking article along part of its
length.
Preferably, the rear portion of the combustible heat source overlain by the
single heat-
conducting element is between about 2 mm and about 8 mm in length, more
preferably between
about 3 mm and about 5 mm in length.
Preferably, the front portion of the combustible heat source not overlain by
the first heat-
conducting element is between about 4 mm and about 15 mm in length, more
preferably
between about 5 mm and about 8 mm in length.
In certain embodiments, the single heat-conducting element overlies the entire
length of
the aerosol-forming substrate. In such embodiments, the downstream end of the
single heat-
conducting element may be aligned with the downstream end of the aerosol-
forming substrate.
Alternatively, the single heat-conducting element may extend beyond the
aerosol-forming
substrate in the downstream direction.
In other embodiments, the single heat-conducting element overlies only a front
portion of
the aerosol-forming substrate. In such embodiments, the aerosol-forming
substrate extends
beyond the single heat-conducting element in the downstream direction.
In embodiments in which the single heat-conducting element overlies only a
front portion
of the aerosol-forming substrate, the aerosol-forming substrate may extend at
least about 3 mm
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beyond the single heat-conducting element in the downstream direction. For
example, the
aerosol-forming substrate may extend between about 3 mm and about 10 mm beyond
the
single heat-conducting element in the downstream direction. Alternatively, the
aerosol-forming
substrate may extend less than 3 mm beyond the single heat-conducting element
in the
downstream direction.
In embodiments in which the single heat-conducting element overlies only a
front portion
of the aerosol-forming substrate, the front portion of the aerosol-forming
substrate overlain by
the single heat-conducting element may be between about 1 mm and about 10 mm
in length,
For example, the front portion of the aerosol-forming substrate overlain by
the single heat-
conducting element may be between about 2 mm and about 8 mm in length or
between about
2 mm and about 6 mm in length.
Smoking articles according to the invention may comprise a blind combustible
heat
source.
It is known to include additives in the combustible heat sources of heated
smoking
articles in order to improve the ignition and combustion properties of the
combustible heat
sources.
However, the inclusion of ignition and combustion additives can give rise
to
decomposition and reaction products, which may disadvantageously enter air
drawn through
such known heated smoking articles during use thereof.
The inclusion of a blind combustible heat source may advantageously
substantially
prevent or inhibit combustion and decomposition products and other materials
formed during
ignition and combustion of the blind combustible heat source from entering air
drawn through
smoking articles according to the invention during use thereof. This is
particularly
advantageous where the blind combustible heat source comprises one or more
additives to aid
ignition or combustion of the blind combustible heat source.
In smoking articles according to the invention comprising a blind combustible
heat
source, it is particularly important to optimise the conductive heat transfer
between the
combustible heat source and the aerosol-forming substrate. The inclusion of a
single heat-
conducting element radially separated from the combustible heat source and the
aerosol-
forming substrate has been found to have a particularly advantageous effect on
the smoking
performance of smoking articles including blind heat sources, where there is
little if any heating
of the aerosol-forming substrate by forced convection.
It will be appreciated that smoking articles according to the invention may
comprise blind
combustible heat sources comprising one or more closed or blocked passageways
through
which air may not be drawn for inhalation by a user.
For example, smoking articles according to the invention may comprise blind
combustible heat sources comprising one or more closed passageways that extend
from the
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front face at the upstream end of the blind combustible heat source only part
way along the
length of the blind combustible heat source.
The inclusion of one or more closed air passageways increases the surface area
of the
blind combustible heat source that is exposed to oxygen from the air and may
advantageously
facilitate ignition and sustained combustion of the blind combustible heat
source.
Alternatively, smoking articles according to the invention may comprise a non-
blind
combustible heat source wherein there are one or more airflow channels
extending from the
front face to the rear face of the non-blind combustible heat source.
The one or more airflow channels may comprise one or more enclosed airflow
channels.
As used herein, the term 'enclosed' is used to describe airflow channels that
extend
through the interior of the non-blind combustible heat source and are
surrounded by the non-
blind combustible heat source.
Alternatively or in addition, the one or more airflow channels may comprise
one or more
non-enclosed airflow channels. For example, the one or more airflow channels
may comprise
one or more grooves or other non-enclosed airflow channels that extend along
the exterior of
the non-blind combustible heat source.
The one or more airflow channels may comprise one or more enclosed airflow
channels
or one or more non-enclosed airflow channels or a combination thereof.
In certain embodiments, smoking articles according to the invention comprise
one, two
or three airflow channels extending from the front face to the rear face of
the non-blind
combustible heat source.
In certain preferred embodiments, smoking articles according to the invention
comprise
a single airflow channel extending from the front face to the rear face of the
non-blind
combustible heat source.
In certain particularly preferred embodiments, smoking articles according to
the invention
comprise comprises a single substantially central or axial airflow channel
extending from the
front face to the rear face of the non-blind combustible heat source.
In such embodiments, the diameter of the single airflow channel is preferably
between
about 1.5 mm and about 3 mm.
It will be appreciated that in addition to one or more airflow channels
through which air
may be drawn for inhalation by a user, smoking articles according to the
invention may
comprise non-blind combustible heat sources comprising one or more closed or
blocked
passageways through which air may not be drawn for inhalation by a user.
For example, smoking articles according to the invention may comprise non-
blind
combustible heat sources comprising one or more airflow channels extending
from the front
face to the rear face of the combustible heat source and one or more closed
passageways that
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extend from the front face of the non-blind combustible heat source only part
way along the
length combustible heat source.
The inclusion of one or more closed air passageways increases the surface area
of the
non-blind combustible heat source that is exposed to oxygen from the air and
may
advantageously facilitate ignition and sustained combustion of the non-blind
combustible heat
source.
Smoking articles according to the invention comprising a non-blind combustible
heat
source further comprise a non-combustible substantially air impermeable
barrier between the
non-blind combustible heat source and the one or more airflow channels
extending from the
front face to the rear face of the non-blind combustible heat source.
Inclusion of a non-combustible substantially air impermeable barrier between
the non-
blind combustible heat source and the one or more airflow channels extending
from the front
face to the rear face of the non-blind combustible heat source may
advantageously substantially
prevent or inhibit combustion and decomposition products formed during
ignition and
combustion of the non-blind combustible heat source from entering air drawn
into the smoking
article through the one or more airflow channels as the drawn air passes
through the one or
more airflow channels. This is particularly advantageous where the non-blind
combustible heat
source comprises one or more additives to aid ignition or combustion of the
non-blind
combustible heat source.
The barrier between the non-blind combustible heat source and the one or more
airflow
channels may be adhered or otherwise affixed to the non-blind combustible heat
source.
In certain preferred embodiments, the barrier comprises a non-combustible
substantially
air impermeable barrier coating provided on an inner surface of the one or
more airflow
channels. In such embodiments, preferably the barrier comprises a barrier
coating provided on
at least substantially the entire inner surface of the one or more airflow
channels. More
preferably, the barrier comprises a barrier coating provided on the entire
inner surface of the
one or more airflow channels.
As used herein, the term 'coating' is used to describe a layer of material
that covers and
is adhered to the combustible heat source.
In other embodiments, the barrier coating may be provided by insertion of a
liner into the
one or more airflow channels. For example, where the one or more airflow
channels comprise
one or more enclosed airflow channels that extend through the interior of the
non-blind
combustible heat source, a non-combustible substantially air impermeable
hollow tube may be
inserted into each of the one or more airflow channels.
Depending upon the desired characteristics and performance of the smoking
article, the
barrier may have a low thermal conductivity or a high thermal conductivity.
Preferably, the
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barrier has a low thermal conductivity.
The thickness of the barrier may be appropriately adjusted to achieve good
smoking
performance. In certain embodiments, the barrier may have a thickness of
between about
30 microns and about 200 microns. In a preferred embodiment, the barrier has a
thickness of
between about 30 microns and about 100 microns.
The barrier may be formed from one or more suitable materials that are
substantially
thermally stable and non-combustible at temperatures achieved by the non-blind
combustible
heat source during ignition and combustion. Suitable materials are known in
the art and
include, but are not limited to, for example: clays; metal oxides, such as
iron oxide, alumina,
titania, silica, silica-alumina, zirconia and ceria; zeolites; zirconium
phosphate; and other
ceramic materials or combinations thereof.
Preferred materials from which the barrier may be formed include clays,
glasses,
aluminium, iron oxide and combinations thereof. If desired, catalytic
ingredients, such as
ingredients that promote the oxidation of carbon monoxide to carbon dioxide,
may be
incorporated in the barrier. Suitable catalytic ingredients include, but are
not limited to, for
example, platinum, palladium, transition metals and their oxides.
Where the barrier comprises a barrier coating provided on an inner surface of
the one or
more airflow channels, the barrier coating may be applied to the inner surface
of the one or
more airflow channels by any suitable method, such as the methods described in
US-A-5,040,551. For example, the inner surface of the one or more airflow
channels may be
sprayed, wetted or painted with a solution or a suspension of the barrier
coating. In certain
preferred embodiments, the barrier coating is applied to the inner surface of
the one or more
airflow channels by the process described in WO-A2-2009/074870 as the
combustible heat
source is extruded.
Smoking articles according to the invention may further comprise a non-
combustible
substantially air impermeable barrier between the rear face of the combustible
heat source and
the aerosol-forming substrate.
Where smoking articles according to the invention comprise a non-blind
combustible
heat source and a non-combustible, substantially air impermeable barrier
between the rear face
of the combustible heat source and the aerosol-forming substrate, the barrier
should allow air
entering the smoking article through the one or more airflow channels
extending from the front
face to the rear face of the non-blind combustible heat source to be drawn
downstream through
the smoking article.
The barrier may abut one or both of the rear face of the combustible heat
source and the
aerosol-forming substrate. Alternatively, the barrier may be spaced apart from
one or both of
the rear face of the combustible heat source and the aerosol-forming
substrate.
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The barrier may be adhered or otherwise affixed to one or both of the rear
face of the
combustible heat source and the aerosol-forming substrate.
In certain preferred embodiments, the barrier comprises a non-combustible
substantially
air impermeable barrier coating provided on the rear face of the combustible
heat source. In
such embodiments, preferably the barrier comprises barrier coating provided on
at least
substantially the entire rear face of the combustible heat source. More
preferably, the barrier
comprises a barrier coating provided on the entire rear face of the
combustible heat source.
The barrier may advantageously limit the temperature to which the aerosol-
forming
substrate is exposed during ignition and combustion of the combustible heat
source, and so
help to avoid or reduce thermal degradation or combustion of the aerosol-
forming substrate
during use of the smoking article. This is particularly advantageous where the
combustible heat
source comprises one or more additives to aid ignition of the combustible heat
source.
To facilitate aerosol formation, the aerosol-forming substrates of heated
smoking articles
typically comprise a polyhydric alcohol, such as glycerine, or other known
aerosol-formers.
During storage and smoking, such aerosol-formers may migrate from the aerosol-
forming
substrates of known heated smoking articles to the combustible heat sources
thereof. Migration
of aerosol-formers to the combustible heat sources of known heated smoking
articles can
disadvantageously lead to decomposition of the aerosol-formers, particularly
during smoking of
the heated smoking articles.
Inclusion of a non-combustible substantially air impermeable barrier between
the rear
face of the combustible heat source and the aerosol-forming substrate of
smoking articles
according to the invention may advantageously substantially prevent or inhibit
migration of
components of the aerosol-forming substrate to the combustible heat source
during storage of
the smoking article.
Alternatively or in addition, inclusion of a non-combustible substantially air
impermeable
barrier between the rear face of the combustible heat source and the aerosol-
forming substrate
of smoking articles according to the invention may advantageously
substantially prevent or
inhibit migration of components of the aerosol-forming substrate to the
combustible heat source
during use of the smoking article.
Inclusion of a non-combustible substantially air impermeable barrier between
the rear
face of the combustible heat source and the aerosol-forming substrate is
particularly
advantageous where the aerosol-forming substrate comprises at least one
aerosol-former.
In such embodiments, inclusion of a non-combustible substantially air
impermeable
barrier between the rear face of the combustible heat source and the aerosol-
forming substrate
of smoking articles according to the invention may advantageously prevent or
inhibit migration
of the at least one aerosol-former from the aerosol-forming substrate to the
combustible heat
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source during storage and use of the smoking article. Decomposition of the at
least one
aerosol-former during use of the smoking article may thus be advantageously
substantially
avoided or reduced.
Depending upon the desired characteristics and performance of the smoking
article, the
non-combustible substantially air impermeable barrier between the rear face of
the combustible
heat source and the aerosol-forming substrate may have a low thermal
conductivity or a high
thermal conductivity. In certain embodiments, the barrier may be formed from
material having a
bulk thermal conductivity of between about 0.1 W per metre Kelvin (W/(m=K))
and about 200 W
per metre Kelvin (W/(m=K)), at 23 C and a relative humidity of 50% as measured
using the
modified transient plane source (MTPS) method.
The thickness of the barrier may be appropriately adjusted to achieve good
smoking
performance. In certain embodiments, the barrier may have a thickness of
between about
10 microns and about 500 microns.
The barrier may be formed from one or more suitable materials that are
substantially
thermally stable and non-combustible at temperatures achieved by the
combustible heat source
during ignition and combustion. Suitable materials are known in the art and
include, but are not
limited to, clays (such as, for example, bentonite and kaolinite), glasses,
minerals, ceramic
materials, resins, metals and combinations thereof.
Preferred materials from which the barrier may be formed include clays and
glasses.
More preferred materials from which the barrier may be formed include copper,
aluminium,
stainless steel, alloys, alumina (A1203), resins, and mineral glues.
In certain preferred embodiments, the barrier comprises a clay coating
comprising a
50/50 mixture of bentonite and kaolinite provided on the rear face of the
combustible heat
source. In other preferred embodiments, the barrier comprises a glass coating,
more preferably
a sintered glass coating, provided on the rear face of the combustible heat
source.
In certain particularly preferred embodiments, the barrier comprises an
aluminium
coating provided on the rear face of the combustible heat source.
Preferably, the barrier has a thickness of at least about 10 microns.
Due to the slight permeability of clays to air, in embodiments where the
barrier
comprises a clay coating provided on the rear face of the combustible heat
source, the clay
coating more preferably has a thickness of at least about 50 microns, and most
preferably of
between about 50 microns and about 350 microns.
In embodiments where the barrier is formed from one or more materials that are
more
impervious to air, such as aluminium, the barrier may be thinner, and
generally will preferably
have a thickness of less than about 100 microns, and more preferably of about
20 microns.
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In embodiments where the barrier comprises a glass coating provided on the
rear face of
the combustible heat source, the glass coating preferably has a thickness of
less than about
200 microns.
The thickness of the barrier may be measured using a microscope, a scanning
electron
microscope (SEM) or any other suitable measurement methods known in the art.
Where the barrier comprises a barrier coating provided on the rear face of the
combustible heat source, the barrier coating may be applied to cover and
adhere to the rear
face of the combustible heat source by any suitable methods known in the art
including, but not
limited to, spray-coating, vapour deposition, dipping, material transfer (for
example, brushing or
gluing), electrostatic deposition or any combination thereof.
For example, the barrier coating may be made by pre-forming a barrier in the
approximate size and shape of the rear face of the combustible heat source,
and applying it to
the rear face of the combustible heat source to cover and adhere to at least
substantially the
entire rear face of the combustible heat source. Alternatively, the barrier
coating may be cut or
otherwise machined after it is applied to the rear face of the combustible
heat source. In one
preferred embodiment, aluminium foil is applied to the rear face of the
combustible heat source
by gluing or pressing it to the combustible heat source, and is cut or
otherwise machined so that
the aluminium foil covers and adheres to at least substantially the entire
rear face of the
combustible heat source, preferably to the entire rear face of the combustible
heat source.
In another preferred embodiment, the barrier coating is formed by applying a
solution or
suspension of one or more suitable coating materials to the rear face of the
combustible heat
source. For example, the barrier coating may be applied to the rear face of
the combustible
heat source by dipping the rear face of the combustible heat source in a
solution or suspension
of one or more suitable coating materials or by brushing or spray-coating a
solution or
suspension or electrostatically depositing a powder or powder mixture of one
or more suitable
coating materials onto the rear face of the combustible heat source. Where the
barrier coating
is applied to the rear face of the combustible heat source by
electrostatically depositing a
powder or powder mixture of one or more suitable coating materials onto the
rear face of the
combustible heat source, the rear face of the combustible heat source is
preferably pre-treated
with water glass before electrostatic deposition. Preferably, the barrier
coating is applied by
spray-coating.
The barrier coating may be formed through a single application of a solution
or
suspension of one or more suitable coating materials to the rear face of the
combustible heat
source. Alternatively, the barrier coating may be formed through multiple
applications of a
solution or suspension of one or more suitable coating materials to the rear
face of the
combustible heat source. For example, the barrier coating may be formed
through one, two,
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three, four, five, six, seven or eight successive applications of a solution
or suspension of one or
more suitable coating materials to the rear face of the combustible heat
source.
Preferably, the barrier coating is formed through between one and ten
applications of a
solution or suspension of one or more suitable coating materials to the rear
face of the
combustible heat source.
After application of the solution or suspension of one or more coating
materials to the
rear face thereof, the combustible heat source may be dried to form the
barrier coating.
Where the barrier coating is formed through multiple applications of a
solution or
suspension of one or more suitable coating materials to the rear face thereof,
the combustible
heat source may need to be dried between successive applications of the
solution or
suspension.
Alternatively or in addition to drying, after application of a solution or
suspension of one
or more coating materials to the rear face of the combustible heat source, the
coating material
on the combustible heat source may be sintered in order to form the barrier
coating. Sintering
of the barrier coating is particularly preferred where the barrier coating is
a glass or ceramic
coating. Preferably, the barrier coating is sintered at a temperature of
between about 500 C
and about 900 C, and more preferably at about 700 C.
Smoking articles according to the invention may comprise one or more first air
inlets
around the periphery of the aerosol-forming substrate.
As used herein, the term 'air inlet' is used to describe a hole, slit, slot or
other aperture
through which air may be drawn into the smoking article.
Where smoking articles according to the invention comprise one or more first
air inlets
around the periphery of the aerosol-forming substrate, in use, cool air is
drawn into the aerosol-
forming substrate of the smoking article through the first air inlets. The air
drawn into the
aerosol-forming substrate through the first air inlets passes downstream
through the smoking
article from the aerosol-forming substrate and exits the smoking article
through the proximal end
thereof.
During puffing by a user, the cool air drawn through the one or more first air
inlets
around the periphery of the aerosol-forming substrate advantageously reduces
the temperature
of the aerosol-forming substrate. This advantageously substantially prevents
or inhibits spikes
in the temperature of the aerosol-forming substrate during puffing by a user.
As used herein, the term 'cool air' is used to describe ambient air that is
not significantly
heated by the combustible heat source upon puffing by a user.
By preventing or inhibiting spikes in the temperature of the aerosol-forming
substrate,
the inclusion of one or more first air inlets around the periphery of the
aerosol-forming substrate,
advantageously helps to avoid or reduce combustion or pyrolysis of the aerosol-
forming
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substrate under intense puffing regimes. In addition, the inclusion of one or
more first air inlets
around the periphery of the aerosol-forming substrate advantageously helps to
minimise or
reduce the impact of a user's puffing regime on the composition of the
mainstream aerosol of
the smoking article.
In certain preferred embodiments, the one or more first air inlets are located
proximate to
the downstream end of the aerosol-forming substrate.
In certain embodiments, the aerosol-forming substrate may abut the rear face
of the
combustible heat source.
As used herein, the term 'abut' is used to describe the aerosol-forming
substrate being in
direct contact with the rear face of the combustible heat source or a non-
combustible
substantially air impermeable barrier coating provided on the rear face of the
combustible heat
source.
In other embodiments, the aerosol-forming substrate may be spaced apart from
the rear
face of the combustible heat source. That is, there may be a space or gap
between the
aerosol-forming substrate and the rear face of the combustible heat source.
As used herein, the term 'spaced apart' is used to describe the aerosol-
forming
substrate not being in direct contact with the rear face of the combustible
heat source or a non-
combustible substantially air impermeable barrier coating provided on the rear
face of the
combustible heat source.
Alternatively or in addition to one or more first air inlets, in such
embodiments smoking
articles according to the invention may comprise one or more second air inlets
between the rear
face of the combustible heat source and the aerosol-forming substrate. In use,
cool air is drawn
into the space between the combustible heat source and the aerosol-forming
substrate through
the second air inlets. The air drawn into the space between the combustible
heat source and
the aerosol-forming substrate through the second air inlets passes downstream
through the
smoking article from the space between the combustible heat source and the
aerosol-forming
substrate and exits the smoking article through the proximal end thereof.
During puffing by a user, cool air drawn through the one or more second inlets
between
the rear face of the combustible heat source and the aerosol-forming substrate
may
advantageously reduce the temperature of the aerosol-forming substrate.
This may
advantageously substantially prevent or inhibit spikes in the temperature of
the aerosol-forming
substrate during puffing by a user.
Alternatively or in addition to one or more first air inlets or one or more
second air inlets,
smoking articles according to the invention may comprise one or more third air
inlets
downstream of the aerosol-forming substrate.
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It will be appreciated that smoking articles according to the invention may
comprise one
or more first air inlets around the periphery of the aerosol-forming
substrate, or one or more
second air inlets between the rear face of the combustible heat source and the
aerosol-forming
substrate, or one or more third air inlets downstream of the aerosol-forming
substrate, or any
combination thereof.
The number, shape, size and location of the air inlets may be appropriately
adjusted to
achieve a good smoking performance.
Preferably, the combustible heat source is a carbonaceous heat source. As used
herein,
the term 'carbonaceous' is used to describe a combustible heat source
comprising carbon.
Preferably, combustible carbonaceous heat sources for use in smoking articles
according to the
invention have a carbon content of at least about 35 percent, more preferably
of at least about
40 percent, most preferably of at least about 45 percent by dry weight of the
combustible heat
source.
In some embodiments, combustible heat sources according to the invention are
combustible carbon-based heat sources. As used herein, the term 'carbon-based
heat source'
is used to describe a heat source comprised primarily of carbon.
Combustible carbon-based heat sources for use in smoking articles according to
the
invention have a carbon content of at least about 50 percent. For example,
combustible
carbon-based heat sources for use in smoking articles according to the
invention may have a
carbon content of at least about 60 percent, or at least about 70 percent, or
at least about
80 percent by dry weight of the combustible carbon-based heat source.
Smoking articles according to the invention may comprise combustible
carbonaceous
heat sources formed from one or more suitable carbon-containing materials.
If desired, one or more binders may be combined with the one or more carbon-
containing materials. Preferably, the one or more binders are organic binders.
Suitable known
organic binders, include but are not limited to, gums (for example, guar gum),
modified
celluloses and cellulose derivatives (for example, methyl cellulose,
carboxymethyl cellulose,
hydroxypropyl cellulose and hydroxypropyl methylcellulose) flour, starches,
sugars, vegetable
oils and combinations thereof.
In one preferred embodiment, the combustible heat source is formed from a
mixture of
carbon powder, modified cellulose, flour and sugar.
Instead of, or in addition to one or more binders, combustible heat sources
for use in
smoking articles according to the invention may comprise one or more additives
in order to
improve the properties of the combustible heat source. Suitable additives
include, but are not
limited to, additives to promote consolidation of the combustible heat source
(for example,
sintering aids), additives to promote ignition of the combustible heat source
(for example,
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oxidisers such as perchlorates, chlorates, nitrates, peroxides, permanganates,
zirconium and
combinations thereof), additives to promote combustion of the combustible heat
source (for
example, potassium and potassium salts, such as potassium citrate) and
additives to promote
decomposition of one or more gases produced by combustion of the combustible
heat source
(for example catalysts, such as CuO, Fe203 and A1203).
Where smoking articles according to the invention comprise a barrier coating
provided
on the rear face of the combustible heat source, such additives may be
incorporated in the
combustible heat source prior to or after application of the barrier coating
to the rear face of the
combustible heat source.
In certain preferred embodiments, the combustible heat source is a combustible
carbonaceous heat source comprising carbon and at least one ignition aid. In
one preferred
embodiment, the combustible heat source is a combustible carbonaceous heat
source
comprising carbon and at least one ignition aid as described in WO-A1-
2012/164077.
As used herein, the term 'ignition aid' is used to denote a material that
releases one or
both of energy and oxygen during ignition of the combustible heat source,
where the rate of
release of one or both of energy and oxygen by the material is not ambient
oxygen diffusion
limited. In other words, the rate of release of one or both of energy and
oxygen by the material
during ignition of the combustible heat source is largely independent of the
rate at which
ambient oxygen can reach the material. As used herein, the term 'ignition aid'
is also used to
denote an elemental metal that releases energy during ignition of the
combustible heat source,
wherein the ignition temperature of the elemental metal is below about 500 C
and the heat of
combustion of the elemental metal is at least about 5 kJ/g.
As used herein, the term 'ignition aid' does not include alkali metal salts of
carboxylic
acids (such as alkali metal citrate salts, alkali metal acetate salts and
alkali metal succinate
salts), alkali metal halide salts (such as alkali metal chloride salts),
alkali metal carbonate salts
or alkali metal phosphate salts, which are believed to modify carbon
combustion. Even when
present in a large amount relative to the total weight of the combustible heat
source, such alkali
metal burn salts do not release enough energy during ignition of a combustible
heat source to
produce an acceptable aerosol during early puffs.
Examples of suitable oxidizing agents include, but are not limited to:
nitrates such as, for
example, potassium nitrate, calcium nitrate, strontium nitrate, sodium
nitrate, barium nitrate,
lithium nitrate, aluminium nitrate and iron nitrate; nitrites; other organic
and inorganic nitro
compounds; chlorates such as, for example, sodium chlorate and potassium
chlorate;
perchlorates such as, for example, sodium perchlorate; chlorites; bromates
such as, for
example, sodium bromate and potassium bromate; perbromates; bromites; borates
such as, for
example, sodium borate and potassium borate; ferrates such as, for example,
barium ferrate;
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ferrites; manganates such as, for example, potassium manganate; permanganates
such as, for
example, potassium permanganate; organic peroxides such as, for example,
benzoyl peroxide
and acetone peroxide; inorganic peroxides such as, for example, hydrogen
peroxide, strontium
peroxide, magnesium peroxide, calcium peroxide, barium peroxide, zinc peroxide
and lithium
peroxide; superoxides such as, for example, potassium superoxide and sodium
superoxide;
iodates; periodates; iodites; sulphates; sulfites; other sulfoxides;
phosphates; phospinates;
phosphites; and phosphanites.
While advantageously improving the ignition and combustion properties of the
combustible heat source, the inclusion of ignition and combustion additives
can give rise to
undesirable decomposition and reaction products during use of the smoking
article. For
example, decomposition of nitrates included in the combustible heat source to
aid ignition
thereof can result in the formation of nitrogen oxides.
Where smoking articles according to the invention comprise a non-blind
combustible
heat source, the inclusion of a non-combustible substantially air impermeable
barrier between
the one or more airflow channels and the non-blind combustible heat source may
advantageously substantially prevent or inhibit such decomposition and
reaction products from
entering air drawn into smoking articles according to the invention through
the one or more
airflow channels as the drawn air passes through the one or more airflow
channels.
The inclusion of a non-combustible substantially air impermeable barrier
between the
rear face of the combustible heat source and the aerosol-forming substrate may
also
advantageously substantially prevent or inhibit such decomposition and
reaction products from
entering air drawn through smoking articles according to the invention.
Combustible carbonaceous heat sources for use in smoking articles according to
the
invention may be prepared as described in prior art that is known to persons
of ordinary skill in
the art.
Combustible carbonaceous heat sources for use in smoking articles according to
the
invention, are preferably formed by mixing one or more carbon-containing
materials with one or
more binders and other additives, where included, and pre-forming the mixture
into a desired
shape. The mixture of one or more carbon containing materials, one or more
binders and
optional other additives may be pre-formed into a desired shape using any
suitable known
ceramic forming methods such as, for example, slip casting, extrusion,
injection moulding and
die compaction or pressing. In certain preferred embodiments, the mixture is
pre-formed into a
desired shape by pressing or extrusion or a combination thereof.
Preferably, the mixture of one or more carbon-containing materials, one or
more binders
and other additives is pre-formed into an elongate rod. However, it will be
appreciated that the
mixture of one or more carbon-containing materials, one or more binders and
other additives
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may be pre-formed into other desired shapes.
After formation, particularly after extrusion, the elongate rod or other
desired shape is
preferably dried to reduce its moisture content and then pyrolysed in a non-
oxidizing
atmosphere at a temperature sufficient to carbonise the one or more binders,
where present,
and substantially eliminate any volatiles in the elongate rod or other shape.
The elongate rod or
other desired shape is pyrolysed preferably in a nitrogen atmosphere at a
temperature of
between about 700 C and about 900 C.
In certain embodiments, at least one metal nitrate salt is incorporated in the
combustible
heat source by including at least one metal nitrate precursor in the mixture
of one or more
carbon containing materials, one or more binders and other additives. The at
least one metal
nitrate precursor is then subsequently converted in-situ into at least one
metal nitrate salt by
treating the pyrolysed pre-formed cylindrical rod or other shape with an
aqueous solution of
nitric acid. In one embodiment, the combustible heat source comprises at least
one metal
nitrate salt having a thermal decomposition temperature of less than about 600
C, more
preferably of less than about 400 C. Preferably, the at least one metal
nitrate salt has a
decomposition temperature of between about 150 C and about 600 C, more
preferably of
between about 200 C and about 400 C.
In preferred embodiments, exposure of the combustible heat source to a
conventional
yellow flame lighter or other ignition means should cause the at least one
metal nitrate salt to
decompose and release oxygen and energy. This decomposition causes an initial
boost in the
temperature of the combustible heat source and also aids in the ignition of
the combustible heat
source. After decomposition of the at least one metal nitrate salt, the
combustible heat source
preferably continues to combust at a lower temperature.
The inclusion of at least one metal nitrate salt advantageously results in
ignition of the
combustible heat source being initiated internally, and not only at a point on
the surface thereof.
Preferably, the at least one metal nitrate salt is present in the combustible
heat source in an
amount of between about 20 percent by dry weight and about 50 percent by dry
weight of the
combustible heat source.
In other embodiments, the combustible heat source comprises at least one
peroxide or
superoxide that actively evolves oxygen at a temperature of less than about
600 C, more
preferably at a temperature of less than about 400 C.
Preferably, the at least one peroxide or superoxide actively evolves oxygen at
a
temperature of between about 150 C and about 600 C, more preferably at a
temperature of
between about 200 C and about 400 C, most preferably at a temperature of about
350 C.
In use, exposure of the combustible heat source to a conventional yellow flame
lighter or
other ignition means should cause the at least one peroxide or superoxide to
decompose and
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release oxygen. This causes an initial boost in the temperature of the
combustible heat source
and also aids in the ignition of the combustible heat source. After
decomposition of the at least
one peroxide or superoxide, the combustible heat source preferably continues
to combust at a
lower temperature.
The inclusion of at least one peroxide or superoxide advantageously results in
ignition of
the combustible heat source being initiated internally, and not only at a
point on the surface
thereof.
The combustible heat source preferably has a porosity of between about 20
percent and
about 80 percent, more preferably of between about 20 percent and 60 percent.
Where the
combustible heat source comprises at least one metal nitrate salt, this
advantageously allows
oxygen to diffuse into the mass of the combustible heat source at a rate
sufficient to sustain
combustion as the at least one metal nitrate salt decomposes and combustion
proceeds. Even
more preferably, the combustible heat source has a porosity of between about
50 percent and
about 70 percent, more preferably of between about 50 percent and about 60
percent as
measured by, for example, mercury porosimetry or helium pycnometry. The
required porosity
may be readily achieved during production of the combustible heat source using
conventional
methods and technology.
Advantageously, combustible carbonaceous heat sources for use in smoking
articles
according to the invention have an apparent density of between about 0.6 g/cm3
and about
1 g/cm3.
Preferably, the combustible heat source has a mass of between about 300 mg and
about 500 mg, more preferably of between about 400 mg and about 450 mg.
Preferably, the combustible heat source has a length of between about 7 mm and
about
17 mm, more preferably of between about 7 mm and about 15 mm, most preferably
of between
about 7 mm and about 13 mm.
Preferably, the combustible heat source has a diameter of between about 5 mm
and
about 9 mm, more preferably of between about 7 mm and about 8 mm.
Preferably, the combustible heat source is of substantially uniform diameter.
However,
the combustible heat source may alternatively be tapered so that the diameter
of a rear portion
of the blind combustible heat source is greater than the diameter of a front
portion thereof.
Particularly preferred are combustible heat sources that are substantially
cylindrical. The
combustible heat source may, for example, be a cylinder or tapered cylinder of
substantially
circular cross-section or a cylinder or tapered cylinder of substantially
elliptical cross-section.
Smoking articles according to the invention preferably comprise an aerosol-
forming
substrate comprising at least one aerosol-former and a material capable of
releasing volatile
compounds in response to heating. The aerosol-forming substrate may comprise
other
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additives and ingredients including, but not limited to, humectants,
flavourants, binders and
mixtures thereof.
Preferably, the aerosol-forming substrate comprises nicotine. More preferably,
the
aerosol-forming substrate comprises tobacco.
The at least one aerosol-former may be any suitable known compound or mixture
of
compounds that, in use, facilitates formation of a dense and stable aerosol
and that is
substantially resistant to thermal degradation at the operating temperature of
the smoking
article. Suitable aerosol-formers are well known in the art and include, for
example, polyhydric
alcohols, esters of polyhydric alcohols, such as glycerol mono-, di- or
triacetate, and aliphatic
esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate
and dimethyl
tetradecanedioate. Preferred aerosol formers for use in smoking articles
according to the
invention are polyhydric alcohols or mixtures thereof, such as triethylene
glycol, 1,3-butanediol
and, most preferred, glycerine.
The material capable of emitting volatile compounds in response to heating may
be a
charge of plant-based material. The material capable of emitting volatile
compounds in
response to heating may be a charge of homogenised plant-based material. For
example, the
aerosol-forming substrate may comprise one or more materials derived from
plants including,
but not limited to: tobacco; tea, for example green tea; peppermint; laurel;
eucalyptus; basil;
sage; verbena; and tarragon.
Preferably, the material capable of emitting volatile compounds in response to
heating is
a charge of tobacco-based material, most preferably a charge of homogenised
tobacco-based
material.
The aerosol-forming substrate may be in the form of a plug or segment
comprising a
material capable of emitting volatile compounds in response to heating
circumscribed by a
paper or other wrapper. As stated above, where an aerosol-forming substrate is
in the form of
such a plug or segment, the entire plug or segment including any wrapper is
considered to be
the aerosol-forming substrate.
Preferably, the aerosol-forming substrate has a length of between about 5 mm
and
about 20 mm, more preferably of between about 8 mm and about 12 mm.
In preferred embodiments, the aerosol-forming substrate comprises a plug of
tobacco-
based material wrapped in a plug wrap. In particular preferred embodiments,
the aerosol-
forming substrate comprises a plug of homogenised tobacco-based material
wrapped in a plug
wrap.
Smoking articles according to the invention preferably comprise a mouthpiece
downstream of the aerosol-forming substrate. The mouthpiece is located at the
proximal end of
the smoking article.
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Preferably, the mouthpiece is of low filtration efficiency, more preferably of
very low
filtration efficiency. The mouthpiece may be a single segment or component
mouthpiece.
Alternatively, the mouthpiece may be a multi-segment or multi-component
mouthpiece.
The mouthpiece may comprise a filter comprising one or more segments
comprising
suitable known filtration materials. Suitable filtration materials are known
in the art and include,
but are not limited to, cellulose acetate and paper. Alternatively or in
addition, the mouthpiece
may comprise one or more segments comprising absorbents, adsorbents,
flavourants, and
other aerosol modifiers and additives or combinations thereof.
Smoking articles according to the element preferably further comprise a
transfer element
or spacer element between the aerosol-forming substrate and the mouthpiece.
The transfer element may abut one or both of the aerosol-forming substrate and
the
mouthpiece. Alternatively, the transfer element may be spaced apart from one
or both of the
aerosol-forming substrate and the mouthpiece.
The inclusion of a transfer element advantageously allows cooling of the
aerosol
generated by heat transfer from the combustible heat source to the aerosol-
forming substrate.
The inclusion of a transfer element also advantageously allows the overall
length of smoking
articles according to the invention to be adjusted to a desired value, for
example to a length
similar to that of conventional cigarettes, through an appropriate choice of
the length of the
transfer element.
The transfer element may have a length of between about 7 mm and about 50 mm,
for
example a length of between about 10 mm and about 45 mm or of between about 15
mm and
about 30 mm. The transfer element may have other lengths depending upon the
desired overall
length of the smoking article, and the presence and length of other components
within the
smoking article.
Preferably, the transfer element comprises at least one open-ended tubular
hollow body.
In such embodiments, in use, the air drawn through the smoking article passes
through the at
least one open-ended tubular hollow body as it passes downstream through the
smoking article
from the aerosol-forming substrate to the proximal end thereof.
The transfer element may comprise at least one open-ended tubular hollow
bodies
formed from one or more suitable materials that are substantially thermally
stable at the
temperature of the aerosol generated by the transfer of heat from the
combustible heat source
to the aerosol-forming substrate. Suitable materials are known in the art and
include, but are
not limited to, paper, cardboard, plastics, such a cellulose acetate, ceramics
and combinations
thereof.
Alternatively or in addition, smoking articles according to the invention may
comprise an
aerosol-cooling element or heat exchanger between the aerosol-forming
substrate and the
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mouthpiece. The aerosol-cooling element may comprise a plurality of
longitudinally extending
channels.
The aerosol-cooling element may comprise a gathered sheet of material selected
from
the group consisting of metallic foil, polymeric material, and substantially
non-porous paper or
cardboard. In certain embodiments, the aerosol-cooling element may comprise a
gathered
sheet of material selected from the group consisting of polyethylene (PE),
polypropylene (PP),
polyvinylchloride (PVC), polyethylene terephthalate (PET), polylactic acid
(PLA), cellulose
acetate (CA), and aluminium foil.
In certain preferred embodiments, the aerosol-cooling element may comprise a
gathered
sheet of biodegradable polymeric material, such as polylactic acid (PLA) or a
grade of Mater-Bi
(a commercially available family of starch based copolyesters).
Smoking articles according to the invention may comprise one or more aerosol
modifying agents downstream of the aerosol-forming substrate. For example, one
or more of
the mouthpiece, transfer element and aerosol-cooling element of smoking
articles according to
the invention may comprise one or more aerosol modifying agents.
Suitable aerosol-modifying agents include, but are not limited to:
flavourants; and
chemesthetic agents.
As used herein, the term 'flavourant' is used to describe any agent that, in
use, imparts
one or both of a taste or aroma to an aerosol generated by the aerosol-forming
substrate of the
smoking article.
As used herein, the term `chemesthetic agent' is used to describe any agent
that, in use,
is perceived in the oral or olfactory cavities of a user by means other than,
or in addition to,
perception via taste receptor or olfactory receptor cells. Perception of
chemesthetic agents is
typically via a "trigeminal response," either via the trigeminal nerve,
glossopharyngeal nerve, the
vagus nerve, or some combination of these. Typically, chemesthetic agents are
perceived as
hot, spicy, cooling, or soothing sensations.
Smoking articles according to the invention may comprise one or more aerosol
modifying agents that are both a flavourant and a chemesthetic agent
downstream of the
aerosol-forming substrate. For example, one or more of the mouthpiece,
transfer element and
aerosol-cooling element of smoking articles according to the invention may
comprise menthol or
another flavourant that provides a cooling chemesthetic effect.
Smoking articles according to the invention may be assembled using known
methods
and machinery.
The invention will be further described, by way of example only, with
reference to the
accompanying drawings in which:
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Figure 1 shows a schematic longitudinal cross-section of a smoking article
according to
a first embodiment of the invention;
Figure 2 shows a schematic longitudinal cross-section of a smoking article
according to
a third embodiment of the invention;
Figure 3a shows a graph of the temperature of the rear portion of the
combustible heat
source of a smoking article according to the invention during smoking; and
Figure 3b shows a graph of the temperature of the aerosol-generating substrate
of the
smoking article according to the invention during smoking.
The smoking article 2 according to the first embodiment of the invention shown
in Figure
1 comprises a blind combustible heat source 4 having a front face 6 and an
opposed rear face
8, an aerosol-forming substrate 10, a transfer element 12, an aerosol-cooling
element 14, a
spacer element 16 and a mouthpiece 18 in abutting coaxial alignment..
The blind combustible heat source 4 is a blind carbonaceous combustible heat
source
and is located at the distal end of the smoking article 2. As shown in Figure
1, a non-
combustible substantially air impermeable barrier 22 in the form of a disc of
aluminium foil is
provided between the rear face 8 of the blind combustible heat source 4 and
the aerosol-
forming substrate 10. The barrier 22 is applied to the rear face 8 of the
blind combustible heat
source 4 by pressing the disc of aluminium foil onto the rear face 8 of the
blind combustible heat
source 4 and abuts the rear face 8 of the combustible carbonaceous heat source
4 and the
aerosol-forming substrate 10.
In other embodiments of the invention (not shown), the non-combustible
substantially air
impermeable barrier 22 between the rear face 8 of the blind combustible heat
source 4 and the
aerosol-forming substrate 10 may be omitted.
The aerosol-forming substrate 10 is located immediately downstream of the
barrier 22
applied to the rear face 8 of the blind combustible heat source 4. The aerosol-
forming substrate
10 comprises a cylindrical plug of homogenised tobacco-based material 24
including an aerosol
former such as, for example, glycerine, wrapped in plug wrap 26.
The transfer element 12 is located immediately downstream of the aerosol-
forming
substrate 10 and comprises a cylindrical open-ended hollow cellulose acetate
tube 28.
The aerosol-cooling element 14 is located immediately downstream of the
transfer
element 12 and comprises a gathered sheet of biodegradable polymeric material
such as, for
example, polylactic acid.
The spacer element 16 is located immediately downstream of the aerosol-cooling
element 14 and comprises a cylindrical open-ended hollow paper or cardboard
tube 30.
The mouthpiece 18 is located immediately downstream of the spacer element 16.
As
shown in Figure 1, the mouthpiece 18 is located at the proximal end of the
smoking article 2 and
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comprises a cylindrical plug of suitable filtration material 32 such as, for
example, cellulose
acetate tow of very low filtration efficiency, wrapped in filter plug wrap 34
The smoking article may further comprise a band of tipping paper (not shown)
circumscribing a downstream end portion of the outer wrapper 20.
As shown in Figure 1, the smoking article 2 further comprises a single heat-
conducting
element 36 of suitable material such as, for example, aluminium foil,
overlying a rear portion of
the blind combustible heat source 4, the entire length of the aerosol-forming
substrate 10 and
the entire length of the transfer element 12.
In other embodiments of the invention (not shown), the transfer element 12 may
extend
beyond the single heat-conducting element 36 in the downstream direction. That
is the single
heat-conducting element 36 may overlie only a front portion of the transfer
element 12. In other
embodiments of the invention (not shown), the single heat-conducting element
36 may not
overlie any of the transfer element 12.
In further embodiments of the invention (not shown), the aerosol-forming
substrate 10
may extend beyond the single heat-conducting element 36 in the downstream
direction. That is
the single-heat-conducting element 36 may overlie only a front portion of the
aerosol-forming
substrate 10.
The single heat-conducting element 36 is radially separated from the blind
combustible
heat source 4 and the aerosol-forming substrate 10 by a wrapper 38 of heat
insulative sheet
material such as, for example, cigarette paper, of low air permeability, which
is wrapped around
the aerosol-forming substrate 10, transfer element 12 and a rear portion of
the blind
combustible heat source 4.
In the smoking article 2 according to the first embodiment of the invention
shown in
Figure 1, the single heat-conducting element 36 and the wrapper 38 radially
separating the
single heat-conducting element 36 from the blind combustible heat source 4 and
the aerosol-
forming substrate 10 extend to approximately the same position on the blind
combustible heat
source 4 in the upstream direction, such that the upstream ends of the single
heat-conducting
element 36 and the wrapper 38 are substantially aligned over the blind
combustible heat source
4.
However, it will be appreciated that in other embodiments of the invention
(not shown),
the wrapper 38 radially separating the single heat-conducting element 36 from
the blind
combustible heat source 4 and the aerosol-forming substrate 10 may extend
beyond the single
heat-conducting element 36 in the upstream direction.
The smoking article 2 according to the first embodiment of the invention
comprises one
or more first air inlets 38 around the periphery of the aerosol-forming
substrate 10.
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As shown in Figure 1, a circumferential arrangement of first air inlets 40 is
provided in
the plug wrap 26 of the aerosol-forming substrate 10, the wrapper 38 radially
separating the
single heat-conducting element 36 from the blind combustible heat source 4 and
the aerosol-
forming substrate 10 and the single heat conducting element 36 to admit cool
air (shown by
dotted arrows in Figure 1) into the aerosol-forming substrate 10.
In use, a user ignites the blind combustible heat source 4 of the smoking
article 2
according to the first embodiment of the invention and then draws on the
mouthpiece 18. When
a user draws on the mouthpiece 18, cool air (shown by dotted arrows in Figures
1) is drawn into
the aerosol-forming substrate 10 of the smoking article 2 through the first
air inlets 40.
The front portion of the aerosol-forming substrate 10 is heated by conduction
through
the rear face 8 of the blind combustible heat source 4 and the barrier 22.
The heating of the aerosol-forming substrate 10 by conduction releases
glycerine and
other volatile and semi-volatile compounds from the plug of homogenised
tobacco-based
material 24. The compounds released from the aerosol-forming substrate 10 form
an aerosol
that is entrained in the air drawn into the aerosol-forming substrate 10 of
the smoking article 2
through the first air inlets 40 as it flows through the aerosol-forming
substrate 10. The drawn air
and entrained aerosol (shown by dashed arrows in Figures 1 and 2) pass
downstream through
the transfer element 12, aerosol-cooling element 14 and spacer element 16,
where they cool
and condense. The cooled drawn air and entrained aerosol pass downstream
through the
mouthpiece 18 and are delivered to the user through the proximal end of the
smoking article 2
according to the first embodiment of the invention. The non-combustible
substantially air
impermeable barrier 22 on the rear face 8 of the blind combustible heat source
4 isolates the
blind combustible heat source 4 from air drawn through the smoking article 2
such that, in use,
air drawn through the smoking article 2 does not come into direct contact with
the blind
combustible heat source 4.
In use, the single heat-conducting element 36 retains heat within the smoking
article 2 to
help maintain the temperature of the aerosol-forming substrate 10 and so
facilitate continued
and enhanced aerosol delivery. In addition, the single heat-conducting element
36 transfers
heat along the aerosol-forming substrate 10 so that heat is dispersed through
a larger volume of
the aerosol-forming substrate 10. This helps to provide a more consistent puff-
by-puff aerosol
delivery.
A smoking article according to a second embodiment of the invention (not
shown) is of
largely identical construction to the smoking article according to the first
embodiment of the
invention shown in Figure 1. However, in the smoking article according to the
second
embodiment of the invention, the wrapper 38 radially separating the single
heat-conducting
element 36 from the blind combustible heat source 4 and the aerosol-forming
substrate 10 is
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omitted and the single heat-conducting element 36 is formed of a laminate
material comprising
an outer layer of heat conductive material and an inner layer of heat
insulative material. In the
smoking article according to the second embodiment of the invention, the outer
layer of heat
conductive material of the single heat-conducting element 36 is radially
separated from the blind
combustible heat source 4 and the aerosol-forming substrate 10 by the inner
layer of heat
insulative material of the single heat-conducting element 36.
The smoking article 42 according to the third embodiment of the invention
shown in
Figure 2 is of largely identical construction to the smoking article according
to the first
embodiment of the invention shown in Figure 1. However, in the smoking article
42 according
to the second embodiment of the invention, the first air inlets 40 around the
periphery of the
aerosol-forming substrate 10 are omitted and the combustible heat source 4 is
a non-blind
combustible carbonaceous heat source comprising a single central airflow
channel 44 extending
from the front face 6 to the rear face 8 of the non-blind combustible heat
source 4.
As shown in Figure 2, a non-combustible substantially air impermeable barrier
46 is
provided between the combustible heat source 4 and the central airflow channel
44. The barrier
46 comprises a non-combustible substantially air impermeable barrier coating
provided on the
entire inner surface of the single central airflow channel 44.
In use, a user ignites the non-blind combustible heat source 4 of the smoking
article 42
according to the third embodiment of the invention and then draws on the
mouthpiece 18.
When a user draws on the mouthpiece 18, cool air (shown by dotted arrows in
Figures 2) is
drawn into the aerosol-forming substrate 10 of the smoking article 2 through
the central airflow
channel 44. The non-combustible substantially air impermeable barrier 22 on
the rear face 8 of
the non-blind combustible heat source 4 and the non-combustible substantially
air impermeable
barrier 46 on the inner surface of the single central airflow channel 44
isolate the non-blind
combustible heat source 4 from air drawn through the smoking article 42 such
that, in use, air
drawn through the smoking article 42 does not come into direct contact with
the non-blind
combustible heat source 4.
In other embodiments of the invention (not shown), the non-combustible
substantially air
impermeable barrier 22 between the rear face 8 of the non-blind combustible
heat source 4 and
the aerosol-forming substrate 10 may be omitted.
A smoking article according to a fourth embodiment of the invention (not
shown) is of
largely identical construction to the smoking article according to the third
embodiment of the
invention shown in Figure 2. However, in the smoking article according to the
fourth
embodiment of the invention, the wrapper 38 radially separating the single
heat-conducting
element 36 from the blind combustible heat source 4 and the aerosol-forming
substrate 10 is
omitted and the single heat-conducting element 36 is formed of a laminate
material comprising
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an outer layer of heat conductive material and an inner layer of heat
insulative material. In the
smoking article according to the fourth embodiment of the invention, the outer
layer of heat
conductive material of the single heat-conducting element 36 is radially
separated from the non-
blind combustible heat source 4 and the aerosol-forming substrate 10 by the
inner layer of heat
insulative material of the single heat-conducting element 36.
Example A
A smoking article according to the invention of largely identical construction
to the
smoking article according to the second embodiment of the invention described
above is
assembled. The smoking article comprises a single heat-conducting element
formed of a
laminate material comprising an outer layer of aluminium and an inner layer of
paper. The
smoking article does not comprise an outer wrapper, such that the outer layer
of aluminium of
the single heat-conducting element is visible on the exterior of the smoking
article. Instead of a
circumferential arrangement of first air inlets around the periphery of the
aerosol-forming
substrate, the smoking article comprises a circumferential arrangement of
third air inlets around
the periphery of the transfer element.
In the smoking article according to the invention, the outer layer of
aluminium of the
single heat-conducting element is radially separated from the blind
combustible heat source and
the aerosol-forming substrate by the inner layer of paper of the single heat-
conducting element.
Comparative Example B
For the purposes of comparison, a smoking article not according to the
invention is
assembled. The smoking article not according to the invention comprises a
single heat-
conducting element formed of a laminate material comprising an inner layer of
aluminium and
an outer layer of paper. Otherwise, the smoking article not according to the
invention is of
identical construction to the smoking article according to the invention of
Example A.
In the smoking article not according to the invention, the inner layer of
aluminium of the
single heat-conducting element is in direct contact with the blind combustible
heat source and
the aerosol-forming substrate.
The temperature of the rear portion of the blind combustible heat sources of
the
smoking article according to the invention of Example A and the smoking
article not according
to the invention of Comparative Example B during combustion of the combustible
heat source
are measured in the smoking articles using a thermocouple attached to the
surface of the
smoking articles at a position 1 mm upstream of the aerosol-generating
substrates thereof.
The results are shown in Figure 3a.
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The temperature of the rear portion of the aerosol-forming substrates of the
smoking
article according to the invention of Example A and the smoking article not
according to the
invention of Comparative Example B during combustion of the combustible heat
source are
measured in the smoking articles using a thermocouple attached to the surface
of the smoking
articles at a position 6 mm downstream of the combustible heat sources
thereof. The results
are shown in Figure 3b.
To measure the temperatures of the rear portion of the blind combustible heat
sources
and the aerosol-forming substrates, the smoking articles are ignited using a
conventional yellow
flame lighter and smoked under a Health Canada smoking regime over 12 puffs
with a puff
volume of 55 ml, puff duration of 2 seconds and a puff interval of 30 seconds
using a smoking
machine. Conditions for smoking and smoking machine specifications are set out
in ISO
Standard 3308 (ISO 3308:2000). The atmosphere for conditioning and testing is
set out in ISO
Standard 3402.
As shown in Figures 3a and 3b, the temperature of the rear portion of the
blind
combustible heat source and the aerosol-forming substrate of the smoking
article not according
to the invention of Comparative Example B are reduced compared to the smoking
article
according to the invention, particularly during later puffs. This results in
the dry total particulate
matter (DTPM) delivery of the smoking article not according to the invention
of Comparative
Example B (10.3 mg) being lower than the dry total particulate matter (DTPM)
delivery of the
smoking article according to the invention of Example A (17.4 mg).
The specific embodiments described above are intended to illustrate the
invention.
However, other embodiments may be made without departing from the spirit and
scope of the
invention as defined in the claims, and it is to be understood that the
specific embodiments
described above are not intended to be limiting.
