Note: Descriptions are shown in the official language in which they were submitted.
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AEROSOL-GENERATING ARTICLE WITH VENTILATED HOLLOW SEGMENT
The present invention relates to an aerosol generating article comprising an
aerosol-
generating substrate and adapted to produce an inhalable aerosol upon heating.
Aerosol-generating articles in which an aerosol-generating substrate, such as
a tobacco-
containing substrate, is heated rather than combusted, are known in the art.
Typically in such
heated smoking articles, an aerosol is generated by the transfer of heat from
a heat source to a
physically separate aerosol-generating substrate or material, which may be
located in contact
with, within, around, or downstream of the heat source. During use of the
aerosol-generating
article, volatile compounds are released from the aerosol-generating substrate
by heat transfer
from the heat source and are entrained in air drawn through the aerosol-
generating article. As
the released compounds cool, they condense to form an aerosol.
A number of prior art documents disclose aerosol-generating devices for
consuming
aerosol-generating articles. Such devices include, for example, electrically
heated aerosol-
generating devices in which an aerosol is generated by the transfer of heat
from one or more
electrical heater elements of the aerosol-generating device to the aerosol-
generating substrate of
a heated aerosol-generating article.
Substrates for heated aerosol-generating articles have, in the past, typically
been produced
using randomly oriented shreds, strands, or strips of tobacco material. As an
alternative, rods for
heated aerosol-generating articles have been proposed, for example in
international patent
application WO-A-2012/164009, that are formed from gathered sheets of tobacco
material. The
rods disclosed in WO-A-2012/164009 have a longitudinal porosity that allows
air to be drawn
through the rods. Effectively, folds in the gathered sheets of tobacco
material define longitudinal
channels through the rod.
Alternative rods for heated aerosol-generating articles are known from
international patent
application WO-A-2011/101164. These rods are formed from strands of
homogenised tobacco
material, which may be formed by casting, rolling, calendering or extruding a
mixture comprising
particulate tobacco and at least one aerosol former to form a sheet of
homogenised tobacco
material. In an alternative embodiments, the rods of WO-A-2011/101164 may also
be formed
from strands of homogenised tobacco material obtained by extruding a mixture
comprising
particulate tobacco and at least one aerosol former to form continuous lengths
of homogenised
tobacco material.
Substrates for heated aerosol-generating articles typically further comprise
an aerosol
former, that is, a compound or mixture of compounds that, in use, facilitates
formation of the
aerosol and that preferably is substantially resistant to thermal degradation
at the operating
temperature of the aerosol-generating article. Examples of suitable aerosol-
formers include:
polyhydric alcohols, such as propylene glycol, triethylene glycol, 1,3-
butanediol and glycerin;
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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.
It is also common to include in an aerosol-generating article for producing an
inhalable
aerosol upon heating one or more additional elements that are assembled with
the substrate in a
same wrapper. Examples of such additional elements include a mouthpiece
filtration segment, a
support element adapted to impart structural strength to the aerosol-
generating article, a cooling
element adapted to favour cooling of the aerosol prior to reaching the
mouthpiece, and so forth.
However, although the inclusion of such additional elements has been proposed
in view of their
advantageous effects, it generally complicates the overall structure of the
aerosol-generating
article and makes it manufactures more complex and costly. In fact,
manufacturing such multi-
element aerosol-generating articles typically requires rather complex making
machinery and
combining machinery.
In view of this, aerosol-generating articles have also been proposed that have
a simpler
structure. However, in the absence of certain additional components, such as,
for example, an-
aerosol-cooling element, it may become more difficult to manufacture aerosol-
generating articles
that consistently provide the consumer with a satisfactory aerosol delivery
and RTD.
Thus, it would be desirable to provide an aerosol generating article that
enables the
provision of a consistently satisfactory aerosol delivery to the consumer
during use. Further, it
would be desirable to provide one such improved aerosol-generating article
that has a satisfactory
RTD value. It would be equally desirable to provide one such aerosol-
generating article that can
be manufactured efficiently and at high speed, preferably with a low RTD
variability from one
article to another. The present invention aims at providing a technical
solution adapted to achieve
at least one of the desirable results described above.
According to an aspect of the present invention, there is provided an aerosol-
generating
article for producing an inhalable aerosol when heated, the aerosol-generating
article comprising:
a rod of aerosol-generating substrate; a mouthpiece segment comprising a plug
of filtration
material, the mouthpiece segment being arranged downstream of the rod and in
longitudinal
alignment with the first segment; and a hollow tubular segment at a location
between the rod and
the mouthpiece segment. The hollow tube segment is in longitudinal alignment
with the rod and
the mouthpiece segment. Further, the hollow tubular segment defines a cavity
extending all the
way to an upstream end of the mouthpiece segment. The aerosol-generating
article further
comprises a ventilation zone at a location along the hollow tubular segment.
An equivalent
internal diameter of the hollow tubular segment at the location of the
ventilation zone is at least
about 5 millimetres. The rod of aerosol-generating substrate comprises at
least an aerosol
former, the rod of aerosol-generating substrate having an aerosol former
content of at least about
10 percent on a dry weight basis.
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The term "aerosol generating article" is used herein to denote an article
wherein an aerosol
generating substrate is heated to produce an deliver inhalable aerosol to a
consumer. As used
herein, the term "aerosol generating substrate" denotes a substrate capable of
releasing volatile
compounds upon heating to generate an aerosol.
A conventional cigarette is lit when a user applies a flame to one end of the
cigarette and
draws air through the other end. The localised heat provided by the flame and
the oxygen in the
air drawn through the cigarette causes the end of the cigarette to ignite, and
the resulting
combustion generates an inhalable smoke. By contrast, in heated aerosol
generating articles, an
aerosol is generated by heating a flavour generating substrate, such as
tobacco. Known heated
aerosol generating articles include, for example, electrically heated aerosol
generating articles
and aerosol generating articles in which an aerosol is generated by the
transfer of heat from a
combustible fuel element or heat source to a physically separate aerosol
forming material. For
example, aerosol generating articles according to the invention find
particular application in
aerosol generating systems comprising an electrically heated aerosol
generating device having
an internal heater blade which is adapted to be inserted into the rod of
aerosol generating
substrate. Aerosol generating articles of this type are described in the prior
art, for example, in
EP 0822670.
As used herein, the term "aerosol generating device" refers to a device
comprising a heater
element that interacts with the aerosol generating substrate of the aerosol
generating article to
generate an aerosol.
In the present specification, the term "tubular segment" is used to denote an
elongate
element defining a lumen or airflow passage along a longitudinal axis thereof.
In particular, the
term "tubular" will be used in the following with reference to a tubular
element having a
substantially cylindrical cross-section and defining at least one airflow
conduit establishing an
uninterrupted fluid communication between an upstream end of the tubular
element and a
downstream end of the tubular element. However, it will be understood that
alternative
geometries of the cross-section of the tubular element may be possible.
As used herein, the term "longitudinal" refers to the direction corresponding
to the main
longitudinal axis of the aerosol-generating article, which extends between the
upstream and
downstream ends of the aerosol-generating article. As used herein, the terms
"upstream" and
"downstream" describe the relative positions of elements, or portions of
elements, of the aerosol-
generating article in relation to the direction in which the aerosol is
transported through the
aerosol-generating article during use.
During use, air is drawn through the aerosol-generating article in the
longitudinal direction.
The term "transverse" refers to the direction that is perpendicular to the
longitudinal axis. Any
reference to the "cross-section" of the aerosol-generating article or a
component of the aerosol-
generating article refers to the transverse cross-section unless stated
otherwise.
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The term "length" denotes the dimension of a component of the aerosol-
generating article
in the longitudinal direction. For example, it may be used to denote the
dimension of the rod or
of the elongate tubular elements in the longitudinal direction.
The term "thickness of a peripheral wall of the tubular element" is used in
the present
specification to denote the minimum distance measured between the outer
surface and the inner
surface of the wall delimiting peripherally the tubular element. In practice,
the distance at a given
location is measured along a direction locally substantially perpendicular to
the outer surface and
the inner surface of the tubular element. For a tubular element having a
substantially circular
cross-section, the distance is measured along a substantially radial direction
of the tubular
element.
In some embodiments, the thickness of the peripheral wall of the tubular
element is
constant. In alternative embodiments, the thickness of the peripheral wall of
the tubular element
varies along the length of the tubular element. This may be because the
tubular element is formed
from a material having an irregular surface finish (for example, the tubular
element is provided in
the form of a cellulose acetate tube). Alternatively, this may be because the
tubular element is
designed to include a tapered section or the like. In embodiments wherein the
thickness of the
peripheral wall of the tubular element varies along the length of the tubular
element, the "thickness
of a peripheral wall of the tubular element" is taken as the average value
calculated on the basis
of several values measured as the minimum distance between the outer surface
and the inner
surface of the wall at different locations along the length of the tubular
element.
In any embodiment, a particularly significant parameter is the thickness of
the peripheral
wall of the tubular element at the location of the ventilation zone.
The expression "air-impervious material" is used throughout this specification
to mean a
material not allowing the passage of fluids, particularly air and smoke,
through interstices or pores
in the material. If the hollow tubular segment is formed of a material
impervious to air and aerosol
particles, air and aerosol particles drawn through the hollow tubular segment
are forced to flow
through the airflow conduit internally defined by the hollow tubular segment,
but cannot flow
across the peripheral wall of the hollow tubular segment.
As used in the present specification, the term "homogenised tobacco material"
encompasses any tobacco material formed by the agglomeration of particles of
tobacco material.
Sheets or webs of homogenised tobacco material are formed by agglomerating
particulate
tobacco obtained by grinding or otherwise powdering of one or both of tobacco
leaf lamina and
tobacco leaf stems. In addition, homogenised tobacco material may comprise a
minor quantity
of one or more of tobacco dust, tobacco fines, and other particulate tobacco
by-products formed
during the treating, handling and shipping of tobacco. The sheets of
homogenised tobacco
material may be produced by casting, extrusion, paper making processes or
other any other
suitable processes known in the art.
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The term "porous" is used herein to refer to a material that provides a
plurality of pores or
openings that allow the passage of air through the material.
The term "ventilation level" is used throughout the present specification to
denote a volume
ratio between of the airflow admitted into the aerosol-generating article via
the ventilation zone
(ventilation airflow) and the sum of the aerosol airflow and the ventilation
airflow. The greater the
ventilation level, the higher the dilution of the aerosol flow delivered to
the consumer.
As briefly described above, the aerosol-generating article of the present
invention
comprises a rod of aerosol-generating substrate; a mouthpiece segment
comprising a plug of
filtration material, and a hollow tubular segment at a location between the
rod and the mouthpiece
segment. All three elements are longitudinally aligned. The rod of aerosol-
generating substrate
comprises at least an aerosol former.
In contrast to known aerosol-generating articles, the rod of aerosol-
generating substrate
has an aerosol former content of at least about 10 percent on a dry weight
basis. Further, the
hollow tubular segment defines a cavity that extends all the way to an
upstream end of the
mouthpiece segment, and a ventilation zone is provided at a location along the
hollow tubular
segment. In addition, an equivalent internal diameter of the hollow tube
segment is at least about
5 millimetres.
By providing an aerosol-generating article wherein a hollow tubular element is
arranged
between the rod of aerosol-generating substrate and the mouthpiece, wherein
the hollow tubular
element defines a cavity extending all the way to an upstream end of the
mouthpiece segment,
the overall structural complexity of the article may be significantly reduced
compared with existing
aerosol-generating articles. This advantageously simplifies the manufacturing
process and
reduces the complexity of the making and combining apparatus required for
implementing the
manufacturing process.
One such aerosol-generating article does not necessarily comprise an aerosol-
cooling
element adapted to lower the temperature of a stream of aerosol drawn through
the aerosol-
generating article ¨ as is the case, for example, with the aerosol-generating
articles described in
international patent application WO 2013/120565.
The inventors have found that a satisfactory cooling of the stream of aerosol
generated
upon heating the article and drawn through the hollow tubular element is
achieved by providing a
ventilation zone at a location along the hollow tubular segment. Further, the
inventors have
surprisingly found that, by utilising a hollow tubular segment having an
equivalent internal
diameter of at least about 5 millimetres, it may be possible to counter the
effects of the increased
aerosol dilution caused by the admission of ventilation air into the article.
Without wishing to be bound by theory, it is hypothesised that, because the
temperature
of the aerosol stream is rapidly lowered by the introduction of ventilation
air as the aerosol is
travelling towards the mouthpiece segment, the ventilation air being admitted
into the aerosol
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stream at a location relatively close to the upstream end of the hollow
tubular segment (that is,
sufficiently close to the heat source and to the rod of aerosol-generating
substrate), a dramatic
cooling of the aerosol stream is achieved, which has a favourable impact on
the condensation
and nucleation of the aerosol particles. Accordingly, the overall proportion
of the aerosol
particulate phase to the aerosol gas phase may be enhanced compared with
existing, non-
ventilated aerosol-generating articles.
At the same time, utilising a hollow tubular element with an equivalent
internal diameter of
5 millimetres or more ensures that the overall internal volume of the hollow
tubular element ¨
which is made available for the aerosol to begin the nucleation process as
soon as the aerosol
components leave the rod of aerosol-generating substrate ¨ and the cross-
sectional surface area
of the hollow tubular segment are effectively maximised, whilst at the same
time ensuring that the
hollow tubular segment has the necessary structural strength to prevent a
collapse of the aerosol-
generating article as well as to provide some support to the rod of aerosol-
generating substrate,
and that the RTD of the hollow tubular segment is minimised. Greater values of
cross-sectional
surface area of the cavity of the hollow tubular segment are associated with a
reduced speed of
the aerosol stream travelling along the aerosol-generating article, which is
understood to favour
aerosol nucleation. In practice, without wishing to be bound by theory, by
providing a cavity
having one such large volume as is the case with articles in accordance with
the invention, a
cooling chamber is effectively provided within which the condensation of
aerosol particles
upstream of a mouth end of the article may be favoured, as nucleation
phenomena are enhanced
by slowing down the flow of the aerosol stream.
The provision of a sufficiently wide tubular cavity downstream of the rod of
aerosol-
generating substrate is understood to favour the formation of a satisfactory
amount of aerosol
during use. In turn, a greater fraction of the generated aerosol particles to
begin to condense
.. prior to reaching the mouth end of the article.
In fact, the inventors have surprisingly found how the favourable effect of
enhanced
nucleation may significantly counter the less desirable effects of dilution,
such that satisfactory
values of aerosol delivery are consistently achieved with aerosol-generating
articles in
accordance with the invention. This is particularly advantageous with "short"
aerosol-generating
articles, such as ones wherein a length of the rod of aerosol-generating
substrate is less than
about 40 millimetres, preferably less than 25 millimetres, even more
preferably less than 20
millimetres, or wherein an overall length of the aerosol-generating article is
less than about 70
millimetres, preferably less than about 60 millimetres, even more preferably
less than 50
millimetres. As will be appreciated, in such aerosol-generating articles,
there is little time and
space for the aerosol to form and for the particulate phase of the aerosol to
become available for
delivery to the consumer.
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Further, because the hollow tubular element substantially does not contribute
to the RTD
of the aerosol-generating article, in aerosol-generating articles in
accordance with the invention
the overall RTD of the article can advantageously be fine-tuned by adjusting
the length and
density of the rod of aerosol-generating substrate or the length and density
of the segment of
filtration material of the mouthpiece. This enables the manufacture of aerosol-
generating
substrates having a predetermined RTD consistently and with great precision,
such that
satisfactory levels of RTD can be provided for the consumer even in the
presence of ventilation.
Aerosol-generating articles in accordance with the invention can be made in a
continuous
process which can be efficiently carried out at high speed, and can be
conveniently manufactured
on existing production lines for the manufactured of heated aerosol generating
articles without
requiring extensive modifications of the manufacturing equipment.
The rod of aerosol generating substrate preferably has an external diameter
that is
approximately equal to the external diameter of the aerosol generating
article.
Preferably, the rod of aerosol generating substrate has an external diameter
of at least 5
millimetres. The rod of aerosol generating substrate may have an external
diameter of between
about 5 millimetres and about 12 millimetres, for example of between about 5
millimetres and
about 10 millimetres or of between about 6 millimetres and about 8
millimetres. In a preferred
embodiment, the rod of aerosol generating substrate has an external diameter
of 7.2 millimetres,
to within 10 percent.
The rod of aerosol generating substrate may have a length of between about 5
millimetres
and about 100 mm. Preferably, the rod of aerosol generating substrate has a
length of at least
about 5 millimetres, more preferably at least about 7 millimetres. In
addition, or as an alternative,
the rod of aerosol generating substrate preferably has a length of less than
about 80 millimetres,
more preferably less than about 65 millimetres, even more preferably less than
about 50
millimetres. In particularly preferred embodiments, the rod of aerosol
generating substrate has a
length of less than about 35 millimetres, more preferably less than 25
millimetres, even more
preferably less than about 20 millimetres. In one embodiment, the rod of
aerosol generating
substrate may have a length of about 10 millimetres. In a preferred
embodiment, the rod of
aerosol generating substrate has a length of about 12 millimetres.
Preferably, the rod of aerosol generating substrate has a substantially
uniform cross-
section along the length of the rod. Particularly preferably, the rod of
aerosol generating substrate
has a substantially circular cross-section.
In preferred embodiments, the aerosol-generating substrate comprises one or
more
gathered sheets of homogenised tobacco material. Preferably the one or more
sheets of
homogenised tobacco material are textured. As used herein, the term 'textured
sheet' denotes a
sheet that has been crimped, embossed, debossed, perforated or otherwise
deformed. Textured
sheets of homogenised tobacco material for use in the invention may comprise a
plurality of
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spaced-apart indentations, protrusions, perforations or a combination thereof.
According to a
particularly preferred embodiment of the invention, the rod of aerosol-
generating substrate
comprises a gathered crimped sheet of homogenised tobacco material
circumscribed by a
wrapper.
As used herein, the term 'crimped sheet' is intended to be substantially
synonymous with
the term `creped sheet' and denotes a sheet having a plurality of
substantially parallel ridges or
corrugations. Preferably, the crimped sheet of homogenised tobacco material
has a plurality of
ridges or corrugations substantially parallel to the cylindrical axis of the
rod according to the
invention. This advantageously facilitates gathering of the crimped sheet of
homogenised
tobacco material to form the rod. However, it will be appreciated that crimped
sheets of
homogenised tobacco material for use in the invention may alternatively or in
addition have a
plurality of substantially parallel ridges or corrugations disposed at an
acute or obtuse angle to
the cylindrical axis of the rod. In certain embodiments, sheets of homogenised
tobacco material
for use in the rod of the article of the invention may be substantially evenly
textured over
substantially their entire surface. For example, crimped sheets of homogenised
tobacco material
for use in the manufacture of a rod for use in an aerosol-generating article
in accordance with the
invention may comprise a plurality of substantially parallel ridges or
corrugations that are
substantially evenly spaced-apart across the width of the sheet.
Sheets or webs of homogenised tobacco material for use in the invention may
have a
tobacco content of at least about 40 percent by weight on a dry weight basis,
more preferably of
at least about 60 percent by weight on a dry weight basis, more preferably or
at least about 70
percent by weight on a dry basis and most preferably at least about 90 percent
by weight on a
dry weight basis.
Sheets or webs of homogenised tobacco material for use in the aerosol-
generating
substrate may comprise one or more intrinsic binders, that is tobacco
endogenous binders, one
or more extrinsic binders, that is tobacco exogenous binders, or a combination
thereof to help
agglomerate the particulate tobacco. Alternatively, or in addition, sheets of
homogenised tobacco
material for use in the aerosol-generating substrate may comprise other
additives including, but
not limited to, tobacco and non-tobacco fibres, aerosol-formers, humectants,
plasticisers,
flavourants, fillers, aqueous and non-aqueous solvents and combinations
thereof.
Suitable extrinsic binders for inclusion in sheets or webs of homogenised
tobacco material
for use in the aerosol-generating substrate are known in the art and include,
but are not limited
to: gums such as, for example, guar gum, xanthan gum, arabic gum and locust
bean gum;
cellulosic binders such as, for example, hydroxypropyl cellulose,
carboxymethyl cellulose,
hydroxyethyl cellulose, methyl cellulose and ethyl cellulose; polysaccharides
such as, for
example, starches, organic acids, such as alginic acid, conjugate base salts
of organic acids,
such as sodium-alginate, agar and pectins; and combinations thereof.
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Suitable non-tobacco fibres for inclusion in sheets or webs of homogenised
tobacco
material for use in the aerosol-generating substrate are known in the art and
include, but are not
limited to: cellulose fibres; soft-wood fibres; hard-wood fibres; jute fibres
and combinations
thereof. Prior to inclusion in sheets of homogenised tobacco material for use
in the aerosol-
generating substrate, non-tobacco fibres may be treated by suitable processes
known in the art
including, but not limited to: mechanical pulping; refining; chemical pulping;
bleaching; sulphate
pulping; and combinations thereof.
Preferably, the sheets or webs of homogenised tobacco material comprise an
aerosol
former. As used herein, the term "aerosol former' describes any suitable known
compound or
mixture of compounds that, in use, facilitates formation of an aerosol and
that is substantially
resistant to thermal degradation at the operating temperature of the aerosol-
generating article.
Suitable aerosol-formers are known in the art and include, but are not limited
to: polyhydric
alcohols, such as propylene glycol, triethylene glycol, 1,3-butanediol and
glycerine; 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 are polyhydric alcohols or mixtures thereof, such as
propylene
glycol, triethylene glycol, 1,3-butanediol and, most preferred, glycerine.
The sheets or webs of homogenised tobacco material may comprise a single
aerosol
former. Alternatively, the sheets or webs of homogenised tobacco material may
comprise a
combination of two or more aerosol formers.
The sheets or webs of homogenised tobacco material have an aerosol former
content of
greater than 10 percent on a dry weight basis. Preferably, the sheets or webs
of homogenised
tobacco material have an aerosol former content of greater than 12 percent on
a dry weight basis.
More preferably, the sheets or webs of homogenised tobacco material have an
aerosol former
content of greater than 14 percent on a dry weight basis. Even more preferably
the sheets or
webs of homogenised tobacco material have an aerosol former content of greater
than 16 percent
on a dry weight basis.
The sheets of homogenised tobacco material may have an aerosol former content
of
between approximately 10 percent and approximately 30 percent on a dry weight
basis.
Preferably, the sheets or webs of homogenised tobacco material have an aerosol
former content
of less than 25 percent on a dry weight basis.
In a preferred embodiment, the sheets of homogenised tobacco material have an
aerosol
former content of approximately 20 percent on a dry weight basis.
Sheets or webs of homogenised tobacco for use in the aerosol-generating
article of the
present invention may be made by methods known in the art, for example the
methods disclosed
in International patent application WO-A-2012/164009 A2. In a preferred
embodiment, sheets of
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homogenised tobacco material for use in the aerosol-generating article are
formed from a slurry
comprising particulate tobacco, guar gum, cellulose fibres and glycerine by a
casting process.
Alternative arrangements of homogenised tobacco material in a rod for use in
an aerosol-
generating article will be known to the skilled person and may include a
plurality of stacked sheets
of homogenised tobacco material, a plurality of elongate tubular elements
formed by winding
strips of homogenised tobacco material about their longitudinal axes, etc.
As a further alternative, the rod of aerosol-generating substrate may comprise
a non-
tobacco-based, nicotine-bearing material, such as a sheet of sorbent non-
tobacco material loaded
with nicotine (for example, in the form of a nicotine salt) and an aerosol-
former. Examples of such
rods are described in the international application WO-A-2015/052652. In
addition, or as an
alternative, the rod of aerosol-generating substrate may comprise a non-
tobacco plant material,
such as an aromatic non-tobacco plant material.
In the rod of aerosol-generating substrate of articles in accordance with the
invention, the
aerosol-generating substrate is preferably circumscribed by a wrapper. The
wrapper may be
formed of a porous or non-porous sheet material. The wrapper may be formed of
any suitable
material or combination of materials. Preferably, the wrapper is a paper
wrapper.
The mouthpiece segment comprises a plug of filtration material capable of
removing
particulate components, gaseous components or a combination. Suitable
filtration materials are
known in the art and include, but are not limited to: fibrous filtration
materials such as, for example,
cellulose acetate tow, viscose fibres, polyhydroxyalkanoates (PHA) fibres,
polylactic acid (PLA)
fibres and paper; adsorbents such as, for example, activated alumina,
zeolites, molecular sieves
and silica gel; and combinations thereof. In addition, the plug of filtration
material may further
comprise one or more aerosol-modifying agent. Suitable aerosol-modifying
agents are known in
the art and include, but are not limited to, flavourants such as, for example,
menthol. In some
embodiments, the mouthpiece may further comprise a mouth end recess downstream
of the plug
of filtration material. By way of example, the mouthpiece may comprise a
hollow tube arranged
in longitudinal alignment with, and immediately downstream of the plug of
filtration material, the
hollow tube forming a cavity at the mouth end that is open to the outer
environment at the
downstream end of the mouthpiece and of the aerosol-generating article.
A length of the mouthpiece is preferably at least about 4 millimetres, more
preferably at
least about 6 millimetres, even more preferably at least about 8 millimetres.
In addition, or as an
alternative, a length of the mouthpiece is preferably less than 25
millimetres, more preferably less
than 20 millimetres, even more preferably less than 15 millimetres. In some
preferred
embodiments, a length of the mouthpiece is from about 4 millimetres to about
25 millimetres,
more preferably from about 6 millimetres to about 20 millimetres. In an
exemplary embodiment,
a length of the mouthpiece is about 7 millimetres. In another exemplary
embodiment, a length of
the mouthpiece is about 12 millimetres.
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The hollow tubular segment is preferably an annular tube delimiting and
defining an air
gap within the aerosol-generating article. In practice, the hollow tubular
segment provides a
chamber for the volatilised aerosol components released upon heating the
aerosol-generating
substrate to accumulate and flow in. As described briefly above, this chamber
extends
longitudinally all the way to an upstream end of the mouthpiece. This means
that no intermediate
element is provided between the hollow tubular segment and the mouthpiece, and
that when the
aerosol flowing through the aerosol-generating article reaches the downstream
end of the hollow
tubular segment, the aerosol flowing through the aerosol-generating article
effectively also
reaches the upstream end of the mouthpiece. In more detail, the aerosol
flowing through the
aerosol-generating article generally reaches the upstream end of the segment
of filtration material
of the mouthpiece.
Thus, in aerosol-generating articles in accordance with the invention, the
hollow tubular
segment maintains the rod of aerosol-generating substrate at a predetermined
distance from the
mouthpiece and provides an elongate airflow conduit for the aerosol to form
and flow towards the
mouthpiece. During use, a thermal gradient is established along this airflow
conduit. In practice,
a temperature differential is provided, such that a temperature of the
volatilised aerosol
components entering the hollow tubular segment at the upstream end is greater
than a
temperature of the volatilised aerosol components exiting the hollow tubular
segment at the
downstream end (that is, the upstream end of the mouthpiece).
On the one hand, the hollow tubular segment is required to withstand any axial
compressive load or bending moment that may be applied on the hollow tubular
segment during
manufacture of the aerosol-generating article. Further, the hollow tubular
segment is required to
impart structural strength to the aerosol-generating article, such that it can
easily be handled by
the consumer and inserted into an aerosol-generating device for use. On the
other hand, it is
desirable that the overall volume of the chamber internally defined by the
hollow tubular element
is as large as possible, so as to favour the formation of aerosol and enhance
the delivery of
aerosol to the consumer.
To satisfy these requirements, as described briefly above, an equivalent
internal diameter
of the hollow tubular segment is at least about 5 millimetres. The term
"equivalent internal
diameter" is used herein to denote the diameter of a circle having the same
surface area of a
cross-section of the airflow conduit internally defined by the hollow tubular
segment. A cross-
section of the airflow conduit may have any suitable shape. However, as
described briefly above,
a circular cross-section is preferred ¨ that is, the hollow tubular segment is
effectively a cylindrical
tube. In that case, the equivalent internal diameter of the hollow tubular
segment effectively
coincides with the internal diameter of the cylindrical tube.
More preferably, an equivalent internal diameter of the hollow tubular segment
is at least
about 5.25 millimetres, even more preferably at least about 5.5 millimetres.
In some
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embodiments, an equivalent internal diameter of the hollow tubular segment is
at least about 6
millimetres or at least about 6.5 millimetres or at least about 7 millimetres.
In addition, an equivalent internal diameter of the hollow tubular segment is
preferably less
than about 10 millimetres. More preferably, an equivalent internal diameter of
the hollow tubular
segment is less than about 9.5 millimetres, even more preferably less than 9
millimetres.
The equivalent internal diameter of the hollow tubular segment is measured at
the location
of the ventilation zone.
In preferred embodiments, the equivalent internal diameter of the hollow
tubular segment
is substantially constant along the length of the hollow tubular segment. In
other embodiments,
the equivalent internal diameter of the hollow tubular segment may vary along
the length of the
hollow tubular segment.
The inventors have surprisingly found that aerosol-generating articles in
accordance with
the invention that comprise a hollow tubular segment having an equivalent
internal diameter within
the ranges described above could provide particularly satisfactory values of
aerosol delivery.
Without wishing to be bound by theory, it is hypothesized that the aerosol
stream flowing along a
hollow tubular segment having an equivalent internal diameter falling within
the ranges described
above is caused to flow at a relatively low speed when the incoming flow of
cooler ventilation air
is received into and mixed with the aerosol stream. Because the aerosol stream
advances
relatively slowly along the hollow tubular segment, the favourable impact of
cooling on aerosol
nucleation is expected to be maximised under such conditions.
Preferably, an equivalent internal diameter of the hollow tubular segment is
substantially
constant along the length of the hollow tubular segment. However, in some
embodiments, the
cross-sectional surface area of the hollow tubular segment may vary along the
length of the hollow
tubular segment. In such embodiments, the equivalent internal diameter is
measured at the
location of the ventilation zone.
In preferred embodiments a thickness of a peripheral wall of the hollow
tubular segment
is less than 1.5 millimetre. More preferably, the thickness of the peripheral
wall of the hollow
tubular segment is less than 1250 micrometres, even more preferably less than
1000
micrometres, most preferably less than 900 micrometres. In particularly
preferred embodiments,
the thickness of the peripheral wall of the hollow tubular segment is less
than 800 micrometres.
In addition, or as an alternative, the thickness of the peripheral wall of the
hollow tubular
segment is at least about 100 micrometres. Preferably, the thickness of the
peripheral wall of the
hollow tubular segment is at least about 200 micrometres.
Without wishing to be bound by theory, it would appear that by utilising a
hollow tubular
segment having a peripheral wall with a thickness falling within the ranges
described above, it is
advantageously possible to limit or even substantially prevent diffusion of
the ventilation air prior
to its contacting and mixing with the stream of aerosol. This is understood to
further favour
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nucleation phenomena. In practice, by providing a more controllably localised
cooling of the
stream of volatilised species being drawn through the hollow tubular segment,
it is possible to
enhance the effect of cooling on the formation of new aerosol particles.
As described briefly above, aerosol-generating articles in accordance with the
present
invention comprise a ventilation zone at a location along the hollow tubular
segment. Preferably,
the ventilation zone is provided at a location less than about 18 millimetres
from an upstream end
of the hollow tubular segment. Preferably, a distance between the ventilation
zone and an
upstream end of the hollow tubular segment is less than about 15 millimetres.
Even more
preferably, a distance between the ventilation zone and upstream end of the
hollow tubular
segment is less than about 10 millimetres.
In addition, or as an alternative, a distance between the ventilation zone and
an upstream
end of the hollow tubular segment is preferably at least 2 millimetres. More
preferably, a distance
between the ventilation zone and an upstream end of the hollow tubular segment
is at least about
4 millimetres. Even more preferably, a distance between the ventilation zone
and an upstream
end of the hollow tubular segment is at least about 6 millimetres.
Preferably, the ventilation zone is provided at a location along the hollow
tubular segment
at least 2 millimetres from the upstream end of the mouthpiece. Preferably,
the ventilation zone
is provided at a location along the hollow tubular segment at least 4
millimetres from the upstream
end of the mouthpiece. Even more preferably, the ventilation zone is provided
at a location along
the hollow tubular segment at least 6 millimetres from the upstream end of the
mouthpiece.
As the mixture of air and aerosol particles flowing through the aerosol-
generating article
reaches the ventilation zone, external air drawn into the hollow tubular
segment via the ventilation
zone is mixed with the aerosol. This rapidly reduces the temperature of the
aerosol mixture whilst
partially diluting the mixture of air and aerosol particles. As will be
discussed in greater detail
below, however, by providing the ventilation zone at a distance from the
upstream end of the
mouthpiece segment falling within the ranges described above, a cooling
chamber is effectively
provided immediately upstream of the mouthpiece, wherein nucleation and growth
of aerosol
particles is advantageously favoured. As such, the diluting effect of the
ventilation air admitted
into the hollow tubular segment is at least partly countered, which
advantageously enables the
provision of aerosol delivery levels that are satisfactory for the consumer.
In some embodiments, a ratio between the distance between the ventilation zone
and an
upstream end of the hollow tubular segment and an equivalent internal diameter
of the hollow
tubular segment at the location of the ventilation zone is less than 4.
Preferably, a ratio between
the distance between the ventilation zone and an upstream end of the hollow
tubular segment
and an equivalent internal diameter of the hollow tubular segment at the
location of the ventilation
zone is less than 3.5. More preferably, a ratio between the distance between
the ventilation zone
and an upstream end of the hollow tubular segment and an equivalent internal
diameter of the
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hollow tubular segment at the location of the ventilation zone is less than 3.
Even more preferably,
a ratio between the distance between the ventilation zone and an upstream end
of the hollow
tubular segment and an equivalent internal diameter of the hollow tubular
segment at the location
of the ventilation zone is less than 2.5.
In particularly preferred embodiments, a ratio between the distance between
the
ventilation zone and an upstream end of the hollow tubular segment and an
equivalent internal
diameter of the hollow tubular segment at the location of the ventilation zone
is less than 2, more
preferably less than 1.5, even more preferably less than 1.2.
Preferably, the ventilation zone is provided at a location along the hollow
tubular segment
at least 10 millimetres from a downstream end of the mouthpiece segment. More
preferably, the
ventilation zone is provided at a location along the hollow tubular segment at
least 12 millimetres
from a downstream end of the mouthpiece segment. Even more preferably, the
ventilation zone
is provided at a location along the hollow tubular segment at least 15
millimetres from a
downstream end of the mouthpiece segment. This is advantageous in that is
ensures that, during
use, the ventilation zone is not occluded by the consumer's lips.
In addition, or as an alternative, the ventilation zone is preferably at a
location along the
hollow tubular segment less than 25 millimetres from a downstream end of the
mouthpiece
segment. More preferably, the ventilation zone is at a location along the
hollow tubular segment
less than 20 millimetres from a downstream end of the mouthpiece segment.
This
advantageously ensures that during use, when the aerosol-generating article is
received within a
heating chamber of an electrically heated aerosol-generating device, the
ventilation zone is
effectively at a location along the hollow tubular segment that projects
outside of the heating
chamber, such that external cooling air can easily be drawn into the hollow
tubular segment.
In some preferred embodiments, the ventilation zone is provided at a location
along the
hollow tubular segment from about 10 millimetres to about 25 millimetres from
a downstream end
of the mouthpiece segment, more preferably from about 12 millimetres to about
20 millimetres
from a downstream end of the mouthpiece segment. In an exemplary embodiment,
the ventilation
zone is provided at a location along the hollow tubular segment 18 millimetres
from the
downstream end of the mouthpiece segment. In another exemplary embodiment, the
ventilation
zone is provided at a location along the hollow tubular segment 13 millimetres
from the
downstream end of the mouthpiece segment.
The aerosol-generating article may typically have a ventilation level of at
least about 10
percent, preferably at least about 20 percent.
In preferred embodiments, the aerosol-generating article has a ventilation
level of at least
about 30 percent. More preferably, the aerosol-generating article has a
ventilation level of at least
about 35 percent. In addition, or as an alternative, the aerosol-generating
article preferably has
a ventilation level of less than about 60 percent. More preferably, the
aerosol-generating article
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has a ventilation level of less than about 50 percent. In particularly
preferred embodiments, the
aerosol-generating article has a ventilation level from about 30 percent to
about 60 percent. More
preferably, the aerosol-generating article has a ventilation level from about
35 percent to about
50 percent. In some particularly preferred embodiments, the aerosol-generating
article has a
ventilation level of about 40 percent.
Without wishing to be bound by theory, the inventors have found that the
temperature drop
caused by the admission of cooler, external air into the hollow tubular
segment via the ventilation
zone may have an advantageous effect on the nucleation and growth of aerosol
particles.
Formation of an aerosol from a gaseous mixture containing various chemical
species
depends on a delicate interplay between nucleation, evaporation, and
condensation, as well as
coalescence, all the while accounting for variations in vapour concentration,
temperature, and
velocity fields. The so-called classical nucleation theory is based on the
assumption that a fraction
of the molecules in the gas phase are large enough to stay coherent for long
times with sufficient
probability (for example, a probability of one half). These molecules
represent some kind of a
critical, threshold molecule clusters among transient molecular aggregates,
meaning that, on
average, smaller molecule clusters are likely to disintegrate rather quickly
into the gas phase,
while larger clusters are, on average, likely to grow. Such critical cluster
is identified as the key
nucleation core from which droplets are expected to grow due to condensation
of molecules from
the vapour. It is assumed that virgin droplets that just nucleated emerge with
a certain original
diameter, and then may grow by several orders of magnitude. This is
facilitated and may be
enhanced by rapid cooling of the surrounding vapour, which induces
condensation. In this
connection, it helps to bear in mind that evaporation and condensation are two
sides of one same
mechanism, namely gas¨liquid mass transfer. While evaporation relates to net
mass transfer
from the liquid droplets to the gas phase, condensation is net mass transfer
from the gas phase
to the droplet phase. Evaporation (or condensation) will make the droplets
shrink (or grow), but
it will not change the number of droplets.
In this scenario, which may be further complicated by coalescence phenomena,
the
temperature and rate of cooling can play a critical role in determining how
the system responds.
In general, different cooling rates may lead to significantly different
temporal behaviours as
concerns the formation of the liquid phase (droplets), because the nucleation
process is typically
nonlinear. Without wishing to be bound by theory, it is hypothesised that
cooling can cause a
rapid increase in the number concentration of droplets, which is followed by a
strong, short-lived
increase in this growth (nucleation burst). This nucleation burst would appear
to be more
significant at lower temperatures. Further, it would appear that higher
cooling rates may favour
an earlier onset of nucleation. By contrast, a reduction of the cooling rate
would appear to have
a favourable effect on the final size that the aerosol droplets ultimately
reach.
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Therefore, the rapid cooling induced by the admission of external air into the
hollow tubular
segment via the ventilation zone can be favourably used to favour nucleation
and growth of
aerosol droplets. However, at the same time, the admission of external air
into the hollow tubular
segment has the immediate drawback of diluting the aerosol stream delivered to
the consumer.
The inventors have surprisingly found that the diluting effect on the aerosol
¨ which can
be assessed by measuring, in particular, the effect on the delivery of
glycerin included in the
aerosol-generating substrate as the aerosol former ¨ is advantageously
minimised when the
ventilation level is between 30 percent and 50 percent. In particular,
ventilation levels between
35 percent and 42 percent have been found to lead to particularly satisfactory
values of glycerin
delivery.
In addition, the inventors have found that in aerosol-generating articles in
accordance with
the invention the cooling and diluting effect caused by the admission of
ventilation air at the
location along the conduit defined by the hollow tubular segment described
above has a surprising
reducing effect on the generation and delivery of phenol-containing species.
The ventilation zone may comprise one or more rows of perforations formed
through the
peripheral wall of the hollow tubular segment. Preferably the ventilation zone
comprises only one
rows of perforations. This is understood to be advantageous in that, by
concentrating the cooling
effect brought about by ventilation over a short portion of the cavity defined
by the hollow tube
segment, it may be possible to further enhance aerosol nucleation. This is
because a faster and
more drastic cooling of the stream of volatilised species is expected to
particularly favour the
formation of new nuclei of aerosol particles.
Preferably, the one or more rows of perforations are arranged
circumferentially around the
wall of the hollow tube. Where the ventilation zone comprises two or more rows
of perforations
formed through the peripheral wall of the hollow tubular segment, the rows are
longitudinally
spaced apart from one another along the hollow tubular segment. By way of
example, adjacent
rows of perforations may be longitudinally spaced from one another by a
distance of between
about 0.25 millimetres and 0.75 millimetres.
An equivalent diameter of at least one of the ventilation perforations is
preferably at least
about 100 micrometres. Preferably, an equivalent diameter of at least one of
the ventilation
perforations is at least about 150 micrometres. Even more preferably, an
equivalent diameter of
at least one of the ventilation perforations is at least about 200
micrometres. In addition, or as an
alternative, an equivalent diameter of at least one of the ventilation
perforations is preferably less
than about 500 micrometres. More preferably, an equivalent diameter of at
least one of the
ventilation perforations is less than about 450 micrometres. Even more
preferably, an equivalent
diameter of at least one of the ventilation perforations is less than about
400 micrometres. The
term "equivalent diameter" is used herein to denote the diameter of a circle
having the same
surface area of a cross-section of the ventilation perforation. A cross-
section of the ventilation
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perforations may have any suitable shape. However, circular ventilation
perforations are
preferred.
The ventilation perforations may be of uniform size. As an alternative, the
ventilation
perforations may vary in size. By varying the number and size of the
ventilation perforations, it is
possible to adjust the amount of external air admitted into the hollow tubular
segment when the
consumer draws on the mouthpiece of the aerosol-generating article during use.
As such, it is
advantageously possible to adjust the ventilation level of the aerosol-
generating article.
The ventilation perforations can be formed using any suitable technique, for
example by
laser technology, mechanical perforation of the hollow tubular segment as part
of the aerosol-
generating article or pre-perforation of the hollow tubular segment before it
is combined with the
other elements to form the aerosol-generating article. Preferably, the
ventilation perforations are
formed by online laser perforation.
A length of the hollow tubular segment is preferably at least about 10
millimetres. More
preferably, a length of the hollow tubular segment is at least about 15
millimetres. In addition, or
.. as an alternative, a length of the hollow tubular segment is preferably
less than about 30
millimetres. More preferably, a length of the hollow tubular segment is less
than about 25
millimetres. Even more preferably, a length of the hollow tubular segment is
less than about 20
millimetres. In some preferred embodiments, a length of the hollow tubular
segment is from about
10 millimetres to about 30 millimetres, more preferably from about 12
millimetres to about 25
millimetres, even more preferably from about 15 millimetres to about 20
millimetres. By way of
example, in a particularly preferred embodiment the length of the hollow
tubular segment is about
18 millimetres. In another particularly preferred embodiment the length of the
hollow tubular
segment is about 13 millimetres.
An overall length of an aerosol-generating article in accordance with the
invention is
preferably at least about 40 millimetres. In addition, or as an alternative,
an overall length of the
aerosol-generating article in accordance with the invention is preferably less
than about 70
millimetres, more preferably less than 60 millimetres, even more preferably
less than 50
millimetres. In preferred embodiments, an overall length of the aerosol-
generating article is from
about 40 millimetres to about 70 millimetres. In an exemplary embodiment, an
overall length of
the aerosol-generating article is about 45 millimetres.
The hollow tubular segment is preferably formed from a substantially air-
impervious
material. Accordingly, air and aerosol particles drawn through the hollow
tubular segment are
forced to flow through the hollow tubular segment from its upstream end to its
downstream end,
but cannot flow across the peripheral wall of the hollow tubular element.
In some embodiments, the hollow tubular segment comprises a wrapper, the
wrapper also
circumscribing the rod and the mouthpiece segment. In practice, a wrapper
having a thickness
falling within the ranges described above is used for circumscribing and
connecting the rod of
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aerosol-generating substrate and the mouthpiece segment, the wrapper
effectively forming the
peripheral wall of the hollow tubular element.
By way of example, one such combining wrapper connecting the rod and the
mouthpiece
segment may have a basis weight of less at least about 70 grams/square metre
(gsm).
Preferably, one such combining wrapper connecting the rod and the mouthpiece
segment has a
basis weight of at least about 80 grams/square metre, more preferably at least
about 90
grams/square metre. In particularly preferred embodiments, the combining
wrapper connecting
the rod and the mouthpiece segment has a basis weight of at least about 110
grams/square
metre, more preferably at least about 130 grams/square metre.
In other embodiments, the hollow tubular segment comprises a tube formed from
a
polymeric material or a cellulosic material, the heated aerosol-generating
article further
comprising a wrapper circumscribing the rod, the tube and the mouthpiece
segment. By way of
example, the cellulosic material may comprise paper or cardboard or a mixture
thereof.
By way of example, the hollow tubular segment can comprise a tube formed from
an
extruded plastic tube. As an alternative, the hollow tubular segment may
comprise a tube formed
from a plurality of overlapping paper layers, such as a plurality of parallel
wound paper layers or
a plurality of spirally wound paper layers. Forming tube from a plurality of
overlapping paper
layers can help to further improve resistance to collapse or deformation.
Preferably the tube
comprises two or more paper layers. Alternatively, or additionally, the tube
preferably comprises
fewer than eleven paper layers.
One such tube may be made air-impervious by using a substantially air-
impermeable
paper. The term "substantially air-impermeable paper" is used herein to denote
a paper having
an air permeability of less than about 20 CORESTA units, more preferably less
than about 10
CORESTA units, most preferably less than about 5 CORESTA units as measured in
accordance
with ISO 2965:2009. As an alternative, adjacent paper layers in the tube may
be held together
with an adhesive imparting sealing properties to the tube.
Suitable materials for forming the tube are known in the art and comprise, but
are not
limited to, cellulose acetate, stiff paper (that is, paper having a basis
weight of at least 90
grams/square metre), polymeric films, such as cellulosic films, and cardboard.
In some embodiments, a ratio between a weight of the hollow tubular segment
and a
volume of the internal cavity defined by the hollow tubular segment is
preferably less than 1
milligram/cubic millimetre. More preferably, a ratio between a weight of the
hollow tubular
segment and a volume of the internal cavity defined by the hollow tubular
segment is less than
0.5 milligrams/cubic millimetres.
In particularly preferred embodiments, a ratio between a weight of the hollow
tubular
segment and a volume of the internal cavity defined by the hollow tubular
segment is less than
0.25 milligrams/cubic millimetres. More preferably, a ratio between a weight
of the hollow tubular
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segment and a volume of the internal cavity defined by the hollow tubular
segment is less than
0.2 milligrams/cubic millimetres. Even more preferably, a ratio between a
weight of the hollow
tubular segment and a volume of the internal cavity defined by the hollow
tubular segment is less
than 0.1 milligrams/cubic millimetres.
In hollow tubular segments having a ratio between a weight of the hollow
tubular segment
and a volume of the internal cavity defined by the hollow tubular segment
falling within the ranges
described above, the volume of the cavity is advantageously maximised, whilst
ensuring that the
hollow tubular segment contributes to the overall structural strength of the
aerosol-generating
article and effectively maintains the rod of aerosol-generating substrate
spaced from the
mouthpiece.
In an exemplary embodiment, the hollow tubular segment has an internal
equivalent
diameter of 7 millimetres and is formed from a wrapper having a basis weight
of 110 gsm, with a
weight of 2.5 milligram/millimetre. For one such hollow tubular segment, the
ratio between a
weight of the hollow tubular segment and a volume of the internal cavity
defined by the hollow
tubular segment is about 0.065 milligrams/cubic millimetres.
In another exemplary embodiment, a hollow tubular segment has an internal
equivalent
diameter of 5.3 millimetres may be provided as a cellulose acetate tube with a
weight of 9.5
milligram/millimetre. For one such hollow tubular segment, the ratio between a
weight of the
hollow tubular segment and a volume of the internal cavity defined by the
hollow tubular segment
is about 0.43 milligrams/cubic millimetres.
In aerosol-generating articles in accordance with the present invention the
overall RTD of
the article depends essentially on the RTD of the rod and on the RTD of the
mouthpiece, as the
hollow tubular segment is substantially empty and, as such, substantially only
marginally
contribute to the overall RTD. In practice, the hollow tubular segment may be
adapted to generate
a RTD in the range of approximately 0 millimetre H20 (about 00 Pa) to
approximately 20 m
millimetres H20 (about 200 Pa). Preferably, the hollow tubular segment is
adapted to generate a
RTD between approximately 0 millimetres H20 (about 00 Pa) to approximately 10
millimetres H20
(about 100 Pa).
The aerosol-generating article preferably has an overall RTD of less than
about 90
millimetres H20 (about 900 Pa). More preferably, the aerosol-generating
article has an overall
RTD of less than about 80 millimetres H20 (about 800 Pa). Even more
preferably, the aerosol-
generating article has an overall RTD of less than about 70 millimetres H20
(about 700 Pa).
In addition, or as an alternative, the aerosol-generating article preferably
has an overall
RTD of at least about 30 millimetres H20 (about 300 Pa). More preferably the
aerosol-generating
article has an overall RTD of at least about 40 millimetres H20 (about 400
Pa). Even more
preferably, the aerosol-generating article has an overall RTD of at least
about 50 millimetres H20
(about 500 Pa).
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The RTD of the aerosol-generating article may be assessed as the negative
pressure that
has to be applied, under test conditions as defined in ISO 3402, to downstream
end of the
mouthpiece in order to sustain a steady volumetric flow of air of 17.5 ml/s
through the mouthpiece.
The values of RTD listed above are intended to be measured on the aerosol-
generating article
on its own (that is, prior to inserting the article into an aerosol-generating
device) without blocking
the perforations of the ventilation zone.
If desired or required, for example to achieve a sufficiently high RTD of the
aerosol-
generating article, the length and density (denier per filament count) of the
filtration material of
the mouthpiece may be adjusted. In addition, or as an alternative, an
additional filter section may
be included in the aerosol-generating article. By way of example, such
additional filter section
may be included between the rod of aerosol-generating substrate and the hollow
tubular segment.
Preferably, such additional filter section comprises a filtration material
such as, for example,
cellulose acetate. Preferably, the length of the additional filter section is
between about 4
millimetres and about 8 millimetres, preferably, between about 5 millimetres
and about 7
millimetres.
In some embodiments, the aerosol-generating article in accordance with the
invention
may comprise an additional support element arranged between, and in
longitudinal alignment
with, the rod of aerosol-generating substrate and the hollow tubular segment.
In more detail, the
support element is preferably provided immediately downstream of the rod and
immediately
.. upstream of the hollow tubular element.
The support element is provided as a tubular element. The support element may
be
formed from any suitable material or combination of materials. For example,
the support element
may be formed from one or more materials selected from the group consisting
of: cellulose
acetate; cardboard; crimped paper, such as crimped heat resistant paper or
crimped parchment
paper; and polymeric materials, such as low density polyethylene (LDPE). In
preferred
embodiment, the support element is provided as a hollow cellulose acetate
tube.
The support element preferably has an external diameter that is about equal to
the
external diameter of the aerosol-generating article. The support element may
have an external
diameter of between about 5 millimetres and about 12 millimetres, for example
of between about
.. 5 millimetres and about 10 millimetres or of between about 6 millimetres
and about 8 millimetres.
In a preferred embodiment, the support element has an external diameter of
about 7.2 millimetres.
A peripheral wall of the support element may have a thickness of at least 1
millimetre,
preferably at least about 1.5 millimetres, more preferably at least about 2
millimetres.
The support element may have a length of between about 5 millimetres and about
15
.. millimetres. In an preferred embodiment, the support element has a length
of about 8 millimetres.
During insertion of a heating element of an aerosol-generating device into an
aerosol-
forming substrate of an aerosol-generating article, a user may be required to
apply some force in
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order to overcome the resistance of the aerosol-forming substrate of the
aerosol-generating
article to insertion of the heating element of the aerosol-generating device.
This may damage
one or both of the aerosol-generating article and the heating element of the
aerosol-generating
device. In addition, the application of force during insertion of the heating
element of the aerosol-
generating device into the aerosol-forming substrate of the aerosol-generating
article may
displace the aerosol-forming substrate within the aerosol-generating article.
This may result in
the heating element of the aerosol-generating device not being fully inserted
into the aerosol-
forming substrate, which may lead to uneven and inefficient heating of the
aerosol-forming
substrate of the aerosol-generating article. The support element is
advantageously configured to
resist downstream movement of the aerosol-forming substrate during insertion
of the heating
element of the aerosol-generating device into the aerosol-forming substrate of
aerosol-generating
article.
Preferably, a distance between the ventilation zone and an upstream end of the
aerosol-
generating article is less than about 50 millimetres. More preferably, a
distance between the
ventilation zone and an upstream end of the aerosol-generating article is less
than about 45
millimetres. Even more preferably, a distance between the ventilation zone and
an upstream end
of the aerosol-generating article is less than about 40 millimetres.
In addition, or as an alternative, a distance between the ventilation zone and
an upstream
end of the aerosol-generating article is preferably at least about 12
millimetres. More preferably,
a distance between the ventilation zone and an upstream end of the aerosol-
generating article is
preferably at least about 15 millimetres. Even more preferably, a distance
between the ventilation
zone and an upstream end of the aerosol-generating article is preferably at
least about 20
millimetres. In particularly preferred embodiments, a distance between the
ventilation zone and
an upstream end of the aerosol-generating article is preferably at least about
25 millimetres.
Preferably, a distance between the ventilation zone and a downstream end of
the rod of
aerosol-generating substrate is at least about 2 millimetres. More preferably,
a distance between
the ventilation zone and a downstream end of the rod of aerosol-generating
substrate is at least
about 5 millimetres. Even more preferably, a distance between the ventilation
zone and a
downstream end of the rod of aerosol-generating substrate is at least about 10
millimetres. In
some, particularly preferred embodiments, a distance between the ventilation
zone and a
downstream end of the rod of aerosol-generating substrate may be at least
about 15 millimetres.
In addition, or as an alternative, a distance between the ventilation zone and
a
downstream end of the rod of aerosol-generating substrate is preferably less
than about 35
millimetres. More preferably, a distance between the ventilation zone and a
downstream end of
the rod of aerosol-generating substrate is less than about 30 millimetres.
Even more preferably,
a distance between the ventilation zone and a downstream end of the rod of
aerosol-generating
substrate is less than about 25 millimetres.
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In practice, the ventilation zone divides the cavity internally defined by the
hollow tubular
segment into an upstream sub-cavity, which extends longitudinally from an
upstream end of the
hollow tubular segment to the location of the ventilation zone, and a
downstream sub-cavity, which
extends longitudinally from the location of the ventilation zone to the
downstream end of the
hollow tubular segment. Without wishing to be bound by theory, it is
understood that in the
upstream sub-cavity the volatilised species of the aerosol stream advance
along the hollow
tubular segment slowly cool down by yielding some of the heat to the
peripheral wall of the hollow
tubular segment and thus aerosol particles begin to nucleate. On the other
hand, in the
downstream sub-cavity, the aerosol stream and the ventilation air rapidly mix
up, which causes a
quick cooling of the volatilised species of the aerosol stream and so favours
the nucleation of new
aerosol particles and the growth of already existing aerosol particles as the
aerosol advances
towards the mouthpiece.
Preferably, a ratio between a length of the upstream cavity and a length of
the downstream
cavity is less than 1.5. More preferably, a ratio between a length of the
upstream cavity and a
.. length of the downstream cavity is less than 1. Even more preferably, a
ratio between a length
of the upstream cavity and a length of the downstream cavity is less than
0.67.
In addition, or as an alternative, a ratio between a length of the upstream
cavity and a
length of the downstream cavity is preferably at least about 0.15. More
preferably, a ratio between
a length of the upstream cavity and a length of the downstream cavity is
preferably at least about
0.2. Even more preferably, a ratio between a length of the upstream cavity and
a length of the
downstream cavity is preferably at least about 0.35.
Similarly, the ventilation zone divides the aerosol-generating article in two
sections,
upstream and downstream of the location of the ventilation zone, respectively.
Preferably, a ratio between a length of the upstream section of the aerosol-
generating
article and a length of the downstream section of the aerosol-generating
article is less than 2.5.
More preferably, a ratio between a length of the upstream section of the
aerosol-generating article
and a length of the downstream section of the aerosol-generating article is
less than 2. Even
more preferably, a ratio between a length of the upstream section of the
aerosol-generating article
and a length of the downstream section of the aerosol-generating article is
less than 1.5. In
particularly preferred embodiments, a ratio between a length of the upstream
section of the
aerosol-generating article and a length of the downstream section of the
aerosol-generating
article is less than 1.
In addition, or as an alternative, a ratio between a length of the upstream
section of the
aerosol-generating article and a length of the downstream section of the
aerosol-generating
article is preferably at least about 0.25. More preferably, a ratio between a
length of the upstream
section of the aerosol-generating article and a length of the downstream
section of the aerosol-
generating article is at least about 0.33. Even more preferably, a ratio
between a length of the
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upstream section of the aerosol-generating article and a length of the
downstream section of the
aerosol-generating article is at least about 0.5.
In aerosol-generating articles in accordance with the invention it is
advantageously easy
to adjust and control the overall RTD of the article. This is because the
overall RTD of the article
depends on the RTD of a finite, small number of components and the provision
of the ventilation
zone also contributes to lowering the overall RTD of the article. Therefore,
it is advantageously
possibly to reduce an RTD variability between aerosol-generating articles.
Accordingly, the invention may also provide a pack comprising ten or more
aerosol-
generating articles as described above, wherein a difference between an RTD of
the aerosol-
generating article having the highest RTD among the at least ten aerosol-
generating articles and
an RTD of the aerosol-generating article having the lowest RTD among the at
least ten aerosol-
generating articles is less than 10 mm H20 (about 100 Pascal). Preferably, in
one such pack, the
difference between an RTD of the aerosol-generating article having the highest
RTD among the
at least ten aerosol-generating articles and an RTD of the aerosol-generating
article having the
lowest RTD among the at least ten aerosol-generating articles is less than 9
mm H20 (about 90
Pascal, more preferably less than 8 mm H20 (about 80 Pascal), even more
preferably less than
7 mm H20 (about 70 Pascal).
In the following, the invention will be further described with reference to
the drawings of
the accompanying figures, in which:
Figure 1 shows a schematic side sectional view of an aerosol-generating
article in
accordance with the invention;
Figure 2 shows a schematic side sectional view of another example of an
aerosol-
generating article in accordance with the invention; and
Figure 3 shows a schematic side sectional view of a further example an aerosol-
generating article in accordance with the invention.
The aerosol-generating article 10 shown in Figure 1 comprises a rod of aerosol-
generating
substrate 12, a hollow cellulose acetate tube 14, a hollow tubular segment 16
and a mouthpiece
segment 18. These four elements are arranged in end-to-end, longitudinal
alignment and are
circumscribed by a wrapper 20 to form the aerosol-generating article 10. The
aerosol-generating
article 10 has a mouth end 22 and an upstream, distal end 24 located at the
opposite end of the
article to the mouth end 22. The aerosol-generating article 10 shown in Figure
1 is particularly
suitable for use with an electrically operated aerosol-generating device
comprising a heater for
heating the rod of aerosol-generating substrate.
The rod of aerosol-generating substrate 12 has a length of about 12
millimetres and a
diameter of about 7 millimetres. The rod 12 is cylindrical in shape and has a
substantially circular
cross-section. The rod 12 comprises a gathered sheet of homogenised tobacco
material. The
sheet of homogenised tobacco material comprises 10 percent by weight on a dry
basis of
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glycerine. The hollow cellulose acetate tube 14 has a length of about 8
millimetres and a
thickness of 1 millimetre.
The mouthpiece segment 18 comprises a plug of cellulose acetate tow of 8
denier per
filament and has a length of about 7 millimetres.
The hollow tubular segment 16 is provided as a cylindrical tube having a
length of about
18 millimetres and a thickness of the tube wall is about 100 micrometres.
In more detail, the hollow tubular segment 16 may for example be formed from a
paper
having a basis weight of 110 gsm and has a weight of 45 milligrams (that is,
2.5
milligrams/millimetre of length). An equivalent internal diameter of the
hollow tubular segment 16
is about 7 millimetres. Thus, a volume of the cavity internally defined by the
hollow tubular
segment 16 is about 693 cubic millimetres. As such, a ratio between the weight
of the hollow
tubular segment and the volume of the internal cavity defined by the hollow
tubular segment 16
is about 0.065. The aerosol-generating article 10 comprises a ventilation zone
26 provided at
about 5 millimetres from an upstream end of the mouthpiece segment 18. Thus,
the ventilation
zone 26 is at about 12 millimetres from the downstream end of the aerosol-
generating article, and
about 13 millimetres from the upstream end of the hollow tubular segment.
Thus, the ventilation zone 26 is at about 21 millimetres from a downstream end
of the rod
12. Figure 2 illustrates another example of an aerosol-generating article in
accordance with the
invention. The aerosol-generating article 30 of Figure 2 has the same
structure of the aerosol-
generating article 10 of Figure 1 and differs from the aerosol-generating
article 10 substantially
only in the length of certain components, and will be described below only
insofar as it differs from
the aerosol-generating article 10. In the following the same reference
numerals will be used,
wherever possible, for corresponding components having the same structural or
functional
function.
In the aerosol-generating article 30 of Figure 2, the rod 12 and the hollow
cellulose acetate
tube 14 have the same length as in the aerosol-generating article 10 of Figure
1. However, the
mouthpiece segment comprises a plug of cellulose acetate tow of 11 denier per
filament and
having a length of about 12 millimetres, and a hollow tubular segment 14
having a length of about
13 millimetres. The ventilation zone 26 is provided at about 6 millimetres
from the upstream end
of the mouthpiece segment 18, and at about 7 millimetres from the upstream end
of the hollow
tubular segment. Thus, the ventilation zone 26 is at about 15 millimetres from
a downstream end
of the rod 12.
In the embodiment of Figure 2, the hollow tubular segment 16 may for example
be
provided as a cylindrical tube of cellulose acetate having a length of about
18 millimetres and a
peripheral wall thickness of about 1 millimetre, with a weight of 171
milligrams (that is, 9.5
milligrams/millimetre of length).
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An equivalent internal diameter of the hollow tubular segment 16 may be about
5.3
millimetres. Thus, a volume of the cavity internally defined by the hollow
tubular segment 16 is
about 397 cubic millimetres. As such, a ratio between the weight of the hollow
tubular segment
and the volume of the internal cavity defined by the hollow tubular segment 16
is about 0.43.
Figure 3 illustrates yet another example of an aerosol-generating article in
accordance with the
invention. The aerosol-generating article 40 of Figure 3 differs structurally
from the aerosol-
generating articles 10 of Figure 1 and 30 of Figure 2 in that it does not
include a hollow cellulose
acetate tube as a support element. Accordingly, the lengths of the three main
components are
also different. In the following the same reference numerals will be used,
wherever possible, for
corresponding components having the same structural or functional function.
In the aerosol-generating article 40 of Figure 3, the rod 12 has a length of
about 12
millimetres, the hollow tubular segment 14 has a length of about 26
millimetres, and the
mouthpiece segment 18 comprises a plug of cellulose acetate tow has a length
of about 12
millimetres and 11 denier per filament. The ventilation zone 26 is provided at
about 5 millimetres
from the upstream end of the mouthpiece segment 18, and at about 21
millimetres from the
upstream end of the hollow tubular segment, which in this embodiment coincides
with the
downstream end of the rod 12.
The following example records experimental results obtained during tests
carried out on
a specific embodiment of an aerosol-generating article in accordance with the
present invention.
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.
EXAMPLE 1 This experiment is performed to assess the effect of incorporation
of a hollow
tubular segment wherein a ventilation zone is provided at a location along the
hollow tubular
segment in accordance with the present invention. The experiment investigates
the effect of the
ventilation level on the delivery of nicotine and aerosol former (glycerin). A
comparative
measurement with a reference aerosol-generating article without ventilation is
also provided.
Materials and methods
Article A is an aerosol-generating article formed of: a rod of aerosol-
generating substrate
comprising a gathered sheet of homogenised tobacco material and about 18
percent on a dry
weight basis of glycerin, the rod having a length of 12 millimetres; a support
element in the form
of a hollow cellulose acetate tube in alignment with and immediately
downstream of the rod, the
support element having a length of 8 millimetres; a hollow tubular segment in
the form of a
cardboard tube in alignment with and immediately downstream of the rod, the
hollow tubular
segment having a length of 13 millimetres; a mouthpiece segment of filtration
material in
alignment with and immediately downstream of the hollow tubular segment, the
mouthpiece
segment having a length of 12 millimetres. A ventilation zone is provided at a
location along the
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hollow tubular segment at 18 millimetres from a downstream end of the
mouthpiece segment. A
level of ventilation of aerosol-generating article A is 30 percent.
Article B is a reference aerosol-generating article having the same structure
of article A,
but without the ventilation zone. Thus, a level of ventilation of aerosol-
generating article B is 0
percent.
Nicotine and glycerin deliveries are measured by gas chromatography/time-of-
flight mass
spectrometry (GC/MS-TOF) on the nicotine and glycerin collected on a Cambridge
filter
pad. Runs were performed as described in example 1
Results. The average nicotine and glycerin deliveries from Article A and
Article B are
shown in the following Table 1.
Table 1. Effect of ventilation level on nicotine and glycerin deliveries.
Nicotine
Ventilation Glycerin
delivery
roi [mg] [mg]
Article A 30 1.41 5.6
Article B 0 1.17 3.5
