Note: Descriptions are shown in the official language in which they were submitted.
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Filter for a Smoking Article
Description
The present invention relates to a filter for a smoking article such as a
cigarette.
Background
Smoke from the combustion of smoking articles is made up of gaseous components
and particulate matter, which is commonly referred to as "tar". Various types
of
filter constructions are known in the art for removing undesirable components
from
the smoke as the consumer draws on the smoking article.
Many different filter arrangements for smoking articles have been described
including composite filters wherein the filter comprises a plurality of
separate filter
sections with different filtering capacities, and filters comprising different
materials
such as cellulose acetate and charcoal particles.
Measures aimed at reducing the level of undesirable components of smoke which
are inhaled by the consumer frequently consist of diluting the smoke by
introducing
ambient air into the smoking article as the consumer draws. The most common
method of introducing ventilating air is by the incorporation of holes in the
smoking article filter. This approach to reducing the concentration of
undesirable
components has several associated advantages. In particular, the smoker
continues
to receive the desired components and associated taste effects of the smoke.
Furthermore, the cooler ambient air lowers the temperature of the smoke
entering
the mouth and throat, producing a more pleasant and agreeable smoking effect.
One major disadvantage of ventilating smoking articles in this way however, is
that
it may result in the over-dilution of the smoke, with consequent loss of
flavour.
Another disadvantage is that as the amount of ventilation is increased the
sucking
effort that the user is required to impart is decreased, resulting in
frustration for the
consumer and a less enjoyable smoking experience.
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Consumers purchase and use smoking articles to obtain the effects of inhaling
the
products produced by combustion of the smokable material. When ventilating
structures are introduced into the filter of the smoking article, the level of
combustion products that the smoker receives is reduced. To compensate, it is
known that consumers may increase the strength with which they draw on the
smoking article, thereby increasing the flow rate through the smoking article,
to
increase the total volume of aerosol (a mixture of smoke and ventilating air)
inhaled.
The most common method of providing for the entry of ventilating air into the
smoking article is by the provision of small ventilation holes in the form of
perforations or conduits through the outer wall of the smoking article. The
flow
rate of air through these ventilation holes into the smoking article is not a
linear
function of the strength of the draw. At higher strengths of draw, the
proportion of
air entering the smoking article via these ventilation holes is reduced as
compared
with the proportion of smoke from the combustion of the smoking article. This
phenomenon, hereinafter referred to as "the restricted orifice effect", is a
consequence of the ventilation holes having a small diameter, typically of the
order
of less than 1mm. Smaller holes impose greater inertial and viscous impedances
on
the gas that is drawn through the hole, and this effect is reduced as the
diameter of
the hole is increased. Therefore, a consequence of the restricted orifice
effect is that
as the strength of draw is increased, the volume of diluting air that can
enter the
smoking article is limited. The ignition end of the smoking article has a much
larger
diameter than the narrow ventilation holes and thus the air entering the
smoking
article via this route is not subject to the restricted orifice effect. As a
result, as the
strength of draw is increased, the concentration of smoke products inhaled
also
increases because the amount of ventilating air is essentially limited, but
the amount
of smoke is not.
The restricted orifice effect can be overcome by increasing the diameter of
the
ventilation holes. However, if the size of the perforations is increased then
smoke
will undesirably escape through these holes. Furthermore, the strength of draw
that
the consumer is required to impart will be reduced to the detriment of the
smoking
experience. It is therefore not a simple matter to construct a smoking article
having
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a filter which is not subject to the restricted orifice effect, especially in
the case of
filters which are required to give a high level of ventilation.
Statements of Invention
According to a first aspect of the present invention, a filter is provided for
use in
conjunction with a smoking article, the filter comprising first and second
filter
passageways operable to impart different filtration efficiencies. The filter
is arranged
so that the amount of smoke passing through one of the passageways relative to
the
other passageway is controlled by the restricted orifice effect. As the draw
is
increased, the level of smoke filtration may be increased.
The restricted orifice effect may be provided by a plurality of holes. The
holes may
be the only means by which smoke is able to pass between the first and second
filter
passageways. The diameter of the holes may be sufficiently small so that with
increased draw the amount of smoke passing through the holes is increasingly
restricted. The holes may be between 0.01mm and 2mm in diameter, preferably
the
holes may be between 0.1mm and 1mm in diameter.
At least one of the passageways may comprise material capable of filtering
smoke.
One of the passageways may comprise a void. Both passageways may comprise
material capable of filtering smoke, the first passageway having a lower
capacity to
filter smoke than the second passageway.
As the draw is increased, the amount of smoke that is drawn via the first
passageway may be limited by the restricted orifice effect and excess smoke is
thus
drawn via the second passageway.
The filter may be ventilated, and this ventilation may be by means of deep
vents.
Alternatively, the filter may not be ventilated.
The filter may comprise a plurality of longitudinally abutted filter sections
and at
least one of these filter sections may be an annular filter section.
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The smoking article to which the filter may be attached may be a cigarette.
According to a second aspect of the present invention, a smoking article is
provided, comprising a filter and a rod of smokable material.
Brief Description of the Drawings
For a fuller understanding of the invention, embodiments of the invention will
be
described by way of illustrative example with reference to the accompanying
drawings in which:
Figure 1 is a schematic sectional side elevation view, not to scale, of the
filter of an
individual filter cigarette according to a first embodiment of the invention,
Figure la indicates the route taken by smoke drawn with a low strength through
the
filter of Figure 1,
Figure lb indicates the route taken by smoke drawn with a high strength
through
the filter of Figure 1,
Figure 2 is a schematic sectional side elevation view, not to scale, of the
filter of an
individual filter cigarette according to a second embodiment of the invention,
Figure 3 is a schematic sectional side elevation view, not to scale, of an
individual
filter cigarette according to a third embodiment of the invention, and
Figure 4 is a schematic sectional side elevation view, not to scale, of an
individual
filter cigarette according to a fourth embodiment of the invention.
Detailed Description
Described herein is a filter for a smoking article which is arranged to
utilise the
restricted orifice effect to manipulate the passage of smoke and the level of
smoke
filtration.
As disclosed herein "high resistance section" is intended to refer to a
section of
material possessing a high capacity to resist the passage of smoke. This
material is
also capable of efficiently filtering the undesirable components from smoke,
for
example, by virtue of having a high density. The terms "high resistance
section",
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"high filtration efficiency material", and "high resistance material" are
therefore to
be understood to have a common interpretation. On the other hand, "low
resistance
section", "low filtration efficiency material", and "low resistance material"
and
similar terms are used to refer to a section of material (or a void)
possessing a low
(or absent) capacity to resist the passage of smoke and a low (or absent)
efficiency
for filtering smoke. In describing these materials, the terms "high" or
"higher" and
"low" or "lower" are intended to reflect the density, resistance, or
filtration
efficiency of the materials relative to one another; that is, the high
resistance section
simply has a higher resistance than the low resistance section, although in
fact it
may possess a low capacity to resist smoke in comparison to other filter
materials
known in the art. Similarly, the low resistance section may actually possess a
relatively high absolute capacity to resist smoke.
One embodiment of a smoking article incorporating a filter is shown in Figure
1 in
which the smoking article is a cigarette comprising a rod of smokable material
1
(shown partially) and a filter 2. The filter comprises filter material 3 which
is
composed of a high resistance material (shaded). As shown in Figure 1, the
filter is
composed of a first section of filter material 3a and a second section of
filter
material 3b, the two sections being arranged in a longitudinally abutting
relationship.
As shown in Figure 1, the section of filter material 3a at the distal end 4 of
the filter
(away from the mouth end) has substantially the same diameter as the rod of
smokable material 1. This is to ensure that all of the smoke drawn along the
rod of
smokable material 1 enters the filter material 3a.
The section of filter material 3b at the mouth proximal end 5 of the filter
has a
reduced diameter and thus a cavity 6 exists between the filter material 3 and
the
tipping paper 9 which circumscribes the filter 2 of the smoking article. This
cavity 6
forms a low resistance section. The length of this cavity 6 may be equivalent
to 10 -
90% of the total length of the filter 2. In some embodiments, the cavity is 20
- 80%
of the total length of the filter. Preferably the cavity is 30 - 70% of the
total length
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of the filter. More preferably the cavity is 40 - 60% of the total length of
the filter.
The cavity is most preferably 50% of the total length of the filter.
The mouth proximal end filter section 3b is circumscribed with non-porous
plugwrap 7, and a non-porous annular ring member 27 separates the distal end
filter
section 3a and the cavity 6. This annular ring 27 is non-porous with the
exception
of a series of small perforations 8. As a consequence, as the consumer draws
on the
smoking article, smoke is only able to pass from the filter material 3a (the
high
resistance section) to the cavity 6 (the low resistance section) via the
perforations 8
in the non-porous annular ring member 27. The rate at which smoke may pass
from
the high resistance section to the low resistance section through the holes 8
is
limited by the restricted orifice effect when the user draws on the smoking
article.
The perforations 8 are preferably between 0.01mm and 2mm in diameter, more
preferably the perforations are between 0.1mm and 1mm in diameter.
In use, smoke is drawn into the mouth from the filter material 3 (the high
resistance
section) from a first passageway I that is defined within the tubular plug
wrap 7 and
also via the cavity 6 (the low resistance section) which provides a
concentric, second
passageway H. Smoke passing to the user's mouth along the first passageway I
undergoes a greater amount of filtration than smoke that passes to the mouth
through the second passageway H.
Figure 1 a illustrates the situation of the smoker drawing on the smoking
article with
a low strength of draw, i.e. low negative pressure created by the user sucking
on the
filter. In this scenario, smoke is drawn through the filter material 3 along
the first
passageway I within the tubular plug wrap 7. Additionally, some smoke is drawn
from the filter material 3 through the perforations 8 and into the cavity 6 as
result
of negative pressure produced by drawing on the mouthpiece. In taking the
second
passageway, the smoke is subject to a lower level of filtration than smoke
that
reaches the user along the first passageway.
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At higher strengths of draw, however, as indicated in Figure 1b, the
restricted
orifice effect imposes a limit on the amount of smoke that is able to pass
through
the perforations 8 and enter the second passageway that extends through the
cavity
6. The remaining smoke is thus drawn into the mouth though the first
passageway
described above which exclusively comprises the high resistance filter
material 3. As
a result, the proportion of smoke that passes along the first passageway as
compared with the second passageway increases with increasing draw and thus
overall, the smoke drawn by the user is subject to an increased level of
filtration
with increasing draw.
As shown in Figure 1, a means of supporting the tipping paper 9 at the
proximal
end 5 of the filter material 3 is provided. To this end, a band of corrugated
paper 10
encapsulates a portion of the length of the mouth proximal section of filter
material
3b and is arranged so that a series of substantially longitudinal channels 11
are
formed. The outermost circumference of the corrugated wrapper 10 is
substantially
the same as the circumference of both the tobacco rod 1 and the distal end
section
of filter material 3a.
In alternative arrangements, the low resistance section is not in the form of
a single
circumferential cavity, but instead a plurality of low resistance sections may
exist.
An example of such an arrangement is shown in Figure 2, in which the filter
material 3 is shaped to provide multiple grooves or channels 28.
As described above, in the filter arrangement of Figure 2, smoke is only able
to pass
from the filter material (the high resistance section) to the grooves (the low
resistance sections) via a series of small holes 29 in a non-porous plug wrap
30 that
provides an otherwise non-porous interface between the sections of high and
low
resistance. The restricted orifice effect imposes a limit on the rate at which
smoke
may pass from the high resistance section to the low resistance section when
the
user draws on the smoking article.
According to alternative embodiments, the low resistance section is not
peripheral
to the high resistance section, but is encapsulated by it.
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Another embodiment is shown in Figure 3. According to this embodiment, the
high
resistance section is a cylindrical section of filter material 12, extending
the entire
length of the filter 13, and having a diameter substantially the same as the
diameter
of the rod of smokable material 14.
The low resistance section is a conical-shaped cavity 15 cut into the mouth
end of
the filter material 12. The length of this cavity 15 may be equivalent to 10 -
90% of
the total length of the filter 13. In some embodiments, the cavity is 20 - 80%
of the
total length of the filter. Preferably the cavity is 30 -- 70% of the total
length of the
filter. More preferably the cavity is 40 - 60% of the total length of the
filter. The
cavity is most preferably 50% of the total length of the filter.
The inner surface of the conic cavity is covered in a non-porous coating 16.
This
may be achieved, for example, by inserting a pre-formed cone, of a non-porous
material such as plastic that has been pre-perforated with holes, directly
into the end
of the filter material.
The non-porous lining 16 of the cavity is characterised by one or more bands
of
perforations 17. The perforations 17 are preferably between 0.01mm and 2mm in
diameter, more preferably the perforations are between 0.1mm and 1mm in
diameter.
Under conditions of a low strength of draw, smoke is drawn through the filter
material 12 (high resistance section). Some of the smoke passes through the
filter
material 12 directly to the mouthpiece end, with the filter material providing
the
first passageway I, whereas some of the smoke passes into the conical cavity
15 (low
resistance section) from the filter material 12 via the perforations 17
whereby the
cavity 15 provides the second passageway II. As the strength of draw is
increased
the restricted orifice effect limits the amount of smoke that is able to pass
through
the perforations 17 into the second passageway and the remaining smoke is
therefore drawn into the mouth via the first passageway that comprises a route
composed entirely of high resistance material 12. As a result, the proportion
of
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smoke that passes along the first passageway as compared with the second
passageway increases with increasing draw and thus overall, the smoke drawn by
the
user is subject to an increased level of filtration with increasing draw.
In alternative embodiments, the cavity 15 in the mouth end of the filter is
not conic
but may be substantially cylindrical, or indeed any other suitable shape.
In alternative embodiments, the restricted orifice effect is harnessed to
limit the
passage of smoke from low resistance section to high resistance section.
Another embodiment is shown in Figure 4 in which *the filter arrangement shown
in
Figure 1 is abutted to the rod of smokable material in a longitudinally
reversed
orientation. According to this arrangement, the mouth distal end of the filter
material 18 (the high resistance section) has a diameter which is less than
that of the
rod of smokable material 19. As a result, a cavity 20 (low resistance section)
exists
between the filter material 18 and the tipping paper 21. Smoke may therefore
become drawn from the rod of smokable material 19 into either high resistance
section 18 or low resistance section 20.
The filter material 18 is covered in a non-porous plug wrap 22. At the mouth
end of
the cavity 20 an annular ring 28 is situated which is non-porous except for a
series
of small perforations 23. The perforations 23 are preferably between 0.01mm
and
2mm in diameter, more preferably the perforations are between 0.1mm and 1mm in
diameter.
Under conditions of a low strength of draw, smoke is drawn into the low
resistance
section 20, and is then subsequently drawn into the high resistance section 18
via
the perforations 23 in the annular ring 28.
On the other hand, under conditions of a high strength of draw, the restricted
orifice effect imposes a limit on the rate at which smoke is able to be drawn
through
the perforations 23 from the low resistance section 20 to the high resistance
section
18. As a result, smoke becomes drawn directly from the rod of smokable
material 19
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into the high resistance section 18. Smoke therefore passes along the filter
and into
the mouth via a route composed entirely of high resistance material. Under
conditions of a high strength of draw smoke is therefore subject to an
increased
level of filtration.
In some embodiments in which the low resistance section and the rod of
smokable
material are in physical contact, there is a non-porous barrier preventing
smoke
from directly entering the low resistance section. According to this
arrangement,
smoke is drawn from the rod of smokable material into the high resistance
section
and may then pass into the low resistance section via small holes as described
above. Obviously these embodiments also encompass a mechanism whereby smoke
can exit the low resistance section and pass into the mouth without being
further
restricted. Such a mechanism may encompass re-entry of smoke into the high
resistance section.
In the embodiment shown in Figure 4, a means of supporting the tipping paper
21
about the cavity 20 is provided, comprising a band of corrugated paper 24 that
encapsulates a portion of the length of the filter material 18 and arranged so
that a
series of substantially longitudinal channels 25 are formed. The outermost
circumference of the corrugated wrapper 24 is substantially the same as the
circumference of the rod of smokable material 19.
The low resistance section need not be a cavity but can comprise a second
filter
material which has a lower resistance than the filter material comprising the
high
resistance section. The smoke is subject to an increased total level of
filtration as
compared with an arrangement where the low resistance section is simply a
cavity.
The entire filter can be encapsulated by non-porous tipping paper that may be
provided with a circumferential band of perforations which permit diluting air
to
pass into the filter material comprising the high resistance section.
Many techniques are known in the prior art for establishing perforations. For
example, tipping paper may be perforated before (pre-perforated; PP) or after
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cigarette construction, and perforations may be introduced via an array of
pins or
using an on machine laser (OML) system. According to some embodiments, the
perforations in the tipping paper and/ or the plug wrap of the filter are
manufactured using PP or OML technology and consequently do not penetrate
substantially into the filter material comprising the high resistance section.
Recently an OML system for generating perforations which penetrate deep into
the
cigarette filter (deep vent OML; DVOML) has been disclosed (GB Patent
Application Number 0809865.9).
In some embodiments, the tipping paper perforations comprise deep vents, which
may be manufactured by DVOML, via alternative suitable methods, and which
extend substantially towards the diametric centre of the filter material
comprising
the high resistance section. Via the use of deep vents, diluting air is drawn
into the
centre of the filter and this has the effect of modifying the flow of smoke
drawn
from the rod of smokable material. For example, in the preferred embodiment
shown in Figure 1 in which the perforations 26 comprise deep vents, air drawn
through these holes will enter the filter material 3 close to the diametric
centre of
the filter material. This will have the effect of concentrating the smoke
drawn from
the rod of smokable material 1 into a diametrically peripheral zone of the
filter
material 3. The mixture of smoke and ventilating air exiting the filter
material via
the perforations 8 therefore contains a higher proportion of smoke than is the
case
when the perforations 26 only penetrate the tipping paper 9.
However, the filter need not be ventilated, or may be ventilated by
alternative
means, such as via an area of porous tipping paper and plug wrap.
The skilled artisan will understand that different embodiments of the
invention will
be more suitable for different types of smoking article, in particular,
depending on
the level of ventilation required. For example, in low tar products comprising
a high
degree of ventilation, it may be preferable for the perforations through which
the
passage of smoke may be restricted to be situated upstream (nearer to the rod
of
smokable material) than the site of ventilation, in order to maximise the
effect.
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For higher tar products on the other hand, in which ventilation is not such an
important consideration, it may be advantageous to site the perforations
through
which the passage of smoke is be restricted towards the mouth end of the
smoking
article.
In some embodiments, the filter material comprising the sections of high and/
or
low resistance comprises a plurality of abutted filter sections made of
similar or
different materials. Each of the filter sections may consist of one or a
combination
of cellulose acetate, polypropylene, paper or any other suitable material. The
filter
section(s) may alternatively or additionally comprise carbonaceous material,
for
example, activated charcoal, a resin material such as amberlite or duolite,
and/ or
catalytic material.
In some embodiments in which the filter comprises a plurality of
longitudinally
abutted filter sections, one or more of the filter sections may comprise an
annular
filter section. In this case the annulus may be a cavity or may be composed of
filter
material with a lower resistance, thus the annulus comprises the low
resistance
section.
In other embodiments, the filter is constructed from a plurality of filter
sections and
one or more annular sections are used wherein the annulus comprises the high
resistance section. .
In some embodiments the filter material may be shaped by heat moulding,
embossing, crimping or any other suitable method.
Above is described what is believed to be the preferred embodiments of the
current
invention. However, those skilled in the art will recognise that changes and
modifications may be made without departing from the scope of the invention.
