Note: Descriptions are shown in the official language in which they were submitted.
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Tobacco Smoke Filter and Methods of Making the Same
Field of the Invention
The invention relates generally to devices for filtration of tobacco smoke,
their
manufacture and use. More specifically, the invention relates to filters
suitable for use in
smoking devices.
Background of the Invention
Single-use, disposable filters have been incorporated in smoking products for
decades.
Filters are commonly made of cellulose acetate, relying on a process whereby
cellulose acetate is
dissolved in a solvent such as acetone, and polymer filarrients are spun out
of the solution. The
filaments are lubricated and bundled, then crimped and dried. Alternative
filter materials include
polypropylene and cellulose. Filters may be segmented, potentially with
different materials in
different segments; they may incorporate granular additives such as carbon.
The filter is located at one end of the tobacco rod so that smoke from the
burning tobacco
rod, which comprises a particle phase and a vapour phase, passes through the
filter before being
inhaled by the user. The fibres of the filter form a mechanical barrier which
entraps particulate
matter in the smoke stream. Early filters relied solely on this mechanical
filtration; see for
example US Patent No. 4,502,495.
More recent approaches include providing ventilation holes along the paper
wrapper
outside the filter to dilute the inhaled smoke. They also target the volatile
constituents of the
smoke, which are typically unaffected by the physical barrier of the filter.
For example,
adsorbent or absorbent materials are often added to selectively remove
volatile elements from the
smoke stream.
Activated carbon, porous minerals such as meerschaum, silica gel, and cation-
or anion-
exchange resins are frequently used as filter additives. Carbon or charcoal
can be useful for
removing acidic gases. Meerschaum has a strong adsorption affinity for charged
species. Silica
gels readily adsorb aldehydes and hydrogen cyanide. Cation exchange resins
have been proposed
for nicotine removal, while anion exchange resins have been proposed for the
removal of smoke
acids. Researchers are continually developing new additives which target
classes of or specific
smoke constituents.
One challenge faced with the addition of granular or particulate material to
the filter
filaments is how to adhere the individual particles in such a way that they
remain active. For
example, adhesives which ensure particles stay in position on fibers can block
reaction sites on
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the particles. One solution has been to form cavities in the filter and load
them with batches of
particles, although that presents a different problem, namely, how to channel
the smoke stream
through such a loose bed of particles during use.
A further solution to containment of particles is to enclose them in tubes
running parallel
to the direction of smoke flow, whereby the smoke passes through the tubes and
contacts the
particles therein. By making the tubes non-linear, the route of filtration is
longer, see US Patent
No. 4,373,539.
Other examples of known filters are disclosed in WO 86/03381, US 2003/0200973,
and
EP-A 0033772, which describe various filters having a helical channel for
smoke.
As reducing particulate and vapour constituents in smoke remains a pressing
need in the
art, new materials and methods for improving upon existing filters are
desired. Particularly,
solutions which can be used in conjunction with any variety of conventional or
novel filter
materials and additives would be of particular benefit.
Summary of the Invention
In accordance with the present invention, there is provided a smoke filter for
a tobacco
product comprising an axially extending filter section defining a path along
which, in use, smoke
passes through filtration material, wherein the path extends helically around
the axis of the filter.
By providing a smoke path that thus winds around the axis of the filter, the
contact time of the
smoke with the filtration material and the surface area of filtration material
contacted may be
increased.
According to an embodiment of the invention, a tobacco smoke filter is
provided which
comprises a generally cylindrical enclosure having an inner diameter and a
helical element
having a diameter and disposed in the enclosure, where the diameter of the
helical element is
approximately equal to the inner diameter of the enclosure. The filter further
comprises filtration
means disposed between the helical element and the enclosure.
The enclosure may comprise plug wrap, which may comprise a plurality of
ventilation
holes. If provided, ventilation holes may be positioned to correspond to
regions of the enclosure
which do not overlie the helical element. The enclosure may be at least two
layers, for example,
an outer layer of plug wrap and an inner layer of cellulose acetate adjoining
the helical element.
The helical element may comprise polypropylene, polyethylene, paper, carbon
paper,
impregnated paper or any other materials as taught herein and may comprise a
coating layer on
an outer surface thereof. The coating layer may comprise activated charcoal,
activated coconut
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carbon, activated coal-based carbon, zeolite, silica gel, meerschaum,
aluminium oxide,
carbonaceous resin, and combinations thereof. The helical element may comprise
compressible
edges at the point where the element may contact the inner diameter of the
enclosure.
Alternatively or in addition, the central portion of-the spiral core may be
compressible.
The filtration means may comprise at least one material selected from the
group
consisting of cellulose acetate, polypropylene, polyethylene, gathered paper,
and combinations
thereof, for example, randomly orientated cellulose acetate. The filtration
means may further
comprise activated carbon, flavourant, adsorbent, or absorbent.
In one embodiment, the filtration means occupies substantially all of the
space between
the helical element and the inner diameter of the enclosure. This ensures that
the smoke flowing
along the helical element must pass through the filtration means, thereby
providing good
filtration behaviour. In addition, tight packing of the filtration means
within the filter imparts a
solid and reassuring feel to the filter. This tight packing can be achieved by
using small fibres or
such-like of filtration materials.
According to another embodiment, a smoking article is provided which comprises
a
tobacco smoke filter according to the present invention.
According to another embodiment, the invention relates to a method of making a
tobacco
smoke filter which comprises the steps of providing a generally cylindrical
helix having intra
helical turn space and having an outer edge, placing filtration means in the
intra helical turn
space, and enclosing the outer edge of the filled helix in an enclosure.
As used herein, "tobacco" refers to any part, e.g., leaves, flowers, stems, of
any member
of the genus Nicotiana and reconstituted materials thereof. It includes
derivatives such as
specific compounds found in natural tobacco, e.g., nicotine, whether extracted
or synthesized, as
well as structural derivatives such as the fibrous portion of a tobacco leaf.
It further includes
tobacco substitutes which comprise individual chemicals and/or complex
chemical entities
which, when appropriately prepared, physically resemble natural tobacco.
As used herein, "tobacco smoke filter" means any element which is intended for
use as a
unit through which tobacco smoke passes and in which certain components in the
tobacco smoke
are slowed, cooled, and/or retained. Tobacco smoke includes both the by-
product of tobacco
combustion and the by-product of tobacco heating in the absence of actual
combustion.
Brief Description of the Drawing Fir-ures
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So that the subject invention may be easily understood and readily carried
into effect,
reference will now be made, by way of example, to the accompanying
diagrammatic drawings,
in which:
Figure 1 represents a perspective, partially broken away view of a filter of
the invention;
Figure 2 shows a side elevation, partly longitudinal cross-section and
partially broken
away view of a filter of the invention;
Figure 3 shows a cross sectional view of a filter of the invention taken along
lines A-A of
Figure 2;
Figure 4 represents a perspective, partially broken away view of a filter of
the invention;
Figure 5 shows an axial cross-section view of a filter of the invention;
Figures 6A and 6B show two views of the element B of Figure 5, one when a
filter of the
invention is uncompressed and one when a filter of the invention is
compressed;
Figures 6C and 6D show alternate configurations for element B of Figure 5;
Figure 7 is a schematic diagram of a manufacturing process according to the
present
invention;
Figure 8 shows a portion of an embodiment of a machine for producing filters
of the
invention;
Figure 9 shows a side elevation view of an embodiment of a machine for packing
intra
helical space of filters according to the invention; and
Figure 10 shows a cross sectional view taken along lines A-A of Figure 9.
Detailed Description
The invention relates to tobacco smoke filters which comprise a helical
element centred
axially therein. The element may take on any number of configurations in cross-
section, although
it will generally be described herein as a single helix. Referring to Figure
1, a tobacco smoke
filter 10 is shown with a spiral core 11. The spiral core is provided as shown
in the embodiment
of Figure 1 with filter means 12. Spiral core 11 and filter means 12 are
visible due to partial
breakaway of the enclosure 13, here depicted as plug wrap.
Spiral core 11 has a diameter which is approximately equal to an inner
diameter of
enclosure 13. That is, the outer edges of the helix generally abut the
enclosure. Filter means 12
is located in grooves formed by edges of the helix between spiral core 11 and
enclosure 13.
As is well known to product engineers, a helix's curve can either move from
the lower
left to the upper right, making it a right-handed helix, or from the lower
right to the upper left,
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thus being a left-handed helix. Either right- or left- handed helices may be
used as a spiral core in
the practice of the present invention.
The pitch of the helix, that is, the length of one complete helical turn, is
selected based on
a balancing of the desire to increase the filtration route with the need to
permit easy inhalation.
5 The pitch that will be employed with any filter according to the invention
can be optimised by a
skilled worker based on variables such as material for the helix element,
particularly whether or
not it is porous; material surrounding the helix and how densely it is packed,
and ventilation,
among others. The pitch might be 1-4 mm, for example 2-3 mm.
Permeability of the material used in the spiral core may preferably be low in
certain
applications, so that it is effectively non-porous. This, combined with the
placement of a less
porous enclosure tightly against the helix, ensures that as smoke is inhaled
it is forced to travel in
a spiral fashion through the filter. This increases physical filtration and
provides an opportunity
for additional removal of volatile components from the tobacco smoke. Extruded
plastics, foils
or coated papers are some examples of materials which may be used to form the
spiral core.
According to another embodiment, the material used in the spiral core is
porous. Pores in
the material may be formed to specifically capture select smoke constituents.
For example, the
material can be polymer, molecularly imprinted with target constituents. The
pores in the
material may be impregnated with an additive such as flavourant or diluent,
which additive could
be inhaled in the first few puffs during use leaving behind empty pores
capable of interacting
with subsequent smoke streams passing there through. The spiral core may be
formed of
activated carbon, which may have a density such that the majority of smoke is
encouraged
around the helix and a minority of the smoke passes through the carbon
structure of the spiral
core. A binder may be utilized to allow granules of activated carbon to be
formed into and retain
the spiral shape.
According to another embodiment the spiral core is non-porous but provided
with a
porous surface for interacting with smoke components. Alternatively or in
addition, the spiral
core may be coated, for example with flavourant or with an agent designed to
entrap, neutralize,
or otherwise interfere with smoke constituents.
The width and length of the spiral core is preferably approximately equal to
the width and
length of a standard tobacco smoke filter. For example, a standard cigarette
filter is typically in
the range of 10-30 mm long and 25-30 mm in circumference. The width of the
spiral core may
be less than the standard thus allowing a co-axial or multi-component
enclosure.
Where the spiral core is of firm and inflexible material, it may be preferred
to provide a
region of tightly packed cellulose acetate co-axially around the outside of
the spiral to cause the
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filter, when it use, to more closely approximate the feel of a standard
filter. The length may also
be adjusted, for example it may be part of the length of a standard filter to
accommodate one or
more filter elements on either or both ends.
To provide a standard looking filter it may be preferred to have a filter
segment of
cellulose acetate at the mouth end of the smoking article visible to the user,
so a multiple
segment filter incorporating_the invention could be half cellulose acetate at
the user end and half
novel tobacco smoke filter at the tobacco rod end. Where the helical element
forms only one part
of a multi-element filter it may be preferred to refrain from adding filter
means within the helix.
The thickness of the material forming the spiral core is also a product
variable. Where the
helix is impermeable to smoke it may be on the order of 0.5-2 mm. When the
helix is intended to
be selectively permeable to smoke constituents and/or ambient air, the
thickness may be 0.5-3
mm. It need not be the same across the entire cross-section, for ease of
production or good
product feel it may be that the centre of the spiral is thicker than the
furthest edges. Alternatively
or in addition, the central axis of the spiral core may be solid, forming a
circle with outwardly
radiating flanges in cross section. In conjunction with manipulation of the
thickness of the
material forming the spiral, pitch can be adjusted to help provide the desired
draw resistance or
pressure drop.
Ventilation holes, commonly known in the art, may be incorporated in a filter
according
to the invention. Such holes would increase dilution of tobacco smoke and
facilitate inhalation
through the circuitous filtration path. It may be most effective to provide
ventilation holes in a
spiral pattern corresponding to the spiral core, at locations where the
enclosure does not abut the
edge of the spiral core. Pressure drop may be considered when determining
whether to use
ventilation holes, the number and location being dependent on the shape and
material of the helix
as well as consideration of any filter means used.
A spiral core of the present invention could be manufactured according to any
appropriate method. Specific manufacturing requirements vary depending on the
material and
dimensions chosen, and on whether there is a coating on the spiral core. For
example, an
extruded core could be entrained in cellulose acetate during the conventional
filter-making
process.
The spiral core and its location in relation to the enclosure causes an
inhaled smoke
stream to take a longer than standard, circuitous path through the filter
before reaching the user.
This provides the possibility of increased surface area and increased time for
filtration to occur.
Accordingly, the spiral core itself comprises a type of filtration means
itself.
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If the enclosed spiral core were surrounded only by ambient air, inhaled smoke
would not
be maximally filtered as it would merely need to travel a longer path prior to
entering the user's
mbuth. The longer path would serve to cool the air and some particulate matter
may settle out
and adhere to the core or surrounding paper. Even where the spiral itself core
comprises filtration
material, and even where such a spiral core is used as one segment of a multi-
segment filter, such
a design fails to maximize the opportunities to filter smoke which are
available and thus might
only be preferred embodiments for special uses.
Thus, additional materials are provided in the space around the helix up to
the enclosure
to maximize filtration opportunities for standard uses. For example, randomly
orientated acetate
fibres, i.e. pieces of standard filter material can be packed more or less
tightly around the helix to
provide filtration means while still allowing smoke inhalation. Acetate fibres
having any size
range which allows incorporation in the filter, for example, 2 mm, could be
employed.
Other options for material around the spiral core include any filtration
materials which
are appropriate for use with filtering inhaled smoke, and may be fragments,
twists, or other. The
material placed around the spiral core may incorporate any number of additives
such as
adsorbents, absorbents, diluents, flavours, and the like. Materials and
methods for incorporating
them into various filter components are known in the art. For example, both
activated charcoal
and resins are commonly used and could be provided.
Conventional means for producing smoking articles may be used in accordance
with the
invention. Tobacco smoke filter material according to the invention having the
same dimensions
and handling properties as standard filters can be provided to the machinery.
The machinery will
incorporate the novel filter with tobacco rods, wrapping paper and tipping
paper to produce an
article resembling conventional products_in size and appearance but provided
with a novel filter
according to the invention.
The enclosure containing the spiral core may be conventional plug wrap. It may
be
coated on one or both sides with any desired additive, such as colourant and
fragrance along the
outer surface, to resemble a cork pattern and to have an appealing scent, and
inner coating of
diluent, flavourant, materials which improve filtration such as activated
carbon particles, and the
like. A layer of material may be provided along the inner surface to improve
the tactile qualities
of the filter, for example, a layer of cellulose acetate forming the inner
diameter of the enclosure
may cause the filter to feel similar to conventional filters, which may
increase user appeal.
Under present manufacturing conditions, a filter portion is compressed by
about lmm in
circumference when tipping papers is added to connect the filter element to
the tobacco rod. In
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an embodiment of the invention which is provided with a layer of cellulose
acetate between the
plug wrap and the spiral core the cellulose acetate layer might be able to
accommodate the
compression. However, and particularly in the case of spiral cores which
directly will be directly
compressed during addition of a single layer enclosure, it may be preferred to
provide some
flexibility or compressibility in the spiral core.
Figure 5 depicts one example of a cross section of a spiral core 11 surrounded
by an
enclosure 12. Circled region B is -shown in more detail in Figures 6A and 6B.
Figure 6A shows
how the edge of spiral core 11 can be configured in the region where it is
intended to contact
enclosure 12. The edge has a deformable flange-type feature which, upon
compression, flexes to
allow inward pressure from enclosure 12. Figure 6B shows how the region
accommodates
compression. After the compressing forces are released the edge of spiral core
11 re-positions
itself to the configuration of Figure 6A.
An added benefit of the type of configuration shown in Figures 6A and 6B is
that it has a
sealing effect between the core and the enclosure, further ensuring that smoke
inhaled through
the filter is forced through the spiral route. Depending on the configuration
and materials used
for spiral core, the compressibility may also provide improved tactile feel
for the user. For
example, the material used for the spiral core may be elastic and provide
tension when deformed
so that it re-expands to the original configuration after application of the
tipping paper.
Alternative tipping paper application steps can be taken where, for example,
it would be
economically preferred or where spiral cores are provided which are not
designed to be
compressible.
Alternatively, the spiral core may be compressible. Preferably it is also
expandable so as
to return to its original size after compression. Such an embodiment may be
provided with
rounded edges along the _portion of the spiral core that is-in contact with
the enclosure to avoid
puncture or tearing during compression or handling, see Figure 6C. Another
alternative would be
to provide a flattened edge which flattened portion sits flush with the
enclosure, also reducing the
risk of tearing and possibly also improving the sealing effect and tactile
feel, see Figure 6D.
One method for manufacturing a filter according to the invention is
represented
schematically in Figure 7. A device 70 comprises a spiral material supply 71
which could be a
bale of extruded plastic helix. A filter means supply 72 could be a batch of
cellulose acetate
fibres. An enclosure supply 73 provides means for enclosing the filter
components, and could be
a roll of plug wrap.
While standard methods typically produce filter materials as a long cylinder
which is cut
into smaller units for individual use, it may be that certain spiral cores are
advantageously made
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unit by unit then incorporated into a filter and joined to a tobacco rod. They
may form the entire
length of the filter region, alternatively they may be part of a multi-segment
filter.
In use, device 70 feeds spiral material from supply 71 to a filter means
addition area 74.
Therein materials from filter means supply 72 are provided to the spiral. An
additive application
means 75 is provided, which could be a single means as shown or a series of
means, potentially
each supplying a different additive. A drying means 76 is provided whicr- may
cure the inner
filter components prior to or after addition of enclosure from enclosure
supply 73. A cut off 77 is
situated to cut prepared filter material to the desired length.
Any known or developed alternative methods could be used to produce a tobacco
smoke
filter according to the invention. For example, as shown in Figure 8 a multi-
segment filter is
being produced. A continuous rod 81 is shown, which is intended for eventual
division into a
plurality of individual filter units 82. Each filter unit 82 comprises a first
filter segment 83, a
second filter segment 84, and a third filter segment 85. In the embodiment
shown, the spiral core
portion is provided in second filter segment 84.
Particles 86 are added to the spiral core of second filter portion 84 by a
dispensing means
87. Particles 86 could be filter means, additives, or a mixture of the two.
One option for an
embodiment such as that shown in Figure 8 would be to have a first filter
segment of cellulose
acetate, a second filter segment of non-porous spiral provided with
flavourants in the intra-
helical space, and a third filter segment comprising carbon such as a cavity
filter filled with
carbon particles or carbon paper formed into a filter segment. As should be
evident to the skilled
person, there are a plurality of existing methods which could be employed
similar to the
dispensing means of Figure 8.
It is contemplated that a plurality of dispensing means could be provided to
the same rod,
wherein each would supply a different material to the spiral core. For-
example, a first means
supplying a first flavourant, a second means supplying an absorbent, and a
third means supplying
a second flavourant. The three means could be provided side by side to fill
separate regions of
the same spiral core with respective additives; alternatively they could be
adding their respective
materials throughout each spiral core one after the other.
Where spiral cores are designed such that differential smoke travel paths are
observed,
one or the other of these configurations may be preferred. For example, where
it is observed that
the beginning portion of an inhaled puff of smoke travels primarily along the
central region of
the core and the latter portion of the same puff travels along the outer
regions of the core, toward
the enclosure, a multi-step or multi-layer fill might be preferred to provide
first materials that
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will affect the beginning portion of a puff and second materials that will
affect the latter portion
of a puff.
A further example is shown in Figure 9, where a spiral core 11 is passed
through a
5 rotating feeder 91 which simultaneously provides material 92 around the core
and provides for
containment of the filled core in an enclosure 13. A cross-section along lines
A-A is. shown in
Figure 10, where it is evident that materia192 is passed into feeder 91 and
fills any space present
around core 11.
While addition of filter or additive material to the spiral core after
formation may be a
10 preferred method for certain placations, where materials and design allow a
single process step
could handle all functions. For example, a rotating head could extrude a
spiral core while
simultaneously filling the intra-helical space with filter and/or additive
material. A plurality of
materials may be mixed first then added as a mixture, alternatively there
could be one or more
streams of each additive fed discretely. This latter form may be preferred
where the added
materials handle differently or where settling or other problems occur in a
mixture.
Although Figures 7-10 relate to a single line for working with spiral cores of
the present
invention, it should be apparent to skilled persons that manufacturing
efficiencies may best be
met by providing a plurality of units or a series of steps in parallel. For
example, the means
shown in Figures 9 and 10 could be provided in duplicate or triplicate, thus
producing two or
three times as much filter material as would otherwise be made.
Example 1 Filter Manufacture
Activated carbon is moulded into a helical shape approximately 6 mm in
diameter. An
average pitch and low porosity, i.e., low permeability, are used. The carbon
is cut into lengths of
approximately 20 mm. Units of standard cellulose acetate tow approximately 6
mm in diameter
and approximately 10 mm long are provided and arranged in alternating fashion
with lengths of
carbon helix.
The intra helical space of the carbon helix is provided with a mixture of
flavourant and
adsorbent before the length of helix/cellulose acetate tow is wrapped with an
approximately 0.5
mm thick layer of cellulose acetate about its circumference. Plug wrap may
optionally be
provided around the cellulose acetate layer as known in the art.
This provides a length of filter material which may be cut along the middle of
the
approximately 10 mm lengths of cellulose acetate tow to provide a plurality of
filter units each
approximately 30 mm in length and each comprising an approximately 5 mm
cellulose acetate
tow at either end, surrounding a carbon helix with additives in the intra
helical space.
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The filters thus produced may be incorporated in smoking articles, for example
cigarette
holders or water pipe mouthpieces, to provide an effective yet disposable
filtration material for
the smoke inhaled therethrough. Different lengths and thicknesses can be
provided depending on
the expected use. For uses with slightly flattened mouthpieces, the spiral
core may be formed- to
have a slightly oval shape in cross-section. This would be regarded as still
having a generally
cylindrical shape as taught by the present invention.
Example 2 Cigarette Manufacture
A resin commonly used in tobacco smoke filters is extruded through a die to
produce a
tight helical shape approximately 7 mm in diameter and 10 meters long. The
shape is fed into a
machine which applies suction or vacuum, for example a suction garniture, to
pack fibres of
cellulose acetate around the helix. The packed helix is wrapped in plug wrap
and cured on a
drying garniture. The cured filter is cut to 60 mm lengths which are provided
to a cigarette
making machine.
The cigarette making machine uses the filter to produce cigarettes according
to known
methods. In brief, two tobacco rods are positioned at either end of the filter
and, once secured,
the filter is cut at the middle. An optional end segment, for example, a pad
of cellulose acetate, is
added at the mouth end of the cigarette to mask the helical core unit. The
resultant product is a
cigarette incorporating a novel tobacco smoke filter according to the
invention.
The foregoing description and examples have been set forth merely to
illustrate the
invention and are not intended to be limiting. Since modifications of the
described embodiments
incorporating the spirit and substance of the invention may occur to persons
skilled in the art, the
invention should be construed broadly to include all variations within the
scope of the appended
claims and equivalents thereof.
