Note: Descriptions are shown in the official language in which they were submitted.
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TOBACCO SMOKE FILTER
The present invention relates to filters and filter elements for
smoking articles such as cigarettes, in particular slim cigarettes.
Conventional cigarettes have a circumference around 24.5 mm ¨
'slim' cigarettes (circumference around 21 ¨ 23.2 mm) and isuperslim'
cigarettes (Circumference around 16 ¨ 18 mm) are also known. It is also
possible to manufacture cigarettes with even narrower circumferences,
e.g. in the range 14 -16 mm, although these are not generally
commercially available. In the context of this document, the term 'slim'
should be construed as including all cigarettes and/or cigarette filters with
a circumference between around 14.0 and 23.2 mm.
Selective filtration occurs when the yield of selected chemicals in
cigarette smoke is proportionally reduced to a greater extent than the
majority of compounds in smoke (e.g. tar). Phenolic compounds ¨ for
example phenol, cresols, catechol and resorcinol ¨ are known constituents
of cigarette smoke. They are toxic compounds ¨ in particular, phenol and
catechol are included on the so-called "Hoffmann" list of the most
hazardous compounds found in cigarette smoke. It is con.sidered
desirable, to potentially selectively reduce the quantities of these
compounds delivered to the smoker.
The usual filtering material used in cigarette filters is a continuous
tow of filamentary cellulose acetate plasticised with triacetin, which is
gathered together in rod form to form the filter or filter element In such a
continuous tow (and in filters and filter elements formed therefrom) the
filaments of cellulose acetate tow are predominantly aligned in the
longitudinal direction. It is well known that cellulose acetate exhibits a
selective filtering action towards phenolic compounds. A filter for a "slim"
cigarette will naturally include a reduced volume of cellulose acetate
filtering material compared to a standard filter; any selective filtering
effect
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,.
may be reduced as there is less material available to act upon a similar
quantity
of smoke. It is desirable, therefore, to provide a slim filter which
potentially
selectively reduces the quantities of phenolic compounds delivered to the
smoker of a slim cigarette.
The specification of a filter tow is described in terms of the denier per
filament (dpf); total denier; and the fibre cross-sectional shape. The
filament
denier is defined as the weight in grams of 9000 metres of a single filament;
the
total denier is then simply the dpf multiplied by the number of filaments in
the
tow. Thus, for example, a 5Y30,000 tow describes a material with a filament
with a dpf of 5 grams per 9000 metres in the shape of a Y, comprising 6,000
filaments giving a total denier of 30,000 grams per 9000 metre length. In
order
to manufacture a standard cellulose acetate ("monoacetate") cigarette filter
having a low circumference (i.e. a slim monoacetate filter), it is necessary
to
use a cellulose acetate tow with a low total denier because there are
limitations
on the amount of material than can be packed into the slim product. It is well
known in the industry that low total denier tows are more expensive (per unit
weight) than higher total denier tows and there is also limited commercial
availability of low total denier tows. It is desirable, therefore, to provide
a slim
filter, which can be made from a wider range of total denier of cellulose
acetate
tows than conventional slim or superslim monoacetate filters.
According to the present invention there is provided a tobacco smoke
filter or filter element comprising a cylindrical plug of a substantially
homogeneous filtering material of circumference between 14.0 and 23.2 mm
(for example, between 16 and 23.2 mm), wherein the substantially
homogeneous filtering material comprises a plurality of randomly oriented
staple fibres, wherein the staple fibres are randomly oriented in three
dimensions.
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Herein, the term "substantially homogeneous filtering material"
means a filtering material which has substantially uniform physical
characteristics throughout any cross-section therethrough.
Herein, the term "staple fibres" means individual, discrete, fibres of
specific length. The
staple fibres may be randomly oriented with
reference to one another. The substantially homogeneous filtering
material may comprise a plurality of randomly oriented staple fibres
wherein a portion of the randomly oriented staple fibres generally extend
transversely to the longitudinal axis of the cylindrical plug. The
substantially homogeneous filtering material may comprise a plurality of
randomly oriented staple fibres at least 10% (for example, 20%, 30%,
40%, 50%, 60%, 70%, 80% or 90%) of which by weight extend
substantially transversely to the longitudinal axis of the cylindrical plug.
The term randomly oriented staple fibres means that the staple
fibres are randomly oriented in three dimensions (in the filter or filter
element). The
term randomly oriented staple fibres, herein, is not
intended to (and does not) mean a continuous cellulose acetate tow, the
individual strands of which are predominantly aligned in the longitudinal
direction (although it will be appreciated that staple fibres may be formed
from such tows, as discussed below). The term randomly oriented staple
fibres, herein, is not intended to (and does not) mean a web or sheet of
filtering material which is formed (from e.g. pulp and/or fibres) and then
shaped as a whole or substantially whole web or sheet into rod form (by
e.g. wrapping). The term randomly oriented staple fibres does not mean a
two dimensional paper-like artefact which is taken up in a roll form. The
term randomly oriented staple fibres, herein, is not intended to (and does
not) mean a web or sheet of filtering material which is formed (from e.g.
pulp and/or fibres) and then shredded and then shaped into rod form.
Sheets or webs may have random orientation in two dimensions but (even
when shredded) undergo processes (such as embossing) so they retain
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some integrity when drawn through a filter making machine. Thus, the
fibres in a filter or filter element made from a sheet or web (even a
shredded sheet or web) will be predominantly aligned along the
longitudinal axis of the filter or filter element, and are therefore not
randomly oriented (in three dimensions) staple fibres.
The plurality of randomly oriented staple fibres may form a porous
matrix providing a labyrinth of passages ¨ these may act as passages for
smoke when utilised as a cigarette filter. The applicants have found that
the performance of the filter or filter element of the invention may be
comparable to existing products (e.g. a "monoacetate" product formed of a
continuous tow of longitudinally oriented filaments of cellulose acetate tow
plasticised with triacetin gathered together in rod form), but the applicants
have found that 20-30% less filtering material (e,g. cellulose acetate) is
required when it is used in the form of randomly oriented staple fibres. In
addition to the requirement for less filtering material per filter, there is
the
further advantage that it is possible to use much higher total denier
cellulose acetate tows than for a conventional superslim product. Thus, in
addition to the cost benefits of the weight saving arising due to the
applicant's invention (because less filtering material is required), the unit
cost of the tow used itself may also be cheaper, because there is no
longer the need to use (expensive and less readily available) low total
denier tows.
The applicants have unexpectedly found that tobacco smoke filters
or filter elements of the invention may provide enhanced removal of
phenols from tobacco smoke (in a slim cigarette), compared to e.g. a
standard monoacetate filter or filter element (which does not comprise
randomly oriented staple fibres). The unexpected reduction in phenolic
compounds by filters and filter elements of the invention is even more
significant when the lower weight of filtering material (cellulose acetate) is
taken into account. The applicants have also unexpectedly found that
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tobacco smoke filter or filter elements of the invention may be more readily
and swiftly degraded under e.g. environmental conditions, compared to
e.g. a standard monoacetate filter or filter element.
The staple fibres may be made of filamentary material. The staple
fibres may be crimped, as is well known in the art. The staple fibres may
be, for example, cellulose acetate or polypropylene fibres. The staple
fibres may be made of (or formed from) a fibre tow, for example cellulose
acetate tow, polypropylene tow, The staple fibres may be, for example,
natural and/or synthetic fibres; fibres formed from natural plant material(s)
etc. The staple fibres may be cellulose pulp fibres (e.g. which have been
fiberized via a hammermill). The staple fibres may be cut herbs (e.g. cut
tobacco leaf), or obtained from reconstituted tobacco sheet. The staple
fibres may impart flavouring and/or filtration properties to the final
product.
The staple fibres may be of substantially the same length (of substantially
uniform length). The staple fibres may be of a variety of different lengths.
The stable fibres may be for example of length between 4 mm and 20 mm,
e.g. between 5 mm and 19 mm, e.g. between 6 mm and 18 mm, e.g.
between 7 mm and 16 mm. The staple fibres may be made of, or formed
from, a fibre tow, for example cellulose acetate tow, of total denier of from
14,000g to 55,000g per 9,000m length, e.g. from 20,000g to 50,000g per
9,000m length, e.g. from 23,000g to 45,000g per 9,000m length, e.g. from
25,000g to 40,000g per 9,000m length.
The substantially homogeneous filtering material may optionally
include other material, for example a liquid additive (such as a flavourant,
e.g. menthol solution). The substantially homogeneous filtering material
comprising a plurality of randomly oriented staple fibres may be formed
from a plurality of staple fibres, and may optionally include other material,
for example a plasticiser, a binder material or other additive. The staple
fibres may be bonded to each other (e.g. due to action of a plasticiser) at a
multiplicity of contact points.
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The substantially homogeneous filtering material may optionally
include a binder material. The substantially homogeneous filtering
material may optionally include a water soluble binder material. Examples
of water soluble materials include water soluble polymer materials such as
polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl ether, starches,
polyethylene glycols and polypropylene glycols; blends of water soluble
binders with plasticisers such as triacetin; and hot melt water soluble
binders in particulate form. The inclusion of a water soluble binder
material may further enhance the ability of the filter or filter element to be
readily and swiftly degraded e.g. under environmental conditions.
The filter or filter element may include one or more particulate
additives ¨ e.g. within the body of the filter or filter element. The (or
each)
particulate additive may be a powder (e.g. particles of 50 to 150 pm
diameter) or granular (e.g. particles of 0.15 to 1.0 mm diameter).
Examples of suitable particulate additives include flavourants or sorbents ¨
e.g. activated carbon, zeolite, ion exchange resin (e.g. a weakly basic
anion exchange resin), sepiolite, silica gel, alumina, molecular sieves,
carbonaceous polymer resins and diatomaceous earths.
The filter or filter element may include more than one type of staple
fibre, For example, staple fibres which are fibres (of e.g. cellulose pulp)
which have been fiberized via a hammermill may be included in the filter in
addition to (e.g. mixed with) staple fibres formed from a filamentary tow.
The staple fibres (e.g. of fibre tow, e.g. cellulose acetate tow) may
be plasticised. In other words, the substantially homogeneous filtering
material may optionally include a plasticiser. The formation of plasticised
tow is well known in the art. The plasticiser (which plasticises the staple'
fibres) may be, for example, triacetin, triethyleneglycol diacetate (TEGDA)
or polyethylene glycol (PEG). The staple fibres may be fibres of
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plasticised cellulose acetate tow. The staple fibres may be cellulose
acetate tow which has been plasticised with e.g. triacetin.
The circumference of the cylindrical plug may be for example
between 14.0 mm and 23.2 mm, for example between 16 and 23.2 mm,
for example between 16.0 mm and 20mm, for example between 16.2mm 1
and 20mm, for example between 16.2 mm and 17 mm.
The plurality of randomly oriented staple fibres may form a porous
matrix providing a labyrinth of passages in the filtering material. The
labyrinth passages may function as passages for smoke when utilised as a
cigarette filter.
The tobacco smoke filter or filter element may have substantially
uniform physical characteristics throughout any cross-section thereof,
rather than the more uneven structure that results from formation from a
sheet of filter material.
In filters and filter elements according to aspects of the invention,
the tobacco smoke filtering material may be over wrapped with a wrapper
or plugwrap, for example a wrapper of paper, for example a wrapper of an
air-permeable paper. Particulate additives such as those discussed above
may be applied to the wrapper or plugwrap surrounding the filter material,
for example as described in GB 2261152.
According to the invention in a further aspect there is provided a
multiple rod comprising a plurality of filters or filter elements as described
above and/or herein integrally joined end-to-end in a mirror image =
relationship.
A filter element according to the invention may be used as a
segment of a multi-segment slim filter, e.g. a dual, triple, other multiple
filter. Such filters are well known in the art. If the filter element is used
as
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or in a segment of a multi-segment filter, it may be used at (or in) the
mouth or buccal end segment of the filter, or as (or in) any other segment
of the filter. A filter element according to the invention may be used on its
own e.g. as a single segment slim filter (e.g. in the same way as a
monoacetate filter). Such filters are well known in the art.
In a filter cigarette according to the invention, a filter of the invention
(or a filter which includes a filter element of the invention) is joined to a
wrapped tobacco rod with one end of the filter towards the tobacco. The
filter may, for example, be joined to the wrapped tobacco rod by ring
tipping [which engages around just the adjacent ends of a (wrapped) filter
and rod to leave much of the filter wrap exposed] or by a full tipping
overwrap (which engages around the full filter length and the adjacent end
of the tobacco rod). Any filter or filter cigarette according to the invention
may be unventilated, or may be ventilated by methods well known in the
art, e.g. by use of a pre-perforated or air-permeable plugwrap, and/or laser
perforation of plugwrap and tipping overwrap.
According to the invention in a further aspect there is provided the
use of a tobacco smoke filter or filter element comprising a cylindrical plug
of a substantially homogeneous filtering material comprising a plurality of
randomly oriented staple fibres for selectively reducing one or more
phenolic compounds in tobacco smoke. According to the invention in a
further aspect there is provided the use of a cylindrical plug of a
substantially homogeneous filtering material comprising a plurality of
randomly oriented staple fibres, as, or in the manufacture of, a filter or
filter
element for selectively reducing one or more phenolic compounds in
tobacco smoke.
According to the invention in a further aspect there is provided the
use of a cylindrical plug of a substantially homogeneous filtering material
comprising a plurality of randomly oriented staple fibres, as, or in the
" 30 manufacture of, a filter or filter element having enhanced
degradability.
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The present invention will now be illustrated with reference to the
following Examples and the attached drawings in which FIGURE 1 is a
plan view, not to scale, of an individual filter in an embodiment of the
invention; and FIGURE 2 shows a cross-section of the filter of Figure 1.
The filter 1 shown in Fig.1 includes a porous elongated cylindrical
plug 2 of circumference 16.9 mm and length 27 mm, which comprises a
plurality of randomly oriented individual or staple filamentary fibres 3
formed from a 5Y30,000 cellulose acetate tow plasticised with triacetin.
As shown in Figs. 1 and 2 the staple fibres 3 generally extend transversely
to the longitudinal axis of the element and tie back slightly to form a
multiplicity of contact points at which the staple fibres 3 are bonded to
each other. The bound fibres provide a substantially homogeneous
filtering material which forms the plug 2. The substantially homogeneous
filtering material so-formed may be described as a porous matrix, which
16 provides a labyrinth of smoke passages when used as a cigarette
filter.
The filter element 1 has substantially uniform physical characteristics
throughout the cross-section.
The filter may be manufactured by known methods, for example the
method disclosed in US 3, 552, 400. Thus, a raw tow of the cellulose
acetate is passed through a conventional banding device so as to
separate the individual filaments thereof, and a further conventional
banding device, which may be utilised to spread the tow into a relatively
thin filamentary layer. The filamentary layer is then passed through a
conventional plasticising device wherein a suitable plasticiser (triacetin in
the present example) is sprayed by suitable jets onto one or both sides of
the filamentary layer to form a plasticised tow. A conventional feeding
means such as a pair of rollers is utilised to deliver the plasticised tow to
a
processing apparatus for making staple fibres and forming these into a
continuous rod. A suitable apparatus is described in full detail in US
3,552,400 and shown in Fig.1 of that document. The plasticised tow is fed
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through a funnel to a chopper which severs the continuous tow into a
multiplicity of discrete staple fibres, the length of which depends upon the
=
relationship between the speed of the chopper and the rate of the feed of
the continuous tow into the chopper. The staple fibres produced by the
chopper are sucked from the chopper by means of a turbulent air stream
which disperses the staple fibres (and provides or increases their random
orientation) and directs these through a porous frusto-conical screen, the
smaller or outlet end of which feeds onto a moving porous belt. Particulate
or other additives (not shown) may, if desired, be fed into the turbulent air
stream and dispersed throughout the filter material at this stage. The
porous enclosing means is tapered and slows the speed of the staple
fibres passing therethrough, and also tends to dispose the staple fibres so
the length of a portion of fibres is disposed substantially transversely to
the
longitudinal axis of the product filter rod. The staple fibres are fed onto
the
porous belt, which moves the fibres longitudinally into a steam treating
chamber. A bore at the entrance to the steam-treating chamber forms the
longitudinal edges of the porous belt about the staple fibres as the belt and
fibres thereon are drawn longitudinally through the bore. The drawing of
the belt around the fibres thus completes the formation of the staple fibres
into a rod surrounded by the porous belt. Steam is applied to the porous
surface of the belt and passes continuously and directly therethrough to
treat the staple fibres held therein. The bonding constituents of the staple
fibres (e.g. the triacetin) are thus activated by the steam while the fibres
are carried in cylindrical rod shaped form enclosed by the belt. It is noted
that this processing is well known in the art and is described in the US
patent mentioned above. The belt and staple fibres entrained therein are
then drawn through a cooling station as is also well known in the art and
thus the drying and cooling of the element (and setting of the bonding
constituents) takes place in the cooling station. The cylindrical rod so-
formed may be wrapped in a plugwrap paper (not shown) and sealed with
a lap adhesive by means that are well-known in the prior art. The resulting
dried and cooled continuous cylindrical rod formed of randomly oriented
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staple fibres is peeled from the belt as it leaves the cooling station, [the
belt being substantially flattened and continuously orbited back to a
position in the region of the screen to gather further additional staple
fibres
from the screen and draw these into the steam chamber]. The initial
continuous cylindrical rod formed of randomly oriented staple fibres as it
issues continuously from the machine outlet is cut into finite lengths for
subsequent use. It may be severed by cutting means for example to form
single filters (such as filter 1 of Figure 1) each of which is then attached
to
an individual wrapped tobacco rod to form a filter cigarette, or to form
individual filter elements. More usually, however, the continuously issuing
rod is first cut into double or higher multiple (usually quadruple or
sextuple)
length rods of filters 1 (or filter elements) for subsequent use. The
formation of multiple length filters (and their subsequent incorporation into
filter cigarettes) is well known in the art.
Example 2 Phenol Reduction
The following Table 1 compares Sample A, a filter made according
to the method of US 3, 552, 400, and which includes a filtering material
formed from a plurality of randomly oriented staple fibres of plasticised
cellulose acetate, with a prior art monoacetate filter of the same
dimensions. The hardness values (defined as the compressed diameter of
the filter rod as a percentage of the initial rod diameter, the compression of
the rod being caused by a known weight applied through a circular foot for
a specific period of time) and pressure drop (PD) (expressed in mm Water
Gauge) were measured for the samples. The yields of phenolic
compounds were measured for all samples smoked under ISO conditions;
cresols are the combined yields of o-, m- and p-cresol, whilst Di Hydroxy
Phenols are the combined yields of Hydroquinone, Resorcinol and
Catechol. The tar yields from the cigarettes were also measured in order
that the changes in the ratios of phenols to tar could be assessed. The
values for Sample A are expressed as a % value of that for the prior art
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monoacetate filter (i.e. the value for the monoacetate filter is taken as 100,
and that for Sample A expressed as a percentage of that value).
Table 1
Parameter Sample A Monoacetate
Tow Weight 77.5 100
Rod Hardness 99.9 100
Pressure Drop 100.6 100
Tar yield* 103.1 100
Nicotine yield* 95 100
CO yield* 103.8 100
Phenol yield* 78.1 100
Total Cresols yield* 78.5 100
Di Hydroxy Phenols yield* 95.9 100
Phenol+Cresols** 75.7 100
Di Hydroxy Phenols** (ug per mg of tar) 92.9 100
Phenol Reduction per unit weight tow 141 100
Total Cresols Reduction per unit weight 145 100
tow
* based on results expressed as "absolute" figures (i.e. mass/cigarette)
** based on results expressed as pg per mg of tar
As indicated above, it is desirable to reduce the levels of phenolic
compounds in cigarette smoke. It is known that cellulose acetate exhibits a
selective filtration effect towards phenols, so it would be expected that
filters according to the invention which include randomly oriented staple
fibres of cellulose acetate would be less effective in removing phenols than
comparable monoacetate filters of similar pressure drop and hardness,
because the former contain e.g. 20 to 30% less cellulose acetate. In fact,
the results show that, surprisingly, Sample A gave reduced yields of
phenolic compounds expressed on both an absolute basis and per mg of
tar than an equivalent monoacetate product. The reductions in phenolic
compounds in Sample A are even more significant when the lower weight
of cellulose acetate in Sample A (which includes the filtering material
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formed from a plurality of randomly oriented staple fibres of plasticised
cellulose acetate) compared to the monoacetate product is taken into
account (Sample A includes 77.5% by weight of the amount of tow of the
monoacetate filter).
The results indicate that filters and filter elements of the invention
provide a surprising and marked selective reduction of phenolic
compounds.
Example 3 Degradability
Different types of cigarette filters were placed in wire mesh cages
on a rooftop site and their weights monitored periodically over a 12-month
period. After 12-months, it was found that the weight of standard
monoacetate filters had reduced by 23-30%, whilst the weight of a
dimensionally comparable filter which includes a filtering material formed
from a plurality of randomly oriented staple fibres of plasticised cellulose
acetate had reduced by 46%. This is surprising because it would have
been expected that a similar weight loss would have occurred.
Example 3 ¨ type of tow
The properties of two superslim multiple filter rods A and B (each
comprising four 27mm length filters of the invention of structure similar to
the embodiment of Figs 1 and 2), and a comparable standard
monoacetate superslim product "Control" are given below:
A B 'Control'
Tow Item 5Y30,000 4.2Y33,000 6Y17,000
Rod Length (mm) 108 108 108
Circumference (mm) 16.9 16.9 16.8
Rod Weight (g) 0,291 0.281 0.416
Rod Hardness (%) 88 89 91
27mm Tip Pressure Drop (mm) 102 100 115
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27mm Tip Tar Retention (%) 29.4 30.5 33.6
27mm Tip Nicotine Retn (%) 27.1 29.7 29.3
The tows used in samples A and B are the same as those used in any
standard (c. 24.5 mm) circumference product; whereas the above
monoacetate control superslim sample required a more expensive low
total denier tow. This example illustrates that filters of the invention
provide acceptable characteristics using much higher total denier cellulose
=
tows than for a conventional superslim product.
=
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