U.S. patent number 3,894,545 [Application Number 05/413,348] was granted by the patent office on 1975-07-15 for filters for tobacco smoke.
This patent grant is currently assigned to Brown & Williamson Tobacco Corporation. Invention is credited to Robin A. Crellin, Henry G. Horewell.
United States Patent |
3,894,545 |
Crellin , et al. |
July 15, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
FILTERS FOR TOBACCO SMOKE
Abstract
The invention relates to a tobacco-smoke filter comprising
regions extending substantially longitudinally of the filter and
separated by a diaphragm or diaphragms of vapour-porous material
into at least one region providing a through path for smoke and at
least one region which is filled with carbon and is closed against
smoke flow through the filter. The regions may be formed by two
co-axial tubes, an inner diaphragm tube of the porous material and
an outer tube of substantially smoke-impervious material.
Alternatively the carbon may be contained in one or more closed
bags or envelopes of the porous material enclosed within an outer
tube providing a through path for the smoke.
Inventors: |
Crellin; Robin A. (Romsey,
EN), Horewell; Henry G. (Totton, EN) |
Assignee: |
Brown & Williamson Tobacco
Corporation (Louisville, KY)
|
Family
ID: |
10463572 |
Appl.
No.: |
05/413,348 |
Filed: |
November 6, 1973 |
Current U.S.
Class: |
131/342; 131/332;
131/207; 131/339 |
Current CPC
Class: |
A24D
3/04 (20130101) |
Current International
Class: |
A24D
3/00 (20060101); A24D 3/04 (20060101); A24b
015/02 () |
Field of
Search: |
;131/10,10.1-10.9,261-269,202,200,207 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
|
|
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287,594 |
|
Nov 1966 |
|
AU |
|
823,690 |
|
Nov 1959 |
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GB |
|
Primary Examiner: Rein; Melvin D.
Attorney, Agent or Firm: Smith; Vance A.
Claims
We claim:
1. A filter for a smokeable article intended to be disposed
downstream from a smokeable charge, comprising a smoke treating
chamber formed by a substantially cylindrical outer wall of the
filter element in close proximity to the downstream end of a
smokeable charge, a longitudinally oriented vapor porous membrane
mounted within said cylinder, said membrane containing a charge of
particulate carbon, the upstream and downstream ends of said carbon
charged membrane being effectively sealed or blocked against the
passage of smoke, the space not occupied by said membrane defining
longitudinally extending continuous and uninterrupted passageway or
passageways extending for a length at least equal to that of the
contained carbon charge, such that the smoke emerging from the
downstream end of a smokeable charge preferentially courses through
the said continuous and uninterrupted passageways without being
forced through said contained carbon charge.
2. A filter according to claim 1 wherein the porous membrane is
tubular and the carbon charge is contained within.
3. A filter according to claim 1 wherein the porous membrane is
tubular and the carbon charge is contained within the space between
the tube and said outer wall.
4. A filter according to claim 1 wherein the carbon charge is
contained within at least one closed envelope of porous membrane
enclosed within said outer wall.
5. A filter according to claim 4 wherein a plurality of said
envelopes are disposed in a triangular form within said outer
wall.
6. A filter according to claim 1 wherein the carbon charge is
contained in at least one closed envelope of porous membrane, said
envelope being folded within and longitudinally of said outer
wall.
7. A filter according to claim 1, disposed as a centre section
between two end sections of fibrous material.
8. A filter according to claim 1, wherein the vapor porous membrane
is made of highly porous paper with a porosity of at least 32,000
cm.sup.3 /min/10 cm.sup.2 per 10 cm water gauge pressure.
Description
Many forms of filters for tobacco smoke are known which remove the
particulate phase of the smoke by mechanical means. These filters,
composed for example of filamentary or fibrous materials, have,
however, a low efficiency for the retention of volatile
constituents of tobacco smoke. It is known that such constituents
in vapour form can be removed from the smoke to some extent by
adsorption on a suitable surface or by chemical reaction. An
effective material for this purpose is, for example, carbon,
possibly in the form of activated charcoal. The material may be
provided as a granular bed between two filter plugs of fibrous or
filamentary filtering material or may be dispersed in or on other
filtering material. It is, however, known that carbon, thus used,
may have an adverse effect on the taste of the tobacco smoke by
producing a so-called "off flavour." It is an object of the
invention to provide a filter containing carbon which removes the
volatile or vapour-phase constituents to an acceptable degree, but
which has little or no adverse effect on the taste of the smoke.
More particularly, it is an object to provide a filter in which the
carbon is protected against the deposition of smoke particles,
while allowing the adsorption of vapours.
According to the invention, a tobacco-smoke filter comprises
regions extending longitudinally of the filter and separated by a
diaphragm or diaphragms of vapour-porous material, for example
highly porous paper, into at least one region providing a through
path for smoke and at least one region which is filled with carbon,
possibly in the form of activated charcoal, and is closed against
smoke flow through the filter. Conveniently the diaphragm may be
tubular and the said regions located one within another.
Thus such a filter may comprise two concentric tubes, an inner tube
of the vapour porous material and an outer tube of substantially
smoke-impervious material, the annular space between the tubes
being filled with carbon granules or powder and being blocked at
each end, while the inner tube, without a carbon filling, is open
at both ends to afford a smoke channel. Suitably the ratio of the
diameter of the inner tube to that of the outer tube may be of the
order of from 1:4 to 1:2.
Alternatively, the inner tube may be filled with carbon and blocked
similarly at each end, the outer tube being spaced from the inner
tube, possibly by longitudinal ribs, to leave an open-ended annular
smoke channel. Suitably the tube-diameter ratio may be of the order
from 5:10 to 9:10.
The packing of the carbon particles may be significant in that the
greater the surface area available, the more favourable are
conditions for the diffusion and thus the removal of the vapour
constituents. Defined in terms of weight per unit length of filter
a range of 10-150 mg/cm, preferably 40-100 mg/cm, is suitable. The
particle size is preferably within a range of 12 to 150 British
Standard Specification mesh.
The "porosity" of the porous material, preferably paper, should be
at least 1000 cm.sup.3 /min/10cm.sup.2 per 10 cm water-gauge
pressure and is preferably within the range of 32,000 to
600,000.
Such a filter is preferably used as a centre section between two
end sections of fibrous material, such as cellulose acetate or
paper, or in dual filter adjacent to the tobacco rod. The whole
filter may be enclosed within a customary sleeve of tipping paper
and attached to a cigarette in conventional manner.
On smoking a cigarette through such a filter, the smoke particles
pass through the smoke path, the inner tube or annular space as the
case may be, without flowing through the carbon. Analysis of the
smoke shows that a reduction in the amount of volatile
constituents, particularly aldehydes and hydrogen sulphide is
obtained, although the taste of the smoke is unaffected. The
reduction is achieved because volatile constituents diffuse through
the inner tube into the carbon-filled region in which they are
adsorbed. The particulate matter does not diffuse through this
tube. Substantially, therefore, the carbon is prevented from being
contaminated by smoke particles and carbon/particle interactions do
not occur. A further advantageous effect observed is that the
proportion of total volatile constituents remains more uniform,
from puff to puff, than is the case if the smoke flows through a
carbon bed.
Examples of ways of carrying out the invention and of results
thereby achieved will now be more fully described with reference to
the accompanying diagrammatic drawings, in which:
FIG. 1 is a longitudinal section through a cigarette filter with an
annular carbon-filled region,
FIG. 2 a similar view of a filter with a central carbon-filled
region,
FIG. 3 a similar view of a filter with a bag-like carbon-filled
region,
FIGS. 3a and 3b being opposite end views of the filter,
FIG. 4 a graphical representation of filter-efficiency results
obtained,
FIG. 5 a perspective view of a carbon-filled bag,
FIG. 6 a perspective view of a filter section comprising three such
bags, and
FIGS. 7 and 8 are a cross section and a longitudinal section, on
the line VIII--VIII in FIG. 7, of a filter with a rolled, carbon
filled, bag.
In all of the following examples, cigarettes with filters having an
outer-tube diameter of 8 mm were smoked under standard conditions
of 1 puff of 2 seconds duration every minute and 35 ml volume. The
measured filtration efficiency for total volatile aldehydes was
taken as an index of the effectiveness with which the carbon
removed vapour-phase constituents from cigarette smoke.
Example 1
the triple filter illustrated in FIG. 1 comprises a section 1 in
accordance with the present invention interposed between
filter-plug sections 2 and 3 of cellulose acetate at the mouth end
and adjoining the tobacco rod 4 respectively, all enclosed within a
smoke-impervious wrapper tube 5. The section 1 comprises an inner
tube 6 of highly vapour-porous paper which extends co-axially
within the tube 5 and bounds a central smoke channel 7 the annular
space 7' between the tubes being filled with carbon particles and
being blocked at both ends by impervious annular closures 8. These
closures may be produced from a plastics material, for example a
polyvinyl acetate adhesive, used as a sealing compound or by discs
of smoke-impervious material having a central hole in register with
the tube 6.
In a specific instance, the overall length of the filter was 71 mm.
The tube 5 was made of smoke-impervious paper and the tube 6 of a
paper having a porosity of 34,000 cm.sup.3 /min/10cm.sup.2 per 10cm
water-gauge pressure. The tube 6 was 58 mm in length and 4.5 mm in
diameter. The space 7' between the tubes 5 and 6 contained 720 mg
of a granular carbon known as grade 203B (available from Sutcliffe
Speakman Ltd). The total pressure drop of the filter was 7.1 cm
water gauge. The filter removed 45 percent of the total volatile
aldehydes from the smoke. For comparison purposes, cigarettes were
prepared with filters which contained a bed of 50 mg of the carbon
granules positioned between two cellulose acetate sections and
designed to remove the same proportion of volatile aldehydes from
the smoke.
Cigarettes with the two kinds of filters were offered to a panel of
smokers with particular experience of evaluating the flavour
characteristics of carbon-filter cigarettes. The panel found that
the comparison, granular-bed, filter produced a high level of the
undesirable off-flavour characteristic of carbon-filter cigarettes,
whilst the other filter, with the porous inner tube 6, produced
none of this flavour.
Example 2
The filter construction of FIG. 2 differs from that of FIG. 1 in
that the granular carbon is disposed in the space 9' within the
tube 6. This space is blocked at both ends, at 10, whereas the
annular smoke channel 9 is open at both ends. With one filter of
this kind, 53 mm long, the outer tube 5 was made of a plastics
material. The inner tube was made of paper having a porosity of
200,000 cm.sup.3 /min/10cm.sup.2 per 10 cm water gauge. It was 40
mm in length and 4.5 mm in diameter and was filled with 282 mg of
the same granular carbon as in Example 1. The filter, whose
pressure drop was 3.2 cm water gauge, removed 48 percent of the
total volatile aldehydes from the smoke. A comparison filter was
prepared in the same manner as in Example 1, but with a 55 mg
carbon bed expected to have the same aldehyde-filtration
efficiency. The panel of smokers again noted a high level of the
characteristic off-flavour from the comparison cigarettes, but none
from the cigarettes with filters containing carbon within the
porous tube.
Example 3
In the filter of FIG. 3, the granular carbon is contained in a
porous bag 11 disposed within the tube 5. The ends of the bag 11
are sealed along straight lines 12,13 at right angles to each
other, as shown in FIGS. 3a and 3b, producing fin-like formations
14 which support the bag 11 within the tube 5 and assist in
ensuring favourable smoke-flow around the bag.
With one filter of this kind, 53 mm long, the tube 5 was of
impervious paper. The bag 11, of paper of 200,000 cm.sup.3 /min/10
cm.sup.2 per 10 cm water gauge porosity, was 40 mm in length and
4.5 mm diameter. It was filled with 235 mg of granular carbon,
grade BPL available from Pittsburgh Activated Carbon Co. The
pressure drop of the filter was 4.5 cm water gauge. On smoking
under standard conditions, a reduction of 40 percent of the total
volatile aldehydes was observed. When compared by the panel with
cigarettes with a granular-bed filter having 70 mg of carbon giving
the same filtration efficiency, cigarettes having filters as
described with reference to FIG. 3 did not produce the off-flavour
imparted by the carbon-bed filter.
Example 4
Further filters were prepared as described in Example 3, but with
the bag 30 mm long and containing 150 mg of the same carbon, the
overall pressure drop being 3.0 cm water gauge. The total volatile
aldehyde filtration efficiency was determined on a puff by puff
basis for these filters (A) and for a conventional filter (B),
containing a 50 mg bed of carbon, which removed substantially the
same average percentage (29 percent) of the volatile aldehydes. The
puff by puff results, given in the following table, are shown in
FIG. 4 as efficiency n plotted against the puff number PN.
______________________________________ Filtration Efficiency Puff
Number for Total Volatile Aldehydes (%) A B
______________________________________ 1 27 70 2 36 60 3 31 49 4 27
41 5 28 33 6 30 37 7 26 22 8 29 12 9 25 0 10 28 0 11 21 0 Average
(all puffs) 28 29 ______________________________________
Filter A removed a similar fraction of the total volatile aldehydes
for each puff. In contrast, filter B removed a very high fraction
of the aldehydes from the first puff, but rapidly declined in
performance, removing none of the aldehydes from the final three
puffs.
Example 5
Filters were prepared as described in Example 3, but the bag 11 was
made of porous paper which had been so perforated that the overall
porosity was raised to 600,000 cm.sup.3 /min/10 cm.sup.2 per 10 cm
water gauge. The bag, 30 mm long, contained 161 mg of carbon of the
same grade. The filter had a total pressure drop of 2.9 cm water
gauge and removed 31 percent of the total volatile aldehydes.
Compared with control filters containing 50 mg of carbon and having
similar filtration efficiency, the former filters did not produce
the off-flavour observed with the latter filters.
Example 6
Filters were prepared as described in Example 3, but the bag 11, 30
mm in length and 6 mm in diameter, was filled with 259 mg of carbon
of the same grade. The pressure drop of the filter was 3.1 cm water
gauge. These filters removed 32 percent of total volatile aldehydes
without producing the off-flavour, as detected from comparison
filters having granular beds of 54 mg of carbon.
Example 7
Filters were produced as in Example 3, but containing 3 bags, each
of 2.75 mm diameter and 30 mm length and each filled with 51 mg of
carbon of the same grade. These filters, which had a pressure drop
of 3.3 cm water gauge removed 34 percent of the total volatile
aldehydes. A panel could not detect the off-flavour found with
comparison filters having granular beds of 59 mg of carbon.
Example 8
Further filters were prepared as described in Example 3. The
annulus between the bag 11 and the tube 5 was filled with: (a)
1,700 mg of inert granules of unglazed porcelain, known as
anti-bumping granules, or (b) open-cell polyethylene foam supplied
by Monsanto Chemicals Ltd, or (c) bloomed cellulose-acetate tow.
The bag 11 was 30 mm long and contained 155 mg of carbon of the
same grade. The pressure-drops for the complete filters were 3.5,
5.7 and 4.8 cm water gauge and the total volatile aldehyde
filtration efficiencies 46 percent, 32 percent and 43 percent
respectively.
Granular-bed filters, of comparable efficiency, containing 82 mg,
51 mg and 74 mg of carbon respectively produced high levels of the
characteristic carbon flavour, which was absent with the former
filters.
Example 9
Filters were prepared as described in Example 3. The bags 11, 30 mm
long and 4.5 mm in diameter, contained other grades of carbon,
namely (a) 140 mg of MF3, supplied by Chemviron Ltd, and (b) 114 mg
of AC45, supplied by The British C.E.C.A. Co. Ltd, the pressure
drops being 2.8 and 3.0 cm water gauge and the total
aldehyde-filtration efficiency 30 percent and 33 percent
respectively. The off-flavour was absent from these filters.
Comparable granular-bed filters containing 36 mg of MF3 and 40 mg
of AC45 carbon respectively produced high levels of the
off-flavour.
Example 10
Further filters were prepared as described in Example 3, but using
polyethylene for the outer tube 5. The tube was ventilated near the
cellulose-acetate section 2 at the mouth end by making holes in the
tube 5 and then wrapping the whole filter in a porous tipping
paper, supplied by Papeteries de Malaucene.
The ventilation reduced the cigarette pressure drop by 55 percent.
The porous bag, 30 mm long and 4.5 mm in diameter, contained 149 mg
of the same grade of carbon as in Example 3. The combination of
ventilation and porous bag reduced the delivery of total volatile
aldehydes by 73 percent. Comparable carbon-bed, non-ventilated,
filters containing 183 mg of the same carbon produced high levels
of the characteristic off-flavour, which was absent with the former
filters.
Example 11
To prepare the filter illustrated by FIGS. 5 and 6, carbon powder
(52-100 British Standard Specification mesh) of the grade AC45
referred to above was placed on a sheet of paper of porosity
200,000 cm.sup.3 /min/10 cm.sup.2 per 10 cm water gauge and the
sheet was folded over to the form of a bag 15 and sealed down the
longitudinal edge 16 and at both ends 16'. Three such bags, 30 mm
long and approximately 7 mm wide each contained 40 mg of carbon.
The three bags 15 were assembled in a triangular configuration
(FIG. 6) between two cellulose acetate sections (not shown), within
an impervious paper tube 5. The filter, which had a pressure drop
of 2.7 cm water gauge, removed 55 percent of total volatile
aldehydes from the smoke. In smoking-panel tests, a comparable
cigarette with a granular-bed filter containing 79 mg of the same
carbon was found to produce a high level of the characteristic off
flavour, which was absent from cigarettes with filters prepared as
described.
Example 12
For the filter illustrated in FIGS. 7 and 8, 115 mg of carbon
powder (100-150 British Standard Speciification mesh) of the
aforesaid grade AC45 was laid between two 100 mm .times. 25 mm
sheets of very porous paper (porosity 200,000 cm.sup.3 /min/10
cm.sup.2 per 10 cm water gauge). All of the edges of the two sheets
were glued together to form a closed bag 17 containing the carbon
18. The bag 17 was rolled from the flat form to the spiral form
shown in FIG. 7 and as in previous examples, was placed between
cellulose-acetate sections 2, 3 to form a 25 mm long filter,
enclosed in an impervious paper tube 5, with a pressure drop of 3.5
cm water gauge. The filter removed 57 percent of total volatile
aldehydes from the smoke. A comparable cigarette with a
granular-bed filter containing 84 mg of the same grade of carbon
produced high levels of the characteristic off flavour, which was
absent from the filter of the Example.
Preferably, the bag 17 is rolled with a sheet of longitudinally
corrugated paper in the spiral space 19 between the turns of the
rolled bag. This will ensure that different parts of the bag do not
come into contact with one another, thus increasing the effective
area of bag surface through which smoke constituents can diffuse
and also the number of smoke passage ways.
The same end can be achieved by making the bag 17 itself from
corrugated porous paper. Contact between different parts of the
paper is then limited to a number of points. The corrugations also
increase the surface area for a given length of bag.
A bag or bags produced in one of the ways described in Example 12
may be disposed in the filter otherwise than in a single spiral
form, as seen in cross section. For example, such a bag may be
rolled in the form of a C with both free ends further rolled
inwardly. Indeed, the bag may be incorporated in the filter with a
random disposition in the cross section.
The bag or bags need not occupy the entire cross section within the
tube 5. A bag may be rolled or folded into the filter together with
a longitudinally extending filter material, such as a cellulose
acetate tow or paper.
Indeed, in all cases, the smoke channel or channels, whether
central and/or peripheral, may be packed with a filtering material
(not carbon) for the removal of particulate matter, for example
with fibrous or filamentary cellulose acetate, paper or the
like.
Alternatively, the smoke channel may be packed with an inert
granular material, as described in Example 8, or with glass spheres
or chippings. Such a packing will provide more intimate contact
between the smoke and the porous paper, thus assisting the
diffusion of volatile smoke constituents into the carbon. The
filtration efficiency of the filter for volatile constituents can
thereby be enhanced above the value obtained for the filter without
such a packing, again without adverse effect on the taste.
Preferably and as described above, the carbon is in the form of
loose granules or powder. However it could alternatively be used in
the form of a charcoal or other carbon rod or tube disposed as
previously described. Carbon may be bonded by a resin such a
polyethylene, an organic material such as paraffin wax or an
inorganic material such as trisodium phosphate.
* * * * *