U.S. patent application number 10/576659 was filed with the patent office on 2007-12-27 for tobacco smoke filter.
Invention is credited to Anthony McCormack, Thomas Ryan, Michael Taylor, Andrew Warburton.
Application Number | 20070295346 10/576659 |
Document ID | / |
Family ID | 29559572 |
Filed Date | 2007-12-27 |
United States Patent
Application |
20070295346 |
Kind Code |
A1 |
McCormack; Anthony ; et
al. |
December 27, 2007 |
Tobacco Smoke Filter
Abstract
A tobacco smoke filter containing a high activity activated
carbon impregnated with a metal impregnant. The use of a relatively
low level of impregnant, in combination with a base carbon having
higher activity than that use in standard cigarette filters, is
highly effective in removing HCN from cigarette smoke.
Inventors: |
McCormack; Anthony;
(Northumberland, GB) ; Taylor; Michael; (Tyne and
Wear, GB) ; Warburton; Andrew; (Greater Manchester,
GB) ; Ryan; Thomas; (Cheshire, GB) |
Correspondence
Address: |
FLYNN THIEL BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1631
US
|
Family ID: |
29559572 |
Appl. No.: |
10/576659 |
Filed: |
October 19, 2004 |
PCT Filed: |
October 19, 2004 |
PCT NO: |
PCT/GB04/04418 |
371 Date: |
February 2, 2007 |
Current U.S.
Class: |
131/341 ;
131/361 |
Current CPC
Class: |
A24D 3/163 20130101;
A24D 3/16 20130101 |
Class at
Publication: |
131/341 ;
131/361 |
International
Class: |
A24D 3/16 20060101
A24D003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2003 |
GB |
03 24464.7 |
Claims
1. A tobacco smoke filter containing activated carbon impregnated
with a metal impregnant, wherein the activated carbon is high
activity activated carbon.
2.-26. (canceled)
27. A tobacco smoke filter according to claim 1, wherein the metal
impregnant is one or more of copper, molybdenum, manganese, cobalt,
zinc and iron.
28. A tobacco smoke filter according to claim 1, wherein the metal
impregnant(s) is present in an amount which is not more than 10% of
the dry weight of the high activity activated carbon.
29. A filter according to claim 28, wherein the metal impregnant(s)
is present in an amount which is from 1 to 5% of the dry weight of
the activated carbon.
30. A tobacco smoke filter according to claim 1, wherein the metal
impregnant is copper.
31. A tobacco smoke filter containing activated carbon which is
impregnated with copper and molybdenum, wherein the ratio of copper
to molybdenum is greater than 1.3 to 1.
32. A tobacco smoke filter containing activated carbon which is
impregnated with copper and molybdenum, wherein the activated
carbon is a high activity activated carbon.
33. A filter according to claim 1, wherein the activated carbon has
an activity of greater than 90% CTC prior to impregnation.
34. A filter according to claim 1, wherein the activated carbon has
an activity of greater than 100% CTC prior to impregnation.
35. A filter according to claim 1, wherein the activated carbon has
an activity of greater than 80% CTC after impregnation.
36. A filter according to claim 1, wherein the activated carbon has
an activity of greater than 90% CTC after impregnation.
37. A filter according to claim 1, in which substantially all of
the activated carbon is of particle size between 2 mm and 0.15 mm,
preferably between 0.6 mm and 0.212 mm.
38. A filter according to claim 1, which contains between 10 mg and
150 mg of activated carbon, preferably between 30 mg and 60 mg of
activated carbon.
39. A filter according to claim 1, which further comprises one or
more additional adsorbents.
40. A filter according to claim 39, wherein the additional
adsorbent(s) selectively removes a compound(s) present in the VP
fraction of cigarette smoke other than HCN.
41. A filter cigarette comprising a filter according to claim 1
joined at its upstream end to a wrapped tobacco rod.
Description
[0001] The present invention relates to tobacco smoke filters,
especially for cigarettes.
[0002] The use of activated carbon to remove undesirable vapour
phase (VP) components from tobacco smoke is well known.
[0003] There are over 400 compounds in the VP fraction of cigarette
smoke (for example aldehydes, ketones and hydrocarbons). Activated
carbon is a strong adsorbent; it is effective in removing a large
number of these compounds from tobacco smoke. However, the
compounds in the VP fraction all tend to be reduced by activated
carbon to a similar extent; activated carbon may be described as an
effective "blanket adsorbent".
[0004] In recent years, there has been a growing interest in
selective filtration by cigarette filters, that is, the enhanced
removal of specific compounds from tobacco smoke compared to
removal of the other smoke components. One compound for which
selective removal is particularly desirable is hydrogen cyanide
(HCN), because HCN is generally recognised as being one of the most
toxic compounds found in the VP fraction. HCN is removed by
standard activated carbons when used in cigarette filters, but it
is not selectively removed compared to other VP compounds. Indeed,
its removal is usually lower than other VP compounds.
[0005] It is well known to add various chemicals to activated
carbon to enhance the removal of particular compounds. These
"impregnated carbons" are able to remove particular compounds
through chemical reaction as well as by physical adsorption. Such
carbons are used widely in, for example, gas mask and respirator
applications, where the activated carbon is generally impregnated
with one or more of a number of chemical entities to target the
removal of specific poisons. Our experiments have shown that such
respirator-grade carbons are comparatively ineffective when used in
cigarette filter applications because only low levels of overall
removal are obtained. It is clear that respirator-grade carbons are
not suited to a cigarette filter environment where contact times
between the carbon and the gas are much less than those in gas
mask/respirator applications. These respirator grade carbons also
displayed little evidence of enhanced selectivity towards HCN. The
above would lead one to expect that a high loading of impregnant
would be required for effective removal of HCN in cigarette filter
applications.
[0006] We have unexpectedly found that use of a relatively low
level of impregnant, in combination with a base carbon having
higher activity than that used in standard cigarette filters, is
highly effective in removing HCN from cigarette smoke.
[0007] According to the present invention there is provided a
tobacco smoke filter containing a high activity activated carbon
impregnated with a metal impregnant.
[0008] Preferably the metal impregnant is present in an amount
which is up to 10% of the dry weight of the high activity activated
carbon. More preferably the impregnant is present in an amount
which is from 1 to 5% of the high activity activated carbon. The
metal impregnant may be, for example, one or more of copper,
manganese, molybdenum, cobalt, iron, zinc. In one preferred
embodiment, the impregnant is copper. In another preferred
embodiment the metal impregnant is a combination of copper and
molybdenum.
[0009] In the present specification, by "metal impregnant",
"copper" and "molybdenum" etc. it is meant the metals themselves
and/or their ions, in any form (e.g. salts, complexes, chelates
etc.).
[0010] The activated carbon of the invention may be derived from
any raw material for which it is possible to prepare an activated
carbon [these raw materials from which activated carbons may be
prepared include, for example, wood, coal, nutshell such as
coconut, peat, petroleum coke and bone; and synthetic sources such
as poly(acrylonitrile) or phenol-formaldehyde].
[0011] The activated carbon is a "high activity" activated carbon.
"Activity" in this context refers to percentage by weight of a
particular vapour (e.g. carbon tetrachloride--CTC) adsorbed under
equilibrium conditions by the base activated carbon (the base
activated carbon refers to the activated carbon prior to
impregnation by impregnant e.g. copper and/or molybdenum). Levels
of activity herein are given as % CTC values. Thus, a value of
carbon activity of 95% CTC refers to a level of adsorption of 95%
by weight of CTC under equilibrium conditions. "High activity"
refers to a base activated carbon (that is, an activated carbon
prior to metal impregnation) which adsorbs more than about 90% CTC
under equilibrium conditions. Preferably the activity is greater
than 90% prior to impregnation. More preferably the activity of the
activated carbon is greater than 100% prior to impregnation (that
is, the base activated carbon adsorbs more than about 100% CTC
under equilibrium conditions).
[0012] Preferably the activated carbon has an activity of greater
than 80% CTC, more preferably greater than 90% CTC, after
impregnation.
[0013] According to the present invention in a further aspect there
is provided a tobacco smoke filter containing activated carbon
which is impregnated with copper and molybdenum, wherein the ratio
of copper to molybdenum is greater than 1.3 to 1.
[0014] A preferred ratio of copper to molybdenum (by weight) in the
impregnated activated carbon is greater than 2:1. Particularly
preferred are ratios of between 3.5:1 and 4.5:1. A particularly
preferred ratio of copper to molybdenum in the impregnated
activated carbon is 4:1.
[0015] Preferably the activated carbon is a high activity activated
carbon.
[0016] According to the present invention in a further aspect there
is provided a tobacco smoke filter containing activated carbon
which is impregnated with copper and molybdenum, wherein the
activated carbon is a high activity activated carbon.
[0017] High activity activated carbons are discussed above.
Preferably, the activity of the activated carbon is greater than
90% CTC, more preferably greater than 100% CTC.
[0018] Preferably the copper and molybdenum are present in a
combined amount which is not more than 10% of the dry weight of the
activated carbon. Preferably the copper and molybdenum are present
in the activated carbon in an amount which is from 1 to 5% of the
dry weight of the activated carbon.
[0019] Preferably, the ratio of copper to molybdenum is greater
than 1.3 to 1. More preferably, the ratio of copper to molybdenum
is greater than 2 to 1, preferably between 3.5 to 1 and 4.5 to 1. A
particular preferred ratio of copper to molybdenum is 4 to 1.
[0020] We have most unexpectedly found that a dramatic reduction of
the metal impregnant concentration (e.g. the copper/molybdenum
impregnant concentration), compared to the concentrations of
impregnants commonly used in military or civilian respirators, does
not lead to a discernable deterioration in the removal of HCN.
[0021] The particle size of the activated carbon of the invention
depends on the performance required and the filter configuration.
In the specification mesh sizes given are US Mesh. Suitable
impregnated activated carbon is of particle size between 2 mm (mesh
size 10) and 0.15 mm (100 mesh). Preferably, substantially all of
the impregnated activated carbon is of particle size between 0.6 mm
(30 mesh) and 0.212 mm (70 mesh). More preferably, substantially
all of the impregnated activated carbon is of particle size between
0.425 mm (40 mesh) and 0.212 mm (70 mesh).
[0022] The impregnated activated carbon of tobacco smoke filters
according to the invention may display surprising selective removal
of HCN without detrimental effect on overall VP reduction.
Impregnated carbons have not previously found favour in cigarette
applications because chemical reactions between the impregnated
component (e.g. metal ion) and components present in smoke (and/or
the products of these reactions) have a detrimental effect on the
taste of the cigarette which reduces smoker satisfaction. The
tobacco smoke filters of the invention may include a rather lower
amount of e.g. impregnated copper, impregnated copper and
molybdenum than previously thought necessary for acceptable removal
of HCN; this is likely to reduce any adverse effects on taste.
[0023] The applicants have also shown that the benefits of the
activated carbon of filters according to the invention are
surprisingly effective at lower levels of activated carbon weight.
This may reduce costs associated with filter manufacture. Preferred
tobacco smoke filters contain less than 150 mg activated carbon
impregnated with metal impregnant (e.g. copper and molybdenum).
Particularly preferred tobacco smoke filters contain from 10 mg to
70 mg impregnated activated carbon, more preferably 30 mg to 60 mg
impregnated activated carbon.
[0024] The filter according to the invention may be of any design
previously proposed for particulate adsorbent--containing tobacco
smoke filters. For example the impregnated activated carbon
according to the invention may be dispersed throughout the filter
plug, carried on the tow or fibres or sheet material which is
gathered to form the plug; it may instead adhere to one or more
threads which extend through the matrix of the filter plug or be
adhered to the inner face of a wrapper around the filter plug (as
described for example in GB-A-9124535 and GB-A-9221545, to which
attention is directed for more information); or it may form a bed
sandwiched between a pair of plugs (e.g. of cellulose acetate tow)
in a common wrapper.
[0025] Filters according to the invention may additionally include
one or more particular adsorbents other than the activated carbon
required by the invention (e.g. silica gel, a different activated
carbon or zeolite), which may or may not selectively remove other
compounds present in the VP fraction of cigarette smoke (e.g.
aldehydes). The additional adsorbent(s) may be mixed with the
activated carbon required by the invention and/or separated from
this.
[0026] Tobacco smoke filters according to the invention may also
provide efficient removal of HCN even after prolonged periods (e.g.
in storage) following filter or cigarette manufacture. The carbon
used in known filters adsorbs volatile species present in the
filter or tobacco during storage, thereby reducing the efficiency
with which the filter carbon can remove VP compounds when the
cigarette is smoked. This has the result that the efficiency with
which the known filters remove HCN also decreases on ageing.
Surprisingly, the ability of filters according to the invention to
remove HCN does not deteriorate significantly even after storage
for prolonged periods (e.g. six months).
[0027] The present invention also provides a filter cigarette
comprising a filter according to any preceding claim joined at its
upstream end to a wrapped tobacco rod. The cigarette filter
according to the invention will usually be attached to a wrapped
tobacco rod with conventional tipping overwrap, which may be a
ventilated or non-ventilated overlap.
[0028] The invention is illustrated by the following examples and
with reference to the attached drawings, in which
[0029] FIGS. 1 and 2 respectively are schematic sectional side
elevation views, not to scale, of an individual filter and filter
cigarette according to one embodiment of the invention; and
[0030] FIG. 3 is a schematic sectional side elevation view, not to
scale, of an individual filter according to a different embodiment
of the invention.
COMPARATIVE EXAMPLES
Respirator Carbons
[0031] Numerous impregnated commercial carbons recommended for the
removal of HCN in respirator applications were obtained from a
number of suppliers and compared to a standard (unimpregnated)
carbon used routinely in cigarette filter applications. These tests
involved assembling cigarettes with "triple granular" filters, each
containing 100 mg of activated carbon in a packed bed between two
cellulose acetate filter segments. The filter cigarettes were
smoked under ISO conditions (35 cm.sup.3 puffs, each of two-second
duration, taken once per minute) and the Hydrogen Cyanide HCN and
mean VP yields were measured.
[0032] The percentage reductions in mean VP and HCN for cigarettes
A to F (each of which includes one of six typical respirator grade
activated carbons) as compared to an equivalent cigarette
containing no carbon in the filter are given in Table 1. The Table
also includes the VP and HCN values for a "Standard" cigarette
containing a filter which includes an unimpregnated activated
carbon derived from coconut shells (as typically used in cigarette
filters). TABLE-US-00001 TABLE 1 Sample reference Mean VP reduction
HCN Reduction (Sample ref.) (%) (%) Standard 55 44 A 22 23 B 27 31
C 25 41 D 29 47 E 23 46 F 39 36 It is clear that the respirator
samples A to F are not suitable for a cigarette filter environment.
It is also clear that the Standard filter is not selective for
HCN.
Preparation of Impregnated Samples
[0033] Samples of impregnated activated carbon were prepared
typically by dissolving basic copper(II) carbonate, ammonium
carbonate and ammonium dimolybdate(VI) into an aqueous, ammoniacal
solution and mixing with the activated carbon according to the
ratios detailed in Table 2 (given for 2% copper; 0.5% molybdenum).
Quantities for other metal concentrations (and ratios) were
adjusted accordingly. The resulting slurry was heat treated to
175.degree. C. to give a dry, free flowing product, which was then
screened to the required mesh size. TABLE-US-00002 TABLE 2
Components Weight (g) activated carbon 1000 basic copper(II)
carbonate 44 ammonium dimolybdate(VI) 12 ammonium carbonate 20
water 460 ammonia solution (0.88) 158
Testing of Impregnated Samples
[0034] Fourteen impregnated activated carbon samples were prepared
by the method above. Filter cigarettes were assembled, each
containing 100 mg of one of the samples, and tested using the
procedures described for the comparative samples above. The results
for the fourteen impregnated samples, and for two unimpregnated
controls (Sample Refs. 3 and 4), are given in Table 3.
[0035] A further sample of impregnated carbon containing 2% copper
only was prepared using the procedure described above, with the
exception that ammonium dimolybdate was omitted from the mix. The
sample (Sample Ref 27) was tested using the same procedure as that
used for the samples included in Table 3, and the results are given
in Table 3a. TABLE-US-00003 TABLE 3 Carbon Carbon activity Mesh HCN
activity (% CTC) Metal size Mean VP Reduc- Sample (% CTC) Impreg-
Content (US Reduction tion Ref. Base nated (%)* Mesh) (%) (%) 1 80
46 >10 20/40 29 46 2 80 47 >10 12/20 15 25 3 95 n/a nil 30/70
77 75 4 60 n/a nil 30/70 51 53 5 101 75 10 30/70 42 92 6 122 82 10
30/70 66 93 7 101 84 5 30/70 56 92 8 103 91 5 30/70 64 83 9 80 73 5
30/70 69 93 10 83 75 5 30/70 46 58 11 101 91 2.5 30/70 81 88 12 101
95 1.25 30/70 83 88 13 101 91 2.5 30/70 77 82 14 108 99 2.5 12/20
57 70 15 125 111 2.5 30/70 90 91 16 125 111 2.5 12/20 65 74
*Expressed as (Copper + molybdenum) in the ratio 4:1.
[0036] TABLE-US-00004 TABLE 3a Carbon Carbon Metal Mesh Mean VP HCN
Sample activity activity (% CTC) Content size Reduction Reduction
Ref. (% CTC) Base Impregnated (%) (Copper) (US Mesh) (%) (%) 27 100
95 2.0 20/40 80 82
[0037] The results show that in order to achieve a high reduction
of VP material (that is reduction of components in the VP fraction
of cigarette smoke) in combination with a high reduction of HCN
(reduction of HCN in the VP fraction of cigarette smoke), in
cigarette filters which are embodiments of the present invention
such as Sample Refs 11, 15 and 27, it is desirable to use a base
carbon with a high activity (greater than around 90% CTC) in
combination with a comparatively low level of metal impregnation
(less than 10%, preferably 1 to 5%).
[0038] The higher CTC activities tend to have both a higher HCN
retention and VP retention. VP retention increases with decreasing
impregnant concentration. HCN retention remains fairly constant
when measured as a function of copper and molybdenum concentration
(Table 3). It is therefore surprising that a dramatic reduction of
the copper/molybdenum impregnant concentrations, relative to those
used in civilian or military respirators, has resulted in no
discernible deterioration of the removal of HCN by filters
containing these carbons.
[0039] Activated carbons derived from different base materials
(e.g. coconut shell and coal) have been prepared; these show there
is little difference in terms of HCN retention between, for
example, coal and coconut for the same mesh size, level of
impregnation and activity.
[0040] The results also clearly show that smaller mesh sizes (e.g.
mesh size 30/70 US mesh) give superior performance in terms of HCN
than the larger mesh sizes (compare, for example, Samples 15 and
16). This is contrary to customarily observed behaviour in
cigarette filters, where variations in mesh size have been found to
have only a relatively minor effect on VP removal.
[0041] Our experiments have also shown that the comparative
benefits of the activated carbon in embodiments of the invention
are even more pronounced at lower levels of carbon weight in the
filter. Sample Refs 8 and 11 were used in the manufacture of
cigarette filters having two different carbon weights (i.e. 5% and
2.5% metal levels respectively) and tested as described above. The
results are given in Tables 4a and 4b. TABLE-US-00005 TABLE 4a
Cigarette filter including Sample Ref 8. Carbon weight Mean VP Mean
HCN (mg/cig) reduction (%) reduction (%) 95 76 87 50 40 80
[0042] TABLE-US-00006 TABLE 4b Cigarette filter including Sample
Ref 11. Carbon weight Mean VP Mean HCN (mg/cig) reduction (%)
reduction (%) 95 72 90 50 56 80
Retention of Performance Over Time
[0043] A disadvantage of known carbon containing filters is that
the carbon in the filter adsorbs volatile species present in the
filter or tobacco during storage, thereby reducing the efficiency
with which the carbon can remove VP compounds on smoking. This has
the effect that the overall efficiency with which known carbons
remove HCN reduces on aging. The applicants tested the change in
performance of filter cigarettes which included filters which
embody the invention. The filters included approximately 95 mg of
carbon per filter.
[0044] The filters embodying the invention where stored as
assembled cigarettes and the change in performance was measured at
0, 3 and 6 months. The results are shown in Table 5. TABLE-US-00007
TABLE 5 Standard carbon* Sample Ref. 8 Sample Ref. 11 Age Mean
redn. Mean redn. Mean redn. months VP (%) HCN(%) VP (%) HCN(%) VP
(%) HCN(%) 0 64 53 76 87 72 90 3 55 41 62 86 63 88 6 45 29 48 85 50
85 *carbon tested in table 1
[0045] It is clear that the HCN reduction (redn.) performance of
filters which embody the invention, those made with Sample Refs. 8
and 11, is not significantly reduced over six months (especially
compared to the sample containing standard carbon).
[0046] FIGS. 1 and 2 respectively are schematic sectional side
elevation views, not to scale, of an individual filter and filter
cigarette according to one embodiment of the invention.
[0047] The FIG. 1 filter has a cylindrical buccal end filtering
plug 2 of cellulose acetate tow, a cylindrical upstream filtering
plug 3 of cellulose acetate tow, and a filter wrapper 4 engaged
around the plugs to form a cavity 6 therebetween. The cavity 6 is
filled with granules 17 of activated carbon impregnated with copper
and molybdenum prepared according to the methods above and of
identical composition to sample ref 11 described above.
[0048] FIG. 2 shows a filter of the FIG. 1 type joined at its
upstream end 7 to a tobacco rod 10 in its own wrap 11 by means of a
full tipping overwrap 12 which surrounds and engages the full
length of the filter and the adjacent end only of the wrapped
tobacco rod 10, 11.
Example 17
[0049] In a specific example of a filter and filter cigarette
according to the invention as described with reference to FIGS. 1
and 2, the filter is 27 mm long and about 25 mm in circumference.
The buccal end plug 2 is a 10 mm long non-wrapped acetate (NWA)
plug--i.e. a preformed non-wrapped plug of plasticised cellulose
acetate filaments gathered and bonded together such as is well
known in the art.
[0050] The upstream end plug 3 is a 10 mm long wrapped acetate (WA)
plug--i.e. a preformed wrapped plug of plasticised cellulose
acetate filaments. The filter wrapper is 27 mm long to give a
cavity 6, which is 7 mm long, extending between plugs 2 and 3. The
cavity 6 is filled with 100 mg of granules 17 of activated carbon
impregnated with copper and molybdenum prepared according to the
methods above and of identical composition to sample ref 11
described above. The filter rod is attached by a ventilating
tipping overwrap 12 to a commercial wrapped tobacco rod 10, 11.
[0051] In a further specific Example (Example 17a), the cavity is
filled with 100 mg of granules 17 of activated carbon impregnated
with copper prepared according to the methods above and of
identical composition to Sample Ref. 27 described above.
[0052] It will be appreciated that Example 17 and Example 17a are
similar in construction to a known triple granular filter but
include activated carbon according to the invention.
[0053] FIG. 3 is a schematic sectional side elevation view, not to
scale, of an individual filter according to a different embodiment
of the invention.
[0054] The FIG. 3 filter has a cylindrical buccal end filtering
plug 52 of cellulose acetate tow and a cylindrical upstream
filtering plug 53, also of cellulose acetate tow. Particles 67 of
activated carbon impregnated with copper and molybdenum prepared
according to the methods above and of identical composition to
sample ref 11 described above are dispersed throughout the upstream
filtering plug 53, carried on the tow or fibres or sheet material
which is gathered to form the plug. A filter wrapper 54 is engaged
around the plugs. It will be appreciated that a filter of the FIG.
3 type may be joined at its upstream end 57 to a tobacco rod in the
manner shown with reference to Example 17 in FIG. 2, for example
(e.g. joined to the tobacco rod in its own wrap by means of a full
tipping overwrap which surrounds and engages the full length of the
filter and the adjacent end only of the wrapped tobacco rod).
Example 18
[0055] In a specific example of a filter according to the invention
as described with reference to FIG. 3, the filter is 27 mm long and
about 25 mm in circumference.
[0056] The buccal end plug 52 is a 14 mm long non-wrapped acetate
(NWA) plug--i.e. a preformed non-wrapped plug of plasticised
cellulose acetate filaments gathered and bonded together such as is
well known in the art.
[0057] The upstream end plug 53 is also a 13 mm long preformed plug
of plasticised cellulose acetate filaments gathered and bonded
together such as is well known in the art. 50 mg of particles 67 of
activated carbon impregnated with copper and molybdenum prepared
according to the methods above and of identical composition to
sample ref 11 described above are dispersed throughout filtering
plug 53, carried on the tow material (filaments) that was gathered
to form the plug. The methods by which the particles may be
introduced to the tow material during the gathering process are
well known in the art. A filter wrapper 54 is engaged around the
plugs and is 27 mm long.
[0058] The filter rod may be attached by a ventilating tipping
overwrap to a commercial wrapped tobacco rod in the manner shown in
FIG. 2 and described with reference thereto.
[0059] In a further specific Example (Example 18a), the cavity is
filled with 50 mg of particles 67 of activated carbon impregnated
with copper prepared according to the methods above, and of
identical composition to Sample Ref. 27 described above, dispersed
throughout filter plug 53, carried on the tow material.
[0060] It will be appreciated that Examples 18 and 18a are similar
in construction to a known active acetate filter but include
activated carbon according to the invention.
[0061] It will be appreciated that the filter according to the
invention may be of any design previously proposed for particulate
adsorbent--containing tobacco smoke filters with the substitution
of the known particulate adsorbent with the impregnated activated
carbon of the invention.
* * * * *