Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
45496
The invention is concerned with improvements re-
lating to filters for smoking articles,particularly cigarettes.
Filters for tobacco smoke comprise two general types,
those which remove the particulate phase of the smoke by
mechanical means and those which reduce the volatile con-
stituents of the smoke by adsorption on a suitable surface or
by chemical reaction.
Filters are also known which will reduce both the
particulate phase and the volatile phase to some extent, for
example filters containing adsorbents. If these filters con-
tain an adsorbent such as activated carbon, the latter commonly
has an adverse effect on the taste. A filter which reduces
the volatile phase, but has no adverse effect on the taste of
tobacco smoke, is disclosed in the specification of our
Canadian Patent No. 992830, dated July 13, 1976, and entitled
"Filters for tobacco smoke". This result is achieved by sub-
stantially preventing the smoke particles from contacting the
carbon.
` 20 It is an object of the present invention to provide
a smoking article, particularly a filter cigarette, which has
a low delivery of volatile, as well as particulate, constituents,
and which has a good taste.
According to the invention, a smoking article is
provided with a filter composed of fibrous or filamentary
material which contains a dispersion of activated carbon, the
filter material being of self-bonded type, i.e. of a rod form
which does not require to be held together by a wrapper, which
filter is joined to the rod of smoking material of the article
by a tipping band of air-pervious material, preferably paper,
which permits an inflow of air through the band of 23% to 86% -
of the puff volume, or approximately 8 cm3 to 30 cm3 per puff
of 35 cm3 measured on a filter length of 15 mm, into the filter
only, around at least a peripheral region of the filter spaced
away from the end thereof adiacent to the end of the tobacco
B
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rod. The band may be of porous paper, having a all-over
porosity ranging from 1,000 to 15,000 cm3 min l(lOcmWG) 1
(lOcm ) 1 (Wiggins Teape method of porosity determination).
Alternatively, the tipping band may be provided with per-
forations over its entire area or in one or more peripheral
bands or rings of perforations, the ring or .................
- la -
1045496
band, being preferably located at a distance from the end of the rod
of smoking material of at least 2 mm. Suitably a total ventilation
area of 0.1 to 7 m~2 per filter is thus provided.
Spacing a ring of holes slightly away from the smoking
material utilizes the filtering material initially to the full extent
for total particulate matter. Also it prevents turbulence which
would occur if air is drawn to a space at the junction of smoking
material and filter. Moreover, since the air inflow occurs through -
filtering material, a better and more even control of the smoke path
is achieved. This is also true with the filter wrapped in paper
having all-over porosity. Generally, the pressure drop of the air
path is higher near the tobacco end and lower near the mouth end.
The inflow cf air is therefore more effective nearer the mouth end.
The rod of smoking material, hereinafter refersed to as
the tobacco ~od, will generally be composed of natural or reconstitut-
ed tobacco, but could be a rod comprising or composed of tobacco
substitute, i so required.
The carbon may be applied to the filter material while
the latter is in tow form in known manner by means of a vibrating
applicator. Suitably, a filter may cont~in 10 to 150 mg of carbon.
On smoking a cigarette throùgh such a filter, the flow
conditlons are such that the inflow of air forces the smoke towards
the central longitudinal axis of the filter~ so that the smoke itself
will contact only a small proportion of the carbon particles present,
namely th ose in the central region of the filter. The degree of off_
taste usually associated with carbon is therefore materially reduced.
However~ volatile constituents of the smoke will, at the same time~
dfffuse towards the carbon particles present in the filtering material
outside the central region, where they will be adsorbed by the carbon,
giving a reduction in the delivery of volatiles. Moreover, as the
tobacco smoke is forced to pass at higher velocity through the central
region, the smoke particles will have less contact with the carbon
there, which also contributes to improvement in taste.
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The diameter of the smoke path through the central region
is controlled by the porosity of the tipping paper or by the size,
number and location or perforations, including their distance from
the tobacco end. Generally the central smoke path in the filter
will decrease from a diameter, at the tobacco end, equal to or less
than that of the filter to a smaller diameter at the mouth end, the
latter diameter being generally within a range of from 1 to 4 mm.
The following Examples illustrate how the~invention may be
carried out, reference being made to Figures 1 to 4 of the accompany-
ing d$agrammatic drawing, each of which shows part of a cigarette,
with filter attached~ in axial section.
Example l
Referring to Figure 1, a filter was composed of a rod section
1~ 15 mm long~ of self-bonded, unwrapped cellulose acetate contain-
ing 70 mg of carbon granules activated for gas adsorption and of a
mesh size of 12-30 (British Standard Specification). The granules
were present as a dispersion in the cellulose acetate tow and evenly
distributed throughout the filter. The filter was attached to the
tobacco rod 2 of a cigarette by a band 3 of naturally porous tipping
paper having a porosity of 10~000 cm3 min 1 (lOcm2) 1 (lOcmWG) 1,
giving an inflow of air of 27 cm3 per 35 cm3 puff, i.e. about 77%
of the puff volu~e~ through the tipping band into the filter. The
band 3 overlapped the cigarette wrapping paper and was adhered there-
to. ~n smoking the cigarette through this filter under the standard
conditions of 1 puff volume~ through the tipping band into the filter. The
duration, the filtration efficiency for aIdehydes was ascertained to
be 45%. The smoke was found to be directed towards the centre of
the filter by the air flowing in through the band 3. The actual
path was apparent, on sectioning the filter, by the staining of the
cellulose acetate, as indicated diagrammatically by the cross-hat~hing
4 in the figure. The smoke path at the mouth end had a diameter of
about 2 mm. When tested by a panel of trained smokers, such
cigarettes had improved taste compared with cigarettes having the
same filter but wrapped in conventional manner.
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Example 2
A filter composed of a similar section 1 of cellulose
acetate containing a dispersion of carbon as in Example 1 was attach-
ed to the tobacco rod 2, as shown in Figure 2, by a band 5 of
substantially non-porous tipping paper provided over its whole area
with electrostatically produced perforations to give again an inflow
of air of 27 cm per puff. On smoking the cigarette through this
filter, the filtration efficiency for aldehydes was again 45%.
The diameter of the smoke path 4 at the mouth end was 2 mm. An
improvement in taste was again apparent.
Example 3
A filter identical with that of Example 1 was attached,
as in Figure 1, to the tobacco rod 2 by a naturally porous paper
tipping band 3 having a porosity of 1000 cm3 min 1 (lOcm2)
(lOcmWG) . This gave an inflow of air through the band of 10 cm
per puff, i.e. 28.5% of the puff volu~e. On smoking the cigarette
through this filter, the filtration efficiency for aldehydes was
ascertained to be 55%. The smoke was again found to be directed
towards the centre of the filter, the smoke path 4 in this case having
2~ a diameter of 7 mm at the mid-length of the filter and 4 mm at the
mouth end. Such cigarettes also had improved taste.
Example 4
A filter 1, again identical with that of Example 1, was
attached, as in Figure 2, to the tobacco rod 2 by a tipping band ~ -
5 of substantially non-porous tipping paper provided with electro-
statically produced perforations to give a porosity of 10,000 and an
inflow of air of 25 cm per puff, i.e. about 71% of the puff volume. '
The filtration efficiency for aiidhydes was ascertained to be 88%.
The dlameter of the smoke path 4 at the mid-length of the filter
was 3 mm and 2 mm at the mouth end. The smoke had improved taste.
Example 5
An identical filter was attached to the tobacco rod 2,
as in Pigure 1 by a naturally porous paper band 3 having a porosity
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of 10,000 and giving an inflow of air of 25 cm per puff, i.e. about
71% of the puff volume. The filtration efficiency for aldehydes was
again 88%. The diameter of the smoke path 4 at the mid-length of
the filter was 3.5 mm and at the mouth end 2.0 m~. The smoke had
improved taste.
Example 6
An identical fllter 1 was attached to the tobacco rod 2,
as in Figure 2, by a tipping band 5 provided with electrostatically
produced perforations to give a porosity of 1000 and an inflow of
air of 8 cm3 per puff, i.e. about 23~h of the puff volume. The
filtration efficiency for aldehydes was 55/O~ The diameter of the
smoke path 4 at the mid-length of the filter was 7 mm and 4 m~ at
the mouth end. An improvement in taste was observed.
Example 7
An identical filter 1 was attached to a cigarette by a
tipping band 6 provided around its periphery with one ring of 32
ventilation holes 7, of 0.25 x 0.25 mm size as shown in Figure 3.
This ring of holes was spaced from the adJacent end of the filter
1 by a distance a of 2 mm. The iinflow of air was 26 cm3 per puff,
i.e. about ~4% of the puff volume. The filtration efficiency for
aldehydes was 80%. The diameter of the smoke path, of substantially
the shape 8 shown in Figure 3, at the tobacco end was reduced to 3 mm.
At about the mid-length of the filter and at the mouth end, the
diameter was about 2 mm. The smoke had improved taste.
Example 8
An identical filter 1 was attached to the tobacco rod 2
by a tipping band 9 provided peripherally with two rings,~each of
32 holes of 0.25 x 0.25 mm sire, of holes 7,7' as shown in Figure 4,
giving an inflow of air of 28 cm3 per puff, i.e. about 80% of the
puff volume. The ring of holes 7 was positioned as in Figure 3 and
the holes 7' at a further distance b of 3 mm. The filtration
efficiency for aldehydes was 90%. The diameter of the smoke path
, ' , . ' . , :'
' :
104S~96
was 4 mm at the tobacco end near the rings and 1.5 mm at about the
mid-length and at the mouth end. An improvement in taste was again
apparent.
Larger numbers of rings of holes may be provided. In all
cases, the first ring of holes 7 should be at a distance a of at
least 2 mm form the adjacent end of the filter 1 and subsequent rings
at least 0.5 mm fr~m the preceding ring.
