Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
IMPROVEME~TS RELATI~G T~ TOBACCO SMOKE FILTERS
This invention relates to tobacco smoke filters
for use with smoking articles, cigarettes for exampl~.
It is well known to provide filter tipped
cigarettes with ventilation means which permit the
ingress of ventilation air into the filter. A purpose
of this is to effect a decrease in the mainstream
delivery of smoke components. It has been observed
that when ventilation air flows into a filter comprising
a plug of fibrous filtration material, cellulose
acetate for example, through a ventilation zone extending
around the filter the tobacco smoke is caused to pass
out of the filter in an axial stream having a diameter
less than the diameter of the end face of the filter plug.
This comparatively narrow stream of smoke impinges on a
limited area of the taste receptors in the mouth of
the smoker. I~ is an object of the present invention to
provide a tobacco smoke filter in the use of which there
occurs a stimulation of the taste receptors over a wider
region in the smoker's mouth.
The present invention provides a smoke filter
including a rod-like plug of filtration material and
having at least one airflow duct at the periphery of
said plug, wherein said at least one airflow duct has an
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outlet opening at the mouth end of said plug and an
inlet opening spaced fxom the mouth end, and wherein
said at least one airflow duct has a region in which
the depth progressively decreases along the airflow
duct in a direction towards the mouth end of the plug.
Conveniently~ said at least one airflow duct
I has its region of decreasing depth extending
substantially up to the mouth end of the plug. Preferably
there may be several said airflow ducts, each defined
partly by a respective one of a plurality of grooves
in the peripheral surface of the filter plug~ and partly
by the i~wardly facing surface of wrapping means around
the filter plus. In this case the width of the grooves
may be constant or it may increase or decrease in the
direction towards the mouth end of the filter plug.
In order that th~ invention may be clearly
understood and readily carried into effect, reference
will now be made, by way of example, to the diagrammatic
drawing hereof, in which:-
Fi~ure 1 shows a part view, in axial section, of a
filter tipped cigarette,
Figure 2 shows a mouth-end view of the filter of
the cigarette of Figure 1,
Figure 3 shows a mouth-end view of a filter of a
somewhat different form from the filter shown in Figure 1
and
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Figure 4 shows a development view of a portion of
the peripheral surface of a filter plug of another form.
The cigarette of Figure 1 comprises a rod 1 of cut
tobacco enwrapped in cigarette paper 2, and a filter 3
comprising a self-sustaining filter plug 4 of fibrous
cellulose acetate filtration material. At the periphery
of the plug 4 there extend a number, eight as shown, of
parallel, axially extending grooves 5 - see also
Figure ~. As may be seen from Figure 1, the grooves 5,
which extend from the mouth end of the plug 4 for a
distance less than the full length of the plug, are so
formed that the depth of each decreases towards and
s~bstantially up to the mouth end of the plug. A
convenient method of forming the grooves 5 is to
subject the plug 4, or preferably a filter rod length
from which the plug was cut, to a hot-moulding process
such as, for example, that disclosed in United Xingdom
Patent Specification No. 1,507,765, using suitably shaped
*orming means. The surfaces of the grooves 5 may be
rendered impervious.
Serving to secure the filter 3 to the cigarette rod
1, 2 is a tipping 7 which, in the portions where it
overlies the grooves 5, defines, together with the walls
of the grooves 5, airflow ducts 8. A row of ventilation
perforations 9, shown in exaggerated form, in the tipping
7 encircles the plug 4 at a location overlying the
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upstream end of the grooves 5, the arrangement being
such that there is in communication with each of the
airflow ducts 8 at least one of the perforations 9.
When the cigarette of Figure 1 is smoked, ambient
air is drawn through ~he ventilation perforations 9 into
the airflow ducts 8. The air passes al-ong the airflow
ducts 8 to the outlet ends thereof unmixed, or
substantially unmixed, with tobacco smoke. Since
the depth of the grooves 5 partly defining the airflow
ducts 8 decreases in the direction of flow of the
ventilation air along the ducts 8, the air exits
the ducts 8 into the smoker's mouth with a component
of velocity directed radially outwardly. There is thus
provided a divergent air stream which entrains smoke
issuing from the mouth end of the filter plug 4 by a
Coanda effect and so causes the smoke to come into contact
with taste receptors over a comparatively wide region of
the smoker's mouth. This is perceived by the smoker as
an enhanced smoke character.
The filter~ a mouth-end view of which is shown in
Figure 3, comprises a plug 4' which, instead of being
provided with ~ number of longitudinally extending
peripheral grooves, comprises a single annular
circumferential groove 5'. In axial section of
the plug 4', the groove 5' has a contour similar to the
contour of the base of each of the grooves 5 of the plug
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4 of Figure l. A stiff wrapper sleeve or mouthpiece
7', which may be formed of plastics material, encases
the plug 4' and receives an end portion of a cigarette
rod in a manner analogous with the tipping 7 of the
cigarette shown in Figure l. The sleeve 7' requires
to be stiff in order that the annular mouth-end opening,
designated 6, of airflow duct 8', defined by the
circumferential annular gro~ve 5' and the sleeve 7',
remains open when the filter is in use.
The effect produced by the filter of Figure 3 is
similar to that of the filter 3 of Figures l and 2.
Ambient air is drawn into the airflow duct 8' through
perforations (not shown) in the wrapper or mouthpiece 7'
and, because of the contour of the groove 5, the air
enters the ~moker's mouth as a divergent stream which
serves to cause smoke to impinge on an extended region
of taste receptors.
Figure 4 shows, as a development view, a pattern of
peripheral grooves which may be utilised as an
alternative to the axially extending grooves 5 of the
filter of Figure l or the single annular circumferential
groove 5' of the filter of Figure 3. In Figure 4
reference numeral lO denotes the mouth end of a
filter plug 11. A first series has per.ipheral, parallel
grooves 13 extending at a small angle to the axis of
the plug 11 and the grooves 14 of a second, similar
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series extend at substantially the same angle to the
axis but with opposite hand. The two sets of grooves
13, 14 intersect to produce a reticular formation. As
with the single series of grooves 5, each of the
grooves 13, 14 has a region of decreasing depth
in the direction towards and substantially up to the
mouth end 10 of the plug 11~ In use the plug 11 is
overwrapped by a wrapper (n~t shown) permitting
ventilation air to flow into the grooves 13, 14
at upstream locations thereof and a smoke-spreading
effect is achieved similar to that exhibited by the
previousl~ described filters.
The wrapping means for the filter plug may
comprise a plug wrapper of pervious nature on the
1~ plug exterior and a longer tipping of impervious nature
overlying the plug wrapper and securing the filter plug
to the tobacco rod 2. In this case the ventilation
perforations need only be present in the impervious
tipping.
The ilter plug may, if desired7 be formed as two
sub-plugs one of which has the grooves 5, 13, 14 or the
single circumferential groove 5' therein, the other
sub-plug being plain.
If desired, the ventilation perforations may
comprise a micro-perforated region of the tipping.
