Note: Descriptions are shown in the official language in which they were submitted.
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UNIEORM TAR DELIVERY PROFILE FILTER
The present invention relates to a novel cigarette
smoke filter element which is able to provide a more
uniform- tar ~delivery profile to the smoker than has
heretofore been possible, and to cigarettes incorporating
such filter elements.
It is well known that when either a smoker or a
smoking machine smokes a conventional filter-tipped
cigarette, the amount of "tar" in each puff increases in
each successlve puff. The "tar" yield of the last few
puffs is usually several times higher than that from the
first few puffs. Consequently the "tar" in the last few
puffs may be perceived by a smoker as "too strong", and
a smoker, therefore, may consider a cigarette as
"smoother", if the "tar" delivery profile can be made
more even.
There have been many attempts in the past to achieve
an "even" puff cigarette by modifying the filter.
Mullor, ~J.S. Patent no. 2,763,267 and Clayton et al, U.S.
Patent no. 3, 809, 097 proposed to use a plurality of discs
to be placed inside a cigarette filter rod and placed
transverse to the smoke flow. These designs, however,
can only improve filtration efficiency, but without any
ability of evening the cigarette "tar" profile.
Patterson, U.S. Patent no. 3, 648, 712 proposed to use
a low gas permeability disc placed transversely inside an
ordinary cellulose acetate filter rod. The disc is of a
diameter which is 5 to 25 percent less than the diameter
of the filter rod and this filter, therefore, can only
achieve improved filtration efficiency, with no ability
to even the "tar" delivery profile.
2 2~ 7~
B.A.T. GB Patent no. 1,339,238 proposed placing a
disc of a blocking plug between a tobacco rod and an
ordinary cellulose acetate filter rod. This disc has an
orifice for smoke to flow through. The disadvantage of
5 this design is that the pressure drop of the cigarette
increases to an unacceptable level as the orif ice of the
plug becomes clogged up at the later puf f s .
Brackmann et al,. U.S. Patent no. 3,882,877
proposed placing a disc of microfine fibres in between
10 two filter rod segments. This filter is designed to
increase filtration efficiency. However, it could not
cause the "tar" delivery to be more even, furthermore
the pressure drop may increase to an unacceptable level
at the later puf f s .
Browne et al., U.S. Patents nos. 4,460,000 and
4,469,112 proposed using a compound filter that contains
a perforated barrier disc through which the whole smoke
passes to a cellulose acetate filter rod segment. As
the smoking process proceeds, more and more "tar" builds
up on the cellulose acetate f ibres around the exit of
the perforations. The disadvantage of this design is
that the build-up of "tar" near the perforations will
greatly increase the flow resistance of the cigarette
f ilter to an unacceptable level .
G.B. Patent nos. 2,102,271 A, 2,103,065 A, and
2,105,566 A of Filtrona (U.K.), proposed to employ two
flow paths, i.e. a low pressure drop path which has low
f iltration ef f iciency and a high pressure drop path
which has high filtration efficiency, for the smoke to
flow in a filter rod. During the initial few puffs of a
cigarette, it is intended that the smoke f low through
the low pressure drop path. The smoke then switches to
f low through the high pressure drop path due to the
presence of a blocking m~ch~niF~ on the low pressure
drop path. The disadvantage of these f ilters is that
they are very complicated and difficult to manufacture.
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U.S Patent no. 4, 747, 418 USQS a filter element in
the form of a membrane having a large number of tiny
openings in combination with openings downstream of the
membrane through which air may be drawn or conventional
5 filter substance in an attempt to produce a more uniform
tar delivery. Again a complicated and expensive
structure is required.
In accordance with the present invention, an
improved filter structure is provided wherein two
lO different filter materials are combined to achieve a more
uniform tar delivery.
Accordingly, in one aspect of the present invention,
there is provided a cigarette smoke filter element,
characterized by an outer elongate cylinder of tobacco
15 smoke filter material, an inner elongate cylinder of
microfine fibres and an axial cigarette smoke path
radially inwardly of the cylinder of microfine fibres.
The outer cylinder of smoke filter material has a greater
resistance to the flow of cigarette smoke therethrough
20 than the axial flow path.
Tobacco smoke flow path directing means is located
at one end of the filter element for directing cigarette
smoke from a cigarette to which the filter element is
attached, only into the outer cylinder of tobacco smoke
25 filter material. In this way, cigarette smoke directed
from a cigarette into the outer cylinder passes first
through the outer cylinder, and then through the inner
cylinder into the axial low resistance flow path.
As smoking of the cigarette proceeds, the tobacco
30 smoke is forced to flow by a progressively-increasing
length of flow path through the outer cylinder as a
progressively greater proportion of the length of the
inner cylinder becomes clogged with tar filtered from the
tobacco smoke. As explained in more detail below,
A
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this effect leads to a more uniform delivery of tar in
the cigarette smoke to the smoker ' s mouth .
The cylinder of microfine fibres may be provided
between two outer porous support layers . The microf ine
5 fibres may be formed as described in the aforementioned
U. S. Patent no. 3, 882, 877, the disclosure of which i8
incorporated herein by reference. The microfine fibres
in the cylindrical layer thereof may have any convenient
diameter to achieve the desired filtration as described
10 herein, generally from about o . 5 to about 10 microns.
The cylindrical layer may have any convenient thickness
to achieve the desired filtration as described herein,
generally from about 0 . 05 to about 4 mm . The microf ine
fibres may be packed to any desired degree to achieve
15 the desired filtration, generally from about 0.05 to
about 0 . 3 g/cc.
The outer annulus of filter material may comprise
any of the well-known filtration materials commonly
employed in cigarette filters, generally cellulose
20 acetate tow with its fibres extending pr~ ~;n~ntly
axially along its length, or a non-woven fibrous
material, such as DANAKLON ES (polypropylene/
polyethylene bicomponent fibres made by Danaklon,
Denmark ) .
The microfine fibres are a highly efficient
cigarette smoke f iltration medium and function to remove
liquid components from the smoke, as described more
fully in U. S . Patent no . 3, 882, 877 . The f iltration is
50 efficient that the filter can rapidly become blocked
30 and permits no further smoke filtration to occur.
The latter effect is employed to advantage in the
novel cigarette smoke f ilter of the invention, where the
cigarette smoke is drawn in the same axial direction as
the direction of extension of the cigarette filter
35 ,~ nPnts. As the first few puffs are taken, smoke
enters the annulus material and then passes through the
2~4~a~3
microfine fibres into the low resistance smoke flow
passage to the smoker ' s mouth . The microf ine f ibres in
the area where the smoke is drawn through rapidly become
clogged, 60 that the smoke is forced to assume a longer
5 path of travel through the annulus material until it can
pass through the microfine fibres into the low
resistance smoke path.
As the cigarette is smoked, it is necessary for
the cigarette smoke to travel for progressively greater
10 di6tances in the annulus material before it can pass
through the microfine fibres. A uniform amount of
droplet material i5 removed from the smoke by the
microfine fibres along the whole of the length of the
filter, since each successive portion of the fibres is
15 able to filter out only the same maximum quantity of
droplets. However, by forcing the smoke to assume a
progressively longer path of travel through the annulus
f ilter material progressively greater quantities of
droplets are removed from the smoke aerosol. The result
20 of this filtration operation is that the smoke entering
the smoker's mouth has a substantially uniform tar
content and the problem of increasing tar yield from the
cigarette is compensated for by providing progressively
increased filtration of the tobacco smoke before it
25 reaches the smoker's mouth, without introducing an
unacceptable level of pressure drop.
Accordingly, in another aspect of the present
invention, there is provided a method of achieving a
more uniform delivery of tar in tobacco smoke entering a
30 smoker's mouth from a cigarette, characterized by
causing the tobacco smoke to pass from a burning
cigarette f irst into an outer cylinder of tobacco smoke
filter material of higher resistance to smoke flow, and
then through an inner cylinder of microfine fibres into
35 an axial flow path to the smoker's mouth of lower
resistance to smoke flow, filtering filterable
6 20~9573
materials, including tar, from the smoke both in the
outer cylinder and the inner cylinder, and causing said
smoke to pass through a progressively longer flow path
through said outer cylinder as a progressively increased
5 proportion of the inner cylinder becomes incapable of
effecting filtration, thereby to remove progressively
greater proportion of filterable materials, including
tar, from the tobacco smoke.
The invention is described further, by way of
10 illustration, with reference to the accompanying
drawings, in which:
Figure l is a schematic sectional view of a novel
cigarette filter constructed in accordance with one
embodiment of the invention.
Referring to the drawing, a cylindrical cigarette 10
includes a cigarette rod 12 and a novel filter 14, having
a construction which the applicants regard as the current
best mode of carrying out the invention. The cigarette
rod 12 has a conventional paper wrapper 16 and is joined
20 to the filter 14 by a conventional cork wrap 18.
The filter 14 comprises an outer annulus 20 of
conventional cellulose acetate tow material having an
outer wrap 22. A cylinder of microfine fibres 24 abuts
the inner radial extremity of the annulus 20 and
25 typically is supported between outer layers of low flow
resistance fabric.
The cylinder 24 is sandwiched between the annulus 20
and an inner plug 26 of low flow resistance material,
such as low flow resistance acetate. The inner plug 26
30 may be omitted entirely, if desired, but preferably is
employed to provide mechanicaI strength and stability to
the structure. Alternative support structures may be
employed, such as an extruded plastic core with a star-
shaped cross-section or other convenient shape providing
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7 2~9573
smoke flow channels radially inwardly of the cylinder
24 .
At the end of the filter 14 opposite to the smoking
end of the cigarette 10, the f ilter is sealed against
5 the f low of cigarette smoke directly from the cigarette
rod 16 to the acetate plug 26, such as by crimping 32
the acetate plug 26, and/or by providing a circular
baffle 34 overlying the end of the acetate plug 26.
The provision of such f low directing means ensures
10 that any smoke drawn by the smoker from the cigarette
rod 12 enters the outer annulus 20 of acetate tow.
Since the inner plug 26 provides a lower resistance flow
path for the cigarette smoke than the higher flow
resistance annulus, the cigarette smoke tends to want to
15 flow radially inwardly from the resistance annulus 20
into the acetate plug 26, which results in the smoke
passing through the cylinder of fibrous filter material
24 .
The 6moke follows the path of lea6t resistance so
20 that, initially, the smoke flows only for a short
distance through the annulus material 20 before flowing
through the microfine fibres into the acetate plug 26.
However, the microfine fibres effect efficient
f iltration of the tobacco smoke to remove smoke-borne
25 particulates including tar-containing droplets and the
fibres eventually are unable to effect further
filtration. Accordingly, the microfine fibres in the
cylinder 24 become, in the direction towards the smoking
end of the cigarette 10, progressively unable to effect
3 0 f i ltration .
The cigarette smoke, therefore, is required to
transverse a progressively longer path through the
annulus filtration material 20 before the smoke can
travel radially inwardly into the acetate plug 26. In
35 this way, a progressively greater degree of filtration
is effected by the annulus material 20 and, thereby, a
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progressively greater degree of overall f iltration is
effected as the cigarette 10 is smoked, thereby
compensating for the progressively greater tar
production by the cigarette rod 12.
In the illustrated f~r~hotl;r--nt, smoke can pass from
the annulus materiAl 20 directly into the smoker's
mouth. However, the predominant smoke flow path is via
the acetate plug 26 because of its lower resistance to
smoke flow. In addition, if desired, an annular barrier
may be provided overlying the smoking end of the annulus
material 20 to force all the smoke to flow to the
6moker's mouth through the acetate plug 26.
The filter element 10 may be formed in any
convenient manner. In one embodiment, the acetate plug
26 is replaced by an extruded plastic core having a
star-shaped cross section so as to provide a plurality
of rhAnnPl c through which the filtered smoke can pass to
the smoker. The plastic core then is reciprocated in
front of a fine fibre extruder on a continuous basis.
The plastic core is rotated about its axis, so that the
fibers are collected in an uniform layer 24 on the
periphery of the core i . e., at the radial extremities of
the points of the star. The relatively few microfine
f ibers which may randomly extend into the air pARsa~Pc
between the points of the star-shaped cross section are
not sufficient to affect significantly the low pressure
drop ducts between the legs of the star.
The continuous rod then i5 passed through a filter-
making machine, wherein the core is periodically crimped
and the normal high efficiency filter material 20 is
placed on the outside of the layer 24 of microfine
fibres. The filter then is wrapped in conventional plug
wrap 22 and cut at the crimped points to provide a
plurality of filter elements 14.
204 95 73
g
The present invention provides a novel cigarette
filter structure to provide a uniform delivery of tar to
a smoker by providing for successively greater degrees of
filtration as the cigarette is smoked, without producing
unacceptable levels of pressure drop. Cigarettes are a
staple item of commerce. Modifications are possible
within the scope of this invention.
