Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02049807 2000-11-14
PM-1322 CIP II
10
SMOKING ARTICLE
This application relates to an invention which is an
improvement in or modification of that disclosed in U.S.
Patents Nos.4,991,606 and 4,966,171.
Background of the Invention
This invention relates to smoking articles which
produce substantially no visible sidestream smoke. More
particularly, this invention relates to a smoking article in
which the sensations associated with the smoking of tobacco
are achieved without the burning of tobacco.
A substantial number of previous attempts have been
made to produce a smoking article which produces an aerosol
or vapor for inhalation, rather than conventional tobacco
smoke. For example, Siegel U.S. Patent 2,907,686 shows a
smoking article consisting of a charcoal rod and a separate
carrier impregnated with flavorants and a synthetic "smoke"
forming agent which is heated by the burning charcoal
1
- 2 -
~04~~~~
rod. The charcoal rod is coated with a concentrated
sugar solution so as to form an impervious layer during
burning. It was thought that this layer would contain
the gases formed during smoking and.concentrate the
heat thus formed.
Another smoking article, shown in Ellis
et al. U.S. Patent 3,258,015, employs burning tobacco
in the form of a conventional cigarette to heat a
metallic cylinder containing a source of nicotine, such
as reconstituted tobacco or tobacco extract. During
smoking, the vapors released from the material inside
the metal tube mix with air inhaled through an open end
of the tube which runs to the burning end of the
smoking article. Ellis et al. U.S. Patent 3,356,094
shows a similar smoking article in which the tube
becomes frangible upon heating, so that it would'~reak
off and not protrude when the surrounding tobacco had
burned away.
Published European patent application
0 177 355 by Hearn et al. shows a smoking article which
produces a nicotine-containing aerosol by heating, but
not burning, a flavor generator. The flavor generator
could be fabricated from a substrate material such as
almumina, natural clays and the like, or tobacco
filler. The flavor generator is impregnated with
thermally releasable flavorants, including nicotine,
glycerol, menthol and the like. Heating of the flavor
generator is provided by hot gases formed as a result
of the combustion of a fuel rod of pyrolized tobacco or
other carbonaceous material.
Banerjee et al. U.S. Patent 4,714,082 shows a
variation of the Hearn et al. article which employs a
short fuel element. The performance of the article is
said to be improved by maximizing heat transfer between
the fuel element and the aerosol generator. This is
effected by preventing heat loss by insulation, and by
enhancing heat transfer between the burning fuel and
the flavor generator by a metallic conductor. A spun
glass fiber insulator surrounds the fuel element and
aerosol generator assembly.
The Banerjee et al. device suffers from a
number of drawbacks. First, the resilient glass fiber
insulating jacket is difficult to handle on modern mass
production machinery without special equipment.
Second, the glass fibers may become dislodged during
shipping and migrate through the pack to rest on the
mouth end of the article, giving rise to the potential
for the inhalation of glass fibers into the smoker's
mouth. Additionally, the use of a metallic heat
conductor may be somewhat inefficient because the
conductor itself absorbs much of the heat produced by
the fuel element. .
It would be desirable to be able to provide a
smoking article in which a flavored aerosol releasing
material is efficiently heated by hot gases formed by
the passage of air through, and by radiation from, a
carbonaceous heat source. J'
It further would be desirable to avoid the
potential for inhalation of glass fibers by a smoker of
such an article.
It still further would be desirable to
provide such:an article which has both the look and
feel of a conventional cigarette.
Summary of the Invention
It is an object of this invention to provide
a smoking article in which a flavored aerosol releas-
ing material is efficiently heated by hot gases formed
by the passage of air through, and by radiation from, a
carbonaceous heat source. ',
._
- 4 -
It is a further object of this invention to
avoid the potential for inhalation of glass fibers by a
smoker of such an article.
It is a still further object of this inven-
°' S tion to provide such an article which has both the look
and feel of a conventional cigarette.
In accordance with this invention, there is
provided a smoking article having a mouth end and a
distal end remote from the mouth end. The smoking
article includes an active element at the distal end in
fluid communication with the mouth end, and may include
a filter adjacent the mouth end. The active element
includes a heat reflective substantially cylindrical
hollow sleeve having internal and external walls, and
having a first end at the distal end and a second end
- closer to the mouth end. At least a portion of the
sleeve at the first end is metallic. A heat source is
inserted in the sleeve adjacent the first end of the
sleeve. Preferably, the heat source is suspended in
the sleeve adjacent the first end and spaced from the
interior wall of the sleeve, defining an annular space
around the heat source. The heat source has a fluid "'
-- passage therethrough. A flavar bed is provided in the
sleeve adjacent the second end thereof, in radiative
and convective heat transfer relationship with the heat
source. A spacer element maintains the flavor bed in
spaced-apart relationship with the heat source. The
sleeve is air-permeable adjacent the heat source for
admitting air to support combustion of the heat source,
and is air-impermeable adjacent the flavor bed to
prevent combustion of material in the flavor bed. When
the heat source is ignited and air is drawn through the
smoking article, air is heated as it passes through the
fluid passage. The heated air flows through the flavor
R.~~~~~3 d
- 5 -
bed, releasing a flavored aerosol, and carrying.it to
the mouth end.
Brief Description of the Drawincrs
The above and other objects and advantages of
the invention will be apparent upon consideration'of
the following detailed description, taken in con-
junction with the accompanying drawings, in which like
reference characters refer to like parts throughout,
and in which:
FIG. 1 is an exploded perspective view of a
first preferred embodiment of a smoking article
according to the present invention;
FIG. 2 is a longitudinal cross-sectional view
of the smoking article of FIG. l, taken from line 2-2
Z5 of FIG. 1;
FIG. 3 is an end view of the smoking article
of FIGS. Z and 2, taken from line 3-3 of FIG. 2;
FIG. 4 is a radial cross-sectional view of
the smoking article of FIGS. ~.-3, taken from line 4-4
of FIG. 2;
FIG. 5 is a radial cross-sectional view of --
the smoking article of FIGS. 1-4, taken from li-ne 5--5
of FIG. 2 ;
FIG. 6 is a radial cross-sectional view of
the smoking article of FIGS. 1-5, taken from line 6-6
of FIG. 2;v
FTG. 7 is an exploded perspective view of the
active element of the smoking article of FIGS. ~.-6;
FIG. 8 is a longitudinal cross-sectional view
of the active element of the smoking article of-
FIGS. 1-7 taken from line 8-8 of FIG. 7;
FIG. 9 is a diagram of testing apparatus for
measuring permeability of smoking articles according to
the invention; _
- 6 -
FIG. l0 is a longitudinal cross-sectional
view of a second preferred embodiment of a smoking
article according to the invention;
FIG. 11 is a radial cross-sectional view of _
the smoking article of FIG. 10, taking from line 11-11
of FIG. 10; , '
FIG. 12 is an exploded perspective view of
the active element of the smoking article of FIGS.
10-11;
FIG. 13 is a longitudinal cross-sectional
view of the active element of the smoking article of
FIGS. 10-12, taken from line 13-13 of FIG. 12;
FIG. 14 is an exploded perspective view of a
third preferred embodiment of a smoking article
according to the present invention;
FIG. 15 is a longitudinal cross-sectional
view of the smoking article of FIG. 14, taken from
line 15-15 of FIG. 14;
FIG. 16 is an exploded perspective view of
the active element of the smoking article of
FIGS. 14-15;
FIG. 17 is a longitudinal cross-sectional -y
view of the active element of the smoking article of
FIGS. 14-16, taken from line 17-17 of FIG. 16;
FIG. 18 is an end view of the smoking article
of FIGS: 14-17, taken from line 18-18 of FIG. 15;
. FIG: l9.is a radial cross-sectional view of
the smoking article of FIGS. 14-18, taken from
line 19-19 of FIG. 15;
FIG. 20 is an end view of the smoking article
of FIGS. 14-19, taken from line 20-20 of FTG. 15; and
FIG. 21 is a radial cross-sectional view of
the smoking article of FIGS. 14-20, taken from
line 21-21 of FIG. 15.
CA 02049807 2000-11-14
_7_
Detailed Description of the Invention
A first preferred embodiment of a smoking article
according to the present invention is shown in Figs. 1-8.
Smoking article 10 consists of an active element 11 and an
expansion chamber tube 12, overwrapped by cigarette wrapping
paper 14, and a filter element 13 attached by tipping paper
205. Wrapping paper 14 preferably is a cigarette paper
treated to minimize thermah degradation, such as a paper
having magnesium hydroxide filler, or other suitable
refractory type cigarette paper, or paper treated with an
aluminum oxide sol gel. As discussed in more detail below,
active element 11 includes a heat source 20 and a flavor bed
21 which releases flavored vapors and gases when contacted
by hot gases flowing through the heat source. The vapors
pass into expansion chamber tube 12, forming an aerosol
which passes to mouthpiece element 13, and thence into the
mouth of a smoker.
As explained in more detail in EP-A-0352108, to which
reference is made, heat source 20 may contain substantially
pure carbon, preferably with some catalysts or burn
additives. Heat source 20 may be formed from charcoal and
has one or more longitudinal passageways therethrough.
These longitudinal passageways may be in the shape of multi-
pointed stars have long narrow points and a small inside
circumference. Heat source 20 may have a void volume
greater than about 50% with a pore size between the charcoal
particles of about one to about 2 microns. Heat source 20
may have a weight of about 81 mg/10 mm and a density between
about 0.2 g/cc and about 1.5 g/cc. The BET surface area of
the charcoal
CA 02049807 2000-11-14
particles used in heat source 20 may be in the range of
about 50 m2/g to about 2000 m2/g.
Flavor bed 21 can include any material that releases
desirable flavors and other compounds when contacted by hot
gases. In a smoking article, the flavors and other
compounds may be those associated with tobacco, as well as
other desirable flavors. Thus, suitable materials for
flavor bed 21 may include tobacco filler or an inert
substrate on which desirable compounds have been deposited.
In a preferred version, described in detail in United States
Patent No. 4,981,522, issued Jan. 1, 1991, to which
reference may be made, flavor bed 21 is a packed~bed of
pelletized tobacco. The pellets are preferably formed by
combining in an extruder particularized tobacco materials
having a size of from about 20 mesh to about 400 mesh,
preferably about 150 mesh, an aerosol precursor, for
example, glycerine, 1,3-butanediol or propylene glycol, or
mixtures thereof, that can be widely dispersed among the
tobacco particles, and a finely divided filler material, for
example, calcium carbonate or alumina, to increase the
thermal load to prevent the hot gases from raising the
temperature of the pellets above their thermal decomposition
temperature. The materials are mixed to form a mixture, and
the mixture is extruded out a die typically having a
plurality of orifices into spaghetti-like strands of about
the same diameter. The extruded strands are cut into
lengths, preferably of uniform length. The pellets
preferably are uniformly dimensioned and comprise a mixture
of about 15% to about 95% tobacco material, about 5% to
about 35% aerosol precursor, and about 0% to about 50%
filler material.
_ g
Given sufficient oxygen, as discussed in more
detail below, heat source 20 will burn to produce
mostly carbon dioxide. As also discussed below,
radiant energy reflector sleeve 22 of active element 11
is substantially non-combustible, and does not burn
during smoking of article 10. Further, article 10 is
constructed in such a way that the gases flowing
through flavor bed 21 have a reduced oxygen content,
also discussed below, so that the constituents of
flavor bed 21 undergo pyrolysis and not combustion even
if their temperature is high enough to ignite them
otherwise. There is substantially no visible side-
stream smoke when article 10 is smoked.
Turning to the details of the construction of
article 10, active element 11 is housed in a composite
sleeve including radiant energy reflector sleeve 22
and, preferably, an inner sleeve 23 within radiant
energy reflector sleeve 22. (As used herein, unless
otherwise indicated, the word ''sleeve" refers to the
composite sleeve.) Inner sleeve 23 is folded to
provide a lip 24 which holds carbon heat source 20
suspended away from the interior wall of radiant energy
reflector sleeve 22, leaving an annular space 25.
Flavor bed 21 is held within inner sleeve 23 between
lip 24 and heat source 20 on one end, and a screen-
like clip or~cup 26, which holds in the pellets of
bed 21 while allowing the aerosol to pass through into
expansion chamber tube 12, on the other end. Expansion
chamber tube 12 gives article 10 the length, and thus
the appearance, of an ordinary cigarette. The mouth
end portion 120 of inner sleeve 23 extends beyond the
mouth end of radiant energy ref lector sleeve 22 and
f its into expansion chamber tube 12. Wrapper 14 holds
active element 11 and expansion chamber tube 12-~~
together. Preferably, cigarette wrapping paper 14 will
- to -
have sufficient porosity to allow air to be admitted
through paper 14 and radiant energy reflector sleeve 22
to support combustion of heat source 20.
Alternatively, paper 14 may be perforated, such as by
5- electrostatic or laser perforation, in the region of
radiant energy reflector sleeve 22 which surrounds heat
source 20.
Preferably, aluminum insert 27, fitted into
inner sleeve 23 behind clip 26, closes off the mouth
end of active element 11, leaving only an orifice 28
for the passage of the hot vapors. Passage through
orifice 28 causes the hot vapors to increase their
velocity and then expand into expansion chamber
tube 12. Expansion of the vapors and gases into the
expansion chamber causes cooling of the saturated
- vapors to form a stable aerosol, thereby minimizing
condensation on either of mouthpiece segments 29, 200,
increasing the delivery of aerosol to the smoker. The
degree of expansion, and therefore of cooling, may be
controlled by varying the size of orifice 28 and the
volume of expansion chamber 12.
Mouthpiece element 13 may be a hollow tube or
--may include a filter segment 29. Mouthpiece element 13
preferably includes two mouthpiece segments 29, 200.
Mouthpiece ~oegment 29 is a cellulose acetate filter
plug 201 wrapped in plug wrap 202. Segment 200 is a
rod of tobacco filler or other tobacco-containing
material, wrapped in plug wrap 203, which, in addition
to further cooling the aerosol and providing some
filtration, may impart additional tobacco taste. The
_tobacco filler in segment 200 is preferably cut at the
i
standard 30 cuts per inch, but may be coarser to
minimize filtration. For example, the tobacco filler
may be cut at about 15 cuts per inch. The two v
segments 29, 200 of mouthpiece element 13 are jointly
11 _ 2~6~:~~r~'~
overwrapped by plug wrap 204, and the entire mouthpiece
element 13 is attached to the remainder of article 10
by tipping 205. Alternatively, segment 200 may be of
another material, or there may be no segment 200.
Returning to the structure of active
element 11, annular space 25 is provided so that there
is sufficient air flow to heat source 20 to allow for
sustained combustion and so that conduction of heat to
the outside is minimized. For the former reason,
radiant energy reflector sleeve 22 is perforated and
preferably has at least about 9.5% open area and a
permeability of about 9.1 to abaut 15.1, measured as
follows:
A permeability test apparatus 90 as shown in
FIG. 9 is assembled from tubing sections 91, 92, 93, 94
all having the same diameter as radiant energy
reflector sleeve 22, which is integrated into apparatus
90. Nitrogen gas is pumped into opening 95 at a rate
of 2 liters per minute. Opening 96 is open to the
atmosphere. Gas is pumped out of opening 97 at a rate
of 1 liter per minute. Because resistance to the flow
of air through the wall of sleeve 22 is less than that
through the tubing of apparatus 90, air will be drawn
in through 'the wall of radiant energy reflector sleeve
22 and out 'through opening 97 along with a quantity of
nitrogen gas. A mass spectrometer probe 98 is
positioned at the end of tube section 93 below tube
section 94, and is connected by cable 99 to mass
spectrometer 900. Cable 99 passes out of tube 94 at
901. The opening through which cable 99 passes is
sealed so that no oxygen enters apparatus 9 0 except
through the wall of radiant energy reflector sleeve 22.
The permeability of radiant energy reflector sleeve 22
is defined as the number of milliliters of oxygen per
minute per square centimeter of surface area of the
- 12 -
outer wall of radiant energy reflector sleeve 22
detected by probe 98 as determined by mass spectrometer
900.
The permeability of radiant energy reflector
sleeve 22 determines the mass burn rate of heat
source 20. It is desirable for article 10 to provide
about 10 puffs under FTC conditions (a two-second,
thirty-five milliliter puff taken once a minute). If
the mass burn rate of heat source 20 is too high; each
puff taken by a smoker will deliver added flavor
because the gases reaching flavor bed 21 will be
hotter. However, because more of heat source 20 is
consumed in each puff, heat source 20 may be consumed
in fewer than l0 puffs. Similarly, if the mass burn
rate is too low, more than 10 puffs will be available,
but each will deliver less flavor because the gases
will be cooler. In addition, if the mass burn rate is
too low, heat source 20 may extinguish before the
smoker is ready to take another puff. A preferable
mass burn rate has been found to be between about
9 mg/min and about 11 mg/min. To achieve such a range
of mass burn rates, a permeability of between about 9.1 --
and about 15.1, measured in accordance with the method
described, is preferred.
The air flow in element 11 into flavor bed 21
is through passage 206 in heat source 20. It is
desirable that as large as possible a surface area of
heat source 20 be in contact with the air flow to
maximize the convective heat transfer to flavor bed 21,
and also so that combustion is as complete as possible.
For that same reason, passage 206 is not a simple
cylindrical passage. Rather, it has a many-sided cross
section, such as the eight-pointed star shown in the
FIGURES. In fact, the surface area of passage 206 in
- 13 -
2~4~~~'~
the preferred embodiment is greater than the surface
area of the outer surface of heat source 20.
In order to minimize radiative heat loss from
article 10, all inner surfaces of active element 11
are reflectorized. For example, radiant energy
reflector sleeve 22 can be made from metallized paper.
More preferably, as seen in FIGS. 7 and 8, radiant
energy reflector sleeve 22 is made up of a paper
layer 70 and an inner foil layer 71. Foil layer 71
reflects heat radiated by heat source 20 back into heat
source 20 to keep it hot and thus to ensure that it
does not cool below its ignition temperature and bFCOme
extinguished. The reflection of heat back into active
element 11 also means that more heat is available for
transfer to flavor bed 21.
_ Paper layer 70 may be made by spiral winding
a paper strip or using other well-known techniques of
paper tube-making. Preferably, however, paper layer 70
and foil layer 71 are passed together through a garni-
tore, similar to that used in the making of conven-
tional cigarettes, which forms them into a tube. In
that preferred embodiment, the edges of paper layer 70 J'
overlap and are glued to one another. Paper layer 70
is either porous or perforated, so that the required
permeability, referred to above, can be achieved. Foil
layer 71 is preferably made by taking 0.0015-inch
-aluminum foil, embossing it to provide raised holes,
and then calendering it to flatten the holes so that
the perforated foil is more nearly smooth. Although
calendering closes up the holes somewhat, the desired
permeability is achieved as long as the embossed
aluminum sheet has~at least 4% open area, preferably
about 9.5% open area.
Althoughfoil layer 71 reflects a substan-
tial portion of the heat produced by heat source 20,
~~~98(3'~
- 14 -
some of the heat may escape to the outside. For that
reason, the paper used in paper layer 70 preferably is
modified to prevent combustion so that it does not
ignite when article 10 is smoked.
Inner sleeve 23 is also-reflective, made of
an outer aluminum layer 80, an inner aluminum layer 82,
and an intermediate paper layer 81. Inner sleeve 23
may be made by taking two identical paper/foil laminate
strips and spiral winding them paper side to paper
side, so that the two paper sides together form
intermediate layer 81. The paper layers are preferably
hard-calendered paper. In the preferred embodiment,
intermediate layer 81 also includes up to three layers
of a paper which may be treated to reduce thermal
degradation, such as a paper having magnesium hydroxide
filler, or other suitable refractory type cigarette
paper, or paper treated with an aluminum oxide sol gel,
wound between the paper/foil laminate strips. Inner
sleeve 23 is not made air permeable because flavor
bed 21 is to be kept oxygen-deprived, so that no
ignition of tobacco can take place which might intro-
duce off tastes and thermal decomposition constituents
to the aerosol. The foil layers 8.0, 82 keep air out,
as well as reflecting radiant heat back in for maximum
flavor generation. Of course, air could be kept out of
flavor bed 21 in other ways, such as overwrapping
radiant energy reflector sleeve 22 with an air-
impermeable material (not shown) in the region of
flavor bed 21. Foil layers 80, 82 should be as thin as
possible so that they have low heat capacity, making
more heat available to flavor bed 21, but not so thin
as to allow paper layer 81 to overheat.
' Inner sleeve 23 is folded over to make
lip 24, which must be wide enough so that heat
source 20 can be held securely in place.
~~4~~fl'~r
- 15 -
Finally, active element 11 is provided with a
reflective end cap 15 which is crimped into radiant
energy reflector sleeve 22. Cap 15 has one or more
openings 16 which allow air into active element 11.
Openings 16 preferably are located at the periphery of -
cap 15. In the preferred embodiment, there are six
equiangularly spaced openings each having a diameter of
0.080 in. Cap 15 increases the reflection of radiation
back into active element 11, and also keeps heat
source 20 from falling out of article 10 if it somehow
becomes loose, cracked or broken. This is important
when it is considered that heat source 20 smolders at a
high temperature between puffs, and is even hotter
during puffs. Cap 15 also keeps in any ash that may
form; during burning of heat source 20. .
It is preferred that article 10 have an outer
diameter of 7.9 mm, similar to a conventional
cigarette. Carbon heat source 20 preferably has a
diameter of 4.6 mm and a length of 10.1 mm, while
active element 11 preferably has an overall length of
26 mm. Mouthpiece element 13 preferably has a length
of 21 mm, divided between a 10 mm cellulose acetate -'
filter portion 29 and an 11 mm tobacco rod portion 200.
Expansion chamber tube 12 preferably is 33 mm long, so
that article 10 overall is 79 mm long, which is com-
parable to a:conventional '°long-size°° cigarette. In
the preferred embodiments, Zip 24 is 2.6 mm wide.
A second, more particularly preferred
embodiment of a smoking article according to the
present invention is shown in FIGS. 10-13, any views of
the second embodiment which are not shown in
FIGS. 10-13 being the same as the corresponding views
of the first preferred embodiment.
In the embodiment 100 of FIGS. 10°13, a
spacer 101 within active element 110 holds the pellets
- 16 -
of flavor bed 21 in spaced-apart relation from the end
of carbon heat source 20. It has been found that, as
compared to the embodiment of FIGS. 1-8, the inclusion
of spacer 101 provides more even heating of the end of
the flavor bed adjacent heat source 20, because the jet
of hot gases drawn through passage 206 has time to
spread out before reaching flavor bed 21, so that it
heats more of the end of flavor bed 21. Similarly,
inclusion of spacer 101 prevents flashing of flavor bed
21 on lighting of smoking article 100. In the absence
of spacer 101, flame drawn through passage 206 during
lighting could causes flavor bed 21 to ignite, or flash,
but with spacer 101 in place, any such flame spreads
out over spacer 101. Spacer 101 preferably is a
metallic -- e.g., aluminum -- disk, which preferably .
has a surface that is treated -- e.g., blackened -- sa
that it will absorb heat from heat source 20 and
radiate it to flavor bed 21.
The inclusion of spacer 101 provides other
advantages, as well. For example, it prevents small
particles from flavor bed 21, such as broken pieces of
tobacco pellets, from falling through passage 206, and -"
obstructing the front end of smoking article 100
between end cap 15 and heat source 20, or falling out
of article 100 altogether if end cap 15 is not
provided. In addition, spacer 101 permits different
degrees of packing of the same amount of pellets in
flavor bed 21, by moving spacer 101 closer to or
further from clip 26. Different~degrees of packing of
flavor bed 21 give rise to different degrees of
resistance-to-draw of article 100, as well as different
flavor characteristics. Finally, spacer 101, which
holds the pellets of flavor bed 21 away from heat
source 20, also prevents migration of flavor compounds
from the pellets to heat source 20, where they might
~~~~~~"~
- 17 -
undergo pyrolysis and give rise to off tastes or
thermal decomposition products.
A third, even more particularly preferred
embodiment of a smoking article according to the
present invention is shown in FIGS. 14-21. Any views
of the third embodiment that are not shown in
FIGS. 14-21 are the same as the corresponding views of
the second preferred embodiment, or the first preferred
embodiment if there is no corresponding view of the
second preferred embodiment.
In the third preferred embodiment 300,
aluminum insert 27 bearing orifice 28 has been
eliminated. Instead, clip 26 is used to provide the
necessary flow restriction to achieve the desired
expansion effect in expansion chamber tube 212
(although not drawn to scale, expansion chamber
tube 212 is preferably longer than expansion chamber
tuba 12). The sizes of the openings in clip 26 can be
adjusted to achieve the desired flow restriction.
In addition, in third preferred
embodiment 300, the shape of the fluid passage through.
heat source 220 is different. Tnstead of a passage
with a multi-pointed star cross_section, such as
passage 206, heat source 220 in the third preferred
embodiment has a passage 226 which has a flower-shaped
cross section, each lobe of the passage resembling a
flower petal. Preferably, there are six lobes in
passage 226. The flower-shaped cross section provides
more efficient or even heat transfer than the star
shape, as well as more thermal control through, e.g.,
reduced ashing propensity. Heat;. source 220 itself,
instead of being substantially pure carbon, contains
carbon along with a metal nitride, as well as the
necessary additives as above. A particularly preferred
metal nitride for heat source 220 is an iron nitride.
CA 02049807 2000-11-14
-18-
Such a heat source, and its advantages, are described in
more detail in EP 0430658 published July 5, 1991, to which
reference may be made. One such advantage is the reduction
of smoke constituents other than carbon dioxide. Another
advantage is a higher burning temperature.
Finally, in third preferred embodiment 300, metallized
paper radiant energy reflector sleeve 22 and perforated
metallic end cap 15 of active element 11 are replaced in
active element 211 by a one-piece cup 222 having end face
215. Cup 222 is preferably made from drawn aluminum.
Perforations 216 of end fact 15 are similar to perforations
16 of end cap 16, but end face 215 is flat, unlike end cap
which is curved. Of course, the drawing technique
permits the use of any desired perforation configuration.
15 Perforations 216 allow the ignition flame (from a match or
lighter) used to light article 300 to spread more evenly
over the end of heat source 220. Cup 222 is fluted, having
an outer diameter defined by aluminum layer 270, and flutes
272 defined by pushed-in areas 271. The outer diameter of
cup 222 is the same as that of expansion chamber tube 12, so
that a uniform surface is presented for wrapper 14. The
inner diameter of cup 222 at flutes 272 is such that cup 222
fits snugly and securely on inner sleeve 23.
Cup 222 may have elongated openings 273 or 274 or both
to admit air to support combustion of heat source 220. In a
preferred embodiment, all of the elongated openings are
openings 274. However, other configurations of openings,
including openings outside flutes 272 in layer 270, may be
used. Wrapper 14 may be air-permeable over openings 274
either because it is
P~~r~~c~c
- 19 -
made of inherently porous paper, or because ~_t is
perforated in the regions over openings 273, 274 as
described above. However, wrapper 14 may also be of
low permeability, as flutes 272 form air ducts to the
- 5 front end of article 300, allowing sufficient air to
reach openings 274 to support ignition and static
burning of heat source 220.
The use of a metal cup 222 instead of metal-
and-paper sleeve 22 eliminates the need for paper
layer 70. In addition, because of the greater heat
capacity of cup 222, it can act as a heat sink when a
user attempts to relight article 300, not realizing
that it is already lit. In articles 10 and 100, an
attempt at relighting could result in ignition of
wrapper 14. That is also true with a conventional
_ cigarette. However, the likelihood of such an ignition
is reduced in article 300 because paper layer 70 is
absent and because cup 222 has greater heat sinking
capacity than sleeve 22. Furthermore, because the
metal expands when heated, when article 300 is being
used, the degree of contact between cup 222 and inner
sleeve 23 decreases. Therefore, there is less heating
- of sleeve 23, and thus less chance of ignition of
wrapper 14.
Thus it is seen that a smoking article in
which a flavored aerosol releasing material is effi-
ciently heated by a carbonaceous or partly carbonaceous
heat source, Which avoids the potential for inhalation
of glass fibers by the smoker, which minimizes heat
loss to the walls of the flavor bed, and which has both
the look and feel of a conventional cigarette, is
provided. One skilled in the art will appreciate that
the present invention can be practiced by other than
the described embodiments, which are presented for pur-
poses of illustration and not of limitation, and the
'.
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present invention is limited only by the claims which
follow.
