Note: Descriptions are shown in the official language in which they were submitted.
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Aerosol generating material for a smoking article
Description
The present invention relates to an aerosol generating material for a smoking
article.
In particular, the present invention relates to an aerosol generating material
for a
smoking article comprising particulate sorbent material coated and/or
impregnated
with diluent, and products comprising the same. The particulate material has a
high
BET specific surface area, or is calcium carbonate.
It is known to include diluents in smoking articles such as cigarettes.
Diluents are
compounds that are vapourised during smoking and transfer to the mainstream
smoke in aerosol form. They are generally selected such that they transfer to
the
smoke substantially intact. Other components of the smoke (tobacco-derived
components in the case of tobacco-containing smoking articles, or nicotine
and/or
flavour components in the case of non-tobacco-containing smoking articles) are
therefore diluted by this means.
A cigarette can comprise a filter at the mouth end, a tobacco rod comprising
smokable filler material, and cigarette paper wrapped around the rod. When
diluent
is present in the smokable filler material, this may be as a simple mixture
with the
other ingredients (particularly for diluents in solid form), or the diluent
may be
carried on one or more of the other ingredients (particularly if the diluent
is in
liquid form). If incorporated into the filler material as a simple mixture,
this may
present disadvantages during manufacturing, and the diluent may be easily
dislodged
from the finished product, especially if it is in fine powder form.
Accordingly, it is
preferred for the diluent to be held in intimate contact with another
ingredient of
the filler material.
It has been discovered that, although the diluent is vapourised during smoking
in
the course of performing its function, vapourisation of the diluent at lower
temperatures can cause problems during storage of the cigarettes.
Specifically, the
diluent can migrate during storage and subsequently be lost to the atmosphere
or
interact with other parts of the product such as the cigarette paper. This may
also
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lead to staining or marking of the cigarette paper, either by the diluent
itself or by
compounds released from the diluent interaction. Those in the art have
therefore
sought to immobilize the diluent until it is required.
US 2008/0110470 describes the immobilization of a diluent in a porous sorbent,
which is then incorporated into a tobacco rod. It focuses on silica gel as the
sorbent. However, the smoke data disclosed in this document reveals that the
use
of the silica gels therein caused an increase in the acrolein, B [a]A and B
[a]P content
of the smoke. Furthermore, the diluent loading capacity for a free-flowing
sample
is relatively low; for instance, this document states that glycerol can be
loaded at
about 120 % by weight of the silica gel, whereas propylene glycol can be
loaded at
about 100 % by weight of the silica gel.
There is therefore a need in the art to carry diluents on alternative sorbents
in a
manner that overcomes one or more of the problems outlined above.
Accordingly, the present inventors have devised the invention defined in the
claims.
Figure 1 is a schematic illustration of a precipitated calcium carbonate
particle
carrying and/or impregnated with a diluent in accordance with an embodiment of
the invention, and a similar precipitated calcium carbonate particle
additionally
coated with a barrier material in accordance with another embodiment of the
invention.
Figure 2 is a schematic illustration of a cigarette containing an aerosol
generating
material in accordance with another embodiment of the invention.
In the first aspect of the invention, the particulate porous material having a
BET
specific surface area of at least 1200 m2/g is a sorbent material, preferably
an
adsorbent material. Such materials are known to the skilled person and, in
many
cases, commercially available. For instance, examples of sorbent resins having
a
BET specific surface area of at least 1200 m2/g include the polystyrene-
divinylbenzene resin Chromabond HR-P from Macherey-Nagel GmbH & Co.,
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KG, Duren, Germany and the styrene-based resin Sepabeads from Sorbent
Technologies Inc., Atlanta, US.
Preferably, the particulate porous material is a carbon material, a resin or a
metal-
organic framework, preferably carbon, preferably activated carbon. The
activation
level can be measured by standard techniques in the art. For instance,
activated
carbon can be weighed, exposed to carbon tetrachloride (CTC) and then
reweighed,
and the percentage weight increase determined. In an embodiment, the CTC
activation level of the particulate porous material before loading with the
diluent is
at least 50 %, 60 %, 70 %, 80 %, 90 %, or 100%.
Preferably, the particulate porous material has a BET specific surface area of
at least
1300 m2/g, preferably at least 1400, 1500, 1600, 1700 or 1800 m2/g. In
general, the
greater the BET specific surface area, the greater the amount of diluent that
can be
carried by the particles. However, the brittleness can increase if the surface
area is
too high. Preferably, the BET specific surface area is 3000 m2/g or less,
preferably
2500 m2/g or less, preferably 2000 m2/g or less.
In an embodiment, the particles of the porous material have an average
particle size
in the range 3 - 45 m, preferably 5 - 30 m, preferably 6 - 20 m, preferably
8 -
15 m.
In an embodiment, the pore volume of the porous material is at least 0.5 cc/g,
preferably at least 0.6, 0.7 or 0.8 cc/g.
In the second aspect of the invention in which the aerosol generating material
comprises particulate calcium carbonate carrying and/or impregnated with a
diluent,
any suitable calcium carbonate particles may be used. The calcium carbonate is
preferably precipitated calcium carbonate, which is crystalline.
Preferably, the particles have a surface morphology with a plurality of
indentations
and/or protrusions, in or between which a substantial quantity of the diluent
can
reside. For example, each particle may be an agglomeration of scalenohedral
calcite
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and/or acicular aragonite crystals. Figure 1 illustrates one suitable
structure
schematically: a precipitated calcium carbonate particle (1) formed by an
agglomeration of scalenohedral calcite crystals has crystalline protrusions
(2) on its
surface. Although not wishing to be limited by theory, it is thought that,
upon
exposure to the diluent, the diluent (3) may become trapped between these
protrusions, in addition to entering the pores of the material. A further
advantage
of this type of structure is that the protrusions may interlock effectively in
the
aerosol generating material of the invention to form a strongly bound entity.
In an embodiment, the calcium carbonate has an average particle size in the
range
0.05 - 200 m, preferably 0.5 - 50 m, 1 - 45 m, 1.5 - 30 m, 1.8 - 20 m or
2 -
10 m.
In both these aspects of the invention, application of the diluent to the
sotbent is
by any suitable method known to the skilled person or described herein. The
diluent may be applied in pure form or in a vehicle of, or mixture with, one
or more
other materials, which may include a barrier material as described below but,
in an
embodiment, do not include a barrier material.
In an embodiment, the diluent is comprised in a liquid in which the sorbent is
washed or soaked. Alternatively, the sorbent can be sprayed with the diluent
in a
liquid or gel format. For instance, diluents that are solid at room
temperature may
be melted, or incorporated into a liquid vehicle such as methanol or ethanol,
and
those that are liquid at room temperature may be applied in pure form or
dissolved
or emulsified with another liquid. Simple admixture may also be suitable, for
instance admixture of the liquid with the sorbent, allowing the liquid to seep
into
the pores of the material. Further processing steps may be employed such as
curing
or pressure treatment.
When using calcium carbonate, such methods may result in a surface covering of
the diluent, and/or the diluent may seep into its pores. When using the
material
specified in the first aspect of the invention, however, it is required for
the diluent
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to enter the pores of the particulate porous material to take advantage of the
high
BET surface area of the particles, thereby allowing a higher loading of the
diluent.
The diluent is at least one aerosol forming agent which may be, for instance,
a
polyol aerosol generator or a non-polyol aerosol generator, preferably a non-
polyol
aerosol generator. It may be a solid or liquid at room temperature, but
preferably is
a liquid at room temperature. Suitable polyols include sorbitol, glycerol, and
glycols
like propylene glycol or triethylene glycol. Suitable non-polyols include
monohydric
alcohols, high boiling point hydrocarbons, acids such as lactic acid, and
esters such
as diacetin, triacetin, triethyl citrate or isopropyl myristate. A combination
of
diluents may be used, in equal or differing proportions. Triacetin, triethyl
citrate
and isopropyl myristate are particularly preferred.
There may be several factors influencing the stability and migration of
diluents
under ambient conditions. These factors may include hydrophobicity or
hydrophilicity, viscosity, saturated vapour pressure at room temperature,
boiling
point, molecular structure (such as hydrogen bonding or Van der Waals forces)
and
the absorptive/adsorptive interaction between diluent and the substrate. Some
diluents will suffer from migration problems to a greater extent than others;
for
instance, it has been found that triacetin, isopropyl myristate and triethyl
citrate
particularly benefit from immobilisation as in the present invention.
Another relevant factor is the loading level of the diluent. For instance, if
a diluent
such as glycerol is included in a large amount, migration problems can still
be
significant.
The diluent loading level in the present invention may depend upon the
specific
diluent. In an embodiment of the first aspect of the invention, however, the
particulate porous material is loaded with up to 500 % by weight of the
diluent,
preferably 80 - 450 %, 130 - 400 %, 140 - 350 %, 150 - 300 % or 160 - 250 % by
weight of the diluent, preferably triacetin. In an embodiment of the second
aspect
of the invention, the calcium carbonate is loaded with 20 - 100 %, preferably
30 -
95 % or 50 - 90 %, by weight of the diluent.
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The particulate sorbent material, once impregnated and/or loaded with diluent,
may
be encapsulated in a barrier material, which provides further hindrance to
migration
of the diluent during storage of the smoking article but allows release of the
diluent
during smoking of the smoking article. This is particularly advantageous for
the
second aspect of the invention, since calcium carbonate tends to bind diluents
relatively weakly. Figure 1 shows the barrier material (4) encapsulating a
calcium
carbonate particle loaded with diluent. Use of a barrier material also assists
in
hindering dislodging of powder in the finished cigarette.
The barrier material may be one that melts, decomposes, reacts, degrades,
swells or
deforms to release the diluent at a temperature above room temperature but at
or
below the temperature reached inside a smoking article during smoking. For
instance, the physical expansion occurring with vapourisation of sufficient
levels of
diluent may break down the structure of the barrier material. In embodiments
of
the invention, the barrier material releases substantial amounts of the
diluent above
50 C, preferably above 60 C, 70 C, 80 C or 90 C.
The barrier material may be, for example, a polysaccharide or cellulosic
barrier
material, a gelatin, a gum, a gel or a mixture thereof. Suitable
polysaccharides
include an alginate, dextran, maltodextrin, cyclodextrin and pectin. Suitable
cellulosic materials include methyl cellulose, ethyl cellulose, hydroxyethyl
cellulose,
hydroxypropyl cellulose, carboxymethyl cellulose, and cellulose ethers.
Suitable
gums include gum Arabic, gum ghatti, gum tragacanth, Karaya, locust bean,
acacia,
guar, quince seed and xanthan gums. Suitable gels include agar, agarose,
carrageenans, furoidan and furcellaran.
In a preferred embodiment of the invention, the barrier material comprises a
polysaccharide. An alginate is especially preferred, due to its encapsulation
properties. The alginate may be, for instance, a salt of alginic acid, an
esterified
alginate or glyceryl alginate. Salts of alginic acid include ammonium
alginate,
triethanolamine alginate, and group I or II metal ion alginates like sodium,
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potassium, calcium and magnesium alginate. Esterified alginates include
propylene
glycol alginate and glyceryl alginate.
In an embodiment, the barrier material is sodium alginate and/or calcium
alginate.
Calcium alginate provides a greater inhibition of migration of the diluent at
ambient
temperature than sodium alginate, but also may release the diluent at a higher
temperature than the latter.
Application of the barrier material to the particulate sorbent material
carrying the
diluent is by any suitable method known to the skilled person or described
herein,
which does not cause complete loss of the diluent in the process. Preferably,
substantially no diluent is lost due to the step of applying the barrier
material. In an
embodiment, the barrier material or a precursor thereto is sprayed onto the
particulate sorbent material.
For instance, the particulate sorbent material carrying the diluent can be
sprayed
with an aqueous sodium alginate solution and dried to form a water-soluble
film of
sodium alginate on the surface. Alternatively, the particulate material can be
sprayed with sodium alginate and then treated with a source of calcium ions,
to
form a water-insoluble film or gel covering of calcium alginate.
In the resulting product of the invention, individual diluent-carrying
particles are
surrounded by barrier material and migration of the diluent is further
hindered
under ambient conditions. This should be contrasted with a comparative
situation
in which the diluent is combined with "barrier" material before application to
the
sorbent, such that in the resulting product the barrier material resides only
in
homogeneous admixture with the diluent, or the diluent has been pre-
encapsulated
with the barrier material before application to the sorbent (and so is not in
intimate
contact with the sorbent).
In addition to or instead of encapsulation with barrier material as described
above,
the particulate sorbent material carrying the diluent may be combined with
other
materials to form a slurry that is cast and dried to form a sheet, which is
then cut or
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shredded to form the aerosol generating material of the invention. The other
materials may comprise a filler material such as ground chalk, a binder such
as
alginate, and/or a plasticizer such as glycerol. For instance, the use of up
to around
25 % glycerol by weight of the sheet renders the sheet suitably flexible. This
glycerol may have the advantage of being transferred to the smoke along with
the
triacetin upon smoking, providing an additional diluent effect.
Preferably, the sheet is cut or shredded so as to have dimensions similar to
those of
cut tobacco. For instance, the sheet may be cut at 35 - 40 cuts per inch,
preferably
36 - 39, 37 or 38 cuts per inch. The shredded portions may have a width of 0.5
- 2
mm and a length of 5 mm - 5 cm. This has the advantage that the aerosol
generating material may be processed using the same apparatus as cut tobacco.
In
addition, when the aerosol generating material is incorporated into the
smokable
filler material of the invention, the presence of the aerosol generating
material is not
readily apparent.
In a preferred embodiment, the CTC activation level of the particulate porous
material in the first aspect of the invention after loading with the diluent
is less than
%, preferably less than 10 %, 5 % or 3 %. This affords substantial advantages
20 when forming a sheet material from the impregnated material, including
improved
processing.
Alternatively, the slurry may be extruded to form lengths of material, which
may
then be cut into pieces, e.g. having the dimensions described above. Further,
the
aerosol generating material may be in the form of flakes.
The aerosol generating material of the invention may comprise a mixture of the
impregnated particulate porous material, described above in connection with
the
first aspect, with the particulate calcium carbonate carrying and/or
impregnated
with the diluent, described above in connection with the second aspect.
The third aspect of the invention relates to a smokable filler material. This
smokable filler material comprises smoking material and the aerosol generating
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material of the invention, preferably a blend of these substances. The smoking
material may be tobacco, a tobacco-containing material or a non-tobacco-
containing
material such as a non-tobacco reconstituted material. Preferably, the smoking
material is a tobacco-containing material, but more preferably the smoking
material
is tobacco.
The tobacco may be, for example, stem, lamina, dust or a mixture thereof.
Suitable
tobacco materials include the following tobacco types: Virginia or flue-cured
tobacco, Burley tobacco, Oriental tobacco, or a blend of tobacco materials.
The
tobacco may be expanded, such as dry ice expanded tobacco (DIET), or processed
by any other means such as extrusion.
Tobacco or other smoking materials can also or alternatively be incorporated
in the
sheet material described above.
Preferably, the aerosol generating material is present in the smokable filler
material
in an amount of 1 - 95 % by weight, and preferably 3 - 80 %, 5 - 60 %, 10 - 30
%
or 15 - 25 % by weight.
The fourth aspect of the invention relates to a smoking article comprising the
aerosol generating material of the invention. The aerosol generating material
can be
incorporated into the smoking article by conventional means. As used herein,
the
term "smoking article" includes smokeable products such as cigarettes, cigars
and
cigarillos whether based on tobacco, tobacco derivatives, reconstituted
tobacco or
tobacco substitutes. The term also includes so-called "heat-not-burn"
products,
which produce smoke or a smoke-like aerosol. The smoking article may be
provided
with a filter for the particulate and gaseous flow drawn by the smoker.
Preferably,
the smoking article is a cigarette.
The smoking article may contain a smokable filler material that consists of
the
aerosol generating material of the invention, i.e. no other smoking or aerosol
generating material is incorporated into the smoking article. This may be
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particularly suitable for heat-not-burn smoking articles. Alternatively, the
smoking
article may contain the aerosol generating material as an additive.
Figure 2 illustrates an embodiment of the invention in which the smoking
article is a
cigarette (5) that contains a filter (6) and a smoking rod (7). The aerosol
generating
material (8) is in shredded sheet form and is incorporated in the rod together
with
other components of the smokable filler material.
The invention will now be illustrated by way of the following examples.
Example 1
Triacetin diluent was admixed with Picactif PNC100 carbon particles from Pica
Carbons, France, which were activated to 100 % CTC and had a surface area of
1800 m2/g and mean particle diameter of 8 - 15 m. Separately, an aqueous
solution of sodium alginate binder was prepared and glycerol was added. The
diluent-impregnated carbon particles were then added to this liquid and formed
into
a slurry along with a ground chalk filler, which had a particle size of around
170 m.
This was then cast to form a sheet and shredded to 37 cuts per inch to form an
aerosol generating material of the invention. Various shredded sheet
formulations
were prepared by this method, having the compositions (given in percentage by
weight) shown in Table 1.
Table 1. Formulations used for sheet manufacture (percentage by weight)
Sheet Carbon Triacetin Ground Alginate Glycerol
No. (adsorbent) diluent chalk (filler) (binder) (plasticiser)
1 7.5 17.6 62.4 7.5 5.0
2 7.5 17.6 60.9 9.0 5.0
3 4.0 12.0 70.0 9.0 5.0
The shredded sheet was blended with lamina tobacco at two levels, 20% sheet /
80% tobacco and 50% sheet / 50% tobacco. These blends were then used in the
manufacture of cigarettes. A control cigarette with 100% lamina tobacco blend
was
also manufactured. The compositions are shown in Table 2. The cigarettes were
made with a 27 mm cellulose acetate filter, cork on white tipping paper, and
50
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Coresta Unit wrapper. The cigarettes were tip ventilated to give a target tar
yield of
7 mg.
Table 2. Cigarette formulations
Cigarette Sheet number Sheet inclusion Lamina tobacco
in blend in blend (%) inclusion in blend (%)
1A 1 20 80
1B 1 50 50
2A 2 20 80
2B 2 50 50
3A 3 20 80
3B 3 50 50
Control - - 100%
The cigarettes were smoked under ISO conditions (35 ml puff of 2 second
duration
every minute). The results are shown in Table 3.
Table 3 shows that the control cigarette with no triacetin in the blend had a
small
yield of triacetin in the smoke of 0.3 mg/cigarette. This is likely to be the
result of
elution of triacetin from the filter where it is used as a plasticiser. The
results also
clearly show that triacetin incorporated as a diluent in and on carbon
particles in the
tobacco rod is effectively transferred to the smoke. Increasing the triacetin
inclusion level increases the dilution.
Further analysis of smoke analytes revealed that the test cigarettes exhibited
no
increase in benzo[a]pyrene (B[a]P) or acrolein levels in their smoke compared
with
the control.
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Example 2
Triacetin diluent is admixed with precipitated calcium carbonate particles
having an
agglomerated scalenohedral calcite crystal structure (SturcalOO L), obtained
from
Speciality Minerals Inc.. Separately, an aqueous solution of sodium alginate
binder
is prepared, and glycerol and colorant are added. The diluent-carrying calcium
carbonate particles are then added to this liquid and formed into a slurry. In
this
instance, the calcium carbonate serves a dual role as diluent carrier and
filler; no
additional chalk filler is required. The slurry is cast to form a sheet and
shredded to
form an aerosol generating material of the invention. Various shredded sheet
/0 formulations are prepared by this method, having the compositions (given in
percentage by weight) shown in Table 4.
Table 4. Sheet formulations (percentage by weight)
Sheet Calcium Triacetin Alginate Glycerol E150a
No. carbonate (diluent) (binder) (plasticiser) (colourant)
(adsorbent
and filler)
4 78.5 7.5 7.5 5 1.5
5 71.5 15 7.5 5 1.5
6 71.5 7.5 7.5 12.5 1.5
7 71 17 7.5 3 1.5
