Note: Descriptions are shown in the official language in which they were submitted.
CA 02553459 2001-05-08
1
Tobacco Reconstitution
This application is divided from Canadian Patent
Application Serial Number 2,407,430, filed May 8, 2001.
The present invention relates to tobacco reconstitution
and particularly to the extrusion of filamentary strands of
reconstituted tobacco. More specifically the present
invention relates to the production of filamentary strands of
reconstituted tobacco downstream of a tobacco reconstitution
extruder.
There have been many prior proposals for the production
of tobacco based material utilising particulate tobacco.
According to these proposals, the particulate tobacco may be
tobacco dust inadvertently produced during smoking article
manufacturing processes, cigarette manufacturing processes
for example, or may be obtained by grinding tobacco leaf
lamina or stem portions. The materials produced from the
particulate material may take the form of flat webs or
sheets, rods, filaments or hollow cylinders. Processes
producing these materials are commonly referred to as tobacco
reconstitution processes.
Components additional to tobacco which have been
proposed for inclusion in materials produced by
reconstitution processes are water; binding agents, e.g.
pectin, starch, pullulan and cellulosic binders; fillers;
humectants; expansion agents; reinforcing agents; and
flavourants.
CA 02553459 2001-05-08
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A prior proposed reconstituted tobacco process by the
applicant was disclosed in UK Patent Specification Nos. 2 201
081B and 2 201 080B. The process involved feeding a mixture
of particulate tobacco, starch and binder, with the 'addition
of water to an extruder to provide a sheet form extrudate, the
extrusion being carried out under such conditions that .the
extrudate assumes a cross-section greater than that of the
exit orifice of the extruder die, i.e. undergoes an expansion
process, It was suggested that it is advantageous to draw
down the sheet form extrudate, so to effect an increase in the
machine direction dimension of the extrudate and a decrease in
the thickness thereof.
A further reconstituted tobacco process is disclosed in
GB 2 291 778B.
A disadvantage of the reconstituted tobacco processes
described in these patent specifications is that production of
sheet material can be problematic. For example, the
thickness, strength and elasticity of the sheet material may
be difficult to regulate and if any of these parameters is
outside of tolerance limits downstream manipulation of the
sheet material (i.e. through cutters) can be adversely
affected.
A 'further disadvantage of this prior art reconstituted
tobacco process is that once cold the resultant sheet product
has an upper skin and a lower skin with a honeycomb structure
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therebetween. Thus degradation of the product may occur at
transverse faces of the product, i.e. faces not constituted
by a skin. Thus the product is frangible. It is, therefore,
undesirable or practically impossible to pneumatically convey
such a product.
US 4,632,131 discloses the extrusion of strands or
filaments of reconstituted tobacco wherein a plurality of
strands are extruded from a die, comprising a circular array
of exit orifices, and are subsequently adhered to one another
so as to form a reconstituted tobacco rod having passageways
extending generally longitudinally thereof.
A disadvantage of such strand extrusion methods for
reconstituted tobacco, when it is required to produce
discrete strands, is that the strands exiting the exit
orifices of the extruder die are difficult to handle without
the strands becoming co-adhered.
The present invention provides an improved filamentary
reconstituted tobacco product.
The present invention also provides a reconstituted
tobacco product of appropriate dimensions for incorporation
into a smoking article, i.e. a cigarette.
Accordingly, the present invention provides an extruded
reconstituted tobacco filament, wherein said filament is of a
substantially rectangular or square cross-section, said
filamer~t comprising a cellular interior and an integral skin
extending over at least the four sides of said filament.
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This structure provides a strong product, which product
can be subsequently transported pneumatically without being
substantially degraded.
A method of handling an extruded reconstituted tobacco
filament downstream of die means through which said filament
is being extruded is described, wherein said filament is
transferred in a direction longitudinal of said filament away
from said die by pneumatic conveyance means, said conveyance
means effecting draw down of said filament such that the
cross-sectional dimensions of said filament are reduced.
Advantageously, the method may further comprise a
cutting step, in which step the extruded filament is cut
transversely at intervals along the length thereof into a
plurality of elements. For example, the filament may be cut
at intervals in the range of about lOmm to about 50mm.
Preferably, the extruded filament is cut subsequent to the
reduction in the cross-sectional dimensions of the filament.
The cutting means utilised in the cutting step may suitably
be a rotary cutter.
Advantageously in some instances the method may further
comprise a cooling step, whereby cooling air is brought into
contact with the extruded filament to effect cooling thereof.
The temperature of the extruded filament at the cutting
means, when present, should advantageously be low enough to
ensure
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that the extrudate is insufficiently tacky to cause problems
in the operation of the cutter means. Suitably, the
temperature of the extruded filament at the cutting stage is
within the range of about 20° to about 60° Celsius, preferably
with the range of about 30° to about 50° Celsius.
Preferably, the pneumatic conveyance means comprises a
gaseous medium transfer means and duct means, the transfer
means being operable to cause transfer of gaseous medium, as a
continuous flow thereof, through the duct means. The gaseous
medium transfer means may comprise, for example, suction
means, which suction means may suitably' he provided by fan
means. Preferably, the inlet end of the duct means is
positioned adjacent to the extruder die such that when the
filament emerges from the die orifice the filament is readily
transferred in a direction longitudinal of the filament away
from the die under the action of the continuous flow of
gaseous medium through the duct means. Advantageously the
inlet end of the duct means is located within about 5mm -
about 20mm from the extruder die, and preferably within the
range of about lOmm - about l5mm. The transfer in a direction
longitudinal of the filament is advantageously initially
perpendicular to the die face. Thereafter the transfer may be
in a substantially horizontal or vertical plane.
In normal practice the gaseous medium will be air, and
thus air only is referred to hereinbelow.
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The draw down of the filament, to reduce the cross-
sectional dimensions thereof, is effected by the velocity of
the air flowing in a direction which corresponds with the
transfer direction of the filament being greater than the
extrusion velocity. Therefore, the filament downstream of the
extruder die is tensioned and drawn down by the air. Draw
down may be enhanced by tensioning the filament further by
drawing the filament over a tensioning means. The tensioning
means inay be, for example, a driven roller.
Draw down is effected advantageously by an air velocity
in the range of 60-180 m/s, and is preferably at least 100
m/s. The drawn down velocity required is dependent on the
formulation chosen and the throughput selected in the
extruder. The air velocity can be varied using the suction
means, the cross-sectional area of the duet, or both. The
conveying velocity after draw down is suitably in the range of
30-6o m/s, and is preferably at least 35 m/s, and more
preferably in the range of 40-60 m/s.
Much to be preferred is a pneumatic conveyance means
configuration and the selection of a mass airflow value which
ensure that the filaments) does not in its transference
through the duct means come into contact with any inner
surface of the duct means.
Much by preference the cross-sectional shape of the
extruded reconstituted tobacco filament resemble the cross-
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sectional shape of cut tobacco, particularly cut lamina
tobacco. In order to achieve this resemblance the extruded
tobacco filament should be of a substantially rectangular or
square cross-section. Expansion of the extrudate may occur
upon exit thereof from the extruder die. Therefore, in a case
when expansion of the extrudate occurs, in order to provide an
extruded filament of a rectangular or square cross-section,
the exit orifice of the die should be of a generally square or
rectangular configuration, the sides of the square or
rectangle being concave. By use of an appropriate concavity in
relation to the.degree of expansion of the extrudate there may
be produced a filament the cross-sectional shape of which is a
substantially straight sided square or rectangle.
The cross-section of a filament following draw down
thereof, advantageously has dimensions of about 0.7mm x about
lmm, preferably of about 0.3mm x about 0.8mm. Suitably the
filament has a length, post-cutting, in a range of about lOmm
to about 50mm. By use of the present invention, the beneficial
result of a filament of constant cross-sectional dimensions
post-draw down is achieved.
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The filamentary reconstituted tobacco product of the
present invention has a filling value in the range of about
3.8 to about 5.Omm3/mg, and may suitably in the range of about
4.Omm3/mg - about 4.6mm3/mg. This represents the potential
for an increase in filling value of 10-20% over the filling
value of products produced in accordance with the processes
described in UK Patent Specification Nos. 2 201 081B and 2
201 080B. The product density may be in the range of about
150 mg/mm3 to about 600 mg/mm3, and preferably less than about
4 0 0 mg / mm3 .
In normal practice, a reconstituted tobacco product
manufactured according to the present invention will form a
proportion of a cigarette filler blend, other tobacco
constituents of which blend may be, or include, cut lamina
and cut stem.
Much by preference, a plurality of reconstituted tobacco
filaments are co-extruded. Suitably, when it is the case
that a plurality of filaments are co-extruded, a die
comprising a plurality of exit orifices is employed.
Preferably, the exit orifices of such an extrusion die are
arranged in such a manner that the filaments issuing
therefrom are in a side-by-side, advantageously horizontal,
array. It is preferable that each filament of the plurality
of filaments is maintained out of contact with each of the
other filaments. Thus, adherence of the filaments one with
another is avoided.
An extruder die plate may be used to form the extruded
reconstituted tobacco filament of the present invention. The
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die plate includes die orifices of a generally square or
rectangular configuration, and the sides of the square or
rectangle being concave.
Suitably, the exit face of the die is oblong in
configuration and the exit orifices thereat are arranged in a
single row across the face. Alternatively, the exit orifices
may be arranged in two, upper and lower, longitudinal rows
across the face, the orifices of the upper row being
vertically out of registration with the orifices of the lower
row. Suitably, when a plurality of filaments is extruded,
the duct of the pneumatic conveyance means may be of an
oblong cross-section so as to enable the plurality of
filaments to travel side-by-side of one another through the
duct. The number of orifices in the die is selected in
accordance with the desired throughput from the extruder.
Preferably, the extrusion mixture comprises particulate
tobacco, starch and binder. Water is preferably added to the
above mixture when the mixture is in the barrel of the
extruder.
The starch is preferably present in the
tobacco/starch/binder mixture at a level within the range of
about 5~ to about 35~ by weight and preferably ~.Nithin a range
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1~
of about 10~ to about 20% by weight. The starch, is preferably
present in the mixture in an amount by weight exceeding that
of binder 'by two times and more preferably by three or more
times. The level of binder in the mixture preferably does not
exceed 10°s by weight and more preferably does not exceed 5~ by
weight.
The starch may, for example, be maize or corn starch.
The starch, or a proportion thereof, may be a modified starch.
Suitably the binder comprises a cellulosic binder.
Cellulosic binder materials for use in practising the present
invention may be hydroxypropyl cellulose, carboxymethyl
cellulose, hydroxyethyl cellulose, methyl cellulose and ethyl
cellulose. Other binders suitable for use in practising the
present invention include gums, such as xanthan gum, guar gum
and locust bean gum. Further suitable binder materials will
readily occur to those skilled in the art. Binder of the
mixture may be provided.by two or more binder materials.
Binders of lesser quality, i.e. those which tend to be
less expensive can be used in the present invention vis-~-vis
the high quality binders which are typically required in
reconstituted tobacco products as disclosed in GB 2 201 080.
Alternatively, lower quantities of the high quality binder may
be used in the present invention. The requirement for a lower
quality binder and/or a lower quantity of binder for use in
the present invention is predicated upon the fact that the
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resultant particulate filamentary reconstituted tobacco
product of the present invention comprises a cellular interior
with an integral skin extending over, when the particle is a
square or oblong cross-section,~at least the four longitudinal
sides of the particle. This contrasts with the sheet
reconstituted tobacco product of GB'2 201 080 which comprises
merely an upper skin and a lower skin with a honeycomb
structure therebetween.
Furthermore, as mentioned above the increase in filling
value obtaining with product produced according to the
invention provides the possibility of decreasing the amount of
binder in the formulation, whilst maintaining a comparable
filling value to the product described in GB 2 201 08OB.
In addition to tobacco, starch and binder, sugar may be
fed to the extruder. The sugar, if present, may comprise one
or more sugars, such for example as fructose, glucose or
sucrose. Suitably, the sugar is present at a level not_
exceeding about 5% by weight of the tobacco/starch/binder
mixture, but may be present up to a level of about 10%.
Advantageously, the total water present in the extruder
is such that, without an extrudate drying step being utilised,
the moisture content of the filament post-draw down is within
a range of about 5% to 20% by weight (wet basis). By "total
water" is meant the sum of any moisture present in the "dry"
components of the tobacco/starch/binder mixture and any added
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water. Water may be~added to one or more of the components of
the mixture before the components are fed to the extruder
and/or by way of injection via a barrel ports) of the
extruder barrel. A convenient practice is to mix the
components of the mixture and then to feed the mixture in a
dry or substantially dry state to the extruder, water being
added by injection into the extruder barrel.
Suitably, a humectant and/or plasticises, such a~ for
example glycerol or propylene glycol is fed to the extruder
with the components of the above referred to mixture and/or by
way of injection into the extruder barrel. The inclusion
level of the plasticises may be within a range of about 1 to
about 10% by weight on a wet basis.
Advantageously, filaments with optimised characteristics
are obtained by ensuring that the processing within the
extruder of the materials fed thereto takes place
adiabatically or close to adiabatically. It is also important
to operate with an extruder barrel temperature profile up to
the extruder die such that the temperature of the tobacco
portion of the materials in the extruder does not attain a
value which would be deleterious to the tobacco and is
suitably in a range of about 80° Celsius to about 180°
Celsius.
Advantageously, the processing takes place under such
conditions that immediately upon it issuing from the die, the
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extrudate is expanded by water therein flashing off to steam.
There is thereby effected an increase in the cross-section of
the extrudate and the establishment of a cellular interior
structure.
As will be readily appreciated by those skilled in the
tobacco reconstitution art, possibilities arise for feeding
flavourant materials to the extruder. Such materials may be
nature-identical or artifidial flavourants or botanical
extracts.
The particulate tobacco used in the above-described
process can be derived from the stem and/or the lamina
portions of tobacco leaf, for example tobacco dust. The
particle size of the particulate tobacco is preferably less
than about 500~.m, and is more preferably less than about
370~cm. Particle size will usually be determined by the
smallest dimension of the die orifice.
In order that the present invention may be clearly
understood and readily carried into effect reference will now
be made, by way of example, to the diagrammatic drawings
hereof, in which:-
Figure 1 shows an apparatus suitable for carrying out the
method of the present invention;
Figure 2 shows an alternative apparatus suitable for
carrying out the method of the present.invention; and
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Figure 3 shows a view of the front face of an extrusion
die and the exit orifices thereof.
Wherever possible reference numerals in respect of each
part of the apparatus shown in the figures have been conserved
between the figures.
As shown in Figure 1, the apparatus 1 comprises a twin-
screw extruder 2 (manufactured by APV Baker, of Peterborough,
U.~K. , under Model designation number MPF50-15) including a die
3 and a barrel 4. The extruder die 3 is mounted at the outlet
end of the barrel 4 of the extruder 2. A steam extraction
unit 5 is located above the extruder die 3 and is operable to
remove steam issuing from the die 3 during the extrusion
process. The apparatus 1 further comprises pneumatic
conveyance means including a gaseous medium (i.e. air? duct
means 6 extending from a position adjacent to the extruder die
3, and gaseous medium transfer means 8. As may be seen from
Figures 1 and 2, the duct means 6 comprises at the upstream
end thereof a curved inlet portion 6'. The duct means 6 is of
an oblong cross-section, the major dimension of the cross-
section extending perpendicularly to the view depicted in
Figure 1. The gaseous medium transfer means 8 comprises
suction means provided by a suction fan. A cool air intake
port 9 is in communication with the duct means 6 at the lower
end thereof, which air intake port 9 is operable to allow
cooling air to be drawn into the duct means 6. A cutting means
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10, i.e. a rotary cutter, is situated in.the duct means 6 and
is operable to cut. the extruded reconstituted tobacco
filaments 7 into particles of filamentary reconstituted
tobacco product 12: Incorporated in the duct means 6 is a
particle/air separator 11 whereby air flowing through duct
means 6 is separated from the particles of filamentary
reconstituted tobacco product 12 and any other particulate
matter being conveyed through the duct means ~6. The
tilamentary tobacco product Z2 is conveyed through an air lock
13, i.e, a rotary air lock, to feed means 14, which feed means
14 conveys the filamentary tobacco product 12 to a silo (not
shown) .
In Figure 2 an alternative apparatus to, that of Figure 1
is shown, wherein the duct means 6 is orientated such that the
filaments ? are transferred in a direction longitudinal of the
filaments ? away from the die 3 in a substantially horizontal
plane. This contrasts with the apparatus 1 of Figure 1 in
which the duct means 6 is orientated such that the filaments ?
are transferred, at least over a portion of the duct means 6,
in a substantially vertical plane. The apparatus of Figure 2
otherwise resembles that depicted in Figure 1 excepting that
in Figure 2 the apparatus 1 comprises a storage container 15,
in to which container 15, in operation of the apparatus 1, cut
product l2 is pneumatically conveyed..
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A view of the front face 3' of the die' 3 is shown in
Figure 3. As an be seen from Figure 3, the die 3 is provided
with a,plurality of exit orifices 16, 16'. Only a small
number of exit orifices 16, 16' have been depicted in Figure
3. However, the die 3 is, in fact, provided with a total of
about one hundred exit orifices 16, 16' . Thus, a plurality of
reconstituted tobacco filaments 7 are co-extruded. Each exit
orifice 16, 16' of the die 3 is of a generally square or
rectangular configuration, the sides of the square or
rectangle being concave. By use of an appropriate concavity
in relation to the degree~of expansion of the extrudate upon
exit'thereof from the die 3, there may be produced filaments 7
the cross-sectional shape of each being a' substantially
straight sided square or rectangle. The exit orifices 16, 16'
of the die 3 are arranged in such a manner that the filaments
7 issuing therefrom are in a side-by-side, horizontal array.
Each filament 7 of the plurality of filaments 7 is maintained
out of contact with each other of the filaments 7. The die 3
is of oblong. configuration and the exit orifices 16, 16' are
arranged in two, upper and lower, longitudinal rows'across the
face 3' . The orifices of the upper row 16 are vertically out
of registration with the orifices of the lower row 16', as can
be seen from Figure 3.
In operation of either of the Figure 1 or the Figure 2
apparatus a dry mixture of 80% particulate tobacco dust, 15%
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starch and 5% cellulosic binder is fed at a rate of about 145
kg/hour to the extruder 2. A feed unit (not shown) of the
extruder 2 serves to feed the mixture through a feed pipe (not
shown) to the inlet end of the barrel 4 of the extruder 2.
Water drawn from a tank (not shown) is injected at a rate of
about 21 kg/,hour into the barrel 4 under the action of a, pump
(not shown). Similarly, glycerol is drawn from a further tank
(not shown) and is injected into the barrel 4 at a rate of
about 5 kg/hour. The total water in the wet mix in the barrel
4 may, for example, represent 16% by weight of the wet mix.
The barrel 4 is provided with heating means (not
depicted) by the operation of which a desired temperature
profile can be maintained along the barrel 4. The barrel
temperature may, for 1 example, be maintained at 4.0 ° Celsius at
the inlet end increasing to 95% Celsius at the outlet end.
The pressure within the extruder. is maintained at a high
enough value to ensure that water therein remains in the
liquid phase. A pressure within the range of 500 psig (3,400
kPa or 34.5 Bar) to.2000 psig (13,600 kPa or 137.8 Bar) may
thus be used, such as 1000 psig (6,800 kPa or 68.9 Bar) to
1500 psig (102,000 kPa or 103.4 Bar).
At these temperatures and pressures the starch fed to the
extruder 3 is caused to gelatinise.
As the extruded filament 7 issues from the plurality of
exit orifices 16, 16', water therein flashes off to steam, as
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1$
a result of which the cross-sectional shape of each filament
changes due to expansion, such that the resultant cross-
sectional shape of each filament 7 is a substantially straight
sided square or rectangle when the shape of each exit orifice
is as that shown in Figure 3.
The approximately 100 co-extruded filaments 7 issue from
the die 3 at a total mass rate of about 157 kg/hour, the
linear speed of each extruded filament 7 being about 1
metre/second. The steam extraction unit_5 removes the flashed
off steam.
The filaments 7 issuing from the orifices 16, Z6' are
directed into the duct means 6 and are transferred through the
duct means 6 in a direction longitudinal of the filaments 7
away from the die 3. Upon entry of the filaments 7 into the
duct means 6, the filaments 7 become entrained in a continuous
stream of air flowing through the duct means 6. Thus the
filaments 7 are pneumatically conveyed through the duct means
6. The airflow in the duct means 6 is effected by the suction
fan 8. During conveyance of the plurality of~ filaments 7 in
the oblong duct means 6 each filament 7 of the plurality of
filaments 7 is maintained out of contact with each other of
the filaments 7. Thus, adherence of the filaments 7 one with
another is avoided.
The filaments 7 .are drawn down to. reduce the cross-
sectional dimensions thereof . - The draw down is effected as a
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result of the velocity of the air flowing in the duct means 6
being greater than the extrusion velocity, which velocity
differential engenders a drag force of the air on each of the
filaments 7. Therefore, the filaments 7 downstream of the
extruder die 3 are tensioned and thus drawn down by the air.
By way of example, a velocity of the airflow which is
effective to tension and draw down the ~ filaments 7 is in the
range of about 60 metres/second to about 180 metres/second
when the extrusion velocity is about l metre/second. Such an
airflow velocity is provided at least at an initial portion of
the duct means 6, in order to effect draw down of the
filaments 7 issuing from the orifices 16, 16' of die 3. Draw
down of the filaments 7 is effected until the required cross-
sectional size of the filaments 7 is reached. The velocity of
the airflow in the duct means 6 downstream of the initial draw
down portion of the duct means 6 is suitably at least 35
metres/second, and may be about 50-60 metres/second. This
reduction in airflow velocity is achievable by arranging~that
downstream ~of the draw down portion of the duct means 6, the
cross-sectional area thereof is greater than at the draw down
portion. A downstream airflow velocity such as 35
metres/second is suitable for transporting the filaments 7
without substantial draw down thereof. Thus the cross-
sectional dimensions of the filaments 7 remain constant
following the draw down step. The filaments 7 subsequent to
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draw down are conveyed at a rate of, for example, about 2
metres/second.
The filaments 7 are cut transversely at intervals of
about 30mm along the length thereof by the cutting means 10
thus to provide a product Z2 constituted of filamentary
particles of.recon.stituted tobacco. This cutting step takes
place subsequent to the reduction in the cross-sectional
dimensions of the filaments 7. The particulate product 12 is
then pneumatically conveyed at about 20 metrea/second either
to an air lock 13 (Figure 1) or directly to a storage
container 15 (Figure 2). Silo feed means 14 may be situated
downstream of the air lock 13. The particles of the product
12 and the conveying air are separated by way of an
air/particle separator 11.
The method may further comprise an enhanced cooling step,
whereby cooling air is brought into contact with the extruded
filament 7 to~ effect cooling thereof. The cooling air enters
the duct means 6 through the cool air intake port 9. If
deemed appropriate a plurality of cool air intake ports may be .
provided. Suitably, the cross-sectional area of the bore of
the cool air intake port 9 is the same as that of the bore of
the inlet portion 6' of the duct means 6. Advantageously, the
sum of the cross-sectional area of the intake port 9 and that
of the inlet portion 6' is equivalent to the cross-sectional
area of the run of the duct means 6 extending immediately
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downstream of the inlet portion 6~. Preferably, the air flow
through the cooling air intake port 9 is adjustable; for
-example a position adjustable baffle (not shown) may be
located in the cooling air intake port 9, which baffle is
operable to variably control the air flow rate through the
intake port 9. Advantageously, the temperature of the
filaments 7 at the cutting means 10 should be low enough to
ensure that the ext,rudate does not foul the cutting means 10.
The temperature of the filaments 7 at the cutting means 10
should be between 30° and 50° Celsius.
By way of example, the cross-sectional area of each of
the intake port 9 and the inlet portion 6' of the duct means 6
is in the range of about 10 cma to about 20 cma, the cross-
sectional area of the duct means 6 at the aforementioned
initial draw down portion thereof is in the range of about 20
cma to about 40 cma, and the cross-sectional area of the duct
means 6 at the cutting means 10 is in the range of about 250
cma to about 4 0 0 cm2 .
The cross-section of each filament 7, following draw down
thereof, has dimensions of, for example, about 0.7mm x about
lmm. The particles of filamentary tobacco product 12 (i.e.
the portions of the filament 7 post-cutting) are each of a
length, for example, in the range of about 30mm. The
resultant filamentary reconstituted tobacco product 12
consists of particles each of which particles 12 is
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constituted by a length of a filament 7 and thus comprises a
cellular interior and an integral skin extending over, when
the particle is of a square or oblong cross-section, at least
the four longitudinal sides of the particle.
The extruder may 'be any extruder suitable to provide a
range of throughputs. The throughput may be up to 300 kg/hr,
a suitable extruder for which throughput being the Buhler DNDG~
62. Increasing the throughput of the extruder will require
consequential increases in the gaseous medium transfer means,
such as an increase in power of the suction fan up to about 75
kW - about 100 kW for a throughput of up to about 300 kg/hr.
A throughput of about 150 kg/hr.would require a suction fan of
about 45 kW.
In an alternative arrangement of the subject invention
the pneumatic conveyance means may additionally comprise
pneumatic jet means. It is preferred that the pneumatic jet
means are located adjacent to the extruder barrel such that
when the filament emerges from the die orifice the filament is
readily transferred in a . direction longitudinal of the
filament away from the die under the action of the continuous
flow of gaseous medium provided by the pneumatic jet means,
into and or through the duct means.
Alternat~.vely, the pneumatic conveyance means may
comprise compressed air jets,. In this alternative arrangement
of the subject invention, compressed air may be~delivered from
~Trade-mark
CA 02553459 2001-05-08
23
the compressed air jets in controlled pulses or as a
continuous flow such that when the filament emerges from the
die orifice, the filament is transferred in a direction
longitudinal of the filament. The compressed 'air may be
delivered so as to separate the filaments from one another and
to transfer the filaments in a side-by-side array. It is
preferred that the compressed air jets are arranged relative
to the barrel of the extruder so as to provide compressed air
substantially tangentially to the filament flow direction.
Alternatively the'compressed air jets may be arranged so as to
deliver air through the die plate by means of at least one die
orifice. It is preferred that the die orifices are other than
those through which the filaments are extruded.
In a further alternative arrangement of the subject
invention using compressed air jets the pneumatic conveyance
means may optionally comprise the duct means.
The compressed air jets may be so arranged as to provide
means for breaking the filaments into discrete elements of a
controllable size and transferring the elements away from the
die orifice.
In the arrangements of the subject invention , using
compressed air,~the air is supplied at a pressure in the range
of about 1 to about 200 bar, and is preferably in the range of
about 5 to about l0 bar.
