Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVEMENTS TO SMOKING ARTICLES
This invention concerns smoking articles such
as cigarettes which use a wrapper normally comprising
fibres of organic origin mixed with inorganic fillers
and sometimes containing amounts of soluble chemical
additives, binding agents and processing aids.
In the case of a cigarette a conventional
wrapper would be predominantly comprised of wood
and/or textile fibres mixed with inorganic filler such
as calcium carbonate. These materials may be subject
to a refining process and mixed in various proportions
such that the wrapper properties can be widely varied
to confer on the cigarette different characteristics
such as smoulder rates, air permeability, ash quality,
appearance and taste. ;e
Cigarette paper technology has been developed
sufficiently to establish relationships between paper
parameters such as filler/fibre ratios and properties
such as inherent permeability and opacity. These
relationships are well known, as indeed are many of
the relationships between paper properties and the
performance of cigarettes constructed with these
papers.
It is recognised that cigarette papers
constructed in the conventional way are not
homogeneous mixtures of fillers and fibre throughout
their cross section. The distribution of the filler
tends to change from one side to the other due to the
natuxe of the wet draining process and filtration
effect of the fibre. Hence conventional papers have
normally a degree of asymmetrical fibre/filler mix
which has a moderate but important effect on their
performance especially in relation to ash formation.
By separately constructing papers with quite
different properties, using for example pulps of
different botanical origin and abnormally high and
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abnormally low filler contents, the product of their
combination as a multi or double wrapper behaves quite
differently from a single substantially homogeneous
mix of the same components such as is achieved with
5 conventional cigarette paper manufacture.
It has previously been proposed to use two
substantially different wrappers on cigarette smoking
articles.
US Patent 3395714 describes the use of two
10 thin sheets to form a composite wrapper wherein the
outer sheet is a conventional cigarette paper and the
inner sheet in contact with the tobacco is a heat
insulating plastic film with a melting point below
440C. ~rhe specification also proposes manufacturing
- 15 as two sheets or as a composite with two sheets glued
together or by depositing the plastic film as a
solution upon the sheet of cigarette paper. This
patent proposes benefits for these systems which
benefits include: changes in the low temperature
20 distillation zone affecting smoke taste, reduced
tobacco consumption between puffs and reduced emission
of sidestream smoke.
US Patent 3633589 proposes a composite wrapper
composed of two thin sheets both consisting of
25 vegetable fibre stock so as to provide the benefits
claimed for US 3395714 without the disadvantages of
plastic films.
US 3633589 provides no teaching as to the
method by which the two thin sheets are linked but
30 indicates that the composite wrapper is constructed
out of independently manufactured papers described as
conventional cigarette paper outer sheet and a
calendered inner sheet which is practically impervious
to air.
The present invention seeks to utilise the
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advantages of a multiple layer sheet whilst at the
same time over^oming the practical difficulties of
using double or multi sheet wrappers. Thus it is
desired to have the benefit of combining the
properties of different paper wrappers without the
manufacturing difficulties associated with either
laminating sheets in an off-line process or attempting
to manufactur~ cigarettes with two paper wrappers run
simultaneously on the cigarette making machine.
Furthermore, it is desired to avoid the disadvantages
of laminatin~ adhesives.
According to one aspect of the present
invention there is provided a wrapper for smoking
articles, which wrapper comprises a single paper sheet
which is formed from two or more discrete webs, which
webs are combined while at least one of the webs is
still in its wet stage of formation prior to drying.
Preferably the webs are formed from different
stock. (Stock being the ingredients of the headbox or
reservoir).
Conveniently, said two or more webs are
combined when all of the webs are in the wet stage of
formation prior to drying.
In a preferred embodiment the wrapper is of
low air permeability and preferably said permeability
is lO Coresta or less. In other preferred embodiments
two partially formed webs are combined and one web is
a substantially unfilled web having a low basis
weight. Conveniently said weight is 20 gm~2 or less
and said one web prevents or substantially reduces
staining or said one web contains activated carbon.
Further preferred features are that the other
web is a filled web conferring a conventional
appearance on the wrapper, for example the opacity of
the wrapper is 60~ or more. It may be that the filler
of said other web comprises predetermined amounts of
calcium carbonate (up .o 50~ by weight) or the filler
of said other web comprises predetermined amounts of
selected fillers, e.g. I~g(OH)2, A1203, LiOH and high
surface area CaC03.
Although it is preferable that the total basis
weight of the wrapper is less than 50 gm~2 but in
other arrangements the total basis weight of the
wrapper is less than 35 gm~2.
In certain preferred arrangements one or more
of the webs may contain a burn retardant su^h as
ammonium phosphate or a burn enhancer such as a
soluble salt of a group I or group II metal, may~e up
to 10% by weight.
According to a second aspect of the invention
there is provided a smoking article comprising a rod
of smoking material and a wrapper having any of the
above features.
The term "duplex" as used in this
specification is intended to cover sheets which
comprise two Gr more webs wherein at least one web is
in the partially formed wet stage prior to drying when
the two or more webs are combined or superposed. Thus
the adhesion between the two layers is achieved by the
fibre bonding inherent in the papermaking process.
Furthermore, this method of formation introduces an
interaction between the two or more layers, which
interaction can have a surprising effect on the air
permeability of the final duplex sheet. Clearly the
component webs may be formed from different stocks
arising from separate headboxes or reservoirs on a
multi-wire machine, or at least one web may be
produced off-line and re-introduced as a finished
sheet to the wet stage of a second paper making
machine. In either method of manufacture the
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objectlve is to use the fibre structure to provide an
integral sheet formed of two or more layers which is
capable of being used as a wrapper for smoking
articles.
Whereas conventional papers are also
asymmetric in that the proportion of fibre to filler
may vary from one side of the sheet to the other, it
is possible with duplex papers to provide a radical
change and alteration in properties from one side to
the other rather than the gradual change of properties
associated with single wire sheets of conventional
form.
Thus it is possible using duplex papers to
provide a paper sheet having differing characteristics
on one side of the paper from those on the other.
Compared with the use of laminated material or
the use of two or more different sheets wrapped
together to form a wrapper, the diffi^ulties mentioned
above with laminating techniques and running two or
more wrappers on a cigarette making machine are of
course avoided. Additionally, by utilising a multiple
wire machine supplied with different stock to each
wire to form a single sheet of such different
characteristics across its section, there is observed
a synergism which affects the properties of the duplex
web not previously discovered or alluded to in the
prior art. We have discovered that air permeability
due to the inherent porous structure of the paper is
not a simple function of the flow through the two
component parts but can be very much reduced due to
the integrity of the surfaces. The same does not
occur when two separate wrappers are brought together
after the wet stage following completion of the paper
making process.
Table l shows air permeability data obtained
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with the Gurley system for duplex papers and the
component parts. In .hese and subsequ2nt tests the
component parts, i.e. inner and top layers or webs,
were acquired at the paper making machine by sampling
from each web without the two becoming joined
together. The sample was then finish treated as a
normal sheet.
The Gurley system of air permeability
measurement is suitable for assessment of cigarette
papers which have low permeabilities relative to usual
commercial standards. The method involves
measurement of the time ta~en to displace a fixed
volume of air through a defined area of paper under
the constant load of a weighted falling piston. The
apparatus is sold commercially by W & L E Gurley,
~ulton Street, Troy, New York 12181. The test is set
out in ISO 3687-1976. In the table, adjacent columns
do not correspond.
Table 1
Air Permeability Data (Gurley seconds)
_ _
Sample No Duplex Top Layer Inner Layer Double Wrap
_
3 30 000 11 4.5 13
23 375 10 5 14
6 17
11 10
6 760 000 65 670 5500
725075 57 550 6950
64 830 4950
523140
68
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The interaction between the two surfaces has
also been found to secure even lower levels of air
permeability than would be achieved with a double wrap
comprising each of the components of the duplex paper.
Clearly, this is a benefit for formulations where low
air permeability is an objective as in the case of
cigarettes where a low sidestream smoke may be
required.
Additionally it has been observed that the
limitations normally imposed on the manufacture of
individual webs by poor tensile strength, low basis
weight and poor appearance, no longer apply because
the duplex paper exhibits properties that are
determined by the composite system and these are
generally found to be superior to any individual
component. As a result it becomes possible to
consider duplex characteristics which would not be
achievable as a double wrap. Table 2 provides data on
tensile strength, basis weight and opacity of duplex
papers and its component parts. Opacity being
measured on a standard EEL machine (according to BS
4432), on which standard cigarette papers have
opacities of 60~ or more.
Table 2
Tensile Strength, Basis Weight and Opacity Data
. ___ . ...__
Tensile Strengt~ Basis Weight, Opacity
Sample g mm~l g m~2
No Dup Top Inner Dup Top Inner Dup Top Inner
3o
1 195 95 62 32.6 19;1 13.5 71.6 60.4 20.2
2 211 31 79 37.4 24.1 13.3 71.0 68.2 19.4
207 66 69 38.3 23.7 14.6 78.4 66.2 22.0
7 207 14 86 36.3 18.9 17.4 69.4 62.2 18.8
9 311 42 114 47 7 29.6 18.1 77.8 72 4 21.0
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In one application the duplex sheet has been
formed from two stocks, one of which provides the
characteristics of highly impermeable paper and the
other of which provides some of the characteristics of
conventional cigarette paper, particularly in relation
to appearance.
One particular embodiment of the present
invention provides a duplex paper for use in the
manufacture of cigarettes, which paper has been formed
from two or more stocks one of which has a composition
that provides the characteristics of a highly
impermeable paper and the other of which is stock
suited to the manufacture of chalk filled cigarette
papers.
There are many uses for wrappers of smoking
articles having unusual non-homogeneous cross-
sectional characteristics, but one of particular
interest is for use with the product of our co-pending
British application No 8901579.6 of 25 January 1989,
which forms the basis for European application No
90300750.8.
In application 8901579.6, a cigarette paper is
required which will produce a self-extinguishing
smoking article. This is, of course, contrary to the
normal requirement of traditional cigarettes which are
expected to smoulder readily and maintain combustion
between puffs. The purpose of this construction is to
achieve low and even negligible sidestream smoke
deliveries between puffs.
~ paper can be made which will readily self-
extinguish the cigarette but such papers are normally
of the Papirossi type having a high fibre density and
low opacity characteristic of impermeable paper
sheets.
Such highly impermeable papers are
unattractive for use on cigarettes since, although
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they may achieve the objectives set out in our co-
pending application, they do not have an appearance
which is acceptable to the smoker and, furthermore,
readily exhibit uneven burning and excessive charline
formation and show staining during smoking.
To overcome this disadvantage the highly
impermeable, low opacity paper could be overwrapped
with conventional cigarette paper. However, the
disadvantage of this proposal is that the overwrapping
must be done on the cigarette making machine or the
two wraps must be laminated thus suffering from the
disadvantages outlined above.
Double wrapping has been employed commercially
in the U.S.A. by Philip Morris on the Virginia
Superslims brand, but in this construction it results
in a total paper basis weight of 70 gm~2 compared to
conventional papers at about 25 gm~2. Thus to achieve
more conventional weights of paper the two components
of the double wrap must be exceptionally low basis
weight and may be low in strength which would
therefore be difficult and in some cases impossible to
make or use commercially as a single sheet.
In one embodiment of the present invention the
problem can be solved by forming a duplex paper in
~5 which a stock for highly impermeable low opacity paper
is used to produce a partially formed web which is
combined with a partially formed web made from stock
of a more conventional cigarette paper, the two
partially formed webs being combined before drying to
3 form a duplex sheet having differing characteristics
from one side of the sheet to the other.
By using such duplex papers in making
cigarettes, the conventional appearance can be placed
on the outside of the cigarette with a lower opacity
reverse side against the tobacco, thus providing the
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characteristics required for the product without
detracting from the appearance, and without staining
etc.
Furthermore, as an integral duplex sheet the
interaction between the two components increases
tensile strength and creates an opportunity to
manufacture low basis weight sheets with properties
that, as single sheets, would be unacceptable for
manufacturing reasons. Paper manufacturing
developments have produced a duplex cigarette paper
with a weight of 32 gm~2; this being comprised sf a
dense low permeability, low opacity layer of 15 gm~2
and a higher permeability, higher opacity chalk-filled
layer. The data for this paper.are given in table 3.
Conventional cigarette paper making methods will not
produce a paper with the same properties as this
duplex sheet. Further reductions in basis weight are
feasible with this system whilst still maintaining
acceptable appearance, strength etc.
Table 3
Data for 32 gm~2 Duplex Paper
Basis Weight CaC03 Air Perm Opacity
Sample gm~2 % Gurley(s)
No Dup Top Inner Top Dup Top Inner Dup Top Inner
.
4 32.0 18.2 14.8 27.9 13900 1 640 68 61 18
31.3 18.2 15.3 93000 1 1470 68 61 19
30.8 18.0 14.0 21050 1 67 60 18
_ _ _ 665C 2 _ 67 61 20
Additionally, the experience of manufacturing
duplex papers has shown that it has reduced thickness
compared with the sum of the thicknesses of the two
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layers from which it is formed, thus further
emphasising the integrity of the forming process.
Table 4 shows thickness data for a range of duplex
formulations.
Table 4
Thickness Data for Duplex Paper and Component Parts
(micrometres)
Sample NoDuplex Top Inner
1 0
1 49 38 22
3 57 49 25
8 65 46 34
It will be appreciated that there are many
other applications of duplex papers in cigarette
making. Unusual characteristics required for the
wrapper may be achieved without detriment to
appearance or handling in cigarette manufacture.
These unusual characteristics can be provided by the
inner face of the duplex wrapper whilst maintaining
the desired appearance with the outer surface.
The paper characteristics may be designed to
modify taste, burn rate, sidestream smoke delivery,
ignition proclivity or even to achieve changes in
appearance.
The construction can provide opportunities to
include paper additives or fillers with beneficial
effect such as improvements to the ideas contained in
the patent literature. For example, the outer surface
may include a disproportionately high level of calcium
carbonate of normal or enhanced specific surface area
such as is suggested in GB Patent 2191930A while the
inner surface provides control of air permeability,
strength and staining, and where this construction has
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as its objective reductions in sidestream smoke.
Further examples are achieved by the
replacement of calcium carbonate in the outer surface
with an alternative filler chosen from a list of those
which demonstrate sidestream reducing properties when
used as single sheets, conferring on them the benefits
of duplex manufacture that is strength, control of air
permeability, resistance to staining and enhanced
reduction of sidestream smoke. Suggested fillers are:
10magnesium hydroxide as detailed in US 4231377 and GB
2118986B; aluminium hydroxide, calcium hydroxide or
lithium hydroxide (US 4721120); gamma alumina (US
4108151) or those contained in GB 2191930, although
this list is by no means exhausti~e.
15Other wrapper modifications have been
suggested in the literature to improve taste and
reduce smoke deliveries as for example in US 4225636
and US 4505282 where a carbon inner liner is proposed.
A similar objective could be achieved with a duplex
wrapper where the external surface provides
conventional appearance and the internal surface
contains a suitable proportion of activated carbon.
The resulting wrapper might even be designed to
provide a suitable combustion source to meet the
requirements of one of the embodiments described in
co-pending UK patent application No 8901579.6.
The system might also be designed with a low
absorbing inner surface as a solution to yellow
spotting during storage of cigarettes without a need
3 for double wraps which has been proposed by at least
one commercial paper manufacturer.
A duplex wrapper for cigars may also be
devised as a means of replacing the binder and
overwrap currently used in the manufacture of the
majority of cigars. The advantage of a duplex
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construction is to provide scope in the formulation of
the two surfaces not achievable with conventional
paper made wrappers in order to enable the desired
appearance, burning properties and taste to be
achievedt
It will of course be appreciated that the
duplex papers discussed in this specification are
formed from stocks which are made up in accordance
with recognised paper making techniques and which can
contain, either separately or as chosen mixtures,
textile fibres (such as flax or hemp), hard wood
fibres, soft wood fibres and other fibres (such as
esparto).
The invention will now be illustrated by way
of some examples.
Example 1
This example refers to our co-pending patent
application No 8901579.6 for which a duplex cigarette
paper has been developed to provide control over free
smoulder and achieve a reduction in sidestream smoke
emissions. (A definition for sidestream smoke is
given in the 8901579.6 application).
Papers were initially developed to provide
rapid self-extinguishing and later modified with burn
promoters for reasons explained in the co-pending
application.
The requirement for low porosity, which
affects cigarette coal shape and propagation was
dictated by the need to trap condensable vapour phase
which normally emerges from behind the coal as
sidestream "smoke" and also to reduce the consumption
of tobacco between puffs, thereby reducing the
production of sidestream emissions. Initially this
need was met with a double wrap in which the inner
wrap provided low porosity and high density but was
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translucent and burn-t unevenly. The outer wrap was
normal cigarette paper and provided good appearance
and even burning.
The idea of a lightweight duplex paper was
pursued as a solution to the problems of manufacturing
double wrapped cigarettes, a desire for a low weight
of paper and a dislike of and lack of success with
adhesive laminations and coatings.
The duplex paper used predominantly with
examples quoted in co-pending application No 8901579.6
had the following specification:
Table 5
Duplex Paper Specification used for Co-pending
Application 8901579.6
Basis Weight, gm~2 Fibre Type
Duplex 37
Top 25 40% Pine 20% Birch
40% Eucalyptus
Inner 12 70% Pine 30% Birch
20 Calcium Carbonate, % 22
(Top Layer)
Air permeability, Gurley(s) 385000
Sample Code 0589987
Cigarettes were made with expanded tobacco
blend to a density of 143 Kgm~3 and incorporating the
fuel element described in the co-pending application.
These were compared in smoking test with commercial
cigarettes to establish mainstream and sidestream
3 total particulate matter (TPM) deliveries. The
results in Table 6 were obtained.
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Table 6
Type No Puffs Mainstream Sidestream Oven Dry
TPM TPM Density
mg cig~l mg min~l Kgm~3
Vantage x 6.3 11.4 1.3 142
Excel
(RJR- SD 0.5 1.9 o,og
10 USA)
n 30 10 10
Embassy x 9.0 9.4 2.32 234
Mild
(ITL- SD 0.4 0.9 0.12
15 UX)
n 24 7 8
Testx 13.8 6.6 0.55 143
Sample
SD 1.0 0.8 0.05
n 29 9 9
These results show the substantial reduction
in rate of sidestream production for the test
cigarette compared with a commercial low sidestream
product (Vantage) available from R J Reynolds of
U.S.A. and a typical low tar UK brand. The results
also show the significantly increased puff number
obtained from an equal or lower density and therefore
lower weight of tobacco. (These cigarettes had
3 similar circumferences and tobacco length).
Additionally the appearance of the cigarette
paper was consistent with commercial brands and there
: was no appreciable yellow spotting prior to smoking or
staining durins smoking.
35Ash characteristics were improved compared
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with ordinary low air permeability papers and further
improvements were observed with the use of ash
conditioning additives, for example potassium citrate
applied at levels up to 7% of paper weight.
Example 2
An early attempt at manufacturing a duplex
cigarette paper produced a relatively high
permeability chalk "free" inner layer and a lower
permeability chalk filled top layer. The pulps used
were a mixture of eucalyptus and flax. Two samples
were produced to achieve different levels of
permeability in the chalk filled layer. Paper details
are given in Table 7 below, the fibres in both webs of
both samples comprising 50% Flax 50% Eucalyptus.
Table 7
Duplex Paper 0189969A and B
Basis weight, gm~2 0189969A 0189969B
Duplex 43.6 42.3
Top 24.8 25.6
Inner 17.3 17.3
Air Permeability, Coresta Units
Duplex 10 8
Top 59 29
Inner 94 94
Calcium Carbonate, % Top Layer 34 36
Opacity, ~ (Duplex) 84.6 84.5
Coresta permeability is a standard measure
used in the tobacco industry for cigarette paper air
permeability. The apparatus involves a sample clamp
which exposes a 2 cm2 sample to a constant pressure of
1 kilo Pascal and provides a means of measuring the
flow rate through the sample. Results are quoted in
units of ml/min/cm2/K Pa.
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Cigarette samples were made for mainstream and
sidestream smoking tests to a specification which is
consistent with some UK low tar commercial cigarettes,
i.e. 59mm tobacco rod, 25 mm filter, 24.9 mm
circumference, 210 kg m~3 oven dry tobacco density,
and 45% tip ventilation.
In smoking tests these cigarettes were found
to free smoulder without the assistance of a puffing
source. They produced about 8 mg of total particulate
matter (TPM) from 10 puffs with a standard smoking
regime using a 35 ml puff volume over 2 seconds,
repeated every minute.
Sidestream smoke deliveries were measured as
TPM collected on a filter pad and as an aerosol
density index according to methods described in co-
pending patent application 8901579.6.
Table 8
Conventional Low
2~ Tar Cigarettes0189969A0189969B
Mainstream
TPM, mg cig~l 9.4 7.8 9.2
Puffs 9.0 10.3 10.1
Carbon Monoxide,
mg cig~l 14.4 18.0
Sidestream
TPM, mg min~l 2.32 1.3 1.4
Visible Sidestream 5.7 2.7 2.8
3 Index, (average value)
Reductions in the sidestream smoke in excess
of 40% were obtained with this construction whilst
maintaining a paper of good appearance and capable of
sustaining free smoulder without the use of burn
-18-
enhancing additives.
Example 3
In this example we have demonstrated a means
of achieving an alternative wrapper for a free
smouldering low sidestream cigarette which improves
upon the reductions in sidestream smoke delivery
obtained in example 2. In summary, we have taken the
knowledge gained in the development of papers and
product specifications for our co-pending patent
8901579.6 and with the use of burn promoters (already
well known to the industry) applied to the paper we
have been able to produce a free smouldering (self
sustaining coal) low sidestream cigarette with typical
UK cigarette dimensions, appearance and mainstream
smoke deliveries.
The duplex paper samples were selected on the
basis of previous test data and were treated with a
solution of potassium citrate to achieve the levels
shown in Table 9 below. Treatment was carried out by
surface contact between the top side of the duplex
paper and the liquid reservoir, followed by subsequent
drying and rewinding. The process could be replicated
through the usual on-line cigarette paper machine
soluble additive application facilities such as a size
press, and other soluble additives selected from the
range of cigarette paper additives known in the prior
art would be suitable.
The additive level was checked after
application and cigarettes were made with each of the
39 treated papers for mainstream and sidestream smoke
delivery measurements. Details of the cigarette
papers are given in Table 9.
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Table 9
Cigarette Paper Details
0389978B 0989923
Basis weight, gm~2
Duplex 37.1 37.8
Top Layer 25.4 26.4
Inner Layer 14.5 11.3
Fibres Top Layer 43/17/40% 40/20/40
(Pine/Birch/Eucalyptus)
Inner Layer 70/30% 70/30%
(Pine/Birch)
Air Permeability, Gurley(s)
Duplex 240,000 27,600
Top Layer 4 10
Inner Layer 1480 6
Calcium Carbonate, % Top Layer 23.2 33.5
Opacity, % Duplex 74 80
20 Tensile, g mm~l Duplex - 168
% Potassium Citrate 6.9 5.3
The cigaxette dimensions were typical of UK
commercial brands but tobacco density was reduced to
25110 kg m~3 using cut tobacco expanded by at least 75~
of its bulk volume using a commercially available
tobacco expansion process~ The precise level of
expansion or mixture of expanded and non-expanded
tobacco is a matter for determination in order to
achieve an acceptable balance of cigarette draw
resistance, tobacco rod firmness and combustion rate.
The cigarette construction was as follows: 59
n~ tobacco rod, 25 mm filter, 24.8 mm circumference,
110 kg m~3 oven dry density, 50% tip ventilation, and
100~ of highly expanded cut tobacco blend.
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Smoking tests were carried out according to
standard procedures to assess mainstream deliveries
and sidestream measurements were confined to an
assessment of the aerosol density using the "visible
index" method described in our co-pending application
8901579.6. The following data was obtained:
Table 10
:
Conventional Low
Tar Cigarettes 0389978B 09899923
Mainstream
TPM, mg cig-1 9.4 10.2 8~8
Puffs 9.0 7.0 6.8
Carbon Monoxide,
mg cig~l - 13.0 11.9
Static burn time,
s mm~l 12 11.9 10.3
Sidestream
20 Visible Index 5.7 o.5 0.5
(average value)
These results demonstrate very substantial
improvements in sidestream reduction compared wiih the
previous example and are achieved with a paper that
has good visual and burning characteristics and is
substantially free of unsightly staining. Furthermore
these products will free smoulder without the need for
an additional fuel source and permit substantial
reductions in tobacco weight.
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