EP0475580A1

EP0475580A1 - Improvements to smoking articles

Info

Publication number: EP0475580A1
Application number: EP91307224A
Authority: EP
Inventors: Christopher George Drewett; Brian Chester Chard; Colin Dennis Luton; Brian William Attwood
Original assignee: Imperial Tobacco Company of Great Britain and Ireland Ltd; Imperial Tobacco Ltd Great Britain
Current assignee: Imperial Tobacco Company of Great Britain and Ireland Ltd; Imperial Tobacco Group Ltd
Priority date: 1990-08-09
Filing date: 1991-08-06
Publication date: 1992-03-18
Also published as: FI913763A0; GB9017451D0; FI913763A

Abstract

There is disclosed a wrapper for a smoking article, the wrapper comprising a single paper sheet. The stock has at least two plies, each formed from a paper stock. The stock for one of the plies is applied to the other components of the sheet without said one stock forming a discrete web. Different stocks can be used to make the plies so as to impart different qualities.

Description

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 a smoulder rates, air permeability, ash quality, appearance and taste.
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 nature 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 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 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 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 400°C. The specification also proposes manufacturing 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 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 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 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 advantages of a multiple layer sheet whilst at the same time overcoming 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 manufacture cigarettes with two paper wrappers run simultaneously on the cigarette making machine. Furthermore, it is desired to avoid the disadvantages of laminating adhesives.
Various solutions have been put forward in our co-pending European Application No 90305610.9, namely the provision of a wrapper for smoking articles, which wrapper is formed from two or more discrete webs, which 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 and all the webs are in the wet stage of formation prior to drying.
According to the present invention there is provided a wrapper for a smoking article, which wrapper comprises a single paper sheet having two or more plies, each ply being formed from a paper stock, the stocks being applied to each other whilst at least one of the stocks if unformed.
The term 'unformed' means that the stock has not been allowed to form a discrete web.
Preferably the plies are formed from different stocks (stock being the ingredients of the headbox or reservoir) and two plies are provided.
In preferred arrangements one stock is in the form of a discrete web when the other stock is applied in an unformed state and the discrete web is still in its wet stage of formation or both stocks are applied to each other in an unformed state by means of a two-channel headbox.
Conveniently, said other component or components are still 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 10 Coresta or less. In other preferred embodiments there are two plies, one ply being a substantially unfilled ply having a low basis weight. Conveniently said weight is 20 gm⁻² or less and said one ply prevents or substantially reduces staining or said one ply contains activated carbon.
Further preferred features are that the other ply is a filled ply conferring a coriventional appearance on the wrapper, for example the opacity of the wrapper is 60% or more. It may be that the filler of said other ply comprises predetermined amounts of calcium carbonate (up to 50% by weight) or the filler of said other ply comprises predetermined amounts of selected fillers, e.g. Mg(OH)₂, Al₂O³, LiOH and high surface area CaCO₃.
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 plies may contain a burn retardant such as ammonium phosphate or a burn enhancer such as a soluble salt of a group I or group II metal, maybe 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.
According to a third aspect of this invention there is provided a method of making a wrapper for a smoking article, which wrapper comprises a single paper sheet having two or more plies each ply being formed from a paper stock said method comprising the step of applying the stock for at least one of said plies while it is unformed.
The term "multiplex" as used in this specification is intended to cover sheets which comprise two or more plies or layers wherein either at least one ply is in the partially formed wet stage prior to drying when the two or more plies are combined or superposed or the stocks are applied to each other whilst at least one of the stocks is unformed in other words one of the stocks is applied to the remainder without said one stock forming a discrete web. Thus adhesion between the plies is achieved by the fibre bonding inherent in the papermaking process. Furthermore, these methods of formation introduce an interaction between the two or more plies, which interaction can have a surprising effect on the air permeability of the final multiplex sheet. Clearly the component plies may be formed from different stocks arising from separate headboxes or reservoirs on a single wire or multi-wire machine.
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 multiplex 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 multiplex 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 difficulties mentioned above with laminating techniques and running two or more wrappers on a cigarette making machine are of course avoided. Additionally, there is observed a synergism which affects the properties of the multiplex paper not previously discovered or alluded to in the prior art. It has been 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 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 multiplex 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 multiplex paper exhibits properties that are determined by the composite system and these are generally found to be superior to any individual component.
In one application the multiplex 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 addition 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.
A 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 they may achieve the objectives set out in our copending 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 multiplex paper in which stock for highly impermeable low opacity paper is applied to a partially formed web made from stock of a more conventional cigarette paper or vice-versa. The multiplexsheet having differing characteristics from one side of the sheet to the other.
By using such multiplex 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 characteristics required for the product without detracting from the appearance, and without staining etc.
Furthermore, as an integral multiplex 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.
It will be appreciated that there are many other applications of multiplex 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 multiplex 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 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: magnesium 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 exhaustive.
Other 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 can be achieved with a multiplex 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 for double wraps which has been proposed by at least one commercial paper manufacturer.
A multiplex 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 multiplex 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 achieved.
It will of course be appreciated that the multiplex 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).
Embodiments of the present invention will now be illustrated in more detail, reference being made to the following diagrammatic drawings in which:

Figure 1a to 1f show schematic side views of examples of prior art paper making arrangements;
Figure 2 shows a schematic side view of a paper making arrangement according to the present invention;
Figure 3 shows a schematic side view of another paper making arrangement according to the present invention;
Figure 4 shows a schematic side view of another paper making arrangement according to the present invention;
Figure 5 shows a schematic side view of another paper making arrangement according to the present invention;
Figure 6 shows a schematic side view of another paper making arrangement according to the present invention;
Figure 7 shows a schematic side view of another paper making arrangement according to the present invention;
Figure 8 shows a schematic side view of another paper making arrangement according to the present invention; and
Figure 9 shows a schematic side view of another paper making arrangement according to the present invention.

Figure 1a shows a basic arrangement for forming a two ply multiplex cigarette paper according to our co-pending European Application No 90305610.9. A first headbox 1 containing a first stock forms a first web on a first Fourdrinier wire 2. A second headbox 3 containing a second stock forms a second web on a second Fourdrinier wire 4. The two webs are brought together while at least one of the webs is still in its wet stage prior to drying.
Figure 1b shows an extension of the Figure 1a arrangement in which a third headbox 5 containing a third stock forms a third web on a third Fourdrinier wire 6. The second and third webs are combined whilst say web 3 is still in its wet stage and this pair of webs is combined with the first web to form a three ply multiplex cigarette paper.
Figure 1c shows a series of rotary formers 7, 8, 9 and associated vats 10, 11, 12 containing the stocks. Each former 7, 8, 9 produces a partially formed web and the webs are combined on wire 13.
Figure 1d is similar to Figure 1c in that there are rotary formers 7, 8, 9 but each former is associated with a pressure former 14, 15, 16 which forms web on the rotary former.
In Figure 1e a Fourdrinier wire 17 and headbox 18 are used in conjunction with a rotary former 19, vat 20 and wire 21 to produce a two ply multiplex cigarette paper by combining two discrete webs whilst one web at least is still in its wet stage of formation prirr to drying.
In Figure 1f there is shown a first Fourdrinier wire 22 and headbox 23 for forming a first discrete web and a second Fourdrinier wire 24 and headbox 25 for forming a second discrete web. A transfer mechanism 26 is provided to divert the first web so as to be combined with the second web between rollers 27 to form a two ply multiplex cigarette paper 28.
It will be appreciated that many combinations of the above and other arrangements would be suitable to form the known cigarette papers. However, all these envisaged techniques bring together discrete webs at least one of which is still in its wet stage of formation. None of the stocks are therefore applied whilst unformed.
One method of producing a cigarette paper according to the present invention is shown in Figure 2. There is shown a single Fourdrinier wire 30 and a first headbox 31 containing a first stock. A partially formed web is formed on the wire 30 and passes beneath a secondary headbox 32 which applies a layer of second stock directly onto the first web. A two ply multiplex cigarette paper is thus formed without actually forming a discrete second web. A liquid removal section 33 is provided so as that the first web reached the secondary headbox 32 either in a partially formed wet state or in a dry state. In addition a further liquid removal section 33 is provided to treat the combined sheet.
The Figure 3 arrangement has the headbox 31 and Fourdrinier 30 wire of the Figure 2 arrangement but for the second stock a flow box 35 employing the Coanda Effect is used. The second stock is gently applied onto the partially formed first ply without disturbing the formation of the first ply. A third flow box 36 similar to flow box 35 is shown and of course other flow boxes could also be added if more than three plies were required. Again water removal stations 33, 34 are provided at locations dependent on the desired paper properties.
By using the flow boxes 35 and 36 it has been found that the consistency of each ply may be relatively low and still the previous ply is not disturbed during application of the subsequent ply. This means that the equipment is well suited to the production of lightweight multiplex papers.
Figure 4 shows another suitable arrangement in which a sloping forming wire 37 is used in conjunction with forming boxes 38, 39 over which a multi-layer headbox 40 is fitted. The equipment is useful for producing non woven materials and can operate at low stock consistencies and at modest speeds. The second stock is applied to the first partially formed web but clearly does not form a discrete web before the application to the first web.
In Figure 5 a rotary forming roll 41 is used in conjunction with a two component pressure former 42. Again the second stock is applied to the partially formed first web without the stage of forming a discrete second web.
Figure 6 is similar in principal to the arrangement in Figure 5 except that a standard forming wire 43 is employed instead of the rotary forming roll 41.
The Figure 7 arrangement is a modification of the Figure 6 arrangement except that separate pressure formers 44, 45, 46 are used in series. Of course any number of pressure formers can be used.
In Figure 8 there is an arrangement very similar to Figure 2 in that there is provided a Fourdrinier wire 30 and first and second headboxes 31, 32. Additionally there is an on-top forming arrangement comprising a second wire 48 and an upward water removal arrangement 49.
Figure 9 shows apparatus comprising a twin wire former comprising two wires 50, 51 and a multichannel headbox 52. In this method no partially formed webs are produced, the separate stocks being applied to each other simultaneously and then the partially formed sheet being retained between the two wires 50, 51. The whole paper sheet is thus formed in one action whilst still retaining the properties of the separate plies. The apparatus has been found to work best at very high speeds.

Claims

A wrapper for a smoking article, which wrapper comprises a single paper sheet having two or more plies, each ply being formed from a paper stock, the stocks being applied to each other whilst at least one of the stocks is unformed.
A wrapper as claimed in claim 1 wherein all the stocks are different.
A wrapper as claimed in claim 1 or 2 wherein the sheet has two plies.
A wrapper as claimed in claim 3 wherein one stock is in the form of a discrete web when the other stock is applied in an unformed state.
A wrapper as claimed in claim 4 wherein the discrete web is still in its wet stage of formation.
A wrapper as claimed in claim 3 wherein both stocks are applied to each other in an unformed state by means of a two-channel headbox.
A wrapper as claimed in any of claims 3 to 6 wherein the wrapper is of low air permeability.
A wrapper as claimed in claim 7 wherein said permeability is 10 Coresta or less.
A wrapper as claimed in any one of claims 3 to 8 wherein one stock forms a substantially unfilled ply having a low basis weight.
A wrapper as claimed in claim 9 wherein said weight is 20 gm⁻² or less.
A wrapper as claimed in claim 9 or claim 10 wherein said one ply prevents or substantially reduces staining during smoking and yellow spotting during storage.
A wrapper as claimed in any one of claims 9 to 11 wherein said one ply contains activated carbon.
A wrapper as claimed in any one of claims 9 to 12 wherein the other ply is a filled web conferring a conventional appearance on the wrapper.
A wrapper as claimed in claim 13 wherein the opacity of the wrapper is 60% or more.
A wrapper as claimed in claim 13 or claim 14 wherein the filler of said other ply comprises predetermined amounts of calcium carbonate.
A wrapper as claimed in claim 15 wherein said other ply comprises up to 50% weight of calcium carbonate.
A wrapper as claimed in any one of claims 13 to 16 wherein the filler of said other ply comprises predetermined amounts of selected fillers, e.g. Mg(OH)₂, Al₂O₃, LiOH and high surface area CaCO₃.
A wrapper as claimed in any one of claims 1 to 17 wherein the total basis weight of the wrapper is less than 50 gm⁻².
A wrapper as claimed in claim 18 wherein the total basis weight of the wrapper is less than 40 gm⁻².
A wrapper as claimed in claim 19 wherein the total basis weight of the wrapper is less than 35 gm⁻².
A wrapper as claimed in any one of claims 1 to 20 wherein one or more of the plies contains a burn retardant and/or a burn enhancer.
A wrapper as claimed in claim 21 wherein the burn retardant is ammonium phosphate.
A wrapper as claimed in claim 21 or claim 22 wherein the burn enhancer is less than 10% weight of a soluble salt of a group I or group II metal.
A smoking article comprising a rod of smoking material and a wrapper as claimed in any one of claims 1 to 23.
A smoking article as claimed in claim 24 wherein a filter is provided, which filter may or may not be ventilated.
A smoking article as claimed in claim 24 or claim 25 wherein the rod of smoking material contains between 0 and 100% expanded tobacco, the oven dry density of the smoking material in the article is between 80 and 260 Kgm⁻³, the circumference of the rod is between 10 and 30 mm and the length of the rod is between 25 and 100 mm.
A smoking article as claimed in claim 24 or claim 25 wherein the smoking article is adapted to extinguish the smoking material between puffs, and a combustion source is incorporated in the smoking article and is adapted to reignite the smoking material during puffs thereby causing the smoking material to combust, the smoking material being contained in said wrapper.
A smoking article as claimed in claim 24 or claim 25 wherein the wrapper permeability is about 10 Coresta and the basis weight is about 43 gm⁻², the tobacco rod is 59 mm long and has a circumference of 24.9 mm and a tobacco density of 210 Kgm⁻³, and a filter having a 25 mm length and giving 45% ventilation is provided.
A smoking article as claimed in claim 24 or claim 25 wherein the wrapper air permeability is 27600 Gurley seconds or more and the basis weight is about 37 gm⁻², the tobacco is 100% expanded and the density is 110 Kgm⁻³, the rod is 59 mm long and has a 24.8 mm circumference, a filter having a 25 mm length and giving 50% ventilation is provided and the wrapper also contains up to 10% weight of potassium citrate.
A method of making a wrapper for a smoking article, which wrapper comprises a single paper sheet having two or more plies each ply being formed from a paper stock said method comprising the step of applying the stock for at least one of said plies whilst it is unformed.
A method as claimed in claim 30 wherein said paper has two plies and said other stock is in the form of a discrete web onto which web said one stock is applied.
A method as claimed in claim 31 wherein the discrete web is still in its wet stage of formation.
A method as claimed in claims 30 to 32 wherein different stocks are used for the respective plies.
A method as claimed in claim 30 wherein the sheet has two or more plies and the stocks are applied to each other using a multi-channel headbox.