Smoking article

Abstract: The present invention relates to a smoking article, preferably in cigarette form, which produces an aerosol that resembles tobacco smoke. The article preferably comprises a short combustible fuel element (10) having a density greater than 0.5 g/cc, a separate substrate (12) bearing an aerosol forming material, a heat conducting member (14) recessed from the lighting end of the fuel element, which preferably encloses the substrate, a resilient insulating jacket (72) encircling at least a portion of the fuel element (10), and an optional tobacco jacket (88) encircling at least a portion of the aerosol forming material.

Description: The present invention relates to a smoking article as described in the preamble of claim 1. Such a smoking article is known from US-A-4 340 072 which describes a proposed cigarette type smoking article with a rod-like fuel element having a central axial passage, an aerosol generating means defined by a chamber and a short filter tip all of which are arranged one behind another. The overall length of the smoking article is 70 mm, and its diameter is 7 mm. The fuel element is a moulding or extrusion of reconstituted tobacco and/or tobacco substitute, e. g. of a mixture of carbon and a binder (SCMC), and the front end of its axial passage may be closed by a plug made from the same material and serving the purpose of preventing a lighting flame from entering the central axial passage of the fuel element. The chamber of the aerosol generating means contains inhalant material which, when contacted by hot gases produced by the burning fuel element and sucked through its axial passage and through the chamber of the aerosol generating means, purportedly forms and aerosol for inhalation by the smoker. According to the drawings of US-A-4 340 072 the length of the rod-like fuel element is about 73 % of the overall length of the cigarette type smoking article and therefore about 51 mm. The rod-like fuel element may have a conventional cigarette paper wrapped around it. EP-A-0 117 355 describes a proposed cigarette type smoking article having a carbon heat source with an axial passageway and a separate flavor generator. The heat source (page 2, line 23 to page 7, line 14) is formed by pyrolyzing a preformed, tube-shaped ligno-cellulosic material of e. g. 90 mm or 65 mm length (see Comparative Example 1 and Example 4, respectively) under specified conditions, followed by at least one additional specified process step. The purported flavor generator (page 8, lines 8 to 27) comprises a substrate material, which may be tobacco, alumina, etc., adjacent the mouth end, which is impregnated with or inherently contains at least one thermally releasable flavorant. The flavor generator also may comprise a flavored, foamed core inside the heat source. A conventional filter may be placed after the flavor generator. The purported formation of an aerosol during use is described from page 8, line 28 to page 9, line 8. During pyrolysis the tube-shaped ligno-cellulosic material experiences a maximum dimensional shrinkage of 37,5 % (see page 12, lines 3 and 4) so that from a tube-shaped ligno-cellulosic material with a length of 65 mm a carbon heat source with a length of more than 40 mm is obtained. Despite decades of interest and effort, there is still no smoking article on the market which provides the benefits and advantages associated with conventional cigarette smoking, without delivering considerable quantities of incomplete combustion and pyrolysis products generated by a conventional cigarette. It is the object of the present invention to provide a smoking article of the type having a fuel element and a separate aerosol generating means which is more efficient during smoking. According to subject invention this object is achieved by the characterizing features of claim 1. In such a smoking article the layer of heat insulating material acts as an insulating member for the fuel element and/or helps to simulate the feel of a conventional cigarette, whereas the inventive paper wrapper restricts air flow to the burning fuel element, thereby helping to control the temperature at which the fuel element burns and the subsequent heat transfer to the aerosol generating means. US-A-2 890 704 discloses a cigarette having a tobacco rod encircled by a wrapper in the form of a non-combustible glass fiber sheet which serves the purpose of retaining the ash produced by the tobacco rod during smoking of the cigarette. A preferred embodiment of the inventon comprises a smoking article, preferably in cigarette form, which utilizes a small, high density combustible fuel element in conjunction with a physically separate aerosol generating means which includes one or more aerosol forming materials. Preferably, the aerosol generating means is in a conductive heat exchange relationship with the fuel element and/or at least a portion of the fuel element is circumscribed by a resilient insulating jacket to reduce radial heat loss. Upon lighting the fuel element generates heat which is used to volatilize the aerosol forming materials in the aerosol generating means. These volatile materials are then drawn toward the mouth end, especially during puffing, and into the user's mouth, akin to the smoke of a conventional cigarette. Smoking articles of the invention are capable of producing substantial quantities of aerosol, both initially and over the useful life of the product, and are capable of providing the user with the sensations and benefits of cigarette smoking. The aerosol produced by the aerosol generating means is produced without significant thermal degradation and is advantageously delivered to the user with substantially reduced amounts of pyrolysis and incomplete combustion products than are normally delivered by a conventional cigarette. The small fuel element utilized in the invention is less than about 30 mm in length, preferably less than about 20 mm in length, and has a density of at least about 0.5 g/cc, more preferably of at least about 0.7 g/cc, as measured, e.g., by mercury displacement. Suitable fuel elements may be molded or extruded from comminuted or reconstituted tobacco and/or a tobacco substitute, and preferably contain combustible carbon. Preferred fuel elements also are provided with one or more longitudinal passageways, more preferably from 5 to 9 passageways or more, which help to control the transfer of heat from the burning fuel element to the aerosol forming materials in the aerosol generating means. Advantageously, the aerosol generating means includes a substrate or carrier, preferably of a heat stable material, bearing one or more aerosol forming materials. In addition, at least a part of the fuel element is provided with a peripheral insulating member, such as a jacket of insulating fibers, the jacket preferably being of resilient, non-burning material at least 0.5 mm thick. This member reduces radial heat loss and assists in retaining and directing heat from the fuel element toward the aerosol generating means and in reducing the fire-causing property of the fuel. The insulating member circumscribes at least part of the fuel element, and advantageously at least part of the aerosol generating means, which helps simulate the feel of a conventional cigarette. The materials used to insulate the fuel element and the aerosol generating means may be the same or different. Because the fuel element is relatively short, the hot, burning fire cone is always close to the aerosol generating means, which maximizes heat transfer thereto and the resultant production of aerosol, especially in embodiments which are provided with a multiple passageway fuel element, and/or an insulating member. A relatively high density fuel material is used to help insure that the small fuel element will burn long enough to simulate the burning time of a conventional cigarette and that it will provide sufficient energy to generate the required amounts of aerosol. Because the aerosol forming substance is physically separate from the fuel element, it is exposed to substantially lower temperatures than are present in the burning fire cone, thereby minimizing the possibility of thermal degradation of the aerosol former. The smoking article of the present invention normally is provided with a mouthend piece including means, such as a longitudinal passage, for delivering the volatile material produced by the aerosol generating means to the user. Alternatively, the smoking article may be produced without a built-in mouthend piece including aerosol delivery means, for use with a separate, disposable or reusable mouthend piece. Smoking articles of the present invention normally utilize substantially less fuel on a volume basis, and preferably on a weight basis, than conventional cigarettes to produce acceptable aerosol levels. Moreover, the aerosol delivered to the user normally is lower in pyrolysis and incomplete combustion products, due to the undegraded aerosol from the aerosol generating means and because the short, high density fuel element, especially in embodiments having a plurality of longitudinal passageways, produces substantially reduced amounts of pyrolysis and/or incomplete combustion products in comparison to a conventional cigarette, even when the fuel element comprises tobacco or other cellulosic material. As used herein, and only for the purposes of this application, "aerosol" is defined to include vapors, gases, particles, and the like, both visible and invisible, and especially those components perceived by the user to be "smoke-like," generated by action of the heat from the burning fuel element upon substances contained within the aerosol generating means, or elsewhere in the article. As so defined, the term "aerosol" also includes volatile flavoring agents and/or pharmacologically or physiologically active agents, irrespective of whether they produce a visible aerosol. As used herein, the term "conductive heat exchange relationship" is defined as a physical arrangement of the aerosol generating means and the fuel element whereby heat is transferred by conduction from the burning fuel element to the aerosol generating means substantially throughout the burning period of the fuel element. Conductive heat exchange relationships can be achieved by locating the aerosol generating means in contact with the fuel element and in close proximity to the burning portion of the fuel element. As used herein, the term "insulating member" applies to all materials which act primarily as insulators. Preferably, these materials do not burn during use, but they may include slow burning carbons and like materials, and especially materials which fuse during use, such as low temperature grades of glass fibers. Suitable insulators have a thermal conductivity in g-cal/(sec) (cm²)(°C/cm), of less than about 0.05, preferably less than about 0.02, most preferably less than about 0.005. See, Hackh's Chemical Dictionary , 34 (4th ed., 1969) and Lange's Handbook of Chemistry , 10, 272-274 (11th ed., 1973). According to the invention it is proposed to use a fuel element which is less than about 30 mm in length. Advantageously, the fuel element has a density of at least about 0,5 g/cm³. It is advantageous to use a fuel element which is provided with a plurality of longitudinal passageways. Most preferably, the fuel element is less than about 20 mm in length and has a density of at least about 0,7 g/cm³. Preferably, the layer of heat insulating material is a resilient, non-burning member at least 0,5 mm thick. In a preferred embodiment the insulating layer fuses during use. It is suggested to design the article such that a resilient insulating member encircles at least a portion of the aerosol generating means. Preferably, the insulating member is a resilient non-burning material at least about 1 mm thick. In preferred embodiments the insulating member comprises ceramic or glass fibers. More advantageously, the fuel element has a density of at least 0,5 g/cm³ and is less than about 30 mm in length and at least a portion of the fuel element is circumscribed by a resilient insulating material at least about 0,5 mm thick. Preferably, the insulating material has a softening temperature of about 650°C or less. It is advisable to use a resilient material which fuses during use of the smoking article and is at least about 1 mm thick. Also in this embodiment it is advisable to have a resilient insulating member which circumscribes at least a portion of the aerosol generating means. In preferred embodiments at least a part of the aerosol generating means is encircled by a tobacco containing material. Preferably, a fuel element is used which comprises primarily carbon as such and has a density greater than about 0,7 g/cm³. Also for these embodiments it is advantageous to have a fuel element which is less than about 20 mm in length and is provided with a plurality of longitudinal passageways. Further advantageous features are subject of the enclosed claims 2 to 25. Preferred embodiments of the smoking article according to the present invention are described in greater detail in the accompanying drawings and in the detailed description of the invention which follow. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 through 4 are longitudinal sectional views of various embodiments of the invention; Fig. 1A is a sectional view of the embodiment of Fig. 1, taken along lines 1A-1A in Fig. 1; Figures 2A, 2B, 2C, 3A, and 4A are end views showing various fuel element passageway configurations suitable for use in embodiments of the invention; Fig. 3B is an enlarged rear end view of the metallic container employed in the embodiment of Fig. 3; and Fig. 4B is a longitudinal sectional view of a preferred fuel element passageway configuration suitable for use in embodiments of the invention. DETAILED DESCRIPTION OF THE INVENTION The embodiment of the invention illustrated in Fig. 1, which preferably has the overall dimensions of a conventional cigarette, includes a short combustible fuel element 10, an abutting aerosol generating means 12, and a paper tube 14, which forms the mouthend 15 of the article. In this embodiment, the fuel element 10 is provided with three longitudinally extending holes 16. The aerosol generating means 12 includes a porous carbon mass 13 which is provided with one or more passages 17 and is impregnated with one or more aerosol forming materials, such as triethylene glycol, propylene glycol, glycerin, or mixtures thereof. The paper tube 14 surrounds the aerosol generating means 12 and a part of fuel element 10. The tube 14 also forms an aerosol delivery passage 18 between the aerosol generating means 12 and mouth end 15 of the article. The article illustrated in Fig. 1 also includes an optional mass or plug of tobacco 20 to contribute flavor to the aerosol. This tobacco charge 20 may be placed at the mouth end of carbon mass 13, as shown in Fig. 1, or it may be placed in passage 18 at a location spaced from aerosol generator 12. For appearance sake, the article may include an optional low efficiency cellulose acetate filter 22, positioned at or near the mouth end 15. The embodiments shown in Figures 1 to 4 include a resilient insulating jacket which encircles or circumscribes the fuel element to insulate and help concentrate the heat in the fuel element. These embodiments also help to reduce any fire causing potential of the burning fire cone and, in some cases, help simulate the feel of a conventional cigarette. In the embodiment of Fig. 1, the fuel element 10 is circumscribed by a resilient jacket 72 about 0,5 mm thick, as shown in Fig. 1A. This jacket is formed of insulating fibers, such as ceramic (e. g., glass) fibers or nonburning carbon or graphite fibers. In the embodiment shown in Fig. 1 the aerosol generating means 12 has a single, axial hole 17. In the embodiment of Figure 2, the resilient, glass fiber insulating jacket 72 surrounds the periphery of both fuel element 10 and aerosol generating means 12 and is preferably a low temperature material which fuses during use. This jacket 72 is overwrapped with a non-porous paper 73, such as P 878-5 obtained from Kimberly-Clark. In this embodiment, the fuel element is about 15 to 20 mm long and is preferably provided with three or more holes 16 to increase air flow through the fuel. Three suitable passageway arrangements are illustrated in Figures 2A, 2B, and 2C. In this embodiment, the aerosol generating means 12 comprises a metallic container 74 which encloses a granular substrate 38 and/or densified tobacco 76, one or both of which include an aerosol forming material. As illustrated, the open end 75 of container 74 overlaps the rear 3 to 5 mm portion of fuel element 10. Alternatively, the open end 75 may abut the rear end of fuel element 10. The opposite end or container 74 is crimped to form wall 78, which is provided with a plurality of passages 80 to permit passage of gases, tobacco flavors, and/or the aerosol forming material into aerosol delivery passage 18. Plastic tube 44 abuts or preferably overlaps walled end 78 of metallic container 74 and is surrounded by a section of resilient, high density cellulose acetate tow 42. A layer of glue 82, or other material, may be applied to the fuel end of tow 42 to seal the tow and block air flow therethrough. A low efficiency filter plug 45 is provided at the mouth end of the article, and tow 42 and filter plug 45 are preferably overwrapped with a conventional plug wrap paper 85. Another layer of cigarette paper 86 may be used to join the rear portion of the insulating jacket 72 and the tow/filter section. In a modified version or the embodiment of Figure 2, the insulating jacket may also be used in lieu of the cellulose acetate tow 42, so that the jacket extends from the lighting end to the filter plug 45. In embodiments of this type, a layer of glue is preferably applied to the annular section of the filter plug which abuts the end of the insulating jacket, or a short annular section of tow is placed between the insulating jacket and the filter piece, with glue applied at either end. Figure 3 illustrates an embodiment in which a 10 to 15 mm long fuel element 10 is overwrapped with an insulating jacket 72 of glass fibers and the aerosol generating means is circumscribed by a jacket of tobacco 88. The glass fibers used on this embodiment preferably have a softening temperature below about 650°C, such as experimental fibers 6432 and 6437 obtained from Owens-Corning, Toledo, Ohio, so that they will fuse during use. The glass fiber and tobacco jackets are each wrapped with a plug wrap 85, such as Ecusta 646, and are joined by an overwrap of cigarette paper 89, such as 780-63-5 or P 878-16-2, obtained from Kimberly-Clark. In this embodiment, the metallic capsule 90 overlaps the rear 3 to 4 mm of the fuel element so that it is spaced about 6 to 12 mm from the lighting end, and the rear portion of the capsule 90 is crimped into a lobe shape, as shown in Figure 3B. A passage 91 is provided at the mouth end of the capsule, in the center of the capsule. Four additional passages 92 are provided at the transition points between the crimped and uncrimped portion of the capsule. Alternatively, the rear portion of the capsule may have a rectangular or square cross section in lieu of the lobes, or a simple tubular capsule with a crimped mouth end may be employed, with or without peripheral passages 92. At the mouth end of tobacco jacket 88 is a mouthend piece 40 including an annular section of cellulose acetate tow 42, a plastic tube 44, a low efficiency filter piece 45, and layers of cigarette paper 85 and 89. The mouth end piece 40 is joined to the jacketed fuel/capsule end by an overwrapping layer of tipping paper 86. As illustrated, the capsule end of plastic tube 44 is spaced from the capsule 90. Thus, the hot vapors flowing through passages 92 pass through tobacco jacket 88, where volatile components in the tobacco are vaporized or extracted, and then into passage 18 where the tobacco jacket abuts the cellulose acetate tow 42. In embodiments of this type having low density fuel insulating jackets 72, some air and gases pass through jacket 72 and into tobacco jacket 88. Thus, the peripheral passage 92 in the capsule may not be needed to extract tobacco flavor from the tobacco jacket 88. In the embodiment or Figure 4, the jacket 94 comprises tobacco or an admixture of tobacco and insulating fibers, such as glass fibers. As shown, the tobacco jacket 94 extends just beyond the mouth end of metallic container 96. Alternatively, it may extend over the entire length of the article, up to the mouth end filter piece. In embodiments of this type, container 96 is preferably provided with one or more longitudinal slots 99 on its periphery (preferably two slots 180° apart) so that vapors from the aerosol generator pass through the annular section of tobacco which surrounds the aerosol generator to extract tobacco flavors before entering passage 18. As illustrated, the tobacco at the fuel element end of jacket 94 is compressed. This aids in reducing air flow through the tobacco, thereby reducing the burn potential thereof. In addition, the container 96 aids in extinguishing the tobacco by acting as a heat sink. This heat sink effect helps quench any burning of the tobacco surrounding the capsule, and it also helps to evenly distribute heat to the tobacco around the aerosol generating means, thereby aiding in the release of tobacco flavor components. In addition, it may be desirable to treat the portion of the cigarette paper overwrap 85, 89 near the rear end of the fuel with a material, such as sodium silicate, to help extinguish the tobacco, so that it will not burn significantly beyond the exposed portion of the fuel element. Alternatively, the tobacco itself may be treated with a burn modifier to prevent burning of the tobacco which surrounds the aerosol generator. Upon lighting any of the aforesaid embodiments, the fuel element burns, generating the heat used to volatilize the aerosol forming material or materials present in the aerosol generating means. These volatile materials are then drawn toward the mouthend, especially during puffing, and into the user's mouth, akin to the smoke of a conventional cigarette. Because the fuel element is relatively short, the hot, burning fire cone is always close to the aerosol generating body, which maximizes heat transfer to the aerosol generating means and any optional tobacco charges, and the resultant production of aerosol and optional tobacco flavor, especially when the preferred heat conducting member is used. Because the fuel element is short, there is never a long section of nonburning fuel to act as a heat sink, as was common in previous thermal aerosol articles. The small fuel source also tends to minimize the amount of incomplete combustion or pyrolysis products, especially in embodiments which contain carbon and/or multiple passageways. Heat transfer, and therefor aerosol delivery, also is enhanced by the use of passageways through the fuel, which draw hot air to the aerosol generator, especially during puffing. In addition, the preferred insulating member tends to confine, direct, and concentrate the heat toward the central core of the article, thereby increasing the heat transferred to the aerosol forming substance. Because the aerosol forming material is physically separate from the fuel element, it is exposed to substantially lower temperatures than are present in the burning fire cone. This minimizes the possibility of thermal degradation of the aerosol former and attendant off taste. This also results in aerosol production during puffing, but minimal aerosol production from the aerosol generating means during smolder. In the preferred embodiments of the invention, the short fuel element, the recessed heat conducting member, the insulating member, and/or the passages in the fuel cooperate with the aerosol generator to provide a system which is capable of producing substantial quantities of aerosol and optional tobacco flavor, on virtually every puff. The close proximity of the fire cone to the aerosol generator after a few puffs, together with the conducting member, the insulating member, and/or the multiple passageways in the fuel element, results in high heat delivery both during puffing and during the relatively long period of smolder between puffs. While not wishing to be bound by theory, it is believed that the aerosol generating means is maintained at a relatively high temperature between puffs, and that the additional heat delivered during puffs, which is significantly increased by the preferred passageways in the fuel element, is primarily utilized to vaporize the aerosol forming material. This increased heat transfer makes more efficient use of the available fuel energy, reduces the amount of fuel needed, and helps deliver early aerosol. Furthermore, by the appropriate selection of the fuel element composition, the number, size, configuration, and arrangement of fuel element passageways, the insulating jacket, and the paper overwrap, it is possible to control the burn properties of the fuel source to a substantial degree. This provides significant control over the heat transferred to the aerosol generator, which in turn, can be used to alter the number of puffs and/or the amount of aerosol delivered to the user. In general, the combustible fuel elements which may be employed in practicing the invention are less than about 30 mm long. Preferably the fuel element is about 20 mm or less, more preferably about 15 mm or less in length. Advantageously, the diameter of the fuel element is about 8 mm or less, preferably between about 3 and 7 mm, and more preferably between about 4 to 6 mm. The density of the fuel elements which may be employed herein range from about 0.5 g/cc to about 1.5 g/cc as measured, e.g., by mercury displacement. Preferably, the density is greater than 0.7 g/cc., more preferably greater than 0.8 g/cc. In most cases, a high density material is desired because it helps to ensure that the fuel element will burn long enough to simulate the burning time of a conventional cigarette and that it will provide sufficient energy to generate the required amount of aerosol. The fuel elements employed herein are advantageously molded or extruded from tobacco substitute materials, such as modified cellulosic materials, degraded or pre-pyrolyzed tobacco, and the like. Suitable materials include those described in U.S. Patent No. 4,347,855 to Lanzilotti et al., U.S. Patent No. 3,931,824 to Miano et al., and U.S. Patent Nos. 3,885,574 and 4,008,723 to Borthwick et al. and in Sittig, Tobacco Substitutes , Noyes Data Corp. (1976). Other suitable combustible materials may be employed, as long as they burn long enough to simulate the burning time of a conventional cigarette and generate sufficient heat for the aerosol generating means to produce the desired level of aerosol from the aerosol forming material. Preferred fuel elements normally include combustible carbon materials, such as those obtained by the pyrolysis or carbonization of cellulosic materials, such as wood, cotton, rayon, tobacco, coconut, paper, and the lake. In most cases, combustible carbon is desirable because of its high heat generating capacity and because it produces only minimal amounts of incomplete combustion products. The fuel elements useful in practicing this invention are carbonaceous fuel elements (i.e., fuel elements primarily comprising carbon). Carbonaceous fuel elements are particularly advantageous because they produce minimal pyrolysis and incomplete combustion products, produce little or no visible sidestream smoke, and minimal ash, and have high heat capacity. In especially preferred embodiments, the aerosol delivered to the user has no significant mutagenic activity as measured by the Ames test. See Ames et al., Mut. Res. , 31:347-364 (1975); Nagas et al., Mut. Res. , 42:335 (1977). Burn additives or combustion modifying agents also may be incorporated into the fuel to provide the appropriate burning and glow characteristics. If desired, fillers, such as diatomaceous earth, and binders, such as sodium carboxymethyl cellulose (SCMC), also may be incorporated into the fuel. Flavorants, such as tobacco extracts, may be incorporated into the fuel to add a tobacco or other flavor to the aerosol. Preferably, the fuel element is provided with one or more longitudinally extending passageways. These passageways help to control transfer of heat from the fuel element to the aerosol generating means, which is important both in terms of transferring enough heat to produce sufficient aerosol and in terms of avoiding the transfer of so much heat that the aerosol former is degraded. Generally, these passageways provide porosity and increase early heat transfer to the substrate by increasing the amount of hot gases which reach the substrate. They also tend to increase the rate of burning. Generally, a large number of passageways, e.g., about 5 to 9 or more, especially with a relatively wide spacing between the passageways, as in Figures 1A, 2A, and 4A, produce high convective heat transfer, which leads to high aerosol delivery. A large number of passageways also generally helps assure ease of lighting. High convective heat transfer tends to produce a higher CO output in the mainstream. To reduce CO levels, fewer passageways or a higher density fuel element may be employed, but such changes generally tend to make the fuel element more difficult to ignite, and to decrease the convective heat transfer, thereby lowering the aerosol delivery rate and amount. However, it has been discovered that with passageway arrangements which are closely spaced, as in Figure 2B, such that they burn out or coalesce to form one passageway, at least at the lighting end, the amount of CO in the combustion products is generally lower than in the same, but widely spaced, passageway arrangement. The optimum arrangement, configuration, and number of fuel element passageways should delivery a steady and high supply of aerosol, allow for easy ignition, and produce low CO. Various combinations have been examined for passageway arrangement/configuration and/or number in carbonaceous fuel elements used in various embodiments of the invention. In general, it has been discovered that fuel elements having from about 5 to 9 passageways, relatively closely spaced such that they burn away into one large passageway, at least at the lighting end of the fuel element, appear to most closely satisfy the requirements of a preferred fuel element for use in this invention, especially for the preferred carbonaceous fuel elements. Variables which affect the rate at which the fuel element passageways will coalesce upon burning include the density and composition of the fuel element, the size, shape, and number of passageways, the distance between the passageways, and the arrangement thereof. For example, for a 0.85 g/cc carbonaceous fuel source having seven passageways of about 0.5 mm, the passageways should be located within a core diameter, i.e., the diameter of the smallest circle which will circumscribe the outer edge of the passageways, between about 1.6 mm and 2.5 mm in order for them to coalesce into a single passageway during burning. However, when the diameter of the seven passageways is increased to about 0.6 mm, the core diameter which will coalesce during burning increases to about 2.1 mm to about 3.0 mm. Another preferred fuel element passageway arrangement useful in embodiments of the invention is the configuration illustrated in Figure 4B, which has been found to be particularly advantageous for low CO delivery and ease of lighting. In this preferred arrangement, a short section at the lighting end of the fuel element is provided with a plurality of passages, preferably from about 5 to 9, which merge into a large cavity 97 which extends to the mouth end of the fuel element. The plurality of passages at the lighting end provide the large surface area desired for ease of lighting and early aerosol delivery. The cavity, which may be from about 30% to 95%, preferably more than 50%, of the length of the fuel element, helps assure uniform heat transfer to the aerosol generating means and tends to delivery low CO to the mainstream. The aerosol generating means used in practicing the invention is physically separate from the fuel element. By physically separate it is meant that the substrate, container, or chamber which contains the aerosol forming materials is not mixed with, or a part of, the burning fuel element. As noted previously, this arrangement helps reduce or eliminate thermal degradation or the aerosol forming material and the presence of sidestream smoke. While not a part of the fuel, the aerosol generating means is preferably in a conductive heat exchange relationship with the fuel element, and preferably abuts or is adjacent to the fuel element. More preferably, the conductive heat exchange relationship is achieved by a heat conducting member, such as a metal tube or foil, which is preferably recessed or spaced from the lighting end of the fuel. Preferably, the aerosol generating means includes one or more thermally stable materials which carry one or more aerosol forming materials. As used herein, a thermally stable material is one capable of withstanding the high temperatures, e.g., 400°C-600°C, which exist near the fuel without decomposition or burning. While not preferred, other aerosol generating means, such as heat rupturable microcapsules, or solid aerosol forming substances, are within the scope of the invention, provided they are capable of releasing sufficient aerosol forming vapors to satisfactorily resemble tobacco smoke. Thermally stable materials which may be used as a substrate or carrier for the aerosol forming materials are well known to those skilled in the art. Useful substrates should be porous and must be capable of retaining an aerosol forming material when not in use and capable of releasing a potential aerosol forming vapor upon heating by the fuel element. Substrates, especially particulates, may be placed within a container, preferably formed from a conductive material. Useful thermally stable materials include thermally stable adsorbent carbons, such as porous grade carbons, graphite, activated, or nonactivated carbons, and the like. Other suitable materials include inorganic solids such as ceramics, glass, alumina, vermiculite, clays such as bentonite, and the like. Preferred carbon substrate materials include porous carbons such as PC-25 and PG-60 available from Union Carbide, and SGL carbon available from Calgon. A preferred alumina substrate is SMR-14-1896, available from the Davidson Chemical Division of W.R. Grace & Co., which is sintered at elevated temperatures, e.g., greater than about 1000°C, washed, and dried prior to use. It has been found that suitable particulate substrates also may be formed from carbon, tobacco, or mixtures of carbon and tobacco, into densified particles in a one-step process using a machine made by Fuji Paudal KK of Japan, and sold under the trade name of "Marumerizer". This apparatus is described in German Patent No. 1,294,351 and U.S. Patent No. 3,277,520 (now reissued as No. 27,214) as well as Japanese published specification No. 8684/1967. The aerosol generating means used in the invention is advantageously spaced no more than about 40 mm, preferably no more than 30 mm, most preferably no more than 20 mm from the lighting end of the fuel element. The aerosol generator may vary in length from about 2 mm to about 60 mm, preferably from about 5 mm to 40 mm, and most preferably from about 20 mm to 35 mm. The diameter of the aerosol generating means may vary from about 2 mm to about 8 mm, preferably from about 3 to 6 mm. If a non-particulate substrate is used, it may be provided with one or more holes, to increase the surface area of the substrate, and to increase air flow and heat transfer. The aerosol forming material or materials used in the invention must be capable of forming an aerosol at the temperatures present in the aerosol generating means when heated by the burning fuel element. Such materials preferably will be composed of carbon, hydrogen and oxygen, but they may include other materials. The aerosol forming materials can be in solid, semisolid, or liquid form. The boiling point of the material and/or the mixture of materials can range up to about 500°C. Substances having these characteristics include polyhydric alcohols, such as glycerin and propylene glycol, as well as aliphatic esters of mono-, di-, or poly-carboxylic acids, such as methyl stearate, dodecandioate, dimethyl tetradodecandioate, and others. The preferred aerosol forming materials are polyhydric alcohols, or mixtures of polyhydric alcohols. Especially preferred aerosol formers are glycerin, propylene glycol, triethylene glycol, or mixtures thereof. The aerosol forming material may be dispersed on or within the aerosol generating means in a concentration sufficient to permeate or coat the substrate, carrier, or container. For example, the aerosol forming substance may be applied full strength or in a dilute solution by dipping, spraying, vapor deposition, or similar techniques. Solid aerosol forming components may be admixed with the substrate and distributed evenly throughout prior to formation. While the loading of the aerosol forming material will vary from carrier to carrier and from aerosol forming material to aerosol forming material, the amount of liquid aerosol forming materials may generally vary from about 20 mg to about 120 mg, preferably from about 35 mg to about 85 mg, and most preferably from about 45 mg to about 65 mg. As much as possible of the aerosol former carried on the aerosol generating means should be delivered to the user as WTPM. Preferably, above about 2 weight percent, more preferably above about 15 weight percent, and most preferably above about 20 weight percent of the aerosol former carried on the aerosol generating means is delivered to the user as WTPM. The aerosol generating means also may include one or more volatile flavoring agents, such as menthol, vanillin, artificial coffee, tobacco extracts, nicotine, caffeine, liquors, and other agents which impart flavor to the aerosol. It also may include any other desirable volatile solid or liquid materials. Alternatively, these optional agents may be placed between the aerosol generating means and the mouthend, such as in a separate substrate or chamber in the passage which leads from the aerosol generating means to the mouthend, or in the optional tobacco charge. If desired, these volatile agents may be used in lieu of part, or all, of the aerosol forming material, so that the article delivery a nonaerosol flavor or other material to the user. One particularly preferred aerosol generating means comprises the aforesaid alumina substrate containing spray dried tobacco extract, tobacco flavor modifiers, such as levulinic acid, one or more flavoring agents, and an aerosol forming material, such as glycerin. This substrate may be mixed with densified tobacco particles, such as those produced on a "Marumerizer", which particles also may be impregnated with an aerosol forming material. Articles of the type disclosed herein may be used, or may be modified for use, as drug delivery articles, for delivery of volatile pharmacologically or physiologically active materials such as ephedrine, metaproterenol, terbutaline or the like. As shown in the illustrated embodiments, the smoking article of the present invention also may include a charge of tobacco or a tobacco containing material downstream from the fuel element, which may be used to add a tobacco flavor to the aerosol. In such cases, hot vapors are swept through the tobacco to extract and vaporize the volatile components in the tobacco, without combustion or substantial pyrolysis. One preferred location for the tobacco charge is around the periphery of the aerosol generating means, as shown in Figures 3 and 4, which increases heat transfer to the tobacco, especially in embodiments which employ a heat conducting member or conductive container between the aerosol forming material and the peripheral tobacco jacket. The tobacco in these embodiments also acts as an insulating member for the aerosol generator and helps simulate the feel and aroma of a conventional cigarette. The tobacco containing material may contain any tobacco available to the skilled artisan, such as Burley, Flue Cured, Turkish, reconstituted tobacco, extruded or densified tobacco mixtures, tobacco containing sheets and the like. Advantageously, a blend of tobaccos may be used to contribute a greater variety of flavors. The tobacco containing material may also include conventional tobacco additives, such as fillers, casings, reinforcing agents, such as glass fibers, humectants, and the like. Flavor agents may likewise be added to the tobacco material, as well as flavor modifying agents. The insulating members which may be employed in practicing the invention are preferably formed into a resilient jacket from one or more layers of an insulating material. Advantageously, this jacket is at least 0.5 mm thick, preferably at least 1 mm thick, and more preferably from about 1.5 to about 2 mm thick. Preferably, the jacket extends over more than half the length of the fuel element. More preferably, it extends over substantially the entire outer periphery of the fuel element and all or a portion of the aerosol generating means. As shown in the embodiment of Figure 3, different materials may be used to insulate these two components of the article. Insulating members which may be used in accordance with the present invention generally comprise inorganic or organic fibers such as those made out of glass, alumina, silica, vitreous materials, mineral wool, carbons, silicons, boron, organic polymers, cellulosics, and the like, including mixtures of these materials. Nonfibrous insulating materials, such as silica aerogel, pearlite, glass, and the like, formed in mats, strips or other shapes, may also be used. Preferred insulating members are resilient, to help simulate the feel of a conventional cigarette. Preferred insulating materials should fuse during use and should have a softening temperature below about 650-700°C. Preferred insulating materials also should not burn during use. However, slow burning carbons and like materials may be employed. These materials act primarily as an insulating jacket, retaining and directing a significant portion of the heat formed by the burning fuel element to the aerosol generating means. Because the insulating jacket becomes hot adjacent to the burning fuel element, to a limited extent, it also may conduct heat toward the aerosol generating means. Currently preferred insulating materials for the fuel element include ceramic fibers, such as glass fibers. Two suitable glass fibers are available from the Manning Paper Company of Troy, New York, under the designations Manniglas 1000 and Manniglas 1200. Preferred glass fiber materials have a low softening point, e.g., below about 650°C, using ASTM test method C 338-73. Preferred glass fibers include experimental materials produced by Owens-Corning of Toledo, Ohio under the designations 6432 and 6437, which have a softening point of about 640°C and fuse during use. Several commercially available inorganic fibers are prepared with a binder, e.g., PVA, which acts to maintain structural integrity during handling. These binders, which would exhibit a harsh aroma upon heating, should be removed, e.g., by heating in air at about 650°C for up to about 15 min. before use. If desired, pectin, at about 3 wt. percent, may be added to the fibers to provide mechanical strength to the jacket without contributing harsh aromas. Alternatively, the insulating material may be replaced, in whole or in part, by tobacco, either loosely packed or tightly packed. The use of tobacco as a substitute for part or all of the insulating jacket serves an additional function by adding tobacco flavors to the mainstream aerosol and producing a tobacco sidestream aroma, in addition to acting as an insulator. In preferred embodiments where the tobacco jacket encompasses the aerosol generating means, the jacket acts as a non-burning insulator, as well as contributing tobacco flavors to the mainstream aerosol. In embodiments where the tobacco encircles the fuel, the tobacco is preferably consumed only to the extent that the fuel source is consumed, i.e., up to about the point of contact between the fuel element and the aerosol generating means. This may be achieved by compressing the tobacco around the fuel element and/or using a conductive heat sink, as in the embodiment of Figure 4. It also may be achieved by treating the cigarette paper overwrap and/or the tobacco with materials which help extinguish the tobacco at the point where it overlaps the aerosol generating means. When the insulating member comprises fibrous materials other than tobacco, there may be employed a barrier means between the insulating member and the mouth end of the article. One such barrier means comprises an annular member of high density cellulose acetate tow which abuts the fibrous insulating means and which is sealed, at either end, with, for example, glue, to block air flow through the tow. In most embodiments of the invention, the fuel/aerosol generating means combination will be attached to a mouthend piece, such as a foil lined paper or cellulose acetate/plastic tubes illustrated in the Figures, although a mouthend piece may be provided separately, e.g., in the form of a cigarette holder. This element of the article provides the passageway which channels the vaporized aerosol forming materials into the mouth of the user. Due to its length, preferably about 35 to 50 mm or more, it also keeps the hot fire cone away from the mouth and fingers of the user and provides sufficient time for the hot aerosol to form and cool before it reaches the user. Mouthend pieces useful in articles of the invention may include an optional "filter" tip, which is used to give the article the appearance of the conventional filtered cigarette. Such filters include low efficiency cellulose acetate filters and hollow or baffled plastic filters, such as those made of polypropylene. Such filters do not appreciably interfere with aerosol delivery. The entire length of article or any portion thereof may be overwrapped with cigarette paper. Preferred papers at the fuel element end should not openly flame during burning of the fuel element. In addition, the paper should have controllable smolder properties and should produce a grey, cigarette-like ash. In an article utilizing an insulating jacket wherein the paper burns away from the jacketed fuel element, maximum heat transfer is achieved because air flow to the fuel source is not restricted. However, papers can be designed to remain wholly or partially intact upon exposure to heat from the burning fuel element. Such papers provide restricted air flow to the burning fuel element, thereby helping to control the temperature at which the fuel element burns and the subsequent heat transfer to the aerosol generating means. To reduce the burning rate and temperature of the fuel element, thereby maintaining a low CO/CO₂ ratio, a non-porous or zero-porosity paper treated to be slightly porous, e.g., non-combustible mica paper with a plurality of holes therein, may be employed as the overwrap layer. Such a paper controls heat delivery, especially in the middle puffs (i.e., puffs 4 through 6). To maximize aerosol delivery which otherwise would be diluted by radial (i.e., outside) air infiltration through the article, a non-porous paper may be used from the aerosol generating means to the mouth end. Papers such as these are known in the cigarette paper art and combinations of such papers may be employed to produce various functional effects. Preferred papers used in the articles of the present invention include Ecusta 01788 and 646 plug wrap manufactured by Ecusta of Pisgah Forest, North Carolina, and Kimberly-Clark's KC-63-5, P 878-5, P 878-16-2, and 780-63-5 papers. Preferred embodiments of the invention are capable or delivering at least 0.6 mg of aerosol, measured as wet total particulate matter (WTPM), in the first 3 puffs, when smoked under FTC smoking conditions. (FTC smoking conditions consist of two seconds of puffing (35 ml total volume) separated by 58 seconds of smolder.) More preferred embodiments of the invention are capable of delivering 1.5 mg or more or aerosol in the first 3 puffs. Most preferably, embodiments of the invention are capable of delivering 3 mg or more of aerosol in the first 3 puffs when smoked under FTC smoking conditions. Moreover preferred embodiments of the invention deliver an average of at least about 0.8 mg of wet total particulate matter per puff for at least about 6 puffs, preferably for at least about 10 puffs, under FTC smoking conditions.

Claims: A smoking article including a fuel element (10) comprising primarily carbon as such, a physically separate aerosol generating means (74, 38, 76; 90; 96) comprising at least one aerosol forming material, and a physically separate paper wrapper (14; 73; 85, 89), characterized in that the fuel element (10) is structured and arranged to burn throughout smoking to generate heat to volatilize aerosol forming material during puffing throughout smoking of the article, that at least a portion of the fuel element (10) is circumscribed by a layer of heat insulating material (72; 94), and that the paper wrapper (14; 73; 85, 89) encircles said insulating layer (72; 94) and is designed to remain at least partially intact during smoking to restrict air flow to the burning fuel element. Article according to claim 1, wherein the wrapper (14; 73; 85, 89) comprises a non-combustible inorganic material. Article according to claim 1 or 2, wherein the wrapper (14; 73; 85, 89) comprises a non-porous or zero porosity paper treated to be slightly porous. Article according to one of the preceding claims, wherein the wrapper (14; 73; 85, 89) comprises a non-combustible mica paper with a plurality of holes therein. Article according to one of the preceding claims, wherein a non-porous paper wrapper (14; 73; 85, 89) is used from the aerosol generating means (74, 38, 76; 90; 96) to the mouth end (15; 45). Article according to one of the preceding claims, wherein the layer of insulating material (72; 94) is at least 0,5 mm thick. Article according to claim 6, wherein the layer of insulating material (72; 94) is at least 1 mm thick. Article according to claim 7, wherein the layer of insulating material (72; 94) is from about 1,5 to about 2 mm thick. Article according to one of the preceding claims, wherein the insulating material (72; 94) comprises inorganic fibers. Article according to one of the preceding claims, wherein the fuel element (10) is located at the lighting end of the article. Article according to one of the preceding claims, wherein the fuel element (10) includes at least one longitudinally extending passageway (16). Article according to claim 11, wherein the fuel element (10) has a plurality of such passageways (16). Article according to claim 11 or 12, wherein at least one passageway (16) is in the form of a hole. Article according to one of the preceding claims, wherein the fuel element (10) is about 30 mm or less in length prior to smoking. Article according to claim 14, wherein the fuel element (10) is about 20 mm or less in length prior to smoking. Article according to claim 15, wherein the fuel element (10) is about 15 mm or less in length before smoking. Article according to one of the preceding claims, wherein the fuel element (10) has a diameter between about 3 and 8 mm. Article according to one of the preceding claims, wherein the fuel element (10) has a diameter of from about 4mm to about 6 mm. Article according to one of the preceding claims, wherein the fuel element (10) has a density of at least 0,5 g/cm³. Article according to one of the preceding claims, wherein the fuel element (10) has a density range from about 0,5 g/cm³ to about 1,5 g/cm³. Article according to claim 20, wherein the fuel element (10) has a density of more than about 0,7 g/cm³. Article according to one of the preceding claims, wherein the fuel element (10) has a density of at least about 0,8 g/cm³. Article according to one of the preceding claims, wherein the fuel element (10) is a pressed or extruded mass. Article according to one of the preceding claims, wherein the fuel element (10) is substantially free of volatile organic material. Article according to one of the preceding claims, wherein the constituents forming the mass of the fuel element (10) are selected to avoid any substantially visible sidestream smoke during smolder.

Inventors: BANERJEE CHANDRA KUMAR, FARRIER ERNEST GILBERT, HARRIS JAMES LUTHER, NORMAN ALAN BENSON, RESCE JAMES LEE, REYNOLDS JOHN HUGHES IV, RIDINGS HENRY THOMAS, SENSABAUGH ANDREW JACKSON JR, SHANNON MICHAEL DAVID, SHELAR GARY ROGER, BANERJEE, CHANDRA KUMAR, FARRIER, ERNEST GILBERT, HARRIS, JAMES LUTHER, NORMAN, ALAN BENSON, RESCE, JAMES LEE, REYNOLDS, JOHN HUGHES IV, RIDINGS, HENRY THOMAS, SENSABAUGH, ANDREW JACKSON, JR., SHANNON, MICHAEL DAVID, SHELAR, GARY ROGER
Applicants: REYNOLDS TOBACCO CO R, R.J. REYNOLDS TOBACCO COMPANY
Application year: 1986
Main classification: A24D1
IPC codes: A24F47, A24B15