Smoking article

Abstract: A smoking article (300) in which a flavored aerosol is generated by heat transfer to a flavor bed (221) from the combustion of a heat source (220) is provided. The article generates substantially no sidestream smoke. The transfer of heat from the heat source to the flavour bed is accomplished by convective and radiative heat transfer and is assisted by a hollow sleeve (222) surrounding the heat source.

Description: This application relates to an invention which is an improvement in or modification of our copending Application No. 89 307361.9 (EP-A-352109, see the preamble of claim 1), which corresponds to US-A-4,991,606, and US-A-4,966,171. Background of the Invention This invention relates to smoking articles which produce substantially no visible sidestream smoke. More particularly, this invention relates to a smoking article in which the sensations associated with the smoking of tobacco are achieved without the burning of tobacco. A substantial number of previous attempts have been made to produce a smoking article which produces an aerosol or vapor for inhalation, rather than conventional tobacco smoke. For example, Siegel U.S. Patent 2,907,686 shows a smoking article consisting of a charcoal rod and a separate carrier impregnated with flavorants and a synthetic "smoke" forming agent which is heated by the burning charcoal rod. The charcoal rod is coated with a concentrated sugar solution so as to form an impervious layer during burning. It was thought that this layer would contain the gases formed during smoking and concentrate the heat thus formed. Another smoking article, shown in Ellis et al. U.S. Patent 3,258,015, employs burning tobacco in the form of a conventional cigarette to heat a metallic cylinder containing a source of nicotine, such as reconstituted tobacco or tobacco extract. During smoking, the vapors released from the material inside the metal tube mix with air inhaled through an open end of the tube which runs to the burning end of the smoking article. Ellis et al. U.S. Patent 3,356,094 shows a similar smoking article in which the tube becomes frangible upon heating, so that it would break off and not protrude when the surrounding tobacco had burned away. Published European patent application 0 117 355 by Hearn et al. shows a smoking article which produces a nicotine-containing aerosol by heating, but not burning, a flavor generator. The flavor generator could be fabricated from a substrate material such as almumina, natural clays and the like, or tobacco filler. The flavor generator is impregnated with thermally releasable flavorants, including nicotine, glycerol, menthol and the like. Heating of the flavor generator is provided by hot gases formed as a result of the combustion of a fuel rod of pyrolized tobacco or other carbonaceous material. Banerjee et al. U.S. Patent 4,714,082 shows a variation of the Hearn et al. article which employs a short fuel element. The performance of the article is said to be improved by maximizing heat transfer between the fuel element and the aerosol generator. This is effected by preventing heat loss by insulation, and by enhancing heat transfer between the burning fuel and the flavor generator by a metallic conductor. A spun glass fiber insulator surrounds the fuel element and aerosol generator assembly. The Banerjee et al. device suffers from a number of drawbacks. First, the resilient glass fiber insulating jacket is difficult to handle on modern mass production machinery without special equipment. Second, the glass fibers may become dislodged during shipping and migrate through the pack to rest on the mouth end of the article, giving rise to the potential for the inhalation of glass fibers into the smoker's mouth. Additionally, the use of a metallic heat conductor may be somewhat inefficient because the conductor itself absorbs much of the heat produced by the fuel element. Summary of the Invention It is an object of this invention to modify the smoking article known from EP-A-352109 in which a flavored aerosol releasing material is heated by hot gases formed by the passage of air through, and by radiation from, a carbonaceous heat source, so that the passage of air to the heat source is more efficient. It is a further object of the invention to avoid the potential for inhalation of glass fibers by a smoker of such an article. It is still further object of this invention to provide such an article which has both the look and feel of a conventional cigarette. In accordance with this invention, these objects are achieved by a smoking article as defined in the claims. The preferred smoking article includes an active element at the distal end in fluid communication with the mouth end. The active element includes a heat reflective substantially cylindrical hollow sleeve having internal and external walls, and having a first end at the distal end and a second end closer to the mouth end. At least a portion of the sleeve at the first end is metallic. A heat source is inserted in the sleeve adjacent the first end of the sleeve. Preferably, the heat source is suspended in the sleeve adjacent the first end and spaced from the interior wall of the sleeve, defining an annular space around the heat source. The heat source has a fluid passage therethrough. A flavor bed is provided in the sleeve adjacent the second end thereof, in radiative and convective heat transfer relationship with the heat source. A spacer element maintains the flavor bed in spaced-apart relationship with the heat source. The sleeve has longitudinal flutes in the surface thereof adjacent the heat source for admitting air to support combustion of the heat source, and is air-impermeable adjacent the flavor bed to prevent combustion of material in the flavor bed. When the heat source is ignited and air is drawn through the smoking article, air is heated as it passes through the fluid passage. The heated air flow through the flavor bed, releasing a flavored aerosol, and carrying it to the mouth end. Brief Description of the Drawings The above and other objects and advantages of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which figures 1-13 relate, for illustrative purposes, to the embodiments of EP-A-352109: FIG. 1 is an exploded perspective view of the first embodiment of a smoking article according to EP-A-352109, not forming part of the present invention. FIG. 2 is a longitudinal cross-sectional view of the smoking article of FIG. 1, taken from line 2-2 of FIG. 1; FIG. 3 is an end view of the smoking article of FIGS. 1 and 2, taken from line 3-3 of FIG. 2; FIG. 4 is a radial cross-sectional view of the smoking article of FIGS. 1-3, then from line 4-4 of FIG. 2; FIG. 5 is a radial cross-sectional view of the smoking article of FIGS. 1-4, taken from line 5-5 of FIG. 2; FIG. 6 is a radial cross-sectional view of the smoking article of FIGS. 1-5, taken from line 6-6 of FIG. 2; FIG. 7 is an exploded perspective view of the active element of the smoking article of FIGS. 1-6; FIG. 8 is a longitudinal cross-sectional view of the active element of the smoking article of FIGS. 1-7 taken from line 8-8 of FIG. 7; FIG. 9 is a diagram of testing apparatus for measuring permeability of smoking articles according to the invention; FIG. 10 is a longitudinal cross-sectional view of the second embodiment of a smoking article according to EP-A-352109, not forming part of the present invention. FIG. 11 is a radial cross-sectional view of the smoking article of FIG. 10, taking from line 11-11 of FIG. 10; FIG. 12 is an exploded perspective view of the active element of the smoking article of FIGS. 10-11; FIG. 13 is a longitudinal cross-sectional view of the active element of the smoking article of FIGS. 10-12, taken from line 13-13 of FIG. 12; FIG. 14 is an exploded perspective view of the smoking article according to the present invention; FIG. 15 is a longitudinal cross-sectional view of the smoking article of FIG. 14, taken from line 15-15 of FIG. 14; FIG. 16 is an exploded perspective view of the active element of the smoking article of FIGS. 14-15; FIG. 17 is a longitudinal cross-sectional view of the active element of the smoking article of FIGS. 14-16, then from line 17-17 of FIG. 16; FIG. 18 is an end view of the smoking article of FIGS. 14-17, then from line 18-18 of FIG. 15; FIG: 19 is a radial cross-sectional view of the smoking article of FIGS. 14-18, taken from line 19-19 of FIG. 15; FIG. 20 is an end view of the smoking article of FIGS. 14-19, taken from line 20-20 of FIG. 15; and FIG. 21 is a radial cross-sectional view of the smoking article of FIGS. 14-20, taken from line 21-21 of FIG. 15. Detailed Description of the Invention The first embodiment of the smoking article according to EP-A-352109 is shown in FIGS. 1-8. Smoking article 10 consists of an active element 11 and an expansion chamber tube 12, overwrapped by cigarette wrapping paper 14, and a filter element 13 attached by tipping paper 205. Wrapping paper 14 preferably is a cigarette paper treated to minimize thermal degradation, such as apaper having magnesium hydroxide filler, or other suitable refractory type cigarette paper, or paper treated with an aluminum oxide sol gel. As discussed in more detail below, active element 11 includes a heat source 20 and a flavor bed 21 which releases flavored vapors and gases when contacted by hot gases flowing through the heat source. The vapors pass into expansion chamber tube 12, forming an aerosol which passes to mouthpiece element 13, and thence into the mouth of a smoker. As explained in more detail in copending Application No. 89 307360.1, published as EP-A-0352108, to which reference is made, heat source 20 may contain substantially pure carbon, preferably with some catalysts or burn additives. Heat source 20 may be formed from charcoal and has one or more longitudinal passageways therethrough. These longitudinal passageways may be in the shape of multi-pointed stars having long narrow points and a small inside circumference. Heat source 20 may have a void volume greater than about 50% with a pore size between the charcoal particles of about one to about 2 microns. Heat source 20 may have a weight of about 81 mg/10 mm and a density between about 0.2 g/cc and about 1.5 g/cc. The BET surface area of the charcoal particles used in heat source 20 may be in the range of about 50 m²/g to about 2000 m²/g. Flavor bed 21 can include any material that releases desirable flavors and other compounds when contacted by hot gases. In a smoking article, the flavors and other compounds may be those associated with tobacco, as well as other desirable flavors. Thus, suitable materials for flavor bed 21 may include tobacco filler or an inert substrate on which desirable compounds have been deposited. In a preferred version, described in detail in copending Application No 89 307359.3, published as EP-A-352107 to which reference may be made, flavor bed 21 is a packed bed of pelletized tobacco. The pellets are preferably formed by combining in an extruder particularized tobacco materials having a size of from about 20 mesh to about 400 mesh, preferably about 150 mesh, an aerosol precursor, for example, glycerine, 1,3-butanediol or propylene glycol, or mixtures thereof, that can be widely dispersed among the tobacco particles, and a finely divided filler material, for example, calcium carbonate or alumina, to increase the thermal load to prevent the hot gases from raising the temperature of the pellets above their thermal decomposition temperature. The materials are mixed to form a mixture, and the mixture is extruded out a die typically having a plurality of orifices into spaghetti-like strands of about the same diameter. The extruded strands are cut into lengths, preferably of uniform length. The pellets preferably are uniformly dimensioned and comprise a mixture of about 15% to about 95% tobacco material, about 5% to about 35% aerosol precursor, and about 0% to about 50% filler material. Given sufficient oxygen, as discussed in more detail below, heat source 20 will burn to produce mostly carbon dioxide. As also discussed below, radiant energy reflector sleeve 22 of active element 11 is substantially non-combustible, and does not burn during smoking of article 10. Further, article 10 is constructed in such a way that the gases flowing through flavor bed 21 have a reduced oxygen content, also discussed below, so that the constituents of flavor bed 21 undergo pyrolysis and not combustion even if their temperature is high enough to ignite them otherwise. There is substantially no visible side-stream smoke when article 10 is smoked. Turning to the details of the construction of article 10, active element 11 is housed in a composite sleeve including radiant energy reflector sleeve 22 and, preferably, an inner sleeve 23 within radiant energy reflector sleeve 22. (As used herein, unless otherwise indicated, the word "sleeve" refers to the composite sleeve.) Inner sleeve 23 is folded to provide a lip 24 which holds carbon heat source 20 suspended away from the interior wall of radiant energy reflector sleeve 22, leaving an annular space 25. Flavor bed 21 is held within inner sleeve 23 between lip 24 and heat source 20 on one end, and a screen-like clip or cup 26, which holds in the pellets of bed 21 while allowing the aerosol to pass through into expansion chamber tube 12, on the other end. Expansion chamber tube 12 gives article 10 the length, and thus the appearance, of an ordinary cigarette. The mouth end portion 120 of inner sleeve 23 extends beyond the mouth end of radiant energy reflector sleeve 22 and fits into expansion chamber tube 12. Wrapper 14 holds active element 11 and expansion chamber tube 12 together. Preferably, cigarette wrapping paper 14 will have sufficient porosity to allow air to be admitted through paper 14 and radiant energy reflector sleeve 22 to support combustion of heat source 20. Alternatively, paper 14 may be perforated, such as by electrostatic or laser perforation, in the region of radiant energy reflector sleeve 22 which surrounds heat source 20. Preferably, aluminum insert 27, fitted into inner sleeve 23 behind clip 26, closes off the mouth end of active element 11, leaving only an orifice 28 for the passage of the hot vapors. Passage through orifice 28 causes the hot vapors to increase their velocity and then expand into expansion chamber tube 12. Expansion of the vapors and gases into the expansion chamber causes cooling of the saturated vapors to form a stable aerosol, thereby minimizing condensation on either of mouthpiece segments 29, 200, increasing the delivery of aerosol to the smoker. The degree of expansion, and therefore of cooling, may be controlled by varying the size of orifice 28 and the volume of expansion chamber 12. Mouthpiece element 13 may be a hollow tube or may include a filter segment 29. Mouthpiece element 13 preferably includes two mouthpiece segments 29, 200. Mouthpiece segment 29 is a cellulose acetate filter plug 201 wrapped in plug wrap 202. Segment 200 is a rod of tobacco filler or other tobacco-containing material, wrapped in plug wrap 203, which, in addition to further cooling the aerosol and providing some filtration, may impart additional tobacco taste. The tobacco filler in segment 200 is preferably cut at the standard 30 cuts per inch, but may be coarser to minimize filtration. For example, the tobacco filler may be cut at about 15 cuts per inch. The two segments 29, 200 of mouthpiece element 13 are jointly overwrapped by plug wrap 204, and the entire mouthpiece element 13 is attached to the remainder of article 10 by tipping 205. Alternatively, segment 200 may be of another material, or there may be no segment 200. Returning to the structure of active element 11, annular space 25 is provided so that there is sufficient air flow to heat source 20 to allow for sustained combustion and so that conduction of heat to the outside is minimized. For the former reason, radiant energy reflector sleeve 22 is perforated and preferably has at least about 9.5% open area and a permeability of about 9.1 to about 15.1, measured as follows: A permeability test apparatus 90 as shown in FIG. 9 is assembled from tubing sections 91, 92, 93, 94 all having the same diameter as radiant energy reflector sleeve 22, which is integrated into apparatus 90. Nitrogen gas is pumped into opening 95 at a rate of 2 liters per minute. Opening 96 is open to the atmosphere. Gas is pumped out of opening 97 at a rate of 1 liter per minute. Because resistance to the flow of air through the wall of sleeve 22 is less than that through the tubing of apparatus 90, air will be drawn in through the wall of radiant energy reflector sleeve 22 and out through opening 97 along with a quantity of nitrogen gas. A mass spectrometer probe 98 is positioned at the end of tube section 93 below tube section 94, and is connected by cable 99 to mass spectrometer 900. Cable 99 passes out of tube 94 at 901. The opening through which cable 99 passes is sealed so that no oxygen enters apparatus 90 except through the wall of radiant energy reflector sleeve 22. The permeability of radiant energy reflector sleeve 22 is defined as the number of milliliters of oxygen per minute per square centimeter of surface area of the outer wall of radiant energy reflector sleeve 22 detected by probe 98 as determined by mass spectrometer 900. The permeability of radiant energy reflector sleeve 22 determines the mass burn rate of heat source 20. It is desirable for article 10 to provide about 10 puffs under FTC conditions (a two-second, thirty-five milliliter puff taken once a minute). If the mass burn rate of heat source 20 is too high, each puff taken by a smoker will deliver added flavor because the gases reaching flavor bed 21 will be hotter. However, because more of heat source 20 is consumed in each puff, heat source 20 may be consumed in fewer than 10 puffs. Similarly, if the mass burn rate is too low, more than 10 puffs will be available, but each will deliver less flavor because the gases will be cooler. In addition, if the mass burn rate is too low, heat source 20 may extinguish before the smoker is ready to take another puff. A preferable mass burn rate has been found to be between about 9 mg/min and about 11 mg/min. To achieve such a range of mass burn rates, a permeability of between about 9.1 and about 15.1, measured in accordance with the method described, is preferred. The air flow in element 11 into flavor bed 21 is through passage 206 in heat source 20. It is desirable that as large as possible a surface area of heat source 20 be in contact with the air flow to maximize the convective heat transfer to flavor bed 21, and also so that combustion is as complete as possible. For that same reason, passage 206 is not a simple cylindrical passage. Rather, it has a many-sided cross section, such as the eight-pointed star shown in the FIGURES. In fact, the surface area of passage 206 in the preferred embodiment is greater than the surface area of the outer surface of heat source 20. In order to minimize radiative heat loss from article 10, all inner surfaces of active element 11 are reflectorized. For example, radiant energy reflector sleeve 22 can be made from metallized paper. More preferably, as seen in FIGS. 7 and 8, radiant energy reflector sleeve 22 is made up of a paper layer 70 and an inner foil layer 71. Foil layer 71 reflects heat radiated by heat source 20 back into heat source 20 to keep it hot and thus to ensure that it does not cool below its ignition temperature and become extinguished. The reflection of heat back into active element 11 also means that more heat is available for transfer to flavor bed 21. Paper layer 70 may be made by spiral winding a paper strip or using other well-known techniques of paper tube-making. Preferably, however, paper layer 70 and foil layer 71 are passed together through a garniture, similar to that used in the making of conventional cigarettes, which forms them into a tube. In that preferred embodiment, the edges of paper layer 70 overlap and are glued to one another. Paper layer 70 is either porous or perforated, so that the required permeability, referred to above, can be achieved. Foil layer 71 is preferably made by taking 0.0015-inch aluminium foil, embossing it to provide raised holes, and then calendering it to flatten the holes so that the perforated foil is more nearly smooth. Although calendering closes up the holes somewhat, the desired permeability is achieved as long as the embossed aluminium sheet has at least 4% open area, preferably about 9.5% open area. Although foil layer 71 reflects a substantial portion of the heat produced by heat source 20, some of the heat may escape to the outside. For that reason, the paper used in paper layer 70 preferably is modified to prevent combustion so that it does not ignite when article 10 is smoked. Inner sleeve 23 is also reflective, made of an outer aluminum layer 80, an inner aluminum layer 82, and an intermediate paper layer 81. Inner sleeve 23 may be made by taking two identical paper/foil laminate strips and spiral winding them paper side to paper side, so that the two paper sides together form intermediate layer 81. The paper layers are preferably hard-calendered paper. In the preferred embodiment, intermediate layer 81 also includes up to three layers of a paper which may be treated to reduce thermal degradation, such as a paper having magnesium hydroxide filler, or other suitable refractory type cigarette paper, or paper treated with an aluminum oxide sol gel, wound between the paper/foil laminate strips. Inner sleeve 23 in not made air permeable because flavor bed 21 is to be kept oxygen-deprived, so that no ignition of tobacco can take place which might introduce off tastes and thermal decomposition constituents to the aerosol. The foil layers 80, 82 keep air out, as well as reflecting radiant heat back in for maximum flavor generation. Of course, air could be kept out of flavor bed 21 in other ways, such as overwrapping radiant energy reflector sleeve 22 with an air-impermeable material (not shown) in the region of flavor bed 21. Foil layers 80, 82 should be as thin as possible so that they have low heat capacity, making more heat available to flavor bed 21, but not so thin as to allow paper layer 81 to overheat. Inner sleeve 23 is folded over to make lip 24, which must be wide enough so that heat source 20 can be held securely in place. Finally, active element 11 is provided with a reflective end cap 15 which is crimped into radiant energy reflector sleeve 22. Cap 15 has one or more openings 16 which allow air into active element 11. Openings 16 preferably are located at the periphery of cap 15. In the preferred embodiment, there are six equiangularly spaced openings each having a diameter of 0.080 in. Cap 15 increases the reflection of radiation back into active element 11, and also keeps heat source 20 from falling out of article 10 if it somehow becomes loose, cracked or broken. This is important when it is considered that heat source 20 smolders at a high temperature between puffs, and is even hotter during puffs. Cap 15 also keeps in any ash that may form during burning of heat source 20. It is preferred that article 10 have an outer diameter of 7.9 mm, similar to a conventional cigarette. Carbon heat source 20 preferably has a diameter of 4.6 mm and a length of 10.1 mm, while active element 11 preferably has an overall length of 26 mm. Mouthpiece element 13 preferably has a length of 21 mm, divided between a 10 mm cellulose acetate filter portion 29 and an 11 mm tobacco rod portion 200. Expansion chamber tube 12 preferably is 33 mm long, so that article 10 overall is 79 mm long, which is comparable to a conventional "long-size" cigarette. In the preferred embodiments, lip 24 is 2.6 mm wide. The second embodiment of the smoking article according to EP-A-352109 is shown in FIGS. 10-13, any views of the second embodiment which are not shown in FIGS. 10-13 being the same as the corresponding views of the first preferred embodiment. In the embodiment 100 of FIGS. 10-13, a spacer 101 within active element 110 holds the pellets of flavor bed 21 in spaced-apart relation from the end of carbon heat source 20. It has been found that, as compared to the embodiment of FIGS. 1-8, the inclusion of spacer 101 provides more even heating of the end of the flavor bed adjacent heat source 20, because the jet of hot gases drawn through passage 206 has time to spread out before reaching flavor bed 21, so that it heats more of the end of flavor bed 21. Similarly, inclusion of spacer 101 prevents flashing of flavor bed 21 on lighting of smoking article 100. In the absence of spacer 101, flame drawn through passage 206 during lighting could cause flavor bed 21 to ignite, or flash, but with spacer 101 in place, any such flame spreads out over spacer 101. Spacer 101 preferably is a metallic -- e.g., aluminum -- disk, which preferably has a surface that is treated -- e.g., blackened -- so that it will absorb heat from heat source 20 and radiate it to flavor bed 21. The inclusion of spacer 101 provides other advantages, as well. For example, it prevents small particles from flavor bed 21, such as broken pieces of tobacco pellets, from falling through passage 206, and obstructing the front end of smoking article 100 between end cap 15 and heat source 20, or falling out of article 100 altogether if end cap 15 is not provided. In addition, spacer 101 permits different degrees of packing of the same amount of pellets in flavor bed 21, by moving spacer 101 closer to or further from clip 26. Different degrees of packing of flavor bed 21 give rise to different degrees of resistance-to-draw of article 100, as well as different flavor characteristics. Finally, spacer 101, which holds the pellets of flavor bed 21 away from heat source 20, also prevents migration of flavor compounds from the pellets to heat source 20, where they might undergo pyrolysis and give rise to off tastes or thermal decomposition products. The smoking article according to the present invention is shown in FIGS. 14-21. Any views of the third embodiment that are not shown in FIGS. 14-21 are the same as the corresponding views of the second embodiment of EP-A-352109, or the first embodiment of EP-A-352109 if there is no corresponding view of the second embodiment thereof. In the smoking article 300 of the present invention aluminum insert 27 bearing orifice 28 has been eliminated. Instead, clip 26 is used to provide the necessary flow restriction to achieve the desired expansion effect in expansion chamber tube 212 (although not drawn to scale, expansion chamber tube 212 is preferably longer than expansion chamber tube 12). The sizes of the openings in clip 26 can be adjusted to achieve the desired flow restriction. In addition, the shape of the fluid passage through heat source 220 is different. Instead of a passage with a multi-pointed star cross-section, such as passage 206, heat source 220 in the third preferred embodiment has a passage 226 which has a flower-shaped cross section, each lobe of the passage resembling a flower petal. Preferably, there are six lobes in passage 226. The flower-shaped cross section provides more efficient or even heat transfer than the star shape, as well as more thermal control through, e.g., reduced ashing propensity. Heat source 220 itself, instead of being substantially pure carbon, contains carbon along with a metal nitride, as well as the necessary additives as above. A particularly preferred metal nitride for heat source 220 is an iron nitride. Such a heat source, and its advantages, are described in more detail in copending, commonly-assigned US-A-5188130, which is hereby incorporated by reference in its entirety. One such advantage is the reduction of smoke constituents other than carbon dioxide. Another advantage is a higher burning temperature. Finally, metallized paper radiant energy reflector sleeve 22 and perforated metallic end cap 15 of active element 11 are replaced in active element 211 by a one-piece cup 222 having end face 215. Cup 222 is preferably made from drawn aluminum. Perforations 216 of end face 15 are similar to perforations 16 of end cap 15, but end face 215 is flat, unlike end cap 15 which is curved. Of course, the drawing technique,permits the use of any desired perforation configuration. Perforations 216 allow the ignition flame (from a match or lighter) used to light article 300 to spread more evenly over the end of heat source 220. Cup 222 is fluted, having an outer diameter defined by aluminum layer 270, and flutes 272 defined by pushed in areas 271. The outer diameter of cup 222 is the same as that of expansion chamber tube 12, so that a uniform surface is presented for wrapper 14. The inner diameter of cup 222 at flutes 272 is such that cup 222 fits snugly and securely on inner sleeve 23. Cup 222 may have elongated openings 273 or 274 or both to admit air to support combustion of heat source 220. In a preferred embodiment, all of the elongated openings are openings 274. However, other configurations of openings, including openings outside flutes 272 in layer 270, may be used. Wrapper 14 may be air-permeable over openings 274 either because it is made of inherently porous paper, or because it is perforated in the regions over openings 273, 274 as described above. However, wrapper 14 may also be of low permeability, as flutes 272 form air ducts to the front end of article 300, allowing sufficient air to reach openings 274 to support ignition and static burning of heat source 220. The use of a metal cup 222 instead of metal-and-paper sleeve 22 eliminates the need for paper layer 70. In addition, because of the greater heat capacity of cup 222, it can act as a heat sink when a user attempts to relight article 300, not realizing that it is already lit. In articles 10 and 100, an attempt at relighting could result in ignition of wrapper 14. That is also true with a conventional cigarette. However, the likelihood of such an ignition is reduced in article 300 because paper layer 70 is absent and because cup 222 has greater heat sinking capacity than sleeve 22. Furthermore, because the metal expands when heated, when article 300 is being used, the degree of contact between cup 222 and inner sleeve 23 decreases. Therefore, there is less heating of sleeve 23, and thus less chance of ignition of wrapper 14. Thus it is seen that a smoking article in which a flavored aerosol releasing material is efficiently heated by a carbonaceous or partly carbonaceous heat source, which avoids the potential for inhalation of glass fibers by the smoker, which minimizes heat loss to the walls of the flavor bed, and which has both the look and feel of a conventional cigarette, is provided. One skilled in the art will appreciate that the present invention can be practiced by other than the described embodiment, which is presented for purposes of illustration and not of limitation, and the present invention is limited only by the claims which follow.

Claims: A smoking article having a mouth end and a distal end and comprising: an active element (211) at said distal end in fluid communication with said mouth end, said active element comprising: a substantially non-combustible substantially cylindrical hollow sleeve having a first end at said distal end and a second end closer to said mouth end, at least a portion of which at said first end is metallic, and said sleeve including a substantially air-impermeable inner sleeve (23) adjacent said flavor bed (221), said hollow sleeve being air-permeable adjacent said heat source for admitting air to support combustion of said heat source, and air-impermeable adjacent said flavor bed to prevent combustion of material in said flavour bed; a heat source (220) suspended in said hollow sleeve adjacent said first end thereof, said heat source having a fluid passage (226) therethrough and being spaced from the interior wall of said hollow sleeve, so defining an annular space (25) around said heat source; a flavor bed (221) in said hollow sleeve adjacent said second end thereof, in radiative and convective heat transfer relationship with said heat source; spacer means (101) for maintaining said flavor bed in spaced-apart relationship with said heat source: and an expansion chamber (212) for cooling said aerosol adjacent said flavor bed (221) toward said mouth end, said expansion chamber comprising a tube having an inner diameter equal to the outer diameter of said inner sleeve (23), and fitting over a portion (120) of said inner sleeve toward said mouth end; characterized in that said substantially non-combustible hollow sleeve comprises a drawn metallic sleeve (222) having the outer diameter of said tube, and that said drawn sleeve has longitudinal flutes (272) in the surface thereof and an inner diameter in the areas of said inner sleeve (23), said metal reflecting heat produced back toward said heat source, to aid in maintaining combustion thereof. The smoking article of Claim 1, characterized in that said flutes (272) extend to the distal end of said drawn metallic sleeve (222), forming air ducts communicating between openings (274) in the walls of said sleeve and the atmosphere. The smoking article of Claim 1 or 2, characterized in that said hollow sleeve comprises a drawn metallic cup including a perforated end face (215) at said distal end of said element. The smoking article of Claim 3, characterized in that said end face (215) is reflective of radiant energy. The smoking article of any of Claims 1 to 4, characterized in that said metal is aluminium. The smoking article of any of Claims 1 to 5, characterized in that said inner sleeve (23) comprises a lip (24) for receiving said heat source (220). The smoking article of any of Claims 1 to 6, or 11, characterized in that said inner sleeve (23) is a laminate of a metallic foil, preferably aluminum, and paper. The smoking article of Claim 7, characterized in that said inner sleeve (23) comprises two metallic foil layers, preferably aluminum, and paper. The smoking article of any of Claims 1 to 8, characterized by a mouthpiece element (13) comprising a cellulose acetate filter plug (201) adjacent said mouth end. The smoking article of Claim 9, characterized in that said mouthpiece element (13) further comprises a rod (200) of tobacco-containing material adjacent an end of said filter plug (201) remote from said mouth end. The smoking article of any of Claims 1 to 10, characterized in that said heat source (220) is solid, ignitable, and self-sustaining. The smoking article of any of Claims 1 to 11, characterized in that said heat source (220) is substantially cylindrical and said fluid passage extends substantially through the centre thereof. The smoking article of any of Claims 1 to 12, characterized in that said flavor bed (221) comprises tobacco, preferably a plurality of tobacco-containing pellets. The smoking article of any of Claims 1 to 13, characterized in that said spacer means comprises a metallic clip, preferably of aluminum. The smoking article of Claim 14, characterized in that the surface of said spacer means (101) is blackened to increase absorption and radiation of radiant energy, whereby aid spacer means serves to absorb heat from said heat source (220) and radiate heat to said flavor bed (221).

Inventors: FLEISCHHAUER GRIER S, HAYWARD CHARLES R, HEARN JOHN R, HOUCK WILLIE G, HOUGHTON KENNETH S, LANZILLOTTI HARRY V, LILLY CLIFTON A JR, LOSEE BRUCE D JR, SANDERS EDWARD B, SERRANO MARK A, FLEISCHHAUER, GRIER S., HAYWARD, CHARLES R., HEARN, JOHN R., HOUCK, WILLIE G., HOUGHTON, KENNETH S., LANZILLOTTI, HARRY V., LILLY, CLIFTON A., JR., LOSEE, BRUCE, D., JR., SANDERS, EDWARD B., SERRANO, MARK A.
Applicants: PHILIP MORRIS PROD, PHILIP MORRIS PRODUCTS INC.
Application year: 1991
Main classification: A24F47
IPC codes: A24D1, A61M15, A24F47