Patent Publication Number: US-2012042885-A1

Title: Segmented smoking article with monolithic substrate

Description:
TECHNICAL FIELD 
     The present invention relates to products made or derived from tobacco, or that otherwise incorporate tobacco, and are intended for human consumption. The present application relates particularly to components and configurations of segmented-type smoking articles. 
     BACKGROUND 
     Popular smoking articles, such as cigarettes, have a substantially cylindrical rod-shaped structure and include a charge, roll or column of smokable material, such as shredded tobacco (e.g., in cut filler form), surrounded by a paper wrapper, thereby forming a so-called “smokable rod”, “tobacco rod” or “cigarette rod.” Normally, a cigarette has a cylindrical filter element aligned in an end-to-end relationship with the tobacco rod. Preferably, a filter element comprises plasticized cellulose acetate tow circumscribed by a paper material known as “plug wrap.” Preferably, the filter element is attached to one end of the tobacco rod using a circumscribing wrapping material known as “tipping paper.” It also has become desirable to perforate the tipping material and plug wrap, in order to provide dilution of drawn mainstream smoke with ambient air. Descriptions of cigarettes and the various components thereof are set forth in Tobacco Production, Chemistry and Technology, Davis et al. (Eds.) (1999) and U.S. Pat. No. 7,503,330 to Borschke et al, which is incorporated herein by reference. A cigarette is employed by a smoker by lighting one end thereof and burning the tobacco rod. The smoker then receives mainstream smoke into his/her mouth by drawing on the opposite end (e.g., the filter end) of the cigarette. 
     Certain types of cigarettes that employ carbonaceous fuel elements have been commercially marketed under the brand names “Premier” and “Eclipse” by R. J. Reynolds Tobacco Company. See, for example, those types of cigarettes described in Chemical and Biological Studies on New Cigarette Prototypes that Heat Instead of Burn Tobacco, R. J. Reynolds Tobacco Company Monograph (1988) and Inhalation Toxicology, 12:5, p. 1-58 (2000). More recently, a cigarette has been marketed in Japan by Japan Tobacco Inc. under the brand name “Steam Hot One. It has also been suggested that the carbonaceous fuel elements of segmented types of cigarettes may incorporate ultrafine particles of metals and metal oxides. See, for example, U.S. Pat. App. Pub. No. 2005/0274390 to Banerjee et al., which is incorporated by reference herein in its entirety. 
     Yet other types of smoking articles, such as those types of smoking articles that generate flavored vapors by subjecting tobacco or processed tobaccos to heat produced from chemical or electrical heat sources are described in U.S. Pat. Nos. 5,285,798 to Banerjee et al. and 7,290,549 to Banerjee et al., and U.S. Pat. App. Pub. No. 2008/0092912 to Robinson et al., which are incorporated by reference herein in their entirety. One type of smoking article that has employed electrical energy to produce heat has been commercially marketed by Philip Morris Inc. under the brand name “Accord.” 
     Smoking articles that employ sources of heat other than tobacco cut filler to produce tobacco-flavored vapors or tobacco-flavored visible aerosols have not received widespread commercial success. However, it would be highly desirable to provide smoking articles that demonstrate the ability to provide to a smoker many of the benefits and advantages of conventional cigarette smoking, without delivering considerable quantities of incomplete combustion and pyrolysis products. 
     SUMMARY 
     Embodiments of the present invention relate to smoking articles, and in particular, to rod-shaped smoking articles, such as cigarettes. A smoking article includes a lighting end (i.e., an upstream end) and a mouth end (i.e., a downstream end). The smoking article also includes an aerosol-generation system that includes (i) a heat generation segment, and (ii) an aerosol-generating region or segment located downstream from the heat generation segment. The smoking article may be configured in a variety of ways, including various insulative configurations related to the heat generation segment that may include one or more of glass or non-glass fiber materials that may or may not be woven, foamed monolithic material selected from metal, ceramic, and ceramic-metal composite (e.g., cermet), or other materials, which materials may also be incorporated in a buffer region between the heat generation and aerosol-generation segments. 
     Further features and advantages of the present invention are set forth in more detail in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments may better be understood with reference to the following drawings, which are illustrative only and are not limiting. 
         FIG. 1  and  FIG. 2  provide longitudinal cross-sectional views of representative smoking articles; 
         FIG. 3  shows a representative fuel element; 
         FIGS. 4A-4G  show representative fuel element and insulation embodiments; 
         FIG. 5  shows another representative smoking article embodiment; 
         FIGS. 6A-6D  show representative monolithic substrate element embodiments; and 
         FIGS. 7-9  each show a longitudinal cross-sectional view of a representative smoking article including a monolithic substrate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Aspects and embodiments of the present invention relating to various smoking articles, the arrangement of various components thereof, and the manner that those smoking articles incorporate overwrap components, are illustrated with reference to  FIGS. 1 and 2 . Like components are given like numeric designations throughout the figures. For the various figures, the thicknesses of the various wrapping materials and overwraps of the various smoking articles and smoking article components are exaggerated. Most preferably, wrapping materials and overwrap components are tightly wrapped around the smoking articles and smoking article components to provide a tight fit, and provide an aesthetically pleasing appearance. Exemplary smoking article construction may include features such as fibrous filter elements, foamed ceramic monoliths formed as insulators or fuel elements, and other features disclosed in U.S. patent application Ser. No. 12/546,107 to Sebastian, et al., filed Aug. 24, 2009, which is incorporated herein by reference in its entirety. 
     Referring to  FIG. 1 , a representative smoking article  10  in the form of a cigarette is shown. The smoking article  10  has a rod-like shape, and includes a lighting end  14  and a mouth end  18 . 
     At the lighting end  14  is positioned a longitudinally extending, generally cylindrical smokable lighting end segment  22 , incorporating smokable material  26 . A representative smokable material  26  can be a plant-derived material (e.g., tobacco material in cut filler form). An exemplary cylindrical smokable lighting end segment  22  includes a charge or roll of the smokable material  26  (e.g., tobacco cut filler) wrapped or disposed within, and circumscribed by, a paper wrapping material  30 . As such, the longitudinally extending outer surface of that cylindrical smokable lighting end segment  22  is provided by the wrapping material  30 . Preferably, both ends of the segment  22  are open to expose the smokable material  26 . The smokable lighting end segment  22  can be configured so that smokable material  26  and wrapping material  30  each extend along the entire length thereof. 
     Located downstream from the smokable lighting end segment  22  is a longitudinally extending, generally cylindrical heat generation segment  35 . The heat generation segment  35  includes a heat source  40  circumscribed by insulation  42 , which may be coaxially encircled by wrapping material  45 . The heat source  40  preferably is configured to be activated by combustion of the smokable material  26 . Ignition and combustion of the smoking material preferably provide a user with a desirable experience (with respect at least to flavor and time taken to light the smoking article  10 ). The heat generated as the smokable material is consumed most preferably is sufficient to ignite or otherwise activate the heat source  40 . 
     The heat source  40  may include a combustible fuel element that has a generally cylindrical shape and can incorporate a combustible carbonaceous material. Carbonaceous materials generally have high carbon contents. Preferred carbonaceous materials are composed predominately of carbon, typically have carbon contents of greater than about 60 percent, generally greater than about 70 percent, often greater than about 80 percent, and frequently greater than about 90 percent, on a dry weight basis. Fuel elements can incorporate components other than combustible carbonaceous materials (e.g., tobacco components, such as powdered tobaccos or tobacco extracts; flavoring agents; salts, such as sodium chloride, potassium chloride and sodium carbonate; heat stable graphite fibers; iron oxide powder; glass filaments; powdered calcium carbonate; alumina granules; ammonia sources, such as ammonia salts; and/or binding agents, such as guar gum, ammonium alginate and sodium alginate). A representative fuel element has a length of about 12 mm and an overall outside diameter of about 4.2 mm. A representative fuel element can be extruded or compounded using a ground or powdered carbonaceous material, and has a density that is greater than about 0.5 g/cm 3 , often greater than about 0.7 g/cm 3 , and frequently greater than about 1g/cm 3 , on a dry weight basis. See, for example, the types of fuel element components, formulations and designs set forth in U.S. Pat. No. 5,551,451 to Riggs et al. and U.S. Pat. App. Pub. No. 2009/0090373 to Borschke et al., which are incorporated herein by reference in their entirety. Particular embodiments of fuel elements are described below with reference to  FIG. 3 . 
     Another embodiment of a fuel element  40  may include a foamed carbon monolith formed in a foam process. In another embodiment, the fuel element  40  may be co-extruded with a layer of insulation  42 , thereby reducing manufacturing time and expense. Still other embodiments of fuel elements may include those of the types described in U.S. Pat. No. 4,922,901 to Brooks et al. or U.S. Pat. App. Pub. No. 2009/0044818 to Takeuchi et al., each of which is incorporated herein by reference. 
     A representative layer of insulation  42  can comprise glass filaments or fibers. The insulation  42  can act as a jacket that assists in maintaining the heat source  40  firmly in place within the smoking article  10 . The insulation  42  can be provided as a multi-layer component including an inner layer or mat  47  of non-woven glass filaments, an intermediate layer of reconstituted tobacco paper  48 , and an outer layer of non-woven glass filaments  49 . These may be concentrically oriented or each overwrapping and/or circumscribing the heat source. 
     In one embodiment, the inner layer  47  of insulation may include a variety of glass or non-glass filaments or fibers that are woven, knit, or both woven and knit (such as, for example, so-called 3-D woven/knit hybrid mats). When woven, an inner layer  47  may be formed as a woven mat or tube. A woven or knitted mat or tube can provide superior control of air flow with regard to evenness across the insulation layer, including as any thermal-related changes may occur to the layer). Those of skill in the art will appreciate that a woven, knit, or hybrid material may provide more regular and consistent air spaces/gaps between the filaments or fibers as compared to a non-woven material which is more likely to have irregularly closed and open spaces that may provide comparatively non-uniform and/or decreased air-flow. Various other insulation embodiments may be molded, extruded, foamed, or otherwise formed. Particular embodiments of insulation structures are described below with reference to  FIGS. 4A-4G . 
     Preferably, both ends of the heat generation segment  35  are open to expose the heat source  40  and insulation  42  to the adjacent segments. The heat source  40  and the surrounding insulation  42  can be configured so that the length of both materials is co-extensive (i.e., the ends of the insulation  42  are flush with the respective ends of the heat source  40 , and particularly at the downstream end of the heat generation segment). Optionally, though not necessarily preferably, the insulation  42  may extend slightly beyond (e.g., from about 0.5 mm to about 2 mm beyond) either or both ends of the heat source  40 . Moreover, smoke produced when the smokable lighting end segment  22  is burned during use of the smoking article  10  can readily pass through the heat generation segment  35  during draw by the smoker on the mouth end  18 . 
     The heat generation segment  35  preferably is positioned adjacent to the downstream end of the smokable lighting end segment  22  such that those segments are axially aligned in an end-to-end relationship, preferably abutting one another, but with no barrier (other than open air-space) therebetween. The close proximity of the heat generation segment  35  and the smokable lighting end segment  22  provides for an appropriate heat exchange relationship (e.g., such that the action of burning smokable material within the smokable lighting end segment  22  acts to ignite the heat source of the heat generation segment  35 ). The outer cross-sectional shapes and dimensions of the smokable lighting end and heat generation segments  22 ,  35 , when viewed transversely to the longitudinal axis of the smoking article, can be essentially identical to one another (e.g., both appear to have a cylindrical shape, each having essentially identical diameters). 
     The cross-sectional shape and dimensions of the heat generation segment  35 , prior to burning, can vary. Preferably, the cross-sectional area of the heat source  40  makes up about 10 percent to about 35 percent, often about 15 percent to about 25 percent of the total cross-sectional area of that segment  35 ; while the cross-sectional area of the outer or circumscribing region (comprising the insulation  42  and relevant outer wrapping materials) makes up about 65 percent to about 90 percent, often about 75 percent to about 85 percent of the total cross-sectional area of that segment  35 . For example, for a cylindrical smoking article having a circumference of about 24 mm to about 26 mm, a representative heat source  40  has a generally circular cross-sectional shape with an outer diameter of about 2.5 mm to about 5 mm, often about 3 mm to about 4.5 mm. 
     A longitudinally extending, cylindrical aerosol-generating segment  51  is located downstream from the heat generation segment  35 . The aerosol-generating segment  51  includes a substrate material  55  that, in turn, acts as a carrier for an aerosol-forming agent or material (not shown). For example, the aerosol-generating segment  51  can include a reconstituted tobacco material that includes processing aids, flavoring agents and glycerin. 
     The foregoing components of the aerosol-generating segment  51  can be disposed within, and circumscribed by, a wrapping material  58 . A wrapping material  58  can be configured to facilitate the transfer of heat from the lighting end  14  of the smoking article  10  (e.g., from the heat generation segment  35 ) to components of the aerosol-generating segment  51 . That is, the aerosol-generating segment  51  and the heat generation segment  35  can be configured in a heat exchange relationship with one another. The heat exchange relationship is such that sufficient heat from the heat source  40  is supplied to the aerosol-formation region to volatilize aerosol-forming material for aerosol formation. In some embodiments, the heat exchange relationship is achieved by positioning those segments in close proximity to one another. A heat exchange relationship also can be achieved by extending a heat conductive material from the vicinity of the heat source  40  into or around the region occupied by the aerosol-generating segment  51 . Particular embodiments of substrates are described below with reference to  FIG. 5 . 
     A representative wrapping material  58  for the substrate material  55  may include heat conductive properties to conduct heat from the heat generation segment  35  to the aerosol-generating segment  51 , in order to provide for the volatilization of the aerosol forming components contained therein. The substrate material  55  may be about 10 mm to about 22 mm in length, with certain embodiments being about 11 mm to about 12 mm in length, and other embodiments ranging up to about 21 mm. 
     The substrate material  55  can be provided from a blend of flavorful and aromatic tobaccos in cut filler form. Those tobaccos, in turn, can be treated with aerosol-forming material and/or at least one flavoring agent. The substrate material can be provided from a processed tobacco (e.g., a reconstituted tobacco manufactured using cast sheet or papermaking types of processes) in cut filler form. Certain cast sheet constructions may include about 270 to about 300 mg of tobacco per 10 mm of linear length. That tobacco, in turn, can be treated with, or processed to incorporate, aerosol-forming material and/or at least one flavoring agent, as well as a burn retardant (e.g., diammonium phosphate or another salt) configured to help prevent ignition and/or scorching by the heat-generation segment. A metal inner surface of the wrapping material  58  of the aerosol-generating segment  51  can act as a carrier for aerosol-forming material and/or at least one flavoring agent. 
     In other embodiments, the substrate  55  may include a tobacco paper or non-tobacco gathered paper formed as a plug section. The plug section may be loaded with aerosol-forming materials, flavorants, tobacco extracts, or the like in a variety of forms (e.g., microencapsulated, liquid, powdered). A burn retardant (e.g., diammonium phosphate or another salt) may be applied to at least a distal/lighting-end portion of the substrate to help prevent ignition and/or scorching by the heat-generation segment. 
     In these and/or other embodiments, the substrate  55  may include marumarized tobacco that has been formed into pellets or beads. Marumarized tobacco is known, for example, from U.S. Pat. No. 5,105,831 to Banerjee, et al., which is incorporated herein by reference. Marumarized tobacco may include about 20 to about 50 percent (by weight) tobacco blend in powder form, with glycerol (at about 20 to about 30 percent by weight), calcium carbonate (at about 40 to about 60 percent by weight), along with binder and flavoring agents. The beads, pellets, or other marumarized forms may be constructed in dimensions appropriate to fitting within a substrate section and providing for optimal air flow and production of desirable aerosol. 
     In these or other embodiments, the substrate  55  may include an open interior section  66  (as shown in  FIG. 2 ). This open region may allow for aerosol condensation and improved transport/aerosolization of vaporizable materials being released by heat during use of the smoking article. The surface of the interior opening  66  may be coated or otherwise treated with flavorants, tobacco extracts, or other materials to provide desirable flavors and/or organoleptic properties to the aerosol traveling therethrough. 
     In still other embodiments, the substrate  55  may include or be constructed from an extruded material. An extruded substrate may be formed in the same manner as described herein with reference to other extruded components. The extruded substrate may include, or may be essentially comprised of, tobacco, glycerin, water, and binder material, although certain formulation may exclude binder. The binder may be any binder commonly used for tobacco formulations including, for example, CMC (carboxymethyl cellulose) or guar gum, or it may include diammonium phosphate. In certain embodiments, a monolithic substrate may include about 10 to about 90 weight-percent tobacco, about 5 to about 50 weight-percent glycerin, about 1 to about 30 weight-percent water (after drying), and about 0 to about 10 weight-percent binder. 
     In one embodiment, the binder may be a custom binder designated here as “T-1.” The T-1 binder includes tobacco, water, and diammonium phosphate. Exemplary T-1 formulations may include about 70 to about 80 percent water (by weight), about 1 to about 5 percent DAP (diammonium phosphate), and about 20 to about 30 percent tobacco. The T-1 may be made by combining those components in a hot water bath and stirring until a thickened slurry is formed. The slurry may be dried (e.g., in a vacuum oven), then ground up and used as a binder. 
     For extrusion, the component mix may be loaded into the barrel of a batch extruder. One end of the barrel preferably will be fitted with an extrusion die for shaping the extrudate as a plastic mass. A female extrusion die may be provided with a tapered surface to facilitate smooth flow of the plastic mass. Such a die may have, for example, five, seven, ten, or more slots and provide extrudate readily separable into segments about 5 to about 50 mm in length and about 0.5 to about 5 mm in diameter, with a mass of about 50 to about 1000 mg. One or more central steel pins may be used to provide one or more corresponding central passageways through the extrudate (e.g., as is shown in  FIGS. 6A-6D , below). Exemplary extruded substrates will have a mass and density configured to provide a desirable flavor profile and air flow. An extruded or other monolithic substrate may have zero to about 15 slots on its surface and zero to about 14 longitudinal holes/channels through its body. A substrate with multiple internal channels may be extruded with a honeycomb, t-shaped, cross-shaped, or other cross-sectional geometry. A die pressure of about 3000 lbs. may be used for extrusion. The wet extruded rods preferably are placed on a well-ventilated tray for approximately one hour, and may then be carefully cut into lengths of about 5 mm to about 50 mm while preferably preserving the shape of the extrudate and the integrity of the axial hole(s). 
     It should also be appreciated that a substrate may be formed using the same formulations and components described herein for an extruded substrate. However, such an alternative embodiment may be formed by press-fit or molding/casting. Thus, the generic term “monolithic substrate” is used herein to include a substrate formed by extrusion or by one of those other methods. Reference to “extruded substrate” should be interpreted to include press-fit and/or molded/cast substrates of the same or substantially similar composition unless contextually excluded. 
     For preferred smoking articles, both ends of the aerosol-generating segment  51  are open to expose the substrate material  55  thereof. Components of the aerosol produced by burning the smokable lighting end segment  22  during use of the smoking article can readily pass through the aerosol-generating segment  51  during draw on the mouth end  18 . 
     Together, the heat generating segment  35  and the aerosol-generating segment  51  form an aerosol-generation system  60 . The aerosol-generating segment  51  is positioned adjacent to the downstream end of the heat generation segment  35  such that those segments  51 ,  35  are axially aligned in an end-to-end relationship. Those segments can abut one another, or be positioned in a slightly spaced apart relationship, which may include a buffer region  53 . The outer cross-sectional shapes and dimensions of those segments, when viewed transversely to the longitudinal axis of the smoking article  10 , can be essentially identical to one another. The physical arrangement of those components preferably is such that heat is transferred (e.g., by means that includes conductive and convective heat transfer) from the heat source  40  to the adjacent substrate material  55 , throughout the time that the heat source is activated (e.g., burned) during use of the smoking article  10 . 
     A buffer region  53  may reduce potential scorching or other thermal degradation of portions of the aerosol-generating segment  51 . The buffer region  53  may mainly include empty air space, or it may be partially or substantially completely filled with a non-combustible material such as, for example, metal, organic, inorganic, ceramic, or polymeric materials, or any combination thereof. The buffer regions may be from about 1 mm to about 10 mm or more in thickness, but often will be about 2 mm to about 5 mm in thickness. 
     The components of the aerosol-generation system  60  and the smokable lighting end segment  22  preferably are attached to one another, and secured in place using an overwrap material  64 . For example, the overwrap material  64  can include a paper wrapping material or a laminated paper-type material that circumscribes each of the heat generation segment  35 , at least a portion of outer longitudinally extending surface of the aerosol-generating segment  51 , and at least a portion of an the lighting end segment  22  that is adjacent to the heat generation segment. The inner surface of the overwrap material  64  may be secured to the outer surfaces of the components it circumscribes by a suitable adhesive. Preferably, the overwrap material  64  extends over a significant portion of the length of the smokable lighting end segment  22 . 
     The smoking article  10  preferably includes a suitable mouthpiece such as, for example, a filter element  65 , positioned at the mouth end  18  thereof. The filter element  65  preferably is positioned at one end of the cigarette rod adjacent to one end of the aerosol-generating segment  51 , such that the filter element  65  and the aerosol-generating segment  51  are axially aligned in an end-to-end relationship, abutting one another but without any barrier therebetween. Preferably, the general cross-sectional shapes and dimensions of those segments  51 ,  65  are essentially identical to one another when viewed transversely to the longitudinal axis of the smoking article. The filter element  65  may include filter material  70  that is overwrapped along the longitudinally extending surface thereof with circumscribing plug wrap material  72 . In one example, the filter material  70  includes plasticized cellulose acetate tow, while in some examples the filter material may further include activated charcoal in an amount from about 20 to about 80 mg disposed as a discrete charge or dispersed throughout the acetate tow in a “Dalmatian type” filter. Both ends of the filter element  65  preferably are open to permit the passage of aerosol therethrough. The aerosol-generating system  60  preferably is attached to filter element  65  using tipping material  78 . The filter element  65  may also include a crushable flavor capsule  76  of the type described in U.S. Pat. No. 7,479,098 to Thomas et al. and U.S. Pat. App. Pub. Nos. 2006/0272663 to Dube et al.; and  2009 / 0194118  to Ademe et al., which are incorporated herein by reference in their entirety. 
     The smoking article  10  may include an air dilution means, such as a series of perforations  81 , each of which may extend through the filter element tipping material  78  and plug wrap material  72  in the manner shown, and/or which may extend to or into the substrate  55 . 
     The overall dimensions of the smoking article  10 , prior to burning, can vary. Typically, smoking articles  10  are cylindrically shaped rods having circumferences of about 20 mm to about 27 mm, have overall lengths of about 70 mm to about 130 mm—often about 83 mm to about 100 mm. Smokable lighting end segments  22  typically have lengths of about 3 mm to about 15 mm, but can be up to about 30 mm. The aerosol-generation system  60  has an overall length that can vary from about 20 mm to about 65 mm. The heat generation segment  35  of the aerosol-generation system  60  may have a length of about 5 mm to about 30 mm; and the aerosol-generating segment  51  of the aerosol-generation system  60  may have an overall length of about 10 mm to about 60 mm. 
     The amount of smokable material  26  employed to manufacture the smokable lighting end segment  22  can vary. Typically, the smokable lighting end segment  22 , manufactured predominantly from tobacco cut filler, includes at least about 20 mg, generally at least about 50 mg, often at least about 75 mg, and frequently at least 100 mg, of tobacco material, on a dry weight basis. The packing density of the smokable material  26  within the smokable lighting end segment  22  preferably will be less than the density of the fuel element (e.g., about 100 to about 400 mg/cm 3 ). Preferably, the smokable lighting end segment  22  essentially comprises smokable material  26 , and does not include a carbonaceous fuel element component. 
     The combined amount of aerosol-forming agent and substrate material  55  employed in the aerosol-generating segment  51  can vary. The material preferably may be employed so as to fill the appropriate section of the aerosol-generating segment  51  (e.g., the region within the wrapping material  58  thereof) at a packing density of about 100 to about 400 mg/cm 3 . 
     During use, the smoker lights the lighting end  14  of the smoking article  10  using a match or cigarette lighter, in a manner similar to the way that conventional smoking articles are lit. As such, the smokable material  26  of the smokable lighting end segment  22  begins to burn. The mouth end  18  of the smoking article  10  is placed in the lips of the smoker. Thermal decomposition products (e.g., components of tobacco smoke) generated by the burning smokable material  26  are drawn through the smoking article  10 , through the filter element  65 , and into the mouth of the smoker. That is, when smoked, the smoking article yields visible mainstream aerosol that resembles the mainstream tobacco smoke of traditional cigarettes that burn tobacco cut filler. 
     Burning the smokable lighting end segment  22  heats the fuel element  40  of the heat generation segment  35  such that it preferably will be ignited or otherwise activated (e.g., begin to burn). The heat source  40  within the aerosol-generation system  60  will burn, and provide heat to volatilize aerosol-forming material within the aerosol-generating segment  51  as a result of the heat exchange relationship between those two segments. Certain preferred heat sources  40  will not experience volumetric decrease during activation, while others may degrade in a manner that reduces their volume. Preferably, the components of the aerosol-generating segment  51  do not experience thermal decomposition (e.g., charring or burning) to any significant degree. Volatilized components are entrained in the air that is drawn through the aerosol-generating region  51 . The aerosol so formed will be drawn through the filter element  65 , and into the mouth of the smoker. 
     During certain periods of use, aerosol formed within the aerosol-generating segment  51 , along with the aerosol (i.e., smoke) formed as a result of the thermal degradation of the smokable material  26  within the smokable lighting end segment  22 , will be drawn through the filter element  65  and into the mouth of the smoker, along with the aerosol (i.e., smoke) formed as a result of the thermal degradation of the smokable material  26  within the smokable lighting end segment  22 . Thus, the mainstream aerosol produced by the smoking article  10  includes tobacco smoke produced by the thermal decomposition of the tobacco cut filler as well as by the volatilized aerosol-forming material. For early puffs (i.e., during and shortly after lighting), most of the mainstream aerosol results from thermal decomposition of the smokable lighting end segment  22 . For later puffs (i.e., after the smokable lighting end segment  22  has been consumed and the heat source  40  of the aerosol-generation system  60  has been ignited), most of the mainstream aerosol that is provided will be produced by the aerosol-generation system  60 . When the smokable material  26  has been consumed, and the heat source  40  extinguishes, the use of the smoking article is ceased (i.e., the smoking experience is finished). 
     Referring to  FIG. 2 , a representative smoking article  10  in the form of a cigarette is shown. The smoking article  10  includes a heat generation segment  35  located at the lighting end  14 , a filter segment  65  located at the other end (mouth end  18 ), and an aerosol-generating segment  51  (which may incorporate tobacco) that is located in between those two segments near the lighting end. The heat generation segment  35  of  FIG. 2  can incorporate a generally cylindrical carbonaceous heat source circumscribed by insulation similar to what is shown in  FIG. 1 . The composition and dimensions of the various segments of the smoking article  10  in  FIG. 2  are generally similar in manner with respect to those set forth previously with reference to  FIG. 1 , but without a charge of smokable material at the distal/lighting end, such that the fuel element is ignited directly rather than by a smokable material that was ignited and burned. 
     A filter element  65  preferably is attached to the cigarette rod so formed using a tipping material  78 , in the general manner set forth previously with reference to  FIG. 1 . The smoking article optionally can be air-diluted by providing appropriate perforations  81  in the vicinity of the mouth end region  18 , as is known in the art. Filters may include materials and may be manufactured by methods such as, for example, those disclosed in U.S. Pat. Publ. Nos. 2008/0029118 to Nelson et al.; 2008/0142028 to Fagg, et al.; 2008/0302373 to Stokes et al.; 2009/028867 to Hutchens et al.; and 2009/009037 to Thomas et al., each of which is incorporated herein by reference. 
     Flavor may be provided or enhanced by capsule or microcapsule materials on or within the substrate material  55  of the aerosol-generating segment  51  ( FIG. 1  may be considered to have microcapsules present therein for illustrative purposes), the wrapping materials, the filter element  65 , or any other component capable of holding and releasing flavorants, preferably with minimal thermal degradation that would undesirably alter the flavor. Other flavor components associated with a filter may also be used; see, for example, U.S. Pat. No. 5,724,997 to Fagg, et al. 
     Cigarettes described with reference to  FIG. 2  may be used in much the same manner as those cigarettes commercially marketed under the trade name “Eclipse” by R. J. Reynolds Tobacco Company. See also the “Steam Hot One” cigarette marketed by Japan Tobacco Inc. 
     Smokable materials of the smokable lighting end segment most preferably incorporate tobacco of some form. Preferred smokable materials are composed predominantly of tobacco, based on the dry weights of those materials. That is, the majority of the dry weight of those materials, and the majority of the weight of a mixture incorporating those materials (including a blend of materials, or materials having additives applied thereto or otherwise incorporated therein) are provided by tobacco of some form. Those materials may be made all of tobacco material, and not incorporate any non-tobacco fillers, substitutes or extenders. The smokable material can be treated with tobacco additives that are traditionally used for the manufacture of cigarettes, such as casing and/or top dressing components. These tobacco components may be understood with reference to the examples and references set forth in U.S. Pat. App. Pub. No. 2007/0215167 to Crooks, et al., which is incorporated herein by reference in its entirety. 
     Fuel elements of the heat generation segment may vary. Suitable fuel elements, and representative components, designs and configurations thereof, and manners and methods for producing those fuel elements and the components thereof, are set forth in U.S. Pat. Nos. 4,714,082 to Banerjee et al.; 4,756,318 to Clearman et al.; 4,881,556 to Clearman et al.; 4,989,619 to Clearman et al.; 5,020,548 to Farrier et al.; 5,027,837 to Clearman et al.; 5,067,499 to Banerjee et al.; 5,076,297 to Farrier et al.; 5,099,861 to Clearman et al.; 5,105,831 to Banerjee et al.; 5,129,409 to White et al.; 5,148,821 to Best et al.; 5,156,170 to Clearman et al.; 5,178,167 to Riggs et al.; 5,211,684 to Shannon et al.; 5,247,947 to Clearman et al.; 5,345,955 to Clearman et al.; 5,469,871 to Barnes et al.; 5,551,451 to Riggs; 5,560,376 to Meiring et al.; 5,706,834 to Meiring et al.; and 5,727,571 to Meiring et al.; and U.S. Pat. App. Pub. Nos. 2005/0274390 and 2010/0065075 to Banerjee et al.; which are incorporated herein by reference. 
     Fuel elements often comprise carbonaceous material and may include ingredients such as graphite or alumina, as well as high carbon content carbonaceous material. Carbonaceous fuel elements include the type that have been incorporated within those cigarettes commercially marketed under the trade names “Premier” and “Eclipse” by R. J. Reynolds Tobacco Company. See also the “Steam Hot One” cigarette marketed by Japan Tobacco Inc. Some other embodiments of fuel elements are set forth in U.S. Pat. Nos. 5,178,167 to Riggs et al. and 5,551,451 to Riggs et al., both which are incorporated herein by reference in their entirety, but certain embodiments may lack the sodium, graphite, and/or calcium carbonate set forth therein. Some fuel element embodiments may include a foamed carbon monolith. In another embodiment, the fuel element  40  may be co-extruded with a layer of insulation  42 , thereby reducing manufacturing time and expense. 
       FIG. 3  shows an example of a carbonaceous fuel element  340  of the type disclosed above with reference to heat source  40 . The following exemplary embodiments are described with reference thereto, but may be applied to fuel elements having different geometries and/or underlying compositions. 
     In a first embodiment, a fuel element  340  may be dip-coated with a mixture of two or more precursors. For example, copper nitrate hemi pentahydrate (available from Alfa Aesar) is mixed with equal weight of cerium nitrate hexahydrate (available from Alfa Aesar). The mixture of nitrates may then be dissolved in water (50% w/w). The fuel element  340  will then be coated with this aqueous solution, and the coated fuels are dried overnight at about 110° C. 
     The treated fuel element  340  is subjected to a heat treatment under nitrogen in a programmable Barnstead THERMOLYNE 62700 furnace by being heated to about 400° C. at a ramp rate of about 5° C. per minute and held for about four hours. The minimum temperatures at which a complete conversion of cerium nitrate hexahydrate to ceria and conversion of copper nitrate hemi pentahydrate to copper oxide take place may be determined by thermo-gravimetric analysis (TGA) using Model STA409 PC analyzer from Netzsch Instruments, Inc. Both transitions typically take place at or below about 300° C. 
     The fuel element  340  may be equilibrated under ambient conditions and inserted into a cigarette  10  similar in construction to that shown in  FIG. 1 . A cigarette  10  thus prepared may be smoked under 50/30/2 smoking conditions (i.e., 50 ml puffs of 2 second duration separated by 28 seconds) and CO in the mainstream measured by nondispersive infrared spectroscopy (NDIR), for example, using an NGA 2000 from Rosemount Inc. Treatment of the fuel with a mixture of cerium nitrate hexahydrate and copper nitrate hemi pentahydrate followed by heat treatment of the fuel will result in at least about 65% (e.g., about 68%) reduction of mainstream CO as compared to a control treated only with water. Nicotine and tar yields of the cigarettes will not be significantly affected by this modified fuel element. This reduction of CO is believed to result from a synergistic effect in the catalytic activity of the two metal oxides. The ratio of copper nitrate hemi pentahydrate and cerium nitrate hexahydrate may be further optimized for maximum catalytic activity. In other preparations of similar embodiments, the fuel element  340  can be dip-coated with the hydrates in sequence or the hydrates can be applied together or in sequence to the finished product either drop wise or by dipping the fuel end of the finished product into the hydrate solution. 
     In another embodiment described with reference to making a fuel element such as, for example, a fuel element  340  shown in  FIG. 3 , two or more metal nitrates or other metal oxide precursors may be mixed and dissolved in water. The solution may then be applied to graphite. The treated graphite may then be dried and calcined to yield metal-oxide coated graphite. Proper selection of metal oxides and processing conditions may yield synergistic catalytic activity. In variant embodiments of this application, the precursor solutions can be added sequentially to graphite, i.e. one metal nitrate solution is added to the graphite, dried and calcined as described before to convert the metal nitrate to metal oxide. The resulting metal oxide coated graphite may then be impregnated with a second metal oxide precursor solution followed by drying and calcination. 
     In yet another embodiment described with reference to making a fuel element such as, for example, a fuel element  340 , about 7.5 grams of cerium (III) nitrate hexahydrate (available from Alfa Aesar) and about 7.5 grams of copper (II) nitrate hemi pentahydrate (available from Alfa Aesar) may be dissolved in about 7 ml of water. Next, about 18 grams of graphite powder (available Superior Graphite Inc.) may be impregnated with the metal nitrate solution and dried overnight in air. The treated graphite may then be calcined at about 300° C. for about one hour under a nitrogen atmosphere in, for example, a programmable Barnstead THERMOLYNE 62700 furnace, where the ramp rate may be set at about 5° C./minute. Calcination will lead to decomposition of both the metal nitrates to their respective metal oxides. 
     The metal oxide-coated graphite may then be ground in a pestle mortar and combined with about 72 grams of milled BKO carbon powder (available from Barnaby and Suttcliffe), and about 10 grams of guar gum. Further mixing may be done in, for example, a Sigma blade mixer (Teledyne) for about an hour at a low speed. Water may then be added to convert the powder into plastic dough by mixing for about two additional hours. Sufficient water preferably will be added to ensure that the plastic mix is stiff enough to hold its shape after extrusion. The moisture content of the dough at this stage will typically be about 42 to 43% (w/w). The dough preferably will be aged overnight in a sealed container at room temperature. 
     For extrusion, the plastic mix may be loaded into the barrel of a batch extruder. One end of the barrel preferably will be fitted with an extrusion die for shaping the extrudate. A female extrusion die may be provided with a tapered surface to facilitate smooth flow of the plastic mass. Such a die may have, for example, five or seven slots and be about 4.2 mm in diameter. An optional central steel pin may be used to provide a central passageway through the extrudate (e.g., as is shown in  FIGS. 4B-4C , below). A die pressure of about 3000 lbs. may be used for extrusion. The wet extruded rods preferably are placed on a well-ventilated tray for approximately one hour, and may then be carefully cut into about 12 mm lengths while preferably preserving the shape of the extrudate and the integrity of the axial hole. The cut fuel rods  340  may then be dried overnight at about room temperature. A cigarette  10  constructed using this embodiment and smoked under 60/30/2 smoking conditions may provide mainstream aerosol having its CO reduced by at least about 50% (for example, about 56%), compared to a cigarette with an untreated control fuel element. 
     Addition of metal oxide precursor solution to graphite occasionally may result in agglomeration of the metal oxide on the graphite surface, leading to reduced catalytic activity. Such agglomeration is believed due to the relatively low surface area and hydrophobic nature of the graphite surface. Adding carbon to graphite before impregnation with precursor solution will minimize agglomeration of the metal oxide and result in a higher catalytic activity. In another embodiment, about 18 grams of graphite may be mixed with about 18 grams of milled BKO carbon. About 15 grams of copper nitrate hemi-penta-hydrate will be dissolved in about 7.5 ml of water. The mixture of graphite and carbon may then uniformly be impregnated with the copper nitrate solution and dried overnight at room temperature. The coated carbon-graphite mixture may thereafter be calcined at about 300° C. for one hour under a nitrogen atmosphere. Fuel elements may be extruded and cut as described earlier. Cigarettes made with this metal nitrate-treated, carbon-graphite mixture will produce about 50% less CO in the mainstream smoke than a control cigarette using an untreated fuel element. 
     Compared to graphite, BKO milled carbon has a large surface area and consequently has a large adsorption capacity for the metal oxide catalyst precursor solution. This results in a highly uniform dispersion of the solution with minimum agglomeration of the metal oxide and thus a good activity of the metal oxide catalyst. 
     In still another embodiment, about 7.5 grams of copper nitrate hemi pentahydrate may be dissolved in 7 grams of water. About 18 grams of BKO milled carbon is impregnated with the solution and the mixture is dried overnight at room temperature. The treated carbon is calcined at about 300° C. for one hour under nitrogen atmosphere. The calcined carbon is mixed with other fuel ingredients and is extruded into fuel rods as described before. A cigarette prepared with this fuel will have about a 50% reduction in mainstream CO compared to cigarettes produced with untreated fuel elements. In addition, cigarettes produced with the treated milled carbon fuel may be easier to light than cigarettes produced with fuel made with precursor-treated graphite described above. 
     The carbonaceous fuel elements commonly in use typically are extruded with a binder that is mostly organic in nature. Some commonly used binders include ammonium alginate, carboxymethyl cellulose, ethyl cellulose and guar gum. These binders provide good flow characteristics and improved physical and mechanical properties for processing the extrudate. However, upon combustion the extruded fuel may produce volatile organic compounds that negatively influence the taste, aroma, and chemistry of the smoke. These volatile organic compounds may nearly be eliminated if the extruded fuel is calcined prior to its use in the cigarette. 
     Accordingly, certain fuel embodiments may be extruded, having been formed using (by weight) about 30% calcium carbonate, about 10% guar gum, about 10% copper nitrate-treated graphite, and about 50% carbon. Treatment of graphite with catalyst precursor and the process of extrusion may be conducted as described above. The extruded fuel may be calcined at about 500° C. for about two hours under nitrogen atmosphere. In test cigarettes constructed with the calcined fuels no significant impact was observed on the yields of tar, nicotine and carbon monoxide of the cigarette but significant improvements were noted with regard to taste and aroma of the mainstream and side stream smoke. 
     The fuel element preferably will be circumscribed or otherwise jacketed by insulation, or other suitable material. The insulation can be configured and employed so as to support, maintain and retain the fuel element in place within the smoking article. The insulation may additionally be configured such that drawn air and aerosol can pass readily therethrough. Examples of insulation materials, components of insulation assemblies, configurations of representative insulation assemblies within heat generation segments, wrapping materials for insulation assemblies, and manners and methods for producing those components and assemblies, are set forth in U.S. Pat. Nos. 4,807,809 to Pryor et al.; 4,893,637 to Hancock et al.; 4,938,238 to Barnes et al.; 5,027,836 to Shannon et al.; 5,065,776 to Lawson et al.; 5,105,838 to White et al.; 5,119,837 to Banerjee et al.; 5,247,947 to Clearman et al.; 5,303,720 to Banerjee et al.; 5,345,955 to Clearman et al.; 5,396,911 to Casey, III et al.; 5,546,965 to White; 5,727,571 to Meiring et al.; 5,902,431 to Wilkinson et al.; and 5,944,025 to Cook et al.; which are incorporated herein by reference. Insulation assemblies have been incorporated within the types of cigarettes commercially marketed under the trade names “Premier” and “Eclipse” by R. J. Reynolds Tobacco Company, and as “Steam Hot One” cigarette marketed by Japan Tobacco Inc. 
       FIGS. 4A-4G  show different embodiments of insulation and fuel elements of a heat generation segment. In certain embodiments, the insulation layer may include about 40 to about 50 percent (by weight) flue-cured tobacco lamina, about 20 to about 25 percent (by weight) water-soluble flue-cured tobacco stems extract, and about 20 to about 25 percent (by weight) wood pulp. In certain embodiments, the layer may include about 20 percent (by weight) carbon fiber, or about 20 percent (by weight) c-glass fiber. Preferred insulation layers thus formed include a treatment of about 5 to about 15 percent ammonium chloride (NH 4 Cl), or of a 50/50 mixture of about 5 percent NH 4 Cl and 5 percent sodium bicarbonate, by which is meant that the compound(s) will be present on the insulation layer sheet(s). These and other flame-retardants may be used in varying amounts. The insulation thus formed may be manufactured on a standard fourdrinier paper-making machine. Preferred insulation layer sheets thus formed will include a porosity of about 50 to about 150 cfm, a basis weight of about 80 to about 150 gsm, and a tensile strength of about 2000 to about 3000 gsm. 
     An insulation layer  42  may include an inner-facing geometry configured to engage and longitudinally retain a heat source  40 . The engagement may be accomplished by a compression fit, co-extrusion of heat-source and insulation materials, or other methods known or developed in the art. Preferred heat sources include those that experience little if any volumetric decrease during a smoking activity. Certain heat sources may degrade and shrink longitudinally and/or circumferentially after being ignited, but—for preferred embodiments incorporating complementarily-shaped insulation elements—heat source embodiments including a matrix or other composition that generally retains volume after ignition are preferable. 
       FIGS. 4A-4B  show, respectively, an end view of an insulation material  442  and heat source  440 , and a perspective view of the heat source  440  without the insulation material  442 . These elements are configured to interlockingly engage with a dovetail connection, where the inward-facing surface insulation material  442  includes an inward-facing geometry with a flared tongue protrusion  442   c  configured to engage in dovetail fashion with a complementarily-shaped flared groove  440   c  in an outward-facing recessed groove geometry of the heat source  440 . The outward-facing geometry of the heat source  440  includes generally elongate rounded grooves  440   d  configured to facilitate airflow. In one embodiment, the dovetail groove  440   c  will be only one-half as wide at its narrowest portion (at the top/edge of the outer heat source surface) as it is at the groove&#39;s widest portion. It should be appreciated that the flared tongue and groove may be constructed in variant fashion, by—for example—reversing the relative position of the dovetailed elements, orienting them other than longitudinally, and/or providing other interengaging tongue/groove geometries. 
       FIGS. 4C-4D  show, respectively, an end view of a heat source  740 , and a longitudinal section view of the heat source  740  with the insulation material  742 . These elements are configured to interlockingly engage, with the insulation forming a retaining lip or shoulder  742   a  at the lighting end  714 . That is, the inward-facing surface of the insulation material  742  includes an inward-facing geometry with a protrusion  742   a  configured to engage around a complementarily-shaped lighting end decreased-diameter cylindrical segment  740   a  of the heat source  740 . The outward-facing geometry of the heat source  740  may include generally elongate rounded exterior grooves  740   d  that are configured to facilitate airflow. A heat source  740  may include one or more generally central longitudinal channels  741 . 
       FIGS. 4E-4F  show, respectively, a perspective view of a generally frustoconical heat source  840 , and a longitudinal section view of the heat source  840  with an insulation material  842 . These elements are configured to engage, with the inward-facing geometry of the insulation  842  forming a generally frustoconical space that houses and complementarily fits the heat source  840 . The outward-facing geometry of the heat source  840  may include generally elongate rounded exterior grooves  840   d  that are configured to facilitate airflow. In many embodiments, five to eight such grooves may provide a desired airflow. This and other embodiments may include features described with reference only in various other embodiments herein. For example, a heat source  840  may include one or more generally central longitudinal channels  841 . 
       FIG. 4G  shows a longitudinal section view of the heat source  940  with an insulation material  942 . These elements are configured to engage, with the inward-facing geometry of the insulation  942  forming a generally columnar space that houses and complementarily fits the heat source  940 . The heat source  940  includes a flared base  940   e  opposite the lighting end  914  that is configured to longitudinally retain it within the insulation  942 . 
     In one specific example, an insulation material may be constructed including about 50 percent (by weight) flue-cured tobacco lamina, about 25 percent (by weight) water-soluble flue-cured tobacco stems extract, and about 25 percent (by weight) wood pulp. After being formed into a sheet, the material may be treated with about 5 to about 15 percent ammonium chloride (NH 4 Cl), or of a 50/50 mixture of about 5 percent NH 4 Cl and 5 percent sodium bicarbonate. The insulation material may be manufactured as a sheet on a standard fourdrinier paper-making machine. The sheet insulation may include a porosity of about 50 to about 150 cfm, a basis weight of about 80 to about 150 gsm, and a tensile strength of about 2000 to about 3000 gsm. 
     In another example, an insulation material may be constructed including about 40 percent (by weight) flue-cured tobacco lamina, about 20 percent (by weight) water-soluble flue-cured tobacco stems extract, about 20 percent (by weight) wood pulp, and about 20 percent (by weight) c-glass fiber. After being formed into a sheet, the material may be treated with about 5 to about 15 percent ammonium chloride (NH 4 Cl), or of a 50/50 mixture of about 5 percent NH 4 Cl and 5 percent sodium bicarbonate. The insulation material may be manufactured as a sheet on a standard fourdrinier paper-making machine. The sheet insulation may include a porosity of about 50 to about 150 cfm, a basis weight of about 80 to about 150 gsm, and a tensile strength of about 2000 to about 3000 gsm. 
     In still another example, an insulation material may be constructed including about 40 percent (by weight) flue-cured tobacco lamina, about 20 percent (by weight) water-soluble flue-cured tobacco stems extract, about 20 percent (by weight) wood pulp, and about 20 percent (by weight) carbon fiber. After being formed into a sheet, the material may be treated with about 5 to about 15 percent ammonium chloride (NH 4 Cl), or of a 50/50 mixture of about 5 percent NH 4 Cl and 5 percent sodium bicarbonate. The insulation material may be manufactured as a sheet on a standard fourdrinier paper-making machine. The sheet insulation may include a porosity of about 50 to about 150 cfm, a basis weight of about 80 to about 150 gsm, and a tensile strength of about 2000 to about 3000 gsm. 
     Flame/burn retardant materials and additives useful in insulation may include silica, carbon, ceramic, metallic fibers and/or particles. When treating cellulosic or other fibers such as—for example—cotton, boric acid or various organophosphate compounds may provide desirable flame-retardant properties. In addition, various organic or metallic nanoparticles may confer a desired property of flame-retardancy, as may diammonium phosphate and/or other salts. Other useful materials may include organo-phosphorus compounds, borax, hydrated alumina, graphite, potassium tripolyphosphate, dipentaerythritol, pentaerythritol, and polyols. Others such as nitrogenous phosphonic acid salts, mono-ammonium phosphate, ammonium polyphosphate, ammonium bromide, ammonium chloride, ammonium borate, ethanolammonium borate, ammonium sulphamate, halogenated organic compounds, thio-urea, and antimony oxides may be used but are not preferred agents. In each embodiment of flame-retardant, burn-retardant, and/or scorch-retardant materials used in insulation, substrate material and other components (whether alone or in any combination with each other and/or other materials), the desirable properties most preferably are provided without undesirable off-gassing or melting-type behavior. 
     An insulation fabric made by any one of the above processes preferably will have sufficient oxygen diffusion capability to sustain a smoking article such as a cigarette lit during a desired usage time. Accordingly the insulation fabric preferably will be porous by virtue of its construction. In knit, woven, or combined woven and knit constructions, the required porosity may be controlled by configuring the assembly machinery to leave sufficient (desirably sized) gaps between fibers to allow for oxygen diffusion into the heat source. For non-woven fabrics, which may not be porous enough to promote evenly sustained combustion, additional porosity may be achieved by perforations into the insulation by methods known in the art including, for example, hot or cold pin perforation, flame perforation, embossing, laser cutting, drilling, blade cutting, chemical perforation, punching, and other methods. Each of the buffer and the insulation may include non-glass material that is woven, knit, or a combination thereof, a foamed metal material, a foamed ceramic material, a foamed ceramic metal composite, and any combination thereof, and the material in the insulation may be the same as or different than that in the buffer. 
     The aerosol-forming material can vary, and mixtures of various aerosol-forming materials can be used, as can various combinations and varieties of flavoring agents (including various materials that alter the sensory and/or organoleptic character or nature of mainstream aerosol of a smoking article), wrapping materials, mouth-end pieces, filter elements, plug wrap, and tipping material. Representative types of these components are set forth in U.S. Pat. App. Pub. No. 2007/0215167 to Crooks, et al., which is incorporated herein by reference in its entirety. 
     The substrate material can incorporate tobacco of some form, normally is composed predominantly of tobacco, and can be provided by virtually all tobacco material. The form of the substrate material can vary. In some embodiments, the substrate material is employed in an essentially traditional filler form (e.g., as cut filler). The substrate material can be otherwise formed into desired configurations. The substrate material can be used in the form of a gathered web or sheet, using the types of techniques generally set forth in U.S. Pat. No. 4,807,809 to Pryor et al, which is incorporated herein by reference in its entirety. The substrate material can be used in the form of a web or sheet that is shredded into a plurality of longitudinally extending strands, using the types of techniques generally set forth in U.S. Pat. No. 5,025,814 to Raker, which is incorporated herein by reference in its entirety. The substrate material can have the form of a loosely rolled sheet, such that a spiral type of air passageway extends longitudinally through the aerosol-generating segment. Representative types of tobacco containing substrate materials can be manufactured from mixtures of tobacco types; or from one predominant type of tobacco (e.g., a cast sheet-type or paper-type reconstituted tobacco composed primarily of burley tobacco, or a cast sheet-type or paper-type reconstituted tobacco composed primarily of Oriental tobacco). 
     The substrate material also can be treated with tobacco additives of the type that are traditionally used for the manufacture of cigarettes, such as casing and/or top dressing components. See, for example, the types of components set forth in U.S. Pat. Publication 2004/0173229 to Crooks et al, which is incorporated herein by reference in its entirety. 
     The manner by which the aerosol-forming material is contacted with the substrate material (e.g., the tobacco material) can vary. The aerosol-forming material can be applied to a formed tobacco material, or can be incorporated into processed tobacco materials during manufacture of those materials. The aerosol-forming material can be dissolved or dispersed in an aqueous liquid, or other suitable solvent or liquid carrier, and sprayed onto that substrate material. See, for example, U.S. Patent Application Pub. No. 2005/0066986 to Nestor et al, which is incorporated herein by reference in its entirety. The amount of aerosol-forming material employed relative to the dry weight of substrate material can vary. Materials including exceedingly high levels of aerosol-forming material can be difficult to process into cigarette rods using conventional types of automated cigarette manufacturing equipment. 
     Cast sheet types of materials may incorporate relatively high levels of aerosol-forming material. Reconstituted tobaccos manufactured using paper-making types of processes may incorporate moderate levels of aerosol-forming material. Tobacco strip and tobacco cut filler can incorporate lower amounts of aerosol-forming material. Various paper and non-paper substrates including gathered, laminated, laminated metal/metallic, strips, beads such as alumina beads, open cell foam, foamed monolith, air permeable matrices, and other materials can be used within the scope of the invention. See, for example, U.S. Pat. Nos. 5,183,062; 5,203,355; and 5,588,446; each to Clearman, and each of which is incorporated herein by reference. 
     In one embodiment, the substrate may be constructed in a novel multilayer fashion not including cast sheet construction, discussed here with reference to  FIG. 5 , which is a longitudinal section view of a cigarette  510  having a lighting end  514  and a mouth end  518 . The substrate  555  (which may be used in other embodiment such as, for example, those discussed with reference to  FIG. 1  and  FIG. 2 ) includes a multilayer construction that preferably is stitch-bonded together. 
     A generally cylindrical or other-shaped substrate core  563  may be centrally located in the substrate  555 . The core  563  may include fabric (which may be treated with glycerin), and may also include an open longitudinal channel  566 . A first outer layer  593  may be disposed coaxially around (i.e., generally encircling) the substrate core  563 . The first outer layer  593  may be constructed including a fabric material such as, for example cotton or rayon. The fabric material preferably has been treated with glycerin such that the glycerin is absorbed into the fabric, which may also include one or more flame-retardant, burn-retardant, and or scorch-retardant agents. The first outer layer  593  may be constructed as a plurality of layers including a multilayer construction with two or more layers. 
     An intermediate layer  592  may be disposed generally coaxially/concentrically around the first outer layer  593 . The intermediate layer  592  is constructed as a layer of aromatic tobacco paper  592 . The tobacco paper may be treated with flavoring agents, including those known for use in treating cut tobacco, tobacco papers, and generally within the tobacco art, as well as agents that may yet be developed. Preferred flavoring agents will help provide a mainstream aerosol including desirable flavor and aroma. A second outer layer  591  may be disposed coaxially around the intermediate layer  592 . Like the first outer layer  593 , the second outer layer may be constructed as a plurality of layers including a multilayer construction with two or more layers. And, it may be constructed of fabric material that preferably has been treated with glycerin such that the glycerin is absorbed into the fabric, which may also include one or more flame-retardant, burn-retardant, and or scorch-retardant agents. 
     At least a portion of the first outer layer  593 , second outer layer  591 , and/or intermediate layer  592  preferably will be stitch-bonded together using a substrate heat-conducting material such as, for example, a metallic material (including as one example, aluminum). Stitch-bonding is known in the art of making non-woven fabrics (e.g., using barbed needles to entangle or otherwise bond fibers together to form a non-woven fabric or web). A stitch-bonding process may be used to form a three-layered substrate (e.g., as shown diagrammatically in  FIG. 5 ) including at least one first outer layer  593 , at least one intermediate layer  592 , and at least one second outer layer  591  by joining one or more portions of two or more of the layers together. The heat-conducting material will help transmit heat from the heat-generation segment  535  in a matter configured to generate a desirable aroma and flavor from the substrate  555 . This construction may be superior to cast sheet substrates, which may experience scorching and/or introduce undesirable flavors, tastes, aromas, etc. The presence of glycerin and the layered construction described with reference to the embodiment of  FIG. 5  will help reduce scorching and minimize undesirable flavors and/or aromas associated with scorching. Embodiments with this and other substrate embodiments may be used with cigarettes including smokable material at the lighting end (e.g., as in  FIG. 1 ). 
     In still other embodiments, the substrate portion of an aerosol-generation segment may include or may be constructed from an extruded or other monolithic material. An extruded substrate may be formed in the same manner as described herein with reference to other extruded components. The extruded or other monolithic substrate may include, or may be essentially comprised of, tobacco, glycerin, water, and binder material. In certain embodiments, a monolithic substrate may include about 10 to about 90 weight-percent tobacco, about 5 to about 50 weight-percent glycerin, about 1 to about 30 weight-percent water (before being dried and cut), and about 0 to about 10 weight-percent binder. It may also include a filler such as, for example, calcium carbonate and/or graphite. 
     For extrusion, the component mix may be loaded into the barrel of a batch extruder. One end of the barrel preferably will be fitted with an extrusion die for shaping the extrudate as a plastic mass. A female extrusion die may be provided with a tapered surface to facilitate smooth flow of the plastic mass. Such a die may have, for example, one, five, seven, ten, or more (or fewer) slots and provide for extrudate with about 5 to about 10 mm outer diameter, although the outer diameter may be larger and the substrate may not necessarily have a circular cross-section. One or more central steel pins may be used to provide one or more corresponding central passageways, which may include up to 14 or more such passages through the extrudate (e.g., as is shown in  FIGS. 6A-6D , discussed below). The passages may be circular and/or polygonal in cross section, including providing a monolithic substrate having a generally honeycomb cross-sectional appearance. 
     Exemplary extruded and other monolithic substrates will have a mass and density configured to provide a desirable flavor profile and air flow. A monolithic substrate may have zero to at least one to about 15 slots/grooves on its exterior surface and zero to about 14 longitudinal holes/channels through its body. Certain preferred embodiments may include at least one generally centered passage that is about 0.025 to about 0.1 inches in diameter. Generally, the passages may have internal diameters of less than 0.001 to about 0.1 inches. A substrate with multiple internal channels may be extruded with a honeycomb geometry. A die pressure of about 3000 lbs. may be used for extrusion. The wet extruded rods preferably are placed on a well-ventilated tray for approximately one hour, and may then be carefully cut into lengths of about 5 mm to about 50 mm while preferably preserving the shape of the extrudate and the integrity of the axial hole(s). The dried weight of the substrate units may range from about 50 to about 1000 mg. 
     Following extrusion, drying, and cutting to a desired length, the substrate may be assembled into a segmented smoking article such as an Eclipse-type cigarette using a manual assembly method or a cigarette-making machine (e.g., KDF or Protus by Hauni Maschinenbau AG). Smaller diameter monolithic substrate elements may be combined by being wrapped, adhered, or otherwise assembled together for use in a smoking article as described for other substrate embodiments herein. Preferred substrate wraps include foil paper, heavy-gauge paper, plug wrap, and/or cigarette paper. 
       FIG. 6A  shows a generally cylindrical slotted/grooved monolithic substrate element  600  including a plurality of external grooves  602 .  FIG. 6B  shows a grooved monolithic substrate element  610  including a plurality of external grooves  612  and a center hole  614  that extends longitudinally through its length. As shown in  FIGS. 6A-6B , the grooves/slots do not have to be the same shape(s) as each other.  FIG. 6C  shows a generally cylindrical non-grooved monolithic substrate element  620  including a center-hole  624  (it should be appreciated that the “center-hole” may actually be off-center in certain embodiments).  FIG. 6D  shows a non-grooved monolithic substrate element  630  including a center-hole  634  and a plurality of holes/channels  636  configured in a honeycomb-like manner and extending through its length. 
     In one embodiment, a smoking article may be constructed with an monolithic substrate  763 , described here with reference to  FIG. 7 , which is a longitudinal section view of a cigarette  710  having a lighting end  714  and a mouth end  718 . The monolithic substrate  763  (which may be used in other embodiments such as, for example, those discussed with reference to  FIGS. 1 ,  2 , and  5 ) may be formed by any appropriate extrusion method and is shown with a center-hole  795  extending longitudinally therethrough. The monolithic substrate, cut to length may comprise about 1/16 to about ⅝ of the total length of the cigarette, often about 1/10 to about ½ thereof (e.g., a 10 mm, 12 mm, or 50 mm long substrate element in an 85 mm or 130 mm long cigarette). The substrate segment  755  of the cigarette body includes a hollow spacing tube  767  disposed between the substrate  767  and the filter  770 . The filter  770  is shown as constructed with overlying layers of plug wrap  772  and tipping paper  778 . The substrate  763  and tube  767  are surrounded by a wrapping material  758 , which may be configured—for example—as a heat-conducting material (e.g., foil paper), heavy-gauge paper, plug wrap, or cigarette paper. A cylindrically-encompassing wrapping material  764  (such as, for example, cigarette paper or heavy-gauge paper) may be provided to connect the heat-generation segment  735 , central substrate segment  755 , and filter segment  765 . The heat-generation segment  735  and other components may be constructed as described herein and elsewhere in this and other embodiments configured to be practiced within the scope of the present invention. 
     In another embodiment, a smoking article may be constructed with an elongate monolithic substrate  863 , described here with reference to  FIG. 8 , which is a longitudinal section view of a cigarette  810  having a lighting end  814  and a mouth end  818 . The elongate monolithic substrate  863  (which may be used in other embodiments) may be formed by any appropriate extrusion method and is shown with a center-hole  895  extending longitudinally therethrough. The filter  870  is shown as constructed with overlying layers of plug wrap  872  and tipping paper  878 . The substrate  863  is surrounded by a wrapping material  858 , which may be configured—for example—as a heat-conducting material (e.g., foil paper), heavy-gauge paper, plug wrap, or cigarette paper. A cylindrically-encompassing wrapping material (such as, for example, cigarette paper or heavy-gauge paper) may be provided to connect the heat-generation segment  835 , central substrate segment  855  (consisting essentially of the substrate in this embodiment), and filter segment  865 . The heat-generation segment  835  and other components may be constructed as described herein and elsewhere in this and other embodiments configured to be practiced within the scope of the present invention. 
     In one embodiment, a smoking article may be constructed with an monolithic substrate  963 , described here with reference to  FIG. 9 , which is a longitudinal section view of a cigarette  910  having a lighting end  914  and a mouth end  918 . The monolithic substrate  963  (which may be used in other embodiments) may be formed by any appropriate extrusion method and is shown with a center-hole  995  extending longitudinally therethrough. The cigarette body includes a tobacco rod  969  disposed between the substrate  967  and the filter  970 . The filter  970  is shown as constructed with overlying layers of plug wrap  972  and tipping paper  978 . The substrate segment  955 , formed by the substrate  963  and tobacco rod  969 , is surrounded by a wrapping material  958 , which may be configured—for example—as a heat-conducting material (e.g., foil paper), heavy-gauge paper, plug wrap, or cigarette paper. A cylindrically-encompassing wrapping material (such as, for example, cigarette paper or heavy-gauge paper) may be provided to connect the heat-generation segment  935 , central substrate segment  955 , and filter segment  965 . The heat-generation segment  935  and other components may be constructed as described herein and elsewhere in this and other embodiments configured to be practiced within the scope of the present invention. 
     In other embodiments, an extruded or other monolithic substrate may be used in place of the substrates discussed herein with reference, for example, to  FIGS. 1 and 2 . For example, in one embodiment, the substrate  55  of  FIG. 1  may be replaced with a monolithic substrate having one or more internal longitudinal channels and/or one or more external grooves. Various other filter designs may be used including perforated filters made of non-cellular acetate materials known in the art, as well as other filter configurations now known or forthcoming, all within the scope of the present invention. The other portions of cigarettes made with extruded or other monolithic substrates may also be modified in accordance with the state of the art, and still be practiced within the scope of the present invention. In the following examples, the monolithic substrate includes about 20 to about 60 weight-percent tobacco, about 20 to about 35 weight-percent glycerin, about 1 to about 20 weight-percent water, and about 1 to about 4 weight-percent binder. 
     Example 1 
     Extruded Substrate in Smoking Article 
     In one example, smoking articles of about 83-85 mm in length were constructed using a heat source of about 12 mm in length, a substrate extruded according to the processes described herein and measuring about 10 mm in length, a hollow/void tube between the substrate and filter measuring about 50 mm in length, and a cellulose acetate filter about 10 mm in length. The exemplary extruded substrate was formed with ten external slots and a 0.032 inch center-hole, and it included the following components: 
                                                 Component   Mass (g)   Weight-Percent                                                        Flue-Cured Tobacco   15   11.8%           Burley Tobacco   9    7.1%           Turkish Tobacco   6   39.4%           CaCo 3     50   39.4%           Glycerin   40   31.5%           CMC (binder)   2    1.6%           Water   5    3.9%                        
The physical construction of the smoking article of Example 1 may be understood with reference to the construction of the cigarette  710  shown in  FIG. 7 .
 
     Example 2 
     Extruded Substrate in Smoking Article 
     In another example, a smoking article was constructed using a heat source of about 12 mm in length, a substrate extruded according to the processes described herein and measuring about 50 mm in length, and a cellulose acetate filter about 10 mm in length with minimal space between the substrate and the filter. The exemplary extruded substrate was formed with ten external slots and a 0.032 inch center-hole, and it included the following components: 
                                                 Component   Mass (g)   Weight-Percent                                                        Flue-Cured Tobacco   50   14.4%           Burley Tobacco   30    8.6%           Turkish Tobacco   20    5.8%           CaCo 3     100   28.8%           Glycerin   80   23.1%           CMC (binder)   12    3.5%           Water   55   15.9%                        
The physical construction of the smoking article of Example 2 may be understood with reference to the construction of the cigarette  810  shown in  FIG. 8 .
 
     Example 3 
     Extruded Substrate in Smoking Article 
     In another example, a smoking article was constructed using a heat source of about 12 mm in length, a substrate extruded according to the processes described herein and measuring about 10 mm in length, a tobacco rod between the substrate and filter measuring about 50 mm in length, and a cellulose acetate filter about 10 mm in length. The exemplary extruded substrate was formed with ten external slots and a 0.032 inch center-hole, and it included the following components: 
                                                 Component   Mass (g)   Weight-Percent                                                        Flue-Cured Tobacco   15   11.8%           Burley Tobacco   9    7.1%           Turkish Tobacco   6    4.7%           CaCo 3     50   39.4%           Glycerin   40   31.5%           CMC (binder)   2    1.6%           Water   5    3.9%                        
The physical construction of the smoking article of Example 3 may be understood with reference to the construction of the cigarette  910  shown in  FIG. 9 .
 
     Example 4 
     Extruded Substrate in Smoking Article 
     In another example, a smoking article was constructed using a heat source of about 12 mm in length, a substrate extruded according to the processes described herein and measuring about 50 mm in length, and a cellulose acetate filter about 10 mm in length with minimal space between the substrate and the filter. The exemplary extruded substrate was formed with ten external slots and a 0.032 inch center-hole, and it included the following components: 
                                                 Component   Mass (g)   Weight-Percent                                                        Flue-Cured Tobacco   100   28.8%           Burley Tobacco   60   17.3%           Turkish Tobacco   40   11.5%           CaCo 3     0     0%           Glycerin   80   23.1%           CMC (binder)   12    3.5%           Water   55   15.9%                        
The physical construction of the smoking article of Example 4 may be understood with reference to the construction of the cigarette  810  shown in  FIG. 8 .
 
     Example 5 
     Extruded Substrate in Smoking Article 
     In another example, a smoking article was constructed using a heat source of about 12 mm in length, a substrate extruded according to the processes described herein and measuring about 50 mm in length, and a cellulose acetate filter about 10 mm in length with minimal space between the substrate and the filter. The exemplary extruded substrate was formed with ten external slots and a 0.032 inch center-hole, and it included the following components: 
                                                 Component   Mass (g)   Weight-Percent                                                        Flue-Cured Tobacco   100   28.0%           Burley Tobacco   60   16.8%           Turkish Tobacco   40   11.2%           Graphite   10    2.8%           Glycerin   80   22.4%           CMC (binder)   12    3.4%           Water   55   15.4%                        
The physical construction of the smoking article of Example 5 may be understood with reference to the construction of the cigarette  810  shown in  FIG. 8 .
 
     Examples 6 and 7 
     Substrates with T-1 Binder 
     In another example, two substrates were formed according to processes described herein, and they included the following components: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Mass (q) 
                 Mass (q) 
               
               
                   
                 Component 
                 (Example 6) 
                 (Example 7) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Tobacco 
                 150 
                 80 
               
               
                   
                 T-1 Binder (formed as 
                 50 
                 50 
               
               
                   
                 73.2 wt-pct water; 
                   
                   
               
               
                   
                 3.6% wt-pct DAP; and 
                   
                   
               
               
                   
                 23.2% wt-pct tobacco 
                   
                   
               
               
                   
                 Glycerin 
                 80 
                 80 
               
               
                   
                 Water 
                 45 
                 55 
               
               
                   
                 CaCO 3   
                 — 
                 70 
               
               
                   
                   
               
            
           
         
       
     
     Examples 8 and 9 
     Substrates with DAP 
     In another example, two substrates may be formed by combining the following components in a heated mixer, then being extruded, press-fit, or molded/cast. The substrates may include the following mixtures of components: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Weight-Percent 
                 Weight-Percent 
               
               
                   
                 Component 
                 (Example 8) 
                 (Example 9) 
               
               
                   
                   
               
             
            
               
                   
                 Tobacco 
                 59.5% 
                 36.8% 
               
               
                   
                 DAP 
                  2.1% 
                  2.0% 
               
               
                   
                 Glycerin 
                 24.6% 
                 23.9% 
               
               
                   
                 Water 
                 13.8% 
                 16.4% 
               
               
                   
                 CaCO 3   
                 — 
                 20.9% 
               
               
                   
                   
               
            
           
         
       
     
     Cigarettes of the present invention may be air-diluted or ventilated such that the amount of air dilution for an air diluted cigarette may be about 10 percent to about 80 percent. As used herein, the term “air dilution” is the ratio (expressed as a percentage) of the volume of air drawn through the air dilution means to the total volume of air and aerosol drawn through the cigarette and exiting the mouth end portion of the cigarette. Higher air dilution levels can act to reduce the transfer efficiency of aerosol-forming material into mainstream aerosol. 
     Preferred embodiments of cigarettes of the present invention, when smoked, yield an acceptable number of puffs. Such cigarettes normally provide more than about 6 puffs, and generally more than about 8 puffs, per cigarette, when machine-smoked under standardized smoking conditions. Such cigarettes normally provide less than about 15 puffs, and generally less than about 12 puffs, per cigarette, when smoked under standardized smoking conditions. Standardized smoking conditions consist of 35 ml puffs of 2 second duration separated by 58 seconds of smolder. 
     Aerosols that are produced by cigarettes of the present invention are those that comprise air-containing components such as vapors, gases, suspended particulates, and the like. Aerosol components can be generated from burning tobacco of some form (and optionally other components that are burned to generate heat); by thermally decomposing tobacco caused by heating tobacco and charring tobacco (or otherwise causing tobacco to undergo some form of smolder); and by vaporizing aerosol-forming agent. As such, the aerosol can contain volatilized components, combustion products (e.g., carbon dioxide and water), incomplete combustion products, and products of pyrolysis. 
     Aerosol components may also be generated by the action of heat from burning tobacco of some form (and optionally other components that are burned to generate heat), upon substances that are located in a heat exchange relationship with tobacco material that is burned and other components that are burned. Aerosol components may also be generated by the aerosol-generation system as a result of the action of the heat generation segment upon an aerosol-generating segment. In some embodiments, components of the aerosol-generating segment have an overall composition, and are positioned within the smoking article, such that those components will have a tendency not to undergo a significant degree of thermal decomposition (e.g., as a result of combustion, smoldering or pyrolysis) during conditions of normal use. 
     Drawings in the figures illustrating various embodiments are not necessarily to scale. Some drawings may have certain details magnified for emphasis, and any different numbers or proportions of parts should not be read as limiting, unless so-designated by one or more claims. Those of skill in the art will appreciate that embodiments not expressly illustrated herein may be practiced within the scope of the present invention, including that features described herein for different embodiments may be combined with each other and/or with currently-known or future-developed technologies while remaining within the scope of the claims presented here. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting. And, it should be understood that the following claims, including all equivalents, are intended to define the spirit and scope of this invention.