Smoking article comprising an isolated combustible heat source

Abstract

A smoking article is provided, including a combustible heat source with opposed front and rear faces; an aerosol-forming substrate downstream of the rear face of the combustible heat source; an outer wrapper circumscribing the aerosol-forming substrate and at least a rear portion of the combustible heat source; and one or more airflow pathways along which air may be drawn through the smoking article for inhalation by a user. The combustible heat source is isolated from the one or more airflow pathways such that air drawn through the smoking article along the one or more airflow pathways does not directly contact the combustible heat source.

Claims

1. A smoking article comprising: a combustible heat source having a front end and a rear end; an aerosol-forming substrate downstream of the rear end of the combustible heat source; a non-combustible, substantially air impermeable, first barrier between a downstream end of the combustible heat source and an upstream end of the aerosol-forming substrate, the first barrier being adhered to or affixed to the downstream end of the combustible heat source and abutting the upstream end of the aerosol-forming substrate; an outer wrapper circumscribing the aerosol-forming substrate and at least a rear portion of the combustible heat source; one or more airflow pathways along which air may be drawn through the smoking article for inhalation; one or more third air inlets downstream of the aerosol-forming substrate for drawing air into the one or more airflow pathways; and an airflow directing element downstream of the aerosol-forming substrate, wherein the one or more airflow pathways comprise an airflow pathway extending between the one or more third air inlets downstream of the aerosol-forming substrate and a mouth end of the smoking article, wherein the airflow pathway comprises a first portion extending from the one or more third air inlets to the aerosol-forming substrate and a second portion extending from the aerosol-forming substrate to a mouth end of the smoking article, wherein the airflow directing element defines the first portion and the second portion of the airflow pathway extending between the one or more third air inlets downstream of the aerosol-forming substrate and the mouth end of the smoking article, wherein the one or more third air inlets are provided between a downstream end of the aerosol-forming substrate and a downstream end of the airflow directing element, and wherein the combustible heat source is isolated from the one or more airflow pathways such that air drawn through the smoking article along the one or more airflow pathways does not directly contact the combustible heat source.

2. The smoking article according to claim 1, wherein the first barrier comprises a first barrier coating provided on the rear face of the combustible heat source.

3. The smoking article according to claim 1, wherein the one or more airflow pathways comprise one or more airflow channels along the combustible heat source.

4. The smoking article according to claim 3, further comprising a non-combustible, substantially air impermeable, second barrier between the combustible heat source and the one or more airflow channels.

5. The smoking article according to claim 4, wherein the second barrier comprises a second barrier coating provided on an inner surface of the one or more airflow channels.

6. The smoking article according to claim 1, further comprising one or more second air inlets about the periphery of the aerosol-forming substrate for drawing air into the one or more airflow pathways.

7. The smoking article according to claim 1, further comprising: a heat-conducting element around and in direct contact with a rear portion of the combustible heat source and a front portion of the aerosol-forming substrate.

8. The smoking article according to claim 1, further comprising: an expansion chamber downstream of the aerosol-forming substrate.

9. The smoking article according to claim 1, wherein the first barrier has a thickness of between about 10 microns and about 500 microns.

10. The smoking article according to claim 1, wherein the first barrier is formed from material having a bulk thermal conductivity of between about 0.1 W per metre Kelvin (W/(m.Math.K)) and about 200 W per metre Kelvin (W/(m.Math.K)), at 23° C. and a relative humidity of 50% as measured using a modified transient plane source (MTPS) method.

11. The smoking article according to claim 1, wherein the first barrier is formed from one or more materials selected from the group consisting of copper, aluminum, stainless steel, alloys, alumina (Al.sub.2O.sub.3), resins, and mineral glues.

12. The smoking article according to claim 1, wherein the combustible heat source is a substantially cylindrical carbonaceous heat source.

13. The smoking article according to claim 1, wherein the airflow directing element extends a distance of up to 0.5 L into the aerosol-forming substrate, where L is the length of the aerosol-forming substrate.

14. The smoking article according to claim 7, wherein the heat-conducting element comprises steel.

Description

(1) The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1a) shows an exploded view of a smoking article according to a first embodiment of the invention comprising a non-blind combustible heat source;

(3) FIG. 1b) shows an exploded view of a smoking article according to a second embodiment of the invention comprising a non-blind combustible heat source;

(4) FIG. 1c) shows an exploded view of a smoking article according to a third embodiment of the invention comprising a non-blind combustible heat source;

(5) FIG. 1d) shows an exploded view of a smoking article according to a fourth embodiment of the invention comprising a blind combustible heat source;

(6) FIG. 1e) shows an exploded view of a smoking article according to a fifth embodiment of the invention comprising a blind combustible heat source;

(7) FIG. 2 shows a schematic longitudinal cross-section of the smoking article according to the first embodiment of the invention shown in FIG. 1a);

(8) FIG. 3 shows a schematic longitudinal cross-section of a smoking article according to a sixth embodiment of the invention comprising a blind combustible heat source; and

(9) FIG. 4 shows a schematic longitudinal cross-section of a smoking article according to a seventh embodiment of the invention comprising a blind combustible heat source.

(10) The smoking article 2 according to the first embodiment of the invention shown in FIGS. 1a) and 2 comprises a combustible carbonaceous heat source 4, an aerosol-forming substrate 6, an elongate expansion chamber 8 and a mouthpiece 10 in abutting coaxial alignment. The combustible carbonaceous heat source 4, aerosol-forming substrate 6, elongate expansion chamber 8 and mouthpiece 10 are overwrapped in an outer wrapper of cigarette paper 12 of low air permeability.

(11) As shown in FIG. 2, a non-combustible, substantially air impermeable, first barrier coating 14 is provided on the entire rear face of the combustible carbonaceous heat source 4.

(12) The combustible carbonaceous heat source 4 comprises a central airflow channel 16 that extends longitudinally through the combustible carbonaceous heat source 4 and the non-combustible, substantially air impermeable, first barrier coating 14. A non-combustible, substantially air impermeable second barrier coating 18 is provided on the entire inner surface of the central airflow channel 16.

(13) The aerosol-forming substrate 6 is located immediately downstream of the rear face of the combustible carbonaceous heat source 4 and comprises a cylindrical plug of tobacco material 20 comprising glycerine as aerosol former and circumscribed by filter plug wrap 22.

(14) A heat-conducting element 24 consisting of a tube of aluminium foil surrounds and is in direct contact with a rear portion 4b of the combustible carbonaceous heat source 4 and an abutting front portion 6a of the aerosol-forming substrate 6. As shown in FIG. 2, a rear portion of the aerosol-forming substrate 6 is not surrounded by the heat-conducting element 24.

(15) The elongate expansion chamber 8 is located downstream of the aerosol-forming substrate 6 and comprises a cylindrical open-ended hollow tube 26 of cardboard which is of substantially the same diameter as the aerosol-forming substrate 6. The mouthpiece 10 of the smoking article 2 is located downstream of the expansion chamber 8 and comprises a cylindrical plug 28 of cellulose acetate tow of very low filtration efficiency circumscribed by filter plug wrap 30. The mouthpiece 10 may be circumscribed by tipping paper (not shown).

(16) In use, the user ignites the combustible carbonaceous heat source 4 and then draws on the mouthpiece 10 to draw air downstream through the central airflow channel 16 of the combustible carbonaceous heat source 4. The front portion 6a of the aerosol-forming substrate 6 is heated primarily by conduction through the abutting rear portion 4b of the combustible carbonaceous heat source 4 and the heat-conducting element 24. The drawn air is heated as it passes through the central airflow channel 16 of the combustible carbonaceous heat source 4 and then heats the aerosol-forming substrate 6 by convection. The heating of the aerosol-forming substrate 6 by conduction and convection releases volatile and semi-volatile compounds and glycerine from the plug of tobacco material 20, which are entrained in the heated drawn air as it flows through the aerosol-forming substrate 6. The heated air and entrained compounds pass downstream through the expansion chamber 8, cool and condense to form an aerosol that passes through the mouthpiece 10 into the mouth of the user.

(17) The airflow pathway through the smoking article 2 according to the first embodiment of the invention is illustrated by the dotted arrow in FIG. 1a). The non-combustible, substantially air impermeable, first barrier coating 14 provided on the rear face of the combustible carbonaceous heat source 4 and the non-combustible, substantially air impermeable second barrier coating 18 provided on the inner surface of the central airflow channel 16 isolate the combustible carbonaceous heat source 4 from the airflow pathway such that, in use, air drawn through the smoking article 2 along the airflow pathway does not directly contact the combustible carbonaceous heat source 4.

(18) Smoking articles according to the first embodiment of the invention shown in FIGS. 1a) and 2 having the dimensions shown in Table 1 were assembled using combustible carbonaceous heat sources produced in accordance with Example 1 and 6 below.

(19) TABLE-US-00001 TABLE 1 First embodiment Smoking article Overall length (mm) 70 Diameter (mm) 7.9 Porous carbonaceous heat source Length (mm) 11 Diameter (mm) 7.8 Diameter of airflow channel (mm) 1.85-3.50 Thickness of first barrier coating (microns) ≤500 Thickness of second barrier coating (microns) ≤300 Aerosol-forming substrate Length (mm) 10 Diameter (mm) 7.8 Density (g/cm.sup.3) 0.8 Aerosol former Glycerine Amount of aerosol former 20% by dry wt. of Expansion chamber Length (mm) 42 Diameter (mm) 7.8 Mouthpiece Length (mm) 7 Diameter (mm) 7.8 Heat-conducting element Length (mm) 9 Diameter (mm) 7.8 Thickness of aluminium foil (microns) 20 Length of rear portion of combustible carbonaceous 4 heat source (mm) Length of front portion of aerosol-forming substrate 5 (mm) Length of rear portion of aerosol-forming substrate 5 (mm)

(20) The smoking article 32 according to the second embodiment of the invention shown in FIG. 1b) is of largely identical construction to the smoking article according to the first embodiment of the invention shown in FIGS. 1a) and 2. However, in the smoking article 32 according to the second embodiment of the invention the combustible carbonaceous heat source 4 and the aerosol-forming substrate 6 are spaced apart from one another along the length of the smoking article. A circumferential arrangement of first air inlets is provided in the cigarette paper 12 and heat conducting element 24 between the downstream end of the combustible carbonaceous heat source 4 and the upstream end of the aerosol-forming substrate 6 to admit cool air into the space between the combustible carbonaceous heat source 4 and the aerosol-forming substrate 6.

(21) In use when a user draws on the mouthpiece 10 of the smoking article 32 according to the second embodiment of the invention, air is drawn downstream through the central airflow channel 16 of the combustible carbonaceous heat source 4 and air is also drawn into the space between the combustible carbonaceous heat source 4 and the aerosol-forming substrate 6 through the first air inlets in the cigarette paper 12 and heat conducting element 24. Mixing of cool air drawn through the first air inlets with heated air drawn through the central airflow channel 16 of the combustible carbonaceous heat source 4 reduces the temperature of the air drawn through the aerosol-forming substrate 6 of the smoking article 32 according to the second embodiment of the invention during puffing by a user.

(22) The airflow pathways through the smoking article 32 according to the second embodiment of the invention are illustrated by the dotted arrows in FIG. 1b). The non-combustible, substantially air impermeable, first barrier coating 14 provided on the rear face of the combustible carbonaceous heat source 4 and the non-combustible, substantially air impermeable second barrier coating 18 provided on the inner surface of the central airflow channel 16 isolate the combustible carbonaceous heat source 4 from the airflow pathways such that, in use, air drawn through the smoking article 2 along the airflow pathway does not directly contact the combustible carbonaceous heat source 4.

(23) The smoking article 34 according to the third embodiment of the invention shown in FIG. 1c) is also of largely identical construction to the smoking article according to the first embodiment of the invention shown in FIGS. 1a) and 2. However, in the smoking article 34 according to the third embodiment of the invention a circumferential arrangement of second air inlets is provided in the cigarette paper 12 and filter plug wrap 22 circumscribing the aerosol-forming substrate 6 to admit cool air into the aerosol-forming substrate 6.

(24) In use when a user draws on the mouthpiece 10 of the smoking article 34 according to the second embodiment of the invention, air is drawn downstream through the central airflow channel 16 of the combustible carbonaceous heat source 4 and air is also drawn into the aerosol-forming substrate 6 through the second air inlets in the cigarette paper 12 and filter plug wrap 22. The cool air drawn through the second air inlets reduces the temperature of the aerosol-forming substrate 6 of the smoking article 32 according to the third embodiment of the invention during puffing by a user.

(25) The airflow pathways through the smoking article 34 according to the third embodiment of the invention are illustrated by the dotted arrows in FIG. 1c). The non-combustible, substantially air impermeable, first barrier coating 14 provided on the rear face of the combustible carbonaceous heat source 4 and the non-combustible, substantially air impermeable second barrier coating 18 provided on the inner surface of the central airflow channel 16 isolate the combustible carbonaceous heat source 4 from the airflow pathways such that, in use, air drawn through the smoking article 2 along the airflow pathways does not directly contact the combustible carbonaceous heat source 4.

(26) The smoking articles 36, 38 according to the fourth and fifth embodiments of the invention shown in FIGS. 1d) and 1e) are of largely identical construction to the smoking articles according to the second and third embodiments of the invention shown in FIGS. 1b) and 1c), respectively, and may be assembled in an analogous manner. However, the smoking articles 36, 38 according to the fourth and fifth embodiments of the invention comprise combustible carbonaceous heat sources 38 that do not comprise a central airflow channel 16. A non-combustible, substantially air impermeable, first barrier coating 14 is provided on the entire rear face of the combustible carbonaceous heat sources 38 of the smoking articles 36, 38 according to the fourth and fifth embodiments of the invention.

(27) In use, when a user draws on the mouthpiece 10 of the smoking articles 36, 38 according to the fourth and fifth embodiments of the invention, no air is drawn through the combustible carbonaceous heat sources 38. Consequently, the aerosol-forming substrate 6 is heated exclusively by conduction through the abutting rear portion 4b of the combustible carbonaceous heat source 4 and the heat-conducting element 24.

(28) The airflow pathways through the smoking articles 36, 38 according to the fourth and fifth embodiments of the invention are illustrated by the dotted arrows in FIGS. 1d and 1e). The non-combustible, substantially air impermeable, first barrier coating 14 provided on the entire rear face of the combustible carbonaceous heat sources 38 of the smoking articles 36, 38 according to the fourth and fifth embodiments of the invention isolates the combustible carbonaceous heat sources 38 from the airflow pathways such that, in use, air drawn through the smoking articles 36, 38 along the airflow pathways does not directly contact the combustible carbonaceous heat sources 38.

(29) The smoking article 42 according to the sixth embodiment of the invention shown in FIG. 3 comprises a combustible carbonaceous heat source 40, an aerosol-forming substrate 6, an airflow directing element 44, an elongate expansion chamber 8 and a mouthpiece 10 in abutting coaxial alignment. The combustible carbonaceous heat source 40, aerosol-forming substrate 6, airflow directing element 44, elongate expansion chamber 8 and mouthpiece 10 are overwrapped in an outer wrapper of cigarette paper 12 of low air permeability.

(30) As shown in FIG. 3, a non-combustible, substantially air impermeable, first barrier coating 14 is provided on the entire rear face of the combustible carbonaceous heat source 40.

(31) The aerosol-forming substrate 6 is located immediately downstream of the combustible carbonaceous heat source 40 and comprises a cylindrical plug 20 of tobacco material comprising glycerine as aerosol former and circumscribed by filter plug wrap 22.

(32) A heat-conducting element 24 consisting of a tube of aluminium foil surrounds and is in direct contact with a rear portion 4b of the combustible carbonaceous heat source 40 and an abutting front portion 6a of the aerosol-forming substrate 6. As shown in FIG. 3, a rear portion of the aerosol-forming substrate 6 is not surrounded by the heat-conducting element 24.

(33) The airflow directing element 44 is located downstream of the aerosol-forming substrate 6 and comprises an open-ended, substantially air impermeable truncated hollow cone 46 made of, for example, cardboard. The downstream end of the open-ended truncated hollow cone 46 is of substantially the same diameter as the aerosol-forming substrate 6 and the upstream end of the open-ended truncated hollow cone 46 is of reduced diameter compared to the aerosol-forming substrate 6.

(34) The upstream end of the open-ended truncated hollow cone 46 abuts the aerosol-forming substrate 6 and is embedded in an air permeable cylindrical plug 48 of cellulose acetate tow circumscribed by filter plug wrap 50, which is of substantially the same diameter as the aerosol-forming substrate 6. It will be appreciated that in alternative embodiments (not shown), the upstream end of the open-ended truncated hollow cone 46 may extend into the rear portion of the aerosol-forming substrate 6. It will also be appreciated that in alternative embodiments (not shown) the cylindrical plug 48 of cellulose acetate tow may be omitted.

(35) As shown in FIG. 3, the portion of the open-ended truncated hollow cone 46 that is not embedded in the cylindrical plug 48 of cellulose acetate tow is circumscribed by an inner wrapper 52 of low air permeability made of, for example, cardboard. It will be appreciated that in alternative embodiments (not shown) the inner wrapper 52 may be omitted.

(36) As also shown in FIG. 3, a circumferential arrangement of third air inlets 54 is provided in the outer wrapper 12 and inner wrapper 52 circumscribing the open-ended truncated hollow cone 46 downstream of the cylindrical plug 48 of cellulose acetate tow.

(37) The elongate expansion chamber 8 is located downstream of the airflow directing element 44 and comprises a cylindrical open-ended hollow tube 26 made of, for example, cardboard which is of substantially the same diameter as the aerosol-forming substrate 6. The mouthpiece 10 of the smoking article 42 is located downstream of the expansion chamber 8 and comprises a cylindrical plug 28 of cellulose acetate tow of very low filtration efficiency circumscribed by filter plug wrap 30. The mouthpiece 10 may be circumscribed by tipping paper (not shown).

(38) The smoking article 42 according to the sixth embodiment of the invention comprises an airflow pathway extending between the third air inlets 54 and the mouth end of the smoking article 42. The volume bounded by the exterior of the open-ended truncated hollow cone 46 and the inner wrapper 52 forms a first portion of the airflow pathway between the third air inlets 54 and the aerosol-forming substrate 6 and the volume bounded by the interior of the open-ended truncated hollow cone 46 forms a second portion of the airflow pathway between the aerosol-forming substrate 6 and the expansion chamber 8.

(39) In use, when a user draws on the mouthpiece 10, cool air is drawn into the smoking article 42 according to the sixth embodiment of the invention through the third air inlets 54. The drawn air passes upstream to the aerosol-forming substrate 6 along the first portion of the airflow pathway between the exterior of the open-ended truncated hollow cone 46 and the inner wrapper 52 and through the cylindrical plug 48 of cellulose acetate tow.

(40) The front portion 6a of the aerosol-forming substrate 6 is heated by conduction through the abutting rear portion 4b of the combustible carbonaceous heat source 40 and the heat-conducting element 24. The heating of the aerosol-forming substrate 6 releases volatile and semi-volatile compounds and glycerine from the plug of tobacco material 20, which are entrained in the drawn air as it flows through the aerosol-forming substrate 6. The drawn air and entrained compounds pass downstream along the second portion of the airflow pathway through the interior of the open-ended truncated hollow cone 46 to the expansion chamber 8, where they cool and condense to form an aerosol that passes through the mouthpiece 10 into the mouth of the user.

(41) The non-combustible, substantially air impermeable, first barrier coating 14 provided on the rear face of the combustible carbonaceous heat source 40 isolates the combustible carbonaceous heat source 40 from the airflow pathway through the smoking article 42 such that, in use, air drawn through the smoking article 42 along the first portion of the airflow pathway and the second portion of the airflow pathway does not directly contact the combustible carbonaceous heat source 40.

(42) The smoking article 56 according to the seventh embodiment of the invention shown in FIG. 4 also comprises a combustible carbonaceous heat source 40, an aerosol-forming substrate 6, an airflow directing element 44, an elongate expansion chamber 8 and a mouthpiece 10 in abutting coaxial alignment. The combustible carbonaceous heat source 40, aerosol-forming substrate 6, airflow directing element 44, elongate expansion chamber 8 and mouthpiece 10 are overwrapped in an outer wrapper of cigarette paper 12 of low air permeability.

(43) As shown in FIG. 4, a non-combustible, substantially air impermeable, first barrier coating 14 is provided on the entire rear face of the combustible carbonaceous heat source 40.

(44) The aerosol-forming substrate 6 is located immediately downstream of the combustible carbonaceous heat source 40 and comprises a cylindrical plug 20 of tobacco material comprising glycerine as aerosol former and circumscribed by filter plug wrap 22.

(45) A heat-conducting element 24 consisting of a tube of aluminium foil surrounds and is in direct contact with a rear portion 4b of the combustible carbonaceous heat source 40 and an abutting front portion 6a of the aerosol-forming substrate 6. As shown in FIG. 4, a rear portion of the aerosol-forming substrate 6 is not surrounded by the heat-conducting element 24.

(46) The airflow directing element 44 is located downstream of the aerosol-forming substrate 6 and comprises an open-ended, substantially air impermeable hollow tube 58 made of, for example, cardboard, which is of reduced diameter compared to the aerosol-forming substrate 6. The upstream end of the open-ended hollow tube 58 abuts the aerosol-forming substrate 6. The downstream end of the open-ended hollow tube 58 is surrounded by an annular substantially air impermeable seal 60 of substantially the same diameter as the aerosol-forming substrate 6. The remainder of the open-ended hollow tube 58 is embedded in an air permeable cylindrical plug 62 of cellulose acetate tow of substantially the same diameter as the aerosol-forming substrate 6.

(47) The open-ended hollow tube 58 and cylindrical plug 62 of cellulose acetate tow are circumscribed by an air permeable inner wrapper 64

(48) As also shown in FIG. 4, a circumferential arrangement of third air inlets 54 is provided in the outer wrapper 12 circumscribing the inner wrapper 64.

(49) The elongate expansion chamber 8 is located downstream of the airflow directing element 44 and comprises a cylindrical open-ended hollow tube 26 made of, for example, cardboard which is of substantially the same diameter as the aerosol-forming substrate 6. The mouthpiece 10 of the smoking article 56 is located downstream of the expansion chamber 8 and comprises a cylindrical plug 28 of cellulose acetate tow of very low filtration efficiency circumscribed by filter plug wrap 30. The mouthpiece 10 may be circumscribed by tipping paper (not shown).

(50) The smoking article 56 according to the seventh embodiment of the invention comprises an airflow pathway extending between the third air inlets 54 and the mouth end of the smoking article 56. The volume bounded by the exterior of the open-ended hollow tube 58 and the inner wrapper 64 forms a first portion of the airflow pathway between the third air inlets 54 and the aerosol-forming substrate 6 and the volume bounded by the interior of the open-ended hollow tube 58 forms a second portion of the airflow pathway between the aerosol-forming substrate 6 and the expansion chamber 8.

(51) In use, when a user draws on the mouthpiece 10, cool air is drawn into the smoking article 56 according to the seventh embodiment of the invention through the third air inlets 54 and the air permeable inner wrapper 64. The drawn air passes upstream to the aerosol-forming substrate 6 along the first portion of the airflow pathway between the exterior of the open-ended hollow tube 58 and the inner wrapper 64 and through the cylindrical plug 62 of cellulose acetate tow.

(52) The front portion 6a of the aerosol-forming substrate 6 is heated by conduction through the abutting rear portion 4b of the combustible carbonaceous heat source 40 and the heat-conducting element 24. The heating of the aerosol-forming substrate 6 releases volatile and semi-volatile compounds and glycerine from the plug of tobacco material 20, which are entrained in the drawn air as it flows through the aerosol-forming substrate 6. The drawn air and entrained compounds pass downstream along the second portion of the airflow pathway through the interior of the open-ended hollow tube 58 to the expansion chamber 8, where they cool and condense to form an aerosol that passes through the mouthpiece 10 into the mouth of the user.

(53) The non-combustible, substantially air impermeable, first barrier coating 14 provided on the rear face of the combustible carbonaceous heat source 40 isolates the combustible carbonaceous heat source 40 from the airflow pathway through the smoking article 56 such that, in use, air drawn through the smoking article 56 along the first portion of the airflow pathway and the second portion of the airflow pathway does not directly contact the combustible carbonaceous heat source 40.

(54) Smoking articles according to the sixth and seventh embodiments of the invention shown in FIGS. 3 and 4 having the dimensions shown in Table 2 were assembled using combustible carbonaceous heat sources produced in accordance with Example 1 and 6 below, but without any longitudinal airflow channels.

(55) TABLE-US-00002 TABLE 2 Seventh Sixth embodiment embodiment Smoking article Overall length (mm) 84 84 Diameter (mm) 7.8 7.8 Porous carbonaceous heat source Length (mm) 8 8 Diameter (mm) 7.8 7.8 Thickness of first barrier coating ≤500 ≤500 (microns) Aerosol-forming substrate Length (mm) 10 10 Diameter (mm) 7.8 7.8 Density (g/cm.sup.3) 0.73 0.73 Aerosol former Glycerine Glycerine Amount of aerosol former 20% by dry wt. of 20% by dry wt. of tobacco tobacco Airflow directing element Length (mm) 18 26 Diameter (mm) 7.8 7.8 Length of plug of porous material 5 24 (mm) Diameter of hollow tube (mm) — 3.5 Number of air inlets 4 4-8 Diameter of air inlets (mm) 0.2 0.2 Distance of air inlets from 27 24 upstream end (mm) Expansion chamber Length (mm) 41 33 Diameter (mm) 7.8 7.8 Mouthpiece Length (mm) 7 7 Diameter (mm) 7.8 7.8 Heat-conducting element Length (mm) 7 8 Diameter (mm) 7.8 7.8 Thickness of aluminium foil 20 20 (microns) Length of rear portion of 3 4 combustible carbonaceous heat source (mm) Length of front portion of aerosol- 4 4 forming substrate (mm) Length of rear portion of aerosol- 6 6 forming substrate (mm)

EXAMPLE 1

Preparation of Combustible Heat Source

(56) Combustible cylindrical carbonaceous heat sources for use in smoking articles according to the invention may be prepared as described in WO2009/074870 A2 or any other prior art that is known to persons of ordinary skill in the art. An aqueous slurry, as described in WO2009/074870 A2, is extruded through a die having a central die orifice of circular cross-section to make the combustible heat source. The die orifice has a diameter of 8.7 mm so as to form cylindrical rods, having a length of between about 20 cm and about 22 cm and a diameter of between about 9.1 cm and about 9.2 mm. A single longitudinal airflow channel is formed in the cylindrical rods by a mandrel mounted centrally in the die orifice. The mandrel preferably has a circular cross-section with an outer diameter of approximately 2 mm or approximately 3.5 mm. Alternatively, three airflow channels are formed in the cylindrical rods using three mandrels of circular cross-section with an outer diameter of approximately 2 mm mounted at regular angles in the die orifice. During extrusion of the cylindrical rods, a clay-based coating slurry (made using clay, such as natural green clay) is pumped through a feed passageway extending through the centre of the mandrel or mandrels to form a thin second barrier coating of about 150 microns to about 300 microns on the inner surface of the airflow channel or channels. The cylindrical rods are dried at a temperature of about 20° C. to about 25° C. under about 40% to about 50% relative humidity for between approximately 12 hours to approximately 72 hours and then pyrolysed in a nitrogen atmosphere at about 750° C. for approximately 240 minutes. After pyrolysis, the cylindrical rods are cut and shaped to a defined diameter using a grinding machine to form individual combustible-carbonaceous heat sources. The rods after cutting and shaping have a length of about 11 mm, a diameter of about 7.8 mm and a dry mass of about 400 mg. The individual combustible carbonaceous heat sources are subsequently dried at about 130° C. for approximately 1 hour.

EXAMPLE 2

Coating of Combustible Heat Source with Bentonite/Kaolinite

(57) A non-combustible, substantially air impermeable, first barrier coating of bentonite/kaolinite is provided on the rear face of a combustible carbonaceous heat source prepared as described in Example 1 by dipping, brushing or spray coating. Dipping involves inserting the rear face of the combustible carbonaceous heat source into a concentrated bentonite/kaolinite solution. The bentonite/kaolinite solution for dipping contains 3.8% bentonite, 12.5% kaolinite and 83.7% H.sub.2O [m/m]. The rear face of the combustible carbonaceous heat source is dipped into the bentonite/kaolinite solution for about 1 second and the meniscus allowed to disappear as the result of penetration of the solution into the carbon pores at the surface of the rear face of the combustible carbonaceous heat source. Brushing involves dipping a brush into a concentrated bentonite/kaolinite solution and applying the concentrated bentonite/kaolinite solution on the brush to the surface of the rear face of the combustible carbonaceous heat source until covered. The bentonite/kaolinite solution for brushing contains 3.8% bentonite, 12.5% kaolinite and 83.7% H.sub.2O [m/m].

(58) After application of a non-combustible, substantially air impermeable, first barrier coating by dipping or brushing, the combustible carbonaceous heat source is dried in an oven at about 130° C. for approximately 30 minutes and placed in a desiccator under about 5% relative humidity overnight.

(59) Spray-coating involves a suspension solution, preferably containing 3.6% bentonite, 18.0% kaolinite and 78.4% H.sub.2O [m/m] and having a viscosity of around 50 mPa.Math.s at a shear rate of about 100 s.sup.−1 as measured with a rheometer (Physica MCR 300, coaxial cylinder arrangement). Spray-coating is done with a Sata MiniJet 3000 spray gun using spray nozzles of 0.5 mm, 0.8 mm or 1 mm on a SMC E-MY2B linear actuator at a velocity of about 10 mm/s to about 100 mm/s. The following spray parameters are used: distance sample-pistol 15 cm; sample velocity 10 mm/s; spray nozzle 0.5 mm; spray jet flat and spray pressure 2.5 bar. In a single spray-coating event, a coating thickness of about 11 microns is typically obtained. Spraying is repeated three times. Between each spray-coating, the combustible carbonaceous heat source is dried at room temperature for about 10 minutes. After application of the non-combustible, substantially air impermeable, first barrier coating, the combustible carbonaceous heat source is pyrolysed at about 700° C. for approximately 1 hour.

EXAMPLE 3

Coating of Combustible Heat Source with Sintered Glass

(60) A non-combustible, substantially air impermeable, first barrier coating of glass is provided on the rear face of a combustible carbonaceous heat-source prepared as described in Example 1 by spray-coating. Spray-coating with glass is performed with a suspension of ground glass using a fine powder. For example, a spray-coating suspension containing either 37.5% glass powder (3 μm), 2.5% methylcellulose and 60% water with a viscosity of 120 mPa.Math.s, or 37.5% glass powder (3 μm), 3.0% bentonite powder, and 59.5% water with a viscosity of 60 to 100 mPa.Math.s, is used. Glass powder having the compositions and physical properties corresponding to Glass 1, 2, 3 and 4 in Table 3 may be used.

(61) Spray-coating is done with a Sata MiniJet 3000 spray gun using spray nozzles of 0.5 mm, 0.8 mm or 1 mm on a SMC E-MY2B linear actuator at a velocity of about 10 mm/s to about 100 mm/s. Spraying is preferably repeated several times. After the spraying is completed, the combustible carbonaceous heat source is pyrolysed at about 700° C. for approximately 1 hour.

(62) TABLE-US-00003 TABLE 3 Composition of glasses in weight percent, transformation temperature Tg, coefficient of thermal expansion A.sub.20-300 and KI-value calculated from composition Glass 1 Glass 2 Glass 3 Glass 4 SiO.sub.2 70 70 65 60 Na.sub.2O 20 15 20 20 K.sub.2O 5 CaO 10 8 10 10 MgO 4 5 5 Al.sub.2O.sub.3 3 T.sub.g (° C.) 517 539 512 465 A.sub.20-300 (10.sup.−6 K.sup.−1) 10.9 9.3 10.2 12.1 KI-value 30 21 35 40

EXAMPLE 4

Coating of Combustible Heat Source with Aluminium

(63) A non-combustible, substantially air impermeable, first barrier coating of aluminium is provided on the rear face of a combustible carbonaceous heat-source prepared as described in Example 1 by laser cutting an aluminium barrier from aluminium bobbin bands having a thickness of about 20 microns. The aluminium barrier has a diameter of about 7.8 mm and a single hole having an outer diameter of about 1.8 mm in the centre thereof to match the cross section of the combustible carbonaceous heat source of Example 1. In an alternative embodiment, the aluminium barrier has three holes, which are positioned to be aligned with three airflow channels provided in the combustible carbonaceous heat-source. The aluminium barrier coating is formed by attaching the aluminium barrier to the rear face of the combustible carbonaceous heat source using any suitable adhesive.

EXAMPLE 5

Methods for Measuring Smoke Compounds

(64) Conditions for Smoking

(65) Conditions for smoking and smoking machine specifications are set out in ISO Standard 3308 (ISO 3308:2000). Atmosphere for conditioning and testing are set out in ISO Standard 3402. Phenols are trapped using Cambridge filter pads. Quantitative determination of carbonyls in aerosols, including formaldehyde, acrolein, acetaldehyde and propionaldehyde, is done by UPLC-MSMS. Quantitative measurement of phenolics such as catechol, hydroquinone and phenol is done by LC-fluorescence. Carbon monoxide in the smoke is trapped using gas sampling bags and measured using a non-dispersive infra-red analyzer as set out in ISO Standard 8454 (ISO 8454:2007).

(66) Smoking Regimes

(67) Cigarettes tested under a Health Canada smoking regime are smoked over 12 puffs with a puff volume of 55 ml, puff duration of 2 seconds and a puff interval of 30 seconds. Cigarettes tested under an intense smoking regime are smoked over 20 puffs with a puff volume of 80 ml, a puff duration of 3.5 seconds and puff interval of 23 seconds.

EXAMPLE 6

Preparation of Combustible Heat Source with Ignition Aid

(68) A carbonaceous combustible heat source comprising an ignition aid is prepared by mixing 525 g of carbon powder, 225 g of calcium carbonate (CaCO.sub.3), 51.75 g of potassium citrate, 84 g of modified cellulose, 276 g of flour, 141.75 g of sugar and 21 g of corn oil with 579 g of deionised water to form an aqueous slurry, essentially as disclosed in WO2009/074870 A2. The aqueous slurry is then be extruded through a die having a central die orifice of circular cross-section with a diameter of about 8.7 mm to form cylindrical rods having a length of between about 20 cm and about 22 cm and a diameter of between about 9.1 mm and about 9.2 mm. A single longitudinal airflow channel is formed in the cylindrical rods by a mandrel mounted centrally in the die orifice. The mandrel has a circular cross-section with an outer diameter of approximately 2 mm or approximately 3.5 mm. Alternatively, three airflow channels are formed in the cylindrical rods using three mandrels of circular cross-section with an outer diameter of approximately 2 mm mounted at regular angles in the die orifice. During extrusion of the cylindrical rods, a green clay-based coating slurry is pumped through a feed passageway extending through the centre of the mandrel to form a thin second barrier coating having a thickness of between about 150 microns and about 300 microns on the inner surface of the single longitudinal airflow channel. The cylindrical rods are dried at between about 20° C. and about 25° C. under about 40% to about 50% relative humidity for between approximately 12 hours and approximately 72 hours and then pyrolysed in a nitrogen atmosphere at about 750° C. for approximately 240 minutes. After pyrolysis, the cylindrical rods are cut and shaped to a defined diameter using a grinding machine to form individual combustible-carbonaceous heat sources having a length of about 11 mm, a diameter of about 7.8 mm, and a dry mass of about 400 mg. The individual combustible carbonaceous heat sources are dried at about 130° C. for approximately 1 hour and then placed in an aqueous solution of nitric acid having a concentration of 38 percent by weight and saturated with potassium nitrate (KNO.sub.3). After approximately 5 minutes, the individual combustible carbonaceous heat sources are removed from the solution and dried at about 130° C. for approximately 1 hour. After drying the individual combustible carbonaceous heat sources are placed once again in an aqueous solution of nitric acid having a concentration of 38 percent by weight and saturated with potassium nitrate (KNO.sub.3). After approximately 5 minutes, the individual combustible carbonaceous heat sources are removed from the solution and dried at about 130° C. for approximately 1 hour, followed by drying at about 160° C. for approximately 1 hour and finally drying at about 200° C. for approximately 1 hour.

EXAMPLE 7

Smoke Compounds from Smoking Articles with Combustible Heat-Sources with a Non-Combustible, Substantially Air Impermeable, First Barrier Coating of Clay or Glass

(69) Combustible cylindrical carbonaceous heat sources comprising an ignition aid are prepared as described in Example 6 with a single longitudinal airflow channel having a diameter of 1.85 mm and a bentonite/kaolinite second barrier coating. The combustible cylindrical carbonaceous heat sources are provided with a non-combustible, substantially air impermeable, first barrier coating of clay as described in Example 2. Additionally, combustible cylindrical carbonaceous heat sources comprising an ignition aid as described in Example 6 with a single longitudinal airflow channel having a diameter of 1.85 mm and a glass second barrier coating are provided with a non-combustible, substantially air impermeable, first barrier coating of sintered glass as described in Example 3. In both cases, the length of the combustible cylindrical carbonaceous heat sources is 11 mm. The non-combustible, substantially air impermeable, first barrier coating of clay has a thickness of between about 50 microns and about 100 microns and the non-combustible, substantially air impermeable, first barrier coating of glass has a thickness of about 20 microns, about 50 microns or about 100 microns. Smoking articles according to the first embodiment of the invention shown in FIGS. 1a) and 2 having a total length of 70 mm comprising the aforementioned combustible cylindrical carbonaceous heat sources are assembled by hand. The aerosol-forming substrate of the smoking articles is 10 mm in length and comprises approximately 60% by weight flue-cured tobacco, approximately 10% by weight oriental tobacco and approximately 20% by weight sun-cured tobacco. The heat conducting element of the smoking articles is 9 mm in length, of which 4 mm covers the rear portion of the combustible heat source and 5 mm covers the adjacent front portion of the aerosol-forming substrate. Except as noted in the foregoing description in this Example, the properties of the smoking articles conform to those listed in Table 1 above. Smoking articles of the same construction, but without a non-combustible, substantially air impermeable, first barrier coating, are also assembled by hand for comparison.

(70) The resulting smoking articles are smoked as described in Example 5 under a Health Canada smoking regime. Before smoking, the combustible heat sources of the smoking articles are lit using a regular yellow flame lighter. The formaldehyde, acetaldehyde, acrolein and propionaldehyde in the mainstream aerosol of the smoking articles is measured as described in Example 5. The results are summarised in Table 4 below and show that carbonyls, such as acetaldehyde and especially formaldehyde, are significantly reduced in the mainstream aerosols of smoking articles comprising a combustible heat source with a non-combustible, substantially air impermeable, first barrier coating compared to the mainstream aerosols of smoking articles comprising a combustible heat source without a non-combustible, substantially air impermeable, first barrier coating.

(71) TABLE-US-00004 TABLE 4 Amount of carbonyls (micrograms per sample) measured in mainstream aerosol under Health Canada smoking regime for smoking articles comprising a combustible carbonaceous heat source (a) without a non-combustible, substantially air impermeable, first barrier coating, (b) with a non-combustible, substantially air impermeable, first barrier coating of clay and (c) with a non-combustible, substantially air impermeable, first barrier coating of sintered glass. Non-combustible, substantially air impermeable, first barrier coating (a) None (b) Clay (c) Glass Thickness (microns) 50 100 20 50 100 formaldehyde 22.19 18.2 17.6 14.87 12.99 14.56 acetaldehyde 102.83 103.9 89.4 75.11 69.56 86.89 acrolein 7.09 7.7 7.1 6.22 4.29 5.41 propionaldehyde 5.09 4.9 7.7 4.50 3.64 4.78

EXAMPLE 8

Smoke Compounds of Smoking Articles with Combustible Heat-Sources with a Non-Combustible, Substantially Air Impermeable, First Barrier Coating of Aluminium

(72) Combustible cylindrical carbonaceous heat sources prepared as described in Example 7 (but not treated with nitric acid) having a length of 11 mm, a single longitudinal airflow channel having a diameter of 1.85 mm and a second barrier coating of micaceous iron oxide coating (Miox, Kärntner Montanindustrie, Wolfsberg, Austria) are provided with a non-combustible, substantially air impermeable, first barrier coating of aluminium having a thickness of about 20 microns as described in Example 4. Smoking articles according to the first embodiment of the invention shown in FIGS. 1a) and 2 having a total length of 70 mm comprising the aforementioned combustible cylindrical carbonaceous heat source are assembled by hand. The aerosol-forming substrate of the smoking articles is 10 mm in length and contains approximately 60% by weight flue-cured tobacco, approximately 10% by weight oriental tobacco and approximately 20% by weight sun-cured tobacco. The heat conducting element of the smoking articles is 9 mm in length, of which 4 mm covers the rear portion of the combustible heat source and 5 mm covers the adjacent front portion of the aerosol-forming substrate. Except as noted in the foregoing description within this Example, the properties of the smoking articles conform to those listed in Table 1 above. Smoking articles of the same construction, but without a non-combustible, substantially air impermeable, first barrier coating, are also assembled by hand for comparison.

(73) The smoking articles are smoked as described in Example 5, under a Health Canada smoking regime and an intense smoking regime. Before smoking, the combustible heat sources are lit using a regular yellow flame lighter. The formaldehyde, acetaldehyde, acrolein, propionaldehyde, phenol, catechol and hydroquinone in the mainstream aerosol of the smoking articles are measured as described in Example 5. The results are summarized in Table 5. As can be seen from Table 4, under both the Health Canada and intense smoking regimes, the inclusion of a non-combustible, substantially air impermeable, first barrier coating of aluminium on the rear face of the combustible heat source leads to a significant reduction of phenolics and carbonyls such as formaldehyde and acetaldehyde in the mainstream aerosol.

(74) TABLE-US-00005 TABLE 5 Amount of compounds (micrograms per sample) measured in mainstream aerosol under (i) Health Canada smoking regime and (ii) intense smoking regime for smoking articles comprising a combustible carbonaceous heat source (a) without a non- combustible, substantially air impermeable, first barrier coating and (b) with a non-combustible, substantially air impermeable, first barrier coating of aluminium. (i) Health Canada (ii) Intense smoking regime smoking regime Non-combustible,substantially air impermeable, first barrier coating (a) None (b) Aluminium (a) None (b) Aluminium formaldehyde 21.2 11.6 30.4 17.8 acetaldehyde 26.6 20.9 63.7 54.0 Acrolein 2.88 1.53 4.97 4.58 propion- 1.46 0.88 3.51 2.41 aldehyde Phenol 0.33 0.20 not not measured measured catechol 2.50 1.58 not not measured measured hydroquinone <1.05 <1.05 not not measured measured

(75) As can be seen from Examples 7 and 8, isolating the combustible heat source of smoking articles according to the invention from the one or more airflow pathways through the smoking article by providing a non-combustible, substantially air impermeable, first barrier coating on at least substantially the entire rear face of the combustible heat source and a non-combustible, substantially air impermeable, second barrier coating on at least substantially the entire inner surface of the airflow channel through the combustible heat source results in significantly reduced formation of carbonyl compounds, such as formaldehyde, acetaldehyde, proprionaldehyde and phenolics, in the mainstream aerosol.

(76) The embodiments and examples described above illustrate but do not limit the invention. Other embodiments of the invention may be made without departing from the spirit and scope thereof, and it is to be understood that the specific embodiments described herein are not limiting.