Insulated heat source

Abstract

There is provided a heat source for a smoking article, including an upstream end and an opposed downstream end, and further including a combustible carbonaceous core and an integral, non-combustible, thermally insulating, peripheral layer. The core extends from the upstream end of the heat source the downstream end of the heat source. The peripheral layer extends from the upstream end of the heat source only part way along the length of the heat source and circumscribes an upstream portion of the core.

Claims

1. A smoking article, comprising: a heat source having an upstream end and an opposed downstream end, the heat source comprising: a combustible carbonaceous core; and an integral, non-combustible, thermally insulating, peripheral layer, wherein the core extends from the upstream end of the heat source to the downstream end of the heat source, and the peripheral layer extends from the upstream end of the heat source only part way along a length of the heat source and circumscribes an upstream portion of the core, and wherein a diameter of the heat source is substantially constant and a ratio of the diameter of the heat source to a thickness of the peripheral layer is from 10:3 to 20:1; an aerosol-forming substrate downstream of the heat source; a heat-conducting, combustion-resistant wrapper around and in direct contact with an upstream portion of the aerosol-forming substrate and a downstream portion of the core of the heat source; an outer wrapper that overwraps the heat source, the aerosol-forming substrate, and the heat-conducting, combustion-resistant wrapper; and an additional heat-conducting, combustion-resistant wrapper in direct contact with the outer wrapper, wherein the additional heat-conducting, combustion-resistant wrapper overlies the heat-conducting, combustion-resistant wrapper with the outer wrapper disposed between the additional heat-conducting, combustion-resistant wrapper and the heat-conducting, combustion-resistant wrapper.

2. The smoking article according to claim 1, wherein a length of the peripheral layer is at least about 2 mm less than a length of the heat source.

3. The smoking article according to claim 1, wherein the peripheral layer comprises at least 90% by dry weight of thermally insulating material.

4. The smoking article according to claim 1, wherein the peripheral layer comprises at least one precursor material that decomposes to form at least one thermally insulating material upon ignition of the core of the heat source.

5. The smoking article according to claim 1, wherein the peripheral layer comprises at least one thermally insulating material selected from the group consisting of clays, whiteware ceramics, technical ceramics, and rocks.

6. The smoking article according to claim 1, wherein the peripheral layer comprises at least one thermally insulating material selected from the group consisting of diatomaceous earth, gypsum, and bentonite.

7. The smoking article according to claim 1, wherein the core comprises at least one ignition aid.

8. The smoking article according to claim 7, wherein the core further comprises: a first layer comprising carbon; and a second layer comprising the at least one ignition aid, wherein a composition of the first layer is different from a composition of the second layer.

9. The smoking article according to claim 8, wherein the second layer further comprises carbon.

10. The smoking article according to claim 8, wherein the first layer further comprises the at least one ignition aid.

11. The smoking article according to claim 8, wherein the first layer comprises carbon and the at least one ignition aid, and the second layer comprises carbon and the at least one ignition aid, and wherein a ratio by dry weight of carbon to ignition aid in the first layer is different from a ratio by dry weight of carbon to ignition aid in the second layer.

12. The smoking article according to claim 8, wherein the second layer is downstream of the first layer.

13. The smoking article according to claim 12, wherein the heat-conducting, combustion-resistant wrapper is around and in direct contact with at least a downstream portion of the second layer of the core of the heat source.

14. The smoking article according to claim 2, wherein the non-combustible, thermally insulating, peripheral layer comprises thermally insulating material having a bulk thermal diffusivity of less than or equal to about 0.01 square centimetres per second (cm.sup.2/s) as measured using the laser flash method.

15. The smoking article according to claim 1, wherein the heat source is a blind heat source.

16. The smoking article according to claim 1, wherein the ratio of the diameter of the heat source to the thickness of the peripheral layer is from 14:3 to 16:1.

17. The smoking article according to claim 1, wherein the thickness of the peripheral layer is between 0.5 mm and 1.5 mm.

18. The smoking article according to claim 1, wherein the peripheral layer is a single layer.

19. The smoking article according to claim 1, wherein the ratio of the diameter of the heat source to the thickness of the peripheral layer is from 5:1 to 20:1.

20. A smoking article, comprising: a heat source having an upstream end and an opposed downstream end, the heat source comprising: a combustible carbonaceous core; and an integral, non-combustible, thermally insulating, peripheral layer, wherein the core extends from the upstream end of the heat source to the downstream end of the heat source, and the peripheral layer extends from the upstream end of the heat source only part way along a length of the heat source and circumscribes an upstream portion of the core, and wherein a diameter of the heat source is substantially constant and a ratio of the diameter of the heat source to the thickness of the peripheral layer is from 10:1 to 20:1; an aerosol-forming substrate downstream of the heat source; and a heat-conducting, combustion-resistant wrapper around and in direct contact with an upstream portion of the aerosol-forming substrate and a downstream portion of the core of the heat source.

21. A smoking article, comprising: a heat source having an upstream end and an opposed downstream end, the heat source comprising: a combustible carbonaceous core; and an integral, non-combustible, thermally insulating, peripheral layer, wherein the core extends from the upstream end of the heat source to the downstream end of the heat source, and the peripheral layer extends from the upstream end of the heat source only part way along a length of the heat source and circumscribes an upstream portion of the core, and wherein a diameter of the heat source is substantially constant and a ratio of the diameter of the heat source to a thickness of the peripheral layer is from 10:3 to 20:1 and wherein the thickness of the peripheral layer is 0.5 mm; an aerosol-forming substrate downstream of the heat source; and a heat-conducting, combustion-resistant wrapper around and in direct contact with an upstream portion of the aerosol-forming substrate and a downstream portion of the core of the heat source.

Description

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

(2) FIG. 1 shows a schematic perspective view of a heat source according to the invention;

(3) FIG. 2 shows a schematic longitudinal cross-section of a smoking article according to the invention; and

(4) FIG. 3 shows photographs illustrating the results of ignition propensity tests conducted on three smoking articles according to the invention and a comparative smoking article described in the Examples.

(5) The heat source 2 shown in FIG. 1 is a substantially cylindrical heat source having an upstream end 4 and an opposed downstream end 6 and comprising a substantially cylindrical combustible carbonaceous core 8 and an integral, non-combustible thermally insulating, annular peripheral layer 10. The core 8 extends from the upstream end 4 of the heat source 2 to the downstream end 6 of the heat source 2 and the peripheral layer 10 extends from the upstream end 4 of the heat source 2 only part way along the length of the heat source 2.

(6) The peripheral layer 10 circumscribes an upstream portion 12 of the core 8. As shown in FIG. 1, a downstream portion 14 of the core 8 is not circumscribed by the peripheral layer 10.

(7) The diameter of the upstream portion 12 of the core 8 is less than the diameter of the downstream portion 14 of the core 8. The difference in diameter is substantially equal to twice the thickness of the peripheral layer 10. As a result, the heat source 2 is of substantially constant diameter.

(8) Some exemplary dimensions are provided in Table 1 for a heat source 2 according to the invention as shown in FIG. 1.

(9) TABLE-US-00001 TABLE 1 Dimension mm A 9 B 4 C 7.8 D 1.3

(10) In certain embodiments, the upstream portion 12 of the core 8 that is circumscribed by the peripheral layer 10 and the downstream portion 14 of the core 8 that is not circumscribed by the peripheral layer 10 may have the same composition.

(11) In other embodiments, the upstream portion 12 of the core 8 that is circumscribed by the peripheral layer 10 may be a first layer of the core and the downstream portion 14 of the core 8 that is not circumscribed by the peripheral layer 10 may be a second layer of the core, wherein the composition of the first layer is different from the composition of the second layer.

(12) The smoking article 22 shown in FIG. 1 comprises a heat source 2 according to the invention as shown in FIG. 1, an aerosol-forming substrate 24, an airflow directing element 26, an expansion chamber 28 and a mouthpiece 30 in abutting coaxial alignment. The heat source 2, aerosol-forming substrate 24, airflow directing element 26, expansion chamber 28 and mouthpiece 30 are overwrapped in an outer wrapper 32 of cigarette paper of low air permeability.

(13) The aerosol-forming substrate 24 is located immediately downstream of the heat source 2 and comprises a cylindrical plug 34 of homogenised tobacco material comprising glycerine as aerosol former and circumscribed by a filter plug wrap 36.

(14) A non-combustible, substantially air impermeable barrier may be provided between the downstream end of the heat source 2 and the upstream end of the aerosol-forming substrate 24. For example, as shown in FIG. 2 a non-combustible, substantially air impermeable barrier consisting of a non-combustible, substantially air impermeable, barrier coating 38 may be provided on the entire downstream end face of the heat source 2.

(15) The smoking article 22 further comprises a heat-conducting, combustion-resistant wrapper 40 around and in direct contact with a rear portion 14b of the downstream portion 14 of the core 8 of the heat source 2 and an abutting front portion 24a of the aerosol-forming substrate 24. As shown in FIG. 2, a rear portion of the aerosol-forming substrate 24 is not circumscribed by the heat-conducting, combustion-resistant wrapper 40. The heat-conducting, combustion-resistant wrapper 40 consists of a tubular layer of aluminium foil.

(16) An additional heat-conducting, combustion-resistant wrapper 42 also consisting of a tube of aluminium foil circumscribes and is in direct contact with the outer wrapper 32. The additional heat-conducting, combustion-resistant wrapper 42 overlies the heat-conducting, combustion-resistant wrapper 40, with the outer wrapper 32 disposed between them. The length of the additional heat-conducting, combustion-resistant wrapper 42 is greater than the length of the heat-conducting, combustion-resistant wrapper 40. The additional heat-conducting, combustion-resistant wrapper 42 therefore extends downstream beyond the heat-conducting, combustion-resistant wrapper 40 and overlies a greater length of the aerosol-forming substrate 24.

(17) The airflow directing element 26 is located downstream of the aerosol-forming substrate 24 and comprises an open-ended, substantially air impermeable truncated hollow cone 44 made of, for example, cardboard comprises. The downstream end of the open-ended truncated hollow cone 44 is of substantially the same diameter as the aerosol-forming substrate 24 and the upstream end of the open-ended truncated hollow cone 44 is of reduced diameter compared to the aerosol-forming substrate 24.

(18) As shown in FIG. 2, the upstream end of the open-ended, substantially air impermeable, truncated hollow cone 44 of the airflow directing element 26 extends into the aerosol-forming substrate 24. As also shown in FIG. 2, a circumferential arrangement of air inlets 46 is provided in the outer wrapper 32 circumscribing the open-ended, substantially air impermeable, truncated hollow cone 44.

(19) The expansion chamber 28 is located downstream of the airflow directing element 26 and comprises an open-ended hollow tube 48 made of, for example, cardboard, which is of substantially the same diameter as the aerosol-forming substrate 24.

(20) The mouthpiece 30 of the smoking article 22 is located downstream of the expansion chamber 28 and comprises a cylindrical plug 50 of cellulose acetate tow of very low filtration efficiency circumscribed by a filter plug wrap 52. The mouthpiece 30 may be circumscribed by a band of tipping paper (not shown).

(21) An airflow pathway extends between the air inlets 46 and the mouthpiece 30 of the smoking article 22. The volume bounded by the exterior of the open-ended hollow cone 44 of the airflow directing element 26 and the outer wrapper 32 forms a first portion of the airflow pathway that extends longitudinally upstream from the air inlets 46 to the aerosol-forming substrate 24. The volume bounded by the interior of the open-ended hollow cone 44 of the airflow directing element 26 forms a second portion of the airflow pathway that extends longitudinally downstream towards the mouth piece 30 of the smoking article 22, between the aerosol-forming substrate 24 and the expansion chamber 28.

(22) In use, when a consumer draws on the mouthpiece 30 of the smoking article 22, cool air (shown by dotted arrows in FIG. 2) is drawn into the smoking article 22 through the air inlets 46. The drawn air passes upstream to the aerosol-forming substrate 24 along the first portion of the airflow pathway between the exterior of the open-ended hollow cone 44 of the airflow directing element 26 and the outer wrapper 32.

(23) The front portion 24a of the aerosol-forming substrate 24 is heated by conduction through the abutting rear portion 14b of the downstream portion 14 of the core 8 of the heat source 2 and the heat-conducting, combustion-resistant wrapper 40. The additional heat-conducting, combustion-resistant wrapper 42 retains heat within the smoking article 22 to help maintain the temperature of the heat-conducting, combustion-resistant wrapper 40 during smoking. This in turn helps maintain the temperature of the aerosol-forming substrate 24 to facilitate continued and enhanced aerosol delivery. In addition, the heat-conducting, combustion-resistant wrapper 42 transfers heat along the aerosol-forming substrate 24, beyond the downstream end of the heat-conducting, combustion-resistant wrapper 40. This helps to disperse heat through a larger volume of the aerosol-forming substrate 24, which in turn helps to provide a more consistent puff-by-puff aerosol delivery.

(24) The heating of the aerosol-forming substrate 24 releases volatile and semi-volatile compounds and glycerine from the plug 36 of homogenised tobacco material, which form an aerosol that is entrained in the drawn air as it flows through the aerosol-forming substrate 24. The drawn air and entrained aerosol (shown by dashed and dotted arrows in FIG. 2) pass downstream along the second portion of the airflow pathway through the interior of the open-ended hollow cone 44 of the airflow directing element 26 to the expansion chamber 28, where they cool and condense. The cooled aerosol then passes downstream through the mouthpiece 30 of the smoking article 22 into the mouth of the consumer.

(25) The non-combustible, substantially air impermeable, barrier coating 38 provided on the downstream end face of the heat source 2 isolates the heat source 2 from the airflow pathway through the smoking article 22 such that, in use, air drawn through the smoking article 22 along the first portion and the second portion of the airflow pathway does not directly contact the heat source 2.

(26) The integral, non-combustible thermally insulating, annular peripheral layer 10 circumscribing the upstream portion 12 of the core 8 of the heat source 2 helps to reduce the ignition propensity of the smoking article 22 during and after use by reducing the temperature of the portion of the heat source 2 that is not circumscribed by the heat-conducting, combustion-resistant wrapper 40 and the additional heat-conducting, combustion-resistant wrapper 42.

(27) Some exemplary dimensions are provided in Table 2 for a smoking article 2 according to the invention as shown in FIG. 2 comprising a heat source 2 according to the invention as shown in FIG. 1 having the dimensions shown in Table 1.

(28) TABLE-US-00002 TABLE 2 Distance from upstream end of heat source (mm) E 10 F 13

EXAMPLES

(29) Smoking articles according to the invention as shown in FIG. 2 having the dimensions shown in Table 2 are assembled by hand using heat sources 2 according to the invention as shown in FIG. 1 having the composition shown in Table 3 and the dimensions shown in Tables 1 and 3.

(30) For the purposes of comparison, smoking articles of the same construction and dimensions are assembled by hand using heat sources of the same dimensions having the composition shown in Table 3.

(31) All of the heat sources are made by manual pressing.

(32) The ignition propensity of the smoking articles is tested using three replicates. Ten Whatman filters are placed on top of a standard filter holder and three pieces of cardboard are used to limit the perturbation of airflow.

(33) The heat sources of the smoking articles are lit using a yellow flame lighter. The colour at the surface of the heat sources changes upon ignition due to downstream movement of a deflagration front from the upstream end to the downstream end of the heat sources. Thirty seconds after the deflagration front has reached the downstream end of the heat source, the smoking articles are placed horizontally on top of the ten Whatman filters.

(34) The smoking articles are left on the Whatman filters until extinction or for at least 10 minutes. The Whatman filters are then removed from the filter holder and a photograph is taken of each of the ten Whatman filters.

(35) The photographs of the first (uppermost), third, sixth and tenth (lowermost) Whatman filters for one representative replicate smoking article according to each example shown in Table 3 is shown in FIG. 3.

(36) TABLE-US-00003 TABLE 3 Example Example Example Example Comparative 1 2 3 4 Example Non-combustible thermally insulating, peripheral layer Thickness (mm) 1.3 1.3 0.8 0.8 Diatomaceous earth (% by dry weight) 95 Gypsum (% by dry weight) 95 95 Bentonite (% by dry weight) 95 Carbon (% by dry weight) 45 Calcium peroxide (% by dry weight) 50 Carboxymethyl cellulose 5 (% by dry weight) Combustible Carbonaceous Core Carbon (% by dry weight) 45 Calcium peroxide (% by dry weight) 50 Carboxymethyl cellulose 5 (% by dry weight)

(37) As shown in FIG. 3, the first, third, sixth and tenth filters for the smoking article of the comparative example are all marked. In contrast, the third, sixth and tenth filters for the smoking articles according to the invention of Examples 1, 2 and 4 are unmarked and the sixth and tenth for the smoking articles according to the invention of Example 3 are unmarked.

(38) This demonstrates that the provision of an integral, non-combustible, thermally insulating, peripheral layer circumscribing an upstream portion of the combustible carbonaceous core of heat sources according to the invention reduces the temperature of the surface of smoking articles according to the invention and hence their ignition propensity.

(39) The embodiments and examples described above illustrate but do not limit the invention. Other embodiments of the invention may be made and it is to be understood that the specific embodiments and examples described herein are not limiting.