COMBUSTIBLE HEAT SOURCE COMPRISING CARBON AND CALCIUM PEROXIDE

Abstract

A combustible heat source (4) for an aerosol-generating article (2) comprises carbon and calcium peroxide. The calcium peroxide has a purity of greater than or equal to about 90 percent. A method of producing a combustible heat source for an aerosol-generating article, the method comprising the steps of: mixing a carbon material and calcium peroxide having a purity of greater than or equal to about 90 percent; forming the mixture of the carbon material and the calcium peroxide into an elongate rod; and drying the elongate rod.

Claims

1. A combustible heat source for an aerosol-generating article, the combustible heat source comprising carbon and calcium peroxide, wherein the calcium peroxide has a purity of greater than or equal to about 90 percent.

2. A combustible heat source according to claim 1 wherein the calcium peroxide has a purity of between about 90 percent and about 98 percent.

3. A combustible heat source according to claim 1 wherein the calcium peroxide has a purity of between about 92 percent and about 98 percent.

4. A combustible heat source according to claim 1 comprising at least about 20 percent by dry weight of the calcium peroxide.

5. A combustible heat source according to claim 1 comprising between about 20 percent by dry weight and about 65 percent by dry weight of the calcium peroxide.

6. A combustible heat source according to claim 1 comprising at least about 35 percent by dry weight of the carbon.

7. A combustible heat source according to claim 1 comprising between about 35 percent by dry weight and about 80 percent by dry weight of the carbon.

8. A combustible heat source according to claim 1 further comprising a binding agent.

9. A combustible heat source according to claim 8 wherein the binding agent includes at least one organic polymeric binder material and at least one carboxylate burn salt.

10. A combustible heat source according to claim 8 comprising between about 2 percent by dry weight and about 10 percent by dry weight of the binding agent.

11. A combustible heat source according to claim 1 wherein the combustible heat source is formed by a pressing process.

12. An aerosol-generating article comprising a combustible heat source according to claim 1 and an aerosol-forming substrate.

13. Use of calcium peroxide having a purity of greater than or equal to about 90 percent as an ignition aid in a carbonaceous combustible heat source for an aerosol-generating article.

14. A method of producing a combustible heat source for an aerosol-generating article, the method comprising the steps of: mixing a carbon material and calcium peroxide having a purity of greater than or equal to about 90 percent; forming the mixture of the carbon material and the calcium peroxide into an elongate rod; and drying the elongate rod.

Description

[0235] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0236] FIG. 1 shows a schematic longitudinal cross-section of an aerosol-generating article according to an embodiment of the invention; and

[0237] FIG. 2 shows a graph of the temperature profiles of combustible heat sources according to the invention and the temperature profiles of comparative combustible heat sources.

[0238] The aerosol-generating article 2 according to the embodiment of the invention shown in FIG. 1 comprises a combustible heat source 4 according to the invention and an aerosol-forming substrate 10 downstream of the combustible heat source 4. The combustible heat source 4 is a blind combustible heat source having a front end face 6 and an opposed rear end face 8 and is located at the distal end of the aerosol-generating article 2. The aerosol-generating article 2 further comprises a transfer element 12, an aerosol-cooling element 14, a spacer element 16 and a mouthpiece 18. The combustible heat source 4, aerosol-forming substrate 10, transfer element 12, aerosol-cooling element 14, spacer element 16 and mouthpiece 18 are arranged in abutting coaxial alignment. As shown in FIG. 1, the aerosol-forming substrate 10, transfer element 12, aerosol-cooling element 14, spacer element 16 and mouthpiece 18 and a rear portion of the combustible heat source 4 are wrapped in an outer wrapper 20 of sheet material such as, for example, cigarette paper.

[0239] As shown in FIG. 1, a non-combustible substantially air impermeable barrier 22 in the form of a disc of aluminium foil is provided between the rear end face 8 of the combustible heat source 4 and the aerosol-forming substrate 10. The barrier 22 is applied to the rear end face 8 of the combustible carbonaceous heat source 4 by pressing the disc of aluminium foil onto the rear end face 8 of the combustible heat source 4 and abuts the rear end face 8 of the combustible carbonaceous heat source 4 and the aerosol-forming substrate 10.

[0240] The combustible heat source 4 comprises carbon and calcium peroxide, wherein the calcium peroxide has a purity of greater than or equal to about 90 percent.

[0241] The aerosol-forming substrate 10 is located immediately downstream of the barrier 22 applied to the rear end face 8 of the combustible heat source 4. The aerosol-forming substrate 10 comprises a gathered crimped sheet of homogenised tobacco material 24 and a wrapper 26 around and in direct contact with the gathered crimped sheet of homogenised tobacco material 24. The gathered crimped sheet of homogenised tobacco material 24 comprises a suitable aerosol former such as, for example, glycerine.

[0242] The transfer element 12 is located immediately downstream of the aerosol-forming substrate 10 and comprises a cylindrical open-ended hollow cellulose acetate tube 28.

[0243] The aerosol-cooling element 14 is located immediately downstream of the transfer element 12 and comprises a gathered sheet of biodegradable polymeric material such as, for example, polylactic acid.

[0244] The spacer element 16 is located immediately downstream of the aerosol-cooling element 14 and comprises a cylindrical open-ended hollow paper or cardboard tube.

[0245] The mouthpiece 18 is located immediately downstream of the spacer element 16. As shown in FIG. 1, the mouthpiece 18 is located at the proximal end of the aerosol-generating article 2 and comprises a cylindrical plug of suitable filtration material 30 such as, for example, cellulose acetate tow of very low filtration efficiency, wrapped in filter plug wrap 32.

[0246] The aerosol-generating article may further comprise a band of tipping paper (not shown) circumscribing a downstream end portion of the outer wrapper 20.

[0247] As shown in FIG. 1, the aerosol-generating article 2 further comprises a heat-conducting element 34 formed from a suitable thermally conductive material such as, for example, aluminium foil around and in contact with a rear portion 4b of the combustible heat source 4 and a front portion 10a of the aerosol-forming substrate 10. In the aerosol-generating article 2 according to the embodiment of the invention shown in FIG. 1, the aerosol-forming substrate 10 extends downstream beyond the heat-conducting element 34. That is, the heat-conducting element 34 is not around and in contact with a rear portion of the aerosol-forming substrate 10. However, it will be appreciated that in other embodiments of the invention (not shown), the heat-conducting element 34 may be around and in contact with the entire length of the aerosol-forming substrate 10. It will also be appreciated that in other embodiments of the invention (not shown), one or more additional heat-conducting elements may be provided that overlie the heat-conducting element 34.

[0248] The aerosol-generating article 2 according to the embodiment of the invention shown in FIG. 1 comprises one or more air inlets 36 around the periphery of the aerosol-forming substrate 10. As shown in FIG. 1, a circumferential arrangement of air inlets 36 is provided in the wrapper 26 of the aerosol-forming substrate 10 and the overlying outer wrapper 20 to admit cool air (shown by dotted arrows in FIG. 1) into the aerosol-forming substrate 10.

[0249] In use, a user ignites the combustible carbonaceous heat source 4. Once the combustible carbonaceous heat source 4 is ignited the user draws on the mouthpiece 18 of the aerosol-generating article 2. When a user draws on the mouthpiece 18, cool air (shown by dotted arrows in FIG. 1) is drawn into the aerosol-forming substrate 10 of the aerosol-generating article 2 through the air inlets 36.

[0250] The periphery of the front portion 10a of the aerosol-forming substrate 10 is heated by conduction through the rear end face 8 of the combustible heat source 4 and the barrier 22 and through the heat-conducting element 34.

[0251] The heating of the aerosol-forming substrate 10 by conduction releases aerosol former and other volatile and semi-volatile compounds from the gathered crimped sheet of homogenised tobacco material 24. The compounds released from the aerosol-forming substrate 10 form an aerosol that is entrained in the air drawn into the aerosol-forming substrate 10 of the aerosol-generating article 2 through the air inlets 36 as it flows through the aerosol-forming substrate 10. The drawn air and entrained aerosol (shown by dashed arrows in FIG. 1) pass downstream through the interior of the cylindrical open-ended hollow cellulose acetate tube 28 of the transfer element 12, the aerosol-cooling element 14 and the spacer element 16, where they cool and condense. The cooled drawn air and entrained aerosol pass downstream through the mouthpiece 18 and are delivered to the user through the proximal end of the aerosol-generating article 2. The non-combustible substantially air impermeable barrier 22 on the rear end face 8 of the combustible carbonaceous heat source 4 isolates the combustible heat source 4 from air drawn through the aerosol-generating article 2 such that, in use, air drawn through the aerosol-generating article 2 does not come into direct contact with the combustible heat source 4.

[0252] Combustible heat sources according to a first embodiment of the invention are produced in accordance with Example 1 below.

EXAMPLE 1

[0253] A combustible heat source according to the invention having the composition shown in Table 1 is prepared by the method described below.

TABLE-US-00001 TABLE 1 Percentage on a dry Amount weight Component Function (g) basis Charcoal Combustible fuel 1020 51.0 Calcium peroxide Ignition aid 840 42.0 (92 percent purity) Carboxymethyl cellulose Organic polymeric binder 94 4.7 Tri-potassium citrate Carboxylate burn salt 40 2.0 Bentonite Non-combustible 6 0.3 inorganic binder Total 2000 100.0

[0254] The powdered raw materials listed under Mix A in Table 2 (charcoal, calcium peroxide and carboxymethyl cellulose) are pre-blended in a mixer. A first granulation fluid is prepared by dissolution of the remaining raw materials listed under Mix A in Table 2 in water (potassium citrate (4% solution in water)). The pre-blended powdered raw materials are introduced into a fluidized bed reactor and the air flow adjusted to keep the pre-blended powdered raw materials in air suspension. The first granulation fluid is pumped (typically at a fluid rate of 50 to 70 ml/min) into a nozzle and atomized with compressed air in a spray that is added onto the air fluidized pre-blended powdered raw materials.

TABLE-US-00002 TABLE 2 Mix A Mix B Amount Amount Raw Material Function (g) (g) Charcoal Combustible fuel 1020 — (powder) Calcium peroxide Ignition aid  840 (92 percent purity) (powder) Carboxymethyl cellulose Organic polymeric binder  94 — (powder) Tri-potassium citrate Carboxylate burn salt  40 — (solution) Bentonite Non-combustible —  6 inorganic binder (slurry) Water 1000 400

[0255] A second granulation fluid is prepared by dissolution of the remaining raw material listed under Mix B in Table 2 in water (bentonite (1.5% slurry in water)). The second granulation fluid is pumped (typically at a fluid rate of 50 to 70 ml/min) into a nozzle and atomized with compressed air in a spray. The atomized second granulation fluid is combined with the raw materials of Mix A to form granules. The granules are air dried, typically at ambient temperature, 60 or 80° C., and the level of residual moisture is controlled by weight, typically 24-28%). The granules are sieved through a 0.8 to 1.0 mm sieve to remove chunks.

[0256] The granules are moulded to form cylindrical combustible heat sources having a length of about 9 mm and a diameter of about 7.8 mm. Moulding is operated with a single cavity press equipped with an automated feeding system. The force of compaction is <2KN for a cycle time of 3 s/stroke. Optionally, a disc of aluminium foil, typically about 20 μm thickness, is punched onto the upper surface of the combustible heat source during the compaction stroke. In such embodiments, a coating of carboxymethyl cellulose covering the surface of the aluminium foil may be used for good adhesion. The punch is designed with a chamfer and with a specific diameter to reduce the risk of aluminium loss during pressing. The diameter of the punch is designed to create a clearance with the mould cavity surface that corresponds to the aluminium foil thickness. The moulded combustible heat sources are dried in an oven for about 30 minutes at about 100° C.

[0257] The temperature of combustible heat sources according to the invention having the compositions shown in Examples (a) to (d) of Table 3 are measured using a thermocouple inserted into the middle of the combustible heat sources. To generate the profiles, the combustible heat sources are ignited using a conventional yellow flame lighter. The results are shown in FIG. 2.

TABLE-US-00003 TABLE 3 Component Comparative (percentage on a Examples Examples dry weight basis) (a) (b) (c) (d) (e) (f) Charcoal 57.4 55.2 53.4 51.5 47.5 45.5 Calcium peroxide 36.0 38.0 40.0 42.0 0.0 0.0 (96 percent purity) Calcium peroxide 0.0 0.0 0.0 0.0 48.0 50.0 (75 percent purity) Calcium hydroxide 0.4 0.4 0.4 0.4 0.0 0.0 Carboxymethyl cellulose 3.7 3.9 3.7 3.6 3.7 3.7 Tri-potassium citrate 1.0 1.0 1.0 1.0 0.0 0.0 Bentonite 1.5 1.5 1.5 1.5 0.8 0.8 Total 100.0 100.0 100.0 100.0 100.0 100.0

[0258] For the purposes of comparison, the temperature of comparative combustible heat sources having the compositions shown in Comparative Examples (e) and (f) of Table 3 are measured under similar experimental conditions. The comparative combustible heat sources are the same size and mass as the combustible heat sources according to the invention and are produced in the same manner as the combustible heat sources according to the invention. The results are also shown in FIG. 2.

[0259] As shown in FIG. 2, the combustible heat sources according to the invention comprising (a) 36% by dry weight of calcium peroxide having a purity of 96 percent, (b) 38% by dry weight of calcium peroxide having a purity of 96 percent, (c) 40% by dry weight of calcium peroxide having a purity of 96 percent and (d) 42% by dry weight of calcium peroxide having a purity of 96 percent advantageously exhibit a longer combustion lifetime than the comparative combustible heat sources comprising (e) 48% by dry weight of calcium peroxide having a purity of about 73 percent and (f) 50% by dry weight of calcium peroxide having a purity of about 73 percent. These results demonstrate an improvement in the combustion properties of the combustible heat sources according to the invention provided through the use of calcium peroxide having a purity of at least 90 percent, as described above.

[0260] The specific embodiments and examples described above illustrate but do not limit the invention. It is to be understood that other embodiments of the invention may be made and the specific embodiments and examples described herein are not exhaustive.