COMBUSTIBLE HEAT SOURCE COMPRISING AN IGNITION AID AND A BINDING AGENT

Abstract

A combustible heat source for an aerosol-generating article, the combustible heat source comprising: carbon; an alkaline earth metal peroxide ignition aid; and a binding agent comprising at least one non-cellulosic film-forming polymer.

Claims

1-15. (canceled)

16. A combustible heat source for an aerosol-generating article, the combustible heat source comprising: carbon; an alkaline earth metal peroxide ignition aid; and a binding agent comprising a combination of carboxymethyl cellulose and at least one non-cellulosic film-forming polymer selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, polyvinyl acetate and graft-copolymers thereof.

17. The combustible heat source according to claim 16 wherein the alkaline earth metal peroxide ignition aid is calcium peroxide.

18. The combustible heat source according to claim 16 wherein the combustible heat source comprises between about 20 percent by weight and about 60 percent by weight of the alkaline earth metal peroxide ignition aid.

19. The combustible heat source according to claim 16 wherein the combustible heat source comprises at least about 3 percent by weight of the binding agent.

20. The combustible heat source according to claim 16 wherein the combustible heat source comprises between about 4 percent by weight and about 15 percent by weight of the binding agent.

21. The combustible heat source according to claim 16 wherein the combustible heat source comprises at least about 0.5 percent by weight of the at least one non-cellulosic film-forming polymer.

22. The combustible heat source according to claim 16 wherein the combustible heat source comprises between about 0.75 percent by dry weight and about 4 percent by weight of the at least one non-cellulosic film-forming polymer.

23. The combustible heat source according to claim 16 wherein the carboxymethyl cellulose is present in the combustible heat source in an amount of at least about 1.5 percent by dry weight.

24. The combustible heat source according to claim 23 wherein the ratio of the percentage by weight of carboxymethyl cellulose to the percentage by weight of the at least one non-cellulosic film-forming polymer in the combustible heat source is at least about 1:1.

25. The combustible heat source according to claim 16 wherein the combustible heat source comprises between about 30 percent by weight and about 55 percent by weight of carbon.

26. The combustible heat source according to claim 16 further comprising one or more carboxylate burn salts.

27. The combustible heat source according to claim 26 wherein the combustible heat source comprises at least about 1 percent by weight of the one or more carboxylate burn salts.

28. An aerosol-generating article comprising: the combustible heat source according to claim 16; and an aerosol-forming substrate downstream of the combustible heat source.

Description

[0342] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0343] FIG. 1 shows a schematic longitudinal cross-section of an aerosol-generating article according to an embodiment of the invention; and

[0344] FIG. 2 shows a graph of the calcium peroxide content of a combustible heat source according to a first embodiment of the invention, a combustible heat source according to a second embodiment of the invention and a comparative combustible heat source not according to the invention as a function of time.

[0345] 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.

[0346] 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.

[0347] The combustible heat source 4 comprises carbon, an alkaline earth metal peroxide ignition aid, and a binding agent comprising at least one non-cellulosic film-forming polymer.

[0348] 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.

[0349] 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.

[0350] 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.

[0351] 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.

[0352] 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.

[0353] The aerosol-generating article may further comprise a band of tipping paper (not shown) circumscribing a downstream end portion of the outer wrapper 20.

[0354] 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.

[0355] 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.

[0356] 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.

[0357] 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.

[0358] 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.

[0359] 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.

[0360] Combustible heat sources according to a first embodiment of the invention are produced having the composition shown in Table 1:

TABLE-US-00001 TABLE 1 Content (percentage by Component Function weight) Charcoal Fuel 43.3 Calcium Peroxide Alkaline earth metal 48.0 (about 80 percent purity) peroxide ignition aid Carboxymethyl cellulose Binding agent 4.7 Polyvinyl alcohol Binding agent 2.0 Tri-potassium citrate hydrate Carboxylate burn salt 2.0 Total 100.0

[0361] The components in Table 1 are combined to form a granulate mixture by wet granulation. The charcoal, calcium peroxide and carboxymethyl cellulose are mixed to form a particulate mixture. The particulate mixture of charcoal, calcium peroxide and carboxymethyl cellulose is air fluidized and sprayed with a liquid solution of tri-potassium citrate hydrate and an aqueous solution of polyvinyl alcohol to form a granulate mixture.

[0362] The granulate mixture is formed into a cylindrical shape by pressing. About 400 milligrams of the granulate mixture is pressed in a single cavity press to form a cylindrical combustible heat source having a length of about 9 millimetres, a diameter of about 7.7 millimetres and a density of about 0.9 grams per cubic centimetre. The cylindrical combustible heat source is removed from the single cavity press and dried in a drying oven at a temperature of between about 85 degrees Celsius and about 105 degrees Celsius for about 3 hours.

[0363] Combustible heat sources according to a second embodiment of the invention are produced having the composition shown in Table 2:

TABLE-US-00002 TABLE 2 Content (percentage by Component Function weight) Charcoal Fuel 43.3 Calcium Peroxide Alkaline earth metal 48.0 (about 80 percent purity) peroxide ignition aid Carboxymethyl cellulose Binding agent 4.7 Polyvinyl alcohol-polyethylene Binding agent 2.0 glycol graft-copolymer Tri-potassium citrate hydrate Carboxylate burn salt 2.0 Total 100.0

[0364] The components in Table 2 are combined to form a granulate mixture by wet granulation. The charcoal, calcium peroxide and carboxymethyl cellulose are mixed to form a particulate mixture. The particulate mixture of charcoal, calcium peroxide and carboxymethyl cellulose is air fluidized and sprayed with a liquid solution of tri-potassium citrate hydrate and an aqueous solution of polyvinyl alcohol-polyethylene glycol graft-copolymer to form a granulate mixture.

[0365] The granulate mixture is formed into a cylindrical shape by pressing. About 400 milligrams of the granulate mixture is pressed in a single cavity press to form a cylindrical combustible heat source having a length of about 9 millimetres, a diameter of about 7.7 millimetres and a density of about 0.9 grams per cubic centimetre. The cylindrical combustible heat source is removed from the single cavity press and dried in a drying oven at a temperature of between about 85 degrees Celsius and about 105 degrees Celsius for about 3 hours.

[0366] Comparative combustible heat sources not according to the invention having the composition shown in Table 3 are also produced:

TABLE-US-00003 TABLE 3 Content (percentage by Component Function weight) Charcoal Fuel 45.0 Calcium Peroxide Alkaline earth metal 48.0 (about 80 percent purity) peroxide ignition aid Carboxymethyl cellulose Binding agent 4.7 Bentonite Binding agent 0.3 Tri-potassium citrate hydrate Carboxylate burn salt 2.0 Total 100.0

[0367] The components in Table 3 are combined to form a granulate mixture by wet granulation. The charcoal, calcium peroxide and carboxymethyl cellulose are mixed to form a particulate mixture. The particulate mixture of charcoal, calcium peroxide and carboxymethyl cellulose is air fluidized and sprayed with a liquid solution of tri-potassium citrate hydrate and then an aqueous solution of bentonite to form a granulate mixture.

[0368] The granulate mixture is formed into a cylindrical shape by pressing. About 400 milligrams of the granulate mixture is pressed in a single cavity press to form a cylindrical combustible heat source having a length of about 9 millimetres, a diameter of about 7.7 millimetres and a density of about 0.9 grams per cubic centimetre. The cylindrical combustible heat source is removed from the single cavity press and dried in a drying oven at a temperature of between about 85 degrees Celsius and about 105 degrees Celsius for about 3 hours.

[0369] To simulate environmental conditions to which combustible heat sources may be exposed during transport and storage, the combustible heat sources according to the first embodiment of the invention, the combustible heat sources according to the second embodiment of the invention and the comparative combustible heat sources not according to the invention are conditioned at about 30 degrees Celsius and about 75 percent relative humidity for 7 days. The calcium peroxide content (percentage by weight) of the combustible heat sources according to the first embodiment of the invention, the combustible heat sources according to the second embodiment of the invention and the comparative combustible heat sources not according to the invention is measured as a function of time by titration with potassium permanganate (KMnO.sub.4) solution. The results are shown in FIG. 2; the upper line in FIG. 2 shows the measured calcium peroxide content of the combustible heat sources according to the first embodiment of the invention as a function of time, the middle line in FIG. 2 shows the measured calcium peroxide content of the combustible heat sources according to the second embodiment of the invention as a function of time and the lower line in FIG. 2 shows the measured calcium peroxide content of the comparative combustible heat sources not according to the invention as a function of time. The values shown in FIG. 2 are the average of the measurements for three replicates of each combustible heat source.

[0370] As shown in FIG. 2, the rate of degradation over time of the calcium peroxide in the combustible heat sources according to the first and second embodiments of the invention is advantageously significantly lower than the rate of degradation over time of the calcium peroxide in the comparative combustible heat sources not according to the invention.

[0371] The ignition propagation speed of ten combustible heat sources according to the first embodiment of the invention, ten combustible heat sources according to the second embodiment of the invention and ten comparative combustible heat sources not according to the invention is also measured. The results are shown in Table 4. The combustible heat sources according to the first embodiment of the invention, the combustible heat sources according to the second embodiment of the invention and the comparative combustible heat sources not according to the invention are conditioned at about 22 degrees Celsius and about 50 percent relative humidity for about 24 hours prior to measurement of the ignition propagation speed. To measure the ignition propagation speed, thermocouples are inserted into the combustible heat sources according to the first embodiment of the invention, the combustible heat sources according to the second embodiment of the invention and the comparative combustible heat sources not according to the invention at two positions, a first position 1 millimetre from the front end face of the combustible heat source and a second position 8 millimetres from the front end face of the combustible heat source. The front end faces of the combustible heat sources according to the first embodiment of the invention, the combustible heat sources according to the second embodiment of the invention and the comparative combustible heat sources not according to the invention are ignited using an electrical lighter. The difference in the time taken for the temperature measured by the thermocouples at the first position and the second position to reach 350 degrees Celsius is measured. The ignition propagation time shown in Table 4 is the average time measured for the ten combustible heat sources according to the first embodiment of the invention, ten combustible heat sources according to the second embodiment of the invention and ten comparative combustible heat sources not according to the invention.

TABLE-US-00004 TABLE 4 Ignition propagation time (seconds) Combustible heat sources according to the first 2.0 ± 0.1 embodiment of the invention Combustible heat sources according to the 2.0 ± 0.2 second embodiment of the invention Comparative combustible heat sources not 3.0 ± 0.3 according to the invention

[0372] As shown in Table 4, the ignition propagation time of the combustible heat sources according to the first and second embodiments of the invention is advantageously significantly lower than the ignition propagation time of the comparative combustible heat sources not according to the invention.

[0373] The results in FIG. 2 and Table 4 demonstrate an improvement in the chemical and physical stability and combustion properties of combustible heat sources according to the invention due to the inclusion of a binding agent comprising at least one non-cellulosic film-forming polymer.

[0374] The results in FIG. 2 demonstrate that inclusion of a binding agent comprising at least one non-cellulosic film-forming polymer in combustible heat sources according to the invention advantageously significantly reduces degradation of the alkaline earth metal peroxide ignition aid as a result of exposure to environmental conditions. In particular, the results in FIG. 2 demonstrate that inclusion of a binding agent comprising at least one non-cellulosic film-forming polymer in combustible heat sources according to the invention advantageously significantly reduces degradation of the alkaline earth metal peroxide ignition aid as a result of exposure to high humidity.

[0375] The results in Table 4 demonstrate that inclusion of a binding agent comprising at least one non-cellulosic film-forming polymer in combustible heat sources according to the invention also advantageously significantly improves the ignition propagation speed of combustible heat sources according to the invention.