METHOD OF PRODUCING A COMBUSTIBLE HEAT SOURCE COMPRISING CARBON AND A BINDING AGENT

Abstract

A method of producing a combustible heat source for an aerosol-generating article, the method comprising: forming a combustible heat source comprising carbon and a binding agent, wherein the binding agent comprises polyvinyl alcohol; and heating the formed combustible heat source at a temperature of at least about 90 degrees Celsius for a period of at least about 45 minutes.

Claims

1. A method of producing a combustible heat source for aerosol-generating article, the method comprising: forming a combustible heat source comprising carbon, a binding agent and an ignition aid, wherein the binding agent comprises polyvinyl alcohol and the ignition aid comprises an alkaline earth metal peroxide; and heating the formed combustible heat source at a temperature of at least about 90 degrees Celsius for a period of at least about 45 minutes.

2. A method according to claim 1 wherein the combustible heat source comprises between about 15 percent by weight and about 65 percent by weight of the alkaline earth metal peroxide ignition aid.

3. A method according to claim 1 wherein the ignition aid comprises calcium peroxide.

4. A method according to claim 1 comprising heating the combustible heat source at a temperature of between about 90 degrees Celsius and about 150 degrees Celsius.

5. A method according to claim 1 comprising heating the combustible heat source at a temperature of between about 100 degrees Celsius and about 140 degrees Celsius.

6. A method according to claim 1 comprising heating the combustible heat source for a period of between about 45 minutes and about 24 hours.

7. A method according to claim 1 comprising heating the combustible heat source for a period of at least about 90 minutes.

8. A method according to claim 1 wherein the polyvinyl alcohol has a molecular weight of between about 20,000 grams per mole and about 200,000 grams per mole.

9. A method according to claim 1 wherein the polyvinyl alcohol has a molecular weight of less than or equal to about 125,000 grams per mole.

10. A method according to claim 1 wherein the combustible heat source comprises at least about 0.1 percent by weight of polyvinyl alcohol.

11. A method according to claim 1 wherein the combustible heat source comprises between about 0.5 percent by weight and about 2 percent by weight of polyvinyl alcohol.

12. A method according to claim 1 wherein the binding agent further comprises carboxymethyl cellulose.

13. A method according to claim 12 wherein the combustible heat source comprises at least about 2 percent by weight of carboxymethyl cellulose.

14. A method according to claim 12 wherein the ratio of the percentage by weight of carboxymethyl cellulose to the percentage by weight of polyvinyl alcohol in the combustible heat source is at least about 2:1.

15. An aerosol-generating article comprising: a combustible heat source produced by a method according to claim 1; and an aerosol-forming substrate downstream of the combustible heat source.

Description

[0391] The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

[0392] FIG. 1 shows a schematic longitudinal cross-section of an aerosol-generating article according to an embodiment of the invention; and

[0393] FIGS. 2 and 3 show the time taken for the calcium peroxide content of combustible heat sources produced by methods according to the invention and comparative combustible heat sources produced by methods not according to the invention to reach a lower limit of 32.7 percent by weight.

[0394] The aerosol-generating article 2 according to the embodiment of the invention shown in FIG. 1 comprises a combustible heat source 4 produced by the method 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.

[0395] 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.

[0396] The combustible heat source 4 produced by the method according to the invention comprises carbon, a binding agent comprising a combination of carboxymethyl cellulose and polyvinyl alcohol and an alkaline earth metal peroxide ignition aid.

[0397] 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.

[0398] 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.

[0399] 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.

[0400] 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.

[0401] 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.

[0402] The aerosol-generating article may further comprise a band of tipping paper (not shown) circumscribing a downstream end portion of the outer wrapper 20.

[0403] 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.

[0404] 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.

[0405] 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.

[0406] 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.

[0407] 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

Examples (a)(i) to (a)(vii)

[0408] Combustible heat sources having the composition shown in Example (a) of Table 1 are formed by methods according to the invention:

TABLE-US-00001 TABLE 1 Component (percentage by Comparative Comparative dry weight) Function Example (a) Example (b) Example (c) Charcoal Fuel 46.3 46.3 45.0 Calcium Peroxide Alkaline earth metal 48.0 48.0 48.0 peroxide ignition aid Carboxymethyl cellulose Binding agent 4.7 4.7 4.7 Polyvinyl alcohol Binding agent 1.0 1.0 0.0 Bentonite Binding agent 0.0 0.0 0.3 Tri-potassium citrate hydrate Carboxylate burn salt 0.0 0.0 2.0 Total 100 100 100

[0409] The components in Example (a) of 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 an aqueous solution of polyvinyl alcohol to form a granulate mixture.

[0410] 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 formed cylindrical combustible heat source is removed from the single cavity press.

[0411] Formed cylindrical combustible heat sources having the composition shown in Example (a) of Table 1 are heated in air in a ventilated drying oven at the temperatures shown in Examples (a)(i) to (a)(iv) of Table 2 for a period of 5 hours:

TABLE-US-00002 TABLE 2 Example Example Example Example (a)(i) (a)(ii) (a)(iii) (a)(iv) Temperature 45 65 95 120 (degrees Celsius)

[0412] The combustible heat sources are removed from the oven and allowed to cool to room temperature.

[0413] Formed cylindrical combustible heat sources having the composition shown in Example (a) of Table 1 are also heated in air in a ventilated drying oven at a temperature of 120 degrees Celsius for the periods of time shown in Examples (a)(v) to (a)(vii) of Table 3:

TABLE-US-00003 TABLE 3 Example (a)(v) Example (a)(vi) Example (a)(vii) Time 1.5 3 5 (hours)

[0414] The combustible heat sources are removed from the oven and allowed to cool to room temperature.

Comparative Examples (b), (c)(i) and (c)(ii)

[0415] Combustible heat sources having the compositions shown in Example (b) and Example (c) of Table 1 are formed by methods not according to the invention:

[0416] The components in Example (b) of 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 an aqueous solution of polyvinyl alcohol to form a granulate mixture.

[0417] 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 formed cylindrical combustible heat source is removed from the single cavity press.

[0418] The formed cylindrical combustible heat sources having the composition shown in Example (b) of Table 1 are not heated as shown in Example (b) of Table 4.

[0419] The components in Example (c) of 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 then an aqueous solution of bentonite to form a granulate mixture.

[0420] 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 formed cylindrical combustible heat source is removed from the single cavity press.

[0421] Formed cylindrical combustible heat sources having the composition shown in Example (c) of Table 1 are not heated as shown in Example (c)(i) of Table 4.

[0422] Formed cylindrical combustible heat sources having the composition shown in Example (c) of Table 1 are heated in air in a ventilated drying oven at the temperature and for the period of time shown in Example (c)(ii) of Table 4:

TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Example (b) Example (c)(i) Example (c)(ii) Temperature Not applicable Not applicable 120 (degrees Celsius) (not heated) (not heated) Time (hours) 5

[0423] The combustible heat sources are removed from the oven and allowed to cool to room temperature.

[0424] To simulate environmental conditions to which combustible heat sources may be exposed during transport and storage, the combustible heat sources produced by the methods according to the invention of Examples (a)(i) to (a)(vii) and the comparative combustible heat sources produced by methods not according to the invention of Example (b), (c)(i) and (c)(ii) are conditioned at about 30 degrees Celsius and about 75 percent relative humidity. The calcium peroxide content of the combustible heat sources produced by the methods according to the invention and the comparative combustible heat sources produced by methods not according to the invention is measured as a function of time by titration with potassium permanganate (KMnO.sub.4) solution. The time taken for the measured calcium peroxide content of the combustible heat sources produced by the methods according to the invention and the comparative combustible heat sources produced by methods not according to the invention to reach a lower limit of 32.7 percent by weight is shown in FIGS. 2 and 3. The values shown in FIGS. 2 and 3 are the average of the measurements for three replicates of each combustible heat source.

[0425] The results in FIGS. 2 and 3 demonstrate an improvement in the chemical and physical stability of the combustible heat sources produced by the methods according to the invention due to inclusion of a binding agent comprising polyvinyl alcohol in the formed combustible heat source and heating of the formed combustible heat source to a temperature of at least 90 degrees Celsius for a period of at least 45 minutes.

[0426] The results in FIGS. 2 and 3 demonstrate that inclusion of a binding agent comprising polyvinyl alcohol in the formed combustible heat source and heating of the formed combustible heat source to a temperature of at least 90 degrees Celsius for a period of at least 45 minutes 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 FIGS. 2 and 3 demonstrate that inclusion of a binding agent comprising polyvinyl alcohol in the formed combustible heat source and heating of the formed combustible heat source to a temperature of at least 90 degrees Celsius for a period of at least 45 minutes advantageously significantly reduces degradation of the alkaline earth metal peroxide ignition aid as a result of exposure to high humidity.

[0427] 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.