Abstract
There is provided a filter for a smoking article, the filter including a hollow tube of filter material having an outer diameter and an inner diameter. The filter further includes a flow restrictor disposed in the hollow tube. At least one cross sectional dimension of the flow restrictor is larger than the inner diameter of the hollow tube, such that the flow restrictor engages with the hollow tube to retain the flow restrictor in the hollow tube. There is also provided a smoking article including such a filter.
Claims
1. A filter for a smoking article, the filter comprising: a hollow tube of filter material, the hollow tube having an outer diameter and an inner diameter; and a flow restrictor disposed in the hollow tube, wherein at least one cross sectional dimension of the flow restrictor, in a direction perpendicular to the longitudinal axis of the hollow tube, is larger than the inner diameter of the hollow tube such that the flow restrictor engages with the hollow tube to retain the flow restrictor in the hollow tube, wherein the at least one cross sectional dimension of the flow restrictor is between about 70% and about 80% of the outer diameter of the hollow tube, wherein the flow restrictor is configured to divert flow of smoke between the flow restrictor and the outer diameter of the hollow tube, wherein the filter forms a mouth end cavity, and wherein the flow restrictor is substantially spherical and includes at least one air flow channel, the at least one cross sectional dimension of the flow restrictor being a diameter of the spherical flow restrictor.
2. The filter according to claim 1, wherein the inner diameter of the hollow tube is between about 75% and about 99% of the at least one cross sectional dimension of the flow restrictor.
3. The filter according to claim 2, wherein the inner diameter of the hollow tube is between about 80% and about 95% of the at least one cross sectional dimension of the flow restrictor.
4. The filter according to claim 1, wherein the flow restrictor has a compressive yield strength greater than about 8.0 kPa.
5. The filter according to claim 1, wherein the flow restrictor has a compressive strength at a deformation of 10% greater than about 50.0 kPa.
6. The filter according to claim 1, further comprising a filter wrapper circumscribing at least the hollow tube of filter material.
7. The filter according to claim 1, wherein the centre of the flow restrictor is at least about 6 mm from the mouth end of the filter.
8. The filter according to claim 1, further comprising a filter plug disposed upstream of the hollow tube of filter material, and an additional hollow tube disposed downstream of the hollow tube of filter material.
9. A smoking article, comprising: a tobacco rod; and a filter, comprising a hollow tube of filter material, the hollow tube having an outer diameter and an inner diameter; and a flow restrictor disposed in the hollow tube, wherein at least one cross sectional dimension of the flow restrictor, in a direction perpendicular to the longitudinal axis of the hollow tube, is larger than the inner diameter of the hollow tube such that the flow restrictor engages with the hollow tube to retain the flow restrictor in the hollow tube, wherein the at least one cross sectional dimension of the flow restrictor is between about 70% and about 80% of the outer diameter of the hollow tube, wherein the flow restrictor is configured to divert flow of smoke between the flow restrictor and the outer diameter of the hollow tube, wherein the filter forms a mouth end cavity, and wherein the flow restrictor is substantially spherical and includes at least one air flow channel, the at least one cross sectional dimension of the flow restrictor being a diameter of the spherical flow restrictor.
10. The smoking article according to claim 9, further comprising tipping material attaching the tobacco rod and the filter, the tipping material including a ventilation zone comprising perforations through the tipping material.
11. The smoking article according to claim 10, wherein the tipping material includes at least one circumferential row of perforations at least about 1 mm downstream of the centre of the flow restrictor.
12. The smoking article according to claim 9, further comprising a filter plug disposed upstream of the hollow tube of filter material, and an additional hollow tube disposed downstream of the hollow tube of filter material.
13. A flow restrictor to restrict air flow in a filter for a smoking article, wherein the flow restrictor is disposed in a hollow tube of filter material having an outer diameter and an inner diameter, wherein at least one cross sectional dimension of the flow restrictor, in a direction perpendicular to the longitudinal axis of the hollow tube, is larger than the inner diameter of the hollow tube such that the flow restrictor engages with the hollow tube to retain the flow restrictor in the hollow tube, wherein the at least one cross sectional dimension of the flow restrictor is between about 70% and about 80% of the outer diameter of the hollow tube, wherein the flow restrictor is configured to divert flow of smoke between the flow restrictor and the outer diameter of the hollow tube, wherein the filter forms a mouth end cavity, and wherein the flow restrictor is substantially spherical and includes at least one air flow channel, the at least one cross sectional dimension of the flow restrictor being a diameter of the spherical flow restrictor.
14. The flow restrictor according to claim 13, wherein the flow restrictor is disposed in the hollow tube of filter material between a filter plug disposed upstream of the hollow tube of filter material, and an additional hollow tube disposed downstream of the hollow tube of filter material.
Description
(1) The invention will be further described, by way of example only, with reference to the accompanying drawings in which:
(2) FIG. 1 is a perspective view of a smoking article according to one embodiment of the invention;
(3) FIG. 2 is a cross sectional view of a filter according to a first embodiment of the invention; and
(4) FIG. 3 is a cross sectional view of a filter according to a second embodiment of the invention.
(5) FIG. 1 is a perspective view of a smoking article 100 according to one embodiment of the invention. The smoking article 100 includes a generally cylindrical tobacco rod 101 and a generally cylindrical filter 103. The tobacco rod 101 and filter 103 are axially aligned in an end-to-end relationship, preferably abutting one another. The tobacco rod includes an outer wrapper 105 circumscribing the smoking material. The outer wrapper 105 may be a porous wrapping material or paper wrapper. The tobacco is preferably a shredded tobacco or tobacco cut filler. The tobacco rod 101 has an upstream, lit end 107 and a downstream end 109. The filter 103 has an upstream end 111 and a downstream, mouth end 113. The upstream end 111 of the filter 103 is adjacent the downstream end 109 of the tobacco rod 101. Although not visible in FIG. 1, a flow restrictor is disposed in the filter 103.
(6) The filter 103 is attached to the tobacco rod 101 by tipping material 115 which circumscribes the entire length of the filter 103 and an adjacent region of the tobacco rod 101. The tipping material 115 is shown partially removed from the smoking article in FIG. 1, for clarity. The tipping material 115 is typically a paper like product. However, any suitable material can be used. In this embodiment, the tipping material 115 includes a circumferential row of perforations 117 aligned with the filter 103. The perforations are provided for ventilation of the mainstream smoke.
(7) In this specification, the upstream and downstream relative positions between smoking article components are described in relation to the direction of mainstream smoke as it is drawn from the tobacco rod 101 and through the filter 103.
(8) FIG. 2 is a cross sectional view of a filter 103 according to a first embodiment of the invention. The filter 103 may be used in the smoking article of FIG. 1. In FIG. 2, the filter 103 comprises a hollow tube 201 of filter material 203. The hollow tube 201 has an outer diameter 207 and an inner diameter 209. The filter 103 further comprises a flow restrictor, in the form of bead 205. In the embodiment of FIG. 2, the flow restricting bead 205 comprises air-impermeable material. The flow restricting bead 205 is substantially spherical, with a diameter 211. The flow restricting bead 205 is disposed in the hollow tube 201. Diameter 211 of the flow restricting bead 205 is slightly larger than inner diameter 209 of the hollow tube 201, so the flow restricting bead 205 causes the filter material adjacent the bead 205 to distort slightly and the flow restricting bead 205 is retained in the hollow tube 201 by friction. As shown schematically by the arrows, air drawn through the filter 103 during use of the smoking article is forced to flow around the flow restricting bead 205 and through a reduced cross section of filter material 203 of the hollow tube 201. Because the filter 103 is open at the mouth end, thereby forming a mouth end cavity, visible staining of the mouth end is reduced. The filter may be manufactured by inserting the flow restricting bead 205 into the hollow tube 201.
(9) In FIG. 2, the outer diameter 207 of the hollow tube 201 is 7.7 mm, the inner diameter 209 of the hollow tube 201 is 5.3 mm, the diameter of the flow restricting bead 205 is 6.0 mm, the length of the filter 103 is 21 mm and the centre of the flow restricting bead 205 is 11 mm from the downstream end of the filter 103. When the filter is circumscribed by tipping material, the diameter of the filter may be 7.73 mm.
(10) FIG. 3 is a cross sectional view of a filter 103 according to a second embodiment of the invention. The filter 103 may be used in the smoking article of FIG. 1. In the embodiment of FIG. 2, the hollow tube 201 comprises the entire filter 103. However, in the embodiment of FIG. 3, the filter 103 includes additional elements. Specifically, in FIG. 3, the filter 103 comprises a hollow tube 301 of filter material 303. The hollow tube 301 has an outer diameter 307 and an inner diameter 309. The filter 103 further comprises a flow restrictor in the form of bead 305. In the embodiment of FIG. 3, the flow restricting bead 305 comprises air-impermeable material. The flow restricting bead 305 is substantially spherical, with a diameter 311. The flow restricting bead 305 is disposed in the hollow tube 301. Diameter 311 of the flow restricting bead 305 is slightly larger than inner diameter 309 of the hollow tube 301, so the flow restricting bead 305 causes the filter material adjacent the bead 305 to distort slightly and the flow restricting bead 305 is retained in the hollow tube 301 by friction.
(11) The filter 103 further comprises a filter plug 313 and an additional hollow tube 315. The hollow tube 301, filter plug 313 and additional hollow tube 315 are axially aligned in an end-to-end relationship. In FIG. 3, the filter plug 313 is upstream of the hollow tube 301 and the additional hollow tube 315 is downstream of the hollow tube 301. The filter plug 313 may comprise any suitable filter material. The additional hollow tube 315 may comprise any suitable material, for example paper or filter material. As shown schematically by the arrows, air drawn through the filter 103 during use of the smoking article is forced to flow around the flow restricting bead 305 and through a reduced cross section of filter material 303 of the hollow tube 301. Because the filter 103 is open at the mouth end, thereby forming a mouth end cavity, visible staining of the mouth end is reduced. The filter may be manufactured by inserting the flow restricting bead 305 into the hollow tube 301, then assembling the hollow tube 301 adjacent the filter plug 313 and additional hollow tube 315.
(12) In FIG. 3, the outer diameter 207 of the hollow tube 301 is 7.7 mm, the inner diameter 209 of the hollow tube 301 is 5.3 mm, the diameter of the flow restricting bead 305 is 6.0 mm, the length of the whole filter 103 is 27 mm, the length of the filter plug 313 is 9 mm, the length of the hollow tube 301 is 8 mm, the length of the additional hollow tube 315 is 10 mm, and the centre of the flow restricting bead 305 is 14 mm from the tubular mouth end of the filter 103 and 4 mm from the downstream end of the hollow tube 301. When the filter is circumscribed by tipping material, the diameter of the filter may be 7.73 mm.
(13) In FIG. 3, the filter includes additional filter elements both upstream and downstream of the hollow tube 301. However, it will be appreciated that an additional element may be included only downstream of the hollow tube 301 or only upstream of the hollow tube 301. Alternatively, no additional filter elements may be provided, as shown in FIG. 2. In addition, in FIG. 3, the upstream additional filter element comprises a plug of filter material. However, any suitable filter element, including but not limited to a disc of filter material and a hollow tube, may alternatively be provided upstream of the hollow tube 301. Similarly, in FIG. 3, the downstream additional filter element comprises a hollow tube. However, any suitable filter element, including but not limited to a plug of filter material or a disc of filter material, may alternatively be provided downstream of the hollow tube 301.
(14) When either the filter 103 of the FIG. 2 or the filter 103 of FIG. 3 is incorporated into a smoking article like that shown in FIG. 1, preferably the perforations 117 are at least about 1 mm downstream of the flow restricting bead 205, 305. The combination of the ventilation provided by the perforations 117, the flow restricting bead 205, 305 and the filter material 203, 303 of the hollow tube provides the desired RTD.
