Abstract
There is provided a filter for a smoking article, the filter including a filter segment of filter material and a flow restrictor. The flow restrictor is embedded in the filter segment and surrounded on all sides by the filter material. A cross sectional dimension of the flow restrictor measured perpendicular to a longitudinal direction of the filter is between about 60% and about 95% of the diameter of the filter segment. There is also provided a smoking article including such a filter.
Claims
1. A filter for a smoking article, the filter comprising: a filter segment of filter material, the filter segment having a diameter measured perpendicular to a longitudinal direction of the filter; and a flow restrictor embedded in the filter segment and surrounded on all sides by the filter material, wherein the flow restrictor is solid, a cross sectional dimension of the flow restrictor measured perpendicular to a longitudinal direction of the filter is between about 60% and about 95% of the diameter of the filter segment, and wherein the flow restrictor is substantially spherical, the cross sectional dimension of the flow restrictor measured perpendicular to the longitudinal direction of the filter being a diameter of the flow restrictor, and wherein the flow restrictor has a compressive strength at a deformation of 10% greater than about 50.0 kPa.
2. The filter according to claim 1, wherein the cross sectional dimension of the flow restrictor is between about 70% and about 80% of the diameter of the filter segment.
3. The filter according to claim 1, wherein the flow restrictor has a compressive yield strength greater than about 8.0 kPa.
4. The filter according to claim 1, wherein the filter forms a mouth end cavity.
5. The filter according to claim 1, further comprising a hollow tube axially aligned with the filter segment.
6. The filter according to claim 1, further comprising a filter wrapper circumscribing at least the filter material.
7. The filter according to claim 1, wherein the centre of the flow restrictor is at least about 6 mm from the downstream end of the filter.
8. A smoking article, comprising: a tobacco rod; and a filter according to claim 1.
9. The smoking article according to claim 8, further comprising tipping material attaching the tobacco rod and the filter, the tipping material including a ventilation zone comprising perforations through the tipping material.
10. The smoking article according to claim 9, 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.
11. A method for manufacturing a filter according to claim 1, the method comprising the steps of: providing a continuous rod of filter material having flow restrictors embedded in the filter material and spaced apart in the longitudinal direction of the rod, wherein each flow restrictor is solid and substantially spherical, and a diameter of each flow restrictor measured perpendicular to the longitudinal direction of the rod is between about 60% and about 95% of the diameter of the rod; and cutting the continuous rod of filter material at longitudinally spaced cut lines, to produce filter segments of filter material, each filter segment including a flow restrictor embedded in the filter segment and surrounded on all sides by the filter material.
12. The method according to claim 11, further comprising the steps of: axially aligning a hollow tube with each filter segment; and overwrapping the filter segment and hollow tube with a filter wrapper.
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;
(4) FIG. 3 is a cross sectional view of a filter according to a second embodiment of the invention; and
(5) FIG. 4 is a cross sectional view of a continuous filter rod for manufacturing filters according to an embodiment of the invention.
(6) 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 embedded in the filter 103.
(7) 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.
(8) 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.
(9) 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 filter segment 201 of filter material 203. 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 embedded in the filter segment 201 and is surrounded on all sides by the filter material 203. 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. In FIG. 2, the diameter of the filter 103 is 7.7 mm, the diameter of the flow restricting bead 205 is 6.0 mm (about 78% of the diameter of the filter), 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 filter segment 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 filter segment 301 of filter material 303. The filter 103 further comprises a flow restrictor, in the form of bead 305, embedded in the filter segment 301 and surrounded on all sides by the filter material 303. In the embodiment of FIG. 3, the flow restricting bead 305 comprises air-impermeable material. The filter 103 further comprises a filter plug 307 and a hollow tube 309. The filter segment 301, filter plug 307 and hollow tube 309 are axially aligned in an end-to-end relationship. In FIG. 3, the filter plug 307 is upstream of the filter segment 301 and the hollow tube 309 is downstream of the filter segment 301. The filter plug 307 may comprise any suitable filter material. The hollow tube 309 may comprise any suitable material, for example paper or filter material. Because the filter 103 is open at the mouth end, thereby forming a mouth end cavity, visible staining of the mouth end is reduced. 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. In FIG. 3, the diameter of the filter 103 is 7.7 mm, the diameter of the flow restricting bead 305 is 6.0 mm (about 78% of the diameter of the filter), the length of the whole filter 103 is 27 mm, the length of the filter plug 307 is 9 mm, the length of the filter segment 301 is 8 mm, the length of the hollow tube 309 is 10 mm, and the centre of the flow restricting bead 305 is 14 mm from the downstream end of the filter 103 and 4 mm from the downstream end of the filter segment 301. When the filter is circumscribed by tipping material, the diameter of the filter may be 7.73 mm.
(11) In FIG. 3, the filter includes additional filter elements both upstream and downstream of the filter segment 301. However, it will be appreciated that an additional element may be included only downstream of the filter segment 301 or only upstream of the filter segment 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 filter segment 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 and a disc of filter material, may alternatively be provided downstream of the filter segment 301.
(12) When either the filter 103 of 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 1 mm downstream of the flow restricting bead 205, 305. The combination of the ventilation provided by perforations 117, the flow restricting bead 205, 305 and the filter material 203, 303 provides the desired RTD.
(13) It will be appreciated by the skilled person that the filter 103 of FIG. 2 may be manufactured from a continuous rod of filter material, in accordance with conventional manufacturing techniques. For example, as shown in FIG. 4, a continuous filter rod 401 of filter material 203 can be manufactured, with flow restricting beads 205 longitudinally spaced along the continuous filter rod 401. The flow restricting beads 205 are embedded in the continuous filter rod 401 and surrounded on all sides by the filter material 203. The flow restricting beads 205 are preferably incorporated as the raw filter material (for example, cellulose acetate) is spun as continuous synthetic fibres into a bundle (for example, cellulose acetate tow) in the form of the continuous filter rod. The continuous rod 401 may then be cut into individual filters 103 by cutting along cut lines 403. The longitudinal spacing of the flow restricting beads 205 and the cut lines 403 may be set according to the desired length of the filter and the desired position of the flow restricting beads within the filter.
(14) Similarly, the filter segment 301 of the filter 103 of FIG. 3 may be manufactured from a continuous rod of filter material, in a similar way to that shown in FIG. 4. The longitudinal spacing of the flow restricting beads and the cut lines may be set according to the desired length of the filter segment and the desired position of the flow restricting beads within the filter segment.
