WO2007135414A1

WO2007135414A1 - Tobacco smoke filter

Info

Publication number: WO2007135414A1
Application number: PCT/GB2007/001880
Authority: WO
Inventors: Paul Clarke; Barry Stevenson
Original assignee: Filtrona International Limited
Priority date: 2006-05-22
Filing date: 2007-05-21
Publication date: 2007-11-29
Also published as: TW200806205A; KR101538002B1; KR20090025251A

Abstract

A tobacco smoke filter (1) comprising an air-permeable axial extending core (2), a first wrapper (3) of air-permeable material around the peripheral surface of the core, and a second wrapper (4) around the first, the first wrapper defining at least with the second wrapper at least one channel extending longitudinally from the upstream end of the filter, and at least one channel extending longitudinally from the downstream end of the filter, each channel extending only part of the core length, wherein at least one portion of the filter includes no longitudinally extending channels.

Description

TOBACCO SMOKE FILTER

The present invention relates to tobacco smoke filters, especially for cigarettes.

Cigarette filters are known comprising a filtering core and two filter wrappers, an inner wrap and an outer wrap. The inner wrap is subjected to an embossing process whereby it is grooved along regular sections of its length. Each filter will include a length of grooved inner wrap ("flutes") and non-grooved inner wrap ("bars"). The filters are produced as a continuous rod including flutes and bars, the continuous rod being cut into finite lengths (either a single filter or several filters) for use in later production steps; the cuts are made in the middle of flutes and bars. Thus, one end of a filter will have a grooved end appearance caused by a flute, and the other end will have a non-grooved or blank appearance due to a bar. The grooved end appearance may be located at the mouth end of the filter if a novel end appearance is desired, or at the tobacco end if a conventional end appearance is desired.

A limitation with this kind of filter is that there is the potential for variation in pressure drop of the product filters, especially under large- scale production conditions, if slight drifting of the bar/flute configuration of the continuous rod with relation to the cutting apparatus occurs. This is discussed in more detail below.

The applicants have found that by locating the bar region within the filter, rather than at one end, the filter will always be cut at both ends in a fluted region. The bar length will not be affected by variation in cutting, and the performance (e.g. the pressure drop) of the final filter will be more consistent.

According to the present invention there is provided a tobacco smoke filter comprising an air-permeable axial extending core, a first wrapper of air-permeable material around the peripheral surface of the core, and a second wrapper around the first, the first wrapper defining at least with the second wrapper at least one channel extending longitudinally from the upstream end of the filter, and at least one channel extending longitudinally from the downstream end of the filter, each channel extending only part of the core length, wherein at least one portion of the filter includes no longitudinally extending channels.

Preferably, the length of each channel is 2mm or greater, preferably between 2.5mm and 23mm, more preferably between 3mm and 15mm, more preferably between 3.5mm and 9mm. The channel or channels extending from one end (upstream or downstream) may be a different length to those extending from the other end, or they may be the same length. The channels at both ends of the filter may be between 7 and 8mm long. The channels at both ends of the filters may be between 3 and 4mm long, for example 3.75mm long. Provision of channels of these dimensions means that the performance of the filter (tar retention etc) will be acceptable and should additionally ensure that the advantages of the present invention (e.g. consistent pressure drop, enhanced retention) are obtained.

The channels will preferably be of substantially uniform depth over their longitudinal extent, although there may be variation, for example where a channel approaches a closed end.

The first wrapper may, for example, be a sheet having a profiled (e.g. corrugated) surface, the sheet being wrapped with the profiled surface facing the second wrapper. The first wrapper preferably has longitudinally (e.g. axially) extending corrugations which define at least with the second wrapper the longitudinally extending channels. Each channel may be provided by the corrugation of the first wrapper being closed or blocked at the end remote from the end of the filter from which the channel extends. The first wrapper is corrugated on both surfaces, and may define longitudinally extending channels with the core as well as with the second wrapper. The enwrapped core surface may however conform to the corrugated inner surface of the first wrapper in the finished filter, leaving channels only between the first and second wrapper.

The completed filters of the invention may have a second wrapper which is air permeable (which may be of inherently permeable material and/or perforate) around the first (e.g. corrugated) wrapper. This permeable outer wrapper may be the tipping overwrap by which the filter is incorporated in a filter cigarette, such overwrap being applied only at the cigarette manufacturing stage. In this case the filter rod is initially produced with the first wrapper exposed, and the invention includes such rods as well as the completed filters with the outer wrapper attached. The filters can also be used in conjunction with a second wrapper which is air- impermeable, e.g. tipping overwrap.

The (or each) portion of the filter which includes longitudinal channels (e.g. which includes corrugations) is referred to herein as a flute or fluted portion. The (or each) part or portion of the filter which does not include longitudinal channels (over the filter cross section) is referred to herein as a bar or bar portion. In one example a filter according to the invention includes a 3mm flute portion at each end and a single central bar portion as the remaining full length of the filter. Such a configuration has a further advantage that the amount of filtering material in the core (e.g. cellulose acetate tow) may be reduced because the pressure drop (PD/mm) of bar is higher than that of flute. This configuration may also give a more desirable end appearance.

The invention also provides a method of making a tobacco smoke filter which comprises providing an air-permeable axially extending core, forming around the core a first wrapper of air-permeable material and enwrapping a second wrapper around the wrapped core, the first wrapper defining at least with the second wrapper at least one channel extending longitudinally from the upstream end of the filter, and at least one channel extending longitudinally from the downstream end of the filter, each channel extending only part of the core length, wherein at least one portion of the filter includes no longitudinally extending channels, wherein the filter is formed as a continuous rod of a plurality of filters, and wherein the step (or steps) of cutting the continuous rod to form individual filters is arranged so the cut ends form the upstream end of the filter and the downstream end of the filter.

The tobacco smoke filter may include up to 23 channels, preferably between 14 and 20 channels, extending longitudinally from each (upstream and downstream) end of the filter (for a filter of around 25mm circumference). The total cross-sectional area of these channels may amount to between 2 and 12%, preferably at least 4%, more preferably between 4 and 8%, of the overall cross-sectional area of the filter. Thus, careful control over the number and/or depth of the channels (e.g. by controlled embossing of the first wrapper) can give improved filtering performance. This may be achieved by increasing the depth of the corrugations, preferably with increase in surface area of the corrugations available to smoke, and optionally along with increase in the corrugation pitch - that is, widening of the corrugations with reduction in their number. For example, a filter according to the invention may have 15 channels at each end of the filter which are about 0.45mm deep and at a pitch of about 1.5mm; another filter may have 0.32mm deep channels, the number of channels (at each end) being 23, at a pitch of 1.05mm. The area of the corrugated wrap available for smoke filtration in these examples is generally a little less than the total corrugated surface area, since the crest of corrugations will generally be against the outer wrapper and hence not effective to filter.

A filter according to the invention may be applied to a cigarette by conventional means, e.g. by ring tipping, i.e. by a narrow strip of paper adhered around the abutting ends only of the tobacco rod and filter; in this case, the second wrapper is exposed. In other cases, the cigarette and filter may be joined by, for example, a tipping overwrap, which surrounds the second wrapper over the whole of its length.

As indicated by the following Examples, with the typical configuration according to the invention, the full length of bar portion (or bar portions) per filter is always wholly within the filter tip. Thus, although there is a potential for the bar/flute configuration or registration to drift slightly during manufacturing, there will always be the same length of bar portion and fluted portion within a tip; accordingly, the bar/flute ratio remains constant and a potential source of PD variation is eliminated.

Further, because there is a point where flute portion meets the bar portion in the filter (at the end of the or each channel), the high tar reduction performance of this type of filter will be maintained, as discussed below.

In a further example of the invention, the tobacco smoke filter further comprises at least one channel defined by the first wrapper and at least the second wrapper which extends longitudinally of the filter and which extends only part of the core length but which does not extend from either the upstream or downstream ends of the filter. In this example of the invention, the tobacco smoke includes one or more longitudinal channels at the upstream end of the filter (a first fluted portion); one or more longitudinal channels at the downstream end of the filter (a second fluted portion); and a further longitudinal channel or channels within the filter (a further fluted portion). In such an example, there is more than one portion or section of the filter having no longitudinal channels (more than one bar portion). The filter may have additional fluted and/or bar areas. In a further example of the invention, the second wrapper is made of coloured material, e.g. coloured paper.

Herein "coloured material" means material (e.g. paper) which is a different colour (i.e. is of different hue) to white or slightly off-white. The filters of the invention include an air permeable axially extending core of tobacco smoke filtering material. Filters are generally made of (or include) tobacco smoke filtering material which is white or slightly off-white, such as cellulose acetate tow. Coloured, herein, means having a pigment or hue or colour which is not white or slightly off-white, e.g. not the colour of cellulose acetate tow, e.g. of a colour which provides a noticeable (visible) difference or contrast between the coloured material of the second wrapper, and the air permeable axially extending core of tobacco smoke filtering material, e.g. of a colour such as black, red, yellow, pink, green, orange, brown, purple or blue and/or various tones thereof.

The applicants have surprisingly found that the inclusion of a second wrapper of coloured material e.g. coloured paper around the first, e.g. corrugated, wrapper of air-permeable material (which is of non coloured or white or off white material), provides a remarkably striking visual impression of flute definition [which is, unexpectedly, rather more striking than when a coloured first, e.g. corrugated, wrapper is used with a non-coloured (white or off-white) second wrapper]. This remarkably striking visual impression of flute definition [which may be further enhanced or changed by variation of the number of corrugations (longitudinal channels) and/or depth of corrugations (longitudinal channels) of the first wrapper] may be used as an anti-counterfeiting measure, because it is visible at the mouth or buccal end of the filter (whether or not it is applied to a cigarette).

The coloured second wrapper may be surrounded by a further wrapper of material, (which may be, e.g. a tipping overwrap), which may be white or off white or coloured, which may further enhance the visual impression/contrast.

It will be appreciated that filters according to this example may be applied to a cigarette by conventional means as set out above.

According to the present invention in a further aspect, there is provided a tobacco smoke filter comprising an air-permeable axial extending core (of tobacco smoke filtering material), a first wrapper of air- permeable material around the core, and an air-permeable second wrapper around the first wrapper, the first wrapper having longitudinally extending corrugations providing, at least between the first wrapper and the second wrapper, channels extending longitudinally of the filter from at least one end thereof, the second wrapper being of coloured material.

Preferably, the channels extend longitudinally from the buccal or mouth end of the filter, so that the channels (flutes) are visible from the buccal end of the filter when the filter is attached to the rod of tobacco material to form a cigarette.

The tobacco smoke filter may include up to twenty-three channels, preferably between fourteen and twenty channels, extending longitudinally from at least one end of the filter (for a filter of around 25 mm circumference). The total cross-sectional area of these channels may amount to between 2 and 12%, preferably at least 4%, more preferably between 4 and 8%, of the overall cross-sectional area of the filter. As discussed above, careful control over the number and/or depth of the channels (e.g. by controlled embossing of the first wrapper) can give improved filtering performance. Further, careful control of the number and/or depth of the channels in combination with the coloured second wrapper may provide a remarkably striking visual impression of the channel (flute) definition, which may be used as an anti-counterfeiting measure. The present invention will now be illustrated by way of example with reference to the accompanying drawings, in which:

FIGURE 1 shows a perspective view, not to scale, with parts broken away, of a filter according to one example of the invention;

FIGURE 2 is a schematic sectional side elevation view, not to scale, of a multiple length rod of the prior art showing how it may be cut to form multiple and eventually individual filter lengths;

FIGURE 3 is a similar view of a multiple length rod according to the invention showing how it may cut to form multiple and individual filter lengths according to the invention, and illustrating the potential advantages of the invention with regards to elimination of a potential source of PD variation; and

FIGURE 4 shows a perspective view, not to scale, with parts broken away, of a filter according to a further example of the invention.

In the filter illustrated in Figure 1 a filter 1 comprises a core 2 of crimped filaments of cellulose acetate. These are bonded to each other at their points of contact by a solvent plasticiser such as triacetin. Immediately surrounding the core 2 is a wrapper 3 of air-permeable filtering paper (or corrugated cellulose acetate) which is corrugated longitudinally over all of its length apart from a circumferential portion 6 in the central portion or section of the filter 7. The core surface conforms to the corrugations in wrapper 3. Immediately surrounding the wrapper 3 and forming channels 5a, 5b with the corrugations is an uncorrugated wrapper of air-permeable paper 4. The core and the wrappers 3 and 4 extend over the entire length of the filter 1. The inclusion of an uncorrugated circumferential portion 6 of wrapper 3 in the central portion of the filter means that there are no channels in this portion and that the channels 5a, 5b do not run the full length of the filter. Thus, filter 1 has a set of channels 5a of length 7.5mm, formed at the first, or downstream, end 9 of the filter (formed between the corrugated portion of wrapper 3 and the uncorrugated wrapper of air-permeable paper 4), and a second set of channels 5b of length 7.5mm at the second or upstream end 11 of the filter (formed between the corrugations in the wrapper 3 and the uncorrugated wrapper of air-permeable paper 4) at the second end; these corrugations form fluted portions or flutes at each end 9, 11 of the filter 1. In the centre of the filter the uncorrugated area of wrapper 3 in the circumferential portion 6 forms an uncorrugated or non-fluted bar portion (bar) of length 6mm in the centre of the filter. This bar portion blocks the end of each channel opposite the end of the filter from which it extends. This bar portion of the filter includes no longitudinally extending channels over the cross section of the filter 1 along the full length of the bar portion.

In use, with the filter attached at end 11 to a cigarette, some of the smoke enters directly into the core 2 and passes to the end of the filter 1 , being filtered by contact with the filaments which form the core. In this example, because there is air permeable wrapper 4, diluting air will also be drawn into the filter. Smoke, along with diluting air drawn in through permeable wrapper 4, also enters the channels 5b up to the uncorrugated portion 6 and the diluted smoke then enters the core 2 after passing through the corrugated wrapper 3 and passes out of the filter at the other end; this smoke is thus filtered both by wrapper 3 and by core 2. It will be understood that filters according to the invention may also be used with non-ventilating wrappers, in which case there will be no diluting air drawn into the filter through the wrapper.

Filter 1 may be attached to a cigarette by ring-tipping or by a full tipping overwrap, for example, such methods are well known in the art. It will be appreciated that other materials that are well known in the art may be used to form core 2, and wrappers 3, 4. Figure 2 shows a multiple length rod 51 of filters of the prior art. The rod 51 is made up of a filtering core and two filter wrappers, an inner wrap and an outer wrap (not shown). The multiple length filter rod is made by a process which is well known in the art. Thus a known device supplies a tow of crimped plasticised filaments of cellulose acetate to a garniture. In this they are enwrapped by a strip of corrugated cellulose acetate or paper. The strip is formed by feeding a tow of crimped plasticised filaments (or paper) to a steam block and thence to heated grooved rollers having short longitudinally spaced non-embossing regions. Thus the inner wrap is a first layer of air permeable material, and is subjected to an embossing process whereby it is grooved along regular sections of its length. An adjustable guide positions the strip of inner wrap before it enters the garniture so that in the latter it is wrapped longitudinally to enclose the tow, the opposite edges of the inner wrap strip being abutted. From a bobbin, a strip of paper (the second wrapper) enters an adhesive printing device which applies to it transverse lines of adhesive in positions upon the strip such that when the strip of corrugated cellulose acetate (or paper) of the inner wrap and the strip of paper of the second wrapper meet in garniture, the lines of adhesive material contacts unembossed regions of the strip of corrugated cellulose acetate (paper) of the inner wrap. The adhesive device also applies the adhesive such that when the strip of paper of the second wrapper enters the garniture and wraps the filaments and strip of inner wrap, the overlapping edges of the strip of paper of the second wrapper are sealed by a heater in a known manner. A guide positions the strip of paper in the correct way. Thus, a continuous rod made up of a filtering core and two filter wrappers, an inner wrap and an outer wrap, is formed which passes to a cut-off which divides into multiple length rods 51 , such as that shown in Fig 2, each of which is a multiple of the length of the finished filter to be attached to a smoking article. The multiple length rod 51 so-produced includes lengths of grooved inner wrap ("flutes") 52 and lengths of non-grooved inner wrap ("bars") 53, 54. During the manufacturing process (using techniques which are well known in the art) the multiple length rod 51 is cut in the areas shown by arrows 55 through flutes 52 and bars 54 to give four filters each configured with a single flute at one end and a bar at the other. One end of each filter will have a grooved end appearance caused by the flutes, and the other end will have a non-grooved or blank appearance due to the bars. The grooved end appearance may be located at the mouth end of the filter if a novel end appearance is desired, or at the tobacco end if a conventional end appearance is desired.

In a production run of 21mm filter tips with a specified flute length of 15mm and a specified bar length of 6mm, the filters would be produced as a continuous rod with 30mm flutes 52 and 12mm bars 54. The continuous rod is cut into finite lengths and the nature of the large-scale production process is that there is the potential for slight drifting of the bar/flute configuration with relation to the cutting apparatus. If this occurs, there is the possibility that the cut might not be as desired, directly in the middle of the flute or bar. Thus, if drifting of plus or minus 1mm were to occur, the desired 15mm flute plus 6mm bar specified configuration could potentially vary between 16mm flute plus 5mm bar and 14mm flute and 7mm bar. The pressure drop in millimeters of water (PD-mm) of a bar portion is considerably higher than the PD-mm of a fluted portion, so variation from the desired length of bar and flute in a filter has the potential to lead to PD variability; a tip PD variation of between 77 to 90mm has been seen in testing. The bottom part of Fig 2 shows that if multiple rod 51 drifts to the position shown by rod 51a (and cut in the position shown by arrows 55 which are set to cut a rod in the true position corresponding to rod 51), the amount of flute and bar in each cut portion may vary from that desired.

Figure 3 shows a multiple length rod 61 of filters according to the invention (for example filters according to Figure 1). The rod 61 is again made up of a filtering core and two filter wrappers, an inner wrap and an outer wrap. The inner wrap is subjected to an embossing process whereby it is grooved along regular sections of its length. These processes are well known in the art and they are as described with reference to Fig 2 above. The multiple length rod 61 includes lengths of grooved inner wrap ("flutes") 63, 63a and 63b and lengths of non-grooved inner wrap ("bars") 62. The length of each bar portion 62 is 6mm and the length of each flute portion 63 is 15mm. During the manufacturing process (using techniques which are well known in the art) the multiple length rod 61 is, in accordance with an example of the invention, cut in the areas shown by arrows 65 through flutes 63 to give four filters each configured with a flute at each end and a bar 62 between the flutes.

In a production run of 21mm filter tips with specified flute lengths of 7.5mm at either end and a specified bar length of 6mm, such as those described with reference to, and shown in, Figure 1 , the filters would be produced as a continuous rod with 15mm flutes and 6mm bars. The continuous rod is cut into finite lengths. If slight drifting of the bar/flute configuration with relation to the cutting apparatus occurs, even if the cut might not be as desired, directly in the middle of the flute, there will always be the same length of flute and bar within a tip. Thus, Fig 3a shows a schematic diagram of the filter as desired, which has two flutes of length 7.5mm (5a, 5b) separated by a bar 6 of length 6mm. If drifting were to occur, the configuration could be, for example, such as that shown in Fig 3b. This includes a 6mm flute 5e and a 9mm flute 5f separated by a 6mm bar 6g; the overall bar flute ratio of the filter remains constant and a potential source of PD variation is eliminated.

In the filter illustrated in Figure 4 a filter 101 comprises a core 102 of crimped filaments of cellulose acetate. These are bonded to each other at their points of contact by a solvent plasticiser such as triacetin. Immediately surrounding the core 102 is a wrapper 103 of air-permeable filtering paper which is corrugated longitudinally over all of its length apart from two circumferential portions 106, 106a. The core surface conforms to the corrugations in wrapper 103. Immediately surrounding the wrapper 103 and forming channels 105a, 105b, 105c with the corrugations is an uncorrugated wrapper of air-permeable paper 104. The core and the wrappers 103 and 104 extend over the entire length of the filter 1. The inclusion of uncorrugated circumferential portions 106, 106a of wrapper 103 in the filter means that there are no channels in these portions and that the channels do not run the full length of the filter. Thus, filter 1 has a set of channels 105a of length 3.75mm, formed at the first, or downstream, end 109 of the filter (formed between the corrugated portion of wrapper 103 and the uncorrugated wrapper of air-permeable paper 104), and a second set of channels 105b of length 3,75mm at the second or upstream end 111 of the filter (formed between the corrugations in the wrapper 103 and the uncorrugated wrapper of air-permeable paper 104) at the second end; these corrugations form fluted portions at each end 109, 111 of the filter 101. In the centre of the filter there is a third set of channels 105c of length 7.5mm (formed between the corrugations in the wrapper 103 and the uncorrugated wrapper of air-permeable paper 104). The uncorrugated area of wrapper 103 in the circumferential portions 106, 106a forms two uncorrugated or non-fluted bar portions of length 3mm (separated by the third set of channels 105c) between the ends of the filter. The bar portions blocks the end of each channel which abuts thereto. The bar portions of the filter include no longitudinally extending channels over the cross section of the filter 101 along the full length of the bar portions.

Filter 101 may be attached to a cigarette by ring-tipping or by a full tipping overwrap, for example, such methods are well known in the art.

The example of Fig 4 may be used, for example, wherein the filter is ventilated and it is desired to put a further fluted area (105c) beneath the ventilation zone.

It will be appreciated that the filter 101 of Fig 4 is symmetrical (as is that of Fig 1). As the skilled man would appreciate, asymmetrical arrangements are possible and within the scope of the invention. For example, a filter similar to that of Fig 1 of length 21mm with 5mm flute and 11mm flute separated by a bar of 5mm is another example of the invention.

In a further example of the invention (not shown) a filter similar to that shown in Fig.1 , above, has an uncorrugated wrapper of blue air- permeable paper 504 in place of wrapper of air-permeable paper 4. This provides a surprisingly striking visual impression of the corrugation (flute) definition at the buccal end of the filter. In a further example of the invention (not shown) a filter similar to that shown in Fig.4, above, has an uncorrugated wrapper of red air-permeable paper 504 in place of wrapper of air-permeable paper 104. This provides a surprisingly striking visual impression of the corrugation (flute) definition at the buccal end of the filter.

Further example

Three different cigarette filter designs were manufactured. Two of these [Comparative Examples A and B] were according to the prior art (e.g. made by the method described with reference to Fig 2), in which filters were cut nominally in the middle of the flute and bar regions. The third filter type [Example C] was according to the present invention (e.g. made by the method described with reference to Fig 3). The filter tips of Comparative Examples A and B had the configuration 4mm bar plus 5mm flute, whilst the filter tips of Example C were of the same overall dimensions, but configured as 2.5mm flute + 4mm bar + 2.5mm flute.

After manufacture, a single cut was made along the length of the wrapper of each filter tip, and the inner wraps carefully removed from the tips. The length of the bar region in each filter tip was measured. Twenty tips of each design were measured in this way and the results obtained are summarised below:

^* standard deviation

It can be seen that the present invention eliminated variability in the measured bar length.

Claims

C L A I M S

1. A tobacco smoke filter comprising an air-permeable axial extending core, a first wrapper of air-permeable material around the peripheral surface of the core, and a second wrapper around the first, the first wrapper defining at least with the second wrapper at least one channel extending longitudinally from the upstream end of the filter, and at least one channel extending longitudinally from the downstream end of the filter, each channel extending only part of the core length, wherein at least one portion of the filter includes no longitudinally extending channels.

2. A filter according to claim 1 wherein the length of each channel is 2mm or greater.

3. A filter according to claim 1 wherein the length of each channel is between 2.5mm and 23mm.

4. A filter according to claim 1 , 2 or 3 wherein the first wrapper has longitudinally extending corrugations which define at least with the second wrapper the longitudinally extending channels, each channel provided by the corrugation of the first wrapper being closed or blocked at the end remote from the end of the filter from which the channel extends.

5. A filter according to any preceding claim further comprising at least one further channel defined by the first wrapper and at least the second wrapper which extends longitudinally of the filter and which extends only part of the core length but which does not extend from either the upstream or downstream ends of the filter.

6. A filter according to any preceding claim including up to 23 channels extending longitudinally from each end of the filter, the total cross-sectional area of these channels amounting to between 2 and 12% of the overall cross-sectional area of the filter.

7. A filter according to claims 6 including longitudinal channel(s) at each end of the filter which contribute at least 4% of the overall filter cross- sectional area.

8. A filter according to any preceding claim wherein the second wrapper is air permeable.

9. A filter according to any of claims 1 to 7 wherein the second wrapper is air-impermeable.

10. A filter according to any preceding claim wherein the second wrapper is of coloured material.

11. A filter substantially as hereinbefore described with reference to Fig. 1 or 4, or a method of making a filter substantially as hereinbefore described with reference to Fig. 3.

12. A filter according to any preceding claim without the second wrapper.

13. A filter cigarette comprising a filter according to any preceding claim joined at one end to a wrapped tobacco rod.

14. A method of making a tobacco smoke filter which comprises providing an air-permeable axially extending core, forming around the core a first wrapper of air-permeable material and enwrapping a second wrapper around the wrapped core, the first wrapper defining at least with the second wrapper at least one channel extending longitudinally from the upstream end of the filter, and at least one channel extending longitudinally from the downstream end of the filter, each channel extending only part of the core length, wherein at least one portion of the filter includes no longitudinally extending channels, wherein the filter is formed as a continuous rod of a plurality of filters, and wherein the step (or steps) of cutting the continuous rod to form individual filters is arranged so the cut ends form the upstream end of the filter and the downstream end of the filter.

15. A tobacco smoke filter comprising an air-permeable axial extending core, a first wrapper of air-permeable materia! around the core, and an air- permeable second wrapper around the first wrapper, the first wrapper having longitudinally extending corrugations and thereby providing at least between the first wrapper and the second wrapper channels extending longitudinally of the filter from at least one end thereof, the second wrapper being made of coloured material.

16. A filter cigarette comprising a filter according to claim 15 joined at one end to a wrapped tobacco rod.