EP2073651A1

EP2073651A1 - Tobacco smoke filter

Info

Publication number: EP2073651A1
Application number: EP07824051A
Authority: EP
Inventors: Paul Francis Clarke
Original assignee: Filtrona International Ltd
Current assignee: Filtrona International Ltd
Priority date: 2006-10-09
Filing date: 2007-10-08
Publication date: 2009-07-01
Also published as: GB0619958D0; KR20090078804A; JP2010505439A; WO2008043988A1

Abstract

A tobacco smoke filter or filter element comprising a longitudinally extending core which includes activated carbon, and a wrapper arranged around the core, the wrapper comprising carbon paper.

Description

Tobacco Smoke Filter

The present invention relates to tobacco smoke filters, especially for cigarettes. In particular, it relates to tobacco smoke filters which include activated carbon, and which are designed to have higher loadings of activated carbon.

According to the present invention there is provided a tobacco smoke filter or filter element comprising a longitudinally extending core which includes activated carbon, and a wrapper arranged around the core, the wrapper comprising carbon paper.

The longitudinally extending core is of air permeable material. The longitudinally extending core which includes activated carbon may include activated carbon in the form of particles e.g. granules. Preferably the longitudinally extending core which includes activated carbon is in the form of, or includes, a cellulose acetate plug - e.g. cellulose acetate tow - which is combined with particles of carbon e.g. particles, preferably granules, of activated carbon; e.g. carried on the cellulose acetate tow or filaments or fibres or sheet material which is gathered to form the plug. Cellulose acetate tow impregnated with activated carbon in this way is known in the art, and is often referred to as "active acetate".

Herein, the term "carbon paper" is intended to mean sorbent particles of activated carbon included in a web of fibres which forms the paper, for example cellulose fibres; this is known in the art (and will also be referred to herein) as carbon-impregnated paper. Such carbon paper is commercially available as e.g. that available under the mark CP60 from Tela-Kimberly of Balsthal, CH. The term "carbon paper" herein is not intended to mean activated carbon (or similar sorbent additive) adhered to (or otherwise held or disposed on) a surface of a wrapper of e.g. paper. However, as seen below, in embodiments of the invention, further activated carbon or other particulate adsorbent additive (e.g. in the form of granules or particles) may be adhered to the surface of the carbon paper.

The carbon paper wrapper may be conveniently applied around the longitudinally extending core as the core is being formed, using conventional garniture apparatus. Preferably the carbon paper has a metric basis weight (by metric basis weight it is meant the weight, in grams, of one sheet of 1 square metre (m²) paper) of between 30gsm and 160gsm, preferably between 50gsm and 85gsm, more preferably between 60gsm and 80gsm. Preferably the carbon paper has carbon content (by weight) between 10% and 70%, more preferably between 40% and 60%, most preferably between 45% and 55%. The carbon paper wrapper may be air permeable or air-impermeable.

Thus, it is preferred that filters and filter elements of the invention include activated carbon in the form of a carbon paper wrapper and in the form of activated carbon, in e.g. granular or particulate form, which is within the longitudinally extending core, or part thereof (e.g. activated carbon in particulate or granular form in the longitudinally extending core which is not in the form of carbon paper). Preferably, the carbon paper wrapper has particulate sorbent additive - e.g. activated carbon, other granular or particulate materials such as zeolite, or an ion exchange resin - adhered to one or more portions of the radially inner face thereof. The carbon paper wrapper may, also or alternatively, have additive adhered to one or more portions of the radially outer face thereof. The carbon paper wrapper may be free of the adhered additive around its circumference at one or both ends of the longitudinally extending core. The adhered particulate sorbent additive - e.g. activated carbon - preferably extends only partially around the inner circumference of the carbon paper wrapper - the wrapper, for example, having an overlapping longitudinal edge which is free of said adhered additive and provides a lapped and stuck seam holding the carbon paper wrapper around the longitudinally extending core. The adhered particulate additive may cover a single region of the inner surface of the carbon paper wrapper extending from one end of the longitudinally extending core partially towards the other; it may cover a single region which is spaced from both ends of the core; it may be disposed in separate regions spaced longitudinally and/or circumferentially from one another as e.g. stripes or patches.

Formation of the longitudinally extending core and application of the coated carbon paper wrapper may occur substantially simultaneously. The carbon paper wrapper is preferably pre-coated with the adhering particulate sorbent additive immediately before application to the longitudinally extending core. The particulate additive is suitably adhered to the carbon paper wrapper by hot melt adhesive, e.g. high melting point polyethylene glycol, starch based adhesive, or emulsion type adhesive such as PVA. Suitable hot melt adhesives for use in the invention are various polyester adhesives. The tobacco smoke filter or filter element may comprise a further wrapper arranged around the longitudinally extending core, the further wrapper having particulate sorbent additive - e.g. activated carbon - adhered to one or more portions of the radially inner face thereof. The further wrapper may, also or alternatively, have additive adhered to one or more portions of the radially outer face thereof. The further wrapper may be free of additive around its circumference at one or both ends of the longitudinally extending core. The particulate sorbent additive - e.g. activated carbon - preferably extends only partially around the inner circumference of the further wrapper - the wrapper, for example, having an overlapping longitudinal edge which is free of said additive and provides a lapped and stuck seam holding the wrapper around the longitudinally extending core. The particulate additive may cover a single region of the inner surface of the wrapper extending from one end of the longitudinally extending core partially towards the other; it may cover a single region which is spaced from both ends of the core; it may be disposed in separate regions spaced longitudinally and/or circumferentially from one another as e.g. stripes or patches. The further wrapper may be carbon paper.

The further wrapper may be arranged around the longitudinally extending core (or portion thereof) so that it is positioned between the longitudinally extending core (or portion thereof) and the carbon paper wrapper; or the further wrapper may be engaged around the carbon paper wrapper (or portion thereof) so that it surrounds both the carbon paper wrapper (or portion thereof) and the longitudinally extending core (or portion thereof). The further wrapper is preferably coated with the adhering particulate sorbent smoke-modifying additive. Formation of the longitudinally extending core and application of the coated further wrapper (and carbon paper wrapper) may occur substantially simultaneously. The particulate additive is suitably adhered to the wrapper in the same manner as for the carbon paper wrapper.

The carbon paper wrapper (if coated with particulate additive) and/or the optional further wrapper may be coated with adhesive over the restricted regions where particulate additive coating is required (e.g. by a printing wheel), and then with particulate additive (e.g. by drawing through a reservoir, fluidised bed, circulated stream or other supply of the additive whilst the adhesive is active) as part of an in-line continuous manufacturing process. Adhesive-coated carbon paper or further wrapper strip may be separately produced or obtained from an outside supplier, with activation (e.g. heat-softening) of the adhesive and application of particulate additive being conducted in-line and continuously with filter production.

Preferably the tobacco smoke filter or element comprises a longitudinally extending core having a carbon loading of between 2 and 20 mg/mm, preferably 3 and 10 mg/mm, more preferably between 3 and 6mg/mm; these figures representing the amount in mg of activated carbon per mm filter length, assuming a standard filter of around 25mm circumference, which may typically be between 24 and 25mm. The range of 3 to 6 mg/mm (for a standard filter of around 25mm circumference) is the preferred loading for an active acetate filter or filter element; the activated carbon loading for a coated thread or strip filter or filter element, discussed below, may be rather higher, e.g. up to 20mg/mm (for a standard filter of around 25mm circumference).

Preferably, the wrapper comprising carbon paper is carbon paper, which has a carbon loading (of impregnant, that is within the carbon paper web) of between 0.075mgs/mm and 2.8mgs/mm, more preferably 0.50 mgs/mm and 1.275 mgs/mm, more preferably 0.675 mgs/mm and 1.1 mgs/mm, these figures again representing the amount in mg of activated carbon per mm filter length, assuming a standard filter of around 25mm circumference. If the carbon paper has particulate sorbent additive - e.g. activated carbon - adhered to one or more portions - e.g. of the radially inner face thereof - it is preferred that the loading of additive adhered to the carbon paper is between 1 and 7 mgs/mm, preferably 2 and 3 mgs/mm (for a standard filter of around 25mm circumference). Preferably, the further coated wrapper (if present) has a carbon loading of between 1 and 7 mgs/mm, preferably 2 and 3 mgs/mm (for a standard filter of around 25mm circumference). It will be appreciated by the skilled man that, for a narrower or broader filter, the carbon loading ranges may be adjusted accordingly.

It will be seen from the above (and below) that filters and filter elements with high carbon loading can be quickly and efficiently produced on existing machinery with relatively little modification to the machinery or the process.

In a preferred embodiment the filter or filter element includes a longitudinally extending core; a wrapper comprising carbon paper; wherein the wrapper of carbon paper includes particulate active carbon adhered to one or more portions (preferably of the radially inner face) thereof (the "coated carbon paper wrapper"), wherein the ratio of carbon loading (mgs/mm) of the longitudinally extending core to the coated carbon paper wrapper is between 20:1 and 1 :1 , more preferably between 9:1 and 1.4:1. The carbon loading in these ratios includes the carbon which is impregnated into the carbon paper wrapper, as well as the additive adhered thereon (the coating).

In another embodiment the filter or filter element includes a longitudinally extending core; a wrapper comprising carbon paper; and a further wrapper having particulate active carbon adhered to one or more portions of the radially inner face thereof (the "coated further wrapper"), wherein the ratio of carbon loading (mgs/mm) of the longitudinally extending core to the coated further wrapper is between 20:1 and 1:1, more preferably between 9:1 and 1.4:1.

As described below, a filter according to the invention may have a longitudinally extending core, which includes more than one longitudinally adjacent portion. Preferably, one or more of these portions may not include activated carbon. In the above carbon loading ranges and ratios, the figures refer to the portion (or portions) which include activated carbon. Thus, for a dual filter, described below, which has a longitudinally extending core comprising a first, downstream plug of cellulose acetate tow which does not include activated carbon, and a second, upstream plug of cellulose acetate tow which does include activated carbon, the preferred loading of the upstream plug is between 3 and 6 mgs/mm for an Active Acetate plug of standard circumference (around 25mm). The longitudinally extending core may be a unitary body, or it could be a composite - e.g. - incorporating its own sleeve and/or having longitudinally (and/or radially) adjacent portions.

The tobacco smoke filter or filter element may comprise a longitudinally extending core which includes activated carbon, a first wrapper comprising a carbon paper arranged around the core, and a second wrapper around the carbon paper wrapper, the carbon paper wrapper defining at least with the second wrapper at least one channel extending longitudinally over at least a part of the length of the filter or filter element. The first wrapper may, for example, be a sheet of carbon paper having a profiled (e.g. corrugated) surface. The carbon paper wrapper may have longitudinally (e.g. axially) extending corrugations which define at least with the second wrapper a longitudinally extending channel or channels (grooves). The carbon paper wrapper is corrugated on both surfaces, and may define longitudinally extending channel or channels with the core as well as the further wrapper. The carbon paper and wrapped surface of the longitudinally extending core may however conform to the corrugated inner surface of the carbon paper wrapper in the finished filter, leaving channel or channels only between the first and second wrapper. Preferably the longitudinally extending channel or channels extend longitudinally over a part of the length of the carbon paper wrapper, so the carbon paper wrapper includes a channelled region and an unchanneled (ungrooved) region. More preferably the carbon paper wrapper has particulate additive adhered to a portion (e.g. the radially inner face) thereof, in the unchannelled or ungrooved region thereof. It will be appreciated by the skilled man that such a filter or filter element may be modified within the invention, for example so that the first wrapper is a standard paper wrapper (which may be corrugated) and the second wrapper is the carbon paper wrapper; in this formation the first wrapper will define at least with the second (carbon paper) wrapper at least one channel extending longitudinally over at least a part of the length of the filter or filter element.

In a preferred embodiment the longitudinally extending core includes a buccal, or mouth, end portion, and a tobacco end portion. The buccal end portion is the downstream portion of the longitudinally extending core which, when the filter is included with a tobacco rod as part of a completed smoking article such as a cigarette, is presented to the mouth of the smoker; the tobacco end portion is the upstream portion of the longitudinally extending core which is towards or closest to the tobacco rod. This is a dual filter.

As indicated above, it is preferred that the longitudinally extending core which includes activated carbon is in the form of a cellulose acetate plug which includes particles of activated carbon (e.g. which are carried on the cellulose acetate tow which forms the plug). The particles of activated carbon on or in the cellulose acetate plug may lead to an unfavourable end appearance (due to the granules of carbon). Thus, it is preferred that if the longitudinally extending core includes this material, the core includes two (or more) longitudinally adjacent portions. The first, downstream, or buccal, end portion is preferably of cellulose acetate tow which does not include activated carbon - e.g. a longitudinally extending plug of filamentary cellulose acetate tow. The buccal end portion may be wrapped. A NWA (non-wrapped acetate) filtering plug may be used for the buccal end portion - made, for example, as described in GB-A-1 , 169,932. A further portion, located towards the tobacco end (i.e. upstream of the buccal end portion and referred to as the upstream portion) is the longitudinally extending core which includes activated carbon in the form of a cellulose acetate plug which includes particles of activated carbon (e.g. which are carried on the filamentary cellulose acetate tow which forms the plug). The upstream portion includes a wrapper around the longitudinally extending core which comprises carbon paper. Optionally, the carbon paper includes particulate sorbent additive - e.g. activated carbon - adhered to one or more portions (e.g. of the radially inner face) thereof. Optionally, there is a further wrapper arranged around the longitudinally extending core having particulate sorbent additive - e.g. activated carbon - adhered to one or more portions (e.g. of the radially inner face thereof). In a preferred embodiment, the buccal end portion abuts the upstream portion at the upstream end of the buccal portion and the two portions (including the carbon paper wrapper and coated further wrapper, if present) are preferably wrapped in a further wrapper of e.g. plugwrap.

In a further embodiment the longitudinally extending core which includes activated carbon comprises substrate threads and/or strips individually pre- coated with activated carbon adhering thereto and gathered together and held in rod form. Such cores are themselves known (from e.g. GB 2,236,239). The threads and/or strips in the product filter or filter element usually extend generally longitudinally of the rod. The threads and/or strips may be held in rod form by the carbon paper wrapper engaged therearound (which may itself be coated with activated carbon), and/or the coated further wrapper engaged around the core portion (if present). This embodiment is referred to as a coated thread or coated strip filter or filter element. The longitudinally extending core which includes activated carbon may be a composite having three (or more) sections. In a further preferred embodiment the longitudinally extending core which includes activated carbon includes a first, downstream, or buccal, end portion; a central portion (which abuts the buccal end portion); and a further portion, located towards the tobacco end (i.e. upstream of the central portion) and referred to as the upstream portion. This is frequently referred to as a triple solid filter. The first, downstream, or buccal, end portion is preferably of cellulose acetate tow which does not include activated carbon - e.g. a longitudinally extending plug of filamentary cellulose acetate tow - similar to that described for the dual filter above. The central portion (located upstream of the buccal end portion) comprises a longitudinally extending core which includes activated carbon in the form of a cellulose acetate plug which includes particles of activated carbon (e.g. which are carried on the filamentary cellulose acetate tow which forms the plug). In an alternative filter, e.g. if higher active carbon loading is required, a coated thread or coated strip filter element, as discussed above, may be used as the central portion. The central portion includes a wrapper around the longitudinally extending core which comprises carbon paper. Optionally, the carbon paper includes particulate sorbent additive - e.g. activated carbon - adhered to one or more portions (e.g. of the radially inner face) thereof. Optionally, there is a further wrapper arranged around the longitudinally extending core having particulate sorbent additive - e.g. activated carbon - adhered to one or more portions (e.g. of the radially inner face thereof). The upstream portion may be of cellulose acetate tow which does not include activated carbon, and may be similar to the buccal end portion. A preformed WA (wrapped acetate) upstream filter plug may be used for the upstream plug. Other fibrous and non-fibrous filtering plug materials and structures can however be used (e.g. a plug of staple fibres or cellular plasties material or a plug of plasties - e.g. HDPE - fibres or filaments). The upstream plug may be a more specialised filter element, depending on the overall filter performance required. Thus, the upstream plug may be, for example, a further filter element according to the invention (i.e. longitudinally extending core which includes activated carbon, and a wrapper arranged around the core, the wrapper comprising carbon paper, with optional further wrapper), a filter element which includes a further sorbent additive (which may be active carbon or other sorbent additive) such as a filter element known in the art as an "active patch" filter element etc. It will also be appreciated that the configuration of the "central portion" and the "upstream portion" may be swapped, so that the portion of the longitudinally extending core which includes activated carbon and which includes a carbon paper wrapper is at the upstream end of the filter.

In a preferred embodiment, the buccal end portion abuts the central portion at the upstream end of the buccal portion, and the central portion abuts the upstream portion at the upstream end of the central portion, and the three portions (including the carbon paper wrapper and coated further wrapper, if present) are preferably wrapped in a further wrapper of e.g. plugwrap.

The filter wrapper may have one or more ventilating apertures. The filter wrapper may have no ventilating apertures. The downstream filtering plug preferably extends to the buccal end face of the filter. The upstream filtering plug preferably extends to the upstream end face of the filter. Filters and elements according to the invention may have a further outer containing sleeve or sleeves e.g. an extruded sleeve or a plugwrap with a lapped and stuck seam; such a plugwrap could be of air-permeable or air-impermeable material, and in either case may be perforated. The carbon paper wrapper and/or the particulate coated further wrapper (if present) may be adhered (e.g. with heat activatable adhesive) to the core portion to give a bonded product which is dimensionally stable without a containing sleeve.

The invention may provide a filter or filter element which carries a higher loading of activated carbon and which may present an acceptable, plain, additive- free appearance at the buccal end of a filter cigarette. It also permits incorporation of high loads of activated carbon or other particulate sorbent additive in tobacco smoke filters using conventional apparatus without introducing production or apparatus problems and in particular with ready achievement of uniform additive loading - and simple and accurate variation of this loading when required. Filters according to the invention allow the activated carbon in the carbon paper wrapper (and optionally, particulate additive adhered to the carbon paper wrapper and/or further coated wrapper) to exercise, unhindered or substantially so, its filtering effect on the tobacco smoke stream; thus filters according to the invention containing particulate sorbent can give good retention of vapour phase smoke components.

In a filter cigarette according to the invention a filter is joined to a wrapped tobacco rod with one end towards the tobacco. The filter may for example be joined to the wrapped tobacco rod by ring tipping (which engages around just the adjacent ends of filter and rod to leave much of the filter wrapper exposed) or by a full tipping overwrap (which engages around the full filter length and the adjacent end of the rod). Any filter or filter cigarette according to the invention may be ventilated by methods well known in the art, e.g. by use of a pre- perforated or air permeable plug wrap, and/or laser perforation of plugwrap and tipping overwrap. Where ventilation in a filter or filter cigarette according to the invention is localised longitudinally of the product, this localisation is preferably to one or two regions selected from upstream of, downstream of, and in register with the longitudinally extending core, or portion thereof, which includes activated carbon, depending upon the ventilation and filtering performances required; ventilation upstream of and/or in register with the longitudinally extending core (or portion of the core) which includes activated carbon is frequently preferred.

The present invention will now be illustrated with reference to the attached drawings in which: FIGURES 1 and 2 respectively are schematic sectional side elevation views, not to scale, of an individual filter and filter cigarette according to an embodiment of the invention;

FIGURE 3 shows a schematic sectional side elevation view, not to scale, of an individual filter according to a further embodiment of the invention; FIGURES 4 and 5 respectively are schematic sectional side elevation views, not to scale, of an individual triple solid filter and filter cigarette according to a still further embodiment of the invention; and

FIGURE 6 is a diagrammatic perspective view, with part broken away, of a filter element according to a further embodiment of the invention, which is a fluted filter element. FIGURE 1 is a diagrammatic longitudinal sectional view of a filter 1 according to the invention. Filter 1 is 27mm long and has a circumference of around 25mm. Filter 1 includes a longitudinally extending core 2 which includes activated carbon, which includes a first, downstream, or buccal, end portion 3 of filamentary cellulose acetate tow which does not include activated carbon in the form of a longitudinally extending cylindrical plug of filamentary cellulose acetate tow of length 10mm. In the illustrated embodiment, the buccal end portion is a NWA (non-wrapped acetate) filtering plug which is well known in the art - made, for example, as described in GB-A-1 ,169,932. However, it will be appreciated that wrapped plugs of filamentary cellulose acetate tow may be used for the buccal end portion 3. The longitudinally extending core 2 also includes a second, upstream portion 4, which includes activated carbon, abutted to the upstream end of portion 3. Upstream portion 4 is a cylindrical cellulose acetate plug of length 17mm which includes particles of activated carbon (particles not shown) at a carbon loading of 5mgs/mm plug length. The activated carbon is carried on the filamentary cellulose acetate tow which forms the plug, as is well known in the art as "active acetate". Upstream portion 4 is surrounded by a wrapper 5 of carbon paper which is commercially available under the mark CP60 from Tela-Kimberly of Balsthal, CH. The carbon paper wrapper 5 is of length 17mm and positioned so as to extend around and engage the full circumference of upstream portion 4, and secured around upstream portion 4 by a lapped and stuck seam (not shown). The longitudinally extending core 2 (that is downstream portion 3, and carbon wrapped upstream portion 4) is surrounded by a non-porous plugwrap 6 which extends around and engages the full circumference of longitudinally extending core 2 and is secured around the core 2 by a lapped and stuck seam (not shown). It will be appreciated that the plugwrap may be porous, in which case ventilation would need to be added later, if required (e.g. using a pre-perforated tipping paper). It will be appreciated that the above embodiment is a modification of the known active acetate dual filter, the skilled man would readily appreciate how, in the manufacture of filters or filter elements of the invention, carbon paper wrapper 5 could be wrapped around portion 4 of cellulose acetate tow which includes activated carbon (e.g. conveniently applied around portion 4 as portion 4 is being formed, using conventional garniture apparatus) in the conventional method of making active acetate dual filters, to give dual filters of the invention as shown in Fig.1.

FIGURE 2 shows a filter of the Fig.1 type joined at its upstream end 7 to a tobacco rod 10 in its own wrap 11 by means of a full tipping overwrap 12 which surrounds and engages the full length of the filter and the adjacent end only of the wrapped tobacco rod 10, 11.

FIGURE 3 is a diagrammatic longitudinal sectional view of a filter 21 which is a further embodiment of the invention. Filter 21 is 27mm long and has a circumference of around 25mm. Filter 21 includes a longitudinally extending core 22 which includes activated carbon, which includes a first, downstream, or buccal, end portion 23 of filamentary cellulose acetate tow which does not include activated carbon in the form of a longitudinally extending cylindrical plug of filamentary cellulose acetate tow of length 10mm. In the illustrated embodiment, the buccal end portion is a NWA (non-wrapped acetate) filtering plug which is well known in the art - made, for example, as described in GB-A-1 ,169,932. However, it will be appreciated that wrapped plugs of filamentary cellulose acetate tow may be used for buccal end portion 23. The longitudinally extending core 22 also includes a second, upstream portion 24, which includes activated carbon, abutted to the upstream end of portion 23. Upstream portion 24 is a cylindrical cellulose acetate plug of length 17mm which includes particles of activated carbon at a carbon loading of 5mgs/mm plug length. The activated carbon (not shown) is carried on the filamentary cellulose acetate tow which forms the plug, as is well known in the art as "active acetate". Upstream portion 24 is surrounded by a wrapper 25 of carbon paper of length 17mm which is commercially available under the mark CP60 from Tela-Kimberly of Balsthal, CH, with impregnant as described above. The carbon paper wrapper 25 has particulate sorbent additive 36 in the form of granules of active carbon adhered to its inner surface so as to extend around and engage the full circumference of upstream portion 24, and is secured around upstream portion 24 by a lapped and stuck seam (not shown). The carbon loading of the active carbon adhered to the carbon paper (i.e. in addition to the active carbon impregnated into the paper) is 2.5mgs/mm length of the carbon paper. It will be appreciated that the particulate sorbent additive may be applied to the carbon paper by known methods, e.g. by those disclosed in GB-A- 2261152. As with the embodiment of Fig 1, the longitudinally extending core 22 (that is downstream portion 23, and carbon wrapped upstream portion 24) is surrounded by a plugwrap 26 which extends around and engages the full circumference of longitudinally extending core 22 and is secured around the core 22 by a lapped and stuck seam (not shown). It will be appreciated that the embodiment of Fig 3 may be attached to and used with a cigarette in, for example, the manner illustrated in and described with reference to Fig 2.

As indicated with reference to Fig.1, the embodiment of Fig.3 is a further modification of the known active acetate dual filter, and the skilled man would readily appreciate how to provide the filter of Fig.3 by adapting conventional methods. The carbon paper wrapper 25 having particulate sorbent additive 36 in the form of granules of active carbon adhered to its inner surface may be preformed and conveniently applied around core 24 as the core is being formed, using conventional garniture apparatus.

It will be appreciated that upstream longitudinally extending portions 4, 24, which include activated carbon and are surrounded by (optionally coated) carbon paper wrappers 5, 25, which are components of the finished filters 1 , 21, may be termed filter elements of the invention.

The Figure 4 filter is 30mm long and of circumference of around 25mm and has a longitudinally extending core 102 which includes activated carbon made up of a cylindrical buccal end filtering plug 103 of length 10mm which is a preformed non-wrapped plug of cellulose acetate filaments gathered and bonded together; a cylindrical upstream filtering plug 108 of length 10mm which is a preformed wrapped plug of cellulose acetate (preformed wrap not shown); and a central portion 104. Central portion 104 is a cylindrical cellulose "active acetate" plug of length 10mm which includes activated carbon (particles not shown) at a carbon loading of 5mgs/mm length. Central portion 104 has a carbon wrapper 105 of CP60 carbon paper of length 10mm engaged around portion 104. The amount of carbon impregnated in the CP60 carbon paper is as set out above. The longitudinally extending core 102, that is plugs 103, 104, 108, is surrounded by a porous plugwrap 106 which extends around and engages the full circumference of longitudinally extending core 102 and is secured therearound by a lapped and stuck seam. It will be appreciated that the plugwrap may be porous or non-porous, as is well known in the art. In an alternative filter, e.g. if higher active carbon loading is required, a coated thread or coated strip filter element, as discussed above, may be used as the central portion 104; if a coated thread/strip is used, the central portion may have a higher active carbon loading, e.g. of up to 20mg/mm.

FIGURE 5 shows a filter of the Fig.4 type joined at its upstream end 107 to a tobacco rod 110 in its own wrap 111 by means of a full tipping overwrap 112 which surrounds and engages the full length of the filter and the adjacent end only of the wrapped tobacco rod 110, 111. The filters of Figs.1 , 3 and 4 might alternatively be attached to wrapped tobacco rod 10, 110, 11 , 111 by ring tipping which extends only around the adjacent ends of the filter and tobacco rod, so that most of filter wrapper (6, 26, 106) is directly exposed to atmosphere. Filter wrapper 6, 26, 106 would then usually be of air-permeable material, and/or provided with one or more apertures (before or after filter cigarette assembly), to give ventilation.

FIGURE 6 is a diagrammatic perspective view, part broken away, of a filter element 201 according to the invention which includes a longitudinally extending core 202 which includes activated carbon in the form of a cylindrical cellulose acetate plug 224 of length 17mm which includes particles of activated carbon at a carbon loading of 5mgs per millimetre plug length. The activated carbon is carried on the filamentary cellulose acetate tow which forms the plug, as is well known in the art as "active acetate". Immediately surrounding the core 202 (plug 224) is a wrapper 225 of air-permeable carbon paper, which is corrugated longitudinally over part of its length to a form corrugated circumferential portion 231 which extends from upstream end 217 of the filter element towards the downstream end 219; the corrugations stopping short of downstream end 219 so wrapper 225 includes an uncorrugated circumferential portion 230 at downstream end 219. The core surface conforms to the corrugations in wrapper 225. Immediately surrounding the carbon paper wrapper 225 and forming channels 234a, 234b with the corrugations is an uncorrugated further wrapper of air-permeable paper 232. The core and the wrappers 225 and 232 extend over the entire length of the filter element 201. The inclusion of an uncorrugated circumferential portion 230 of wrapper 225 means that there are no channels in this portion and that the channels 234a, 234b do not run the full length of the filter. The carbon paper wrapper 225 has particulate sorbent additive 236 in the form of granules of active carbon adhered the inner surface of the uncorrugated circumferential portion 230.

It will be appreciated by the skilled man that filter element 201 may be used as an alternative to, for example, upstream filter plug 4 shown in Figs.1 and 2. Thus filter element 201 (of Fig 6) could be used in place of upstream filter plug 4 in Fig

1 and abutted (at downstream end 219) to the upstream end of portion 3 of Fig 1.

As with the embodiment of Fig 1 , portion 3 and carbon wrapped filter element 201 may be surrounded by a plugwrap 6 which extends around and engages the full circumference of the longitudinally extending core (portion 3 and filter element

201), and which is secured around the core 2 by a lapped and stuck seam (not shown). In a still further embodiment, filter element 201 does not include separate uncorrugated further wrapper of air-permeable paper 232; the uncorrugated further wrapper of air permeable paper is provided by plugwrap 6 which extends around and engages the full circumference of the longitudinally extending core (portion 3 and filter element 201 ) to form channels between the corrugations in the carbon paper wrapper of filter element 201 and the inner surface of plugwrap 6.

The filters or filter elements according to the invention may be made by techniques well known in the art as continuous rods. The continuous rod as it issues continuously from the production machine outlet is cut into finite lengths for subsequent use. This cutting may be into individual filters or filter elements as defined and described above, each of which is then attached to an individual wrapped tobacco rod to form a filter cigarette. More usually, however the continuously issuing rod is first cut into double or higher multiple (usually quadruple or sextuple) lengths for subsequent use; when the initial cut is into quadruple or higher lengths, then the latter are subsequently cut into double lengths for the filter cigarette assembly - in which the double length filter rod is assembled and joined (by ring tipping or full tipping overwrap) between a pair of wrapped tobacco rods with the combination then being severed centrally to give two individual filter cigarettes. The invention includes double and higher multiple length filter rods (and/ or filter element rods).

Claims

1. A tobacco smoke filter or filter element comprising a longitudinally extending core which includes activated carbon, and a wrapper arranged around the core, the wrapper comprising carbon paper.

2. A tobacco smoke filter or filter element comprising a longitudinally extending core which includes activated carbon, a first wrapper comprising a carbon paper arranged around the core, and a second wrapper around the carbon paper wrapper, the carbon paper wrapper defining at least with the second wrapper at least one channel extending longitudinally over at least a part of the length of the filter or filter element.

3. A filter or filter element according to claim 1 or 2 wherein the longitudinally extending core which includes activated carbon comprises a cellulose acetate plug which includes activated carbon.

4. A filter or filter element according to claim 1 , 2 or 3 wherein the carbon paper has a basis weight of between 30gsm and 160gsm,

5. A filter or filter element according to any preceding claim wherein the carbon paper has carbon content (by weight) between 10% and 70%.

6. A filter or filter element according to any preceding claim wherein the carbon paper wrapper has particulate sorbent additive adhered thereto.

7. A filter or filter element according to any preceding claim comprising a further wrapper arranged around the longitudinally extending core, the further wrapper having particulate sorbent adhered thereto.

8. A filter or filter element according to any preceding claim comprising a longitudinally extending core having a carbon loading of between 2 and 20 mg per mm filter or filter element length, for a standard filter or element of around 25mm circumference.

9. A filter or filter element according to any preceding claim comprising carbon paper having activated carbon additive adhered thereto, wherein the loading of additive adhered to the carbon paper is between 1 and 7 mgs per mm length of carbon paper for a standard filter or element of around 25mm circumference.

10. A filter or filter element according to any preceding claim wherein the longitudinally extending core includes a first, downstream end portion which does not include activated carbon; and a second upstream portion which includes activated carbon; and a wrapper around at least part of the second upstream portion of the longitudinally extending core which comprises carbon paper.

11. A filter or filter element according to any of claims 1 , 2 or 4 to 9 wherein the longitudinally extending core which includes activated carbon comprises substrate threads and/or strips individually pre-coated with activated carbon adhering thereto and gathered together and held in rod form.

12. A filter or filter element according to any of claims 1 to 9 or 11 wherein the longitudinally extending core includes a first, downstream, end portion which does not include activated carbon; a second portion which includes activated carbon, and a further filtering portion; and a wrapper around at least part of the second portion of the longitudinally extending core which comprises carbon paper.

13. A filter according to claim 12 wherein the second portion is located between the downstream end portion and the further filtering portion.

14. A filter or filter element substantially as hereinbefore described with reference to any of Figs. 1 , 3, 4 or 6.

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

16. A filter cigarette substantially as hereinbefore described with reference to any of Figs. 2 or 5.