GB2118424A

GB2118424A - Tobacco smoke filter

Info

Publication number: GB2118424A
Application number: GB08309057A
Authority: GB
Inventors: Ernest Brian Hayes
Original assignee: Filtrona PLC
Current assignee: Essentra PLC
Priority date: 1982-04-07
Filing date: 1983-03-31
Publication date: 1983-11-02
Also published as: IT8320476A0; ATA122783A; DE3312548A1; ES281071Y; GB2118424B; AT385633B; IT1194190B; NO159834C; CH659174A5; NO831227L; NL8301226A; NO159834B; BR8301853A; BE896380A; FR2524774A1; HK86689A; ES281071U; AU566029B2; GB8309057D0; FR2524774B1

Abstract

A tobacco smoke filter element comprises a wrapped core (4). The wrapper (2) is longitudinally corrugated to provide, externally thereof, passages (6) extending longitudinally of the filter. The wrapper also has a circumferential groove (8) into which the said passages open. For use the filter element can be provided with an air-permeable wrap, which may be a ventilating tipping overwrap incorporating the element in a filter cigarette; such an overwrap suitably has ventilating perforations opening directly into the circumferential groove. <IMAGE>

Description

SPECIFICATION Tobacco smoke filter This invention concerns smoke filters and provides a tobacco smoke filter element having a longitudinally extending core and a wrapper around this core, the wrapper being pre-configured to provide externally thereof passages extending longitudinally of the filter to or towards at least one end thereof, the wrapper also having a circumferential groove into which the said passages open. It also provides a smoke filter having such an element having tipping material around the wrapper; the tipping material may be longitudinally co-extensive with the element, or it may be a tipping overwrap incorporating the element in a filter cigarette; the tipping material may be air-permeable or air-impermeable, and where it is a ventilating tipping it preferably provides for ventilation directly into the circumferential groove.

The wrapper will usually be longitudinally corrugated to provide the external passages, though it could be otherwise configured (e.g. dimpled) for this purpose.

The core surface may conform to the inner surface of the wrapper, or the latter can also define internal passages between itself and the core, these likewise extending from the circumferential groove to or towards at least one end of the element or filter; such internal passages will usually be closed by the external circumferential groove.

The invention also provides a method of making a tobacco smoke filter element which comprises providing a longitudinally extending core, embossing a wrapping strip at longitudinally spaced regions to form therein longitudinally extending channels spaced from further such channels by an unembossed region, and wrapping the wrapping material around the core with said channels outermost whereby the said unembossed region of the wrapping adopts the form of a circumferential groove around the wrapped core into which the external longitudinal passages open.

The core of the element and filter according to the invention can be of any of the whole range of cigarette filter materials, e.g. of bonded or unbonded staple fibres or filamentary tow (of cellulose acetate, or polyolefin etc), creped paper, or air-permeable foamed material. The core may be of uniform structure and composition along its length, or may instead be of composite structure - e.g. of separate plugs of differing characteristics (e.g. pressure drop); the core may extend wholly or only partially the length of the element, and where the core is a composite of two or more plugs adjacent plugs may abut or be spaced apart. The core may be unwrapped or include a plugwrap which is perforate and/or of inherently smoke-permeable material; the core could instead have an impermeable plugwrap or integral (e.g. heat- or solvent-fused) skin.The core could instead be impermeable or non-filtering.

The wrapper when impermeable is suitably a paper/thermoplastics polymer laminate, e.g. a paper/thermoplastics/paper laminate, the plastics layer preferably being of polyolefin, e.g. polyethylene.

Such a laminate has good embossing characteristics and retains its impermeability and embossed configuration well. The wrapper might instead be permeable, e.g. of permeable paper plugwrap and/or perforate. The wrapper is preferably secured around the core by way of a lapped and stuck seam; it may also be secured to the core by one or more longitudinal adhesive lines.

The tipping material may be airpermeable; for ventilated filters it may be inherently permeable, but when it is the tipping overwrap joining the element to a tobacco column it is more usually of substantially impermeable material having perforations in communication with the external passages e.g. via the circumferential groove. The element may have a wrap of air-permeable material, giving a filter of plain external appearance and around which the tipping overwrap (or ring tipping) is engaged in filter cigarette manufacture, but this is not usually necessary.

In use as part of a filtered cigarette, some filters according to the invention can provide, via passages between wrapper and core, for some by-pass of smoke around part of the core length, various controlled effects being thereby obtainable according to the filter structure adopted; in these cases, of course, the core does not have a smokeimpermeable layer between itself and the impermeable wrapper.

In ventilated filters according to the invention the external passages, between wrapper and tipping material, may be open only to the buccal end of the filter, so that ventilation air drawn thereinto passes directly into the smokers mouth without previous mixing with smoke. Where the external passages open instead only at the end of the filter abutting the tobacco rod, ventilation air drawn thereinto passes upstream to the tobacco rod and then downstream through the filter core.

Elements according to the invention are suitably made by first forming the core (as a continuous or discrete finite length rod), corrugating the wrapper to the required configuration, and wrapping and securing the corrugated wrapper around the core.

Tipping material can subsequently be wrapped around the wrapper; this tipping material may be the tipping overwap which is employed to join filter and tobacco rod together during formation of filtered cigarettes in conventional manner.

Normally the core will be formed as a continuous rod which is then continuously wrapped in the corrugated wrapper, the resulting continuous composite then being cut transversely into finite lengths.

Awrap of air-permeable or-impermeable material may if desired be applied continuously around the composite of core and corrugated wrapper before the cutting into finite lengths. For filter cigarette manufacture, double length such products are disposed with wrapped tobacco rods abutting either end, tipping overwrap or ring tipping being applied to join the tobacco rods and intervening filter rods together, and the resulting combination is cut through the double lengths to produce individual filter cigarettes. The initially produced continuous filter rod is normally cut into even multiple (e.g.

sextuple) length units for supply to the filter cigarette manufacturer who then cuts these multiple lengths into double lengths for use in filter cigarette production as described above. It will be appreciated that, in the case of individual filter lengths according to the invention in which the first and further passages extend from one end only of the filter to terminate short of the other end so that the two filter ends are different, the initial even multiple length rods supplied by the filter manufacturer and from which the individual lengths are eventually formed can have identical ends - e.g. the even multiple length rod could have passages extending from both ends or closed at both ends, according to whether the passages in the final filter cigarette are to be open to the tobacco or at the buccal end respectively.Such even multiple length filter rods also form part of the present invention.

Whilst the core of filters and elements according to the invention may be a composite structure as mentioned above, e.g. made up of abutting or longitudinally spaced plugs, the corrugated wrapper usually extends the full filter or element length to render it overall a coherent, unitary structure.

There may be used as or in the core of filters and elements according to the invention a high pressure drop, low retention plug of gathered coarse fibres or of gathered embossed plastics, metal (e.g. aluminium) orotherfoil.

In filter cigarettes employing elements according to the invention, there can be ventilation through the tipping material directly into the circumferential groove and hence into all of the external passages; for example, ventilating perforations may be provided in the tipping material in a circumferential ring in register with the circumferential groove.

Various configurations of element according to the invention are possible; for example, the circumferential groove may be disposed mid-way along the wrapper, with external (and optionally internal) passages extending therefrom in opposite directions to both ends of the element; or the circumferential groove may be towards one end of the element where the wrapper is circumferentially corrugated or otherwise conformed to close the circumferential groove from that end, the external (and optionally internal) passages extending from the circumferential groove to the other end of the element; in another variant, the circumferential groove is at one end of the wrapper, being open to that end with the external(and optionally internal) passages extending therefrom to the other end; other embodiments have a plurality of the circumferential grooves spaced along the wrapper, e.g. at opposite ends thereof. The wrapper to be employed in the production of this type of element according to the invention can simply be profiled in the normal way to provide the required corrugations, with each region to constitute a circumferential groove being left plain and unprofiled; when the corrugated wrapper is applied round the core, it is found that the said plain unprofiled regions naturally adopt the conformation of circumferential grooves.

This feature of a filter element with a core having a longitudinally corrugated wrapper providing an external circumferential groove into which the external channels of the corrugations open, and the method of forming this structure by wrapping around the core a pre-corrugated wrapper with plain portions left as described above, are generally useful and applicable, whatever the nature of the core, whatever the nature of the corrugated wrap (e.g. impermeable or permeable and/or perforate), and whatever the nature of the tipping material employed therewith. Furthermore, instead of being corrugated, the said wrapper could be otherwise conformed (e.g.

dimpled) to provide the said external channels.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which like reference numerals indicate like parts and in which: Figure lisa longitudinal sectional view of a filter and filter cigarette according to the invention; Figure 2 and 3 are cross sectional views along lines ll-ll and Ill-Ill respectively of Figure 1; Figure 4 is a perspective view of the filter element according to the invention employed in the filter of Figure 1; Figures5and 13 are views similarto Figure 1 of other filters and filter cigarettes according to the invention;; Figures 6 and 11 are perspective views of the filter elements according to the invention employed in Figures 5 and 13 respectively; Figure 7is a view, similarto that of Figure 6, of another filter element according to the invention; and Figures 8to 10 and 12 are schematic longitudinal sectional views of multiple length filter rods accord ing to the invention.

In some Figure 1 to 7 embodiments the filter element or rod comprises a filtering core 4 (which incorporates a plain smoke-permeable or -impermeable plugwrap 1) wrapped in a smoke-impermeable wrapper 2 with longitudinal corrugations 3 providing longitudinal passages 5 between wrapper and core and external longitudinal passages 6; in the elements of Figures 1 to 7 the impermeable wrapper also provides a circumferential groove 8 communicating with the said external grooves 6 which extend therefrom as shown to an end of the filter. In use, surrounding the filter element and joining it to a wrapped tobacco rod 10 is a ventilating tipping overwrap 12 having a ring of ventilating perforations 14 opening into the said circumferential groove.

In the embodiment of Figure 1 to 4, internal and external passages extend longitudinally from the circumferential groove to both ends of the filter rod.

In the embodiment of Figures 5 and 6, the impermeable wrapper at the end of the filter abutting the tobacco rod has circumferential corrugations 20 which close off the circumferential groove and the external channels from the tobacco rod, the circumferential groove being directly adjacent to the circumferential corrugations and the longitudinal corrugations of the wrapper extending therefrom to the buccal end of the filter. In the Figure 7 element, which can be incorporated in a filter cigarette in the same manner as shown for Figures 1 and 5, the circumferential groove 8 is open to one end of the element, channels 5 and 6 extending therefrom to the opposite end.

As indicated above, in the formation of the illustrated filter elements, the initially flat wrapper 2 is first embossed with its sets of corrugations 3 (Figures 1 to 4 and 7) or 3 and 20 (Figures 5 and 6) with the spaces therebetween being left plain and unembossed. When the pre-corrugated wrapper is engaged around the core 4, the unembossed wrapper portions naturally distort to provide the circumferential groove 8 into which the channels 6 open.

As previously explained, a filter element according to the invention such as any of those illustrated will initially be produced in a continuous length from which even multiple length rods (i.e. each rod being an even multiple of the eventual individual element) are cut, the multiple length rods subsequently being further subdivided into double length elements and then, during filter cigarette production, into the final single length elements. Examples of sextuple length rods according to the invention, which can be further subdivided into individual elements according to the invention, are illustrated schematically in Figure 8 to 10. Figure 8 shows a sextuple length rod from which single elements as in Figure 4 can be produced by cutting midway through the inboard longitudinally corrugated sections.A similar multiple length rod, but with appropriately different relative dimensions of the corrugated and circumferentially groove regions could be cut midway through the grooves to yield individual elements as shown in Figure 7.

Figure 9 shows a sextuple length rod which can be cut midway through the circumferentially corrugated regions and midway through the inboard longitudinally corrugated regions to yield individual elements of the type shown in Figure 6. Figure 10 shows a sextuple length rod which can be cut through the circumferentially corrugated regions 20 to yield individual elements according to the invention (not shown) having circumferential corrugations at one end with the longitudinal corrugations extending therefrom to the other end.

Whilst in all the above embodiments the filtering core 4 incorporates a plain plugwrap 1, the latter need not always be present, and when it is it may be smoke-permeable or -impermeable. The individual elements and multiple length rods illustrated in Figures 4 and 7 to 10 can be provided, as part of the filter manufacturing procedure, with a plain airpermeable plugwrap. The wrapped elements or filters could then be incorporated in filter cigarettes by a ventilating tipping overwrap as shown in Figures 1 and 5, or by ring tipping.

As also indicated above, whilst the embodiments of Figure 1 to 10 employ a filtering core 4, and an impermeable wrapper 2 providing both internal and external passages 5 and 6, any one or more of these features may be absent or modified. For example, the core may conform to the wrapper, leaving no internal passages 5; the core may be permeable or impermeable and of high, low or zero filtering efficiency; and the wrapper 2 may be of permeable or impermeable material and perforate or imperforate. The comments above concerning even multiple length rods apply equall to these modified embodi ments. Furthermore these elements may be used with either permeable or impermeable tipping overwrap.As another modification, wrapper 2 need not be longitudinally corrugated, but could be of any other configuration - e.g. dimpled - to provide the external channels extending from groove 8 to or towards an end of the element.

In one particular type of modified embodiment according to the invention, the core may be of low (or even zero) permeability with the said passages and circumferential groove providing externally of the core a path which extends from end to end of the core and which is of lower enclosed pressure drop than the core.In use, most at least of the smoke is thus constrained or encouraged to pass via the passages and circumferential groove rather than via the core, so that there is little or no mechanical filtration of the smoke; adequate tar and CO reduction can however be achieved by providing high levels (e.g. 50% or more) of air dilution through ventilating tipping material into the peripheral smoke path, preferably directly into the circumferential groove; because of the flow-obstructing core and of the relatively restricted smoke flow path therearound, however, this high degree of air dilution can be provided whilst retaining acceptably high overall filter and filter cigarette pressure drops. By this means there can thus be provided a cigarette filter which achieves most or substantially all of its tar etc.

reduction by air dilution rather than by mechanical retention whilst retaining an acceptable draw resistance in use; this is a distinct advance over conventional filter structures where high air dilution and low mechanical retention have inevitably led to filter and filter cigarette pressure drops too low to be acceptable. Filters according to the invention of the described type can also give a CO/tar yield appreciably lower (e.g. 0.5 or less) than that obtainable with conventional filters (generally about unity) of the same enclosed pressure drop and tar retention.

Enclosed pressure drop and tar retention etc. are those measured with air dilution prevented.

Referring again to the drawings, such a filter element, filter and filter cigarette according to the invention may be as variously shown in Figure 1 to 4.

In one case the filter element as shown in Figure 4 has a very low permeability core 4 of Transorb (a dense drawndown rod of bonded cellulose acetate filaments) with an impermeable plugwrap 1 (e.g. of paper of plastics film), the wrapper 2 being impermeable (e.g. a paper/thermoplastics/paper laminate as previously described) and providing via the two sets of passages 6 and intervening circumferential groove 8 a peripheral longitudinal flow path of lower enclosed pressure drop than that of the core.

The characteristics of Transorb rods, and methods for their production (which can remove the initial filament crimp) are described in U.K. Patent Specification No. 970817 to which attention is directed for further detail. In the corresponding filter and filter cigarette according to the invention (Figure 1 to 3) the element is surrounded by ventilating tipping material 12 providing for a high degree of high dilution (e.g. 50% or more) into the peripheral smoke flow path, in this case by way of a ring of ventilating perforations 14 in register with circumferential groove 8; the tipping 12 is here of inherently impermeable material, but it could instead be inherently permeable, with or without perforations 14. In a similar embodiment the wrapped Transorb core 4, 1 is replaced by an impermeable extruded rod of closed cell plastics foam.

The element illustrated in Figure 7 can likewise be of the same components as described immediately above, with a closed cell foam or wrapped Transorb core and an impermeable wrapper 2 providing via 6 and 8 a peripheral smoke flow path of lower enclosed pressure drop than the core; this element will be incorporated in a high air dilution filter and filter cigarette as described in connection with Figures 1 to 3. The components of the multiple length rod shown in Figure 8 may likewise be as just described for Figures 4 and 7.

in another particular type of modified embodiment, the core is of filtering material, the wrapper 2 is smoke-permeable, and the peripheral path provided by the circumferential groove and longitudinal passages communicating therewith terminates short of at least one end of the element. Such an element can be used with ventilating or non-ventilating tipping material, and in use smoke is constrained or encouraged to pass through the wrapper between the core and the peripheral flow path.Such an element may for element may for example be as shown in Figure 6, and its multiple length version as shown in Figure 9, with the core 4 being a porous filtering rod of bonded crimped cellulose acetate filamentary tow, the plugwrap 1 being (e.g. highly) permeable or omitted altogether, and the wrapper 2 being (e.g. highly) permeable. in other cases, however, the core 4 will not have a plain cylindrical surface, but will conform to the inner corrugated face of wrapper 2 so that there are no internal channels 5; this is conveniently achieved in practice by enwrapping the freshly produced core rod 4 in the preconfigured wrapper 2 whilst the gathered tow of the core is still "live" and uncured, the wrapper then impressing its profile into the core surface.A corresponding filter and filter cigarette according to the invention may be as illustrated in Figure 5 except that the ventilating perforations 14 are preferably not present in impermeable tipping material 12 and that, as indicated above, plugwrap 1 (which is permeable, preferably highly permeable, when present) may be omitted. In the latter case the core 4 may conform to the inner profile of wrapper 2 and hence fill the passage 5. Figures 11,12 and 13 illustrate respective ly a filter element. multiple length element, and filter and filter cigarette according to the invention where the filtering core 4 has no plugwrap and conforms to the Drofile of wrapper 2 which in use is surrounded by non-ventilating tipping material 12. The illustrated element is preferably employed in the reverse orientation to that shown in Figure 13, i.e. with the passages 6 towards the tobacco and the circumferential corrugations 20 at the buccal end, and indeed this is the filter cigarette which would be formed, by the conventional method previously described,from double length elements cut (through the inbrandlorgitudinally corrugated sections) from the Figure 12 rod. Sextuple length rods for the Figure 13 (or 5) filters would normally be as in Figure 12 (or 9) but with the circumferential corrugations 20 at each end.

Claims

1. A tobacco smoke filter having a longitudinally extending core, around the core a wrapper which is preconfigured to provide externally thereof passages extending longitudinally of the filter to or towards at least one end thereof and which also has a circumferential groove into which the said passages open, and tipping material around the wrapper.

2. A filter according to claim 1 wherein the core is of low or zero permeability and the circumferential groove and the passages provide a peripheral flow path from end to end of the core which is of lower enclosed pressure drop than the core.

3. A filter according to claim 1 wherein the core is a permeable filtering core and the wrapper is a permeable wrapper through which smoke can pass to or from the core.

4. A filter according to claim 1,2 or 3 wherein the tipping material is air-permeable and,or perforate.

5. A filter according to claim 4 wherein the tipping material provides in use for the ingress of external air laterallytherethrough into the circumferential groove.

6. A filter according to claim 3 wherein the tipping material is non-ventilating.

7. A tobacco smoke filter element having a longitudinally extending core of low or zero permeability, and a wrapper around this core, the wrapper being configured to provide externally thereof passages extending longitudinally of the element to at least one end thereof, the wrapper aiso having at least one circumferential groove into which the said passages open and which with the passages provides from end to end of the core a peripheral flow path of lower enclosed pressure drop than the core.

8. A tobacco smoke filter element having a longitudinally extending permeable filtering core, and permeable wrapper around the core, the wrapper being configured to provide externally thereof passages extending longitudinally or the filter and a circumferential groove into which the said passages open, the peripheral flow path provided by the passages and circumferential groove terminating short of at least one end of the element.

9. A method of making a tobacco smoke filter element which comprises providing a longitudinally extending core, embossing a wraping strip at longitudinally spaced regions to form therein longitudinally extending channels spaced from further such channels by an unembossed region, and wrapping the wrapping material around the core with said channels outermost whereby the said unembossed region of the wrapping adopts the form of a circumferential groove around the wrapped core into which the external longitudinal passages open.

10. A filter cigarette incorporating a filter or element according to any of claims 1 to 6.

11. A filter cigarette according to claim 10 where in the tipping material comprises a tipping overwrap joining the filter to the tobacco rod.

12. An integral multiple length rod which can be cut into individual elements or filters according to any of claims 1 to 8.

13. Afilter element substantially as hereinbefore described with reference to any one of Figure 4, 6,7 and 11 of the accompanying drawings.

14. A tobacco smoke filter substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 5 or Figure 13 of the accompanying drawings.

15. Afilter cigarette substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 5 or Figure 13 of the accompanying drawings.

16. A multiple length filter element substantially as hereinbefore described with reference to any one of Figure 8to 10 and 12 oftheaccompanying drawings.

17. A method of making a tobacco smoke filter element, the method being substantially as hereinbefore described.