IE53810B1 - Improvements relating to smoke filters - Google Patents

Abstract

A smoke filter (3) for a smoking article (e.g. a cigarette) comprises a filter plug (3) having ducts (5) extending part way along the plug from the mouth end thereof, and opening in register with inlets (9) through wrapping means (7) around the plug (4) to provide segregated peripheral venting of the filter. Further apertures (10) in the wrapping means (7) communicate directly with the filter plug away from the ducts (5), to permit ambient air to enter the filter plug to mix with and dilute the smoke being filtered within the plug. In one embodiment of the invention mixing of ambient air with smoke being filtered within the plug is facilitated by provision of a circumferentially extending channel (13) which is in register with said further apertures.

Description

This invention relates to smoke filters for use with smoking articles, cigarettes for example.

A number of proposals have heretofore been made for cigarette filters having provision for the ingress of ventilation air into ducts extending at the periphery of the filter to the mouth end thereof and serving to convey the air to the smoker's mouth without any, or substantially any,' mixing of the air within the filter with tobacco smoke drawn through the filter. Such mode of filter ventilation may be referred to as segregated peripheral ventilation.

It has been claimed for segregated peripheral ventilation filters that they enhance the quality of the tobacco smoke as perceived by the smoker.

The present invention provides a smoke filter comprising a rod-like plug of filtration material and having at least one airflow duct moulded in the periphery of the rod-like plug with air-impervious walls, said at least one duct extending along said plug between a first end of the duct open at the mouth end of said plug and a second end open at the periphery of said plug, said at least one duct being shorter than said plug; and wrapping means enwrapping said plug and permitting the ingress of a first stream of ambient air into said at least one airflow duct at a location spaced from said first end and also permitting the ingress of a second stream of ambient air into the interior of said plug, other than by way of the said at least one air duct and other than by way of the end face of the plug at the end opposite the mouth end, wherein said wrapping means is generally air-permeable but has a less permeable outer layer provided with first and second ventilation perforations to pass the respective first and second streams of ambient air. Suitably, the second ventilation perforations are located over a region of the periphery of the filter plug longitudinally spaced from a region thereof at which extend the airflow ducts. Conveniently, the airflow duct is partly defined by a number of grooves in the peripheral surface of the filter plug, as well as by the wrapping means or inner layer thereof. The grooves may extend parallel to the axis of the filter plug or may be helical. There may be two sets of helical grooves of opposite hand so that the grooves of one set intersect the grooves of the other set.

The plug of filtration material may be other than of unitary form. For example, it may comprise two abutting sub-plugs, in which case one sub-plug may be provided with grooves bounding the airflow duct.

By use of a filter according to the invention on a cigarette, an unexpected improvement in the taste of the mainstream smoke is obtainable over that perceived when a filter is employed of which the only mode of ventilation is segregated peripheral ventilation· In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing,in which:FIGURE 1 shows a part view, in axial section, of a 10 filter-tipped cigarette? FIGURE la shows a cross-sectional view of half of the cigarette of Figure 1 taken along line A-A thereof; FIGURE 2 shows a filter plug of an alternative form from that of the cigarette of Figure 1; and FIGURE 3 shows, partially in axial section, a further alternative form of filter plug· The cigarette of Figure 1 comprises a rod 1 of cut tobacco enwrapped in cigarette paper 2, and a filter 3 comprising a self-sustaining filter plug 4 of fibrous cellulose acetate filtration material. At the periphery of the plug 4 there extend a series of grooves 5 - see also Figure la. The grooves 5 open at the mouth end of the plug 4 and extend parallel to the plug axis for about half the length of the plug 4. A convenient method'of forming the grooves 5 is to subject the plug 4, or preferably a piece of filter rod material fran which everal of the plugs 4 are to be cut, to a hot moulding process such as, for example, that disclosed in British Patent Specification No. 1,507,765. Sealing of the walls of the grooves 5 may be assured by the application thereto of a sealant material, polyethylene for instance* Serving to secure the filter 3 to the cigarette rod 1, 2 is a tipping 7. In the portions where it overlies the grooves 5, the tipping 7 defines, together with the walls of the grooves 5, airflow ducts 8. In the tipping 7 are two rows of ventilation perforations 9 and 10. As is indicated in Figure 1, the row of perforations 9 encircles the plug k at that portion thereof at which the grooves 5 extend, the arrangement being such that at least one of the perforations 9 is in communication with each of the airflow ducts 8. lhe row of perforations 10 encircles a portion of the plug 4 into which tbe grooves 5 do not extend.

The perforations 9 and 10 may, if desired, be formed as micro-perforated regions of the tipping 7.

The tipping 7 overlies a plug wrapper of airpervious quality so that the tipping serves as a less permeable outer layer in which the ventilation perforations are provided. •6 :g When the cigarette of Figure 1 is smoked, ambient air is drawn in through the perforations 10 directly into the filter plug 4 and mixes with tobacco smoke passing through the latter. Ambient air is also drawn inseparately through the perforations 9 into the airflow ducts β and passes along the ducts to the outlet ends thereof unmixed, or substantially unmixed, with smoke.

The filter plug shown in Figure 2 and generally designated 11 is one which may be used in place of the plug 4 of Figure 1. The plug 11 is provided with a number of equally-spaced longitudinal grooves 12 which open at the mouth end of the plug and extend therefrom for substantially less than the full length of the plug 15 In a portion of the plug 11 clear of the longitudinal grooves 12 the plug is provided with a deep annular circumferential channel 13. The longitudinal grooves 12 and circumferential channel 13 may conveniently be formed by a hot; moulding process. When the plug 11 20 is incorporated in a filter-tipped cigarette, it is enwrapped in a wrapping which is constructed to permit the ingress of a first stream of air directly into airflow ducts bounded by the walls of the longitudinal grooves 12 and by the inwardly facing surface of the wrapping, and a second, separate stream of air into the circumferential channel 13. The second stream of air directly enters the interior of the plug 11, mainly through the downstream side wall of the circumferential channel 13.

If a tipping wrapper surrounding the filter plug 11 is provided with a row of perforations (like the perforations 9 of Figure 1) in register with the portion of the plug in which the longitudinal grooves 12 extend and if sane intermediate ones of the perforations in that row are disposed between the longitudinal grooves, air may be prevented fran entering the interior of the plug 11 through such intermediate perforations by applying a sealant to the peripheral surface of the plug 11. Alternatively, the plug 11, or a piece of filter rod of which the plug 11 initially formed part, may be enwrapped in a non-pexmeable wrapper of thermoplastic character prior to being hot-moulded to provide the longitudinal grooves 12 and the circumferential channel 13. In the latter case the hot-moulding of the comparatively shallow longitudinal grooves 12 leaves the non-permeable wrapper substantially intact, whereas little or no remnant of the wrapper is observable in the deep circumferential channel 13* Thus the walls of the longitudinal grooves 12 are air-impermeable and at least the side walls of the circumferential channel 13 are air-permeable· Figure 3 shows another form of filter plug, generally designated 14, which may be used in place of the plug 4 of Figure 1. Plug lU is provided with a number of equally-spaced, helical grooves 15 which extend from the mouth end of the plug 14 and may be formed by a hot-moulding process· Plug 14 is also provided, clear of the grooves 15. with a number of holes 16 extending radially inwardly fran the peripheral surface of the plug· The holes 16 may be formed mechanically or by a laser, formation of the holes conveniently taking place after assembly of the plug 14 with a cigarette rod so that the step of forming the holes 16 also results in the perforation of the wrapper.

Although the above described filter plugs are of a unitary nature, dual element plugs could be used, such that a first element has grooves formed in it extending fran the mouth end of the first element, and the second element has means for permitting the ingress of air into the interior of the second element. The grooves in the first element could extend for the full length of the first element. If such dual element plugs are wrapped :όίθ in respective plug wrappers, conveniently the wrapper of the first element ia air-impervious and that of the second element is air-pervious.

The air/smoke regime issuing fran each of the above 5 described filters, as far as it is due to the segregated peripheral ventilation, is modified by the establishment within the filter of an air/smoke flow by virtue of the direct ventilation air flow into the interior of the filter plug. This modification effect results in an unexpected improvement in the taste of the mainstream smoke.

The various perforations 9, 10 and lfeshown in the drawing are not to scale and are exaggerated for ease of illustration.

Claims (11)

1. A smoke filter comprising a rod-like plug of filtration material and having at least one airflow duct moulded in the periphery of the rod-like plug with air-impervious walls, said at least one duct extending 5 along said plug between a first end of the duct open at the mouth end of said plug and a second end open at the periphery of said plug, said at least one duct being shorter than said plug; and wrapping means enwrapping said plug and permitting the ingress of a first stream 10 of ambient air into said at least one airflow duct at a location spaced from said first end and also permitting the ingress of a second stream of ambient air into the interior of said plug, other than by way of the said at least one air duct and other than by way of the end 15 face of the plug at the end opposite the mouth end, wherein said wrapping means is generally air-permeable but has a less permeable outer layer provided with first and second ventilation perforations to pass the respective first and second streams of ambient air. 20

2. A filter according to claim 1, wherein the at least one airflow duct extends over a first region of the plug and the second ventilation perforations are located over a second region of the periphery of the 'plug which is spaced longitudinally from said first region.

3. A filter according to claim 2. and including a circumferentially extending channel in the plug at said second region; said channel being in register with the permitted ingress of the second stream of ambient air, and being effective to admit the second stream directly into the interior of the plug.

4. A filter according to any one of claims 1 to 3, wherein said ventilation perforationscomprise micro-perforated regions of the wrapping means to permit the ingress of at least one of said first and second streams of ambient air through the wrapping means.

5. A filter according to any one of the preceding claims, wherein there is a plurality of said airflow ducts eguiangularly spaced around the periphery of said plug.

6. A filter according to claim 5, wherein each said airflow duct is defined partly by a respective groove in the peripheral surface of the plug and also partly by the radially inwardly facing surface of said wrapping means.

7. A filter according to any one of the preceding claims, wherein said plug comprises two abutting sub-plugs, one of said sub-plugs being provided with said at least one airflow duct, and the other being devoid of such airflow ducts.

8. A filter according to any one of claims 1 to 7, wherein said at least one airflow duct extends helically of said filter plug starting frcm the mouth end of the plug. 5

9. A filter according to any one of the preceding claims wherein said location is at said second end of said at least one airflow duct.

10. A filter substantially as hereinbefore described with reference to, and as illustrated in, Figures 1 and la, 10 or Figure 2, or Figure 3, of the accompanying drawings.

11. A smoking article including a tobacco rod and a filter according to any one of the preceding claims.