GB2091078A - Ventilated cigarette filter - Google Patents

Abstract

A cigarette filter rod comprises a plug (10) of tobacco smoke filtering material, a tubular wall (12) in longitudinal alignment with the plug and extending to one end of the rod, and wrapping (14) around the plug and tubular wall, the rod thus having a cavity (18), extending from the plug and defined by the tubular wall, which opens at that end of the rod, the wrapping or the wrapping and the tubular wall providing, when the filter rod is drawn on in use, for the ingress of external air laterally into the cavity. Such a rod (6) may be attached to a wrapped tobacco rod (2), with tubular wall (12) open to the latter or to the buccal end, by means of a tipping overwrap (8) having perforations (16) for the passage of ventilation air. The rods may be made in continuous lengths which are cut into finite lengths as convenient for storage and handling and subsequent application to cigarettes. <IMAGE>

Description

SPECIFICATION Cigarette filter This invention relates to cigarette filters, and provides a cigarette filter rod comprising a plug of tobacco smoke filtering material, a tubular wall in longitudinal alignment therewith and extending to one end of the rod, and wrapping around the plug and tubular wall, the rod thereby having a cavity extending from the plug and centrally of the tubular wall to open at the one end of the rod, and said wrapping or wrapping and tubular wall providing, when the filter rod is drawn on in use, for the ingress of external air laterally therethrough into said cavity.

In some embodiments, the tubular wall extends from the plug and is of porous air-permeable material, e.g. tobacco smoke filter material, with the wrapping therearound being perforate and/or of inherently air-permeable material; the tubular wall could instead be of inherently air-impermeable material (e.g. a plastics or cardboard sleeve) with holes therethrough, the wrapping therearound being of airpermeable material and/or having perforations in communication with the holes in the tubular wall.

When the tubular wall is of air-permeable material, it may also have holes therethrough to facilitate the said lateral ingress of external air.

In other embodiments the tubular wall is spaced longitudinally from the plug, the wrapping providing for the ingress of external air laterally through the wrapping into the space between the plug and tubular wall. In these cases the tubular wall may be impermeable, all of the ventilation being directly into the said space; orthe wrapping and tubular wall can be as described for the first-mentioned embodiments, allowing for some lateral ingress of external air through the wrapping and wall. As in all embodiments the wrapping may be perforate and/or of inherently air-permeable material where the air is to pass laterally therethrough.

The above types of embodiment of filter rod according to the invention, when used in a filter cigarette, will usually be attached to the wrapped tobacco rod by a tipping overwrap; the tipping overwrap will normally be of substantially airimpermeable material having perforations in a region where it surrounds the tubular wall and/or (in the embodiments where there is such a space) around the space between plug and tubular wall.

In filter rods according to the invention there will usually be substantially no lateral ingress of external air into the plug. The said lateral ingress of external air into the cavity may be the sole air dilution or ventilation provided by the plug/tubular wall/wrap- ping combination in the use of filter rods according to the invention. In filter cigarettes incorporating filter rods according to the invention, the cigarette paper around the tobacco rod is preferably substantially air-impermeable, with air dilution or ventilation in use occurring substantially only via the filter rod; if the cigarette paper is appreciably air permeable the degree of air dilution and of CO removal vary unacceptably as the smoking of the cigarette proceeds, decreasing from first to last puff, with unacceptably low taste delivery over the first puffs.

The various dimensions of the filter rods according to the invention (e.g. lengths of plug and tubular wall and of any space therebetween, thickness of tubular wall), and the structure and composition of the components, may be chosen to give the overall properties - e.g. pressure drop, degree of air dilution, filtration efficiency - required; the filter characteristics will preferably be designed, according to the characteristics of the wrapped tobacco rod with which the filter is to be used, to provide a filtered cigarette having the required smoking properties.

In filter rods according to the invention, the arrangement is preferably such that the majority (most preferably the great majority, e.g. subftantially all) of the pressure drop due to the plug/tubular wall combination is provided by the plug, with correspondingly little (e.g. substantially no) pressure drop being provided by the tubular wall portion.

Ventilated or air dilution cigarette filters are known to reduce the proportion of harmful CO delivered by the filter cigarette; with prior filter structures, however, the reduction in CO delivery has been generally proportional to the degree of air dilution but with corresponding proportional reduction in the delivery of taste components to the smoker, so that desirable high CO reduction due to a high degree of air dilution has resulted in an unacceptably tasteless smoke.

Tests on cigarettes provided with filters according to the invention, with the open end of the said cavity against the tobacco rod, have shown an unexpectedly high degree of CO reduction in the delivered smokeforthe degree of air dilution concerned, without undue reduction in the delivery of taste components.

In other embodiments of the invention, the filter cavity is open at the buccal end of the filter cigarette, the arrangement preferably being such that most or substantially all of the filter pressure drop occurs upstream (i.e. towards the tobacco rod) from the region of lateral ingress of external air into the cavitye.g. where filter and tobacco rod are joined by a tipping overwrap having ventilating perforations, the latter will preferably be disposed downstream of the plug. In such filter cigarettes according to the invention, particularly those with the filter pressure drop substantially all upstream of the ventilation region, the tar yield may be reduced more by air dilution than by mechanical filtration.Prior conventional filters designed for low mechanical filtration efficiency with high air dilution suffer the severe disadvantage of exhibiting an unduly low pressure drop which is frustrating and unacceptable to the smoker. In the filter cigarette according to the invention, however, with the plug portion towards the tobacco rod and the cavity portion open at the buccal end, high levels of ventilation can be provided at acceptable overall pressure drops and desired low retention (mechani cal filtration) levels. The high air dilution/lovv retention filter cigarettes according to the invention, with cavity open at the buccal end, can have CO/tar yields lowerthan those obtainable by use of conventional filters.The filters according to the invention with cavity open to the buccal end can provide a pieasing end appearance both before and to the end of smoking; as the smoke passes out along the cavity, the material of the tubular wall remains substantially unstained during smoking and so retains its initial clean appearance throughout.

Filter rods according to the invention will normally be produced continuously in continuous lengths which are cut to the required finite lengths for handl ig and use. Thus, in filter cigarette production, a double length filter rod is normally assembled and joined by tipping overwrap between a pair of tobacco rods, the assembly being severed centrally to give two filter cigarettes; and the initially produced continuous rod will normally be cut initially into multiple (e.g. sextuple) lengths for delivery to the filter cigarette manufacturer who would cut these multiple length units into the double length units for use in the assembly as previously described.Accordingly, the invention also embraces the continuously produced rod of alternating plugs and tubular walls with the wrapping therearound, and the multiple and double length rods obtained therefrom by cutting transversely through the plug andssor tubular wall sections. The plug and tubular wall sections may abut or be longitudinally spaced.

The invention is illustrated, by way of example only, by the accompanying drawing, in which: Figure 1 is a schematic longitudinal sectional view of a filter cigarette provided with a filter rod according to the invention, with the filter cavity open to the tobacco; Figure 2 is a similar schematic view of a filter cigarette provided with a different filter rod according to the invention, the filter cavity still being open to the tobacco; and Figures 3 and 4 are similar schematic views of respective filter cigarettes with filters according to the invention with the filter cavity open at the buccal end.

The Figures, in which like reference numerals indicate like parts, are not to scale.

The filter cigarette illustrated in Figure 1 has a conventional tobacco rod 2 wrapped in conventional substantially air-impermeable cigarette paper 4 and joined to a filter 6 according to the invention by a conventional tipping overwrap 8 of substantially airimpermeable paper. The filter 6 has a plug 10 of tobacco smoke filtering material abutting a tubular wall 12 of tobacco smoke fiitering material, the two being joined by air-permeable wrap 14. Plug 10 may be any conventional smoke filter element e.g. one made of corrugated paper or of cellulose acetate filaments bonded at points of contact, and separate tubular wall 12 may similarly be of smoke filtering material.Tipping overwrap 8 has a circumferential ring of perforations therethrough around the tubular wall 12 providing vents 16 through which, when the filtered cigarette is drawn on during smoking, exter nal air is drawn via wrap 14 andtubularwall 12 into the cavity 18.

The plug 10 may for example be of bonded cellulose acetate filaments and made as described in UK specification No. 1,169,932; tubular wall 12 maybe of like material, made for example as described in the latter specification but with a central mandrel extending through the bore of the steam chamber or as described in UK specification No. 970817. Tubular wall 12, even though of inherently permeable material, may have lateral perforations, as indicated in broken iines at 20, to facilitate the air dilution; such holes are essential for the purposes of the invention when, as in other embodiments with the illustrated structure, tubular wall 10 is of inherently impermeabie material.

The embodiment illustrated in Fig. 2 differs in that the plug 10 and tubular wall 12 are separated by a space 22, with the perforations 16 in overwrap 8 being provided in a ring around this space. Plug 10 may for example be about 10 mm. long, space 22 about 5 mm. long, and tubular wall 12 about 15 mm.

long, and the plug, tubular wall and plug wrap may be ofthe materials mentioned in connection with Fig. 1.

The following is a specific example of a filter cigarette incorporating a filter according to the invention of the type of construction illustrated in the accompanying drawing.

EXAMPLE Filter cigarettes of the type shown in Fig. 1 were made by assembling standard cigarette tobacco rods 2 (wrapped in conventional low-porosity cigarette paper 4) with respective filter rods 6 using conventional Ecusta (Registered Trade Mark) tipping overwrap 8; the latter is of impermeable paper with three rings of perforations 16 instead of the single ring shown in the drawing.

In each case plug 10 was a 10 mm. long nonwrapped porous plug of bonded cellulose acetate filaments (2.5 filament denier, 56 x 103total denier) having a pressure drop (PD) of about 67 mm.; tubularwall 12 was similarly a porous wall of bonded cellulose acetate filaments, being 15 mm. long and 1 to 2 mm. thick and being without any lateral holes 20; plug 10 and tubular wall 12 were held together to form a filter rod according to the invention by a porous paper plugwrap 14 having an air permeability of 100 K ascertained as described below. The filtered cigarettes were designed to give about 50 vol.% air dilution (ventilation).

Twenty substantially identical such filter cigarettes were smoked (on a standard smoking machine according to the standard smoking test regime) with the vents 16 open, and another 20 were likewise smoked with the vents closed; the results were averaged and are shown in the following Table. In the Table, the pressure drops (PD) are expressed in mm.

Wg. (mm. water gauge) as measured at an air flow rate of 17.5 ml/sec; TPM means total particulate matter; and WNF means water- and nicotine-free.

TABLE Vents Vents Open Closed Ventilation vol.% via filter rod 6 47.7 via cigarette wrapper 4 7.5 Total Cigarette PD mm. Wg. 89 113 Filter Rod PD mm. Wg. 67 TPM Yield mg/cigarette 10.8 21.0 TPM (WNF) Yield mg/cigarette 8.6 16.5 Nicotine Yield mg/cigarette 1.13 1.55 COYieldmg/cigarette 4.99 16.73 Nicotine Retention % 37.5 37.5 Puffs/cigarette 9.4 8.1 % Reduction TPM 48.6 TPM (WNF) 47.9 Nicotine 27.1 CO 70.1 CO/TPM(WNF) ratio 0.58 It will be seen that the filter rods according to the invention (vents 16 open) gave excellent reduction in CO delivery, this reduction being greater than that obtainable with conventional ventilated filters at the same percentage air dilution.

Figures 3 and 4 illustrate filter cigarettes according to the invention made of components essentially the same as those of the Figures 1 and 2 embodiments but with the filter portion reversed so that the cavity 18 is open at the buccal end. Thus in Figures 3 and 4 the plug 10, tubular wall 12, wrapping 14 and tipping overwrap 8 may be of the same respective materials and dimensions as suggested above in connection with Figures 1 and 2. In each case, plug 10 adjacent to the wrapped tobacco rod 2 may give relatively little particulate retention but provide virtually all of the filter pressure drop, with the air dilution via perforations 16 into cavity 18 occurring wholly downstream of plug 10, thus allowing for high levels of air dilution and low mechanical retention at an acceptably high overall pressure drop.

Herein, an air permeability of nK means an air permeability of n x 1000 mis/minute /10 square cms. 100 mm Wg. pressure - as determined by measuring the pressure "p" in mm.Wg. (water gauge) generated by a flow of 1050 mls. of air per minute through 10 square cms. of the paper, and calculating from the equation: air permeability = 1050 x 100 P

Claims (23)

1. Acigarette filter rod comprising a plug of tobacco smoke filtering material, a tubular wall in longitudinal alignment therewith and extending to one end of the rod, and wrapping around the plug and tubular wall, the rod thereby having a cavity extending from the plug and centrally of the tubular wall to open at the one end of the rod, and said wrapping or wrapping and tubular wall providing, when the filter rod is drawn on in use, for the ingress of external air laterally therethrough into said cavity.

2. A filter rod according to claim 1 wherein the tubular wall extends from the plug and is of airpermeable material.

3. Afiiter rod according to claim 1 or 2 wherein the tubular wall is a perforate element abutting the plug.

4. A filter rod according to claim 1 wherein the tubular wall is a separate element longitudinally spaced from the plug, the portion of the wrapping around the space between the plug and tubular wall being of air-permeable material and/or perforate.

5. A filter cigarette provided with a filter rod according to any preceding claim with tubular wall between the plug and tobacco rod.

6. A filter cigarette provided with a filter rod according to any of claims 1 to 4 with plug between tubular wall and tobacco rod.

7. Afilter rod which is cuttable transversely into individual cigarette filter rods according to claim 1 and comprises plugs of tobacco smoke filtering material alternating along the rod with tubular walls in longitudinal alignment therewith, and wrapping around plugs and tubular walls, the rod thereby having cavities extending from each plug and centrally of each adjacent tubular wall, said wrapping or wrapping and tubular walls providing for the ingress of external air laterally therethrough into said cavities.

8. A filter rod according to claim 7 having a cavity at each end.

9. Afilter rod according to claim 7 having a plug at each end.

10. A filter rod according to any of claims 7 to 9 wherein each tubular wall abuts against the adjacent plug and is perforate and/or of air-permeable material.

11. A filter rod according to any of claims 7 to 9 wherein adjacent plugs and tubular walls are longitudinally spaced, said wrapping around each said space being perforate and/or of air-permeable material.

12. A cigarette filter rod substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

13. A cigarette filter rod substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

14. A cigarette filter rod substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

15. A cigarette filter rod substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

16. A filter cigarette substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

17. A filter cigarette substantially as herein before described with reference to Fig. 2 of the accompanying drawings.

18. A filter cigarette substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

19. A filter cigarette substantially as herein before described with reference to Fig. 4 of the accompany- ing drawings.

20. A cigarette filter rod substantially as herein before described in the Example.

21. A fi Iter cigarette substantially as hereinbefore described in the Example.

22. A multiple-length filter rod substantially as hereinbefore described.

23. A sextuple-length filter rod substantially as hereinb#ore described.