GB2064293A - Fibrous carbon cigar filter - Google Patents

Abstract

A cigar is provided with a filter section (2) composed of a mass of flexible fibres of a carbonaceous material which has been produced by the controlled pyrolysis of a fibrous cellulose precursor. <IMAGE>

Description

SPECIFICATION Cigar Cigars are conventionally not provided with filter tips.The reasonforthis is not entirely clear. It may be because the cigar smoker expects a rich smoke and filtering might reduce the richness of the smoke.

Another possible reason is that the outer wrapper of a cigar is usually natural leaf extending from end to end of the cigar and this precludes the attachment of a preformed filter tip section by a subsidiary end wrapper. Also the incorporation of a preformed cylindrical filter tip section would be difficult in cigars having a shaped and tapering buccal end.

Nevertheless it is desirable to achieve some control of cigar smoke yields so that products having different characteristics may be produced. This is most readily achieved by filtration of the smoke.

In accordance with the present invention, a cigar comprises an outer wrapper of synthetic or natural tobacco leaf surrounding a filler which incorporates, adjacent to a buccal end of the cigar, a filter section composed of a mass of flexible fibres of a carbonaceous material which has been produced by the controlled pyrolysis of a fibrous cellulose based pre cursor, the organic residue of the precursor, exclud- ing additives, containing at least 80% carbon by weight.

By appropriate choice of precursor material, dimensions, and extent of pyrolysis, the mass of carbonaceous fibrous material can be arranged to have properties of packing hardness, porosity, and other handling characteristics not unlike that of the natural cigar filler so that the filter section can be integrated with the filler with the minimum of inter- ference with the appearance and feel of the cigar, and its assembly.

The filter section might be exposed at the buccal end of the cigar or, in order that the smoker can still appreciate the taste of the tobacco filler on his tongue at the buccal end, the filter section may be sandwiched between the bulk of the tobacco filler and a short section of the tobacco filler immediately at the buccal end. Experiments have shown that the filter section is undetectable to the smoker if positioned at least 5 mm. from the buccal end and sandwiched by tobacco filler. In any case the fibrous mass of filter material will preferably be dark in colour so that it will appear as tobacco fillerto the casual glance. If necessary, it may be stained to a brown colour, thus more accurately reproducing the colour of natural substitute tobacco filler.

We find that the fibrous mass of filter material forms an effective mechanical filter for the particulate matter in the smoke and also an effective filter for vapour phase constituates such as hydrogen cyanide, formaldehyde and other volatile aldehydes.

A reduction in these components leads to a reduction in harshness and consequently an improvement in taste of the smoke. The filtration from the tobacco smoke of selected vapour phase components may be enhanced if the carbonaceous fibrous material is activated in conventional manner.

A particular advantage of the use of a carbonaceous filter material is that, unlike some more conventional filter materials it produces no noxious or potentially toxic products when strongly heated or burned. This is particularly so when the organic content of the precursor contains only carbon, hydrogen and oxygen. The organic residue of the precursor contains at least 80% carbon by weight, implying that the pyrolysis has been carried out up to a temperature of between 700" and 900"C or more. The essential combustion products of the pyrolysed material will then be carbon dioxide and water.

It is not in fact necessary for the filter material to be combustible and indeed if it is essentiaily incombustible, when the cigar is burnt down to the filter section, it will extinguish. However the resulting exposed carbonaceous fibres of the filter material may be somewhat unsightly and this would normally be avoided if the filter material is combustible.

If it is combustible, the filter material may be treated with a combustion modifying agent, such as an inert oxide or salt of calcium, magnesium or zinc whereby if it is accidentally burned, it will produce a ash similarto that produced by cigar filler so that the smoker still receives the impression that he is smoking a conventional all tobacco cigar. Of the available combustion modifying agents, calcium ions are preferred. These may be applied to the precursor prior to pyrolysis in the form of calcium carbonate, calcium nitrate or calcium formate.

The fibrous carbonaceous material may be manufactured by the pyrolysis of a fibrous cellulose precursor, particularly viscose fibres, preferably having a denier of between 0.5 and 20. The denier is important as viscose fibres with a denier of greater than 20 tend to produce carbonaceous fibres which are too brittle to be easily processed, while fibres with a denier of less than 0.5 may result in an unacceptably high pressure drop in the finished filter section. Carbonaceous fibres derived from 8 denier viscose appear to be close to the optimum, resulting in desirable filtration characteristics and an acceptable firmness in the finished cigar. It is also desirable that the viscose fibres should be crimped, preferably with between 4 and 8 crimps per cm., as this increases the firmness of the filter section.

The viscose fibres may be in the form of a tow, a sliver of staple fibres, or a non-woven, e.g. needled, mass of staple fibres. A strand, i.e. a tow or sliver may be simplerfor mass production of the filter sections, the strand being pyrolysed and treated as necessary prior to being chopped to length. The linear mass of the strand will depend upon the cross sectional area of the cigar. However irrespective of the origin of the fibrous carbonaceous filter material, it is desirable that the carbonaceous fibres be packed in the filter section at a density of between 0.05 and 0.18 g/cm3.

The viscose or other cellulose based fibres are preferably pyrolysed in a non-oxidising atmosphere, such as nitrogen, to a final temperature of between 600 and 900"C. The pyrolysis is preferably such that the organic residue of the precursor contains at least 95% carbon by weight, and has an oxygen content between 1 and 4% and a hydrogen content of less than 1% by weight. The production of activated car bon fibres may be brought about by using, in con ventional fashion, atmospheres of carbon dioxide, steam, or chlorine for all or part of the pyrolysis cycle. Additional activating pretreatments and yield improving agents, such as calcium formate, phosphoric acid, or a chloride of calcium, aluminium, zinc or copper, may be used.

Further details of the preparation of a suitable fibrous mass of carbonaceous filter material are disclosed in our British Patent Specification No.

1,431,045, and our DOS 2744728 which corresponds with the cognate Complete Specification filed on our British Patent Application No. 41271/76 et al. These specifications refer to the preparation of a flexible fibrous carbonaceous fuel but the same process is applicable to the production ofthe present filter material. However, the physical dimensions of the fibres and the pre-treatments of the material referred to in our earlier specifications, are of lesser importance in the present context.

Example of cigars incorporating filter sections in accordance with the invention will now be described: Example A.

A medium sized cigar of approximately 12.7 cm. in length and 12 x 10 mm. in cross section is provided adjacent to its buccal end with a filter section composed of a substantially incombustible mass of carbonaceous fibres packed to a density of 0.125 g/cm3.

The fibrous filter material had been produced from a sliver of staple, round cross-section, 8 denier, viscose staple fibres having four crimps per cm. and containing 1.5% by weight titanium dioxide, supplied by Courtaulds under the trade name Evlan. The sliver of viscose fibres had been subjected to a controlled pyrolysis in an atmosphere of nitrogen to a final temperature of 780"C. The linear contraction of the sliver during the pyrolysis was found to be substantially 13% and the pyrolysis yield 15%. Various lengths of filter section and correspondingly varying weights of filter material were incorporated in the cigar and the reduction in particulate matter and nicotine when the cigar is smoked is apparent from Figures 1 and 2 of the accompanying drawings. The reduction in such smoke components was deter mined using standard methods.Thus the cigar was smoked to a 40 mm. butt length using a puff volume of 35 cm3., a puff duration of 2 seconds and an inter puff interval of 58 seconds.

Example B.

Example A was repeated except that the strand of viscose fibres was pretreated prior to the pyrolysis by being dipped in an aqueous solution of calcium formate and dried to leave a deposit of between 1.0 and 2.5, preferably 1.5% weight for weight calcium formate to viscose. In this case the pyrolysis yield was 16% and the resulting carbonaceous fibres were combustible. The reduction in particulate matter and nicotine for various lengths/weights of filter material also appear in Figures 1 and 2.

Example C.

Example A was repeated except that in this case the strand of viscose fibres was given a yield improving pretreatment with zinc chloride to leave a deposit of 0.4 moles/Kg. of viscose. In this case the pyrolysis yield was 23% and the resulting carbonaceous fibres were substantially incombustible. Again the reduction in particulate matter and nictone when the cigar was smoked are shown in Figures 1 and 2.

Example D.

Example Cwas repeated except that in this case the pyrolysis was carried out under an atmosphere of carbon dioxide, the heating rate being 8"C per minute up to 780"C, this temperature being held for 15 minutes before cooling. This treatment results in activated carbon fibres and a pyrolysis yield of 20%.

A filter section of length 20 mm. and weight 300 mg.

in the cigar resulted in a whole smoke formaldehyde reduction of 21%, obtained using a similar procedure as before.

We believe that the maximum desirable reduction in tar and nicotine levels for average size cigars is about 25% with an optimum range between 5 and 15%. The above examples indicate that such level reductions can be obtained utilizing filter section lengths of between 5 and 15 mm. with an optimum length of about 10 mm.

Figure 3 of the accompanying drawings is a diagrammatical axial section through a typical cigar in accordance with the invention. The illustrated cigar has a conventional tobacco filler 1 and a filter section 2 of the carbonaceous fibres sandwiched between the main filler 1 and a buccal end section 3 of natural tobacco all within a binder 4. A conventional outer leaf wrapper 5 surrounds the binder 4.

Claims (9)

1. A cigar comprising an outer wrapper of synthetic or natural tobacco leaf surrounding a filler which incorporates, adjacent to a buccal end of the cigar, a filter section composed of a mass of flexible fibres of a carbonaceous material which has been produced by the controlled pyrolysis of a fibrous cellulose based precursor, the organic residue of the precursor, excluding additives, containing at least 80% carbon by weight.

2. A cigar according to claim 1, in which the organic content of the precursor contains only carbon, hydrogen and oxygen.

3. A cigar according to claim 1 or claim 2, in which the fibrous cellulose based precursor comprises viscose fibres.

4. A cigar according to claim 3, in which the viscose fibres have a denier of between 0.5 and 20.

5. A cigar according to claim 3 or claim 4, in which the viscose fibres are crimped.

6. A cigar according to any one of the preceeding claims, in which the carbonaceous fibres are packed in the filter section at a density of between 0.05 and 0.18 g/cm3.

7. A cigar according to any one of the preceding claims, in which the carbonaceous fibres are com bustible and incorporated a combustion modifying agent.

8. A cigar according to claim 7, in which the combustion modifying agent includes calcium ions.

9. A cigar according to claim 1, substantially as described with reference to any one of the examples.