GB2118423A - Tobacco smoke filter - Google Patents

Abstract

A ventilated tobacco smoke filter whose retention of particulate matter is due more to air dilution than to mechanical filtration comprises a ventilating wrapper around a rod providing a multiplicity of capillaries extending longitudinally of the rod and formed by a bundle of coarse filaments extending longitudinally of the rod or by longitudinally corrugated and/or at least partially fibrillated sheet, film or foil of zero or low smoke permeability material gathered laterally into rod form.

Description

SPECIFICATION Tobacco smoke filter The present invention concerns tobacco smoke filters and provides a ventilated tobacco smoke filter comprising a ventilating wrapper around a rod providing a multiplicity of capillaries extending longitudinally of the rod and formed by a bundle of coarse filaments extending longitudinally of the rod or by longitudinally corrugated and/or at least partially fibrillated sheet, film, or foil of zero or low smoke permeability material gathered laterally into rod form.

The multi-capillary rod around which the ventilating wrapper is engaged is preferably a laminarflow body, i.e. such that in normal use (e.g. when incorporated in a filter cigarette and smoked on a standard smoking machine at through-flow rates of up to 17.5 ccs. per second) the flow of air and smoke therethrough is substantially laminar rather than turbulent.

The coarse fibres, preferably of 20 or more (e.g.

about 100) denier per filament (dpf), are preferably smooth surfaced and of low or zero absorbency; coarse cellulose acetate or polyolefin (e.g. polypropylene) filaments are suitable. Suitable sheet, film or foil for use in the invention includes plastics (e.g.

polyolefin, such as polyethylene), metal (e.g. aluminium) and cellulose (e.g. cellophane) sheet, film or foil, and preferably has a maximum air permeability of 0.1 K Filtrona units.

Herein, an air permeability of nK Filtrona units 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 sheet, film or foil and calculating from the equation 1050 x 100 air permeability = Filters according to the invention permit the achievement of high degrees of air dilution (e.g. 50% or more) to give good particulate matter reduction whilst retaining an acceptable perceived pressure drop.Thus they may reduce tar yield mainly by air dilution ratherthan mechanical filtration, whilst maintaining a relatively high filter pressure drop (PD) compared to that of a conventional filter with the same tar retention and air dilution. Afilter according to the invention may reduce CO preferentially with respect to tar. This is achieved by using a filter with a relatively low mechanical efficiency in conjunction with relatively high air dilution (e.g. 50% or more).

Conventional filters, constructed for example of 12 dpf (denier per filament) cellulose acetate, which provide relatively low mechanical efficiency, have the disadvantage that when used in conjunction with high levels of air dilution, unacceptably low filter and filter cigarette PD's are obtained. Filters according to the present invention provide low mechanical retentions, whilst maintaining a relatively high PD compared to that of conventional filters.

In a filter cigarette employing a ventilated filter according to the invention, the percentage air dilution via the filter is preferably greater than the percentage "non-ventilated" or "enclosed" tar retention of the filter - i.e. that measured for an equivalent filter and cigarette with air dilution via the filter prevented.

Cigarettes provided with filters according to the invention may yield a CO/tar ratio lower than that of cigarettes of the same tar yield using conventional ventilated filters (for which the ratio is generally about unity), by increasing the contribution of ventilation and decreasing the contribution of mechanical retention to tar reduction, but maintaining a similar cigarette draw resistance.

The percentage air dilution as referred to herein is the percentage by volume of ventilating air added via the filter in the total mixture delivered by the filter; thus 50% ventilation or air dilution means that in each puff there is a 50/50 volume ratio of added air to original smoke, and 40% air dilution indicates a 40/60 ratio, and so on.

Preferably the enclosed filter (i.e. with air dilution prevented) will have a PD of at least 80 or 90 mm.

and a mechanical tar retention of at most 45%.

Standard length (about 25 mm) cigarette filters according to the invention may for example exhibit an enclosed pressure drop of 80 to 100 mm.Wg. at an enclosed total particulate matter retention of 12 to 40%.

Filters according to the invention can be designed, by choice of length, of core material, structure, and packing density etc., and of percentage air dilution, to provide with any given tobacco rod any acceptable predetermined overall ventilated filter cigarette PD - e.g. 80 to 120 mm.Wg., currently preferably about 80 or about 90 or about 100 mm.Wg. However, much higher or much lower (e.g. 70, 60, 50, 40, 30 or even 25 mm.Wg.) ventilated filter cigarette PD's can be provided as current requirements dictate, in each instance more satisfactorily than is possible with conventional filter structures.

The ventilating wrapper may be of inherently air-permeable and/or perforate material. It may be the tipping overwrap by means of which the filter is incorporated in a filter cigarette, in which case it will normally be of air-impermeable material and provided with ventilating perforations. Otherwise, the ventilated wrapper could be one applied during initial production of the filter and hence extend only the length of the filter; the resulting filter could then be incorporated in a filter cigarette either by ring tipping or by means of more conventional ventilating tipping overwrap.

The rod portion of filters according to the invention can be made continuously by continously advancing a coarse fibre bundle or longitudinally pre-corrugated and/or-fibrillated sheet, film orfoil longitudinally through a former which condenses it to rod form, and cutting the continuously produced rod into finite lengths.The rod formation may involve localised bonding of contacting portions of the rod material (e.g. by application of heat when the rod material is thermoplastic or pretreated with heat-activatable adhesive) so that the product is dimensionally stable without a wrapper, in which case the ventilating wrapper can be applied after rod formation; thus cut lengths of the unwrapped bonded rod may be incorporated in filter cigarettes by ventilating tipping overwrap; or the bonded rod may be wrapped, before or after cutting to length, in air-permeable plugwrap and the resulting filters incorporated in filter cigarettes by ring-tipping or ventilating tipping overwrap.Likewise, if an airpermeable plugwrap is applied around the rod material as the rod (whether bonded or not) is formed, the initially formed continuous wrapped rod can be cut into lengths and the resulting filters incorporated in filter cigarettes by ring tipping or ventilating tipping overwrap. The wrapped or unwrapped rod is usually supplied for filter cigarette manufacture in lengths an even multiple (e.g. sextuple) of that of the eventual individual filter; double lengths can then be abutted end to end between wrapped tobacco rods and joined thereto by ring tipping or ventilating full tipping overwrap (as appropriate), and the resulting assembly cut through said double lengths to give individual filter cigarettes.

Filters according to the invention may be used alone, or as a component of a multiple filter along with at least one additional plug - e.g. of low pressure drop and low tar retention - longitudinally aligned therewith. The aligned core components may abut or be spaced apart, and will usually be joined by a common ventilating wrapper.

Unless otherwise specified, the flow rates, PD's and retention, delivery and air dilution values quoted herein are measured by the accepted procedures recommended by CORESTA (Centre de Cooperation pour les Recherches Scientifiques Relatives au Tabac).

The invention is illustrated, by way of example only, by the accompanying drawings, in which: Figure 1 is a schematic longitudinal sectional view through one filter and filter cigarette according to the invention; and Figure 2 is a schematic cross sectional view through a second filter according to the invention.

The filter of Figure 1 comprises a bundle 2 of 100 dpf smooth surfaced polypropylene filaments wrapped in plugwrap 4 of air-permeable paper. A tipping overwrap 6, of impermeable paper having a ring of ventilating perforations 8, joins the filter to a wrapped tobacco rod 9 to form a filter cigarette. In use at total flow rates of up to 17.5 cos/sec, the wrapped bundle of filaments provides for laminar flow of air and smoke through the filter.

The Figure 2 filter has a body 12 of longitudinally corrugated polyethylene film held in rod form by plugwrap 4 of air-permeable paper and of similar laminar flow characteristics to the bundle 2 of Figure 1. This filter may be incorporated in a filter cigarette in the manner of Figure 1. In both embodiments, if the gathered filaments or film are bonded so as to form a self-sustaining dimensionally stable rod, plugwrap 4 might be omitted, a tipping overwrap such as 6 serving also as the filter wrapper. Whilst rods 2 and 12 have been shown used alone, the invention also encompasses the use of either such rod in end-to-end abutting or spaced combination with another core rod or plug, the assembly sharing and being held together by a common ventilating wrapper such as 4 or 6.

When the said rod of a filter according to the invention is made from plain sheet, film or foil, the latter is corrugated or fibrillated before gathering to rod form. Embossing to effect corrugation can result also in fibrillation, before or after rod formation, and such fibrillation may in fact be more apparent than the corrugations.

The following are specific Examples of the inven tion: Example 1 A smoke filter according to the invention consisted of a rod of partially longitudinally fibrillated cellulose film gathered laterally and held in rod form by a permeable plugwrap. The filter was 20 mm. long and about 8 mm. in diameter, and had an enclosed PD of 85 mm.Wg. and an enclosed tar retention of 19%; the lattertar retention is measured by machine smoking via the enclosed filter a cigarette which (when unfiltered and unventilated) has a PD of 55 mm.Wg. and delivers 30 mg. tar and 16 mg. CO.

Afilter cigarette according to the invention consisted of a filter as above joined to a cigarette as above by a perforated tipping overwrap giving an air dilution of 50%. This filter cigarette had a perceived PD of 92 mm.Wg. and on smoking delivered 12 mg.

tar and 6.4 mg.CO. The PD and tar reduction and delivery were thus as required with a CO/ta r yield ratio of 0.53 which is much better than that (about unity) for conventional filters of similar PD and tar reduction.

Example 2 Example 1 was repeated using a perforated tipping overwrap giving 70% air dilution. This filter cigarette according to the invention had a perceived PD of 74 mm.Wg. and delivered 7.2 mg.tar and 2.24 mg. CO - a CO/tar yield ratio of 0.31.

Claims (15)

1. A ventilated tobacco smoke filter comprising a ventilating wrapper around a rod providing a multiplicity of capillaries extending longitudinally of the rod and formed by a bundle of coarse filaments extending longitudinally of the rod or by longitudinally corrugated and/or at least partially fibrillated sheet, film or foil of zero or low smoke permeability material gathered laterally into rod form.

2. Afilter according to claim 1 wherein the rod is of coarse fibres of at least 20 denier per filament, e.g.

about 100 denier per filament.

3. Afilter according to claim 1 or2whereinthe rod is of coarse fibres which are smooth surfaced and substantially impermeable.

4. A filter according to claim 1 wherein the rod is of corrugated and/or at least partially fibriliated sheet, film orfoil of cellulose material, plastics or metal.

5. A filter according to any preceding claim wherein the rod is one which provides substantially laminar flow of smoke and air in use.

6. Afilter according to any preceding claim wherein the said rod is longitudinally aligned with an additional plug.

7. Afilter according to any preceding claim wherein the ventilating wrapper is a ventilating tipping overwrap incorporating the filter in a filter cigarette.

8. A filter according to any of claims 1 to 6 incorporated in a filter cigarette.

9. A filter according to claim 7 or 8 in which the percentage air dilution via the filter is greater than the percentage enclosed tar retention of the filter.

10. Afilter element comprising a dimensionally stable self-supporting rod providing a multiplicity of capillaries extending longitudinally of the rod and formed by a bonded bundle of coarse filaments extending longitudinally of the rod or by longitudinally corrugated and/or at least partially fibrillated sheet, foil or film of zero or low smoke permeability material laterally gathered and bonded into rod form.

11. Afilter element according to claim 10 and substantially as herein before described.

12. A ventilated tobacco smoke filter substantially as herein before described with reference to Figure 1 or Figure 2 of the accompanying drawings.

13. A filter cigarette substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

14. A ventilated tobacco smoke filter substantially as hereinbefore described in Example 1 or Example 2.

15. A filter cigarette substantially as herein before described in Example 1 or Example 2.