GB2113066A

GB2113066A - Tobacco smoke filter

Info

Publication number: GB2113066A
Application number: GB08235897A
Authority: GB
Inventors: Ernest Brian Hayes
Original assignee: Filtrona PLC
Current assignee: Essentra PLC
Priority date: 1981-12-18
Filing date: 1982-12-16
Publication date: 1983-08-03
Also published as: NO157124B; SE8207227L; BE895390A; DK560282A; IT1155005B; IT8224837A1; ZA829280B; IT8224837A0; NL8204909A; DE3246898A1; NO157124C; AU9153382A; FR2518374A1; PT76005B; AU556902B2; SE8207227D0; JPS58155073A; CH651184A5; GB2113066B; FR2518374B1

Abstract

A ventilated tobacco smoke filter reduces tar yield mainly by air dilution rather than mechanical filtration (and/or which enhances reduction of CO yield in comparison to that of tar yield), whilst maintaining a relatively high pressure drop, wherein the filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core and is itself surrounded by an air-permeable wrapper. The filtering material is suitably of bonded crimped cellulose acetate filaments and the flow- obstructing core is suitably a zero or low permeability drawn-down rod of bonded substantially uncrimped filaments, e.g. of cellulose acetate. The filter is incorporated in a filter cigarette by means of a ventilating (e.g. perforate) tipping overwrap, which may constitute said wrapper. Also provided is a tobacco smoke filter rod comprising a layer of tobacco smoke filtering material around a denser flow-obstructing drawn-down core of bonded filaments. <IMAGE>

Description

SPECIFICATION Tobacco smoke filter The present invention relates to tobacco smoke filters. It provides a novel nonhomogenous tobacco smoke filter rod, and a ventilated tobacco smoke filter which incorporates a rod of the same general type and which reduces tar yield mainly by air dilution rather than 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. The invention also provides a tobacco smoke filter of novel nonhomogeneous construction which reduces 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.

Conventional filters, constructed homogeneously of, for example, 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 made according to the present invention provide low mechanical retentions, whilst maintaining a relatively high PD compared to that of conventional, homogeneously constructed filters.

The present invention uses a filter rod in which the filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core; the latter may be impermeable or of very low permeability to smoke.

In one aspect, the present invention provides a tobacco smoke filter rod comprising a layer of tobacco smoke filtering material around a denser flow-obstructing drawn-down core of bonded filaments.

According to a further aspect it provides a ventilated tobacco smoke filter which reduces CO preferentially to tar and in which smoke filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core and is itself surrounded by an air-permeable wrapper.

According to another aspect it provides a ventilated tobacco smoke filter which reduces tar yield more by air dilution than by mechanical filtration, in which smoke filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core and is itself surrounded by an air-permeable wrapper; in a filter cigarette employing such a ventilated filter, the percentage air dilution via the filter is preferably greater than the percentage "non-ventilated" tar retention of the filter - i.e that measured for an equivalent filter and cigarette with air dilution via the filter prevented.

The filter according to the invention will of course have an air-permeable wrapper, e.g. of substantially impermeable paper having perforations therethrough; in use there is preferably at least 50% air dilution of the smoke.

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 said 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 pressure drop (PD) of the complete filter is maintained at a reasonably high level because of the restricted cross-sectional area of the filtering material. The mechanical efficiency of the filter is low due to this restricted cross-sectional area, as well as to the low efficiency of the said filtering material itself.

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 90 mm Wg (water gauge) and a mechanical tar retention of at most 45%.

The filtering material may be of conventional material of low filtering efficiency e.g. cellulose acetate or other fibre of 8 dpf or more (as filamentary tow or staple fibres) or gathered corrugated web material.

The flow-obstructing denser fibrous or filamentary core may be impermeable or of low permeability material e.g. low permeability fibrous or filamentary material such as "Transorb" (Registered Trade Mark), a dense drawn down rod of bonded cellulose acetate filaments. The characteristics of 'Transorb" rods, and methods for their production (which can remove the initial filament crimp) are described in UK Patent Specification No.970,817, to which attention is directed for further detail.

In the case of a low permeability core, radial flow of smoke or air between the flow-obstructing core and the filtering material may be prevented by a wrap or sleeve (e.g. of non-porous paper or impermeable film) or integral skin around the core.

The flow-obstructing core surrounded by the filtering material may extend fully or partially the length of the filter. In cases where the flow-obstructing core does not extend from one end of the filter to the other it may extend from one exposed end, or be spaced from both ends. The obstructing core will normally be parallel to the filter axis and will preferably be coaxial with the filter, but this is not absolutely essential. The filter according to the invention may of course have two or more obstructing cores as described above.Filters according to the invention are readily made by continuously advancing longitudinally a web or band of the smoke filtering material, continuously feeding thereonto a continuous obstructing core or depositing thereon at longitudinally spaced intervals lengths of obstructing core, continuously condensing the assembly into rod form with the filter material surrounding the obstructing core, continuously wrapping the said rod form in the air-permeable wrapper, and continuously cutting the resulting continuously produced product into individual lengths.

Where there is a perforate tipping overwrap and a part-length core, the latter may with advantage be disposed downstream or upstream of the overwrap perforations, i.e. respectively at or remote from the filter buccal end.

Filters according to the invention may be used alone, or as a component of a multiple filter along with at least one additional plug of low pressure drop and low tar retention.

The pressure drops and retention and air dilution values quoted herein are measured by the accepted procedures recommended by CORESTA (Centre de Cooperation pour les Recherehes Scientifiques Relatives au Tabac).

Where the assembly of obstructing core and surrounding filter material as produced is selfsustaining, the air permeable wrapper may be applied after the continuously produced assembly has been cut into individual lengths - it may for example be the tipping overwrap joining the filter to a wrapped tobacco rod in a filter cigarette.

Instead an air-permeable wrap may be applied as the assembly is continuously produced; then the filter may be incorporated in a cigarette by ring tipping, or the air dilution in use may be through both this wrap and a tipping overwrap.

As indicated above the flow-obstructing core may be wholly and inherently impermeable to smoke, or it may be of such structure and composition that it is in itself of measurable or appreciable smoke-permeability but contributes little or nothing to thesmoke-permeabilityofthefilterasa whole. The or each flow-obstructing core could for example be a bonded filamentary or fibrous body having some permeability which is nonetheless markedly less in use of the filter than that of the said surrounding smoke filtering material. Where the or each flow-obstructing core has some inherent smoke-permeability, it may have a smoke-impermeable wrapper or skin separating it from the surrounding smoke filtering material.

In one preferred type of embodiment of the invention, the or each flow-obstructing core is a "Transorb" rod of bonded filamentary cellulose acetate and is surrounded by conventional smoke filtering material, if desired with an impermeable wrap between the two.

In one set of such embodiments, the flow-obstructing core rod is an unwrapped "Transorb" rod of bonded substantially de-crimped cellulose acetate filaments, made as described in UK Specification No.970817, and the filter material therearound is bonded crimped cellulose acetate filaments. The core and surrounding filter rod each extend the full length of the filter, which has a highly permeable (1 50 K) plugwrap. For the filter cigarette performance tests reported below, such wrapped filter tips are attached to conventional wrapped tobacco rod (of 45 mm.Wg.PD) by conventional tipping overwrap which is of impermeable material but with perforations to give a required degree of air dilution into the tip on normal smoking.Details of three specific Exampies are given in Table 1:

FILTER MATERIAL CORE MATERIAL CORE Tip Tip Enclosed Tip Non-Ventilated Diameter mm Length mm Circumfer- P.D. tar tetention % ence mm mm.Wg. Example 1 8/54 tow 1.6/70 tow 4.5 25 24.61 101 42 Example 2 8/54 tow 1.6/70 tow 4.6 25 24.61 118 45 Example 3 8/54 tow 1.6/70 tow 4.5 25 24.61 92

In Table 1 "8/54 tow" means a tow of 8 filament denier and 54 x 103 total denier, "1.6/70 towv has corresponding meaning, and the "enclosed tip PD" is that of the filter tip alone as measured in mm.Wg.(water gauge) with lateral entry of air prevented. The "non-ventilated tar retention" is that on smoking the filter cigarette as described above under standard conditions on a Filtrona 300 smoking machine with the tipping overwrap perforations ciosed.

Table 2 compares the pressure drop characteristics of the filter along and the ventilated filter cigarette of Example 1 with those of filters and filter cigarettes in which the filter is a uniform plug of bonded crimped cellulose acetate filaments of coarse or conventional gauge. The comparison data, as for Example 1, refers to 25 mm. tip length, 42% non-ventilated tar retention, and a tobacco rod PD of 45 mm.Wg.

TABLE 2

P.D. Measurement Example 1 Coarse (12 dpf) Conventional cellulose acetate cellulose acetate (2.5-5 dpf) Enclosed Tip 101 67 35-60 Filter cigarette Vents open at 102 84.5 50--70 50% Ventilation Table 3 gives performance data on Examples 1 to 3; the smoking tests were conducted under standard conditions on a Filtrona 300 smoking machine with the tipping overwrap perforations open.

Example 1 of Table 3 differs from that reported in Table 2 only in that in the latter test the air dilution (ventilation was limited to 50%, in each Example the unfiltered cigarette has a PD of 45 mm.Wg., a tar yield (WNF) of 29 mg., and a CO yield of 15.7 mg. The ventilated filter cigarette of Example 1 has a PD of 95 mm.Wg.

TABLE 3

Example 1 2 3 EnclosedtipPDmm.Wg. 101 118 92 Yield-TPM (WNF). mg. 5.5 6.2 9.7 Yield-COmg. 4.1 4.8 5.85 Ratio CO/TPM (WNF) 0.75 , 0.77 0.6 Tip Ventilation % 62 58 50 TPM (WNF) refers to Total Particulate Matter (Water, Nicotine Free).

In Table 4 below, a commercial filter cigarette and its conventional (homogeneous bonded cellulose acetate tow) ventilated filter are compared with a filter (of the same dimensions) and filter cigarette (Example 4) according to the invention; the tobacco rods of Example 4 and its conventional commercial comparison are of course identical.

TABLE 4

Ventilated filter cigarette EXAMPLE 4 Conventional Commercial Comparison PD, mm Wg. 80 89 Tip Ventilation % 65.3 56.4 TPM (WNF) yield mg 5.7 5.0 CO yield mg 2.94 4.09 CO/TPM (WNF) Ratio 0.52 0.82 Non-ventilated tip PD mm Wg. 126 98 Non-ventilated tar retention % 42 '53 Herein, an air permeability of nK means an air permeability of n x 1000 mls/minute/l0 square cm./1 00 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:: airpermeability= 1050 x 100 P The invention also provides a tobacco smoke filter rod comprising a layer of tobacco smoke filtering material around a denser flow-obstructing drawn-down core of bonded filaments, this being the preferred form of filter rod per se for use according to the invention with a ventilating tipping overwrap in a filter cigarette. The core filaments, e.g. of cellulose acetate, are preferably substantially uncrimped.

e.g. having been decrimped by the drawing-down of the core material during core formation. The filter material is suitably of bonded crimped filaments, e.g. of cellulose acetate. The composite rod may have therearound a plugwrap of high (e.g. 1 50 K) air permeability. If the rod per se is unwrapped, it will be incorporated in a filter cigarette by means of a ventilating tipping overwrap; if the rod per se includes a highly permeable plugwrap, then it might be incorporated in a filter cigarette by ring tipping or by a ventilating tipping overwrap, most usually the latter.

Filters according to the invention can be designed, by choice of length, of core and surrounding filter materials, structure, packing density and relative cross-sectional areas 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.

Claims

1. A ventilated tobacco smoke filter which reduces tar yield more by air dilution than by mechanical filtration, in which smoke filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core and is itself surrounded by an air-permeable wrapper.

2. A filter according to claim 1 whose percentage air dilution is greater than its percentage non ventilated mechanical tar retention, both values being measured in conjunction with equivalent tobacco rods.

3. A ventilated tobacco smoke filter which enhances reduction of CO yield in comparison to that of tar yield and in which smoke filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core and is itself surrounded by an air-permeable wrapper.

4. A filter according to any preceding claim having a nonventilated pressure drop of at least 90 mm.Wg. and a non-ventilated mechanical tar retention of at most 45%.

5. A filter according to any preceding claim having a wrap or sleeve separating the core from the surrounding filtering material.

6. A filter according to any preceding claim wherein the core extends the full length of the filter.

7. A filter according to any of claims 1 to 5 wherein the core extends only partially the length of the filter.

8. A filter according to any preceding claim wherein the core is a drawn-down rod of bonded substantially decrimped cellulose acetate filaments, and the filtering material is of bonded crimped cellulose acetate filaments.

9. A filter according to any preceding claim having a highly permeable plugwrap therearound.

10. A filter according to any preceding claim wherein the wrapper comprises a tipping overwrap incorporating the filter in a filter cigarette.

11. A filter cigarette having a filter according to any preceding claim.

12. A tobacco smoke filter rod comprising a layer of tobacco smoke filtering material around a denser flow-obstructing drawn-down core of bonded filaments.

13. A filter rod according to claim 1 2 wherein the filaments of the core are substantially uncrimped.

14. A filter rod according to claim 12 or 13 wherein the filtering material is of bonded crimped filaments.

1 5. A filter rod according to claim 12, 13 or 14 wherein the filaments are of cellulose acetate.

16. A filter rod according to any of claims 12 to 15 having a highly permeable plugwrap therearound.

17. A filter or filter rod according to any of claims 1 to 9 and 12 to 16 incorporated in a filter cigarette by a ventilating tipping overap.

18. A filter substantially as hereinbefore described in Example 1,2,3 or 4.

19. A filter cigarette substantially as hereinbefore described in Example 1,2, 3 or 4.

20. A method of making smoke filters which comprises continuously advancing longitudinally a web or band of the smoke filtering material, continuously feeding thereonto a continuous obstructing core or depositing thereon at longitudinally spaced intervals of denser flow-obstructing fibrous or filamentary core, continuously condensing the assembly into rod form with the filter material surrounding the obstructing core, continuously wrapping the said rod form in the air-permeable wrapper, and continuously cutting the resulting continuously produced product into individual lengths.

21. A method according to claim 20 and substantially as hereinbefore described.

22. A filter rod in which smoke filtering material forms a layer around a denser flow-obstructing fibrous or filamentary core, the rod being substantially as hereinbefore described in Example 1, 2, 3 or 4.