GB2118819A - Cigarette filter - Google Patents

Abstract

A cigarette filter element comprises a core (4, 10) of relatively high or infinite pressure drop material. Around the core a longitudinally grooved or corrugated wrapper or integral surface region (3) provides channels (1, 2) which extend from end to end of the core out of communication therewith and which, when the wrapper or skin is in turn surrounded by tipping material (7), are of less pressure drop longitudinally of the element than the core. <IMAGE>

Description

SPECIFICATION Cigarette filter The present invention relates to cigarette filters which achieve much of their reduction of delivery of particulate matter due to air dilution of the smoke. Difficulties have been encountered in the past in achieving this whilst retaining a satisfactorily high perceived pressure drop for the filter in use.

According to the invention an element for such a filter comprises a core of relatively high or infinite pressure drop longitudinally of the element, and around the core a longitudinally grooved or corrugated wrapper or integral surface region providing channels which extend from end to end of the core out of communication therewith and which are of less enclosed pressure drop longitudinally of the element than the core. In filters according to the invention, such elements are wrapped with ventilating tipping material, i.e.

that which in use provides for the ingress of external air laterally therethrough into the filter and thence into the smokers mouth; according to the filter structure and composition, this ventilating air may fully or partially mix with the smoke stream within the filter, or remain substantially separate therefrom until mixing with the smoke in the smokers mouth.

In filters according to the invention, comprising an element as defined above with a ventilating wrap of tipping material, this tipping material can be a conventional tipping overwrap joining the element end to end with a wrapped tobacco rod in a filter cigarette. It could instead be a ventilating plugwrap applied as a step in the initial filter production, in which case the filter could be incorporated in a filter cigarette by means of ring tipping or conventional ventilating tipping overwrap. The tipping material may be inherently air-permeable and/or perforate; where the tipping material is a tipping overwrap, it will normally be an impermeable material provided with ventilating perforations.

By means of the core or low or zero permeability (high or infinite pressure drop), and by the provision therearound of said longitudinal channels of such dimensions as to exhibit a lower (yet still high) pressure drop, elements and filters according to the invention can constrain most or all of the smoke to travel along the channels (with little or no mechanical filtering effect) rather than through the core; the invention can thus provide for low mechanical filtering efficiency with retention of an acceptably high overall pressure drop even at high levels (e.g. 50% or more) of the air dilution which is responsible for most or substantially all of the total particulate matter reduction provided by the filter in use. The ratio of the enclosed pressure drop (i.e. that measured with air dilution prevented) of the core to that of the channels is preferably at least 4:1.

The element according to the invention may be used alone, in which case the ventilation through the tipping material is directly into the channels. It may be employed instead in abutting or longitudinally spaced end to end combination with another filter plug or plugs, which would usually be of low pressure drop and low mechanical filtering efficiency; in use, air dilution through the tipping material could then be directly into the said channels and/or into a portion of the composite rod upstream or downstream of the channels.

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 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. A filter 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.

Standard length (about 25 mm) cigarette filters according to the invention may for example exhibit an enclosed pressure drop of 60 to 100 mm.Wg.

at an enclosed total particulate matter retention of 10 to 40%.

Filters according to the invention can be designed, by choice of length, of core material, structure, and permeability etc., of channel size, and of percentage air dilution, to provide with any given tobacco rod any acceptable predetermined overall ventilated filter cigarette PD - e.g. 50 or 60 or 70 or 80 and up to 120 mm.Wg. However, much higher or much lower (e.g. 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.

Unless otherwise specified, the flow rates, pressure drops 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 core of an element used according to the invention may be a plain (i.e. without grooves or corrugations) rod which is inherently smokeimpermeable or of smoke-impermeable lateral periphery - e.g. incorporating a smokeimpermeable wrap or integral (e.g. heat- or solvent-fused) skin - the core then having a corrugaged or grooved wrapper therearound which can be air- or smoke-permeable (inherently and/or by way of perforations) or -- impermeable and can provide said longitudinal channels both externaily and between itself and the core. In other embodiments, the core cross section conforms to a corrugated or grooved wrapper or skin, in which case the latter is air- or smoke-impermeable and provides said longitudinal channels only externally thereof.

The invention provides such filter elements per se (i.e. before wrapping with ventilating tipping material to constitute a filter). Such elements comprise a core of relatively high or infinite pressure drop longitudinally of the element, and around the core a longitudinally grooved or corrugated wrapper or integral skin providing channels which extend from end to end of the core out of communication therewith and which are of less enclosed pressure drop longitudinally of the element than the core.

In these cases the wrapper or skin is distinguishable from the core; however, in filters according to the invention (i.e. when ventilating tipping material is present around the element), this need not be so and the core may constitute the element, e.g. be an inherently smokeimpermeable grooved or fluted rod (such as an extrusion of gear-wheel or serrated cross-section).

It is to be understood that the term "wrapper" is used herein to indicate any form of surrounding sleeve which wraps the core - e.g. one extruded, or preformed and slid over the core.

The invention is further illustrated by the following description of preferred embodiments, to be taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic cross sectional view through one element and filter according to the invention, Figure 2 is a similar view of a second filter and element according to the invention; Figure 3 is a longitudinal sectional view of a filter and filter cigarette according to the invention; and Figure 4 is a similar view of another filter and filter cigarette according to the invention.

The Figure 1 element has a low or zero permeability core 4 (e.g. of Transorb) surrounded by an impermeable plugwrap 10 and by an impermeable longitudinally corrugated wrapper 3 providing internal and external channels 2 and 1 extending from end to end of the core 4. Around wrapper 3 is a wrap 7 of ventilating tipping material which could extend merely from end to end of the element but which would more usually be a tipping overwrap incorporating the element in a filter cigarette as shown in Figure 3. The channels 1 and 2 provide in use a fiow path whose pressure drop is high but nonetheless lower than that of the core; the smoke is thus encouraged to pass along the channels with little or no mechanical filtration, but with retention of high pressure drop.

Figure 2 illustrates a similar arrangement; in this case, however, the periphery of the core 4 conforms to the inner surface of wrapper 3 so that only external channels 1 are provided.

Figure 3 shows one embodiment of a filter and filter cigarette incorporating an element of the type shown in Figure 1 or 2. In this case the wrapper 7 is a perforated tipping overwrap joining the element to a wrapped tobacco rod 6, the perforations 12 through the tipping overwrap opening directly into the channels 1 of the element.

In Figure 4 the element of Figure 1 or Figure 2 is employed in combination with a low pressure drop, low filtering efficiency plug 8, the two being held together by an inherently permeable plugwrap. This composite is again joined to a wrapped tobacco rod 6 by a perforate tipping overwrap 7, though in this case the perforations of the latter are disposed downstream of the element channels.

Suitable materials for the core 4 of Figure 1 are for example a "Transorb" rod - a dense drawndown rod of bonded cellulose acetate filamentary tow - or very high pressure drop embossed paper gathered into rod form. Core 4 in Fig. 2 might for example be a closed-cell foam, with an integral fused skin 3, or it might also be of gathered filamentary (e.g. cellulose acetate) tow conforming to a separate wrapper 3.

Standard length (""25 mm) cigarette filters according to the invention may for example exhibit an enclosed pressure drop (i.e. one measure with air dilution prevented) of 80 to 100 mm water gauge at an enclosed total particulate matter retention of 1 2 to 40%. One particular such filter according to the invention as illustrated in Figure 3, using a Fig. 1 element with a "Transorb" core 4 had an enclosed pressure drop of 88 mm water gauge and an enclosed total particulate matter retention of 1 8z%; for another of like structure and composition the figures were 100 mm water gauge and 21% respectively.

The Figure 2 embodiment could be a uniform extruded inherently smoke-impermeable rod (e.g.

of plastics material) of the cross-section shown, with a surface region essentially the same as its main body and so not evident as a skin around a core.

The following are specific Examples of elements, filters and filter cigarettes according to the invention: EXAMPLE 1 A filter element according to the invention as shown in Fig. 1 had a zero permeability core 4 of closed cell foam (Ethafoam) with a plain impermeable plugwrap 10 and an impermeable corrugated wrapper 3. This element, 20 mm long and of about 8 mm outer diameter, had an enclosed PD of 51 mm.Wg. and an enclosed tar retention of 10.5%; the latter tar 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.

EXAMPLE 2 A further filter element of the Example 1 structure and diameter but 1 9 mm long had an enclosed PD of 50 mm.Wg. and a said tar retention of 10%. A filter according to the invention consists of a composite of this element and an abutting 6 mm long plug (of the same diameter) of non-wrapped bonded cellulose acetate crimped filamentary tow, joined by a permeable plugwrap; it had an enclosed PD of 57 mm.Wg. and a said tar retention of 12.8%.

EXAMPLE 3 Another filter according to the invention, of the size and structure given in Example 2 but employing a different 6 mm plug of non-wrapped bonded cellulose acetate crimped filamentary tow, had an enclosed PD of 61 mm.Wg. and a said tar retention of 20.3%.

EXAMPLE 4 A filter'cigarette according to the invention, having a cigarette as in Example 1 joined to a filter as in Example 2 by a ventilating tipping overwrap giving 50% air dilution, delivered on machined smoking 13.1 mg tar and 6.4 mg CO; the CO/tar yield ratio of 0.49 is much better than that (about unity) conventionally obtainable at acceptable perceived PD's and tar reductions and deliveries.

EXAMPLE 5 A filter cigarette according to the invention as in Example 4 but using instead a filter as in Example 3 gave with 50% air dilution a tar yield of 12.0 mg and a CO yield of 6.4 mg CO, a CO/tar yield ratio of 0.53.

Filter cores or elements according to the invention, with or without air-permeable plugwrap, are preferably made initially in continuous rod form and then cut to convenient lengths. Cores or elements without air-permeable plugwrap can be incorporated in filter cigarettes by ventilating tipping overwrap, and those with such plugwrap by such overwrap or by ring tipping. For use with other plugs in dual or multiple filters, cores or elements according to the invention are aligned with such other intervening plugs and the whole wrapped in air-permeable plugwrap to form a continuous wrapped rod which is then cut to lengths for joining to cigarettes by ring tipping or ventilating tipping overwrap.The wrapped or unwrapped element or core 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.

EXAMPLE 6 A filter element as in Example 1 had an enclosed PD of 80 mm.Wg. and an enclosed tar retention of 14%. A filter cigarette having this element attached to an abutting wrapped tobacco rod by a tipping overwrap giving (by way of ventilating perforations around the overwrap and in register with the corrugations) 85% air dilution had a tar yield of 1.5 mg and a CO yield of 0.6 mg - a CO/tar yield ratio of 0.4 - and a perceived (open) PD of 80 mm.Wg.

Claims (14)

1. A cigarette filter which comprises ventilating tipping material around a filter element, the filter element comprising a core of relatively high or infinite pressure drop longitudinally of the element, and around the core a longitudinally grooved or corrugated wrapper or integral surface region providing channels which extend from end to end of the core out of communication therewith and which are of less pressure enclosed drop longitudinally of the element than the core.

2. A filter according to claim 1 wherein the element comprises an inherently smokeimpermeable grooved or fluted rod.

3. A cigarette filter element comprising a core of relatively high or infinite pressure drop longitudinally of the element, and around the core a longitudinally grooved or corrugated wrapper or integral skin providing channels which extends from end to end of the core out of communication therewith and which are of less enclosed pressure drop longitudinally of the element than the core.

4. A filter or element according to claim 1 or 3 wherein the core is a plain rod which is inherently smoke-impermeable or of smoke-impermeable lateral periphery, the core havng a longitudinally corrugated or grooved wrapper therearound.

5. A filter or element according to claim 1 or 3 wherein the core cross-section conforms to a longitudinally corrugated or grooved wrapper or skin therearound.

6. A filter according to claim 1, 2, 4 or 5 wherein the element is longitudinally aligned with at least one further plug and the assembly is held together by a common air-permeable wrap.

7. A filter according to any of claims 1, 2 and 4 to 6 wherein the ventilating tipping material comprises a tipping overwrap incorporating the filter in a filter cigarette.

8. A ventilated filter cigarette including a filter or element according to any of claims 1 to 6.

9. A cigarette filter element substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

10. A cigarette filter substantially as hereinbefore described with reference to any one of Figs. 1 to 4 of the accompanying drawings.

11. A filter cigarette substantially as hereinbefore described with reference to Fig. 3 or Fig. 4 of the accompanying drawings.

1 2. A cigarette filter element substantially as hereinbefore described in Example 1 or 2.

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

14. A filter cigarette substantially as hereinbefore described in Example 4 or 5.

1 5. A multiple length rod from which individual elements or filters according to any of claims 1 to 6, 9, 10, 13 and 14 can be cut.