The present invention relates to tobacco smoke filters, especially for cigarettes. Tobacco smoke filters can be manufactured from a number of different materials. The majority of commercial cigarette filters are manufactured from cellulose acetate. Other filtration media, such as paper, non-woven webs made from natural and/or synthetic fibres, and other fibre tows (for example polypropylene), are used to only a limited extent.

Paper filters have a number of advantages over cellulose acetate, notably reduced cost, higher particulate removal efficiency at equivalent pressure drop, higher adsorption capacity for flavourings such as menthol, more rapid biodegradability, and less tendency to collapse during smoking. However, paper filters have a number of disadvantages compared to cellulose acetate, for example inferior end appearance and less acceptable taste. The disadvantages mentioned above have prevented paper filters from gaining widespread commercial usage.

A further limitation with paper filters is their reduced retention of toxic phenolic compounds - for example phenol, cresols, catechol and resorcinol - found in volatile and semi-volatile phases of cigarette smoke, compared to cellulose acetate filters; this results in higher relative yields of phenolic compounds from cigarettes with paper filters. This is caused by the well-known selectivity of cellulose acetate filters towards phenolic

compounds, rather than any inherent deficiency with paper filters. However, it is, of course, still desirable to enhance phenol retention of paper filters so a smoker would not be exposed to higher levels of phenolic compounds when smoking a paper filtered cigarette compared to a cellulose acetate filtered cigarette.

According to the present invention in a first aspect there is provided a tobacco smoke filter or filter element including (e.g. formed from) a coherent web comprising (e.g. formed from materials including) a first filter material and a second filter material and, optionally, one or more further filter materials; wherein the first filter material comprises a cellulose acetate tow having a total denier of 44,000 or less and a filament denier of from 2.1 to 8.3 (for example 2.1 to 6.3 or 6.5 to 8.3, for example 2.1 to 6.3, for example from 3 to 6.2); and the second filter material comprises a paper. The filter or filter element may be (or include) a rod including (e.g. formed from) the coherent web.

The first filter material comprises a cellulose acetate tow and the second filter material comprises a paper. As can be seen from Figure 3, the end appearance of filters formed from a coherent web comprising these first and second filter materials has a much enhanced and desirable end appearance, compared to a mono paper filter, because the first filter material (cellulose acetate tow) tends to fill in the small channels in the paper folds that are normally associated with mono paper filters (see the prior art mono paper filter illustrated in Figure 2). The filter or filter element of the invention may provide the combination of satisfactory end appearance, efficient manufacture and cost, and effective filtration.

The present Applicants have surprisingly found that filter or filter elements of the invention may also provide a remarkable selective filtration of phenolic compounds (e.g. phenol and/or cresols) from cigarette smoke. It is well known that the tar retention of filters and filter elements which include cellulose acetate and paper is proportional to the ratio of cellulose acetate to paper in the filter, and it would be expected that the retention of phenolic compounds would follow a similar trend. The Applicants have found that use of a cellulose acetate tow with paper in a coherent web wherein the cellulose acetate tow has specific characteristics (and/or wherein there are specific amounts of cellulose acetate tow and paper) may provide unexpectedly high retention of phenolic compounds, thereby resulting in lower deliveries of these toxic compounds to the smoker.

The first filter material comprises a cellulose acetate tow which may be of continuous filaments, as is well known in the art. Preferably, the first filter material comprises a cellulose acetate tow having total denier from 11 ,000 to 40,000, preferably from 15,000 to 40,000, preferably from 16,000 to 39,000, preferably from 17,000 to 38,000, preferably from 21 ,000 to 37,500. The first filter material may comprise a cellulose acetate tow of filament denier from 3.1 to 4.9, for example from 3.5 to 4.8. The first filter material may comprise a cellulose acetate tow of filament denier from 3.6 to 4.0, 4.5 to 4.9, 5.7 to 6.3, or 7.8 to 8.2.

In an example the first filter material comprises a cellulose acetate tow of filament denier between 3.6 and 4.0 and, optionally, total denier between 25,000 and 39,000, for example a cellulose acetate tow of filament denier 3.8 and, optionally, total denier 37,000. In another example the first filter material includes a cellulose acetate tow of filament denier from 4.5 to 4.9 and, optionally, total denier from 19,000 to 24,000, for example filament denier 4.7 and, optionally, total denier 22,000. In a still further example the first filter material comprises a cellulose acetate tow of filament denier from 5.8 to 6.2 and, optionally, total denier from 15,000 to 19,000, for example a cellulose acetate tow of filament denier 6.0 and, optionally, total denier 17,000. In a still further example the first filter material comprises a cellulose acetate tow of filament denier from 7.8 to 8.2 and, optionally, total denier from 26,000 to 30,000, for example a cellulose acetate tow of filament denier 8.0 and, optionally, total denier 28,000.

The second material comprises a paper. Preferably the second filter material comprises a filtration paper, for example filtration paper to which a smoke modifying agent (e.g. flavour) has been applied (see below). The second filter material may comprise a paper (e.g. filtration paper) of basis weight from 20 to 40 g/m ² , for example from 32 to 40 g/m ² , for example 36 g/m ² .

The amount of first filter material in the coherent web may be from 20 to 80% by weight, for example 25, 30, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 , 52, 53, 54, 55, 56, 57, 58, 59, 60, 61 , 62, 63, 64, 65, 70, 75% by weight of the coherent web. The amount of second filter material in the coherent web may be from 20 to 80% by weight, for example 25, 30, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 , 52, 53, 54, 55, 56, 57, 58, 59, 60, 61 , 62, 63, 64, 65, 70, 75% by weight of the coherent web.

The filter or filter element may include a further filter material. If present, the further filter material may comprise, for example, a cellulose acetate tow (the same or different to that of the first filter material), a paper, a non-woven web made from a natural and/or a synthetic fibre, and/or other fibre tow, for example polypropylene. The coherent web may include a web of first filter material and a web of second filter material and a web of further filter material, wherein the first and further materials are the same, and the second filter material is different (e.g the first and further filter materials may be cellulose acetate, and the second material may be paper).

One (or more) of the first, second or further filter materials may include a smoke modifying agent which, in use, becomes entrained in smoke passing through the filter or filter element. The smoke modifying agent may be one which imparts an additional taste or aroma to the smoke passing through the filter in use, or an agent which has another effect (e.g. that of suppressing certain flavours or aromas). Examples of flavour imparting agents include menthol, tobacco flavour, liquorice etc. The application of smoke modifying agents e.g. flavours, is well-known, for example by direct injection of flavour to filter tow prior to entry into the garniture during filter manufacture or by applying a flavour solution to cotton thread that is subsequently entrained in a filter. However, these and other methods have the disadvantage that only small amounts of smoke modifying agent may be applied due to e.g. limited adsorption capacity (of cellulose acetate) or limited quantity of material (in the case of cotton thread) to which to apply the solution. Preferably the smoke modifying agent is included on or in the second filter material which comprises paper, e.g. filtration paper, e.g. a web of paper. Paper, e.g. filtration paper, is a naturally adsorbent material which is available for the application of smoke modifying agent (e.g. flavour).

The filter or filter element may include granular additives such as activated carbon, silica gels, zeolites, ion exchange resins or sepiolite. These granules may, for example, be applied in a further step after production of the coherent web; may be included in one or more of the filter materials (for example as carbon-impregnated paper); or may be applied onto one (or more) of the filter materials prior to their facial alignment and formation into a coherent web.

If granular materials are used, it may be desirable to use the combined material filter as a segment of a dual, or other multi component, filter, as set out below.

The filter or filter element (e.g. the coherent web) may be over wrapped with a wrapper, for example a wrapper of an air-permeable paper.

The tobacco smoke filter or filter element according to the invention may be of circumference 14 to 28 mm, for example 16 to 26 mm, for example 16 to 17 mm or 24 to 25 mm. A tobacco smoke filter of the invention may be of length 10 to 40 mm, e.g. 15 to 35 mm, e.g. 20 to 30 mm. A tobacco smoke filter element of the invention may be of length 5 to 30mm, e.g. 6 to 20mm, e.g. 8 to 15 mm, e.g. 10 to 12 mm.

The present applicants have surprisingly found that filter or filter elements of the invention may have advantageous hardness characteristics. The definition of filter rod hardness is known in the art (CORESTA Technology Group) and is defined as the compressed diameter (DL) expressed as a percentage of the point of contact diameter (DP) when the filter rod is subject to the following conditions (i) filter rods tested singly and initially preloaded with a typically 10 g weight prior to the measurement of the point of diameter (DP). Filter rods are then compressed under a static load of 300 grams in the form of a flat disc of 12 mm diameter, the filter rod being supported by a flat surface at least 15 mm long immediately opposite and parallel to the flat disc; (ii) the filter rod must be located exactly on the centre line of the disc without restricting the rod in the vicinity of the test area; (iii) the load is applied for 15 seconds, and then the compressed diameter (DL) taken. The filter rod should be tested with the lap joint (of the filter paper, if present) not directly in line with the applied load, and preferably at 90° thereto. Filter rods should ideally be conditioned for at least 48 hours at 22 ± 1°C and 60 ± 3% RH prior to testing and where possible the tests should be carried out in an environment controlled to 22 ± 2°C and 60 ± 5% RH.

A tobacco smoke filter or filter element of the invention may have a hardness of 85% or above, preferably 90% or above as measured by the above defined test.

A filter element according to the invention may be used as a segment of a dual, triple, or other multi component (multiple segment), filter. Dual and other multiple component filters are known in the art. In an example, a dual, triple, or other multi component, filter includes a granular additive(s) such as activated carbon, silica gels, zeolites, ion exchange resins or sepiolite. It is preferred that the granular additive is not included in the filter element of the invention (i.e. is included in one of the other segments of the multi component filter). In an example the filter element of the invention forms the mouth end segment of a dual segment filter, while tobacco end segment of the dual filter includes a granular additive. It will be appreciated that a filter element according to the invention which includes a granular additive (e.g. to which a granular additive has been applied) may be used towards the tobacco end of a dual or other multiple filter. In such instances, the mouth end filter element may be of any construction that does not include a granular additive.

Filters according to the invention may be used in machine made cigarettes (e.g. those mass produced and packaged). Filters according to the invention may also be used as a filter tip for use with a individually rolled cigarette (e.g a hand rolled cigarette) or a Roll Your Own or Make-your-own product.

According to the present invention in a further aspect, there is provided the use of a coherent web comprising a first filter material and a second filter material and, optionally, one or more further filter materials as, or in the production of, a filter or filter element for selectively filtering phenolic compounds (e.g. phenols and/or cresols) from smoke, for example tobacco smoke. The first filter material may comprise a cellulose acetate tow having a total denier of 44,000 or less and a filament denier of from 2.1 to 8.3 (for example 2.1 to 6.3 or 6.5 to 8.3, for example 2.1 to 6.3, for example from 3 to 6.2). The second filter material may comprise a paper, eg., filtration paper. The present invention also provides a method of production of a tobacco smoke filter or filter element comprising aligning facially a web of a first filter material and a web of second filter material (and, optionally, one or more further webs each comprising a further filter material); and combining the facially aligned webs into a coherent web; in which the first filter material comprises a cellulose acetate tow having a total denier of 44,000 or less and a filament denier of from 2.1 to 8.3 (for example 2.1 to 6.3 or 6.5 to 8.3, for example 2.1 to 6.3, for example from 3 to 6.2); and the second filter material comprises a paper. The webs of filter material may be combined using, for example, a pair of rollers (e.g. nip rolls), the facially aligned webs being passed (at e.g. the same linear speed) between the nip of the pair of rollers under sufficient nip pressure to combine the webs. One or both of the rollers may have a specific surface pattern thereon - e.g. embossed thereon. Passing the aligned webs through the nip of the pair of rollers may add (e.g. emboss) a patterned surface to the combined, coherent, web. The coherent web may then be passed into the garniture arrangement of a conventional filter making machine for conversion into cigarette filter rods. The applicants have found that forming a coherent web prior to passing the filter material (e.g. the first and second filter materials) into the garniture arrangement provides a uniform distribution of the plurality of filter materials (e.g. the first and second filtration materials) across the cross section of the filter or filter rod. It has been found that if the first and second (and further) filter materials are simply passed into the garniture arrangement without being formed into a coherent web there tends to be a non-uniform distribution of filter materials to the detriment of the filtering characteristics of the product rod. The coherent web may be formed by forming (e.g. compressing or sandwiching) the second filter material (paper) between the first (cellulose acetate) and the further filter materials, or by forming (e.g. compressing or sandwiching) the first filter material (cellulose acetate) between the second (paper) and the further filter materials.

In a filter cigarette according to the invention, a filter of the invention (or a filter which includes a filter element of the invention) is joined to a wrapped tobacco rod with one end toward the tobacco. The filter may, for example, be joined to the wrapped tobacco rod by ring tipping (which engages around just the adjacent ends of a [wrapped] filter and rod to leave much of the filter wrapper exposed) or by a full tipping overwrap (which engages around the full filter length and adjacent end of the tobacco rod). Any filter or filter cigarette according to the invention may be unventilated, or may be ventilated by methods well known in the art, e.g. by use of a pre-perforated or air-permeable plugwrap, and/or laser perforation of plugwrap and tipping overwrap.

According to the present invention in a further aspect, there is provided a filter cigarette which includes a tobacco smoke filter or filter element according to the invention.

The filters or filter elements according to the invention may be made (as discussed above) as continuous rods. The continuous rod as it issues continuously from the production machine outlet is cut into finite lengths for subsequent use. This cutting may be into individual filters or filter elements as defined and described above, each of which is then attached to an individual wrapped tobacco rod to form a filter cigarette. More usually, however the continuously issuing rod is first cut into double or higher multiple (usually quadruple or sextuple) lengths for subsequent use; when the initial cut is into quadruple or higher lengths, then the latter are subsequently cut into double lengths for the filter cigarette assembly - in which the double length filter rod is assembled and joined (by ring tipping or full tipping overwrap) between a pair of wrapped tobacco rods with the combination then being severed centrally to give two individual filter cigarettes. The invention includes double and higher multiple length filter rods (and/ or filter element rods).

The term denier is well known in the art, and expresses weight per unit length (linear density) measure of a continuous filament or yarn. The term denier expresses weight in grams of nine kilometers (9000 meters) length of the material. Therefore the lower the denier number, the finer the material; the higher the denier number, the coarser the material.

The present invention will now be illustrated with reference to the attached drawings in which :

FIGURE 1 is a schematic side elevation view of an apparatus for forming filters according to the invention;

FIGURE 2 is a photograph of the end of a conventional (i.e. prior art) mono paper filter; and

FIGURE 3 is a photograph of the end of a filter or filter element according to the present invention.

Figure 1 shows a schematic side elevation view of an apparatus for forming filters or filter elements according to the invention. A band (1 ) of first filter material is drawn from a bale (not shown) over a guide (2) into two sets of rollers (3, 3a and 4, 4a). The first filter material comprises continuous cellulose acetate filaments in the form of a 3.8Y37 cellulose acetate tow [expressed as filament denier/filament shape/total denier (x1000), an expression well known in the art, so the 3.8Y37 tow has Filament denier 3.8, a Y shaped cross section and a total denier of 37,000], Such a tow is well known and readily commercially available. Rollers (4, 4a) rotate faster than rollers (3, 3a) causing the tow to be stretched and opened to form a web of first filter material of width of approximately 250 mm. The web of tow then passes into a spray booth (5) where it is sprayed with glycerol triacetate before exiting the spray booth via a set of delivery rollers (6, 6a). These operations are well known in the manufacture of cellulose acetate filters. A web of second filter material in the form of a web of paper (7) with characteristics suited for the manufacture of cigarette filters (a 90 mm width of a 36 g/m ² paper supplied by Swiss Quality Paper) is unwound from a reel (8) and is fed into the nip of a pair of nip rolls (9, 9a) at the same time, in the same linear direction, and at the same speed, as the sprayed web of first filter material (tow). The web of cellulose acetate tow (first filter material) and the web of filtering paper (second filter material) are thus aligned facially (with one face of the web of cellulose acetate tow facing one face of the web of filter paper) as they pass between the nip of the pair of nip rollers (9, 9a). The nip rollers (9, 9a) have a specific grooved pattern and are similar to those typically used to emboss filtration paper so that it can be subsequently formed into a cylindrical rod (although the use of nip rolls (9, 9a) in the processing of cellulose acetate filters is not normal) and are positioned transversely or substantially transversely to the paths of the web of paper (7) and the web of tow. The nip rolls (9, 9a) are at sufficient nip pressure to combine and compress/emboss the web of filtering paper and the web of cellulose acetate tow into a coherent web that then passes into the garniture arrangement of a conventional filter making machine (not shown) for conversion into cigarette filter rods. A filter wrapper of air permeable paper is applied around the filter rods by conventional means. In one example of the invention, ("Sample 8", see Example 1 and Table 1 below) the apparatus of Figure 1 is used to produce filter rods (and filter tips) using 90 mm width of a 36 gsm paper supplied by Swiss Quality Paper and a 3.8Y37 cellulose acetate tow. The amount of cellulose acetate tow (first filter material) is 57% by weight of the coherent web and the amount of paper (second filter material) is 43% by weight of the coherent web. The resulting rod is cut into filter tips are of length 11 mm (and circumference of around 25 mm). Samples A, C, D and E (Table 1) are made by a similar method, using the first (cellulose acetate tow) and second (paper) filter materials set out in Table 1.

In a further example of the invention, the apparatus of Figure 1 includes (not shown) a means for imparting a flavouring agent (e.g. menthol) into the web paper (7). The web of menthol flavoured paper (i.e. filter paper with menthol adsorbed thereon) is included (with the web of cellulose acetate tow) in the coherent web, which is then formed into filter rods. The resulting filters combine satisfactory end appearance with ready and efficient adsorption of menthol into the body of the filter.

It will be appreciated by the skilled man how a further web or webs of further filter material (e.g. further web of paper or tow) may be included (e.g. incorporated) into the coherent web by aligning the further web(s) facially with the other webs as they pass between the nip of the pair of nip rollers (9, 9a).

Figure 2 shows the end appearance of a mono paper filter of the prior art. It can be seen that the end appearance is not satisfactory.

Figure 3 shows a photograph of the end appearance of a filter according to the present invention, for example produced by the methods discussed with reference to Figure 1. It will be appreciated that the end appearance is greatly improved because the cellulose acetate (first filter material) has a tendency to fill the small channels in the paper (second filter material) folds. It will be appreciated that variation of the amounts of cellulose acetate and paper will have some effect on the end appearance of the filters, although the inclusion of cellulose acetate at an amount of greater than 20% by weight of the filter should ensure an improved end appearance over a paper only filter, and effective filtration. Filters according to the present invention, for example produced by the methods discussed with reference to Figure 1, may advantageously have hardness of 85% or greater, for example 90% or greater, for example 95% or greater.

Example 1 A series of five sample filters (Samples A, B, C, D and E) of similar pressure drop were made from cellulose acetate tow and paper to provide filters with a range of cellulose acetate:paper ratios. This was achieved through the use of cellulose acetate tows of different total deniers in combination with a 36 g/m ² paper of different widths. Comparable control filters comprising 100% of the individual materials were also manufactured. Table 1 lists the properties of these filters.

Table 1

1. expressed as Filament Denier/Filament Shape/Total Denier (x1000) an expression well known in the art, so the 3.8Y37 tow has Filament denier 3.8, a Y shaped cross section and a total denier of 37,000; 4.7Y22 tow has Filament denier 4.7, a Y shaped cross section and a total denier of 22,000, and so on.

2. per 66mm filter rod

3. expressed as % (by weight) of the total weight of the coherent web, i.e. % by weight of the total weight of acetate and paper in the sample filter.

Cigarettes were constructed using these filters, smoked under ISO conditions and their yields of tar, phenol and cresols measured. As expected, the tar yields from filter cigarettes with higher contents of paper decreases as a consequence of the higher filtration efficiency of paper as compared to cellulose acetate. Table 2 lists the results obtained together with the expected and measured values of the ratio of phenol:tar and cresols:tar. The quoted expected values are based on an anticipated linear relationship between the values obtained from the acetate and paper controls. It can be seen that the all five samples unexpectedly gave measured ratios lower than expected. Filters A, B and C gave particularly selective filtration of phenol.

Table 2

Sample Tar Phenol Cresols Expected Ratio Measured Ratio

Yield Yield Yield

Phenol: Cresols: Phenol: Cresols: (mg/cig) (pg/cig) (MQ/cig) Tar Tar Tar Tar

Acetate 16.7 25.5 21.3 1.53 1.28 1.53 1.28

A 15.8 25.7 21.3 1.84 1.47 1.63 1.35

B 15.7 25.3 20.8 1.89 1.50 1.61 1.32

C 16.5 30.2 24.0 1.91 1.51 1.83 1.45

D 16.5 28.7 23.0 1.99 1.56 1.74 1.39

E 14.8 27.2 21.9 2.08 1.62 1.84 1.48

Paper 13.9 32.9 24.9 2.37 1.79 2.37 1.79