Tobacco smoke filter

Abstract

A tobacco smoke filter or filter element including a longitudinally extending core of tobacco smoke filtering material of circumference 14 to 17 mm which includes a channel which extends longitudinally from an end of the core; wherein the core further includes a plasticiser in an amount of 17 to 19% by weight of the tobacco smoke filtering material.

Claims

1. A tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of circumference 14 to 17 mm which defines a channel which extends longitudinally from an end of the core; wherein the core further comprises a plasticiser in an amount of 17 to 19% by weight of the tobacco smoke filtering material; wherein the plasticiser is applied to a surface of the tobacco smoke filtering material; wherein the core has a hardness of 93% or more Filtrona hardness units; and wherein the channel has a circumference of 8.8 mm to 9.42 mm.

2. A tobacco smoke filter or filter element according to claim 1 comprising a longitudinally extending core of tobacco smoke filtering material of circumference 16 to 17 mm.

3. A tobacco smoke filter or filter element according to claim 1 wherein the tobacco smoke filtering material is cellulose acetate.

4. A tobacco smoke filter or filter element according to claim 3, wherein the cellulose acetate is of density in the range of 0.25 to 0.41 g/cc.

5. A tobacco smoke filter or filter element according to claim 3, wherein the cellulose acetate is of total filament denier of 30-36,000.

6. A tobacco smoke filter or filter element according to claim 1 wherein the plasticiser is triacetin.

7. A tobacco smoke filter or filter element according to claim 1 wherein the longitudinally extending core of tobacco smoke filtering material is substantially cylindrical.

8. A tobacco smoke filter or filter element according to claim 1 wherein the channel is cylindrical.

9. A tobacco smoke filter or filter element according to claim 1 wherein the channel extends from one end, to the other, of the longitudinally extending core.

10. A tobacco smoke filter or filter element according to claim 1 further comprising a wrapper engaged around the longitudinally extending core.

11. A tobacco smoke filter or filter element according to claim 1 of length 12 to 40 mm.

12. A tobacco smoke filter comprising a filter element according to claim 1 joined at its upstream end to a further filter element.

13. A filter cigarette comprising a filter or filter element according to claim 1 joined to a wrapped tobacco rod with one end of the filter towards the tobacco.

14. A multiple rod comprising a plurality of filters or filter elements according to claim 1 integrally joined end-to-end in a mirror image relationship.

15. A tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of circumference 14 to 15 mm which defines a channel which extends longitudinally from an end of the core; wherein the core further comprises a plasticiser in an amount of 15 to 21% by weight of the tobacco smoke filtering material; wherein the plasticiser is applied to a surface of the tobacco smoke filtering material; wherein the core has a hardness of 93% or more Filtrona hardness units; and wherein the channel has a circumference of 8.8 mm to 9.42 mm.

16. A tobacco smoke filter or filter element according to claim 15 wherein the channel extends from one end, to the other, of the longitudinally extending core.

17. A tobacco smoke filter or filter element according to claim 15 wherein the channel is cylindrical.

18. A tobacco smoke filter or filter element according to claim 15 wherein the tobacco smoke filtering material is cellulose acetate.

19. A tobacco smoke filter or filter element according to claim 18, wherein the cellulose acetate is of density in the range of 0.25 to 0.41 g/cc.

20. A tobacco smoke filter or filter element according to claim 18 wherein the cellulose acetate is of total filament denier of 30-36,000.

21. A tobacco smoke filter or filter element according to claim 15 wherein the plasticiser is triacetin.

22. A tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of circumference 14 to 17 mm which defines a channel which extends longitudinally from an end of the core; wherein the core further comprises a plasticiser in an amount of 15 to 20% by weight of the tobacco smoke filtering material; wherein the plasticiser is applied to a surface of the tobacco smoke filtering material; wherein the tobacco smoke filtering material is of wall density in the range of 0.25 to 0.41 g/cc; wherein the core has a hardness of 93% or more Filtrona hardness units; and wherein the channel has a circumference of 8.8 mm to 9.42 mm.

23. A method of production of a tobacco smoke filter or filter element comprising a longitudinally extending core of tobacco smoke filtering material of circumference 14 to 17 mm which defines a channel with extends longitudinally from an end of the core; wherein the core furthercomprises a plasticizer in an amount of 15.5 to 21% by weight of the tobacco smoke filtering material; wherein the core has a hardness of 93% or more Filtrona hardness units; and wherein the channel has a circumference of 8.8 mm to 9.42 mm; the method comprising: continuously d rawingthe tobacco smoke filtering material from a single source; applying plasticizerto a surface of the filtering material; and thermoforming tobacco smoke filtering material to which plasticizer has been applied.

Description

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

(2) FIG. 1 is an end view of a tobacco smoke filter element according to an example of the invention;

(3) FIG. 2 shows the effect of hardness, visual quality and filter condition of the amount of plasticiser (triacetin); and

(4) FIG. 3 shows the results of hardness testing of filter elements according to an example of the invention.

(5) FIG. 1 shows one end (the downstream or mouth end) of a filter element according to one embodiment of the invention. The filter element comprises a thermoformed longitudinally extending core 1 of plasticised cellulose acetate filtering material of circumference 16.5 mm. The longitudinally extending (annular) core defines a channel or bore 2 of circular cross section which extends longitudinally through the longitudinally extending core. The channel or bore 2 has inner diameter of approximately 2.8 mm (circumference 8.8 mm) and extends from one end, to the other, of the core. Thus, the core 1 has substantially annular cross section.

(6) The longitudinally extending core 1 is made by thermoforming a plasticised cellulose acetate filamentary tow of total filament denier 30,000 to 36,000 (e.g. 34,000) which includes a triacetin plasticiser in an amount of 17% to 19% (e.g. 18%) by weight of the cellulose acetate.

(7) It will be appreciated that the filter element of FIG. 1 may be joined (abutted) at its upstream end to another filter element (not shown), and the abutted filter elements wrapped with plugwrap, to form a dual filter, as is well known in the art. A dual filter incorporating the filter element of FIG. 1 may be joined at its upstream end to a wrapped tobacco rod (not shown) by means of, for example, a full tipping overwrap which surrounds and engages the full length of the dual filter and the adjacent end only of the wrapped tobacco rod, to form a filter cigarette. Cigarettes which include dual filters are well known.

(8) The filter element of FIG. 1 is made by thermoforming a longitudinally advancing flow of plasticised tow of cellulose acetate around a shaped die (of circular cross section) to form a continuous longitudinally advancing tube, by methods which are well known in the art, for example as in GB 2091078 and references therein. The continuously advancing thermoformed tube is then cut into finite length products (e.g. dual (or other multiple length) product rods comprising two (or other multiple) filter elements of FIG. 1 joined end to end). The dual product rods may be further processed into dual filters (e.g. using a filter maker) and filter cigarettes, by methods well known in the art.

(9) As seen in FIG. 1, the cross section of the channel 2 is immediately visible at the mouth end of filter and is therefore visible at the mouth end of the ultimate product (dual filter or filter cigarette), and hence presents a distinctive image to the smoker (which may also be useful as an anti counterfeiting measure). Provision of filters having a controlled and acceptable visual appearance provided by the channel is therefore highly important.

(10) The applicants have determined, following extensive trials, the following values for optimum characteristics for the manufacture of superslim tubular cigarette filters: Triacetin level: 17-19% by weight of cellulose acetate Hardness: 93-97% (Filtrona hardness units) Filter circumference: 16-17 mm (5.09-5.41 mm diameter) Tube diameter: 2.8-3.0 mm (8.8-9.42 mm circumference)
Some of these trials are described in the following Examples 1 and 2.

EXAMPLE 1

(11) 6 variants (labelled A-F) of superslim tube filter rods were produced. These filter rods may be thought of a number of filter elements similar to that shown in FIG. 1 joined end to end (to form a multiple filter rod). Each filter rod had an outer circumference of 16.5 mm, an inner tube (channel or bore) diameter of approx. 2.8 mm, and a wall thickness of the longitudinally extending core (annular core) of approx. 1.2 mm. These filter rods were cut to a length of 84 mm. Details are given below (CA=cellulose acetate).

(12) TABLE-US-00001 CA Wall Weight of CA Triacetin Level Density Trial CA Tow Type* (g/rod) (%) (g/cc) A 7.3Y36000 0.352 18.30 0.287 B 7.3Y36000 0.373 17.79 0.303 C 8.0Y32000 0.342 18.96 0.279 D 8.0Y32000 0.370 17.15 0.301 E 5.0Y30000 0.333 17.88 0.272 F 5.0Y30000 0.352 18.14 0.288 *The CA Tow type is expressed as filament denier/fibre cross-section/total denier, as is well known in the art.

(13) The rods were tested for hardness using a standard method for determining hardness in terms of Filtrona hardness units, the Filtrona Hardness Unit scale of hardness being well known in the art. The hardness results are shown in FIG. 3. All rods had satisfactory hardness of 93-97% Filtrona hardness units.

(14) Further, all rods having this hardness had acceptable visual (hairiness) characteristics, especially rods C, D and E.

(15) The applicants have concluded on the basis of these, and other results, that a cellulose acetate wall density in the range of 0.25-0.33 g/cc is preferred for acceptable hardness and visual characteristics. The applicants found that when a tow weight is used that falls below that required for this minimum density and/or triacetin levels of less than 17% w/w are used, hardness falls below the minimum 93%, and it is also becomes difficult to achieve the desired shape definition.

EXAMPLE 2

(16) Dual filter tips of 16.75 mm circumference and 27 mm length were prepared (A), with a downstream 7 mm long circular bore mouth end filter element (section) which is a filter element of the invention. The downstream filter element comprised a longitudinally extending substantially cylindrical core of length 7 mm of cellulose acetate tow of circumference 16.75 mm. The core defined a cylindrical channel or bore of bore 3.0 mm diameter which extends longitudinally from one end to the other of the core. The dual filter tip (filter of the invention) also includes an upstream filter element of 20 mm length comprising plasticised cellulose acetate. The two filter elements are joined with a paper plugwrap as is well known in the art.

(17) Filter cigarettes incorporating these filters were then compared with similar filter cigarettes (not of the invention) of 23.1 and 24.2 mm circumference (B and C respectively). A filter nicotine retention test was carried out on each sample. Retention is defined as the proportion of nicotine retained by the filter expressed as a percentage of the nicotine yield of the equivalent unfiltered cigarette, when the cigarette is smoked under ISO smoking conditions. In the retention test to measure the nicotine retention of the tube filter element, the tubes were separated after smoking and individually measured for nicotine content. The results are summarised in the following table:

(18) TABLE-US-00002 A B C Filter Circumference (mm) 16.75 23.10 24.20 Tube Bore (mm) 3.0 4.6 5.0 7 mm Tube Pressure Drop 1 0 0 (mm water) 7 mm Tube Nicotine Retention 2.2 3.1 2.2 (%) Tube Surface Area (mm2) 66.0 101.2 110.0 Tube Volume (mm3) 49.5 116.3 137.5 Surface Area/Volume 1.33 0.87 0.80

(19) The filter elements of the invention surprisingly make a small contribution to the retention of the filter. Without wishing to be bound by theory it is believed that the filtering effect is due to smoke being deposited on the inner wall of the narrow tube or bore (i.e. a surface effect). The data shows that the nicotine retention is surprisingly consistent, despite differences in surface area/volume ratio of these filters. This effect supports the use of tubes with a diameter of 3 mm (or less), particularly when used in a superslim filter.

EXAMPLE 3

(20) The following parameters were examined:

(21) Using different mandrel sizes to create different internal diameters for super slim shape filters (3 mm mandrel and 4 mm mandrel);

(22) Using different tow types to determine the best material to use;

(23) Comparing both single bale and double bale tow processes; and

(24) Using different bobbins to create different outer sized circumference (i.e. down to 14.5 mm circumference, termed nano filters).

(25) Method

(26) Filter rod samples were made using the methodologies described for Examples 1 and 2 above. These were manufactured at three different sizes:

(27) Super Slim (SS) Tube Filter Rods of 16.5 mm circumference80 mm length and nominal 3 mm bore diameter;

(28) Super Slim Tube Thin Walled (SSTW) Tube Filter Rods of 16.5 mm circumference80 mm length having nominal 4 mm diameter bore; and

(29) Nano Slim Tube (N) Filter Rods of 14.5 mm circumference80 mm length having nominal 3 mm bore diameter.

(30) These products gave wall thicknesses of around 1.2 mm, 0.8 mm and 0.9 mm respectively.

(31) A total of six different types of cellulose acetate tow of differing numbers of bales, filament denier and total denier were used, as follows:

(32) Single bale: 7.3Y/36,000; 8.0Y32,000; 5.0Y/30,000 Dual bales: 28.0Y/15,000; 26Y/17,000; 24.7Y/22,000
The filter rods produced were tested for the following parameters: Hardness Bore Size Circumference (as measured seven days after manufacture) Visual quality (especially ovality and hairiness in the bore of the tube) Fibre densityas calculated from the weight and dimensional data
The results obtained are given in the table below:

(33) TABLE-US-00003 No. Triacetin Bore Filter Fibre of level Hardness diam. circum. density Visual Sample Type.sup.1 Tow.sup.2 Bales (%) (%) (mm) (mm) (g/cc) Quality 1 SS 7.3Y/36 1 16.7 94.6 2.9 16.6 0.30 2 SS 5Y/30 1 18.1 92.5 2.9 16.7 0.26 3 SS 6Y/17 2 17.0 93.3 3.0 16.6 0.29 4 SSTW 8Y/32 1 17.4 91.4 3.8 16.8 0.37 Excellent 5 SSTW 5Y/30 1 19.5 93.7 3.7 16.6 0.36 6 SSTW 8Y/15 2 16.9 92.3 3.7 16.6 0.38 7 SSTW 6Y/17 2 17.9 93.7 3.7 16.5 0.40 8 SSTW 4.7Y/22 2 15.3 95.3 3.5 16.6 0.32 Hairy (poor) 9 N 7.3Y/36 1 16.9 96.9 2.8 14.6 0.40 10 N 8Y/32 1 15.1 97.0 2.9 14.6 0.40 11 N 5Y/30 1 20.0 96.8 2.9 14.5 0.37 Excellent 12 N 8Y/15 2 17.9 96.8 2.9 14.7 0.40 13 N 6Y/17 2 14.5 97.1 2.9 14.6 0.42 Hairy (poor) 14 N 4.7Y/22 2 15.8 98.1 2.8 14.5 0.48 Notes .sup.1SS = Superslim; SSTW == Superslim Thin Walled; N = Nano tube .sup.2Tow denier given as: filament/total 1000

(34) The visual qualities of the filters were tested using a Dinolite digital microscope measuring system at 30 magnification to assess the incidence of hairy fibres in the tube bore, shape deformity and ovality, from which it was concluded that the present invention may be used to provide superslim filters having thin walls, and nano filters of diameter 14 to 15 mm, of satisfactory hardness and end appearance.

(35) At comparable hardness, and tow weight, a single bale process provided a product with a better visual quality than a filter produced from a double bale process. Further, a higher occurrence of hairy filters was observed with double bale filters. In addition, a double bale tow process provided a higher tow weight on average (which is undesirable because the resultant filters would be more costly). This applied to SSTW and N filters, in addition to SS filters.