Cigarette smoke filter

Abstract: A novel cigarette smoke filter (10) element is provided which achieves an increased removal of tar from cigarette smoke while retaining a higher flavour level than is achieved using conventional filter materials. The filter comprises an elongate cylinder (14) of microfine fibers which is closed (16) at the upstream end of the filter element and tobacco smoke filter material (18) located both externally and internally of the cylinder of microfine fibers. A tobacco smoke flow path blocking means (20,24,26,28,32) is provided at the downstream end of the filter element to permit filtered tobacco smoke to pass from the filter element only from the tobacco smoke filter material located internally of the cylinder of microfine fibers.

Description: FIELD OF INVENTION The present invention relates to a novel manner of achieving cigarette smoke filtration and to a specific embodiment of a filter structure for a cigarette. BACKGROUND TO THE INVENTION It is considered desirable for cigarettes to provide relatively low levels of tar in the cigarette smoke entering the smoker's mouth. This result is achieved by the utilisation of filtration, air dilution or, most commonly, a combination of the two. Generally, as the tar level falls, so does the flavour level in the cigarette smoke. It is considered desirable to increase the flavour level of smoke entering the mouth of the smoker for the same tar level and this can be achieved to some extent by using more highly-flavoured tobaccos. However, serious limitations exist with the current technology. There is an upper level of venting of the cigarette which is possible before the cigarette smoke becomes "airy" and, in addition, there is an upper pressure drop limitation associated with conventional filter material. It is known from U.S Patent No. 3,882,877, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, to place a disc of microfine fibres between two filter rod segments of conventional tow material in a cigarette smoke filter. However in use, this type of filter exhibits a tendency to plug and inhibit the flow of cigarette smoke through the filter. It is also known from EP-A-0364253 to provide a filter element having the structure of the preamble of claim 1. SUMMARY OF INVENTION Nevertheless, a filter structure may be provided utilising such fine fibres to achieve desirable smoking characteristics. In particular, in accordance with one aspect of the present invention, there is provided a procedure for controlling the flavour/tar ratio of cigarette smoke to achieve a higher level of flavour for the same level of tar when compared to the prior art employing such fine fibres. One manner of achieving the desired result is to employ a low pressure drop filter comprising microfine fibres. The presence of the microfine fibres enables efficient filtration of the cigarette smoke to occur to remove tar from the cigarette smoke while permitting more flavour components to pass through the filter. According to a first aspect of the invention we provide a cigarette smoke filter element, with (a) an elongate cylinder of microfilm fibres which is closed at the upstream end of the filter element in the intended direction of flow of tobacco smoke through the filter element; (b) tobacco smoke filter material comprising cellulose acetate tow material located externally of said cylinder of microfine fibres in the form of an elongate cylinder located between and in engagement with an outer filter element wrapping and the external surface of said elongate cylinder of microfine fibres; (c) tobacco smoke filter material comprising low pressure drop, low filtration efficiency cellulose acetate tow material located internally of said cylinder of microfine fibres in the form of an elongate plug in engagement with the inner surface of said elongate cylinder of microfine fibres; and (d) tobacco smoke flow path blocking means located at the downstream end of said filter element in the intended direction of flow of tobacco smoke through the filter element to permit filtered tobacco smoke to pass from internally of said cylinder of microfine fibres, characterised in that the cellulose acetate tow material located externally of said cylinder is low pressure drop, low filtration efficiency material. The plugging problem referred to above when a disc of such microfine fibres is employed is overcome by configuring the microfine fibres in an orientation with respect to the direction of flow of the cigarette smoke which provides a significantly-greater area of microfine fibres through which the tobacco smoke may pass. The microfine fibres may have any convenient diameter to achieve the desired filtration, as described herein, generally about 0.5 to about 10 microns. The cylinder of microfine fibres may have any convenient thickness to achieve the desired filtration, generally about 0.05 to about 4mm. The microfine fibres may be packed to any degree to achieve the desired filtration, generally about 0.05 to about 0.3 g/cc. The remainder of the filter is comprised of low resistance filtration materials. The ability to provide an increased flavour/tar ratio in the cigarette smoke according to the invention enables higher flavour tar ratio tobaccos to be employed than has hitherto been provided and thereby obtain a further enhanced flavour/tar ratio in the smoke. Both flavour and tar are decreased, with the flavour being decreased to a usable level. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a sectional view of a cigarette filter provided in accordance with one embodiment of the invention; and Figures 2 to 4 also contain a sectional view of a cigarette filter provided in accordance with the present invention illustrating alternative blocking means for the filter. DESCRIPTION OF PREFERRED EMBODIMENTS Referring to Figure 1, a cigarette smoke filter 10 comprises an outer paper wrapper 12, a cylinder 14 of microfine fibers, crimped at the upstream end 16 of the filter 10 with respect to the direction of flow of cigarette smoke, and low pressure drop, low efficiency tow 18 surrounding the cylinder 14 of microfine fibers, both internally and externally. At the downstream end of the filter 10 is provided an annular blocking means 20 having a central opening 22 to permit cigarette smoke to pass out of the filter 10 to the smoker's mouth. By providing the annular blocking means 20 at the downstream end and the crimping 16 at the upstream end, any smoke passing through the filter 10 to the smoker's mouth passes through the cylinder 14 of microfine fibers and is filtered by the fibers, thereby removing liquid components from the smoke, including tar-containing droplets. Since the microfine fibers are provided in the form of a cylinder 14, there is provided a sufficient quantity of microfine fiber material such that all the material does not become blocked or plugged before smoking of the cigarette is finished. Figures 2 to 4 illustrate alternative forms of annular blocking means. As seen in Figure 2, the annular blocking means comprises a very high density, high pressure drop tow material 24 and a plastic tube 26. In Figure 3, the annular blocking means comprises an outer annulus of very high density, high pressure drop tow material 28 and an inner plug 30 of low resistance filter material. In Figure 4, the annular blocking means comprises an annular plastic plug 32. SUMMARY OF DISCLOSURE In summary of this disclosure, the present invention provides a novel cigarette smoke filtration procedure to obtain an increased flavour/tar ratio in smoke entering the smoker's mouth, as well as a novel filter structure which is able to efficiently remove liquid droplet components of cigarette smoke therefrom by utilizing a cylinder of microfine fibers. Modifications are possible within the scope of this invention as defined by the claims.

Claims: A cigarette smoke filter element, with (a) an elongate cylinder (14) of microfilm fibres which is closed (16) at the upstream end of the filter element (10) in the intended direction of flow of tobacco smoke through the filter element (10); (b) tobacco smoke filter material (18) comprising cellulose acetate tow material located externally of said cylinder (14) of microfine fibres in the form of an elongate cylinder located between and in engagement with an outer filter element wrapping (12) and the external surface of said elongate cylinder (14) of microfine fibres; (c) tobacco smoke filter material (18) comprising low pressure drop, low filtration efficiency cellulose acetate tow material located internally of said cylinder (14) of microfine fibres in the form of an elongate plug in engagement with the inner surface of said elongate cylinder of microfine fibres; and (d) tobacco smoke flow path blocking means (20, 24, 26, 28, 32) located at the downstream end of said filter element (10) in the intended direction of flow of tobacco smoke through the filter element (10) to permit filtered tobacco smoke to pass from internally of said cylinder (14) of microfine fibres, characterised in that the cellulose acetate tow material (18) located externally of said cylinder (14) is low pressure drop, low filtration efficiency material. A filter element according to claim 1, characterised in that the microfine fibres in said cylinder (14) thereof each has a diameter of about 0.5 to about 10 microns. A filter element according to claim 2, characterised in that the said cylinder of microfine fibres has a thickness of about 0.05 to about 4mm and a density of about 0.05 to about 0.3 g/cc. A filter element according to any one of claims 1 to 3, characterised in that said tobacco smoke flow path blocking means comprises an annular plate (20) having a diameter corresponding to that of the filter element (10) and a central opening (22) in communication with the downstream end of the region located internally of the cylinder of microfine fibres. A filter element according to any one of claims 1 to 3, characterised in that said tobacco smoke path blocking means comprises an outer elongate cylinder (24) of very high density, high pressure drop tow material resistant to tobacco smoke flow therethrough and having an outside diameter corresponding to that of the filter element (10) and an inner elongate cylinder (26) of plastic material bearing against the internal wall of and having the same length as said outer elongate cylinder (24) of very high density, high pressure drop tow material and a central bore communicating with the downstream end of the region located internally of the cylinder of microfine fibers. A filter element according to any one of claims 1 to 3, characterized in that said tobacco smoke flow path blocking means comprises an elongate cylinder (28) of very high density, high pressure drop tow material resistant to tobacco smoke flow therethrough and having an external diameter corresponding to that of the filter element (10) and a plug (30) of low resistance filter material located in said cylinder and communicating with the downstream end of the region located internally of the cylinder of microfine fibers. A filter element claimed according to any one of claims 1 to 3, characterized in that said tobacco smoke flow path blocking means comprises an elongate cylinder (32) of plastic material and having an external diameter corresponding to that of the filter element (10) and a central bore communicating with the downstream end of the region located internally of the cylinder of the microfine fibers.

Inventors: BRACKMAN WARREN A, LIEW TOW PIN, BRACKMAN, WARREN A., LIEW, TOW PIN
Applicants: ROTHMANS BENSON & HEDGES, ROTHMANS INTERNATIONAL LTD, ROTHMANS INTERNATIONAL SERVICES LIMITED, ROTHMANS, BENSON & HEDGES INC.
Application year: 1991
Main classification: A24D3
IPC codes: A24D3