Cigarette filter assembly

Abstract: A cigarette filter assembly (10) has a non-porous wrap­ per comprising a pair of wrappings (18, 20) and attaching the assembly to the tobacco cylinder (12) of the cigarette, the wrapper surrounding a filter plug (14) adjacent the tobacco cylinder and an open mixing chamber (24) between the filter plug and the distal end (22) of the filter assembly. The portion of the wrapper (18, 20) surrounding the mixing chamber (24) contains perforations (28) to allow the drawing in of diluting air to mix with the filtered smoke drawn into the mixing chamber through the filter plug (14) when the cigarette is smoked. The filter assembly is constructed to allow the smoke and diluting air to pass substantially unimpeded from the mixing chamber (24) through the distal end (22) into the smoker's mouth, either directly or through a hollow mouthpiece (26) or a very low flow resistance secondary filter (15) contained by the wrapper adjacent the distal end.

Description: The present invention relates to a filter assembly of the ventilated type for a cigarette or other similar article for smoking. A filter of the ventilated type may be defined as a filter which is contructed in a manner such that outside air is drawn into the filter for admission. with the tobacco smoke. to the smoker's mouth. in effect diluting the smoke which is taken in. A ventilated filter makes it possible to use a higher density filtering medium for removal of greater quantities of smoke components while not reducing the draw that the smoker expects. It is well known, however, that the method of obtaining the air dilution generally affects the taste characteristics of the cigarette or other article. Modifications of the filter construction to vary the manner in which the diluting air is added to the smoke can have either a positive or a negative effect on the taste. This is demonstrated by the fact that there are a number of known ventilated filter designs involving a variety of porous or perforated filter wrap constructions in combination with various types of porous or perforated tipping papers. In a common form of cigarette filter, the perforations for admitting diluting air into the smoke mainstream are located over some portion of the filter section, so that the air is drawn into the filter. Due to the fact that the outside air is drawn in through the filter periphery, it must follow a tortuous route through the filter wrap and filtering material, toward the core of the filter plug, before encountering the smoke mainstream. Rather than flowing into the centre of the filter, the diluting air tends to channel along the perimeter of the filter, resulting in an inefficient mixing of air and smoke, and also tending to confine the smoke stream to the core of the filter. As a result, only a portion of the cross-sectional area of the filter is utilized to filter smoke, reducing the filter efficiency. U.S. Patent No. 3,490,461 and U.S. Patent No. 4,256,122 describe another type of ventilated filter. Channels extending along the length of the filter provide a passage for outside air to be drawn, together with the smoke, into the smoker's mouth. Unlike the ventilated filter constructions described above, the filter wrapping is impervious and prevents any mixing of the air stream and the smoke stream until such time as the two streams enter the smoker's mouth. The fact that the air and smoke remain separated affects the taste characteristics of the product. Also, the proper functioning of such a design is dependent upon the channels remaining open while the article is being smoked and on the air stream having free access to the mouth. If either of these two factors are changed. there can be a drastic change in the air-to-smoke ratio taken in. U.S. Patent No. 3,496,945 discloses yet another construction of a ventilated filter, which employs a flow-restricting plate to maintain a constant air-to-smoke throughout the smoking cycle. Outside air is drawn into the filter assembly, either into a filter plug, or into a chamber, located upstream of the flow-restricting plate, for mixing with the smoke. The air and smoke mixture is drawn through a restrictive flow orifice in the plate and thereafter either through a second filter or directly out through an open end of the mouth-piece. This construction, introducing air upstream of a flow-restricting plate, is intended to regulate the flow pattern of the smoke tnrough the filter plug and the flow pattern of the incoming dilution air so as to control the ratio of smoke-to-air. The fact that mixed smoke and air are drawn through the plate orifice will affect the taste characteristics of the cigarette or other article, as well as increasing its draw resistance. The presence of a flow-restricting plate, having only a small orifice for passing the combined flow streams, may also affect the uniformity of flow of the smoke through the filter plug upstream of the p!ate and thus the performance of the filter. BE-A-891,728 discloses yet another filter assembly for a cigarette, this assembly being of the ventilated type and comprising a filter mass, wrapper means surrounding the filter inass and, in use, attaching the filter assembly to the cigarette or other article such that the filter mass is retained in end-to-end relation thereto, the wrapper means including at least one substantially non-porous wrapping and having a distal end spaced from the filter mass to provide the filter assembly with an open mixing chamber between the filter mass and the distal end, and at least one perforation in the wrapper means located to allow diluting air to be drawn from outside directly into the mixing chamber to mix with the mainstream smoke drawn into the chamber through the filter mass when the cigarette or other article is smoked, the filter assembly including a mouthpiece disposed within the wrapper means and extending from the mixing chamber to the distal end, said mouthpiece having an open cross-section formed by at least one longitudinal channel. With the aim of providing a filter assembly of the ventilated type for a cigarette or other similar article for smoking which is an improvement over known assemblies of this type, particularly with regard to smoking taste characteristics, according to one aspect of this invention, a filter assembly is as defined in Claim 1. According to another aspect of the invention, a filter assembly is as defined in claim 2. The filter assembly disclosed in BE-A-891,728 and in particular in Figure 4 of this specification, has a number of important differences from the various aspects of the present invention. Firstly the wrapper means includes a porous, but imperforate, wrapping surrounding and directly engaging the filter mass. Secondly and most importantly it has a tubular filter mass within the wrapping means and extending from the mixing chamber to the distal end. The tubular filter mass has only a small bore and presents a substantial restriction of between 65% and 75% to the free flow passage of smoke and air from the chamber to the distal end of the filter assembly. The present invention, in all its aspects, accordingly provides an improvement over all the prior art including BE-A-891,728 in that when a cigarette having a filter assembly in accordance with the invention is smoked, the diluting air does not have to penetrate various porous wraps or penetrate the filtering material prior to mixing with the smoke stream. Direct access is provided by the perforations into the mixing chamber, where the air and smoke commingle. After this the mixed air and smoke can flow in an at least substantially unimpeded manner to the smoker's mouth. As a result, the product exhibits significantly improved taste characteristics. Furthermore, in contrast to prior constructions described earlier, the filter assembly of the present invention avoids airstream channelling and smoke stream compression, and thereby ensures that the full cross-section of the filter is utilized. The integrity of the dilution system is maintained throughout the smoking process, inasmuch as the inlet for the diluting air and the filter path of the smoke stream are less likely to clog or become blocked. A thorough mixing of the air stream occurs prior to the two streams entering the smoker's mouth. Preferably the wrapper means which circumscribes the filter plug, the mixing chamber and the mouthpiece or secondary filter comprises an inner wrapping (a combined wrap) surrouding and directly engaging the filter mass, and an outer wrapping (a tipping paper) surrounding the inner wrapping and serving to attach the filter assembly to the cigarette or other article. One or both of the inner and outer wrappings are substantially non-porous. The filter plug is composed of cellulose acetate. The perforations aerating the mixing chamber may be made by piercing holes through the wrapping mears (i.e. the tipping paper and combined wrap) by laser or mechanical means either during the making of the product, or afterwards in a separate operation. The perforations through the wraps surrounding the mixing chamber ensure that the smoke mainstream and the diluting air stream are allowed to commingle freely after filtration has occurred and prior to the mixture entering the smoker's mouth. Two examples of a filter assembly in accordance with the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a cigarette together with the first example, the filter assembly being shown partly opened up and cut away to illustrate its construction; and Figure 2 is a view similar to that of Figure 1, but showing the second example. Figure 1 illustrates a cigarette having a ventilation-type filter assembly 10 in accordance with the invention. The filter assembly 10 includes a filter mass or plug 14, of cellulose acetate. Filter plugs are normally manufactured with a filter plug wrapper 16 as shown, and in the following description any reference to a filter plug or filter mass will mean the filter plug and its wrapper. if it has one. The filter plug 14 is positioned in end-to-end relation with the tobacco body 12 of the cigarette and is circumscribed by a pair of wrapper elements, a noin-porous combiner wrap 18 and a non-porous tipping paper 20. The combined wrap 18 surrounds the filter plug 14 and forms a tube extending beyond the end of the plug 14 remote from the tobacco body 12, and the tipping paper 20 surrounds the combiner wrap 18 and the end portion of the tobacco wrapper to attach the filter assembly 10 to the tobacco cylinder of the cigarette. The portion of the combiner wrap 18 which extends beyond the filter plug 14 surrounds a space which is directly adjacent the plug 14 and which forms an cpen mixing chamber 24, and also surrounds an extruded plastics mouthpiece 26 situated between the mixing chamber 24 and the distal end 22 of the filter assembly. The plastics mouthpiece 26 may, for example, be constructed as shown and described in U.S. Patent Specification No. 3,396,733, comprising a plastics tube having a plurality of radially and longitudinally extending ribs. The mouthpiece 26 reinforces the tip of the cigarette which is received in the mouth of the smoker, and permits the unimpeded longitudinal flow of smoke and air from the mixing chamber 24 through the distal end 22 to the smoker. A plurality of perforations 28 are formed through the combiner wrap 18 and the tipping paper 20 so as to communicate the mixing chamber 24 with the outside air. The perforations are made during the manufacture of the cigarette, such as by a laser or by a mechanical perforator. When the cigarette is smoked, diluting air enters the chamber 24 through the perforations 28, as illustrated by the arrow, and mixes with the smoke drawn into the chamber 24 through the filter plug 14. The number and size of the perforations 28 are selected so that the overall resistance to the flow of incoming air into the mixing chamber 24, relative to the resistance produced by the filter element 14 to the flow of smoke into the chamber 24, results in the desired ratio of air-to-smoke and the desired draw. Figure 2 illustrates a cigarette having a triple section filter assembly 10'' which is similar to that of Figure 1 except that it comprises a secondary filter 15 in place of the mouthpiece 26. The main filter plug 14'' is of cellulose acetate material and the secondary filter 15 may be of acetate material, and are axially spaced to define an open mixing chamber 24'' between them. The filters 14'' and 15 and the chamber 24'' are surrounded by a combiner wrap 18'' and by a tipping paper 20'' which attaches the assembly 10'' to the tobacco cylinder 12''. The perforations 28'' through the wraps 18'' and 20'' are located so that dilution air will enter the mixing chamber 24' between the filter elements 14'' and 15 when the cigarette is smoked. With the filter assembly shown in Figure 2, in order to obtain the desired effect in a cigarette, it is essential that the majority of the filtration (in the range of 80 to 90% or more) is effected by the main filter plug 14''. Accordingly, the main filter element 14'' is made with a small denier per filament tow material and a large total denier, and the final pressure drop (flow resistance) must be relatively high. The exact reverse is true for the filter 15, in that a filter element is utilized providing an extremely low pressure drop and therefore minimal filtration. In organoleptic evaluations, cigarettes having filter assemblies in accordance with the invention were judged to have significantly enhanced taste characteristics. In order to substantiate the organoleptic evaluations, the nicotine-to-tar ratio (nicotine/tar x 10) and the transference efficiency of menthol were determined and compared with conventional cigarettes. Nicotine and menthol bracket the volatility zone of cigarette smoke which contains the majority of the flavour components of smoke ("semi-volatile fraction"). An increase in the values of the nicotine-to-tar ratio and menthol transfer efficiency indicates that a large amount of the particulate matter is composed of the most flavourful smoke components. Cigarettes with filters constructed in accordance with the invention were found to have a nicotine-to-tar ratio of 1.5 and a menthol transfer efficency value of 1.7. A typical filter cigarette at a comparable particulate matter level generally has a nicotine-to-tar ratio of approximately 1.0 and a menthol transfer efficiency of about 1.3. Although the difference is not targe in absolute terms, the percentage difference is quite significant, and this fact is reflected in the judgment of significant taste enhancement in the resulting cigarette product. If desired, as with other filters of the ventilated-type, the filter plug may comprise a high density filter mass in order to effect a larger degree of smoke filtration. While the presence of a high density filter mass produces a draw reistance greater than in normal filter cigarettes, the increased draw through the filter plug is compensated by the introduction of the outside air. Also, the pattern, number, and spacing of the perforations may be varied from the examples shown in the drawings.

Claims: A filter assembly (10) for a cigarette or other similar article for smoking, the filter assembly (10) being of the ventilated type consisting of a filter plug (14) wrapper means (18, 20) and a mouthpiece (26), the filter plug (14) being composed of cellulose acetate the wrapper means (18, 20) surrounding the filter plug and, in use, attaching the filter assembly (10) to the cigarette or other article such that the filter plug (14) is retained in end-to-end relation thereto, the wrapper means including at least one substantially non-porous wrapping (18) and having a distal end (22) spaced from the filter plug (14) to provide the filter assembly (10) with an open mixing chamber (24) between the filter plug (14) and the distal end (22), and at least one perforation (28) in the wrapper means located to allow diluting air to be drawn from outside directly into the mixing chamber to mix with the mainstream smoke drawn into the mixing chamber (24) through the filter plug (14) when the cigarette or other article is smoked, the filter assembly (10) including a mouthpiece (26) disposed within the wrapper means (18, 20) and extending from the mixing chamber (24) to the distal end (22), said mouthpiece having an open cross-section formed by at least one longitudinal channel, the substantially non-porous wrapping (18) surrounding and directly engaging the filter plug (14) and the perforation (28) extending completely through the wrapper means (18, 20), and said mouthpiece having its longitudinal channel substantially co-extensive with the open cross-section of the mixing chamber such that the filter assembly will pass smoke and diluting air substantially unimpeded from the mixing chamber (24) to the distal end (22). A filter assembly (10'') for a cigarette or other similar article for smoking, the filter assembly (10'') being of the ventilated type consisting of a filter plug (14''), wrapper means (18'', 20'') and a secondary filter (15), the filter plug (14'') being composed of cellulose acetate, the wrapper means (18'', 20'') surrounding the filter plug and, in use, attaching the filter assembly to the cigarette or other article such that the filter plug is retained in end-to-end relation thereto, the wrapper means including at least one substantially non-porous wrapping (18'') and having a distal end (22'') spaced from the filter plug to provide the filter assembly with an open mixing chamber (24'') between the filter plug and the distal end, at least one perforation 428'') in the wrapper means located to allow diluting air to be drawn from outside directly into the mixing chamber to mix with the mainstream smoke drawn into the chamber through the filter plug when the cigarette or other article is smoked, the substantially non-porous wrapping (18'') surrounding and directly engaging the filter plug (14'') and the perforation (28'') extending completely through the wrapper means (18'', 20''), the secondary filter (15) being disposed within the wrapper means (18'', 20'') between the open mixing chamber (24'') and the distal end (22'') so that the mixing chamber (24'') extends between the filter plug (14'') and the secondary filter (15), and the secondary filter (15) having a flow resistance value substantially lower than the flow resistance value of the filter plug (14'') such that smoke and diluting air are passed substantially unimpeded from the mixing chamber (24'') to the distal end (22''), the filter plug (14'') and the secondary filter (15) being constructed such that at least 80% of the filtration is effected by the filter plug (14''). A filter assembly according to either of the preceding claims, in which there are a plurality of perforations (28) spaced about the periphery of the wrapper means (18, 20).

Inventors: HUDSON ALBERT B, JESSUP TERRY D, HUDSON, ALBERT B., JESSUP, TERRY D.
Applicants: LORILLARD INC, LORILLARD, INC.
Application year: 1983
Main classification: A24D3
IPC codes: A24D3