Filter for tobacco smoke

Abstract

A tobacco smoke filter, particularly for use in cigarettes, consists wholly of or includes elements consisting wholly of non-crimped fibers of thermoplastic polymeric non-adsorbent materials having a diameter less than 5 microns. A filter of this type reduces tar and nicotine levels in the smoke to low values while at the same time the filter has satisfactory draw properties and the smoke has enhanced "taste."

Description

FIELD OF THE INVENTION

This invention relates to filters for tobacco smoke, more particularly to cigarette filters.

BACKGROUND TO THE INVENTION

Tobacco smoke essentially consists of a dispersion of solid and liquid particles in air, and this dispersion will be referred to as an aerosol in this specification. The aerosol is extremely stable due to the small size of the particles concerned and hence gravity has a negligible effect compared with the effect of convection currents and Brownian movement. Tobacco smoke is thought to contain constituents injurious to health and many suggestions have been made of filters to at least partially remove constituents of the smoke prior to entry into the smoker's mouth.

Tar and nicotine values of tobacco smoke entering the smoker's mouth, ie. after filtration, are considered by Government bodies to be a significant indication of the effectiveness of a filter to remove injurious components of tobacco smoke. While it is possible to achieve very low levels of tar and nicotine values in tobacco smoke, frequently this is at the expense of taste and smoker satisfaction. For example, the filter may not allow adequate quantities of smoke to pass through the filter and hence the "draw" of the cigarette may not be satisfactory to the consumer.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a filter for tobacco smoke which reduces tar and nicotine levels in the smoke to low values while at the same time providing a filter having satisfactory draw properties and enhanced "taste" properties. Further, the invention is concerned with methods of making the filter material.

Accordingly, the present invention is concerned with filters consisting wholly of or including elements consisting wholly of non-crimped fibers of thermoplastic natural or synthetic polymeric, non-absorbent material, the fibers having a diameter less than 5 microns.

BRIEF DESCRIPTION OF DRAWING

The accompanying drawing is a part-sectional view of a cigarette filter in accordance with one embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Tobacco smoke filters of polyolefin have been suggested heretofore in U.S. Pat. No. 2,966,157. However, the fibers forming this prior art filter medium have diameters considerably in excess of 5 microns and are crimped. If fibers having diameters greater than 5 microns are used, it is found that the superior tar and nicotine removal values observed for the filters of the present invention are not achieved for reasons outlined below.

Crimping of the filamentary material for tobacco smoke filters usually is considered necessary in order to displace portions of the individual filaments at angles to the axis of the filter tow so that, in the filter, these displaced portions of the filaments will be disposed across the flow path of the tobacco smoke for intercepting the particles to be filtered from the smoke. The crimping and crimp-deregistering operations are particularly critical to the production of high quality filters from cellulose acetate filaments and have been thought to be necessary for polyolefins fibers, as described in U.S. Pat. No. 2,966,157 referred to above. However, such operations add materially to the cost of production, and unless they are carried out with care, products lacking in uniformity are apt to result. It has been found that the filters of the present invention wherein micro-fine fibers are used do not require the crimping of the individual fibers to provide effectiveness.

As indicated above, the filter elements provided in accordance with the present invention consist of a mass of noncrimped fibers of a thermoplastic material in which the individual fibers have a particle size less than 5 microns. The thermoplastic material fibers used preferably have substantially all of the fibers below 2 microns diameter, more preferably the fibers have an average diameter of about 1 micron. This element is positioned in the path of the cigarette smoke and is found to provide superior tar and nicotine reducing properties.

The mass of fibers in the filter element may be in the form of a scrambled mass of long fibers which may be self-sustaining or a mat of short fibers, generally supported on a tobacco smoke-permeable backing.

The filter elements of the present invention when utilized with cigarettes may be the sole filter element of the cigarette, although this may provide some crush problems if a paper sleeve is employed since the filter elements lack physical strength. The required structural strength, however, could be provided by the use of a plastic or cardboard sleeve.

In a preferred construction in accordance with this invention, the filter element of this invention forms one element of a multi-element filter. In accordance with this preferred aspect of the present invention there is provided a cigarette filter element comprising an outer sleeve, at least a pair of plugs of cellulose acetate filter material, or other commonly employed filter material, disposed within the sleeve in longitudinally spaced apart relation and a filter element consisting of a mass of thermoplastic fibers, each of the fibers having a diameter less than 5 microns and positioned between the plugs.

In this way there is provided a filter element which has substantially the strength of the conventional cellulose acetate fiber filter and the enhanced tar and nicotine reducing properties of the microfine polymeric fibers.

A cigarette filter in accordance with this embodiment of the invention as shown in the accompanying drawing, wherein a cylindrical filter 10, suitable for a cigarette, consists of three elements. An outer sleeve 12 of cork paper, plastic or any other convenient material, surrounds the elements. Two elements 14 and 16 constitute the majority of the length of the filter and are constructed of conventional filter material, such as cellulose acetate fibers. The elements 14 and 16 are longitudinally displaced from each other a short distance and in the gap 18 is positioned a third filter element 20. More than two such elements 14 and 16 may be provided, if desired. The third filter element 20 consists of a disc of a mass of polymeric fibers, each of which has a fiber size less than 5 microns. Preferably, in the disc 20 the majority of the fibers are positioned in the disc so that they are transverse to the flow of tobacco smoke. The gap 18 usually is substantially filled by the third filter element 20.

It will be seen that the filter disc 20 engages the inside wall of the sleeve 12 and hence is positioned in such a manner that tobacco smoke passing through the filter 10 all passes through the disc. The element 20 may have other forms, for example, a ball or similar mass of fibers positioned in the gap 18 and engaging the inner wall of the sleeve 12. In order to have efficient reduction of tar and nicotine levels from the smoke, it is necessary for the element 20 in whatever form it may take to be positioned in the path of the tobacco smoke so that substantially all of the smoke passes through the filter.

The precise mechanism whereby efficient filtration is achieved using the filters of the present invention is not fully understood, but the following theory is proposed. The diameter of the particles of the smoke aerosol is about 0.1 to 0.6 microns. Due to the small diameter of the fibers used in the filters of the present invention, the particles collide with the fibers and are removed from the aerosol. This action is in contrast to the situation when the conventional thicker fibers are employed, typically in conventional cellulose acetate filters and in the polyolefin fiber filters proposed in U.S. Pat. No. 2,966,157 discussed above, in which the particles are displaced by air flow slip lines round the fiber and hence are not impinged on the fibers. Therefore, when fibers of conventional filter fiber size are employed (typically about 10 to 25 microns average diameter), the quantity of particles removed from the aerosol is considerably less than when the filter of the present invention is employed.

Conventional filter materials, such as cellulose acetate, absorb materials from the aerosol, including tar and nicotine, and as noted above have fibre sizes in excess of 10 microns. Therefore, when a cellulose acetate cigarette filter is examined after use it is found to be substantially dry, although stained. In contrast, the filters provided in accordance with the present invention are constructed of non-absorbent, thermoplastic fibres having fibre sizes less than 5 microns and it is found that the filter material of the invention after use is wet with impinged material removed from the aerosol.

It is observed that the "taste" of tobacco smoke filtered using the filter of the present invention is superior to that of conventionally-filtered tobacco smoke. It is theorized that this observed effect is due to the essentially different manner of removel of material from the aerosol by the present invention as compared with conventional filters. In the absorption of material using cellulose acetate fibers, taste-producing volatile materials may be absorbed in addition to the tar and nicotine, whereas in the impingement of materials on fine diameter non-absorbent fibers when the filters of the present invention are used, it is possible for the flavorful volatiles to pass to the smoker's mouth.

The polymeric materials used in the filters of the present invention may be any natural or synthetic thermoplastic material capable of formation into the fiber diameters required in the present invention. In addition, the material must be capable of withstanding the temperature of the tobacco smoke without substantial degradation and must be substantially inert to chemical attack by the tobacco smoke. Typical examples of materials which may be utilized to provide the fibers are polyolefins, polyesters and polyamides. Polyolefins which may be employed include polyethylene and polypropylene, or polymers of substituted olefins, such as, polytrifluorochloroethylene. Many polyesters may be used, such as polyethylene terephthalate. Among the polyamides which may be utilized are nylon 6, nylon 66 and nylon 610. Other thermoplastic polymeric materials also may be employed in the filters of the invention, such as polystyrene, and poly(methylmethacrylate. Fibers formed from copolymers also may be used.

While generally the filter element consists of a mass of a single polymeric material, it is possible to utilize a mass of fibers which is a mixture of fibers of two or more polymeric materials.

In the mass of fibers, the orientation of the fibers relative to the stream of tobacco smoke may be varied. Althoug it is possible to employ a mass of fibers in which the fibers are randomly oriented, it is preferred to employ a mass of fibers in which the individual fibers substantially are oriented transverse to the flow of smoke. It has been found that statistically orienting the fibers in this manner results in higher tar and nicotine removal than when a randomly-oriented mass of fibers is employed.

The filters of the present invention may be formed in any convenient manner. For example, fibers may be melt spun from a die having a plurality of openings therein, so that a mass of fibers is extruded. The mass may be collected and used as such, or may be subjected to physical treatment before use. Polymeric materials having low melting points and low melt viscosities are preferred since the heat required in the spinning operation thereby may be minimized.

EXAMPLE

The invention is illustrated further by the following Example.

EXAMPLE

Cigarettes were tested in a smoking apparatus capable of collecting and measuring total particulate solids which includes tar and nicotine, in smoke. Cigarettes tested, at the same pressure drop along the length thereof, were a cigarette with no filter, a cigarette with a conventional cellulose acetate filter and a cigarette with a filter including a disc of Acrylite fibers having an average diameter about 1 micron. The results are reproduced below:

Total Particulate solids ______________________________________ cigarette with Acrylite fiber filter 8.4 mg cigarette with cellulose acetate filter 16.5 mg cigarette with no filter 30.5 mg ______________________________________

These results show the effectiveness of a filter constructed in accordance with the present invention in removing tar and nicotine from cigarette smoke as compared to a conventional filter and no filter at all.

While the invention has been described with particular reference to cigarettes, the filters provided by the present invention may be utilized with other tobacco smoking articles, such as, pipes and cigarette and cigar holders.

Modifications are possible within the scope of the invention.

Claims

What we claim is:

1. A self-sustaining filter for tobacco smoke comprising a plurality of filter elements, and including a substantially airtight tubular holder, a pair of cylindrical cellulose acetate filter elements positioned within and in contact with the inner wall of the holder, said pair of filter elements being spaced apart from each other to define a gap therebetween, said pair of filter elements and said tubular holder combining to provide sufficient crush-resistance to provide a self-sustaining filter, and a third filter element consisting wholly of a plurality of randomly-oriented, non-crimped, smooth-surfaced, solid fibers of a thermoplastic polymeric non-absorbent material selected from polyolefins, polyesters, polyamides and polystyrene, each of said fibers having a uniform diameter less than about 5 microns, with substantially all of the fibers being below 2 microns in diameter and having an average fiber diameter of about 1 micron, the majority of the said fibers being oriented transverse to the flow of the tobacco smoke, said third filter element being positioned in the gap between said pair of filter elements, said third filter element having a diameter substantially that of said tubular holder and being in engagement with said inner wall.

2. The filter of claim 1 wherein said thermoplastic polymeric material is a nylon.

3. The filter of claim 1 wherein said thermoplastic polymeric material is poly (methylmethacrylate).

4. The filter of claim 1 wherein said third filter element is in the form of a disc.

5. The filter of claim 4 wherein the faces of said disc engage the opposed ends of the pair of elements.