Tobacco Smoke Filter and Methods of Making the Same

Abstract

A tobacco smoke filter (10) can comprise a spiral core (11) of impermeable or semi-permeable material. A filter spiral core (11) is surrounded by filter material (12) such as cellulose acetate and wrapped in paper (13).

Description

FIELD OF THE INVENTION

The invention relates generally to devices for filtration of tobacco smoke, their manufacture and use. More specifically, the invention relates to filters suitable for use in smoking devices.

BACKGROUND OF THE INVENTION

Single-use, disposable filters have been incorporated in smoking products for decades. Filters are commonly made of cellulose acetate, relying on a process whereby cellulose acetate is dissolved in a solvent such as acetone, and polymer filaments are spun out of the solution. The filaments are lubricated and bundled, then crimped and dried. Alternative filter materials include polypropylene and cellulose. Filters may be segmented, potentially with different materials in different segments; they may incorporate granular additives such as carbon.

The filter is located at one end of the tobacco rod so that smoke from the burning tobacco rod, which comprises a particle phase and a vapour phase, passes through the filter before being inhaled by the user. The fibres of the filter form a mechanical barrier which entraps particulate matter in the smoke stream. Early filters relied solely on this mechanical filtration; see for example U.S. Pat. No. 4,502,495.

More recent approaches include providing ventilation holes along the paper wrapper outside the filter to dilute the inhaled smoke. They also target the volatile constituents of the smoke, which are typically unaffected by the physical barrier of the filter. For example, adsorbent or absorbent materials are often added to selectively remove volatile elements from the smoke stream.

Activated carbon, porous minerals such as meerschaum, silica gel, and cation- or anion-exchange resins are frequently used as filter additives. Carbon or charcoal can be useful for removing acidic gases. Meerschaum has a strong adsorption affinity for charged species. Silica gels readily adsorb aldehydes and hydrogen cyanide. Cation exchange resins have been proposed for nicotine removal, while anion exchange resins have been proposed for the removal of smoke acids. Researchers are continually developing new additives which target classes of or specific smoke constituents.

One challenge faced with the addition of granular or particulate material to the filter filaments is how to adhere the individual particles in such a way that they remain active. For example, adhesives which ensure particles stay in position on fibers can block reaction sites on the particles. One solution has been to form cavities in the filter and load them with batches of particles, although that presents a different problem, namely, how to channel the smoke stream through such a loose bed of particles during use.

A further solution to containment of particles is to enclose them in tubes running parallel to the direction of smoke flow, whereby the smoke passes through the tubes and contacts the particles therein. By making the tubes non-linear, the route of filtration is longer, see U.S. Pat. No. 4,373,539.

Other examples of known filters are disclosed in WO 86/03381, US 2003/0200973, and EP-A 0033772, which describe various filters having a helical channel for smoke.

As reducing particulate and vapour constituents in smoke remains a pressing need in the art, new materials and methods for improving upon existing filters are desired. Particularly, solutions which can be used in conjunction with any variety of conventional or novel filter materials and additives would be of particular benefit.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a smoke filter for a tobacco product comprising an axially extending filter section defining a path along which, in use, smoke passes through filtration material, wherein the path extends helically around the axis of the filter. By providing a smoke path that thus winds around the axis of the filter, the contact time of the smoke with the filtration material and the surface area of filtration material contacted may be increased.

According to an embodiment of the invention, a tobacco smoke filter is provided which comprises a generally cylindrical enclosure having an inner diameter and a helical element having a diameter and disposed in the enclosure, where the diameter of the helical element is approximately equal to the inner diameter of the enclosure. The filter further comprises filtration means disposed between the helical element and the enclosure.

The enclosure may comprise plug wrap, which may comprise a plurality of ventilation holes. If provided, ventilation holes may be positioned to correspond to regions of the enclosure which do not overlie the helical element. The enclosure may be at least two layers, for example, an outer layer of plug wrap and an inner layer of cellulose acetate adjoining the helical element.

The helical element may comprise polypropylene, polyethylene, paper, carbon paper, impregnated paper or any other materials as taught herein and may comprise a coating layer on an outer surface thereof. The coating layer may comprise activated charcoal, activated coconut carbon, activated coal-based carbon, zeolite, silica gel, meerschaum, aluminium oxide, carbonaceous resin, and combinations thereof. The helical element may comprise compressible edges at the point where the element may contact the inner diameter of the enclosure. Alternatively or in addition, the central portion of the spiral core may be compressible.

The filtration means may comprise at least one material selected from the group consisting of cellulose acetate, polypropylene, polyethylene, gathered paper, and combinations thereof, for example, randomly orientated cellulose acetate. The filtration means may further comprise activated carbon, flavourant, adsorbent, or absorbent.

In one embodiment, the filtration means occupies substantially all of the space between the helical element and the inner diameter of the enclosure. This ensures that the smoke flowing along the helical element must pass through the filtration means, thereby providing good filtration behaviour. In addition, tight packing of the filtration means within the filter imparts a solid and reassuring feel to the filter. This tight packing can be achieved by using small fibres or such-like of filtration materials.

According to another embodiment, a smoking article is provided which comprises a tobacco smoke filter according to the present invention.

According to another embodiment, the invention relates to a method of making a tobacco smoke filter which comprises the steps of providing a generally cylindrical helix having intra helical turn space and having an outer edge, placing filtration means in the intra helical turn space, and enclosing the outer edge of the filled helix in an enclosure.

As used herein, “tobacco” refers to any part, e.g., leaves, flowers, stems, of any member of the genus Nicotiana and reconstituted materials thereof. It includes derivatives such as specific compounds found in natural tobacco, e.g., nicotine, whether extracted or synthesized, as well as structural derivatives such as the fibrous portion of a tobacco leaf. It further includes tobacco substitutes which comprise individual chemicals and/or complex chemical entities which, when appropriately prepared, physically resemble natural tobacco.

As used herein, “tobacco smoke filter” means any element which is intended for use as a unit through which tobacco smoke passes and in which certain components in the tobacco smoke are slowed, cooled, and/or retained. Tobacco smoke includes both the by-product of tobacco combustion and the by-product of tobacco heating in the absence of actual combustion.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

So that the subject invention may be easily understood and readily carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:

FIG. 1 represents a perspective, partially broken away view of a filter of the invention;

FIG. 2 shows a side elevation, partly longitudinal cross-section and partially broken away view of a filter of the invention;

FIG. 3 shows a cross sectional view of a filter of the invention taken along lines A-A of FIG. 2;

FIG. 4 represents a perspective, partially broken away view of a filter of the invention;

FIG. 5 shows an axial cross-section view of a filter of the invention;

FIGS. 6A and 6B show two views of the element B of FIG. 5, one when a filter of the invention is uncompressed and one when a filter of the invention is compressed;

FIGS. 6C and 6D show alternate configurations for element B of FIG. 5;

FIG. 7 is a schematic diagram of a manufacturing process according to the present invention;

FIG. 8 shows a portion of an embodiment of a machine for producing filters of the invention;

FIG. 9 shows a side elevation view of an embodiment of a machine for packing intra helical space of filters according to the invention; and

FIG. 10 shows a cross sectional view taken along lines A-A of FIG. 9.

DETAILED DESCRIPTION

The invention relates to tobacco smoke filters which comprise a helical element centred axially therein. The element may take on any number of configurations in cross-section, although it will generally be described herein as a single helix. Referring to FIG. 1, a tobacco smoke filter 10 is shown with a spiral core 11. The spiral core is provided as shown in the embodiment of FIG. 1 with filter means 12. Spiral core 11 and filter means 12 are visible due to partial breakaway of the enclosure 13, here depicted as plug wrap.

Spiral core 11 has a diameter which is approximately equal to an inner diameter of enclosure 13. That is, the outer edges of the helix generally abut the enclosure. Filter means 12 is located in grooves formed by edges of the helix between spiral core 11 and enclosure 13.

As is well known to product engineers, a helix's curve can either move from the lower left to the upper right, making it a right-handed helix, or from the lower right to the upper left, thus being a left-handed helix. Either right- or left- handed helices may be used as a spiral core in the practice of the present invention.

The pitch of the helix, that is, the length of one complete helical turn, is selected based on a balancing of the desire to increase the filtration route with the need to permit easy inhalation. The pitch that will be employed with any filter according to the invention can be optimised by a skilled worker based on variables such as material for the helix element, particularly whether or not it is porous; material surrounding the helix and how densely it is packed, and ventilation, among others. The pitch might be 1-4 mm, for example 2-3 mm.

Permeability of the material used in the spiral core may preferably be low in certain applications, so that it is effectively non-porous. This, combined with the placement of a less porous enclosure tightly against the helix, ensures that as smoke is inhaled it is forced to travel in a spiral fashion through the filter. This increases physical filtration and provides an opportunity for additional removal of volatile components from the tobacco smoke. Extruded plastics, foils or coated papers are some examples of materials which may be used to form the spiral core.

According to another embodiment, the material used in the spiral core is porous. Pores in the material may be formed to specifically capture select smoke constituents. For example, the material can be polymer, molecularly imprinted with target constituents. The pores in the material may be impregnated with an additive such as flavourant or diluent, which additive could be inhaled in the first few puffs during use leaving behind empty pores capable of interacting with subsequent smoke streams passing there through. The spiral core may be formed of activated carbon, which may have a density such that the majority of smoke is encouraged around the helix and a minority of the smoke passes through the carbon structure of the spiral core. A binder may be utilized to allow granules of activated carbon to be formed into and retain the spiral shape.

According to another embodiment the spiral core is non-porous but provided with a porous surface for interacting with smoke components. Alternatively or in addition, the spiral core may be coated, for example with flavourant or with an agent designed to entrap, neutralize, or otherwise interfere with smoke constituents.

The width and length of the spiral core is preferably approximately equal to the width and length of a standard tobacco smoke filter. For example, a standard cigarette filter is typically in the range of 10-30 mm long and 25-30 mm in circumference. The width of the spiral core may be less than the standard thus allowing a co-axial or multi-component enclosure.

Where the spiral core is of firm and inflexible material, it may be preferred to provide a region of tightly packed cellulose acetate co-axially around the outside of the spiral to cause the filter, when it use, to more closely approximate the feel of a standard filter. The length may also be adjusted, for example it may be part of the length of a standard filter to accommodate one or more filter elements on either or both ends.

To provide a standard looking filter it may be preferred to have a filter segment of cellulose acetate at the mouth end of the smoking article visible to the user, so a multiple segment filter incorporating the invention could be half cellulose acetate at the user end and half novel tobacco smoke filter at the tobacco rod end. Where the helical element forms only one part of a multi-element filter it may be preferred to refrain from adding filter means within the helix.

The thickness of the material forming the spiral core is also a product variable. Where the helix is impermeable to smoke it may be on the order of 0.5-2 mm. When the helix is intended to be selectively permeable to smoke constituents and/or ambient air, the thickness may be 0.5-3 mm. It need not be the same across the entire cross-section, for ease of production or good product feel it may be that the centre of the spiral is thicker than the furthest edges. Alternatively or in addition, the central axis of the spiral core may be solid, forming a circle with outwardly radiating flanges in cross section. In conjunction with manipulation of the thickness of the material forming the spiral, pitch can be adjusted to help provide the desired draw resistance or pressure drop.

Ventilation holes, commonly known in the art, may be incorporated in a filter according to the invention. Such holes would increase dilution of tobacco smoke and facilitate inhalation through the circuitous filtration path. It may be most effective to provide ventilation holes in a spiral pattern corresponding to the spiral core, at locations where the enclosure does not abut the edge of the spiral core. Pressure drop may be considered when determining whether to use ventilation holes, the number and location being dependent on the shape and material of the helix as well as consideration of any filter means used.

A spiral core of the present invention could be manufactured according to any appropriate method. Specific manufacturing requirements vary depending on the material and dimensions chosen, and on whether there is a coating on the spiral core. For example, an extruded core could be entrained in cellulose acetate during the conventional filter-making process.

The spiral core and its location in relation to the enclosure causes an inhaled smoke stream to take a longer than standard, circuitous path through the filter before reaching the user. This provides the possibility of increased surface area and increased time for filtration to occur. Accordingly, the spiral core itself comprises a type of filtration means itself.

If the enclosed spiral core were surrounded only by ambient air, inhaled smoke would not be maximally filtered as it would merely need to travel a longer path prior to entering the user's mouth. The longer path would serve to cool the air and some particulate matter may settle out and adhere to the core or surrounding paper. Even where the spiral itself core comprises filtration material, and even where such a spiral core is used as one segment of a multi-segment filter, such a design fails to maximize the opportunities to filter smoke which are available and thus might only be preferred embodiments for special uses.

Thus, additional materials are provided in the space around the helix up to the enclosure to maximize filtration opportunities for standard uses. For example, randomly orientated acetate fibres, i.e. pieces of standard filter material can be packed more or less tightly around the helix to provide filtration means while still allowing smoke inhalation. Acetate fibres having any size range which allows incorporation in the filter, for example, 2 mm, could be employed.

Other options for material around the spiral core include any filtration materials which are appropriate for use with filtering inhaled smoke, and may be fragments, twists, or other. The material placed around the spiral core may incorporate any number of additives such as adsorbents, absorbents, diluents, flavours, and the like. Materials and methods for incorporating them into various filter components are known in the art. For example, both activated charcoal and resins are commonly used and could be provided.

Conventional means for producing smoking articles may be used in accordance with the invention. Tobacco smoke filter material according to the invention having the same dimensions and handling properties as standard filters can be provided to the machinery. The machinery will incorporate the novel filter with tobacco rods, wrapping paper and tipping paper to produce an article resembling conventional productsin size and appearance but provided with a novel filter according to the invention.

The enclosure containing the spiral core may be conventional plug wrap. It may be coated on one or both sides with any desired additive, such as colourant and fragrance along the outer surface, to resemble a cork pattern and to have an appealing scent, and inner coating of diluent, flavourant, materials which improve filtration such as activated carbon particles, and the like. A layer of material may be provided along the inner surface to improve the tactile qualities of the filter, for example, a layer of cellulose acetate forming the inner diameter of the enclosure may cause the filter to feel similar to conventional filters, which may increase user appeal.

Under present manufacturing conditions, a filter portion is compressed by about 1 mm in circumference when tipping papers is added to connect the filter element to the tobacco rod. In an embodiment of the invention which is provided with a layer of cellulose acetate between the plug wrap and the spiral core the cellulose acetate layer might be able to accommodate the compression. However, and particularly in the case of spiral cores which directly will be directly compressed during addition of a single layer enclosure, it may be preferred to provide some flexibility or compressibility in the spiral core.

FIG. 5 depicts one example of a cross section of a spiral core 11 surrounded by an enclosure 12. Circled region B is shown in more detail in FIGS. 6A and 6B. FIG. 6A shows how the edge of spiral core 11 can be configured in the region where it is intended to contact enclosure 12. The edge has a deformable flange-type feature which, upon compression, flexes to allow inward pressure from enclosure 12. FIG. 6B shows how the region accommodates compression. After the compressing forces are released the edge of spiral core 11 re-positions itself to the configuration of FIG. 6A.

An added benefit of the type of configuration shown in FIGS. 6A and 6B is that it has a sealing effect between the core and the enclosure, further ensuring that smoke inhaled through the filter is forced through the spiral route. Depending on the configuration and materials used for spiral core, the compressibility may also provide improved tactile feel for the user. For example, the material used for the spiral core may be elastic and provide tension when deformed so that it re-expands to the original configuration after application of the tipping paper. Alternative tipping paper application steps can be taken where, for example, it would be economically preferred or where spiral cores are provided which are not designed to be compressible.

Alternatively, the spiral core may be compressible. Preferably it is also expandable so as to return to its original size after compression. Such an embodiment may be provided with rounded edges along the portion of the spiral core that is-in contact with the enclosure to avoid puncture or tearing during compression or handling, see FIG. 6C. Another alternative would be to provide a flattened edge which flattened portion sits flush with the enclosure, also reducing the risk of tearing and possibly also improving the sealing effect and tactile feel, see FIG. 6D.

One method for manufacturing a filter according to the invention is represented schematically in FIG. 7. A device 70 comprises a spiral material supply 71 which could be a bale of extruded plastic helix. A filter means supply 72 could be a batch of cellulose acetate fibres. An enclosure supply 73 provides means for enclosing the filter components, and could be a roll of plug wrap.

While standard methods typically produce filter materials as a long cylinder which is cut into smaller units for individual use, it may be that certain spiral cores are advantageously made unit by unit then incorporated into a filter and joined to a tobacco rod. They may form the entire length of the filter region, alternatively they may be part of a multi-segment filter.

In use, device 70 feeds spiral material from supply 71 to a filter means addition area 74. Therein materials from filter means supply 72 are provided to the spiral. An additive application means 75 is provided, which could be a single means as shown or a series of means, potentially each supplying a different additive. A drying means 76 is provided which may cure the inner filter components prior to or after addition of enclosure from enclosure supply 73. A cut off 77 is situated to cut prepared filter material to the desired length.

Any known or developed alternative methods could be used to produce a tobacco smoke filter according to the invention. For example, as shown in FIG. 8 a multi-segment filter is being produced. A continuous rod 81 is shown, which is intended for eventual division into a plurality of individual filter units 82. Each filter unit 82 comprises a first filter segment 83, a second filter segment 84, and a third filter segment 85. In the embodiment shown, the spiral core portion is provided in second filter segment 84.

Particles 86 are added to the spiral core of second filter portion 84 by a dispensing means 87. Particles 86 could be filter means, additives, or a mixture of the two. One option for an embodiment such as that shown in FIG. 8 would be to have a first filter segment of cellulose acetate, a second filter segment of non-porous spiral provided with flavourants in the intra-helical space, and a third filter segment comprising carbon such as a cavity filter filled with carbon particles or carbon paper formed into a filter segment. As should be evident to the skilled person, there are a plurality of existing methods which could be employed similar to the dispensing means of FIG. 8.

It is contemplated that a plurality of dispensing means could be provided to the same rod, wherein each would supply a different material to the spiral core. For- example, a first means supplying a first flavourant, a second means supplying an absorbent, and a third means supplying a second flavourant. The three means could be provided side by side to fill separate regions of the same spiral core with respective additives; alternatively they could be adding their respective materials throughout each spiral core one after the other.

Where spiral cores are designed such that differential smoke travel paths are observed, one or the other of these configurations may be preferred. For example, where it is observed that the beginning portion of an inhaled puff of smoke travels primarily along the central region of the core and the latter portion of the same puff travels along the outer regions of the core, toward the enclosure, a multi-step or multi-layer fill might be preferred to provide first materials that will affect the beginning portion of a puff and second materials that will affect the latter portion of a puff.

A further example is shown in FIG. 9, where a spiral core 11 is passed through a rotating feeder 91 which simultaneously provides material 92 around the core and provides for containment of the filled core in an enclosure 13. A cross-section along lines A-A is shown in FIG. 10, where it is evident that material 92 is passed into feeder 91 and fills any space present around core 11.

While addition of filter or additive material to the spiral core after formation may be a preferred method for certain placations, where materials and design allow a single process step could handle all functions. For example, a rotating head could extrude a spiral core while simultaneously filling the intra-helical space with filter and/or additive material. A plurality of materials may be mixed first then added as a mixture, alternatively there could be one or more streams of each additive fed discretely. This latter form may be preferred where the added materials handle differently or where settling or other problems occur in a mixture.

Although FIGS. 7-10 relate to a single line for working with spiral cores of the present invention, it should be apparent to skilled persons that manufacturing efficiencies may best be met by providing a plurality of units or a series of steps in parallel. For example, the means shown in FIGS. 9 and 10 could be provided in duplicate or triplicate, thus producing two or three times as much filter material as would otherwise be made.

Example 1 Filter Manufacture

Activated carbon is moulded into a helical shape approximately 6 mm in diameter. An average pitch and low porosity, i.e., low permeability, are used. The carbon is cut into lengths of approximately 20 mm. Units of standard cellulose acetate tow approximately 6 mm in diameter and approximately 10 mm long are provided and arranged in alternating fashion with lengths of carbon helix.

The intra helical space of the carbon helix is provided with a mixture of flavourant and adsorbent before the length of helix/cellulose acetate tow is wrapped with an approximately 0.5 mm thick layer of cellulose acetate about its circumference. Plug wrap may optionally be provided around the cellulose acetate layer as known in the art.

This provides a length of filter material which may be cut along the middle of the approximately 10 mm lengths of cellulose acetate tow to provide a plurality of filter units each approximately 30 mm in length and each comprising an approximately 5 mm cellulose acetate tow at either end, surrounding a carbon helix with additives in the intra helical space.

The filters thus produced may be incorporated in smoking articles, for example cigarette holders or water pipe mouthpieces, to provide an effective yet disposable filtration material for the smoke inhaled therethrough. Different lengths and thicknesses can be provided depending on the expected use. For uses with slightly flattened mouthpieces, the spiral core may be formed to have a slightly oval shape in cross-section. This would be regarded as still having a generally cylindrical shape as taught by the present invention.

Example 2 Cigarette Manufacture

A resin commonly used in tobacco smoke filters is extruded through a die to produce a tight helical shape approximately 7 mm in diameter and 10 meters long. The shape is fed into a machine which applies suction or vacuum, for example a suction garniture, to pack fibres of cellulose acetate around the helix. The packed helix is wrapped in plug wrap and cured on a drying garniture. The cured filter is cut to 60 mm lengths which are provided to a cigarette making machine.

The cigarette making machine uses the filter to produce cigarettes according to known methods. In brief, two tobacco rods are positioned at either end of the filter and, once secured, the filter is cut at the middle. An optional end segment, for example, a pad of cellulose acetate, is added at the mouth end of the cigarette to mask the helical core unit. The resultant product is a cigarette incorporating a novel tobacco smoke filter according to the invention.

The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.

Claims

1. A tobacco smoke filter comprising:

a generally cylindrical enclosure having an inner diameter;

a helical element having a diameter and disposed in the enclosure, wherein the diameter of the helical element is approximately equal to the inner diameter of the enclosure; and

filtration means disposed between the helical element and the enclosure.

2. A tobacco smoke filter according to claim 1, wherein the enclosure comprises plug wrap.

3. A tobacco smoke filter according to claim 2, wherein the plug wrap comprises a plurality of ventilation holes.

4. A tobacco smoke filter according to claim 3, wherein the ventilation holes are positioned to correspond to regions of the enclosure which do not overlie the helical element.

5. A tobacco smoke filter according to claim 1, wherein the enclosure is at least two layers.

6. A tobacco smoke filter according to claim 6, wherein the enclosure is an outer layer of plug wrap and an inner layer of cellulose acetate.

7. A tobacco smoke filter according to any preceding claim, wherein the helical element comprises polypropylene, polyethylene, paper, carbon paper, or impregnated paper.

8. A tobacco smoke filter according to any preceding claim, wherein the helical element comprises a coating layer on an outer surface thereof.

9. A tobacco smoke filter according to claim 8, wherein the coating layer comprises activated charcoal, activated coconut carbon, activated coal-based carbon, zeolite, silica gel, meerschaum, aluminium oxide, carbonaceous resin, and combinations thereof.

10. A tobacco smoke filter according to any preceding claim, wherein the helical element is in contact with the inner diameter of the enclosure;

the helical element is laterally compressible; and

the helical element maintains contact with the inner diameter of the enclosure after compression.

11. A tobacco smoke filter according to any preceding claim, wherein the filtration means comprises at least one material selected from the group consisting of cellulose acetate, polypropylene, polyethylene, gathered paper, carbon, and combinations thereof.

12. A tobacco smoke filter according to claim 11, wherein the filtration means comprises randomly orientated cellulose acetate.

13. A tobacco smoke filter according to any preceding claim, wherein the filtration means further comprises flavourant, adsorbent, or absorbent.

14. A tobacco smoke filter according to any preceding claim, wherein the filtration means occupies substantially the entire space between the helical element and the inner diameter of the enclosure.

15. A smoking article, comprising a tobacco smoke filter according to any of claims 1-14.

16. A method of making a tobacco smoke filter, comprising:

providing a generally cylindrical helix having intra helical turn space and having an outer edge defining a generally cylindrical shape;

placing filtration means in the intra helical turn space; and

enclosing the outer edge of the filled helix in an enclosure.