Filter For A Smoking Article

Abstract

The present invention relates to smoking articles incorporating an improved filter in which the amount of smoke filtration varies with increased strength of draw. In particular, the filter comprises a plurality of passageways, at least one primary passageway I comprising a section of material which extends from the rod of smokable material to the mouth end of the smoking article and which has a high capacity to filter smoke and a high capacity to resist the passage of smoke. Via a series of small holes in an otherwise non-porous interface between the different passageways, smoke may be drawn between the primary passageway I and one or more secondary passageways II which have a low capacity to filter and resist the passage of smoke. At lower strengths of draw, smoke may become drawn through the small holes between the primary and secondary passageways. At higher strengths of draw, however, the rate at which smoke may pass through the small holes is limited by the restricted orifice effect and in this way the level of filtration of the smoke at different strengths of draw may be controlled.

Description

The present invention relates to a filter for a smoking article such as a cigarette.

BACKGROUND

Smoke from the combustion of smoking articles is made up of gaseous components and particulate matter, which is commonly referred to as “tar”. Various types of filter constructions are known in the art for removing undesirable components from the smoke as the consumer draws on the smoking article.

Many different filter arrangements for smoking articles have been described including composite filters wherein the filter comprises a plurality of separate filter sections with different filtering capacities, and filters comprising different materials such as cellulose acetate and charcoal particles.

Measures aimed at reducing the level of undesirable components of smoke which are inhaled by the consumer frequently consist of diluting the smoke by introducing ambient air into the smoking article as the consumer draws. The most common method of introducing ventilating air is by the incorporation of holes in the smoking article filter. This approach to reducing the concentration of undesirable components has several associated advantages. In particular, the smoker continues to receive the desired components and associated taste effects of the smoke. Furthermore, the cooler ambient air lowers the temperature of the smoke entering the mouth and throat, producing a more pleasant and agreeable smoking effect.

One major disadvantage of ventilating smoking articles in this way however, is that it may result in the over-dilution of the smoke, with consequent loss of flavour. Another disadvantage is that as the amount of ventilation is increased the sucking effort that the user is required to impart is decreased, resulting in frustration for the consumer and a less enjoyable smoking experience.

Consumers purchase and use smoking articles to obtain the effects of inhaling the products produced by combustion of the smokable material. When ventilating structures are introduced into the filter of the smoking article, the level of combustion products that the smoker receives is reduced. To compensate, it is known that consumers may increase the strength with which they draw on the smoking article, thereby increasing the flow rate through the smoking article, to increase the total volume of aerosol (a mixture of smoke and ventilating air) inhaled.

The most common method of providing for the entry of ventilating air into the smoking article is by the provision of small ventilation holes in the form of perforations or conduits through the outer wall of the smoking article. The flow rate of air through these ventilation holes into the smoking article is not a linear function of the strength of the draw. At higher strengths of draw, the proportion of air entering the smoking article via these ventilation holes is reduced as compared with the proportion of smoke from the combustion of the smoking article. This phenomenon, hereinafter referred to as “the restricted orifice effect”, is a consequence of the ventilation holes having a small diameter, typically of the order of less than 1 mm. Smaller holes impose greater inertial and viscous impedances on the gas that is drawn through the hole, and this effect is reduced as the diameter of the hole is increased. Therefore, a consequence of the restricted orifice effect is that as the strength of draw is increased, the volume of diluting air that can enter the smoking article is limited. The ignition end of the smoking article has a much larger diameter than the narrow ventilation holes and thus the air entering the smoking article via this route is not subject to the restricted orifice effect. As a result, as the strength of draw is increased, the concentration of smoke products inhaled also increases because the amount of ventilating air is essentially limited, but the amount of smoke is not.

The restricted orifice effect can be overcome by increasing the diameter of the ventilation holes. However, if the size of the perforations is increased then smoke will undesirably escape through these holes. Furthermore, the strength of draw that the consumer is required to impart will be reduced to the detriment of the smoking experience. It is therefore not a simple matter to construct a smoking article having a filter which is not subject to the restricted orifice effect, especially in the case of filters which are required to give a high level of ventilation.

STATEMENTS OF INVENTION

According to a first aspect of the present invention, a filter is provided for use in conjunction with a smoking article, the filter comprising first and second filter passageways operable to impart different filtration efficiencies. The filter is arranged so that the amount of smoke passing through one of the passageways relative to the other passageway is controlled by the restricted orifice effect. As the draw is increased, the level of smoke filtration may be increased.

The restricted orifice effect may be provided by a plurality of holes. The holes may be the only means by which smoke is able to pass between the first and second filter passageways. The diameter of the holes may be sufficiently small so that with increased draw the amount of smoke passing through the holes is increasingly restricted. The holes may be between 0.01 mm and 2 mm in diameter, preferably the holes may be between 0.1 mm and 1 mm in diameter.

At least one of the passageways may comprise material capable of filtering smoke. One of the passageways may comprise a void. Both passageways may comprise material capable of filtering smoke, the first passageway having a lower capacity to filter smoke than the second passageway.

As the draw is increased, the amount of smoke that is drawn via the first passageway may be limited by the restricted orifice effect and excess smoke is thus drawn via the second passageway.

The filter may be ventilated, and this ventilation may be by means of deep vents. Alternatively, the filter may not be ventilated.

The filter may comprise a plurality of longitudinally abutted filter sections and at least one of these filter sections may be an annular filter section.

The smoking article to which the filter may be attached may be a cigarette.

According to a second aspect of the present invention, a smoking article is provided, comprising a filter and a rod of smokable material.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, embodiments of the invention will be described by way of illustrative example with reference to the accompanying drawings in which:

FIG. 1 is a schematic sectional side elevation view, not to scale, of the filter of an individual filter cigarette according to a first embodiment of the invention,

FIG. 1 a indicates the route taken by smoke drawn with a low strength through the filter of FIG. 1,

FIG. 1 b indicates the route taken by smoke drawn with a high strength through the filter of FIG. 1,

FIG. 2 is a schematic sectional side elevation view, not to scale, of the filter of an individual filter cigarette according to a second embodiment of the invention,

FIG. 3 is a schematic sectional side elevation view, not to scale, of an individual filter cigarette according to a third embodiment of the invention, and

FIG. 4 is a schematic sectional side elevation view, not to scale, of an individual filter cigarette according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

Described herein is a filter for a smoking article which is arranged to utilise the restricted orifice effect to manipulate the passage of smoke and the level of smoke filtration.

As disclosed herein “high resistance section” is intended to refer to a section of material possessing a high capacity to resist the passage of smoke. This material is also capable of efficiently filtering the undesirable components from smoke, for example, by virtue of having a high density. The terms “high resistance section”, “high filtration efficiency material”, and “high resistance material” are therefore to be understood to have a common interpretation. On the other hand, “low resistance section”, “low filtration efficiency material”, and “low resistance material” and similar terms are used to refer to a section of material (or a void) possessing a low (or absent) capacity to resist the passage of smoke and a low (or absent) efficiency for filtering smoke. In describing these materials, the terms “high” or “higher” and “low” or “lower” are intended to reflect the density, resistance, or filtration efficiency of the materials relative to one another; that is, the high resistance section simply has a higher resistance than the low resistance section, although in fact it may possess a low capacity to resist smoke in comparison to other filter materials known in the art. Similarly, the low resistance section may actually possess a relatively high absolute capacity to resist smoke.

One embodiment of a smoking article incorporating a filter is shown in FIG. 1 in which the smoking article is a cigarette comprising a rod of smokable material 1 (shown partially) and a filter 2. The filter comprises filter material 3 which is composed of a high resistance material (shaded). As shown in FIG. 1, the filter is composed of a first section of filter material 3a and a second section of filter material 3b, the two sections being arranged in a longitudinally abutting relationship.

As shown in FIG. 1, the section of filter material 3a at the distal end 4 of the filter (away from the mouth end) has substantially the same diameter as the rod of smokable material 1. This is to ensure that all of the smoke drawn along the rod of smokable material 1 enters the filter material 3a.

The section of filter material 3b at the mouth proximal end 5 of the filter has a reduced diameter and thus a cavity 6 exists between the filter material 3 and the tipping paper 9 which circumscribes the filter 2 of the smoking article. This cavity 6 forms a low resistance section. The length of this cavity 6 may be equivalent to 10-90% of the total length of the filter 2. In some embodiments, the cavity is 20-80% of the total length of the filter. Preferably the cavity is 30-70% of the total length of the filter. More preferably the cavity is 40-60% of the total length of the filter. The cavity is most preferably 50% of the total length of the filter.

The mouth proximal end filter section 3b is circumscribed with non-porous plugwrap 7, and a non-porous annular ring member 27 separates the distal end filter section 3a and the cavity 6. This annular ring 27 is non-porous with the exception of a series of small perforations 8. As a consequence, as the consumer draws on the smoking article, smoke is only able to pass from the filter material 3a (the high resistance section) to the cavity 6 (the low resistance section) via the perforations 8 in the non-porous annular ring member 27. The rate at which smoke may pass from the high resistance section to the low resistance section through the holes 8 is limited by the restricted orifice effect when the user draws on the smoking article.

The perforations 8 are preferably between 0.01 mm and 2 mm in diameter, more preferably the perforations are between 0.1 mm and 1 mm in diameter.

In use, smoke is drawn into the mouth from the filter material 3 (the high resistance section) from a first passageway I that is defined within the tubular plug wrap 7 and also via the cavity 6 (the low resistance section) which provides a concentric, second passageway II. Smoke passing to the user's mouth along the first passageway I undergoes a greater amount of filtration than smoke that passes to the mouth through the second passageway II.

FIG. 1 a illustrates the situation of the smoker drawing on the smoking article with a low strength of draw, i.e. low negative pressure created by the user sucking on the filter. In this scenario, smoke is drawn through the filter material 3 along the first passageway I within the tubular plug wrap 7. Additionally, some smoke is drawn from the filter material 3 through the perforations 8 and into the cavity 6 as result of negative pressure produced by drawing on the mouthpiece. In taking the second passageway, the smoke is subject to a lower level of filtration than smoke that reaches the user along the first passageway.

At higher strengths of draw, however, as indicated in FIG. 1b, the restricted orifice effect imposes a limit on the amount of smoke that is able to pass through the perforations 8 and enter the second passageway that extends through the cavity 6. The remaining smoke is thus drawn into the mouth though the first passageway described above which exclusively comprises the high resistance filter material 3. As a result, the proportion of smoke that passes along the first passageway as compared with the second passageway increases with increasing draw and thus overall, the smoke drawn by the user is subject to an increased level of filtration with increasing draw.

As shown in FIG. 1, a means of supporting the tipping paper 9 at the proximal end 5 of the filter material 3 is provided. To this end, a band of corrugated paper 10 encapsulates a portion of the length of the mouth proximal section of filter material 3b and is arranged so that a series of substantially longitudinal channels 11 are formed. The outermost circumference of the corrugated wrapper 10 is substantially the same as the circumference of both the tobacco rod 1 and the distal end section of filter material 3a.

In alternative arrangements, the low resistance section is not in the form of a single circumferential cavity, but instead a plurality of low resistance sections may exist. An example of such an arrangement is shown in FIG. 2, in which the filter material 3 is shaped to provide multiple grooves or channels 28.

As described above, in the filter arrangement of FIG. 2, smoke is only able to pass from the filter material (the high resistance section) to the grooves (the low resistance sections) via a series of small holes 29 in a non-porous plug wrap 30 that provides an otherwise non-porous interface between the sections of high and low resistance. The restricted orifice effect imposes a limit on the rate at which smoke may pass from the high resistance section to the low resistance section when the user draws on the smoking article.

According to alternative embodiments, the low resistance section is not peripheral to the high resistance section, but is encapsulated by it.

Another embodiment is shown in FIG. 3. According to this embodiment, the high resistance section is a cylindrical section of filter material 12, extending the entire length of the filter 13, and having a diameter substantially the same as the diameter of the rod of smokable material 14.

The low resistance section is a conical-shaped cavity 15 cut into the mouth end of the filter material 12. The length of this cavity 15 may be equivalent to 10-90% of the total length of the filter 13. In some embodiments, the cavity is 20-80% of the total length of the filter. Preferably the cavity is 30-70% of the total length of the filter. More preferably the cavity is 40-60% of the total length of the filter. The cavity is most preferably 50% of the total length of the filter.

The inner surface of the conic cavity is covered in a non-porous coating 16. This may be achieved, for example, by inserting a pre-formed cone, of a non-porous material such as plastic that has been pre-perforated with holes, directly into the end of the filter material.

The non-porous lining 16 of the cavity is characterised by one or more bands of perforations 17. The perforations 17 are preferably between 0.01 mm and 2 mm in diameter, more preferably the perforations are between 0.1 mm and 1 mm in diameter.

Under conditions of a low strength of draw, smoke is drawn through the filter material 12 (high resistance section). Some of the smoke passes through the filter material 12 directly to the mouthpiece end, with the filter material providing the first passageway I, whereas some of the smoke passes into the conical cavity 15 (low resistance section) from the filter material 12 via the perforations 17 whereby the cavity 15 provides the second passageway II. As the strength of draw is increased the restricted orifice effect limits the amount of smoke that is able to pass through the perforations 17 into the second passageway and the remaining smoke is therefore drawn into the mouth via the first passageway that comprises a route composed entirely of high resistance material 12. As a result, the proportion of smoke that passes along the first passageway as compared with the second passageway increases with increasing draw and thus overall, the smoke drawn by the user is subject to an increased level of filtration with increasing draw.

In alternative embodiments, the cavity 15 in the mouth end of the filter is not conic but may be substantially cylindrical, or indeed any other suitable shape.

In alternative embodiments, the restricted orifice effect is harnessed to limit the passage of smoke from low resistance section to high resistance section.

Another embodiment is shown in FIG. 4 in which the filter arrangement shown in FIG. 1 is abutted to the rod of smokable material in a longitudinally reversed orientation. According to this arrangement, the mouth distal end of the filter material 18 (the high resistance section) has a diameter which is less than that of the rod of smokable material 19. As a result, a cavity 20 (low resistance section) exists between the filter material 18 and the tipping paper 21. Smoke may therefore become drawn from the rod of smokable material 19 into either high resistance section 18 or low resistance section 20.

The filter material 18 is covered in a non-porous plug wrap 22. At the mouth end of the cavity 20 an annular ring 28 is situated which is non-porous except for a series of small perforations 23. The perforations 23 are preferably between 0.01 mm and 2 mm in diameter, more preferably the perforations are between 0.1 mm and 1 mm in diameter.

Under conditions of a low strength of draw, smoke is drawn into the low resistance section 20, and is then subsequently drawn into the high resistance section 18 via the perforations 23 in the annular ring 28.

On the other hand, under conditions of a high strength of draw, the restricted orifice effect imposes a limit on the rate at which smoke is able to be drawn through the perforations 23 from the low resistance section 20 to the high resistance section 18. As a result, smoke becomes drawn directly from the rod of smokable material 19 into the high resistance section 18. Smoke therefore passes along the filter and into the mouth via a route composed entirely of high resistance material. Under conditions of a high strength of draw smoke is therefore subject to an increased level of filtration.

In some embodiments in which the low resistance section and the rod of smokable material are in physical contact, there is a non-porous barrier preventing smoke from directly entering the low resistance section. According to this arrangement, smoke is drawn from the rod of smokable material into the high resistance section and may then pass into the low resistance section via small holes as described above. Obviously these embodiments also encompass a mechanism whereby smoke can exit the low resistance section and pass into the mouth without being further restricted. Such a mechanism may encompass re-entry of smoke into the high resistance section.

In the embodiment shown in FIG. 4, a means of supporting the tipping paper 21 about the cavity 20 is provided, comprising a band of corrugated paper 24 that encapsulates a portion of the length of the filter material 18 and arranged so that a series of substantially longitudinal channels 25 are formed. The outermost circumference of the corrugated wrapper 24 is substantially the same as the circumference of the rod of smokable material 19.

The low resistance section need not be a cavity but can comprise a second filter material which has a lower resistance than the filter material comprising the high resistance section. The smoke is subject to an increased total level of filtration as compared with an arrangement where the low resistance section is simply a cavity.

The entire filter can be encapsulated by non-porous tipping paper that may be provided with a circumferential band of perforations which permit diluting air to pass into the filter material comprising the high resistance section.

Many techniques are known in the prior art for establishing perforations. For example, tipping paper may be perforated before (pre-perforated; PP) or after cigarette construction, and perforations may be introduced via an array of pins or using an on machine laser (OML) system. According to some embodiments, the perforations in the tipping paper and/or the plug wrap of the filter are manufactured using PP or OML technology and consequently do not penetrate substantially into the filter material comprising the high resistance section.

Recently an OML system for generating perforations which penetrate deep into the cigarette filter (deep vent OML; DVOML) has been disclosed (GB Patent Application Number 0809865.9).

In some embodiments, the tipping paper perforations comprise deep vents, which may be manufactured by DVOML, via alternative suitable methods, and which extend substantially towards the diametric centre of the filter material comprising the high resistance section. Via the use of deep vents, diluting air is drawn into the centre of the filter and this has the effect of modifying the flow of smoke drawn from the rod of smokable material. For example, in the preferred embodiment shown in FIG. 1 in which the perforations 26 comprise deep vents, air drawn through these holes will enter the filter material 3 close to the diametric centre of the filter material. This will have the effect of concentrating the smoke drawn from the rod of smokable material 1 into a diametrically peripheral zone of the filter material 3. The mixture of smoke and ventilating air exiting the filter material via the perforations 8 therefore contains a higher proportion of smoke than is the case when the perforations 26 only penetrate the tipping paper 9.

However, the filter need not be ventilated, or may be ventilated by alternative means, such as via an area of porous tipping paper and plug wrap.

The skilled artisan will understand that different embodiments of the invention will be more suitable for different types of smoking article, in particular, depending on the level of ventilation required. For example, in low tar products comprising a high degree of ventilation, it may be preferable for the perforations through which the passage of smoke may be restricted to be situated upstream (nearer to the rod of smokable material) than the site of ventilation, in order to maximise the effect.

For higher tar products on the other hand, in which ventilation is not such an important consideration, it may be advantageous to site the perforations through which the passage of smoke is be restricted towards the mouth end of the smoking article.

In some embodiments, the filter material comprising the sections of high and/or low resistance comprises a plurality of abutted filter sections made of similar or different materials. Each of the filter sections may consist of one or a combination of cellulose acetate, polypropylene, paper or any other suitable material. The filter section(s) may alternatively or additionally comprise carbonaceous material, for example, activated charcoal, a resin material such as amberlite or duolite, and/or catalytic material.

In some embodiments in which the filter comprises a plurality of longitudinally abutted filter sections, one or more of the filter sections may comprise an annular filter section. In this case the annulus may be a cavity or may be composed of filter material with a lower resistance, thus the annulus comprises the low resistance section.

In other embodiments, the filter is constructed from a plurality of filter sections and one or more annular sections are used wherein the annulus comprises the high resistance section.

In some embodiments the filter material may be shaped by heat moulding, embossing, crimping or any other suitable method.

Above is described what is believed to be the preferred embodiments of the current invention. However, those skilled in the art will recognise that changes and modifications may be made without departing from the scope of the invention.

Claims

1. A smoking article filter that provides an increased level of smoke filtration with increasing strength of draw, the filter comprising: first and second filter passageways, the first passageway having a higher smoke filtration capacity than the second passageway, wherein smoke from the first passageway is directed to the second passageway by means of one or more perforations, andwherein as the strength of draw is increased, the amount of smoke passing through the perforations is limited by the restricted orifice effect.

2. The smoking article filter as claimed in claim 1, wherein the diameter of the perforations is sufficiently small so that with increased draw the proportion of smoke passing through the perforations is increasingly restricted.

3. The smoking article filter as claimed in claim 1, wherein the perforations are between 0.01 mm and 2 mm in diameter.

4. The smoking article filter as claimed in claim 1, wherein one of the passageways comprises a void.

5. The smoking article filter as claimed in claim 1, wherein the first and second passageways comprise smoke filtration material, the filtration capacity of the smoke filtration material of the first passageway being higher than that of the second passageway.

6. The smoking article filter as claimed in claim 1, wherein the filter is ventilated.

7. The smoking article filter as claimed in claim 6, wherein the ventilation is facilitated by deep vents.

8. The smoking article filter as claimed in claim 1, wherein the filter is not ventilated.

9. The smoking article filter as claimed in claim 1, wherein the filter comprises a plurality of longitudinally abutted filter sections.

10. The smoking article filter as claimed in claim 9, wherein at least one of the filter sections is an annular filter section.

11. The smoking article filter as claimed in claim 1, wherein the smoking article is a cigarette.

12. A smoke filtration method correlated with draw strength, the method comprising: configuring a smoking article with a filter comprising first and second filter passageways, the first passageway having a higher smoke filtration capacity than the second passageway, wherein smoke from the first passageway is directed to the second passageway by means of one or more small perforations, wherein at lower strengths of draw, smoke passes through the perforations, and as the strength of draw is increased, the amount of smoke that passes through the perforations is limited by the restricted orifice effect.

13. The method as claimed in claim 12, wherein the diameter of the perforations is sufficiently small so that with increased draw the amount of smoke passing through the perforations is increasingly restricted.

14. The method as claimed in claim 12, wherein as the strength of draw is increased, the amount of smoke that is drawn via the first passageway is limited by the restricted orifice effect and excess smoke is drawn via the second passageway.

15. The smoking article filter as claimed in claim 1, wherein the perforations are between 0.1 mm and 1 mm in diameter.

16. A smoking article filter, comprising: first and second longitudinally abutting filter sections;a first passageway disposed in the second filter section and a second passageway circumscribing the first passageway;an annular section separating the first filter section from the second passageway; anda plurality of perforations disposed on the annular ring member.

17. The smoking article filter of claim 16, wherein the first passageway is a high resistance passageway and the second passageway is a low resistance passageway.

18. The smoking article filter of claim 17, wherein smoke drawn through the smoking article passes from the first filter section through the high resistance first passageway in the second filter section for a higher amount of smoke filtration.

19. The smoking article of claim 17, wherein smoke drawn through the smoking article passes from the first filter section to the second passageway through the plurality of perforations disposed on the annular section.

20. The smoking article filter of claim 19, wherein smoke passing through the low resistance second passageway undergoes a reduced amount of smoke filtration.