WO2013034512A1

WO2013034512A1 - Smoking article filter with flow restriction element and cavity

Info

Publication number: WO2013034512A1
Application number: PCT/EP2012/067065
Authority: WO
Inventors: Christophe Blanc; Blaise Walter Ryter
Original assignee: Philip Morris Products S.A.
Priority date: 2011-09-09
Filing date: 2012-09-03
Publication date: 2013-03-14
Also published as: EP2753198A1; JP6044908B2; EP2753198B1; PL2753198T3; ES2595159T3; JP2014528711A; RU2600911C2; RU2013157183A

Abstract

A smoking article (10) includes a flow restriction element (24) comprising a transverse barrier (28) including one or more orifices (38). The smoking article (10) defines a mouth end cavity (22) extending from the transverse barrier (28) of the flow restriction element (24) to the mouth end of the smoking article. The flow restriction element (24) is preferably provided in the filter (14) and the mouth end cavity (22) is preferably at least partially defined by a filter wrapper (26).

Description

SMOKING ARTICLE FILTER WITH FLOW RESTRICTION ELEMENT AND CAVITY

The present invention relates to a smoking article filter including a flow restriction element in combination with a mouth end cavity, and to a smoking article incorporating such a 5 filter.

Filter cigarettes typically comprise a cylindrical filter aligned in an end-to-end relationship with a wrapped tobacco rod, with the filter attached to the tobacco rod by tipping paper. In conventional filter cigarettes, the filter may consist of a plug of a fibrous filtration material, such as cellulose acetate tow, wrapped in porous plug wrap. During smoking, particulate matter from i o the mainstream smoke is deposited in the plug of cellulose acetate tow as the smoke is drawn through the filter. This may result in discolouration or staining of the cellulose acetate tow plug, which is usually visible at the mouth end of the smoking article.

Filters incorporating one or more structural inserts are also known. For example, it is known to provide filters including one or more flow restriction elements for increasing the

15 resistance to draw (RTD) of the smoking article. Flow restriction elements are typically provided in combination with ventilation at a position along the filter, in order to provide a filter that lowers the delivery of gas phase constituents in the mainstream smoke whilst maintaining an acceptable RTD. In previously proposed filters including a flow restriction element, one or more plugs of cellulose acetate tow are provided at the mouth end of the filter, downstream of the flow

20 restriction element. After smoking, there is usually visible staining of the cellulose acetate filter plug at the mouth end of the smoking article.

It would be desirable to provide a smoking article filter with reduced staining or reduced visibility of staining at the mouth end of the filter. It would also be desirable to provide a smoking article filter that enables improved mixing of the mainstream smoke with ventilation air

25 entering the filter. It would be particularly desirable if a smoking article incorporating such a smoking article filter could provide an improved smoking experience to the consumer during smoking.

According to the invention there is provided a smoking article comprising a flow restriction element comprising a transverse barrier including one or more orifices. The smoking

30 article defines a mouth end cavity extending from the transverse barrier of the flow restriction element to the mouth end of the smoking article. The smoking article also comprises a first downstream tubular portion downstream of the transverse barrier, the first downstream tubular portion at least partially defining the mouth end cavity. One or more openings are provided in the first downstream tubular portion to form a communication path between the external

35 periphery of the first downstream tubular portion and the mouth end cavity.

The provision of the openings in the flow restriction element has been found to advantageously improve the mixing of ventilation air and the mainstream smoke and to further improve the dispersion of the smoke stream that is delivered to the consumer. The occurrence of staining at the mouth end of the filter is thereby further reduced. Furthermore, the effects of the dispersion of the smoke on the taste and mouth feel of the smoke are enhanced.

Preferably, smoking articles according to the invention include a filter comprising the flow restriction element and a filter wrapper circumscribing the filter, wherein the filter defines the mouth end cavity.

According to the invention there is further provided a filter comprising: a flow restriction element comprising a transverse barrier including one or more orifices; and a filter wrapper circumscribing the filter. The filter defines a mouth end cavity extending from the transverse barrier of the flow restriction element to the mouth end of the filter. The mouth end cavity is a space at the mouth end of the filter formed by one or more of the components of the filter. The filter also comprises a first downstream tubular portion downstream of the transverse barrier, the first downstream tubular portion at least partially defining the mouth end cavity. One or more openings are provided in the first downstream tubular portion to form a communication path between the external periphery of the first downstream tubular portion and the mouth end cavity.

In the following description, any references to filters according to the invention also apply to the filters of smoking articles according to the invention, unless stated otherwise.

Filters according to the present invention may advantageously be used in filter cigarettes and other smoking articles in which tobacco material is combusted to form smoke. Filters according to the present invention may also be used in smoking articles in which tobacco material is heated to form an aerosol, rather than combusted. Filters according to the present invention may also used in smoking articles in which a nicotine-containing aerosol is generated from a tobacco material, tobacco extract, or other nicotine source, without combustion or heating.

As used herein, the term "smoke" is used to describe smoke produced by combustible smoking articles, such as filter cigarettes, and aerosols produced by non-combustible smoking articles, such as heated or non-heated smoking articles of the types described above.

The term "flow restriction element" is used to refer to a structural filter insert that restricts the flow of the mainstream smoke through the filter by providing a pathway of reduced size or cross section through which the mainstream smoke must be drawn. The reduction in the size of the pathway relative to the overall size of the filter makes it more difficult for the smoke to be drawn through the filter, so that the resistance to draw is increased. In filters according to the invention, the flow restriction element comprises a transverse barrier including one or more orifices. The mainstream smoke is restricted to passing through the orifices only. Preferably, the transverse cross sectional area of the passage or passages through which the mainstream smoke must be drawn is less than about 75% of the transverse cross sectional area of the overall filter, more preferably less than about 50%, and most preferably less than about 10%.

The terms "upstream" and "downstream" are used to describe the relative position of components of the filters according to the invention with reference to the direction of the flow of the mainstream smoke through the filter during smoking of a smoking article incorporating the filter.

The term "mouth end" refers to the end of the filter that is intended to be placed between the lips of the consumer during smoking. In the assembled smoking article, the mouth end of the filter is located at the opposite end to the end of the smoking article that is lit.

The term "transverse" describes a component or direction that is substantially perpendicular to the longitudinal or principal axis of the filter and smoking article.

Filters according to the present invention incorporate a flow restriction segment to increase the resistance to draw (RTD) of the filter. Flow restriction elements find particular application in ventilated filters. Ventilation is incorporated into filters in order to reduce the delivery of mainstream smoke constituents, such as tar or carbon monoxide. However, high levels of ventilation can result in unacceptably low levels of RTD. A flow restriction element can therefore advantageously be incorporated into the filter to achieve a filter with an acceptable RTD which can still provide reduced delivery of tar and carbon monoxide.

Filters according to the present invention comprise a mouth end cavity. The cavity is formed or defined by one or more of the filter components, as described in more detail below. The filters therefore provide an open space at the mouth end of the filter such that there are no additional filter components between the flow restriction element and the mouth end of the filter. During smoking, the mainstream smoke will therefore pass through the orifices in the transverse barrier of the flow restriction element and will then flow substantially unobstructed through the mouth end cavity and out of the mouth end of the filter.

The arrangement of the filter with a mouth end cavity means that the transverse barrier of the flow restriction element is visible from the mouth end of the filter. The internal surfaces of the mouth end cavity will also be visible. Advantageously, the use of a cavity at the mouth end of the filter in place of a fibrous filtration material has been found to significantly reduce the visible staining of the filter after smoking. The arrangement of the filter is such that there is minimal filtration of the mainstream smoke downstream of the transverse barrier of the flow restriction element and therefore minimal deposition of particulate matter from the mainstream smoke. In particular, there will be minimal deposition of particulate matter on the visible surfaces at the mouth end of the filter.

The provision of a mouth end cavity downstream of the transverse barrier of the flow restriction element additionally changes the flow dynamics of the mainstream smoke as it is drawn through the filter, compared with the flow dynamics observed in a conventional filter arrangement. In a conventional filter comprising a plug of filtration material as the most downstream element of the filter, the mainstream smoke tends to be delivered to the consumer from the mouth end of the filter in a channelled, concentrated smoke stream. In filters according to the invention, the mainstream smoke passes through the one or more orifices in the transverse barrier into the mouth end cavity, where the smoke expands and disperses before being delivered to the consumer.

Where ventilation is provided in the filter, the mouth end cavity also provides a space in which the mainstream smoke can more effectively mix with any ventilation air before the diluted smoke is delivered from the mouth end of the filter.

The dispersed smoke stream is likely to provide a different sensation in the mouth of the consumer, which may be preferred over the more concentrated smoke stream of conventional filters.

In order to provide sufficient space for adequate mixing and expansion of the mainstream smoke, the mouth end cavity may extend at least about 2 mm from the transverse barrier to the mouth end of the filter. Preferably, the mouth end cavity extends at least about 5 mm from the transverse barrier, more preferably at least about 10 mm, and most preferably at least about 12 mm. Ventilation holes for providing the ventilation air may be at least about 8 mm from the mouth end of the filter, preferably at least about 10 mm, and more preferably at least about 12 mm.

The mouth end cavity of filters according to the invention is preferably at least partially defined by a filter wrapper. The term "partially defined" is intended to mean that the filter wrapper defines the mouth end cavity along only a part of its length. In preferred embodiments, the mouth end cavity is at least partially defined by the plug wrap of the filter, which extends beyond the downstream end of the flow restriction element to define a hollow, cylindrical tube. The inner periphery of the tube defines a cylindrical cavity providing all or part of the mouth end cavity of the filter. Where the plug wrap defines only a downstream part of the mouth end cavity in a longitudinal direction, the remainder of the mouth end cavity is preferably defined by the flow restriction element, as described below.

Preferably, where the plug wrap at least partially defines the mouth end cavity, the plug wrap is formed of a paper material having a higher basis weight than conventional plug wrap materials. This provides a stiffer plug wrap which forms a rigid hollow tube at the mouth end, to avoid the collapse of the mouth end cavity when the filter is compressed between the lips of the consumer.

The plug wrap may have a basis weight between about 40 grams per square meter and about 130 grams per square meter. More particularly, the plug wrap may have a relatively low basis weight between about 40 grams per square meter and about 60 grams per square meter, or a relatively high basis weight between about 60 grams per square meter and about 130 grams per square meter.

The plug wrap may alternatively be formed of a plastics material, for example, a transparent plastics material. The basis weight of the plastics materials may be between about 5 40 grams per square meter and about 70 grams per square meter and the plastics material may have a thickness between about 25 micron and 50 micron. In some embodiments, the plug wrap may be substantially non-porous, for example having a porosity of less than about 20 Coresta units, more preferably less than about 10 Coresta units. In other embodiments, the plug wrap may be porous, for example having a porosity of greater than about 20 Coresta units, i o more preferably greater than about 100 Coresta units, and most preferably greater than about 1000 Coresta units.

In certain embodiments of smoking articles according to the invention, the tipping paper attaching the filter to the rod of tobacco material may at least partially define the mouth end cavity, in addition to or instead of the plug wrap. For example, in certain embodiments, both the

15 plug wrap and the overlying tipping paper are coextensive, extending beyond the downstream end of the flow restriction element to at least partially define the mouth end cavity. In alternative embodiments, the tipping paper extends beyond the flow restriction element and the plug wrap to at least partially define the mouth end cavity.

The flow restriction element of filters of the present invention includes a transverse

20 barrier having one or more orifices providing restricted pathways for the smoke passing through the barrier. The transverse barrier is formed of a smoke impermeable material such that the orifices effectively provide the only pathway through the filter for the smoke. The number of orifices provided in the transverse barrier and the dimensions of each orifice may be selected in order to achieve a desired RTD. Preferably, the transverse barrier comprises a single,

25 substantially central orifice. Alternatively, the transverse barrier may comprise a plurality of spaced apart orifices.

The size of each orifice in the transverse barrier is preferably between about 0.2 mm and about 1 .2 mm, more preferably between about 0.3 mm and about 0.8 mm, most preferably between about 0.5 mm and about 0.7 mm. Each orifice preferably also has a length of between

30 about 0.2 mm and about 2.0 mm, more preferably between about 0.5 mm and about 0.7 mm.

The term "length" is used to denote the length of the pathway of the orifice from an upstream entrance of the orifice to a downstream exit of the orifice. In preferred embodiments, the length of the orifice is typically approximately equal to the thickness of the transverse barrier. The "size" of the orifice is used to denote the largest dimension across the orifice. In preferred

35 embodiments, the orifice is circular in shape and the size of the orifice is the diameter of the circular shape. The transverse barrier of the flow restriction element may be of any suitable shape. For example, the transverse barrier may be a substantially flat disc that is preferably substantially perpendicular to the longitudinal axis of the filter. Alternatively, the transverse barrier may be frustoconical and convergent or divergent relative to the direction of the mainstream smoke drawn through the filter. In further embodiments, the transverse barrier may be concave or convex relative to the direction of the mainstream smoke drawn through the filter. Preferably, the transverse barrier is concave relative to the direction of the mainstream smoke, that is, concave in the upstream direction. This advantageously eases compression of the flow restriction element during manufacture of the filters according to the invention.

The inner periphery of the first downstream tubular portion at least partially defines the mouth end cavity. The mouth end cavity may be fully defined by the first downstream tubular portion in filters where the first downstream tubular portion extends from the transverse barrier to the mouth end of the filter. Alternatively, the mouth end cavity may include an upstream portion defined by the first downstream tubular portion and an integral downstream portion of the cavity defined by a filter wrapper extending beyond the end of the first downstream tubular portion, as described above.

Preferably, the first downstream tubular portion has a reduced external diameter compared to the external diameter of the filter. In the wrapped filter, there is therefore an annular space between the filter wrapper and the outer surface of the first downstream tubular portion. This may advantageously be used to provide a ventilation zone within the filter, as described in more detail below.

This arrangement enables air to be drawn in through the ventilation zone during smoking and channelled through the openings in the first downstream tubular portion directly into the mouth end cavity.

The flow restriction element may further comprise a second downstream tubular element, downstream of the first downstream tubular element. The second downstream tubular element is preferably connected to the first downstream tubular element such that no gap exists between the adjacent ends of the downstream tubular elements. Particularly preferably, the first and second downstream tubular portions are integrally formed. The inner periphery of the second downstream tubular portion defines a portion of the mouth end cavity, together with the portions defined by the first downstream tubular element and optionally the filter wrapper. The second downstream tubular portion preferably has an external diameter substantially corresponding to the external diameter of the filter. This advantageously provides structure and reinforcement to the filter to prevent collapse of the filter, in particular where the first downstream tubular portion is of reduced external diameter compared to the second downstream tubular portion. Alternatively or in addition to the one or more downstream tubular portions, the flow restriction element preferably comprises an upstream tubular portion extending upstream from the transverse barrier. The inner periphery of the upstream tubular portion defines an upstream cavity. The external diameter of the upstream tubular portion is preferably substantially the same as the external diameter of the filter. The upstream cavity may advantageously allow the mainstream smoke to concentrate around the one or more orifices in the transverse barrier before being drawn downstream through the orifices. In addition, the upstream cavity may help to prevent blockage of the one or more orifices during smoking.

The flow restriction element may comprise a second upstream tubular portion, upstream of the first upstream tubular portion, in a similar arrangement as described above in relation to the first and second downstream tubular portions. Where two upstream tubular portions are provided, the first upstream tubular portion adjacent to the transverse barrier is preferably of a reduced external diameter compared to the overall diameter of the filter and the second upstream tubular portion is preferably of substantially the same external diameter as the filter.

In a particularly preferred embodiment, two integral tubular portions are provided downstream of the transverse barrier and a single tubular portion is provided upstream of the transverse barrier.

The tubular portions on either side of the transverse barrier may be of substantially the same size and shape as each other to provide a flow restriction element having symmetry about the transverse barrier. Alternatively, the tubular portions on either side of the transverse barrier may have a different size or shape to each other to provide a flow restriction element that is asymmetric about the transverse barrier.

Preferably, the components of the flow restriction element are integrally formed as a single, one-piece element although it may also be possible to form the flow restriction element of two or more connected portions. Preferably, the flow restriction element is formed by extrusion or injection moulding.

The flow restriction element may be made from any suitable material or combination of materials. Preferably, the flow restriction element is formed from a material that is suitable for extrusion or injection moulding. Preferably, the flow restriction element is formed of a material with a lower particulate efficiency than conventional cellulose acetate filter materials, so that the flow restriction element retains less of the particulate matter of the mainstream smoke passing through. Suitable materials from which the flow restriction element may be formed include but are not limited to plastic (for example, polypropylene, polyethylene, polystyrene, nylon, polysulfone, polyester, polyurethane, poly(hydroxyalkanoates), poly(butylene succinate), poly (vinyl acetate), poly(hydroxybutyrate-co-hydroxyvalerate, poly(butylene adipate co-terephthalate or polycaprolactone), cellulosic material, starch based material, polylactic acid, polyvinyl alcohol and combinations or composites thereof. Preferably, the flow restriction element is formed from a dissolvable polymeric material formed of one or more water soluble polymers. Particularly preferably the dissolvable polymeric material is formed of one or more water soluble thermoplastics. The term "dissolvable" means that the polymeric material is capable of dissolving into a solution with a water solvent. This is 5 achieved through the use of one or more water soluble materials to form the material. The flow restriction element may be made entirely of the dissolvable polymeric material or the dissolvable polymeric material may be combined with inert components, such as inert inorganic fillers, which may or may not be dissolvable. The use of a dissolvable material to form the flow restriction element advantageously increases the rate of disintegration of the filter after it has i o been discarded.

Particularly preferably, the flow restriction element is formed from a biodegradable polymeric material. Preferred polymers are fully biodegradable as defined in the Aqueous Aerobic Biodegradation Test (Sturm test) outlined in European standard EN13432. Preferred biodegradable polymers include starch, polyvinyl alcohol and combinations thereof.

15 Preferably, the thickness of the material forming the flow restriction element is between about 0.2 mm and about 2.0 mm, more preferably between about 0.5 mm and about 0.7 mm. For example, the thickness of the transverse barrier and the walls forming the upstream and downstream tubular portions are preferably between these ranges.

Preferably, the length of the flow restriction element is between about 6 mm and about

20 20 mm, more preferably between about 6 mm and about 14 mm. The ratio of the length of the flow restriction element to the diameter of the flow restriction is preferably at least about 1 .2, more preferably at least about 1 .5, and most preferably at least about 1 .8. Where the flow restriction element includes one or more tubular portions, the length of each tubular portion is preferably at least about 3 mm, more preferably at least about 4 mm. Preferably, the external

25 diameter of the flow restriction element is between about 6 mm and about 9 mm, more preferably between about 7 mm and about 8.5 mm, most preferably between about 7.5 mm and about 7.9 mm for standard sized cigarettes or between about 6.6 mm and about 7.6 mm for reduced diameter cigarettes.

Filters and smoking articles according to the invention are preferably provided with a

30 ventilation zone at a location along the filter to admit air into the filter during smoking. The ventilation air that enters the filter dilutes the mainstream smoke and reduces the carbon monoxide and tar delivery during smoking. Preferably, the ventilation zone is in the form of one or more circumferential rows of perforations through the tipping paper attaching the filter to the rod of tobacco material. Where the underlying plug wrap is substantially air impermeable, the

35 perforations are preferably provided through both the tipping paper and the plug wrap. Where the underlying plug wrap is at least partially air permeable, the perforations may extend only through the tipping paper. The ventilation zone may provide ventilation air upstream of the transverse barrier of the flow restriction element or downstream of the transverse barrier. Preferably, the ventilation air is provided downstream of the transverse barrier. The ventilation air is preferably provided into the first downstream tubular portion.

As described above, the first downstream tubular portion preferably has a reduced external diameter compared to the overall external diameter of the filter. This is particularly advantageous in embodiments in which the ventilation zone is provided over the first downstream tubular portion, since the annular space formed between the tipping paper and the outer periphery of the first downstream tubular portion provides a space into which the ventilation air can be drawn. This arrangement improves the ventilation of the mainstream smoke.

Each opening in the first downstream tubular portion preferably comprises a passageway extending through a wall of the first downstream tubular portion from the external surface to the internal surface. When viewed in longitudinal cross-section, the passageway may be angled in an upstream direction, angled in a downstream direction, or be perpendicular with respect to the longitudinal axis of the filter. The passageway preferably extends at an angle alpha (a) that is non-perpendicular with respect to the longitudinal axis of the filter. For example, the angle alpha (a) is preferably between about 30 degrees and about 90 degrees in an upstream or downstream direction, more preferably between about 45 degrees and about 90 degrees in an upstream or downstream direction. The angle alpha (a) is measured as the smallest angle between the central axis of the passageway and the longitudinal axis of the filter. In cases where the passageway is not straight, the angle alpha (a) is measured between the longitudinal axis of the filter and the direction of the exit of the passageway.

In some embodiments, all of the passageways direct the air in a downstream direction, towards the mouth end. In other embodiments, all of the passageways direct the air in an upstream direction, away from the mouth end. In yet other embodiments, some of the passageways direct the smoke in an upstream direction and others direct the smoke in a downstream direction.

The provision of openings or passageways that are angled relative to the longitudinal direction of the smoking articles means that during smoking the ventilation air is directed into the mouth end cavity at an angle to the flow of the mainstream smoke. This advantageously optimises the mixing of the air with the smoke and breaks up the stream of the mainstream smoke. The mixing may also increase the turbulence of the flow of smoke and air through the mouth end cavity. These effects on the flow dynamics of the mainstream smoke may enhance the benefits described above.

Preferably, in the transverse cross section of the flow restriction element, each passageway extends either along a radius of the transverse cross section or along a line that is offset from a radius by an angle beta (β). The 'radius' refers to any line extending from the centre of the transverse cross section to the edge of the transverse cross section. The angle beta (β) is measured as the smallest angle between the intersection of the radius and the central axis of the passageway. In cases where the passageway is not straight, the angle can be measured between the longitudinal axis of the filter and of the exit of the passageway.

When viewing the cross section from a downstream direction, the angle beta (β) may be directed in a clockwise direction or a counter-clockwise direction with respect to a radius.

Where the passageway is offset from the radius, the angle beta (β) is preferably less than about 60 degrees, more preferably less than about 45 degrees, and most preferably less than about 15 degrees, either in the clockwise direction or counter-clockwise direction. The mixing of the smoke and the ventilated air may be enhanced in the case where the angle beta (β) is offset from the radius. In some cases, all of the passageways may be directed in a clockwise direction or in a counter-clockwise direction, or some of the passageways are directed in the clockwise direction and some of them are directed in a counter-clockwise direction.

The size of the openings or passageways in the first downstream tubular portion preferably provide a total open area between about 1 .0 and about 4.0 square mm (mm²), more preferably between about 1 .5 and about 3.5 square mm (mm²). Preferably, the openings or passageways are substantially circular or oval, although other shapes of transverse cross section are also possible.

A single opening or passageway may be provided in the first downstream tubular portion. Alternatively, two or more spaced apart openings or passageways may be provided in the first downstream tubular portion. For example, in one preferred embodiment a pair of substantially opposed passageways is provided. Where there are two or more openings or passageways, the openings or passageways may have the same open area as each other or different open areas. Two or more passageways may be provided at the same or a different angle alpha (a) to the longitudinal axis and with the same or a different angle beta (β) to a radius of the transverse cross-section of the flow restriction element. The openings or passageways may be positioned at substantially the same position along the length of the first downstream portion, or at different longitudinal positions to each other.

In alternative embodiments in which the ventilation zone is provided upstream of the transverse barrier, the ventilation zone preferably overlies an upstream tubular portion of the flow restriction element. In such embodiments, the upstream tubular portion may include one or more openings to form a communication path between the ventilation zone and the upstream cavity formed by the upstream tubular portion, as described above in relation to the openings in the first downstream tubular portion. In such embodiments, the mixing of the ventilation air with the mainstream smoke takes place before the smoke passes through the transverse barrier.

Where the flow restriction element includes two upstream tubular portions, the openings are preferably provided in the first upstream portion adjacent to the transverse barrier. Preferably, the first upstream portion has a reduced external diameter compared to the overall diameter of the filter in order to form an annular channel between the outer surface of the first upstream tubular portion and the overlying plug wrap.

Filters according to the invention may further comprise one or more additional filter segments upstream of the flow restriction element. Preferably, one or more plugs of fibrous filtration material, such as one or more of cellulose acetate tow, cellulose nonwoven (for example a paper), cellulose-based yarn, water soluble fibres, and biodegradable fibres, are provided upstream of the flow restriction element. Preferably, the length of each plug of filtration material is between about 5 mm and about 12 mm, more preferably between about 6 mm and about 8 mm. The fibres forming the fibrous filtration material may be substantially aligned in the longitudinal direction along the segment, or the fibres may be randomly oriented.

Where one or more upstream plugs of fibrous filtration material are provided, at least one plug may include a sorbent capable of removing at least one gas phase constituent from mainstream smoke drawn through the filter. Preferably, the at least one sorbent is selected from the group consisting of activated carbon, activated alumina, zeolites, sepiolites, molecular sieves and silica gel. Alternatively or in addition, at least one plug of fibrous filtration material may include one or more flavourants, preferably one or more liquid flavourants, to further enhance flavour delivery to the consumer during smoking.

Preferably, the flow restriction element and, where present, the one or more upstream plugs of fibrous filtration material are circumscribed by a band of plug wrap. The plug wrap may be substantially air permeable or substantially air impermeable. As described above, the band of plug wrap preferably extends beyond the downstream end of the flow restriction element to at least partially define the mouth end cavity.

Preferably, the band of plug wrap is affixed to the circumferential outer surface of at least a part of the flow restriction element. Preferably, the band of plug wrap is affixed to the flow restriction element so as to establish a substantially air-tight seal at the outer surface of the flow restriction element. This advantageously prevents the leakage of the mainstream smoke around the outside of the flow restriction element during smoking, so that substantially all of the mainstream smoke is forced through the one or more orifices in the transverse barrier. In this way, the flow restriction element can effectively maintain the desired level of RTD.

Where the filter additionally comprises one or more upstream plugs of fibrous filtration material, the band of plug wrap is preferably affixed to the circumferential outer surface of each plug. Preferably, the plug wrap is formed of a paper material. However, the plug wrap may alternatively be formed of a plastic material, for example, a transparent plastic material. The band of plug wrap may be affixed to the flow restriction element and any filter plugs using a suitable adhesive.

Preferably, filters according to the present invention have an overall RTD of between about 250 mm WG and about 500 mm WG, more preferably between about 275 mm WG and about 400 mm WG, most preferably between about 300 mm WG and about 400 mm WG, wherein the RTD is measured with all ventilation blocked. Preferably, smoking articles according to the invention have an overall RTD of at least about 30 mm WG, more preferably at least about 40 mm WG, wherein the RTD is measured prior to smoking with all ventilation blocked.

The RTD of a filter or smoking article is expressed herein with the units of pressure 'mm WG' or 'mm of water gauge' and is measured in accordance with ISO 6565:2002.

Preferably, the overall length of filters according to the present invention is between about 18 mm and about 36 mm, more preferably about 27 mm. Preferably, the overall length of smoking articles according to the present invention is between about 70 mm and about 128 mm, more preferably about 84 mm. Preferably, the external diameter of filters and smoking articles according to the invention is between about 5 mm and 8.5 mm, more preferably about 7.9 mm.

Filters according to the present invention may advantageously be incorporated into a wide variety of different types of smoking article. For example, the filters may be incorporated into combustible smoking articles, such as filter cigarettes, having a rod of tobacco cut filler or other smokable material, which is combusted during smoking. Preferably, the rod of smokable material comprises tobacco circumscribed by a wrapper, more preferably, tobacco cut filler circumscribed by a wrapper.

Alternatively, the filters may be incorporated into heated smoking articles of the type described above in which material is heated to form an aerosol, rather than combusted. For example, filters according to the present invention may be incorporated into a heated smoking article comprising a combustible heat source, such as that disclosed in WO-A-2009/022232, which comprises a combustible heat source and an aerosol-generating substrate downstream of the combustible heat source. Filters according to the present invention may also be incorporated into heated smoking articles comprising non-combustible heat sources, for example, chemical heat sources or electrical heat sources such as electrical resistive heating elements.

Alternatively, filters according to the invention may be incorporated into smoking articles in which a nicotine-containing aerosol is formed from a tobacco material or other nicotine source without combustion and without heating, such as those described in WO-A-2008/121610 and WO-A-2010/107613.

Smoking articles according to the invention may be packaged in containers, for example in soft packs or hinge lid packs. The smoking articles within the container may be wrapped in an inner liner, which may optionally have a flavourant applied to at least one surface.

Filters according to the invention may be produced in a continuous method comprising the steps of: providing a continuous array of filters including the flow restriction elements and any additional upstream filter segments; wrapping the continuous array of filters with a continuous sheet of plug wrap; and cutting the continuous wrapped filter rod to form individual filters, or multiple filters such a double or quadruple filters. The filters are preferably arranged in the continuous array such that a space is provided adjacent the downstream end of the flow restriction element. The individual or multiple wrapped filters rods are subsequently combined with wrapped rods of tobacco material in a known process to provide assembled smoking articles. The filter rod is cut at a position of the space to provide filters having a mouth end cavity formed by the plug wrap, as described above.

The flow restriction elements and any additional upstream filter segments can be aligned and arranged in an appropriate order to form the continuous array of filters using conventional filter making apparatus and techniques. When the flow restriction element is asymmetric along its length, it may be necessary to alternate the direction of the flow restriction element so that the correct direction is obtained in all assembled filters. The continuous wrapped filter rod can be cut in the appropriate position using conventional cutting apparatus, with the use of suitable means for registering the position of the cut such that mouth end cavities of a consistent length are produced.

During the production of the filters, a suitable adhesive is preferably applied to the inner surface of the plug wrap, the outer surface of the filter components, or both, so that the plug wrap adheres to the outer circumferential surfaces of the filter components after it has been wrapped around the continuous array of filters.

The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a smoking article according to the invention, with the tipping paper and plug wrap partially unwrapped to reveal the internal components of the filter;

Figure 2 shows a longitudinal cross section of the filter of the smoking article of Figure 1 ; Figure 3 shows a transverse cross section of the filter taken at the position of the line of perforation; and

Figure 4 shows a longitudinal cross section of a filter according to an alternative embodiment of the present invention. The smoking article 10 shown in Figure 1 comprises a cylindrical tobacco rod 12 and a filter 14. The tobacco rod 12 comprises a plug of tobacco cut filler circumscribed by a paper wrapper 16. The filter 14 is attached to the tobacco rod 12 by a band of tipping paper 18, which circumscribes the filter 14 and an adjacent portion of the tobacco rod 12.

The filter 14 comprises an upstream filter segment 20 adjacent to and abutting the tobacco rod 12, a mouth end cavity 22 at the mouth end of the smoking article 10 and a one piece, injection moulded flow restriction element 24 disposed between the upstream filter segment 20 and the mouth end cavity 22. The upstream filter segment 20 is formed of a plug of cellulose acetate tow. The upstream filter segment 20 is spaced apart from the upstream end of the flow restriction element 24 by a small distance.

The upstream filter segment 20 and the flow restriction element 24 are circumscribed by a band of plug wrap 26. The band of plug wrap 26 extends beyond the downstream end of the flow restriction element 24 to partially define the mouth end cavity 22 of the filter. The band of tipping paper 18 extends the full length of the filter such that the tipping paper 18 overlies the plug wrap 26, including over the mouth end cavity 22.

The flow restriction element 24 is formed of polyvinyl alcohol which has been blended with an organic or inorganic filler material and injection moulded to form the flow restriction element 24. As shown in Figure 2, the flow restriction element 24 includes a central, transverse barrier 28, an integral downstream tubular portion 30 extending from the downstream side of the barrier 28 and an integral upstream tubular portion 32 extending from the upstream side of the barrier 28.

The inner periphery of the downstream tubular portion 30 defines a downstream cavity 34 adjacent the transverse barrier 28, wherein the downstream cavity 34 forms part of the mouth end cavity 22, together with the space defined by the plug wrap 26. The inner periphery of the upstream tubular portion 32 similarly defines an upstream cavity 36 adjacent the transverse barrier 28 on the opposite side. The tubular portions 30, 32 are of approximately the same length as each other and both have an external diameter substantially corresponding to the outer diameter of the filter 14.

The transverse barrier 28 is in the form of a circular disc having an outer diameter corresponding to the outer diameter of the filter 14. The circular disc includes a single, central orifice 38 that provides a passageway between the downstream cavity 34 and the upstream cavity 36. As shown in Figure 1 , the outer surfaces of the transverse barrier 28, the downstream tubular portion 30 and the upstream tubular portion 32 are integral such that the outer surface of the flow restriction element 24 as a whole is substantially cylindrical. The transverse barrier 28 and the walls of the tubular portions 30, 32 have a thickness of between 0.5 mm and 0.7 mm. A pair of substantially opposed passageways 40 is provided in the downstream tubular portion 30. Each passageway 40 extends all of the way through the wall of the downstream tubular portion 30 at an angle alpha (a) of approximately 90 degrees to the longitudinal axis of the smoking article.

5 As shown in Figure 3, when viewed in transverse cross-section, each passageway 40 extends circumferentially around the downstream tubular portion 30 such that the passageway 40 extends at an angle beta (P) to the radius of the transverse cross section of the flow restriction element. In alternative embodiments, the angle beta (β) may be zero degrees, such that each passageway extends along a radius of the downstream tubular portion or the angle i o beta (β) may be offset less than about 45 degrees from the radius in a clockwise direction as shown.

A circumferential row of perforations 50 is provided through the band of tipping paper 18 and the band of plug wrap 26. The perforations 50 are located at a position along the filter 14 overlying the openings of the passageways 40 at the external surface of the downstream

15 tubular portion 30. The passageways 40 therefore provide a communication path between the outside of the filter and the mouth end cavity 22, for ventilation air to be drawn into the mouth end cavity 22. In use, ventilating air is drawn through the perforations 50, along the passageways 40 in the downstream tubular portion and into the mouth end cavity 22 where it mixes with mainstream smoke drawn through the central orifice 38 of the transverse barrier 28.

20 The arrangement of the passageways 40 means that the ventilation air is directed into the mainstream smoke at an angle that is perpendicular to the direction of the mainstream smoke. This provides mixing of the ventilation air with the mainstream smoke and generates a turbulent stream of smoke and air.

The filter 1 14 shown in Figure 4 is similar in construction to the filter 14 described above

25 but incorporates an alternative flow restriction element 124. The flow restriction element 124 comprises a central, transverse barrier 128 as described above, a first integral downstream tubular portion 130, a second integral downstream tubular portion 131 and an upstream integral tubular portion 132. The transverse barrier 128 is concave in the upstream direction.

The first downstream tubular portion 130 extends from the downstream side of the

30 transverse barrier 128 and has a reduced external diameter compared to the overall diameter of the filter. The second downstream tubular portion 131 extends from the downstream end of the first downstream tubular portion 130. The upstream tubular portion 132 extends from the upstream side of the transverse barrier 128. Both the second downstream tubular portion 131 and the upstream tubular portion 132 have an external diameter which is substantially the same

35 as the diameter of the filter 1 14.

The inner peripheries of the first downstream tubular portion 130 and the second downstream tubular portion 131 define a downstream cavity 134 adjacent the transverse barrier 128, wherein the downstream cavity 124 forms part of the mouth end cavity 122 together with the space defined by the plug wrap 26, as in the filter 14.

Due to the reduced external diameter of the first downstream tubular portion 130 compared to the tubular portions on either side, the inner surface of the plug wrap 126 is spaced apart from the circumferential outer surface of the first downstream tubular portion 130, as shown in Figure 2. The annular space between the plug wrap 26 and the outer surface of the first downstream tubular portion 130 forms a ventilation zone. One or more circumferential rows of perforations 140 are provided through the plug wrap 26 and tipping paper 18 overlying the first downstream tubular portion 130.

As in the filter 14, a pair of substantially opposed passageways 140 is provided in the first downstream tubular portion 130. The passageways have the same configuration as described above in relation to filter 14.

When the filters 14, 1 14 described above are viewed from the mouth end the inner surfaces of the mouth end cavity 22,122 are visible. At the mouth end of the mouth end cavity, the inner surface corresponds to the inner surface of the plug wrap 126. In the portion of the mouth end cavity 122 defined by the flow restriction element 124, the inner surface corresponds to the inner surface of the downstream portion 30 or portions 130,131 . The transverse barrier 28,128 with the central orifice 38 is also visible from the mouth end. After smoking of a smoking article 10 incorporating the filter 14 or the filter 1 14 by combustion of the tobacco material in the tobacco rod 12, the level of staining on the visible surfaces of the mouth end cavity 22,122 and transverse barrier 28,128 is relatively low.

The filters 14,1 14 are constructed using the method described above. A continuous array of the flow restriction elements 24,124 is arranged with an upstream filter segment 20 adjacent to the upstream side of each flow restriction element 24, 124 and a space provided on the downstream side. A continuous sheet of plug wrap material is also provided and the sheet of plug wrap is wrapped around the array of filter segments and glued in place. The continuous wrapped filter rod is then cut to provide individual, double, or quadruple wrapped filters and the wrapped filters are combined with a wrapped tobacco rod by affixing the band of tipping paper around the filter. This step may be carried out using existing machinery employed for attaching filters to tobacco rods during the manufacture of known filter cigarettes.

Claims

1 . A smoking article comprising:

a flow restriction element comprising:

a transverse barrier including one or more orifices wherein the smoking article defines a mouth end cavity extending from the transverse barrier of the flow restriction element to the mouth end of the smoking article;

and

a first downstream tubular portion downstream of the transverse barrier, the first downstream tubular portion at least partially defining the mouth end cavity, wherein one or more openings are provided in the first downstream tubular portion to form a communication path between the external periphery of the first downstream tubular portion and the mouth end cavity.

2. A smoking article according to claim 1 including a filter comprising the flow restriction element and a filter wrapper circumscribing the filter, wherein the filter defines the mouth end cavity.

3. A smoking article according to claim 2 wherein the filter wrapper at least partially defines the mouth end cavity in the filter.

4. A smoking article according to any claims 1 to 3 wherein the first downstream tubular portion of the flow restriction element is of reduced external diameter compared to the external diameter of the smoking article.

5. A smoking article according to any of the preceding claims wherein the one or more openings comprise one or more passageways extending through a wall of the first downstream tubular portion at a non-perpendicular angle alpha (a) of between 30 degrees and 90 degrees to the longitudinal axis of the smoking article.

6. A smoking article according to any of claims 1 to 4 wherein the one or more openings extend substantially perpendicularly to the longitudinal axis of the smoking article.

7. A smoking article according to any of the preceding claims wherein the one or more openings comprise one or more passageways extending through a wall of the first downstream tubular portion and wherein the passageways extend at an angle beta (P) with respect to a radius of a transverse cross section of the flow restriction element, the angle beta (β) being offset from the radius by less than about 45 degrees.

8. A smoking article according to any preceding claim wherein the flow restriction element further comprises a second downstream tubular portion, downstream of the first downstream tubular portion and at least partially defining the mouth end cavity.

9. A smoking article according to any preceding claim wherein the mouth end cavity of the filter extends at least 2 mm from the transverse barrier of the flow restriction element in the downstream direction of the smoking article.

10. A smoking article according to any preceding claim wherein the flow restriction element further comprises one or more upstream tubular portions, upstream of the transverse barrier and defining an upstream cavity.

1 1 . A smoking article according to any preceding claim wherein a ventilation zone is provided at a location along the smoking article, the ventilation zone comprising at least one circumferential row of perforations provided through a portion of a smoking article wrapper.

12. A smoking article according to claim 1 1 wherein the ventilation zone is provided over the first downstream tubular portion to form a communication path between the ventilation zone and the mouth end cavity through the one or more openings.

13. A smoking article according to claim 1 1 or 12, wherein the ventilation zone further comprises an annular space between the inner surface of a portion of the smoking article wrapper and the outer surface of the first downstream tubular portion.

14. A filter for a smoking article, the filter comprising:

a flow restriction element comprising a transverse barrier including one or more orifices, the flow restriction element further comprising a first downstream tubular portion downstream of the transverse barrier; and

a filter wrapper circumscribing the filter, wherein the filter defines a mouth end cavity extending from the transverse barrier of the flow restriction element to the mouth end of the filter, and the first downstream tubular portion at least partially defines the mouth end cavity, wherein one or more openings are provided in the first downstream tubular portion to form a communication path between the external periphery of the first downstream tubular portion and the mouth end cavity.