CH649448A5 - Filter element, especially for cigarette method for manufacturing and rod with several such items. - Google Patents

Description

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1. Smoke filter element, characterized in that it comprises a filtering core (2), an envelope (6) impermeable to smoke and surrounding the core, at least one internal passage (14) defined between the envelope impermeable and the core and opening at one end of the element, and at least one external passage (16) defined by the external surface of the impermeable envelope and extending to one end of the element.

2. Element according to claim 1, characterized in that the impermeable envelope (6) has a profile providing said passage.

3. smoke filter element according to claim 1, characterized in that the envelope (6) impermeable to smoke is corrugated and defines internal passages between the envelope and the core, extending longitudinally to one end of the element, as well as external passages (16) located outside the envelope and which extend longitudinally to one end of the element.

4. Element according to one of claims 1 to 3, characterized in that said passages extend from one end of the element to the other.

5. Element according to one of claims 1 to 3, characterized in that it comprises at least one passage extending only over a part of the length of the core.

6. Element according to claim 4, characterized in that said passages are terminated or interrupted by a circumferential ripple (12) of the envelope.

7. Element according to one of claims 1 to 3, characterized in that the impermeable envelope has a circumferential groove in which at least one external passage opens.

8. Element according to one of claims 1 to 3, characterized in that at least one of said passages comprises an external or intermediate constriction.

9. Filter element according to one of the preceding claims, characterized in that the core is formed of buffers of different filtering characteristics surrounded by an envelope.

10. Filter element according to claim 9, characterized in that the buffers cause different pressure drops.

11. Filter element according to one of the preceding claims, characterized in that the filter core comprises a filter envelope permeable to smoke, which the smoke passes through in use, and which acts as a filter aid.

12. Filter element according to one of claims 1 to 11, characterized in that said core comprises a perforated envelope and / or permeable to smoke, that the smoke passes through in use, and which is gradually blocked by the passage of smoke.

13. Filter element according to one of the preceding claims, characterized in that the smoke-impermeable envelope is a paper / thermoplastic polymer / paper laminate.

14. Element according to one of the preceding claims, characterized in that it comprises a nozzle material in peripheral contact with the impermeable envelope, defining at least one external passage between the impermeable envelope of the nozzle and open to one end of the element, the nozzle serving when the filter element is used for the entry of outside air laterally through the outside passage.

15. Element according to claim 14, characterized in that the internal and external passages open at the same end of the element and extend only partially towards the other end of the element.

16. Element according to one of claims 14 or 15, characterized in that the impermeable envelope comprises a circumferential groove into which opens at least one of said external passages and in that the end-piece material ensures, when the element of filter is subjected to suction during use, a lateral air intake from the outside directly in this circumferential groove.

17. Element according to one of claims 14,15 or 16, characterized in that the tip material comprises an outer surround of the buffer which does not project beyond the ends of the core.

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18. Filter element according to one of claims 14, 15 or 16, characterized in that the tip material is constituted at least in part by an external cap ensuring the junction of the filter element with a tobacco rod wrapped.

5 19. Rod comprising several unitary elements according to one of claims 1 to 17 arranged end to end and joined by a common impermeable envelope extending over the entire length of the rod, each unitary element being arranged symmetrically with respect to an element unit integrated in an adjacent position, io 20. A method of manufacturing the smoke filter element according to claim 1, characterized in that a filter core is formed, in that the impermeable envelope is given the necessary profile and that the waterproof profiled envelope is wound and fixed around the core so as to form said internal and external passages.

The present invention relates to smoke filtration, in particular to tobacco smoke filtration. It relates to filters and filter elements which are widely applicable to smoke filtration and other filtration applications, but which are shown and described below essentially in connection with cigarette filters, this application constituting that which is of the greatest commercial interest. The invention relates to a smoke filter element comprising a filter core, at least one (internal) passage defined between the impermeable envelope and the core and opening at one end of the element, and at least one other passage ( external) defined by the external surface of the impermeable envelope and extending to one end of the element. Preferably, the impermeable envelope is profiled so as to form the internal and external passages; for example, it can be grooved or corrugated longitudinally to form said passages; in corres-35 pondance, the invention also relates to a smoke filter element comprising a filter core and a corrugated envelope impermeable to smoke and defining between it and the core first (internal) passages which extend longitudinally to one end of the element and, outside of said envelope, 40 other (external) passages which extend longitudinally to one end of the element.

The filter element according to the invention is characterized in that it comprises a filtering core, an envelope impermeable to smoke and surrounding the core, at least one internal passage defined 45 between the impermeable envelope and the core and opening out at one end of the element, and at least one external passage defined by the external surface of the impermeable envelope and extending to one end of the element.

Elements according to the invention are mainly intended to be used as filters provided with a nozzle which ensures, when the filter is subjected to a suction during use, an outside air inlet laterally through of the filter so that it passes through said other (external) passages. Such a ventilation nozzle can be placed around the impermeable envelope 55 in a step of the filter manufacturing process, or it can constitute the nozzle cap which is put in place to join the element to the rod. tobacco during the manufacture of filter cigarettes. In addition, a cigarette filter can comprise a filtering core, a shell impermeable to smoke and surrounding the core, a nozzle surrounding the impermeable envelope, at least one (internal) passage defined between the impermeable envelope and the core and opening at one end of the filter, and at least one other (external) passage defined between the impermeable envelope and the nozzle and opening at one end of the filter, the nozzle ensuring, when the filter is "subjected to a suction in progress service, the external air intake laterally in the other passage (s) (external).

The passages may extend only over part of the length of the element or filter, but one, several or all of them pass

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ges may instead extend from one end of the filter or element to the other; a given passage can have a cross section that is essentially constant over its length, or else (in particular when it extends from one end of the filter or element to the other), it can be throttled in an extreme and / or intermediate zone. The passages can extend in the axial direction of the element or filter or follow a curved profile.

When the waterproof casing is provided with longitudinal grooves or corrugations to form said passages, said grooves or corrugations can therefore extend over the entire length of the casing (although it is possible that the grooves or corrugations are smaller in an extreme or intermediate zone), or they can end (for example in a non-wavy or circumferentially grooved or wavy zone) so as to close one or more passages (at least in the finished filter) in an extreme or intermediate part of the envelope. It is possible to give the waterproof envelope other profiles to define said passages (for example the shape of streaks).

In particularly preferred embodiments of the present invention, the impermeable envelope comprises a circumferential groove into which at least one of said external passages opens, this groove conventionally ensuring simultaneously the closing of the internal passage or passages. In filter cigarettes using such elements, ventilation can be created through the material of the nozzle directly towards the circumferential groove and, therefore, towards the communicating external passage (s); for example, ventilation perforations can be provided in the material of the nozzle in a circumferential annular zone coinciding with the circumferential groove. Different configurations are possible; for example, the circumferential groove can be placed halfway along the envelope, internal and external passages starting from said groove in opposite directions up to the two ends of the element; or the circumferential groove may be directed towards one end of the element, where the impermeable envelope is corrugated circumferentially or otherwise shaped so as to close the circumferential groove at this end, the internal and external passages extending from the circumferential groove to the other end of the element; in another variant, the circumferential groove is placed at one end of the envelope and it is open at this end, the internal and external passages extending from said groove to the other end; in other embodiments, there are provided several circumferential grooves which are distributed along the envelope, for example at opposite ends thereof. The waterproof envelope to be used in the manufacture of this type of element, in accordance with the present invention, can be simply pre-profiled in the normal manner to establish the necessary passages, each region having to constitute a circumferential groove being left full and not profiled; when the profiled envelope is placed around the core, we realize that the non-profiled and smooth regions naturally take the shape of the circumferential grooves. This is particularly effective in the case of undulations to form the passages.

When an embossed or otherwise profiled waterproof envelope establishes said passages, the core advantageously has a substantially constant circular section and the end piece is similarly in the form of a substantially straight circular cylinder.

When they do not extend over the entire length of the envelope, the internal and external passages are usually open at the same end of the element or filter and they are usually closed in the same position in the direction of their length, for example at their other end, but neither one nor the other of these characteristics is essential; the internal and external passages can be closed in different longitudinal positions, that is to say that each of them can be closed at one end of the element or filter, or between its ends.

The filter core of the element or filter according to the invention can

be made up of any of the whole range of materials for cigarette filters, for example bundles of fibers or filaments linked or unbound (in cellulose acetate, polyolefin, etc.), crepe paper or a expanded material permeable to air. The core can have a uniform or non-uniform structure and composition along its length; it can be formed of a homogeneous or composite structure, comprising for example an envelope and / or provided with separate pads having characteristics (for example pressure drop) and / or identical or different compositions; the core can extend over all or only part of the length of the element or filter and, when this core is formed from a composite set of two or more buffers, the adjacent pads can abut one against the other the other or be spaced from each other. The core may not be enveloped or may comprise an envelope or cap which is perforated and / or formed of a material intrinsically permeable to smoke; the core could on the contrary comprise an impermeable envelope or else an integrated skin (for example by hot fusion or by solvent). The core can comprise particles of additive which are uniformly dispersed or else located in at least one inter-buffer zone or space; the core may have a profiled periphery (for example longitudinally grooved) and it may be provided with one or more internal passages or cavities which may or may not be filled. The core may include one or more components which do not fulfill a filtering function but which are simply used to increase the pressure drop; in addition, it is possible to use, as or in the filter core of elements and filters according to the invention, a buffer establishing a large pressure drop, having a low retaining power and formed from an assembly of coarse fibers, or else an assembly of embossed sheets formed of plastic, metal (for example aluminum) or another material. In certain embodiments, the impermeable envelope surrounds a cavity or recess open at one end of the filter element or the filter and, in service, this recess or cavity can be placed against the wrapped tobacco rod, or else it may be exposed to the mouth of the filter cigarette.

Although the element filtering core according to the invention may have a composite structure as mentioned above, for example a structure formed from pads placed end to end or spaced apart longitudinally, the profiled waterproof envelope which extends over the entire length of the element gives it an overall structure which is unitary and coherent.

The waterproof jacket is suitably formed of a laminate product comprising paper and a thermoplastic material of the polymer type, for example a laminate product paper / thermoplastic material / paper, the layer of plastic material preferably being made of a polyolefin. , for example polyethylene. A laminate product of this kind has good embossing characteristics and retains its impermeability and embossed profile well. The impermeable envelope is preferably fixed around the core by means of a glued lap joint; it can also, or on the contrary, be fixed to the core by one or more longitudinal gluing lines.

The material of the nozzle may be breathable but, when it constitutes the nozzle cap connecting the element to a column of tobacco, it is more usually formed of an essentially impermeable material comprising perforations which are in open communication with said other passages. The element may include an envelope formed of a material permeable to air, which creates a filter with a smooth external appearance and around which the cap cap (or annular cap) is placed in the production line. filter cigarettes, but this is not usually necessary.

When used as part of a filter cigarette, the filter according to the invention can establish (by means of the internal passage or passages between the impermeable envelope and the core) a certain bypass of the smoke around of a part of the length of the core, different controlled effects can thus be obtained in relation to the filter structure adopted, such as

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indicated in some of the specific embodiments which will be described below; in certain cases, obviously, it is not necessary for the core to have a layer impermeable to smoke between it and the impermeable envelope. The external passage or passages between the impermeable envelope and the mouthpiece can open into the buccal end, so that the ventilation air is sucked in by said passages and passes directly into the smoker's mouth with little or no mixing. beforehand with smoke. On the contrary, an external passage can open out at the end adjacent to the tobacco rod and it can be arranged so that ventilation air sucked by this passage flows upstream towards the tobacco rod, then downstream through the filter core. A constriction of a passage may affect or determine the degree and direction of flow in the constricted portion (s). A filter according to the invention may include at least one external passage open only at the mouth end and at least one other corresponding passage open only at the other end; similarly, at least one internal passage can open only at the buccal end and at least one other passage can open only at the other end.

Elements according to the invention are produced in an appropriate manner by first forming the core (in the form of a continuous rod or of finite finite length), by profiling (for example by waving) the envelope impermeable to the configuration necessary, and by winding and fixing the profiled waterproof envelope around the core; the tip material can then be wrapped around the impermeable envelope; this tip material may be the tip cap which is used to join the filter element to the tobacco rod during the manufacture of filter cigarettes, in a conventional manner.

Normally, the core is in the form of a continuous rod which is then continuously surrounded by the pre-profiled waterproof envelope, the resulting continuous composite product then being cut transversely into finite lengths. An envelope formed of a material permeable to air can optionally be placed continuously around the composite structure constituted by the core and the profiled envelope before cutting into finite lengths. For the manufacture of filter cigarettes, a product of this kind and of double length is arranged so that a wrapped tobacco rod abuts against one or the other of its ends, a cap of ventilation nozzle is set up to join the tobacco rods and the element or intermediate filter rod, and the resulting assembly is cut in the middle to produce two filter cigarettes. The initially produced continuous element or filter is normally cut into units of multiple lengths (eg sixfold) for supply to the cigarette manufacturer who then cuts these units of multiple length into units of double length usable for the production of cigarettes with filter, as described above. It should be noted that, in the case of sections of elements or filters according to the invention where the internal and external passages start only from one end and end at a short distance from the other end, so that the two ends of the filter element are different, the initial rods of multiple multiple length, supplied by the filter manufacturer and from which the individual lengths are finally formed, may have identical ends; for example, the rod of multiple even length could have passages starting from the two ends or closed at both ends, depending on whether the passages of the final cigarette must lead respectively to the tobacco end or to the buccal end. Such rods of double length and multiple lengths also come within the scope of the present invention.

The impermeable envelope preferably exerts practically no radical compression on the core and, advantageously, it does not imprint its profiled configuration in the surface of the core. The waterproof envelope is preferably pre-profiled with grooves or undulations extending longitudinally; they may be discontinuous, lengths longitudinally grooved or wavy being spaced from one another by parts (for example smooth, or else wavy or grooved transversely) which ensure, in the final filter, a sealing of the longitudinal passages created by the envelope. Instead of the corrugations, the waterproof envelope could be embossed with bosses which would create in the final product a network of passages arranged randomly or in an orderly fashion, the embossed lengths of the envelope being again optionally spaced. from each other by smooth segments or else profiled so as to close passages in io the final product.

The advantages and characteristics of the invention will be highlighted in the following description, given by way of nonlimiting example, with reference to the appended drawings in which:

fig. 1 is a view in longitudinal section, taken along line 15 I-I of FIG. 3, a filter and an element according to the invention, incorporated in the filter cigarette according to the invention;

fig. 2 is a sectional view of the filter and the element of FIG. 1,

made along line II-II of fig. 1;

fig. 3 is a sectional view of the filter and the element of FIG. 1, 20 made along line III-III of FIG. 1;

fig. 4 to 8 are views in longitudinal section, similar to that of FIG. 1, five other filters and different elements arranged in accordance with the present invention and incorporated into filter cigarettes according to the invention;

25 fig. 9 is a similar longitudinal section view of yet another filter and element according to the invention;

fig. 10 is an elevational and end view, on an enlarged scale, of the element and filter of FIG. 9;

fig. 11 is a view in longitudinal section of other elements, filter and filter cigarette according to the invention;

fig. 12 and 13 are sectional views taken respectively along lines XII-XII and XIII-XIII of FIG. 11;

fig. 14 is a perspective view of the filter element according to the invention, used in the filter of FIG. 11;

35 fig. 15 is a view similar to that of FIG. 11 of another element, another filter and another filter cigarette according to the invention;

fig. 16 is a perspective view of a filter element according to the invention and used in FIG. 15;

40 fig. 17 is a view, similar to that of FIG. 16, of another filter element according to the invention, and FIGS. 18 and 20 are schematic longitudinal section views of elements of multiple lengths according to the present invention.

The filter element shown in figs. 1 to 3 comprises a filter core formed by a pad 2 made up of a filtering material and enveloped by an envelope 4 permeable to smoke (intrinsically permeable to smoke and / or perforated) or else impermeable to smoke, and an envelope 6 impermeable to smoke and in contact with the core; a tip material 8 surrounding the waterproof envelope completes the filter. The impermeable envelope 6 has longitudinal undulations 10 closed at one end 22 of the filter by circumferential undulations 12, the longitudinal undulations 10 forming passages 14 (FIG. 3) between the core and 55 the impermeable envelope, as well as passages 16 between the impermeable envelope and the tip material, all these passages being open at the end 18 of the filter. The tip material 8 is formed of a material impermeable to smoke, but it comprises a cir-conference ring of perforations 20 which are in communication, through the intermediary of passages 16, with the external atmosphere.

The tip material 8 constitutes an outer cap which protrudes from the core and from the envelope 6 to join the element to a wrapped tobacco rod 23 at the end 22; on the contrary, it could join the element to said tobacco rod wrapped at the opposite end 18. 65 The waterproof envelope 6 is constituted by a laminated paper / polyethylene / paper product which has been provided by embossing with longitudinal and transverse corrugations. shown and which is fixed around the core by a conventional glued lap joint; he can

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also be glued to the core along one or more longitudinal gluing lines. The waterproof envelope 6 does not compress the core and does not print its pattern on its surface.

The pad 2 can be formed from a conventional smoke filtering material, for example bound or unbound fibers, or else a bundle of filaments (for example cellulose acetate, viscose, polyester or polyolefin), crepe paper, expanded plastic, etc. When the pad 2 itself constitutes a dimensionally stable body (for example a bundle of continuous cellulose acetate filaments which have been hardened and bonded together), and when smoke must be allowed to flow between the core and the passages 14, it is possible to remove the buffer envelope 4. When the buffer 2 is formed from a composite assembly of two or more elements end to end or spaced apart longitudinally, it may be preferable to use a buffer envelope 4.

As indicated above, the filter can be fixed on a tobacco rod either at the end 18 or at the end 22. In the first case, a suction exerted on the mouth end 22 causes that external air flows through the perforations 20, along the passages 16 to the end 18 of the filter then, through the body of the filter, from the end 18 to the end 22, by diluting the smoke passing through the filter. When the end 22 of the filter is placed against the tobacco rod, a suction exerted at the mouth end 18 causes external air to pass through the perforations 20 and along the passages 16 towards the end mouth 18, so that the ventilation air passes directly into the smoker's mouth before mixing with the inhaled smoke. When the tampon envelope 4 is omitted or is perforated and / or intrinsically permeable to smoke, smoke passes, during the use of the filter, from the tampon 2 in the passages 14, then directly into the mouth of the smoker (when the filter end 22 is fixed on the tobacco rod), or directly in the passage 14, then in the mouth of the smoker, via the pad 2 (when the end 18 is fixed on the rod tobacco).

When the buffer envelope 4 is formed of a permeable filter material, for example of paper, this makes it possible to improve the total capacity for retaining particles of the filter.

The filters and elements of fig. 4 to 6 have a structure similar to that of FIG. 1 and their appearance in sectional view made through the circumferentially and longitudinally grooved parts is similar to what has been shown respectively in FIGS. 2 and 3.

In fig. 4, the pad 2 comprises a carrier envelope 4 which initially establishes a low pressure drop to allow the passage of smoke, but which can be easily closed by components of tobacco smoke; the filter is fixed by the end 18 on a wrapped tobacco rod 23. When the cigarette shown is smoked, the initial puffs cause an appreciable smoke bypass along the passage 14, the degree of bypass decreasing as the envelope is obstructed so that, during subsequent puffs, an additional quantity of smoke is forced to pass through the entire length of the filter pad 2. This arrangement contributes to uniformizing the transmission of the taste while the cigarette is smoked. The taste transmission obtained with a conventionally ventilated filter cigarette increases, while the cigarette is smoked, from a low initial value, often unsatisfactory, to a high level, often unacceptable; for a given total degree of taste transmission, the filter of fig. 4 establishes by comparison an increased initial value and a reduced final value; it therefore gives more uniformity to the smoke.

In the embodiment of FIG. 5, the pad 2 is constituted by a composite structure comprising two elements 24 and 26 having different filtering characteristics. For example, the element 24 can be an element having a high pressure drop while the element 26 can create a low pressure drop; in this case, the tampon envelope 4 is made in a naturally porous manner and / or has perforations at least around the element with low pressure drop 26, the filter being fixed on the wrapped tobacco rod 23 by the end 18 so that the element to

high pressure drop 24 is applied against tobacco. In the initial phase of cigarette consumption, smoke is therefore encouraged to bypass the high pressure drop element 24 by flowing along the passages 14 to enter the low pressure drop element 26. As in the previously described embodiment, the tampon envelope 4 can be easily sealed, so that the degree of smoke derivation varies while the cigarette is smoked. The individual segments can be different and can be chosen to obtain the necessary overall filtering characteristics.

In the embodiment of FIG. 6, when the filter is again fixed on the tobacco rod by the end 18, the tampon envelope 4 is made of an impermeable material which is provided with perforations 29 at the closed ends of the grooves 14. The tampon 2 can be of a unitary structure, or it can again be formed by a composite structure consisting of a high pressure drop element adjacent to the tobacco and abutting against a low pressure drop element surrounded by the perforations 29. During initial puffs, smoke coming from the tobacco rod flows along the passages 14 and through the perforations 29 to penetrate the tampon 2, the perforations 29 being finally closed, so that more smoke is forced to cross the entire length of buffer 2.

In the filter shown in fig. 7, the core consists of a pad 30 with a relatively high pressure drop which is placed against a pad 32 with a relatively low pressure drop and which is wrapped and joined by a pad envelope 4 made of smoke-impermeable material. In this case, the impermeable envelope 6 has circumferential undulations 12 placed in an intermediate zone of its length, as well as longitudinal undulations 10 extending from the circumferential undulations 12 to the opposite ends 18 and 22 of the filter. The filter is fixed by one end 18 to the wrapped tobacco rod 23 by the outer cap 8, the ring of ventilation perforations 20 communicating with the passages 16 existing between the impermeable envelope 16 and the outer cap 8 to the buccal end 22 of the filter. At the other end of the filter, the passages 14 formed between the impermeable envelope 6 and the core are open in the direction of the tobacco. These passages 14 extend beyond the pad 30 with high pressure drop and, in the zone where they terminate around the upstream end of the pad with low pressure drop 32, the casing 4 is provided with fine perforations. 29 which initially allow the smoke coming from the passages 14 to pass through them easily but, after a few puffs, these perforations are closed, so that an increasing quantity of smoke is forced to travel the entire length of the core by crossing the tampon 30 and the pad 32. The effect of the embodiments of FIGS is not only obtained. 4 to 6 but, moreover, the degree of dilution of the air in the mouth of the smoker through the perforations 20 and the passages 16 increases from a relatively low initial value (when the perforations of the tampon envelope 4 are open, so that the resistance against the flow of smoke is low) up to a relatively large final value (when said perforations are closed, so that the resistance against the flow of smoke is maximum) ; the overall effect is therefore to better standardize the transmission of taste from the first to the last puff.

In the embodiment of FIG. 8, there is provided a filtering core formed of a pad 50 consisting of a bundle of cellulose acetate filaments and a pad 52 placed end to end and formed of crepe paper, the two pads being held together by a smoke-proof envelope 4. The smoke-tight envelope has longitudinal undulations 10 extending over the entire length of the core in order to form passages 14 and 16 each opening at the two ends of the filter. The outer cap 8, formed of a material impermeable to smoke and comprising a ring of perforations 20 opening into the passages 16, ensures the junction of the filter with a wrapped tobacco column 23 and constitutes the end piece of the filter.

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■ In the embodiments of FIGS. 1 to 8, the filter nozzle consists of an outer cap ensuring the junction of the filter element with a wrapped tobacco rod. The tip of a filter according to the invention can however be constituted by a surrounding of a breathable, smooth and traditional pad, as shown in FIG. 9. In this embodiment, the core is constituted by a filter pad 2 provided with a smoke-permeable envelope 4, the impermeable envelope 6 placed around the core comprising intermediate circumferential 12 and longitudinal longitudinal corrugations 10, as shown in fig. 7. A smooth tampon envelope 40, formed of an air permeable paper, is fixed around the waterproof envelope 6 by a glued lap joint of conventional type, this envelope being put in place in a production step. of the filter in the form of a continuous rod which is then cut transversely to produce the filter section shown. The tampon envelope 40 could on the contrary be formed of an air-impermeable material, comprising perforations opening into the passages 16. The filter can be joined at either end with a wrapped tobacco rod using an annular nozzle or else an external nozzle cap comprising ventilation perforations communicating with the passages 16 existing between the envelope 6 and the external tampon envelope 40. It should be noted that, to clarify the representation, the drawings were not made to scale; in general, the radial depth of the corrugations 10 is greatly exaggerated and their number and the diameter of the core are reduced in correspondence. In practice, essentially the entire diameter (approximately 8 mm) of a filter according to the invention is occupied by the filtering core, the corrugations 10 (and 12) having a radial depth of, for example, between approximately 0.25 and 1 mm, especially 0.5 mm. Where only one perforation 20 has been shown for each passage 16, the perforations may be more closely spaced, two or more perforations communicating with each passage 16. FIG. 10 shows a filter element of the type indicated in FIG. 9 and on an enlarged scale, the figure constituting an elevation view of the end 22. In practice, the core pad 2 has a diameter of approximately 8 mm and the corrugations 10 of the envelope 6 create approximately 22 passages internal 14 and 22 external passages 16, each having a depth of about 0.5 mm. Similar dimensions apply in practice to the other embodiments shown in FIGS. 1 to 9 and 11 to 20.

Although reference is frequently made above and below to the use of a corrugated waterproof envelope, it is possible to envisage other forms of profiled waterproof envelope. For example, the waterproof envelope could be formed from thick paper (with a density for example of 100 g / m 2 or more), for example from a cartridge paper comprising preformed longitudinal grooves, advantageously using profiled printing rollers; the surface of the paper could be left smooth in the areas where the passages created by the envelope end.

On each of fig. 11 to 20, the filter element or rod comprises a filtering core (comprising a pad 2 and a smooth and permeable or smoke-proof envelope 4) surrounded by a smoke-proof envelope 6, which has longitudinal undulations 10 providing longitudinal passages 14 between the casing and the core and external longitudinal passages 16; in the elements of fig. 11 to 17, the impermeable envelope also establishes a circumferential groove 80 communicating with said external grooves 16 which extend from the latter, as indicated at one end of the filter. In the cigarette, there is provided around the filter element, to ensure its junction with a wrapped tobacco rod 23, a ventilation end cap 8 comprising a ring of ventilation perforations 20 opening into the circumferential groove.

In the embodiment of FIGS. 11 to 14, internal and external passages extend longitudinally from the circumferential groove to the two ends of the filter rod. In the embodiment of FIGS. 15 and 16, the waterproof envelope placed at

the end of the filter and abutting against the tobacco rod has circumferential corrugations 12 which close the circumferential groove and the external passages starting from the tobacco rod, the circumferential groove being placed in a position directly adjacent to the circumferential corrugations and longitudinal undulations of the envelope extending from the latter to the buccal end of the filter. In the element of fig. 17, which can be incorporated into a filter cigarette in the same manner as that indicated in FIGS. 11 and 15, the circumferential groove 80 is open towards one end of the element, passages 14 and 16 starting therefrom at the opposite end.

As indicated above, during the manufacture of the filter elements shown, the initially planar envelope 6 is first provided by embossing the series of corrugations 10 (fig. 11 to 14 and 17) 15 or else 10 and 12 (fig. 15 and 16), the spaces between corrugations being left smooth and not embossed. When the pre-corrugated envelope is engaged around the core, the non-embossed parts of the envelope are naturally deformed to form the circumferential groove 80 into which the passages 16 open.

m As explained above, a filter element according to the invention, such as any of those shown in the figures, is initially produced in the form of a continuous strip in which rods of multiple even lengths ( that is, each rod is an even multiple of the final individual element) are cut, the rods of multiple lengths then being subdivided into elements of double length and then, during the manufacture of filter cigarettes, into elements single length final. Examples of six-length rods according to the invention, which can be subdivided into individual elements according to the invention, have been shown diagrammatically in FIGS. 18 to 20. Fig. 18 shows a rod six times in length from which simple elements can be produced, such as that of FIG. 14, by a mid-distance cutting of the longitudinally corrugated inner sections, first operating in positions 82 to produce rods of double length, then, during the manufacture of the filter cigarettes as described above , in positions 84. A rod of similar multiple length, but having different dimensions for the corrugated and circumferentially grooved areas, can be sectioned through corrugations and grooves to produce the elements shown in FIG. 17. Fig. 19 shows a rod of sixfold length which can be cut first at 82 midway through the corrugated areas longitudinally inward, then at 84 midway through the circumferentially wavy areas 12, so as to produce dual individual elements of the type indicated in FIG. 16; in finished filter cigarettes, the filter element would in this case be inverted by comparison with that of FIG. 15, the circumferential undulations 12 being placed at the buccal end. To realize the structure of fig. 15, we start with a rod such as that of FIG. 19, which has 50 corrugations 12 at each end. Fig. 20 shows a rod of sixfold length which can be cut through the wavy zones 10 and 12 to produce individual elements, filters and filter cigarettes according to the present invention (for example fig. 1) having circumferential corrugations at a end of the element, the longitudinal undulations extending from the latter to the other end; in this case, the filter cigarette has the element oriented in the same way as in FIG. 1, the corrugations 12 extending to the tobacco rod.

Although, in all the embodiments shown, the filtering core 60 includes a smooth casing 4, the latter need not always be provided and, when it occurs, it may or may not be permeable to smoke. The individual elements and the multiple length rods shown in Figs. 14 and 16 to 20 can be provided, in a part of the filter manufacturing process, 65 with a smooth and breathable envelope. The wrapped elements or filters can then be incorporated into cigarettes using an external ventilation cap, as shown in figs. 11 and 15, or by an annular end-piece.

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