IL26609A - Bonded fibrous materials and process and apparatus for their manufacture - Google Patents

Description

'ΠΙΪΙΙΙ fi13 TJini"! "11 PATENT ATTORNEYS · □ ' D ] D 3 PATENTS AND DESIGNS ORDINANCE SPECIFICATION Bonded fibrous materials and process and apparatus for their manufacture D»jpnni ο'ο^πη , o*neipa D»»a»o D'noiit X fwe) CIGARETTE C0MP0HBITS LIMITED, a British company, of Friendly House, 21-24 Chis ell Street, London E.C.I, England do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement :- This invention relates to a bonded fibrous rod having an evenly deformable peripheral surface such that on transaxial compression of the rod the said surface deforas without the formation of irregularities, and to a process and apparatus for its production. Such rods may be used as tobacco smoke filters. In prior art bonded fibrous rods the peripheral surface comprises a layer of coalesced fibres, or a paper wrapper, which when the rod is compressed trans-axially is liable to form ridges or folds. Thus it has heretofore been essential that the circum erence of cigarette filters be almost exactly equal to the circumference of the tobaceo rod to which they are to be attached, so that the tipping paper which attaches a rod to a cigarette does not so compress the rod that folds or grooves through which ssoke may by pass the filter are formed in the periphery of the rod. The rods of this invention are preferably made slightly larger than the cigarette to which they are to be attached to ensure that some compression and consequently intimate contact with the tipping paper occurs when they are enveloped by the latter. Thus a tight seal is formed around the periphery of the rod. The rods of thid invention have a generally uniform cross section and retain to a large degree the surface area of the fibrous material from which they are formed? they are made from crimped continuous filaments and the fibres at the surface of the rods retain their crimp* According to the invention there is provided a porous self-sustaining rod comprising continuous crimped filaaents which extend between the ends of the rod and are bonded to adjacent filaments at points of contact, the rod having an evenly deformable peripheral surface in which the crimped filaments are bonded to adjacent filaments at points of contact so that upon transaxial compression of the rod the surface of the rod deforms without the formation of longitudinally extending irregularities* The rods ma be formed from continuous filamentary tows such as are used in the manufacture of tobacco smoke filters. Such a continuous filamentary tow comprises a large number of filaments commonly in excess of 5,000, The filaments of the tow are generally longitudinally aligned in parallel orientation, but include crimped portions which diverge or converge from the longitudinal alignment. Continuous filamentary tows of this type comprising fibres of cellulose acetate are used for the manufacture of tobacco smoke filters.

The tows are conventionally supplied in the form of a bale from which they ma be easily withdrawn in a continuous manner by a processing machine* This machine separates the filaments, applies a plasticiser to the filaments and then wraps the filaments in a continuous enveloping strip of paper having a lapped and stuck seam to form a continuous rod which is further sub-divided by transverse cuts into short rods commonly of between 60 and 120 mm. length. Thus paper covered rods are produced* Proposals describing processes for manufacturing rods without a paper cover have been published. However, only one of these processes has proved to be of any practical use. In it plastieised fibres are drawn through a steam heating nozzle which envelops the fibres whilst they are being bonded together. The surface of the rods however, is smoothed by the internal surface of the nozzle. The tension needed to draw the fibres through the nozzle results in substantial reraoval of the crimp in the surface fibres and thus makes the rods less satisfactory by reducing their resistance to radial deformation. These features are undesirable for subsequent processing. A well known drawback of the paper wrapped rod is that after cutting it must be left unused for a period during which the plasticiser will act upon the fibres to bond them together* It is therefore impossible at the time of manufacture to determine whether the rod is of satisfactory quality, A further drawback of the paper wrapped rod is that the pressure drop, i«e. the difference in pressure between its ends when 17,5 ccs. of air per second is passed through it, can only be determined by the taking of samples from the machine and making intermi tent adjustments to the machine to vary the amount of fibrous material $his invention provides a process or bonding continuous crimped filaments including a heat-aetiv able bonding constituent into a porous self-supporting rod comprising continuously gathering the filaments into rod form and conveying then, longitudinally through a heating enclosure in an enveloping previous tape, a heating fluid being passed through the tape into contact with the enveloped filaments during their passage through the enclosure so as to activate the bonding constituent and bond the fibrous material into a rod having a peripheral surface in which the crimped filaments are bonded to adjacent filaments at points of contact whereby the resulting rod has a peripheral surface which on transaxial compressions deforms without the formation of longitudinally extending irregularities. The invention also provides an apparatus fo carrying out the process comprising a heating enclosure having a conduit for the supply of a heating fluid, an endless flexible tape pervious to the heating fluid and extending through the heating enclosure, a drive for conveying the tape through the heating enclosure, means £©r continuously feeding onto the tape crimped continuous filamentst means for a plying a heat-ae ivfttable bonding constituent to the filaments before passage through the heating enclosure, and means for forming the tape into a tube enveloping the continuous filaments for conveying them through the heating enclosure, whereby in operation the heating fluid passes through the pervious tape during its passage through the heating enclosure to activate the bonding constituent and bond each filament to adjacent filaments at points of contact. Continuous measurement of the pressure drop of the fo med reds and continuous control thereof is preferably effected during operation.

A preferred erimped continuous filamentary material upon which to practice the invention is cellulose acetate tow. However, other ^ stp d continuous filamentary materials may be used including pelyslefinsj e.g. polyethylene, polypropylene, and copolymers of ethylene and propylene with other olefins* Also pol aisidesj e.g. nylon,} Polyesters? e.g. polyethylene terephthaia e, may be used* As bonding constituent fusible resins j e.g. lew density polyethylene, may be used. Where a resinous bonding eon-stitueat is used it should have a fusion or so ening point below the fusion or softening point of the filaments.

Sorben material ia particulate form may be addedj e»g# by dusting, shaking or spraying, to the filaments especially when a filter is to be made. Such materials way include activated carbon, silica gel, activated aiumin and molecular sieves. — 4t> — Pig. 1 is a di grammatic elevation of a complete apparatus according to the invention.

Fig. 2 is an elevation of a specific embodiment of the invention.

Fig. 3 is a slightly enlarged plan view of parts of the apparatus of Fig. 2.

Fig. 4 is an end view of Fig. 3 shoving the tongue piece adjustment devices.

Fig. 5 is a cross—sectional view taken on line 5-5 of Fig. 3.

Fig. 6 is a eross-seetional view taken on line 6-6 of Fig. 3.

Fig. 7 is a cross-sectional view taken on line 7-7 of Fig. 3. preferred, form of a portion of the apparatus showing a cooling block having means for adjusting the circumference of the main bore therethrough.

In all the drawings like numbers refer to like parts of the apparatus.

The invention will now be described in a preferred embodiment in which the fibrous material is a secondary cellulose acetate tosr , and in which the bonding constituent is glyceryl triacetate. Referring now to Figure 1, from a bale 1 of cellulose acetate tow the tow 2 is drawn through an air banding jet 4 over a cylindrical guide 5 by rollers 3· Rollers 6, which rotate faster than rollers 3» stretch the tow between themselves and rollers 3· A further air banding jet 7 forms the tow into a band approximately 250 mm. wide before it ass s into a box 10 where it is sprayed with glyceryl triacetate by spray guns 8 and 9. e banding jets 4 and 7 are of known form and comprise a narrow slot through which the tow passes. On one side of the slot is a perforate wall communicating with a supply of compressed air and on the other side of the slot an imperforate wall retains the tow whilst the air impinges upon it. Rollers 11 hold the tow in the band form which fora is continued as the tow passse beneath applicator 12 comprising a hopper 13 for containing a particulate additive, the additive falling upon an inclined shaking trough 1.4 which deposits the additive evenly upon the band of tow.

The machine may be operated without the use of the applicator 12 if it is not desired to apply any additive, fhe tow then passes through funnel 15 which converts it from a band form into a cylindrical form before it enters beneath a tongue 16 which may be seen in greater detail in Figures 3 and 4· The tongue serves to guide the tow into a heating enclosure 18 as well as correctly to position a pervious tape 19 around the tow. The pervious tape whic is drawn through the heating enclosure by drum 20 and which is further trained round rollers 21, 22, 23 and 24 has an open structure and may be made from woven nylon or polyethylene terephthalate monofilament. The tape may have a surface coating of silicone resin or polyetrafluroethylene in order to prevent the tow 2 from adhering to it. The heating enclosure 18 is provided with a conduit 25 connected to a supply of steam which passes through passageways in the enclosure thence through the tape and into the tow in order to heat it and cause the glyceryl triacetate to bond the filaments of cellulose acetate to each other.

Thus by the bonding of the filaments a rod 26 is formed. The longitudinal edges of the tape 19 do not generally meet each other perfectly so that some of the filaments of the tow press between the edges forming a ridge. This ridge is removed by a presser foot 27 which lies between the edges of the tape and serves to press upon the ridge thus reforming the rod into a substantially cylindrical shape. Then the rod passes into a cooling enclosure 28 wherein air or other gas supplied through conduit 30 passes through the tape and into contact with the filaments of the rod in order to cool them and to remove any condensate from the rod 26. Preferably, the cooling air passes through the tape at a multiplicity of points spaced along the length of the cooling enclosure 28. After passing through the rod, the air, with any entrained condensate, passes into receiver 17, which is vented towards the rear of the machine. The result of the action of the air is also to cause the rod to become more rigid. On leaving the Whilst the tape is passing about the drum 20 and the rollers 21 to 24 it occupies a flat form. During its passage from roller 2 to the drum 20 it is folded into an incomplete cylindrical form with a slight gap between its edges. On leaving the cooling enclosure 28 it opens out and is separated from the rod. The apertures in the tape are of sufficient size to provide an easy passage for the steam and the air to pass into the filaments and to effect heat transfer. The surface finish of the rod 26 is dependent upon the surface characteristics of the tape since the filaments of the tow press against the tape whilst they are in a softened condition under the influence of the steam. If a deeply embossed finish to the rod is desired a coarse weave tape may be used. If a smoother rod is required a finely woven tape may be used. The embossing serves to inhibit fibre separation upon the peripheral surface of the rod without the need, in general of causing coalescence of the peripheral fibres of the rod.

If desired it may be arranged that the bore of the heating enclosure is slightly greater than the bore of the cooling enclosure. The latter then serves to set the rod in its final desired diameter.

The action of the steam is to cause the formation of local surface solvation bonds at the points where the droplets of glyceryl triacetate rest upon the filaments of cellulose acetate. Owing to the high latent heat of condensation of steam the cellulose acetate and glyceryl triacetate are rapidly heated so that the bonding of the fibres to each other is substantially complete by the time that the tow leaves the heating enclosure 18. The rate of supply of steam is adjusted according to the speed of travel " of the t w throu h the machine a minimum uantit b i for example that a tow having a cross section of approx-imately 0.5 cms moving at 117 metres per minute may be satisfactorily bonded by approximately 18 Kg per hour of steam at a pressure slightly above atmospheric pressure. In this manner the bonding constituent; i.e. glyceryl triacetate, is activated by the steam whilst the tow is in a relaxed condition, being carried by the belt rather than pulled through a nozzle device as in the prior art. Under these conditions approximately 550 litres per minute of air at room temperature; e.¾. 21-29°C at a pressure of 1.8 atmospheres is supplied to conduit 30 to cool and thereby to harden the rod so that it may be further cut and handled without being damaged or distorted by these operations.

The absence of a paper overwrap on the continuous rod 26 enables a continuously operating pressure drop measuring apparatus; for example the apparatus 33 shown schematically in Figure 1, to be used in determining the resistance to air flow of the continuous rod 26. This apparatus which may take any conventional form, and include a pressure responsive device; e.g. the manometer 35 which may be operatively connected, as shown schematically by the dotted line 34 through any desired linkage means, to the driving mechanism for the rollers 3. In this manner, feeding of the tow 2 may be automatically and continuously varied in response to any changes in pressure drop of the rod 26 whereby substantially constant pressure drop characteristics may be maintained. In order to provide automatic control of the pressure drop the rate of rotation of rollers 3» ma be varied in approximately inverse proportion to the pressure drop so as to vary the degree of crimping of the filaments, hence the weight per unit length It will "be understood that in a finished cigarette these filters will normally be attached to the tobacco rod by means of an enveloping piece of tipping paper; e.g. cork tipping, which overlaps the whole of the length of the filter and 2-3 mm of the tobacco rod. This differs from the conventional filter cigarettes which have a core having a thin paper overwrap to which the tipping paper is stuck. The cores of some types of cigarette filters having a thin paper overwrap may shrink during storage or smoking, so as to leave a gap between them and the thin paper overwrap. Thus smoke may pass through the gap without being filtered. This cannot arise with cigarette filters made by the process of this invention.

Further the tipping paper, which is a thick paper, may be so well bonded by adhesives to the filter so that it may assist in preventing shrinkage of the filter during smoking.

Whilst the rod product made by this process finds a primary use as a cigarette filter it may be used for other purposes such as ink absorbers within felt tipped pens, or as filters for coal gas or water.

The following examples illustrate the application of the process: EXAMPLE 1: The procedure shown in Figure 1 was followed utilizing a tow speed of approximately 117 metres per minute of cellulose acetate tow. After banding, approximately 10 per cent by weight of the tow of glyceryl triacetate was sprayed on to the thin layer of filaments and the thus plasticised tow was formed into a generally circular shape 2 of approximately 0.5 cm cross sectional area. Steam at a rate of approximately 11 Kg per hour was passed into the plasticised tow in the steam-treating enclosure and the air at 24°G. and 1.8 atmosph Individual filter rods 80 mm long were cut from the continuous rod. After 24 and 72 hours of storage the 80 mm. long rods were analysed. The following results were found: TABLE 1 Control Weight Acetate* Plast- Water Total (gram/10 i icizer i io rods ) As produced 5.95 82.3 10.0 7.7 100.0 After 24 hours 5.85 83.8 10.2 6.0 100.0 After 72 hours 5.77 84.6 10.0 5.4 100.0 * including lubricant The above data shows a reduction in water content during storage, but the final moisture can be varied by modifying the characteristics of the cooling enclosure as well as the relative humidity of the storage area.

The following results were obtained on rods which had come into equilibrium with atmospheric moisture: TABLE 2 Oontrol Average Maximum Minimum Weight of 10 rods grms. 5.85 5.95 5.75 Pressure-drop cms. water gauge 12.2 13.0 11.2 Circumference mm 24.55 24.65 24.45 Length mm 79.7 79.8 79.5 EXAMPLE 2: Example 1 was repeated with the dispersion of approximately 30 per cent by volume of finely divided flake carbon particles utilizing the applicator 13 of Figure 1. Filtration efficiency particularly in respect of vapour phase constituents of tobacco smoke of the final EXAMPLE 3: The apparatus of Figure 1 was used, the spray guns 8 and 9 however, being switched off. A homogeneous mixture of activated carbon particles having a particle size between 20 mesh and 50 mesh (U.S. Standard Sieve) and polyethylene particles having a mean diameter of approximately 50 x 10"^ metres was placed in hopper 13. The proportions by weight of the two constituents was approximately 75 carbon and 25$ polyethylene.

The apparatus was started and an addition of approximately 25$ by weight of the mixture was put on a cellulose acetate tow by the operation of applicator 12. Steam and air was passed through the tow in the manner described in Example 1. Well bonded rods containing carbon and polyethylene were produced.

Figures 2 and 3 show the general arrangement of a preferred form of the apparatus of this invention. It will be seen that various parts of the apparatus are carried by a long common supporting member 40 of 'U' shaped cross section, upon which the heating and cooling enclosures, the tongue piece and the ridge remover are mounted.

Conventional plug making machinery of which the tape, drum and rollers only are illustrated, can be used to support the member 40 which thus takes the place of the conventional garniture normall . fitted . The conventional cut off and tape drives shown in Figure 1 remain in place. The receiver 17 has a conduit 39 for removal of condensate and a conduit 49 which may be connected to an exhaust pump for better removal of cooling air. This adaptation is simple and inexpensive.

In Figures 3 and 4 can be seen an entrance block 41 which seats in member 40 and has an upwardly opening section. Two support members 43 and 44 are mounted upon member 40 and serve to carry the rib 42 and hence the tongue piece 16. Set screws 45 serve to effect vertical adjustment of the member 44» the screw 46 being used to clamp it in position. Set screws 47 serve to effect horizontal adjustment of the rib 42 and hence the tongue piece 16, screw 48 being used to clamp rib 42 to member 44 after adjustment has been made. The tongue piece 16 and the groove of the entrance block 41 together provide a tapering passage way for the guidance of the tow and the reduction of its cross section as it enters the steam heating enclosure 18. The path of the tape is such that the edges thereof pass over the tip of the tongue piece so as to meet or approach closely during their passage through heating enclosure 18.

This differs from the path of the tapes used in the manufacture of paper wrapped rods.

Referring now to Figures 3 and 5, the heating enclosure 18 comprises a steam block 50 which seats in the supporting member 40 and has a longitudinal bore 51 for the passage of the tow and the enveloping tape 19. Orifices 52 join the bore 51 to a chamber 53 which communicates with conduit 25 for the admission of steam to the tow and tape in the bore 51. The bore 51 is axially aligned with the tapering space lying between tongue piece 16 and the groove in the entrance block 41* It is further aligned with a 51 _2. ' bore in the cooling enclosure 28» The diameter of the bore 51 may approximate the diameter of the space formed between the smaller end of the tongue piece 16 and the entrance block 41 and may be equal to or slightly larger than the bore in the cooling enclosure 28. The chamber 53 may have any convenient form but must in any case provide a sufficient passageway for the admission of steam and for feature of this embodiment is the provision of an auxiliary bore 55 which communicates by way of a slot 56 with the main bore 51. The bore 55 extends through the heating enclosure and is connected with the atmosphere by way of a further slot 57. The slots 56 and 57 extend the full length of the respective bores and are so dimensioned that the endless tape 19 may be passed through them into the main bores 51 and 54. In this manner the tape can readily be engaged with or disengaged from the heating enclosure and the cooling enclosure before manufacture is begun, and after it is completed without the necessity of providing a split block which would otherwise be required, since the belt is endless.

In order to avoid escape of steam through the slot 56 a sealing device in the form of a tube 58 of heat resistant polyvinylchloride or other suitable deformable 55 plastic is inserted into the bore f>f> after the tape has been passed into the bore 51 and is expanded by fluid pressure into contact with the walls of the bore 55. The end of the tube projects through the bore and is brought to a clamp 59 where it is compressed and thereby closed. Fluid pressure is then fed into the opposite end to expand the tube and to maintain the sealing during the use of the apparatus.

By this means of sealing, after the initial assembly of the heating enclosure, it is not necessary to remove any of the parts of the apparatus other than the tube 58 for insertion and removal of the tape 19. A metal elbow 60 may be fitted around the end of the tube 58* A metal sleeve 61, also to be seen in Figure 6, may be fitted around the portion of the tube 58 between the inflation of the same. Such precautions are only necessary in the vicinity of the heating enclosure as the tubing has sufficient resistance to radial expansion at room temperature to make these precautions unnecessary. The bore 54 is so dimensioned that the sleeve 61 may be fitted at the appropriate place around the tube 58 before the latter is inserted into the bores 51 and 54, the expansion of the tube 58 and the diameter of the bores 51 and 54 being such as to permit this.

Referring now to Figures 3 and 6 the construction of the ridge removing device 27 may be seen. This serves to remove the ridge in the rod 26 which is present after the latter leaves the steam heating enclosure 18. The ridge removing device includes a ridge remover 65 carried by a portion of the cooling block 66 at the end adjacent the steam heating enclosure 18. A pair of set screws 67 co-operate with a screw 68 which slides in an elongated slot 69 in the ridge remover 65 and seats in a tapped bore 70 in an upwardly extending portion of the cooling block 66 to provide for adjustment of the ridge remover 65, the remainder of the cooling block adjacent this e d being cut away to permit an element 71 carried by the ridge remover to extend downwardly between the edges of the tape and press upon the ridge in the rod so as to remove it.

A groove 72 in the cooling block 66 receives the sleeve 61 which is positioned around the tube at this open portion of the apparatus. The groove is aligned with the auxiliary bore 55. A box like enclosure 73 seating on the heating and cooling enclosures and upon the support member 40 has a conduit from the heating enclosure 18. Orifices 81 permit cooling air coming from the cooling enclosure to pass through slot 82 into receiver 17.

Referring now to Figure^ -«¾ 7 the construction of the cooling enclosure 28 may be seen. It comprises a cooling block 66 having three bores. Bores 51 and 54 are the main bore for the rod and tape and the auxiliary bore for the sealing tube 58 respectively. Bore 77 which runs nearly the full length of the cooling block 66 connects with conduit 30 to receive compressed air therefrom and to distribute it via orifices 78 which connect with bore 51 so as to pass through the tape and the rod and to cool them.

Slots 79 and 80 permit the insertion and removal of the tape 19 in the same way as the similar slots in the steam heating enclosure 18. A source of compressed air not shown, is connected to conduit 30. Orifices 81 permit the egress of cooling air and condensate from the rod and the tape into the receiver 17 via a slot 82 which runs substantially the full length of the cooling block 66 and the part of the support member 40 which underlies it« An exit block 83, to be seen in Figure 3» is also carried by the channel 40 and has a tapered upwardly opening groove to facilitate separating the tape 19 from the rod 26.

Referring now to Figure 8 a cross sectional view -i-e—efeown- of a modified and preferred cooling block which incorporates means for adjusting the circumference of the main bore is shown. This provides a small in the provision of a deep groove 85 formed in the side wall of the cooling block 66 opposite to the slots 79 and 80 and a plurality of screws 86 which pass through the portion of the cooling block 66 above the groove 85 and engage in threaded bores 87 in the portion below the groove 85» The part 88 of the block 66 lying between the groove 85 and the bore 51 is so dimensioned that by tightening the screws 86 the part 88 may bend so that the effective diameter of the bore 51 may be increased.

Adjacent to each screw 86 is a further screw not shown, which bears upon the lower face of the groove 85, and is threaded into the upper part of the block 66. By slackening the screws 86 and tightening the further screws the part 88 may bend in the opposite direction to that just described so as to reduce the effective diameter of the bore 51. Modifications to the bore 51 by these means is only intended to produce minor alterations in the diameter of the rod 26, With this modified cooling block, the portion upon which the ridge remover is mounted may be arranged not to move, when adjustments of the screws are made by omitting the screws 86 at the end adjacent to the heating enclosure, by providing a vertically directed slit connecting the groove 85 with the top of the block 66 and by cutting away the end of the block adjacent to the end of the heating enclosure. With such a construction any movement caused by adjustment of the cooling block bore will not affect the positioning of the ridge remover which remains stationar .

Similar adjustment may if desired, be provided 266S9/2

Claims (30)

1. A porous self-sustaining rod of continuous crirabed filaments which extend between th© ends of the rod and are bonded to adjacent filaisents at points of contact, the rod having an evenly deforiaable perij>heral surface in which the crimped filaments are bonded to adjacent filaments at points of contact so that upon transaxial compression of the rod the surface of the rod deforms without the formation of longitudinally extending irregularities.

2. A rod according to Claim 1 having an embossed peripheral surface*

3. A cigarette comprising a tobacco rod in endwise abutting relationship with a filter rod according to Claim 1 or 2 and secured thereto by an adhered enveloping strip overlapping a part of the tobacco rod and the whole of the length of the filter rod.

4. » A process ior bonding continuous crimped filaments including a heat-aetivatable bonding constituent into a porous self-supporting rod Efomprising continuously gathering the filaments into rod form and conveying them longitudinally through a heating enclosure in an enveloping pervious tape, a heating fluid being passed through the tape into contact with the enveloped filaments during their passage through the enclosure so as to activate the bonding constituent and bond the fibrous material into a rod having a peripheral surface in which the crimped filaments are bonded to adjacent filaments at points of contact whereby the resulting rod has a peripheral surface whieh on transaxial compressions deforms without the formation of longitudinally extending irregularities. 26609/2 - 18 -

5. * A process according to Claim 4 wherein the resulting heated rod is passed through a cooling enclosure to which a cooling gas is supplied so as to contact the rod.

6. A process according to Claim 5 wherein the heated rod is carried through the cooling enclosure in a pervious tape through which the cooling gas is passed.

7. A process according to Claim 6 in which the same jervious tn-pe is used to carry the fibrous material through both the heating enclosure and the cooling enclosure.

8. A process according to any of Claims 4 to 7 in which the pressure drop of the formed rod is continuously measured, the feed of filaments to the heating enclosure being controlled so as to maintain the pressure drop reading substantially constant.

9. A process according to any of Claims 4 to 8 in which after leaving the heating enclosure, the heated rod is subjected to a forming operation to cause its cross s ectional shape or dimensions to be altered.

10. A process according to Claim 9 in which a longitudinal ridge is produced in the heated rod between adjacent edges of the enveloping tape, and in which the forming operation comprises pressing the ridge to eliminate it.

11. A process according to any of Claims 4 to 10 wherein the bonding constituent for the filaments comprises a fusible resin.

12. A process according to any of Claims 4 to 10 in which the bonding constituent comprises a thermoplastic material and is applied to the filaments in admixture with a particulate 26609/2 · - 19 - additive before they are gathered into rod form.

13. A process according to any of Claims 4 to 10 wherein the filaments are rendered self-adhesive by plasticiser which serves as a bonding constituent.

14. * A process according to Claim 13 wherein the filaments comprise filaments of cellulose acetate.

15. A process according to any of Claims 4 to 13 wherein the filaments are supplied in the form of a continu-ousfilamentary tow.

16. · A process according to Claims 12 and IS wherein the particulate additive comprises particles of carbon, the thermoplastic particles of polyethylene, and the filaments comprise cellulose acetate filaments.

17. * A process according to any of Claims 4 to 16 wherein the heating fluid is steam.

18. Apparatus for performing the process according to Claim 4 comprising a heating enclosure having a conduit for the supply of a heating fluid, an endless flexible tape pervious to the heating fluid and extending through the heating enclosure, a drive for conveying the tape through the heating enclosure, means for continuously feeding onto the tape crimped continuous filaments, means for applying a heat-activatable bonding constituent to the filaments before passage through the heating enclosure, and means for forming the tape into a tube enveloping the continuous filaments for conveying them through the heating enclosure, whereby in operation the heating fluid passes through the pervious tape during its passage through the heating enclosure to activate the bonding 26609/2 - 20 - constituent and bond eaeh filament to adjacent filaments at points of contact.

19. · Apparatus according to Claim 18 including a cooling enclosure haring a conduit for the supply thereto of a cooling medium, and means for conveying a formed rod from the heating enclosure through the cooling enclosure.

20. · An apparatus according to Claim 18 or 19 including a device for pressing upon the formed rod so as to alter its cross sectional shape or dimensions.

21. · An apparatus according to Claims 19 and 20 wherein the device for pressing upon the rod comprises a strip arranged between the heating enclosure and the cooling enclosure and between adjacent longitudinal edges of the tape*

22. An apparatus according to any of Claims 18 to 21 including a pressure responsive device for indicating continuously the pressure drop of the formed rod*

23. An apparatus according to Claim 22 in which the pressure responsive device controls the action of a feed roller for the continuous filaments by varying its rate ef rotation to maintain the said pressure drop substantially constant.

24. Apparatus according to any of the Claims 18 to 23 in which the heating enclosure has a main bore for passage of the enveloping pervious tape and filaments and orifices opening into the bore for supply of the heating fluid.

25. An apparatus according to any of the Claims 18 to 24 in which the heating enclosure comprises a bore for the longitudinal passage therethrough of the filaments and » » 26609/2 - 21 the enveloping pervious tape, a longitudinal slot connecting said bore to an external face of said enclosure over the full length thereof and so dimensioned as to permit the passage of the tape vhen the latter is inserted into or removed from the said enclosure , and a device for sealing the said slot along its length.

26. » An apparatus according to Claim 25 wherein the device for sealing the slot comprises a further auxiliary bore substantially parallel with the bore for the passage of the filaments and the tape, said auxiliary bore forming an axial enlargement of the slot, an expansible tube extending through said auxiliary bore having means for the application of fluid pressure to the interior of said tube for expanding said tube so as to seal the said slot.

27. · Apjsaratus according to Claim 25 or 26 including means for changing the dimensions of on© transverse axis of the bore by altering the distance of separation of opposed faces of the slot.

28. · A process for manufacturing a bonded fibrous rod substantially as described w ith reference to the accompanying dravin s.

29. · An apparatus for manufacturing a bonded fibrous rod substantially as described with reference to the accompanying dravings.

30. A tobacco smoke filter comprising a rod according to Claim 1 and substantially as hereinbefore described. For the Ap licants DR. TNERS