IL35766A - A tobacco smoke filter and method and apparatus for its manufacture - Google Patents

Description

*rp»¾>yn a'jpnm ηβ»©ι pao †wy 730D A tobacco ainoko filter and method and apparatus for its manufacture CIGARETTE COMPONENTS LIMITED This invention is concerned with a tobacco sraoke filter, for example a cigarette filter, and with a method for its manufacture. Tobacco smoke filters in common use are made of cylinders filled with creped paper, bonded crimped fibres or bonded crimped filaments. They generally have a paper wrapper around their circumference. Recently tobacco smoke filters have been described in which a hollow air permeable inner tube or a lamina of filter material is arranged within an impermeable outer tube in such a way that smoke passes through the material, at right angles to its face. Such filters may have high retention of tobacco smoke solids yet a moderate pressure drop. The production of an inner tube or a lamina and the combination of it with the outer tube is not as simple as the production of a filter comprising a cylinder made of creped paper, bonded filaments or bonded fibres. This invention has as its object to provide a filter which may have a similarly high retention of tobacco smoke solids without an excessive pressure drop and an apparatus and a method for making it.

This invention provides a tobacco smoke filter comprising- an axially extending tubixlar outer member, within said member an axially extending air permeable rod having a circum erential wall of filtering material encloses an air permeable supporting-part, at a first longitudinal position the outer circumferential surface of the filtering material being in engagement with the inner surface of the outer member, so as substantially to preclude passage of smoke in the axial direction between the rod and the outer member, and at a second position, longitudinally spaced from the first, the inner surfa.ces of the wall being in engagement so as substantially to preclude passage of smoke in the axial direction betieen them, . so that tobacco smoke drawn through the filter passes through the wall of filtering material.

In the drawings Figure 1 shows, partly in section, a filter cigarette which includes a filter of the invention. Figures 2, 3 and h show alternative forms- whic the rod in the filter may have. Figure 5 shows one form of the apparatus for performing the method and making the filter.

The embodiment shown in Figure 1 consists a of a filter 1, comprising/rod 2, enclosed by a tubular outer member 3 of stiff paper. The filter is attached to a paper wrapped tobacco rod h by means of an enveloping strip of cork tipping paper 5, which is adhered to the whole of the outer surface of member 3 and to part of the tobacco rod . , The. rod 2 has a circum erential wall 6 of air permeable filtering paper. Enclosed by the wall there is an air permeable supporting part 7 which consists of crimped filaments of cellulose acetate which are bonded to each other at their points of contact.

The outer circum erential surface of the rod 2 has an end portion 10 in the form of a right circular cylinder with an outside diameter equal to the inside diameter of the outer member 3· Thus the end 10 is in engagement with the outer member 3 around its whole periphery so that no significant amount of tobac - h ' - smoke can pass in the axial direction, shown by the arrow, between the outer circumferential surface of the rod at the end 10 and the inner surface of the outer member 3· The othei" end 11 of the rod has a cruciform cross section with a smaller cross sectional area than that of the end 10. Four ribs .12 form the cross and in each rib the inner surfaces of the filter paper 6 are pressed together, a small quantity of fused cellulose acetate, produced by a the fusion of/part of the. supporting part during form an impermeable bond the manufacturing .process , serving to /ardhero-frhem— between them. tfl-eae1¾—t ^hr&y. ^Between the ends 11 and 10 lies a tapering portion 13 and a substantially cylindrical portion 1 , which has grooves 15» in its peripheral surface. These increase, the area through which tobacco smoke can pass. Smoke passing in the direction shown by the arrow enters the filter at the end 10, passes into the air permeable supporting part 7» and, since it cannot get out of the end 11 of the rod 2, the inner surfaces of the wall of filtering material are adhll separated by the impermeable fused cellulose acetate to which being/ sealed effectively to each other, it travels through the wall 6 of the filtering material and is filtered.

This construction provides a large area of filtering material through which the tobacco smoke can pass so that the packing density of the material can, be high without the pressure drop of the filter being high. The paper of which, the tubular outer member 3 is made should be sufficiently thick and stiff to bend evenly over the ribs 12 without departing from a circular form. A paper weighing at least k 5 g/m2 is usually needed.

In Figure 2 an alternative form of rod 20, has two ends 21 and 21' which have the form of right circula . cylinders . Contiguous with these are two tapering portions 3 and 23' which meet in a central portion 22. This comprises three ribs 2 k , of which two are to be seen, which are arranged around . the axial portion 5 so that portion 22 has a Y shaped cross section. The air permeable supporting part 26, which fills the ends and tapering portions of the rod, is surrounded by a wall of filtering material 27» which forms the whole of the outer surface of the rod 20. The circumference of the ends 21 and 21' and the peripheral length of the portion 22 are approximately the same, so that it is possible to provide good support for the tubular outer member 3» by means of the tips of the ribs 2 , making the rod by deforming a cylindrical rod, without significantly altering the length of the periphery at the position of deformation. The tips of the ribs 2 k lie thus on a circle coaxial with and of the same diameter as the ends 21 and 21'.

The permeability of the .paper which forms the wall 27 must be higher than that of the paper used to form the wall 6 of Figure .1 since the smoke has to pass through two layers of paper. An air permeability of greater than 30,000 cc per ininute is desirable.

In Figure 3 a rod 3 is shown.- This comprises ribs 31 i a tapering portion 32 and a cylindrical end portion 33 · It has the shape of one ► half of the rod shown in Figure 2 , In this embodiment however the ai permeability of the paper should preferably be about 30 » 000 cc per minute, or less, since it is a single pass filter. A further rod is shown in Figure . This comprises a central cylindrical portion hO having crimped cruciform end portions hi and k2. The wall and the supporting part which is within it are made of similar materials to those used in the embocliment of Figure 2 .

In Figure 5 an, embodiment of the apparatus for performing the method and making the filters of the invention is show . diagrammatically . A known device 50 supplies an opened filamentary tow 51 of cellulose acetate, having upon it droplets of triacetin, to the entry part 52 of a known' filter rod forming machine 53 · The latter comprises a garniture ^ through which a rotating drum 56 draws an endless tape 55 · Rollers 57 tension the tape. A bobbin 60 supplies an elongate strip 6l of air . permeable filtering paper, and. a printing device 62 applies transverse stripes of adhesive to the strip 6l. Within the garniture 5^ the strip 6l is enveloped around the filaments 5-1» its edges are overlapped and adhered in place by an adhesive which comes from 'applicator 63. This enters a deforming devic four heated rotating whe projections on their circumferences which meet each other as they contact the rod 65. The rod 67 coming from device 66 comprises alternating portions in which the cross sectional area changes. For example, circular portions may alternate with cruciform portions, tapering or grooved portions lying between them generally as shown in Figures 1-k, The rod 67 enters the garniture 8.0, through which a drum 81 draws an endless tape 82, rollers 83 tensioning the tape. A bobbin 8^1 supplies an elongate strip 85 of substantially impermeable paper to the garniture 80 where it is enveloped around the rod 67. The strip 8 is held in place by a seam in which overlapping edges are adhered by an adhesive, which comes from the applicator 86, and is. dried by heater 87. This forms a continuous rod 88. The tube formed from the strip 85 is in engagement with the undeformed portions of the rod 67 and enclose the deformed portions of reduced cross sectional area.. A cut off 0 divides the continuous rod 88 into lengths 91» each of which comprises an even number of filters. The cut is made by the cut off 0 at the positions of deformation, or midway between the position of deformation. This may be seen by reference to Figures 1-h .

The triacetin, after an hour or two, causes the filaments of cellulose acetate to bond to each other. The adhesive stripes on the strip 6l, are deposited in register with the positions of deformation to ensure the sealing of the inner surfaces of the filtering material to each other.

A printing device similar to the printing device 62 may be used to apply stripes, in register with the undeformed portions of. the rod.67» to the strip 85 to seal the inner surface of the tubular outer member to the outer surface of rod between the points of deformation.

If desired the parts of the apparatus between deforming device 66 and the cut off 90 may be dispensed with so that the latter divides the continuous rod 67 directly. The cut pieces may be fed, for example, to a . suitable . filter cigarette machine wherein they are assembled directly to tobacco rods and a strip of cork tipping paper,' such as that indicated by reference ; numeral .5 of Figure 1, may serve as a tubular outer member and as a means of attachment to the tobacco rod. They may also be assembled with other types of filter to form multiple filters in a known manner. If the strip 6l is made of paper having sufficient wet strength, the deformation of the rod 65 by the deforcing device 66 may be' facilitated by the provision of a steam heating jet arranged betiveen heater 6h and device 66. This applies steam directly upon the rod 65. Other means of heating may also be employed to preheat the rod 65. If the filtering material. or the supporting part are of thermoplastic material,its temperature during preheating or deformation should be raised to its softening point.

Suitable materials for forming the air . permeable supporting part include, other thermoplastic materials such as fibres or filaments of polypropylene, 0 polyethylene and lightweight longitudinally air permeable extruded section's which permit longitudinal passage of the smoke and access to the wall of filtering material. Other air permeable materials may be used for the supporting part, for example, a web of creped, porous paper. When using this material stripes sich a.s those applied by device 62 of Figure 5 should be vised so as to adhere the inner surfaces of the wall of filtering material to each other and to the creped paper. The material to be used to form the wall which encloses the supporting part is chosen to suit the shape and size of the rod which is to be made. For example a rod such as that shown in Figure 3 and having an area exposed to tobacco smoke of about 2.5 cm3 a length of 20 mm and a diameter of 8 mm may be made with filtering wall of paper weighing about 75 g/m2 , an air permeability, of about 30» 000 cc per minute and a thickness of about 0.25 mm. The air permeabilities referred to in this . speci ication are the volume of air which passes ,per minute through a piece of the material, 10 cm2 in area, when the pressure difference between the faces of the material is. 10 cm Water Gauge. In filters of the dimensions which are at present practical, the area of the outer circumferential wall exposed to the tobacco smoke lies between 2.0 and 7.0 cm For these the wall should preferably be formed of a laminar material with an air permeability between 2,000 and 40,000 cc per .minute, the thickness between 0.05 mm and 0.^ mm. and the weight between ho and 100 g/m2. In general ve'ry thin paper is. unsuitable , even when used in the embodiment shown in. Figure 2, as the pores of the paper may clog very easily if the paper is dense enough to be strong. If the pores are . larger ' it may be too weak. For such a rod the weight of the paper, is preferably not less than ^5 g/m2 in order to provide the desired thickness. Laminar materials other than paper, such as bonded fibrous or filamentary webs and porous plastics, may be used.

Then using as the supporting part bonded filaments of cellulose acetate or other thermoplastic fibres or filaments of a suitably small diameter, the wall of filtering material may be formed from the outer layer of these fibres or filaments by applying heated tools to compact the said layer, and hold the fibres or filaments in place by partial.. fusion. For this purpose a rod substantially . larger in diameter than the. intended diameter of the rod in the completed filter is made. This is- compressed into the appropriate shape, for example, that shown in Figures 1- by the heated tools.

The following examples the invention. Filters 20 mm lon were made with the inner supporting part of 5000 cellulose acetate filaments with a Y shaped cross section . and a titer of 8 denier. A paper having a weight per unit area of 75 g/m2 and an air porosity · of ,000 cc per minute was wrapped around the rods by the method shown in Figure 5 to form the filtering wall. The inner members' vere deformed to give cruciform or Y cross section portions at one end only of the filter. The results are given below: Filter Outer Crimp Pressure Tar Nicotine Circumference Type Drop mm Retention Retention mm ■ '.' · -■ Water Gauge 1. 2k.95 ■ . + ·· 68 68.0$ 65.0$ 2. 2^1.80 + 5h 6h.k<$> 62.9$ 3. 2*1.80 Ϋ . ,·' .67/ 65.^$ , 61.6$ The pressure drop was measured by drawing air at a flow rate of 17·5 cc per second through the filters.

•Such 'results cannot be obtained with prior art filters of packed paper or filaments.

, The fibres of which paper is formed usually . have a suitable diameter, however the .synthetic fibres or filaments or non fibrous porous synthetic materials for use in this invention should have a small fibre or filament diameter, or the dimensions of the material between the pores, in the case of non fibrous porous material, should be small. It is preferable, in order to obtain a satisfactory retention, that these dimensions should not exceed l'l microns.

In a further embodiment the rod was formed of a crimped continuous filamentary cellulose acetate tow, 8 denier per filament 20,000 total denier which · formed the supporting part and a tow with smaller filaments, 1.6 denier per filament, total denier 6l,000. which formed the filtering material. Each tow was opened, banded and sprayed with plastic! ser in a known manner. The first tow was brought through an inner tubular guide, and the second was brought through an outer tubular guide, coaxial with and surrounding the first, so that at ' the exit of the guides the first tow had a circular cross section and the second an annular cross section surrounding the first. Immediately adjacent the outle,t o the guides was a steam treating enclosure connected to a supply of saturated steam and having an internal diameter appropriate to that desired in the . ... r rod'.' . The steam passed into the combined tows, causing the filciments to adhere- firmly to each other. At the exit of the guides was an air coolin device of a known form. After the air cooling device a deforming device, such as device 66, was mounted. This deformed the continuous rod into an alternating succession of pieces having the form shown in Figure 2, Upon leaving the deforming device the tube entered a garniture, such as garniture 80, in which it was enveloped in a continuous paper strip, which was kept tightly in place around the tube, by a lapped and stuck seam. This formed the tubular outer member. The rod was then cut into pieces by a cut off.

The space "between the rod and the tube in :.·- ·-,· · the filter embodiment shown in Figure 2 may be filled with particulate filtering materials. - l'l - such as disintegrated plastic foam or activated carbon g-ram.iles. These may be incorporated using known apparatus mounted betAiiee the deforming device 66 and the garniture 80. 35766/2

Claims (42)

1. » A tobacco smoke filter comprising an axially extending tubular outer member, within the said member an axially extending air permeable rod comprising a circumferential wall of filtering material, within which is an air permeable supporting part, at a first longitudinal position the outer circumferential surface of the filtering material being in engagement with the Inner surface of the outer member so as substantially to preclude passage of smoke in the axial direction between the rod and the outer member, and at a second position, longitudinally spaced from the first, opposed parts of the wall of filtering material, with between them a compressed portion of the supporting part, are brought togethe so that a the second position, axial passage of the smoke between the opposed parts of the wall of filtering material is substantiall prevented and the smoke, which is drawn through the filter, passes through the filtering material.

2. A tobacco smoke filter according to Claim 1, the filtering material being an air permeable material chosen from the group comprising paper, bonded fibrous and filamentar webs, porous plastics, plastic foam, bonded fibres and bonded filaments.

3. A tobacco smoke filter according to claim 1, the rod comprising bonded fibres or filaments of cellulose acetate.

4. Λ tobacco smoke filter according to claims 2 or 3 , the diameter of. the fibres or filaments or the dimension of the inter pore material in the wall of the filtering material being not more than about 14 microns.

5. A tobacco smoke filter according to any of the preceding claims, the material of which the supporting part is made. being chosen from the group comprising fibres, filaments, thermoplastic 'materials, creped paper, polyethylene and polypropylene.

6. A tobacco smoke filter according to claim 2,. the wall being formed of a laminar material v/eighing . between 40 and 100 g/m .

7. A tobacco smoke filter according to claim 6 wherein the wall has a air permeability of between 2000 and ¾Q,000 cc per minute per 10 cm 2 under a pressure of 10 cm water gauge.

8. ; A tobacco smoke filter according to any of the preceding claims . wherein, the thickness of the wall lies between 0.05 mm and 0.4 mm.

9. A tobacco smoke filter according to any of the preceding claims wherein the area of the outer circumferential wall exposed to the tobacco smoke lies between 2.0 and 7.0 cm

10. A tobacco smoke, filter according to any of claims 2-9, the tubular outer member being of paper having a weight of not less than 45 g/m2..

11. A tobacco .smoke filter according to claim 8, the wall of filtering material comprising paper weighing approximately 75 g/m~.

12. A tobacco smoke filter according to claim 1 "wherein at least one of the said engaged surfaces is provided with an. adhesive.

13. A tobacco smoke filter according to any of the preceding claims wherein at the said second position the rod is formed into a plurality of ribs.

14. A tobacco smoke filter according to claim 13, the ribs being arranged in the form of a Y.

15. A tobacco smoke filter according to any of the preceding claims wherein the said first position lies at one of the ends of. the filter and the said second position lies at the other end. of the filter.

16. A tobacco smoke filter according to any of claims 1-6, 8, 9, 12-14 wherein the rod is in engagement with the outer member at its ends and that the said second position lies between its ends.

17. A tobacco smoke filter, according to claim . 16 wherein the wall. of filtering material comprises paper having an air porosit in excess of 30,000 cc per minute per 10 cm. ? under a. pressure of 10 cm water gauge.

18. A tobacco smoke filter according to claim 1 wherein the supporting part and the wall of filtering material are formed of continuous filamentary tows, the filaments . of the tow forming the wall of filtering material being smaller than those forming the supporting part.

19. A tobacco smoke filter according to claim 16 wherein between the rod and the outer member a particulate filtering material is retained, at the said second position. 35766/2

20. A method of making tobacco smoke filters comprising the steps of forming an axially extending air permeable rod comprising a circumferential wall of filterin material, within which is an air permeable supporting part, deforming the rod at a position along its length to brin opposed parts of the wall of filtering material towards each other with a compressed portion of the supporting part between them, so as substantially to preclude passage of smoke in the axial direction between them, enclosing the rod by a tubular outer member and bringin the inner surface of the outer member into engagement with the ofcfcer member and bringing the inner surface of the outer member into engagement with the outer surface of the rod at a positio longitudinally spaced from the position of deformation, so as substantially to preclude passage of smoke in the axial direction between them.

21. A method according to claim 20 wherei the rod is formed in a continuous length and that after being deformed it is divided into pieces by transverse cuts at the positions of deformation,

22. Δ method according to claim 20 wherein the rod is formed as a continuous length and that after being deformed It is divided into pieces by transverse cuts between the positions of deformation.

23. A method according to any of claims 20-22 wherein' at at least one of the said longitudinal positions the engaged surfaces are provided with an adhesive.

24. A method according to any of claims 21-23 wherein the circumferential wall is formed ' from an elongate strip of air permeable material which is longitudinally enveloped around the supporting part, to form the continuous length of rod, and retained in place by- a longitudinal seam.

25. A method according to claim 24 wherein . ■transverse stripes of adhesive in register with the positions of deformation, are deposited upon the strip of air permeable material before the latter is enveloped around the supporting part.

26. A method according to any of the claims 20-25 v/herein deformation is accomplished with the aid of heat.

27. A method according' to claim 26 wherein the supporting part>or the wall. of filtering material, comprise thermoplastic materials which are heated to their softening temperatures during or before deformation.

28. A method according to any of "claims 20-27 wherein the supporting part is formed by bonding filaments or fibres to each other whilst they are enclosed by the wall of filtering material.

29. A method according to any of claims 20-22 wherein a rod of bonded filaments or fibres is made, the material of the peripheral region thereof being thereafter compacted to form the wall of filtering' material , and deformed at a specified position to bring the inner limits of the compacted. material into engagement.

30. A method according to claim 20 wherein the supporting part comprises^ fibres or filaments of cellulose acetate, which are bonded to each other at their points of contact by means of a liquid plasticiser, which is applied to them, the fibres or filaments being thereafter enwrapped by an elongate paper strip which is retained around the filaments by a lapped and stuck seam, before being deformed, enwrapped by an elongate paper strip which forms the tubular outer member, and transversely cut at the positions of deformation, or midway between positions of deformation, to form lengths each of which comprises an even numbe of tobacco smoke filters^.

31. A method according to any of claims 20-30 wherein before deformation the rod is heated, preferably by direct contact with steam.

32. ' A method according to any of claims 20-31 wherein the rod is deformed into a plurality of ribs.

33. A method according to claim 32. wherein the . rod is deformed without significantly altering the length of the periphery at the position of deformation.'

34. A method according to claims 21 or 22 wherein the rod is cut into pieces before it is enveloped by the outer member.

35. An apparatus for performing the method according to. claim 20 comprising a device for 'forming an axially extending air permeable rod, having a circumferential wall of filtering material, which encloses an air. permeable supporting part, a device for deforming the rod at a position along its length so as to. bring the inner surfaces of the wall of ; fiIt ering material into engagement, and a, device for enclosing the rod by a tubular outer member, the inner surface of which engages the outer surface of the rod.

36. An apparatus according to claim 35 wherein the device for forming the rod by enclosing the supporting part by the filtering material comprises a garniture.

37.. An apparatus according to claim 36 wherein the device for enclosing the rod by a tubular outer member comprises a garniture to which an endless strip of material may be supplied.

38. An apparatus according, to claim 37 wherein between the garnitures a deforming device is fitted. . ',

39. An apparatus according to claim 36' wherein the deforming device comprises heated deforming members which press the rod coming from the garniture.

40. A method for making tobacco smoke filters substantially as described with reference to 'Figure 5.

41. An apparatus . for performing the method according to claim 20 substantially as described with reference to Figure 5.

42. A tobacco smoke filter substantially as described with reference to Figures 1-4. 24 - ERS