IL35360A - A cigarette filter and method and apparatus for its manufacture - Google Patents

Description

mis"1? Δ cigarette filter and method and apparatus for ito manufacture This invention relates to a cigarette and apparatus filter and the method/for its manufacture." Cigarette filters are already known comprising crimped fibres or filaments which are bonded to each other at points of contact to form air permeable deformation resistant rods. Such filters are limited in the amount of tobacco tar and nicotine that they can retain without their constituent fibres or filaments being so closely packed that the filter has an excessive pressure drop. This invention is concerned with improving the retention of filters such as these without raising the pressure drop. - The inventio provides a tobacco smoke filter having an axially extending tubular outer member, within said member an axiall extending air permeable inner member comprising an air solid permeable/rod of filaments or fibres which are bonded to each other at their points of contact, at a first position the outer surface of the inner member being in engagement with the inner surface of the outer member so as substantially to preclude axial passage of the smoke between the members whil at a second position, longitudinally spaced from th first, the filaments or fibres are formed into a portion of substantially smaller cross sectional area to leave a hollow space through which 'smoke drawn through the filter may pass. The area of the rod bounding the space at the second position is substantially greater, preferably four times as great as the cross sectional area of the rod at the first position.

The invention also comprises a method for manufacturing the filters of the invention including forming an air permeable inner member comprising an solid axially extending/rod of bonded filaments or fibres, deforming it at longitudinally separated positions to agglomerate the filaments or fibres in portions of substantially smaller cross sectional area, enclosing the said member by an axially extending tubular outer member and bringing the inner surface thereof into engagement with the outer surface of the inner member. The deformation of the rod must be sufficient to cause its cross sectional area substantially and permanently to drop, so that its pressure drop as herein defined, is substantially less than before deformation.

Preferably such a drop should not be less than #.

Figure I shows a perspective view, with parts removed, of a cigarette filter element attached to a paper wrapped tobacco rod.

Figure 2 shows an elevation of the inner member of the filter of Figure I and Figure 3 shows a transverse cross section along lines III-III 1 of Figure 2. Figure shows a view of an alternative form of the inner air permeable member. Figure 5 shows a transverse cross section along lines V-V · of Figure k. Figures 6 and 7 show further forms which the inner member of the filter element may have. Figure 8 shows in diagrammatic form an apparatus for carrying out the method of manufacture.

Referring now to Figures 1, 2 and 3 an. embodiment of the invention comprises a rod 1 which forms the inner member, made of crimped continuous filaments of cellulose acetate which are bonded to each other at their points of contact. End portions 2 and 2' of the rod 1 have a circular cross section and a centre portion 3 has a cruciform cross section. The tips k of the ribs 5 of portion 3 lie upon a circle coaxial with and having the same diameter - k - as that of the portions 2 and 2 ' . The filaments within the ribs 5 from the tips k to the axis 6 are closely agglomerated so that the fibre density is far greater than in the portions 2 and 2'. The part of the rod 1, lying between the parts of the rib 7 and 7' and the dotted lines 8 and 8' is tapered, air permeable, and fibrous, the density gradually decreasing from 7 and 8 and from 7 ' and 8 ' . Surrounding the rod 1 is a substantially impermeable tubular paper wrapper 9 which is tightly engaged about the circumferential surface of the rod at the parts 2 and 21. Thus no significant bypass of smoke occurs between the surface of the rod and the inner surface of the enveloping paper wrapper 9 · Advantageously the rod 1 and the wrapper 9 may be sealed, e.g. by means of an adhesive.

The filter is attached to a paper wrapped tobacco rod 12 by an enveloping overlapping strip 15, of cork tipping paper. Upon drawing smoke from the lighted end 13» in the direction shown by the arrow it will pass through the portion 2 ' at the upstream end of the filter element and, meeting great resistance in the ribs 5» pass through the surface of the tapering portion of the rod lying between 7 and 8 into the spaces lh surroundin the ribs, thence into the portion 2 at the mouth end of the cigarette.

The filter element shown in Figures 1, 2 and 3 was made as follows. Cylindrical rods 25 mm long having the circular cross section of the portions 2 and 21 were manufactured in accordance with United Kingdom Patent Specification 1,169,932 from crimped continuous filaments of cellulose acetate.

These were placed in a device having four heated mating dies. Each die comprised a central part, having a V shaped cross section, at each side a sloping part. These dies gripped and deformed the rod around the centre of its length into the crimped portion 3 and tapering portions at each end of the crimped portion. The heat caused the cellulose acetate filaments at the crimped portion 3 to fuse superficially and adhere with very little space between them. After deformation, the rod was tightly wrapped by a strip of paper to form the tube 9» the paper being held in place by a lapped and stuck seam.

The pressure drop of a cigarette filter is defined as the pressure needed to draw 17· 5 cc per second of air through it. When a fibrous or filamentary rod is deformed according to the method of the invention its pressure drop falls but the ratio of the tar retention to the pressure drop rises. The greater is the fall in the pressure drop the greater is the improvement in the above ratio. In general the best tar retention/pressure drop ratio is found when the denier of the filaments is below 5·0, preferably 2.5· The weight per unit length of the filters is substantially constant the filaments being pressed into a small cross sectional area, as seen in Figures 3 and 5 without stretching or compressing them much in the longitudinal direction. The shape of the deforming dies should be such that the area of the rod through which the smoke passes to enter or leave the space should be, for best results, at least four times as great as the cross sectional area in the undeformed portion of the rod.

In Figures k and 5 an example of an air permeable inner member 20 is shown. It has two ends 21 and 21' which have a circular cross section between which lies a portion 22 around which parts 23 and 23' taper almost to a point and are surrounded by three ribs 2k of which the tips 25 lie upon a circle coaxial with and having the same diameter as the portions 21 and 21'. To form the tobacco smoke filter element of the invention this is tightly enveloped so as to seal around portions 21 and 21' by a wrapper such as the wrapper 9 shown in Figure 1 and thereafter attached to a cigarette rod by means of a tipping paper such as the cork tipping paper 15 of Figure 1. Alternatively the tipping paper 15 may be wrapped around inner member. 20 to seal the portions 21 and 21' to its inner surface and at the same time to attach the tobacco rod 12. Thus the tipping paper serves as means of attachment to the tobacco rod and as the tubular outer member.

The inner member 50 of Figure 6 resembles the inner member 1 of Figure 1 in all respects except that the centre is cylindrical and the crimped ends 51 and 52 are cruciform. The inner member 55 of Eigure 7 comprises one cylindrical portion 56 one crimped cruciform portion 57 and between them a tapering portion 58, and alternating ribs 60 and valleys 6l. The inner members 0 and 55 are employed in the same way as the inner member 1 of Figure 1 and have similar filtering effects.

The portion of the rod having a substantially reduced cross sectional area need not comprise ribs having a Y shaped or cruciform arrangement but may have any convenient form. It should give the smoke a greater area through which to pass into the undeformed portion or portions. It should cause the pressure drop to fall below that of a rod of identical composition and of constant cross sectional shape.

Referring now to Figure 8, an embodiment of the method of manufacturing tobacco smoke filter elements, in this case from cellulose acetate filaments is shown. A known apparatus 30 for example that described in United Kingdom Patent Specification 765, 61 is supplied with crimped cellulose acetate filaments. It separates the filaments and deregisters their crimps, applies to the filaments a fine spray of glyceryl triacetate and delivers a band 31 of the filaments to a rod forming device 32 in which, they are formed into an unwrapped deformation resistant continuous cylindrical rod 33» for example by use of the method described in United Kingdom Patent Specification 1,169,932. In the deforming device }"h the continuous rod is shaped at the desired locations into a continuous rod 36 comprising continuous alternating portions such as those shown in Figures 1-7» by heated crimping members which enter and leave the path of the rod 33 and compress spaced portions into a form having a substantially reduced cross sectional area.

The crimping members may comprise reciprocating or rotative members. These have mated deforming surfaces arranged and driven in synchronism with the movement of the rod 33 to produce the shaped portions of reduced cross sectional area in the deformed rod 36 which emerges. A bobbin kO supplies a continuous strip kl of paper which passes to garniture h2 where it is enwrapped around continuous rod 36 to form the tubular outer member. The edges of the strip l are overlapped and held in place by a lapped and stuck seam in a known manner A tape drum hh drives a tape h3 through the garniture hZ and past tensioning roller h5. A heater 6 dries the adhesive in the seam in the tubular outer member so as to complete the formation of a continuous rod kj which contains a unitary succession of portions of bonded filaments the cross sectional area of which changes from place to place along its length. A cut-off h8 divides the rod k7 approximately equidistantly between the positions of deformation into multiple length filter rods 50 each of which contains a number of deformed and undeformed portions. The cut is made only through deformed portions to produce filters having inner members such as those of Figures 6 and 7· It is made through the undeformed portions to produce filters having inner members such as those of Figures 1-5· The rods 50 are used in the usual way that is they are divided by the filter cigarette machines into double length pieces, each of which is assembled to a tobacco rod at its ends and cut in its centre to produce filter cigarettes.

Any space between the inner member and the tubular outer member may be filled with particles or granules of filtering material such as active carbon, thermoplastic foam or fine denier bonded filaments. To facilitate the filling of the space by the filtering material the crimp preferably has the form of a single straight rib . When making such a filter by the method of Figure 8 the paper strip hi is formed into a U around the rod J6 and the granules dropped on to each deformed portion to flow on each side of the rib. The garniture 42 folds and adheres the strip 4l to hold the granules in place.

Examples Filters were made in accordance with the methods described above from crimped continuous filaments of cellulose acetate.

The results are summarised in the table. Under 'Tow' the filament and total deniers are given and the percentage tar retention of the prior art filters (of uniform cross section, and made of the same tow and lengthened to give the same pressure drop as the filters of the invention) are quoted for purposes of comparison.

Length CircumCrimp Tow Pressure 7¾ TAR RETENTION (mm) ference Type Drop Prior (mm) (mm W.G. ) Example Art 24.8 Y centre 3.5/53000 35 37.0 31.5 24.9 + centre 3.5/53000 37 36.5 32.5 25 .1 centre 2. 1/57000 54 46.0 40.0 24.9 + at one 2. 1/57000 51 45.5 39.0 end 25.0 + at 2. 1/57000 53 43.5 39.5 each end 24.0 + centre 1.6/48000 68 50.0 46.0 24.8 + centre 5/40000 33 27.0 30.0 Y centre see Figures 4 and 5· + centre see Figures 1 , 2 and 3. + at one end see Figure 7. + at each end see Figure 6.

Claims (3)

1. 35360/2 1. . A tobacco smoke filter having an axxally extending tubular solid outer member, within said member an axially extending air permeable/ rod of fibres or filaments which are bonded to each other at their points of contact, at a first longitudinal position the rod being in engagement with the inner surface of the outer member so as substantially to preclude axial passage of smoke between itself and the outer member, and at a second longitudinal position, spaced from the first, the fibres or filaments of the rod being formed into a portion of smaller cross-sectional area to leave a hollow space through which smoke drawn through the filter passes.

2. A filter according to claim 1 wherein the area of the surface of the rod through which the smoke passes to enter or leave the space is four times as great as its cross sectional area at the first position.

3. A filter according to any of the preceding claims wherein the portion of smaller cross sectional area lies between the ends of the filter. , A filter according to claim . 1 or' 2 wherein a portion of smaller cross sectional area lies at one or both of the ends of the filter. 35360/2 5.» A filter according to any of the preceding claims wherein at the said second position the filaments or fibres are formed into ribs. 6. A filter according to claim 5 wherein the ribs are arranged in the form of a cross. 7· A filter according to claim 5 wherein the ribs are arranged in the form of a 1 Y' . ·¾ - 8. A filter according to any one of claims 5 to 7 wherein the tips of the ribs lie upon a circle, the diameter of which is approximately equal to the internal diameter of the tubular outer member. 9· A filter according to any of the preceding claims wherein between the first and second positions the surface of the rod through which the smoke passes is formed with protrusions or depressions to increase its surface area. 10. A filter according to claim 9 wherein the said protrusions or depressions comprise longitudinally directed ribs or valleys. 11. A filter according to any of the preceding claims wherein the filaments or fibres have a denier of less than 5· 3S360/2 12, A filter accordin to claim 11 wherein the denier is 2.5 or less. , 13· filter according to any of the preceding claims forming-part of a cigarette the outer member being formed by the tipping material which attaches the rod to the tobacco rod. ½. A filter according to any of the preceding claims wherein the filameni.s or . fibres are of cellulose acetate. 5· A filter according to any" of the preceding claims in which the weight per unit length is substantially constant. 16. A method for manufacturing a filter comprising forming an solid air permeable axially extending/rod of fibres or filaments which are bonded to each other at their points of contact, deforming the rod at separated positions along its length to form the fibres or filaments into portions of smaller cross sectional area, enclosing the said rod by an axially extending tubular outer member, bringin the inner surface thereof into engagement with the outer surface of the rod between positions of deformation and cutting the enclosed rod into filter lengths. 17· A method according to claim 16 wherein the inner member comprises thermo-plastic material and is deformed with the aid of heat. 3S360/2 18. A method according to claim 17 wherein heated crimping members are employed. 19· method according to any of claims 16 to 18 wherein the rod is deformed so that its pressure drop falls. 20. A method according to claim 19 wherein the pressure drop falls by not less than 30%. 21. A method according to any of claims 16 to 20 wherein the rod is made in a continuous endless form, the deformation, enwrapment and cutting being carried out in succession on continuously moving portions of the rod. 22. A method according to any of claims 16 to 21 wherein the outer member is formed by enwrapping the deformed rod with a continuous strip of material and adhering the overlapping edges of the strip to form a seam. 23» A method accordin'g to any of claims 16 to 22 in which after enwrapment the rod is cut through the positions at which it was deformed. 2 » A method according to any of claims 16 to 22 wherein the rod is cut approximately equidistantly between the positions at which it was deformed. 25· method according to any of claims 16 to 22 wherein the rod is cut at t>oth the positions of deformation and between successive positions of deformation. 26. Apparatus for making a tobacco smoke filter comprising solid. a device for forming an axially extending air permeable/rod of fibres or filaments which are bonded to each other at their points of contact, a device for deforming the rod, t longitudinally separated positions into portions of smaller cross sectional area, a device for enclosing the deformed rod by an axially extending enclosed tubular outer member, and a cut off for dividing the /roA into lengths. 27. A tobacco smoke filter. substantiall as described with reference to the drawings. 28. A method for manufacturing a tobacco smoke filter substantially as described -with reference to the drawings. 29. An apparatus for. manufacturing a tobacco smoke filter substantially as described with reference to the drawings. For the Applicants DR. REINHC XOHN AND PARTNERS By : N