GB2284138A - Material for smoking article filters,method of making it,and filters and smoking articles incorporating it - Google Patents

Abstract

A cigarette filter material is prepared by slitting a sheet into a plurality of equal width strips by means of rotating intermeshing grooved rollers and restraining the strip at the exit side of the nip to prevent its free egress from the nip, whereby the strip is corrugated into the vicinity of the groove of the roller in a substantially regular series of oppositely-directed parallel folds transverse of the width of the strip. The method may further include gathering up a plurality of such corrugated strips with their lengths generally parallel but in random alignment and subjecting the mass thus formed to pressure across its thickness whereby randomly to flatten a proportion of the corrugations. <IMAGE>

Description

MATERIAL FOR SMOKING ARTICLE FILTERS, METHODS OF MAKING IT, AND FILTERS AND SMOKING ARTICLES INCORPORATING IT The present invention relates to a material particularly intended for use in a filter of a smoking article such as a cigarette. It relates also to method of making that material, to filters incorporating it and to the finished smoking article incorporating the filter.

Conventional filters are made usually from one of two types of material. Most common is tow material, usually of cellulose acetate. This is crimped individually-spun fibres of material laid lengthwise and compressed into the characteristic cylindrical tube of a filter.

Another conventional material is sheet material specially of paper or of tobacco sheet which is compressed or crumpled as a sheet into the cylinder.

Again, this material has to be crimped before being crumpled up, otherwise there would be a substantial risk of complete blockage of flow.

Both these materials have disadvantages; cellulose acetate tow in that the manufacturing process is quite complex and in that the material is chemically more active and adsorbent than would ideally be desirable, and paper or the like in that despite the crimping there can be irregularity and unpredictability in performance as between one filters or another, or as between different portions of one filter.

The present invention uses strips of material as the filter medium.

In the prior art, there have been quite numerous proposals for using a strip of material as the starting point for making a fibre or a mock-fibre for tow. See for example EP-A-357258 and 359387, US-A3675541 and JP-A-475719. In each case a comparatively narrow strip of material is prepared from a sheet and is then given complex treatments including often orientations and heat treatments in order to approximate it to a fibre. The stated advantage of these treatments is that the "fibres" remain from point to point attached to each other in what was the strip so that they are more easily handleable and do not fall out of the finished filter.A further approach using a strip of film is seen in GB-A-1145976 where an oriented film is projected through a nozzle while at the same time being treated with very high velocity air such that the strip became "fibrillated" and roughened so as once again to have essentially fibrous qualities.

Finally in CA-A-846546 there is a proposal for the use of a sheet of cellophane which is corrugated and held in its corrugation on a base sheet of paper which is then rolled up to form the filter cylinder.

In the present invention a material primarily intended for use in a filter of a smoking article is a strip of material prepared by sub-division of a sheet into a plurality of such strips, the strip after subdivision being corrugated about parallel fold lines transverse to its width. Preferred thicknesses of the sheets are in the range 5 ym to 100 ym, most preferably in the range 20 m to 50 ym. Preferred widths of the strips are in the range 0.2 mm to 20 mm, most preferably in the range 1 mm to 3 mm.

The corrugated strip material if chemically and physically suitable may be used as it is as the material of a filter by the juxtaposition side by side of a plurality of such strips and their disposition in the cylinder of a filter with the direction of their length generally parallel to the axis of the cylinder.

The residual strength of the material causes the adjacent strips to maintain, over a given cross-section with the filter, sufficient spacing between them that a labyrinthine path is afforded along the length of the filter. The material of the strip is most suitably a cellulose film such as for example Cellophane, or polymeric films such as polyvinyl alcohol (PVA) polypropylene and polyethylene. Most preferred are such films as have, in the strip, the property of forming a dead fold", that is to say they exhibit little or no recovery when the fold lines of the zigzag are imposed upon them. Cellophane is particularly suitable from this point of view.

Although the material as above mentioned may be used directly in a filter, it is preferred that before being so used it is subjected to a second process step.

In this step a plurality of such strips lying generally parallel to each other but randomly assembled in other respects into a mass are subjected to pressure across the thickness of the mass. This is conveniently done by rolling. The effect of the rolling will be that some of the corrugations will be lost or substantially so; but others will be completely flattened so that instead of a regular zigzag there is an irregular formation in each strip consisting of a random sequence of completely flattened folds and of largely opened-out former corrugations. It is found that a mass of material subjected to this treatment and having the characteristics mentioned is superior in two respects to the merely corrugated strip.Firstly it has greater resistance to being flattened by traction (a certain amount of which is necessary in a conventional garniture of a filter-making machine) and secondly and more importantly the randomisation of the corrugation and the partial flattening of the material in the second stage renders the filter produced much more predictable and uniform in its characteristics, especially its pressure drop characteristics.

It is a particular advantage of the present materials that they can be handled with little or no adaptation in conventional garnitures of filter-making machines, one example of which is seen highly diagrammatically in the above-mentioned US-A-3675571.

The materials which can be used in the present invention can be those such as Cellophane or PVA which have a low chemical affinity and adsorption, and the filters produced from the present materials can if wished be structured to have a high pressure drop but only a low to medium filtration efficiency. This is the situation which is otherwise achieved by the socalled ventilated filters. The filters of the present invention will therefore be, in that configuration, particularly valuable for so-called low tar cigarettes.

Furthermore, Cellophane and especially PVA are substantially more readily biodegradable than conventional materials.

In another aspect, the invention provides a method of preparing a material particularly suitable for a filter for a smoking article which consists of slitting a sheet into a plurality of equal width strips by means of rotating intermeshing grooved rollers and restraining the strip at the exit side of the nip to prevent its free egress from the nip, whereby the strip is corrugated into the vicinity of the groove of the roller in a substantially regular series of oppositelydirected parallel folds transverse of the width of the strip. The method may further include gathering up a plurality of such corrugated strips with their lengths generally parallel but in random alignment and subjecting the mass thus formed to pressure across its thickness whereby randomly to flatten a proportion of the corrugations. The process may then include taking the product of either the first or the second step and compressing the strips into a filter cylinder with the general direction of their length parallel to the axis of the cylinder.

The invention also includes a filter formed of such material or by that method and smoking articles incorporating those materials or those filters.

A particular embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 shows diagrammatically a laboratory scale machine suitable for making the material; Figure 2 shows a plan view of inter-fingering grooved rollers; Figure 3 is a side view of the rollers; Figures 4, 5, 6 and 7 show the-machine in various stages of production of the material; Figure 8 illustrates diagrammatically the compression of the material into a filter tube; Figure 9 shows a smoking article incorporating the material; Figure 10 shows diagrammatically the product of a first stage of the process; Figure 11 shows diagrammatically the product of the second stage; Figure 12 shows a plan view of another embodiment of the inter-fingering grooved rollers; and Figure 13 shows diagrammatically another embodiment of the product of a first stage of the process.

The machine illustrated as being suitable for laboratory scale production of the material is essentially a domestic pasta-making machine 31 having two pairs of inter-fingering grooved rollers 1 and 2 and a third pair of plain rollers 3 which are able to exert pressure at the nip.

Figure 2 shows the inter-fingering grooved rollers in a plan vew. They are intended to counter rotate in the directions indicated by arrows 7 and 8 and having grooves 6 of equal width and depth along their length.

A nip is formed at 9,10 and into this is fed a sheet 14 of the thin sheet material which is to be transformed into a smoking article filter material. A particularly preferred material is a cellulose sheet such as Cellophane but others such as PVA film or polypropylene or polyethylene sheet may alternatively be used. Particularly preferred for reasons which will become apparent is a material which has a dead fold" characteristic, namely one which involves substantially no recovery when a fold line is imposed upon it.

The sheet material is led between the rollers of the roller pair 3, here being used as simple guide rollers and upwardly through the nip between the rollers 4 and 5. Upon rotation of those rollers it is severed into a large number of parallel and equal strips which at the moment of severence are not subjected to any special orientation, heating or other regime and are at that time plain portions of the sheet.

The leading end 19 of the bundle of strips 18 produced can be bound up or tied in a knot to maintain the strips generally parallel.

Guide plates 17 are placed each side of the egress from the nip over the scraper comb 16 and between them is slid a weight 20 which has a shaped lower end designed to constrain the severed strips into maintained contact with the grooves 6 of the grooved rollers. The weight 20 is of between 0.5 and 5 kg, for example about 1 kg, so that it has a substantial restraining effect.

This causes the strips, as stated, to be compressed into and around the grooves in the manner diagrammatically illustrated in Figure 3 with the corrugations being imposed as sheet, converted into strip, is progressively piled up behind the resistance offered by the weight 20.

The result is that each of the equal width strips forming the bundle 18 has had crimps imposed upon it, as is seen in more detail in Figure 10, a more or less regular corrugation in zigzag formation about parallel fold lines. The crimp width is generally affected by the groove width b, groove depth a, weight 20 and the type of material used.

As more and more material piles up due to the rotation of the rollers, the weight 20 gradually rises in the direction of the arrow 22 and a mass 21 of compressed corrugated strip builds up in the hopper formed by the side plates 17.

Clearly, what is being described is essentially a batch process but is readily adaptable to continuous production.

The batch formed by the mass 21 is now taken from the hopper and loosened out to form a tassel of corrugated strips.

This tassel may itself be used directly as filter material, being subjected to a conventional feeding and compression process as very diagrammatically indicated in Figure 8. Here, the tassel is given a reference 26 and is being fed into progressively narrower tubes 27 and 28 by pulling at one end 30. The compressed filter material inside the tube 28 represents the desired rod-shape article used as a cigarette filter after it has been enveloped by a conventional plugwrap.

This laboratory rod-forming process can be readily adopted in a conventional filter rod making machine where the filter material forms a continuous cylindrical rod wrapped by a plugwrap in a garniture (not shown here). A trumpet is usually fitted to channel the filter material into the garniture.

However, although conventional filter rod making machines assure feed into the compression with as little as possible traction, there is some, and this "first stage material may to a certain extent be straightened by that traction. It is therefore preferred to subject the tassel of strips produced in the first stage to a second stage process in which the tassel 18, Figure 7., is passed through the compression nip of the pair of plain roller pair 3 so that it is flattened in the direction of its thickness to a mass 25. One or more other webs 24 may be fed into the nip additionally so as to increase the pressure on the tassel 18 if need be, but are separated and taken away immediately.

The effect of the compression is to compress more or less randomly the corrugations so that some become largely flattened out and some are completely bent over, so that each individual strip has a highly irregular shape diagrammatically indicated in Figure 11 which may include doublings back and foldings over so that the strip is now bent both across lines transverse to its width as before, but at sharper or lesser angles, but also may be folded about lines not directly transverse so that it is no longer a straight strip.

This second stage treatment therefore has the effect of rendering the material more suitable for use as a filter material partly because it renders unnecessary any de-phasing effect which might be necessary with the first step product and because with the randomisation that it incurs, it is statistically more likely that both as between different filters and within the length of a given filter there will be a more standardized response. Also the second process renders the bundle less susceptible to being distorted by traction upon it and therefore it is able to be treated more robustly in a filter-forming machine; in other words, the bundle designated 18' at Figure 11, which is a teased out and loosened version of the mass 25, can be the input material 26 of Figure 8.

Finally there is illustrated in Figure 9 a conventional smoking article, in this case a cigarette, with a tobacco rod 40, plug wrap 43, surrounding a filter 42 made of the material described and held to the tobacco rod by an overwrap 44. The plugwrap 43 may be porous or non-porous material. Tipping paper 44 may contain ventilation holes (not shown here) to form a tip-ventilated cigarette.

Of course the amount of material fed will affect the compression in the final filter tip and the performance and characteristics of the filter. In particular the product of the slitting of one or more sheets may be fed in common to a single filter-making machine. Other treatments such as heat, steam, plasticizer and flavouring additives may be included which will also affect the performance of the filters.

The following example of the effect of one such material is given: A cellulose film (Cellophane 325P32, noncoated, softener-added cellulose film, ca. 30 ym thick, ca. 33 gsm from Courtaulds Films) of 100 mm width is used. In a first stage as described above a 3 m length of film is converted into a bundle of crimped ribbon of about 1.5 m length. Either two, three, four or five bundles of this crimped ribbons are further processed into compressed masses in a second stage as described above. The "bloomed" (separated) ribbons of each variation are made into 25 mm cigarette filter tips of 7.8 mm diamter.The pressure drop and filtration efficiency are presented below: Sample *Number of Weight of Pressure +Filtration Number Bundle of Filter per Drop per Efficiency Ribbons 25mm tip (g) 25mm Tip (k) (mmWG) 1 2 0.32 15 negligible 2 3 0.41 43 0-5 3 4 0.51 110 20 4 5 0.78 438 (not measured) 5 **Cellulose 0.16 25 24 Acetate Tow Notes: *Each bundle of ribbons is produced from a 4m length of 325 P32 Cellophane film (l00mm width) +Figure expressed as nicotine retention efficiency **Cigarette filter made from cellulose acetate tow (8Y/30000 tow) is quoted for comparison.

Figure 12 shows another embodiment of roller pair 1.

In this embodiment, roller pair 1 consists of a pair of identical rollers 32 and 33. These rollers consist of grooves 38 of substantially equal width and depth along the length. This pair of rollers is designed to cut the thin sheet at alternate cutting edges of these rollers. For example, edges 34 and 35 are cutting edges, but edge 36 located between edges 34 and 35 is blunt and thus a ribbon of width h is cut from the sheet. The ribbon with width h is crimped in the same manner as that described with reference to Figures 2 and 3. However, as each alternate edge does not cut, the ribbon is folded into and around the two separate groove spaces on each roller. This has the advantageous effect that the crimped ribbons are much easier to move out of rollers 32 and 33 after they are cut and crimped.

Figure 13 shows a section of ribbon 18" cut from thin sheet by rollers according to Figure 12. Ribbon 18" is shown to have a width h. Line 37 represents the line made by the blunt edges of the rollers. Line 37 may be undetectable or may represent a severe dent made by the blunt edges, depending on the crimping condition. This additional line 37 provides an additional advantage in that the final crimps after the second stage are more stable.

Claims (13)

CLAIMS:

1. A cigarette filter material comprising a plurality of juxtaposed strips, each strip being corrugated transverse touts length about parallel fold lines.

2. A cigarette filter material according to Claim 1 in which each strip contains a sequence of corrugations irregularly interspersed with partially or completely flattened folds.

3. A cigarette filter material according to Claim 1 or Claim 2 in which said strips have a generally parallel alignment.

4. A cigarette filter material according to any preceding claim in which the thickness of each strip is in the range 5 ym to 10 ym.

5. A cigarette filter material according to any preceding claim in which the width of each strip is in the range 20 tcm to 50 Fm.

6. A cigarette filter composed of a cigarette filter material according to any preceding claim, said strips being juxtaposed side-by-side with sufficient spacing between them that a labyrinthine path is afforded along the length of the filter.

7. A method of preparing a cigarette filter material comprising the step of slitting a sheet into a plurality of equal width strips by means of rotating intermeshing grooved rollers and restraining each strip at the exit side of the nip to prevent its free egress from the nip, whereby the strip is corrugated in parallel folds transverse to the width of the strip.

8. A method of preparing a cigarette filter material according to Claim 7 further comprising the steps of gathering up the strips with their lengths generally parallel but in random alignment, and of subjecting the mass thus formed to pressure across its thickness whereby to flatten a proportion of the corrugations.

9. A method of preparing a cigarette filter comprising the step of compressing a cigarette filter material prepared by a method according to Claim 7 or Claim 8 into a filter cylinder, with the general direction of said strips parallel to the axis of said cylinder.

10. A cigarette filter material substantially as herein described with reference to the accompanying drawings.

11. A cigarette filter substantially as described herein with reference to the accompanying drawings.

12. A method of preparing a cigarette filter material substantially as described herein with reference to the accompanying drawings.

13. A method of preparing a cigarette filter substantially as described herein with reference to the accompanying drawings.