US3599646A

US3599646A - Cigarette filter

Info

Publication number: US3599646A
Application number: US820355A
Authority: US
Inventors: Richard M Berger; Elwin W Brooks
Original assignee: American Filtrona Corp
Current assignee: Filtrona Richmond Inc
Priority date: 1969-04-30
Filing date: 1969-04-30
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

A cigarette filter means is constructed to provide a pair of elongated, high surface area, cavities defined on opposite sides of a relatively thin wall formed of filtering material. Preferably, only the ends of the filter means contact an overwrapped outer tube which provides maximum available surface area to provide a filter element with a relatively high filtration efficiency and satisfying ordinary commercial standards regarding ''''taste,'''' pressure drop and manufacturing cost. The filter comprises an outer elongated member in which an inner crimped filter is disposed. The latter has major portions of the outer surface spaced from the inner surface of the outer member to define cavity means therebetween into which the smoke is compelled to pass.

Description

United States Patent Inventors Richard M. Berger Richmond; Elwin W. Brooks, Mechanicsville, both of, Va. Appl. No. 820,355 Filed Apr. 30, 1969 Patented Aug. 17, 1971 Assignee American Filtrona Corporation Richmond, Va.

Continuation-impart of application Ser. No. 727,477, May 8, 1968, now Patent No. 3,533,416, dated Oct. 13, 1970.

6/1963 Davidson 131/10x 10/19 67 L1oyd... 131/10.7x

Primary Examiner- Melvin D. Rein Attorneys-Holman & Stern and Samuel L. Davidson ABSTRACT: A cigarette filter means is constructed to provide a pair of elongated, high surface area, cavities defined on opposite sides of a relatively thin wall formed of filtering material. Preferably, only the ends of the filter means contact an overwrapped outer tube which provides maximum available surface area to provide a filter element with a relatively high filtration efficiency and satisfying ordinary commercial standards regarding taste," pressure drop and manufacturing cost. The filter comprises an outer elongated member in which an inner crimped filter is disposed. The latter has major portions ofthe outer surfacespaced from the inner surface of the outer member to define cavity means therebetween into which the smoke is compelled to pass.

PATENTED mm 1 Ian 31; 599 '54s SHEET 1 [IF 3 INVENTORS RICHARD M. BERGER ELWIN W. BROOKS BY Jm Ma i M ATTORNEYS SHEET 30F 3 PATENTEU mm 1 an INVENTORS RICHARD M. BERGER ELWIN W. BROOKS Y MZZM /M ATTORNEYS CIGARETTE FILTER Thisapplication is a continuation-in-part of copending application Ser. No.'727,477, filed May 8, I968, for Tobacco Smoke Filter, now US. Pat. No. 3,533,416 granted on Oct. 13,1970.

This invention relates to filters, particularly filters for tobacco smoke. Known filters differ in their resistance to air flow through them. This resistance is usually expressed as the pressure drop in cm. water gauge when air at a flow rate of 17.5 cc./se c. is passed through the filter. The retention of tobacco smoke solids is expressed as the percentage of such materials retained by the filter when the smoke of one cigarette is drawn through it. Filters at present in commercial production comprise packed rods of bonded filaments or fibers, gathered paperwebs or bonded particulate adsorbents. The pressure drop and retention of such filters is approximately proportional to their length. Such filters cannot provide a retention of greater than 55 percent without an excessive pressure drop. Filters comprising a laminar member enclosed within a tube and having diaphragms, baffles or other barriers to direct the smoke from one face to the other of the laminar member, are

known. Such filters may have a higher retention and lower pressure drop than the current commercial filters. However the assembly of the parts of such a filter is difficult and this, it is believed, is the reason why such filters have not been produced commercially. It is an object of this invention to provide a filter comprising a laminar filtering member which may havea high retention and a low pressure drop and which will be economical to manufacture and to provide a method and apparatus for manufacturing the same. This invention provides a tobacco smoke filter element comprising an axially extending tubular outer member, within said member an axially extending hollow inner member comprising an axially extending air permeable wall, the arrangement being such that smoke passing in an axial direction must travel through said wall of said inner member and be filtered thereby characterized in that the outersurface of the wall of the inner member is in engagement with the innersurface of the outer member at a first axial position so as substantially to preclude axial passage of smoke between the members, and at a second axial position the inner surfaces of the wall of the inner member are in engagement so as substantially to preclude axial passage of the smoke between them at the said second position.

The tubular outer member is formed of a material to provide sufficient rigidity for handling in conventional filter cigarette machines. It may be of plastic, paper, cardboard or bonded fibers. The wall of the inner hollow member is formed of air permeable materials, for example, filter paper or bonded fibers such as crimped cellulose acetate fibers, porous plastic, plastic foam, blends of paper fibers with thermoplastic fibers especially secondary cellulose acetate fibers. Enclosedby or retained within the material of the inner member, adsorbent materials for the removal of vapor phase constituents of tobacco smoke, for example active carbon, or-materials for flavoringthe smoke, may be provided. Thus it is possible to produce-a filter with high retention for both vapor phase constituents and tobacco smoke solids.

In the drawings FIG. Ishows a typical'filter with a portion of a tobacco rod attached.

FIG. 2, shows an apparatus for formingthe filter of the invention.

FIG. 3 shows a strip offilter material during conversion into an inner hollow member.

FIG. 4.shows a stage in.the production of a pair of filter cigarettes;

FIGS. 5, 6, 7 and 8 are perspective-views of three different I forms of the innerfiltering member.

FIG. 9 shows an apparatus for forming a filter from cellulose acetate filaments.

FIG. 10 is an enlarged view of part of the apparatus of FIG. 9.

The invention will now be described in an embodiment. In FIG. 1 a portion of a filter cigarette 20 comprises a paper wrapped tobacco rod 22 and a filter 30 secured to each other by a tipping overwrap 32. The filter 30 includes a tubular outer member 34 and a hollow inner member 36. Member 34 comprises a cylinder of stiff paper of the type usedin the manufacture of cigarette mouthpieces. The member 36 comprises an air permeable tube, the wall of which is of bonded cellulose acetate fibers, or of one of the other filtering materials described herein. One end portion 38 is cylindrical and is in engagement around the whole of its periphery with the inner surface of outer member 34 thereby substantially preventing passage of smoke at this point between

members

34 and 36. An adhesive may be used to secure end portion 38 as well as to seal it more effectively to member 34. Integral portions 42 of inner member 36 are crimped as described hereinafter so that the inner surfaces thereof are in engagement. Thus the inner member'36 divides an upstream cavity 40 from a downstream cavity 48. Tobacco smoke coming from tobacco rod 22 passes into cavity 40 through the perme able wall of inner member 36 into cavity 48. The position of filter 30 may be reversed so that cavity 48 faces the tobacco rod 22. The edges 44 of the crimped portion 42contact the inner surface of outer member 34 and assist in positioning the inner member 36 within the outer member 34 and ensuring that the permeable wall of the inner member 36 between

portions

38 and 42 is available for smoke filtration. Alternative forms of crimping are shown in FIGS. 5, 6, 7 and 8. The inner surfaces of the walls of member 36 are engaged at 42 so as substantially to preclude passage of smoke between them. They may, when the material of the walls is at least partly thermoplastic, be fused to each other and the part 42 made impervious by coalescence. However, for the purposes of this invention, the surfaces are sufficiently engaged if the smoke is directed substantially to pass through the portion 46 of wall of member 36 lying between the

parts

38 and 42. Likewisethe parts 38 are sufficiently engaged with the inner surface of member 34 if there is no significant bypass of smoke between them, though complete sealing is clearly desirable.

In FIGS. 5 and 6 alternative forms of crimp in the inner member 36 are shown. The support given to the outer member 34 by the Y-shaped or cruciform ribs is better than that given by the simpler S or Z crimp shown in FIG. 1.

In FIG. 7 a further alternative form of inner member 36 is shown. In this the walls of member 36 are crimped so as to leave ribs which are arranged helically around the longitudinal axis of the member 36. By this means good support is given to the outer member 34 and the cross section of the latter may, when it is made of thin materials, be kept substantially circular.

In FIG. 8 an embodiment is shown of the inner member 36 having a flared portion 38 and a closed end 42 formed by twisting.

In a further embodiment the inner member 36 of FIGS. 1 5, 6, 7 and 8-may be made in a double form shown for example by the dotted lines with the crimped portion 42 lying midway between the ends of the filter. This embodiment providesa circular end, which facilitates attachment to a cigarette and a circular recessed end next to the mouth, which is preferred by many smokers. This form facilitates the incorporation of granules of adsorbent or other material. These may be placed in the space around the crimped portion 42 of the inner member 36, and retained in place by outer member34 and the two circular ends 38.- The material contributes to the radial rigidity of the filter rod at this part of its length.-

The outer member 34 may, if desired, be dispensed with and its function performed by the use of a stiff tipping overwrap 32; The use of this embodiment is dependent upon the provision ofa cigarette filter machine able satisfactorily to handle the crimped inner member 36.

By lengthening the filter, the area of-the permeable wall of the inner member 36 may be increased and the pressure drop reduced thereby. Additional filtering materials 52in granular form may be located within the cavity 48 and retained therein by a permeable disc 50, thereby providing a three element filter comprising the inner member 36, the material in the cavity 48 and the disc 50. Such granular materials may include activated carbon, silica gel or other adsorbents. Alternatively the cavity 48 may be closed by a plug 51, shown by the dotted lines.

In the embodiment of FIGS. 2 and 3, a method and means for forming filter elements, of the type shown in FIG. 1, from a stripof web of material is shown. A web of filtering material such as paper or like air permeable material comes from roll 62, passes to a tubular gamiture 64 wherein it is brought into cylindrical form by an endless belt 66 so as to form a tube 68. The edges 70 of the web are joined by overlapping or butting as shown at 72 and may be adhered and sealed to each other by a molten plastic material coming from a nozzle 74. Stripes 76 of an adhesivematerial such as a molten plastic may be applied at spaced locations on one side of the web by a reciprocating intermittently acting dispenser 78. The stripes 76 may be axially spaced a distance equal to the length of a single filter or twice this length. The tube 68 thus has the stripes on its inner surface. A crimper 80 has reciprocating shaped jaws within it, which crimp the tube 68 into a form such as is shown in FIGS. 1, 5, and 6, and seal the molten plastic so as to form a continuous rod 86 of the crimped inner element comprising alternating crimped and hollow portions. Other adhesives such as heat seal or liquid adhesives may be used'in place of the molten plastic, in which case heated jaws in the crimper'80 are employed to bring the inner surfaces o the tube 68 into engagement.

The crimped element 86 is then overwrapped with a strip of heat seal paper coming from reel 88 by means of a further garniture 90. This has the conventional drive belt 92 and heater 96-for forming a longitudinal lapped and stuck seam to secure the strip around the inner element 86. A cut off 100 divides the combined inner and outer elements 98 into multiple length filter rods I02. These may include four filter elements which may be subdivided into the double unit 94 in FIG. 4 which is shown attached to tobacco rods 108, by a tipping overwrap 110. A cut at line 112 severs the double unit with the tobacco rods 108 into two filter cigarettes.

Other'tec'hniques for forming the inner element from a web or strip, include helical winding. In this process, which is commonly used for the manufacture of cardboard tubes, oneor more strips are helically wound and adhered at overlapping portions to each other around a mandrel. More than one layer of material may beused, thus'it is possible to produce the inner hollow member with inner and outer layers of different material. For example, the inner layer may comprise athermoplastic material for facilitating thesealing of the crimped portions 42 by the application of heat. Heat may additionally be used to bond the thermoplastic layer to the adjacent layer. Other materials may be incorporated in one or more of the layers, to provide specific filtering, chemical or flavoring effects.

The hollow inner element may also be formed by a laminate. This is a convenient way of incorporating a thermoplastic inner layer by the method of FIG. 2. The sealing of the-longitudinal margins 70 of the strip of filtering material and of the crimped portions 42 of the inner element are, in this case, effected solely by the application of heat. The filtering material of the inner member may comprise thermoplastic and a nonthermoplastic fiber in admixture, for example, a sheet of porous paper formed of pulp fibers and secondary cellulose acetate.

In the embodiment of the invention shown in FIGS. 9 and 10, a known tow preparation device indicated by block diagram 130, supplies opened, crimped, continuousfilamentary cellulose acetate two 132, having about 9 percent triacetin in fine droplets distributed upon its surface, to an air nozzle 134. This is generally as shown in British Pat. No. 933,227 and comprises two frustoconical tubes, fixed one inside the other, having a supply of compressed air applied to connection 136 to pass in the space between the frusta and escape from the end 138, thus drawing the tow 132 with it. A mandrel, not shown, passesthrough nozzle 134 into jet 140. The latter is generally as shown in British Pat. l\ lo. 970,817 and is provided with a supply of. steam to connection 142. The steam passes into the bore of the nozzle through radial orifices and serves to bond the filaments of cellulose acetate to each other as they pass through the annulus between the mandrel and the bore. Thus a tube 156 of bonded cellulose acetate filaments is formed. This passes into a crimper 144 which'comprises a heated enclosure 146 within which is a chain 148 carrying crimping devices 150 shown in FIG. 10. Each of the devices comprises a block 152 having a slot 154 for receiving the tube 156 coming from jet 140. Four sliding spring loaded dies 158 having ends directed towards the rod 156, are shaped to cooperate to produce the desired form of crimp in the tube, for example, that shown in FIG. 6. The cellulose acetate flows under heat to adhere the filaments to each other and form and retain thedesired shape. The crimped tube 160 coming from the crimper 144 then enters the garniture 162 which is.of known form and includes an endless belt 164 driven by a' drum 166. A paper strip 174 envelops the crimped tube 160, which now forms the hollow inner member, to form the outer member as described in the embodiment of FIG. 2. A cutoff 168 divides the rod 170 into plugs 172 of any desired multiplicity of filter units. To incorporate granular material, the paper strip 174 is formed into a trough around the member 160 as shown by the-dotted line, and granules are dropped from a hopper 176 so that they flow around the member 160 and fill up the space between it and the paper strip 174. The latter is then folded around the member 160 andsealed with a lapped and stuck seam by heater 178 to form a composite rod. The cutoff 168 is timed to cut only through the uncrimped parts of the member 160. i

In acomparative trial, filters of the type shown in FIG. 1 were made from commercially available air permeable papers having different pressure drops. Each filter was 25 mm. long and was attached to a tobacco rod 65 mm. long. Table I compares the percentage retention of these filters, with filters made according to the prior art processes. Myria is a longitudinally grooved paper filter, Acetate is the conventional filter made of crimped continuous filaments of cellulose acetate. The filter of this invention can be seen to be much more retentive at a given pressure drop.

In Table II a comparison is made of a filter made in accordance with FIG. 1, having a coating of activated carbon on its inner surface, with a conventional filter plug of the same length of bonded carbon made according to the prior art. Acrolein is chosen as a typical vapor phase compound, the removal of which from tobacco smoke by the filter, indicates its vapor phase retentivity. This invention in a single filter provides, at a low pressure drop, a high retention of vapor phase constituents with a high retention of tobacco smoke solids.

Filter The area of the filtering material through which smoke is drawn in filters of this invention may be varied. Generally it lies between 3 and 16 cm'. The packed filters of the prior art have an area equal to that of the end of the cigarette, that is about 0.5 cm. In consequence of the greater area, the filtering material may have a greater packing density, that is the ratio of the volume of the solid material in the filtering material, to the'total volume of the material. The packing density may lie between 0.1 and 0.4, preferably about 0.35. A packing density of this magnitude has not so far been used for the filtration of cigarette smoke. The velocity of the smoke stream through the filter at the normal puffing rate may lie between 2.5'and-5.7 ems/second. This much lower velocity permits filtration to be more effective at any given pressure drop than with the prior art commercial filters. Particularly good results are obtained with fibers of a diameter below 25 microns, fibers around 14 microns diameter having proved particularly effective in making theinnerrnember sufficiently rigid and retentive, while still retaining an acceptably low pressure drop. that is not greatly in excess of6 cms. water gauge.

The filter and method of its manufacture have. been described above, principally in terms of the preferred materials and apparatus. However it is apparent that simple trial in accordance with the principles disclosed in the embodiments will show the suitability of other materials. Thus,-for example, other thermoplastic filaments and fibers may be used instead of cellulose acetate, and paper made from synthetic plastics may replace the paper of the embodiment of FIG. 2'. Likewise in place of the continuous rod method of FIGS. 2 and 9, a method involving the sequence of forminga permeable tube, cutting it into lengths, and deforming them to bring their inner surfaces into engagement, could be employed.

We claim:

l. A filter means including a filter element comprising a. an axially elongated outer member;

b. an axially elongated inner member disposed withinsaid outer member;

c. said outer member including an inner surface, and an outersurface and having spaced end portions;

d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions;

e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween;

f. the major portions of said outer surface of said innerv member being spaced from said inner-surface of said outer member to define first elongated cavity1meanstherebetween; g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of V smoke as said filtering material, said first portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extending across the interior of said inner member 1 which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced fromsaid first portions toward said peripheral portions; 1 1 I the interior of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material;

j. the area of the wall of the inner member through which smoke is drawn lying between 3.0 and 16.0 cm.

2. A filter means including a filter element comprising a. an axially elongated outer member;

b. an axially elongated inner member disposed within said outer member; 1 i

c. said outer member including an inner surface and an outer surface and having spaced end portions;

. integral peripheralportions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween;

f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween;

integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions;

. second portions of said inner member defining a second area extending across the interior'of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions;

. the interior of said inner member between said first and second portions defining secondelongated cavity means,

whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material;

j. the wall ofthe inner member comprising filtering materi al, the packing density -of which lies between 0.1 and 0.4

3. A filter means including a filter element comprising:

a. an-axially elongated outer member;

b. anaxially elongated inner member disposed within said outer member;

d.- said inner member comprising a filtering material and including an inner surface and an outer surface-and having spaced end portions; e. integral peripheralportions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween;

g. integral first portions of said inner member defining a first area extending across the interior of saidinn'ermember which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the .area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions;

. the interior of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between'opposite ends thereof must travel through both said cavity means and through said filtering material;

j. the wall of the inner member comprising substantially of fibers having a diameter of less than microns.

4. A filter means including a filter element comprising a. an axially elongated outer member;

b. an axially-elongated inner member disposed within said outer member;

c. said outer member including an inner surface and a outer surface and having spaced end portions;

d. said inner member comprising a filtering materialand including an inner surface and an outer surface and having spaced end portions; v e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween;

f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebe'tween;

g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke'as said filtering material, said first portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smokethan the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions;

. the interior of said inner member between said first and second portions defining secondelongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material;

j. the pressure drop being not greater than 6 cm. water gauge.

5. A filter rod comprising a plurality of filter means integrally joined in end-to-end relationship for subsequent separation, said filter means comprising;

a. an axially elongated outer member;

b. an axially elongated inner member disposed within said outer member;

c. said outer member including an inner surface and an .outer surface and having spaced end portions;

d. said inner member comprising a filtering material and including an inner surface and an outer surfaceand having spaced end portions;

e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially" preclude axial passage of smoke across the area therebetween;

. the major portions of said outer surface of. said inner member being spaced from said inner surface'of said outer member to define first elongated cavity means therebetween;

g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions;

h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; v

i. the interior of said inner member between said first and second portions defining a second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material.

6. The filter rod of claim 5 wherein said filter element has a pressure drop no greater than about 2.5 inches of water and a total particulate matter filtration efficiency of at least about 60 percent.

7. The filter rod of claim 6 wherein said filter element has a total particulate matter filtration efficiency of at least percent.

8. The filter rod of claim 5 wherein said filtering material comprises at least about 25 weight percent secondary cellulose acetate.

9. The filter rod of claim 8 wherein said 'filtering material comprises a blend of secondary cellulose acetate and pulp.

10. The filter rod of claim 5 wherein said filtering material comprises a tubular layer of fibrous filtering material in sheet form carrying a sorbent particulate filtering material.

11. The filter rod of claim 10 wherein said sorbent particulate filtering material is activated carbon.

12. The filter rod of claim 5 wherein said filtering material comprises a pair of tubular layers of fibrous filtering material in sheet form with a sorbent particulate filtering material therebetween.

13. The filter rod of claim 12 wherein said sorbent particulate filtering material is activated carbon. I

14. The filter rod of claim 5 wherein said second area is defined by one of said end portions of said inner member being open.

15. The filter rod of claim 5 wherein said second area is defined by a plug of material extending across one of said end portions of said inner member, said plug beingformed of a material offering less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member.

16. The filter rod of claim 15 further including a quantity of a further smoke-modifying material carried in said second cavity means between said first portions and said plug.

17. The filter rod of claim 16 wherein said further smokemodifying material is a loose, sorbent, particulate filtering material.

18. The filter rod of claim 17 wherein said sorbent particulate filtering material is activated carbon.

19. The filter rod of claim 5 wherein said peripheral portions of said inner member are formed by integral flared portions of said inner member atone of said end portions of said inner member.

20. The filter rod of claim 5 wherein said first area is defined by integral portions of said inner member crimped together at one of said end portions of said inner member.

21. The filter rod of claim 20 wherein said crimped portions are sealed together by a bonding means.

22. The filter rod of claim 20 wherein spaced parts of the periphery of said crimped portions contact said inner surface of said outer member to assist in centering said inner member within said outer member to assist in centering said inner member. within said outer member and in defining said first cavity means.

2 3.-T he filter rod of claim 22 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said one end portions of said inner member, the entire outer surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions.

24. The filter rod of claim wherein said inner member is tubular, the outer surface of one end portion of said inner member defining said peripheral portions, the other end portions of said inner member being crimped and sealed together to define said first area, spaced parts of the periphery of said crimped portions contacting said inner surface of said outer member to assist in centering said inner member within said outer member and in defining said first cavity means, the inner surface of said one end portion of said inner member being open to define said second area.

25. The filter rod of claim 24 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said other end portions of said inner member, the entire outer surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions 26. The filter rod of claim 25 wherein said other end portion of said inner member is crimped to form a generally S-shaped cross section, only the laterally terminal edges of the S-shaped portions and said peripheral portions of said outer surface of said inner member contacting said inner surface of said outer member.

27. The filter rod of claim 25 wherein said other end portion of said inner member is crimped to form a generally cruciform-shaped cross section, only the laterally terminal edges of the cruciform-shaped portions and said peripheral portions of said outer surface of said inner member contacting said carrying a bonding means sealing said crimped portions of said inner member.

30. The filter rod of claim 25 wherein said inner surface of said inner member comprises a porous thermoplastic material and said outer surface of said inner member comprises filtering material, said thermoplastic material defining a bonding means sealing said crimped portions of said inner element.

31. The filter rod of claim 30 wherein said inner surface of said inner member is formed of a helically wound strip of said thermoplastic material and said outer surface of said inner member is formed of a helically wound strip of said filtering material overlying said thermoplastic material, juxtaposed edges of said helically wound strip of said filtering material I being axially offset with respect to underlying juxtaposed edges of said helically wound strip of said filtering material being axially offset with respect to underlying juxtaposed edges of said helically wound strip of said thermoplastic material.

Claims

2. A filter means including a filter element comprising a. an axially elongated outer member; b. an axially elongated inner member disposed within said outer member; c. said outer member including an inner surface and an outer surface and having spaced end portions; d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions; e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween; f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween; g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions; h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; i. the interiOr of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material; j. the wall of the inner member comprising filtering material, the packing density of which lies between 0.1 and 0.4.
3. A filter means including a filter element comprising: a. an axially elongated outer member; b. an axially elongated inner member disposed within said outer member; c. said outer member including an inner surface and an outer surface and having spaced end portions; d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions; e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween; f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween; g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions; h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; i. the interior of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material; j. the wall of the inner member comprising substantially of fibers having a diameter of less than 25 microns.
4. A filter means including a filter element comprising a. an axially elongated outer member; b. an axially elongated inner member disposed within said outer member; c. said outer member including an inner surface and an outer surface and having spaced end portions; d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions; e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween; f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween; g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions; h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; i. the interior of said inner member between said first and second portions defining second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through Both said cavity means and through said filtering material; j. the pressure drop being not greater than 6 cm. water gauge.
5. A filter rod comprising a plurality of filter means integrally joined in end-to-end relationship for subsequent separation, said filter means comprising: a. an axially elongated outer member; b. an axially elongated inner member disposed within said outer member; c. said outer member including an inner surface and an outer surface and having spaced end portions; d. said inner member comprising a filtering material and including an inner surface and an outer surface and having spaced end portions; e. integral peripheral portions of said outer surface of said inner member being juxtaposed to portions of said inner surface of said outer member to at least substantially preclude axial passage of smoke across the area therebetween; f. the major portions of said outer surface of said inner member being spaced from said inner surface of said outer member to define first elongated cavity means therebetween; g. integral first portions of said inner member defining a first area extending across the interior of said inner member which offers at least as much resistance to passage of smoke as said filtering material, said first portions being axially spaced from said peripheral portions; h. second portions of said inner member defining a second area extending across the interior of said inner member which offers less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member, said second portions being axially spaced from said first portions toward said peripheral portions; i. the interior of said inner member between said first and second portions defining a second elongated cavity means, whereby smoke passing through said filter element between opposite ends thereof must travel through both said cavity means and through said filtering material.
6. The filter rod of claim 5 wherein said filter element has a pressure drop no greater than about 2.5 inches of water and a total particulate matter filtration efficiency of at least about 60 percent.
7. The filter rod of claim 6 wherein said filter element has a total particulate matter filtration efficiency of at least 90 percent.
8. The filter rod of claim 5 wherein said filtering material comprises at least about 25 weight percent secondary cellulose acetate.
9. The filter rod of claim 8 wherein said filtering material comprises a blend of secondary cellulose acetate and pulp.
10. The filter rod of claim 5 wherein said filtering material comprises a tubular layer of fibrous filtering material in sheet form carrying a sorbent particulate filtering material.
11. The filter rod of claim 10 wherein said sorbent particulate filtering material is activated carbon.
12. The filter rod of claim 5 wherein said filtering material comprises a pair of tubular layers of fibrous filtering material in sheet form with a sorbent particulate filtering material therebetween.
13. The filter rod of claim 12 wherein said sorbent particulate filtering material is activated carbon.
14. The filter rod of claim 5 wherein said second area is defined by one of said end portions of said inner member being open.
15. The filter rod of claim 5 wherein said second area is defined by a plug of material extending across one of said end portions of said inner member, said plug being formed of a material offering less resistance to passage of smoke than the area between said peripheral portions of said inner member and said inner surface of said outer member.
16. The filter rod of claim 15 further including a quantity of a further smoke-modifying material carried in said second cavity means between said first portions and said plug.
17. The filter rod of claim 16 wherein said further smoke-modifying material is a loose, sorbent, particulate filtering material.
18. The filter rod of claim 17 wherein said sorbent particulate filtering material is activated carbon.
19. The filter rod of claim 5 wherein said peripheral portions of said inner member are formed by integral flared portions of said inner member at one of said end portions of said inner member.
20. The filter rod of claim 5 wherein said first area is defined by integral portions of said inner member crimped together at one of said end portions of said inner member.
21. The filter rod of claim 20 wherein said crimped portions are sealed together by a bonding means.
22. The filter rod of claim 20 wherein spaced parts of the periphery of said crimped portions contact said inner surface of said outer member to assist in centering said inner member within said outer member and in defining said first cavity means.
23. The filter rod of claim 22 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said one end portions of said inner member, the entire outer surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions.
24. The filter rod of claim 5 wherein said inner member is tubular, the outer surface of one end portion of said inner member defining said peripheral portions, the other end portions of said inner member being crimped and sealed together to define said first area, spaced parts of the periphery of said crimped portions contacting said inner surface of said outer member to assist in centering said inner member within said outer member and in defining said first cavity means, the inner surface of said one end portion of said inner member being open to define said second area.
25. The filter rod of claim 24 wherein said spaced parts of the periphery of said crimped portions contact said inner surface of said outer member only at said other end portions of said inner member, the entire outer surface of said inner member being spaced from said inner surface of said outer member except at said spaced end portions.
26. The filter rod of claim 25 wherein said other end portion of said inner member is crimped to form a generally S-shaped cross section, only the laterally terminal edges of the S-shaped portions and said peripheral portions of said outer surface of said inner member contacting said inner surface of said outer member.
27. The filter rod of claim 25 wherein said other end portion of said inner member is crimped to form a generally cruciform-shaped cross section, only the laterally terminal edges of the cruciform-shaped portions and said peripheral portions of said outer surface of said inner member contacting said inner surface of said outer member.
28. The filter rod of claim 25 wherein said other end portion of said inner member is crimped to form a generally Y-shaped cross section, only the laterally terminal portions of the Y-shaped portions and said peripheral portions of said other surface of said inner member contacting said inner surface of said outer member.
29. The filter rod of claim 25 wherein said inner member includes a tubular element comprising filtering material, said inner surface of said other end portion of said tubular element carrying a bonding means sealing said crimped portions of said inner member.
30. The filter rod of claim 25 wherein said inner surface of said inner member comprises a porous thermoplastic material and said outer surface of said inner member comprises filtering material, said thermoplastic material defining a bonding means sealing said crimped portions of said inner element.
31. The filter rod of claim 30 wherein said inner surface of said inner member is formed of a helically wound strip of said thermoplastic material and said outer surface of said inner member is formed of a helically wound strip of said filtering material overlying said thermoplastic material, juxtaposed edges of said helically wound strip of said filtering material beinG axially offset with respect to underlying juxtaposed edges of said helically wound strip of said filtering material being axially offset with respect to underlying juxtaposed edges of said helically wound strip of said thermoplastic material.