U.S. patent number 3,599,646 [Application Number 04/820,355] was granted by the patent office on 1971-08-17 for cigarette filter.
This patent grant is currently assigned to American Filtrona Corporation. Invention is credited to Richard M. Berger, Elwin W. Brooks.
United States Patent |
3,599,646 |
Berger , et al. |
* August 17, 1971 |
CIGARETTE FILTER
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.
Inventors: |
Berger; Richard M. (Richmond,
VA), Brooks; Elwin W. (Mechanicsville, VA) |
Assignee: |
American Filtrona Corporation
(Richmond, VA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to October 13, 1987 has been disclaimed. |
Family
ID: |
25230556 |
Appl.
No.: |
04/820,355 |
Filed: |
April 30, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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727477 |
May 8, 1968 |
3533416 |
Oct 13, 1970 |
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Current U.S.
Class: |
131/340; 131/342;
493/47 |
Current CPC
Class: |
A24D
3/0283 (20130101) |
Current International
Class: |
A24D
3/02 (20060101); A24D 3/00 (20060101); A24f
007/04 (); A24d 001/04 () |
Field of
Search: |
;131/9,10,10.3,10.5,10.7,10.9,261,262,267 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,118,860 |
|
Mar 1956 |
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FR |
|
559,115 |
|
Mar 1957 |
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IT |
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795,666 |
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May 1958 |
|
GB |
|
Primary Examiner: Rein; Melvin D.
Parent Case Text
This application is a continuation-in-part of copending application
Ser. No. 727,477, filed May 8, 1968, for Tobacco Smoke Filter, now
U.S. Pat. No. 3,533,416 granted on Oct. 13, 1970.
Claims
We claim:
1. 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 area of the wall of the inner member through which smoke is
drawn lying between 3.0 and 16.0 cm.sup.2.
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.
Description
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./sec. 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 paper webs 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 have a 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
outer surface of the wall of the inner member is in engagement with
the inner surface 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. Enclosed by 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 flavoring the 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. 1 shows a typical filter with a portion of a tobacco rod
attached.
FIG. 2 shows an apparatus for forming the filter of the
invention.
FIG. 3 shows a strip of filter 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 forms
of the inner filtering 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 used in 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
permeable 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 42 contact 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. Likewise the 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 provides a 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
member 34 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 of a
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 52 in 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 strip or 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
garniture 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 adhesive material 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 of 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 102. 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 techniques 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, one or more strips are
helically wound and adhered at overlapping portions to each other
around a mandrel. More than one layer of material may be used, 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 a thermoplastic material for facilitating the sealing
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, continuous filamentary cellulose acetate tow 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, passes through nozzle 134 into jet 140. The
latter is generally as shown in British Pat. No. 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 the desired 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 and sealed 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.
In a comparative 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.
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TABLE I
Type P.D.(cms.) % retention
__________________________________________________________________________
Invention 0.8 64 `Myria` 0.8 18 Acetate 0.8 11 Invention 2.4 81
`Myria` 2.4 36 `Acetate` 2.4 25 Invention 3.6 93 `Myria` 3.6 47
`Acetate` 3.6 35 Invention 4.6 94 `Myria` 4.6 54 `Acetate` 4.6 41
__________________________________________________________________________
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.
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TABLE II
Acrolein Weight of Through Carbon Filter Material P.D. Micrograms
Milligrams
__________________________________________________________________________
Cotton linter pulp and carbon 1.1" 11 71 Bonded carbon Filter 1.0"
19 197
__________________________________________________________________________
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.sup.2. 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.sup.2. 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 cms./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 the inner member sufficiently
rigid and retentive, while still retaining an acceptably low
pressure drop, that is not greatly in excess of 6 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 forming
a permeable tube, cutting it into lengths, and deforming them to
bring their inner surfaces into engagement, could be employed.
* * * * *