U.S. patent number 3,852,007 [Application Number 05/237,904] was granted by the patent office on 1974-12-03 for apparatus for making filters.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to Charles H. Keith, William E. Levers.
United States Patent |
3,852,007 |
Levers , et al. |
December 3, 1974 |
APPARATUS FOR MAKING FILTERS
Abstract
Improved tobacco smoke filters, particularly cigarette filters,
are prepared from a web of synthetic polymeric fibers having
applied to at least one surface thereof a film-forming derivative
of cellulose. Continuous processes and apparatus for the production
of the web and filter are also described.
Inventors: |
Levers; William E. (Charlotte,
NC), Keith; Charles H. (Charlotte, NC) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
26713465 |
Appl.
No.: |
05/237,904 |
Filed: |
March 24, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
36746 |
May 13, 1970 |
|
|
|
|
Current U.S.
Class: |
425/66; 19/66T;
28/282; 425/102; 425/363; 19/65T; 28/100; 156/167; 425/289 |
Current CPC
Class: |
A24D
3/022 (20130101) |
Current International
Class: |
A24D
3/00 (20060101); A24D 3/02 (20060101); B29c
017/02 () |
Field of
Search: |
;425/66,92,102,105,106,109,4,223,224,392,371,373,363 ;156/166,167
;28/1CF ;19/65T,66T |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spicer, Jr.; Robert L.
Attorney, Agent or Firm: Kasa; Pamela D.
Parent Case Text
This is a division, of application Ser. No. 36,746, now abandoned.
Claims
What is claimed is:
1. An apparatus for preparing improved cigarette filters comprising
a supply means for providing a web of synthetic thermoplastic
organic fibers having at least one surface thereof impregnated with
a film-forming derivative of cellulose which renders the web stiff,
flexing and fracturing means for receiving, flexing and fracturing
said film-forming derivative of cellulose on said web, patterning
means for embossing said web, plasticizing means for applying a
plasticizer to at least one surface of the flexed and embossed web,
which plasticizer means softens the fractured web and means for
converting the plasticized web into a substantially cylindrical
tobacco smoke filter rod.
2. The apparatus of claim 1 additionally comprising stretching
means positioned after said flexing means for transversely
stretching said web.
3. The apparatus of claim 1 additionally comprising patterning
means after said flexing means for impressing a patterned
configuration into at least one surface of said web, said
patterning means comprising a pair of circumferentially or
helically grooved rolls having 5 to 80 grooves per inch, said
grooves being from about 0.035 to 0.005 inch in depth.
4. The apparatus of claim 1 wherein said flexing means comprises a
plurality of roll pairs at least one roll of each pair being
circumferentially grooved.
5. The apparatus of claim 1 additionally including liquid
applicator means for applying a film-forming derivative of
cellulose in liquid form to said web and drying means for drying
said applied cellulose.
6. The apparatus of claim 1 wherein the patterning means are heated
rolls.
7. The apparatus of claim 3 wherein said grooved rolls have
substantially rectangular grooves, wherein the angle from the
vertical of the groove walls is 0.degree. to 30.degree..
Description
BACKGROUND OF THE INVENTION
An acceptable tobacco smoke filter, particularly a cigarette
filter, must exhibit a high degree of filtration of tobacco smoke
particles, i.e., have high smoke removal efficiency, at an
acceptable draw resistance, i.e., pressure drop. The filter must
also be capable of economical continuous production. Furthermore,
it must be of a firmness sufficient to avoid collapse during
smoking and must not unduly distort the taste and odor of the
tobacco smoke.
Many materials including cellulose fibers and a variety of
synthetic fibers have been suggested for use in tobacco smoke
filters. Of these materials, only continuous filament cellulose
acetate tow, and to a lesser degree, paper, have met with any
degree of commercial acceptance.
There is a continuing search for new tobacco smoke filters meeting
the above criteria and having improved smoke removal
efficiencies.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved
tobacco smoke filters exhibiting a high degree of smoke removal
efficiency with acceptable taste, firmness, draw resistance and
economics.
It is another object to provide improved intermediate products
useful in the formation of filters having the above
characteristics.
Other objects of the present invention reside in the provisions for
apparatus and processes for manufacture of the aforesaid filters
and intermediate products.
Still other objects, if not specifically set forth herein, will be
obvious to the skilled artisan upon reading the detailed
description of the invention with reference to the drawings.
DRAWINGS
FIG. 1 is a perspective view of an apparatus suitable for the
practice of the present invention.
FIG. 2 is a side view of an apparatus suitable for use in forming
the intermediate product.
FIG. 3 is a side view of an apparatus suitable for use in forming
tobacco smoke filters from the intermediate product.
DETAILED DESCRIPTION OF THE INVENTION
Generally, the filters of the present invention are comprised of a
condensed web of small diameter synthetic thermoplastic filaments,
preferably of non-cellulosic composition, which are bound together
by a film-forming derivative of cellulose.
Briefly, the intermediate products used in the preparation of the
aforesaid filters are prepared by coating the fibers on at least
one surface of a web of synthetic organic thermoplastic fibers and
preferably substantially uniformly impregnating the web, with a
solution or dope of a filmforming organic derivative of cellulose,
removing solvent from the dope to at least partially produce a
film, flexing the web to fracture or substantially destroy the film
and produce a multiplicity of particles of the organic derivative
of cellulose adhered to the fibers, applying a plasticizer to the
web to render the particles tacky and condensing the web into
filter form while the particles are in a tacky state.
Fibrous webs finding utility in the present invention may be
prepared from a variety of synthetic, organic fibers including
polyolefin, polyester, polyamide, and cellulosic fibers. The fibers
in the web may be in the form of a tow of continuous filaments, a
staple roving or randomly arranged as in a non-woven web.
Preferably, the web to be coated will have a total denier of from
about 25,000 to about 120,000, and preferably from about 45,000 to
about 65,000; a width of from about 2 to about 24 inches, and, for
shipping purposes, preferably from 2 to about 8 inches; and a
thickness from about 0.02 to about 0.25 inches.
The individual fibers comprising the web will ordinarily have a
denier per filament of from about 0.01 to about 16 (equal to about
1-45 microns in diameter) with the lower denier per filament
fibers, e.g., from about 0.01 to about 1.0 (equal to about 1-12
microns in diameter) being preferred.
If a tow of continuous filaments is employed, the tow will
ordinarily have a total denier of from about 45,000 to 120,000 and
be comprised of crimped continuous filaments having up to about 40,
and preferably from about 5 to about 15 crimps per inch and a dpf
of from about 0.5 to about 16. Such tows may be conveniently
prepared, for example, from cellulose acetate or polyolefin
filaments.
The preferred fibrous web for use in the present invention is a
spray spun web having a surface area of from about 0.1 to about 2.0
M.sup.2 /gm, and preferably, from about 0.4 to about 1.5 M.sup.2
/gm, comprised of a randomly arranged reticulate mass of fibers
composed of a non-cellulosic polymer, preferably a polyolefin such
as polypropylene or polyethylene. Ideally, the fibers are composed
of a polyolefin having an intrinsic viscosity of from about 0.4 to
about 1.25, and preferably, from about 0.6 to 0.75.
The dope applied to the web is comprised of a solution of a
film-forming organic derivative of cellulose in a suitable solvent.
Particularly desirable film-forming materials are the celulose
esters and cellulose ethers, including, but not limited to,
cellulose acetate, cellulose propionate, cellulose acetate
butyrate, cellulose acetate propionate, ethyl cellulose, methyl
cellulose, sodium carboxymethyl cellulose, carboxymethyl
hydroxyethyl cellulose, and mixtures thereof. Cellulose acetate,
because of its cost and previous commercial acceptance is
particularly suitable.
The solvent employed in the preparation of the dope is not critical
and will vary somewhat depending on the film-forming compound
employed. Organic solvents such as acetone, methyl ethyl ketone, or
methylene chloride, normally liquid organic ethers and esters are
ordinarily suitable. Water may also be used as a solvent with
cellulose derivatives such as sodium carboxymethyl cellulose and
cellulose acetates of certain acetyl values and molecular
weights.
Ordinarily the dope will contain from about 3 to about 30 percent
and preferably from about 6 to about 10 percent of the film-forming
derivative based on the total amount of dope. Percentages outside
the broader range may be used but difficulties in application or
solvent removal may occur.
In the preferred embodiment of the invention, web 10 is withdrawn
from a supply source 12, illustrated in the drawing as roll
although other sources such as a bale may be used, and directed to
dope applicator 14 where dope 16 is applied to at least one surface
of the web.
In the drawing, dope applicator 14 is shown as a transfer roll
device. It is to be understood, however, that other types of
applicators may be employed. For example, the cellulose acetate
dope can also be readily applied with wick applicators, spray
devices, and the like.
After web 10 is coated on at least one surface with dope 16, and
preferably substantially, uniformly impregnated, it is passed to a
dryer 18 where the solvent is removed and the web is dried.
Ordinarily, dryer 18 will be comprised of a suitably heated chamber
with a vacuum source which directs evaporated solvent to a recovery
systen, not shown. The structure of the particular device is not
critical, however, so long as the web is substantially freed of
solvent.
After solvent removal, treated web 10 may be taken up on a suitable
collection means 20, which may be a roll or bale, for subsequent
processing or shipment, or the web may be directly processed into
tobacco smoke filter rods.
The intermediate product or treated web 10, will be comprised of
from about 10 to about 40 and preferably from about 20 to about 30
percent of the film-forming cellulosic derivative, the derivative
forming a film-like coating around and between at least a portion
of the fibers. During collection for storage, the dried film may
become somewhat fractured and discontinuous. This fracturing is not
detrimental to the properties of the web, however, for reasons
which will become apparent.
In the preparation of filter rods, the web is directed from
collector 20, or drier 18, to flexing device 22 which further
fractures or partially destroys the continuous structure of the
film and increases the flexibility of the web, and a multiplicity
of particles of the cellulosic derivative adhered to the
fibers.
As earlier noted, the intermediate product of the present invention
is desirably from about 2 to about 8 inches in width to facilitate
packaging and shipping. If webs of this width are employed, it is
desirable at this stage to transversely stretch the web to a width
of from 8 to 24 inches, in order to obtain the optimum filtration
properties upon condensation of the web into a tobacco smoke
filter. While this transverse stretching or opening can also occur
after plasticizing of the web, prior stretching is preferred in
order to obtain optimum plasticizer distribution.
Flexing device 22 as illustrated in the drawing is comprised of a
plurality of roll pairs at least one roll of each pair being
circumferentially grooved. A flexing device of this type is
particularly suitable in the present invention in that it causes
both flexing and stretching of the web to the desired width. This
particular device does not constitute part of the present invention
except as being illustrative of the fact that flexing and
transverse stretching of the web can occur simultaneously.
Significant improvements in filtration properties are observed if,
after flexing and optional transverse stretching, web 10 is passed
through the nip of a pair of patterning rolls 24. In the drawing,
patterning rolls 24 form part of flexing device 22. It is to be
understood, however, that in the general aspects of the invention,
patterning rolls 24 may be a device separate from flexing device
22.
Essentially, patterning rolls 24, at least one roll of the roll
pair having a patterned surface, are adapted to afford a plurality
of permanently depressed areas in the substrate. Said rolls 24 are
positioned substantially transverse to the tow path and are
arranged with parallel axes. Ordinarily, one roll of the pair will
be adjacent the upper surface of the tow path, while the second
roll will be mounted opposite said roll and below the tow path.
However, the web may also follow a vertical path with a patterned
roll mounted of either side of such path. The rolls 24 may be
mounted yieldably in contact or slightly separated. The rolls
should be of a proximity, however, sufficient to cause at least
some permanent depression of the tow as it passes therebetween.
Preferably, the separation of the rolls is from 0 to about 0.02
inches, and even more desirably from 0 to about 0.01 inches. The
separation, of course, will depend upon a thickness of the tow as
determined by the total denier and width thereof. Webs processed
through rolls of the above separation will have an overall
thickness of from about 0.1 to about 2.5 mm.
In order to obtain the advantages of the present invention, a
variety of patterns may be imparted to the surface of the web
material. Such patterns may comprise continuous depressed areas
and/or continuous lands. For example, a waffle or quilted surface
as illustrated in FIG. 2 may be imparted to the surface of the web.
In this pattern, either the continuous or discontinuous area may be
compressed. The waffle or quilted pattern may also be oriented so
that the edges of the pattern are at an angle to the longitudinal
axis of the web, in effect imparting a diamond-shaped pattern as
shown in FIG. 3 to the surface of the web. Generally, it has been
found that the preferred patterns of the present invention from the
standpoint of the greatest relative reduction in pressure drop
comprise grooves defining a path substantially parallel to the
longitudinal axis of the web. These longitudinal grooves preferably
form a straight line along the web, i.e., accordian pleats;
sinusoidal or zig-zag grooves are also possible, however.
Desirably, the preferred rolls employed in the present invention
are circumferentially or helically grooved, and will have from
about 5 to about 80 and preferably from about 20 to about 45
grooves per inch. The lands of the rolls will ordinarily be of
about 0.03 to about 0.005 inch and more preferably from about 0.015
to about 0.008 inch in width. The grooves will ordinarily be about
0.035 to about 0.005 and preferably from about 0.002 to about 0.001
inch in depth. The lands of a given roll will ordinarily, but not
necessarily, be of uniform width. In fact, lands which
progressively decrease in width outwardly from the center of the
patterned area may aid in the construction of a more uniform
filter. Similarly, the depths of the grooves may be of differential
dimensions across the web.
Rod firmness can be improved by using rectangular or substantially
rectangular grooves, since such grooves tend to yield a material
which, upon gathering into rod form, has self-supporting,
triangular-shaped, difficultly compressible channels. The term
substantially rectangular grooves is intended to define a groove
wherein the angle from the vertical of the wall is from 0.degree.
to 45.degree. and preferably from 0.degree. to 30.degree.. It is,
of course, within the scope of the present invention to use other
grooved shapes, e.g., semi-circular, trapezoidal, or triangular
grooves.
In some instances, the use of heated patterned rolls has been found
to be of value in obtaining improved corrugation. When used, the
heated rolls will generally have a temperature of from about
25.degree. to 225.degree.C and preferably from about 110.degree. to
about 160.degree.C.
Preferably, patterning rolls 24 are at least 2 inches in diameter,
and more preferably, from about 4 to about 8 inches in diameter.
The width of the patterned portion of the rolls will, of course, be
determined, to some extent, by the width of the web being
structured. Generally, a total patterning width of from about 8 to
about 16 inches is sufficient for most operations.
After flexing and optional transverse stretching and/or patterning,
web 10 is directed to plasticizer applicator 26 where a
plasticizer, i.e., a solvation agent, is applied to the web to
cause the cellulosic particles to become tacky. In the drawing,
plasticizer applicator 26 is a cylindrical plasticizer applicator
of the type described in U.S. Pat. No. 3,387,992, issued June 11,
1968. Essentially applicator 26, is comprised of a housing, a
rotatable disc located within the housing below the path of the web
and substantially transverse thereto, means for conveying a
plasticizer to the rotatable disc and means for recycling unused
plasticizer. Other applicators which are adapted to apply
plasticizer to a continuous fibrous web may also be used for this
purpose.
For example, applicators utilizing wicks or spray nozzles are also
usable.
Ordinarily, from about 3 to about 25 percent plasticizer based on
the amount of cellulosic derivative will be applied, with about 6
to about 15 percent being preferable. Triacetin will normally be
employed after plasticizing, particularly when the cellulosic
derivative is cellulose acetate. However, other organic solvents
such as triethyl citrate, dimethyl ethyl phthalate, or the dimethyl
ethers of triethylene or tetraethylene glycol may also be used.
Water will also find utility as a plasticizer with certain of the
hereinbefore described cellulosic derivatives.
The web, after being treated with a plasticizer, is directed into
filter rod maker 28 where the web is condensed into tobacco smoke
filter rods which will ordinarily be of about 8 mm in diameter and
severed to 60 to 180 mm in length. Filter rods of this length are
desirable in that they are readily severable into 6 filters of 10
to 30 mm in length for attachment to tobacco columns.
The following examples are presented for the purpose of
illustration only and are not to be taken as in limitation of the
present invention.
EXAMPLES 1-6
Spray spun webs of polypropylene fibers were substantially,
uniformly impregnated with a dope of cellulose acetate polymer
dissolved in acetone. The coated webs were then dried and flexed to
destroy the film-like properties of the cellulose acetate film
produced. A triacetin plasticizer was applied to the webs which
were then patterned with 20 parallel, longitudinal, rectangular
grooves per inch. The web was then condensed into cigarette filters
of 20 mm in length and 24.8 mm in circumference. The composition,
based on total weight of product, and surface area of the webs were
as follows:
TABLE I ______________________________________ FILTER TIP
PROPERTIES Specific Intermediate % % % Surface Product
Polypropylene CA Triacetin Area M.sup.2 /gm
______________________________________ 1 70.8 25.8 3.4 0.50 2 67.9
28.4 3.7 0.53 3 70.6 26.5 2.9 0.40 4 67.1 29.2 3.7 0.54 5 68.8 27.7
3.5 0.41 6 70.8 25.8 3.4 0.50
______________________________________
The pressure drops of filaments prepared from the above
intermediate product was determined. The filaments were then
attached to 65 mm tobacco columns and smoke nicotine and "tar"
(total particulate matter, less nicotine and water) removal
efficiencies were determined. The following results were
obtained.
TABLE II ______________________________________ SMOKING PERFORMANCE
Intermediate .DELTA.P & & & & Com. Product
mm,H.sub.2 O SRE NRE TRE pressibility
______________________________________ 1 64 66.5 61.0 62.1 31.6 2
62 59.3 53.2 53.7 NOT TESTED 3 65 53.7 48.6 48.0 NOT TESTED 4 60
59.6 55.6 54.4 38.2 5 55 56.3 50.6 48.3 43.8 6 70 67.3 64.0 62.4
31.6 ______________________________________
For purposes of comparison, conventional cellulose acetate filters
having a pressure drop of from 55 to 70 mm water have a smoke
removal efficiency of about 42 to about 52 percent, a nicotine
removal efficiency of about 32 to about 42 percent, and a tar
removal efficiency from about 35 to about 45 percent.
EXAMPLE 7
A band of crimped, continuous polypropylene filaments having
approximately 20 crimps per inch, a denier per filament of 0.9 and
a total denier of 50,500 was substantially uniformly impregnated
with a dope of 6 percent, based on the weight of dope, of cellulose
acetate polymer dissolved in acetone, and dried to produce an
intermediate product comprised of approximately 60 percent
polypropylene fiber and 40 percent cellulose acetate. This material
was flexed and patterned with 20 rectangular, longitudinal,
parallel grooves per inch. Ten percent triacetin based on the
cellulose acetate was applied thereto. The plasticized material was
then formed into cigarette filters exhibiting desirable smoke
removal efficiencies, pressure drop, and firmness.
While the foregoing description has dealt only with the preparation
of a filter from an impregnated web of a fibrous material, it is
also possible to prepare satisfactory and often improved filters by
incorporation of one or more other filtration materials into the
web material prior to corrugation. Such materials include carbon,
silica gel or other high surface area absorbents, granular
polyurethanes, cellulose acetate flake, wood pulp, flock, liquid
additives and other gas adsorbents or selective absorbents.
Generally, up to about 20 percent of these materials based on the
weight of the filter may be employed, with from about 5 percent to
about 10 percent being preferably utilized. Obviously, a
multiplicity of, and tows comprising the same of different
filamentary materials could be combined to form suitable filter
structures as described herein.
Filters prepared by the above method may be used as the sole
filtration means on a cigarette. It is, of course, possible to use
filters prepared by the present invention as part of a dual or
segmented filter. In this context, the present filters are
particularly suitable in combination with paper filters and
conventional cellulose acetate filters.
It is to be understood that the foregoing detailed description is
given merely by way of illustration and that many variations may be
made therein without departing from the spirit and scope of the
invention.
* * * * *