U.S. patent number 3,607,512 [Application Number 04/788,903] was granted by the patent office on 1971-09-21 for extruding tow filled mouthpiece rod having serrated inner surfaces clenching the tow.
This patent grant is currently assigned to Philip Morris Incorporated. Invention is credited to George L. Mathe.
United States Patent |
3,607,512 |
Mathe |
September 21, 1971 |
EXTRUDING TOW FILLED MOUTHPIECE ROD HAVING SERRATED INNER SURFACES
CLENCHING THE TOW
Abstract
A method with which a continuous length, tubular article filled
with a tow of a fibrous material and having serrated or grooved
inner surfaces clenching the tow is disclosed. The article is
formed by extruding thermoplastic material as a tubular sheath
having a smooth inner surface at extrusion around an advancing tow
of fibers, the serrations or grooves being formed by spraying a
cooling fluid against the inner wall surface of the plastic sheath
at circularly spaced locations therein as it leaves the extrusion
aperture. The cooling fluid functions to chill and set the inner
wall surface sufficiently so that when the tubular sheath is
thereafter pulled down from an initial to a final size, the sheath
will pull down to a lesser extent at said spaced locations than at
the still more plastic surfaces intervening said spaced locations
thereby forming longitudinal grooves in the sheath inner wall
surface.
Inventors: |
Mathe; George L. (Richmond,
VA) |
Assignee: |
Philip Morris Incorporated (New
York, NY)
|
Family
ID: |
25145936 |
Appl.
No.: |
04/788,903 |
Filed: |
January 3, 1969 |
Current U.S.
Class: |
156/178; 156/198;
156/213; 156/244.12; 156/294; 131/340; 156/199; 156/244.25 |
Current CPC
Class: |
F16L
11/118 (20130101); B29C 48/15 (20190201); Y10T
156/103 (20150115); B29L 2023/003 (20130101); Y10T
156/1007 (20150115); Y10T 156/1005 (20150115); B29C
48/06 (20190201); B29C 48/12 (20190201) |
Current International
Class: |
B29C
47/02 (20060101); B29C 47/00 (20060101); F16L
11/118 (20060101); F16L 11/11 (20060101); B32b
005/00 () |
Field of
Search: |
;156/166,178,244,293,294,303.1,198,199,213 ;131/10 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Padgett; Benjamin R.
Assistant Examiner: Lechert, Jr.; Stephen J.
Claims
What is claimed is:
1. A method for forming an article comprising a mass of fibrous
material enclosed in a tubular sheath, said tubular sheath having
an inner wall surface provided with grooves extending
longitudinally of said sheath with lands intervening adjacent
grooves, said method comprising
extruding a thermoplastic material through an extrusion aperture to
form a continuous tubular workpiece having a generally smooth inner
wall surface and cross-sectional dimensions substantially larger
than the intended final cross-sectional dimensions of said
sheath,
conveying said tubular workpiece away from said aperture,
simultaneously advancing a cohesive tow of plural filaments of said
fibrous material into and codirectionally with said continuous
tubular workpiece,
spraying streams of cooling fluid against said inner wall surface
of said workpiece at a circle of spaced locations thereon as it
leaves said extrusion aperture to thereby chill said inner surface
at said locations, and
pulling down said tubular workpiece against said continuous tow to
form a sheath therearound and to an extent sufficiently tightly to
radially compress said tow by advancing said tubular workpiece
through a closing aperture of substantially the same dimension as
the intended final external dimension of said sheath, the inner
surface of said tubular workpiece being chilled sufficiently to
initiate setting thereof whereby said tubular workpiece in its
passage to and through said closing aperture pulls down to a lesser
extent at said locations than at the surfaces intervening said
locations thereby forming grooves in said wall surface at said
intervening surfaces, the tow of filler material becoming clenched
in said grooves during the pull down of said tubular workpiece.
2. The method of claim 1 wherein the thermoplastic material is
polyethylene and the fibrous filler material is cellulose acetate.
Description
BACKGROUND OF THE INVENTION
The present invention is concerned with forming in continuous
operation, a filled tubular article, such as cigarette filter rod.
It is common practice in the cigarette-making art to form filter
rod in a continuous operation by wrapping a continuous tow of
filaments of a filter medium, most usually cellulose acetate, in a
continuous paper wrapper customarily referred to as "plug wrap."
However, this known method of making cigarette filter rod has
shortcomings which makes it unsuitable for use in modern
cigarette-making technology where very high manufacturing speeds
are desirable. For example, the use of an adhesive joint or seam
usually limits production line speed to a speed not greater than
about 300 feet per minute.
A filter rod overcoming the aforementioned problem is described in
presently pending application Ser. No. 747,279 filed July 24, 1968
by Richard N. Thomson et al. The mouthpiece described in said
application is made by extruding plastic over a tow of fibers. The
advantages of making mouthpiece rod in this manner are numerous
particularly with respect to the accurate control of rod size as
well as improved uniformity of product manufacture. However,
certain uses of the filter rod described in said Thomson et al.
application make it desirable that enhanced securement of the tow
within the plastic sheath be provided to enable it to withstand
higher gas flow pressure therethrough than normally encountered in
the smoking of a cigarette.
SUMMARY OF THE INVENTION
The present invention is concerned with a method with which a
thermoplastic tubular article filled with a gas or liquid pervious
filler such as a tow-filled cigarette filter rod can be produced in
continuous length by continuous forming operation, the production
of the article being characterized by procedures which enable
formation on the inner wall surface of the rod of longitudinally
directed grooves which serve to clench or anchor the tow to the
plastic in which it is enclosed. The article itself is of novel
character and is susceptible to uses for purposes other than merely
as a filtering device in a smoking article particularly for such
uses as involve passage of fluid at relatively high pressure
through a filter device. The invention is further characterized by
a constancy of processing in the finished product as well as
density of the filter medium enclosed within the tubular plastic
workpiece.
In accordance with the present invention, filter rod is made by
extruding a tubular, preferably circular section thermoplastic
workpiece in continuous operation from an extruder die, the
extrudate leaving the die at a diameter somewhat greater than that
of the hardened finished workpiece but with an external shape
substantially conforming to that of the finished product and with a
smooth inner wall surface. Simultaneously, a partially compressed
tow of filaments of a filter material is advanced axially into and
in codirectional movement with the plastic extrudate as the latter
leaves the forming die. The tow of filaments is not connected by
the extrudate until the latter has advanced some distance
downstream of the exit aperture of the die from whence it issues,
the first contact being made when the extrudate is drawn down
against the tow, to form a sheath covering the latter and as the
two enter the portal gland of a cooling chamber in which heat is
removed from the plastic extrudate and the latter is sized so that
its external dimension and shape are accurately controlled within
prescribed limits. To form longitudinally extending grooves
intervened by lands on the inner wall surface of the workpiece,
streams of a cooling fluid are sprayed against said inner surface
in correspondence to the locations of the lands. Thus the surfaces
defining lands immediately are chilled sufficiently to initiate a
setting of them. Thereafter when the workpiece is drawn or pulled
down from an initial to a final smaller size, the sheath will pull
down or stretch to a lesser extent at the surfaces which were
sprayed with the cooling fluid than at the wall surfaces
intervening the sprayed surfaces. The greater degree of pulldown or
stretch of the sheath at the unsprayed surfaces thereby forms
circularly spaced grooves on the sheath inner wall surface in which
the tow filler becomes anchored. The character of the anchorage of
the tow within the sheath is such as to prevent blowout of the tow
when subjected to passage through the article of a gas or fluid
flow at pressures substantially above those normally encountered in
the testing and smoking of cigarettes thereby making the article
more suitable for those purposes but also adapted for other uses
including filters for media other than smoke. The apparatus and
procedure by which the cooling of the extrudate to set its external
surface in the manner aforesaid is the same as that described in
the presently pending U.S. Pat. application of Charles Gatto, Ser.
No. 747,370, filed July 24, 1968.
In accordance with the present invention and also as described in
the earlier mentioned Thomson et al. application, various types of
material may be used as the filler and various types of
thermoplastic material can be utilized for the tubular workpiece in
which the filler is sheathed. Most commonly, however, cellulose
acetate is employed as the filter medium. For the purpose of
providing uniform density and overall cohesive character to the
filler, it is customary as is also done in prior art filter rod
making methods, to treat the filaments thereof with a plasticizer
to thereby promote interfiber bonding of the various filaments
comprising the tow.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts, which will be
exemplified in the construction hereinafter set forth and the scope
of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWING
A fuller understanding of the nature and objects of the invention
will be had from the following detailed description taken in
conjunction with the accompanying drawing in which:
FIG. 1 is a vertical sectional view of apparatus with which the
tow-filled rod of the present invention is formed.
FIG. 2 is a transverse sectional view through the tubular workpiece
as it leaves the extrusion aperture of the extruder shown in FIG.
1, the view being taken along line II-II in that Figure.
FIG. 3 is a perspective view of a representative length of the
tow-filled filter rod made according to the invention.
FIG. 4 is an end view of the length of rod shown in FIG. 3
illustrating the manner in which the tow is clenched in the grooves
of the plastic tubular workpiece.
Throughout the following description like reference numerals are
used to denote like parts in the drawing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is concerned with a method for forming filled
plastic tubing in continuous operation, as for example, a
continuous hollow tube having the bore thereof filled with a tow of
fibrous material. It is more particularly concerned with an
improvement in the method and article described in the
aforementioned Thomson et al. patent application. The article of
the present invention is useful as a device for filtering gaseous
or liquid media including cigarette smoke, but because of the
manner of clenching the tow in the grooves in the plastic sheath,
the article is particularly suited for use as a gas or fluid filter
wherein high flow pressure is encountered. Furthermore, the article
lends itself for use as an ink cartridge, a hospital throwaway
antiseptic swab and similar inexpensively mass produced fibrous
material filled devices. Turning now to a description of a
representative embodiment of the invention reference is made to
FIG. 3 wherein it will be noted, the filter rod 10 is comprised of
a thin-walled plastic sheath 12 of generally circular section,
which encloses a filler 14 such as a tow of filaments of cellulose
acetate, the tow functioning as a filter medium. The overall
diameter of the depicted sheath 12, which is intended for
embodiment in a cigarette, is approximately 0.3 inch with a wall
thickness ranging between 0.005 inch to 0.015 inch- 0.020 inch
although it will be understood that variations in these dimensions
can occur depending upon the intended use of the article. The rod
shown in FIG. 3 for example, can be employed as the mouthpiece
component in the ventilated cigarette described in presently
pending U.S. Pat. application Ser. No. 632,336 filed Apr. 20, 1967.
As will be noted, the sheath 12 is provided at its inner wall
surface with an alternating arrangement of grooves 5 and lands 6
intervening said grooves with the grooves 5 serving to receive the
filler 14 and functioning as anchorages or clenching means to
secure more firmly the filler within the sheath. By providing a
greater measure of anchorage of the filler, the filter rod is
capable of withstanding considerable fluid or gas pressure flow
therethrough.
The rod 10 shown in FIG. 3 desirably has an external dimension
within prescribed limits and when used as a filter plug for a
ventilated-type cigarette, the circumference of a circle
circumscribing the peaks of the flutes 16 preferably should measure
23.9 mm..+-. 0.05 mm. The reasons for controlling this
circumferential dimension with such accuracy are set out more
elaborately in the earlier mentioned application of Charles Gatto,
but in brief it is done so as to minimize conditions which can
cause upset in cigarette-making machinery when the filter plugs are
joined with tobacco cylinders.
FIG. 1 illustrates apparatus denoted generally at 20 with which
cigarette filter rod 10 of the present invention can be made. The
apparatus 20 is generally similar to that described in said earlier
filed Gatto application being modified to the extent of the
construction of the extrusion die details of which will be given
shortly herein. As a preliminary to forming the cigarette filter
rod 10, the filter medium which is described in representative form
as being a tow of filaments of cellulose acetate is fed through a
blooming and coating chamber (not shown) wherein the filaments are
coated with a plasticizer comprising by way of example, a solution
of 3 %- 12 % (but preferably 9%) triacetin. The plasticizer is
employed to promote interfiber bonding in the tow at the points of
crossing or contact of the respective fibers and thereby produces
cohesiveness in the mass of the tow. The tow is advanced through a
suitable feed device to relieve all but a slight tension of about
20-50 grams pull in the tow feed in the longitudinal direction
since it is preferable that the tow be processed with but a minimum
of tension being present therein. The tow is then partially
compressed and shaped in known manner into a generally continuous
cylindrical body just prior to delivery of same to the crosshead
die. The tow entering the die has a diameter larger than the
intended final internal dimension of the sheath 12 but, and for
reasons as will appear, has a diameter smaller than the internal
diameter of the extrudate leaving the die. The extruder die which
is a crosshead-type includes a body part 28 wherein is supported in
known manner a mandrel 30, the mandrel being spaced from the
internal bore of the body part 28 so as to define therewith an
annular space in the body part in which can be received molten
plastic 32 entering the crosshead die laterally from a reservoir
(not shown). Depending on the speed with which the extruder screw
(not shown) feeding the molten plastic 32 is rotating, a continuous
tubular stock 12 of heated plastic issues from and is conveyed away
from the mouth or extrusion aperture of the extruder die as at 34
by means of puller rolls 64 downstream in the apparatus line, the
extrudate upon exit from the extrusion aperture having
cross-sectional dimensions substantially larger than the intended
final cross-sectional dimensions of the finished filter rod and
being sufficiently heated to be plastically deformed and the inner
surfaces as at 35 being tacky or in a plastic state. Also, the
extrudate possesses at that point an external surface configuration
in substantial conformance with that of the finished product and to
that end, the crosshead die 22 may be fitted with a suitable
shaping means to impart the required external configuration to the
extrudate. As for example, a faceplate or adapter 21 can be
removably secured to the housing 28, the adapter having an
extrusion aperture designed to produce the particular internal and
external surface configuration on the extrudate. Simultaneously,
with the issuance of the tubular workpiece 12 from the die, the
compressed tow 14 of filter medium transits through a central
cylindrical passage formed in the mandrel as at 38. The tow upon
leaving the die 22 advances axially into and codirectionally with
the extrudate, the tow mass having at that point a diameter at
least slightly greater than the inside diameter of the sheath when
the latter is fully processed. As will be noted the codirectional
movement of the extrudate 12 and tow 14 downstream of the point of
exit from the crosshead die 22 is for some short distance one in
which the hot extrudate does not contact the tow. The foregoing is
provided to allow the extrudate to be drawn down in size in that
distance of travel with the extrudate making first contact with the
tow only as the composite structure enters the closing aperture of
portal gland 42 of the cooling chamber 40. In drawing down the
heated extrudate, its overall sectional dimensions can be reduced
as much as 100 percent from the initial as extruded dimensions to
the smaller final rod dimensions. For example and with respect to
rod 10 as used for a cigarette component, the sheath 12 generally
will have at extrusion, a wall thickness of 0.050 inch, whereas
after drawing down, the sheath at its thicker portions generally
has a thickness in the range 0.005 -0.015 inch.
In extruding the tubular workpiece or sheath 12, the present
invention makes it possible to form the longitudinally extending
grooves 6 on the inner surface thereof as part of the extrusion
operation in a relatively simple yet highly effective manner.
Mandrel 30 is provided with a circle of passages 110 extending
therethrough from end to end and being in communication at one end
with a manifold 112 formed in plate 114 and outletting as ports 121
at the other end adjacent the aperture from whence issues workpiece
12, such outlet being at the inside of the workpiece. Manifold 112
is connected by means of a conduit 116 with a source 118 of
compressed air or other fluid under pressure. Such other fluid of
course would be one compatible with the overall forming procedure.
For example, the plasticizer with which the tow is coated might be
used for the purpose of cooling although it will be understood that
gaseous coolants are preferred. Thus, it will be noted that as the
heated extrudate 12 issues from the extrusion aperture, cooling
streams of air are sprayed against the smooth inner wall surface
thereof at a circle of locations as shown in FIG. 2 in
correspondence to the locations of the lands 6, the streams
preferably issuing in a direction parallel to extrusion axis. The
effect of the cooling jets of air striking said surfaces is to
chill them and initiate a certain degree of set or hardening of
these surfaces. The degree of set initiated is such that when the
workpiece is thereafter pulled down as it advances toward and
through the closing aperture, the sheath will pull down
differentially, that is, to a lesser extent longitudinally along
the surfaces defining the lands 6 than at the surfaces intervening
said lands. Thus the sheath will pull down disproportionately along
the adjacent longitudinal bands defining the lands and grooves, the
greater pull down at said intervening surfaces forming the grooves
5. The overall pull down of the inner wall surfaces which form the
grooves is shown in dashed lines in FIG. 2. As the sheath is pulled
down in size the tow at the surface of the mass thereof becomes
clenched in the grooves 5 providing an anchoring of the mass.
Moreover, the tow becomes adhered to the tacky surfaces in the
grooves to secure the mass within the sheath. Since the grooves
provide an increased surface area at which such adhesion can occur,
they enhance the total character of the tow anchorage. The tow also
adheres to the surfaces of the lands 6 since while the setting of
these surfaces has been initiated by spraying them with cooling
fluid, they retain sufficient tackiness to effect this additional
adhesion.
Cooling of the composite article occurs as it enters the cooling
chamber 40 through portal gland 42, with the plastic sheath being
drawn down sufficiently and uniformly tightly against the tow and
to about the optimum final dimension it is intended to have on
entry to the gland. In pulling the sheath down, the tow mass of
filler 14 is subjected to a further and final radial compression.
As was indicated earlier, the portal gland serves as a closing
aperture having substantially the same diameter and shape as the
final external diameter of the sheath. Thus in the finished
article, the sheath 12 will enclose the tow mass with a positive
constraint of the latter and the tow will invest fully the
anchorages provided by the grooves 5.
In its passage through the cooling chamber, the composite article
is submerged in the bath of cooling water 46 and passes through a
series of apertured sizing plates in the manner taught in the
earlier mentioned Gatto patent application to control accurately
the circumferential dimension of the sheath 12, one such plate 120
being shown. In effecting the sizing of the sheath which is done in
the same manner as described in the prior mentioned Gatto
application, the sleeve can be subjected to an internal pressure
that tends to expand it radially to thus hold same tightly in
sizing relationship with the sizing plates. The force of expansion
is provided by maintaining the cooling chamber 40 and the fluid 46
therein under a condition of vacuum whereas the space enclosed by
the sheath can be communicated with atmospheric pressure, in
addition to having the presence of pressurized air therein
introduced as the cooling streams to set the workpiece inner
surface as earlier described.
On leaving the cooling chamber 40, the sheathed article passes
between the puller device wheels 64 which feed the article through
a cutting unit (not shown) wherein the continuous length article
can be cut into short lengths as shown in FIG. 2 and adaptable for
use in further processing such as utilization in cigarette-making
machines.
The tubular article produced according to the present invention is
advantageously employed as the mouthpiece component of a ventilated
cigarette. It is also suited for use as a filter for other purposes
including in hydraulic systems wherein relatively high fluid
pressure is to be encountered. A 10 mm. long cigarette filter plug
made from rod produced by the present invention was subjected to
both a negative pressure of almost absolute vacuum and a positive
pressure of 25 p.s.i.g. without noticeable pullout of tow from the
sheath. The tow of filters preferably is comprised of a plurality
of filaments of cellulose acetate extending longitudinally and
coextensively of the tow mass. When used in conjunction with a
polyethylene mouthpiece for a ventilated cigarette of the type
previously described the cellulose acetate preferably should have a
total denier of 25,000 to 75,000 but more preferably in the range
of 30,000 to 50,000 the foregoing being based on a fiber denier of
about 1 to 16 and preferably 3 to 6 denier. Other materials are
suitable for use as filler and can include polyalkenes,
polyethylene, and paper tows. The sheath 12 can be formed from
various types of thermoplastic materials including polyolefins,
polypropylene, cellulose acetate and polyethylene, and can have
various external and internal dimensions as well as external
surface configuration depending on the use.
It will be seen from the foregoing then that the present invention
is particularly suited for forming a fibrous filled thermoplastic
rod wherein the filler is anchored in the workpiece in
longitudinally extending grooves formed in the workpiece. This is
accomplished very effectively by the present invention by directing
the cooling streams of air at ambient temperature against the inner
surfaces of the tubular extrudate as it leaves the annular
extrusion aperture. The degree of securement of the filler within
the workpiece is believed to be better with respect to rod produced
according to the present invention than with rod which is formed by
extruding thermoplastic material through an extrusion aperture
having teethlike projections therein corresponding to the grooves
to be formed. A greater degree of clenching is believed to be
achieved because a more pronounced pull down of the extrudate along
the groove surfaces is possible when pulling down the workpiece
structure along bands located between already set surfaces. A
further advantage of the present invention is that it allows for
production of either plastic rod with a serrated inner
configuration such as shown in FIG. 4 or of a smooth inner surface
rod without the need for changing adapter pieces on the extrusion
die. To produce smooth inner surface rod, all that need be done is
to shut down the air supply.
It will thus be seen that the objects set forth above among those
made apparent from the foregoing description, are efficiently
attained and, since certain changes in carrying out the above
method and in the construction set forth, which embody the
invention may be made without departing from its scope, it is
intended that all matter contained in the above description shall
be interpreted as illustrative and not in a limiting sense. For
example, the pressure at which the cooling streams of air are
supplied to the manifold 112 can vary depending on the type of
material being extruded as long as the pressure is not above one
which would cause a rupture of the workpiece 12 issuing from the
die. Furthermore, the range of diameters of the passages 110 will
vary depending upon specific requirements. For example for a sheath
12 of dimensions early discussed, the passages may have a diameter
of one sixty-fourth inch- one thirty-second inch.
* * * * *