U.S. patent number 3,787,265 [Application Number 05/237,832] was granted by the patent office on 1974-01-22 for process and apparatus for producing fibrous structures.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to Paul H. McGinnis, William D. McLaughlin, Jr., Robert E. Swander.
United States Patent |
3,787,265 |
McGinnis , et al. |
January 22, 1974 |
PROCESS AND APPARATUS FOR PRODUCING FIBROUS STRUCTURES
Abstract
Apparatus and method for producing filamentary material by
extruding substantially axially through an orifice comprising
contacting the extruded filament stream downstream of the orifice
and prior to hardening with a plurality of converging,
substantially planar, high velocity gas streams, each moving
substantially in the direction of the filament stream such that
they converge upon the filament stream at an angle of from about
45.degree. to 5.degree. from the axis of the polymer extrusion
nozzle. The planes of the gas streams intersect at a point which is
at a distance measured perpendicularly from the axis of the
extrudate stream at least equal to the diameter of the extrudate
stream.
Inventors: |
McGinnis; Paul H. (Kings
Mountain, NC), McLaughlin, Jr.; William D. (Charlotte,
NC), Swander; Robert E. (Charlotte, NC) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
22895391 |
Appl.
No.: |
05/237,832 |
Filed: |
March 24, 1972 |
Current U.S.
Class: |
156/167; 156/229;
156/441; 156/181; 156/433; 264/103 |
Current CPC
Class: |
D04H
3/07 (20130101); D04H 3/16 (20130101); D01D
5/0985 (20130101) |
Current International
Class: |
D04H
3/16 (20060101); D04H 3/02 (20060101); D01D
5/08 (20060101); D01D 5/098 (20060101); D04H
3/07 (20060101); D04h 003/16 () |
Field of
Search: |
;156/161,167,180,181,229,306,441,433 ;264/12,103,210 ;425/72 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fritsch; Daniel J.
Attorney, Agent or Firm: Thomas J. Morgan et al.
Claims
1. The process of producing a nonwoven self-bonded structure of
randomly arranged synthetic fibrous material comprising first
positioning a collection surface at a distance of from about 6 to
48 inches from a polymer extrusion nozzle, extruding through said
nozzle toward said collection surface a substantially continuous
filament-forming synthetic organic polymer material in liquid phase
at a filament stream under conditions to form a fibrous material,
attenuating the extrudate utilizing a plurality of converging
substantially planar gas streams all having the major force
component in the direction of the filament stream, the planes of
all the attenuating gas streams intersecting the axis of the
extrudate stream at an angle of from less than 45.degree. to more
than 5.degree., the planes of all the gas streams intersecting each
other at a point which is at a distance, B, measured
perpendicularly from the axis of the extrudate stream at least
equal to the diameter of the extrudate stream at a point along the
extrudate stream in juxtaposition to the point of intersection of
the gas streams, the perpendicular distance, A, from the extrusion
nozzle to the point of intersection of the gas streams ranging from
about 2 to 7 inches, the fibrous material when it hits said
collection surfaCe being tacky and adhering to previous layers
thereof and
2. The process of claim 1 wherein the collection surface is
positioned at a distance of from about 10 to 30 inches from the
polymer extrusion nozzle.
3. The process of claim 1 wherein the polymer stream is attenuated
from 10
5. The process of claim 1 wherein the angle of intersection of the
gas
6. The process of claim 1 wherein a polyolefin is extruded at a
temperature of from about 150.degree. to 350.degree. centigrade
above its melting point.
Description
BACKGROUND OF THE INVENTION
This invention relates to the production of filamentary material.
It is particularly concerned with novel apparatus and process for
spray spinning molten fiber-forming polymers to form nonwoven
structures.
Various proposals have been advanced heretofore in connection with
integrated systems for forming fibrous assemblies, such as nonwoven
fabrics and the like, directly from molten, fiber-forming
materials. In general, the proposed systems envisioned an extrusion
operation followed by collection of the extruded filamentary
material in the form of a continuous fabric, web or other desired
fibrous assembly. When details are considered, however, the various
proposals differed in substantial ways.
In recently issued U.S. Pat. No. 3,543,332, a novel method for
spray spinning molten fiber-forming polymers is shown. Filamentary
material is extruded substantially axially through an orifice and
contacted downstream prior to hardening by a plurality of high
velocity gas streams, each moving in a direction having a major
component in the direction of extrusion of the filament stream in a
shallow angle of tangential convergence therewith to attenuate the
filament stream. The axis of the gas passages and corresponding
gaseous streams are skewed about the extrusion orifice such that
they have non-intersecting axes spaced about the axis of the
extrusion orifice.
The present invention is concerned with an improved method and
apparatus for the direct production of filamentary materials. It is
an object of the present invention to provide improved method and
apparatus for spray spinning molten fiber-forming materials at
production rates much higher than the prior art processes. At the
same time, it is a further object of the invention to produce a
substantially uniform spray-spun fibrous structure while minimizing
the formation of shot or objectionally short fibers which detract
from the desirability of the collected fibrous assembly.
In accordance with an embodiment of the invention, spinning nozzle
means are provided with an extrusion orifice with a fiber-forming
material and with a plurality of substantially rectangular gas
outlet passages spaced apart from the extrusion orifice to supply
jets of high velocity gas for attenuating the extruded filament
stream prior to hardening of the filaments. The molten polymer and
attenuating gas do not flow through the same nozzle or any other
part of the spray-spinning equipment. The gas passages are
separated from the extrusion orifice by an insulating means such as
an air space. As a consequence, the gas flow, if it is not heated,
would not cause heat transfer from the polymer to the gas. Such an
arrangement eliminates the need for either heating the attenuating
gas or heating the polymer to a sufficiently high degree above the
required extrusion temperature such that the heat transfer would
only lower the polymer temperature to the required extrusion
temperature. The direction of the gas jets are such that
substantial drag forces are applied to the extruded filament stream
in the direction of extrusion for attenuating or drawing the
material leaving the extrusion orifice. Further, the gas passages
are positioned such that the planar gas streams are directed
substantially in the direction of flow of the extrudate stream in
such a manner that the gas streams converge upon the extrudate
stream. The planes of the gas streams and the planar projections of
the gas outlet passages intersect at a point which is at a distance
measured perpendicularly from the axis of the extrudate stream at
least equal to the diameter of the extrudate stream. The planes of
the attenuating gas streams contact the polymer extrudate stream at
an angle of from about 45.degree. to 5.degree. from the axis of the
polymer extrusion nozzle to project it away from the extrusion
orifice.
Briefly, a relatively heavy monofil is extruded and a plurality of
streams of gas, e.g., steam or air, are directed at a shallow angle
in the direction of flow of the freshly extruded monofil. This
attenuates the monofil into relatively finer denier material and,
like the more conventional drawing, also increases the tenacity of
the solidified extrudate. Depending upon the conditions of
extrusion, the filamentary material will be one or more
substantially continuous structures, or relatively long staple
fibers, or conventional length fibers, possibly mixed with varying
amounts of solid debris or "shot."
The severity of the gas streams varies the attenuation and
determines the denier of the resulting fibrous material which may
range from about 0.1 up to about 50, although for maximum surface
and strength the fiber denier is preferably mostly below about 25
denier. Actually each product will include a range of deniers which
will add to its strength and performance.
The extrudate is discharged onto a suitable collection surface such
as a rotating collector drum. The height or length of the resulting
structure can be set by traverse or by use of multiple side-by-side
extruders whose spray patterns overlap. The duration of spray
obviously controls the thickness of the resulting structures. The
conditions of extrusion and collection are such that each new layer
when deposited is sufficiently tacky so as to adhere to the
preceding layer so that the total structure will be shape-retaining
without further treatment.
The filament-forming material may comprise any known suitable
polymeric material which is plasticizable, soluble or fusible. If
soluble materials are used in conjunction with a solvent, the
problem of solvent removal is encountered which, of course, is
avoided where fusible materials are employed. Representative
fusible materials include polyolefins such as homopolymers and
copolymers of olefins, e.g. ethylene and propylene, especially
stereospecific or crystalline polyethylene and polypropylene;
polyamides such as nylon 66, nylon 6, and the like; polyesters such
as polyethyleneterephthalate; cellulose esters such as cellulose
acetate, and especially the secondary triacetate; polyurethanes;
polystyrene; polymers of vinylidene monomers such as vinyl
chloride, vinyl acetate, vinylidene chloride, and especially
acrylonitrile; and mixtures thereof.
DESCRIPTION OF THE DRAWINGS
A more complete understanding of these and other features of the
invention will be gained from a consideration of the following
detailed description of an embodiment illustrated in the
accompanying drawings in which:
FIG. 1 is a schematic illustration of an extrusion and collection
apparatus in accordance with the present invention;
FIG. 2 is a schematic plan view of the extrusion apparatus and
process in accordance with the present invention;
FIG. 3 is a graph illustrating vectorially the forces resulting
from two converging planar gas streams;
FIG. 4 is a schematic illustration showing how the vector force
component illustrated in FIG. 3 both deflect and accelerate the
filament stream.
FIG. 5 is a front elevation of one embodiment of an extrusion
nozzle and planar attenuating gas jets useful in the apparatus and
process illustrated in FIG. 2;
FIG. 6 is a schematic perspective illustration of an extrusion
nozzle having a pair of planar attenuating gas jets positioned on
each side of the extrusion nozzle;
FIG. 7 is a perspective view of a planar attenuating gas jet shown
in FIG. 6.
FIG. 8 is a schematic front elevation of the preferred arrangement
for utilizing four extrusion nozzles.
Referring now more particularly to the drawings, in FIG. 1 a
fiber-forming, thermoplastic polymer, preferably a polyolefin, is
fed to an extruder 10 provided with an adapter section 12 to which
a gas, such as steam or air, is supplied. While extrusion
temperatures may be anywhere above the melting point of the
polymer, it has been found that best results are obtained by
heating the polymer to at least 150.degree.C., and preferably from
about 250.degree. to about 350.degree.C. above the softening point
of the polymer being extruded. For example, polypropylene having
hereinafter defined characteristics will generally be heated to
temperatures of from about 325.degree. to about 400.degree.C.
Polyethylene, on the other hand, will be heated to from about
350.degree. to about 450.degree.C. A hot, molten stream of polymer
16 is discharged through a nozzle 14.
It is to be understood that nozzles having one or more polymer
orifices may be used. Also, a plurality of nozzles per collector
may be employed. However, there must be at least two planar gas
streams per polymer orifice. The attenuating gas orifices 18 are of
an elongated rectangular cross section, as shown in FIGS. 5 and 6,
to emit substantially planar gas streams 17.
The gas streams 17 act on the polymer stream 16 in convergence
region 20 to form an attenuated filament 22 wherein it cools and
partially solidifies while moving toward collection surface 24 on
which it is collected as a cylindrical structure 26. The collection
surface 24 is ordinarily rotated at a speed sufficient to provide a
moving surface of from about 25 to about 125 feet per minute by a
motor drive. Collection surface 24 is in surface contact with
roller 28, which acts as an idler roll and whose bias against the
mandrel can be adjusted; the extent of the bias will effect how
tightly the tacky filament packs against previous layers on the
cartridge 26. Both the collection surface 24 and the roller 28 are
reciprocated laterally by a traversing mechanism 30 whose throw
determines the shape of the cylinder; the throw may be of constant
length or may change in the course of package build-up to produce a
particular shape as may be needed for acceptance in a receptacle of
predetermined corresponding shape.
The force of the attenuating gas on the polymer stream causes the
polymer to attenuate greatly, e.g., from 10 to 500 times, based on
diameter ratios, and possibly fibrillate to a slight degree to
produce a substantially continuous fiber. Some turbulence and
resultant whipping about of the polymer stream occurs.
Consequently, a generally random, stereo reticulate structure of
fiber results as the material impinges on the collector. Since the
polymer is still in a somewhat molten or tacky state when it
strikes the collector, some sticking together occurs at the points
where fiber intersects. For brevity, this sticking will be referred
to as interfiber bonding, although it is to be understood that this
bonding will ordinarily result from an individual fiber looping
about and sticking or bonding to itself.
For best results, the collection surface 24 should be from about 6
to about 48 inches, preferably 10 to 30 inches, from polymer exit
nozzle 14. With greater distances the spray pattern is difficult to
control and the resultant web tends to be nonuniform. Shorter
distances result in a web which contains too great a quantity of
shot, i.e., beads of non-attenuated polymer, which undesirably
affects subsequent processing, web uniformity and surface area.
In FIG. 2 there is schematically shown a top view of the apparatus
of this invention. A plurality of converging substantially planar
gas streams 18 (corresponding substantially to planar projections
of gas outlet passages 17) issue from substantially rectangular gas
outlet passages 17. The axis 19 of the nozzle 14 corresponds to the
direction in which the polymer stream is extruded. The gas jets 17
are positioned along side the extrusion nozzle 14 in such a manner
that the gas streams 18 are directed substantially in the direction
of flow of the polymer extrudate along the nozzle axis 19. The
planes of the gas streams and planar projections of the gas outlet
passages intersect at a point 21 which is at a distance B measured
perpendicularly from intersection point 21 to the nozzle axis 19.
The distance B is at least equal to the diameter of the extrudate
stream at a point 23 along the nozzle axis in juxtaposition to the
point of intersection 21. Preferably B is at least 0.06 inch, most
preferably from about 0.2 to 2.0 inches. The point 23, which
defines the perpendicular distance from the nozzle 14 to the
intersection point 21 is a distance A of at least 2.0 inches from
the point of extrusion nozzle 14, preferably from about 2.5 to 7.0
inches. The attenuating gas jets 17 are positioned along side the
extrusion nozzle such that the planes of the attenuating gas
streams 18 intersect the nozzle axis 19 (also the axis of the
extrudate stream) at an angle (.alpha..sub.1 and .alpha..sub.2)
less than 45.degree. to more than about 5 degrees, preferably from
about 10 to 40 degrees, to project the extrudate stream away from
the extrusion nozzle.
In FIG. 3 the force of the gas streams 18 are shown vectorially.
The Y force component is in the direction of the extrusion nozzle
axis and polymer extrudate stream, and serves to accelerate and
attenuate the extrudate stream.
Angles .alpha..sub.1 and .alpha..sub.2, shown in FIG. 2, are not
the same so that the intersection point of the planes of the gas
streams is off the nozzle axis and extrudate stream. FIG. 4 shows
that the effect of this is to deflect the extrudate stream 16,
first to one side and then to the other, in addition to attenuating
the extrudate. If .alpha..sub.1 and .alpha..sub.2 are identical,
the planar filament streams 18 would intersect on the nozzle axis
and substantially on the extrudate stream. As can be seen from the
examples, this leads to much lower surface area when compared to
the method of this invention illustrated in FIG. 2. It is probable
that the effect of the gas streams intersecting on the extrudate
stream is to cut the stream and produce a less open, lower surface
area product.
The illustrated extrusion nozzle 14 has a center polymer exit
orifice 15, as shown in FIG. 5, which ordinarily has a diameter of
from about 0.01 to about 0.10 inch, and preferably from about 0.015
to about 0.030 inch.
In the preferred embodiment, polymer is generally extruded through
the nozzle at 1 to about 30 lb./hr., and desirably at 5 to 15
lb./hr.
Along side polymer exit orifice 15, as shown in FIGS. 5 and 6, are
a plurality of attenuating substantially rectangular elongated gas
orifices 18 having a width of from about 0.002 to about 0.050 inch,
preferably from about 0.004 to about 0.025 inch, and a length of at
least about 0.5 inch, preferably from about 1.0 to about 3.0
inches. Attenuating gas nozzles 18 emit substantially planar gas
streams 17 and are positioned, as illustrated in FIGS. 2 and 8.
FIGS. 6 and 7 show, in perspective, a preferred embodiment of a gas
jet for emitting a substantially planar gas stream. The gas enters
through gas inlet passage 25 and is emitted through rectangular
elongated gas orifice 18.
EXAMPLE 1
Isotactic polypropylene having an intrinsic viscosity of 1.5 and a
melt flow rating of 30 is spray-spun at a melt temperature of
390.degree.C. through four extrusion orifices arranged as shown in
FIG. 8. Each orifice is of a substantially circular cross-section
having a diameter of about 0.016 inch. Referring to FIG. 8, two
planar attenuating gas jets, as shown in FIG. 6, were spaced at a
distance of 2 inches from the axis of each extrusion nozzle, in
approximately parallel relationship to each other along side each
extrusion orifice. The elongated rectangular air jets had an
orifice width of 0.010 inch and a length of about 1.88 inches and
each emitted ambient air flowing at a rate of about 56 cubic feet
per minute at a pressure of about 65 p.s.i.g.
Referring to FIG. 2, the gas jets 17 are positioned so that the
planes of gas streams 18 intersect at a point 21 which is at a
distance B of five-sixteenths inch from the axis of the extrudate
stream which corresponds to nozzle axis 19. The distance A which
defines the distance from the orifice 14 to the intersection point
21, is 4 inches. As a result, the planes of the gas streams
intersect the axis of the extrudate stream at angles .alpha..sub.1
and .alpha..sub.2 of about 30.degree. and 25.degree. respectively.
The polypropylene extrudate is collected on a metal drum having a
diameter of 1 inch to produce annular cylindrical structures. The
total through put of polypropylene is about 6 lb./hr.
The procedure is repeated, except that the extruder throughput is
increased such that the total throughput of polypropylene being
spray spun is 9 lb./hr.
EXAMPLE 2
Polypropylene, as in Example 1, is spray spun through one or more
circular orifices, utilizing planar attenuating gas jets, as shown
in FIG. 6, spaced at a distance of 2 inches from the axis of each
extrusion orifice. The spray spun structure was collected on a
cylindrical drum. The process conditions for 14 runs are summarized
in Table 1 below: ##SPC1##
The molecules in the surface layer of a solid are bound on one side
to inner molecules but there is an imbalance of atomic and
molecular forces on the other. The surface molecules attract gas,
vapor, or liquid molecules in order to satisfy these latter forces.
The attraction may be either physical or chemical, depending on the
system i volved and the temperature employed. Physical adsorption
(frequently referred to as van der Waal's adsorption) is the result
of a relatively weak interaction between a solid and a gas. This
type of adsorption has one primary characteristic. Essentially all
of a gas adsorbed can be removed by evacuation at the same
temperature at which it was adsorbed.
While the first gas molecules to contact a clean solid are held
more or less rigidly by van der Waal's forces, the forces active in
the condensation of vapors become increasingly responsible for the
binding energy in subsequent layer development. The expression
V.sub.a = V.sub.m CP/(P.sub.s - P) [1 + (C-1) P/P.sub.s ] (1)
where V.sub.a is the volume of gas adsorbed at pressure P, V.sub.m
the volume adsorbed when the entire adsorbing surface is covered by
a monomolecular layer, C a constant, and P.sub.s the saturation
pressure of the gas (actually the vapor pressure at a given
temperature of a large quantity of gas condensed into a liquid), is
obtained by equating the rate of condensation of gas molecules onto
an adsorbed layer to the rate of evaporation from that layer and
summing for an infinite number of layers. The expression describes
the great majority of low temperature adsorption data. Physical
measurements of the volume of gas adsorbed as a function of
pressure at a fixed temperature, therefore, permit calculation of
V.sub.m, the volume of gas required to form a layer one molecule
thick. Equation 1 can be rearranged to the linear form
P/V.sub.a (P.sub.s - P) = 1/V.sub.m C + (C-1/V.sub.m C)
P/P.sub.s
Then a plot of data for P/V.sub.a (P.sub.s - P) versus P/P.sub.s
gives a straight line, the intercept and slope of which are
1/V.sub.m C and (C - 1)V.sub.m C, respectively. The value of
V.sub.m is thus readily extracted from a series of measurements.
From this information and knowledge of the physical dimensions of
single molecules, the surface area of the adsorbing solid is
computed.
As shown in Table 1 above, surface area measurements were taken
utilizing Orr Surface -- Area Pore -- Volume Analyzer (Model
2100A). The runs using the preferred process of this invention (2,
2a, 2b, 2c, 2f, 2g, 2k and 2m) exhibited a higher surface area than
the runs wherein the attenuating gas streams intersected on the
axis of the extrudate stream. A direct comparison can be between
runs 2f and 2h, 2g and 2i, 2j and 2k, and 2l and 2m. Increases in
surface area of from 0.05 to 0.17 meters.sup.2 /gram are
achieved.
The higher the surface area, the greater the filtration efficiency
of the structure.
The preferred fiber-forming polymers employed in the present
invention are the polyolefins, such as polyethylene or
polypropylene. The melt index of the polyolefin prior to extrusion
will ordinarily be from about 5 to 60 and preferably from about 15
to 40. The intrinsic viscosity will be from about 1.0 to about 2.5
and preferably from about 1.0 to about 2.0.
Instead of the polyolefins, one may also employ other
thermoplastic, melt-extrudable, fiber-forming polymers such as
polyamides, polyesters, phenol-formaldehyde resins, polyacetals,
and cellulose esters, e.g., cellulose acetate. With some of the
polymers, spray spinning is aided by mixing the polymer with a melt
depressant to facilitate melting without decomposition.
Air will normally be employed as the attenuating gas for reasons of
economy. Other gases, e.g., steam, nitrogen, helium, etc., are also
suitable. Usually, the attenuating gas will be at ambient
temperature. Heated gas, e.g., at a temperature of 250.degree. to
500.degree.C., may also be advantageously used, however.
It will be appreciated that the instant specification and examples
are set forth by way of illustration and not limitation, and that
various modifications and changes may be made without departing
from the spirit and scope of the present invention.
* * * * *