Note: Descriptions are shown in the official language in which they were submitted.
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MEI-HOD AND APPARATUS FOR THE PRODUCTION OF ARTIFICU~L FIBERS, NON-WOVEN
WEBS AND SORBEN~CY NON-WOVEN FABRICS
Field Of The Invention
This invention relates generally to the production of
man-made fibers, and particularly, to the field of production
of man-made ~ibers using melt-blown, coform and spunbond
technigues.
Backqround Of The Invention
The production of man-made ~ibers has long used melt-
blown, coform and spunbond techniques to produce fibers for
use in forming non-woven webs of material. Figures la
]o through 3b illustrate prior art machines which manufacture
non-woven webs from melt-blown and spunbond techniques.
Additionally, prior art coform techniques are discussed in
greater detail hereinafter.
Figures la-lc illustrate a typical approach for
1~ producing melt-blown fibers. Referring to Figure la, a
hopper 10 contains pellets of resin. Extruder 12 melts the
resin pellets by a conventional heating arrangement to form a
molten extruda~le composition which is extruded through a
melt-blowing die 14 by the action of a turning extruder screw
(not shown) located within the extruder 12. As shown in
Figure lc, the extrudable composition is fed to the orifice
18 through ext]usion slot 28. The die 14 and the gas supply
fed therethrough are heated by a conventional arrangement
(not shown).
Figure lb illustrates the die 14 in greater detail. The
tip 16 of die ~4 contains a plurality of melt-blowing die
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orifices 18 which are arranged in a linear array across the
face 16. Referring now to Figure lc, inlets 20 and 21 feed
heated gas to the plenum chambers 22 and 23. The gas then
exits respectively through the passages 24 and 25 to converge
S and form a gas stream which captures and attenuates the
polymer or resin threads extruded from orifice 18 to form a
gas borne stream of fibers 26 as is seen in Figure la.
The melt-blowing die 14 includes a die ~rh~l~ 36 having
a base portion 38 and a protruding central portion 39 within
which an extrusion slot 28 extends in fluid communication
with the plurality of orifices 18, the outer ends of which
terminate at the die tip. The gas borne stream of fibers 26
is projected onto a collecting device which in the embo~; ~nt
illustrated in Figure la includes a foraminous endless belt
30 carried on rollers 31 and which may be fitted with one or
more stationary vacuum chambers (not shown) located beneath
the collecting surface on which a non-woven web 34 of fibers
is formed. The collected entangled fibers form a coherent
web 34, a segment of which is shown in plan view in Figure 2.
The web 34 may be removed from the belt 30 by a pair of pinch
rollers 33 (shown in Fig. la) which press the entangled
fibers together. The prior art melt-blowing apparatus of
Figs. la-lc may optionally include pattern-embossing means as
by patterned calender nip or ultrasonic embossing equipment
(not shown) and web 34 may thereafter be taken up on a
storage roll or passed to subse~uent manufacturing steps.
Other embossing means may be utilized such as the pressure
nip between a calender and an anvil roll, or the embossing
step may be omitted altogether.
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Figure 3a illustrates a prior art apparatus 44 for
producing spunbond fibers. The spunbond apparatus typically
contains a fil:)er draw unit 46 positioned above an endless
belt 78 which is supported on rollers 76. Figure 3b
S illustrates the fiber draw unit in greater detail. Fiber
draw unit 46 includes upper air regions 48 and 50 and a
longitudinal air chamber which contains an upper portion 52,
a mid--portion 54, and a lower portion or tail pipe 56. The
fiber draw unit also includes a first air plenum 58 and an
air inlet 60 leading from the first air plenum 58 to mid-
portion 54 of the fiber draw unit. Additionally, a second
air plenum 62 also communicates with mid--portion 54 of the
fiber draw unit via air inlet 64. The spunbond apparatus 44
also includes standard equipment for melting an extruding
lS resin through dies to create fibers 68. Typically, this
equipment feeds resin fed from a supply to a hopper extruder,
through a filter, and finally through a die to create the
fibers 68.
High velocity air is admitted into the fiber draw unit
through plenums 58 and 62 via inlets 72 and 74, respectively.
The addition of air to the fiber draw unit through inlet 60
and 64 aspirates air through inlets 50 and 48. The air and
fibers then exit through tail pipe 56 into exit area 70.
Generally, air admitted into the fiber draw unit through
inlets 50 and 48 draws fibers 68 as they pass through the
fiber draw unit. The drawn fibers are then laid down on
endless belt 78 to form a non-woven web 80 as is seen in
Figure 3a. Rollers 82 may then remove the non-woven web from
the endless belt 78 and further press the entangled fibers
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together to assist in forming the web. The web 80 is then
bonded, such as by embossing by calender and anvil,
ultrasonic embossing, or other known technique, to form the
finished material.
S It is well known in the art to vary a number of
processing parameters in both melt-blown and spunbond fiber
forming processes to obtain fibers of desired properties in
order to form fabrics with desired characteristics.
However, the majority of prior art techniques for varying
fiber characteristics required more time consuming changes in
machinery or process, such as changing dies or changing the
resins. Therefore, those techniques required that the
production line be halted while the necessary changes were
made, which resulted in inefficiency when a new material was
to be run.
The prior art has previously taught that various effects
can be obtained by the manipulation of air flow near the
fiber exit in melt-blown and spunbond fiber producing
equipment. For example, Shambaugh, U.S. Patent No.
5,405,559, teaches that the air flow provided in the melt-
blown process can be alternately turned on and off on both
sides of the die, thus reducing the energy required to
produce melt-blown fiber. However, this teaching of
Shambaugh has several drawbacks. Under some conditions, the
complete shutting off of the air on either side will tend to
blow the li~uefied resin onto the air plates on the other
side of the die, thereby clogging the machinery for typical
production airflow rates (especially with high MFR polymers
or other polymers normally used in non-woven web production).
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Further, such t~hn i ques would likely result in the
deposition of resin globs or "shot", on the production web
since the resin would be affected only ;n;~lly during the
transition from airflow on one side of the die to the other.
Finally, while the ~h~h~ugh reference teaches switchi.ng air
on and off for the purposes of reducing fiber size for a
given flow, its main emphasis is that such switching saves
energy by reducing the overall airflow requirements in the
melt-blown process. Moreover, the low frequencies taught
by Shambaugh would result in poor formation on a high speed
machine. Fibers produced as given in the examples are
coarser, e.g. larger diameters than typically found in non-
woven commercial production. Finally, Shambaugh teaches no
applicability of selective alteration of airflow
characteristics for varying fiber parameters in a spunbond
fiber production environment.
SummarY Of The Invention
The above and further objects are realized in a process
and apparatus for the production of fibers in accordance with
disclosed and preferred embodiments of the present invention
and resulting non-woven webs and sorbent products for
absorbing oil and other uses.
Generally, the present invention relates to an apparatus
for forming artificial fibers from a liquefied resin and for
2~ forming a non-woven web. The apparatus may include means for
generating a substantially continuous airstream for
entraining fibers along a primary axis, at least a first
extrusion die located next to the airstream for extruding the
liquefied resin, and perturbation means for selectively
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perturbing the air stream by varying the air pressure on
either side or both sides of the primary axis. The apparatus
may also include a substrate disposed below the first die,
substrate translation means for moving the substrate relative
S to the die, wherein the entrained fibers are deposited on the
substrate to form a non-woven web.
The apparatus may include a first supply of air
connected to first and second air plenum chambers located on
opposite sides of the axis, wherein plenum chambers outlets
provide a substantially continuous air stream for fiber
attenuation. The perturbation means may include a valve for
selectively varying the airflow rate to the first and second
plenums, thereby providing airflow perturbation to the
entrained fibers. Additionally, airstream perturbation may
be achieved by superimposing a perturbed secondary air supply
on the first air supply within the plenum chambers.
Alternatively, the perturbation means may include first and
second pressure transducers adjacent or attached to the first
and second plenum chambers, and means for selective
activation of the first and second pressure transducers for
selectively varying the pressure in the first and second
plenum ch~h~rs~ Generally, the perturbation means varies a
steady state pressure in the first and second plenum chambers
at a perturbation fre~uency of approximately less than 1000
Hertz, and varies an average plenum pressure in the first and
second plenum chamber up to about 100% of the total average
plenum pressure in the absence of activation of the
perturbation means.
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~ he apparatus may also include a fiber draw unit
disposed below the first die and adapted to channel the
primary air flow therethrough. The fiber draw unit may
include a fiber inlet at a top portion thereof for receiving
fluid flow and fibers entrained therein, an outlet for
dispensing the air entrained fibers onto the substrate. The
apparatus may also include a multiple die arrangement for
extruding seve~ral types of resin simultaneously, as well as
means for adding other fibers or particulates (coform).
lo The apparatus may also include first and second
secondary pert:urbing air supplies disposed on opposite sides
of said axis and near the die or fiber draw unit for
alternatingly perturbing the substantially continuous flow of
air.
The preseint invention also relates to a method for
forming artificial fibers from a liquefied resin and forming
a non-woven web thereby, comprising the steps of generating a
substantially continuous air stream along a primary axis,
extruding the liquefied resin through a first die located
adjacent to the air stream, entraining the liquefied resin in
the air stream to form fibers, selectively perturbing the
flow of air in the airstream by varying the air pressure on
either side of the primary axis.
Brief DescriPtion of the Drawings
Figures la-lc illustrate schematic representations of a
prior art apparatus for producing melt-blown fibers.
Figure 2 is a surface representation of a non-woven web
made in accordance with prior art methods.
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g
Figures 3a and 3b illustrate schematic representations
of a prior art apparatus for producing spunbond fibers.
Figure 4 is a photograph of a surface of a non-woven web
manufactured without airstream perturbation.
s Figure 5 is a photograph of a surface of a non-woven web
manufactured in accordance with the present invention.
Figures 6a-6d illustrate schematic representations of
apparati for producing melt-blown fibers according to the
present invention.
Figures 7a-7e illustrate schematic representations of
three-way valve embodiments which may be utilized in
accordance with the present invention.
Figures 8a and 8d illustrate plenum pressure as a
function of time for a prior art apparatus for producing
melt-blown fibers.
Figures 8b-8c illustrate plenum pressure as a function
of time for an apparatus for producing melt-blown fibers in
accordance with the present invention.
Figure 9 illustrates fiber diameter distribution for
melt-blown fibers manufactured in accordance with the prior
art.
Figure 10 illustrates fiber diameter distribution for
melt-blown fibers manufactured in accordance with the present
lnventlon .
2~ Figure 11 illustrates Frazier porosity as a function of
perturbation frequency for a melt-blown non-woven web
manufactured in accordance with the present invention.
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Figure 1-! illustrates hydrohead as a function of
perturbation frequency for a melt-blown non-woven web
manufactured in accordance with the present invention~
Figure 13 is a photograph of the surface of a non-woven
web manufactured in the absence of airstream perturbation.
Figure 14 is a photograph of the surface of a non-woven
web manufactured in accordance with the present invention.
Figure 15 illustrates peak load as a function of
perturbation frequency of a non-woven web of spunbond fibers.
Figure 16 is a schematic representation of a coform
apparatus configured in accordance with the present
invention.
Figures 17a-17d and 19 illustrate various apparatus
configurations for manufacturing a non-woven web of spunbond
fibers in accc,rdance with the present invention.
Figures 18a-18f, 20a and 20b, and 21a-21d illustrate
various configurations of secondary jets for use with the
present invention.
Figures 22 and 23 are X-Ray Diffraction Scans of a prior
art meltblown fiber and a fiber made in accordance with the
present invention.
Figure 24 is a DSC (Differential Scanning Calorimetry)
comparing the calorimetric characteristics of a prior art
meltblown fiber and a fiber made in accordance with the
present invention.
Detailed Description Of The Preferred Embodiments
The following te~hni~ues are applicable to the melt-
blown, spunbond and coform fiber forming processes. For the
sake of clarity, the general principles of the invention will
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be discussed with reference to these techniques. Following
the general description of the t~chn; ques, the specific
application of these techniques in the melt-blown, spunbond,
and coform fields will be described. For ease in following
the discussion, sub-headings are provided below; however,
these sub-heading are for the sake of clarity and should not
be considered as limiting the scope of the invention as
defined in the claims. As used herein, the term
"perturbation" means a small to moderate change from the
steady flow of fluid, or the like, for example up to 50% of
the steady flow, and not having a discontinuous flow to one
side. Furthermore, as used herein, the term fluid shall mean
any liquid or gaseous medium; however, in general the
preferred fluid is a gas and more particularly air.
Additionally, as used herein the term resin refers to any
type of li~uid or material which may be liquefied to form
fibers or non-woven webs, including without limitation,
polymers, copolymers, thermoplastic resins, waxes and
emulsions.
General Description of the Air Flow Perturbation Process
As was described previously, the production of fibers
having various characteristics has been known in the prior
art. However, the preferred embodiments of the present
invention provide for a much greater range of variation in
fiber characteristics and provide for a greater range of
control for forming various non-woven web materials from such
fibers, these techniques allow one to "tune in" the
characteristics of the non-woven web formed thereby with
little or no interruption of the production process. The
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basic t~hn; que involves perturbing the air used to draw the
fiber from the die. Preferably, the airflow in which the
fiber travels is alternately perturbed on opposite sides of
an axis paral]!el to the direction of travel of the fiber.
s Thus, the airstream carrying the forming fiber is perturbed,
resulting in perturbation of the fiber during formation.
Airstream pert:urbation according to the methods and apparati
of the present: invention may be implemented in melt-blown and
spunbond manufacturing, but is not limited to those
processes.
In general, the airflow may be perturbed in a variety of
ways; however, regardless of the method used to perturb the
airflow, the perturbations have two basic characteristics,
frequency and amplitude. The perturbation frequency may be
defined as the number of pulses provided per unit time to
either side. As is common the frequency will be described in
Hertz (number of cycles per second) throughout the
specification. The amplitude may also be described by the
percentage increase or difference in air pressure (~P/P)
X lO0 in the perturbed stream as compared to the steady
state. Additionally, the perturbation amplitude may be
described as the percentage increase or difference in the air
flow rate during perturbation as compared to the steady
state. Thus, the primary variables which may be controlled by
the new fiber forming techniques are perturbation frequency
and perturbation amplitude. The techniques described below
easily control these variables. A final variable which may
be changed is the phase of the perturbation. For the most
part, a 180~ phase differential in perturbation is described
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1~
below (that is, a portion of the airflow on one side of an
axis parallel to the direction of flow is perturbed and then
the other side is alternately perturbed); however, the phase
differential could be adjusted between 0~ to 180~ to achieve
any desired result. Tests have been conducted with the
perturbation being symmetric (in phase) and with varying
phase relationships. ~his variation allows for still more
control over the fibers made thereby and the resulting web or
material.
lo The perturbation of the air stream and fibers during
formation has several positive effects on the fiber formed
thereby. First, the particular characteristics of the fiber
such as strength and crimp may be adjusted by variation of
the perturbation. Thus, in non-woven web materials,
increased bulk and tensile strength may be obtained by
selecting the proper perturbation frequency and amplitude.
Increased crimp in the fiber contributes to increased bulk in
the non-woven web, since crimped fibers tend to take up more
space. Additionally, preliminary investigation of the
characteristics of meltblown fibers made in accordance with
the present invention, as compared to those made with prior
art techniques, appear to indicate that fibers made in
accordance with the present invention exhibit different
crystalline and heat transfer characteristics. It is
believed that such differences are due to heat transfer
effects (including quenching) which result from the movement
of fibers in a turbulent airflow. It is further believed
that such differences contribute to the e~h~nc~A
characteristics of fibers and non-woven materials made in
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accordance with the techniques of the present invention.
Additionally, the perturbation of the airflow also results in
improved deposition of the fibers on the forming substrate,
which enhances the strength and other properties of the web
formed thereby.
Furthermore, since the variables of frequency and
amplitude of the perturbation are easily controlled, fibers
of different characteristics may be made by changing the
frequency and/or amplitude. Thus, it is possible to change
lo the character of the non-woven web being formed during
processing (or "on the fly"). By this type of adjustment, a
single machine may manufacture non-woven web fabrics having
different characteristics required by different product
specification 1while eliminating or reducing the need for
lS major hardware or process changes, as is discussed above.
Additionally, the present invention does not preclude the use
of conventional process control techniques to adjust the
fiber characteristics.
Referring now to Figures 4 and 5, magnified photographs
of melt-blown webs made in accordance with prior art
t~chn;ques (Fig. 4) and according to the present invention
(Fig. 5) may be compared. As is seen in Figure 4, the
individual fibers of the web are relatively linear. However,
as is seen in Figure 5, the fibers in the web made in
accordance Wit]l the perturbation techniques of the present
invention are much more crimped and are not predominantly
aligned in the same direction. Thus, as will be seen in the
results described below, webs made in accordance with the
present invent:ion tend to exhibit greater bulk for a given
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weight and fre~uently have greater machine and cross
direction strengths (the machine direction is the direction
of movement, relative to the forming die, of the substrate on
which the web is formed; the cross direction is perpendicular
to the machine direction). It is believed that the increase
crimp will provide many more points of contact for the fibers
of the web which will enhance web strength. As a note, at
first glance it would appear that many more and larger voids
are present in the web of Figure 5 as compared to that of
Figure 4; however, in fact, the web of Figure 5 does not
contain more or larger voids than that of Figure 4. Since
the SEM photographs of these Figures present views of the top
surface of the material, the increased bulk of the web of
Figure 5 is not seen in the photograph and the bulk manifests
in a manner to make it appear that there are a greater number
of larger voids. Conversely, since the web of Figure 4 has
less bulk, a greater number of fibers of that web are located
in the plane of the photograph, giving the appearance of
fewer and small voids. As is seen below, the barrier
properties of webs made in accordance with the present
invention can be selected to be superior to those made in
accordance with the prior art, thus demonstrating that the
appearance of voids in the photograph of Figure 5 is
misleading.
2~ Melt-Blown Applications
Figures 6a through 6d illustrate various embodiments of
the present invention which utilize alternating air pulses to
perturb air flow in the vicinity of the exit of a melt-blown
die 59. Each melt-blown embodiment of the present invention
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includes diametrically opposed plenum/manifolds 22 and 23 and
air passages ~4 and 25 which lead to a tip of the melt die 59
to create a st:ream of fibers in a jet stream 26. ~he
function of the present invention is to maintain a steady
flow and to superimpose an alternating pressure perturbation
on that steady flow near the tip of melt die 59 by
alternatingly increasing or reducing the pressure of the
manifolds 22 and 23. This t~chn;que assures controlled
modifications in the gas borne stream of fibers 26 an~
therefore facilitates regularity of pressure fluctuations in
the gas borne stream of fibers. Additionally, the relatively
high steady state air flow with respect to perturbation air
flow amplitude also serves to prevent the airborne stream of
fibers from becoming tangled on air plates 40 and 42. The
jet structure air entrainment rate (and therefore quenching
rate) and fiber entanglement are thus modified favorably.
Figures 7a through 7d illustrate a few examples of
valves that alternatingly augment the pressure in plenum
chambers 22 and 23 shown in Figs. 6a-6d. Referring to Figure
7a, perturbation valve 86 is essentially comprised of a
bifurcation of main air line 84 into inlet air lines 20 and
21. In the immediate vicinity of the bifurcation, a pliant
flapper 98 alternatingly traverses the full or partial width
of the bifurcation. This provides a means for alternatingly
restricting air flow to one of air inlet lines 20 and 21
thereby superimposing a fluctuation in air pressure in
manifolds 22 and 23. Alternatively, an activator may
mech~n;cally oscillate the flapper across the bifurcation to
produce the appropriate fluctuation in air pressure in
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plenums 22 and 23. Flapper valve 98 may traverse the
bifurcation of mainline 84 in an alternating ~nn~ simply by
the turbulence of air in mainline 84 using the natural
frequency of the flapper. Oscillation frequency of valve 86
S as disclosed in Figure 7a may be varied ?~hAnically by an
activator which reciprocates the flapper, or by simply
adjusting the length of the flapper 98 to change its natural
frequency.
Figure 7b illustrates a second embodiment of the
perturbation valve 86. This embodiment may include a motor
100 which rotates a shaft 102. The shaft 102 may be fixed to
a rotation plate 109 which has a plurality of apertures 108
disposed thereon. Behind rotation plate 109 is a stationary
plate 104 containing a plurality of apertures 106. Both
lS disks may be mounted so that flow is realized through fixed
disk openings only when apertures from the rotation plate 109
are aligned with apertures in the stationary plate 104. The
apertures on each plate may be arranged such that a steady
flow may be periodically augmented when apertures on each
plate are aligned. The frequency of the augmented flow may
be controlled through a speed control of motor 100.
Figure 7c illustrates yet another embodiment of
perturbation valve 84. In this embodiment a motor 100 is
rotatingly coupled to a shaft 112 which supports a butterfly
2s valve 110 having essentially a slightly smaller cross-section
than main air line 84. Turbulence created downstream from
rotating butterfly 110 may then provide an alternatingly
augmented air pressure in air inlet lines 20 and 21 and also
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in air plenums 22 and 23 to achieve the flow conditions in
accordance with the present invention.
Figure 7d represents yet another embodiment of a
perturbation valve 86 in accordance with the present
invention. There, a motor 100 is coupled to a shaft 112 and
butterflies 110 and 114 within inlet air lines 20 and 21
respectively. As is seen from Figure 7d, butterflies 110 and
114 are mounted on shaft 112 approximately 90~ to each other.
Additionally, each of the butterflies 110 and 114 may include
apertures 111 so as to provide a constant air flow to each of
the plenums while alternatingly augmenting pressure in each
of the plenums 22 and 23 when the appropriate butterfly is in
an open position.
Figure 7e represents still another embodiment of the
perturbation valve 86. In this embodiment an actuator 124 is
coupled to a shaft 122 which in turn is mounted to a spool
123. Spool 123 includes channels 118 and 120 which
communicate with air inlet lines 20 and Z1 respectively,
depending on the longitudinal position of the spool 123.
Each of the channels 118 and 120 is fluidly connected to main
channel 116 which is fluidly connected to main air line 84.
In this embodiment, perturbation valve 86 may achieve
alternatingly augmented air pressures in each of the plenums
by reciprocation of rod 122 from actuator 124. Additionally,
channels 118 and 120 may simultaneously be connected to main
air line 84 while activator 124 reciprocates spool 123 to
vary an amount of overlap, and thus air flow restriction,
between channels 118 and 120 with lines 20 and 21,
respectively, to achieve alternating augmented pressures in
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Ig
~ the plenum chambers 22 and 23, respectively. Actuator 124
may include any known means for achieving such reciprocation.
This may include but is not limited to pneumatic, hydraulic
or solenoid means.
Figures 8a-8d illustrate, respectively, plenum air
pressures in both the prior art melt-blown apparatus and in
the melt-blown apparatus according to the present invention.
As is seen in Figure 8a, a prior art air pressure in the
plenum chambers is essentially constant over time whereas in
Figures 8b and 8c the air pressure in the plenum chambers is
essentially augmented in an oscillatory manner. As an
example, the point at which the mean pressure intersects the
ordinate can be about 7 psig. Fig. 8d illustrates a prior
art air pressure in the vicinity of a prior art extrusion die
where air is turned on and off. In this case, the mean
pressure meets the ordinate at about 0.5 psig, for example.
The on/off control of prior art air flow as illustrated in
Fig. 8d is conducive to die clogging due to the intermittent
flow, as explained above. Additionally, the prior art on/off
air flow control illustrated in Fig. 8d (implemented by
Shambaugh) utilizes a lower average pressure, a lower
fre~uency and less pressure amplitude than the present
invention. Although the airflow characteristic illustrated
in Fig. 8a is not conducive to die clogging, no control may
be implemented over fiber crimping or web characteristics,
since the flow is virtually constant with respect to time.
Perturbation valve 86 may be placed in a multitude of
arrangements to achieve the alternatingly augmented flow in
plenum chambers 22 and 23 of the melt-blown apparatus
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Iq
according to the present invention. For example, Figure 6b
shows another embodiment according to the present invention.
In this embodiment, main air line 84 bifurcates constant air
flow to inlet air lines 20 and 21 while bleeding an
appropriate flow of air to perturbation valve 86 via bleeder
valve 90. Therefore, in this embodiment plenum ch~rh~rs 23
and 22 each include two inlets. The first inlet introduces
essentially constant flow from air inlet lines 20 and 21.
The second inlet of each plenum chamber introduces the
alternating flow to the chamber, thereby superimposing
oscillatory flow on the constant flow from lines 20 and 21.
The amount of air bled from bleeder valve 88 will control the
amplitude of the pressure augmentation for precise adjustment
of fiber characterization, as explained in greater detail
below, while perturbation valve 86 controls frequency.
Figure 6c represents yet another embodiment of the
present invention. In this embodiment, main air line 84
bifurcates into air lines 21 and 22 to supply air pressure to
plenum chambers 22 and 23. Additionally, an auxiliary air
line 92 bifurcates at perturbation valve 86. The
perturbation valve 86 then superimposes an alternatingly
augmented air pressure onto plenum chambers 22 and 23 to
achieve the oscillatory flow conditions in accordance with
the present invention. Here, pressure on the air line 92
controls the amplitude of air pressure perturbation, while
perturbation valve 86 controls perturbation frequency, as
explained above.
Figure 6d represents yet another embodiment of the
present invention. In this embodiment, main air line 84
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bifurcates into inlet air lines 20 and 21 which lead to
plenum chambers 22 and 23 respectively. The alternatingly
augmented pressure in plenum chambers 22 and 23 may be
provided by transducers 94 and 96 respectively. Transducers
94 and 96 are actuated by means of an electrical signal. For
example, the transducers may actually be large speakers which
receive an electrical signal to pulsate 180~ out of phase in
order to provide the alternating augmented pressures in
plenum chambers 22 and 23. However, any type of appropriate
transducer may create an augmented air flow by using any
means of actuation. This may include but is not limited to
electromagnetic means, hydraulic means, pneumatic means or
~ech~nical means.
As was discussed previously, all of the described
embodiments allow for the precise control of the perturbation
frequency and amplitude, preferably without interrupting the
operation of the fiber forming machinery. As will be
described below, this ability to precisely control the
perturbation parameters allows for relatively precise control
of the characteristics of the fibers and web formed thereby.
Typically, there are a wide variety of fiber parameters and
while a particular set of parameters may be desired for
making one type of non-woven material, such as filter
material, a different set of fiber parameters may be desired
for making a different type of material, such as for
disposable garments.
For example, in filter applications, the material is
preferably made of small diameter fibers. However, larger
diameter fibers may be desired for other materials.
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Furthermore, many end products consist of layers of material
having a variety of characteristics. For example, disposable
diapers generally consist of a wicking layer designed to move
moisture away from contact with the skin of an infant and to
s keep such moisture away. A middle, absorbent layer is used
to retain the moisture. Finally, an outer, barrier layer is
desired to prevent the absorbed moisture from seeping out of
the diaper. l~he fiber characteristics for each layer of the
diaper are different in order to achieve the specific
functions of each type of material. With the present
~hn;ques, various portions of the web can be formed by
varying the perturbation parameters with respect to time so
that each layer of the diaper is formed sequentially in one
non-woven web. Then the single web may be folded to provide
the layered finished material.
Sorbent structures for oil are described, for example,
in U.S. Patent No. 5,364,680 to Cotton which is incorporated
herein in its entirety by reference. For oil sorbent
applications it is desired to have a microfiber web that is
oleophilic andL characterized by a bulk in terms of density of
no more than about O.lg/cc, preferably no more than about
0.06g/cc. In general, lower densities are preferred but
densities belc,w O.Olg/cc are difficult to handle. Such webs
have the ability to soak up and retain oil in an amount of at
least about lO times the web weight, preferably at least
about 20 times the web weight. For certain applications it
may be desired to provide a treatment with one or more
compositions to increase wettability by aqueous liquids.
Such treatments are well known and described, for example, in
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coassigned U.S. Patent No. 5,057,361 which is incorporated
herein in its entirety. Prior attempts to produce such webs
by meltblowing techniques, while resulting in useful fine
fiber materials, have lacked the desirable bulk and
absorbency due to the manner in which the air streams applied
the still tacky fibers to the forming ~urface.
Thus, with precise control of the fiber and material
characteristics by control of the perturbation
characteristics, a great degree of flexibility is possible in
the formation of non-woven webs. This control, in turn,
allows for greater efficiency and the ability to design a
greater range of materials which may be produced with little
interruption of the production process.
one shortcoming of prior art melt-blown equipment is the
relative inability to precisely control the diameter of
fibers produced thereby. The formation of materials with
particular characteristics often requires precise control
over the diameter of the fibers used to form the non-woven
web. With the perturbation technique of the present
invention, it is possible to provide for much less variation
in fiber diameter than was previously possible with prior art
t~chn;ques.
Figures 9 and 10 illustrate fiber diameter distribution
for samples taken from prior art melt-blown techniques and
the melt-blown fiber producing technique according to the
melt-blown apparatus embodiment of Figure 6c. Figure 9 shows
a diameter distribution in accordance with the prior art.
Figure 10 represents a fiber diameter distribution chart for
melt-blown fibers made in accordance with the inventive
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t~c-hn; ~ue. The fiber distribution in Figure 10 illustrates a
fiber diamete:r sample which has a distribution that is
centered on a peak between about 1 and 2 microns. Here, the
narrow band o:E fiber distribution achieved by the
S perturbation ]nethod and apparatus illustrates the great
extent to which fiber diameter may be controlled by only
varying perturbation frequency or amplitude.
Figure l:L represents the Frazier porosity of a non-woven
melt-blown web made in accordance with the present invention
as a function of perturbation frequency in the plenum
chambers 22 and 23. The Frazier Porosity is a stA~rd
measure in the non-woven web art of the rate of airflow per
square foot through the material and is thus a measure of the
permeability of the material (units are cubic feet per square
foot per minut:e). For all samples the procedure used to
determine Frazier air permeability was conducted in
accordance wit:h the specifications of method 5450, Federal
Test Methods Stand No. 191 A, except that the specimen sizes
were 8 inches by 8 inches rather than 7 inches by 7 inches.
The larger size made it possible to ensure that all sides of
the specimen extended well beyond the retaining ring and
facilitated cl.amping of the specimen securely and evenly
across the ori.fice.
As is ill.ustrated in Figure 11, the Frazier porosity
generally falls first to a minimum and then increases with
perturbation frequency from a steady state to approximately
500 hertz. Th.us, one can observe that to make a material
with a desired Frazier porosity with the present invention,
it is only necessary to vary the oscillation frequency
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(and/or the amplitude). With prior art techniques, changes
in porosity often required changes to the die or starting
materials or the duplication of machinery. Thus, with the
present t~chn;ques, it is possible to easily change the
porosity of a material once a run is completed; it is only
necessary to adjust the perturbation frequency (or
amplitude), which can easily be done with simple controls and
without stopping production. Therefore, the melt-blowing
apparati according to the present invention may quickly and
easily manufacture filtering materials of varying porosity by
simply changing perturbation frequency.
Figure 12 illustrates a plot of hydrohead as a function
of perturbation frequency. The Hydrohead Test is a measure
of the liquid barrier properties of a fabric. The hydrohead
test determines the height of water (in centimeters) which
the fabric will support before a predetermined amount of
liquid passes through. A fabric with a higher hydrohead
reading indicates it has a greater barrier to liquid
penetration than a fabric with a lower hydrohead. The
hydrohead test is performed according to Federal Test
Standard No. l91A, Method 5514. Generally, hydrohead first
increases and then decreases with increasing perturbation
frequency in a frequency range of approximately 75 hertz to
525 hertz. Since perturbation frequency directly affects
hydrohead, an appropriate adjustment of the perturbation
valve 86 provides the type of barrier to liquid required by a
particular application. Perturbation frequency may be used to
vary hydrohead to suit the particular use f or the material.
ExamPles
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The following examples provide a basis for demonstrating
the advantages of the present invention over the prior art in
the production. of melt-blown, coform and spunbond webs and
materials. These examples are provided solely for the
purpose of illustrating how the methods of the present
invention may be implemented and should not be interpreted as
limiting the scope of the invention as set forth in the
claims.
Exam~le 1
Process Condition
Die Tip Geometry: Recessed
Die Width = 20"
Gap = 0.090"
30 hpi
Primary Airflow: Heated (~608~F in heater)
488 scfm
Pressure PT = 6.6 psig
Auxiliary Airflow: Unheated (ambient air temp.)
60 scfm
Inlet Pressure = 20 psig
Polymer: Copolymer of butylene and propylene
polypropylene* - 79%
polybutylene - 20%
blue pigment - 01%
*800 MFR polypropylene coated with peroxide -
final MFR ~ 1500
Polymer Throughput: 0.5 GHM
Melt Temperature: 470~F
Perturbation Frequency: 0 Hz, 156 Hz, 462 Hz
- Basi-; Weight: 0.54 oz/yd2
Form:ing Height: 10"
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Test Results
Barrier
Table 1-1
Perturbation Freauency 0 Hz 1~6 Hz 462 Hz
Frazier Porosity 45.18 35.70 65.89
(cfm/ft2 )
Hydrohead (cm) 86.40 103 74.60
In this example, the melt-blown process was configured
as described above and corresponds to the embodiment shown in
FIG. 6c, in which the primary airflow is supplemented with an
auxiliary airflow. In the example, the unit hpi
characterizes the number of holes per inch present in the
die. PT is defined as the total pressure measured in a
stagnant area of the primary manifold. GHM is defined as the
flow rate in grams per hole per minute; thus, the GHM unit
defines the amount, by weight, of polymer flowing through
each hole of the melt-blown die per minute. As discussed
above, Frazier Porosity is a measure of the permeability of
the material (units are cubic feet per minute per square
foot). The hydrohead, measured as the height of a column of
lS water supported by the web prior to permeation of the water
into the web, measures the liquid barrier qualities of the
web.
The above configuration and results provide a baseline
comparison of a typical melt-blown production run with no air
perturbation (a frequency of perturbation of 0 Hz) with runs
conducted with perturbation frequencies of 156 and 462 Hz.
As can be seen from Table 1-1, in general, the barrier
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characteristics of materials made using perturbed airflows
improve with increasing perturbation frequency. Thus, by
merely varying the perturbation frequency, a relatively easy
process, materials or webs with desired barrier
characteristics may be made without major changes to the
process conditions. This ability to adjust barrier
properties was not previously possible in the prior art
without substantial changes to the process conditions which
required significant time and effort. As can be seen there
is an initial decrease in Frazier Porosity (which represents
an decrease in the permeability of the web or material to
air) at the 156 Hz perturbation frequency. Similarly, at the
156 Hz frequency, there is an increase in the supported
hydrohead. Thus, at the 156 Hz frequency, the web material
produced is a ~ore effective barrier. At the 462 Hz
perturbation frequency, the Frazier Porosity has increased
and the Hydroh,ead has decreased from both the 0 Hz (prior
art) and 156 Hz production runs. Thus, at the higher
perturbation frequency, the web material is a less effective
barrier, but is more suitable for use as an absorbent or
wicking material.
The change in barrier properties with respect to change
in perturbation frequency is also demonstrated in Figures 11
and 12 (for different process conditions from those of
Example 1). As Figure 11 shows, there is an initial drop in
Frazier Porosifcy as the process is changed from no
perturbation to a perturbation frequency between 1 and 200
Hz. As the perturbation frequency is increased above about
200 Hz, the Frilzier Porosity increases, until the original 0
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~ Hz Frazier Porosity is exceeded between about 300 to 400 Hz.
Above 400 Hz, the Frazier Porosity increases relatively
steeply with increasing perturbation frequency. Similarly,
referring to Figure 12, supported hydrohead initially
S increases between about 1 to 200 Hz perturbation frequency.
Then the hydrohead steadily decreases with increasing
perturbation frequency until the supported hydrohead at
between about 400 to 500 Hz is less than that at the 0 Hz
(steady flow) frequency. Thus, as these Figures demonstrate,
with no variation in the basic process conditions such as
polymer type, flow conditions, die geometry, aside from a
simple change in the frequency of perturbation of the
airflow, a wide variety of different web materials can be
made having desired barrier properties. For example, by
lS merely setting the perturbation frequency in the 100 to 200
Hz range, with all of the other process conditions remaining
unchanged, a more effective barrier material can be made.
Then, if less effective barrier material was desired, the
only process change necessary would be an increase in the
perturbation frequency, which could be accomplished with a
simple control and without necessitating the interruption of
the production line. In prior art techniques, alteration of
the production run barrier properties may require substantial
changes in the process conditions, thereby requiring a
2s production line shut-down to make the changes. In actuality,
such changes are not typically made on a given machine;
multiple machines typically produce a single type of web
material (or an extremely narrow range of materials) having
desired properties.
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Fxam~le 2
Process C'onditions
Die Tip Geometry: Recessed
Die Width = 20~'
Gap = O.O9o"
30 hpi
Primary Airflow: Heated (~608~F in heater)
317 scfm
Pressure PT = 2.6 psig
Auxiliary Airflow: Unheated (ambient air temp.)
80 scfm
Inlet Pressure = 20 psig
~oly~: ~lg~ MF~ PR*
*e.g. 800 MFR polypropylene coated with peroxide -
final MFR ~ 1500
Polymer Throughput: 0.5 GHM
Melt Temperature: 470~F
Perturbation Frequency: 0 Hz (control), 70 Hz
Basis Weight: 5 oz/yd2
Forming Height: 10"
Test Results
In this example the bulk of the web made using a 70
Hz perturbation frequency was compared to a control web (0 Hz
perturbation frequency).
Control - 0.072" (thickness)
70 Hz - 0.103"
Thus, it can be seen that using a modest 70 Hz
perturbation frequency results in a 43% increase in bulk over
- the prior art. Increased bulk is often desired in the final
web or material because the increased bulk often provides for
better feel and absorbency.
Furthermore, with respect to desired texture or
appearance, the use of the perturbation techniques of the
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present invention allows for custom texture or appearance
control. Referring to the photographs of Figures 13 and 14,
Figure 13 represents the appearance of the web produced with
the O Hz perturbation frequency while the web of Figure 14
represents that produced using the 70 Hz perturbation
frequency. As can be seen from the Figures, the web of
Figure 14 has a leather like appearance and texture which is
not present in the web of Figure 13. Thus, to the extent
such appearance and texture is desired, the techniques of the
present invention allow for added control and variety in
production of various types of webs having such
characteristics.
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Examples 2A - 2I
Process Conditions
Die Tip Geometry: Die Width 100 in
30 hpi
Primary Airflow: 1500-1800 scfm (general range)
2A 1800 scfm
2B 1750 scfm
2C 1750 scfm (per bank)
2D 1750 scfm (per bank)
2E 1800 scfm
lS 2F 1800 scfm
2G 1600 scfm
2H 1500 scfm
2I 1750 scfm
Primary Air Temp: 575~F - 625~F (general range)
2A 625~F
2B 600~F
2C 600~F (per bank)
2D 600~F (per bank)
2E 625~F
2F 575~F
2G 575~F
2H 575~F
2I 600~F
Perturbation Fretluency: 75 Hz - 200 Hz
Polymer: PF-015 - polypropylene
Throughput: 4.8PIH
Melt Temperature: 600~F
This series of examples illustrates the high bulk and
oil capacity results obtainable with meltblown webs in
accordance with the present invention. Using an arrangement
as shown in Figure 6B, meltblown webs were produced using the
processing conditions shown. These materials were tested for
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3~-
bulk and oil capacity, and in addition, the roll samples were
tested for oil absorption rate.
Qil Absorption Tests
s
Oil absorption test results were obtained using a test
procedure based on ASTM D 1117-5.3. Four square inch samples
of fabric were wieghed and submerged in a pan cont~;n;ng oil
to be tested (white mineral oil, +30 Saybolt color, NF grade,
80-90 S.U. viscosity in the case of roll samples and 10W40
motor oil in the case of hand samples) for two minutes. The
samples were then hung to dry (20 minutes in the case of roll
samples and 1 minute in the case of hand samples). The
samples were weighed again, and the difference calculated as~5 the oil capacity.
The variation in results for bulk and oil capacity
between the rolled samples and hand samples results from
compression in the rolled configuration. In both cases the
improvement o~ the invention is apparent. Since the control
was not perturbed, it was compressed as formed and was
relatively unaffected by being formed into a roll.
Oil Rate Tests
2s Oil rate results were obtained in accordance with TAPPI
St~n~rd Method T 432 su-72 with the following changes:
To measure oil absorbency rate, 0.1 ml of white mineral
oil is used as the test liquid.
Three separate drops are timed on each specimen, rather
than just one drop.
Five specimens are tested from each sample rather than
ten, i.e. a total of 15 drops is timed for each sample
instead of ten drops.
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Oilsorb Data
Table 2-1 - roll sa~les
ExamplePerturbation Bulk Density Oil Oil
Conditions inches gm/cm3 Capacity Rate
g/g sec
2A OHz 0.1294 0.05711.91 1.847
Control 1 Bank (18.21*)
2B 200Hz 0.1678 0.04712.84 1.673
1 Bank
2C200Hz/150Hz 0.1537 0.05011.25 1.805
2 Bank
2D OHz 0.0987 0.0759.79 2.200
Control 2 Bank
*Test method for hand samples - Table 2-2
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Example 3
Process Conditions
Die ~rip Geometry: Recessed
Gap = 0.090~'
30 hpi
Primary Airflow: Heated (~608~F in heater)
426 scfm
Pressure PT = 5 psig
Auxiliary Airflow: Unheated (ambient air temp.)
80 scfm
Inlet Pressure = 20 psig
Polymer: High MFR PP*, 1% Blue pigment
*e.g. 800 MFR polypropylene coated with peroxide --
final MFR ~ 1500
Polymer Throughput: 0.6 GHM
Melt Temperature: 480~F
Perturbation Fre~uency: 0 Hz (control), 192 Hz,
436 Hz
Basis Weight: 0.54 oz/yd2
Forming Height: 10"
Test Results
Softness - Cup Crush -- 0 Hz - 1352
192 Hz -- 721
Cup Crush is a measure of softness whereby the web is
draped over the top of an open cylinder of known diameter, a
rod of a diameter slightly less than the inner diameter of
the cup cylinder is used to crush the web or material into
the open cylinder while the force required to crush the
material into the cup is measured. The cup crush test was
used to evaluate fabric stiffness by measuring the peak load
required for a 4.5 cm diameter hemispherically-shaped foot to
crush a 22.9 cm by 22.9 cm piece of fabric shaped into an
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approximately 6.5 cm diameter by 6.5 centimeter tall inverted
cup while the cup shaped fabric was surrounded by an
approximately 6.5 cm centimeter diameter cylinder to maintain
a uniform deformation of the cup shaped fabric. The foot and
cup were aligned to avoid contact between the cup walls and
the foot which could affect the peak load. The peak load was
measured while the foot was descending at a rate of about
0.64 cm/s utilizing a ~odel 3108-128 10 load cell available
from the MTS S~ystems Corporation of Cary, North Carolina. A
total of seven to ten repetitions were performed for each
material and then averaged to give the reported values.
The lower cup crush number achieved by the material made
using the l9Z Hz perturbation frequency indicates that the
material made thereby is softer. Subjective softness tests
such as by hand or feel also confirm that the material made
by using the 1'32 Hz perturbation frequency is softer than
that made using the prior art techniques.
Strenqth
Table 3-1
Perturbation 0 Hz 192 Hz 436 Hz
Frequency
MD Peak I,oad (lbs) 1.989 2.624 2.581
MD Elongation (in) 0.145 0.119 0.087
CD Peak Load (lbs) 1.597 1.322 1.743
CD Elongation (in) 0.202 0.212 0.135
As can be seen from Table 3-1, the machine direction
strength increases for runs in which the perturbation
frequency is greater than 0 Hz. In the production runs of
Example 3, the direction of perturbation was generally
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parallel to the machine direction (MD). Applicants believe
that the increased strength in MD is due to more controlled
and regular overlap in the lay-down of the web on the
substrate as the fibers oscillate as a result of the
S perturbation. A similar result is demonstrated in Figure 15
which is a graph showing the variation of Peak Load in MD and
CD as a function of perturbation frequency. As is seen in
the Figure 15, strength in the MD increases as the
perturbation frequency increases. Typically, CD strength
r~;n~ relatively constant (with slight variations)
regardless of perturbation frequency. It is applicants'
belief that increases in CD strength can be achieved by
varying the angle of the perturbation relative to the MD.
Thus, by having the perturbation occur at some angle between
1~ parallel to MD and perpendicular to MD, CD strength can be
improved as well as MD strength.
Barrier
Table 3-2
Perturbation Frequency 0 Hz 192 Hz
Frazier Porosity 31.5 22.3
(cfm/ft2 )
Hydrohead (cm of H2O) 90.8 121.6
Equiv. Pore Diameter (~ 13.2 10.8
m)
As Table 3-2 demonstrates, and as was demonstrated in
Example 1, at relatively low perturbation frequencies
(between about 100 to 200 Hz) the barrier properties of a web
produced thereby increase. This result is explained by the
measured Equivalent Circular Pore Diameter in the 0 Hz case
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37
and the 192 H~ case. As is shown in Table 3-2, the pore size
for web material produced using a 192 Hz perturbation
frequency is 2.4 microns less than that for a material
produced with no perturbation. Thus, since the pores in the
material are smaller, the permeability of the material is
less and the barrier properties are greater.
~mple 4
Process Conditions
Die Tip Geometry: Recessed
Die Width = 20"
Gap = 0.090
30 hpi
Primary Airflow: Heated (~608~F in heater)
422 scfm
Pressure PT = 5 psig
Auxiliary Airflow: Unheated (ambient air temp.)
40 scfm
Inlet Pressure = 15 psig
Polymer: Copolymer of butylene and propylene
polypropylene* - 79%
polybutylene - 20%
blue pigment - 01%
*800 MFR polypropylene coated with peroxide -
final MFR ~ 1500
Polymer Throughput: 0.6 GHM
Melt Temperature: 471~F
Perturbation Frequency: 0 - 463 Hz
Basis Weight: 0.8 oz/ydZ
Forming Height: 12"
Test Results
Barrier
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38'
Table 4-1
Perturbation Frequency 0 Hz 305 Hz 463 Hz
Frazier Porosity 46.27 26.85 59.34
( (cfm/ft2 )
once again, it can be seen that the porosity of the web
material initially decreases when the airflow is perturbed.
However, as the perturbation frequency increases, the
porosity also increases. The results in Example 4 agree with
the other barrier property results from the other examples
and with the results reported in Figures 11 and 12.
Although the above referenced examples utilize a
polypropylene or mixture of high melt flow polypropylene and
polybutylene resins for non-woven web production, a multitude
of thermoplastic resins and elastomers may be utilized to
create melt-blown non-woven webs in accordance with the
present invention. Since it is the structure of the web of
the present invention which is largely responsible for the
improvements obtained, the raw materials used may be selected
lS from a wide variety. For example, and without limiting the
generality of the foregoing, thermoplastic polymers such as
polyolefins including polyethylene, polypropylene as well as
polystyrene may be used. Additionally, polyesters may be
used including polyethylene, terepthalate and polyamides
including nylons. While the web is not necessarily elastic,
it is not intended to exclude elastic compositions.
Compatible blends of any of the foregoing may also be used.
In addition, additives such as processing aids, wetting
agents, nucleating agents, compatibilizers, wax, fillers, and
the like may be incorporated in amounts consistent with the
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~9
fiber forming process used to achieve desired results. Other
fiber or filanent forming materials will suggest themselves
to those of ordinary skill in the art. It is only essential
that the composition be capable of spinning into filaments or
s fibers of some form that can be deposited on a forming
surface. sinc:e many of these polymers are hydrophobic, if a
wettable surface is desired, known compatible surfactants may
be added to the polymer as is well-known to those =skilled in
the art. Such surfactants include, by way of example and not
limitation, anionic and nonionic surfactants such as sodium
diakylsulfosuccinate (Aerosol OT available from American
Cyanamid or Triton X-100 available from Rohm ~ Haas). The
amount of surfactant additive will depend on the desired end
use as will also be apparent to those skilled in this art.
Other additives such as pigments, fillers, stabilizers,
compatibilizers and the like may also be incorporated.
Further discussion of the use of such additives may be had by
reference to, for example, U.S. Patent Nos. 4,374,888 issued
on Bornslaeger on February 22, 1983, and 4,070,218 issued to
Weber on January 24, 1978
Additionally, a multitude of die configurations and die
cross-sections may be utilized to create melt-blown non-woven
webs in accordance with the present invention. For example
orifice diameters of 20 to 50 holes per inch (hpi) are
preferred, however, virtually any appropriate orifice
diameter may be utilized. Additionally, star-shaped,
elliptical, circular, square, triangular, or virtually, any
other geometrical shape for the cross-section of an orifice
may be utilized for melt-blown non-woven webs.
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Coform ApPlications
Applicant hereby incorporates by reference U.S. Patent
No. 4,818,464, issued to Lau on April 4, 1989 which discloses
coform methods of polymer processing by combining separate
s polymer melt streams into a single polymer melt stream for
extrusion through orifices in forming non-woven webs.
Additionally, applicant hereby incorporates by reference U.S.
Patent No. 4,818,464, issued to Lau on April 4, 1989 which
discloses the introduction of super absorbent material as
lo well as pulp, cellulose, or staple fibers through a
centralized chute in an extrusion die for combination with
resin fibers in a non-woven web. Referring now to Figure 16,
a description of the coform process is provided. In essence,
a coform die 170 is basically a combination of two melt-blown
die heads 173, 175. Air flows 176 and 178 are provided
around die 172 and air flows 180 and 182 are provided around
die 174. A chute 184 is provided through which pulp, staple
fibers, or other material may be added to vary the
characteristics of the resulting web. Since any of the above
described techniques to vary the airflow around a melt-blown
die may be used in the coform technique, specific
descriptions of all of the valving techniques will not be
repeated. However, it will be apparent to one skilled in the
art, that to vary the four air flows present in the coform
die, the equipments used to control the perturbation of the
air flows will have to be doubled.
In the coform technique, there are a variety of possible
perturbation combinations. The most basic is to perturb each
side of a given die 172 or 174 just as described above with
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Lll
respect to the melt--blown techniques (basically, air flows
176 and 178 a]ternating with each other and the same for
airflows 180 and 182). However, it is also possible to
perturb the air flows around die 172 relative to those around
die 174. Thus" air flows 176 and 182 could be perturbed in
phase with each other, but out of phase with air flows 178
and 180 to achieve a desired characteristic in the fibers or
web. To achieve a different effect it may be desirable for
air flows 176 and 180 to be perturbed in phase with each
other, but out. of phase with air flows 178 and 182. It
should be read~ily apparent that with four air flows, many
perturbation combinations are possible, all of which are
within the scope of the present invention. For example, a
centralized chute may be located between the two centralized
air flow for introducing pulp or cellulose fibers and
particulates. Such a centralized location facilitates
integration of the pulp into the non-woven web and results in
consistent pulp distribution in the web.
Example 5
As described above with reference to Figure 16, coform
materials are essentially made in the same manner as melt-
blown materials with the addition of a second die. Thus,
there are two airflows around each die, for a total of four
air flows, which may be perturbed as described above.
Additionally, there is typically a gap between the two dies
through which pulp or other material may be added to the
fibers produced and incorporated into the web being formed.
The following example utilizes such a coform-form head, but
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otherwise, with respect to the airflow perturbation, conforms
to the previous description of the melt-blown process.
Process Conditions
Die Tip Geometry: Recessed
Gap = 0.070"
Die Width = 20"
Primary Air Flow: 350 scfm per bank (20" bank)
Primary Air Temperature: 510~F
Auxiliary Air Flow: 40 scfm per MB bank
Polymer: PF-015 (polypropylene)
Polymer Ratio: 65/35
Basis Weight: 75 gsm (2.2 osy)
Test Results
Table 5-1
Perturbation 0 Hz 67 Hz 208 Hz 320 Hz
FrequencY
MD Peak Load 1.578 1.501 1.67 2.355
MD Elongation (%) 23.86 22.48 24.21 20.23
CD Peak Load 0.729 0.723 0.759 0.727
CD Elongation (%) 49.75 52.46 58.08 71.23
Cup Crush (gm/mm) 2518 2485 2434 2281
From table 5-1, it can be seen that the results
generally agree with those shown in the melt-blown examples.
Generally, with increasing perturbation frequency, aligned
along the MD, MD strength increased while CD strength remains
about the same. Similarly, the softness, measured as cup
crush, generally increases as the perturbation frequency
increases (a lower cup crush value indicates increased
softness). Thus, this example shows that the techniques
previously described can be applied to coform-forming
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technology to achieve the process and material control by
simple adjustnlent of the perturbation frequency in the same
manner as the~ were applied to the melt-blown process~
S~unbond Applications
Figures 17a through 17d represent various ~hoA; m~nts
which utilize alternatingly augmented air pressure in plenum
chambers 58 and 62 of a standard fiber draw unit, as
illustrated i~ Figure 3b. In a manner similar to that of the
valving arrangements for the melt-blown unit, the fiber draw
unit may receive alternatingly augmented air pressure into
plenum chambers 62 and 58 via lines 72 and 74, respectively,
through the bifurcation of main air lines 66 via perturbation
valve 86. Alternatively, as is illustrated in Figure 17b,
main air line 66 may be bifurcated by valve 86 into supply
lines 130 and 128 with a third bleeder portion supplying
perturbation valve 86. While lines 128 and 130 receive air
from bleeder valve 88 at a relatively constant pressure,
perturbation valve 86 receives bleed air from bleeder valve
88 and perturbs that air to create an oscillatory pressure
which is then superimposed onto supply lines 128 and 130 to
create alternatingly augmented pressure in lines 74 and 72
for supply to plenum chambers 58 and 62, respectively. In
yet another embodiment illustrated in Figure 17c, main supply
line 66 bifurcates into lines 128 and 130. This embodiment
utilizes an auxiliary air supply 92 which is perturbed by
valve 86 superimposed onto the constant air pressure of lines
128 and 130 to create an alternatingly augmented air flow
supply in lines 72 and 74 so as to supply air plenum chambers
62 and 58 of the fiber draw unit, respectively. Finally,
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Figure 17d represents still another embodiment of the present
invention which utilizes a perturbation valve 86 which
provides an alternatingly perturbing air flow prior to the
bifurcation of the main air supply line.
Figures 18a through 18f illustrate various locations for
secondary perturbation jets which may be used with a stAn~rd
prior art fiber draw unit such as the one illustrated in
Figure 3b to create the proper flow conditions for increasing
desirable properties of fibers made in accordance with the
present invention. For example, Figure 18a illustrates the
tail pipe 56 of a fiber draw unit which utilizes secondary
perturbation jets 132 and 134. As described above, these
secondary perturbation jets impose alternating augmented flow
in a direction which is perpendicular to the main air flow
through the tail pipe 56 of the present invention. This
orthogonal relationship between primary and secondary air
flow increases both the degree and order of turbulence of the
air flow in the vicinity of the tail pipe 56.
As illustrated in Figure 18b, tail pipe 56 may also
include alternatingly, or otherwise activated, co-flowing
jets 136 and 138 create turbulent flow in accordance with the
present invention near the tail pipe of the fiber draw unit.
Figure 18c illustrates secondary perturbing jets 142 and 140
disposed near a top portion of the fiber draw unit upstream
of plenum chamber inlets 60 and 64. Figure 18d represents
yet another embodiment of the present invention that utilizes
alternatingly augmented flow through Coanda nozzles 144 and
146 at an exit of tail pipe 56 to create turbulent air flow
in the vicinity of tail pipe 56. Additionally, Figure 18e
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illustrates ~oAn~-like nozzles 190 and 192 disposed at mid
portion 54 of the fiber draw unit. Finally, Figure 18f
illustrates jets at inlet portions 48 and 50 of the fiber
draw unit. Each of those jets illustrated in Figures 18a
S through 18f may alternatingly perturb air flow through the
fiber draw unit in addition to any perturbation which may be
implemented upstream of the jets. Additionally, each of the
jets illustrated in Figures 18a-18f may also be implemented
without additional perturbation means upstream therefrom.
Figure 19 represents yet another embodiment of the
present invention. The alternatingly augmented pressure in
plenum chambers 147 and 150 may be provided by transducers
148 and 152 via inlets 150 and 154, respectively.
Transducers 148 and 152 are preferably actuated by means of
an electrical signal. For example, the transducers may
actually be large speakers which receive an electrical signal
to activate 0~ to 180~ out of phase in order to provide the
alternating augmented pressures in plenum chambers 147 and
150. However, any type of appropriate transducer may create
an augmented air flow by using any means of actuation. This
may include but is not limited to electromagnetic means,
hydraulic means, pneumatic means or mechanical means.
Figures 20a and 20b illustrate yet another embodiment of
the present invention wherein hot and cold jets are
alternatingly used to increase fiber crimp. Referring to
Figure 20a, fiber draw unit 69 includes secondary
perturbation jets 156 and 158. Oscillatory jet 156 supplies
hot air whereas oscillatory air jet 158 supplies cold air.
Alternatively, Figure 20b illustrates perturbation air jets
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164, 166, which alternatingly supply hot air to the primary
air flow and fiber bundle exiting from the tail pipe of the
fiber draw unit. Both Figures 20a and 20b illustrate the
fiber bundle deflection upon application of secondary
perturbation. This secondary perturbation creates fiber
bundle deflection and heating or cooling effects which lead
to added crimp of the fibers being distributed within a web
on an endless belt. The temperature varied perturbation
provides for additional parameters which may be varied and
controlled during production. The jets may be symmetrically
or asymmetrically oriented to achieve desired fiber
characteristics, namely fiber crimp. As with perturbation
frequency and amplitude, the temperature of the air may be
controlled without interruption of the production process,
although this control is more complex. Thus, materials having
different properties can be made without requiring the line
to be substantially delayed and without the need for
additional equipment. This technique may be applied to
processes utilizing the homopolymer fibers as well as to
multi-component fibers and materials.
Figures 21(a) through 21(d) represent yet another
embodiment of the present invention, wherein a stAn~Ard fiber
draw unit includes secondary perturbation jets at an exit of
the tail pipe thereof wherein at least one bank of
2~ perturbation jets is rotated with respect to the machine
direction to create a crimp or fiber movement in a cross
direction with respect to travel of the belt within the fiber
draw unit apparatus to increase tensile strength in the cross
direction of the non-woven web. For example, as shown in
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Figure 21(a), jet bank 162 is disposed at an angle with
respect to the machine direction while jet bank 160 is
essentially parallel to the machine direction. Figure 21(b)
illustrates jet: banks 202 and 200 which are both disposed at
s an angle with respect to the machine direction but oppose one
another. Furthermore, Figure 21(c) illustrates yet another
configuration f.or jet orientation. There, jet banks 202 and
204 are each rotated with respect to the machine direction
and face in the same direction. Finally, Figure 21(d)
illustrates opposing jet banks 208 and 210.
Finally, Figure 15 illustrates the peak load of a non-
woven web sampl.e as a function of perturbation frequency of
secondary perturbation jets for the embodiment utilized in
Example 6. As is illustrated in the chart, machine direction
strength of the. non-woven web increases with increasing
perturbation frequency. In the process run used to generate
the data for Fi.gure 15, the direction of perturbation was
parallel to the machine direction, as illustrated in Figure
21(d). Furthermore, by varying the direction of the
perturbation jets or airstreams relative to the machine
direction, it is possible to increase cross-direction
strength.
The following examples show the application of the
techn;ques of the present invention to the production of
fibers and non-woven webs in the spunbond process. The
processes and apparati are described using terms and units
well known in the prior art. The initial example describes
fibers and a web formed using prior art techniques to provide
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a basis for ~ o~ison for fibers and webs formed using the
tPchn; ~ues of the present invention.
Exam~le 6
The following examples show the application of
s perturbing airflows to the spunbond process. In this
particular example, the perturbing airflows were applied to
the air stream carrying the fibers at the exit of the fiber
draw unit (FDU), which corresponds to the embodiment shown in
Figure 21(d). However, as was previously described, the
process is equally applicable to perturbing the airflow in
the FDU itself, or by application of auxiliary air, or
bleeding airflow, at the manifolds prior to the FDU.
Process Conditions
FDU Draw Pressure: 4 psi
Draw unit width = 14"
Polymer Throughput: 0.5 GHM
Polymer: 3445 Polypropylene*
*Exxon brand 3445 polYmer~ peroxidè coated
Melt Temperature: 430~F
Auxiliary Flow: 40 scfm
Basis Weight: 0.5 osy (17 gsm)
Test Results
Table 6-1
Perturbation Frequency O 67 227 338 463
(Hz)
MD Peak Load (lb) 0.921 1.687 1.844 2.108 2.452
CD Peak Load (lb) 0.824 0.645 0.462 0.586 0.521
MD Elongation (%) 23.85 52.79 18.03 11.08 23.05
CD Elongation (~) 60.84 46.5 42.31 38.76 57.10
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Total Tensile 1.24 1.81 1.90 2.19 2.51
(MD2 +CD2 ) ~
As can be~ seen from the Table, the use of perturbing
airflows in the spunbond process provides substantially
increased MD strength (in this example, the perturbing
airflows were aligned with the machine direction). As was
the case with the melt-blown process with perturbed airflows,
the CD strength remained relatively constant after a slight
decrease. As the total tensile strength calculation
indicates, however, the overall strength of the web is
increased by the application of the perturbing airflows.
Once again, as was demonstrated with the use of perturbation
of airflow in the melt-blown process, the use of airflow
perturbation provides for a range of selectable
characteristics in the final web material, merely by
adjusting the perturbation frequency. This ease of process
control is not currently available in the spunbond art.
Typically, to prepare spunbond web materials with varying
properties, the processing equipment must be completely shut
down and the process conditions changed, such as by changing
the die or other substantial change to the equipment. Though
the present invention does not preclude those processes, with
the present process, such changes to the web material may be
accomplished on the fly by merely changing the perturbation
frequency while the other process conditions remain constant.
This feature of the present invention allows for much greater
flexibility and efficiency in the operation of spunbond
equipment.
~ nle 7
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In this example, the spunbond process was adapted, using
the te~hn;ques disclosed herein to provide for perturbing
airflows disposed at the exit of the FDU. For the purposes
of this example, the perturbing airflows were not disposed
S immediately opposite each other, as was the case in Example
6, but rather one bank of auxiliary air nozzles was directed
parallel to the machine direction, while the other was
directed at an angle with respect to the cross direction to
provide a slight cross direction trajectory (as shown
schematically in Fig. 21(a)).
Process Conditions
Fiber Draw Pressure: g psi
Polymer Throughput: 0.75 GHM
Basis Weight: 1.0 oz/ydZ
Polymer: 3445 Polypropylene*
*Exxon brand 3445 polymer, peroxide coated
Melt Temperature: 450~F
Auxiliary Air Flow: 75 scfm
~est Results
Table 7-1
Perturbation FrequencY 0 115 195 338 500
(Hz)
MD Peak Load (lb) 12.00 19.96 21.00 21.13 20.00
MD Elongation (%) 34.75 37.36 38.36 39.77 37.48
CD Peak Load (lb) 8.965 11.30 10.53 10.34 12.69
CD Elongation (%) 40.10 49.78 52.84 43.18 47.94
Once again, it can be seen that by simply varying the
perturbation frequency of the airflow, a variety of changes
can be effectuated in the final non-woven web. Thus, to the
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extent that a material having different characteristics is
desired, varying the perturbation frequency of the perturbing
airflow can re~sult in substantial changes in the final non-
woven material. This change represents a substantial
departure from prior art spunbond techniques in which other
process condit:ions, which are much more difficult to achieve,
must be varied to vary the characteristics of the final
material.
As is seen from the above Examples 1-7 of meltblown,
coform and spwlbond non-wovens made in accordance with the
present invention, the techniques of the present invention
allow for the i-ormation of a non-woven webs of various
characteristics with relatively simple adjustments to process
controls. Whi]e some of the differences can be attributed to
the lay-down of the fibers on the forming surface,
prel;~; n~ry investigation indicates that the present
inventive techniques also result in flln~ental changes to
the fibers formed thereby. Referring now to Figures 22 and
23, there are shown X-Ray diffraction scans of a meltblown
fiber made according to prior art techniques (Figure 22) and
a meltblown fiber made in accordance with the present
invention (Figure 23) both otherwise under identical
processing conditions and polymer type. As can be seen from
comparison of Figures 22 and 23, the X-Ray scan of the
meltblown fiber made with the inventive techniques has two
peaks, while that of the prior art meltblown fiber has
several peaks. It is believed that the differences observed
in Figure 23 result from the presence of smaller crystallites
in the fiber, which possibly result from better quenching of
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the fiber during formation. In summary, these X-Ray
diffraction scans indicate that the fibers made in accordance
with the present t~r-hn; que are more amorphous than prior art
fibers and may have a broader bonding window than fibers made
in accordance with prior art techniques.
Additional evidence of the believed characteristic
differences between fiber made in accordance with the present
invention and those made in accordance with the prior art are
shown in Figure 24. Figure 24 is a graph showing the results
of a Differential Scanning Calorimetry (DSC) test conducted
on a prior art meltblown fiber (indicated by the dashed line
on the graph) and with a fiber made in accordance with the
present t~chn; ques (the solid line). The test basically
observes the absorbance or emission of heat from the sample
l~ while the sample is heated. As can be seen from Figure 24,
the DSC scan of the prior art fiber is significantly
different from that of the present fiber. A comparison of
DSC scans shows two main features in the present fiber that
do not appear in the prior art fiber: (1) heat is given off
from 80-110~C (apparent exotherm) and (2) a double melting
peak. It is believed that these DSC results confirm that the
present formation techniques produce fibers having
significant differences from fibers produced with prior art
techniques. Once again, it is believed that these
2~ differences relate to crystalline structure and quenching of
the fiber during formation.
While preferred embodiments of the present invention
have been described in the foregoing detailed description,
the invention is capable of numerous modifications,
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5~
substitutions, additions and deletions from the embodiments
described above without departing from the scope of the
following claims. For example, the teachings of the present
application could be applied to the atomizing of liquids into
s a mist (or entraining a liquid in a fluid flow such as air).
An apparatus for entraining such liquids is very similar, in
cross section, to the melt-blown apparatus shown in Figures
6A-6D. In this embodiment, the apparatus simply would not
have the typical melt-blown width of several inches to
several feet. Additionally, the components of an atomizer
would typically be several orders of magnitude smaller. In
any event, the perturbation techniques in an atomizing
embodiment provide for narrow droplet size distribution and
more even distribution of the small liquid droplets in the
entraining air flow. This embodiment could be employed in
many applications such as creating fuel/air mixtures for
engines, improved paint sprayers, improved pesticide
applicators, or in any application in which a liquid is
entrained in an airflow and an even distribution of the
liquid and narrow particle size distribution in the airflow
is desired.
