Note: Descriptions are shown in the official language in which they were submitted.
~ 092/18677 2 i ~ ~ 0 7 ~ PCT/Usg2/~l381
ORIENTED MELT-BLOWN FIBERS, PROCESSES FOR NAXING SUCH
FIBER6, AND WEBS MADE FRON SUCH FIBERS
TechnicaI_Fi ld
The present invention is directed to melt-
blown fibrous webs, i.e., webs prepared by extruding
molten fiber-forming material through orifices in a
die into a high-velocity gaseous stream which impacts
the extruded material and attenuates it into fibers,
often of microfiber size averaging on the order of 10
micrometers or less.
Background Art
During the over twenty-year period that melt-
blown fibers have come into wide commercial use, for
uses such as filtration, battery electr~de separation
and insulation, there has been a recognized need for
fibers of extremely small diameters and webs of good
tensile strength. However, there has always been a
recognition that the tensile strength of melt-blown
fibers was low, e.g., lower than that of fibers -
prepared in conventional melt-spinning processes (see
the article "Melt-Blowing - A One-Step Web Process
For New Nonwoven Products," by ~obert R. Buntin and
Dwight D. Lohkcamp, Volume 56, No. 4, April 1973,
Tappi, Page 75, paragraph bridging columns 2 and 3).
At least as late as 1981, the art generaIly doubted
"that melt-blown webs, per se, will ever possess the
strengths associated with conventional nonwoven webs
produced by melt spinning in which fiber attenuation
occurs below the polymer melting point bringing about
crystalline orientation with resultant high fiber
strength" (see the paper "Technical Developments In
40~ The Melt-Blowing Process And Its Applications ~In
Absorbent Products" by Dr. W~. John McCulloch and ~r.
7 ~
WO92~ 77 PCT/US92/0138 ~ i ;
Robert A. VanBrederode presented at Insight '81,
copyright Marketing/Technology service, Inc., of
Kalamazoo, MI, page 18, under the heading "Strength"). -
The low strength of melt-blown fibers limited
the utility of the fibers, and as a result there have
been various attempts to combat this low strength.
One such effort is taught in Prentice, U.S. Pat. No.
3,704,198, where a melt-blown web is "fuse-bonded," as
by calendering or point-bonding, at least a portion of
the web. Although web strength can be improved
somewhat by calendering, fiber strength is left
unaffected, and overall strength is still less than
desired.
Other prior workers have suggested blending
high-strength bicomponent fibers into melt-blown
fibers prior to collection of the web, or lamination
of the melt blown web to a high strength substrate
such as a spunbond web (see U.S. Pat. Nos. 4,041,203,
4,302,495 and 4,196,245). Such steps add costs and
dilute the microfiber nature of the web, and are not
satlsfactory for many purposes.
With regard to fiber diameter, there is a
recognized need for fibers of uniformly small
diameters and extremely high aspect ratios, as -~
discussed, for example in Hauser U.S. Pat. No.
4,118,531 (col. 5) and Kubik et al. U.S. Pat. No.
4,215,582 (cols. 5 and 6). However, as recognized by
Hauser, despite the ability to get melt-blown fibers
with very small average fiber diameters, the fiber
size distribution is quite large, with fibers in the 6
to 8 micrometer range present for use with fibers of
an average fiber diameter of 1 to 2 micrometers -
(Examples 5-7). Problems are also present in
eliminating }arger diameter "shot", discussed in the
above Buntin et al. article, page 74, first paragraph
of col. 2. Shot is formed when the fibers break in
the turbulence from the impinging air of the
.
~ :,
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2~507~
092~18677 PC~/US9~/0138i
melt-blown process. Buntin indicates that shot is
unavoidable and of a diameter greater than that of the
fibers.
McAmish et al, U.S. ~at. No. 4,622,259, is
directed to melt-blown fibrous we~s especially
suitable for use as medical fabrics and said to have
improved strength. These webs are prepared by
introducing secondary air at high velocity at a point
near where fiber-forming material is extruded from the
lo melt-blowing die. As seen best in Fig. 2 of the
patent, the secondary air is introduced from each side
of the stream of ~elt-blown fibers that leaves the
melt-blowing die, the secondary air being introduced
on paths generally perpendicular to the stream of
fibers. The secondary air merges with the primary air
that impacted on the fiber-forming material and formed
the fibers, and the secondary air is turned to travel
more in a direction parallel to the path of the
fibers. Th~ merged primary and secondary air then
carries the fibers to a collector. The patent states
that, by the use of such secondary air, fibers are
formed that are longer than those formed by a
conventional melt-blowing process and which exhibit
less autogeneous bonding upon fiber collection; with
the latter property, the patent states it has been
noted that the individual fiber strength is higher. `
Strength is indicated to be dependent on the degree of
molecular orientation, and it is stated (column 9,
lines 21-27) that the
high velocity secondary air employed in the
present process is instrumental in increasing
the time and distance over which the fibers
are attenuated. The cooling effect of the
3s secondary air enhances the probability that
the molecular orientation of the fibers is
not excessively relaxed on the deceleration
of the fibers as they are collected on the
screen.
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21~S~7~
W092/18677 PCT/US92/0138
Fabrics are formed from the collected web by embossing
the webs or adding a chemical binder ~o the web, and
the fabrics are reported to have higher strengths,
e.g., a minimum grab tensile strength-to-weight ratio
greater than 0.8 N per gram per square meter, and a
minimum Elmendorf tear strength-to-weight ratio
greater than 0.04 N per gram per square meter. The
fibers are also reported to have a diameter of 7
micrometers or less. However, there is no indication
that the process yields fibers of a narrow fiber
diameter distribution or fibers with average diameters
of less than 2.0 micrometers, substantially continuous
fibers or fiber webs substantially free of shot.
Disclosure of Invention
The present invention provides new melt- ` -
blown fibers and fibrous webs of greatly improved
fiber diameter size distribution, average fiber
diameter, fiber and web strength, and low-shot levels.
The new melt-blown fibers have much greater
orientation and crystallinity than previous melt-blown
fibers, as a result of preparation by a new method
which, in brief summary, comprises extruding
fiber-forming material to a metering means and then
25 through to the orifices of a die into a controlled -
high-velocity gaseous stream where the extruded
material is rapidly attenuated into fibers; directing
the attenuated fibers and gaseous stream into a first
open end, i.e., the entrance end, of a tubular chamber :
disposed near the die and extending in a direction
parallel to the path of the attenuated fibers as they
~leave the die; introducing air with both radial and
axial components into the tubular chamber such that
the air blowing along the axis of the chamber is at a
velocity sufficient to maintain the fibers under
tension during travel through the chamber, and ~ -
~preferably introducinq air perpendicular to the
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~ 92/18677 2 ~ O ~ 0 7 ~ PCT/US92/01381
longitudinal axis of the chamber along substantially
the entire length of the chamber; optionally directing
the attenuated fibers into a second tubular chamber
where quenched fibers are further drawn by air blowing
along the axis of the chamber; and collecting the
fibers after they leave the opposite, or exit end, of
the last tubular chamber.
Generally, the tubular chamber is a thin
wide box-like chamber (generally somewhat wider than
the width of the melt-blowing die). Orienting air is
generally introduced into the chamber at an angle to
the path of the extruded fibers, but travels around a
curved surface at the first open end of the chamber.
By the Coanda effect, the orienting air turns around
the curved surface in a laminar, non-turbulent manner,
thereby assuming the path traveled by the extruded
fibers and merging with the primary air in which the
fibers are entrained. The amount of the radial flow
component of the air available for intersecting and -
20 directing the extrude~ fibers into the chamber can be - -
adjusted by varying the radius of the coanda surface.
Larger and more gradual areas of radial flow are
obtained with larger radii. A large radial flow
region acts to provide more directioning of the fibers
into the axial centerline of the chamber. Smaller
radii Coanda surfaces decrease the relative amount of
axial flow component of the air available for
intersecting and guiding the fibers into the axial
-centerline of the chamber. ~owever, the greater axial
30 flow components from smaller radii Coanda surfaces -
tend to increase the draw force of the air on the
fibers in the chamb~er1 Generally, the Coànda surfaces
`~ can be used having an infinite range of radii.
However,~as the radii;decreases to nil, the;angle wiIl - -~
be to sharp, and the air will tend to separate from
~ . . -
the;surface. Radii have been used as low as l/8 in
and~ are generally 0.5~to 1.5 in.
- . . . -
2~507~
WO9~18S77 PCT/US92/0138
Preferably, a second perpendicular cooling
stream of air is introduced along the length of the
chamber. This air is introduced into the chamber in a
diffuse manner preferably thru two opposing walls of
the chamber facing the plane of fibers exiting from
the die. This is done, for example, by having at
least a portion of the sidewalls made of a porous
glass composite. This perpendicul~r air further
guides the fibers into the center of the chamber while
preventing stray fibers from sticking to the chamber
walls. The fibers ara drawn into the chamber in an
orderly compact stream and rPmain in that compact
stream through the complete chamber. If only one
chamber is used, preferably, the described tubular
chamber is flared outwardly around the circumference
of its exit end, which has been found to better
provide isotropic properties in the collected or
finished web.
The orienting air and perpendicular cooling
air generally have a cooling effect on the fibers ~the
orienting air flows can be, but usually are not,
heated, but are ambient air at a temperature less than
about 35C; in some circumstances, it may be useful to
cool the orienting air or perpendicular air below
ambient temperature before it is introduced into the
orienting chamber.) The cooling effect is generally
desirable since it accelerates solidification of the
fibers under orienting conditions, strengthening the
fibers. Further, the pulling effect of the orienting
air as it travels through the orienting chamber
provides a tension on the solidifying fibers that
tends to cause them to crystallize.
~ . .....
A secondary tubular chamber can be used to -
impart further orientation to the fibers exiting the
primary tubular chamber. As the fibers are normally
quenched at this point, higher air pressure can be
employed to impart a higher tension on the fibers to
.
~ Og2/18677 2~S07~ PCT/US9~101381
further enhance orientationO The need for the diffuse
perpendicular air flow is less due to the low tack
nature of the ~ibers in this chamber, however,
perpendicular air can be used.
The significant increase in molecular
orientation and crystallinity of the fibers of the
invention over conventional melt-blown fibers is
illustrated by reference to Figs. 4, 7, 8, 10 and 11,
which show WAXS (wide-angle x ray scattering)
photographs of fibers that, respectively, are oriented
fibers of the invention (A photo) and are non-oriented
conventional fibers of the prior art (B photo). The
ring-like nature of the light areas in the B photos
signifies that the pictured fibers of tha invention
are highly crystalline, and the interruption of the
rings means that there is significant crystalline
orientation.
., .
BrieP Description o~_the Drawinqs
Figs. 1 and 2A and 2B are a side view and
perspective views, respectively, of different
apparatuses useful for carrying out methods of the
' invention to prepare fabrics of the invention.
Figs. 3, 5 and 9 are plots of stress-strain
2S curves for fibers of the invention (the 'IA'l drawings)
and comparative fibers (the IlBl' drawings).
Figs. 4, 7, 8, 10 and 11 are WAX photographs
~! of fibers of the invention (the "Al' photographs) and
comparative fibers (IlB~l photographs); and
Fig. 6 comprises scanning electron
mirroscope photographs of a representative fibrous web
of the invention (6A) and a comparative fibrous web
(6B).
Fig. 12 is a ~raph showing the theoretical
relationship of polymer flow rate-to-fiber diameter
for the continuous submicron fibers.
;: ~ ' ,
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W~92~18677 PCT/US92/~138
Fig. 13 is a scanning electron micrograph of
the submicron fibers of Example 33.
Detailed De~criPtion
A representative apparatus useful for
preparing blown fibers or a blown-fiber web of the
invention is shown schematically in Fig. 1. Part of
the apparatus, which forms the blown fibers, can be as `
described in Wente, Van A., t'Superfine Thermoplastic
Fibers" in Industrial Enqineerin~ Chemistry, Vol. 48,
~ page 1342 et seq. (1956), or in Report No. 4364 of the
; Naval Research Laboratories, published May 25, 1954,
- entitled "Manufacture of Superfine Organic Fibers," by
; Wente, V. A.; Boone, C. D.; and Fluharty, E. L. This
portion of the illustrated apparatus comprises a die
10 which has a set of aligned side-by-side parallel
die orifices 11, one of which is seen in the sectional
^ view through the die. The orifices 11 open from the
central die cavity 12.
Fiber-forming material is introduced into
the die cavity 12 through an opening 13 from an
extruder (not illustrated). Air gaps 15, disposed on -
-l either side of the row of orifices 11, convey heated
,1i air at a very high velocity. This air, called the
primary air, impacts onto the extruded ~iber-forming
-j material, and rapidly draws out and attenuates the
extruded material into a mass of fibers. The primary
air is generally heated and supplied at substantially
identical pressures to both air gaps 15. The air is
also preferably filtered to prevent dirt or dust from
interfering with uniform fiber formation. The air
temperature is maintained generally at a temperature
Il greater than that of the melt polymer in the die -
! : : orifices. Preferably, the air is at least 5C above
the temperature of the melt. Temperatures below this
range can cause excessive quenching of the polymer as
it exits the-die, maklng orientation in the chambers
1`
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t ~ 9~/18677 2 ~ 0 5 0 7 4 PCT/US92/0138l
difficult. Too high a temperature can excessively
degrade the polymer or increase the tendency for fiber
breakage.
From the melt-blowing die 10, the fibers
travel to a primary tubular orienting chamber 17.
"Tubular" is used in this specification to mean any
axially elongated structure having open ends at each
axially opposed end, with walls surrounding the axis.
Generally, the chamber is a rather thin, wide, box-
like chamber, having a width somewhat greater than thewidth o~ the die 10, and a height (18 in Fig. 1)
sufficiellt for the orienting air to ~low smoothly
through the chamber without undue loss of velocity,
and for ~ibrous material extruded ~rom the die to
- 15 travel through the chamber without contacting the
walls of t.he chamber. Too large a height would
require unduly large volumes of air to maintain a
tension-applying air velocity. Good results for a
solid walled chamber 17 have been obtained with a
height of about 10 millimeters or more/ and we have
found no need for a height greater than about 25
millimeters.
The walls 26 along the width of the chamber
17 can be made of air-permeable or porous material. A
secondary cooling diffuse airstream can then be
introduced along the width of the chamber. This
airflow serves the function of increasing the polymer
solidification and/or crystallization rate in the
quenching chamber 17. This secondary cooling air also
helps keep the fibers in the center of the chamber 17
and off the walls 26. However, the air pressure of
this cooling airstream should not be so high as to
cause turbulence in the chamber. Generally, a
pressure of from 2 to 15 PSI has been found
acceptable.
orienting air is introduced into the
; orienting chamber 17 through the orificès I9 arranged
- .
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wosz/~ ia~o7,~ PClr/U~j92/0~38~i
near the first open end of the chamber where fibers
entrained in the primary air from the die snter the
chamber. Orienting air is preferably introduced from
both sides of the chamber (i.e., from opposite sides
of the stream of fibers entering the chamber) around
~- curved surfaces 20, which may be called coanda
surfaces. A larger radius Coanda surface is preferred
for the orienting chamber 17 when the polymer used is
less crystalline or has a slow crystallization rate.
Further, with low crystalline polymers, pre~erably the
air exits from an orifice adjacent the Coanda surface
at an angle to a line perpendicular to the axial
- centerline of the chamber. At an angle of zero, the
air would exit the orifice parallel to the axial
centerline. Generally, the orienting air exit anyle
was varied from 0 to 90 degrees, although higher
angles are feasible. An air exit angle of 30 to 60
degrees was found to be generally preferred. A lower
orienting air exit angle is acceptable if a quenching
chamber is used prior to the orienting chamber or a
highly crystalline polymer is melt blown.
~1 The orienting air introduced into the
J! chamber bends as it exits the orifice and travels
around the Coanda surfaces to yield a predominately
' 25 axial flow along the longitudinal axis of the chamber.
The travel of the air is quite uniform and rapid, and
it draws into the chamber, in a uniform manner, the
fibers extruded from the melt-blowing die 10. Whereas
fibers exiting from a melt-blown die typically
! 30 oscillate in a rather wide pattern soon after they
leave the die, the fibers exiting from the melt-
; blowing die in the method of the invention tend to
pass uniformly in a sur~prising planar-like -
distribution into the center of the chamber and travel
lengthwise through the chamber without significant
oscillation.
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~ 092/18677 21~ S 0 7 ~ PCT/US92/0138l
11
After the fibers exit the chamber 17, they
typically exhibit oscillating movement as represented
: by the oscillating line 21 and by the dotted lines 22,
which represent the general outlines of the stream of
fibers. This oscillation results from the expansion
or flaring at the chamber 17 exit. This oscillation,
however, does not result in significant fiber breakage
as it would tend to cause if present close~y adjacent
to the melt-blown die orifica. The orienting chamber
significantly strengthens the fiber so that
post-chamber oscillation, with the resulting increase
in peak stress that the fibers are exposed to, is more
readily endured without ~iber breakage.
As shown in Fig. 1, for the single orienting
chamber 17 embodiment, the chamber 17 is preferably
- flaired at its exit end 23. This flaring has been
found to cause the ~ibers to assume a more randomized
or isotropic arrangement within the fiber stream,
however, without fiber breakage. For example, a
collected web of fibers of the invention passed
through a chamber which does not have a flared exit
tends to have a machine-direction fiber pattern (i.e.,
` more fibers tend to be aligned in a direction parallel
to the direction of movement of the collector than are
aligned transverse to that direction). On the other
1 hand, webs of fibers collected from a chamber with a
flared exit are more closely balanced in machine and
transverse orientation. The flaring can occur both in
its height and width dimensions, i.e., in both the
axis or plane of the drawing and in the plane
perpendicular to the page of the drawings. More
typically, the flaring occurs only in the axis in the
plane of the drawing, i.e., in the large-area sides or
walls on opposite sides of the stream of fibers
passing through the chamber. Flaring at an angle (the
angle 0) bétween a broken line 25 parallel to the
longitudinal axis of the chamber and the flared side
~ .
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.:
21~07~
WO92/1~677 PCT/US~2/0138
12
of the chamber between about 4 and 7 is believed
ideal to achieve smooth isotropic deposit of fibers.
The length 24 of the portion of the chamber over which
flaring occurs (which may be called the randomizing
portion of the chamber) depends on the velocity of the
orienting air and the diameter of fibers being
produced. At lower velocities, and at smaller fiber
diameters, shorter lengths are used. Flaring lengths
between 25 and 75 centimeters have proven useful.
The orienting air enters the orienting
chamber 17 at a high velocity, sufficient to hold the
fibers under tension as they travel lengthwise through
the chamber. Planar continuous travel through the
chamber is an indication that the fibers are
continuous and under stressline tension. The needed
velocity of the air for orientation, which is
` determined by the pressure with which air is
; introduced into the orienting chamber and the
dimensions of the orifices or gaps l9, varies with the
kind of fiber-forming material being used and the
diameter of the fibers. For most situations,
velocities corresponding to pressures of about 70 PSI
(approximately 500 kPa) with a gap width for the
orifice l9 (the dimension 30 in Fig. l) of 0.005 inch
(0.013 cm), have been found optimum to assure adequate
tension. However, pressures as low as 20 to 30 PSI
(140 to 200 kPa) have been used with some polymers,
i such as nylon 66, with the stated gap width. If
chamber 17 is used primarily as a quenching chamber,
pressures as low as 5 PSI can be used for the
orienting air.
Surprisingly, most fibers can travel through
the chamber a long distance without contacting either
the top or bottom surface of the chamber. However, in
~ 35 the first chamber (17 or 37) preferably a ~econdary
i cooling ai~rflow is introduced perpendicular to the
i fibers in a diffuse~manner through the chamber
;:
~ O9~t18677 2 ~ ~ a 0 7 ~ PCT/US92~01381
13
sidewalls. The secondary cooling airflow is preferred
with polymers having a low crystallization rate, as
they have an increased tack and, hence, a tendency for
stray fibers to adhere to the chamber sidewalls. The
cooling airflow also increases fiber strength by its
quenching action, decreasing the likelihood of any
fiber breakage before, in or after the first chamber
~17 or 37).
The chambers are generally at least about 40
centimeters long (shorter chambers can be used at
lower production rates or where the first chamber
functions primarily as an orienting chamber) and
preferably is at least 100 centimeters long to achieve
desired orientation and desired mechanical properties
in the fibers. With shorter chamber lengths, faster
air velocities can be used to still achieve fiber
; orientation. The entrance end of the first chamber is
generally within 3-10 centimeters of the die, and as
previously indicated, despite the disruptive
turbulence conventionally present near the exit of a
~`) melt-blowing die, the fibers are drawn into the
.J. chamber in an organized manner.
~` After exiting from the orienting or last -~
` chamber (17 or 38), the solidified fibers are
decelerating, and, in the course of that deceleration
they are collected on the collector 26 as a web 27 as
a possibly misdirecting mass of entangled fibers. The
collector may take the form of a finely perforated
i cylindrical screen or drum, a rotating mandrel, or a -
i 30 moving belt. Gas-withdrawal apparatus may be
positioned behind the collector to assist in
deposition of fand removal of gas.
The collected web of fibers can be removed
from ~he collector and wound in a storage roll,
35 preferably with a liner separating adjacent windings -
on the roll. At the time of ~iber collection and web
formation, the fibers are totally solidified and
, . .
1 ~ ' ~ : ,..... ... ... .... ..
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WO92/18b77 PCT/US92/0138
14
oriented~ These two features tend to cause the fibers
to have a high modulus, and it is difficult to make
high-modulus fibers decelerate and entangle
sufficiently to form a handleable coherent web. Webs
comprising only oriented melt-blown fibers may not
have the coherency of a collected web of conventional
melt-blown fibers. For that reason, the collected web
of fibers is often fed directly to apparatus for
forming an integral handleable web, e.g., by bonding
the fibers together as by calendering the web
uniformly in areas or points (generally in an area of
about 5 to 40 percent), consolidating the web into a
coherent structure by, e.g., hydraulic entanglement,
ultrasonically bonding the web, adding a binder
material to the fibers in solution or molten form and
solidifying the binder material, adding a solvent to
the web to solvent-bond the fibers together, or
preparing bicomponent fibers and subjecting the web to
conditions so that one component fuses, thereby fusing
together adjacent or intersecting fibers. Also, the
collected web may be deposited on another web, for
example, a web traveling over the collector; also a
second web may be applied over the uncovered surface
of the collected web. The collected web may be
25 unattached to the carrier or cover web or liner, or ~-
~, may be adhered to the web or liner as by heat-bonding ;
~!` or solvent-bonding or by bonding with an added binder
material.
The blown fibers of the invention are
preferably microfibers, averaging less than about 10
micrometers in diameter. Fibers of that size offer
improved filtration efficiency and other beneficial
¦ properties. Very small fibers, averaging less than 5 - ~;
or even 1 or less micrometer in diameter, may b~
blown, but larger fibers, e.g., averaging 25
micrometers or more in diameter, may also be blown, -
. :
1 ~ .
~V092/18677 2l ~ S 0 7~ PCTiUS92/01381
and are useful fox certain purposes such as coarse
filter webs.
The invention is of advantage in forming
fibers of small fiber size, and fibers produced by the
invention are generally smaller in diameter than
fibers formed by the conventional melt-blowing
conditions, but without use of an orienting chamber as
used in the invention. Also, the invention melt-blown
~- fibers have a very narrow distribution of fiber
diameters. For example, in samples of webs of the
invention having average fiber diameters of greater
than 5 micrometers, the diameter of three-quarters or
more of the fibers, ideally, 90 percent or more, have -
tended to lie within a range of about 3 micrometers,
in contrast to a typically much larger spread of
diameters in conventional melt-blown fibers. In a
preferred embodiment where the fiber diameter averages
less than 5 micrometers and more preferably less than
about 2 micrometers, preferably the largest fibers
s1 20 will differ from the mean by at most about l.0
. .......................................................................... .
-~- micrometers, and generally with 90 percent or more of
the fibers are within a range of less than 3.0
~` micrometers, preferably withi`n a range of about 2.0
~r ~
~;' micrometers or less and most preferably within a range
. ~
of l.0 micrometer or less.
An embodiment suitable for forming fibers of
` ~ extremely small average diameters, generally averaging
~ 2 micrometers or less, with a very narrow range of
- fiber diameters (e.g., 90 percent within a range of
30 l.0 micrometers or less) is shown in Fig. 2A. The --
i fiber-forming material from the extruder 30 is passed
;;i into a metering means that comprises at least a
3~ precision meter~ing~pump 31 or purge or the like. The
~ metering pump 31 tends to even out the flow from the
;' 35 extruder 30. It has been found that for exceeding
`1 small diameter, uniform, and substantially continuous
1 ~ fibers, the polymer flow rate must generally be quite
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1 ~ . :
- WO92/18677 PCT/US92/0138
16
low through each ori~ice in the die. Suitable polymer
flow rates for most polymers range from O.Ol to 3
gm/hr/orifice with 0.02 to l.5 gm/hr/orifice preferred
- for average fiber diameters of less than l or 2
micrometers. In order to achieve these low flow
rates, conventional extruders are operated at low
screw rotation rates even with a high density of
` orifices in the die. This results in a polymer flow -:
rate that fluctuates slightly. This slight flow
fluctuation has been found to have a large adverse
effect on the size distrihution and continuity of the
resulting extremely small diameter melt-blown fibers.
. ~ .
The metering means decreases this fluctuation.
Preferably, a system of three precision
pumps is employed as the metering means, as shown in
Fig. 2A. Pumps 32 and 33 divide the flow from
metering pump 31. Pumps 32 and 31 can be operated by
a single drive with the pumps operating at a fixed
;~ ratio to one another. With this arrangement, the
; 20 speed of pump 33 is continuously adjusted to provide polymer feed at a constant pressure to pump 32,
measured by a pressure transducer. Pump 33 generally
acts as a purge to remove excess polymer fed from the
extruder and pump 31, while pump 32 provides a smooth
; 25 polymer flow to the die 35. More than one pump 32 can
be used to feed polymer to a series of dies (not
shown). Preferably, a filter 34 is provided between
`i the pump 32 and the die 35 to remove any impurities.
; Preferably, the mesh size of the filter ranges from
lO0 to 250 holes/in2 and higher. Although this system
is preferred, other arrangements are possible which
1 provide polymer to the orifices at the necessary low
and substantially non-fluctuating flow rate.
The polymer is fed to the die at a flow rate
! 35 per orifice suitable to produce the desired fiber
' diameter as shown, for example, in the hypothetical
~ model shown in Fig.~ 12, wh,-re the y axis represents
... .
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092~18677 21~ S 0 7 4 PCT/US92/D1381
17
the log of the resin flow rate (in grams/min/orifice)
and the x axis represents the corresonding 0.9 density
~: isotactic polypropylene fiber diameter in microns at
two fiber velocities (400 m/sec, upper line, and 200
m/sec, lower line). This models the demonstrated need
for reduction in flow rate to produce uniform diameter
microfibers. As can be seen, a very low polymer flow
- rate is needed to produce very small average diameter
continuous microfibers using the invention process.
The total theoretical polymer feed rate to the die
will depend on the number of orifices. This
appropriate polymer feed rate is then supplied by,
e.g., the metering means. However, the invention
method for obtaining uniform, continuous,
high-strength, small-diameter fibers with such low
polymer flow rates was not known or predictable from
conventional melt~blown techniques.
Suitable orifice diameters for producing
uniform fibers of average diameters of less than 2
micrometers are from 0.025 to 0.50 mm with 0.025 to :
;~ 0.05 being preferred (obtainable from, e.g., Ceccato
Spinnerets, Milan, Italy or Kasen Nozzle Manufacturing
Corporation, Ltd., Osaka, Japan). Suitable aspect
ratios for these orifices would lie in ~he range of
200 to 20, with l00 to 20 being preferred~ For the
, .
preferred orifices, high orifice densities are
preferred to increase polymer throughput. Generally,
i orifice densities of 30/cm are preferred with 40/cm or
, more being more preferred.
,j .
When producing uniform fibers having average
diameters of less than 2 micrometers, the primary air
j; pressure is reduced, decreasing the tendency for fiber
breakage while still attenua~ing and drawing out the
polymeric meltstreams extruded from the die orifices.
~ 35 Generally, air pressures of less than l0 lbs/in2 PSI
j (70 kPa) are preferred, and more preferably, about 5
~ lbs/in2 (35 kPa) or 1ess,~with~an air gap width of
- .
: :
,
.
. .
wo 92/l8677 2 1 0 ~ 0 7 ~ PCT/US92/0138 ~
18
about 0.4 mm. The low air pressure decreases
turbulence and allows a continuous fiber to be blown
into the chamber 17 or 37 prior to fiber breakup from -
turbulence created in the melt blowing. The
continuous fiber delivered to the chamber 17 or 37 is
then drawn by orienting air (in chamber 17 or 37
and/or 38). The temperature of the primary air is
preferably close to the temperature of the polymer
melt ~e.g., about 10C o~er the polymer melt
temperature).
: The fibers must be drawn by the first,
and/or second, chamber from the melt-blown area at the
exit of the dieface to keep the proper stress-line
tension. The chambers (17 in Fig. 1, and 37 and/or 38
in Fig. 2A) keep the fibers from undergoing the
oscillatory effect ordinarily encountered by
melt-blown fiber at the exit of a melt-blown die.
When the fibers do undergo these oscillatory forces,
for randomization purposes, the fibers are strong
enough to withstand the forces without breaking. The
resulting oriented fibers are substantially continuous
and no fiber ends have been observed when viewing the
resulting microfiber webs under a scanning electron
microscope.
From the die orifices, the fiber-forming
material is entrained in the primary air, and then,
the orienting air and secondary cooling air, as
described above for chamber 17 or chamber 37 (which
can be used with or without chamber 38). In a
preferred arrangement, the material exits chamber 37
and is further attenuated in chamber 38. Tubular
chamber 38~operates in a manner similar to chamber 37.
If the secondary chamber 38 is used, this chamber is
used primarily for orientation in which case the air
pressure is generally at least 50 PSI (344 kPa) and
preferably at least 70 PSI (483 kPa) for a gap width
of the air orifice (not shown) of 0.005 inches (0.13
.,
, ::
:
~ O9~tl8677 2 1 ~ ~ 0 7 ~ PCT/US92/013~1
19
mm~. When this secondary chamber 38 is used, the
co~responding pressures in the first chamber 37 for an
identical gap width would genPrally be 5 PSI to 15 PSI
(35 to 103 kPa). The first chamber 37 in this
5 instance would act primarily as a cooling chamber with -
a slight degree of orientation occuring.
The secondary chamber 38 is generally
located from 2 to 5 cm from the exit of the first
chamber, which first chamber would not be flared as
described above. The secondary chamber dimensions are
substantially similar to those of the first chamber
37. If the secondary chamber 38 is employed,
preferably its exit end 40 would be flared as
described above with respect to the Fig. l embodiment.
-
The ramdomization of the fibers is further
enhanced by use of an airstream immediately prior t~
the fibers reaching the flared exit 40. This can be
done by an entangling airstream provided from the
chamber walls. This entangling airstream could be
provided through apperatures in the sidewalls
(preferably widthwise) and preferably close to the
exit end 40 of the chamber 38. Such an airstream
'! could also be used in an arrangement such as described
for Fig. l.
The above-described embodiment is used
primarily for obtaining extremely small-diameter,
substantially continuous fibers, e.g., less than 2
micrometers average diameter fibers, with very a
narrow ranges of fiber diameters and with high-fiber
strength. This combination of propexties in a
microfiber web is unique and highly desirable for uses
such as filtration or insulation.
I . .
As discussed above, the oriented melt-blown
fibers of the inventionlare beIieved to be continuous,
` which is apparently a~fundamental distinction from
fibers formed in conventional melt-blowing processes,
.
wo g2/,867, ~ 1 0 ~ 0 7 ~ PCT/~S~2/~13$1 ~
where the fibers are typically said to be
discontinuous. The fibers are delivered to the
orienting chamber(s) (or to the quenching then
orienting chamber) unbroken, then generally travel
through the orienting chamber without interruption.
The chamber~s) generates a stress line tension which
orients the fibers to a remarkable extent and prevents
the fibers from oscillating significantly until after
they are fully oriented. There is no evidence of
fiber ends or shot (solidified globules of fiber-
forming material such as occur when a fiber breaks and
the release of tension permits the material to retract
back into itself) found in the collected web. These
~ features are present even with the embodiment wherein
- 15 the fibers average diameter is less than 2
micrometers, which is particularly remarkable in view
of the low strength of the extremely small diameter
polymer flowstreams exiting the die orifices. Also,
~i the fibers in the web show little, if any, thermal
-~ 20 bonding between fibers.
Other fibers may be mixed into the fibrous
webs of the invention, e.g., by feeding the other `
fibers into the stream of blown fibers after it leaves
the last tubular chamber and before it reaches a
2S collector. U.S. Pat. No. 4,118,531 teaches a process
and apparatus for introducing into a stream of melt-
blown fibers crimped staple fibers which increase the
loft of the collected web, and such process and
apparatus are useful with fibers of the present
30 invention. U.S. Pat. No. 3,016,599 teaches such a
process for introducing uncrimped fibers. The
additional fibers can have the function of opening or
loosening the web, of increasing the porosity of the
web, and of providing a gradation of fiber diameters
in the web.
Furthermore, added fibers can function to `~
give the collected web coherency. For example,
~ 09~/18677 2 ~ 0 5 0 7 ~ PCT/VS92/Q~381
21
~usible ~ibers, pre~erably bicomponent fibers that
have a component that fuses at a temperature lower
than the fusion temperature of the other component,
can be added and the fusible fibers can be fused at
points of fiber intersection to form a coherent web.
Also, it has been found that addition of crimped
staple fibers to the web, such as described in U.S.
-~ Pat. No. 4,118,531, will produce a coherent web. The
`~ crimped fibers intertwine with one another and with
the oriented fibers in such a way as to provide
coherency and integrity to the web.
Webs comprising a blend of crimped fibers
and oriented melt-blown fibers (e.g., comprising
staple fibers in amounts up to about 90 volume
`~- 15 percent, with the amount preferably being less than
. ~
about 50 volume percent of the web) have a number of
other advantages, especially for use as thermal
insulation. First, the addition of crimped fibers
makes the web more bulky or lofty, which enhances
insulating properties. Further, the oriented
~; melt-blown fibers tend to be of small diameter and to
'!, have a narrow distribution of fiber diameters, both of ;
'rl which can enhance the insulating quaIity of the web
since they contribute to a large surface area per
25 volume-unit of material. Another advantage is that ,
the webs are.softer and more drapable than webs
~ comprising non~-oriented mel~-blown microfibers,
,~ ; apparently~because of the absence of thermal bonding
between the collected fibers. At the same time, the
webs are very durable because of the high strength of
, ; the oriented fibers, and because the oriented nature
.~ of the fiber mak~es it more resistant to high
temperatures, dry cleaning solvents, and the like.
The~latter advantage is especially important with -
; 35 ~ fibsrs of~polyethy1ene terephthalate, which-tends to
;l be amorphous in character when made by conventional
' melt-blowing procedures. When subjected to higher ;
w092/l8677 2 1 0 ~ O ~ ~ 2~ PCT/~592/0138 ~
temperatures the amorphous polyester polymer can
crystallize to a brittle form, which is less durable
during use of the fabric. But the oriented polyester
fibers of the invention can be heated without a
5 similar degradation of their properties. :-
It has also been found that lighter-weight
webs of the invention can have equivalent insulating
value as heavier webs made from non-oriented melt-
blown fibers. One reason is that the smaller diameter
lo of the fibers in a web of the invention, and the
narrow distribution of fiber diameters, causes a
larger effective fiber surface area in a web of the
invention, and the larger surface area effectively
holds more air in place, as discussed in U.S. Pat. No.
4,118,531. Larger surface area per unit weight is
also achieved because of the absence of shot and
"roping" (grouping of fibers such as occurs in
conventional melt-blowing through entanglement or
thermal bonding).
Coherent webs may also be prepared by mixing
oriented mel~-blown fibers with non-oriented melt-
blown fibers. An apparatus for preparing such a mixed
web is shown in Fig. 2B and comprises first and second
melt-blowing dies 10a and 10b having the structure of
the die 10 shown in Fig. 1, and at least one orienting
chamber 28 through which fibers extruded from the
first die lOA pass and die 35 of Fig. 2A. The chamber
28 is like the chamber 17 shown in Fig. l and chambers
37 and 38 of Fig. 2A, except that the randomizing
portion 29 at the end of the orienting chamber has a
different flaring than does the randomizing portion 24
or 40 shown in Figs. 1 and 2A. In the apparatus of
Fig. 2B, the chamber flares rapidly to an enlarged
height, and then narrows slightly until it reaches the
exit. WhiIe such a chamber provides an improved
isotropic character to the web, the more gradual ;
:
:
:
~ 092/18677 2 I O S 0 7 ~ PCT/US92/01381
23
flaring of the chamber shown in Fig. 1 provides more
isotropic character.
Polymer introduced into the second die loB
is extruded through a set of orifices and formed into
fibers in the same way as fibers formed by the first
die lOA, but the prepared fibers are introduced
directly into the stream of fibers leaving the
orienting chamber 28. The proportion of
; oriented-to-non-oriented fibers can be varied greatly
lo and the nature of the fibers (e.g., diameter, fiber
composition, bicomponent nature) can be varied as
- desired. Webs can be prepared that have a good
isotropic balance of properties, e.g , in which the
cross-direction tensile strength of the web is at ~-
least about three-fourths of the machine-direction
- tensile strength of the web.
Some webs of the invention include
particulate matter, which may be introduced into the
web in the manner disclosed in U.S. Pat. No.
3,971,373, e.g., to provide enhanced filtration. The
added particles may or may not be bonded to the
fibers, e.g., by controlling process conditions during
web formation or by later heat treatments or molding
' operations. Also, the~added particulate matter can be
., 25 a supersorbent material such as taught in U.S. Pat.
No. 4~429,001.
The fibers may be formed from a wide variety
~ of fiber-forming materials. Representative polymers
i ~ for forming melt-blown fibers include polypropylene,
; 30 polyethylene, polyethylene terephthalate, and ;-
polyamide. Nylon 6 and nylon 66 are especially useful
materials because they form fibers of very high
strength.
Fibers and webs of the~invention may be
electrically charged to enhance their filtration
capabilities, as by introducing charges into the `~
fibers as they are formed, in the manner described in
:, . : -
~ O 7 ~
WO9~/18677 PC~/US9~ 38
24
u.s. Pat. No. 4,215,682, or by charging the web after
formation in the manner described in U.S. Pat. NoO
3,571,679; see also U.S. Pat. Nos. 4,375,718, :
4,588,537 and 4,592,815. Polyolefins, and especially
polypropylene, are desirably included as a component
in electrically charged fibers of the invention
because they retain a charged condition well.
Fibrous webs o~ the invention may include
`~ other ingredients in addition to the microfibers. For
example, fiber finishes may be sprayed onto a web to
~ improve the hand and ~eel of the web. Additives, such
`~ as dyes, pigments, fillers, surfactants, abrasive
particles, light stabilizers, fire retardants,
~; absorbents, medicaments, etc., may also be added to
`~ 15 webs of the invention by introducing them to the
fiber-forming liquid of the microfibers, or by
spraying them on the fibers as they are formed or
after the web has been collected.
A completed web of the invention may vary
widely in thickness. For most uses, webs have a
; thickness between about 0.05 and 5.0 centimeters. For
~! some applications, two or more separately formed webs
may be assembled as one thicker sheet product~
The invention will be further described by
~i 25 reference to the following illustrative examples.
:, ~
- Exam~le 1
1 Using the apparatus of Fig. 2, minus the
'`! second die lOb, oriented microfibers were made from
, 30 polypropylene resin (Himont PF 442, supplied by Himont
Corp., Wilmington, Delaware, having a melt~flow index
(MFI) of 800-1000)~. The die temperature was 2000C,
and the primary air temperature was 190C. The
~ primary air pressure was 10 PSI (70 kPa), with gap
.j 35 width in the orifices 15 being between 0.015 and 0.018
inch (0.038 and 0~046 cm). The polymer was extruded
.
d
'
09~/18677 2 ~ 7 ~ PCT/US92~1381
through the die orifices at a rate o~ about 0.009
pound per hour per orifice (89 g/hr/orifice).
From the die, the fibers were drawn through
a box-like tubular orienting chamber as shown in ~ig.
2 having an interior height of 0.5 inch (1.3 cm), an
interior width of 24 inches (61 cm), and a length of
18 inches (46 cm). The randomizing or expansion
portion 29 of the chamber was 24 inches (61 cm) long,
and as illustrated in the drawing, was formed by
portions of the large-area walls defining the
orienting chamber, which flared at 90 to the portions
of the walls defining the main portion 28 of the
chamber; the wall flared to a 6 inch (15.24 cm) height
`; at the point of their connection to the main portion
of the chamber, and then narrowed to a 5 inch (12.7
cm) height over its 24 inch (61 cm) length. Secondary
air having a temperature of about 25C was blown into
the orienting chamber at a pressure of 70 PSI (483
kPa) through orifices (like the orifices l9
shown in Fig. l) having a gap width of 0.005 inch
(0.013 cm).
The completed fibers exited the chamber at a
velocity of about 5644 metersjminute and were
collected on a screen-type collector spaced~about 36
inches (9l cm) from the die and moving at a rate of
about 5 meters per minute.~ The fibers ranged in
diameter between l.8 and 5.45 microns and had an
average diameter of about 4 microns. The speed/draw
ratio for the fibers (the ratio of exit
velocity-to-initial extrusion vèlocity) was ll,288 and
thq diameter draw ratio was 106.
The tensile strength of the fibers was
measured by testing a collected embossed web of the
~ibers (emboss~ed~over about 34 percent of its area
with 0.54-square-millimeter-sized diamond-shaped
spots) with an Instron tensile testing machine. The
test was performed using a gauge length, i.e., a .
.::
' ~
W092t18677 2 l ~5 a 7Ll~ ~CT/US92/0138
26
separation of the jaws, of as close to zero as
possible, approximately o.oog centimeter. Results are
shown in Fig. 3A. stress is plotted in dynes/cm2 x 107
on the ordinate and nominal strain in percent on the
abscissa ~stress is plotted in psi x lO2 on ~he right-
hand ordinate). Young's modulus was 4.47 x lo6
dynes/cm2, break stress was 4.99 x 107 dynes/cm2 and
toughness (the area under the curve) was 2.69 x lO9
ergs/cm3. By using a very small spacing between jaws
~ lO of the tensile testing machine, the measured values
; reflect the values on average for individual fibers,
~` and avoid the effect of the embossing. The sample
tested was 2 centimeters wide and the crosshead rate
;i was 2 cm/minute.
For comparative purposes, tests were also
performed on microfibers like those of this example,
~ i.e., prepared from the same polypropylene resin and
- using the same apparatus, except that they were not
passed through the orienting chamber. These
.~ 20 comparative fibers ranged in diameter between 3.64 and
12.73 microns in diameter, and had a mean diameter of
6.65 microns. The stress-strain curve is shown in
~ ,.
~ Fig. 3B. Young's modulus was 1.26 x lO6 dynes/cm2,
i break stress was l.94 x 107 dynes/cm2, and toughness
~; 25 was 8.30 x lOgergs/cm3. It can be seen that the more
oriented microfibers produced by the process of the
present invention had higher values in these
properties by between 250 and over 300% than the~
microfibers prepared in the conventional process.
; 30 WAXS (wide angle x-ray scattering)
i~ photographs were prepared for the oriented fibers of
the invention and the comparative unoriented fibers,
and are pictu~ed in Fig. 4A (fibers of the invention)
and 4B (comparative fibers) (as~is well understood in
35 preparation of WAXS photographs of fibers, the photo : ~i
~ is taken of a bundle of fibers such as obtained by
3- ;: collecting such a bundle on a rotating mandrel placed
: -
,: : .
,~ : :
~ Y092~18677 ~ 7 4 PCT/USg2/01381
27
in the fiber stream exiting from the orientingchamber, or by cutting fiber lengths from a collected
: web and assembling the cut lengths into a bundle).
The crystalline orientation of the oriented
microfibers is readily apparent from the presence of
rings, and the interruption of those rings in Fig. 4A.
Crystalline axial orientation function
; (orientation along the fiber axis) was also determined
; for the fibers of the invention (using proc~dures as
. 10 described in Alexander, L.E., X-Ray Diffraction
Methods in Polymer Science, Chapter 4, published by R.
E. Krieger Publishing Co., New York, 1979; see
particularly, page 241, Equation 4-21) and found to be
. ~
0.65. This value would be very low, at least
approaching zero, for conventional melt-blown fibers.
A value of 0.5 shows the presence of significant
crystalline orientation, and preferred fibers of the
invention exhibit values of 0.8 or higher.
Example 2
Oriented nylon 6 microfibers were prepared
using apparatus generally like that of Example 1,
except that the main portion of the orienting chamber
was 48 inches (122 cm) long. Thè melt-blowing die had
circular smooth-surfaced orifices (25/inchj having a
~; 5:1 length-to-diameter ratio. The die temperature was
~` 270C, the primary air temperature and pressure were,
.; respectively, 270C and 15 PSI ~104 kPa), (0.020-inch
[0.05 cm] gap width), and the polymer throughput rate
was 0.5 lb/hr/in (89 g/hrtcm). The extruded fibers
were oriented using air in the orienting chamber at a
j pressure of 70 PSI (483 kPa) with a gap width of 0.005
inch (0.013~cm?,~and~an approximate air temperature of
25C. The flared randomizing portion of the orienting
chamber was 24 inches (61 cm) long. Fiber exit
velocity was about 6250 meterstminute.
;, ~ - : ~
, , ,
d ; : ~ ~ ;
.~ .: :
'. :
W092"8677 21~^~07~1 ~8 PCT/US9~/~138 ~
Scanning electron microscopy (SEM) of a
representative sample showed fiber diameters of 1O8 to
9.52 microns, with a calculated mean fiber diameter of
5.1 microns.
For comparison, an unoriented nylon 6 web
was prepared without use of the orienting chamber and
with a higher die temperature of 315C chosen to
produce fibers similar in diameter to those of the
oriented fibers of the invention (higher die
temperature lowers the vis osity of the extruded
material, which tends to result in a lower diameter of
the prepared fibers; thereby the comparative fibers
can approach the size of fibers of the invention,
which as noted above, tend to be narrower in diameter
than conventionally prepared melt-blown fibers). The
fiber diameter distribution was measured as 0.3 to
10.5 microns, with a calculated mean fiber diameter of
3.1 microns.
The tensile strength of the prepared fibers
`20 was measured as described in Example 1, and the
resultant stress-strain curves are shown in Figs. 5A
(fibers of the invention) and 5B (comparative
unoriented fibers). Units on the ordinate are in
-pounds/square inch and on the abscissa are in percent.
I 25 Fig. 6 presents SEM photographs of
representative webs of the invention prepared as
described above (6A) and of the comparative unoriented
! webs (6B) to further illustrate the differenae between
them as to fiber diameter. As will be seen, the
i30 comparative web includes very small-diameter fibers,
'apparently produced as a result of the great -
turbulence at the exit of a melt-blowing die in the
conventional melt-blowing process. A much more
uniform air flow occurs at the exit of the die in a
process of;the present invention, and this appears to
contribute toward preparation of fibers that are more
uniform in diameter.
.
: ~ .
: :: : ,
.
- - : ' :'
~ ~ ~ 0 5 ~ 7 ~
r ~ ,. ~ .
29
Fig. 7 presents WAXS photos for the ~ibers
o~ the invention (7A) and the comparative fibers (7B).
,
Example 3
- Oriented microfibers of polyethylene
-- terephthalate (Eastman A150 ~rom Eastman Chemical Co.)
were prepared using the apparatus and conditions of
~; Example 2, except that the die temperature was 315C,
and the primary air pressure and temperature were,
respectively, 20 PSI (138 kPa) and 315C. Fiber exit
velocity was about 6000 meters/minute. The
distribution of fiber diameters measured by SEM was
3.18 to 7.73 microns, with a mean o~ 4.94 microns.
~ 15 Unoriented microfibers were prepared for
`,!~` comparative purposes, using the same resin and
operating conditions except for a slightly higher die
temperature (335C) and the lack of the orienting
chamber. The fiber diameter distribution was O.91 to
8.8 microns with a mean of 3.81 microns.
Fig. 8 shows the WAXS patterns photographed
for the oriented (Fig.-8A) and comparative unoriented
fibers (Fig. 8B). The increased crystalline
orientation of the oriented microfibers was readily
apparent.
Example 4
~I Using the apparatus of Fig. 2A without the
;I secondary chamber 38, a ultrafine submicron fiber was
blown from polypropylene resin (Himont PF 442) the
extruder temperature was 435F (224C) and the die
! temperature was 430F (221C). The extruder operated
at 5RPM (3l4 inch diameter, model No. D-31-T, C.W.
Brabender Intruments of Hackensack, New Jersey) with a
3S purge block. Excess polymer was purged in order to
approximate a polymer ~low rate of less than 1
gm/orifice/hr. The die had 98 orifices, each with an
SIJBSTITIJTE Sl-IFET
r ~ ` r ~
~ 1 0 a ~ 7 ~ r r ~ I ;
ori~ice size of about 0.005 inches (125 micrometers)
and an orifice length of o. 227 inches (o. 57 cm). The
primary air pressure was 30 PSI (206 kPa) and a gap
width of 0.01 in (o. 025 cm). The primary air -
temperature was 200c. The polymer was blown into theorienting chamber. The secondary orienting air had a
pr~ssure of 70 PSI (483 kPa) with an air gap width of
. 0. 03 inches and was at ambient temperature. The
Coanda surface had a radius of 1/8 in (0. 32 cm). The
lo chamber had an interior height of l.0 inches (2. 54
cm), an interior width of 4 inches (10.16 cm), and a
total length of 20 inches (including a flared exit
portion).
The fibers formed had an averaye flber
diameter of 0.6 micrometers with 52~ of the fibers in
the range o~ 0.6 to 0.75 micrometers. Approximately
85% of the fibers were in the range of 0. 45 to 0.75
micrometers. tThe fiber sizes and distributions were
determined by scanning electron micrographs of the web
analyzed by an OmiconTM Image Analysis System made by
, Bausch & Lomb.) Some roping of fibers (approximately
,' 3%) was noted. ~
., .
Example_5
This example again used the apparatus and
, polymer of Example 4 without the chamber 38. In this
; ' ' example, the chamber 37 was provided w~th sidewalls
formied o~ porous glass and had a chamber length of 15
' 1/2 inches excluding the flared exit portion. The air
knives-on the chamber 37 were also adjustable to allow
the air to be deli~ered to the Coanda surface at
! different angles. The Coanda surface had a radius of
1 in (2.54 cm)~and~an air ex~it angle of 45 degrees.
The temperature of the extruder ranged from l90~to
255C from inlet to outlet and rotated at 4 rotations
per minutes (a~0.75 in,~1.7 cm,~ screw diamete~). A
purge block was agaln used~ to keep the polymer flow
SUE~STiTUTE~ SHEET ~ :
2 1 3 ~ a ~ 4 ~ r ~ r
rate down and prevent excessive residence time of the
polymer in the die. The polymer flow rate was 260
gm/hr (2.6 g/min/ori~ice). The die temperature was
186C and had orifices each with an orifice size of
0.005 in (0.01~ cm). The primary air pressure was 10
PSI (70 kPa) with an air gap width of 0. oa5 in (0.013
cm). The secondary orienting air had a pressure of 20
PSI (140 kPa) with an air gap width of 0.03 in (0.0076
cm). Cooling air was introduced through the porous
glass walls at a pressure of 10 PSI (70 kPa). The
collector was located 22 in (56 cm) from the die. The
fibers under microscope appeared to have an average
diameter of one micrometer.
Examples 6-18
- The set-up and polymer was used as in
Example 4 above. The conditions of the process are
set forth in Table I below.
. ::
. :,
.... .
"~ , .
.
! .
., .
~ I .
;~ , .
!:, , , ' .
e
,
,
;l `
~ ,
-1 .
..
'I - .
3 : -:
SUBSTITUTE SHE T
.. .~
~ r
2 1 ~) ~;1 0 i 4
32
. Table I
Ex T1 T2 T3 ~I T~2 ~ ~2 R ~,
6 240 250 250 2302550 80 2 .180
7 240 250 250 2302530 80 15 179
8 240 250 250 2302525 80 10 . 180
9 240 250 250 2302~50 80 4 180
lo 240 250 250 2302510 20 2 180
11 240 250 250 2302510 10 2 177
.~ 10 12 240 250 250 2302515 5 2 180
13 240 250 250 2302535 5 2 lc~O
` 14 240 250 250 2302535 25 2 177
`- 15 240 250 250 2302535 5 2 180
.~ 16 240 250 250 2302530 50 2 180
17 240 250 250230 .2520 50 2 177
`:` 18 240 250 250230 25 5 50 2 177
T~ - extruder exit temperature ~c)
T2 ~ purge block temperature (C)
T3 - temperature of the die (C)
3 T~l-T~2 - temperature of the airstreams (C), the
primary air and the first orienting air,
respectively.
P3l-P,2 - the pressures of the above airstreams (PSI)o
F~ - polymer flow rate was.approximately
. 2.5 gm/hr/orifice, for Examples 31-33.
R - extruder RPM
Tm - temperature of melt (C)
.! ,
~' 30 :.
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';
J85TITUTE SHE~:T ~:
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r r r ~ r ~,
33
The fiber size (in micrometers) distribution
was then determined with the results set forth in
Table II below.
Table II
Ex. Mean Median St.Dev. 90%+ ranqe Ct
6 2~7 2~80~6 1~5-3~5 15
7 4~8 4~62~4 0~1-8~1 16
8 2~2 2~ 4 0~5~4~5 21
9 2.7 2~70~6 2~1-3.7 13
10 1~7 1~70~3 1.4-2~2 15
11 2~0 2~00~5 1~5-3~5 22
12 2.6 2~50~4 1.6-3.4 19
13 2~5 2~31~0 1~0-4~0 28
14 2~4 2~40~6 1~0-4~0 20
15 2~5 2.60~4 1~7-3~8 20
16 0~93 0~820~38 0~6-1~6 37
., .
i 20 17 0~ 80 0~ 810~ 25 0 ~ 3-1 ~ 2101 ,
t 18 0~ 90 0.850~ 07 0~ 78-0~ 92100
.. . . .
In Table II, the 90% range is the size range
in which 90~, or more, of the fibers are found, Ct is
- 25 the number of fibers measured, and St.Dev. represents
the standard deviation. Generally, narrower size
distributions were noted with lower polymer flow
rates. Examples 7 and 8 had higher extruder speeds
and a significantly wider range of fiber diameters
compared to Examples 6 and 9.
The last three examples in Table II (16-18) ;
have smaller mean diameters~than the other examples.
It is beli~ved that this~;arose form the combination of
relatively lower primary press~re and relatively
higher air pressure from the orientation chamber
orifices.
~ . .:
~JBSTITUTE SHEFT
- .
,
~ 2 1 ~ ~i 0 7 4
34
Example 18 yielded extremely small average
diameter fibers of a very narrow range of fiber
diameters. The scanning electron micrograph of the
Example 18 fibers of Fig. 13 shows this uniformity of
fiber diameters (the small line below "5.0 kx"
represents 1 micrometer).
Example 19
In this example, the same arrangement and
~; polymer were used, as in Example 5, except that a
secondary chamber 38 (namely, that used in Example 19)
was used. The extruder and a ratio of metering pumps
were used to control the purge block. The extruder
outlet temperature was 240C and the purge block and
- die were 250C. The extruder was run at 2 RPMs.
The action of purge block was controlled by
three precision pumps (pump 1, "Zenithl' pump, model
^ no. HPB-4647-0.297, pumps 2 and 3, "Zenith" pumps,
model no. HPB-4647-0.160, obtained from the Powell
Equipment Company, Minneapolis, Minnesota). Pumps 1
and 2 were driven by a precision, adjustable, constant
~- speed motor (model number 5BP56KAA62, Boston Gear
Company, of Boston, Massachusetts). These pumps were
~`~ connected by a full-time gear drive which drove pump 1
at five times the speed of pump 2. Pump 3 was driven
by another precision speed motor of the same type.
These pumps divided the onflowing stream of resin into
two streams. The larger polymer stream from pump 3
was removed ("purged") from the system. The smaller
stream from pump 2 was retained.
, 30 The smaller stream was passed through a filter
- bed of small glass beads with a mesh of 240 holes/in2,
capable of removing any foreign matter larger than 1
micron (1 micrometer). It was then conveyed into the
die and extruded through the orifices (0.012 inches
diameter, 0.03 cm).
.
IE3STITUT~: SHEE:~ `
,i, . - .
2 1 U ~i o 7 4
Primary air ("Air 1") was supplied to the die,
` at a controlled temperature (210C), pressure (5 PSI
`~ with an air gap of 0.01 in), and volume per unit time.
Before beginning the actual formation and
collection of the fibers of the invention, the flow
rate of the polymer through the die was m~asured by
collecting samples of the emergent resin stream at a
point just beyond the die by placing a small weighted
piece of mesh/screen at that point. After five
minutes, the screen was re-weighted, the wei~ht of
resin collected and the extruslon rate in
grams/hole/minute were calculated.
` Ater making this measurement, the resin
stream was routed through two separate chambers.
The first orienting airstream was used to
` carry the stream o~ melted-but-cooling resin on
through the first chamber. The pressure of the
orienting air was 10 PSI (70 kPa) with an air gap of
0.03 in (0.0076 cm?. Air was also introduced at 5 PSI
. 20 (3s kPa) through the porous sidewalls of the chamber.
`, The fibers were then intercepted by a second
,;;.! orienting chamber 38, when they were substantially or
completely cooled, this orienting chamber had an
orienting airstream at 60 PSI (412 kPa) with an air
gap of 0.03 in (0.0076 cm) and an entangling airstream
.l adjacent the chamber exit introduced through
apperatures, at 5 PSI (35 kPa). Pump q t31 in Fig.
2A) was operated at 1730 RPMs, pump 2 (32 in Fig. 2A)
~` was driven at one-fifth this speed with pump 3 (33 in
Fig. 2A) operating at approximately 900 RPM at steady
state. The polymer feed rate was 1 gm/hr/orifice.
~!' The fiber formed had a mean diameter of 1.1
;, micrometers with all fibers (6 counted~ in the range `~
of 0.07 to 1.52 micrometers.
, 35 Rs a matter`of comparison, this same polymer
! was blown without either~chamber (37 or 38 of Fig.
2A). All conditions in the remaining steps o~ the
~: SIJBSTITUTE SHE:E:T: ~
!
~: . ~: : , , .
,
2~0~a~Ll
36
melt-blown process were identical with the exception
of the primary air pressure, which was increased to lo
PSI (70 kPa). The fibers collected had an average
fiber size of 1.41 micrometers with a standard
deviation of 0.37 micrometers. All fibers lay in the
range of 0.5 to 2.1 micrometers.
In further comparison, see Example 1 where
~- much higher polymer flow rates were used (89
gm/hr/orifice). This condition resulted in a much
wider range of fiber diameters for both the oriented
and unoriented melt-blown fibers.
.~. ' ,'. ~,.
Example 20
` This example wa~ run in accordance with the
procedure and apparatus of Example l9. The polymer
was a polyethylene (Dow AspunTM 6806, available from
Dow Chemical Co., MidIand, MI). The extruder was run
at 3 RPMs with an exit temperature O~ about 200C.
The die block and purge block were also about 200Co
The gear pump 1 was run at 1616 RPMs with gear pump 3
operating at 1017 RPMs. The polymer feed rate was
about 1.0 gm/hr/orifice. The primary air temperature -
and the melt temperature were both 162C~ The air `
- pressure was of the primary air was 6 PSI~(32 kPa).
The orienting air in chamber 37 was 50 PSI (345 kPa)
(room temperature) with an 0.01 in(0.025 cm) gap width
and the cooling air was at 10 PSI (70 kPa). The
second chamber had orienting air at 50 PSI (345 kPa) ;
and an entangling airstream at 10 PSI (70 kPa). The`
mean fiber diameter was 1.31 micrometers with a
standard deviation of (0.49 micrometers) (12 samples).
All the fibers lay in the size range of 0.76 to 2.94
~ micrometers, 94 percent were between 0.76 and 2.0
d micrometers. The die had 56 orifices, each 0.012 in
~ 35 (0.03 cm).
`
5UE3ST1TVTE` ~S~ET
.
~ 2105~-7~
37
Examp 1 e 21
he polymer of Example 20 was run as per
xample 19 above with a polymer feed rate of 0.992 ',
~m/hr/orifice (gear pump 31, gear pump 33,,and
extruder RPMs of 1670, 922 and 3, respectively). The
primary air (170~C) was at 10 PSI (70 kPa), with an air ,
, gap width of o.o1 in (0.025 cm). The melt temperature
was 140C extruded from a die ~t 200C (the extruder
exit temperature and block temperature were about
lo 170C). The unoriented fibers formed had a mean fiber
diameter of 4.5 micrometers and a standard deviation
',`' ~ of 1.8 micrometers. 93 percent of the fibers were
,, found in the range of 2 to 8 micrometers (47 fibers
~'i sampled). ''
~, 15 For comparison, the polyethylene fibers of
Example 3 had approximately the same fiber size
distribution when unoriented, but a much wider fiber ,'
size distribution when oriented compared to Example ~
~'~ 20. ,
~ Exam 1 23
'^'~ These examples were run in accordance with the
procedure of the previous'example. The polymer used '
,;,~ji was nylon~(BASF KR-4405) using a die insert with 0.005 ,,
in (0.013 cm) and 0.012 (0.03 cm) in diameter orifices ~'
for the unoriented and the oriented examples,
respecti~ely. The~extruder was run at~2 and 20 RPMs,
respectively, with~exit temperatures of 310 and 300C,
respectively. The die and feed block temperatures
were 280 and 270C, and 275 and 270C, respectively.
~,JI ~ The gear pumps 31 and 33 were run at 1300 and 1330
RPMs, respectively. The meIt temperatures were 231
; and 234C, respectively,~with a primary air
temperature~of 2~42~and 249C, respectivel~. Example
' 35 22 was unoriented~using only the primary air at 7
ft3lmin (0.2 m3/min) with an air gap of 0.01 in (0.025
cm). The resulting fibers had~a~mea;n diamete~ of }.4
SUE35TI~UTE S~:E~
~ s~ !s r r 2 ~ ) 7 L~
,. ..
38
micrometers with a standard deviation of 1Ø 95 ~ -
percent of the fibers (62 counted) had fibers in the
range of 0.0 to 3.0 micrometers. In comparison, see
Example 2, where for a higher polymer flow rate, a
much wider range of fiber diameters were obtained.
Example 23 was oriented using a primary air at
- 3.5 ft3/min (10 PSI or 70 kPa with a 0.01 in (0.025 cm)
air gap). The first chamber 37 had orienting air at
` 20 PSI (140 kPa) and sidewall air at 5 PSI (35 kPa).
The second orienting chamber had air at 40 PSI (277
kPa) and entangling air at 5 PSI (35 kPa). The
resulting fibers had a mean diameter of 1.9
; micrometers with a standard deviation of 0.66
micrometers. 91.6 percent of the fibers (2~ counted)
had diameters within the range of l.0 to 3.0
micrometers.
The a~ove examples are for illustrative
purposes only. The various modifications and
-~ alterations of this invention will be apparent to
20 those skilled in the art without departing from the ; ;
` scope and spirit of the invention, and this invention
should not be restricted to that set forth therein for
illustrative purposes.
., :
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: : :
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SUBSTITlJTE~ SHEET
`. ~ ~92/l~677 2 ~ O ~ ~ 7 ~PCT~us92/0l381
39
sxample ls-15
Insulating webs of the invention were
prepared which comprised 80 weight-percent oriented
microfibers of polycyclohexane terephthalate
: 5 (crystalline melting point 295C; Eastman Chemical
- Corp. 3879), made on apparatus as described in Example
2 using conditions as described in Table V, and 20 -:
~` weight-percent 6-denier polyethylene terephthalate
; crimped staple fiber introduced into the stream of
melt-blown oriented fibers in the manner described for
~` Example 13. Two different webs of excellent
. drapability and soft hand were prepared having the
basis weight described below in Table VII. Thermal
insulating properties for the two webs are also given :-
15 in Table VII. . :
~, .
"~ Table VII
" ~ .,
.~ Example No. 14 15 16
" : 20
Weight (g!m2) 133 106 150
Thickness (cm): o. 73 0.71
Insulating Efficiency (c103 1.31 l.S9
25 (clo/cm) ~1.79 2.24
1.63
(clo-m2/kg) 9.8 .15.013.9
~: After Washed 10 Times
Insulating Efficiency
% Retained 103.1 92.2 99.6
. j . .. .',~. Thickness (~ Retained) 97.3 98.6
.. : 35 ~ - Example 16
An insulating web of the invention was made -~
comprising 65 weight-percent oriented melt-blown
,s ~
1: : : ~ :
2~0~07~
WO92~18677 PCT/U~92/01381
~
polycy~lohexane terephthalate microfibers (Eastman
3879) and 35 weight-percent 6-denier polyethylene
terephthalate crimped staple fibers. Conditions for
manufacture of the oriented melt-blow~ microfibers are
as given in Table V, and measured properties were as
given in ~able VII. The web was of excellent
- drapability and soft hand.
Example l7 and_l8
A first web of the invention (Example 17) was
-~ prepared according to Example l, except khat two dies
were used as shown in Fig. 2. For the die l0A, the
die temperature was 200C, the primary air temperature
and pressure were 200C and 15 PSI (103 kPa),
respectively, and the orienting chamber air
`.` temperature and pressure were ambient temperature and
70 PSI (483 kPa), respectively. Polymer throughput
rate was 0.5 lb/hr/in (89 g/hr/cm). The fibers
leaving the orienting chamber were mixed with
-~ 20 non-oriented melt-blown polypropylene fibers prepared
in the die l0b. For die l0B, the die temperature was
270C, and the primary air pressure and temperature
~ were 30 PSI (206 kPa) and 270C, respectively. The
!~:, polymer throughput rate was 0.5 lb/hr/in (89 g/hr/cm).
; 25 As a comparison, another web of the invention
(Example 18) was prepared in the manner of Example 4,
which comprised only orianted melt-blown fibers. Both
the Example 17 and 18 webs were embossed at a rate of
~8 feet per minute in a spot pattern (diamond-shaped
spots about 0.54 square millimeters in area and
; occupying about 34 percent of the total area of the
web) using a temperature of 275F (135C), and a
pressure of 20 PSI (138 kPa~.
~lj Both the Example 17 and 18 embossed webs were
measured on an Instron tester for tensile strength
` versus strain in the machine direction, iOe., the
direction of movement of the collector, and the cross
, , ' '
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:,
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~ 92~18677 2 1 ~ 5 0 7 d Pcr/U~92/0138l ;
41 .
direction, ~nd the results are reported below in Table
VIII.
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Wo 9~18677 PCI/US92~0138
42
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.. ~ o~ I~
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a u~
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~ 092/18677 21~ ~ ~ 7 ~ PCT/US92/01381 ,l
43
E~amDle 19
Using the apparatus of Fig. 2~ without the
secondary chamber 38, a ultrafine submicron fiber was
blown from polypropylene resin (Himont Pf442) the
extruder temperature was 435F (224C) and the die
temperature was 430F (221C). The extruder operated
at 5RPM (3/4 inch diameter, model No. D-31-T, C.W.
Brabender Intruments of Hackensack, New Jersey) with a
purge block. Excess polymer was purged in order to
~`~ 10 approximate a polymer flow rate of less than 1
gm/orifice/hr. The die had 98 orifices, each with an
orifice size o~ about 0.005 inches (125 micrometers)
` and an orifice length of 0.227 inches (0.57 cm). The
primary air pressure was 30 PSI (206 kPa) and a gap
15 width of 0.01 in (0.025 cm). The primary air
temperature was 200C. The polymer was blown into the
orienting chamber. The secondary orienting air had a
pressure of 70 PSI (483 kPa) with an air gap width of
0.03 inches and was at ambient temperature. The
`~ 20 Coanda surface had a radius of 1/8 in (0.32 cm). The
` chamber had an interior height of 1.0 inches (2.54
i cm), an interior width of 4 inches (10.16 cm~, and a
,J~ total length of 20 inches (including a flared exit
d p0rtion).
, 25 The fibers formed had an average~fiber
Y~ diameter of 0.6 micrometers with 52% of the fibers in
the range of 0.6 to 0.75 micrometers. Approximately
85% of the flbers were in the range o~ 0.45 to 0.75
J micrometers. (The fiber sizes and distributions were
determined by scanning electron micrographs of the web
analyzed by an OmiconTM Image Analysis System made by
Bausch ~ Lomb.) Some roping o~ fibers (approximately
.
j 3%) was noted.
Example 20
This example again used the apparatus and
polymer o~ Example l9 without the chamber 38. In this
210507~
WO92~18677 PCT/US92/0138
example, the chamber 37 was provided with sidewalls
formed of porous glass and had a chamber length of 15
1/2 inches excluding the flared exit portion. The air
knives on the chamber 37 were also adjustable to allow
the air to be delivered to the Coanda surface at
different angles. The Coanda surface had a radius of
1 in (2.54 cm) and an air exit angle of 45 degrees.
The temperature of the extruder ranged from 190 to
255OC from inlet to outlet and rotated at 4 rotations
per minutes (a 0,75 in, 1.7 cm screw diameter). A
purge block was again used to keep the polymer flow
rate down and prevent excessive residence time of the
polymer in the die. The polymer flow rate was 260
gm/hr (2.6 g/min/orifice). The die temperature was
186C and had orifices each with an orifice size of
0.005 in (0.013 cm). The primary air pressure was 10
PSI (70 kPa) with an air gap width of 0.005 in (0.013
cm). The secondary orienting air had a pressure of 20
PSI (140 kPa) with an air gap width of 0.03 in (0.0076
cm). Cooling air was introduced through the porous
glass walls at a pressure of 10 PSI (70 kPa). The
collector was located 22 in (56 cm) from the die. The
fibers under microscope appeared to have an average
diameter of one micrometer
Example 21 34
The set-up and polymer was used as in Example
19 above. The conditions of the process are set forth
. .,
in Table IX below.
.. .
. . .
,
~ .
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. : ' .
~:
: - : ~ j . .. .
210507a
O9~/18677 PCTIUS92/01381
Table IX
Ex Tl T2 ~3 ~l '~ P~l P~2 R~ Tm
~ 21 240 250 250 230 2550 80 2 180
'~ . 5 22 240 250 250 230 25 30 80 15 179
23 240 250 250 230 25 25 80 10 180
.~ 24 240 250 250 230 25 50 80 4 180
25 240 250 250 230 25 10 20 2 180 .
26 240 250 250 230 25 10 10 2 .177 ::
~`, 10 27 240 250 250 230 25 15 5 2 180
28 240 250 250 230 25 35 5 2 180
29 240 250 250 230 25 35 25 2 177 ;
30 240 250 250 230 25 35 5 2 ~80
31 240 250 250 230 25 30 50 2 180
' 15 32 240 250 250 230 25 20 50 2 177
" 33 240 250 250 230 25 5 50 2 177
.~ T~ - extruder exit temperature (C)
~ T2 ~ purge block temperature (C)
.. 20 T3 - temperature of the die (C)
~,! T,l-T~2 - temperature of the airstreams (C), the
~t primary air and the first orienting air, : :
.~ respectively.
Pl~-P,2 - the pressures of the above airstreams (PSI).
t ~ 25 Fl -:polym.er flow:rate was approximately~ :
2.5 ~m/hr/orifice, for~Examples 31-33.
- R - extruder RPM :~
Tm - temperature of melt (C):
' 30 :
d ~
~ ' . : ~ . i .
w~Pl~6~77l~ PCr/U~g2/0138~
46
The fiber size tin micrometers) distribution
was then determined with the results set forth in
Table X below.
Table X
Ex. Mean Median St.Dev. 90~ ranae Ct
21 ~.7 2.8 0.6 1.5-3.5 15
22 4.8 4.6 2.4 0.1-8.1 16
23 2.2 2.1 1.4 0.5~4.5 21
24 2.7 2.7 0.6 ~.1-3.7 13
25 1.7 1.7 0.3 1.4-2.2 15
26 2.0 2.0 0.5 1.5-~.5 22
~7 2.6 2.5 0.4 1.6-3.~ 19
` 15 28 2.5 2.3 1.0 1.0-4.0 28
2g 2.4 2.4 0.6 1.0~4.0 20
30 2.5 2.6 0.4 1.7-3.8 20
31 0.93 0.82 0.38 0.6-1.6 37
32 0.80 0.81 0.25 0.3-1.2 101 ;~
33 o.90 0.85 0.07 0.78-0.92lO0
',. '~
In Table X, the 90~ range is the size range in ~
which 90%, or more, of thei fibers are found, Ct is the ~`
number of fibers measured,~ and St.Dev. represents the
standard deviation. Generally, narrower size
distributions were noted with lower polymer flow
rates. Examples 22 and 23 had higher extruder speeds
and a significantly~wider range of fiber diameters
compared to Examples 21 and 24.
The last three examples in Table X (31-33)
have smaller mean diameters than the other examples.
-It is believeid thak this arose form the combination of -
relatively lower primary pressure and relatively
higher air~pressure from the orientation chamber
orifices. ~
: ~ : - ,.
~ 09~/18677 2 1 ~ ~ 0 7 4 PCT/US92/01381
47
Example 33 yielded extremely small average
diameter fibers of a very narrow range of fiber
diameters. The scanning electron micrograph of the
Example 33 fibers of Fig. 13 shows this uniformity of
fiber sizes (the small line below "5.0 kx" represents
l micrometer).
Bxample 34
In this example, the same arrangement and
polymer were used, as in Example 20, except that a
; lO secondary chamber 38 (namely, that used in Example l9)
was used. The extruder and a ratio of metering pumps
were used to control the purge block. The extruder
outlet temperature was 240OC and the purge block and
die were 250C. The extruder was run at 2 RPMs.
The action of purge block was controlled by -
three precision pumps (pump l, "Zenith" pump, model
" no. HPB-4647-0.297, pumps 2 and 3, "Zenith" pumps,
~i model no. HPB-4647-0.160, obtained from the Powell
Equipment Company, Minneapolis, Minnesota). Pumps l
and 2 were driven by a precision, ad~ustable, constant
~! speed motor (model number 5BP56KAA62, Boston Gear
Company, of Boston, Massachusetts). These pumps were
connected by a full-time gear drive which drove pump l
at five times~the speed of pump 2. Pump 3 was driven
by another precision speed motor of the same type.
-i These pumps divided the onflowing st~ream of resin into
~1 ~ two streams. ~The larger;polymer stream from pump 3 -
~ was removed ("purged") from the system. The smaller
-! stream from pump 2 was retained.
,7,; 30 The smaller stream;was passed through a filter
bed of small glass beads with a mesh of 240 holes/in2,
capable of removing any foreign matter larger than l `
micron (l micrometer). It was then conveyed into the
die ~and extruded~through the orifices (0.012 inches
diameter, 0.03 cm).
3 ~ : .
:
U J ~
WO92/1~677 PCT~US9~/0138
~8
Primary air ("Air l"~ was supplied to the die,
at a controlled temperature (210C), pressure (5 PSI
with an air gap of o.ol in), and volume per unit time.
sefore beginning the actual formation and
collection of the fibers of the invention/ the flow
rate of the polymer through the die was measured by
collecting samples of the emergent resin stream at a
point just beyond the die by placing a small weighted
piece of mesh/screen at that pointv After five
minutes, the screen was re-weighted, the weight of
` resin collected and the extrusion rate in
` grams/hol~/minute were calculated.
After making this measurement, the resin
stream was routed through two separate chambers.
The first orienting airstream was used to
carry the stream of melted-but-cooling resin on
through the first chamber. The pressure of the
orienting air was lO PSI (70 kPa) with an air gap of
0.03 in (0.0076 cm). Air was also introduced at 5 PSI
~ 20 (35 kPa) through the porous sidewalls of the chamber.
; The fibers were then intercepted by a second
orienting chamber 38, when they were substantially or
completely cooled, this orienting chamber had an
orienting airstream at 60 PSI (412 kPa) with an air
gap of 0.03 in (0.0076 cm) and an entangling airstream
1 adjacent the chamber exit introduced through
,~j apperatures, at 5 PSI (35 kPa). Pump l (31 in Fig.
2A) was operated at 1730 RPMs with pump 2 (32 in Fig.
2A) was driven at one-fifth this speed with pump 3 (33
in Fig. 2A) operating at approximately 900 RPM at
t steady state. The polymer feed rate was
`1 I gm/hr/orifice. The fiber formed had a mean diameter
of l.l micrometers with all fibers (6 counted) in the
' ~ range of 0.07 to l.52 micrometers.
As a matter of comparison, this same polymer
was blown without either chàmber (37 or 38 of Fig.
2A). All conditions in the remaining steps of the
~! . - .
, ~ ` ,
.
. .
~92/18677 ~ ~J O 7 ~ PCT/US92tOl381
49
melt-blown process were identical with the exception
of the primary air pressure, which was increased to 10
; PSI (70 kPa). The fibers collected had an average
fiber size of 1.41 micrometers with a standard
deviation of 0.37 micrometers. All fibers lay in the
range of 0.5 to 2.1 micrometers.
In further comparison, see Example 1 where
much higher polymer b~own rates were used (89
gm/hr/orifice). This condition resulted in a much
wider range of fiber diameters for both the oriented
and unoriented melt-blown fibers.
Example 35
This example was run in accordance with the
procedure and apparatus of example 34. The polymer
was a polyethylene (Dow AspunTM 6806, available from
~ow Chemical Co., Midland, MIj. The excruder was run
at 3 RPMs with an exit temperature of about 200C. ;
The die block and purge block were also about 200C.
The gear pump 1 was run at 1616 RPMs with gear pump 3
operating at 1017 RPMs. The polymer feed rate was
about 1.0 gm/hr/orifice. The primary air temperature
and the melt temperature were both 162C. The air
pressure was of the primary air was 6 PSI (32 kPa).
The orienting air in chamber~37 was 50 PSI~(345 kPa?
(room temperature) with an 0.01 in (0.0~25 cm) gap
width and the cooling air was at 10 PSI (70 kPa). The
second chamber had orienting air at 50 PSI (345 kPa)
and an entangling airstream at 10 PSI (70 kPa). The
mean fiber diametèr was 1.31 micrometers with a
standard deviation of (0.49 micrometers) (12 samples).
All the fibers lay in the size range of 0.76 to 2.94
micrometers, 94 percent were between 0.76 and 2.0
micro~eters. The~die~had~ 56 orifices, each 0.012 in
(0.03 cm)-~ ~
~.',
:
21~507 ~
WO 92/18677 PCI/US92/0138
Example 36
The polymer of Example 35 was run as per
Example 34 above with a polymer feed rate of 0.992
gm/hr/orifice (gear pump 31, gear pump 33, and
extruder RPMs of 1670, 922 and 3, respectively). The
primary air (170C) was at 10 PSI (70 kPa) with an air
gap width of o.Ol in (0.025 cm). The melt temperature
was 140C extruded from a die at 200C (the extruder
exit temperature and block temperature were about
;~ 10 170C). The unoriented fibers formed had a mean fiber
diameter of 4.5 micrometers and a standard deviation
of 1.8 micrometers. 93 percent of the fibers were ~ ;
~ found in the range of 2 to 8 micrometers (47 fibers
- sampled).
For comparison, the polyethylene fibers of
Example 3 had approximately the same fiber size
distribution when unoriented, but a much wider fiber
size distribution when oriented compared to Example
- 35.
; 20
.~,
i Examples 37 and 38
These examples were run in accordance with the
procedure of the previous example. The polymer used
was nylon (BASF KR-4405) using a die insert with 0.005
in (0.013 cm) and 0.012 t0.03 cm) in diameter orifices
for the unoriented and the oriented examples,
~ respectively. The extruder was run at 2 and 20 RPMs,
;, respectively, with exit temperatures of 310 and 300C,
respectively. The die and feed block temperatures
~! 30 were 280 and 270C, and 275 and 270C, respectively.
The gear pumps 31 and 33 were run at 1300 and 1330
RPMs, respectively. The melt temperatures were 231
~' ~ and 234C, respectively, with a primary air
tempsrature of 242 and 249C, respectively. Example
1 35 37 was unoriented using only the primary air at 7
i ft3/min (0.2 m3/min) with an air gap of 0.01 in (0.025
cm). The resulting fibers had a mean diameter of 1.4
~~ ~ 092/18677 21~ S 0 7 4 PCT/US92/01381
.. : 51
micrometers with a standard deviation of lØ 95
percent of the fibers (62 counted) had fibers in the
range of 0.0 to 3.0 micrometers. In comparison, see
Example 2, where for a higher polymer flow rate, a
much wider range of fiber diameters were obtained.
Example 38 was oriented using a primary air at
- 3.5 ft3/min (lO PSI or 70 kPa with a O.Ol in (0~025 cm)
air gap). The first chamber 37 had orienting air at
20 PSI (140 kPa) and sidewall air at 5 PSI (35 kPa).
- lO The second orienting chamber had air at 40 PSI (277
kPa) and entangling air at 5 PSI (35 kPa). The
resulting fibers had a mean diameter of l.9
'? micrometers with a standard deviation of 0.66
- micrometers. 9l.6 percent of the fibers (24 counted)
15 had diameters within the range of l.0 to 3.0
micrometers. -
The above examples are for illustrative
:, ..
purposes only. The various modifications and
alterations of this invention will be apparent to
20 those skilled in the art without departing from the
scope and spirit of the invention, and this invention
, should not be restricted to that set forth therein for
illustrative purposes.
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