Note: Descriptions are shown in the official language in which they were submitted.
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POLYMERIC STRANDS WITH ENHANCED TENSILE STRENGTH, NONWOVEN WEBS
INCLUDING SUCH STRANDS, AND METHODS FOR MAKING SAME
Technical Field
This invention relates to polymeric strands made by melt-extruding a polymer andnonwoven webs made with such strands.
Cross-R~f~r~.,ce to Related Applications
This app"c~tion is a continuation-in-part of U.S. ~pF'.-~tion Serial No. 08/576,174
filed in the U.S. Patent Office on December 21, 1995 in the names of B. Cohen et al. and
entitled "An Ultrasonic Apparatus and Method For Increasing the Flowrate of a Liquid
Through an Orifice", a continuation-in-part of U.S. Application Serial No. 08/576,543 filed in
the U.S. Patent Office on December 21, 1995 in the names of L. K. Jameson et al. and
entitled "An Apparatus and Method For Emulsifying a Pressurized Multicomponent Liquid",
and a continuation-in-part of U.S. Application Serial No. 08/477,689 filed in the U.S. Patent
Office on June 7, 1995 in the names of L. K. Jameson et al. and entitled "Method And
Apparatus For Increasing the Flowrate of a Liquid Through an Orifice", which is a
continuation-in-part of U.S. Patent Application Serial Number 08/264,548 filed in the U.S.
Patent Office on June 23, 1994 in the name of L.K. Jameson and entitled "Method and
Apparatus for Ultrasonically Assisted Melt Extrusion of Fibers," the subject matter of which
applications is hereby incol~.o,~led by reference in their entirety.
Background of the Invention
The melt-extrusion of liquids, such as, for example, thermoplastic polymers, to form
fibers and nonwoven webs generally involves forcing a molten polymer through a plurality of
orifices to form a plurality of molten threadlines, contacting the molten threadlines with a
fluid, usually air, directed so as to form strands (filaments or fibers) and attenuate them.
The attenuated strands then are randomly deposited on a surface to form a nonwoven web.
The more common and well known processes utilized for the preparation of
nonwoven webs are meltblowing, coforming, and spunbonding.
Meltblowing references include, by way of example, U.S. Patent Nos. 3,016,599 toPerry, Jr., 3,704,198 to Prentice, 3,755,527 to Keller et al., 3,849,241 to Butin et al.,
3,978,185 to Butin et al., and 4,663,220 to Wisneski et al. See, also, V. A. Wente,
"Superfine Thermoplastic Fibers", Industrial and Enqineerinq ChemistrY, Vol. 48, No. 8, pp.
, . ..... .... , . . . --.
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1342-1346 (1956); V. A. Wente et al., "Manufacture of Superfine Organic Fibers", Navy
Research Laboratory, Washington, D.C., NRL Report 4364 (111437), dated May 25, 1954,
United States Depa~ ent of Commerce, Office of Technical Services; and Robert R. Butin
and Dwight T. Lohkamp, "Melt Blowing - A One-Step Web Process for New Nonwoven
roducts", Journal of the Technical Association _ the ~ull~ and PaPer Industry, Vol. 56, No.4,
pp 74-77 (1973)-
Coforming references (i.e., references disclosing a meltblowing process in whichfibers or particles are commingled with the meltblown fibers as they are formed~ include U.S.
Patent Nos. 4,100,324 to Anderson et al. and 4,118,531 to Hauser.
Finally, spunbonding references include, among others, U.S. Patent Nos. 3,341,394
to Kinney, 3,655,862 to Dorschner et al., 3,692,618 to Dorschner et al., 3,705,068 to Dobo
et al., 3,802,817 to Matsuki et al., 3,853,651 to Porte, 4,064,605 to Akiyama et al.,
4,091,140 to Harmon, 4,100,319 to Schwartz, 4,340,563 to Appel and Morman, 4,405,297
to Appel and Morman, 4,434,204 to Hartman et al., 4,627,811 to Greiser and Wagner, and
4,644,045 to Fowells.
Nonwoven webs have many uses including cleaning products such as towels and
industrial wipes, personal care items such as incontinence products, infant care products,
and absorbent feminine care products, and garments such as medical apparel. Polymeric
strands with a high level of strength, particularly, tensile strength or tenacity, are often
desirable for these applications. Typical methods of enhancing the tensile strength of a fiber
or filament include increasing the denier of the fiber or filament, changing the polymer to a
higher strength polymer, or adding strength enhancing ingredients to the polymer. Although
these methods are often suitable, they can affect other physical properties of melt-extruded
polymeric strands and nonwoven materials made therewith, such as softness and feel.
Accordingly, there remains a need for melt-extruded strands and nonwovens with enhanced
strength and methods of making such strands without subsl~ntially altering other physical
properties of the materials.
-
Summary of the Invention
This invention addresses some of the needs described above by providing amelt-extruded polymeric strand having enhanced tensile strength, particularly, an enhanced
tenacity. This invention also encompasses a method for making such a strand by extruding
a melt-extrudable polymer while applying ultrasonic energy to a portion of the
melt-extrudable polymer. This invention further encompasses a nonwoven web and amethod for making a nonwoven web comprising such a melt-extruded polymeric strand.
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More particularly, the melt-extruded polymeric strand of this invention has enhanced
tensile ~ nglh formed by extruding a melt-extrudable polymer while subjecting the a portion
of the polymer to ull,ason.~ energy. The melt-extrudable polymeric strand has a tenacity
which is about 1.5 to about 3 times the tenacity of an otherwise identical strand not made by
applying ultrasonic energy to a portion of the melt-extrudable polymer while themelt-extrudable polymer is extruded. Desirably, the strand has a tenacity within a range
from about 0.3 to about 0.9g/denier.
More particularly, the method of this invention for making polymeric strands with
enhanced sl~nyll, includes extruding a melt-extrudable polymer through a die assembly,
applying ull,dsonic energy to a portion of the melt-extrudable polymer, and attenuating the
extruded polymer to form a strand. The die asse~bly includes a die housing and a device
for applying ull~sonic energy to the melt-extrudable polymer. The die housing comprises a
chamber adapted to receive the melt-extrudable polymer, an inlet adapted to supply the
chamber with the melt-extrudable polymer, and an exit orifice defined by the walls of a die
tip. The exit orifice is adapted to receive the melt-extrudable polymer from the chamber and
pass the melt-extrudable polymer out of the die housing.
The ultl~sonic energy is applied to a portion of the melt-extrudable polymer within
the chamber and without applying ull,dsonic energy to the die tip, while the exit orifice
receives the melt-extrudable polymer from the die housing chamber. Consequently, as the
melt-extrudable polymer passes out of the exit orifice in the die tip, the melt-extrudable
polymer is at least partially orienled and the tensile strength of the strand is enhanced.
Nonwoven webs made with the above-described polymeric strands are made by
depositing the polymeric strands onto a collecting surface such as in meltblowing,
coforming, or spunbonding techniques.
Other objects and the broad scope of the applicability of this invention will become
apparent to those of skill in the art from the details given her~ a~Ler. However, it should be
understood that the detailed description of the preferred e~bodi",ents of the invention is
given only by way of illustration because various changes and modifications well within the
scope of the invention should become apparent to those of skill in the art in view of the
following detailed description.
Brief Desc.i~liG" of D~ i,-ys
FIG. 1 is a cross-sectional elevation view of an apparatus for making an embodiment
of the present invention.
FIG. 2 is a graph ilhlsl,~ g average load versus displacement values for a strand
. ,
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made according to an e",bodi",enL of this invention.
FIG. 3 is a graph illustrating average load versus displacement values for a
conventional polymeric strand made without the use of ulll~sonic energy.
Detailed Desc~i"tion of C."l G.li.nel~t~ of the l~ .niG.I
As su~ ""~ari~ed above, this invention encompasses melt-extruded polymeric strands
with enhanced tensile strength, nonwoven webs made with such strands and methods for
making the foregoing. After defining certain terms used herein, an appar~lus for use in
making strands in accordance with an embodiment of this invention is described, followed by
a description of methods for using the apparatus and particular examples of polymeric
strands made with the appal ~tus.
As used herein, the term "strand" refers to an elongated extrudate formed by
passing a polymer through a forming orifice such as a die. Strands include fibers, which are
discontinuous strands having a definite length, and filaments, which are continuous strands
of material.
As used herein, the term "nonwoven web" means a web of material which has been
formed without use of weaving processes which produce a structure of individual strands
which are interwoven in an identifiable repeating manner. Nonwoven webs may be formed
by a variety of processes such as mel~ "lg processes, spunbonding processes, film
aperturing processes, coforming processes, and staple fiber carding processes.
As used herein, the term "tenacity" means the tensile strength of a strand for a given
size of strand and the term "tensile strength" means the maximum stress a material
subjected to a stretching load can withstand without tearing.
As used herein, the terms "ther",oplaslic polymer" and "thermoplastic material" refer
to a high polymer that softens when exposed to heat and returns to its original condition
when cooled to room temperature. The terms are meant to include any thermoplastic
polymer which is t~;lp~h'c of being melt-extruded. The term also is meant to include blends
of two or more polymers and alternating, random, and block copolymers. Examples of
thermoplastic polymers include, by way of illustration only, end-capped polyacetals, such as
poly(oxymethylene) or polyformaldehyde, poly(trichloroacetaldehyde),
poly(n-valeraldehyde), poly(acetaldehyde), poly(propionaldehyde), and the like; acrylic
polymers, such as polyacrylamide, poly(acrylic acid), poly(methacrylic acid), poly(ethyl
acrylate), poly(methyl methacrylate), and the like; fluorocarbon polymers, such as
poly(tetrafluoroethylene), perfluorinated ethylene-propylene copolymers,
ethylene-tetrafluoroethylene copolymers, poly(ch' rull irluoroethylene),
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ethylene-chlorotrifluoroethylene copolymers, poly(vinylidene fluoride), poly(vinyl fluoride),
and the like; polyamides, such as poly(6-aminocaproic acid) or poly( -caprolactam),
poly(hexar"ell ,ylene adipamide), poly(hexamethylene sebAc~mide),
poly(1 1-aminoundecanoic acid), and the like; polyaramides, such as
poly(imino-1,3-phenyleneiminoisophlllaloyl) or poly(~-phenylene isophthalamide), and the
like; parylenes, such as poly-D-xylylene, poly(chloro-P-xylylene), and the like; polyaryl ethers,
such as poly(oxy-2,6-dimethyl-1,4-phenylene) or poly(E2-phenylene oxide), and the like;
polyaryl sulfones, such as poly (oxy-1,4-phenylenesulfonyl- 1,4-phenyleneoxy-1,
4-phenylene-isopropylidene-1,4-phenylene), poly(sulfonyl-1,4-phenyleneoxy-1,
4-phenylenesulfonyl-4,4'-biphenylene), and the like; polycarbonates, such as poly(bisphenol
A) or poly(carbonyldioxy-1,4-phenylene.so~ropylidene-1,4-phenylene), and the like;
polyesters, such as poly(ethylene terephlhalale), poly(tetr~r"etl ,ylene terephthalate),
poly(cyclohexylene-1,4-dimethylene tert:phll,alate) or
poly(oxymethylene-1,4-cyclohexylenemethyleneoxyterephthaloyl), and the like; polyaryl
sulfides, such as poly(E~-phenylene sulfide) or poly(thio-1,4-phenylene), and the like;
polyimides, such as poly(pyromellitimido-1,4-phenylene), and the like; polyolefins, such as
polyethylene, polypropylene, poly(1-butene), poly(2-butene), poly(1-pentene),
poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene),
1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, polychloroprene,
polyacrylonitrile, poly(vinyl acetate), poly(vinylidene chloride), polystyrene, and the like;
copolymers of the foregoing, such as acrylonitrile-butadiene-styrene (ABS) copolymers, and
the like; and the like.
By way of example, the them~oplaslic polymer may be a polyolefin, exan,ples of
which are listed above. As a further example, the thermoplastic polymer may be a polyolefin
which cor,lai"s only hydrogen and carbon atoms and which is prepared by the addition
pol~,~"eri~lion of one or more unsaturated monomers. Examples of such polyoiefins
include, among others, polyethylene, polypropylene, poly(1-butene), poly(2-butene),
poly(1-pentene), poly(2-pentene), poly(3-methyl-1-pentene), poly(4-methyl-1-pentene),
1,2-poly-1,3-butadiene, 1,4-poly-1,3-butadiene, polyisoprene, polystyrene, and the like, as
well as blends of two or more such polyolefins and alternating, random, and block
copolymers prepared from two or more different unsaturated monomers.
As used herein, the term "node" means the point on the longitudinal excitation axis of
the ultrasonic horn at which no longitudinal motion of the horn occurs upon excitation by
ultrasonic energy. The node sometimes is referred to in the art, as well as in this
specification, as the nodal point.
s
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The term "close proximity" is used herein in a qualitative sense only. That is, the
term is used to mean that the means for applying ultrasonic energy is sufficiently close to
the exit orifice (e.g., extrusion orifice) to apply the ultrasonic energy primarily to the
melt-extrudable polymer passing into the exit orifice (e.g., extrusion orifice). The term is not
used in the sense of defining specific distances from the extrusion orifice.
Generally speaking, the appa~lus of the present invention includes a die housingand a means for applying ull~son _ energy to a portion of a pressurized liquid such as a
molten thermoplastic polymer. The die housing defines a chamber adapted to receive the
melt-extrudable polymer, an inlet (e.g., inlet orifice) adapted to supply the chamber with the
melt-extrudable polymer, and an exit orifice (e.g., extrusion orifice) adapted to receive the
melt-extrudable polymer from the chamber and pass the melt-extrudable polymer out of the
exit orifice of the die housing. The means for applying ultrasonic energy is located within the
chamber. For example, the means for applying ultrasonic energy can be located partially
within the chamber or the means for applying ultrasonic energy can be located entirely
within the chamber.
Referring now to FIG.1, there is shown, not necessarily to scale, an exemplary
apparatus for extruding a melt-extrudable polymer. The apparatus 100 includes a die
housing 102 which defines a chamber 104 adapted to receive a pressurized liquid such as
molten thermoplastic polymer. The die housing 102 has a first end 106 and a second end
108. The die housing 102 also has an inlet 110 (e.g., inlet orifice) adapted to supply the
chamber 104 with the melt-extrudable polymer. An exit orifice 112 ~which may also be
referred to as an extrusion orifice) is located in the first end 106 of the die housing 102; it is
adapted to receive the melt-extrudable polymer from the chamber 104 and pass themelt-extruda~le polymer out of the die housing 102 along a first axis 114. An ultrasonic horn
116 is located in the second end 108 of the die housing 102. The ultrasonic horn has a first
end 118 and a second end 120. The horn 116 is located in the second end 108 of the die
housing 102 in a manner such that the first end 118 of the horn 116 is located outside of the
die housing 102 and the second end 120 of the horn 116 is located inside the die housing
102, within the chamber 104, and is in close proximity to the exit orifice 112. The horn 116
is adapted, upon excitation by ultrasonic energy, to have a nodal point 122 and a
longitudinal mechanical excitation axis 124. Desirably, the first axis 114 and the rnechanical
excitation axis 124 will be substantially parallel. More desirably, the first axis 114 and the
mechanical excitation axis 124 will substantially coincide, as shown in FIG.1.
The size and shape of the apparatus of the present invention can vary widely,
depending, at least in part, on the number and arrangement of exit orifices (e.g., extrusion
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orifices) and the operdli"g frequency of the means for apply;"g ultl dSOll.C energy. For
example, the die housing may be cylindrical, rectangular, or any other shape. Moreover, the
die housing may have a singîe exit orifice or a plurality of exit orifices. A plurality of exit
orifices may be arranged in a pattern, including but not limited to, a linear or a circular
pattern.
The means for applying ull~son c energy is located within the chamber, typically at
least partially surrounded by the melt-extrudable polymer. Such means is adapted to apply
the ull,dson ~ energy to the melt-extrudable polymer as it passes into the exit orifice. Stated
~ifr~,~ nlly, such means is adapted to apply ultrasonic energy to a portion of the
melt-extrudable polymer in the vicinity of each exit orifice. Such means may be located
completely or partially within the chamber.
When the means for applying ultrasonic energy is an ull,dson c horn, the hom
conveniently extends through the die housing, such as through the first end of the housing
as identified in FIG. 1. However, the present invention comprehends other configurations.
For ex~,llple, the horn may extend through a wall of the die housing, rather than through an
end. Moreover, neither the first axis nor the longitudinal excitation axis of the horn need to
be vertical. If desired, the longitudinal mechan _al excitation axis of the horn may be at an
angle to the first axis. Nevertheless, the longitudinal mechanicai excitdtion axis of the
ulll~son.c horn desirably will be subslantially parallel with the first axis. More desirably, the
longitudinal mechanical ex~ lion axis of the ultrasonic horn desirably and the first axis will
suL,~tar,lially coincide, as shown in FIG. 1.
If desired, more than one means for applying ultrasonic energy may be located
within the chamber defined by the die housing. Moreover, a single means may apply
ultl~sonic energy to the portion of the melt-extrudable polymer which is in the vicinity of one
or more exit orifices.
According to the present invention, the ultrasonic horn may be composed of a
magnetostrictive material. The horn may be surrounded by a coil (which may be immersed
in the melt-extrudable polymer) c~p~h'c of inducing a signal into the magnetostrictive
material causing it to vibrate at ultrasonic frequencies. In such cases, the ultrasonic horn
can simultaneously be the transducer and the means for applying ull~sonic energy to the
melt-extrudable polymer.
The application of ultrasonic energy to a plurality of exit orifices, such as in a
meltblowing or spunbonding appar~lus, may be accomplished by a variety of methods. For
example, with reference again to the use of an ultrasonic horn, the second end of the horn
may have a cross-sectional area which is sufficiently large so as to apply ultrasonic energy
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to the portion of the melt-extrudable polymer which is in the vicinity of all of the exit orifices in
the die housing. In such case, the second end of the ultrasonic horn desirably will have a
cross-sectional area approximately the same as or greater than a minimum area which
encompasses all exit orifices in the die housing (i.e., a minimum area which is the same as
or greater than the sum of the areas of the exit orifices in the die housing oriy;"aling in the
same chamber). Alternatively, the second end of the horn may have a plurality ofprotrusions, or tips, equal in number to the number of exit orifices. In this instance, the
cross-sectional area of each protrusion or tip desirably will be app~oxi",ately the same as or
less than the cross-sectional area of the exit orifice with which the protrusion or tip is in close
proximity.
The planar relationship between the second end of the ultrasonic horn and an array
of exit orifices may also be shaped (e.g., parabolically, hemispherically, or provided with a
shallow curvature) to provide or correct for certain spray patterns.
~ s already noted, the term "close proximity" is used herein to mean that the means
for applying ultrasonic energy is suffficiently close to the exit orifice to apply the ulll~sonic
energy pri" ,arily to the melt-extrudable polymer passing into the exit orifice. The actual
distance of the means for applying ultrasonic energy from the exit orifice in any given
situation will depend upon a number of factors, some of which are the flow rate of the
melt-extrudable polymer (e.g., the flow rate, rheological characteristics or the viscosity of
melt-extrudable polymer), the cross-sectional area of the end of the means for applying the
ultrasonic energy relative to the cross-sectional area of the exit orifice, the frequency of the
ultrasonic energy, the gain of the means for applying the ultrasonic energy (e.g., the
magnitude of the longitudinal mechanical excitation of the means for applying ullr~sonic
energy), the temperature of the melt-extrudable polymer, the rheological characteristics of
the melt-extrudable polymer, and the rate at which the melt-extrudable polymer passes out
of the exit orifice.
In general, the distance of the means for applying ultrasonic energy from the exit
orifice in a given situation may be determined readily by one having ordinary skill in the art
without undue experimentation. In practice, such distance will be in the range of from about
0.002 inch (about 0.05 mm) to about 1.3 inches (about 33 mm), although greater distances
can be employed. Such distance determines the extent to which ultrasonic energy is
applied to the melt-extrudable polymer other than that which is about to enter the exit orifice;
i.e., the greater the distance, the greater the amount of melt-extrudable polymer which is
subjected to ultrasonic energy. Consequently, shorter distances generally are desired in
order to minimize degradation of the melt-extrudable polymer and other adverse effects
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which may result from exposure of the melt-extrudable polymer to the ultrasonic energy.
Desirably, the means for applying ultrasonic energy is an immersed ullldson ~ horn having a
longitudinal mechanical ekcilaLion axis and in which the end of the hom located in the die
housing nearest the orifice is in close prc~i"lily to the exit orifice but does not apply
ull,~son.c energy directly to the exit orifice.
One advantage of the foregoing appardl~s is that it is self-cleaning. That is, the
comb.. Ialion of supplied pressure and forces generated by ultrasonically exciting the means
for supplying ultrasonic energy to the melt-extrudable polymer (without applying ulll~sonic
energy directly to the orifice) can remove obstructions that appear to block the exit orifice
(e.g., extrusion orifice). According to the invention, the exit orifice is adapted to be
self-cleaning when the means for applying ull~son c energy is excited with ultrasonic
energy (without applying ullldson c energy directly to the orifice) while the exit orifice
receives pressurized melt-extrudable polymer from the chamber and passes the
melt-extrudable polymer out of the die housing.
In general, melt-extruded polymeric strands are formed with the extruder apparatus
100 illustrated in FIG. 1 by introducing a melt-extrudable polymer into the chamber 104 of
the die housing 102 through the inlet 110 and exciting the ultrasonic horn 116 as the
melt-extrudable polymer is extruded through the exit oriflce 112. The ultrasonic energy
applied by the ultrasonic horn 116 applies ultrasonic energy to a portion of themelt-extrudable polymer within the chamber and without applying ull~asonic energy to the
die tip, while the melt-extrudable polymer is received and extruded through the exit orifice
1 12. After the melt-extrudable polymer is extruded through the exit orifice 112, the extruded
polymer is attenuated to form a strand. The attenuation of the extruded polymer can be
accon,F' shed mechanically or by entraining the fiber in a fluid such as in a meltblowing or
spunbonding process. To form a nonwoven web from the extruded strand, the strand is
Idncl~r, lly deposited on a collecting surface. Nonwoven webs can also be prepared by
extruding the melt-extrudable polymer and forming a strand, cutting the strand into staple
fibers, and carding the staple fibers into a nonwoven web which can be subsequently
bonded by known means.
The physical properties of the resulting melt-extruded polymeric strand depend
largely on the melt-extruded polymer. Suitable melt-extrudable polymers are described
above.
The polymeric strand formed with the melt-extrudable polymer and the application of
ultrasonic energy as described above has a tenacity which is about 1.5 to about 3 times the
tenacity of an otherwise identical strand made without the application of ultrasonic energy.
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More particularly, the tenacity of the strand can range from about 0.3 to about 0.9 g/denier.
In a desirable embodiment, such a melt-extruded high tensile strength polymeric strand has
a denier within the range from about 0.006 to about 250.
The present invention is further described by the examples which follow. Such
exa",,~'es, however, are not to be construed as limiting in any way either the spirit or the
scope of the present invention.
EXAMPLES
Ultrasonic Horn Apparatus
The following is a desc;, il tion of an exe" ,,~,lary ultrasonic hom apparatus of the
present invention generally as shown in FIG.1.
With reference to FIG.1, the die housing 102 of the apparatus was a cylinder having
an outer diameter of 1.375 inches (about 34.9 mm), an inner diameter of 0.875 inch (about
22.2 mm), and a length of 3.086 inches (about 78.4 mm). The outer 0.312-inch (about
7.9-mm) portion of the second end 108 of the die housing was threaded with 16-pitch
threads. The inside of the second end had a beveled edge 126, or chamfer, extendin~ from
the face 128 of the second end toward the first end 106 a distance of 0.125 inch (about 3.2
mm). The chamfer reduced the inner dial "eter of the die housing at the face of the second
end to 0.75 inch (about 19.0 mm). An inlet 110 ~also called an inlet orifice) was drilled in the
die housing, the center of which was 0.688 inch (about 17.5 mm) from the first end, and
tapped. The inner wall of the die housing consisted of a cylindrical portion 130 and a conical
frustrum portion 132. The cylindrical portion extended from the chamfer at the second end
toward the first end to within 0.992 inch (about 25.2 mm) from the face of the first end. The
conical frustrum portion extended from the cylindrical portion a distance of 0.625 inch (about
15.9 mm), te", lindlin9 at a threaded opening 134 in the first end. The diameter of the
threaded opening was 0.375 inch (about 9.5 mm); such opening was 0.367 inch (about 9.3
mm) in length.
A die tip 136 was located in the threaded opening of the first end. The die tip
consist~d of a threaded cylinder 138 having a circular shoulder portion 140. The shoulder
portion was 0.125 inch (about 3.2 mm) thick and had two parallel faces (not shown) 0.5 inch
(about 12.7 mm) apart. An exit orifice 112 (also called an extrusion orifice) was drilled in the
shoulder portion and extended toward the threaded portion a distance of 0.087 inch (about
2.2 mm). The diameter of the extrusion orifice was 0.0145 inch (about 0.37 mm). The
extrusion orifice terminated within the die tip at a vestibular portion 142 having a diameter of
0.125 inch (about 3.2 mm) and a conical frustrum portion 144 which joined the vestibular
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portion with the extrusion orifice. The wall of the conical frustrum portion was at an angle of
30~ from the vertical. The vestihu'~r portion extended from the extrusion orifice to the end of
the threaded portion of the die tip thereby connecting the chamber defined by the die
housing with the extrusion orifice.
The means for applying ull~son c energy was a cylindrical ulll~sor,.~ horn 116. The
hom was machined to resonate at a frequency of 20 kHz. The horn had a length of 5.198
inches (about 132.0 mm) which was equal to one-half of the resonating wavelength and a
dia"~eter of 0.75 inch (about 19.0 mm). The face 146 of the first end 118 of the horn was
drilled and tapped for a 3/8-inch (about 9.5-mm) stud (not shown). The horn was machined
with a collar 148 at the nodal point 122. The collar was 0.094-inch (about 2.4-mm) wide and
extended outwardly from the cylindrical surface of the horn 0.062 inch (about 1.6 mm).
Thus the clia",eter of the horn at the collar was 0.875 inch (about 22.2 mm). The second
end 120 of the horn terminated in a small cylindrical tip 150 0.125 inch (about 3.2 mm) long
and 0.125 inch (about 3.2 mm) in diameter. Such tip was separated from the cylindrical
body of the horn by a parabolic frustrum portion 152 appro~ci,,,~lely 0.5 inch (about 13 mm)
in length. That is the curve of this frustrum portion as seen in cross-section was parabolic
in shape. The face of the small cylindrical tip was normal to the cylindrical wall of the horn
and was located about 0.4 inch (about 10 mm) from the extrusion orifice. Thus the face of
the tip of the horn i.e. the second end of the horn was located immediately above the
vestihl l~-~ opening in the threaded end of the die tip.
The first end 108 of the die housing was sealed by a threaded cap 154 which alsoserved to hold the ul;ldsol- . horn in place. The threads extended upwardly toward the top
of the cap a distance of 0.312 inch (about 7.9 mm). The outside dial"eter of the cap was
2.00 inches (about 50.8 mm) and the length or thickness of the cap was 0.531 inch (about
13.5 mm). The opening in the cap was sized to accommodate the horn; that is the opening
had a dian)eter of 0.75 inch (about 19.0 mm). The edge of the opening in the cap was a
chamfer 156 which was the mirror image of the chamfer at the second end of the die
housing. The thickness of the cap at the chamfer was 0.125 inch (about 3.2 mm) which left
a space between the end of the threads and the bottom of the chamfer of 0.094 inch (about
2.4 mm) which space was the same as the length of the collar on the horn. The diameter of
such space was 1.104 inch (about 28.0 mm). The top 158 of the cap had drilled in it four
1/4-inch dia",~er x 1/4-inch deep holes (not shown) at 90~ intervals to accommodate a pin
spanner. Thus the collar of the horn was compressed between the two chamfers upon
tightening the cap thereby sealing the chamber defined by the die housing.
A Branson elongated aluminum waveguide having an input:output mechanical
11
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W O 97/43478 PCT~US97/07173
excitation ratio of 1:1.5 was coupled to the ultrasonic horn by means of a 3/8-inch (about
9.5-mm) stud. To the elongated waveguide was coupled a piezoelectric transducer, a
Branson Model 502 Converter, which was powered by a Branson Model 1120 Power Supply
operating at 20 kHz (Branson Sonic Power Company, Danbury, Connecticut). Power
consumption was ~onitor~d with a Branson Model A410A Wattmeter.
ExamPle 1
A high tensile s~nylll polymeric strand was made in accordance with an
embodiment of this invention. A Grid Melter, Model GM-25-1 hydraulic pump system,
obtained from J&M Laboratories Inc. of Dawsonville, Georgia was used to pump molten
polymer through the extrusion apparatus. The device has the capability to process up to 25
pounds of polymer per hour (about 11 kilograms per hour), and has an integral variable
speed gear pump with a displacement of 1.752 cclrevolution. Temperature of the melt is
regulated in two zones, premelt and main melt. Pressure is limited and regulated by an
internal variable by-pass valve, and indicated by digital readout resolved to increments of 10
psi. Pump drive speed is controlled by a panel mounted potentiometer.
The Grid Melter was used to melt and pressurize a thermoplastic polymer. The
polymer used was Himont HH~41 (Himont HH~41, Himont Company, Wilmington,
Delaware), a polypropylene having no melt processing additives and a melt flow rate of 400
grams per 10 minutes, or g/10 min. The melt flow rate is expressed in units of mass divided
by time (i.e., gramsl10 minutes). The melt flow rate was determined by measuring the mass
of molten thermoplastic polymer under a 2.160 kg load that flowed through an orifice
diameter of 2.09g5 + 0.0051 mm during a specified time period such as, for example, 10
minutes at a specified temperature such as, for example, 180~C as determined in
accordarIce with ASTM Test Method D1238-82, "Standard Test Method for Flow Rates of
Thermoplastic By Extrusion Plastometer," using a Model VE 4-78 Extrusion Plastometer
(Tinius Olsen Testing Machine Co., Willow Grove, Pennsylvania).
The Grid Melter pump drive speed was arbitrarily set at approximately 30 percent of
the potentiometer range, and pressure was set and controlled by adjusting the by-pass
valve. A 9-inch (about 23-cm) length of 114-inch (about 6.4-mm) diameter stainless steel
tubing was attached from the outlet of the Grid Melter to the inlet of the die housing. The
tubing and the extrusion cup were wrapped with heat tape as two zones, and the two zones
were set and controlled by automatic heat controllers. The heat zones in both the grid
melter and the extrusion apparatus were set to 360~ F and allowed to stabilize.
Pressure of the Grid Melter was adjusted to 140 psi and polymer was extruded at a
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WO 97/43478 PCT/US97/07173
rate of about 1.4g/min through the exit orifice of the extruder appar~lus with ultrasonic
energy applied at 30% of available power, drawing 35 watts. The resulting strand or fiber
was drawn by gravity alone for a d;slance of 40 inches. The strand had a linear density of
123.68 denier.
ExamPle 2 (cG~ rdtive)
A polymeric strand was made in accorJance with the procedure of Example 1 exceptthat the pressure of the grid melter was adjusted to 270 psi, the polymer flow rate was 1.43
grams per minute, and no ull,dson.c energy was applied. The strand had a linear density of
254.46 denier.
Fifteen specimens of the strand from Example 1 and seventeen specimens of the
strand from Example 2 were tested for tensile properties in accordance with ASTM D-3822
using the Instron Corporation Series IV Automated Materials Testing System 6.02. All
specimens were tested at a sample rate of 18.06 points per second, a cross-head speed of
2.0 inches per minute, and a full scale load range of 500 grams under conditions of 50
percent humidity and a temperature of 73~F.
In summary, the mean tenacity at break of the strand from Example 1 was 0.4374
grams per denier and the mean tenacity at break of the strand from Comparative Example 2
was 0.1975 grams per denier. Accordingly, the tenacity of the strand from Example 1 made
acco,d,"g to an embodiment of the present invention was more than twice that of the strand
of Example 2 made without the application of ultrasonic energy. In terms of toughness, or
energy absorbed, however, the values were lower for the strand made according toExample 1 than for the strand made according to Example 2.
The graphs in Figs. 2 and 3 illustrate the difference in the tenacity of the strand of
Example 1 made according to an embodiment of the present invention and the strand of
Example 2 which is made without the application of ultrasonic energy. The graphs and Figs.
2 and 3 plot the average load in grams on the strands versus the clispl-cement of the strand
by the load in inches. The curve illustrated in Fig. 3 for the strand of Example 2 shows a
period of little load increase up to about 7 inches displacement, then a sharp increase in
load up to the average point of break, which was under 10 inches. The curve illustrated in
Fig. 2 for the sample from Example 1, on the other hand, shows an immediate rise in load at
the onset of displacement, and the load increases at a substantially linear rate to the
average point of break. This indicates that the strand made without the application of
ul~,ason.c energy undergoes a period of crystal alignment during the initial displacement,
with ultimate alignment occurring at the point where the load curve turns positive. It also
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i, Idicales that there is a high degree of molecular orientation present in the strand formed in
accordance with Example 1 using ultrasonic energy.
While the specification has been described in detail with respect to specific
embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an
understanding of the foregoing, may readily conceive of alterations to, variations of, and
equivalents to these embodi~enl~. Accordi,,yly~ the scope of the present invention should
be ~sessed as that of the appended claims and any equivalents thereto.
14
