U.S. patent application number 11/145274 was filed with the patent office on 2006-02-16 for polyethylene protective yarn.
This patent application is currently assigned to Honeywell International Inc.. Invention is credited to Alfred L. Cutrone, Thomas Y-T Tam, Chok B. Tan.
Application Number | 20060035078 11/145274 |
Document ID | / |
Family ID | 32682456 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060035078 |
Kind Code |
A1 |
Tam; Thomas Y-T ; et
al. |
February 16, 2006 |
Polyethylene protective yarn
Abstract
High strength polyethylene yarns useful in ballistic-resistant,
cut-resistant and other applications, fabrics produced from these
yarns and the methods by which the yarns and fabrics are made. An
untwisted yarn of the invention comprises a plurality of filaments
in essentially parallel array and from about 0.5 to 5 weight
percent of a water-dispersible binder material covering less than
half the surfaces of the filaments. The yarn has a tenacity greater
than about 17 g/d, a tensile modulus greater than about 300 g/d,
fewer than 20 entanglements/meter in a scoured state and a width
less than given by the formula W.ltoreq.0.055 {square root over
(d)}where W is the yarn width in millimeters under a tensile load
of 0.01 g/d measured on a flat surface and d is the yarn
denier.
Inventors: |
Tam; Thomas Y-T; (Richmond,
VA) ; Tan; Chok B.; (Richmond, VA) ; Cutrone;
Alfred L.; (Orange, TX) |
Correspondence
Address: |
Virginia Szigeti;Honeywell International Inc.
15801 Woods Edge Road
Colonial Heights
VA
23834
US
|
Assignee: |
Honeywell International
Inc.
|
Family ID: |
32682456 |
Appl. No.: |
11/145274 |
Filed: |
June 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10820907 |
Apr 8, 2004 |
6979660 |
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11145274 |
Jun 6, 2005 |
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10444811 |
May 23, 2003 |
6764764 |
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10820907 |
Apr 8, 2004 |
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Current U.S.
Class: |
428/364 |
Current CPC
Class: |
Y10T 428/2933 20150115;
Y10T 442/3065 20150401; D02G 3/404 20130101; Y10S 428/911 20130101;
Y10T 428/2913 20150115; Y10T 428/2938 20150115; D01F 6/04 20130101;
Y10T 442/2402 20150401; Y10T 428/2967 20150115; Y10T 442/2861
20150401; D02G 3/442 20130101; Y10T 442/291 20150401; Y10T 428/2915
20150115 |
Class at
Publication: |
428/364 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. In a process for the preparation of untwisted polyethylene yarns
comprising a plurality of filaments in essentially parallel array,
said yarn having a tenacity greater than about 17 g/d, a tensile
modulus greater than about 300 g/d, and fewer than 20
entanglements/meter: the improvement comprising applying about 0.5
to 5 wt. % of a water-dispersible binder material so as to cover
less than half the surfaces of the filaments during a last drawing
step under a tension of greater than about 2 grams/denier.
10. In a process for the preparation of a very low creep, ultra
high modulus, low shrink, high tenacity multifilament polyethylene
yarn by: a) drawing a high molecular weight polyethylene yarn at a
temperature within 10.degree. C. of its melting temperature to form
a drawn, highly oriented polyethylene yarn, b) then poststretching
said yarn at a drawing rate of less than about 1 second.sup.-1 at a
temperature within 10.degree. C. of its melting temperature, and
cooling said yarn under tension sufficient to retain its highly
oriented state; the improvement comprising applying to the yarn
about 0.5 to 5 weight percent of a water-dispersible binder
material so as to cover less than half the surfaces of the
filaments during one of drawing step a) or poststretching step b)
under a tension greater than about 2 grams/denier.
11. The process of claim 9 wherein the water-dispersible binder
material is a member selected from the group consisting of a salt
of an acrylic copolymer, sodium carboxymethyl cellulose,
polyethylene oxide, polypropylene oxide, ethylene oxide/propylene
oxide copolymers, polyvinyl alcohol, modified starch, esterified
starch, cationic starch, starch-styrene/butadiene copolymer, and
mixtures thereof.
12. The process of claim 10 wherein the water-dispersible binder
material is a member selected from the group consisting of a salt
of an acrylic copolymer, sodium carboxymethyl cellulose,
polyethylene oxide, polypropylene oxide, ethylene oxide/propylene
oxide copolymers, polyvinyl alcohol, modified starch, esterified
starch, cationic starch, starch-styrene/butadiene copolymer, and
mixtures thereof.
13. A process for the preparation of a ballistic-resistant fabric
comprising the steps of: a) weaving a fabric comprising in majority
portion the yarn described by claim 1; and b) flattening and
spreading the yarns in said fabric by additionally applying one or
both steps selected from the group consisting of scouring said
fabric and calendering said fabric.
14. The process of claim 13 wherein said flattening and spreading
step comprises scouring said fabric.
15. The process of claim 13 wherein said flattening and spreading
step comprises calendering said fabric.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to improved, high strength
polyethylene yarns useful in ballistic-resistant, cut-resistant and
other applications, fabrics produced from these yarns and the
methods by which the yarns and fabrics are made.
[0003] 2. Description of the Related Art
[0004] Among the requirements that protective clothing such as
personal body armor, chain saw chaps, and others must meet, in
addition to ballistic-resistance and/or cut resistance, are comfort
and flexibility. Multiple layers of woven fabrics consisting of
high strength and high modulus fibers are commonly used in such
protective clothing.
[0005] The preparation of high strength, polyethylene filaments
and/or multi-filament yarns has been described for example in U.S.
Pat. Nos. 4,411,854, 4,413,110, 4,422,993, 4,430,383, 4,436,689,
4,455,273, 4,536,536, 4,545,950, 4,551,296, 4,584,347, 4,663,101,
5,248,471, 5,578,374, 5,736,244, 5,741,451, 5,972,498 and 6,448,359
B1. Ballistic-resistant articles prepared from such high strength
polyethylene filaments have been described for example in U.S. Pat.
Nos. 4,403,012, 4,457,985, 4,623,574, 4,650,710, 4,737,401,
4,737,402, 4,748,064, 4,883,700, 4,916,000, 5,061,545, 5,160,776,
5,167,876, 5,175,040, 5,187,023, 5,196,252, 5,343,796, 5,376,426,
5,440,965, 5,480,706, 5,677,029, 5,788,907, 5,804,015, 5,958,804,
6,003,424, and 6,276,254 B1.
[0006] U.S. Pat. No. 4,403,012 indicates that the fibers may be
formed into a fabric by any of a variety of conventional
techniques. U.S. Pat. No. 4,737,401 broadly indicates that plain
woven, basket woven, satin and crow feet woven fabrics, etc., can
be made from high strength polyethylene filaments. However, to
efficiently use conventional weaving equipment, the yarns to be
woven must have some minimum degree of yarn coherence to avoid
snags and wild loops which effect fabric quality and may stop the
loom. Weaving is also enhanced when the yarn to be woven is
essentially round in cross-section and does not flatten when
passing over guides. On the other hand, for maximum
ballistic-effectiveness it is desirable that the yarns in woven
fabrics are flat and are spread out into thin layers.
[0007] Methods to achieve yarn coherence have included twisting,
jet entanglement, and application of sizing material. Twisting
improves the roundness of yarn bundles but it is known that
twisting reduces the ballistic effectiveness of fabrics produced
from these yarns. This may be in part because twisting induces
stress in the yarns and in part because twisting prevents the woven
yarns from spreading into thin layers.
[0008] Air jet entanglement of yarn filaments as taught, for
example, by U.S. Pat. No. 5,579,628, provides yarn coherence and
improves ballistic-resistance as compared to twisted yarns.
However, air jet entanglement may also damage the yarn and is an
expensive process in both capital costs for air compressors and in
operating costs for energy consumption.
[0009] Sizing of a plain weave fabric made from untwisted high
strength polyethylene filaments with polyvinyl alcohol has
previously been described in U.S. Pat. No. 4,737,401. A process
that covered virtually all yarn surfaces of synthetic filament
yarns with sizing has been described in U.S. Pat. No.
4,858,287.
[0010] Each of the methods and yarns cited above represented
improvements in the state of their respective arts. Nevertheless,
none described the specific constructions of the yarns and fabrics
of this invention and the methods by which they are achieved.
SUMMARY OF THE INVENTION
[0011] The invention is an untwisted polyethylene yarn comprising:
a plurality of filaments in essentially parallel array and from
about 0.5 to 5 weight percent of a water-dispersible binder
material covering less than half the surfaces of said filaments.
The yarn has a tenacity greater than about 17 grams/denier (g/d)
and a tensile modulus (modulus of elasticity) greater than about
300 g/d as measured by ASTM D2256, fewer than 20
entanglements/meter in a scoured state and has a width satisfying
the following formula W.ltoreq.0.055 {square root over (d)} where W
is the yarn width in millimeters under a tensile load of 0.01 grams
per denier measured on a flat surface, and d is the yarn denier.
The requirement for the yarn width expressed by the above formula
insures sufficient yarn roundness for good weaving capability.
[0012] The invention is also a protective fabric comprising in
majority portion the yarn described above.
[0013] The invention is also an improvement to a process for the
preparation of untwisted polyethylene yarns comprising a plurality
of essentially parallel filaments, said yarns having a tenacity
greater than about 17 g/d, a modulus greater than about 300 g/d,
and fewer than 20 entanglements/meter. The improvement comprises
applying about 0.5 to 5 wt. % of a water-dispersible binder
material so as to cover less than half the surfaces of the
filaments during a last drawing step under a tension greater than
about 2 grams/denier (g/d).
[0014] The invention is also an improvement to a process for the
preparation of a very low creep, ultra high modulus, low shrink,
high tenacity polyethylene multiple filament yarn, comprising:
[0015] a) drawing a high molecular weight polyethylene yarn at a
temperature within 10.degree. C. of its melting temperature to form
a drawn, highly oriented polyethylene yarn; [0016] b) then
poststretching the yarn at a drawing rate of less than about 1
second.sup.-1 at a temperature within 10.degree. C. of its melting
temperature, and cooling the yarn under tension sufficient to
retain its highly oriented state. The improvement comprises
applying to the yarn about 0.5 to 5 wt. % of a water-dispersible
binder material so as to cover less than half the surfaces of the
filaments during one of drawing step a) or poststretching step b)
under a tension greater than about 2 grams/denier.
[0017] The invention is also a process for the preparation of a
protective fabric comprising the steps of: weaving a fabric
comprising in majority portion the yarn described above; scouring
the fabric to remove the water-dispersible binder material and
flattening the yarn.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the accompanying drawing figures:
[0019] FIG. 1 illustrates a method of measuring the width of a
yarn.
[0020] FIG. 2 illustrates a process for producing a yarn of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] An objective of this invention is the provision of a high
strength, high tensile modulus polyethylene yarn having a coherence
and roundness suitable for weaving into a protective fabric and
which flattens and spreads out when the fabric is scoured. The
invention is an untwisted polyethylene yarn comprising a plurality
of filaments in essentially parallel array and from about 0.5 to 5
weight percent of a water-dispersible binder material covering less
than half the surfaces of said filaments. The yarn has a tenacity
greater than about 17 g/d, a tensile modulus greater than about 300
g/d, fewer than about 20 entanglements/meter in a scoured state and
has a width satisfying the following formula W.ltoreq.0.055 {square
root over (d)} where W is the yarn width in millimeters under a
tensile load of 0.01 grams per denier measured on a flat surface,
and d is the yarn denier. The requirement for the yarn width
expressed by this formula insures sufficient yarn roundness for
good weaving. Preferably, the yarn width (W) satisfies the
following formula W.ltoreq.0.040 {square root over (d)} where W is
the yarn width in millimeters under a tensile load of 0.01 grams
per denier measured on a flat surface, and d is the yarn denier.
The woven fabric is especially useful in applications requiring
ballistic-resistance and/or cut resistance, more preferably the
former.
[0022] FIG. 1 illustrates the method of yarn width measurement. A
length of yarn 10 is attached at each end to weights 30 and placed
across a flat plate 20. At least 7 cm of the yarn are in contact
with the flat plate. The flat plate is conveniently chosen to be
the stage of an optical microscope. The weights 30 are chosen in
relation to the yarn denier so as to produce a tension in the yarn
of 0.01 g/d. The width W of the yarn bundle lying on the flat plate
20 is measured by appropriate means, such as an optical microscope,
averaging at least five measurements at different points along a 5
cm length.
[0023] When the yarn has some degree of twist, the yarn width W is
measured along a yarn length at least twice the twist periodicity,
and is the maximum (as opposed to average) measurement taken along
this length.
[0024] The number of entanglements per meter is measured after
scouring the yarn to remove the binding material. "Entanglements"
are interlocked filaments that cannot be readily separated.
Entanglements may be formed during the process of spinning multiple
filaments. The number of entanglements/meter is measured by the
method of ASTM D4724-99, with the modification that the apparatus
used is the Model HW70735 Interlace Tester manufactured by
Industrial Machine Works, Waynesboro, Va. Preferably, the yarn of
the invention has fewer than about 10 entanglements/meter in the
scoured state.
[0025] The percentage of the filament surfaces that are covered by
the water-dispersible binder material is determined using a
microscope with digital image analysis software, such as
IMAGE-PRO.RTM. software from Media Cybernetics, Silver Spring, Md.
To aid in the measurement, the binder material may be selectively
dyed to enhance contrast by using a water-soluble dye that is not
absorbed by polyethylene.
[0026] The water-dispersible binder material is preferably selected
from the group consisting of: a salt of an acrylic copolymer,
sodium carboxymethyl cellulose, polyethylene oxide, polypropylene
oxide, ethylene oxide/propylene oxide copolymers, polyvinyl
alcohol, modified starch, esterified starch, cationic starch,
starch-styrene/butadiene copolymer, and mixtures thereof.
Preferably, the water-dispersible binder forms about 0.5 to about 3
wt. % of the yarn of the invention. It will be understood that the
terms "weight percent" or "wt. %" have the conventional meaning of
weight of binder per weight of filaments plus binder.
[0027] The untwisted yarn of the invention is produced by an
improvement to a process for the preparation of polyethylene yarns
having a plurality of filaments in essentially parallel array, a
tenacity greater than about 17 g/d, a tensile modulus greater than
about 300 g/d and fewer than about 20 entanglements/meter in a
scoured state. The improvement comprises the application of about
0.5 to 5 wt. % of a water-dispersible binder material so as to
cover less than half the surfaces of said filaments during a last
drawing step under a tension of greater than about 2 grams/denier,
more preferably under a tension of greater than about 3
grams/denier. Preferably, the last drawing step is at an elevated
temperature between about 110.degree. C. and about 160.degree.
C.
[0028] Surprisingly, the application of the binder material when
the yarn is under substantial tension is believed to be a key
factor in achieving superior ballistic effectiveness in fabric
woven from the yarn. Without being held to a particular theory of
why the invention works, it is believed that application of the
binder material when the yarn is under substantial tension prevents
complete wetting of the surfaces of the filaments. The binder forms
limited area binding points between filaments sufficient to provide
cohesion to the yarn for weaving, but not sufficient to reduce
ballistic effectiveness. Moreover, the limited area binding points
are more readily removed by scouring to achieve maximum ballistic
effectiveness.
[0029] An untwisted polyethylene yarn having a plurality of
essentially parallel filaments, a tenacity greater than about 17
g/d, a tensile modulus greater than about 300 g/d and fewer than
about 20 entanglements/meter is preferably produced by any of the
processes described by U.S. Pat. Nos. 4,413,110, 4,551,296,
4,663,101, and 6,448,359 B1, all incorporated herein by reference
to the extent not incompatible herewith.
[0030] FIG. 2 illustrates one embodiment of the process of the
invention. Ultra-high molecular weight polyethylene and mineral oil
are charged to a mixer 10 maintained at elevated temperature. The
partially dissolved polyethylene is passed to a screw extruder 20
which may be a single screw extruder or a twin screw extruder
wherein the formation of a polyethylene solution is completed.
Solution filaments 30 are spun through an air gap into a water
quench bath 40 wherein the solution filaments are cooled and
solidified to gel filaments. The solution filaments may be
stretched on passing through the air gap to the quench bath. The
gel filaments are passed in sequence through a washer cabinet 50 in
contact with a low boiling extraction solvent to remove the mineral
oil and then through a drying cabinet 60. The gel filaments may be
stretched between the quench bath and the washer cabinet and
through the washing and drying cabinets. The extracted and dried
multi-filament yarn is passed continuously from the drying cabinet
over a driven heated godet 70 and associated idler roll 76, through
a first heated tube 77 and onto a second driven heated godet 78,
and associated idler roll 79, operating at higher speed. The yarn
is thereby stretched in the heated tube 77. The yarn next passes
under a tension greater than about 2 g/d in kissing contact with an
applicator roll 81 partially immersed in an aqueous solution 80 of
a binding agent. The yarn containing the binding agent is dried and
stretched again on passing through heated tube 82 to driven heated
godet 83 and associated idler roll 84 operating at higher speed
than associated rolls 78 and 79. After the last elevated
temperature stretch, the yarn is passed under tension over a driven
cold godet 85 and associated idler roll 86 and collected without
twist on a winder 90. The heated godets and heated tubes are
typically at temperatures between about 110.degree. C. and about
160.degree. C. As used herein, the term "elevated temperature"
means a temperature within that range.
[0031] The untwisted yarn so produced has filaments in essentially
parallel array, a tenacity greater than 17 g/d, a tensile modulus
greater than about 300 g/d, fewer than 20 entanglements per meter
in a scoured state, about 0.5 to 5 vol % of a water-dispersible
binding agent covering less than half the surfaces of the
filaments, and a width in millimeters less than given by 0.055
times the square root of the yarn denier.
[0032] Preferably the yarn of the invention is produced by an
improvement to the process of U.S. Pat. No. 5,741,451, incorporated
herein by reference to the extent not incompatible herewith. This
process comprises the preparation of a very low creep, ultra high
modulus, low shrink, high tenacity polyethylene multiple filament
yarn by: a) drawing a high molecular weight polyethylene yarn at a
temperature within 10.degree. C. of its melting temperature to form
a drawn, highly oriented polyethylene yarn; b) then poststretching
the yarn at a drawing rate of less than about 1 second.sup.-1 at a
temperature within 10.degree. C. of its melting temperature, and
cooling said yarn under tension sufficient to retain its highly
oriented state. The improvement comprises applying to the yarn
about 0.5 to 5 wt. % of a water-dispersible binder material so as
to cover less than half the surfaces of the filaments during one of
drawing step a) or poststretching step b) under a tension greater
than about 2 grams/denier.
[0033] The protective woven fabric of the invention, preferably
ballistic-resistant, comprises in majority portion an untwisted
polyethylene yarn comprising: a plurality of filaments in
essentially parallel array and about 0.5 to 5 wt. % of a
water-dispersible binder material covering less than half the
surfaces of said filaments. The yarn has a tenacity greater than
about 17 g/d and a tensile modulus (modulus of elasticity) greater
than about 300 g/d as measured by ASTM D2256, fewer than 20
entanglements/meter in the scoured state and a width satisfying the
following formula W.ltoreq.0.055 {square root over (d)} where W is
the yarn width in millimeters under a tensile load of 0.01 grams
per denier measured on a flat surface, and d is the yarn
denier.
[0034] The woven fabric of the invention may be plain woven, basket
woven, satin or crowfeet woven or any other standard weave. It is
preferred that the yarns in the fabric have as few out-of-plane
bends as possible. An eight-harness satin weave is particularly
preferred.
[0035] It is also preferred that the fabrics of the invention are
scoured and/or calendered to flatten and spread the yarns, thereby
enhancing their ballistic-resistance. It is most preferred that the
fabrics of the invention are both scoured and calendered, with
calendering preferably occurring after scouring.
[0036] The ballistic-resistant woven fabric of the invention
possesses at least 5% greater specific energy absorption when
impacted with a 9 mm FMJ bullet at its V50 velocity than a woven
fabric having the same construction using polyethylene yarns having
the same tenacity and tensile modulus but having more than 20
entanglements/meter and/or greater twist.
COMPARATIVE EXAMPLE 1
[0037] The widths were measured of commercially available untwisted
high strength, high modulus polyethylene yarns. Table I below sets
forth the yarn deniers and the measured yarn widths in comparison
with 0.055 times the square root of the yarn denier. Each of these
yarns had about 8 entanglements/meter. TABLE-US-00001 TABLE I Yarn
Width, 0.055{square root over (denier)}, Yarn Denier mm mm 1200 2.5
1.91 650 1.7 1.40 375 2.8 1.07 215 2.1 0.81
[0038] It is seen that each of the prior art, untwisted yarns had
yarn widths that exceeded 0.055 times the square root of the yarn
denier.
COMPARATIVE EXAMPLE 2
[0039] A 60 filament, 650 denier highly oriented polyethylene yarn
having a tenacity of 30 g/d, a tensile modulus of 970 g/d, and a
main melting point of 147.degree. C., as measured by differential
scanning calorimetry (DSC) at a heating rate of 10.degree. C./min,
was prepared by the process of U.S. Pat. No. 4,663,101.
[0040] A number of packages of this yarn were post-stretched by the
process of U.S. Pat. No. 5,741,451. The yarn packages were placed
on a creel and fed from the creel over a set of driven rolls into a
post-stretching oven at a temperature of 156.degree. C. and thence
to a second set of driven rolls operating at a speed 2.63 times
faster than the first set. The yarns were thereby stretched 2.63:1
between roll sets at a temperature within 10.degree. C. of their
melting point. The plurality of yarns leaving the second set of
driven rolls was passed through a second post-stretching oven at
temperature of 154.degree. C. to a third set of driven rolls
operating at a speed 1.2 times faster than the second set. The
yarns passing through the second post-stretching oven were thereby
stretched an additional 1.2:1. Yarn tension between the second and
third sets of driven rolls was 4 g/d. Each yarn leaving the third
set of driven rolls was cooled under a tension of 2 g/d and then
wound on individual packages.
[0041] The wound yarns consisting of 60 essentially parallel
filaments were of 215 denier, having a tenacity of 38 g/d, a
tensile modulus of 1320 g/d, a main melting point of 148.degree. C.
as measured by DSC, no twist, 8 entanglements/meter and a width
measured under a tension of 0.01 g/d of 2.1 mm. As the yarn width
of 2.0 mm exceeded 0.055 times the square root of 215 (0.81 mm),
and as the yarn contained no binder material, this was not a yarn
of the invention.
[0042] Some packages of these yarns were put aside for later
twisting (see Comparative Examples 3 and 4). Other packages of
these yarns were rewound onto a warp beam and placed on a loom
manufactured by Lindauer DORNIER GmbH. Still other packages of
these same yarns were used for the weft. An attempt to weave a
plain weave fabric produced many snags, tight ends and operating
difficulties. A plain weave fabric was nevertheless prepared having
wild filaments, slubs and irregular yarn spacings. On average the
fabric had 17.7 warp and weft yarns per centimeter, an areal
density of 88 g/m.sup.2 and a thickness of 0.15 mm. Forty-two
sheets of this fabric were plied up to an areal density of 3.69
kg/m.sup.2 and subjected to ballistic testing by NIJ Standard
0101.03 using a 9 mm 124 grain FMJ bullet. According to this
method, samples are placed on a clay backing, and shot 16 times.
The protective power of the sample is expressed by citing the
impacting velocity at which 50% of the projectiles are stopped.
This is designated the V50 velocity. The specific energy absorption
(SEA) is the kinetic energy of the projectile at the V50 velocity
in Joules, divided by the areal density of the sample, kg/m.sup.2.
SEA has units of J-m.sup.2/kg.
COMPARATIVE EXAMPLE 3
[0043] Some of the same 60 filament, 215 denier yarns prepared in
Comparative Example 2 were twisted to 1.2 turns/cm on a MEADOWS
Model 805-M ring twister. The twisted yarns were used as the warp
and weft of a plain weave fabric having 17.7.times.17.7 yarns/cm.
No difficulty was experienced in the weaving operation. The woven
fabric had an areal density of 88 g/m.sup.2 and a thickness of 0.15
mm. The fabric was cut into 46 cm squares, stacked to an areal
density of 3.67 kg/m.sup.2 and subjected to ballistic testing by
NIJ Standard 0101.03 using a 9 mm 124 grain FMJ bullet. The V50
velocity was 378 meters/sec and the specific energy absorption was
32.0 J-m.sup.2/kg.
COMPARATIVE EXAMPLE 4
[0044] Some of the same 60 filament, 215 denier yarns prepared in
Comparative Example 2 were twisted to 2 turns/cm on a MEADOWS Model
805-M ring twister. The twisted yarns were used as the warp and
weft of a plain weave fabric having 22.times.22 yarns/cm. No
difficulty was experienced in the weaving operation. The woven
fabric had an areal density of 111 g/m.sup.2 and a thickness of
0.17 mm. The fabric was cut into 46 cm squares, stacked to an areal
density of 3.67 kg/m.sup.2 and subjected to ballistic testing by
NIJ Standard 0101.03 using a 9 mm 124 grain FMJ bullet. The V50
velocity was 421 meters/sec and the specific energy absorption was
39.8 J-m.sup.2/kg.
EXAMPLE OF THE INVENTION
[0045] Sixty-filament polyethylene yarns were produced exactly as
described in Comparative Example 2 with the exception that before
entering the second post-stretching oven and after passing over the
second set of driven rolls, the yarns, while under a tension of 4
g/d, made kissing contact with a roll rotating in a 7.5 wt. %
aqueous emulsion of PENFLEX.TM. starch styrene butadiene copolymer
from Penford Products Co., Cedar Rapids, Iowa. The yarns were dried
and post-stretched and in the second post-stretching oven under the
same conditions as in Comparative Example 2, cooled under 2 g/d
tension and wound on individual rolls.
[0046] The untwisted polyethylene yarns of the invention consisted
of sixty essentially parallel filaments and about 2.5 wt. % of
water-dispersible binder material covering less than half the
surface area of the filaments. The yarns were of 220 denier, had a
tenacity of 37 g/d, a tensile modulus of 1290 g/d, a main melting
point of 148.degree. C. as measured by DSC, no twist, 8
entanglements/meter in a scoured state, and a width of 0.58 mm
measured under a tension of 0.01 g/d. The yarn width was less than
0.055 times the square root of the denier.
[0047] A plain weave fabric having 17.7 warp and weft yarns per
centimeter, an areal density of 90 g/m.sup.2 and a thickness of
0.15 mm was readily woven from these yarns without difficulty.
Sheets of this fabric were plied up to an areal density of 3.69
kg/m.sup.2and subjected to ballistic testing by NIJ Standard
0101.03 using a 9 mm 124 grain FMJ bullet. The V50 velocity was 445
meters/sec. SEA was 44.3 J-m.sup.2/kg.
[0048] The V50 velocity of this fabric of the invention was 17.7%
greater and the SEA was 38% greater than for the fabric of
Comparative Example 3 having the same construction, and woven from
twisted yarns having the same tenacity and tensile modulus.
Suprisingly, the V50 velocity of this fabric of the invention was
also 5.7% greater and the SEA was 11% greater than for the finer
weave fabric of Comparative Example 4, also woven with twisted
yarns.
[0049] Having thus described the invention in rather full detail,
it will be understood that such detail need not be strictly adhered
to but that further changes and modifications may suggest
themselves to one skilled in the art, all falling within the scope
of the invention as defined by the subjoined claims.
* * * * *