Note: Descriptions are shown in the official language in which they were submitted.
WO9~/04X~ 2 0 G ~ CT/US~0/05137
BALLISTIC-RESISTANT ARTICLES
AND
METHOD OF MANUFACUTURE THEREOF
BACKGROUND OF THE INVENTION
The present invention relates to ballistic-
resistant articles of manufacture, as well as to a
method of manufacture thereof. The ballistic-resistant
articles of the present invention comprise high
strength polyolefin fibers.
Ballistic-resistant articles formed from high
strength polyolefin fibers are known from a series of
U.S. Patents assigned of record to Allied Corporation.
These are:
Harpell et al U.S. Patent No. 4,403,012
15 Har~ell et al U.S. Patent No. 4,457,985
Harpell et_al U.SO Patent No. 4,501,856
Harpell et al U.S. Patent No. 4,623,574
Hareell et al U.S. Patent No. 4,650,710; and
Harpell et âL U.S. Patent No. 4,681,792.
Another Allied Corporation patent directed to
high strength polyethylene fiber i9 Kavesh et al, U.S.
Patent No. 4,413,ll0.
These patents describe ballistic-resistant
articles of manufacture comprising a flexi~le network
of polyolefin fibers having, in the case of
polyethylene filament, a weight average molecular
weight of at least about 500,000, a tensile modulus of
at least about 300 g/denier and a tenacity of at leask
about 15 g/denier, and in the case of polypropylene
filament, a weight average molecular weight of at least
WO9l/0485~ ~ O S ~ 7 7 ~' PCT/US90/05137
750,000, a tensile modulus of at least about 160
g/denier and a tenacity of at least about 8 g/denier,
said fibers being formed into a network of sufficient
thickness to absorb the energy of a projectile.
As will be discussed hereinafter, the filament
described in the above patents is a preferred
ingredient for use in forming the ballistic-resistant
articles according to the present invention.
Accordingly, the disclosure of the above patents is
hereby expressly incorporated by reference, to the
extent not inconsistent herewith.
Other patents of general interest with respect to
ballistic-resistant articles include Zeqlen, U.S.
Patent No. 604,870, and Hawkinson, U.S. Patent No.
15 4,428,998.
The Har~ell et al patents listed above are
directed to ballistic-resistant articles formed by
winding a continuous filament of the high strength
polyethylene around a steel plate to form a network of
parallel fibers. This construction was found to be
superior to KEVLAR (trademark of Dupont for aramid
yarn) in arresting projectile penetration.
There remains a need, however, for ballistic
resistant articles capable of arresting projectile
penetration more effectively than those discussed above
at a given basis weight of ballistic-resistant
material, or, correspondingly, that are equally as
Pffective at a lower basis weight.
SUMMARY OF THE INVENTION
A major object of the present invention i5 to
provide ballistic resistant articles of manufacture
that offer improved penetration resistance as compared
to ballistic-resistant articles of the prior art.
W091/048~ 2 0 6 6 7 7 ~' Pcr/us90/05l37
Another object of tne invention is to provide a
method for manufacturing such ballistic-resistant
articles that is easily adapted to an industrial scale,
preferably by modifying conventional processing
apparatus.
A further object of the present invention is to
provide ballistic resistant articles that offer
penetration resistance equal to articles of the prior
art, but at significantly lower material basis weight,
thereby greatly expanding th~ useful applications for
such articles.
These and other objects according to the present
invention are accomplished by ballistic resistant
articles having as a principal ingredient the high
strength polyolefin filament discussed above, but in
which that filament has been converted to discrete
fibers of a much shorter and definite length, and in
which those discrete fibers have been formed into an
agglomerated web together with a minor amount of much
shorter polyolefin fibers.
The ballistic resistant articles according to the
present invention are preferably formed by conventional
papermaking techniques~ In this manner, a uniform web
of the high strength fibers can be readily generated,
and the process can be carried out on an industrial
scale without extensive original plant design.
It has been found that an agglomerated web of the
high strength Allied fiber alone does not offer
significantly improved penetration resistance.
Instead, i is necessary to form the web with a minor
amount of a much shorter, high density polyolefin fiber
such as that marketed commercially under the trademark
PULPEX rademark of ~Prcules Inc., a Delaware
Corporatior., for high density polyethylene pulp having
WO91~0~85~ 2 ~ ~ ~ 7 7 ~ PCT/US90/05137
an avPrage fiber length of 0.6 - 1.2 mm, made water-
dispersible with polyvinyl alcohol treatment).
Accordingly, the present invention relates in one
aspect to ballistic resistant articles of manufacture
comprising an ag~lomerated web of discrete fibers
formed from (1) polyolefin filament having, in the case
of polyethylene filament, a weight average molecular
weight of at least about 500,000, a tensile modulus of
at least about 300 g/denier and a tenacity of at least
about 15 g/denier, and in the case of polypropylene
filament, a weight average molecular weight of at least
750,000, a tensile modulus of at least about 160
g/denier and a tenacity of at least about 8 g/denier;
and ~2) high density polyolefin fibers having an
average fiber length of about 0.5 to about 1.5 mm; said
article having a sufficient thickness to absorb the
energy of a projectile.
In another aspect, the present invention relates
to a process for making such ballistic-resistant
articles, in which an aqueous slurry of the two types
of fibers is de-watered on a wire screen, to form the
agglomerated web according to the invention.
BRIEF DESCRIPTION OF ~HE DRAWING
The Figure of the drawing graphically depicts the
experimental results of Table 1.
DETAIIED DESCRIPTION OF T~ PREFERRED EMBODIMENTS
OF THE PRESENT INVENTION
A high strength polyolefin filament such as that
described in the aforementioned Allied patents is
converted, for use in the present invention, to fibers
having a length from about 0.5 to about 1.5 inches,
WO9l/04X5~ 2 Q ~ 6 ~ 7 ~ PCT/US90/05137
preferably from about 0.5 to about l inch, and
optimally about 0.75 inch (re~erred to hereinafter as
"long fiber"). This fiber i5 then formed into an
aqueous slurry together with a lesser amount of high
density polyethylene fiber having an average fiber
length of about 0.5 to about 1.5 mm, preferably about
0.6 to about 1.2 mm (referred to hereinafter as "short
fiber"). The slurry is then converted to an
agglomerated web, for example by using a Fourdrinier
wire and appropriate suction rolls.
Experimentation with the relative amounts of long
fiber and short fiber, as will be set forth
hereinafter, has revealed the optimum composition to be
one containing from about -75 to about 85% long fiber
and from about 15 to about 25~ short fiber.
Compositions containing from about 65 to about 95% long
fiber and from about 5 to about 35% short fiber,
however, are also within the scope of the invention.
Moreover, because various additives may be included in
the formulations according to the invention, the
optimum ratio of long fiber to short fiber may also be
expressed as preferably 65 to 95 parts long fiber to 35
to 5 parts short fiber, more prPferably 75 to 85 parts
long fiber to 25 to 15 parts short fiber.
The ballistic-resistant articles according to the
invention are formed using conventional papermaking
techniques, such as passing an aqueous slurry of the
admixed long and short fibers onto an endless wire
screen, followed by dewatering and drying o~ the thus-
formed sheet. The sheet is then heat-treated with or
without pressure as is known to those skilled in the
paper-maXing art. The heat treatment is generally of
sufficient temperature and pressure to melt or sinter
the short fiber,-which results in a bonding of the long
WO91/0485~ 2 0 ~ ~ 7 7 ~ PCT/US90/0~137
fibers. It will be appreciated that in such process,
what might otherwise be a conventional technique
interacts with the materials employed to form a
resultant product having properties of penetration
resistance that could not have been predicted from the
starting materials and technique alone.
It is also contemplated to form the agglomerated
web by a hydroentangling process. Hydroentangling is a
process for producing nonwoven fabrics by impinging a
plurality of fine columnar streams of a fluid, such as
water or air, onto a fibrous web carried by an
apertured or patterned conveying means. There is thus
produced a felt like material in which even relatively
short fibers can be mechanically intertwined without
the damaging effects of needling. One example of a
patent describing hydroentangling is U.S. Patent No.
3,485,706, the disclosure of which is hereby expressly
incorporated by reference, to the extent not
inconsistent herewith. In this patent, an apertured
hydroentangled fabric is produced wherein the apertures
in the fabric correspond to knuckles in the wire screen
used to support and convey the fibrous web. Patterned
supporting means are disclosed for imparting to the
resulting hydroentangled fabric a desired ornamental
appearance.
A series of experimental handsheets were
prepared, whose formulations were both within and
without the scspe of the present invention, and
subjected to ballistic testing to determine their
penetration resistance. The handsheets were prepared
by dewatering an aqueous slurry of the constituent
ingredients, to form an agglomerated web, followed by
drying on a steam-heated drum and bonding in a 130C
oven for ten minutes. The handsheets thus formed
WO91/0485~ ~0~S 6 7 7 rd PCT/US90/05137
--7--
measured 8 inches by 8 inches square, and were formed
so as to have a basis weight of 60 pounds per 3000
square feet. The basis weight of a specimen to be
subjected to ballistic testing could easily ~e
increased 2, 4 or 8 times by folding one of these
sheets once, twice or thxee times, respectively. The
specimens tested thus tend to have basis weights
increasing by multiples of eight~ because th~ basis
weight of a specimen was generally increased by adding
an additional 8 inch by 8 inch sheet that had been
folded three times.
The specimens tested were backed either by
plywood or by clay. The first tests were run with
plywood as the backing. When plywood backing was used,
the plywood had a hole formed where the bullet was
expected to pass (or not pass, depending on whether the
specimen stopped the bullet). Clay backing was also
used, primarily since modeling clav is the backing used
for determining the baLlistic resistance of body armor
(U.S. Department of Justice - National Institute of
Justice, NI~ Standard 0101.03).
The firing was done with a .22 caliber rifle
using Winchester high velocity .22 caliber long rifle
bullets. According to literature published by
Winchester, the muzzle velocity of these bullets is
about 1440 feet per second. The target was located
about three feet from the muzzle of the rifle.
The results of these experiments are listed in
Table 1 below. In Table 1, the term "Spectra" is a
trademark of Allied Corporation for high strength
polyethylene as described in the Harpell et al patents,
whereas the term "Pulpex" is a trademark of Hercules
Corporation for their short fiber polyethylene
synth~tic pulp. The Pulpex was used in its
WO 91/04855 2 0 ~ ~ 7 7 .~ Pc-r/lJs9l)/osl37
commercially available form, whereas the Spectra
filament was modified by chopping it to ~orm fibers
haviny an average length of about 0.75 inch. All
number entries are p~rcent by weight, except ~or
"Basis Weight", which is in units of lb/3000 ft2, and
refers to the basis weight of the specimen tested.
TABLE 1
Ex. Spectra PulpexOther Basis P~ne-
AdditivesWeight tration
1 50 25*25 Albacell 2880 N
2 ~ - ll 2400 N
3 " " " 1920 P
4 " 50 - 1440 P
" " - 1920 P
6 " " - 3360 P
7 ~ _ 3840 P
8 " " - 4800 N
9 " " - 5760 N
10 60 40 - 1440 P
ll " " - 1920 P
12 " " - 2~00 P
13 " " - 2880 P
14 " " - 3840 P
" " - 4800 N
16 " 20 20 CA2 1920 N
17 ~ - 14~0 P
18 64 21 15 CA 1920 N
19 " " " 1440 N
20 68 22 10 CA 1920 N
21 ll ll ll 1440 P
22 70 30 - 1440 P,P,N,N
23 " " (dry) 1680 N
24 ll " (wet) 1680 P
" " dry, heat pressed 1680 N
WO ~1/04~55 2 ~ ~ 'o 7 ~ ~ pcr/us~n/osl37
_9_
26 " " wet, heat precsed 1680 P
27 ~ add ' 1 20% EL3 1440 P
28 " " " 1920 P
29 " " " 1440 P
530 " " " 1688 P
31 " " " 1920 P
32 70 25* 5 AL 1920 N
33 " " " 1440 P
34 " 25 5 AP4 960 P
1035 " " " 1440 N
36 " " 5 KF5 960 P
37 " " " 1440 N
38 " 10* 20 AL 1920 N
39 " " " 1440 N
1540 " " " 960 P
41 " 20* 10 AL 1920 N
42 " " " 1440 N
43 " 22*3 AL, 5 M6 1440 N
44 " 25 5 CA 1440 N,P
2045 " " 5 M 1440 P,N
46 i' 30 SC7 1920 P
47 " " " 1680 P
48 " " " 1440 P
49 71 24 5 CA 1440 N
2550 " " " 960 . N, P, P
51 75 25 - 1440 ~-
52 " " - 960 P
53 80 20 - 1440 N,N, P
54 ~ 960 P,P,N
3055 85 15 - 1440 N
- 56 " " - 960 P, P
WO91/0485~ 2 0 ~ ~ 7 7 ~ PC~/US90/05137
--10--
57 90 10 - 1440 P,P,N
58 " " - 1920 N
59 ~ - 960 P
" " - 480 P
Notes: * Pulpex grade A321 - "bondable"
pulp, treated to have increased
hydrogen bonding;
otherwise, Pulpex grade ED (unmodified)
1. Albacel southern softwood kraft pulp
2. Cellulose acetate fibrit (Celanese
Corp'n)
3. Elastoplast resin added as saturant,
about 20% pick up
4. Apyeil (Japanese aramid fibrid)
5. Kevlar Fibrid
6. Microfibrillated cellulose from ITT
7. Caschem - a surfactant based on a castor
oil soap ~glycerol monoricinolate CAS-
1323382),
0.5 g/handsheet added for formation
improvement
In the above table, "N" indicates that the bullet
was stopped by the specimen, whereas "P" indicates that
the bullet passed through the specimen. Where more
than one designation appears, it indicates that the
testing was performed a plurality of times. When a
clay backing was used, the bullet would sometimes
penetrate fairly deeply into the clay backing, yet fail
completely to rupture the paper-like structure of the
specimen. Nevertheless, if the bullet penetrated more
than 0.75 inch into the clay backing, the result was
judged "P". The results of these tests are somewhat
qualitative, because the clay backing appeared to
WO9l/0485~ 2 Q ~ ~ 7 ~ ~ PCT/US90/05137
improve slightly the performance of the specimen.
The data of Table l, for handsheets containing
mixtures of Spectra type fiher and Pulpex fiber, may be
represented graphically, as is shown in the
accompanying Figure, by plotting increasing long
fiber/decreasing short fiber percentage on the
abscissa, and ~tal basis weight of specimen on the
ordinate. From this Figure, it appears that a
composition range of 75-85~ long fiber to 15-25% short
fiber is optimum for use in the invention.
A number of interesting observations can be made
from the above table. If the tensile strength of
varying long fiber/short fiber compositions is
calculated, it appears that specimens with a very high
tensile strength required a much higher basis weight
per specimen to display penetration resistance, as
compared to specimens with a much lower tensile
strength. This is shown below in Table 2, where there
are listed the minimum basis weights at which each of a
variety of long fiber/short fiber compositions
displayed penetration resistance.
TABLE 2
Long Fiber~ 50-50 60-40 70-3080-20 90-10
short fiber
25 Bullet Pene- NO N0 NO NO NO
tration
Total basis 4800 4800 1440 960 1440
weight
Tensile, lb/in 2800 2850 567 256 144
Basis weight 2400 2880 1008 778 1296
long fiber
It is indeed surprising hc poorly the 50-50
composition fared in penetr-ation resistance, as it has
WO91/0485~ 2 0 S ~ 7 7 ~ PCT/US90/05137
-12-
has the highest tensile strength of the specimens
listed. This is entirely contrary to the teaching of
the prior art, notabl~ the Harpell et al patents and
Kevlar ballistic-resistant articles, where high
tensile strength is taught to be directly related to
increased penetration resistance.
The explanation for these discrepant results is
that the present invention operates on an entirely
different principle than the prior art discussed above,
owing to its unique structure and attendant properties.
In the HarPell et al patents, and in woven Kevlar
fabrics, when a bullet strikes the wound or woven
filament, the kinetic eneryy of the bullet causes the
filament to rupture. By contrast, in the present
invention, the filament is present as relatively short
fibers in a ra~domly oriented paper-like agglomeration.
When a bullet strikes this structure, the predominant
mechanism is one in which the relatively short fibers
are caused not to rupture, but rather to be pulled out
from the entangled paper-like structure. It has been
found that more kinetic energy is consumed by pulling a
fiber out of an entangled structure than by rupturing a
fiber.
This can be demonstrated by a kinetic energy
calculation comparing a specimen according to the
present invention (identical to Example 22 of Table l,
but having a slightly higher total basis weight of 1488
lb/300 ft2) with the best performing fabric disclosed
in Harpell et al, U.S. Patent No. 4,650,710, as well as
a another ballistic article prepared according to the
teaching of this same patent. The ~abrics from
Har~ell 1710 are those designated Examples F-l and F-5,
appearing in Table lB at column 9, lines ~0-30. It
should be further noted that the data used for the wet
WO9l/04855 2 0 ~ 6 l ~ ~ Pcr/us~o/os137
-13-
laid nonwoven structure of the present invention is for
no bullet penetration, while the data Of ~3E~ell e~ al
is for 50~ bullet penetration.
Calculations
1. Ballistic resistant article according to the
present invention:
Specimen basis weight = 1488 lb/ream or 2.427
kg/m2
Long fiber basis weight = 1041 lb/ream or 1.7
1 0 kg/m2
Velocity, no penetration = 1250 ft/s = 381 m/s
Bullet = 40 grains = 2.592 g = 0.002593 kg
Kinetic energy = 1/2 mv2 - (0.5)(0.002593)(381)2
= 188 kg m /s
Kinetic energy/specimen basis weight = 188/2.427
= 78 Joules/(kg/m2)
Kinetic energy/long fiber basis weiyht = 188/1.7
= 111 Joules/(kg/m2~
2. Example F-l according to Har~ell '710 (best-
performing):
Fabric basis weight = 1079 lb/ream or 1.76 kg/m2
Velocity, 50gO penetration = 1318 ft/s = 402 m/s
Bullet = 19 grain fragment = 0.0012312 kg
Kinetic energy = 1/2 mv2 = (0.5)(0.0012312)(4022)
= 99-4 kg m2/s2
Kinetic energy/fabric basis weight = 99.4/1.76
= 5~ Joules/tkg/m2)
3. Example F-5 according to Har~ell '710:
Fabric basis weight = 3005 lb/ream or 4.95 kg/m2
W~l/04~ CT/US~J0/~5137
Bullet = 19 grain fragment = 0.0012312 kg
Kinetic energy = 1/2 mv2 = ~0.5)(0.0012312)(4052)
- 101.6 kg m2/s~
Kinetic energy/fabric basis weight = 101.6/4.95
= 21 Joules/(kg/m2)
The above comparison shows that a given basis
weight of the same type of filament as used in the
Har~ell et al patents, when present as relatively short
fibers in a paper-like agglomeration according to the
present invsntion, absorbs nearly twice the kinetic
energy as the most preferred use disclosed by the
teaching of the prior art.
While the present invention has been described in
connection with various preferred embodiments thereof,
it will be appreciated that it should not be construed
to be limited thereby. Modifications remain possible,
without departing from the scope and spirit of the
appended claims.
