An aramid article is disclosed having improved resistance to penetration by sharp implements. The article is woven with tough, low dtex, aramid yarns of low dtex filaments in a tight plain weave configuration; and, when used in several layers, the layers are not stitched together.

BACKGROUND OF THE INVENTION 
There is a need for protective garments exhibiting improved penetration 
resistance from sharp pointed implements. However, attention has been 
directed primarily toward ballistics and toward garments which provide 
protection from ballistic threats. This invention relates to articles 
which protect from penetration, such as stabs or thrusts from sharp 
instruments such as awls or ice picks. 
U.S. Pat. No. 5,578,358, issued Nov. 26, 1996 (U.S. Ser. No. 08/421,350, 
filed Apr. 12, 1995) on the application of Foy and Miner, discloses a 
penetration resistant article made from tightly woven aramid yarn having a 
low linear density and a high toughness. 
U.S. Pat. No. 5,185,195, issued Feb. 9, 1993 on the application of Harpell 
et al., discloses a penetration resistant construction wherein adjacent 
layers of woven aramid or linear polyethylene fabric are affixed together 
by regular, close, paths. The affixing is preferably by means of 
stitching. 
U.S. Pat. No. 4,850,050, issued Jul. 25, 1989 on the application of Droste 
et al., discloses a body armor made from laminated layers of aramid 
fabrics wherein yarns in the fabric are made from filaments with a linear 
density of less than 1.5 dtex. 
SUMMARY OF THE INVENTION 
This invention relates to a penetration resistant article consisting 
essentially of fabric woven to a fabric tightness factor of at least 0.75 
from aramid yarn having a linear density of less than 500 dtex, a 
toughness of at least 30 Joules/gram and filaments in the yarn having a 
linear density of less than 1.67 dtex. The invention also relates to such 
a penetration resistant article wherein at least two layers of the fabric 
are included in the article, and are joined at edges of the article in a 
manner such that adjacent layers of the fabric are free to move relative 
to each other.

DETAILED DESCRIPTION 
The protective article of this invention was specially developed to provide 
protection from penetration by sharp instruments as opposed to protection 
from ballistic threats. There has been considerable effort expended in the 
past on improvement of ballistic garments; and many times the assumption 
has been that improved ballistic garments will also exhibit improved stab 
resistance or penetration resistance. The inventors herein have found that 
assumption to be incorrect and they have discovered a fabric article with 
a combination of several necessary qualities which does, indeed, exhibit 
improved penetration resistance. 
The inventors herein have discovered that the penetration resistance of a 
fabric article is dramatically improved when yarns used to make the fabric 
of the article are made with filaments having a linear density of less 
than about 1.67 dtex. It is believed that filaments of decreased linear 
density yield fabric articles having reduced interfilament spaces thereby 
providing a structure which is more difficult to penetrate with sharp 
instruments. 
While ballistic garments are made using several layers of protective fabric 
and the several layers are nearly always fastened together in a way to 
hold faces of the adjacent layers in position relative to each other, it 
has been found that penetration resistance is improved if adjacent layers 
in a protective garment are not held together; but are free to move 
relative to each other. When adjacent layers are stitched closely 
together, penetration resistance is decreased. 
The invention herein is constructed entirely of woven fabric without rigid 
plates or platelets and without matrix resins impregnating the fabric 
materials. The articles of this invention are more flexible, lighter in 
weight, softer to the touch, and more pliable than penetration resistant 
constructions of the prior art offering comparable protection. 
Fabrics of the present invention are made from yarns of aramid fibers. By 
"aramid" is meant a polyamide wherein at least 85% of the amide 
(--CO--NH--) linkages are attached directly to two aromatic rings. 
Suitable aramid fibers are described in Man-Made Fibers--Science and 
Technology, Volume 2, Section titled Fiber-Forming Aromatic Polyamides, 
page 297, W. Black et al., Interscience Publishers, 1968. Aramid fibers 
are, also, disclosed in U.S. Pat. Nos. 4,172,938; 3,869,429; 3,819,587; 
3,673,143; 3,354,127; and 3,094,511. 
Additives can be used with the aramid and it has been found that up to as 
much as 10 percent, by weight, of other polymeric material can be blended 
with the aramid or that copolymers can be used having as much as 10 
percent of other diamine substituted for the diamine of the aramid or as 
much as 10 percent of other diacid chloride substituted for the diacid 
chloride or the aramid. 
Para-aramids are the primary polymers in yarn fibers of this invention and 
poly(p-phenylene terephthalamide)(PPD-T) is the preferred para-aramid. By 
PPD-T is meant the homopolymer resulting from mole-for-mole polymerization 
of p-phenylene diamine and terephthaloyl chloride and, also, copolymers 
resulting from incorporation of small amounts of other diamines with the 
p-phenylene diamine and of small amounts of other diacid chlorides with 
the terephthaloyl chloride. As a general rule, other diamines and other 
diacid chlorides can be used in amounts up to as much as about 10 mole 
percent of the p-phenylene diamine or the terephthaloyl chloride, or 
perhaps slightly higher, provided only that the other diamines and diacid 
chlorides have no reactive groups which interfere with the polymerization 
reaction. PPD-T, also, means copolymers resulting from incorporation of 
other aromatic diamines and other aromatic diacid chlorides such as, for 
example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl 
chloride or 3,4'-diaminodiphenylether. Preparation of PPD-T is described 
in U.S. Pat. Nos. 3,869,429; 4,308,374; and 4,698,414. 
"Fabric tightness factor" and "Cover factor" are names given to the density 
of the weave of a fabric. Cover factor is a calculated value relating to 
the geometry of the weave and indicating the percentage of the gross 
surface area of a fabric which is covered by yarns of the fabric. The 
equation used to calculate cover factor is as follows (from Weaving: 
Conversion of Yarns to Fabric, Lord and Mohamed, published by Merrow 
(1982), pages 141-143): 
##EQU1## 
Depending on the kind of weave of a fabric, the maximum cover factor may be 
quite low even though the yarns of the fabric are situated close together. 
For that reason, a more useful indicator of weave tightness is called the 
"fabric tightness factor". The fabric tightness factor is a measure of the 
tightness of a fabric weave compared with the maximum weave tightness as a 
function of the cover factor. 
##EQU2## 
For example, the maximum cover factor which is possible for a plain weave 
fabric is 0.75; and a plain weave fabric with an actual cover factor of 
0.68 will, therefore, have a fabric tightness factor of 0.91. The 
preferred weave for practice of this invention is plain weave. 
While aramid yarns are available in a wide variety of linear densities, it 
has been determined that acceptable penetration resistance can be obtained 
only when the linear density of the aramid yarns is less than 500 dtex. 
Aramid yarns of greater than 500 dtex, even when woven to a fabric 
tightness factor of nearly 1.0, are believed to yield between the adjacent 
yarns and permit easier penetration of a sharp instrument. The improvement 
in penetration resistance due to low linear density of the yarns can be 
expected to continue to very low linear densities; but, at about 100 dtex, 
the yarns begin to become very difficult to weave without damage. With 
that in mind, the aramid yarns of this invention have a linear density of 
from 100 to 500 dtex. 
The inventors herein have found that fabrics made from yarns with filaments 
having a linear density less than 1.67 dtex exhibit dramatically improved 
penetration resistance. Reference is made to the FIG. 1 which is a 
graphical representation of the data points from the tests performed in 
Example 1 herein. Each point on the graph represents the test results from 
one of the fabrics and is located by normalized penetration resistance of 
the fabric and linear density of the yarn filaments. 
Reference is made to FIG. 2 which is a graphical representation of data 
points from tests performed in the Supporting Example herein. Each point 
on the graph represents the test results from one fabric, is located by 
tightness factor of the fabric and linear density of the yarn, and is 
identified by the so-called specific penetration resistance determined in 
the test. 
As will be explained later herein, specific penetration resistance 
decreases as resistance to penetration decreases and a value of about 30 
for specific penetration in the tests conducted herein is considered to 
represent adequate penetration resistance for general use. The line 
identified as Y=X 6.25.times.10.sup.-4 +0.69 separates adequate 
penetration resistance from inadequate penetration resistance for fabrics 
in FIG. 2 made from aramid yarns. 
There is one point on the "adequate penetration resistance" side of the 
line which exhibits inadequate penetration resistance; but that point 
represents a fabric made from yarn which was not aramid. 
Good penetration resistance requires a combination of several yarn and 
fabric qualities, among which are yarn linear density and fabric tightness 
factor. From FIGS. 1 and 2, it can be seen that, for aramid fibers, 
improved penetration resistance will be afforded by fabrics with a 
combination of filament linear density which is less than 1.67 dtex, as 
shown in FIG. 1 and a tightness factor and yarn linear density which falls 
under the curve of FIG. 2 in the ranges of 0.75 to 1.0 and 500 to 100 
decitex, respectively. 
The aramid yarns used in this invention must have a high tenacity combined 
with a high elongation to break to yield a high toughness. The tenacity 
should be at least 19 grams per dtex (21.1 grams per denier) and there is 
no known upper limit for tenacity. Below about 11.1 grams per dtex, the 
yarn doesn't exhibit adequate strength for meaningful protection. The 
elongation to break should be at least 3.0 percent and there is no known 
upper limit for elongation. Elongation to break which is less than 3.0 
percent results in a yarn which is brittle and yields a toughness which is 
less than necessary for the protection sought herein. 
"Toughness" is a measure of the energy absorbing capability of a yarn up to 
its point of failure in tensile stress/strain testing. Toughness is 
sometimes, also, known as "Energy to Break". Toughness or Energy to Break 
is a combination of tenacity and elongation to break and is represented by 
the area under the stress/strain curve from zero strain to break. It has 
been discovered that a slight increase in tenacity or elongation to break 
results in a surprisingly large improvement in penetration resistance. A 
yarn toughness of at least 35 Joules/gram is believed to be necessary for 
adequate penetration resistance in practice of this invention; and a 
toughness of at least 38 Joules/gram is preferred. 
A single layer of the woven article of this invention does provide a 
measure of penetration resistance and, therefore, a degree of protection; 
but a plurality of layers are usually used in an ultimate product. It is 
in the use of a plurality of layers that the present invention exhibits 
its most pronounced and surprising improvement. It has been discovered 
that articles of this invention, when placed together in a plurality of 
layers, afford a surprisingly effective penetration resistance when the 
articles are not affixed to one another, thereby permitting relative 
movement between adjacent layers. Adjacent layers or articles may be 
fastened at the edges or there may be some loose interlayer connections at 
relatively great spacings compared with the thickness of the articles. For 
instance, layer-to-layer attachments at point spacings of greater than 
about 15 centimeters would serve, for this application, as being 
substantially free from means for holding the layers together. Layers 
which have been stitched together over the surface of the layers may 
provide more effective ballistics protection; but such stitching causes 
immobility between the layers and, for reasons not entirely understood, 
actually decreases the penetration resistance of the layers as compared 
with expectations based on single layer tests. 
TEST METHODS 
Linear Density 
The linear density of a yarn or a filament is determined by weighing a 
known length of the yarn or filament. "Dtex" is defined as the weight, in 
grams, of 10,000 meters of the material. "Denier" is the weight, in grams, 
of 9000 meters of the material. 
In actual practice, the measured dtex of a yarn or filament sample, test 
conditions, and sample identifica-tion are fed into a computer before the 
start of a test; the computer records the load-elongation curve of the 
sample as it is broken and then calculates the properties. 
Tensile Properties 
Yarns tested for tensile properties are, first, conditioned and, then, 
twisted to a twist multiplier of 1.1. The twist multiplier (TM) of a yarn 
is defined as: 
EQU TM=(twists/cm)/(dtex).sup.-1/2 /30.3=(twists/inch)(denier).sup.-1/2 /73 
The yarns to be tested are conditioned at 25.degree. C., 55% relative 
humidity for a minimum of 14 hours and the tensile tests are conducted at 
those conditions. Tenacity (breaking tenacity), elongation to break, and 
modulus are determined by breaking test yarns on an Instron tester 
(Instron Engineering Corp., Canton, Mass.). 
Tenacity, elongation, and initial modulus, as defined in ASTM D2101-1985, 
are determined using yarn gage lengths of 25.4 cm and an elongation rate 
of 50% strain/minute. The modulus is calculated from the slope of the 
stress-strain curve at 1% strain and is equal to the stress in grams at 1% 
strain (absolute) times 100, divided by the test yarn linear density. 
Tenacity, elongation, and initial modulus of individual filaments are 
determined in the same way as for yarns; but filaments are not subjected 
to twist and a gage length of 2.54 cm is used. 
Toughness 
Using the stress-strain curve from the tensile testing, toughness is 
determined as the area (A) under the stress/strain curve up to the point 
of yarn break. It is usually determined employing a planimeter, to provide 
area in square centimeters; and, for aramids, which generally exhibit a 
nearly straight-line stress-strain curve, toughness can be estimated as 
one-half of the product of tenacity times elongation. Dtex (D) is as 
described above under "Linear Density". Toughness (To) is calculated as 
EQU To=A.times.(FSL/CFS)(CHS/CS)(1/D)(1/GL) 
where 
FSL=full-scale load in grams 
CFS=chart full scale in centimeters 
CHS=crosshead speed in cm/min 
CS=chart speed in cm/min 
GL=gauge length of test specimen in centimeters 
Digitized stress/strain data may, of course, be fed to a computer for 
calculating toughness directly. The result is To in dN/tex. Multiplication 
by 1.111 converts to g/denier. When units of length are the same 
throughout, the above equation computes To in units determined only by 
those chosen for force (FSL) and D. 
Penetration Resistance 
Penetration resistance is determined on articles of a single layer or a few 
layers by a standard method for Protective Clothing Material Resistance to 
Puncture identified as ASTM F1342. In that test, the force is measured 
which is required to cause a sharply pointed puncture probe to penetrate a 
specimen. The specimen is clamped between flat metal sheets with opposing 
0.6 cm holes and placed 2.5 cm below the puncture probe mounted in a 
testing machine set to drive the probe through the specimen at the holes 
in the metal sheets at a rate of 50.8 cm/minute. The maximum force before 
penetration is reported as the penetration resistance. 
Penetration resistance is determined on a plurality of layers of the 
articles using either a tempered steel awl 18 centimeters (7 inches) long 
and 0.64 centimeter (0.25 inch) in shaft diameter having a Rockwell 
hardness of C-45 or an ice pick of the same length, a shaft diameter of 
0.42 centimeter and a Rockwell hardness of C-42. The tests are conducted 
in accordance with HPW test TP-0400.02 (22 Jul. 1988) from H. P. White 
Lab., Inc. The test samples are impacted with the awl, weighted to 7.35 
kilograms (16.2 pounds) and dropped from various heights. 
EXAMPLES 
Example 1 
In this example, several fabrics were woven using 220 dtex (200 denier) 
aramid yarns having filaments of a variety of linear densities. The 
fabrics were plain weave with a yarn density of 70.times.70 ends, 
exhibiting a fabric tightness factor of 1.0. 
The yarns were: 
______________________________________ 
Filament 
Linear Filament Toughness 
##STR1## 
##STR2## 
##STR3## 
##STR4## 
##STR5## 
______________________________________ 
1-1 1.67 25.4 3.8 0.483 
1-2 2.50 24.6 4.0 0.492 
1-3 5.00 22.1 3.8 0.420 
1-4 1.22 24.2 3.9 0.472 
1-5 0.83 24.5 3.7 0.453 
1-6 0.83 23.6 3.6 0.425 
1-7 1.67 23.2 4.0 0.464 
1-8 0.83 23.1 4.0 0.462 
______________________________________ 
Fabrics made from these yarns were tested for penetration resistance, as 
ten-ply configurations, in accordance with the falling awl procedure, as 
previously described. The penetration resistance test results are reported 
in Table 1 as minimum penetrating energy in Joules and as minimum 
penetrating energy in Joules normalized to the toughness of the yarn of 
the fabric identified herein as 1--1. 
Penetration resistance was normalized to a constant yarn toughness to 
eliminate bias which would be introduced by toughness variations. 
TABLE 1 
______________________________________ 
Yarn of the 
Penetration Normalized Penetration 
Fabric Resistance Joules 
Resistance Joules 
______________________________________ 
1-1 98.9 98.9 
1-2 75.0 73.6 
1-3 58.5 67.3 
1-4 106.2 108.7 
1-5 102.5 109.3 
1-6 95.1 108.8 
1-7 80.6 83.9 
1-8 104.3 109.0 
______________________________________ 
The Normalized Penetration Resistance for each fabric was plotted as a 
function of the filament linear density for yarns in the fabrics, and that 
plot is shown in FIG. 1. It is readily seen that fabrics made using yarns 
with filaments having a linear density greater than 2.0 dtex exhibit very 
low penetration resistance and fabrics made using yarns with filaments 
having a linear density less than 1.2 dtex exhibit very high penetration 
resistance. The penetration resistance of these fabrics increases rapidly 
from very low to very high as the linear density of filaments in the 
fabric yarns is decreased from 2.0 dtex to 1.2 dtex, and it appears that 
there is an inflection in the curve of the Figure at about 1.67 dtex. 
All of the above was conducted at a constant, high, fabric tightness factor 
and using yarn of the same linear density. As previously stated, fabrics 
of high penetration resistance are made using yarns having a linear 
density of 100 to 500 decitex and a fabric tightness of greater than 0.75. 
This invention represents an improvement in the discovery that the 
penetration resistance can be increased even more by use of yarns having 
filaments with linear density less than 1.67 dtex. The preferred fabrics 
of this invention require a combination of yarns of 100 to 500 decitex 
made from filaments of less than 1.67 decitex and woven to a fabric 
tightness factor of greater than 0.75. 
Supporting Example 
In this example, several fabrics were woven using a variety of yarns in 
plain weave at a variety of fabric tightness factors. 
The yarns were: 
______________________________________ 
Energy 
Tenacity Elongation 
to Break Linear Density 
Yarn (gm/dtex) (%) (Joules/gm) 
(dtex) 
______________________________________ 
A 30.1 3.4 41.2 220 
B 25.4 3.0 31.2 220 
C 26.6 3.2 33.9 440 
D 25.5 3.4 34.2 1110 
E 30.0 3.4 40.5 440 
F 31.1 3.4 41.4 670 
G 30.0 3.4 40.5 440 
H 38.8 3.1 47.8 415 
______________________________________ 
Yarns A-G are poly(p-phenylene terephthalamide) (PPD-T) yarns sold by E. I. 
du Pont de Nemours and Company. 
Yarn A bears the trademark designation KEVLAR.RTM. 159. 
Yarns B-D bear the trademark designation KEVLAR.RTM. 29. 
Yarns E and F bear the trademark designation KEVLAR.RTM. 129. 
Yarn G bears the trademark designation KEVLAR.RTM. LT. 
Yarn H is high molecular weight linear polyethylene yarn sold by 
AlliedSignal under the trademark designation SPECTRA.RTM. 1000. 
The fabrics were: 
______________________________________ 
Yarn Yarn End Count 
Basis Wt. 
Tightness 
Fabric # 
Used (cm .times. cm) 
(g/m.sup.2) 
Factor 
______________________________________ 
S-1 A 27.6 .times. 27.6 
128 1.0 
S-2 A 24.8 .times. 24.8 
115 0.93 
S-3 A 19.7 .times. 19.7 
89 0.78 
S-4 B 27.6 .times. 27.6 
126 1.0 
S-5 B 24.8 .times. 24.8 
115 0.93 
S-6 B 19.7 .times. 19.7 
89 0.78 
S-7 C 19.7 .times. 19.7 
182 1.0 
S-8 D 12.2 .times. 12.2 
282 0.99 
S-9 E 17.3 .times. 17.3 
159 0.93 
S-10 E 13.4 .times. 13.4 
120 0.75 
S-11 F 14.6 .times. 14.6 
206 0.94 
S-12 F 11.8 .times. 11.8 
164 0.80 
S-13 G 13 .times. 13 125 0.75 
S-14 G 16 .times. 16 139 0.90 
S-15 H 20.1 .times. 19.7 
173 1.0 
______________________________________ 
All of the fabrics were tested, as one and two-ply configurations, in 
accordance with ASTM F1342, as previously described. The test results are 
reported in Table 2 as absolute penetration resistance (grams-force) and 
as specific penetration resistance (absolute/basis weight) for both one 
and two-ply configurations. 
TABLE 2 
______________________________________ 
Penetration 
Tight- Basis Resistance No. 
Fabric 
ness No. of Wt. Absolute 
Specific 
of 
# Factor Plies (g/m.sup.2) 
(grams) 
Resist. 
Tests 
______________________________________ 
S-1 1.0 1 128 6,800 53.1 3 
2 256 15,400 60.2 3 
S-2 0.93 1 115 4,900 42.6 3 
2 230 11,300 40.1 5 
S-3 0.78 1 89 2,300 25.8 6 
2 178 4,400 24.7 3 
S-4 1.0 1 126 5,100 40.5 6 
2 252 11,400 45.2 3 
S-5 0.93 1 114 4,100 36.0 9 
2 229 8,100 35.4 7 
S-6 0.78 1 89 1,600 18.0 9 
2 178 3,600 20.2 7 
S-7 1.0 1 182 6,000 33.0 9 
S-8 0.99 1 282 2,400 8.5 5 
1 (repeat) 2,200 7.8 3 
S-9 0.93 1 159 3,200 20.1 5 
2 318 8,700 27.4 3 
S-10 0.75 1 120 1,200 10.0 5 
2 240 3,900 16.2 3 
S-11 0.94 1 206 2,000 9.7 6 
2 412 4,100 10.0 6 
S-12 0.80 1 164 800 4.9 6 
2 328 2,600 7.9 6 
S-13 0.75 1 139 1,900 13.7 6 
S-14 0.90 1 125 1,000 8.0 6 
S-15 1.0 1 173 2,300 13.3 6 
2 346 4,600 13.3 6 
______________________________________ 
Specific penetration resistance values for the single ply configurations 
from those tests were placed on a graphical field of yarn decitex versus 
fabric tightness factor, as shown in FIG. 2. The values fall into two 
easily-characterized areas. On one side of a line of the equation Y=X 
6.25.times.10.sup.-4 +0.69 (where Y is tightness factor and X is linear 
yarn density in decitex) the fabrics have adequate penetration resistance; 
and, on the other side of the line, penetration resistance is inadequate. 
From these test results, it is seen that penetration resistant fabrics are 
made from yarns of aramid having linear yarn density from 100 to 500 
decitex and which are woven to a fabric tightness factor of at least 0.75 
in accordance with the following formula: 
EQU Y=or&gt;X 6.25.times.10.sup.-4 +0.69 
wherein Y=Fabric Tightness Factor and X=Linear Yarn Density.