Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TTY
CUT RESISTANT YARN AND FABRIC
BACKGROUND OF THE INVENTION
Fabrics used in cut resistant garments can be
generally rather stiff and bulky due the perceived need
for strong yarns with a high modulus. It has been
especially true that cut resistant garments, such as
gloves, aprons, and protective sleeves, have been made
from stiff yarns which yield stiff and uncomfortable
fabrics with a arsh hand; and that modification of the
yarns to yield yabrics with increased cut resistance
hale yielded fabrics which were even stiffer and more
uncomfortable. This invention relates to cut resistant
woven and knitted fabrics which exhibir_ improved cut
resistance while maintaining an equivalent or softer
hand.
F T
This invention relates to apparel of improved
cut resistance made from yarn having a linear density
of 150 to 5900 dtex (133 to 5315 denier) and a twist
factor of less than 26, wherein the yarn includes para-
aramid staple fibers having a linear density of 3 to 6
dtex (2.7 to 5.~ denier) and a length of 2.5 to 15.2
centimeters (1 to 6 inches).
The invention also relates to the yarn and to a
cut resistant fabric having a weight of 135 to 1017
grams per square meter (4 to 30 ounces/square yard) and
made from the yarn.
There has long been a tension in the field of
protective garments, between comfort and effectiveness;
and considerable effort has been expended to increase
the effectiveness while maintaining the comfort. The
present inventic:: represents just such <<n improvement
in the field of c:~t resistant apparel and fabrics. By
use of this invention, it is now possible to increase
the cut resistant effectiveness and maintain the
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comfort, of fabrics and protective garments, such as
cut resistant gloves.
It has been discovered that protective garments
made from spun yarns of para-aramid fibers are softer
if made from yarns which have a low degree of twist.
Moreover, it has been discovered that the cut
resistance of the fabric of such garments is
independent of the degree of twist imparted to the
yarns in the fabric and that the cut resistance of the
i0 fabric is improved by increasing the linear density of
the individual fibers used in the yarns.
By para-aramid fibers is meant fibers made from
para-aramid polymers; and polyp-phenyLene
terephthalamide)(PPD-T) is the preferred para-aramid
polymer. 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 carp be used in
amounts up to as much as about l0 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;
provided, only that the other aromatic diamines and
aromatic diacid chlorides be present in amounts which
do not adversely affect the properties of the para-
aramid.
Additives can be used with the Foara-aramid in
the fibers and it has been found that up to as much as
10 percent, by weight., of other polymeric material can
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be blended with the aramid or that coaolymers can be
used having as much as 10 percent of other diamine
substituted for the diamine of the aramid or as much as
percent of other diacid chloride substituted for the
5 diacid chloride of the aramid.
Staple fibers for use in spindling yarns are
generally of a particular length and c>f a particular
linear density. For use in this invention, the fibers
can have any length which is adequate for manufacture
10 of spun yarns. Staple lengths of 2.5 to 15.2
centimeters (1 to 6 inches) can be used and lengths of
3.8 to 11.4 centimeters (1.5 to 4.5 inches) are
preferred. Yarns made from fibers having staple
lengths of less than 2.5 centimeters have been found to
i5 require excessively high levels of twist to maintain
strength for processing; and yarns made from fibers
having staple lengths of more than 15.2 centimeters are
more difficult to make due to the tendency for long
staple fibers to become entangled and broken resulting
in short fibers. The staple fibers of this invention
are generally made by cutting continuous filaments to
certain predetermined lengths; but staple can be made
by other means, such as by stretch-breaking; and yarns
can be made from such fibers as well as from a variety
or distribution of different staple fiber lengths.
Spun yarns are held together by means of a
twist incorporated into the yarn while spinning.
Crimped staple fibers are spun on a spinning machine to
yield a yarn with a certain twist. The twist helps to
entangle the fibers together to form the yarn. In the
past, it has been the usual practice to use yarns with
a high degree of twist for cut resistant fabrics in
protective garments. It was generally believed that
the high twist was necessary for providing a yarn of
high strength; and that the high strength was necessary
for good cut resistance. That high degree of twist
causes the fibers to be rather tightly bundled in the
yarn corm and creates a rather hard yarn.
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It has now been discovered that 'yarns of high
twist are not necessary for effective protection; and,
in fact, it has been learned that cut resistance is
substantially independent of the degree of twist in
yarns used for the manufacture of protective fabrics.
The degree of twist is, however, very important as a
factor in the softness or comfort of such fabrics. It
has been discovered that fabrics made using yarns of
low twist are much softer with a finer "hand" than
fabrics made using highly twisted yarn... Moreover, it
is believed that decreased twist results in increased
fabric softness, without regard to the kind of yarn or
the material from which it is made.
Twist in yarns is usually represented by a
factor called "Twist Factor", which may, also, be
called twist multiplier. A higher twist factor
indicates a higher degree of twist. Cut resistant
fabrics in protective garments have, up to now, been
made with yarns having a preferred twist factor of
greater than about 28 (tex)1/2(turns/cm) and using
staple fibers with a linear density less than or equal
to 2.5 dtex. The twist factor (TF) of a yarn is a
number denoting the twist of fibers in a yarn, taking
into account the linear density of the yarn, and can be
defined using any of several dimensiona_~ systems:
Tex System -
TF = (turns/centimeter) (tex) 1~~2
Cotton System -
TF = (turns/inch)/(cotton count of yarn)1/2
Metric Count System -
TF = (turns/meter)/(metric count of yarn)1/2
"Cotton Count" of a yarn is the number of
skeins of the yarn 768 meters (840 yards) long to have
a weight of 454 grams (one pound).
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"Metric Count" of a yarn is the number of
kilometers of the yarn to nave a weight of one
kilogram.
For the purposes herein, the z'ex System Twist
Factor using SI units of texl/2 turns/cm will be used.
In fabrics of this invention, it has been found
that yarns with a twist factor of less than about 26
yield a soft fabric which can be fashioned into
comfortable, yet cut resistant, gloves. While it is
l0 necessary to have some degree of twist in the yarns in
order for the yarns to stay together, rests indicate
that cut resistance is not affected by changes in yarn
twist. That is, the additional strength provided to
the yarn by the use of increased twist does not
translate to improved cut resistance. It has been
concluded that, as a practical matter, the yarns of
this invention should have a twist factor of at least
about 10. For a single spun yarn of 1C Cotton Count
(equal to 590 dtex) a twist factor of about 10
translates to a twist of about 1.3 turns per
centimeter. It is preferred that yarns of this
invention have a twist factor of 15 to 22.
Yarns are made of staple fibers. It has been
found that the yarns which are used in practice of this
invention should have a yarn linear density of 150 to
5900 dtex, and preferably 550 to 4700 dtex. The yarns
may be made up of single strands or plied using several
strands and may be twisted together or not.
As to the linear denaity of individual staple
fibers, it has been discovered that increased linear
density in the staple results in increased cut
resistance for the yarr_. In the past, cut resistant
protective garments have utilized yarns having
individual staple fibers of about 2.5 dtex or less.
While those yarns have been adequate for many uses, it
is now known that the cut resistance of a fabric can be
improved by increasing the linear density of the staple
fibers used in the yarns thereof. Moreover, it is
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known that the comfort of such a fabric can be
maintained by decreasing the twist in the yarns
thereof. Thus, by use of this invention, a fabric can
be made having improved cut resistance and comfort
S equivalent with that of known products. For example,
fabrics of improved cut resistance can be made using
yarn with a twist factor of less than 26 which includes
para-aramid staple fibers having a linear density of 3
to 6 dtex. Such fabrics will deliver improved cut
l0 resistance from the increased fiber linear density and
maintained comfort from the decreased yarn twist.
From the. comfort point of view, it has been
found that low twist yarns of this invention should be
made using staple fibers having a linear density of 3
'S to 6 dtex; and, preferably from 4 to 5 dtex. Fibers of
less than about 3 dtex may not yield the improved cut
resistance of this invention. Fibers of more than
about 6 dtex exhibit very good cut resistance; but are
not aesthetically acceptable and may not yield fabrics
20 with adequate comfort.
The yarns of this invention can be made by any
appropriate spinning process among which can be
mentioned, cotton/worsted/woolen ring and open end
spinning.
25 The spun yarn of this invention, having low
twist and high linear density can be made into highly
cut resistant fabrics which have been knittEd or woven
or even laid in unidirectional conformations. Also,
the spun yarn can be made directly into gloves and
~0 other apparel by knitting machines. The cut resistance
is a function of the linear density of filaments in the
yarn and not of the manner that the yarn is presented
in a fabric.
35 TEST METHODS
Cut Resistance. The method used was the
"Standard Test Method for Measuring Cut Resistance of
Fabrics Used in Protective Clothing", proposed as an
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ASTM Standard (ASTM Subcommittee F23.a:0). Tn
performance of the test, a cutting edge, under
specified force, is drawn one time across a sample
mounted on a mandrel. At several different forces, the
distance drawn from initial contact tc cut through is
recorded and a graph is constructed of force as a
function of distance to cut through. From the graph,
the force is determined for cut through at a distance
of 25 millimeters and is normalized to validate the
to consistency of the blade supply. The normalized force
is reported as the cut resistance force.
The cutting edge is a stainless steel knife
blade having a sharp edge 70 millimeters long. The
blade supply is calibrated by using a Load of 400 g on
~5 a neoprene calibration material at the beginning and
end of the test. A new cutting edge i:~ used for each
cut test .
The sample is a rectangular piece of fabric cut
50 x i00 millimeters on the bias at 45 degrees from the
20 warp and fill directions.
The mandrel is a rounded electroconductive bar
with a radius of 38 millimeters and the sample is
mounted thereto using double-face tape. The cutting
edge is drawn across the fabric on the mandrel at a
25 rlgl2t angle with the longitudinal axis of the mandrel.
Cut through is recorded when the cutting edge makes
electrical contact with the mandrel.
EXAMPLES
30 Knitting g oves and fabrics to bA test d.
Para-aramid filament yarns of four different linear
densities were crimped and cut to make :Maple for
spinr_ing test yarns for these examples. The filament
yarns were polyp-phenylene terephthalamide) yarns sold
35 by E. T. du Pont de Nemours and Company under the
tradename Kevlar~ 29, and were made from filaments
havi:.g linear densities of 1.67, 2.50, 4.67, and 6.67
dtex. The staple length was 11.4 centimeters.
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Portions of each-staple fiber were spun by a
worsted system into yarns having a variety of twists.
Two-ply yarns were spun having a linear density of 590
dtex (Cotton Count, 20/2) and twist factors as shown in
Tables 1 and 2.
Sample gloves and sample fabrics were knitted
on a Shima Seiki glove knitting machine using these
yarns and 4- and 6-end set-ups. The 4-end set-up
resulted in a knitted fabric and string knit glove with
an averaged weight of 478 g/square meter (14.1
ounces/square yard); and the 6-end set-up resulted in a
knitted fabric and glove with an averaged weight of 783
g/square meter (23.1 ounces/square yard).
~~~PLE 1.
The gloves prepared above were subjected to cut
resistance tests to yield information relating to the
relationship between cut resistance and the fabric
parameters of staple linear density and yarn twist
factor. Results of those tests are set out in Tables 1
and 2, below, for the 6-end and 4-end fabrics,
respectively.
TABLE 1 (6-End abric)
F
Lin. Den. .1 67 tex 2.50 t ex 4.67 dtex 6.67 dtex
Twist .~ ( Cut Resis tance (KG-for ce)
14 1.4 1.6 1.8 -
17 1.3 1.6 1.7 1.8
19 1.4 1.5 1 6 1.8
22 1.3 1.4 1.6 1.7
24 1.3 1.5 1.9 2.3
26 1.3 1.4 1.8 1.8
29 1.4 1.5 1.9 2.0
31 1-33 1-44 1-7 1,g
avg. 1.3 1.5 1.8 1.9
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TABLE 2 (4-End Fabricl
Lin. Den. 1.67 dtex 2.50 dtex 4.67 dtex 6.67
d tek
Twist ~ t Cut sistance !KG-for ce)
Re
14 1.0 1.1 __.2 -
17 i.0 1.1 ~_.5 1.6
19 1.1 1.2 1..4 1.5
22 1.1 1.2 i..4 1.5
24 0.9 1.2 1.4 1.6
26 1.0 1.0 1.5 1.5
29 1.0 1.2 1.5 1.6
31 I-22 1-11 1-44 2-S5
avg. 1.0 1.1 1.4 1.5
The Cut Resistance data from t:nis example show
that cut resistance is a definite function of staple
linear density and is relatively independent cf twist.
The cut resistance improves dramatically with increase
in staple linear density and the increase is most
dramatic at staple linear densities of greater than 2.5
dtex.
EXAMPLE 2.
The 6-end fabrics prepared above were subjected
to a comfort test wherein the thirty one fabric samples
were evaluated by feel to determine the "hand" of each
sample. Ten persons were asked to feel each sample and
rate the softness on a scale of 1-5 with 1 being
harshest and 5 being softest. All of the ratings of
the ten persons were averaged and are recorded in Table
~ 3, below.
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TABLE 3
Lin. Den.- 1.67 dtex 2.50 dtex 4.67 dtex 6.67 dtex
Twist ~ ( Com fort Rating!Average of ten) _)
14 4.4 4.4 3.2 -
17 4.2 4.4 3.1 2.9
19 4.2 4.0 3.0 2.5
22 3.6 3.5 2.5 2.1
24 3.5 3.5 2.2 2.5
26 3.3 3.2 2.0 1.3
29 3.0 2.4 ~.0 1.8
31 2.B 2.0 L.4 1.4
The Comfort data from this example show that
comfort is a direct function of the degree of yarn
twist. The comfort improves dramatically as twist is
reduced. As stated previously, fabrics usually used in
commercially offered gloves have been made from yarns
with staple linear density of less than about 2.5 dtex
and a preferred twist factor of greater than 28. It is
clear from Table 3 that such fabrics were comfort rated
at 2 to 3 in these tests; and that fab~Yics of this
invention made from yarns with staple :linear density of
4.67 dtex and twist factors of less than 26 were rated
_~ at least as good. Comfort clearly inci:-eases with
decrease in staple linear density and decrease in
twist.
Examples 1 and 2, show that fabrics made from
yarns having staple linear densities of greater than
2.5 dtex exhibit improved cut resistance and fabrics
made from yarns of less than 6.67 dtex and having twist
factors of less than 26 exhibit improved comfort. A
combinaticn of those results show that yarns with
staple linear densities of 3 to 6 dtex and twist
factors of less than 26 will result in fabrics having,
both improved cut resistance and maintained comfort.
