BACKGROUND OF THE INVENTION
[0001] 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 harsh
hand; and that modification of the yarns to yield fabrics with increased cut resistance
have yielded fabrics which were even stiffer and more uncomfortable. This invention
relates to cut resistant woven and knitted fabrics which exhibit improved cut resistance
while maintaining an equivalent or softer hand, as described, for instance, in US-A-4
918 912.
SUMMARY OF THE INVENTION
[0002] 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 5.4 denier) and a length of 2.5 to 15.2 centimeters (1 to 6
inches).
[0003] 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.
DETAILED DESCRIPTION
[0004] 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 invention represents just such an improvement
in the field of out resistant apparel and fabrics. By use of this invention, it is
now possible to increase the cut resistant effectiveness and maintain the comfort,
of fabrics and protective garments, such as cut resistant gloves.
[0005] 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 fabric is improved by increasing the linear density of the individual fibers
used in the yarns.
[0006] By para-aramid fibers is meant fibers made from para-aramid polymers; and poly(p-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 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; 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.
[0007] Additives can be used with the para-aramid in the fibers 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 of the aramid.
[0008] Staple fibers for use in spinning yarns are generally of a particular length and
of a particular linear density. For use in this invention, the fibers can have any
length which is adequate for manufacture 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 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.
[0009] 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 form and creates a rather hard yarn.
[0010] 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
yarns. 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.
[0011] 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 dimensional systems:
Tex System -
Cotton System -
Metric Count System -
[0012] "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).
[0013] "Metric Count" of a yarn is the number of kilometers of the yarn to have a weight
of one kilogram.
[0014] For the purposes herein, the Tex System Twist Factor using SI units of tex
1/2 turns/cm will be used.
[0015] 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 necessary to have some degree of twist in the yarns
in order for the yarns to stay together, tests 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 10 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.
[0016] 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.
[0017] As to the linear density of individual staple fibers it has been discovered that
increased linear density in the staple results in increased cut resistance for the
yarn. 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 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 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 resistance from the increased fiber linear
density and maintained comfort from the decreased yarn twist.
[0018] 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 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 with adequate
comfort.
[0019] 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.
[0020] 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 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.
TEST METHODS
[0021] Cut Resistance. The method used was the "Standard Test Method for Measuring Cut Resistance of Fabrics
Used in Protective Clothing", proposed as an ASTM Standard (ASTM Subcommittee F23.20).
In 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 to 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
consistency of the blade supply. The normalized force is reported as the cut resistance
force.
[0022] 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 a neoprene calibration
material at the beginning and end of the test. A new cutting edge is used for each
out test.
[0023] The sample is a rectangular piece of fabric cut 50 x 100 millimeters on the bias
at 45 degrees from the warp and fill directions.
[0024] 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 right angle with the longitudinal axis of the mandrel.
Cut through is recorded when the cutting edge makes electrical contact with the mandrel.
EXAMPLES
Knitting gloves and fabrics to be tested.
[0025] Para-aramid filament yarns of four different linear densities were crimped and cut
to make staple for spinning test yarns for these examples. The filament yarns were
poly(p-phenylene terephthalamide) yarns sold by E. I. du Pont de Nemours and Company
under the tradename Kevlar® 23, and were made from filaments having linear densities
of 1.67, 2.50, 4.67, and 6.67 dtex. The staple length was 11.4 centimeters.
[0026] 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.
[0027] 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).
EXAMPLE 1.
[0028] 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.
[0029] The Cut Resistance data from this example show that cut resistance is a definite
function of staple linear density and is relatively independent of 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.
[0030] 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.
[0031] 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 fabrics 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 increases with decrease in staple linear density
and decrease in twist.
[0032] 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.
1. A yarn including para-amid staple fibres having a length of 2.5 to 15.2 centimeters,
characterised in that the yarn has a linear density of 150 to 5900 dtex and a twist
factor of less than 26 wherein the para-aramid staple fibers have a linear density
of 3 to 6 dtex.
2. The yarn of Claim 1 wherein the staple fibers have a linear density of 4 to 5 dtex.
3. The yarn of Claim 1 or 2 wherein the staple fibers have a twist factor of 15 to 22.
4. A cut resistant garment made from the yarn of Claim 1.
5. A fabric having a weight of 135 to 1017 grams per square meter and made from the yarn
of anyone of Claims 1, 2 or 3.
6. A cut resistant garment made from the fabric of Claim 5.
7. The garment of Claim 6 in the form of a glove.
8. A woven fabric of Claim 5.
9. A knitted fabric of Claim 5.
1. Garn, das Paraamidstapelfasern umfaßt, die eine Länge von 2,5 bis 15,2 cm aufweisen,
dadurch gekennzeichnet, daß das Garn eine lineare Dichte von 150 bis 5900 dtex und
einen Drehungsfaktor von weniger als 26 aufweist, bei dem die Paraamidstapelfasern
eine lineare Dichte von 3 bis 6 dtex aufweisen.
2. Garn nach Anspruch 1, bei dem die Stapelfasern eine lineare Dichte von 4 bis 5 dtex
aufweisen.
3. Garn nach Anspruch 1 oder 2, bei dem die Stapelfasern einen Drehungsfaktor von 15
bis 22 aufweisen.
4. Schnittfeste Bekleidung. die aus dem Garn nach Anspruch 1 hergestellt wird.
5. Textiles Flächengebilde mit einer Flächenmasse von 135 bis 1017 g/m2, hergestellt aus dem Garn nach einem der Ansprüche 1, 2 oder 3.
6. Schnittfeste Bekleidung, die aus dem textilen Flächengebilde nach Anspruch 5 hergestellt
wird.
7. Bekleidung nach Anspruch 6 in der Form eines Handschuhs.
8. Gewebe nach Anspruch 5.
9. Maschenware nach Anspruch 5.
1. Fil englobant des fibres para-aramides, d'une longueur comprise entre 2,5 et 15,2
centimètres, caractérisé en ce que le fil a une densité linéaire comprise entre 150
et 5900 dtex et un facteur de torsion inférieur à 26, les fibres discontinues para-aramides
ayant une densité linéaire comprise entre 3 et 6 dtex.
2. Fil selon la revendication 1, dans lequel les fibres discontinues ont une densité
linéaire comprise entre 4 et 5 dtex.
3. Fil selon les revendications 1 ou 2, dans lequel les fibres discontinues ont un facteur
de torsion compris entre 15 et 22.
4. Vêtement résistant aux coupures fabriqué à partir du fil selon la revendication 1.
5. Tissu ayant un poids compris entre 135 et 1017 grammes par mètre carré et fabriqué
à partir de fil selon l'une quelconque des revendications 1, 2 ou 3.
6. Vêtement résistant aux coupures fabriqué à partir de tissu selon la revendication
5.
7. Vêtement selon la revendication 6 ayant la forme d'un gant.
8. Tissu tissé selon la revendication 5.
9. Tissu tricoté selon la revendication 5.