Note: Descriptions are shown in the official language in which they were submitted.
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CUT-RESISTANT KNITTED FABRIC
BACKGROUND OF THE INVENTION
This invention relates to cut-resistant fabric
machine-knitted two-ends-in from two different yarns, one
of which contains cut-resistant fiber and the other of
which contains fibers having a hardness that tends to
dull a cutting blade.
Cut-resistant fabric made from yarn containing an
inherently cut-resistant fiber and a fiber having a
hardness above about 3 on the Mohs hardness scale is
disclosed in U.S. patent No. 5,119,512. Cut-resistance
is obtained by combining the two different materials in a
single yarn, the hard material apparently dulling a
cutting edge enough that the fabric is more resistant to
the cutting than would be a fabric of yarn containing
only the cut-resistant fiber. Such yarn has been
proposed for forming cut-resistant garments, including
gloves. Other cut-resistant gloves and yarns have also
been proposed, as set forth in the aforementioned patent,
including a testing procedure for determining cut-
resistance.
A cut-resistant yarn that utilizes a particle-filled
fiber is disclosed in U.'S. patent No. 5,597,649.-
. The particles are a hard material having a
Mohs hardness value of greater than about 3, and the
fiber is a high modulus cut-resistant fiber.
SUMMARY OF THE INVENTION
The present invention offers significant advantages
over the use of the yarn of the aforementioned patents
while utilizing a combination of an inherently cut-
resistant fiber and a hard fiber or fiber containing hard
particles to achieve high cut-resistance. These
advantages are obtained by locating the two different
types of fibers in separate yarns and knitting the yarns
two-ends-in, i.e., both together, on a single knitting
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machine. This structure and process maintains the two
different materials in close proximity so each can
function concurrently in accordance with its specific
property when the fabric so knitted is subjected to the
cutting action of a sharp instrument, such as a knife.
At the same time, the use of separate yarn strands having
the different properties facilitates achieving a desired
cut-resistance and fabric weight by conveniently allowing
either yarn to,be modified independently of the other.
For example, depending upon the intended use of a fabric,
one of the ends or yarn strands can be of lesser or
greater denier for greater flexibility or greater cut-
resistance without changing the other end, resulting in
ease of manufacturing a variety of fabrics. In addition,
one end, e.g., the end having the hard fiber, can be used
with one of a variety of other yarns as the other end,
having different weights (deniers) and/or utilizing
different cut-resistant synthetic fibers that have
different characteristics, such as abrasive resistance,
heat tolerance, shrink-resistance, and chemical
resistance, so optimum fabric construction for an
intended purpose can be achieved with less inventory, to
meet varying functional requirements and price
constraints. Further, the two ends can be controlled in
the knitting process to preferentially locate either of
the ends at a selected surface of the fabric to emphasize
the different characteristic of each end in a way to
achieve maximum cut-resistance and/or increased comfort.
In its broader aspects, the present invention
achieves these features and advantages by providing a
cut-resistant fabric comprised of first and second
separate ends of yarn machine-knitted together two-ends-
in, the first of said ends comprised of a cut-resistant
fiber and essentially free of any fiber having a hardness
of greater than 3 Mohs on the hardness scale, and the
second of said ends comprised of a fiber having a
hardness of greater than 3 P'Iohs on the hardness scale. An
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example of a preferred fiber having a hardness of greater
than 3 Mohs is ECG-150 fiber glass. In a preferred
embodiment, the second of said ends is essentially free
of any cut-resistant fiber.
The present inventioii also achieves these features
and advantages through a process of concurrently knitting
two yarns on a single knitting machine two-ends-in to
form a protective cut-resistant fabric, one of the ends
comprised of a,cut-resistant fiber essentially free of
any fiber having a hardness of greater than 3 Mohs on the
hardness scale and the second of said ends comprised of a
fiber having.a hardness of greater than 3 Mohs.
The invention finds particular usefulness in the
manufacture of cut-resistant protective gloves.
The process can advantageously include the step of
plaiting the two ends of yarn during knitting to locate
one of the ends predominantly at a first surface of a
garment, and the other of the ends predominantly at a
second surface of the garment. This allows placing of
the typically more comfortable end predominantly on the
inside of a garment and locating the other predominantly
on the outside. Apart from comfort, the synthetic cut-
resistant fiber end advantageously can be plated to the
inside, such as the inside surface of a protective glove,
and the hard fiber can be plaited predominantly to the
outside, producing a garinent in which the outer surface,
which is most apt to first encounter any sharp edge,
serves to effectively dull the edge before it encounters
a majority of the cut-resistant fiber.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic plan view of a protective
glove knitted two ends-in, embodying the present
invention;
Figure 2 is a diagrammatic drawing of a composite
yarn having two core strands and two wraps, the yarn
containing cut-resistant fiber and free of hard fiber;
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Figure 3 is a diagrammatic drawing of a composite
yarn having two core strands and two wraps, the yarn
containing hard fiber and free of cut-resistant fiber;
Figure 4 is a diagrammatic drawing of a composite
yarri similar to the yarn of Figure 2, but with a single
core strand;
Figure 5 is a diagrammatic drawing of a yarn formed
of air-entangled fibers containing cut-resistant fiber,
and free of hard fiber;
Figure 6 is a diagrammatic drawing of a yarn formed
of air-entangled fibers containing hard fiber and free of
cut-resistant fiber;
Figure 7 is a diagrammatic plan view of a protective
knit glove embodying the present invention in which two
ends of yarn are plait-knitted; and
Figure 8 is a diagrammatic sectional view taken
along the line 8-8 of Figure 7 and looking in the
direction of the arrows, illustrating the location of one
of the two ends predominantly at the exterior of the
glove and the other predominantly at the interior.
DESCRIPTION OF PREFERRED EMBODIMENTS
With reference to the drawings, a preferred
embodiment of the invention is a cut-resistant fabric A,
shown in Figure 1 in the form of a protective glove G,
machine knit from two ends of yarn B, C (Figures 2 and
3). The glove finds particular use in the meat industry
to protect workers' hands against injury from sharp
implements, such as knives. The fabric in the form of a
glove is advantageously knit on a 10 cut Shima knitting
machine.
The yarn B is a composite yarn having a core 10, a
first helical wrap 12 wound about the core and a second
helical wrap 14 wound about the first wrap in an opposite
direction from that of the wrap 12. The core 10 has two
strands 16, 18 extending lengthwise of the yarn.
The yarn C is a composite yarn having a core 20, a
first helical wrap 22 wound about the core and a second
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helical wrap 24 wound about the first wrap in an opposite
direction from that of the wrap 22. The core 20 has two
strands 26, 28 extending lengthwise of the yarn.
In one preferred embodiment of the invention, the
yarn B contains cut-resistant fiber and is free of fiber
having a hardness of above 3 Mohs on the hardness scale.
The core strand 16 is a cut-resistant continuous-filament
synthetic fiber of 400 denier high strength or normal
strength thermotropic liquid crystalline polymer, such as
Vectran HS or Vectran M, respectively. The core strand
18 is a cut-resistant continuous-filament synthetic fiber
of 375 denier extended chain polyester such as Spectra,
or alternatively 360 denier extended chain polyester such
as Certran. The first and second wraps 12, 14 are each
70 denier nylon, wrapped eight turns per inch, with the
turns of each wrap substantially touching one to the next
to cover the core and preceding wrap.
The yarn C contains fiber having a hardness of above
3 Mohs on the hardness scale and is free of synthetic
cut-resistant fiber. The core strand 26 is 220 denier
normal strength polyester and the core strand 28 is 150
denier ECG-150 fiber glass. The first and second wraps
22, 24 are each 70 denier nylon, wrapped eight turns per
inch, with the turns of each wrap substantially touching
one to the next to cover-ithe core and preceding wrap.
The two yarns B and C are together knitted two-ends-
in, i.e., both yarns or ends are concurrently knitted by
a common needle, on a 10-cut Shima knitting machine to
produce a cut-resistant protective glove as shown at G in
Figure 1.
A second preferred embodiment is identical to the
first, except that a yarn D (Figure 4)containing cut-
resistant fiber and free of fiber having a hardness above
3 Mohs on the hardness scale is substituted for the yarn
B. The yarn D has a core 30 of a single strand of 400
denier high or normal strength thermotropic liquid
crystalline polymer fiber, such as Vectran HS or M,
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respectively. The core is covered with first and second
wraps 32, 34, each of 70 denier nylon wrapped eight turns
per inch, with the turns of each wrap substantially
touching one to the next to cover the core and preceding
wrap.
A thir_d preferred embodiment utilizes a first yarn E
shown in Figure 5 and a second yarn C as shown in Figure
3 and described above. The yarn E is formed of air- ,
entangled continuous length fibers. Air entanglement of
continuous or staple length fibers is a known process for
forming yarn from a multiplicity of individual fibers.
The yarn E contains cut-resistant fibers and is free of
fiber having a hardness of above 3 Mohs on the hardness
scale. The cut-resistant fibers are continuous filament
synthetic fibers of 400 denier high strength or normal
strength thermotropic liquid crystalline polymer, such as
Vectran HS or Vectran M, respectively. Additionally, the
yarn E contains 220 denier normal strength polyester
fibers. The proportion of high strength fibers to normal
strength fi_bers being approximately 2:1 by weight. The
yar_iis E and C are together knitted two-ends-in, i.e.,
both yarns or ends are concurrently knitted by a common
needle, on a 10-cut Shima knitting machine to produce a
cut-resistant protective glove as shown at G in Figure 1.
A fourth preferred 6mbodiment utilizes a first yarn
E as described above and a second yarn F as shown in
Figure 6. The yarn F is formed of air-entangled
continuous length fibers and includes fibers having a
hardness of above 3 Mohs on the hardness scale and is
free of cut-resistant synthetic fiber. The fibers are
220 denier normal strength polyester and 150 denier ECG-
150 fiber glass in proportions of approximately 1:1 by
weight.
The two yarns E and F are together knitted two-ends-
in, i.e., both yarns or ends are concurrently knitted by
a common needle, on a 10-cut Shima knitting machine to
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produce a cut-resistant protective glove G as shown in
Figure 1.
Cut-resistant fibers are considered to be those
synthetic fibers that have a tenacity of above 10 grams
per denier, and/or those synthetic fibers having a
modulus greater than 200 grams per denier as measured by
ASTM Test Method D-3822, and include aramid fibers such
as..Kevlar, high strength extended chain polyethylene
fibers such as.Spectra and Certran, high strength
thermotropic liquid-crystalline polymer fibers such as
Vectran HS, and polybenzazole-containing fibers such as
fibers containing liquid-crystalline polybenzoxazole or
polybenzothiazole polymer (PBO). They also include
thermotropic liquid-crystalline polymer Vectran M fibers
having a tenacity of 10 or below. Cut-resistant fibers
are also those that have a cut-resistance equal to any of
the above-mentioned cut-resistant fibers, as determined
by any one of the following three industry accepted cut-
tests:
(1) A slash test procedure that measurably
simulates a knife under load contacting and moving across
a fabric knitted from yarn. The slash test is performed
to determine and record the load it takes to cut through
the knitted fabric. A relatively higher "slash test
load" is indicative of airelatively more cut-resistant
fabric. A yarn of the fiber to be tested is knitted into
a fabric sample that is then manipulated so it is
substantially flat and placed into a test fixture
constructed to stretch the fabric sample and load each
yarn or thread in the fabric to about a five pound
tensile load. The test fixture and fabric sample are
placed in an Instron model 4465 test machine with the
fabric sample oriented at a 45 angle relative to the
direction that a sharpened test blade is to be moved.
The test blade is moved under load in a straight line
against the fabric sample. The weight or load acting on
the test blade against the fabric sample is variable.
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The test blade is carbide steel and has four sharpened
and independent circumferentially spaced arcuate cutting
sections. Each section of the test blade performs only
one slash test. The test blade is removed and re-
sharpened after all four sections perform a slash test.
A test blade section is deemed "sharp" when a slash test
load in the range of nine pounds to sixteen pounds causes
the blade to cut through a standardized fabric using the
above described procedure. The standardized fabric used
is available from Whizard Protective Wear Corp. under the
name Handguard II. The Handguard II fabric is machine
knitted two-ends-in, five and one half needles per inch
of a specific yarn of about 0.023 inch diameter. Each
yarn has a core consisting of a multifilament strand of
375 denier Spectra 1000 fiber. Each yarn has oppositely
wound helical wraps about the core. These wraps consist
of, in the order set forth, a first and second wrap of a
multifilament strand of 70 denier nylon fiber, six turns
per inch each; a third wrap of one end of 0.0016
stainless steel, eight turns per inch; a fourth wrap of a
multifilament strand of 400 denier Kevlar fiber, ten
wraps per inch; a fifth wrap of multifilament strand of
650 denier Spectra 900 fiber, 10 wraps per inch; and a
sixth wrap of a multifilament strand of 440 denier
polyester fiber, 10 wraps per inch. To determine if a
fiber is cut-resistant, 'a slash test is performed on a
fabric knitted from a yarn of the fiber. The test blade,
under a selected load, is brought into engagement with
the fabric sample three times. Each time, a new cutting
section of the test blade is used and the blade engages a
different portion of the fabric at a different
orientation relative to a knit loop. The three test
orientations are directly across a knit loop, directly
along a knit loop, and diagonally across a knit loop.
The loads sufficient for the test blade to cut through
each fabric sample in the three test directions are
recorded and averaged. Each average slash value is an
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average of 25 readings. The average load in pounds
required to cut completely through the fabric sample may
be referred to as the "slash test load."
(2) A procedure known as the Ashland Cut Protection
Performance Test (CPPT) for determining if a fiber or
yarn is cut-resistant, which i_s disclosed in U.S. patent
No. 5,597,649. In the Ashland test
procedure, a fabric sample of the yarn to be tested is
placed on the convex surface=of a mandrel. A series of
tests is carried out in which a razor blade loaded with a
variable weight is pulled across the fabric until the
fabric at the location of contact is cut all the way -
through. The distance the razor blade travels across the
the location of contact with the fabric, until the blade
cuts completely through the fabric, is measured. The
logarithm of the distance of blade travel required to
make the cut is plotted on a graph as a function of the
load on the razor blade. The data are collected and
plotted for cut distances varying from 0.3 inch to about
1.8 inches. The resulting plot is approximately a
straight line. An idealized straight line is drawn or
calculated through the points on the plot, and the weight
required to cut through the cloth after one inch of
travel across the fabric,;is taken from the plot or
calculated by regression analysis. This is referred to
as the "CPP" value. By forming the fabric of a fiber to
be tested, a value indicative of the cut-resistance of
the fiber is determined.
(3) A Betatec impact cam test for determining if a
fiber or yarn is cut-resistant, which is disclosed in
U.S. patent No. 5,597,649. The method and apparatus are
described in U.S. patent No. 4,864,852.
The determination involves repeatedly contacting a sample
with a sharp edge that falls on the sample, which is
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rotati_ng on a mandrel. These contacts are repeated until
the sample is penetrated by the cutting edge. The
greater the number of cutting cycles (contacts) required
to penetrate the sample, the greater the cut resistance
of the sample. By way of example, the following
conditions can be used: 180 grams cutting weight, a
mandrel speed of 50 rpm, a rotating steel mandrel
diameter of 19 mm, a cutting blade drop height of about
3/4 inch, use of a single edged industrial razor blade
for cutting, a cutting arm distance from pivot point to
center of blade about 15.2 cm (about 6 inches).
While preferred embodiments have been described in
detail, modifications or alterations may be made without
departing from the invention. Thus, any of the above-
mentioned cut-resistant fibers or fibers of equivalent
cut-resistance or mixtures thereof may be substituted for
those of the preferred embodiments, as may other hard
fibers, such as ceramic or carbon fiber or particle-
filled fibers containing hard fillers, or mixtures
thereof, be substituted for the fiber glass of the
preferred embodiments. Particle-filled fibers containing
hard fillers are described in U.S. patent No. 5,597,649
Also, depending upon the cut-resistance required and the
flexibility of the garment, especially the flexibility
and feel required of a glove, deniers of the fibers may
vary from those set forth above in the preferred
embodiments. For example, in the cut-resistant end of
yarn, the total denier of the cut-resistant fiber may
vary between 300 and 800, and the denier of the hard
fibers in the other yarn may vary between 75 and 500, in
the manufacture of knitted protective gloves suitable for
industrial uses such as in the food industry and
particularly in the meat packing industry. Non-cut-
resistant fibers other than the nylon and polyester of
the preferred embodiments may be used, including natural
fibers, along with the cut-resistant and hard fibers, to
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provide desired bulk and softness. The deniers of those
fibers will vary, depending upon the bulk desired.
To assure knittability and good cut-resistance using
two-ends-in on conventional glove-knitting machines, the
overall diameter of each end of yarn is preferably from
about 0.003 to 0.026 inch. It is desirable, although not
essential, that each end be of about the same diameter.
The total of the two diameters individually measured
should not exceed 0.052 inch. This_provides slightly
greater mass than could be knit if used to form a single
yarn, the maximum diameter of a machine-knittable single
yarn being about 0.035 inch. This is because the two
ends are movable relative to each other during knitting
and therefore can be.knitted through the finger crotches
more easily than a single yarn of equivalent mass. The
knitting can be done on a 5-cut, 10-cut, l3=cut, or 15-
cut knitting machine.
While the covering wraps of the composite yarns of
the preferred embodiments are wound eight turns per inch,
this can vary from 2 to 16. It is desirable to use
sufficient wraps and turns per wrap to completely cover
the core of a composite yarn.
The preferred yarns are free of metallic fiber, such
as stainless steel wire, although additional cut-
resistance can be obtained by its inclusion as either a
core strand or a wrap, or its incorporation into the
entangled yarns, but at the cost of increased yarn
stiffness.
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