Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
CUT AND ABRASION RESISTANT FIBROUS STRUCTURE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a high abrasion resistant fibrous
structure comprising a specific construction of a non composite p-aramid
strand and a nylon strand. This structure can be used to manufacture
protective clofihing having a high cut resistance and a high abrasion
resistance.
Description of the Related Art
Aramids and more specifically para-aramids are a relatively new
class of materials, which finds application in the domain of mechanical and
thermal protection. High cut protection performance can be obtained from
textile assemblies made of the para-aramid fibers. Therefore, para-aramid
fibers are often used in the manufacture of protective clothing for industrial
workers, firemen, sportsmen, military and police officers.
One drawback of para-aramid fibers is that they tend to suffer from
a relatively low abrasion resistance due to their fibrillation tendency. The
risk associated with this modest abrasion resistance is the reduction of the
cut performance of the protective clothing with time under service. In this
area of protection against wear and friction and therefore low abrasion,
nylons are superior but they do not offer a sufficient cut performance.
There is still a need to provide a material having both a high and
durable cut performance and a very high abrasion resistance.
There are many factors that influence the abrasion resistance of a
fabric. The abrasion performance may be tailored by the selection of the
type of fiber components, the fiber properties, the textile structures, the
fabric mass per unit area, the number of fibers per unit volume or the
relaxation allowance of the fiber components within the fiber bundle.
Often, the addition of abrasion resistance materials in a given structure
containing cut resistance components generally provides higher abrasion
performance at the expense of the cut resistance.
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U.S. 5, 319, 950 discloses a reinforcing component which is a
composite yarn made of a nylon twisted yarn helically wrapped by another
nylon twisted yarn, this reinforcing component being knitted in a plaited
relationship with a body yarn. The manufacture of such a yarn is complex
and necessitates several steps. Moreover, the reinforced fabric thus
obtained is still not satisfactory as regards cut resistance.
Now, it has been found that by combining specific fiber ingredients
in a specific construction style, it was possible to realize rapidly, directly
and easily very high cut resistant and high abrasion resistant fibrous
material. In particular, it is possible to reach the same cut resistance level
with a higher level of abrasion resistance than if the same fiber ingredients
are either taken separately or combined in a different construction style.
SUMMARY OF THE INVENTION
One aspect of the invention is a fibrous structure comprising at
least one non composite para-aramid strand and at least one nylon strand
maintained in a parallel relationship to each other, the non composite
para-aramid strand being present in the structure in an amount ranging
from about 20 % to about 99'.9 % by weight, relative to the weight of the
structure.
Another aspect of the invention is a process to manufacture the
structure above comprising the step of processing a non composite
para-aramid strand and a nylon strand in a parallel. relationship to each
other.
Another aspect of the invention is a process for providing a fibrous
structure having high cut and abrasion resistance, comprising:
- a) providing strands of at least one non composite para-aramid
strand and at least one nylon strand,
- b) feeding the strands into a knitting or weaving machine without
prior assembly, and
- c) knitting or weaving a fibrous structure without changing the
order in which the strands are fed into the machine, the strands
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being maintained in a parallel relationship to each other during
the whole knitting or weaving process.
A further aspect of the invention is a high cut and abrasion resistant
protective clothing, in particular gloves, aprons or sleeves, made of the
fibrous structure above.
The fibrous structure of the invention has a high resistance to
abrasion. It also has a very high resistance to cutting. With the structure
of the invention, it is possible to manufacture high cut and abrasion
resistant protective clothing like working gloves. The gloves made of the
fibrous structure of the invention are comfortable and, by wearing them,
the user does not lose the natural dexterity of his hands.
The fibrous structure of the invention also finds use in the ballistic
area: it has a very good puncture resistance.
Moreover, since the para-aramid strand of the invention is a non
composite one, the manufacturing process of the fibrous structure is very
simple and direct and does not require any previous treatment or
arrangement of the strand. The manufacturing process can therefore be
completed in a minimum number of steps, allowing for a rapid, easy and
cost effective realization of any fibrous sfiructure.
DETAILED DESCRIPTION
"Fibrous .structure", as used herein, includes two or three-
dimensional structures comprising fibrous material. Preferably, this
structure includes knitted fabrics, woven fabrics, unidirectionals,
nonwovens, and/or combinations thereof. By "combinations", is meant
that structures of different nature and/or construction may be assembled
together, either in the same plane or not, as a multilayer structure for
instance, by any assembling means like sewing, gluing, stitching and the
like. By "nonwovens" is meant fibrous materials combined to a binding
matrix of polyethylene, polypropylene, polyamides, phenols, epoxy resins,
polyester or mixtures thereof.
"Fibrous material", as used herein, includes endless fibers such as
filaments, short fibrous structures, short cut fibers, microfibers,
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multifilaments, cords, yarns, fibers, pulps. The fibers may be made into
yarns of short fibrous structures which are spun into staple fibers, into
yarns of endless fibers or into stretchbroken yarns which can be described
as intermediate yarns between staple and continuous yarns.
"Strand", as used herein, means an ordered assemblage of fibrous
material having a high ratio of length to diameter, preferably having a
length at least 1000 times its diameter. The strand may be round, flat or
may have another cross-sectional shape or it may be a hollow fiber. By
"non composite strand", is meant a single simple strand by opposition to
assembled strands like cotwisted strands, cotextured strands, intermingled
strands, core-spun strands and combinations thereof.
The structure of the invention comprises at least one non composite
para-aramid strand.
Aramids are polymers that are partially, preponderantly or
exclusively composed of aromatic rings, which are connected through
carbamide bridges or optionally, in addition, also through other bridging
structures. The structure of such aramids may be elucidated by the
following general formula of repeating units:
(-NH-A1-NH-CO-A2-CO)n
wherein A1 and A2 are the same or different and signify aromatic and/or
polyaromatic and/or heteroaromatic rings, that may also be substituted.
Typically A1 and A2 may independently from each other be selected from
1,4-phenylene, 1,3-phenylene, 1,2-phenylene, 4,4'-biphenylene,
2,6-naphthylene, 1,5-naphthylene, 1,4-naphthylene, phenoxyphenyl-4,4'-
diyelen, phenoxyphenyl-3,4'-diylen, 2,5-pyridylene and 2,6-quinolylene
which may or may not be substituted by one or more substituents which
may comprise halogen, C1-C4-alkyl, phenyl, carboalkoxyl, C1-C4-alkoxyl,
acyloxy, nitro, dialkylamino, thioalkyl, carboxyl and sulfonyl. The -CONH-
group may also be replaced by a carbonyl-hydrazide (-CONHNH-) group,
azo-or azoxygroup.
These aramids are generally prepared by polymerization of diacid
chloride, or the corresponding diacid, and diamine.
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Examples of aramids are poly-m-phenylene-isophthalamide and
poly-p-phenylene-terephthalamide.
Additional suitable aromatic polyamides are of the following
structure:
(-N H-Ar1-X-Ar2-N H-CO-Ar1-X-Ar2-CO-)n
in which X represents O, S, S02, NR, N2, CR2, CO.
R represents H, C1-C4-alkyl and Ar1 and Ar2 which may be same
or different are selected from 1,2-phenylene, 1,3-phenylene and
1,4-phenylene and in which at least one hydrogen atom may be
substituted with halogen and/or C1-C4-alkyl.
Further useful polyamides are disclosed in U.S. Pat. No. 4,670,343
wherein the aramid is a copolyamide in which preferably at least 80% by
mole of the total A1 and A2 are 1,4-phenylene and phenoxyphenyl-3,4'-
diylene which may or may not be substituted and the content of
phenoxyphenyl-3,4'-diylene is 10% to 40% by mole.
Additives may be used with the aramid and, in fact, it has been
found that up to as much as 10% by weight, of other polymeric materials
may be blended with the aramid or that copolymers may be used having
as much as 10% of other diamine substituted for the diamine of the aramid
or as much as 10% of other diacid chloride substituted for the diacid
chloride of the aramid.
The non composite para-aramid strand of the invention preferably
has an elongation equal to or less than 5%, measured according to ASTM
D885-98. Preferably, the para-aramid strands have a modulus of about 10
to about 2500 g/den, preferably of about 1000 to about 2500 g/den, and a
tenacity of about 3 to about 50 g/den, preferably of about 3 to about 38
g/den. The modulus and the tenacity are measured according to the
ASTM D 885-98 method.
The structure of the invention may comprise several para-aramid
strands. In such a case, these strands are independent from each other.
The para-aramid strands are present in the structure of the invention in an
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amount ranging from about 20 to about 99.9%, preferably from about 30%
to about 70% by weight, relative to the total weight of the structure.
The strands are generally spun from an anisotropic spin dope using
an air gap spinning process such as is well-known and is described in U.S.
Patent No. 3,767,756 or 4,340,559.
The structure of the invention also comprises at least one nylon
strand. By "nylon" is meant a strand made from aliphatic polyamide
polymers. Suitable nylons in the present invention include
polyhexamethylene adipamide (nylon 66), polycaprolactam (nylon 6),
polybutyrolactam (nylon 4), poly(9-aminononanoic acid) (nylon 9),
polyenantholacfiam (nylon 7), polycapryllactam (nylon 8) and
polyhexamethylene sebacamide (nylon 6,10). Preferred nylon is
polyhexamethylene adipamide (nylon 66).
In a preferred embodiment of the invention, the nylon strand is a
textured strand. By "textured strand" is meant a strand which has
undergone a treatment, like air-injection for instance, in order to
intermingle the originally parallel filaments constitufiing the strand.
Preferred nylon strands of the invention have an elongation equal to
or less than 18%, and a tenacity equal to or less than 10 gpd. The
elongation and the tenacity are measured according to ASTM D885-98.
Nylon strands are generally spun by extrusion of a melt of the
polymer through a capillary into a gaseous congealing medium. Such
processes are well-known.
Suitable nylon strands of the invention include the product sold
under the tradename "Cordura~" by E. 1. du Pont de Nemours and
Company, Delaware.
The structure of the invention may comprise several nylon strands.
The non composite para-aramid strand and the nylon strand are
maintained in a parallel relationship to each other in the structure of the
invention. "Parallel", as used herein, means that the angle between one
strand along the entirety of its running length and any other strand along
the entirety of its running length is about zero. All the strands remain
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independent and separate from each other. They are not intimately
blended, they are not cotwisted, they are not intermingled, not
commingled, not interlaced, not intermixed nor textured. One does not
wrap any other one, they do not form a core-spun fiber nor a sheath core.
In a preferred embodiment of fihe fibrous structure of the invention,
the non composite para-aramid strand is present in an amount ranging
from about 30% to about 70% by weight and the nylon strand is present in
an amount ranging from about 30% to about 70% by weight, relative to the
weight of the structure.
In addition to the non composite para-aramid strands and the nylon
strands described above, the structure of the invention may comprise
additional man-made or natural strands. These additional strands include
polyethylene strands, polyester strands, acrylic strands, acetate strands,
meta-aramid strands, glass strands, steel strands, ceramic strands,
polytetrafluoroethylene strands, cellulosic strands, cotton strands, sii(c
strands, wool strands and mixtures thereof. These additional strands may
be present in an amount ranging from about 0.25 weight % to about 25
weight %, relative to the total weight of the structure, as long as their
presence in the structure of the invention does not negatively impact the
specific high abrasion and cut resistance of the structure of the invention.
- These additional strands are also maintained in a parallel relationship to
any other strand present in the structure.
The structure of the invention shows a very good cut resistance. In
a preferred embodiment of the invention, the structure of the invention
shows a combined normalized index CTPCPI.N, measured as described
below, equal or greater than 80 g/mm, more preferably equal or greater
than 90 g/mm. The structure of the invention also shows a very good
abrasion resistance. In a preferred embodiment of the invention, the
structure shows an abrasion resistance, measured according to EN 388
method, equal or greater than 1000 cycles, more preferably equal or
greater fihan 3000 cycles. In a more preferred embodiment of the
invention, the structure shows both a combined normalized index
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CTPCPI.N, measured as described below, equal or greater than 80 and
an abrasion resistance, measured according to EN 388, equal or greater
than 1000 cycles.
The structure of the invention preferably shows a medium weight
ranging from about 20Q g/m2 to about 1500 g/m2, preferably ranging from
about 300 g/m2 to about 800 g/m2, measured according to EN 388
method.
The structure of the invention is prepared according to any classical
textile process allowing for parallel alignment of the strands making the
structure: knitting, weaving, unidirectionally laying down, combining the
strands with a binding matrix to form a nonwoven. For instance, in the
knitting or weaving process, the strands are fed directly to the knitting
machine or the weaving machine without any prior assembly of any sort.
For instance, in the knitting process, the order in which the strands are fed
into the needles of the knitting machine remains the same during the
whole knitting process. Preferred process for making the structure of the
invention is the knitting process.
The structure of the invention may be used in the manufacture of
gloves, aprons, sleeves and any protective clothing requiring a high cut
resisfiance and a high abrasion resistance.
The invention will be explained in more detail with reference to the
following examples.
Test Methods and Examples Description
Abrasion resistance
In the following. examples, the abrasion resistance of the samples
was measured according to the Standard European Method EN388, July
1994, section untitled "Protective Gloves against Mechanical Risks",
subsection 6 "Abrasion resistance".
The apparatus was the Martindale wear and abrasion tester,
designed to give a controlled amount of abrasion between the fabric
surface and the selected abradant afi relatively low contact pressure of (9
+/- 0.2) kPa in continuously changing directions. The circular samples
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were abraded against a standard abrasive glass paper (grade F2 grit 100
quality 117).
The abrasion was continued and the samples were examined at
suitable intervals without removing them from their holder. The
rub-through situation was characterized by broken threads and the
average values of cycle to reach this breakdown was registered and
averaged for 6 samples.
The test is conducted at (23 +/- 2) °C and (50 +/-5) % relative
humidity.
The greater is the number of cycles needed to reach the
breakdown, the higher is the resistance to abrasion of the sample.
Cut resistance
In the following examples, the cut resistance was measured
according to the "Standard test Method for Measuring Cut Resistance of
Materials Used in protective Clothing", ASTM Standard F 1790-97.
In performance of the test, a cutting edge, under a specified force,
was drawn one time across a sample mounted on a cylindrical mandrel,
At several different forces, the distance drawn from initial contact to cut
through was recorded and a graph was constructed of force as a function
of distance to cut through. From the graph, the forces (in grams) were
determined to cut through at a distance of 25.4 millimeters, and 10
millimeters, and were normalized to validate the consistency of the blades.
These normalized forces are hereinafter respectively referred to as NL1
(for the 25.4 mm distance) and NL2 (for the 10 mm distance). The blades
were stainless steel cutter blades with a sharp edge of 70 mm, which were
calibrated using a load of 4 N on a neoprene sheet of about (1.57 +/- 10%)
mm and a hardness of (50 +/- 5} shore A. This was performed at the
beginning and at the end of the test. A new blade was used for each
measurement, i.e. each load. The sample was a rectangular piece of
textile of 50x100 millimeters placed at a biais of 45 degrees. The mandrel
was a rounded electroconductive bar with a radius of 38 millimeters and
the sample was mounted onto it using double-face tapes. The cutting
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edge was drawn across the textile on the mandrel at a right angle with the
longitudinal axis of the mandrel. Cut through was recorded when the
cutting edge makes electrical contact with the mandrel. The normalized
forces were reported as the cut resistance forces, respectively NL1 and
NL2 expressed in grams for a cut length of 25.4 mm and 10 mm.
The test is conducted at (23 +/- 2) °C and (50 +/-5) % relative
humidity.
The 25.4 millimeters cut can be classified as a tear-like-cut and the
10 millimeters cut can be classified as a puncture-like-cut. These two
belong to different regions of the cut-length - cut-force relationship, which
is a non-linear curve. It was therefore convenient to define a combined
index, which has the merit to compound the two behaviors. This index is
hereafter referred to as the Combined Tear Puncture Cut Performance
Index, CTPCPI. It was computed as per the following equation:
CTPCPI = NLl + NL2 2 ~ ~grarras~
2~.4 10 ~/ mrn
This index was further normalized for a constant weight of fabric
composition, hereafter selected at 800 grams per square meters. This
mass per square area is a realistic value with regard to the protective
clothing applications such as gloves for industrial usage.
CTPCPI __ NLl + NL2 2 ~ (800) ~ ~gr~arns~
25.4 10 ~/ (mass per surface area of the sample) mr Jn
This combined normalized index is given in grams per millimeter of
cut length. The higher this index is, the higher is the cut resistance of the
sample.
For each example, 12 samples were tested. The result is the average of
the results of the 12 tests.
Inuredients
Non composite para-aramid strand A: staple para-aramid yarn of
linear density 714dtex, equivalent Nm=28/2 (with dtex=10000/Nm)
commercially available from E.I. du Pont de Nemours and Company under
the tradename Kevlar~ staple aramid fiber, Type 970. The synthetic fiber
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staples were produced from short para-aramid fibers of 38 mm length as
per the state of the art spinning process used for the production of
para-aramid staple yarns. The para-aramid short fibers were obtained by
cutting continuous filament para-aramid yarns made of 1000 filaments of
1.5 dpf (1.6dtex) each.
Nylon strand B: staple yarns of nylon 66 of linear density 370 dtex,
equivalent Nm=55/2 (with dtex=10000/Nm}, commercially available by E. I.
du Pont de Nemours and Company under the trade designation Cordura~
Type 200. The synthetic fiber staples were produced from short aliphatic
polyamide nylon 66 fibers of 38 mm length as per the state of the art
spinning process used for the production of aliphatic polyamide staple
yarns. The aliphatic polyamide short fibers were obtained by cutting
continuous filament yarns made filaments of 1.9 dtex each.
EXAMPLES
Examples 1 and 2 are comparative Examples. Example 3 is an
example according to the invention. In order for the results to be
comparative, all three examples were realized for a relatively constant
value of the total dtex (which is representative of the linear density of a
fiber) and a relatively constant value of the mass per surface area.
Example 1 (Comparative)
Five independent non composite para-aramid strands A were fed to
a circular knitting machine (Fiber Analysis Knitter from Lawson-Hamphill)
without prior assembling of any sort. A sleeve of sufficient length was
knitted to obtain a uniform and reproducible pattern of a mass per surface
area close to 800 g/m2.
The samples were cut to the adequate dimensions and shapes,
circular for the abrasion testing and rectangular for the cut performance
measurement, to perform 6 abrasion tests and 12 cut tests.
Each sample had therefore a total dtex of 3570 (five times 714
dtex).
The abrasion resistance measured was 900 cycles.
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The forces measured in the cut resistance test were 821 g for a cut
length of 25.4 mm and 1666 g for a cut distance of 10 mm. The combined
CTPCPI.N normalized index was given by the following calculation
[(821/25.4 + 1666/10)/2]x800/800 and equaled 99 g/mm.
Example 2 (Comparative)
Ten independent nylon strands B were fed to the same circular
knitting machine as the one used in Example 1 without prior assembling of
any sort. A sleeve of sufficient length was knitted to obtain a uniform and
reproducible pattern of a mass per surface area close to 826 g/m2.
The samples were cut to the adequate dimensions and shapes,
circular for the abrasion testing and rectangular for the cut performance
measurement, to perform 6 abrasion tests and 12 cut tests.
Each sample had therefore a total dtex of 3700 (ten times 370
dtex).
The abrasion resistance measured was 3000 cycles.
The forces measured in the cut resistance test were 759 g for a cut
length of 25.4 mm and 923 g for a cut distance of 10 mm. The combined
CTPCPI.N normalized index was given by the following calculation
[(759/25.4 + 923/10)/2]x800/826 and equaled 59 g/mm.
CTPCPI.N of example 2 reveals an approximate 40% inferior cut
resistance compared to example 1. On the other side the abrasion
resistance of example 2 is three times superior to the one of example 1.
Example 3 (Invention)
Three independent non composite para-aramid strands A and four
independent nylon strands B were fed to the same circular knitting
machine as the one used in Example 1 without prior assembling of any
sort. A sleeve of sufficient length was knitted to obtain a uniform and
reproducible pattern of a mass per surface area close to 843 g/m2.
The samples were cut to the adequate dimensions and shapes,
circular for the abrasion testing and rectangular for the cut performance
measurement, to perform 6 abrasion tests and 12 cut tests.
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Each sample had therefore a total dtex of 3622 (three times 714
dtex plus four times 370 dtex). Each sample comprised 50.1 % by weight,
of non composite para-aramid strand relative to the weight of the sample,
and 40.1 % by weight, of nylon strand, relative to the weight of the sample.
The abrasion resistance measured was 6000 cycles.
The forces measured in the cut resistance test were 1170 g for a
cut length of 25.4 mm and 1400 g for a cut distance of 10 mm. The
combined CTPCPI.N normalized index was given by the following
calculation [(1170/25.4 + 1400/10)/2]x800/843 and equaled 88 g/mm.
CTPCPI.N of Example 3 reveals an approximate equal cut
resistance compared to Example 1. On the other side, the abrasion
resistance of Example 3 is six times superior to the one of Example 1 and
surprisingly two times superior to the one of Example 2.
The following table summarizes the results obtained in Examples 1
to 3.
TABLE I
Example Example Example 3
1 2 invention
com arativecom arative)
Total dtex 3570 3700 3622
w% of p-aramid strands 100 0 59
Mass per square area 800 826 843
(g/m2)
CTPCPI.N in g/mm 99 59 88
Abrasion resistance in 900 3000 6000
cycles
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