Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF INVENTION
ARC RESISTANT GARMENT CONTAINING A MULTILAYER FABRIC
LAMINATE AND PROCESSES FOR MAKING SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention. This invention relates to a multilayer fabric
laminate having improved arc performance and protective garments
containing the multilayer fabric laminate.
2. Description of Related Art. United States Patent Nos. 7,065,950
and 7,348,059 to Zhu et al. disclose modacrylidaramid fiber blends for use
in arc and flame protective fabrics and garments. Arc resistant garments
are used in potentially life-threatening situations; as such, any garment
construction that can provide improved arc protection can potentially
reduce injury and save lives.
SUMMARY OF THE INVENTION
This invention relates to a protective garment having use in an
electrical arc potential environment, the garment having an arc resistant
multilayer fabric laminate comprising a first layer of a woven flame-
resistant fabric forming an outer surface of the garment and comprising a
first fire-resistant fiber made from a synthetic polymer comprising a
halogen, and a second layer of a woven flame-resistant fabric comprising
a second fire-resistant fiber made from a synthetic polymer, wherein the
first fire-resistant fiber has a thermal decomposition temperature that is at
least 70 degrees C less than the second fire-resistant fiber; and wherein
the fabrics in the first and second layers are different and the first layer
is
positioned in the garment to be closer the electrical arc potential
environment than the second layer.
This invention also relates to a process for making a protective
garment having use in a electrical arc potential environment, comprising:
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i) providing a first woven flame-resistant fabric comprising a first
fire-resistant fiber made from a synthetic polymer comprising a
halogen;
ii) providing a second woven flame-resistant fabric comprising a
second fire-resistant fiber made from a synthetic polymer,
wherein the first fire-resistant fiber has a thermal decomposition
temperature that is at least 70 degrees C less than the second
fire-resistant fiber; the first and second woven flame-resistant
fabrics being different;
iii) combining the first and second woven flame-resistant fabrics to
form a arc resistant multilayer fabric laminate, the first and
second woven flame-resistant fabrics being distinct fabric layers
without any shared weft or warp fabric yarns; and
iv) forming an arc resistant garment from the arc resistant
multilayer fabric laminate wherein the first woven flame-resistant
fabric forms an outer surface of the garment and is positioned in
the garment closer to the electrical arc potential environment
than the second layer.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 are thermgravimetric analysis scans in air
illustrating how the thermal decomposition temperature of a fiber can be
determined.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to protective garments that have use in an
electrical arc potential environment. By electrical arc potential
environment, it is meant any situation where a worker could be exposed to
an electrical arc that could cause injury or death.
This invention relates to a protective garment having an arc
resistant multilayer fabric laminate comprising at least two flame-resistant
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fabric layers that have different compositions. The first flame-resistant
fabric layer forms an outer surface of the garment and comprises a first
fire-resistant fiber containing a synthetic polymer comprising a halogen.
The second flame-resistant fabric layer comprises a second fire-resistant
fiber containing a synthetic polymer. In addition, the first and second fire-
resistant fibers have different compositions, and the first fire-resistant
fiber
has a thermal decomposition temperature that is at least 70 degrees C
less than the thermal decomposition temperature of the second fire-
resistant fiber.
The different fabric compositions provide the multilayer fabric
laminate with directionality, and the multilayer fabric laminate is positioned
in the garment such that the first flame-resistant fabric layer is closer the
electrical arc potential environment than the second flame-resistant fabric
layer.
Protective garments of this type include protective coats, jackets,
jumpsuits, coveralls, hoods, etc. used by industrial personnel such as
electricians and process control specialists and others that may work in an
electrical arc potential environment. In a preferred embodiment, the
protective garment is a coat or jacket, including a three-quarter length coat
commonly used over the clothes and other protective gear when work on
an electrical panel or substation is required.
In a preferred embodiment, the protective garments have at least a
Category 2 arc rating or higher as measured by either of two common
category rating systems for arc ratings. The National Fire Protection
Association (NFPA) has 4 different categories with Category 1 having the
lowest performance and Category 4 having the highest performance.
Under the NFPA 70E system, Categories 1, 2, 3, and 4 correspond to a
heat flux through the fabric of 4, 8, 25, and 40 calories per square
centimeter, respectively. The National Electric Safety Code (NESC) also
has a rating system with 3 different categories with Category 1 having the
lowest performance and Category 3 having the highest performance.
Under the NESC system, Categories 1, 2, and 3 correspond to a heat flux
through the fabric of 4, 8, and 12 calories per square centimeter,
respectively. Therefore, a fabric or garment having a Category 2 arc rating
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can withstand a thermal flux of 8 calories per square centimeter, as
measured per standard set method ASTM F1959 or NFPA 70E.
Electrical arcs typically involve thousands of volts and thousands of
amperes of electrical current, exposing the garment to intense incident
energy. To offer protection to a wearer, a garment must resist the transfer
of this incident energy through to the wearer. It has been believed that
this occurs best when the outer shell fabric absorbs a portion of the
incident energy while resisting what is called "break-open". During "break-
open", a hole forms in the fabric. Therefore, garments for arc protection
have been designed to avoid or minimize break-open of any of the fabric
layers in the garment.
It has now been found that improved arc performance can be
achieved by the use of a multilayer fabric laminate having at least two
flame-resistant fabric layers, wherein the fabric layer closer the electrical
arc actually acts as a sacrificial material and breaks open upon exposure
to the arc. It is believed that the decomposition of the outer fabric provides
an energy sink that reduces the transfer of energy through the multilayer
fabric laminate.
The multilayer fabric laminate includes at least one layer of the first
flame-resistant fabric and at least one layer of the second flame-resistant
fabric. In some embodiments, the first flame resistant fabric layer has a
basis weight of about 5 to 9 ounces per square yard and the second
flame-resistant fabric layer has a basis weight of about 4 to 8 ounces per
square yard. In some embodiments, the first flame resistant fabric layer
has a basis weight of about 6.5 to 9 ounces per square yard. In some
embodiments, the second flame resistant fabric layer has a basis weight of
about 4.5 to 7.5 ounces per square yard. In some embodiments, the
multilayer fabric laminate can include two adjacent layers of the first flame-
resistant fabric and one layer of the second flame-resistant fabric. In some
embodiments, the multilayer fabric laminate can include a layer of the first
flame-resistant fabric and two adjacent layers of the second flame-
resistant fabric. In some other embodiments, the multilayer fabric laminate
can include two adjacent layers of the first flame-resistant fabric and two
adjacent layers of the second flame-resistant fabric.
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By flame-resistant fabric, it is meant that when tested, a layer of the
fabric has a vertical char length of 6 inches or more. Char length is a
measure of the flame resistance of a textile. A char is defined as a
carbonaceous residue formed as the result of pyrolysis or incomplete
combustion. The char length of a fabric under the conditions of test of
ASTM 6413-99 is defined as the distance from the fabric edge that is
directly exposed to the flame to the furthest point of visible fabric damage
after a specified tearing force has been applied.
By fire-resistant fiber, it is meant the fiber or a fabric made solely
from that fiber will not support flame, meaning they have a Limiting
Oxygen Index (L01) above the concentration of oxygen in air (that is,
greater than 21 and preferably greater than 25) as measured by ASTM G-
125-00.
The term fabric refers to a single layer structure that has been
assembled by conventional weaving of warp yarns with weft yarns on a
loom. One preferred embodiment is a twill weave; however, plain or satin
weaves made be used. By yarn is meant an assemblage of fibers spun or
twisted together to form a continuous strand that can be used in weaving
or knitting, or otherwise made into a textile material or fabric. The yarns
can be staple fiber yarns. Staple fiber yarns can be produced by yarn
spinning techniques such as, but not limited to ring spinning, core
spinning, and air jet spinning; including air spinning techniques such as
Murata air jet spinning where air is used to twist staple fibers into a yarn.
If
single yarns are produced, they are then preferably plied together to form
a ply-twisted yarn comprising at least two single yarns prior to being
converted into a fabric. Alternatively, multifilament continuous filament
yarns can be used to make the fabric, or combinations of multifilament and
staple fiber yarns can be used.
A first fire-resistant fiber is present in the woven fabric of the first
flame resistant fabric layer in an amount of at least 20 percent by weight,
and is normally present in the yarns of that fabric. The first fire-resistant
fiber contains, and is preferably solely made of, a synthetic polymer
comprising a halogen. One useful halogen is chlorine, but other halogens
can also be used.
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In some embodiments, the first flame resistant fabric contains a
blend of yarns, or the yarns contain a blend of fibers, comprising
modacrylic fiber, meta-aramid fiber, and para-aramid fiber; and optionally
small portions of antistatic fiber. One embodiment of this yarn blend or
fiber blend comprises 20 to 70 weight percent modacrylic fiber, 11 to 64
weight percent meta-aramid fiber, 5 to 15 weight percent para-aramid
fiber, and optionally 0.5 to 4 weight percent antistatic fiber. If desired, FR
rayon, cotton, or wool may be substituted for portions of the modacrylic
fiber as long as at least 20 percent of a halogen-containing fiber remains
in the first flame resistant fabric. Generally this means these substituted
fibers can be be present in an amount of up to about 50% of the blend if
desired.
In one preferred embodiment, the first flame resistant fabric
contains a blend of yarns, or the yarns contain an intimate blend of fibers,
comprising 40 to 70 weight percent modacrylic fiber,15 to 55 weight
percent meta-aramid fiber, and 5 to 15 weight percent para-aramid fiber;
and optionally contains 0.5 to 3 weight percent antistatic fiber. In some
embodiments the blend of yarns or intimate blend of fibers comprises 55
to 70 weight percent modacrylic fiber; 20 to 40 weight percent meta-
aramid fiber, the meta-aramid being poly(metaphenylene isophthalamide;
5 to 10 weight percent para-aramid fiber, the para-aramid being
poly(paraphenylene terephthalamide); and 2 to 3 weight percent carbon
core/polyamide sheath antistatic fiber. In some embodiments, the first
flame resistant fabric contain a blend of yarns, or the yarns contain a blend
of fibers, consisting essentially of modacrylic fiber, meta-aramid fiber, and
para-aramid fiber; and optionally small portions of antistatic fiber in
amounts as previously mentioned. All of the percentages stated herein are
on a basis of the explicitly named components; that is, the total weight of
the named components in the blend of yarns or fibers.
A second fire-resistant fiber is present in the woven fabric of the
second flame resistant fabric layer and is normally present in the yarns of
that fabric. Useful fire-resistant fibers include aramid fiber,
polybibenzimidiazole fiber, or polybenzazole fiber, or a blend of any of
these fibers. In one preferred embodiment, the second flame resistant
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fabric layer contains at least 70 weight percent of these fibers, and a
preferred fiber is meta-aramid fiber. In some preferred embodiments, the
yarn has at least 75 weight percent meta-aramid fibers. In some
embodiments, the preferred maximum amount of meta-aramid fibers is 93
weight percent or less; however, amounts as high as 100 weight percent
can be used.
In some embodiments, the second flame resistant fabric contains a
blend of yarns, or the yarns contain a blend of fibers, comprising meta-
aramid fiber and para-aramid fiber; and optionally, small portions of
antistatic fiber. One embodiment of this yarn blend or fiber blend,
comprises 70 to 93 weight percent meta-aramid fiber and 7 to 30 weight
percent para-aramid fiber. The yarn blend or fiber blend can also contain
0.5 to 3 weight percent antistatic fiber. In some preferred embodiments the
yarn blend or fiber blend comprises 85 to 93 weight percent meta-aramid
fiber, the meta-aramid being poly(metaphenylene isophthalamide; and 7 to
15 weight percent para-aramid fiber, the para-aramid being
poly(paraphenylene terephthalamide); and optionally 2 to 3 weight percent
carbon core/polyamide sheath antistatic fiber. The addition of small
amounts of rigid rod or para-aramid fibers in the yarns can provide some
additional resistance to flame shrinkage for fabrics having a high content
of meta-aramid fiber or other fabric having unacceptable flame shrinkage.
In one preferred embodiment, the second flame resistant fabric
contains a blend of yarns, or the yarns contain an intimate blend of fibers
comprising para-aramid fiber and meta-aramid fiber, and optionally small
portions of antistatic fiber. In some embodiments, the second flame
resistant fabric contains a blend of yarns, or the yarns contain an intimate
blend of fibers consisting essentially of para-aramid fiber and meta-aramid
fiber, and optionally small portions of antistatic fiber in amounts as
previously mentioned. All of the percentages stated herein are on a basis
of the explicitly named components; that is, the total weight of the named
components in the blend of yarns or fibers.
The antistatic component is an optional component in the garment
and can be used in those situations where static electrical discharges can
be hazardous for workers, such as when working with sensitive electrical
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equipment or near flammable vapors. In one embodiment, the antistatic
component is present as a fiber in at least some of the yarns in the
garment fabric. Illustrative examples are steel fiber, carbon fiber, or a
carbon combined with an existing fiber and can be present in a garment
fabric in an amount of 0.5 to 5 weight percent. In some embodiments the
antistatic component is present in a garment fabric in an amount of only 2
to 3 weight percent. U.S. Patent 4,612,150 ( to De Howitt) and U.S. Patent
3,803453 (to Hull) describe an especially useful conductive fiber wherein
carbon black is dispersed within a thermoplastic fiber, providing anti-static
conductance to the fiber. The preferred antistatic fiber is a carbon-core
nylon-sheath fiber. Use of anti-static fibers provides yarns, fabrics, and
garments having reduced static propensity, and therefore, reduced
apparent electrical field strength and nuisance static.
In some embodiments, the yarns having the proportions of the first
and second fire-resistent fibers and optionally other fibers and/or antistatic
fiber, are exclusively present in the fabric. In the case of a woven fabric
these yarns are preferably used in both the warp and fill of the fabric. If
desired, the relative amounts of of the first and second fire-resistent fibers
as previously described and antistatic fiber can vary in the respective warp
and fill yarns as long as the compositions of both yarns falls within the
previously described ranges.
In one embodiment, both the multilayer fabric laminate, the yarns
used in the making of the first and second flame-resistant fabrics, and the
fabrics themselves, consist essentially of the fibers as previously
described, in the proportions described, and do not include any other
additional thermoplastic or combustible fibers or materials, except for
small portions of antistatic fibers as previously mentioned. Other materials
and fibers, such as polyamide or polyester fibers, provide combustible
material to the yarns, fabrics, and garments, and are believed to affect the
protective performance of the garments.
In environments where additional thermal protection is desired, 1 to
4 layers of a thin flame-resistant insulating fabric can be sandwiched
between the first and second flame-resistant fabric and become part of the
multilayer fabric laminate as herein defined. Such nonwoven insulating
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fabrics can include lightweight (0.5 to 3.0 oz/yd2) needlepunched,
hydroentangled, or otherwise consolidated nonwoven fabrics formed from
carded, air-laid, or wet-laid cut fiber webs. Preferably, such fabrics have a
basis weight of 1 to 2 oz/yd2. Especially preferred are fabrics that include
fire-resistant fibers. A suitable flame-resistant fabric is Nomex0 E89, a
spunlaced nonwoven material produced from a blend of meta-aramid and
para-aramid staple fibers and available from E. I. du Pont de Nemours &
Company of Wilimington, Delaware. E89 fabric has a nominal thickness of
19 mil (0.48 mm) and a basis weight of 1.5 oz/yd2 (50.5 g/m2). In one
preferred embodiment all of the layers of fabric in the multilayer fabric
laminate are sewn together only at the edges and/or seams in the
garment, allowing maximum flexibility of the layers of fabric within the
multilayer fabric laminate.
In some embodiments, the multilayer fabric laminate has a total
basis weight of 11 to 25 ounces per square yard. In some preferred
embodiments the total basis weight of the multilayer fabric laminate is 11
to 20 ounces per square yard.
In some preferred embodiments the multilayer fabric laminate has
an arc resistance, normalized for basis weight, of at least 2.0 calories per
square centimenter per ounce per square yard (0.247 Joules per square
centimeter per grams per square meter). In some embodiments the arc
resistance normalized for basis weight is preferably at least 2.2 calories
per square centimenter per ounce per square yard (0.272 Joules per
square centimeter per grams per square meter).
One fiber useful as the first fire-resistant fiber is modacrylic fiber.
By modacrylic fiber it is meant acrylic synthetic fiber made from a polymer
comprising primarily acrylonitrile. Preferably the polymer is a copolymer
comprising 30 to 70 weight percent of a acrylonitrile and 70 to 30 weight
percent of a halogen-containing vinyl monomer. The halogen-containing
vinyl monomer is at least one monomer selected, for example, from vinyl
chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, etc.
Examples of copolymerizable vinyl monomers are acrylic acid, methacrylic
acid, salts or esters of such acids, acrylamide, methylacrylamide, vinyl
acetate, etc.
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The preferred modacrylic fibers are copolymers of acrylonitrile
combined with vinylidene chloride, the copolymer having in addition an
antimony oxide or antimony oxides for improved fire retardancy. Such
useful modacrylic fibers include, but are not limited to, fibers disclosed in
United States Patent No. 3,193,602 having 2 weight percent antimony
trioxide, fibers disclosed in United States Patent No. 3, 748,302 made with
various antimony oxides that are present in an amount of at least 2 weight
percent and preferably not greater than 8 weight percent, and fibers
disclosed in United States Patent Nos. 5,208,105 & 5,506,042 having 8 to
40 weight percent of an antimony compound. Within the yarns, modacrylic
fiber provides a fire resistant, char- forming fiber with an LOI typically at
least 28 depending on the level of doping with antimony derivatives.
In addition, other fibers can be present in the first fire resistant
fabric layer and these include aramid fibers, flame retardant rayon fibers,
cotton fibers, wool fibers, and mixtures of these fibers. These are also
normally present in the yarns of the fabric, either in the form of a mixture
with, for example, modacrylic fibers, or as separate yarns having only one
type of fiber, or separate yarns having a mixture of various fibers.
As used herein, "aramid" is meant a polyamide wherein at least
85% of the amide (-CONH-) linkages are attached directly to two aromatic
rings. Additives can be used with the aramid and, in fact, 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. 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. Meta-aramid are those aramids where the amide linkages are
in the meta-position relative to each other, and para-aramids are those
aramids where the amide linkages are in the para-position relative to each
other. The meta-aramid includes poly(metaphenylene isophthalamide)
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and the para-aramid includes poly(paraphenylene terephthalamide).
Within the yarns, meta-aramid fiber provides a fire resistant fiber with an
LOI typically at least about 25, with para-aramid fiber having a LOI of at
least about 27.
In some embodiments, the meta-aramid fiber has a minimum
degree of crystallinity of at least 20% and more preferably at least 25%.
For purposes of illustration due to ease of formation of the final fiber a
practical upper limit of crystallinity is 50% (although higher percentages
are considered suitable). Generally, the crystallinity will be in a range from
25 to 40%. An example of a commercial meta-aramid fiber having this
degree of crystallinity is Nomex0 T-450 available from E. I. du Pont de
Nemours & Company of Wilimington, Delaware.
The degree of crystallinity of an meta-aramid fiber can be
determined by one of two methods. The first method is employed with a
non-voided fiber while the second is employed on a fiber that is not totally
free of voids.
The percent crystallinity of meta-aramids in the first method is
determined by first generating a linear calibration curve for crystallinity
using good, essentially non-voided samples. For such non-voided
samples the specific volume (1/density) can be directly related to
crystallinity using a two-phase model. The density of the sample is
measured in a density gradient column. A meta-aramid film, determined
to be non-crystalline by x-ray scattering methods, was measured and
found to have an average density of 1.3356 g/cm3. The density of a
completely crystalline meta-aramid sample was then determined from the
dimensions of the x-ray unit cell to be 1.4699 g/cm3. Once these 0% and
100% crystallinity end points are established, the crystallinity of any non-
voided experimental sample for which the density is known can be
determined from this linear relationship:
Crystallinity = 11/non-crystalline density) ¨ (1/experimental density)
(1/non-crystalline density) ¨ (1/fully-crystalline density)
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Since many fiber samples are not totally free of voids, Raman
spectroscopy is the preferred method to determine crystallinity. Since the
Raman measurement is not sensitive to void content, the relative intensity
of the carbonyl stretch at 1650-1 cm can be used to determine the
crystallinity of a meta-aramid in any form, whether voided or not. To
accomplish this, a linear relationship between crystallinity and the intensity
of the carbonyl stretch at 1650 cm-1, normalized to the intensity of the ring
stretching mode at 1002 cm-1, was developed using minimally voided
samples whose crystallinity was previously determined and known from
density measurements as described above. The following empirical
relationship, which is dependent on the density calibration curve, was
developed for percent crystallinity using a N icolet Model 910 FT-Raman
Spectrometer:
% Crystallinity = 100.0 x (1(1650 cm-1) ¨ 0.2601)
0.1247
where 1(1650 cm-1) is the Raman intensity of the meta-aramid sample at
that point. Using this intensity the percent crystallinity of the experiment
sample is calculated from the equation.
Meta-aramid fibers, when spun from solution, quenched, and dried
using temperatures below the glass transition temperature, without
additional heat or chemical treatment, develop only minor levels of
crystallinity. Such fibers have a percent crystallinity of less than 15
percent when the crystallinity of the fiber is measured using Raman
scattering techniques. These fibers with a low degree of crystallinity are
considered amorphous meta-aramid fibers that can be crystallized through
the use of heat or chemical means. The level of crystallinity can be
increased by heat treatment at or above the glass transition temperature
of the polymer. Such heat is typically applied by contacting the fiber with
heated rolls under tension for a time sufficient to impart the desired
amount of crystallinity to the fiber.
The level of crystallinity of m-aramid fibers can be increased by a
chemical treatment, and in some embodiments this includes methods that
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color, dye, or mock dye the fibers prior to being incorporated into a fabric.
Some methods are disclosed in, for example, United States Patents
4,668,234; 4,755,335; 4,883,496; and 5,096,459. A dye assist agent, also
known as a dye carrier may be used to help increase dye pick up of the
aramid fibers. Useful dye carriers include aryl ether, benzyl alcohol, or
acetophenone.
By flame-retardant rayon fiber, it is meant a rayon fiber having one
or more flame retardants and having a fiber tensile strength of at least 2
grams per denier. Cellulosic or rayon fibers containing as the flame
retardant a silicon dioxide in the form of polysilicic acid are specifically
excluded because such fibers have a low fiber tensile strength. Also,
while such fibers are good char formers, in relative terms their vertical
flame performance is worse that fibers containing phosphorous
compounds or other flame retardants.
Rayon fiber is well known in the art, and is a manufactured fiber
generally composed of regenerated cellulose, as well has regenerated
cellulose in which substituents have replaced not more than 15% of the
hydrogens of the hydroxyl groups. They include yarns made by the
viscose process, the cuprammonium process, and the now obsolete
nitrocellulose and saponified acetate processes; however in a preferred
embodiment the viscose process is used. Generally, rayon is obtained
from wood pulp, cotton linters, or other vegetable matter dissolved in a
viscose spinning solution. The solution is extruded into an acid-salt
coagulating bath and drawn into continuous filaments. Groups of these
filaments may be formed into yarns or cut into staple and further
processed into spun staple yarns. As used herein, rayon fiber includes
what is known as lyocell fiber.
Flame retardants can be incorporated into the rayon fiber by adding
flame retardant chemicals into the spin solution and spinning the flame
retardant into the rayon fiber, coating the rayon fiber with the flame
retardant, contacting the rayon fiber with the flame retardant and allowing
the fiber to absorb the flame retardant, or any other process that
incorporates a flame retardant into or with a rayon fiber. Generally
speaking, rayon fibers that contain one or more flame retardants are given
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the designation "FR," for flame retardant. In a preferred embodiment, the
FR rayon has spun-in flame retardants.
The FR rayon has a high moisture regain, which provides a comfort
component to fabrics. It is believed that the yarn should have at least 10
weight percent FR rayon to provide detectable improved comfort in the
fabrics. Further, while larger percentages of FR rayon might provide even
more comfort, it is believed that if the amount of FR rayon exceeds about
30 weight percent in the yarn, the fabric could have negative performance
issues that would outweigh any comfort improvement. In some preferred
embodiments the FR rayon fiber is present in the yarn in an amount of 15
to 25 weight percent.
The FR rayon fiber can contain one or more of a variety of
commercially available flame retardants; including for example certain
phosphorus compounds like Sandolast 9000 available from Sandoz, and
the like. While various compounds can be used as flame retardants, in a
preferred embodiment, the flame retardant is based on a phosphorus
compound. A useful FR rayon fiber is available from Daiwabo Rayon Co.,
Ltd., of Japan under the name DFG "Flame-resistant viscose rayon".
Another useful FR rayon fiber is available from Lenzing AG under the
name of Viscose FR (also known as Lenzing FR available from Lenzing
Fibers of Austria).
Cotton fiber is a well-known natural fiber composed of almost pure
natural cellulose. As taken from plants, it has a fiber length of from about
0.375 to 2 inches. Wool fiber is a well-known natural fiber that is normally
the fleece of sheep, lambs, or Angora or Cashmire goats. The term can
also be used for the hair from the camel, alpaca, llama, and/or vicuna.
By polybibenzimidiazole fiber (PBI), it is meant fiber comprising
polybibenzimidazole polymer such as made by the processes disclosed in
U.S. Patent 2,895,948 and U.S. Reissue 26,065. Polybibenzimidazole
fibers can be made by known processes such as those disclosed in U.S.
Patent 3,441,640 and U.S. Patent 4,263,245. One useful
polybibenzimidazole polymer is poly(2,2'-(m-phenylene)-5,5'-
bibenzimidazole) polymer. One commercial PBI polymer is prepared from
tetra-aminobiphenyl and diphenyl isophthalate.
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By polybenzazole fiber it is meant fiber containing homopolymers
and copolymers of polybenzoxazole (PB0), polybenzothiazole (PBT), and
polybenzimidazole having a LOI of greater than 21. Suitable
polybenzazole homopolymers and copolymers can be made by known
procedures, such as those described in U.S. Patents 4,533,693 (to Wolfe
et al. on Aug. 6, 1985), 4,703,103 (to Wolfe et al. on Oct. 27, 1987),
5,089,591 (to Gregory et al. on Feb. 18, 1992), 4,772,678 (Sybert et al. on
Sept. 20, 1988), 4,847,350 (to Harris et al. on Aug. 11, 1992), and
5,276,128 (to Rosenberg et al. on Jan. 4, 1994). Polybenzimidazoles also
include polybenzobisimidazoles; polybenzothiazoles also include
polybenzobisthiazoles; and polybenzoxazoles also include
polybenzobisoxazoles.
The first fire-resistant fiber of the first flame-resistant fabric has a
thermal decomposition temperature that is at least 70 degrees C less than
the thermal decomposition temperature of the second fire-resistant fiber of
the second flame-resistant fabric. The "thermal decomposition
temperature" of the fiber as used herein is the initial major decomposition
temperature as determined by ThermoGravimetric Analysis (TGA) in air
and is defined as the temperature at the onset point as measured using
the modified weight loss (% weight loss/degreeC) scan of the TGA
analysis. The onset point is determined by using the TA systems Universal
Analysis software program. The onset is defined as the extrapolated
beginning point of any transition as determined by the data analysis.
Alternatively, this can be shown graphically. The onset point is found by
taking the first major derivative peak or shoulder 1 on the derivative weight
scan and drawing tangent lines 2 and 3 corresponding to that peak on the
modified weight scan as shown on Figure 1, which has scans
representative of one embodiment of modacrylic fiber. The intersection of
those two tangents provides point 4, which isthe initial major thermal
decomposition temperature as defined herein. Likewise, as defined herein,
the initial major thermal decomposition temperature of one embodiment of
Nomex0 meta-aramid fiber is shown via representative scans on Figure 2.
Using the first major derivative peak or shoulder 5 on the derivative weight
scan, tangent lines 6 and 7 corresponding to that peak are drawn on the
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modified weight scan, with the intersection of those two tangents providing
the initial major thermal decomposition temperature at point 8. The TGA
measurements are made on the TA Systems Q500TGA under default Hi
Res conditions (sensitivity 1.0/resolution 4.0). To eliminate the effect of
moisture on the analysis, the 100`)/0 Y axis is set at 150 C. As measured
in this manner, modacrylic has a thermal decomposition temperature of
modacrylic is about 225-275 C, while metaphenylene isopthathalamide is
about 400 to 475 C.The first major derivative peak or shoulder is a
deviation in derivative weight from the 0.0 baseline of at least 20 percent.
In one embodiment, this invention also relates to a process for
making a protective garment having use in a electrical arc potential
environment, comprising:
i) providing a first woven flame-resistant fabric comprising a first
fire-
resistant fiber made from a synthetic polymer comprising a halogen;
ii) providing a second woven flame-resistant fabric comprising a
second fire-resistant fiber made from a synthetic polymer, wherein
the first fire-resistant fiber has a thermal decomposition temperature
that is at least 70 degrees C less than the second fire-resistant
fiber; the first and second woven flame-resistant fabrics being
different;
iii) combining the first and second woven flame-resistant fabrics to
form a arc resistant multilayer fabric laminate, the first and second
woven flame-resistant fabrics being distinct fabric layers without
any shared weft or warp fabric yarns; and
iv) forming an arc resistant garment from the arc resistant multilayer
fabric laminate wherein the first woven flame-resistant fabric forms
an outer surface of the garment and is positioned in the garment
closer to the electrical arc potential environment than the second
layer.
The first and second woven fabrics can be provided in several
different ways, including from actual production of the individual yarns
using the fiber as previously described in various proportions as previously
described, followed by weaving the previously described fabrics from
those yarns.
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In one preferred embodiment, the individual yarns are made from
an intimate blend of staple fibers. By "intimate blend" it is meant the
various staple fibers in the composition form a relatively uniform mixture. If
desired, other staple fibers can be combined in this relatively uniform
mixture of staple fibers. The blending can be achieved by any number of
ways known in the art, including processes that creel a number of bobbins
of continuous filaments and concurrently cut the two or more types of
filaments to form a blend of cut staple fibers; or processes that involve
opening bales of different staple fibers and then opening and blending the
various fibers in openers, blenders, and cards; or processes that form
slivers of various staple fibers which are then further processed to form a
mixture, such as in a card to form a sliver of a mixture of fibers. Other
processes of making an intimate fiber blend are possible as long as the
various types of different fibers are relatively uniformly distributed
throughout the blend. The yarns formed from the blend have a relatively
uniform mixture of the staple fibers also. Generally, in most preferred
embodiments the individual staple fibers are opened or separated to a
degree that is normal in fiber processing to make a useful fabric, such that
fiber knots or slubs and other major defects due to poor opening of the
staple fibers are not present in an amount that detract from the final fabric
quality. The yarns can then be combined as previously described herein
and woven together on a conventional loom, forming in a preferred
embodiment a single layer woven structure of either the first or second
woven fabric. The greige fabric can then be finished as desired.
The first and second woven flame-resistant fabrics can then be
combined to form an arc resistant multilayer fabric laminate. One
convenient method of forming the multilayer fabric laminate is to provide a
layer of one of the fabrics on a flat surface, like a cutting table, and then
overlay that fabric with a layer of the other fabric. If desired, multiple
layers
of either the first or second woven flame-resistant fabrics can be used in
the multilayer fabric laminate, or one or more layers of flame resistant
insulating fabrics, such as those previously described herein, can be laid
down or inserted between the first and second flame-resistant fabrics, as
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long as they do not detract from the final garment or the desired properties
of that garment.
Since the first woven flame-resistant fabric will ultimately form an
outer surface of the final garment, care should be taken that when
combining the fabrics to form a multilayer fabric laminate, the first woven
flame-resistant fabric forms an outer surface of the multilayer fabric
laminate. In some embodiments, the second woven flame-resistant fabric
forms the opposing outer surface of the multilayer fabric laminate;
however, in some other embodiments the opposing outer surface of the
multilayer fabric laminate can be another fabric. For example, the
opposing outer surface can be a soft fabric that will ultimately be the
interior lining of the protective garment, because this multilayer fabric
laminate surface will be the interior of the garment and closer to the
wearer.
The first and second flame-resistant fabrics are combined as
separate distinct fabric layers, that is, without any shared weft or warp
fabric yarns that might compromise either layer. This allows the first woven
flame-resistant fabric to be entirely a sacrificial layer and the second
woven flame-resistant fabric to be entirely a thermal protective layer.
Further, this provides flexibility to provide additional fabric layers between
the first and second flame-resistant fabrics, if desired.
The arc resistant garment is then formed from the arc resistant
multilayer fabric laminate. The first woven flame-resistant fabric forms an
outer surface of the garment and is positioned in the garment closer to the
electrical arc potential environment than the second woven-flame resistant
fabric layer when worn.
The garment can be formed by any number of methods; for
example, the previously mentioned multilayer fabric laminate can be
formed on a cutting table and then the laminate can be cut per a
prescribed pattern into fabric shapes suitable for making protective
garments such as coats, coveralls, jumpsuits, hoods, etc. Alternatively,
such fabric shapes can be obtained by forming the multilayer fabric
laminate from individually cut fabric shapes, laying up each layer of fabric
as previously described. The multilayer fabric laminate shapes are then
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sewn together to form the desired garment with the first flame-resistant
fabric of the multilayer fabric laminate forming an outer surface of the final
garment, which in use is the exterior of the garment. In so doing, the first
woven flame-resistant fabric is positioned in the garment closer to the
electrical arc potential environment than the second woven flame-resistant
layer.
TEST METHODS
ThermGravimetric Analysis (TGA) was conducted in air using
ASTM E1131-08 on a TA Instrument Q500 TGA in air from 40-1000 C
under TA Systems Hi-Res with default conditions (sensitivity 1/resolution
4) with a balance gas purge flow of 60 ml/min and a sample gas purge
flow of 40 ml/min.
The arc resistance of fabrics is determined in accordance with
ASTM F-1959-99 "Standard Test Method for Determining the Arc Thermal
Performance Value of Materials for Clothing". The Arc Thermal
Performance Value (ATPV) of each fabric is a measure of the amount of
energy that a person wearing that fabric could be exposed to that would
be equivalent to a 2nd degree burn from such exposure 50% of the time.
The limited oxygen index (L01) of fabrics is determined at room
temperature in accordance with ASTM G-125-00 "Standard Test Method
for Measuring Liquid and Solid Material Fire Limits in Gaseous Oxidants".
The char length of fabrics is determined in accordance with ASTM
D-6413-99 "Standard Test Method for Flame Resistance of Textiles
(Vertical Method)".
Basis weight values were obtained according to FTMS 191A; 5041.
EXAMPLES
The fabrics used in the following examples were made as follows.
Fabric 1 was woven from airjet spun yarn made from an intimate blend of
Nomex0 type 455 fiber, Kevlar0 29 fiber, and P140 fiber. Nomex0 type
455 fiber is non-crystallized poly(m-phenylene isophthalamide)(MPD-I)
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staple fiber; Kevlar0 29 fiber is poly(p-phenylene terephthalamide)(PPD-T)
staple fiber; and P140 fiber is an antistatic staple fiber having a carbon
core and a nylon sheath.
A picker blend sliver of 93 wt.% Nomex0 type 455 fiber, 5 wt.%
Kevlar0 29 fiber, and 2 wt. A) P140 fiber was prepared and then
processed into spun yarn using a conventional cotton system and an airjet
spinning frame. The spun yarn so made was a 15.5 tex (38 cotton count)
singles yarn. Two of these singles yarns were then plied together on a
plying machine to make a two-ply yarn having a ply twist of 12 turns/inch.
The two-ply yarns were then used in both the warp and fill on a
shuttle loom to form a plain weave fabric. The greige fabric had a basis
weight of 136 g/m2 (4.0 oz/yd2). It was scoured in hot water and then jet
dyed using basic dye. The finished fabric basis weight was a nominal 153
g/m2 (4.5 oz/yd2).
Fabric 2 was made in a manner similar to Fabric 1, with the
exception that the spun yarn was a 12.2 tex (30 cotton count) single yarn.
As in Fabric 1, two of these singles yarns are then plied on the plying
machine to make a two-ply yarn having a ply twist of 12 turns/inch. The
resulting greige fabric had a basis weight of 186 g/m2 (5.5 oz/yd2). It was
scoured in hot water and then jet dyed using basic dye. The finished basis
weight was a nominal 203 g/m2 (6.0 oz/yd2).
Fabric 3 was woven from airjet spun yarn made from an intimate
blend of Protex0 C fiber, Nomex0 type 450 fiber, Kevlar0 29 fiber, and
P140 fiber. Protex0 C fiber is a modacrylic staple fiber of
ACN/polyvinylidene chloride co-polymer with ¨10% antimony; Nomex0
type 450 fiber is crystallized poly(m-phenylene isophthalamide)(MPD-I)
staple fiber; and the Kevlar0 29 fiber and P140 fiber are as in Fabrics 1
and 2. A picker blend sliver of 65 wt. A) of Protex0 C fiber, 23 wt.% of
Nomex0 type 450 fiber, 10 wt.% of Kevlar0 29 fiber, and 2 wt. A) of
antistatic fiber was prepared and then processed into spun yarn in a
matter similar to Fabric 1. The spun yarn so made was a 21 tex (28 cotton
count) singles yarn. Two of these singles yarns are then plied together on
a plying machine to make a two-ply yarn having a ply twist 10turns/inch.
The two-ply yarns were then used in both the warp and fill on a shuttle
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1001r1 to form a 2x1 twill weave having a construction of 31 ends x 16 picks
per cm ( 77 ends x 47 picks per inch). The greige twill fabric had a basis
weight of 203.4 g/m2 (6.0 oz/yd2). It was scoured in hot water and then jet
dyed using basic dye. The finished twill fabric basis weight was a nominal
220.3 g/m2 (6.5 oz/yd2).
Fabric 4 was made in a manner similar to Fabric 3, with the
exception that the twill fabric had a construction of 31 ends x 28 picks per
cm ( 77 ends x 70 picks per inch). The greige fabric had a basis weight of
254 g/m2 (7.5 oz/yd2). After scouring and jet dying the fabric had a
Comparative Example A
A multilayer fabric laminate was formed by overlaying Fabric 1 on
Fabric 3. To simulate the electrical arc performance of a garment
simulate a garment having Fabric 1 as the outer layer and Fabric 3 as the
inner layer. The arc rating this multilayer fabric laminate was then
Example 1
The multilayer fabric laminate of Comparative Example A was
reversed in the arc testing apparatus, with Fabric 3 positioned closer to the
30 Comparative Example B
Comparative Example A was repeated, except that Fabric 3 was
replaced with the heavier Fabric 4. The arc rating this laminate was then
determined and is shown in the Table.
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Comparative Example C
Comparative Example A was repeated with the exception that
Fabric 2 was substituted for Fabric 1. The arc rating this laminate was then
determined and is shown in the Table.
Example 2
Example 1 was repeated with the exception that Fabric 2 was
substituted for Fabric 1. The arc rating this laminate was then determined
and is shown in the Table.
Table
Example Outer Inner Arc Rating
Fabric Fabric ( cal / cm2 )
A Fabric 1 Fabric 3 16.7
1 Fabric 3 Fabric 1 28.3
B Fabric 1 Fabric 4 17.2
C Fabric 2 Fabric 3 21.3
2 Fabric 3 Fabric 2 32.2
Example 3
A high arc performance multilayer fabric laminate is formed by
overlaying on Fabric 2 three layers of a 1.5 osy Nomex /Kevlar0
spunlaced fabric known as E-89, followed by overlaying with Fabric 4. This
forms a multilayer fabric laminate having Fabric 4 as the outer layer and
Fabric 2 as the inner layer. This multilayer fabric laminate will provide
superior arc performance when used in a garment with the Fabric 4 layer
positioned closer to the arc generation point and Fabric 1 closer to an
imagined wearer of the garment.
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Example 4
The multilayer fabric laminate of Example 1 is made into a
protective garment in the form of a coat, by cutting the multilayer fabric
laminates into fabric shapes per a pattern and sewing the shapes together
to form a three-quarter length coat. The multilayer fabric laminate of
Example 1 is sewn into the coat such that Fabric 3 forms the outer surface
layer of the coat and Fabric 1 forms a layer closer to the wearer.
Example 5
Example 4 is repeated, but the multilayer fabric laminate of
Example 3 is used and it is positioned in the coat such that Fabric 4 forms
the outer surface layer of the coat and Fabric 1 forms a layer closer to the
wearer. In addition, a light cotton lining fabric is used to line the inside
of
the coat and is positioned between the wearer and Fabric 1.
Example 6
The multilayer fabric laminates of Examples 1, 2, & 3 are used to
make various protective garments, including coveralls, jumpsuits, and
hoods. In each garment the previously designated multilayer fabric
laminate outer layer (Fabrics 3, 3, & 4, respectively) forms the outer
surface layer of the garments.
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