Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLAME AND HEAT RESISTANT STRETCH FABRICS WITH IMPROVED
CHEMICAL RESISTANCE AND DURABILITY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to flame and heat resistant stretch fabrics with
improved
durability. The stretch fabrics comprise crosslinked polyolefin elastic fibers
which may be
combined into a core yarn with inherently flame resistant fibers. The elastic
fibers or yarns can
be conveniently formed into fabrics using well-known techniques such as, for
example,
weaving or by using co-knitting techniques with other flame resistant fibers
or yarns. Such
fabrics are useful in various durable or repeated-use fabric applications such
as, but not limited
to, clothing (in particular protective garments), and upholstery.
Workers whose occupations put them at risk of exposure to heat and/or flame,
such as
foundry workers and workers the chemical and refinery industries, wear
protective garments to
minimize the potential of serious bums or other bodily injury. In attempting
to provide
maximum protection against heat and fire for these workers, the emphasis in
the prior art has
been on using thermal and/or flame resistant fabrics to form protective
garments. The flame
resistant fabrics used for such garments typically are formed of woven
inherently flame
resistant yams which tend to be heavy and stiff. Thus, the garments formed
therefrom tend to
be heavy, bulky and somewhat inflexible. The stiffness and general
inflexibility of such fabrics
tends to restrict the movement of a worker while wearing garments made from
such fabrics.
Attempts have been made in the prior art to develop garments, that protect
against
exposure to extreme heat and fire, but that are flexible so as to enable
greater freedom of
movement to the wearer. One approach has been to use conventional, heavy,
somewhat
inflexible flame resistant fabrics for the majority of the garment, with
portions of the garments
being formed with lighter, less flame and thermally resistant materials for
the joints of the
garments. For example, U.S. Pat. No. 4,922,552 discloses a firefighters'
garment formed from
layers of a thick, flame resistant fabric in which an outer layer of the
protective flame resistant
material has portions cut-away therefrom, and replaced with a layer of a
lighter material having
a significantly less degree of flame resistance and protective properties, but
which has greater
flexibility and less bulk. The problem with such a garment is that the
flexibility of the garment
is limited to specific portions of the garment and some flame resistance
protection is sacrificed
to achieve this enhanced flexibility.
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More recently, U.S. Pat. No, 5,527,597 touted the use of an elastic fiber such
as spandex
or rubber to make protective garments more flexible. This reference teaches
that since the
elastic core years have a low resistance to heat and/or fire, that they need
to be wrapped with a
protective yarn such as fibers made from an aromatic
polyamide/polybenzimidazole (PBI)
blend. The wrap fibers were designed to protect the elastic core yarns from
direct exposure to
heat and fire which would otherwise cause the core yarns to degrade or melt.
However, the
reference acknowledged that the protective wrap would not completely protect
the elastic fiber
(particularly when stretched), and that breaks in the elastic yarn would
eventually occur. This
is particularly true when the garment is subjected to relatively long
exposures to elevated
temperatures, such as during industrial laundering of the garment.
Another approach to making fabrics flame resistance involves chemically
treating
fabrics which would otherwise not be flame resistant. Fabrics of inherently
flame resistant
fibers are generally considered to provide longer lasting protection, while
chemically- treated
fabrics (such as flame resistant cotton) are often considered to provide less
lasting protection
but with more comfort to the wearer. Moreover the chemical treatments used in
such processes
are typically too harsh for elastic fibers to survive, leading to a rapid loss
of elasticity or even
breaks.
Accordingly, there is still a need for a more comfortable elastic heat and/or
flame-
resistant fabric which is durable upon repeated exposures to industrial
laundering. The present
invention relates to such fabric. The fabric is elastic, flame andJor heat-
resistant and durable,
making it particularly well-suited for these applications.
A material is typically characterized as elastic if it has a high percent
elastic recovery
(that is, a low percent permanent set) after application of a biasing force.
Ideally, elastic
materials are characterized by a combination of three important properties,
that is, (i) a low
percent permanent set, (ii) a low stress or load at strain, and (iii) a low
percent stress or load
relaxation. In other words, there should be (i) a low stress or load
requirement to stretch the
material, (ii) no or low relaxing of the stress or unloading once the material
is stretched, and
(iii) complete or high recovery to original dimensions after the stretching,
biasing or straining is
discontinued.
To be used in the elastic, durable, flame and/or heat resistant fabrics of the
present
invention, the fibers making up the fabric should be, inter alia, stable
during dyeing and heat
setting processes as well as industrial laundering conditions. For an elastic
polyolefin fiber to
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be stable under dyeing and heat-setting conditions, it must be crosslinked.
These fibers can be
crosslinked by one or more of a number of different methods, for example, e-
beam or UV
irradiation, silane or azide treatment, peroxide, etc., some methods better
than others for fibers
of a particular composition. For example, polyolefin fibers that are
irradiated under an inert
atmosphere (as opposed to irradiated under air) tend to be highly stable
during dyeing processes
(that is, the fibers do not melt or fuse together). The addition of a mixture
of hindered phenol
and hindered amine stabilizers further stabilized such fibers at higher
temperatures, such as
those encountered during some heat setting procedures (for example, 200-210 C
for
polyethylene terephthalate (PET) fiber).
Spandex (also known as elastane), a segmented polyurethane elastic material is
currently used in various stretch fabrics, including flame and heat-resistant
fabrics (see US
5,527,597). Spandex, however, is not stable at the typical high heat-setting
temperatures used
with some companion fibers, and moreover, spandex fabrics tend to lose their
integrity, shape
and elastic properties when subjected to elevated service temperatures such as
those
encountered in washing, drying and ironing.
It has been discovered that elastic flame and/or heat-resistant fabrics can be
formed
which are capable of surviving exposures that other flame and/or heat
resistant fabrics do not
survive. Particularly the fabrics of the present invention are durable,
meaning the fabrics can
survive c) 50 cycles of industrial laundering at temperatures of at least 65
C, wherein
"surviving" means that the fabric after treatment exhibits growth of less than
about 20 percent,
preferably less than about 10 percent, and more preferably less than about 8
percent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following terms shall have the indicated meaning when used in the present
patent
application:
"Fiber" means a material in which the length to diameter ratio is greater than
about 10.
Fiber is typically classified according to its diameter. Filament fiber is
generally defined as
having an individual fiber diameter greater than about 15 denier, usually
greater than about 30
denier. Fine denier fiber generally refers to a fiber having a diameter less
than about 15 denier.
Microdenier fiber is generally defined as fiber having a diameter less than
about 100 microns
denier.
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"Filament fiber" or "monofilament fiber" means a single, continuous strand of
material
of indefinite (that is, not predetermined) length, as opposed to a "staple
fiber" which is a
discontinuous strand of material of definite length (that is, a strand which
has been cut or
otherwise divided into segments of a predetermined length).
The term "flame resistant" when used in reference to the fabric or article
means that the
fabric or article exhibits 1) response to flame propagation, upon direct
exposure to flame,
graded as A grade as per DIN EN 531:02.95 standard norm (DIN IS015025:02.03
standard
testing method); 2) heat transmission on exposure to flame performances graded
as B 1 grade or
higher (B2,B3, B4 or B5) as per DIN EN 531:02.95 standard norm (DIN EN
367:11.92
standard testing method); 3) heat transmission on exposure to radiant heat
graded as Cl or
higher (C2, C3, or C4), as per DIN EN 531:02.95 standard norm (DIN EN
366:05.93 standard
testing method). Fabrics or articles that can meet or excide those
requirements are considered
suitable for at least "Low risk level: localized exposure to heat and/or
flame" protective
clothing as per ISO 2801:1998 International Standard "Clothing for protection
against heat and
flame - General recommendation for selection, care and use of protective
clothing".
The term "durable" when used in reference to the fabric or article means that
the fabric
or article exhibits growth of less than 20 percent, preferably less than about
10 percent and
more preferably less than about 8 percent, 6 percent or even 5 percent in both
the warp and
weft direction after 50 cycles of industrial laundering at temperatures of at
least 65 C,
alternatively at least 75 C. 85 C or even 95 C.
The term "growth" means residual elongation, or the amount the fabric
lengthens after
applying a load over a given length of time and allowing recovery, expressed
as a percentage of
the initial fabric dimension. Growth can be determined using ASTM D3107.
An "elastic fiber" is one that will recover at least about 50 percent, more
preferably at
least about 60 percent even more preferably 70 percent of its stretched length
after the first pull
and after the fourth to 100 percent strain (double the length). One suitable
way to do this test is
based on the one found in the International Bureau for Standardization of
Manmade Fibers,
BISFA 1998, chapter 7, option A. Under such a test, the fiber is placed
between grips set 4
inches apart, the grips are then pulled apart at a rate of about 20 inches per
minute to a distance
of eight inches and then allowed to immediately recover. It is preferred that
the elastic textile
articles of the present invention have a high percent elastic recovery (that
is, a low percent
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permanent set) after application of a biasing force. Ideally, elastic
materials are characterized
by a combination of three important properties, that is, (i) a low stress or
load at strain; (ii) a
low percent stress or load relaxation, and (iii) a low percent permanent set.
In other words,
there should be (i) a low stress or load requirement to stretch the material,
(ii) zero or low
relaxing of the stress or unloading once the material is stretched, and (iii)
complete or high
recovery to original dimensions after the stretching, biasing or straining is
discontinued.
"Elastic materials" are also referred to in the art as "elastomers" and
"elastomeric". For
purposes of this invention, an "elastic article" is one that comprises elastic
fiber.
"Nonelastic material" means a material, for example, a fiber, that is not
elastic as
defined above.
"Core spun yarn" means a yam which has been made by twisting fibers around a
core
which is another filament or a previously spun yarn, thus at least partially
concealing the core.
One aspect of this invention is an elastic, durable, flame and/or heat
resistant article
such as fabric or an assembled garment that comprises a heat-resistant,
crosslinked elastic fiber.
The fabric may be made flame and/or heat resistant by the incorporation on
inherently flame
resistant materials and/or the article may be subjected to a chemical
treatment to impart the heat
and/or flame resistance.
In one embodiment, the article is a durable stretch fabric made and processed
from one
or more crosslinked, heat-resistant olefin elastic fibers. The fabrics can be
made by any
process, for example, weaving, knitting, etc., and may use a combination of
elastic and inelastic
("hard") fibers. These fabrics exhibit excellent chemical, for example,
chlorine, resistance and
durability, for example, they retain their shape and feel ("hand") over
repeated exposure to
service conditions, for example, washing, drying, etc. The fabric or assembled
garment will
exhibit a change in elasticity no greater than about 10 percent and/or will
retain no more than
about 50 percent of its growth more preferably no more than about 20 percent
of its growth,
more preferably no more than about 10 percent of its growth and most
preferably no more than
about 8 percent of its growth after a treatment of 50 cycles of industrial
laundering at
temperatures of at least 65 C.
The elastic fibers are preferably crosslinked, heat-resistant olefin elastic
fibers. Such
fibers include ethylene polymers, propylene polymers and fully hydrogenated
styrene block
copolymers (also known as catalytically modified polymers). The ethylene
polymers include
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the homogeneously branched and the substantially linear homogeneously branched
ethylene
polymers as well as ethylene-styrene interpolymers. Crosslinked homogeneously
branched and
the substantially linear homogeneously branched ethylene polymers are most
preferred.
The elastic fibers of the present invention may be of any suitable fiber
diameter, for
example, 15, 40, 70, 140 or even higher denier.
Suitable elastic fibers for use in the present invention are disclosed in US
6,437,014, hereby incorporated by reference in its entirety. As described in
that reference, the
fibers can be formed by many processes known in the art, for example the
fibers can be
meltblown, spunbond, or more preferably made by the melt spinning process.
Similarly, as
taught in US 6,437,014, the fibers can be made from many different materials,
including
ethylene-alpha olefin interpolymers, substantially hydrogenated block
polymers, styrene
butadiene styrene block polymers, styrene-ethylene/butene-styrene block
polymers, ethylene
styrene interpolymers, polypropylenes, polyamides, polyurethanes and
combinations thereof.
The crosslinked homogeneously branched ethylene polymers described in that
reference,
particularly the substantially linear ethylene polymers, are particularly well
suited for use in
making articles of this invention.
These elastic fibers may be used neat or may advantageously be used as the
core in a
core spun yarn. Core spun yarns may be easier to process in some commercial
weaving or
knitting machines. Furthermore, by selecting inherently flame-resistant
materials for use as the
wrapping fibers in a core spun yarn, the overall flame and/or heat resistance
of the core spun
yarn (and the articles which include such yams) can be increased. Suitable
fibrous materials
for wrapping an elastic core include polyamides (including aramids), polynosic
rayon,
cellulosics (particularly flame resistant cellulosics), polyester
(particularly flame resistant
polyester), polyvinyl alcohol, polytetrofluoroethylene, wool (particularly
flame resistant wool),
polyvinyl chloride, polyetheretherketone, polyetherinide, polyolefins,
polyimideamide,
polybenoxazole, carbon, modacrylic acrylic, melamine, glass, polybenzimidazole
(PBI) fibers,
poly(phenylene sulphide) PPS fibers, polyacrylate, semicarbon, phenolic or
novoloid fibers,
modacrylic, chlorofibres, FR viscose, nylon and acrylic and combinations
thereof. Aramid
fibers are particularly preferred for their flame resistance.
These fibers, whether neat or more preferably as the core in a core spun yarn,
will
preferably be used together in a weaving or knitting process with other fibers
or yams to make
the fabric of the present invention. To increase the flame-resistant
properties of the article, it
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may be advantageous to combine the elastic fiber or core spun yarn with
inherently flame-
resistant fibers. Suitable fibrous materials for combining with the elastic
fiber or yarns include
those listed above for use as the covering fiber in a core spun yarn. Aramid
fibers may be
particularly preferred for their inherent flame resistance. Usually the
crosslinked, heat-resistant
olefin elastic fibers comprise a minority of the fabric on a weight basis, but
the exact
percentage of each of the fibers may be optimized for any particular use. In
general, the fabrics
will contain at least about 2 percent by weight of the elastic fiber and woven
fabrics will tend to
have less than about 15 percent by weight of the elastic fiber whereas knitted
fabrics may have
up to about 35 percent by weight of the elastic fibers, but amounts outside
these ranges are
possible.
It may also be desirable to include a static dissipating fiber such as
metallic or carbon
fibers into the fabric. Garments including such static dissipating fibers will
provide additional
protection for workers.
The fabric of the present invention can be made according to known fabrication
methods such as weaving or knitting. It will be understood by one of ordinary
skill in the art
that in general, for any given fabric composition, the denser the fabric
construction, the more
flame resistant the fabric will be. At the same time, however, the denser the
fabric the heavier
the fabric will be, which may make a garment made from the fabric less
comfortable.
The fabric of the present invention can be used to make garments. Examples of
garments which can be advantageously made from the fabric of the present
invention include
uniforms, particularly uniforrns which are subject to industrial laundering.
The fabrics of this invention include fabrics known to require harsh and
stringent
processes that utilize chemicals and conditions that would degrade most
conventional stretch
fabrics because these chemicals and conditions would degrade the stretch fiber
component of
these fabrics. The fabrics of this invention, however, comprise a stretch
fiber that is
particularly resistant to such degradation and as such, the fabric containing
these fibers exhibits
surprising durability and chemical resistance.
In another embodiment of the present invention, an elastic fabric can be
chemically
treated to impart flame-resistance. In such methods, the fibers or articles
are treated with
specific chemicals to impart flame resistance to them. Such chemicals are
known in the art,
and include Tetrakis-(hydroxymethyl) phosphonium salts (henceforth designated
THP salts),
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such as THPS, are very effective for imparting flame resistance to cellulosic
materials. The
application of such chemicals can be accomplished by using either a THP/urea
precondensate
salt, which is insolubilized with gaseous ammonia, or by using a
THP/pad/dry/cure process, or
both. Exemplary techniques are described in U.S. Pat. Nos. 4,494,951
4,078,101, and
5,238,464, although any know method of imparting flame resistance may be used.
Treatments
to enhance thermal protective performance on wool based fabrics are also
known, and based on
addition of hexafluorotitanates and hexafluorozirconates to wool fiber, by
exhausting onto
wool at or below the boil. Such treatments are commercially as Zirpro finish
from IWS.
In general the chemical treatments used to impart flame-resistance expose the
fiber to a
harsh environment, which would degrade most elastic fibers. However, the
preferred melt
spun fibers comprising crosslinked homogeneously branched ethylene polymers,
resist
degrada'tion even under the harsh conditions typically seen in these
processes. It is
contemplated that the treatment may be applied to the fiber, the fabric or
even the finished
article as desired.
It is also possible to combine the techniques of creating a flame and or heat
resistant
durable stretch fabric, for example by chemically treating a fabric made from
inherently flame
and/or heat resistant fibers.
The following examples are to illustrate the invention, and not to limit it.
Ratios, parts
and percentages are by weight unless otherwise stated.
EXPERIMENTAL
Fiber Descriptions:
Core spun yam is made via the Siro Spinning process. The corespun yam
comprises 91
percent by weight of Poly(amide-imide)fibers; lpercent by weight carbon fibers
and 8 percent
by weight fiber made from 140 Denier crosslinked ethylene-octene copolymer
fiber available
from The Dow Chemical Company as Dow XLA fiber. Poly(amide-imide)fibers and
carbon
fiber short (cotton like) staple length in intimate blend is spun using a
conventional ring
spinning frame, and can be combined during the twisting process with ethylene-
octene
copolymer 140 den, pre-drafted at 5.2:1 ratio (draft). The process spinning
process leads to
form core yams, of average count equal to Nm 1/26, where ethylene-octene
copolymer 140den
5.2X drafted makes up the core, and of Poly(amide-imide)fibers and carbon
fibers the outer
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covering sheath. Cohesion within the covering fiber is imparted by applying
twist level equal
to: 570 twist per meter.
A fabric is then woven using this core spun yarn as the weft component. Yams
of
similar Nm 1/26 count, based on 99 percent by weight Poly(amide-imide)fibers
and 1 percent by
weight carbon fiber short (cotton like) staple length are used as warp
component. Loom settings
are: total number of warp threads 4867, reed width 201 cm. 2550 weft picks per
m.
Fabric so woven is than finished with a relaxation process in open width form
to promote
shrinkage in the weft direction and allow for the desired extensibility. This
fabric is then tested
for flame resistance as follows:
1) response to flame propagation, upon direct exposure to flame, as per DIN EN
531:02.95 standard norm (DIN IS015025:02.03 standard testing method):
resulting grade A;
2) heat transmission on exposure to flame as per DIN EN 531:02.95 standard
norm (DIN
EN 367:11.92 standard testing method): resulting grade B 1;
3) heat transmission on exposure to radiant heat, as per DIN EN 531:'02.95
standard
norm (DIN EN 366:05.93 standard testing method): resulting grade C 1
Elasticity is tested by the method known in the art as TTM074 DuPont method
(Total
elongation of woven fabrics); while growth is tested by the methods known in
the art as
TTM077 DuPont method (Percentage of fabric growth in stretch woven). The
growth and
elongation on the fabric in this example are elongation 10 percent, growth
after 1 min - 4.0
percent; growth after 1 hour - 3.2 percent.
These fabrics will exhibit similar durability as those reported in WO
03/078723 Al
(hereby incorporated by reference in its entirety), particularly those
described in Example 5
"Laundering".
Although the invention has been described in considerable detail through the
preceding
embodiments, this detail is for the purpose of illustration. Many variations
and modifications
can be made on this invention without departing from the spirit and scope of
the invention as
described in the following claims. All references including patents and patent
applications
cited above are incorporated herein by reference.
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