Note: Descriptions are shown in the official language in which they were submitted.
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MICROWAVE PROCESSING OF BALLISTIC COMPOSITES
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to the production of moldable, ballistic
resistant
articles. As part of the molding process, ballistic resistant fabrics are
heated with
microwave energy as an alternative to conventional preheating heating methods,
reducing heating time and increasing production efficiency.
DESCRIPTION OF THE RELATED ART
Ballistic resistant articles containing high strength fibers that have
excellent
properties against high speed projectiles are known. Articles such as bullet
resistant vests, helmets, vehicle panels and structural members of military
equipment are typically made from fabrics comprising high strength fibers.
High
strength fibers conventionally used include polyethylene fibers, para-aramid
fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon
fibers, glass fibers and the like. For many applications, such as vests or
parts of
vests, the fibers may be used in a woven or knitted fabric. For many of the
other
applications, the fibers are encapsulated or embedded in a matrix material to
form
either rigid or flexible fabrics.
Various ballistic resistant constructions are known that are useful for the
formation of articles such as helmets, panels and vests. For example, U.S.
patents
4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064,
5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are
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incorporated herein by reference, describe ballistic resistant composites
which
include high strength fibers made from materials such as extended chain ultra-
high molecular weight polyethylene. These composites display varying degrees
of
resistance to penetration by high speed impact from projectiles such as
bullets,
shells, shrapnel and the like.
For example, U.S. patents 4,623,574 and 4,748,064 disclose simple composite
structures comprising high strength fibers embedded in an elastomeric matrix.
U.S. patent 4,650,710 discloses a flexible article of manufacture comprising a
plurality of flexible layers comprised of high strength, extended chain
polyolefin
(ECP) fibers. The fibers of the network are coated with a low modulus
elastomeric material. U.S. patents 5,552,208 and 5,587,230 disclose an article
and method for making an article comprising at least one network of high
strength
fibers and a matrix composition that includes a vinyl ester and diallyl
phthalate.
U.S. patent 6,642,159 discloses an impact resistant rigid composite having a
plurality of fibrous layers which comprise a network of filaments disposed in
a
matrix, with elastomeric layers there between. The composite is bonded to a
hard
plate to increase protection against armor piercing projectiles.
In general, ballistic resistant articles are formed by molding a combination
of
fibers, any matrix composition and any additional polymeric layers in a
desired
configuration by subjecting the combination to heat and pressure for a
particular
mold cycle time. In the molding process, it is very important that the molding
temperature is low enough to avoid damage to the component fibers of the
ballistic resistant fabric. Particularly, is very important that the molding
temperature is less than the melting point of the polymer from which the
fibers are
formed or the temperature at which fiber damage occurs. For example, for
extended chain polyethylene fibers, such as SPECTRA@ fibers manufactured by
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Honeywell International, Inc., molding temperatures of about 68 F (20 C) to
about 293 F (145 C) are generally acceptable. However, the fibers are affected
after prolonged exposure to heat above 265 F (129 C), and SPECTRA fibers
melt at 300 F (149 C). Temperatures higher than 265 F may cause the filaments
of the fibrous layers to deform, reducing their ballistic resistance
properties.
Other fiber types may be able to tolerate higher molding temperatures. For
example, for aramid fibers, the upper limitation of the temperature range is
generally about 20 C to about 30 C higher than for extended chain polyethylene
fibers.
Furthermore, in an efficient process, it is also desired to maximize the
molding
temperature to minimize molding times. Using common convection heating,
standard molding times range from about 20 to 60 minutes at a temperature
range
of about 176 F (80 C) to about 293 F (145 C) and at a pressure of from about
10
psi (69 kPa) to about 10,000 psi (69,000 kPa). Moreover, common convection
heating requires the molding machine to be pre-heated for at least 10 minutes
prior to molding. Accordingly, there is a need in the art for a more efficient
fabric
molding process that can effectively form ballistic resistant articles at a
relatively
low temperature with a relatively short molding time.
The present invention provides a solution to this need in the art. The
invention
presents a method of forming ballistic resistant articles with reduced heating
time
in preparation for molding of said articles. Ballistic resistant fabrics, such
as
Spectra Shield fabrics manufactured by Honeywell International, Inc., are
generally poor conductors of heat. Accordingly, a long pre-heating time is
necessary before such fabrics are hot enough to be moldable into ballistic
resistant
articles. By reducing this pre-heating time, production efficiency can be
significantly improved.
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The invention provides a method of molding a ballistic resistant article
comprising heating a ballistic resistant fabric with microwave energy followed
by
molding the heated fabric. By heating with microwave energy, the overall
heating
and molding time is significantly reduced. The inventive process is more
efficient
than conventional heating techniques, and allows for considerably improved
productivity. Additionally, when using conventional heat sources, long
exposures
to high temperatures are necessary to insure good bonding between the fibers
and
can result in fiber degradation. Microwave processing avoids this problem by
allowing short heating times and avoiding significant temperature gradients
within the samples due to even distribution of microwave energy and heating
uniformity.
SUMMARY OF THE INVENTION
The invention provides a method of forming an article comprising:
a) providing a fabric comprising a plurality of fibers arranged in an array,
said
fibers having a tenacity of about 7 g/denier or more and a tensile modulus of
about 150 g/denier or more; said fibers having an optional microwave-reactive
composition thereon; and
b) heating said fabric inside a microwave oven by subjecting the fabric to
microwave energy sufficient to thereby heat the fibers or the optional
microwave-
reactive composition to at least about the softening temperature of the fibers
or
the softening temperature of the optional microwave-reactive composition;
c) molding the heated fabric into an article while said fabric has a
temperature of
at least about the softening temperature of the fibers or the softening
temperature
of the optional microwave-reactive composition due to the application of
microwave energy; and
d) allowing the molded fabric to cool.
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The invention also provides a method of forming a consolidated fiber network,
said consolidated network of fibers comprising a plurality of fiber layers,
each
fiber layer comprising a plurality of fibers having a tenacity of about 7
g/denier or
more and a tensile modulus of about 150 g/denier or more; and said fibers
having
a polymeric matrix composition thereon; which consolidated fiber network is
consolidated under heat and pressure, wherein the heat of consolidation is
generated by the application of microwave energy sufficient to thereby heat
the
polymeric matrix composition to a temperature of at least about the softening
temperature of polymeric matrix composition.
The invention further provides a ballistic resistant article comprising a
ballistic
resistant fabric, the ballistic resistant fabric comprising a plurality of
fibers
arranged in an array, said fibers having a tenacity of about 7 g/denier or
more and
a tensile modulus of about 150 g/denier or more; said fibers having a dry,
microwave-reactive composition coated thereon, which microwave-reactive
composition has been heated above its softening point temperature by the
application of microwave energy.
DETAILED DESCRIPTION OF THE INVENTION
Microwave ovens provide an effective way of uniformly heating many non-
conductive materials, such as ballistic resistant fabrics. Microwave
processing of
ballistic resistant fabrics provides desirable benefits, including economic
benefits
through the saving of energy and time, and increased process yield and
throughput. The materials produced herein ostensibly have uniquely uniform
microstructures that are not achieved by other heating methods due to the even
energy distribution and uniform heating from the microwave.
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For the purposes of the invention, fabrics having superior ballistic
penetration
resistance describe those which exhibit excellent properties against high
speed
projectiles. As used herein, a "fiber" is an elongate body the length
dimension of
which is much greater than the transverse dimensions of width and thickness.
The
cross-sections of fibers for use in this invention may vary widely. They may
be
circular, flat or oblong in cross-section. Accordingly, the term fiber
includes
filaments, ribbons, strips and the like having regular or irregular cross-
section.
They may also be of irregular or regular multi-lobal cross-section having one
or
more regular or irregular lobes projecting from the linear or longitudinal
axis of
the fibers. Most commonly, fibers are single lobed and have a substantially
circular cross-section.
As used herein, a"yarn" is a strand of interlocked fibers. A "parallel array"
describes an orderly parallel arrangement of fibers or yarns. A fiber "layer"
describes a planar arrangement of woven or non-woven fibers or yarns. A fiber
"network" denotes a plurality of interconnected fiber or yarn layers. A fiber
network can have various configurations. For example, the fibers or yarn may
be
formed as a felt or another woven, non-woven or knitted, or formed into a
network by any other conventional technique. In general, a "fabric" may relate
to
either a woven or non-woven material, or a combination thereof. As used
herein,
the term "fabric" describes structures including multiple fibrous layers
either
before or after molding to form a composite.
As used herein, a "high-strength, high tensile modulus fiber" is one which has
a
preferred tenacity of at least about 7 g/denier or more, a preferred tensile
modulus
of at least about 150 g/denier or more, both as measured by ASTM D2256 and
preferably an energy-to-break of at least about 8 J/g or more. As used herein,
the
term "denier" refers to the unit of linear density, equal to the mass in grams
per
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9000 meters of fiber or yarn. As used herein, the term "tenacity" refers to
the
tensile stress expressed as force (grams) per unit linear density (denier) of
an
unstressed specimen. The "initial modulus" of a fiber is the property of a
material
representative of its resistance to deformation. The term "tensile modulus"
refers
to the ratio of the change in tenacity, expressed in grams-force per denier
(g/d) to
the change in strain, expressed as a fraction of the original fiber length
(in/in).
Particularly suitable high-strength, high tensile modulus fiber materials
include
extended chain polyolefin fibers, such as highly oriented, high molecular
weight
polyethylene fibers, particularly ultra-high molecular weight polyethylene
fibers,
and ultra-high molecular weight polypropylene fibers. Also suitable are
extended
chain polyvinyl alcohol fibers, extended chain polyacrylonitrile fibers, para-
aramid fibers, polybenzazole fibers, such as polybenzoxazole (PBO) and
polybenzothiazole (PBT) fibers and liquid crystal copolyester fibers. Each of
these fiber types is conventionally known in the art.
In the case of polyethylene, preferred fibers are extended chain polyethylenes
having molecular weights of at least 500,000, preferably at least one million
and
more preferably between two million and five million. Such extended chain
polyethylene (ECPE) fibers may be grown in solution spinning processes such as
described in U.S. patent 4,137,394 or 4,356,138, which are incorporated herein
by
reference, or may be spun from a solution to form a gel structure, such as
described in U.S. patent 4,551,296 and 5,006,390, which are also incorporated
herein by reference.
The most preferred polyethylene fibers for use in the invention are
polyethylene
fibers sold under the trademark Spectra from Honeywell Intemational Inc.
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Spectra fibers are well known in the art and are described, for example, in
commonly owned U.S. patents 4,623,547 and 4,748,064 to Harpell, et al.
Ounce for ounce, Spectra high performance fiber is ten times stronger than
steel, while also light enough to float on water. The fibers also possess
other key
properties, including resistance to impact, moisture, abrasion chemicals and
puncture.
Suitable polypropylene fibers include highly oriented extended chain
polypropylene (ECPP) fibers as described in U.S. patent 4,413,110, which is
incorporated herein by reference. Suitable polyvinyl alcohol (PV-OH) fibers
are
described, for example, in U.S. patents 4,440,711 and 4,599,267 which are
incorporated herein by reference. Suitable polyacrylonitrile (PAN) fibers are
disclosed, for example, in U.S. patent 4,535,027, which is incorporated herein
by
reference. Each of these fiber types is conventionally known and are widely
commercially available.
Suitable aramid (aromatic polyamide) or para-aramid fibers are commercially
available and are described, for example, in U.S. patent 3,671,542. For
example,
useful poly(p-phenylene terephthalamide) filaments are produced commercially
by Dupont corporation under the trade name of KEVLAR . Also useful in the
practice of this invention are poly(m-phenylene isophthalamide) fibers
produced
commercially by Dupont under the trade name NOMEX . Suitable
polybenzazole fibers for the practice of this invention are commercially
available
and are disclosed for example in U.S. patents 5,286,833, 5,296,185, 5,356,584,
5,534,205 and 6,040,050, each of which are incorporated herein by reference.
Preferred polybenzazole fibers are ZYLON brand fibers from Toyobo Co.
Suitable liquid crystal copolyester fibers for the practice of this invention
are
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commercially available and are disclosed, for example, in U.S. patents
3,975,487;
4,118,372 and 4,161,470, each of which is incorporated herein by reference.
The other suitable fiber types for use in the present invention include glass
fibers,
fibers formed from carbon, fibers formed from basalt or other minerals, M5
fibers and combinations of all the above materials, all of which are
commercially
available. M5 fibers are manufactured by Magellan Systems International of
Richmond, Virginia and are described, for example, in U.S. patents 5,674,969,
5,939,553, 5,945,537, and 6,040,478, each of which is incorporated herein by
reference.
As stated above, a high-strength, high tensile modulus fiber is one which has
a
preferred tenacity of about 7 g/denier or more, a preferred tensile modulus of
about 150 g/denier or more and a preferred energy-to-break of about 8 J/g or
more, each as measured by ASTM D2256. For greater ballistic resistance
properties, the tenacity of the fibers should be about 15 g/denier or more,
preferably about 20 g/denier or more, more preferably about 25 g/denier or
more
and most preferably about 30 g/denier or more; the fibers preferably also have
a
tensile modulus of about 300 g/denier or more, more preferably about 400
g/denier or more, more preferably about 500 g/denier or more, more preferably
about 1,000 g/denier or more and most preferably about 1,500 g/denier or more.
Fibers with increased ballistic protection properties also have a preferred
energy-
to-break of about 15 J/g or more, more preferably about 25 J/g or more, more
preferably about 30 J/g or more and most preferably have an energy-to-break of
about 40 J/g or more. These combined high strength properties are obtainable
by
employing well known solution grown or gel fiber processes. U.S. patents
4,413,110, 4,440,711, 4,535,027, 4,457,985, 4,623,547 4,650,710 and 4,748,064
generally discuss the preferred high strength, extended chain polyethylene
fibers
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employed in the present invention, and their disclosures are incorporated
herein
by reference.
Ballistic resistant fabrics may comprise one or more woven or non-woven
fibrous
layers, or a combination thereo Woven and non-woven fibrous layers may be
formed using techniques that are commonly known in the art. Suitable non-
woven fibrous layers include those comprising randomly oriented fibers, as
with a
felt, and a plurality of fibers or yarns arranged in a substantially parallel
array. In
a common construction, the non-woven fibrous layers of the invention comprise
a
single-layer, consolidated network of fibers in an elastomeric or rigid
polymer
composition, referred to in the art as a matrix composition. In general, a
"polymeric matrix composition" is a binder material that binds the fibers
together
after a consolidation or lamination step. A "consolidated network" describes a
consolidated combination of multiple fiber layers with the matrix composition.
As used herein, a "single layer" structure refers to structure composed of one
or
more individual fiber layers that have been consolidated into a single unitary
structure, wherein consolidation can occur via drying, cooling, heating,
pressure
or a combination thereof. The consolidated network may also comprise a
plurality of yarns that are coated with such a matrix composition, formed into
a
plurality of layers and consolidated into a single fabric layer.
In either a random or parallel non-woven parallel orientation, the individual
fibers
forming the fabric layer may or may not be coated on, impregnated with,
embedded in, or otherwise applied with a matrix composition, using well known
techniques in the art. The matrix composition may be applied to the high
strength
fibers either before or after the layers are formed, then followed by
consolidating
the matrix material-fibers combination together to form a multilayer complex.
Most particularly, the non-woven fibrous layers of the invention comprise: i)
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plurality of layers, each layer comprising a plurality of unidirectionally
aligned,
parallel fibers, wherein said layers are cross-plied at an angle relative to a
longitudinal fiber direction of each adjacent fiber layer; and wherein said
fibers
optionally have a polymeric matrix composition thereon; or ii) one or more
layers
comprising a plurality of randomly aligned fibers; and wherein said fibers
optionally have a polymeric matrix composition thereon.
As is conventionally known in the art, non-woven fabrics achieve excellent
ballistic resistance when the individual component fiber layers are cross-
plied
such that the fiber alignment direction of one layer is rotated at an angle
with
respect to the fiber alignment direction of another layer, such that they are
non-
parallel. For example, a preferred structure has two fiber layers of the
invention
positioned together such that the longitudinal fiber direction of one layer is
perpendicular to the longitudinal fiber direction of the other layer. In
another
example, a five layered structure is formed in which the second, third, fourth
and
fifth layers are rotated +45 , - 45 , 90 and 0 , with respect to the first
layer, but
not necessarily in that order. For the purposes of this invention, adjacent
layers
may be aligned at virtually any angle between about 0 and about 90 with
respect
to the longitudinal fiber direction of another layer, but the about 0 and
about 90
fiber orientations are preferred. While the examples above illustrate fabrics
that
include either two or five individual fiber layers, such is not intended to be
limiting. The non-woven fibrous layers can be constructed via a variety of
well
known methods, such as by the methods described in U.S. patent 6,642,159. It
should be understood that the single-layer consolidated networks of the
invention
may generally include any number of cross-plied layers, such as about 20 to
about
40 or more layers as may be desired for various applications.
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Woven fibrous layers may be formed using techniques that are well known in the
art using any fabric weave, such as plain weave, crowfoot weave, basket weave,
satin weave, twill weave and the like. Plain weave is most common. Prior to
weaving, the individual fibers of each woven fibrous material may or may not
be
coated with a polymeric matrix composition in a similar fashion as the non-
woven
fibrous layers using the same matrix compositions as the non-woven fibrous
layers.
Alternately, the fabrics may comprise a hybrid combination of alternating or
non-
alternating woven and non-woven fibrous layers, such as a non-
woven/woven/non-woven or woven/non-woven/woven structure. Ballistic
resistant fabrics may include any number of combined woven and/or non-woven
layers, and each non-woven layer may comprise single-layer consolidated
networks which incorporate multiple component layers. Adjacent layers may
optionally be attached with an intermediate adhesive layer. Each woven layer,
in
particular, is preferably attached to an adjacent layer via an adhesive layer.
Suitable adhesives non-exclusively include elastomeric materials such as
polyethylene, cross-linked polyethylene, chlorosulfonated polyethylene,
ethylene
copolymers, polypropylene, propylene copolymers, polybutadiene, polyisoprene,
natural rubber, ethylene-propylene copolymers, ethylene-propylene-diene
terpolymers, polysulfide polymers, polyurethane elastomers, polychloroprene,
plasticized polyvinylchloride using one or more plasticizers that are well
known
in the art (such as dioctyl phthalate), butadiene acrylonitrile elastomers,
poly
(isobutylene-co-isoprene), polyacrylates, polyesters, unsaturated polyesters,
polyethers, fluoroelastomers, silicone elastomers, copolymers of ethylene,
thermoplastic elastomers, phenolics, polybutyrals, epoxy polymers, styrenic
block
copolymers, such as styrene-isoprene-styrene or styrene-butadiene-styrene
types,
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and other suitable adhesive compositions conventionally known in the art.
Particularly preferred adhesive compositions include methacrylate adhesives,
cyanoacrylate adhesives, UV cure adhesives, urethane adhesives, epoxy
adhesives, ethylene vinyl acetate adhesives and blends of the above materials.
Most preferably, the adhesive comprises a thermoplastic polymer, particularly
ethylene vinyl acetate. Such adhesives may be applied, for example, in the
form
of a hot melt, film, paste or spray, or as a two-component liquid adhesive.
The woven or non-woven fibrous layers of the invention may be prepared using a
variety of matrix materials, including both low modulus, elastomeric matrix
materials and high modulus, rigid matrix materials. Suitable matrix materials
non-exclusively include low modulus, elastomeric materials having an initial
tensile modulus less than about 6,000 psi (41.3 MPa), and high modulus, rigid
materials having an initial tensile modulus at least about 300,000 psi (2068
MPa),
each as measured at 37 C by ASTM D638. As used herein throughout, the term
tensile modulus means the modulus of elasticity as measured by ASTM 2256 for
a fiber and by ASTM D638 for a matrix material.
An elastomeric matrix composition may comprise a variety of polymeric and non-
polymeric materials. A preferred elastomeric matrix composition comprises a
low modulus elastomeric material. For the purposes of this invention, a low
modulus elastomeric material has a tensile modulus, measured at about 6,000
psi
(41.4 MPa) or less according to ASTM D638 testing procedures. Preferably, the
tensile modulus of the elastomer is about 4,000 psi (27.6 MPa) or less, more
preferably about 2400 psi (16.5 MPa) or less, more preferably 1200 psi (8.23
MPa) or less, and most preferably is about 500 psi (3.45 MPa) or less. The
glass
transition temperature (Tg) of the elastomer is preferably less than about 0
C,
more preferably the less than about -40 C, and most preferably less than about
-
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50 C. The elastomer also has an preferred elongation to break of at least
about
50%, more preferably at least about 100% and most preferably has an elongation
to break of at least about 300%.
A wide variety of matrix materials and formulations having a low modulus may
be utilized as the matrix. Representative examples include polybutadiene,
polyisoprene, natural rubber, ethylene-propylene copolymers, ethylene-
propylene-
diene terpolymers, polysulfide polymers, polyurethane elastomers,
chlorosulfonated polyethylene, polychloroprene, plasticized polyvinylchloride,
butadiene acrylonitrile elastomers, poly(isobutylene-co-isoprene),
polyacrylates,
polyesters, polyethers, fluoroelastomers, silicone elastomers, copolymers of
ethylene, and combinations thereof, and other low modulus polymers and
copolymers curable below the melting point of the polyolefin fiber. Also
preferred are blends of different elastomeric materials, or blends of
elastomeric
materials with one or more thermoplastics.
Particularly useful are block copolymers of conjugated dienes and vinyl
aromatic
monomers. Butadiene and isoprene are preferred conjugated diene elastomers.
Styrene, vinyl toluene and t-butyl styrene are preferred conjugated aromatic
monomers. Block copolymers incorporating polyisoprene may be hydrogenated to
produce thermoplastic elastomers having saturated hydrocarbon elastomer
segments. The polymers may be simple tri-block copolymers of the type A-B-A,
multi-block copolymers of the type (AB)õ (n= 2-10) or radial configuration
copolymers of the type R-(BA),, (x=3-150); wherein A is a block from a
polyvinyl
aromatic monomer and B is a block from a conjugated diene elastomer. Many of
these polymers are produced commercially by Kraton Polymers of Houston, TX
and described in the bulletin "Kraton Thermoplastic Rubber", SC-68-81. The
most preferred matrix polymer comprises styrenic block copolymers sold under
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the trademark KRATONS commercially produced by Kraton Polymers. The
most preferred low modulus matrix composition comprises a polystyrene-
polyisoprene-polystrene-block copolymer.
Preferred high modulus, rigid matrix materials useful herein include materials
such as a vinyl ester polymer or a styrene-butadiene block copolymer, and also
mixtures of polymers such as vinyl ester and diallyl phthalate or phenol
formaldehyde and polyvinyl butyral. A particularly preferred rigid matrix
material
for use in this invention is a thermosetting polymer, preferably soluble in
carbon-
carbon saturated solvents such as methyl ethyl ketone, and possessing a high
tensile modulus when cured of at least about 1 x 106 psi (6895 MPa) as
measured
by ASTM D638. Particularly preferred rigid matrix materials are those
described
in U.S. patent 6,642,159, which is incorporated herein by reference.
The rigidity, impact and ballistic properties of the articles formed from the
fabric
composites of the invention are affected by the tensile modulus of the matrix
polymer. For example, U.S. patent 4,623,574 discloses that fiber reinforced
composites constructed with elastomeric matrices having tensile moduli less
than
about 6000 psi (41,300 kPa) have superior ballistic properties compared both
to
composites constructed with higher modulus polymers, and also compared to the
same fiber structure without a matrix. However, low tensile modulus matrix
polymers also yield lower rigidity composites. Further, in certain
applications,
particularly those where a composite must function in both anti-ballistic and
structural modes, there is needed a superior combination of ballistic
resistance and
rigidity. Accordingly, the most appropriate type of matrix polymer to be used
will vary depending on the type of article to be formed from the fabrics of
the
invention. In order to achieve a compromise in both properties, a suitable
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composition may combine both low modulus and high modulus materials to form
a single matrix composition.
Ballistic resistant fabrics may be used for various applications. For example,
one
or more fabrics of the invention may be arranged together to form flexible
articles, including garments such as vests, pants, hats, or other articles of
clothing,
as is well known in the art. The fabrics of the invention may also be formed
into
other personal protective articles such as helmets, or may be formed into
protective shields, covers or blankets as desired. Other common structures
include flat, planar panels or customized shaped panels. Molded fabrics may be
used, for example, to fortify armored civilian vehicles for NIJ Level I, IIA,
II,
IIIA and III protection; as armored doors and roofs for police cars and other
vehicles; as trauma pads or breast plate inserts for ballistic resistant vests
for NIJ
Level I, IIA, II, IIIA and III protection; for hand-held riot shields at NIJ
Level I,
IIA, II, IIIA and III protection, or for explosion management devices.
Multiple
fabrics may be stacked or arranged in a bonded or non-bonded array. Bonding
may be done using any conventional means in the art, such as stitching or
bonding
together with adhesive materials, other thermoplastic materials, or non-
thermoplastic fibers or materials.
In order to produce such desired articles from ballistic resistant fabrics,
the fabrics
are subjected to a process referred to in the art as molding. In a typical
molding
process, a fabric, which may comprise any number of woven and/or non-woven
layers (also referred to as "plies"), is heated or pre-heated to a desired
molding
temperature which allows it to be formed into a shaped article or panel. The
heated fabric is either shaped or compressed in a suitable molding apparatus,
typically under pressure. Typical molding pressures range from about 50 psi to
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about 5000 psi, more commonly from about 200 psi to about 1500 psi. The
molding step may take from about 4 seconds to about 45 minutes.
In accordance with the invention, the fabric is heated in a microwave oven
instead
of by any other traditional heating method. Microwave heating is a more
efficient
alternative to conventional heating because of its efficient volumetric heat
production. Volumetric heating is defined as heating of the bulk, as opposed
to
transferring heat inward from the surface. Microwaves cause heating within a
material by generating waves that excite molecules, causing them to rotate.
Any
molecule which is "polar" and has positive and negative ends will be rotated
back
and forth to align with the changing electric field of the waves in the oven.
This
rotation produces energy in the form of heat. Unlike conventional heating,
this
effect occurs simultaneously throughout the whole material being microwaved.
Microwaves are electromagnetic waves in the frequency band from 300 MHz (3 x
108 cycles/second) to 300 GHz (3 x 1011 cycles/second). These two frequencies
correspond to wavelengths of 1 m and 1 mm, respectively. All domestic
microwave ovens and laboratory microwave processors operate at 2.45 GHz,
corresponding to a wavelength of about 12.2 cm. Industrial microwaves may
operate at a 2.45 GHz frequency, and may also operate at lower frequencies,
such
as 900MHz or at greater frequencies, such as 10 GHz, and are generally
available
at 1000 watts to 3000 watts power. The present invention is not restricted to
any
particular microwave frequency.
In general, microwave processing systems consist of a microwave source, an
applicator to deliver the power to the sample, and systems to control the
heating.
Microwave generators are generally vacuum tubes or solid state devices. In
microwave ovens, the tubes are generally rated at 1.5 kW. The tubes need a
magnetic field in order to operate, and the field is supplied by either a
permanent
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magnet or an electromagnet. The magnetron is the most common microwave
source in materials processing applications. In general, microwave energy is
applied to materials through multi-mode or single-mode microwave applicators,
and temperature control is typically accomplished by varying input power or
through pulsed sources. The invention encompasses the use of any specialized
microwave, including microwave ovens sufficient for use at home, industrial
microwave ovens, and other unique microwave ovens, which may or may not use
unique wavelengths for unique applications.
One significant factor limiting the potential use of microwaves for materials
processing is the ability of materials to absorb microwave radiation
(essentially
high frequency radio waves). In contrast to conventional heating, microwaves
penetrate the material with penetrating radiation. Whether or not heat is
generated is determined by the specific dielectric properties of the material
itself,
such as the dielectric constant and dielectric loss tangent of the material.
In most materials, the microwave-power absorption is proportional to the water
content of the material. However, in materials processing, unlike microwaving
of
food, coupling of microwave energy is to atoms or atomic groups other than
water. As is commonly known, many polymeric materials are not capable of
absorbing microwave radiation. Particularly, while some types of high strength
fibers suitable for forming fabrics having superior ballistic penetration
resistance
may be capable of absorbing microwave radiation, others are not. However, it
has
been found that blending microwave absorbent additives with a polymeric matrix
composition, or otherwise applying a microwave-reactive composition onto a
material, fabrics that are otherwise not capable of absorbing microwave
radiation
may be suitably processed with microwave radiation. As used herein, a
"microwave-reactive composition" is a composition that absorbs sufficient
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microwave radiation to heat a fiber or a polymeric matrix composition to at
least
the softening temperature of the fiber or polymeric matrix composition,
respectively.
As discussed above, many polymeric materials are not capable of absorbing
microwave radiation. For example, it has been found that aramid fibers are
sufficiently absorbent to microwave radiation, but polyethylene fibers are
not, to
heat a fabric to at least the softening temperature of the fibers, or more
particularly, to at least about 60 C. Particularly, Spectra polyethylene
fibers
have been found to be substantially transparent to microwave radiation. Nylon,
polyester and polyethylene naphthalate fibers are also at least partially
microwave
absorbing.
If a fabric is formed from fibers that are transparent to microwave radiation,
the
fibers must be at least partially coated or contacted with a material that is
sufficiently microwave absorbent to reach the softening temperature of the
fibers
or of the polymeric matrix composition. For example, a microwave absorbent
material, such as a microwave absorbent polymeric matrix composition, may be
coated onto a surface of the fabric. A polymeric matrix composition may be
microwave absorbent by itself, or by being blended with a microwave-reactive
additive. A microwave-reactive additive will absorb the microwave energy and
transfer it to the fibers. Polar materials in particular, including polar
polymeric
fibers, polar polymeric matrix compositions and polar additives, are microwave
reactive. Conductive materials, such as conductive fibers (e.g. carbon fibers)
and
conductive polymeric matrix compositions (polyaniline, polypyrole, etc.) are
microwave reactive. Combining non-microwave absorbent fiber types with one
or more polar polymers, conductive polymers or microwave-reactive additives
provides good coupling to microwave energy.
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Suitable microwave-reactive additives non-exclusively include metal particles,
including but not limited to magnetic particles, and metal powders, dielectric
particles and dielectric powders, insoluble microwave-absorbing polymeric
particles and non-dispersible microwave-absorbing polymeric particles. While
solid metals are known to reflect microwave radiation, powder metals do absorb
microwave radiation and can be heated. Useful dielectric and polymeric powders
include those that allow a polymeric matrix material to be heated to at least
the
softening point of the polymeric matrix material in a conventional microwave
oven. Non-exclusive examples of suitable materials are described in the book
Microwave Processing of Materials III, edited by Ronald L. Beatty, Willard H.
Sutton and Magdy F. Iskander, published by Materials Research Society, vol.
269
(October 1992), which is incorporated herein by reference. Also suitable are
the
materials described in U.S. patents 5,349,168 and 6,066,375, the disclosures
of
which are incorporated herein by reference. Examples of useful microwave-
reactive materials capable of absorbing the electric or magnetic portion of
the
microwave field energy and converting that energy into heat include metal
powders such as powdered nickel, antimony, copper, molybdenum, bronze, iron,
steel, chromium, tin, zinc, silver, gold, cobalt, tungsten, titanium,
aluminum,
including leafing aluminum powder, and alloys thereof. Other useful additives
are conductive materials such as carbon black, carbon fibers, metal fibers,
and
metal flakes, spheres or needles with sizes typically ranging from about 0.1
to 100
m. These microwave-reactive additives are particularly useful when blended
with a polymeric matrix composition.
Other conductive materials such as graphite and semi-conductive materials such
as silicon carbides and magnetic material such as metal oxides (if available
in
particulate form) may also be utilized. These materials are non-exclusive and
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generally any other additive material may be used that allows a polymeric
matrix
material or polymeric fiber to be heated to at least the softening temperature
of the
matrix or fiber in a conventional microwave oven at 2.45 GHz.
Such materials employed are in particulate form, and may be flakes or powders.
The size of such particles will vary in accordance with a number of factors,
including the particular material selected, the amount of heat to be
generated, the
manner in which the coating composition is to be applied, and the like.
Other useful microwave-reactive additives include oils, such as watch oil, as
well
as glycerol, silicon carbide, calcium nitride and calcium aluminates. Other
suitable additives include additives such as organic salts and inorganic salts
having a high freedom of rotational, vibrational or translational movement, as
well as non-conductive additives including metal oxides and metal dioxides,
such
as titanium dioxide, cobalt oxide, iron oxide, nickel oxide and manganese
dioxide.
Suitable organic salts include monosodium glutamate (MSG), potassium citrate,
calcium carbonate, potassium tartrate, ammonium formate, sodium bicarbonate,
maganese carbonate, and combinations thereof, as well as many others. Suitable
inorganic salts include magnesium sulfate, calcium chloride, trisodium
phosphate,
ferrous sulphate, maganese sulphate, zinc sulphate, sodium metabisulphite, and
combinations thereof, as well as many others. Also suitable are the materials
disclosed in U.S. patent 4,219,361, the disclosure of which is incorporated by
reference herein. These microwave-reactive additives are excited by microwaves
of 2.45 GHz frequency and convert the microwave energy into thermal energy
due to molecular friction. Other suitable materials that may be applied onto
the
fabric or blended within a matrix composition further include solutions of
polyacrylate, a polyamide solution, a polyvinyl methyl ether solution, a
polyamide hot melt adhesive, and a polyvinyl methyl based hot melt adhesive.
It
may also be suitable to soak the fabric in a processing fluid, such as water,
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isopropanol or ethanol, which are capable of converting at least a portion of
the
incident microwave energy into heat and transferring the heat to the fabric.
These
materials may be applied by any well known means in the art.
The amount of additive may vary depending on the type of polymeric matrix and
type of additive. Typically, the microwave-reactive additive should comprise
from about 0.01 % to about 10.0% by weight of the polymeric matrix
composition,
more typically 0.01% to about 3.0% and most typically 0.01% to about 1.0% by
weight of the polymeric matrix composition. Greater quantities may be used if
determined to be necessary by one skilled in the art. However, in larger
quantities,
the additive will not stay in the matrix resin mix and will precipitate in the
mixing
tank when the additive is blended with the matrix resin. Depending on the
temperature sensitivity of the composite's raw materials and the temperature
required to achieve consolidation or reaction, both the ultimate temperature
and
the rate at which the composite reaches that temperature may need to be
manipulated. Each specific combination would have its own preferred
concentration of additive, and that concentration may vary greatly. In
general,
metals are more efficient than polymers, salts and other materials at reacting
with
and absorbing microwave radiation. Accordingly, smaller quantities of metallic
based additives are typically needed.
Different substances subjected to the same amount of microwave energy heat up
at different rates. For example, non-symmetrical polar molecules are easily
rotated by microwave energy and heat up quickly. The principal mechanism of
coupling of microwave radiation to polymers is through dipolar reorientation
by
an electric field. Particularly, materials having a high concentration of a
strong
dipole are considered to be active absorbers of microwave energy and are
particularly effective. A dipole is a chemical arrangement where a positive
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charge and a negative charge are held at a fixed distance from each other. As
a
reaction of a material with microwave radiation proceeds, the type and
concentration of dipole moments change, and a phase change occurs, changing
the mobility of the dipoles. A dipole moment is formed by adjacent groups
having different electron withdrawing/donating properties resulting in a net
charge or partial charge localization on one atom or group and can be viewed
as a
small, weak bar magnet. Typical groups which form these dipoles include
hydroxyl, amino, cyanate, etc. The efficiency of this coupling is dependent on
a
number of factors, including dipole strength, the mobility of the dipole and
the
mass of the dipole. Small strong dipoles appear to couple to microwave
radiation
most efficiently and liquids couple the strongest, followed by rubbers, glassy
polymers and crystalline materials.
Water-based resins, as well as solvent-based and 100% solids materials, which
contain dipoles will absorb microwave radiation to some extent. The strength
of
those dipoles, coupled with the concentration of those dipoles and the freedom
of
movement of the polymer, which allows the dipole to try to align itself with
the
oscillating magnetic field, causing friction and heat, will determine how much
energy will be converted to heat. For example, a urethane linkage (-NH-COO-)
is
a strong dipole and polyurethane resins have a high concentration of these
groups.
Accordingly, polyurethane-containing matrix polymers are very effective.
Polymers containing carboxylic acid groups, also a dipole, are also preferred.
Other preferred polymers include poly-electrolytes, ionomers, polyvinyl
alcohol,
polyvinyl butyral, silicones and polyamides.
Other useful polymers that have weaker dipoles or lower concentrations of
dipoles non-exclusively include acrylics, ethylene vinyl acetate and ethylene
acrylic acid. These materials are active to some extent with the magnitude of
the
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warming related to the strength and concentration of the dipoles. Also
suitable are
blends of matrix polymers, such as a two-phase matrix of an active resin
dispersed
in a non-active resin, allowing the non-active resin to be processed with
microwave energy.
The selection of the most effective microwave-reactive additive is generally
dependent upon the frequency, power and duration of the microwave energy to be
absorbed. It is known that heating is accelerated by ionic effects and the
specific
heat of a composite material. For example, oils are useful materials because
of
their low specific heat. Many factors also contribute to the minimum amount of
microwave-reactive additive required. Highly active materials will generally
require a lower weight or volume percentage. Synergistic compositions (some
absorbed free water, induced dipoles in other constituents of the composite,
etc.)
will reduce the required level of active component. Lower targeted process
temperatures would also require lower levels of highly active component, or
higher levels of a lower absorbing material. Typically, the minimum amount of
microwave-reactive additive required will be less than about 10% by weight of
the fabric, more preferably, less than 10% by weight of the polymeric matrix
composition. More preferably, the quantity of microwave-reactive additive will
be from about 1% to about 6% by weight, more preferably from about 3% to
about 6% by weight of the polymeric matrix composition, or by weight of the
fabric if no matrix is present. If the microwave-reactive additive is
dispersed as a
mixture in a solvent, mixture will typically include about 70% to about 80% by
weight of the solvent.
In the method of the invention, a fabric is heated inside a microwave oven by
subjecting the fabric to microwave energy sufficient to thereby heat the
fibers or
the optional microwave-reactive composition to at least about the softening
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temperature of the fibers or of the optional microwave-reactive composition.
Prior to microwave heating, it is preferred that the ballistic resistant
fabric and
optional microwave-reactive composition be completely dry and free of volatile
substances. The material should be heated to a temperature less than a
temperature at which the material is degraded or burned. Immediately after
heating or during heating, the fabric is molded or consolidated into an
article
while said fabric has a temperature of at least about the softening
temperature of
the fibers or the softening temperature of the optional microwave-reactive
composition, if present. As used herein, the term "immediately thereafter"
means
that the fabric is molded or consolidated while still at or above the
softening
temperature due to microwave generated heat. Thereafter, the heated fabric is
molded into an article while said fabric has a temperature of at least about
the
softening temperature of the fibers or the softening temperature of the
optional
microwave-reactive composition, if present. Alternately, the fabric may be
heated
and molded consecutively in a single multifunctional apparatus having both
heating and molding capabilities. While it is envisioned that the optional
transfer
of the heated fabric from the microwave to a separate molding apparatus might
cause the fabric to lose some heat, the process is conducted such that molding
is
commenced while the fabric retains sufficient microwave generated heat to
allow
the fabric to be molded into any desired shape or form, and allowing the
fabric to
retain said shape if so intended. Finally, the molded fabric is allowed to
cool.
As described herein, a fabric of the invention must be heated until it reaches
a
temperature suitable for molding. The minimum molding temperature of a fabric
is typically determined by the softening temperature point of either the
polymeric
matrix composition or the softening temperature point of the fibers if no
matrix
composition is present. As is commonly known in the art, the softening point
of
plastics may be measured by the ASTM D1525 Vicat Softening Temperature
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testing method, which covers determination of the temperature at which a
specified needle penetration occurs when specimens are subjected to specified
controlled test conditions. More particularly, in this testing method, a flat-
ended
needle loaded with a specified mass is placed in direct contact with a test
specimen. The specimen and needle are heated at a permissible rate, and the
temperature at which the needle has penetrated to a depth of 1 0.01 mm is
recorded as Vicat softening temperature.
Suitable minimum molding temperatures typically range from about 60 C to
about 180 C, but vary depending on the particular fiber type, and may be
beyond
this range. For example, Spectra polyethylene fibers are affected after
prolonged exposure to heat above 265 F (129.4 C) and melt at 300 F (148.9 C).
Accordingly, Spectra polyethylene fibers are preferably heated to greater
than
about 200 F (93.3 C) but less than about 257 F (125 C). When heating by
convection, the heating step commonly adds an additional 10 to 30 minutes to
the
fabric processing time and requires pre-heating of the convection oven. This
heating time is substantially reduced by microwaving the fabric. The exposure
time to microwave energy should be enough to sufficiently heat the fabric to
the
desired temperature, while brief enough to avoid degradation of the fibers.
Most
preferably, the fabric is capable of being heated in a microwave oven to 200 F
or
greater within three minutes.
The complete molded fabrics of the invention comprise a combination of fibers,
an optional matrix composition, optional intermediate adhesive layers and an
optional microwave sensitive material. In general, to produce a fabric having
sufficient ballistic resistance properties, the proportion of fibers
preferably
comprises from about 45% by weight to about 95% by weight of the fabric, more
preferably from about 60% to about 90% by weight of the fabric, and most
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preferably from about 65 to about 85% by weight of the composite. As is
commonly known in the art, the matrix composition and/or optional adhesive may
also include other additives such as fillers, such as carbon black or silica,
may be
extended with oils, or may be vulcanized by sulfur, peroxide, metal oxide or
radiation cure systems as is well known in the art.
Depending on the desired structural and ballistic resistance properties of the
articles formed from the fabrics of the invention, various parameters such as
the
number and type of fabric layers and the type of matrix may be controlled. For
example, for the formation of low cost trauma pads for reducing deformation in
ballistic resistant vests, it is preferred to include 2 fabric layers, i.e.
two woven
fibrous layers, or two single layer, consolidated networks of non-woven,
unidirectional fibers, each formed from two fiber layer plies cross-plied at 0
/90 ,
having a rubber layer on either outer surface of the combined fabric. Further,
for
ballistic resistant panels having a ballistic protection level of NIJ Level II
or IIA,
fabrics including 14 fabric layers and 10 fabric layers, respectively, are
preferred.
Whether the component fibers of a fabric are capable of absorbing microwave
radiation or whether a microwave-reactive composition is required, the fabrics
of
the invention are capable of being heated to a temperature of at least about
60 C
by microwave radiation in a microwave oven. The microwave oven may operate
at any frequency and at any microwave power setting. Most preferably, fabrics
of
the invention are capable of being heated in a microwave oven to 200 F (93.3
C)
or greater within three minutes.
The following non-limiting examples serve to illustrate the invention.
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EXAMPLES 1-6 (COMPAR.ATIVE)
Microwave heating trials were conducted on Spectra Shielde ("SS") non-woven
fabric samples formed with Spectra fibers (1300-denier, type 1000), and
KRATON styrene-isoprene-styrene (SIS) polymeric matrix resin (KRATON
D-1161: 40 wt. % supplied solids, diluted to 16 wt. % solids content applied
onto
fabric) or SANCURE 12929 polyurethane matrix resin (commercially available
from Noveon, Inc. of Cleveland, Ohio, a subsidiary of the Lubrizol
Corporation).
In each case, the samples were made with 20 2 wt. % resin content, and had a
non-woven, cross-plied Spectra Shield material (0 , 90 construction).
Ten test coupons (2" x 2") (5.08 cm x 5.08 cm) each including two 0 /90 cross-
plied and consolidated plies, were cut from each sample, stacked and exposed
to
different levels of microwave energy for various durations using a standard
2.45
GHz, 1500 watt home microwave oven. The temperature of the fabric upon
heating was measured. The results are summarized in Table lA.
TABLE 1 A
EXAMPLE Polymeric Matrix Microwave Microwave Highest
(Comparative) Composition Power %) Time (min) Temp ( F
I Kraton SIS Rubber 70 1 113 45 C)
2 Kraton SIS Rubber 70 2 113 45 C
3 Kraton SIS Rubber 70 5 113 (45 C
4 Kraton SIS Rubber 100 1 113 (45 C)
5 Kraton(t SIS Rubber 100 2 113 (45 C)
6 Kraton SIS Rubber 100 5 113 (45 C)
In each of Examples 1-6, the KRA.TON polymeric matrix material failed to
reach a temperature of about 113 F when subjected to microwave radiation at
the
specified conditions, much lower than the softening point of the KRATON
polymer. Accordingly, K.RATON polymer alone is insufficiently microwave
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absorbent to generate the minimum amount of heat required for molding of
Spectra Shield material.
EXAMPLES 7-10
Microwave heating trials were conducted on Spectra Shield ("SS") material,
non-woven fabric samples formed with Spectra fibers (1300-denier, type 1000)
and SANCURE 12929 polyurethane matrix resin (commercially available from
Noveon, Inc. of Cleveland, Ohio, a subsidiary of the Lubrizol Corporation). In
each case, the samples were made with 20f2 wt. % resin content, and had a non-
woven, cross-plied Spectra Shield (0 ,90 ) construction.
Ten test coupons (2" x 2") (5.08 cm x 5.08 cm) each including two 0 /90 cross-
plied and consolidated plies, were cut from each sample, stacked and exposed
to
different levels of microwave energy for various durations using a standard
2.45
GHz, 1500 watt home microwave oven. The temperature of the fabric upon
heating was measured. The results are summarized in Table 1 B.
TABLE 1 B
EXAMPLE Polymeric Matrix Microwave Microwave Highest
Composition Power % Time min Tem F)
7 Sancure 12929 70 1 175 (79.44 C)
8 Sancure 12929 70 2 213 (100.6 C)
9 Sancure 12929 100 1 213 (100.60C
10 Sancure 12929 100 2 213 (100.60C
The above Examples show that Sancure 12929 polymeric matrix resin provides
the microwave heating capability to Spectra Shield for pre-heating.
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EXAMPLES 11-16 (COMPARATIVE)
Similar to Examples 1-10, microwave heating trials were conducted on Spectra
Shield non-woven fabric samples formed with Spectra(t fiber (1300-denier,
type 1000) and Good-Rite SB-1168 styrene-butadiene-styrene (SBS) rubber
polymeric matrix resin (commercially available from Noveon, Inc. of Cleveland,
Ohio). In each case, samples were made with 20 2 wt. % resin content, and had
a
non-woven, cross-plied Spectra Shield (0 , 90 ) construction.
Ten test coupons (2" x 2") (5.08 cm x 5.08 cm) each including two 0 /90 cross-
plied and consolidated plies, were cut from each sample, stacked and exposed
to
different levels of microwave energy for various durations using a standard
2.45
GHz, 1500 watt home microwave oven. The temperature of the fabric upon
heating was measured. The results are summarized in Table 2.
TABLE 2
EXAMPLE Polymeric Matrix Microwave Microwave Highest Temp
(Com arative Composition Power (%) Time (min Melted (F)
11 Good-Rite SB-1168 70 1 113 (45 C)
SBS Rubber
12 Good-Rite SB-1168 70 2 113 (45 C)
SBS Rubber
13 Good-Rite SB-1168 70 5 113 (45 C)
SBS Rubber
14 Good-Rite SB-1168 100 1 113 (45 C)
SBS Rubber
15 Good-Rite SB-1168 100 2 113 (45 C)
SBS Rubber
16 Good-Rite SB-1168 t00 5 113 (45 C)
SBS Rubber
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The above Examples show that Good-Rite SB-1168 SBS Rubber polymeric
matrix resin does not provide a microwave heating capability to Spectra Shield
for pre-heating.
EXAMPLES 17-32
Similar to Examples 1-16, microwave heating trials were conducted on Spectra
Shield non-woven fabric samples formed with Spectra fiber (1300-denier,
type 1000) and various polymeric matrix polymers. In each case, samples were
made with 20 2 wt. % resin content, and had a non-woven, cross-plied Spectra
Shield material (0 , 90 construction).
The tested polymeric matrix polymers were:
Example 17: Airflex 4500, an amide-modified ethylene-vinyl chloride
copolymer available from Air Products and Chemicals, Inc.
Example 18: PermaxTM 230, a polyurethane resin available from Noveon, Inc.
Example 19: Hycar 26523, an acrylic available from Noveon, Inc.
Example 20: Hycar 26-1475, an acrylic available from Noveon, Inc.
Example 21: Hycarg 26-1199, an acrylic available from Noveon, Inc.
Example 22: Sancureg 20023, a polyurethane resin available from Noveon,
Inc.
Example 23: Good-Ritet SB-1168, a carboxyl-modified styrene-butadiene-
styrene copolymer available from Noveon, Inc.
Example 24: Daran SL112, a PVdC polymer available from W. R. Grace & Co.
Example 25: PermaxTM 803, an acrylic-PVdC copolymer available from Noveon,
Inc.
Example 26: Sancure 777, a polyurethane resin available from Noveon, Inc.
Example 27: Sancure 843, a polyurethane resin available from Noveon, Inc.
Example 28: Dispercoll U53, a polyurethane resin available from Bayer AG.
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Example 29: Vycar 460X25 1, a PVC copolymer available from Noveon, Inc.
Example 30: Sancure 20025, a polyurethane resin available from Noveon, Inc.
Example 31: Butvar RS-261, a polyvinylbutyral available from Solutia, Inc.
Example 32: Sancurel) 2026, a polyurethane resin available from Noveon, Inc.
Ten test coupons (2" x 2") (5.08 cm x 5.08 cm) each including two 0 /90 cross-
plied and consolidated plies, were cut from each sample, stacked and exposed
to
microwave energy for 60 seconds using a standard 2.45 GHz home microwave
oven at 50% power. The highest fabric temperature after being microwaved for
one minute was measured, the temperature reached after one minute in a
microwave following forced drying in a conventional oven was measured, and the
time to reach 175 F in a 2.45 GHz microwave oven at 50% power was estimated
for each sample. The results are summarized in Table 3. In column 4, rows with
a dash indicates that the highest fabric temperature after 1 minute in the
microwave was not measured.
For each of the examples, prior to subjecting samples to microwave radiation,
the
samples were heated in an oven to remove any water or other volatile
components
in the resin dispersion. The samples were initially dried in an oven at 150 F
(65.56 C) for five days. Once microwave testing commenced, some samples
popped indicating the presence of residual water or other volatiles. These
samples were then placed back into the oven for another five days at 200 F
(93.33
C) to complete the removal of any water and/or volatiles.
For each of the examples, the response to microwave radiation was evaluated
according to the following procedures:
1. A circular 1" (2.54 cm) thick section of STYROFOAMTM was placed onto the
carousel of a 1500 watt residential-use microwave oven. This
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STYROFOAMTM was used to isolate any heat generated by the sample under
evaluation from any heat generated by the ceramic carousel plate.
2. Four samples of the material being evaluated were placed onto the
STYROFOAMTM section. These samples were placed towards the edge of the
STYROFOAMTM at the 12:00, 3:00, 6:00 and 9:00 positions. The four
samples were spaced 3" (7.62 cm) from each other.
3. Next, Tempilstik temperature indicators, manufactured by Illinois Tool
Works Inc. of Illinois, were used to evaluate temperature thresholds.
4. The desired temperature ranges were tested using two Tempilstik crayons
with
temperature ratings below the targeted temperature and two crayons with
activation ranges above the targeted temperature.
5. Using an indelible pen, each of the four samples of consolidated fabric
were
marked with one of the four temperatures. Shavings were scraped from one of
the crayons onto the fabric sample that has the appropriate temperature
writing on its surface. This was also done with the other three crayons and
the
other three samples.
6. The microwave oven was closed, set to the desired power level, a duration
time was set and the microwave heating was initiated.
7. Thereafter, it was determined which of the waxes melted onto the surface of
the fabric sample.
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TABLE 3
EXAMPLE Polymeric Heated Highest Temp. Estimated
Matrix To 175 F Fabric Reached In Time To
Composition Or Above Temperature Microwave Reach
After One After One After Drying 175 F In
Minute In Minute In In A Microwave
Microwave Microwave Conventional (sec)
( F Oven ( F)
23 Airflex Yes - 175+ 30
4500
24 PermaxTM Yes - 175+ 20
230
25 Hycar No - 125-150 N/A
26523
26 Hycar No 113 <125 N/A
26-1475
27 Hycar Yes 175+ 175+ 45
26-1199
28 Sancure Yes - 175+ 30
20023
29 Good-Rite No 113 <125 N/A
SB-1168
30 Daran Yes 175+ 175+ 44
SLI12
31 Perm,axTM No - <125 N/A
803
32 Sancure(t Yes 175+ 175+ 19
777
33 Sancure Yes 175+ 175+ 30
843
34 Dispercollg Yes 175+ 175+ 25
U53
34
CA 02669761 2009-05-15
WO 2008/140567 PCT/US2007/084531
35 Vycar Yes 175+ 175+ 40
460X251
36 Sancure Yes - 175+ 27
20025
37 Butvar Yes 175+ 175+ 45
RS-261
38 Sancure Yes - 175+ 5
2026
All of the polymeric matrix resins tested in Examples 7-38 were water-based
resin
dispersions. Some were successful and others were unsuccessful at absorbing
microwave radiation. The Kraton D- 1161 resin tested in Examples 1-6 was a
solvent-based resin and was unsuccessful at absorbing microwave radiation.
However, it is expected that other solvent-based resins would be successful,
and it
is not expected that an aqueous polymeric matrix composition is required.
While the present invention has been particularly shown and described with
reference to preferred embodiments, it will be readily appreciated by those of
ordinary skill in the art that various changes and modifications may be made
without departing from the spirit and scope of the invention. It is intended
that
the claims be interpreted to cover the disclosed embodiment, those
alternatives
which have been discussed above and all equivalents thereto.
