Note: Descriptions are shown in the official language in which they were submitted.
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INSECT-REPELLANT FABRICS AND METHODS FOR MAKING THEM
BACKGROUND
[0001] Many occupations (including, but not limited to, industrial (e.g.,
utility workers,
petrochemical workers, etc.), military, rescue, firefighting, construction,
and landscaping) require
that time be spent in outdoor environments. In many instances, these
environments are populated
by a variety of insects. Many of these insects, such as mosquitoes and ticks,
can bite, sting, or
otherwise make undesirable contact with people. Although some insects are
merely a nuisance,
other insects can carry diseases, viruses, or other maladies that may be
transmitted through biting
or other contact with the person. For example, mosquitoes have been known to
carry the West
Nile virus, malaria, yellow fever, dengue fever, encephalitis, and other
maladies. In addition,
ticks can carry Lyme disease. Other insects can carry other serious diseases
or maladies, and have
been known to bite humans or otherwise transmit such diseases through biting
or other types of
contact.
[0002] Insect bites can sometimes be avoided by staying indoors or avoiding
certain
geographical areas. These alternatives may not always be available, however,
when the person is
required by their job duties to spend extended periods of time outdoors. In
these cases, a person
can reduce the possibility or frequency of insect bites by applying a topical
insect repellent to his
or her skin. Although topical insect repellents can reduce the likelihood or
frequency of insect
bites, insects may still bite the person through a garment, such as a shirt or
relatively thin jacket,
that is being worn on the person's body.
[0003] Sometimes people's occupations not only require them to spend time
in outside
environments, but also expose them to the threat of fire. For example,
industrial workers, military
and rescue personnel, and firefighters all work in outside environments that
can expose them to
flames and other heat sources. In these cases, it may be desirable to provide
an insect repellent
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garment that is flame resistant or flame retardant. It is conceivable to
impart insect repellent
properties to a flame resistant garment by spraying a commercial insect
repellant onto the
otherwise flame resistant material. This method of treatment, however, causes
the treated
garment to burn because the applied insect repellant impairs the material's
flame resistant
properties. Moreover, the insect repellant washes off the garment after the
garment has been
laundered or worn for an amount of time. It is therefore desirable to provide
a garment having
both flame resistant and insect repellant properties, whereby the insect
repellency does not impair
the flame resistance, and the garment does not lose effectiveness of either
property upon
laundering of the gannent.
[0004] In view of the above, it would be desirable to produce garments that
repel insects.
[0005] It would also be desirable to produce garments with both insect
repellant and flame
retardant or flame resistant properties.
[0006] It would also be desirable to produce garments that can be laundered
without losing
their insect repellant and flame retardant or flame resistant properties.
SUMMARY OF THE INVENTION
[0007] The above mentioned objectives are accomplished by embodiments of
the present
invention. One embodiment comprises fabrics treated with at least one insect
repellant, wherein
the insect repellant is absorbed, imbibed, or otherwise taken into and locked
in the fibers. Over
time, the insect repellent molecules are slowly released to the surface of the
fibers where they act
as a repellent to insects. While these fabrics repel insects, they can be
laundered without losing
their insect repellant properties.
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[0008] In another embodiment, the fabrics treated with at least one insect
repellant further
comprise at least some fibers having flame resistant properties. These fabrics
repel insects while
maintaining their flame resistant properties and can be laundered without
losing their insect
repellant or flame resistant properties.
[0009] Another embodiment of the invention comprises a method for imparting
insect
repellant properties to fabrics such that the fabrics maintain their insect
repellant properties after
laundering.
DETAILED DESCRIPTION OF THE INVENTION
[0010] In one embodiment of the invention, a garment can comprise a shirt
that can be worn
by a user in environments where the user may encounter one or more disease-
bearing insects.
The shirt is made of material that, as described below, is treated with at
least one insect repellent.
Although a shirt is described for purposes of example, other types of garments
may benefit from
the fabrics and methods described herein. Such garments may include, but are
not limited to, one
or more of jackets, pants, coveralls, vests, and the like that are intended
for use in various
applications. Moreover, the present disclosure is not limited to garments.
More generally, the
present disclosure pertains to any fabric where insect repellency is
desirable. For example, insect
repellency is desirable in fabrics used in curtains that hang over windows or
doors, canopies that
drape over beds or other sleeping accommodations, or fabrics used to make
tents or other flexible
shelters.
[0011] In other embodiments of the invention, the garment can be
constructed from a fabric
having flame resistant properties. Such fabric may comprise inherently flame
resistant fibers,
fibers that are not inherently flame resistant but that, as fibers or yarns,
have been treated with
flame retardant chemicals, or both types of fibers. As used herein,
"inherently flame resistant
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fibers" refers to fibers that do not burn because the chemical structure of
the fiber is extremely
stable. Examples of inherently flame resistant fibers include, but are not
limited to, aramid
(aromatic polyamide), polybenzoxazole (PBO), polybenzimidazole (PBI),
melamine, polyamide,
polyimide, polyimideamide, and modacrylic fibers. Examples of non-inherently
flame resistant
fibers that may be treated with flame retardant chemicals include, but are not
limited to, cellulosic
fibers such as rayon, acetate, triacetate, and lyocell. It is to be understood
that these constructions
are mere examples and are not intended to limit the scope of the present
disclosure.
[0012] Regardless of the types of fibers from which the fabric is
constructed, it is preferable
that the insect repellent be absorbed, imbibed or otherwise taken in by at
least some of the fibers
(rather than merely applied to the surface of the fibers). In this way, the
insect repellency
properties of the fabric are better retained after repeated launderings.
[0013] Insect repellency may be imparted to the fabric (which is
preferably, but not
necessarily, also flame resistant) in a variety of ways. In one embodiment,
the insect repellent is
added to the fabric during a dyeing process or during a finishing process. In
one embodiment, the
fabric can be treated with insect repellant in a dye-bath wherein several
ingredients are mixed
together in liquid faun, and the fabric is immersed in the dye-bath. Examples
of ingredients in
the dye-bath could include any or all of: dye to color the fabric, a dye
assistant (or "carrier"), an
insect repellant, or a flame retardant additive (if applicable). Carriers aid
in the absorption of dye
into the fibers of the fabric. In some cases, the carrier may act as a natural
insect repellant, as
discussed below. Example carriers include dibutylacetamide, dibutylfounamide,
aryl ether,
isophorone, benzyl alcohol, N-cyclohexyl pyrrolidinone (CHP), and N-diethyl-m-
toluamide
("DEET"). Example insect repellents include, but are not limited to,
permethrin (such as
Evercide 2778 available from McLaughlin Gormley King Co. or Permanone 40
available from
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Bayer Environmental Science) and DEBT (available from Fisher Scientific and
from Morflex,
Inc.).
[0014] Once the dye-bath is formed, the fabric is contacted with the dye-
bath, typically by
immersion, and the dye-bath is heated to fix the dye in the fibers. During
this process, the insect
repellent, which can be in the form of the carrier or a separate chemical, is
absorbed, imbibed or
otherwise taken in by at least some of the fibers. Over time, the insect
repellent molecules are
slowly released to the surface of the fibers where they act as a repellent to
insects. It will be
obvious to one of ordinary skill in the art that dyeing need not occur during
this process. Rather,
the process may be carried out without a dye if it is desired to impart insect
repellent properties to
already-dyed or un-dyed fabrics.
[0015] Although the fabric has been described as being treated with an
insect repellant, a
flame retardant, or a combination thereof when the fabric is wholly
constructed, the treatment can
be performed during earlier stages of the process such as on the fibers, yarn,
or other fibrous
textile before it is woven or spun into wholly constructed fabric.
Additionally, a carrier can be
imbibed into the fibers during fiber production prior to treating the fibers
or the fabric constructed
therefrom. This method may be advantageous in that additional carrier may not
be needed in the
bath. Equipment for dyeing textiles includes jig dyeing machines, pad dyeing
machines, beck
dyeing machines, and jet dyeing machines.
[0016] One type of insect repellant is permethrin, which can be added to
the dye-bath in a
concentration that ranges from about 0.15% on weight of fabric ("own to about
2.80% owf.
During the dye-bath process, a carrier may be, but need not always be, used to
solubilize the
permethrin such that the permethrin may be absorbed into the fibers of the
fabric more readily.
The bath may be conducted at temperatures ranging from about 100 F to about
300 F. When the
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bath is conducted below the boiling point, which is 212 F at atmospheric
pressure, CHP or benzyl
alcohol may be particularly effective in achieving insect repellant
absorption. After the fabric has
been treated in the bath, it is removed and heated to dry the fabric. When the
fabric dries, the
fibers contract and lock the insect repellant molecules in the fiber, which
allows the insect
repellant to remain in the garment even after the garment has been laundered.
With such
concentrations, after approximately 20 launderings residual levels of
permethrin are about 0.10 ¨
1.75% owf Table I shows two specific examples of fabrics dyed in dyebaths
containing
permethrin. Fabric 1 is a 4.0 ounce per square yard (osy), 65/35 blend of
Nomex T-462 and FR
rayon, plain weave fabric, and Fabric 2 is a 6 osy, Nomex 1-462, plain weave
fabric.
TABLE I
Fabric % permethrin owf % permethrin owf % permethrin owf
after treatment after 10
launderings _ after 20 launderings
Fabric 1 0.70 0.55 0.51
Fabric 2 0.41 0.41 0.39
Amounts of insect repellant on the fabric were determined using gas
chromatography, such as the
GLC Method of Analysis for Permethrin in Technical Material and Formulations
available from
the McLaughlin Gormley King Company.
[0017] As an example, one possible test method for determining the amount
of permethrin
incorporated into the fabric uses a gas chromatograph equipped with a flame
ionization detector.
The column is 5% OV-1 on ChromosorbTM W(HP) 80/100 mesh, 120 cm x 4 mm i.d.,
glass. The
column temperature is 250 C, and the injection port and detector temperatures
are each 300 C.
Gas flows are N2 at 50 mls/min, air at 240 mls/min, and 112 at 60 mls/min. The
flame ionization
detector has a sensitivity of 5 x 10-11 AFS. The method is as follows: A
sample of permethrin in
acetone is prepared such that the amount of permethrin in the acetone is
approximately 1.0
mg/mi. A standard solution comprising 1.0 mg/ml of permethrin in acetone is
also prepared. The
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sample and standard solution each further comprise one equivalent of
diethylhexyl phthalate as an
internal standard. The sample and standard solutions are injected onto the
column. Retention
time is about 5 minutes for permethrin and about 3 minutes for diethylhexyl
phthalate. This
method does not separate the isomers of permethrin.
[0018] In an alternate embodiment, the insect repellant, such as
permethrin, is incorporated
into the fabric during a finishing process. The finishing process can occur
alternatively or in
addition to treating the fabric with an insect repellant in a dye-bath. One
such finish formulation
can contain 0.9%-6.0% on weight of bath ("owb"), 40% active permethrin. The
finish can be
applied by a finish applicator such as a Pad Roll, Kiss Roll, Knife-over roll,
or foam finish
applicator. The treated fabric can be dried in a drying oven (or tenter) at
around 250 F - 400 F
for a time sufficient to dry the fabric. When the fabric dries, the fibers
contract and lock the
insect repellant in the fiber. In an alternate embodiment, binders such as
melamine formaldehyde
resins, dimethyloldihydroxyethyleneurea (DMDHEU) resins, acrylic polymers,
polyurethane
polymers, etc. may be added to the finishing foimula to assist in maintaining
laundering
durability.
[0019] In addition to permethrin, another insect repellant that may be used
is N-diethyl-m-
toluamide ("DEBT"). As mentioned above, DEBT can also serve as a carrier
during the dyeing
process. Traditionally, carriers are removed as much as possible from the dyed
fabric because of
the flammability of the carriers. However, where DEBT is used as an insect
repellant and is
incorporated in the fabric using the dye-bath method, relatively large amounts
of DEBT can be
used so that a relatively high residual amount of DEBT remains in the fibers
after the bath is
completed. The DEBT may be added to the dye-bath in a concentration that
ranges from about 10
grams per liter (gpL) to about 60 gpL. With such concentrations, residual
levels of DEBT of
about 0.10%-1.75% owf can be achieved. Alternatively or in addition, DEBT can
be incorporated
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into the fibers during a finishing process in a manner similar to that
described above in relation to
permethrin. In such a case, the finishing formula can include DEBT in a
concentration of about
0.9%-6.0% owb.
[0020] A flame retardant compound can also be included in the dye-bath,
applied as a
finishing treatment, or otherwise incorporated into the fibers of the fabric
to enhance flame
resistance or to counteract any deleterious effects of the carrier contained
within the fibers.
Furthermore, other chemicals can be applied to the fibers (e.g., added to the
mixture) including
lubricants, wetting agents, leveling agents, and the like. Incorporating flame
retardant compound
in the fiber matrix may also enhance durability of the fibers and resulting
products.
[0021] Embodiments of this invention were tested by Insect Control &
Research of
Baltimore, Maryland in order to determine the insect repellent properties of
the fabric. The test
method used fabric samples treated with both permethrin and DEET, and further
tested the
samples both before and after laundering. The fabric was wrapped around a tube
constructed of a
screen of the type typically used as a window screen. Fabric that was not
treated with any insect
repellant was wrapped around another tube to serve as the control tube.
Volunteers then placed
their arms in the tubes, and placed their arms into cages containing 250
mosquitoes. The number
of mosquitoes on the fabric was counted after three minutes. Thereafter, the
number of
mosquitoes was counted at thirty-minute intervals until the fabric no longer
repelled mosquitoes.
The repellency of the fabric was calculated using the following equation: R =
(C ¨ T)/C * 100,
wherein R is repellency, C is the number of mosquitos that landed on the
control fabric and T is
the number of mosquitos that landed on the impregnated fabric.
[0022] Table II shows the test results for a 4.5 ounce per square yard
(osy), 65/35 blend of
Nomex T-462 and FR rayon (Fabric A) treated with 1.6% owf of permethrin. The
fabric was
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tested both before and after laundering. As can be appreciated from Table II,
markedly improved
results were achieved with the unlaundered, treated fabric as compared to the
unlaundered,
untreated fabric, with an average repellency increase of about 75% over an
eight-hour time
period. Similarly, improved results occurred for the laundered, treated fabric
as compared to the
laundered, untreated fabric, with an average repellency increase of about 38%
over a period of
approximately two hours.
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TABLE II
Exposure Number of Number Mosquitoes Number Mosquitoes Repellency
Time (Hrs.) Laundry on Control Fabric on Treated Fabric A Increase
Cycles (%)
0.5 0 102 6 94.1
1.0 0 80 5 93.8
1.5 0 47 5 89.4
2.0 0 26 7 73.1
2.5 0 16 3 81.3
3.0 0 91 19 79.1
3.5 0 49 10 79.6
4.0 0 51 11 78.4
4.5 0 37 10 73.0
5.0 0 32 13 59.4
5.5 0 41 11 73.2
6.0 0 24 11 54.2
6.5 0 44 15 65.9
7.0 0 49 12 75.5
7.5 0 46 15 67.4
8.0 0 26 12 53.8
0.5 20 15 7 53.3
1.0 20 31 12 61.3
1.5 20 19 17 10.5
2.0 20 34 25 26.5
[0023] Turning to Table III, a 4.5 osy, 65/35 blend of Nomex T-462 and FR
rayon (Fabric B)
was treated with 24% owf of DEET. A sample of the treated fabric and an
untreated sample (i.e.,
"control") of the same fabric were tested in the same manner described above.
As can be
appreciated from Table 111, markedly improved results were for the most part
achieved with the
unlaundered, treated fabric as compared to the unlaundered, untreated fabric,
with an average
repellency increase of about 46% over a two hour time period. Similarly,
improved results
occurred for the laundered, treated fabric as compared to the laundered,
untreated fabric, with an
average repellency increase of about 64% over a period of approximately two
hours.
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TABLE 111
Exposure Number of Number Number Repellency
Time (Hrs.) Laundry Cycles Mosquitoes on Mosquitoes on Increase (%)
Control Fabric Treated Fabric B
0.5 0 43 6 86.0
1.0 0 24 25 -4.2
1.5 0 45 20 55.6
2.0 0 36 19 47.2
0.5 20 52 3 94.2
1.0 20 37 14 62.2
1.5 20 38 16 57.9
2.0 20 30 17 43.3
[0024] While particular embodiments of insect-repellant fabrics for
protective garments have
been disclosed in detail in the foregoing description and drawings for
purposes of example, it will
be understood by those skilled in the art that variations and modifications
thereof can be made
without departing from the scope of the disclosure.
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