Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Infra-Red Reflective Coverings
FIELD OF THE INVENTION
~ This invention relates to ele_~ùnnagnetic reflective and l,dns",issive
materiais and to the use of the ",alerials as electromagnetic camoufbge
particularly at infra-red wave'enyU,s.
BACKGROUND OF THE INVENTION
Instnuments which detect ll,e""al rddialion are well known. Ra~i~tion
from the human body or other objects can easily be de~cted by infra-red
detecting instruments.
These instruments operate in the al",ospheric lranspa,ency windows of
3 to 5 mic,u"~eters and 8 to 12 micrullleters. Infra-red imaging atwavelengths
outside of these windows is not prd- Ucdl due to dl-"ospheric absorption. In
images obtained with these devices objects with high emissivities and or
objects having a higher temperature relative to the background appear as
bright silhouettes. This is due to the emitted power of these objects. The
emitted power is described by the equ~tion:
W = ~T~
where W = emitted power in BTU/hr.-ft.2 ~ = emissivity ~s = the Stephan-
Bolk-"a" con~ldr,l and T = tei~Iperdl-Jre in degrees Rankine.
From this e~uation it can be seen that there are two ~os .ible approaches
to subdue a U ,e""al image; use low emissivity i"ateri ~ s on the exterior
surface or reduce the exterior surface temperature. The typical approach is to
use low emissivity Illdtel idlS on the exterior surface and then cover the low
emissivity surface with materials which are l.dnspa,t n~ in infrared (IR)
wavelengths but optically opaque to provide visual camouflage. The second
approach is to use ll,e"nal insulation to reduce the e~tenor surface
temperature. A third approach is a CG"~ ~ . ,alion of these methods.
It has long been a desi, ~le goal to develop materials that protect
persons or equipment from dete. Uon by elecl.c""agnetic and esperial~y infra-
red detecting equipment without detracting from the mobility of the personnel
or equipment.
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For example. U.S. Patent 5 281 460 provides a pattem of strips attached
to a porous nylon mesh. The strips are coated with silver copper or pigment.
lJ.S. Patent 4 495 239 employs a base layer of textile fabric having a
vapor deposited metallic reflecting layer on it followed by a camouflage paint.
U.S. Patent 4 659 602 employs a woven material that has a metal foil on
it and a polyethylene sheet containing a conductive partic~ ~~ste.
In U.S. Patent 4 621 012 a textile is coated with a ll,e""opl~slic that has
selected dipole material in it and which has a metallic layer to reflect infra-red.
U.S. Patent 4 467 005 employs a support netting that a carrier web on
each side having an IR reflecting metal coating. The malerial is water vapor
permeable.
U.S. Patent 4 533 591 provides a thermopl~slic resin having disc,t"e
ele~l,o,naynetically pailicles cJispe,~ad in it.
U.S. Patent 4 064 305 provides a knit fomled of strands of
noncontinuous polymeric fibers and nonconl;n.Jous metal fibers which reflect
radar waves.
U.S. patent 4 529 633 teaches an GIE~ l,ur,~agnetic ~lle~ ~ing material
made of a layer of polyethylene a layer of a metal coating an adhesive and a
fabric.
Because of the presence of plastic layers the co",posilions of the
patents do not allow water vapor to escape easily and when wom as
garments are uncomrol i le or when draped over equipment cause sweating
of the aquipment.
An sxceplion is U.S. Patent 4 467 005 which claims water-vapor
permeability but not air permeability. To a person skilled in the art it would be
readily apparent that the te-_l ,n ~ e described to acl ..9ve water vapor
permeability and wdlel~ r~,or"ess would not result in a sufficiently high water
vapor permeability to be of any practical value. Any improvements in water
vapor permeability would result in a con~po,)ding reduotion in
30 walel~,roor.,ess. The ",alelials descnbed in the aro,e-"anlioned patent
provide a salisraclùry surface for metallizatlon and are acceFta~lo for uses
where a high degree of flexibility and mobility are not required such as a
covering for slalionary lo~ ~ ~s but many disad\dnlagas surface when these
materials are used to provide thermal imaging p,utecliûn for an individual
35 person. Chief among these disadvantages are the lack of drape low moisture
vapor permeability and weight. In addilion to the drort,l"entioned
disadvantages the metallized surface is on the exterior of the la", ~dleS where
it is in a position to be damaged or scraped off while moving through brush. It
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is desirable from a physic'~gi~l standpoint to reduce the heat stress of the
person wearing IR camouflage gamlents to the largest extent possible. This
can be accomplished by increasing the evaporali~/e cooling of the body by
allowing moisture vapor to easily permeate through the lami.)a~, and by
5 reducing weight and thickness of the total thermal camouflage package.
SUMMARY OF THE INVENTION
The object of this invention is to provide thermal image masking or
10 suppression in the mid and far infra-red region without coi"pr~.",;sing the
effectiveness of visual and near IR camouflage or co",fc,l level, or the
effectiveness, and mobility of a person. This objective is ach--eved by
inco".ordli"g a met~ ed microporous membrane into a typical article of
clothing or covering, such as tenbng, which suppresses themmal imaging of
15 objects underneath or behind the metallized membrdne.
Specifically the invention is directed to an air peu n ~ ~ t l ~, moisture vaportransmissive, waterproof, drapable heat reflecting material consisting
essentially of at least one metallized microporous me",b,dne laminated to at
least one other layer or textile backing material such as woven, nonwoven or
20 kniKed polyamides, polyolefins, polyester, cotton, silk, etc. or additional
microporous layers, in which the metal in the metallized menJbrane forms a
discontinuous layer on the surface and on the pore walls adjacent the surface
of the ~"ic,~porous me"~brdne.
BRIEF DESCRIPTION OF THE DRl~WINGS
Figures 1a and 1b are cutaway side views of "~.- oporous membrane
used in the invention which depicts how the metal layer can be discontinuous
but sti!l provide an effective barrier to heat l,ana",ission.
Figure 2 is a side view of the metallized ",ai"brd,)e laminated to a
backing material.
DET~ILED DESCRIPTION OF THE INVENTION
Referring to Figure 1a, an enlaryed side cutaway view of a "~.c opor~us
membrane 10 is shown with polymer sheet 11 having irregularly shaped pores
12 running through it from side to side. In Figure 1 b a vapor deposi~ed metal
13 is shown in which the metal is depo~ited from above the membrane so that
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the metal coats the surface and the "open" pore walls, i.e., that portion of thepore walls that are open as viewed from above the membrane. Thus looking
vertically down from the top in the direction of the arrow it appears that the
metal has fommed continuous line-of-sight coverage. This is dep. 'ed by the
dotted lines in Figure 1 b. But from the side, it is seen that the metal coating is
discontinuous, leaving the pores open for passage of water vapor.
The use of metallized i" _ uporûus films and membranes, such as
microporous polyethylene, polypropylene, polyurethane, expanded
polytetrafluoroethylene, etc. in lamination with standard bxtile fabrics
circumvents the disadvantages of the prior art for several reasons. First, the
three dimensional nature of the microporous materials provides for 100% line
of sight metal coverage on the surface as viewed from above, providing the IR
reflection required for adequate thermal image suppression. Second, the
porosity in three dimensions required to allow large quantities of moisture
vapor to permeate through the composite is preserved, thus reducing heat
stress on the wearer. Third, the air entrained in the "~ pores of the
membrane reduces the membranes themmal conductivity by providing an
insulating air space. This forces more of the heat exchange between a human
body and the environment to be through evapordli./e cooling. A large portion
of the heat radiated through the microporous me",brdrle from the body is
reflected back towards the body, in tum reducing the temperature of the
exterior surface, thereby reducing the thermal image. The reflected heat is
removed through the body's natural cooling me.,l,anis"" evaporation.
Microporous materials are also lighter, more flexible and drapeable than the
materials cited in the prior art, which makes them more suit~ for clothing.
The metal used in the metallized n,i 'OpGIuUS films and membranes can
be any metal that can be vapor deposited or sputtered on the film or
membrane and produce the desired reflective effect, such as aluminum, silver,
copper, zinc, or the like.
The mat1t'i~ation is on one side only and can be acco""~' ~hed through
the use of physical vapor deposilion, e.g. sputtering, or chemical vapor
deposition. The metal coating can range from 40 to 1200 angs(,ùms in
thickness, and the mat " :~ membrane will have an optical density between 1
to 6 density units.
The met;~ ed ",-:~upo,ous film or ",e",brd.~e thickness measured as A
in Figure 1b can range from 0.001 to 0.125 inch and will vary depending on
the desired air and moisture vapor permeability. The ll ,i._l~"ess of the metal
coating is not so great as to close the pores of the "~: opor~us film or
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membrane but rather deposition takes place to the extent that the surface and
part of the pore walls are covered to form a line-of-sight coating as explained
further above with reference to Figure 1.
The textile employed should have the desired specific properties e.g. IR
5 transparency visible opacity etc.
The textile is adhered to the metallized membrane on the metal coating
side by laminating with a discontinuously applied adhesive with heat and
pressure or by direct heat fusion.
In one e,.,bo~ ent shown in Figure 2 a .n;croporuus expanded
10 polytetrafluoroethylene (ePTFE) membrane 20 is shown with metal 21 e.g.
aluminum deposited on the membrane. A textile shell material 22 such as
woven silk or nylon is laminated to the coated me---bra"e using a
.Jiscor,~i"uous polyurethane adhesive so that the metallized surface of the
' microporous membrane is facing the shell material. A liner fabric (not shown)
15 such as knitted polypropylene can be attached in the same manner as the
shell. Altemate embodiments could include multiple layers of meP~ ed
microporous membranes of the same or different chemistry addilional textile
Iayers and fusion bonding instead of adhesive bonding. In addition the textile
shell material may be coated with a topical coating of a material such as
20 barium titanate to modify its radiant ll,e"nal characteristics.
EXAMPLE 1
A n.' OpGlOUS ePTFE me~"t"a"e 0.001 inch thick of nominal .2 ~m pore
25 size obtained from W. L. Gore & Asso~ s Inc. was metallized by vapor
depositing aluminum by evapG,dtion and condensalion to an optical density of
3.0 density units (as dete""ined on a Densito-.-~ter of Tobias Assoc. Inc.
(Model TRX-N). Specifically aluminum wire was heated in an oxide crucible at
a high vacuum (2 X 10~ Torr at about 1220 ~C. The aluminum vaporized.
30 The eP'TFE me,.,brdne with a hlm backing to block entry of vapor on one side
was passed over the crucible with the bac~dng on the side away from the
crucible. Vapor from the cruicibl~a rose to form the .~iscontinuous coating on
the adjacent side of the men,brane. The coated "~e"~brdna was then wound
on a roll. After the backing was removed the aluminized ,n-- uporous
35 membrane was laminated to a 2.7 ounce/yard woven nylon taslite shell
material so that the aluminized surface is closest to the shell'material using adiscontinuously applied polyurethane adhesive. A third layer of knitted nylon
was then laminated to the non-metallized side of the ePTFE la"~;ndle.
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To test infrared image suppression, a Hughes/Texas Instruments night
vision system (dielectric volometer - Part #6245935) was used. The dielectric
volometer recorded heat emission from a human object. When the la"~inale
was placed over the object, the image of the object was sub~Le~l)t;e-"y reduced.
EXAMPLE 2
A metallized microporous ePTFE l"e",~re~ne was prepar~d as in
Example 1.
10A piece of one ounce per square yard China silk was placed on a 6 X 9
inch rubber pad. A 6 X 9 inch piece of fusible open, nonwoven adhesive such
as Spunfab #EV3014 was placed over the silk. A piece of the metallized film
was placed over the adhesive layer with the metal side fadng the adhesive.
This rubber pad/silk/adhesive/metallized me",~rdne comhine~lion was placed in
15a press heated to 123~C. The press was closed and pressurized to 2000 PSI
for 10 seconds. The laminated sa",~'ss were then removed. IR image
suppression properties were determined as in Example 1. The image was
substantially reduced.
