Note: Descriptions are shown in the official language in which they were submitted.
CA 02209821 1997-07-08
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LIGHTWEIGHT HARDENED PROTECTIVE
COATING AND METHOD FOR MAKING AND USING SAME
eACKGROUND OF THE INVENTION
1. Field of the In~/entiGn
The pl- s3nl i,)~ention relates paints and other ha,~ened coatings
applied to surfaces requiring eA~ptiondl protective qualities and particularly
to lightwei~ht prvte..ti~a coatin~s for vehides such as aircraft.
2. Description of Related Art
The coating of aircraft and other vehicles for decorative andlor
pl~tG- ti;c purposes is an area of conUnuing interest. Given the costs of such
vehides and their i,lherènt maintenance requir- .~,er,ts there is a de",and for
i,,,~,u~cd p~vt~5- ti~le coatings for these vehides to dec.l~se vfear, and
hopefully i"",rula the laminar flow of air and water over the vehides.
Improved laminar nOw is a major coo~,., in aircraft and water craft
applications, such as with racin~ vehides where high speeds are sought and
in tightening competitive ",a,l~ets where escalating fuel costs must be
constrained.
While there continues to be i~p~u1remanls in the pigments and
solvents used for probctive coaan~s, the availability of a highly protective
coating usually results in a weight gain for the paint product. This is a
particular worry in weight sens;t;,/a envir~r""enb such as the w"""ereial
aircraft industry where every i"~ 2se in weight tl--nslates into Jla",~t;c
i"~ _ases in fuel costs over time.
Due to the reduced coemcient of drag Expe,ienced with
totrafluoroethylene (TFE) monG..,ar or full density polytetrafluoroethylene
(PTFE) poly.--er such as PTFE pol~."ar available from E. I. duPont de
Nemours & Company. Wilmin~ton Delaware under the t~-J--",a,l~ TEFLON~
many investi~ t~,a have su~ested mixing this n~ate,ial with a variety of paints
30 and other coaffngs to reduce friction and improve protective properties. For
example, in United States Patent 4,284,668 issued August 18, 1981 to Nixon
a mixture of tetrafluorue;!~Jl~ne (TFE) ",ono",ar, a TFE dispe.~ion carrier an
abla3;Je compound and an atllo!i;Je Ji_pelaiun carrier are applied to a surface
and buffed in place to ~is ~ir~te the Ji~pe,aion carriers and poly",e.iLe the TFE
35 on the painted surface.
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A number of others have suggested suspending poly",e~ ed TFE in
paint and then apply;ng this sul,alance to the surface to be painted. For
inslance, in United States Patent 4,849,264 issued July 18, 1989, to Gira et
al., PTFE particles are suspended in an oil phase and mixed with a resin film-
5 forming paint composition. Upon arpl :~tion and curing of the resin film, theoil phase sepa,dt~s to form a protective overlayer of oil with PTFE suspended
therein. In United States Patent 5,039,745 issued August 13, 1991, to Riddle
a mixture of silicone~ resin, PTFE poly.,.er and polyun,l; ,ane polymer are
combined to produce a chemical fesialanl paint with a non-stick top layer.
One conce", with this ap,uùach is that a full density PTFE fine
powder, or dispe,~ion of the same, may fibrillate when added to a paint
mixture. This can lead to an inconsial~nl mixture of PTFE material within the
paint. In ,~sponse to this pr b'e -, is the appluacll p,uposed in United States
Patent 5,081,171 issued January 14, 1992, to Nixon. In this case, negatively
charge PTFE particles suspendad in a paint are fused to a positively cl,ar~ed
substrate.
While the various previous dt~ n.pb to combine TFE or PTFE
particles into a paint may have had some limited suc~ss, there are a number
of pre~le."s with this appruac,l,. First, as some of the above patents
recogni~e, without further process steps or other measures, discrete PTFE
particles do not readily bond to a substrate or paint layer. The inher~nt
lubricity of these particles can then result in poor adl ,esion and possible
co,.,rJro",;se of durability
Second, of even greater concem in the aircraft industry where every
measure must be employed to avoid excess weight, full density PTFE (i.e.,
with a density of about 2.2 g/cc) pr~sent~ a possibly needless weight gain for
an aircraft. As a result, even if more durable or slippery cGatings can be
applied to aircraft by inclusion of a PTFE ",at~rial, it may still be more
econG"~ic-' to forgo the improved p~pe,tics of this ,.,~erial in favor of a lighter
coating.
Accordingly, it is a primary purpose of the present invention to
provide a hard coating ~",poaition suitable for use on a variety of surfaces,
and espe~ally for use on aircraft, that is liyl ,t~,ight, durable, chemical
resistanl, and has a low cG~fri~.ient of friction.
It is a further purpose of the present invention to provide a coating
cbmpo~iticn that forms a inte.~,onne~.led polymeric net~vork when applied,
improving durability and aJhesio-, of the coating.
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It is still another purpose of the present invention to provide a coating composition
which includes an additive with a porous structure of PTFE, presenting an improved
surface for binding between paint pigments and the additive.
It is yet another purpose of the present invention to provide a method for
5 producing and using a coating material with the above properties.
These and other purposes of the present invention will become evident from
review of the following specification.
SUMMARY OF THE INVENTION
The present invention is an improved coating material for use on a variety of
suRaces and particularly for use on vehicles such as aircraft where there is a need
for a highly protective but lightweight hardened coating.
The coating material of thQpresent invention comprises a blend of csmminuted
porous expanded PTFE particles within a base paint mixture. The expanded PTFE
15 particles are evenly suspended within the base paint for application and then cured
into a cohesive protective rletworked- grid of expanded PTFE.
With a typical density of expanded PTFE of 1.8 g/cc or less, the composition of
the present invention forms a lightweight coating on the substrate, suit~le for
weight-sensitive applications such as aircraft painting. Moreover, the coating of the
20 present invention is believed to have significantly improved properties in many other
respects, including adhesion, durability, chemical resistance, ultraviolet (UV) light
resistance, and low coeffficient of friction. These properties are also sought to
improve paint quality. The cumulative effect of combining these properties creates a
paint that has enhanced wear resistance, which will thus make it suitabLe for many
25 demanding applications like use on water craft, roads or metals in corrosive
environments.
Due to the availability of expanded PTFE material and the properties of
comminuted expanded PTFE particles which allow for ease in producing and
applying the composition of the present invention, the present invention should be
30 suitable for a wide variety of applications. However, the lightweight properties of
. .
present invention makes it particularly useful for providing protective coatings on
vehicles, and especiaiiy aircraft. ~ - ~ ~
Other improved properties of coating of the present invention include: greater
resistance to heat and flames (in fact, the addition of expanded PTFE
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CA 02209821 1997-07-08
to a material increases the number of fluorine groups to the matrix thus inhibiting
combustion of the material); increased liquid repellence, both hydrophobic and
oleophobic (i.e., expanded PTFE mixed with paint tends to gravitate to the surface of
the mixture, providing a blanket layer of ePTFE, which will assist in repelling water or
other fluids having surface tension energies greater than 31 dynes/crn at 23~C as
per the MTCC 118-1983 Oil Repellency Test); improved resistance to steam and
other gaseous mixtures; increased insulating properties; enhanced chip resistance
capability over paint doped with standard PTFE since the ePTFE particles bond
better in the paint due to their inherent morphology; improved abrasion resistance;
10 when loaded with large expanded PTFE particles, improved durable non-slip surface
properties; resistance to flex and thermal expansion avoiding cracking and
fractures; and enhanced ability to bond to other desirable materials oF active agents,
such as anti-fungal, anti-bacterial, or anti-fouling agents, pigments (e.g., fluorescent
pigments), radar absorbing materials, radar reflecting materials, etc.
DESCRIPTION OF THE DRAWINGS
The operation of the present invention should become apparent from the
following description when considered in conjunction with the accompanying
drawings, in which:
Figure 1 is a graph plotting the average particle sizes of comminuted expanded
PTFE particles generated for use with the present invention, the graph comprising
the cumulative volume and differential volume;
Figure 2 (plate 82) is a scanning electron micrograph (SEM) of a surface of a
coating of the present invention, enlarged 100 times;
Figure 3 (plate 80) is a SEM of the surface shown in Figure 2, enlarged 500
times;
Figure 4 (plate 88) is a SEM of filings scraped off the surface of a cured
coating of the present invention to show its cross-section, enlarged 100 times;
Figure 5 (plate 86) is a SEM of filings scraped off the surface of a cured
30 coating of the presen~ invention, enlarged 500 times;
Figure 6 (plate 91 ) is a SEM of filings scraped off the surface of a cured
coating of the present invention, enlarged 5000 times.
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DETAILED DESCRIPTION OF THE INVENTION
The present invention comprises a coating material which is applied to a
substrate and hardened in place to form a relatively lightweight and durable
protective finish on the substrate. The present invention provides numerous
5 improved properties, including serving as a vehicle for other agents.
Many improved properties can be imparted to polytetrafluoroethylene (PTFE)
by heating and rapidly expanding the PTFE in one or more directions. By forming a
network of polymeric nodes interconnected by fibrils, the PTFE experiences little
decrease in its overall volume, but undergoes a dramatic decrease in its density in
10 this process. As a result, a microporous structure is created that has numerous
unique properties, including low density, porosity, increased tensile strength, and
increased resistance to creep. Such a product can be produced in a known manner,- ~ such as in accordance with the teachings of United States Patent 3,953,566 issued
April 27, 1976, to Gore. ~enerally, this material has a density of less than 2.0 g/cc,
15 and preferably a density of 0.9 to 1.8 g/cc.
The coating compositiori of the present invention comprises a blend of a
conventional paint mixture and comminuted particles of expanded
polytetrafluoroethylene (PTFE). The expanded PTFE comprises a fine powder grind
of expanded PTFE with an average particle size of about 5 to 100 micrometers, a
20 particle size of less than about 40 micrometers being preferred. The expandedPTFE particles and the paint mixture are agitated together to form an even
suspension of the expanded PTFE particles within the paint mixture.
While the expanded PTFE particles can be generated in any known manner, it
is preferred to form these particles by the following procedure:
1. Initially reducing the size of the expanded-PTFE in the form of sheet goods,
- fiber etc., to a particle size of approximately 940 micrometers (20 mesh) using a
shredding type mill; ~
2. Further reducing the size of the 940 micrometers (20 mesh) material using
a modified Morehouse Super 800 series colloid mill. The Morehouse mill is modified
by securing the mill stones as is taught in U.S. Patent Number 4,841,623 James C.
Rine, incorporated by reference. -The mill stones-are ,e~tdined circumferentially as
opposed to the common axia~ mo~nting conf~uration. The circumferentially ~-~
mounting of the stones permits the stones to will,stand higher rotatior~al velocities.
- When the grinding stones rotate at the increased ~otational velocities in the colloid
mill, it is found that expanded PTFE can be sized reduced t~ a mean particle size of
40 micrometers and smaller without severe degradation to the nodal-fibril structure
inherent to the expanded PTFE material. Common size reduction techniques for
PTFE and plastics use radiation to render the material fractal to allow the material to
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O
be size reduced to particles sizes below 100 micrometers. Unfortunately, the
irradiation process destroys the nodal-fibril structure of the expanded PTFE material.
The use of the modified Morehouse Colloid mill provides an alternative to the use of
irradiation to yield particles of sized reduced PTFE and size reduced expanded
5 PTFE below 100 micrometers.
3. Adding tap water to the 940 micrometers (20 mesh) initially sized reduce
material in the hopper which feeds the colloid mill. A water and ePTFE slurry isproduced in the hopper with a concentration of water to ePTFE of 50:50. Note that
the higher the concentration of ePTFE to water is made, the better the efficiency of
10 the mill. Although there does exists a peak concentration ratio since too much
ePTFE to water will result in excessive heat build-up on the stones. The stone must
be kept cool during the milling operation. Excessive heat build-up in the stones will
- render the stone useless. The preferred water and PTFE concentration is 35~0%
PTFE to 65-60% water to allow for adequate cooling of the stones. The size
15 reduced material exits the mill as a slurry.
4. Placing the slurry material on flat aluminum pans in a forced air convection
oven at a temperature of 105 to 150~ C until the water evaporates. This produces a
cake-like material.
5. Removing the pans from the oven and fracturing the cake-like material by
20 blending the material using a standard household food blender or simply by shaking
it in a closed container.
The graph of Figure 1 illustrates a typical range of particle sizes of expanded
PTFE generated through the above procedure. Curve 10 represents the cumulative
25 volume; the bar graphs 12 represent the differential volume. The graph indicates
that the greatest quantity of pa,li.'os (i.e., 50%) produced in this manner are
between 17 to 50 ",icro",eters. To acquire particular particle sizes for use with the
present invention, the ground expanded PTFE material can be separated in any
known manner, such as through screening, thermal air separation, floatation,
30 cyclone rill,ation and cyclone separation, also possibly fluid bed separation.
Preferably the pa, licles are separated through the process of a thermal air separator.
Comminuted expanded PTFE particles- are the preferred matèrial for use in the
present invention for a couple of reàsons. First,- in addilion to ~ow density, with a
typical density of less than 1.8 g/cc, an ek,uanded PTFE fiber can have a very high
35 matrix tensile strength when compared to standard PTFE. For example, a
conventional PTFE particle may have a matrix tensile strength of 211 Kg/sq cm
(3000 psi). By contrast, a comminuted particle of expanded PTFE made from a fiber
stretched with a ratio of 80:1 will have a matrix tensile strength of about 7030 Kg/sq
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cm (100,000 psi). In this context, tensile strength is determined in accordance with
ASTM D-882 (Tensile Properties of Thin Plastic Sheeting) using an INSTRON
Tensile Tester Model 1130 outfitted with clamping jaws suitable fomest,aining sheet
goods. This machine is available from INSTRON Machine of Canton, MA. The
5 tensile strength was determined using sheet goods of expanded PTFE. It is thought
that the material is isotropic.
Depending upon the paint mixtures used and the properties desired, the
particles can be mixed in virtually any proportion, with the understanding that
excessive loading of expanded PTFE particles can lead to an uneven painted
10 surface and, in extreme, possible compromise of adhesion. A proportion of
expanded PTFE in the final composition of 1/8% to 25% by weight is considered
appropriate for most ~pplications. For use as an aircraft or water craft paint, where a
smooth, gloss finish is often desired, the expanded PTFE preferably comprises
, .
'10% by weight of the final blended composition.
The blending of the paint and expanded PTFE is preferably performed using
mechanical agitation, such as~through use of a magnetic stirrer or for more viscous
matter, an electrical lab propeller. This step is performed by slowly adding theground ePTFE particles into the agitated beaker containing the paint. A vibrating
sifter or other powder dispensing device should be used to dispense the co"~",inuted
20 ePTFE material into the container holding the paint. Other suit~'e mixing processes
may include wetting out of the comminuted expanded PTFE with a solvent, such as
isopropyl alcohol (IPA), and suLjecli"g the mixture to ultrasonic agitation, such as
through the use of an ultrasonic horn submerged in a beaker containing the IPA and
then slowly adding the comminuted ePTFE into the beaker using any suitable
25 powder dispensing device or appardtus. Other potential mixing apparatus may
include a mechanical vibrdting table, or a shaker table.
For use with oil-based paint mixtures which are "filmogen" (i.e., film-forming
material or binder), such as vegetable oil, linseed oil, and oleoresinous varnish, the
expanded PTFE may become suspended through mere agitation. However, with
30 most paints, such as water based latex paints (e.g., acrylic, butadiene-styrene,
polyvinylacetate), the hydrophobic nature of expanded PTFE may require the
introduction of a wetting agent, such as a hydrophilic surface coating of
SPECTRACOTE (polyuretl,ane coating) from Flexible Products Company of
Marietta, Georgia, or a surfactant of TRITON X100 from Rohm & Haas or OP10 from
35 ICI, Inc. These materials should be mixed such that the surfactants are less than
3% of the total liquid volume.
Once the final composition is formed in the above manner, it is readily applied
to a substrate through any conventional manner, including but not limited to use of
. .
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CA 0220982l l997-07-08
8 , ' ~ , ~' ' ' '- --.
brushes or other mechanical applicators, spraying equipment, and pad printing.
Once applied, the composition will dry and cure in accordance with the
properties of the paint mixture used. Unlike previous attempts to mix a full density
PTFE or similar material with a paint, the expanded PTFE particles, which are pre-
fibrillated, are believed to form a stronger interlocking grid network within the
hardened paint surface without requiring any further treatment. It is anticipated that
this network will serve both to improve the interface between the expanded PTFE
and the paint pigment and to provide a stronger and more durable finish to the
coating.
Another important property of the expanded PTFE particles is that their
microporous structure and randomized surfaces provide an excellent surface to
which paint pigment can bond. As a result, a far stronger and more cohesive coating
can be provided than is possible with existing fully densified fluorinated paints. In
light of these advantages, it is believed that the preferred size for the ePTFE particle
15 is greater than 5 microns to assure sufficient porosity of the particles.
Without intending to limit the scope of the present invention, the following
examples serve to illustrate how the present invention can be made and used.
EXAMPLE 1:
A comminuted expanded PTFE was produced from unsintered expanded
PTFE material by grinding it using a Morehouse Super 800 series colloid mill. The
Morehouse mill was modified by securing the mill stones as is taught in U.S. Patent
Number 4,841,623 James C. Rine. The 940 micrometers (20 mesh) material was
further size reduced using a modified Morehouse Super 800 series colloid mill. The
25 milling apparatus was equipped with 90 grit stones. The mean particle size of the
comminuted material was about 45 micrometers.
The expanded PTFE material used in this context comprised of 1/2 inch (12.7
mm) diameter PTFE cord material which was expanded 8:1 times longitudinally in
accordance to U.S. Patent No. 3,953,566. This material is commercial expanded
30 PTFE joint sealant material without the adhesive strip and is available from W. L.
Gore & Associates, Inc., Elkton, MD, under the trademark GORE-TEX~). The
expanded beading was then shredded to a mean particle size of approximately 500-700 micrometer using a shredder from Cumberland, Inc. The shredded flake
material was further size reduced using a Morehouse colloid mill which was modified
35 as described above in accordance to U.S. Patent No. 4,841,623. The modification to
the mill involved restraining the stones around the circumference of the mill stones
as opposed to restraining the stones axially, as is commonly done. This novel
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., , . ~,
9 , ~
... .. .. ..
restraining configuration permits the stones to rotate at a greater velocity without
destroying the stones due to centrifugal forces.
One g of comminuted expanded PTFE was added to 10 g of AWL-CAT #2
G3010 (92-C-39) thinner available from U.S. Paint Corporation, Inc. of St. Louis,
5 Missouri. This thinner comprises xylene, toluene, ethyl acetate, cellulose acetate
and aliphatic polyisocyanate. The expanded PTFE particles and thinner were
agitated togéther by hand with a glass stirring rod. The expanded PTFE material
easily wetted-out to produce a homogenous suspension.
Next, 10 g of pigmented polymer were added to the suspension while stirring
10 continued with the glass rod. The pigmented polymer comprised a glossy black G-
2001 Alumi-Grip Linear Polyurethane topcoat paint available from U.S. Paint
Corporation, Inc. of St. Louis, Missouri. This is a common high gloss paint
comprising a base urethane polymer, which is frequently employed for coating
aircraft and race cars. An even suspension of expanded PTFE in the paint material
15 was achieved.
The mixture was then applied by natural bristle paint brush to a piece of
aluminum sheet metal of the kind used in aircraft construction. The sheet metal was
degreased with a toluene based solvent and wiped with lint-free towels. The coating
composition was allowed to cure under the following conditions: Ambient
temperature, under laboratory hood with a face velocity of 0.5 m/sec (100 ft/min) for
24 hours.
Assuming all the thinner volatized during the curing operation, the comminuted
expanded PTFE constitutes about 9.1% of the final mixture.
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The fe" / :.19 results were observed: the mixture easily ~leased
from the paint brush onto the sheet mebl surface. I lo~ cr, brush strokes
were eYident in the final coated product since the paint failed to level
sumciently during curing. The cured surface was somewhat rough and dull in
appea~nca, a suitable finish for water craft deck use, aircraft step areas, and
similar env;.o"",~nts where traction may be desired.
To test the durability of this surface, after the coating had completely
cured for 24 hours, app,uxi,,,alely 1.0 ml of a test solvent was applied to the
painted surface. The solvent cG",p,ised an aircraft hydraulic fluid of
tributyl~JhGsphate, dibutyl phenyl phosphate marketed by MDnsanto Company
of St. Louis, Missouri under the llaJelllalh SI~YDROL. After the fluid was left
in place for 96 hours, no appar~nl effect was observed on the painted surface.
By way of co",parison, a test area was p~pa,e:d on the same sheet
metal a~ply;ng the glossy black G-2001 Alumi-Grip Linear Poly~-,ell,ane
lopcGat paint alone. The paint applied to the surface easily and cured for 24
hours to a glossy black finish. When the hydraulic fluid was applied to the
paint for the same 96 hour period, the painted surface was severely drre.,led,
with the paint ~issolv;, .9 in the solvent, blistering from the surface, and easily
wiping off.
EXAMPLE 2:
Using the same materials, anotl.er test sample was pr~pa,ed
employing 2 9 of comminuted eA~,anded PTFE added to 10 9 of G3010
thinner. The ex~,anded PTFE particles and thinner were gently agih~ed by
hand using a glass stirring rod. Again, the ePTFE material easily wetted-out to
produce a ho",ogeneous suspension. 10 9 of G-2001 pig,.. ented polymer
were added to the suspension while sUrring the mixture with a glass stirring
rod.
The mixture was then applied to the aircraft sheet metal using a
natural bristle paint brush. Assuming 100YO of the thinner is vol t;~ed during
30 the curing operation, the comminuted ex~,anded PTFE constitutes about
16.6% of the final coating.
In this i"slance the mixture easily l~ilcased from the paint brush onto
the sheet metal surface. Similar to Example 1, bNsh strokes were pr~senl in
the fnal coating bec~use the paint did not fully level before curing. The cured
35 surface was more rough and dull in appea,~nce than the surface of produced
in ac~rJance with Example 1.
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When the hydraulic fluid was placed on the surface of the paint for 96
hours, no appaf~nt effect was observed.
Both of these examples de.-,on~t~dted a number of illluG~nt
~r~.pe.ties of the ~r~Gn~ invention. First, that e~pan~ed PTFE pa~ticl2s can
S be readily mixed with solvents and paint to acl..eve an even suspension
without agglo..,or~tion of the eA~anded PTFE particles. Second, that this
suspension can be roadily applied to a sheet mebl surface and fomm a stron
~dl .esion thereto. Third, that the combination of the eApdnded PTFE particles
and the paint produce a finish which is far more chemical resistant than paint
1 0 alone.
Scanning electron mi~u~ hs (SEMs) were then taken of the
product of Example 2. These are shown in Figures 2 and 3. Figure 2, a 1 OOx
magnification of the surface of the coatin~, shows the noda~porous nature of
the coating's surface. Figure 3, a 500 magnification of the surface of the
coating, shows how the ex~anded PTFE particles are enc~ s~ ted and/or
bonded to the epoxy paint. It is in.po, ~n~ to note little shade or co. ~t,~sl
di~fcr~nce between the eA~.andad PTFE partides and the black pigment. This
is believed to indicate that the e~andad PTFE particles have been wetted out
by the pigmont.
Surface filings were s~,3ad off the test sample of Example 2 to
study the cross-section of the cured paint. SEMs of these sc~ed filings are
shown in Figures 4 through 6. Figures 5 and 6 show a defined nodal-fibril
structure in the eApanded PTFE. This structure may have resulted from the
scraping action of the test sample during sample prt,pa~aliûn. Figures 4 and 5
show pookstc of epoxy pigment, but there a~ ."s to be a di_~rupGl tionate
amount of eApandad PTFE on the surface. The in~-,ased amount of
eApanded PTFE on the surface may indicate that the eA~,anded PTF
migrates to the surface of the paint during curing rather than being a
het~n~g2neous mixture across the cross s~ction of the cured paint. This may
explain why the final coating has an e~,~.ely durable and chemically
resistant finish.
The coating of the present i,.l/ention is believed to have numerous
advantages over previous paints. First, low density e,~uandad PTFE when
blended with regular paint will reduce the total weight per gallon of the
combined mixture. Given the substantial cost of fuel, this form of weight
reduction can be a ve~y si4gnificant factor in the aircraft industry.
CA 02209821 1997-07-08
WO96n1700 P~-JI~ 9~103261
-12-
Second, as has been noted, the fibrous nature of e,~panded PTFE
creates an inlerlGcking grid network which should enhance the final codting's
tensile stlell~tll. Further, this material is far more f~.,y;~;,lg to stresses from
thermal cyding or flexing, significantly redudng ~ ~ in~ or fractures in the
S paint underthese conditions. Additionally, when co",pa~d to the sl-~cked
pattern that can occur when full density PTFE spheres are added to paint, the
grid network of expanded PTFE also creates a barrier which greatly enhances
the coat;ny's chemical ,esistance. While convenlional PTFE is UV light
resislant, it is believed that the i"terlo.,ki"g grid fommed with the present
10 invention may present an even more protective coating in this regard. Finally,
the inlerlo~i"g grid may also improve the heat nesisla.lce of the final coating.Third, the density and chemical prupc, lies of the eA~,anded PTFE
particles should cause them to gravibte toward the surface of the coating
during the curing p,ocess. When cured in this position, the ~"~t nalion of
15 eA~anded PTFE and paint binder is believed to offer a far superior barrier to wear, light dey~da~ion, and chemical attack.
Fourth, the inte,lGcking nature of the e~ande.J PTFE partides may
also allow a paint manufacturer to formulab a paint that is SIIIG~JU ,er than one
containing full densitv PTFE. This should lead to i"~pro~ed laminar flow over
20 the coated surface, and improved performance and reduced fuel consumption
in vehides.
Fifth, the eA~,anded PTFE should in~ease the flame retar~an~ of
the mixture since by the addition of PTFE to the matrix, the number of fluorine
compounds presenl are i"ueased thus lende,i"g the mixture less fla,~""able.
25 Fluorine compounds help reduce the degree of flammability of mal~,ials.
Thus, the final product is more flame r~tar~ant.
Sixth, the voids and pores of the expanded PTFE should improve the
illteilGcki"g of pigments with the eA~,andad PTFE. This is a sig"ifieanl
improvement over conventi~aal PTFE sphert,s, where only the minimal surface
30 aJl,esion of the pigments to the sphe,es can be pro~ided. This allows the
eA~.anded PTFE particles to seNe as a skeletal sponge for the paint pigments,
improving the wetting and suspension prupe,~;es of the eA~,anded PTFE
particles while producing an improved final product.
Seventh, the voids and spheres of the eApanded PTFE offer a region
35 for other materials to occupy and be placed into the paint vfh~ lg added
enhance" ,en~s to the paint. Active agents that can be in~i ~,Gra~ed into the
expanded PTFE pa.licles include: anti-fungal agents (e.g., magnesium
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borate), anti-fouling agents (e.g., metallic naphU.-.nate, mercury compounds),
i-.~e ti~id~l agents (e.g., dica"U.on, dieldrin), radar rt~ne~.ti..g medium (e.g.,
aluminum flakes), radar absorbing medium (e.g., soft ferrites), etc.
It should be evident from the above description that the p.esent
S invention has numerous properties particularly suited for use on a variety of
land, water, air, and space vehicles. In fact, the lightwei~ht nature of the
p,esent invention should be especially useful when used in all forrns of aircraft
applicaffons (e.g., conventiondl planes and hel :~pters, space vehides, etc.).
In addition to employment on vehides, it should be und6.:.tood that many of
10 the pn~p."~ies of the pr~sent invention may also be used in other areas,
including: certain machinery coatin~, such as heavy construction equipment
which is subjected to harsh en~l;,ufi,..ent~; building, and especially roof
p~te tion and roadway paint. Additionally since ePTFE is both hyd~phob.e
and o'eoFheb:~, and since the ePTFE particles Send to migrate to the surface
15 of the coating, a coating of the present im/entiûn is particularly suibble as an
improved wabr sealant or chemically ,~:sis~nt finish.
.'JlDreo~ar, as has been nobd, the e~and.,d PTFE p .ticles may
serve as a matrix or carrier for other materials. In this ".anner, various
chemical compounds may be incGI,uGrdted or ena~ps.llated in the comminuted
20 ePTFE material prior to mixing into the paint. One advantage of this ~ncept
is that materials that are resistant to mixing uniformly into a paint alone can be
suc~ssfully and unifommly in~l~GIdted throughout the paint through
di~pe,aion via the ePTFE particles.
The paint of the present im~enl;on has virtually endless possible
25 arF' ~tions. Suitable paints mixtures (e.g., oil based paints) of the pr~senl invention could be used to coat machinery, cement, asphalt, bridges,
buildings, tanks and other surfaces .,~l~osed to harsh env;.~r".,ental
conditions. Fu.llle----Gr~, the comminuted ex~,andad PTFE may mix even
more readily with oil based paints, becoming susp~nd~d through mere
30 agitation. This may make paint production easier and less e)t,uensivc.
Applications for the latex based paints, either in a standard form or which havebeen modified as to be suitable for cl~ct~ùal~tic or ele_~ ophw~:tic applications,
may be used to coat a wide variety of products, including buildings,
autu...at.'es, and other vehicles, and certain aquatic appa-d~us, etc. The
35 matenal of the pl~Sel It invention can also reduce the chance for galvanic
corrosion by minimizing the penetration through the paint of CCill05i'~ liquids,like salt water, thus stopping the electro-chemical process from ever
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beginning.
vVhile pa~ '~ embodiments of the present invention have been
illustrabd and des~.,il,ed herein, the present invention should not be limited to
such illuall~tions and des~i,~tions. It should be appare"t that changes and
5 modifications may be i, IcouJordbd and embodied as part of the present
invention within the scope of the f~IILJ~j~I9 claims.
