WO1996021700A1

WO1996021700A1 - Lightweight hardened protective coating and method for making and using same

Info

Publication number: WO1996021700A1
Application number: PCT/US1995/003261
Authority: WO
Inventors: John W. Dolan; David A. Chopko; Charles E. Singleton
Original assignee: W.L. Gore & Associates, Inc.
Priority date: 1995-01-09
Filing date: 1995-03-14
Publication date: 1996-07-18
Also published as: EP0802952A1; CA2209821A1; JPH10512312A; AU2635195A

Abstract

An improved protective coating is disclosed that hardens to form a lightweight but extremely durable finish for a variety of substrates. The preferred coating comprises a mixture of lightweight comminuted porous expanded polytetrafluoroethylene (PTFE) particles suspended within a base paint mixture. When applied to and cured on a surface, the expanded PTFE particles form an interlocking grid network within the paint which is lightweight, durable, chemical and UV light resistant, and has a low coefficient of friction. The composition of the present invention is particularly suited for applications where a durable but lightweight coating is sought, such as in the aircraft industry.

Description

.1.

LIGHTWEIGHT HARDENED PROTECTIVE COATING AND METHOD FOR MAKING AND USING SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates paints and other hardened coatings applied to surfaces requiring exceptional protective qualities, and particularly to lightweight, protective coatings for vehicles such as aircraft. 2. Description of Related Art The coating of aircraft and other vehicles for decorative and/or protective purposes is an area of continuing interest. Given the costs of such vehicles and their inherent maintenance requirements, there is a demand for improved protective coatings for these vehicles to decrease wear, and hopefully improve the laminar flow of air and water over the vehicles. Improved laminar flow is a major concern in aircraft and water craft applications, such as with racing vehicles where high speeds are sought, and in tightening competitive markets where escalating fuel costs must be constrained.

While there continues to be improvements in the pigments and solvents used for protective coatings, the availability of a highly protective coating usually results in a weight gain for the paint product. This is a particular worry in weight sensitive environments, such as the commercial aircraft industry, where every increase in weight translates into dramatic increases in fuel costs over time. Due to the reduced coefficient of drag experienced with tetrafluoroethylene (TFE) monomer or full density polytetrafluoroethylene (PTFE) polymer, such as PTFE polymer available from E. I. duPont de Nemours & Company, Wilmington, Delaware, under the trademark TEFLON®, many investigators have suggested mixing this material with a variety of paints and other coatings 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 tetrafluoroethylene (TFE) monomer, a TFE dispersion carrier, an abrasive compound and an abrasive dispersion carrier are applied to a surface and buffed in place to dissipate the dispersion carriers and polymerize the TFE on the painted surface. A number of others have suggested suspending polymerized TFE in paint and then applying this substance to the surface to be painted. For instance, 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- forming paint composition. Upon application and curing of the resin film, the oil phase separates to form a protective overiayer 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 polymer and polyurethane polymer are combined to produce a chemical resistant paint with a non-stick top layer. One concern with this approach is that a full density PTFE fine powder, or dispersion of the same, may fibrillate when added to a paint mixture. This can lead to an inconsistent mixture of PTFE material within the paint. In response to this problem is the approach proposed in United States Patent 5,081,171 issued January 14, 1992, to Nixon. In this case, negatively charge PTFE particles suspended in a paint are fused to a positively charged substrate.

While the various previous attempts to combine TFE or PTFE particles into a paint may have had some limited success, there are a number of problems with this approach. First, as some of the above patents recognize, without further process steps or other measures, discrete PTFE particles do not readily bond to a substrate or paint layer. The inherent lubricity of these particles can then result in poor adhesion and possible compromise of durability.

Second, of even greater concern 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) presents a possibly needless weight gain for an aircraft. As a result, even if more durable or slippery coatings can be applied to aircraft by inclusion of a PTFE material, it may still be more economical to forgo the improved properties of this material in favor of a lighter coating.

Accordingly, it is a primary purpose of the present invention to provide a hard coating composition suitable for use on a variety of surfaces, and especially for use on aircraft, that is lightweight, durable, chemical resistant, and has a low coefficient of friction. It is a further purpose of the present invention to provide a coating composition that forms a interconnected polymeric network when applied, improving durability and adhesion of the coating. 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 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 surfaces and particularly for use on vehicles such as aircraft where there is a need for a highly protective but lightweight hardened coating.

The preferred coating material of the present invention comprises a blend of comminuted porous expanded PTFE particles within a base paint mixture. The expanded PTFE particles are evenly suspended within the base paint for application and then cured into a cohesive protective networked 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, suitable for weight-sensitive applications such as aircraft painting. Moreover, the coating of the present invention is believed to have significantly improved properties in many other respects, including adhesion, durability, chemical resistance, ultraviolet (UV) light resistance, and low coefficient 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 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 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 especially aircraft.

Other improved properties of coating of the present invention include: greater resistance to heat and flames (in fact, the addition of expanded PTFE 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/cm at 23°C as per the AATCC 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 moφhology; improved abrasion resistance; 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 or 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 1 , 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 coating of the present 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. 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 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 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. Generally, this material has a density of less than 2.0 g/cc, and preferably a density of 0.9 to 1.8 g/cc.

The coating composition 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 microns, a particle size of less than about 40 microns being preferred. The expanded PTFE 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 from of sheet goods, fiber etc., to a particle size of approximately 20 mesh using a shredding type mill;

2. Further reducing the size of the 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, incoφorated by reference. The mill stones are restrained circumferentially as opposed to the common axial mounting configuration. The circumferentially mounting of the stones permits the stones to withstand higher rotational velocities. When the grinding stones rotate at the increased rotational velocities in the colloid mill, it is found that expanded PTFE can be sized reduced to 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 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 PTFE below 100 micro-meters.

3. Adding tap water to the 20 mesh initially sized reduce material in the hopper which feeds the colloid mill. A water and ePTFE slurry is produced 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 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 35-40% PTFE to 65-60% water to allow for adequate cooling of the stones. The size 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 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 volume; the bar graphs 12 represent the differential volume. The graph indicates that the greatest quantity of particles (i.e., 50%) produced in this manner are between 17 to 50 microns. 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, cyclone filtration and cyclone separation, also possibly fluid bed separation. Preferably the particles are separated through the process of a thermal air separator.

Comminuted expanded PTFE particles are the preferred material for use in the present invention for a couple of reasons. First, in addition to low density, with a typical density of less than 1.8 g/cc, an expanded PTFE fiber can have a very high matrix tensile strength when compared to standard PTFE. For example, a conventional PTFE particle may have a matrix tensile strength of 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 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 for restraining sheet goods. This machine is available from INSTRON Machine of Canton, MA. The 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 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 applications. 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 the ground ePTFE particles into the agitated beaker containing the paint. A vibrating sifter or other powder dispensing device should be used to dispense the comminuted ePTFE material into the container holding the paint. Other suitable mixing processes may include wetting out of the comminuted expanded PTFE with a solvent, such as isopropyl alcohol (IPA), and subjecting 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 powder dispensing device or apparatus. Other potential mixing apparatus may include a mechanical vibrating 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 most paints, such as water based latex paints (e.g., acrylic, butadiene-styrene, polyvinyiacetate), the hydrophobic nature of expanded PTFE may require the introduction of a wetting agent, such as a hydrophilic surface coating of SPECTRACOTE (polyurethane coating) from Flexible Products Company of Marietta, Georgia, or a surfactant of TRITON X100 from Rohm & Haas or OP10 from 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 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 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 20 mesh material was further size reduced using a modified Morehouse Super 800 series colloid mill. The milling apparatus was equipped with 90 grit stones. The mean particle size of the comminuted material was about 45 microns. 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 PTFE joint sealant material without the adhesive strip and is available from W. L. Gore & Associates, Inc., Eikton, MD, under the trademark GORE-TEX®. The expanded beading was then shredded to a mean particle size of approximately 500-700 micro-meter using a shredder from Cumberland, Inc. The shredded flake material was further size reduced using a Morehouse colloid mill which was modified 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 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 Coφoration, Inc. of St. Louis, Missouri. This thinner comprises xylene, toluene, ethyl acetate, cellulose acetate and aliphatic polyisocyanate. The expanded PTFE particles and thinner were agitated together 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 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 Coφoration, 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 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 100 ft/min (0.5 m/sec) for 24 hours. Assuming all the thinner volatized during the curing operation, the comminuted expanded PTFE constitutes about 9.1% of the final mixture. The following results were observed: the mixture easily released from the paint brush onto the sheet metal surface. However, brush strokes were evident in the final coated product since the paint failed to level sufficiently during curing. The cured surface was somewhat rough and dull in appearance, a suitable finish for water craft deck use, aircraft step areas, and similar environments where traction may be desired.

To test the durability of this surface, after the coating had completely cured for 24 hours, approximately 1.0 mi of a test solvent was applied to the painted surface. The solvent comprised an aircraft hydraulic fluid of tributylphosphate, dibutyl phenyl phosphate marketed by Monsanto Company of St. Louis, Missouri under the trademark SKYDROL. After the fluid was left in place for 96 hours, no apparent effect was observed on the painted surface.

By way of comparison, a test area was prepared on the same sheet metal applying the glossy black G-2001 Alumi-Grip Linear Polyurethane topcoat 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 affected, with the paint dissolving in the solvent, blistering from the surface, and easily wiping off. EXAMPLE 2:

Using the same materials, another test sample was prepared employing 2 g of comminuted expanded PTFE added to 10 g of G3010 thinner. The expanded PTFE particles and thinner were gently agitated by hand using a glass stirring rod. Again, the ePTFE material easily wetted-out to produce a homogeneous suspension. 10 g of G-2001 pigmented polymer were added to the suspension while stirring the mixture with a glass stirring rod.

The mixture was then applied to the aircraft sheet metal using a natural bristle paint brush. Assuming 100% of the thinner is volatized during the curing operation, the comminuted expanded PTFE constitutes about

16.6% of the final coating.

In this instance the mixture easily released from the paint brush onto the sheet metal surface. Similar to Example 1 , brush strokes were present in the final coating because the paint did not fully level before curing. The cured surface was more rough and dull in appearance than the surface of produced in accordance with Example 1. When the hydraulic fluid was placed on the surface of the paint for 96 hours, no apparent effect was observed.

Both of these examples demonstrated a number of important properties of the present invention. First, that expanded PTFE particles can be readily mixed with solvents and paint to achieve an even suspension without agglomeration of the expanded PTFE particles. Second, that this suspension can be readily applied to a sheet metal surface and form a strong adhesion thereto. Third, that the combination of the expanded PTFE particles and the paint produce a finish which is far more chemical resistant than paint alone.

Scanning electron micrographs (SEMs) were then taken of the product of Example 2. These are shown in Figures 2 and 3. Figure 2, a 100x magnification of the surface of the coating, shows the nodal-porous nature of the coating's surface. Figure 3, a 500x magnification of the surface of the coating, shows how the expanded PTFE particles are encapsulated and/or bonded to the epoxy paint. It is important to note little shade or contrast difference between the expanded PTFE particles and the black pigment. This is believed to indicate that the expanded PTFE particles have been wetted out by the pigment. Surface filings were scraped off the test sample of Example 2 to study the cross-section of the cured paint. SEMs of these scraped filings are shown in Figures 4 through 6. Figures 5 and 6 show a defined nodal-fibril structure in the expanded PTFE. This structure may have resulted from the scraping action of the test sample during sample preparation. Figures 4 and 5 show pockets of epoxy pigment, but there appears to be a disproportionate amount of expanded PTFE on the surface. The increased amount of expanded PTFE on the surface may indicate that the expanded PTFE migrates to the surface of the paint during curing rather than being a heterogeneous mixture across the cross-section of the cured paint. This may explain why the final coating has an extremely durable and chemically resistant finish.

The coating of the present invention is believed to have numerous advantages over previous paints. First, low density expanded 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 very significant factor in the aircraft industry. Second, as has been noted, the fibrous nature of expanded PTFE creates an interlocking grid network which should enhance the final coating's tensile strength. Further, this material is far more forgiving to stresses from thermal cycling or flexing, significantly reducing cracking or fractures in the paint under these conditions. Additionally, when compared to the stacked 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 coating's chemical resistance. While conventional PTFE is UV light resistant, it is believed that the interlocking grid formed with the present invention may present an even more protective coating in this regard. Finally, the interlocking grid may also improve the heat resistance of the final coating.

Third, the density and chemical properties of the expanded PTFE particles should cause them to gravitate toward the surface of the coating during the curing process. When cured in this position, the combination of expanded PTFE and paint binder is believed to offer a far superior barrier to wear, light degradation, and chemical attack.

Fourth, the interlocking nature of the expanded PTFE particles may also allow a paint manufacturer to formulate a paint that is smoother than one containing full density PTFE. This should lead to improved laminar flow over the coated surface, and improved performance and reduced fuel consumption in vehicles.

Fifth, the expanded PTFE should increase the flame retardancy of the mixture since by the addition of PTFE to the matrix, the number of fluorine compounds present are increased thus rendering the mixture less flammable. Fluorine compounds help reduce the degree of flammability of materials.

Thus, the final product is more flame retardant.

Sixth, the voids and pores of the expanded PTFE should improve the interlocking of pigments with the expanded PTFE. This is a significant improvement over conventional PTFE spheres, where only the minimal surface adhesion of the pigments to the spheres can be provided. This allows the expanded PTFE particles to serve as a skeletal sponge for the paint pigments, improving the wetting and suspension properties of the expanded PTFE particles while producing an improved final product.

Seventh, the voids and spheres of the expanded PTFE offer a region for other materials to occupy and be placed into the paint offering added enhancements to the paint. Active agents that can be incoφorated into the expanded PTFE particles include: anti-fungal agents (e.g., magnesium borate), anti-fouling agents (e.g., metallic naphthenate, mercury compounds), insecticidal agents (e.g., dicapthon, dieldrin), radar reflecting medium (e.g., aluminum flakes), radar absorbing medium (e.g., soft ferrites), etc.

It should be evident from the above description that the present invention has numerous properties particularly suited for use on a variety of land, water, air, and space vehicles. In fact, the lightweight nature of the present invention should be especially useful when used in all forms of aircraft applications (e.g., conventional planes and helicopters, space vehicles, etc.). In addition to employment on vehicles, it should be understood that many of the properties of the present invention may also be used in other areas, including: certain machinery coating, such as heavy construction equipment which is subjected to harsh environments; building, and especially roof protection and roadway paint. Additionally since ePTFE is both hydrophobic and oleophobic, and since the ePTFE particles tend to migrate to the surface of the coating, a coating of the present invention is particularly suitable as an improved water sealant or chemically resistant finish.

Moreover, as has been noted, the expanded PTFE particles may serve as a matrix or carrier for other materials. In this manner, various chemical compounds may be incoφorated or encapsulated in the comminuted ePTFE material prior to mixing into the paint. One advantage of this concept is that materials that are resistant to mixing uniformly into a paint alone can be successfully and uniformly incoφorated throughout the paint through dispersion via the ePTFE particles.

The paint of the present invention has virtually endless possible applications. Suitable paints mixtures (e.g., oil based paints) of the present invention could be used to coat machinery, cement, asphalt, bridges, buildings, tanks and other surfaces exposed to harsh environmental conditions. Furthermore, the comminuted expanded PTFE may mix even more readily with oil based paints, becoming suspended through mere agitation. This may make paint production easier and less expensive.

Applications for the latex based paints, either in a standard form or which have been modified as to be suitable for electrostatic or electrophoretic applications, may be used to coat a wide variety of products, including buildings, automobiles, and other vehicles, and certain aquatic apparatus, etc. The material of the present invention can also reduce the chance for galvanic corrosion by minimizing the penetration through the paint of corrosive liquids, like salt water, thus stopping the electro-chemical process from ever beginning.

While particular embodiments of the present invention have been illustrated and described herein, the present invention should not be limited to such illustrations and descriptions. It should be apparent that changes and modifications may be incoφorated and embodied as part of the present invention within the scope of the following claims.

Claims

The invention claimed is: 1. A process for applying a lightweight coating to a vehicle which comprises: providing a base paint; providing fine ground particles of expanded polytetrafluoroethylene (PTFE) with a density no greater than 1.8 g/cc; mixing the particles of expanded PTFE with the base paint to produce a mixture comprised of a base paint and a suspension of expanded PTFE particles; applying the mixture to the vehicle to provide a hardened coating thereon. 2. The process of claim 1 which further comprises comminuting the expanded PTFE particles to an average particle size of between about 5 and 100 microns. 3. The process of claim 2 which further comprises comminuting the expanded PTFE particles to an average particle size of less than about 40 microns. 4. The process of claim 1 which further comprises mixing the base paint and the expanded PTFE particles in a ratio of 0.125 to 25% by weight expanded PTFE particles. 5. The process of claim 4 which further comprises mixing the base paint and the expanded PTFE particles in a ratio of less than 10% by weight expanded PTFE particles. 6. The process of claim 1 which further comprises mixing the paint and expanded PTFE particles through agitation. 7. The process of claim 6 which further comprises wetting out the expanded PTFE with a solvent prior to applying the agitation. 8. The process of claim 1 which further comprises providing expanded PTFE particles with a matrix tensile strength of > 100,000 psi and an average particle size of about 5 to 100 microns. 9. The process of claim 1 which further comprises forming a coating on the vehicle with the expanded PTFE comprising an interlocking grid network therein. 10. A hardening coating material which comprises: a base paint; and comminuted particles of expanded polytetrafluoroethylene (PTFE), with a density of <1.8 g/cc and an average particle size of about 5 to 100 microns, suspended within the base paint; wherein the expanded PTFE particles comprise 0.125 to 25% by weight of the coating material. 11. The coating material of claim 10 wherein the average particle size of the expanded PTFE is < 40 microns. 12. The coating material of claim 10 wherein the expanded PTFE particles comprises <10% by weight of the coating material. 13. The coating material of claim 10 wherein the base paint includes an organic solvent in which the expanded PTFE particles are wetted out. 14. The coating material of claim 10 wherein the base paint includes an aqueous solvent and the expanded PTFE particles are wetted out therein through use of a wetting agent to place the particles into suspension. 15. The coating material of claim 14 which further includes a wetting agent selected from the group consisting of hydrophilic surface coatings and surfactants. 16. The coating material of claim 10 wherein the expanded PTFE within the coating material forms a protective interlocking grid network within the hardened coating. 17. The coating material of claim 10 which further comprises an active agent incoφorated within the expanded PTFE particles. 18. The coating material of claim 10 comprises the incorporation of particles greater than 5 micrometers to roughen the texture of the paint. 19. A method for providing a lightweight, protective coating to an aircraft which comprises: providing a base paint comprising pigment and solvent; providing comminuted particles of expanded polytetrafluoroethylene (PTFE), the particles of expanded PTFE having a density of <2.0 g/cc and an average particle size of less than 100 microns; mixing the base paint and particles of expanded PTFE to form a mixture with the particles suspended within the base paint, the particles comprising .125 to 25% by weight of the mixture; applying the mixture to the aircraft to form the protective coating, with the expanded PTFE forming an interlocking grid network therein. 20. The method of claim 19 which further comprises providing particles of expanded PTFE with an average size of < 40 microns and mixing the particles with the base paint to form a mixture comprising < 10% by weight expanded PTFE particles.