CA1185731A

CA1185731A - Fluorocarbon compositions and method of spray coating

Info

Publication number: CA1185731A
Application number: CA000345540A
Authority: CA
Inventors: John E. Bacino
Original assignee: WL Gore and Associates Inc
Current assignee: WL Gore and Associates Inc
Priority date: 1979-02-16
Filing date: 1980-02-12
Publication date: 1985-04-16
Also published as: AU541846B2; NL8000931A; KR830002458B1; IT8019963A0; FR2453877B1; JPS55129440A; SE8601039D0; AR218816A1; BR8000990A; SE8601039L; FI800457A; ZA80876B; IN154739B; DE3005785A1; IL59368A; GB2051091B; IL59368A0; SE8001127L; KR830002002A; FR2453877A1

Abstract

Abstract of the Disclosure A new fluorocarbon composition is provided. An amount of polytetrafluoroethylene resin and perfluoro-alkoxy resin is dispersed in water or other suitable carrier liquid by mixing vigorously. The dispersion can be sprayed onto surfaces to coat the surfaces and the fluorocarbon polymer coating can be dried and heated to form a coating thicker than has heretofore been pos-sible. Improved properties of the coating may be ob-tained by addition to the coating of suitable materials in particle, mat or woven forms. A method for coating substrates is provided, as well as a method for molding shaped articles of the new composition.

Description

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Background of the Invention Fluorocarbon polymer coatings on surfaces or substrates for diverse applications are known. Most familiar is the polytetrafluoroethylene ~hereinafter, PTFE) coating applied to pots and pans to provide non-stick suxfaces for cooking applications. Such surfaces are generally coa~ed by first etching the substrate and then coating the substrate with the fluorocarbon followed by coalescing (sintering) the polymer in situ on the substrate~
In addition to the non-stick characteristics o~ 1uorocarbon polymer coatings, such coatings offer high heat resistance, stability at cryogenic temperatures, non-wettable surface characteristics, exceptional dielectric properties, exceptional weather resistance, and provide one of the most chemically inert coating subs-tances presently known.
Methods of spray coating PTFE finishes and enamels onto various substrates are also known. These PTFE finishes and enamels are applied over a primer to obtain satisfactory adhesion. These enamels can be applied in multiple coats, each coating being baked above the melt temp~rature of PTFE to coalesce the polymer. The maximum film thickness which can be applied by this technique is limited by a mud-crackir:c;
phenomenon. Mud-cracking is a common problem associated with coating fluorocarbon polymers on substrates and refers to the~

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surface effect which resembles the mud-cracks which form in sun-parched grownd. Mud-cracks are generally undesirable in fluorocarbon coatings, and represent defects in the coating.
Mud-cracks occur when a film is sprayed too thickly onto a surface and cracks form upon drying.
Most PTFE finishes and enamels can be applied in single coating thicknesses up to about 0.001 inch without mud-cracking. All PTFE finishes will crack if a critical thickness is exceeded in a single coat. These cracks will not heal upon sintering. For example, the maximu~ one-coat dry film thickness without mud-cracking for duPont's 851-214 and 852-201* PTFE
enamels is 0.001 inch, and for the so-called "high build" enamels, the maximum thickness per coat is 0.003 inch.**
Sprayable polyfluorocarbon powders are also known. Poly~:erized perfluoroalkoxy resin (hereinaft,er, the term PFA is used to designate the polymerized perfluoroalkoxy resin) in powder form can be applied to hot or cold substrate surfaces using conventional electrostatic spray equipment. Perfluoroalkoxy resin is a copolymer obtained through the copolymerization of perfluoroalkyl perfluorovinyl ethers and tetrafluoroethylene monomers.

**Teflon Finishes Product and Application Techniques'l, Bulletin No. 1, 14th Edition, published by E.I. duPont de Nemours and Co., Inc. See also "Teflon PTFE Coatings ~,51-Line", ~ulletin No. E-05440, Revision 3, published by duPont.
* denotes trade mark 3 73-~
Using electrostatic powder spray techniques, "TEFLON-P"
PFA resin*, commerclally available from E. I. duPont de Nemours &
Co., Inc., under product designation 532~5010, can be used to provide a continuous film up to 0.002 inch thick without mud-crack-ing. Thick films of PAF of 0.005 inch or more have been achievedthrough the application of multiple coats of PFA sprayable powder.
Application techniques for coatlngs of TEFLON-P PFA powder are contained in the bulletin "TEE'LON coatings Fact Sheet - TEFLON-P
PFA POWDER COATING 532-5010" published by duPont in bulletin number E-054409 dated June, 1977.
Regarding end-use applications, the PAF powders may be used wherever a coating is desired having one or more of the basic properties inherent to fluorocarbon polymers. The sprayable powders are useful in applications where mechanical, electrical, thermal and chemical properties approaching those of PTFE fluoro-carbon resin are required~
Summary of the Invention The present invention relates fo a new composi-tion comprising sheared particles of polytetrafluoroethylene (PTFE) dispersion powder and perfluoroalkoxy (PFA) powder in a carrier liquid, wherein PTFE is contained in an amount between about 5% and 100% by weight and PFA is contained in an amount between about 95% and 0% by weight, based upon the total weight of said PTFE and PFA polymers, said composition being sprayable using conventional paint spraying apparatus to produce a coating substantially free of mud-cracks or blisters on a substrate, the shearing of said particles being sufficiently high to enable spraying to a thickness exceeding 0.003 inch per layer. The sprayable composition according to this invention comprises pre-ferably particles of PTFE and PFA dispersed in a liquid carrierof water.

* TEFLON is a registered trademark of duPont 1/' . i 73~

The inven~ion relates also to a method for coating a substrate with a fluorocarbon polymer composition, said method comprising essentially the following steps:
ta) applyin~ to said substxate at least one coating of a composition in a carrier liquid the composition comprising sheared particles of polytetrafluoroethylene (PTFE) dispersion powder and perfluoroalkoxy (PFA) powder in a carrier liquid, wherein PTFE
is contained in an amount between about 5% and 100% by weight and PFA is contained in an amount between about 95% and 0~
by weight, based upon the total weight of said PTFE and PFA
pol~mers, said composition being sprayable using conventional paint spray.ing apparatus to produce a coating substantially free of mud-cracks or blisters on a substrate, the shearing of said particles being sufficiently high ~o enable spraying to a thickness exceeding 0.003 inch per layer, and -4a-'73~L

(b) heating the resulting coated substrate to evaporate said liquid from the coating and to coalesce the polytetrafluoro~
ethylene and th~ perfluoroalkoxY resins thereofO
As used herein, the tPrm PTFE is intended to designate homopolymers; also the expression "PT~E ~ispersion p~w~er" is intended to designate the extrusion grade PTFE powders used in paste extruslon.
The preferred method oE applying the coating to the substrate is by spraying and the preferred carrier liquid is water.
Substantially nonporous coatings free of mud-cracks can he obtained by applying a force, either a shear force or a compressive force, to the top surface of the coating prior to heating according to step (b) above, in order to densify the coating.
Also provided is a substrate coated with the composition oE this .invention.
The thickness o each layer of the coating of this inven kion exceeds 0.003 inch and can exceed 0.009 inch.
~ method o molding a shaped article and a molded shaped article comprised of the above fluorocarbon compositions, option-ally Eilled and reinforced, are also provided.
Both porous and substantially nonporous compositions, coatings and shaped articles are provided, as well as filled and reinforced products.

Detailed Description of the Invention and Preferred Embodiments According to the present invention, a new sprayable composition is provided comprising be~ween about 5% and about lO0 by weight ofa polytetrafluoroethylene resin and between about 0~
and about 9S% by weight of a perfluoroalkoxy resin, wherein said percentages are based upon the total weight of the polytetrafluoroethylene and the perfluoroalkoxy resins. As used herein, all percentages denote weight percentages unless otherwise indicated.
It has been found that a suspension comprising PTFE
dispersion powder and PFA powder in the above proportions, when mixed vigorously with about two (2) to about six (6) volumes of 73~

conventional sprayin~ equipment such as that employed in the spraying of paint. Other carrier liquids which may be employed include mineral spirits, oils, kerosene and the like. However, water is preferred because it is readily available, simple to use 5 and is free of fire or pollution hazards.

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The PTFE/PFA composition of this invention can be sprayed onto the substrate desired to be coated, the coating can be heated to remove the liquid carrier, and the coated substrate can then be raised to a temperature above the melt temperature* of the polymer particles resulting in coalescing of the particles into a cc,ntinuous coating of perfluorocarbon polymer on the substrate, the coating having a thickness greater than has heretofore been achieved using aqueous spray coating compositions.
Such coatings may be applied several times to a single substrate in order to increase the thickness of the overall coating. By the process of this invention, no noxious fumes or dust ar~ produced. The cost of the coating composition of this invention is much less than prior conventional coatings utilizing PFA powder, since PTFE is presently less expensive t~,~n PE'A. Also, the cost. of applying the coating of this invention is significantly reduced over prior methods. Simple spraying devices are used to prc.d~ce thick coatings herein, as compared to costly electrostatic spray guns or fluidized beds needed to apply PFA powder. A much larger number of coatinss using prior PTFE spray methods are needed to produce thicknesses (where possible) of PTFE coatings comparable to the coatings of this invention.

_ _ _ _ _ _ _ _ _ _ * The melt temperature for virgin PTFE is about 342C
and about 327C :Eor previously melted polymer. The melt temperature for PFA is about 307C.

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The coatings achievable by the method of this invention can be modified if desired. If reinforcement is required to improve the physical properties of the coating or to reduce its thermal expansion, glass flakes, carbon black, the "granul2r" type of PTFE or other fillers can be mixed with the PTFE/PFA powder to provide such reinforcement. Also, a layer of glass cloth or mat, or like reinforcing material, can be placed wi-thin the coating. This may be accomplished by spraying a coating of the PTFE/PEA mixture of this invention onto the substrate desired to be coated, allowing the coating to dry slightly, and applying the cloth or mat to the coating and forcing it into the coating. The mat rnay easily be forced into the coating by using a simple roller device such as a paper hanger's roller. Following installation of the cloth or mat, more coats of the PTFE/PFA mixture may be applied, dried and rolled, followed by sintering in place, to achieve a continuous, essentially nonporous reinforced coating substantially free of mud-cracks.
The sprayable composition and spraying method of this invention have great advantages over the known PTFE enarnel spraying prccess. Thick single coatings may now be applied, having thicknesses exceeding 0.003 inch and being substantially free of mud-cracks, as compared to the maximum Frior art single coating thickness of 0.003 inch. Single layer coa-tings, substantially free of rnud-cracks, can now --73~

be applied having a thickness exceeding 0.009 inch. Multiplelayer coatings can now be applied having thickness grea-ter than 0.100 inch. The surlaces of very large vessels and -tanks can now be coated economically to pr~vide thick, corrosion resis~ant coat-ings. Reinforced coatings are now possible, as discussed above,whereas heretofore such reinforced coatings were not available.
In a preferred embodiment of preparing and applying the coating of this invention, the following procedures are employed.
Fifty grams of PFA resin such as duPont's #532-5010 and 0 50 grams of PTFE fine powder resin such as ~CI's "FLUON"* CD 1, ~L
duPont's "I~EF~ON" 6A or Ugine Kuhlmann's "Soxeflon"** S620 or S630 are added to 175 ml water to which has first been added 2 grams ~ 4c Triton X100 wetting agent and a few drops of Dow Corning antifoaming agent. This fluorocarbon/water mixture is blended vigorously for about 1 to 5 minutes using, for example, a Waring blender. The speciEied quantities and proportions are not precisely re~uired and ~ne skilled in the art can readily alter these quantities and specific proportions to suit particular applications.
The high speed agita-tion of the polymer/water mixture ~ ,,c~
in the Waring blender is an important process step in preparing the coating composition of this invention. Such high speed agitation vigorously mixes the polymer/water suspension at a rapid rate, and the use of such rapid mixing in preparation of sprayable compositions is contrary to prior art teachings. High speed stirring or violent agitation was known to cause irreversible coagulation of PTEE aqueous dispersions, and such rapid agitation was to be avoided.*** Forpurposes of this invention, the mixing of the aqueous polymer suspension must be high enough to break up the agglomerates present in PTFE dispersion powder and permit spraying of the suspension withou-t clogging of the spray gun.

* Registered trademark of Imperial Chemical Industries ** Registered trademark o Uyine Kuhlmann *** See "Teflon 30 TFE-Fluorocarbon Resin", Bulletin No. A-46473, Published by E. I. duPont de Nemours & Co. and Bulletin No.
E-05440, Revision 3, referred to hereinabove.
o ~ .~ / ~

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The surface of the substrate to be coated should be prepared prior to coating to thoroughly clean it and remove all contarni-nants which may affect the continuity and bonding of the coating to be applied. If the surface to be coated is metallic such as steel, it may be prepared prior -to coating by conventional sand-blasting and applying a surface primer such as duPont's ~850-201 prlmer .
The PFA/PTFEjwater suspension or dispersion is then sprayed onto the surface to be coated using conventional paint spraying or similar apparatus. A Model 18 paint spray gun manu-' factured by the Binks Manufacturing Company or a DeVilbls EGA 502 spray gun is suitable.

~ o~/~s i73~

After spraying the coating onto - th~
substratel the coating should be thoroughly dried in any convenient mannerO For ~xample, air from a hot air gun may be directed to the coating to evaporate the liquids. The coated substrate is then placed in an oven maintained at a temperature above the melt temperature of the polymers for a time sufficient to effect coalescing of the polymers into a continuous film bonded to the substrate. The preferred temperature range is 700 to 750F. Alternatively, the coated article may be su~jected to a heating cycle comprising several stages wherein the first heating stage is conducted at lower temperature levels to effect removal o the liquid carrier and a second heating stage is conducted at higher temperature levels to effect coalescing of the polymer particles to provi~e a continuous coating on the substrate.
Additional coats may be applied by repeating the above procedures as many times as desired.
To obtain nonporous coatings it is necessary to denslfy the applied coating. This may be accomplished by rolling the coati~g prior to heating the coating to coalesce it. For this purpose, a roller such as a paper hanger's roller may be used. If the polymer tends to Ctick to the ro~ler, a film or coating of thin plastic such as polyethylene may be applied to the surface of the roller to prevent such sticking.
If multiple cocts are required, it is desirable to spray a light coat of the polymer suspension on the prior coat after rolling and kefore heating to coalesce r in order to obtain good adhesion of subsequent coats to the previous coat.
X

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The compostion and procedures descriked abc~e have been found useful in the spray coating of a variety of substrates. They are particularly useful in the coating of large irregular shapes such as the interior of large chemical reactox vessels. These coatings are especially suited for the repair of glass-lined chemical equipment such as Pfaudler lined vessels and glass-lined metallic piping. Virtually any substrate which can withstand the temperatures required to coalesce the polymers may be coated by the techniques of this invention.
It has also been found that shaped articles can be molded from the composition of this invention, including simple flat sheets as well as very highly irregular shaped articles. In particular, flasks such ag Erlenmeyer flasks and the like can be molded using this composition. This is accomplished by sprairing the composition on the outside of a mold, such as a conventional glass Erlenmeyer flask using the cleaning and coating techniques described above. Preferably several coats are applied until a desired thickness is obtained. Following application of the coating composition, the glass mold is broken and xemoved leaving a flask in the shape of the mold made of the PFA/EqFE coating composition of this invention.
Examples of the invention are given below. The preceding description and the examples are intended to be ful]y illustrative of the invention, but not to limit its scope in any way. Minor modifications or ~ 12 73~

changes from the description can be made by one skilled in the art, and such modifications or changes are deemed to fall within the scope of the claims hereinbelow.
In the examples below, reference is made to a spark test. This test utilizes an electrical holiday detector to locate areas or points on a coated metal surface where there is a great difference in electrical resistance between an exploring electrode passed over the coating and the underlying metal. The holiday detector consists of an electrical energy source such as a batt~ry or high voltage coil, an exploring eleckrode and a connection from the energy source to the coated metal. The device is usually equipped with a vlsual or audible alarm which signals current flow through the apparatus.
In using such spark detector, a high vcltage is applied to the surface oE the coating, ranging usually from 1,000 to 30,000 volts. The exploring electrode can be a wire brush, electrica~ly conductive silicone or a coil spring. When a very thin section of coating is passed over by the electrode, a spark will jump from the electrode through the air gap to the metal, indicating a defect in the coating.
Example 1 A sheet of steel plate was sand-blasted and primed with duPont 850-201* primer.

* denotes trade mark Fifty (50) grams of PFA powder (duPont product designation 532-S010), fifty (50) grams of PTFE
dispersion powder (Imperial Chemical Industries product designation CD-l*), 2 grams Triton X100* surfactant and a drop of anti-foaming agent (Dow Corning Antifoam A) were added to 175 ml water and blended in a Waring blender for about 2 minutes. This mixture was sprayed onto the surface of the primed plate using a DeVilbis EGA 502 spray gun. The coating on the plate was dried using a hot air gun and then the coated plate was baked in an oven at 700F (385~C) for 15 minutes.
A second coating of the above mixture was then sprayed onto the top of the first coating and dried as above. This second coating, after drying, was rolled using a 1.5 inch wide, 1.5 inch diameter wall paper roller -to increase the density of the coating. The coated plate was then baked at 700F for 15 minutes.
A third coat was applied using the same procedures employed for the second coat.
A fourth coat was applied, dried but not baked, followed by a fifth coat which was applied, dried and baked using the same procedures followed in applying the second coat. The thickness of the coating (five layers) was approximately 0.040 inch (0.101 cm).
The average thickness per coating layer was thus 0.008 inch (0.020 cm).

* denotes trade marks 73~

The coated steel plate passed a 10,000 volt spark test over its entire surface, had a good appearance and was free of mud-cracks.
Following these procedures, the mixture was found to be easily sprayable and single coating thicknesses were produced which are greater than the thickness of any prior fluorocarbon coating produced by known spraying techniques.
Example 2 A sheet of steel plate having dimensions of 8 inch x 8 inch x 1/4 inch was sandblasted and primed with duPont 850-201 primer.
A mixture of 50 grams of PFA (duPont 532-50101 and 50 grams of PTFE (ICI CD~l) in 175 ml water was prepared, to which 2 grams Triton X100 surfact~nt had been added. To this mixture, one-fourth teaspoon of carbon black pigment was added and the mixture was blended in a Waring blender for about A minutes~
This mixture was then sprayed on the primed steel plate and hot air dried~ A second coating was sprayed on top of the first coating, dried and baked in an oven at 725F until the resin turned black in color.
A third coat was sprayed onto the plate~ hot air dried and rolled using a sheet of plastic to cover the roller to prevent the resin from sticking to the roll. A futher coat was then applied, dried and baked at 725F for ]5 minutes.

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A fifth and sixth coat were applied by the same technique as the first and second coats, respectively.
A seventh and eighth coat were applied by the same technique as the third and fourth coats, respec-tively.
A ninth coat was applied, dried and a layer o fiberglas veil was pressed into the coating using the plastic covered roller.
A tenth coat was applied over the fiberglas, dried and rolled very hard and an eleventh and twelfth coats were applied using the same techniques as for the Eirst and second coats, respectively.
A thirteenth and fourteenth coat were applied using the same techniques as the third and fourth coats respectively.
Upon rernoval from the sintering oven the coating was firmly bonded to the substrate and had a thickness of about 0.055 inch. The average thickness per coat was thus 0~004 inch. The coating passed a 10,000 volt spark test over its entire surface, was bonded well to the substrate and had no mud-cracks. The black color from the pigment yielded an aesthetically pleasing appearance.
Example 3 Seventy (70) grams of PFA (duPont 532-5010) and thirty (30) grams of PTFE (ICI CD-l) ancl thirty (30) grams of 1/64 inch diameter glass flake were blended in a Waring blender for 5 minutes with 175 ml water to which had been added 2 grams Triton X100 surfactant.
~ 16 73~

This mixture was sprayed onto a sandblasted and primed steel plate as described in Example 2. The coating was dried and then baked at 700F (385C) for 15 minutes.
Three additional coatings were applied, repeating each of the above steps, with the exception that just prior to baking, each coating was rolled with the small roller previously described.
A further top coating was applied by spraying a mixture of seventy ( 70) grams of PFA (532-5010) and thirty (30) grams of PTFE (CD-13 in 175 ml water containing 2 grams Triton X100 but containing no glass flake. This top coating was rolled as above, dried and baked at 700F (385C) for 15 minutes. Upon removal from the oven, the coated plate passed a 10,000 volt spark test and appeared to be a continuous, well-bonded coa-ting.

Ninety-five (95) grams dispersion grade PTFE
(ICI CD-1), five (5) grams PFA (duPont 532-5010), 2 grams Triton X100 surfactant and 2 drops Dow Corning antifoaming agent were added to 175 ml water and blended in a Waring blender for about 2 to 3 minutes.
The mixture was then sprayed onto a steel plate which had been sandblasted and primed as described in Exampl~

2. The coated plate was dried to remove the water and additives and then baked in an oven at 725F. The plate was removed from the oven and water-quenched, and then ~S7~

a second coat of the above mixture was sprayed onto the first coat. This second coat was then dried, rclled with the paper hanger's roller to increase the density of the coating, and baked at 725F.
The thickness of the coating produced was 0.010 inch (0.025 cm) to 0.012 inch (0.027 cm). The average thickness per coat was thus 0.005 inch (0.0125 cm) to 0.006 inch (0~0145 cm). The coating was substantially nonporous and free of mud-cracks.
5uch coating is especially suitable as a thick release coating.
Example 5 Nine-ty~five (95) grams PFA (duPont 532-5010), five (5) grams dispersion grade PTFE (ICI CD-l), 2 grams Triton X100 and 2 drops antifoaming agent were added to 100 ml water and blended in a Waring blender for 2 to 3 minutes. This mixture was then sprayed onto a steel plate which had been sandblasted and primed as in Example 2~ The coated plate was then dried and baked at 700F until the coating gelled. This procedure of spraying, drying and baking was repeated four (4) times to produce a total of five (5) coats on the surface of the plate. No rolling was employed in this example.
The resulting coating had a good physical appearance and passed a 10,000 volt spark test over approximately~

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95% of the surface area of the plate. Such mixture can be applied to surfaces which are very irregular and thus difficult to roll, i.e. in corners, to achieve a thick, acceptable fluorocarbon coating. The thickness of the coating was 0.025 inch. The average thickness per coate was thus 0.005 inch.
Example 6 Fifty (50~ grams of PTFE (ICI CD-l), fifty (50) grams of PFA (duPont 532-5010), 2 grams Triton X100 and 2 grams of carbon black pigment were blended in a Waring blender for 1 to 2 minutes.
This mixture was then sprayed as before onto a 14 inch by 18 inch steel manway cover that had Eirst been sandblasted and primed with duPont primer 850-201. The coating was dried and then baked at 725F until -the coating turned black. The coated cover was then quenched in water. A second coating was applied as above and dried in an oven until the coating turned a whitish color and all the water was evaporated.
The coating on the cover was then rolled with a 1.5 ~nch diameter roller until the coating turnéd grayish in color.
~hird coating oE the above mixture was then sprayed onto the ~0 second coat as above and the coated cover was dried and then baked at 725F until the coa-ting turned black. Upon removal from the oven, the coated cover was quenched in water.

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The above coating, drying, rolliny and baking procedure was then repeated to provide a total of six (6) coats on the surface of the cover.
The coated cover passed a 10,000 volt spark test over its entire surface. The thickness of the coating was approximately 0.050 inch to 0.060 inch. The average thickness per coat was thus 0.008 to 0.010 inch. The coating was free of mud-cracks and had an aes-thetically pleasing appearance.
Example 7 One hundred (100) grams of PTFE (ICI CD 014)*, two (2) drops of Triton X100 and 225 ml water were blended in a Waring blender for 2 to 3 minutes. This mixture was then sprayed onto a steel plate which had been sandblasted and baked in an oven at 750F until the po]ymer coalesced.
A second coating of this mixture was sprayed onto the first coat to a thickness of about 0.015 inch.
This coating was dried in an oven and, upon removal from the oven, mud-cracks had formed. This top coating was then rolled as in Example 6 until substantially all of the mud-cracks disappeared. The coating was baked in an oven at 750F until the polymer coalesced.
The resultant second coating was substantially nonporous, had a smooth appearance and was approximately 0.012 inch thick.

* denotes trade mark

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Example 8 Fifty (50~ grams of PTFE (ICI CD-l), fifty (50) grams of PFA (duPont 532-5010), 2 grams Triton X100 and one-quarter teaspoon carbon black pigment were added to 175 ml water and blended for 1 to 2 minutes in a Waring blender. This mixture was sprayed onto the outside surface o~ a glass, 125 ml, Ehrlenmeyer flask~
The coating was dried and the coated flask was baked in an oven at 725F until the coating turned black.
Seven (7) additional coats were then applied by repeating the above procedure.
The glass f:lask (mold) was then broken and the broken glass removed leaving a flask in the shape oE
the mold comprised of the 50% PTFE/50~ PFA polymeric composition.
By this technique, shaped fluorocarbon articles, including highly complex shapes, can be molded using inexpensive glass or similar molds.
Exampl One hundred (100) grams of PTFE (ICI CD 014) and two ~2) drops of Triton X100 were added to 225 ml water and vigorously blended for 2 to 3 minutes in a Waring blender.
The above mixture was sprayed onto the outside surface of a glass beaker which had been previ~usly sandblasted. The coating was dried and then baked in an oven at 700-750F.

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Six (6) additional coatings were applied, dried and baked as above, to provide a total of seven ~7) coats on the beaker. The glass mold was then broken and removed. The molded PTFE beaker so produced had a wall thickness of 0.045 inch (i.e. 0.006 inch per layer) and the surface of the PTFF did not have visually a~parent mud-cracks.
The PTFE beaker was then filled with water.
Under pressure, the water penetrated the walls of the beaker indicating that the beaker was porous.
Example 10 -A glass-lined steel pipe spool was sand-blasted and primed with duPont 850-201 primer, then placed in an oven at 700F for 10 minutes, and ~hen air cooled. The glass coating had a chip in it, and steel was exposed at the chip location.
Fifty (S0) grams of PTFE (ICI CD-l), fifty (S0) grams of PFA (duPont 532 5010), 2 grams Triton X100 and one-quarter teaspoon ferous black pigment were added to 175 ml water and blended for one to twc minutes in a Waring blender.
This mixture was then sprayed onto the glass-coated steel in the vicinity of the chip and baked in an oven at 750F until the mixture turned black. A second coating was applied and dried in an oven. This seccnd coating was then rolled to densify it, and a third coating was applied, dried and rolled.

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A total of six coats were similarly applied and then the coated spool was baked in an oven at 750F until the coating materials coalesced.
The resultant coating was firmly honded to the spool and passed a 10,000 volt spark test over its entire surface at the location of the chip in the glass.
The total thickness of the coating on the substrate was about 0.050 inch. The average thickness per coat was thus 0.007 inch.
According to this technique, defects in glass-lined equipment may be repaired by application of the polymer composition of this invention.
Comparative Example 11 Eighty (80) grams of PFA (duPont 532-5010) and twenty (20) grams of PTFE (ICI CD-l) were blended with 175 ml water containing 2 grams Triton X100 surfactant and, while mixing, a drop of Dow Corning Antifoam A
antifoaming agent was added.
This mixture was sprayed on a sand-bla~ted and primed steel plate at room temperature. The Water was evaporated using a hot air gun and the dried, coated plate was baked for 15 minutes at 700F.
A mixture of 95 grams of PFA (duPont 532-5010) in 175 ml water to which 2 grams of surfactant had been added was blended for 5 rninutes and this mixture was sprayed on top of the first coat using the technique of X

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Example 1, and the water evaporated using a hot air gun. The coated, dried plate was then baked at 700~F
for 15 minutes.
The PFA top coat was found to have small bubbles over approximately 60% of the surface and had little or no adhesion to the first coat. This comparative example illustrates that a pure PFA coating is unsui-table and failed to provide a uniform, nonporous coating.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition comprising sheared particles of poly-tetrafluoroethylene (PTFE) dispersion powder and perfluoroalkoxy (PFA) resin powder in a carrier liquid, wherein PTFE is contained in an amount between 5% and 100% by weight and PFA is contained in an amount between about 95% and 0% by weight, based upon the total weight of said PTFE and PFA polymers, said compositions being sprayable using conventional paint spraying apparatus to produce a coating substantially free of mud-cracks or blisters on a substrate, the shearing of said particles being sufficiently high to enable spraying to a thickness exceeding 0.003 inch per layer.

2. The composition of claim 1, wherein the perfluoroalkoxy resin is a copolymer obtained through the copolymerization of perfluoroalkyl perfluorovinyl ethers and tetrafluoroethylene monomers.

3. The composition of claim 1 in which the polymer components comprise about 20% polytetrafluoroethylene resin and about 80% perfluoroalkoxy resin.

4. The composition of claim 1 in which the polymer components comprise about 50% polytetrafluoroethylene resin and about 50% perfluoroalkoxy resin.

5. The composition of claim 1 containing, in addition to the polymer components, a particulate filler.

6. The composition of claim 5 wherein the particulate filler is glass.

7. The composition of claim 5 wherein the particulate filler is carbon.

8. The composition of claim 5 wherein the filler is a pigment.

9. The composition of claim 5 wherein the filler is selected from the class consisting of chromium oxide, iron oxide and titanium dioxide.

??

10. The composition of claim 5 wherein the filler is granular polytetrafluoroethylene resin.

11. The method of coating a substrate with a fluorocarbon polymer composition comprising:
(a) applying to said substrate at least one coating of a composition in a carrier liquid, the composition comprising sheared particles of polytetrafluoroethylene (PTFE) dispersion powder and perfluoroalkoxy (PFA) resin powder in a carrier liquid, wherein PTFE is contained in an amount between about 5% and 100% by weight and PFA is contained in an amount between about 95% and 0% by weight, based upon the total weight of said PTFE and PFA polymers, said compositions being sprayable using conventional paint spraying apparatus to produce a coating substantially free of mud-cracks or blisters on a substrate, the shearing of said particles being sufficiently high to enable spraying to a thickness exceeding 0.003 inch per layer, and (b) heating the resulting coated substrate to evaporate said liquid from the coating and to coalesce the polytetrafluoroethylene and the perfluoroalkoxy resins thereof.

12. The method of claim 11 wherein the perfluoroalkoxy resin is a copolymer obtained through the copolymerization of perfluoroalkyl perfluorovinyl ethers and tetrafluoroethylene monomers.

13. The method of claim 11 wherein said dispersion of polymers is applied to the substrate by spraying.

14. The method of claim 11 including applying force to the top surface of said resultant coating prior to heating according to step (c), in order to densify the coating.

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15. The method of claim 14wherein the force applied is a shearing force.

16. The method of claim 14wherein the force applied is a compressive force.

17. The method of claim 11wherein said dispersion comprises about 20% polytetrafluoroethylene resin and about 80% perfluoroalkoxy resin.

18. The method of claim11 wherein said dispersion comprises about 50% polytetrafluoroethylene resin and about 50% perfluoroalkoxy resin.

19. The method of claim11 wherein said carrier liquid is water.

20. The method of claim11 wherein said dispersion contains, in addition, a particulate substance.

21. The method of claim11 including applying reinforcement into at least one of said coatings.

22. A coated substrate having at least one coating layer thereon produced by the method of claim 11.

23. The coated substrate of claim22 wherein each said layer has a thickness greater than 0.003 inch.

24. The coated substrate of claim22 wherein said composition comprises 100% polytetrafluoroethylene resin.

25. The coated substrate of claim22 wherein said composition contains, in addition to the polymer components, a particulate filler.

26. The coated substrate of claim25 wherein said filler is glass.

27. The coated substrate of claim25 wherein said filler is carbon.

28. The coated substrate of claim25 wherein said filler is pigment.

29. The coated substrate of claim25 wherein the filler is selected from the class consisting of chromium oxide, iron oxide and titanium dioxide.

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30. The coated substrate of claim 25wherein the filler is granular polytetrafluoroethylene resin.

31. The coated substrate of claim 22 wherein said composition contains, in addition to the polymer components, a reinforcement.

32. The coated substrate of claim 31 wherein the reinforcement is selected from the class consisting of a cloth, a veil and a mat.

33. The coated substrate of claim 31 wherein the reinforcement is a glass material.

34. The coated substrate of claim 22 wherein said substrate is steel.

35. The coated substrate of claim 22 wherein said substrate is glass-lined steel.
36. The method of molding a shaped article of a fluorocarbon polymer, comprising:
(a) applying onto a mold surface at least one coating of a composition in a carrier liquid, the composition comprising sheared particles of polytetrafluoroethylene (PTFE) dispersion powder and perfluoroalkoxy (PFA) resin powder in a carrier liquid, wherein PTFE is contained in an amount between 5% and 100% by weight and PFA is contained in an amount between about 95%
and 0% by weight, based upon the total weight of said PTFE and PFA polymers, said composition being sprayable using conventional paint spraying apparatus to produce a coating substantially free of mud-cracks or blisters on a substrate, the shearing of said particles being sufficiently high to enable spraying to a thickness exceeding 0.003 inch per layer, ?

(b) heating said coated mold to evaporate said liquid from the coating and to coalesce the polymer components in said coating, and (c) removing the mold, thereby producing a shaped article having the contour of said mold.
37. The method of claim 36 wherein the perfluoroalkoxy (PFA) resin is a copolymer obtained through the copolymerization of perfluoroalkyl perfluorovinyl ethers and tetrafluoroethylene monomers.
38. The method of claim 36 wherein said suspension is applied to the mold by spraying.
39. The method of claim 36 including applying force to the external surface of said coating prior to heating according to step (b), in order to densify the polymer components therein.
40. The method of claim 36 wherein said mixture contains, in addition, a particulate substance.
41. The method of claim 36 including applying a reinforcement into at least one of said coatings.
42. A molded, shaped article produced by the process of

claim 36.