GB2051091A - Fluorocarbon Polymer Compositions and Method of Spray-coating - Google Patents

Abstract

Sprayable fluorocarbon polymer coating compositions comprise 5- 95% polytetrafluoroethylene (PTFE) resins, 95-5% perfluoroalkoxy (PFA) resins and a carrier liquid, preferably water. Methods of producing shaped fluorocarbon polymer articles by the application of fluorocarbon polymer coating compositions to moulds use coating compositions comprising from 5% to 100% by weight of PTFE and from 0% to 95% by weight of PFA.

Description

SPECIFICATION Fluorocarbon Compositions and Method of Spray coating This invention relates to sprayable compositions of poly-tetrafluoroethylene and perfluoroalkoxy resins and to a method of providing a substrate with a fluorocarbon polymer -coating derived therefrom.

Fluorocarbon polymer coatings on surfaces of substrates for diverse applications are known.

Most familiar is the polytetrafluoroethylene (hereinafter, PTFE) coating applied to pots and pans to provide non-stick surfaces for cooking applications. Such surfaces are generally coated 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 of fluorocarbon polymer coatings, such coatings offer high heat resistance, stability at cryogenic temperatures, non-wettable surface characteristics, exceptional dielectric properties and exceptional weather resistance, and provide one of the most chemically inert coating substances 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 temperature of PTFE to coalesce the polymer.

The maximum film thickness which can be applied by this technique is limited by a mudcracking phenomenon. Mud-cracking is a common problem associated with coating fluorocarbon polymers onto substrates and refers to the surface effect which resembles the mudcracks which form in sun-parched ground. Mudcracks 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 causing cracks to form upon drying. Most PTFE finishes and enamels can be applied in single coating thicknesses of up to about 0.001 inch without mud-cracking. All PTFE finshes will crack if a critical thickness is exceeded in a single coat. These cracks will not heal upon sintering. For example, the maximum 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 ("Teflon Finishes Product and Application Techniques", Bulletin No, 1, 14th Edition, published by E.I. duPont de Nemours and Co., Inc. and "Teflon PTFE Coatings 851--Line", Bulletin No, E-05440, Revision 3, published by duPont).

Sprayable polyfluorocarbon powders are also known. Polymerized perfluoroalkoxy resin (the term PFA is used hereinafter to designate polymerized perfluoroalkoxy resin) can be applied in powder form 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.

Using electrostatic powder spray techniques, 'TeflonP" PFA resin (Teflon is a registered Trade Mark of duPont), commercially available from E. I.

duPont de Nemours 8 Co., Inc., under product designation 532-5010, can be used to provide a continuous film up to 0.002 inch thick without mud-cracking. Thick films of PFA of 0.005 inch or more have been achieved through the application of multiple coats of PFA sprayable powder.

Application techniques for coatings of Teflon-P PFA powder are contained in the bulletin "Teflon coatings Fact Sheet-Teflon-P PFA Powder Coatings 532-5010" published by duPont in bulletin number E-05440, dated June, 1977 Regarding end-use applications, PFA powders may be used wherever a coating, having one or more of the basic properties inherent to fluorocarbon polymers, is desired. The sprayable powders are useful in applications where mechanical, electrical, thermal and chemical properties approaching those of PTFE fluorocarbon resin are required.

According to one aspect of the present invention we therefore provide novel sprayable compositions comprising between about 5% and about 95% by weight of a polytetrafluoroethylene (PTFE) resin and between about 5% and about 95% by weight of a perfluoroalkoxy (PFA) resin (advantageously either about 20% PTFE and about 80% PFA or about 50% PTFE and about 50% PFA) in a carrier liquid, preferably water, wherein the percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins.

According to a further aspect of the present invention we provide a method for coating a substrate with a fluorocarbon polymer composition, said method comprising: (a) applying, preferably by spraying, to the said substrate at least one coating of a composition comprising between about 5% and about 95% by weight of a polytetrafluoroethylene resin and between about 5% and about 95% by weight of a perfluoroalkoxy resin (advantageously either about 20% PTFE and about 80% PFA or about 50% PTFE and about 50% PFA) in a carrier liquid, preferably water, wherein the said percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins; and (b) heating the resulting coated substrate to evaporate the said carrier liquid from the said coating and to coalesce the said resins thereof.

According to a still further aspect of the present invention we provide a method of moulding a shaped article of a fluorocarbon polymer, said method comprising: (a) applying, preferably by spraying, to a mould at least one coating of a composition comprising from about 5% to 100% by weight of a polytetrafluoroethylene resin and from 0% to about 95% by weight of a perfluoroalkoxy resin (advantageously 100% PTFE) in a carrier liquid, preferably water, wherein the said percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins; (b) heating the resulting coated mould to evaporate the said carrier liquid from the said coating and to coalesce the said resins thereof; and (c) removing the mould, thereby producing a shaped article having the contour of the said mould.

In the compositions and methods of the present invention the compositions advantageously may further comprise at least one particulate substance or filler such as, for example, glass, carbon, pigment, chromium oxide, iron oxide, titanium dioxide and granular PTFE resin.

Substantially nonporous coatings free of mudcracks can be 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.

The thickness of each layer of the coating of this invention preferably exceeds 0.003 inch and can advantageously exceed 0.009 inch.

As used herein, the term "PTFE" is intended to designate homopolymers and copolymers of tetrafluoroethylene other than copolymers with perfiuoroalkyl perfluorovinyl ethers; also, the expression "PTFE dispersion powder" is intended to designate the extrusion grate PTFE powders used in past extrusion.

Compositions, coatings and shaped articles as well as filled and reinforced products according to the present invention may be either porous or substantially non-porous.

As used herein, all percentages denote weight percentages unless otherwise indicated.

It has been found that compositions comprising PTFE dispersion powder and PFA powder in the above proportions, when dispersed by mixing vigorously with about two (2) to about six (6) volumes of water or other suitable carrier liquid, is sprayable using conventional spraying equipment such as, for example, that employed in the spraying of paint. Other carrier liquids such as, for example, mineral spirits, oils and kerosene may be used. However, water is preferred because it is readily available, simple to use and is free of fire and pollution hazzards.

The PTFE/PFA compositions 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 (about 3420C for virginPTFE, about 3270C for PTFE which has been melted previously and about 3070C for PFA) of the polymer particles resulting in the particles coalescing into a continuous coating of perfluorocarbon polymer on the substrate, the coating having a thickness greater than has hitherto been achieved using aqueous spraycoating 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 the present invention, no noxious fumes or dust are produced. The cost of the coating compositions of the present invention is much less than that for prior conventional coatings utilizing PFA powder, since PTFE is presently less expensive than PFA. Also, the cost of applying the coating of this invention is significantly reduced in comparison to the prior methods. According to the present invention simple spraying be used to produce thick coatings in comparison to the costly electro-static spray guns or fluidized beds needed to apply PFA powder. Using prior PTFE spraying methods a much larger number of coatings would in many cases be needed to produce thicknesses of PTFE coatings comparable to those of the coatings of the present invention.

The coatings achievable by the method of the present 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 "granular" type of PTFE or other fillers can be mixed with the PTFE/PFA powder to provide such reinforcement. Also, a layer or glass cloth or mat, or similariy reinforcing material, can be incorporated within the coating. This may be accomplished by spraying a coating of the PTFE/PFA mixture of this invention onto the substrate desired to be coated, allowing the coating to dry slightly, applying the cloth or mat to the coating and then forcing it into the coating.

The mat may easily be forced into the coating by using a simple roller device such as a paperhanger'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 compositions and spraying methods of the present invention have distinct advantages over the known PTFE enamel spraying process. Single coatings according to the present invention may be applied, having thicknesses exceeding 0.003 inch and being subsantially free of mud-cracks, as compared to the maximum single coating thickness of 0.003 inch previously attainable. According to the present invention single layer coatings, substantially free of mud-cracks, can be applied having a thickness exceeding 0.009 inch.

Furthermore, multiple layer coatings according to the present invention can be applied having thickness greater than 0.100 inch. Thus the surfaces of very large vessels and tanks can be coated economically to provide thick, corrosionresistant coatings. 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 the present invention, the following procedures are employed.

Fifty grams of PFA resin such as duPont's 532-5010 and 50 grams of PTFE powder resin such as ICl's "Fluon" CD-1 (Fluon is a registered Trade Mark of Imperial Chemical Industries) duPont's "Teflon" 6A or Ugine Kuhlmann's "Soreflon" S620 or S630 (Soreflon is a registered Trade Mark of Ugine Kuhlmann) are added to 1 75 ml water to which has first been added 2 grams 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 specified quantities and proportions are not precisely required and one skilled in the art can readily alter these quantities and specific proportions to suit particular applications.

The high speed agitation of the poiymer/water mixture, for example, in the Waring blender is an important process step in preparing the coating compositions of the present invention. Such high speed agitation shears the polymer/water suspension at a rapid rate, and the use of such rapid shearing in preparation of sprayable compositions is contrary to prior art teachings.

Very high speed stirring or violent agitation was known to cause irreversible coagulation of PTFE aqueous dispersions, and such rapid agitation was to be avoided (see "Teflon 30 TFE Fluorocarbon Resin", Bulletin No. A-46473, published by E. I. duPont de Nemours s Co. and Bulletin No. E-05440, Revision 3, referred to hereinabove).

The rapid agitation or vigorous mixing referred to as a step in the dispersion of PTFE/PFA polymer particles in a carrier liquid and effected by apparatus such as, for example, a Waring blender can otherwise be referred to as shearing as it involves the imposition of shear forces to agglomerations of polymer particles to effect their dispersion. For the purpose of the present invention, the agitation of the aqueous polymer suspension must, however, be vigorous enough to break up the agglomerates present in PTFE dispersion powder and permit spraying of the suspension without clogging the spray gun.

The surface of the substrate to be coated should be prepared prior to coating to thoroughly clean it and to remove all contaminants 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 sandblasting and applying a surface primer such as duPont's 850201 primer.

The PFA/PTFE/water suspension or dispersion is then sprayed onto the surface to be coated using conventional paint-spraying or similar apparatus. For example, a Model 18 paint spraygun manufactured by the Binks Manufacturing Company or a DeVilbis EGA 502 spray-gun is suitable.

After spraying the coating onto the substrate, the coating should be thoroughly dried in any convenient manner. For example, 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 7500F. Alternatively, the coated article may be subjected to a heating cycle comprising several stages wherein the first heating stage is conducted at lower temperature levels to affect the removal of the carrier liquid and a second heating stage is conducted at higher temperature levels to effect coalescing of the polymer particles to provide a continuous coating on the substrate.

Additional coats may be applied by repeating the above procedures as many times as desired.

To obtain non-porous coatings it is necessary to densify the applied coating. This may be accomplished by rolling the coating 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 stick to the roller, 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 coats are required, it is desirable to spray a light coat of the polymer suspension on the prior coat after rolling and before heating to coalesce, in order to obtain good adhesion of subsequent coats to the previous coat.

The composition and procedures described above have been 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 reaction 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 moulded from the compositions of the present invention, ranging from simple flat sheets to very highly irregular shaped articles. In particular, flasks such as, for example, Erlenmeyer flasks can be moulded using the compositions of the present invention. This is accomplished by spraying the compositions onto the outside of a mould, such as, for example, a conventional glass Erlenmeyer flask, using the cleaning and coating techniques described above. Preferably several coats are applied until the desired thickness is obtained.

Following application of the coating composition, the glass mould is broken and removed leaving a flask in the shape of the mould made of the PFA/PTFE coating composition of the present invention.

Examples of the present invention are given below. The preceding description and the Examples are intended to be fully illustrative of the invention, but not to limit its scope in anyway.

Minor modifications or 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 the electrical resistance between an exploring electrode passed over the coating and the underlying metal is reduced. The holiday detector consists of an electrical energy source such as a battery or high voltage coil, an exploring electrode and a connection from the energy source to the coated metal. The device is usually equipped with a visual or audible alarm which indicates the flow of current through the apparatus.

In using such spark detector, a high voltage is applied to the surface of the coating, ranging usually from 1,000 to 30,000 volts. The exploring electrode can be a wire brush, electrically 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 sandblasted and primed with duPont 850-201 primer.

Fifty (50) grams of PFA powder (duPont product designation 532-5010), fifty (50) grams of PTFE dispersion powder (Imperial Chemical Industries product designation CD-i), 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 7000F (3850C) for 1 5 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 7000F for t5 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).

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 fluorocarbon polymer composition was found to be easily sprayable and single coating thicknesses were produced which are greater than the thickness of any fluorocarbon coating produced by previously 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 5325010) and 50 grams of PTFE (ICI CD-1) in 175 ml water was prepared, to which 2 grams Triton Xl 00 surfactant 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 4 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 7250F until the resin turned black in colon 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 further coat was then applied, dried and baked at7250Ffor 15 minutes.

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, respectively.

A ninth coat was applied, dried and a layer of fibreglass veil was preseed into the coating using the plastic-covered roller.

A tenth coat was applied over the fibreglass, dried and rolled very hard and an eleventh and twelfth coats were applied using the same techniques as for the first and second coats, respectively.

A thirteenth and fourteenth coat were applied using the same techniques as the third and fourth coats respectively.

Upon removal 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 colour 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-i) and thirty (30) grams of 1/64 inch diameter glass flake were blended in a Waring blender for 5 minutes with 1 75 ml water to which had been added 2 grams Triton X100 surfactant. This mixture was sprayed onto a sandblasted and primed steel plate as described in Example 2.

The coating was dried and then baked at 7000F (3850C) for 1 5 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-1) 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 7000F (3850C) for 1 5 minutes. Upon removal from the oven, the coated plate passed a 10,000 volt spark test and appeared to be a continuous, wellbonded coating.

Example 4 Ninety-five (95) grams dispersion grade PTFE (ICI CD-1 ), five (5) grams PFA (duPont 5325010), 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 has been sandblasted and primed as described in Example 2. The coated plate was dried to remove the water and additives and then baked in an oven at 7250 F. The plate was removed from the oven and water-quenched, and then a second coat of the above mixture was sprayed onto the first coat.

This second coat was then dried, rolled with the paper hanger's roller to increase the density of the coating, and baked at 7250F.

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.

Such coating is especially suitable as a thick release coating.

Example 5 Ninety-five (95) grams PFA (duPont 5325010), five (5) grams dispersion grade PTFE (ICI CD-1), 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 7000F 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 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 coat was thus 0.0005 inch.

Example 6 Fifty (50) grams of PTFE (ICI CD-1), fifty 50 grams of PFA (duPont 532-5010), 2 grams Triton X100 and 2 grams of carbon black pigment were with water blended in a Waring blender for 1 to 2 minutes as above. This mixture was then sprayed as before onto a 14 inch by 1 8 inch steel manway cover that had first been sandblasted and primed with duPont primer 850-201. The coating was dried and then baked at 725"F 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 inch diameter roller until the coating turned grayish in color. A third coating of the above mixture was then sprayed onto the second coat as above and the coated cover was dried and then baked at 7250F until the coating turned black.

Upon removal from the oven, the coated cover was quenched in water.

The above coating, drying, rolling 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 aesthetically pleasing appearance.

Example 7 One hundred (100) grams of PTFE (IDI CD 014), two (2) drops of Triton Xl 00 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 7500F until the polymer 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, it was found that mudcracks 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 7500F until the polymer coalesced.

The resultant second coating was substantially non-porous, had a smooth appearance and was approximately 0.012 inch thick.

Example 8 Fifty (50) grams of PTFE (ICI CD--1), fifty (50) grams of PFA (duPont 532-5010), 2 grams Triton X100 and onequarter 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 of a glass, 125 ml, Ehrlenmeyer flask. The coating was dried and the coated flask was baked in an oven at 7250F until the coating turned black.

Seven (7) additional coats were then applied by repeating the above procedure.

The glass flask (mould) was then broken and the broken glass removed leaving a flask in the shape of the mould comprised of the 50% PTFE/50% PFA polymeric composition.

By this technique, shaped fluorocarbon articles, including highly complex shapes, can be moulded using inexpensive glass or similar moulds.

Example 9 One hundred (100) grams of PTFE (ICI CD 014) and two (2) drops of Triton Xl 00 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 previously sandblasted. The coating was dried and then baked in an oven at 700-7500F.

Six (6) additional coatings were applied, dried and baked as above, to provide a total of seven (7) coats on the beaker. The glass mould was then broken and removed. The moulded PTFE beaker so produced had a wall thickness of 0.045 inch (i.e. 0.006 inch per layer) and the surface of the PTFE did not have visually apparent 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 sandblasted and primed with duPont 850-201 primer, then placed in an oven at 7000Ffor 10 minutes, and then air cooled. The glass coating has a chip in it, and steel was exposed at the chip location.

Fifty (50) grams of PTFE (ICI CD1), fifty (50) grams of PFA (duPont 532-5010), 2 grams Triton Xl 00 and one-quarter teaspoon ferrous black pigment were added to 175 ml water and blended for one to two 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 7500F until the mixture turned black. A second coating was applied and dried in an oven. This second coating was then rolled to densify it, and a third coating was applied, dried and rolled. A total of six coats were similarly applied and then the coated spool was baked in an oven at 7500F until the coating materials coalesced.

The resultant coating was firmiy bonded 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 glasslined equipment may be repaired by the application of the polymer composition of the present invention.

Comparative Example 11 Eighty (80) grams of PFA (duPont 532-5010) and twenty (20) grams of PTFE (ICI CD-i) were blended with 1 75 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 sandblasted and primed steel plate at room temperature. The water was evaporated using a hot air gun and then dried, coated plate was baked for 1 5 minutes at 7000F.

A mixture of 95 grams of PFA (duPont 5325010) in 175 ml water to which 2 grams of surfactant had been added was blended for 5 minutes and this mixture was sprayed on top of the first coat using the technique of Example 1, and the water evaporated using a hot air gun. The coated, dried plate was then baked at 7000F for 1 5 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 unsuitable and failed to provide a uniform, non-porous coating.

Claims (36)

Claims

1. Sprayable compositions comprising between about 5% and about 95% by weight of polytetrafluoroethylene (PTFE) resin and between about 5% and about 95% by weight of a perfluoroalkoxy (PFA) resin in a carrier liquid, wherein the said percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins.

2. Compositions as claimed in claim 1 wherein the said carrier liquid is water.

3. Compositions as claimed in either of claims 1 and 2 wherein the said resins comprise about 20% PTFE and about 80% PFA.

4. Compositions as claimed in either of claims 1 and 2 wherein the said resins comprise about 50% PTFE and about 50% PFA.

5. Compositions as claimed in any of the preceding claims further comprising at least one particulate filler.

6. Compositions as claimed in claim 5 wherein the said filler is glass.

7. Compositions as claimed in claim 5 wherein the said filler is carbon.

8. Compositions as claimed in claim 5 wherein the said filler is a pigment.

9. Compositions as claimed in claim 5 wherein the said filler is selected from chromium oxide, iron oxide and titanium dioxide.

10. Compositions as claimed in claim 5 wherein the said filler is granular PTFE resin.

11. A method for coating a substrate with a fiuorocarbon polymer composition, said method comprising: (a) applying to the said substrate at least one coating of a composition comprising between about 5% and about 95% by weight of a polytetrafluoroethylene resin and between about 5% and about 95% by weight of a perfluoroalkoxy resin in a carrier liquid, wherein the said percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins; and (b) heating the resulting coated substrate to evaporate the said carrier liquid from the said coating and to coalesce the said resins thereof.

12. A method as claimed in claim 11 wherein the said carrier liquid is water.

13. A method is claimed in either of claims 11 and 1 2 wherein the said compositions are applied to the said substrate by spraying.

14. A method as claimed in any of claim 11 to 1 3 wherein a force is applied to the external surface of the said resulting coating prior to heating according to step (b), in order to densify the coating.

15. A method as claimed in claim 14 wherein the said force is applied as a shearing and/or compressive force.

16. A method as claimed in any of claims 11 to 1 5 wherein the said composition comprises about 20% PTFE and about 80% PFA.

1 7. A method as claimed in any of claims 11 to 1 5 wherein the said composition comprises about 50% PTFE and about 50% PFA.

1 8. A method as claimed in any of claims 11 to 1 7 wherein the said composition further comprises a particulate substance.

19. A method as claimed in claim 18 wherein the said particulate substance is selected from glass, carbon, pigment, chromium oxide, iron oxide, titanium dioxide and granular PTFE resin.

20. A method as claimed in any of claims 11 to 1 9 further comprising the incorporation of a reinforcement into at least one of the said coatings.

21. A method as claimed in claim 20 wherein the said reinforcement is in the form of a cloth, veil or mat.

22. A method as claimed in either of claims 20 and 21 wherein the said reinforcement is of vitreous material.

23. Coated substrates whenever produced by a method as claimed in any of claims 11 to 22.

24. Coated substrates as claimed in claim 23 wherein each of the said coatings has a thickness of greater than 0.003 inch.

25. Coated substrates as claimed in either of claims 23 and 24 wherein the said substrate is steel or glass-lined steel.

26. A method of moulding a shaped article of a fluorocarbon polymer, said method comprising: (a) applying to a mould at least one coating of a composition comprising from about 5% to 100% by weight of a polytetrafluoroethylene resin and from 0% to about 95% by weight of a perfluoroalkoxy resin in a carrier liquid, wherein the said percentages are based on the total weight of the polytetrafluoroethylene and perfluoroalkoxy resins; (b) heating the resulting coated mould to evaporate the said carrier liquid from the coating and to coalesce the said resins thereof; and (c) removing the mould, thereby producing a shaped article having the contour of the said mould.

27. A method as claimed in claim 26 wherein the said composition is applied to the said mould by spraying.

28. A method as claimed in either of claims 26 and 27 wherein the said carrier liquid is water.

29. A method as claimed in any of claims 26 to 28 wherein a force is applied to the external surface of the said coating prior to heating according to step (b), in order to densify the polymer components therein.

30. A method as claimed in any of claims 26 to 29 wherein the said composition further comprises a particulate substance.

31. A method as claimed in any of claims 26 to 29 further comprising the incorporation into at least one of the said coatings of a reinforcement.

32. A method as claimed in claim 26 wherein the said composition is a composition as claimed in any of claims 1 to 10.

33. Moulded shaped articles whenever produced by a method as claimed in any of claims; 26 to 32.

34. Compositions as claimed in any of claims 1 to 10 substantially as herein described.

35. A method as claimed in claim 11 wherein the said composition is a composition as claimed in any of claims 1 to 10.

36. A method as claimed in any of claims 11 to 22 and 26 to 32 substantially as herein described.