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Publication numberUS3431136 A
Publication typeGrant
Publication dateMar 4, 1969
Filing dateDec 10, 1964
Priority dateDec 10, 1964
Publication numberUS 3431136 A, US 3431136A, US-A-3431136, US3431136 A, US3431136A
InventorsFrederic B Stilmar
Original AssigneeDu Pont
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Ferrous metal articles with metal galvanic coatings and fluorocarbon copolymer top layers
US 3431136 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent 3,431,136 FERROUS METAL ARTICLES WITH METAL GALVANIC COATINGS AND FLUOROCAR- BON COPOLYMER TOP LAYERS Frederic B. Stilmar, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec. 10, 1964, Ser. No. 417,515 U.S. Cl. 117-70 6 Claims Int. Cl. B44d 1/14; C23f 15/00 ABSTRACT OF THE DISCLOSURE A durable corrosion-resistant composition comprising a ferrous metal substrate, an intermediate layer of a coating containing zinc or aluminum, and a top layer of a copolymer of at least one fluorine-containing olefin and an acid group-containing olefin.

The present invention is directed to corrosion-resistant ferrous metal articles which retain their corrosion resistance and original appearance after long periods of weathering in a corrosive environment.

Ferrous metals are subject to attack by numerous corrosive agents. Accordingly, ferrous metal surfaces or articles are usually painted in order to protect the metal against destruction by corrosive attack. Besides protecting the ferrous metal articles, painting can also be used as a means for enhancing the aesthetic appearance of the metal articles.

A time-honored procedure for protecting ferrous metals from corrosive attack or deterioration is toapply a thin layer of zinc metal on the ferrous metal substrate. A variety of procedures have been devised for applying this thin layer of zinc. Examples of such procedures are galvanizing, electrodeposition, zinc spray, and zinc dust paint. Recently, the method using the zinc dust paint has become particularly important because of ease and convenience of application as well as economy.

Although by themselves the thin layers of zinc or zinccontaining paints on iron or steel provide good long-term corrosion protection, aging causes formation of dull gray zinc salt deposits known as white rust. Thus, while these zinc-containing coatings prevent rusting, they are far from aesthetically pleasing. The aesthetic appearance can be improved by overpainting the zinc-containing primer coating with various formulations based on alkyd, epoxy or other commercial paint binder compositions. However, such overpainted articles remain corrosion resistant and aesthetically pleasing only while the topcoat remains durable. In most corrosive environments, wherein the ferrous metal article is also subject to atmospheric weathering, currently available commercial topcoating compositions fail much more rapidly than do the zinccontaining primers. Thus, although the coated ferrous metal articles in modern commercial use may retain their anticorrosion properties for an extended period of time, they lose their aesthetic appearance after relatively short periods in corrosive environments due to the rapid failure of available topcoat materials.

It is, therefore, an object of this invention to provide ferrous metal articles which retain their original aesthetic appearance and long-term corrosion resistance after long periods of weathering in corrosive environments:

This and other objects will become apparent from the following description and claims.

More specifically, the present invention is directed to a ferrous metal substrate having on at least a portion of the surface thereof (A) a galvanic action coating of from about 0.3 to about 10.0 mils in thickness comprising at least 10% by volume of a metal selected from the group ice consisting of zinc and aluminum, and (B) overlaid and adhered to the galvanic action coating a topcoating composition of from about 0.3 to about 5.0 mils in thickness of a normally solid copolymer of a terminally unsaturated fiuorine-containing olefin, said copolymer being characterized by a fluorine content greater than 30.0% by weight, a sticking temperature greater than 60 C., a glass transition temperature of less than about C. and a melt flow rate of greater than 0.5 g./ 10 minutes at C.

The novel ferrous metal articles of this invention, having been first coated with a zincor aluminum-containing composition and then coated with a fluorocarbon polymer, are useful as components in ships, marine structures, industrial buildings, bridges and vehicles, and wherever else durable, corrosion-resistant, attractive ferrous metal structures are used.

The novel articles of this invention consist of three essential components: 1) a ferrous metal substrate, (2) a zinc or aluminum metal-containing coating adhering to at least a portion of the surface of the ferrous metal substrate, and (3) a topcoat film adhering to the zincor aluminum-containing coating of a normally solid copolymer of a terminally unsaturated fluorine-containing olefin. To provide the combination of corrosion resistance and durable aesthetics of the ferrous metal articles of the present invention, the metal-containing galvanic action coating composition must be from about 0.3 to about 10.0 mls. thick, and the fluorocarbon copolymer-containing topcoat composition must be from about 0.3 to about 5.0 mils thick. If either the metal-containing coating composition or the fluorocarbon copolymer-containing topcoat are present in amounts below these ranges, the desirable combination of durable, long-term corrosion resistance and long-term aesthetic appearance is not obtained. If either of the coatings are present in amounts exceeding these specified ranges, the combination of corrosion resistance and durable aesthetic appearance may be obtained; however, such large quantities are unnecessaril y wasteful and not desirable for obvious economic reasons.

The ferrous metal articles of this invention include articles made of iron or iron alloys including steels, cast irons and wrought irons which under normal use conditions in the atmosphere undergo corrosion, particularly rusting. These articles may take a variety of forms such as sheet, wire and machined, cast or formed bulk articles. Since it is often desired to protect only a portion of such articles, it is fully contemplated that the ferrous metal articles of this invention may be only partially coated with the galvanic action coating and fluorocarbon topcoating.

The galvanic action coatings are characterized by a con-tent of at least 10% by volume of either zinc or aluminum. The zinc and aluminum must be relatively pure since impurities in these metals can reduce their ability to protect steel from corrosion. Thus, it is preferred that the zinc and aluminum used be at least 95% pure. The zinc-containing coatings are particularly preferred under most conditions of use since they give the best over-all protection from corrosion. However, aluminum-containing galvanic action coatings are preferred under certain conditions. For example, aluminum-containing coatings are preferred where the ferrous metal articles are to be immersed in soft water. Mixtures of zinc and aluminum or alloys of zinc and aluminum with other metals may also be used in the galvanic action coatings, although no particular advantage is obtained thereby.

The zinc-containing galvanic action coatings may assume a variety of forms including high content zinc coatings such as those obtained by hot galvanizing, electrogalvanizing, or by metal spraying. The zinc-containing paints may also be used. Such zinc-containing paint coatings normally contain up to 90 volume percent of a binder which may be a fluorine-free, film-forming organic polymer composition, an alkali silicate, tetraalkyl orthosilicate, or a partially hydrolyzed tetraalkyl orthosilicate wherein the alkyl group in said tetraalkyl orthosilicate is a C to C aliphatic hydrocarbyl grouping. Among the useful binders for Zinc dust paints are polystyrene, epoxy resins, chlorinated and cyclized rubber, and alkyd resins. Film-forming binders and vehicles for zinc dust paints are well known in the art and are fully discussed in such works as Joseph J. Mattiellos four-volume text, Protective and Decorative Coatings, John Wiley & Son, Inc. (1943), and in recent articles such as Paint Manfacture, vol. 34, No. 1, pp. 41-6 (1964); vol. 34, N0. 2, pp. 51-3 (1964), and Paint and Varnish Production, vol. 54, No. 5, pp. 87-94 (1964). A particularly preferred class of zinc-containing galvanic action coatings are those wherein the zinc dust or flake is bonded by an inorganic silicate. Such inorganic zinc-rich coatings are described in U.S. Patent 3,056,684, U.S. Patent 3,093,493, and in Paint and Varnish Production, July 1964, pp. 75-76 Aluminum-containing coatings useful in this invention include those applied by metal spraying, dipping and rolling, electrodeposition, and other methods known to those skilled in the art, and aluminum-containing coatings utilizing the same binders as described above for use with zinc.

It is essential, of course, for best protection that the ferrous metal substrate to which the zincor aluminumcontaining coating is applied be free from grease, scale, rust or other foreign matter. Suitable methods for providing such clean surfaces include blasting with a suitable abrasive, vapor degreasing with a substance such as trichloroethylene, rubbing with abrasive paper, wire brushing, and pickling.

The copolymers of terminally unsaturated fluorinecontaining olefins used as the topcoat film of the invention articles are normally solid copolymers characterized by a fluorine content greater than 30% by weight, a sticking temperature greater than 60 C., a second order transition temperature (glass transition temperature, Tg) of less than about 105 C. and a melt flow rate of the polymer itself or of the polymer in admixture with an equal weight of a latent solvent of greater than 0.5 g./ 10 minutes. These copolymers include two-, threeand multicomponent polymers of at least one polymerizable fluorine-containing olefin. Fluorocarbon copolymers containing less than 30% by weight fluorine do not provide, in combination with the ferrous substrate and zincor aluminum-containing coating, the combination of durable corrosion resistance and aesthetic appearance when subjected to atmospheric weathering for long periods of time as do the fluorocarbon copolymers utilized in the present invention. The fluorocarbon copolymers must also possess a sticking temperature greater than 60 C. to be useful when exposed under tropical or desert conditions. Sticking temperature can be defined as the lowest temperature of a heated brass block at which a solid copolymer leaves a molten trail when moved across the brass block. Those fluorocarbon copolymers having a glass transition or second order transition temperature greater than 105 C. are not useful as topcoats for the articles of this invention since they do not possess satisfactory film-forming properties. The phenomena known as glass transition or second order transition and the methods of measuring the glass transition temperature of polymeric materials are fully discussed in Textbook of Polymer Science, Billmeyer, Fred W., Interscience Publishers (1962), pp. 198 et seq. The fluorinecontaining copolymers for utilization in this invention must also possess a melt flow rate of greater than 0.5 g./ 10 minutes. For the purposes of this invention, melt flow rate is defined as the weight of molten polymer in grams that passes through a defined orifice in 10 minutes at an indicated temperature and at an indicated extrusion weight. The copolymers must possess the required flow rate at this temperature either by themselves or in admixture with an equal weight of a latent solvent. For purposes of this invention, the term latent solvent is defined as a solvent which has no significant solvating or swelling action on the fluorocarbon polymers at room temperature but has enough solvating ability at high temperatures to make the' polymers fuse. Latent solvents which are particularly useful are dimethyl phthalate, 2- ethoxyethyl acetate, diethyl adipate, diisobutyl phthalate, diethyl succinate, tetraethyl urea, triethyl phosphate and di(2-ethylhexyl)phthalate. This required melt flow rate is necessary if the polymer is to form the continuous coalesced, adherent topcoat films required. The melt flow rate is measured by ASTM Method D-123 8-62T at C. with a weight of 2160 grams and an orifice size of 0.082 inch in diameter and 0.319 inch in length.

Representative examples of fluorinated polymerizable olefins useful for the fromation of the topcoat film-forming fluorocarbon copolymers of this invention are vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene chlorotrifluoroethylene, hexafiuoropropylene, dichlorodifluoropropylene, dichlorodifluoroethylene and tetrafluoropropylene. Of these, vinyl fluoride, vinylidene fluoride and tetrafluoroethylene are preferred.

Representative examples of specific copolymers which will form the topcoat compositions of this invention include tetrafluoroethylene/vinyl acetate, vinylidene fiuoride/isobutylene, vinyl fluoride/vinylidene fluoride/vinyl acetate, vinylidene fluoride/tet-rafluoroethylene, vinylidene fluoride/tetrafluoroethylene/t-butyl methacrylate, tetrafluoroethylene/chlorotrifluoroethylene/methacrylic acid, vinylidene fluoride/tetrafluoroethylene/bis (2-chloroethyl) vinylphosphonate, vinyl fluoride/trifiuoroethylene, tetrafluoroethylene/isobutylene, tetrafiuoroethylene/isobutylene/ vinyl benzoate, tetrafluoroethylene/isobutylene/ vinyl benzoate/itaconic acid, tetrafluoroethylene/ethylene/vinyl benzoate/bis(2chloroethyl) vinylphosphonate, vinylidene fluoride/chlorotrifluoroethy1ene, vinylidene fluoride/tetrafluoroethylene/vinyl acetate, vinylidene fluoride/tetrafluoroethylene/acrylic acid, vinylidene fluoride/tetrafluoroethylene/vinyl butyrate/dineopentyl vinylphosphomate, and various other copolymers, particularly those more fully described in US. Patents 2,419,009; 2,468,054; 2,468,664 and 2,599,640 and in my copending applications S.N. 286,470, filed June 10, 1963, and now US. Patent 3,318,850; S.N. 407,868; filed Oct. 30, 1964; S.N. 407,856, filed Oct. 30, 1964, and now US. Patent 3,380,974, and S.N. 407,858, filed Oct. 30,1964, and now US. Patent 3,380,971. Other examples of fluorine-containing copolymers which form the topcoat compositions of this invention are also described in pending application S.N. 407,860, filed Oct. 30, 1964, and now abandoned.

The fluorocarbon copolymers which form the topcoating material of this invention must be capable of application to the zincor aluminum-containing coating by a method which yields a continuous coalesced topcoat film. Suitable methods include film lamination; application from solution, organosol, or aqueous dispersion; melt coating, such as melt extrusion; and flame spraying. The particular method used for application of the topcoat film depends on the nature and properties of the particular fluorocarbon polymer used. Thus, topcoat films of tetrafluoroethylene/ ethylene copolymer are best laid, down from organosols containing a compound such as diisobutyl adipate which can serve as a latent solvent for the copolymer as described in Bn'tish Patent 609,586. Tetrafluoroethylene/isobutylene copolymer is preferably applied by melt techniques such as melt extrusion or flame spraying. The ter-, tetraand other multicomponent fluorocarbon copolymers are usually best applied from solution. The particular solvents used are dependent on the composition of the polymer. For example, xylene, toluene, trichloroethylene and l,1,2,2-tetrafluoro-1,3,3,3-tetrachloropropane or combinations of these solvents with each other or with common hydrocarbon, chlorocarbon, ester or ketonic solvents are preferred for the copolymers containing tetrafluoroethylene and isobutylene as principal monomers. For the copolymers containing vinylidene fluoride and tetrafluoroethylene as principal monomers, such solvents as cyclohexanone, methyl ethyl ketone, N,N-dimethylformamide, N,N dimethylaceta-mide and mixed solvents incorporating these compounds are preferred.

Essentially inert materials such as pigments, fillers, dyes or antioxidants may be incorporated into the fluorocarbon copolymer topcoat. This incorporation can be brought about by a variety of well-known methods such as ballmilling or sand-milling of the preformed fluorocarbon copolymers with the additives. Ferrous metal articles wherein the fluorocarbon topcoating contains inert materials are included in the products of this invention.

As hereinbefore discussed, ferrous metal articles which have been protected against corrosion by zinc-containing paints generally lose their aesthetic appearance by the formation of a dull gray zinc salt deposit known as white rust. Topcoating the zinc-containing protective coating with various paint formations prevents white rusting initially, but soon the corrosive atmosphere and weathering conditions cause the topcoat to fail and fall away. The failure of common topcoating materials is generally attributed to their inability to adhere to the zincor alumimum-containing undercoating and their lack of durability to withstand the deteriorating conditions of heat, light and vvater vapor at the interface between the topcoating and the metal-containing undercoating. In order to improve the adhesion between the topcoat material and the zincor aluminum-containing undercoating, it has been the practice to pretreat the metal-containing undercoating, either with a material to change the surface characteristics of the undercoating or with an adhesive material to insure adhesion. Adding an adhesive material has generally failed, since the adhesion-promoting material is just as subject, if not more so, to the deteriorating conditions of weathering, i.e., heat, light and water vapor at the interface. Changing the surface character of the undercoating to improve adhesion is generally successful, but involves a laborious step which adds to the cost of the manufactured ferrous metal articles.

In view of this art-recognized difiiculty in obtaining adherence of any topcoating material directly to a zincor aluminum-containing protective coating, it was most surprising that the fluorocarbon copolymer topcoat materials of the present invention proved to adhere so strongly to the zinc or aluminum undercoating without the aid of any additional adhesive materials or pretreatment. Moreover, the durability of the coating adhesion and the general over-all durability of the coating to the attack of heat, light and water vapor proved most surprising. Accordingly, the ferrous metal articles of this invention are able to withstand the corrosive attack of weathering conditions for many years and still retain their aesthetic appearance due to the adhesive capabilities of the fluorine-containing copolymer topcoatings.

The choice of the fluorocarbon copolymer topcoat film composition utilized in the present invention is in part dependent on the nature of the zincor aluminum-containing coating on the ferrous metal substrate. When the metalcontaining coating is quite smooth and a difficult surface upon which to adhere another material, such as with galvanized coatings, it is preferably to use a fluorocarbon copolymer which contains chain units derived from an olefinically unsaturated polymerizable acid having an acidity constant (pK,,) of from 1.0 to 5.5 or a derivative thereof which hydrolyzes to the free acid. More specifically, a preferred class of fluorocarbon topcoats exhibiting an unusually durable adhesion with the zincor aluminumcontaining primer coatings are those copolymers of at least one terminally unsaturated fluorine-containing olefin and an acid monomer such as (A) the ethylenically unsaturated monoand dicarboxylic acids having from three to eleven carbon atoms, (B) the lower alkyl monoand diesters, the salts and the anhydrides of such carboxylic acids, (C) the ethylenically unsaturated phosphonic acids having up to eighteen carbon atoms, and (D) the lower alkyl monoand diesters, the salts and anhydrides of such acids. Specific representative examples of such acid monomers include unsaturated carboxylic acids such as acrylic, methacrylic, maleic, fumaric, crotonic, itaconic, undecyclenic, 3-methylenecyclobutane carboxylic acid, and similar polymerizable aliphati carboxylic acids. Specific representative examples of phosphonic acid monomers are the alkenephosphonic acids such as vinylphosphonic acid, allylphosphonic acid, butenylphosphonic acid, and l7-octadecenephosphonic acid. In place of the free acids one may use derivatives of the acids which are hydrolyzable to the free acid such as the lower alkyl or haloalkyl esters, the salts and anhydrides of the acids. Useful examples of such esters of the above acids include the various isomeric methyl, ethyl, propyl, butyl, amyl, and hexyl monoand diesters. The sodium and potassium salts of the above acids are the most useful salt derivatives. For this improved adhesion to smooth zinc surfaces, the fluorocarbon copolymer must contain at least 0.01% by weight of the polymerizable acid monomers.

Various other specific film-forming properties required in specific situations can be appreciably enhanced by the addition of units into the polymer of a monomer in addition to the fluoroolefin and acid monomer. Such third monomer is preferably a terminally unsaturated fluoroolefin different from the principal fluoroolefin or a C -C hydrocarbon olefin.

It is to be understood, of course, that the copolymers containing the acid monomer and/or additional fluoroolefin or hydrocarbon olefin must also possess the physical characteristics hereinbefore defined in order for utilization as a durable topcoating over the zinc or aluminum primer coatings. Thus, the fluorocarbon copolymer containing the acid monomer must have a fluorine content greater than 30.0% by Weight, a sticking temperature greater 60 C., a glass transition temperature of less than about C. and a melt flow rate of greater than 0.5 g./ 10 minutes at C.

With other metal-containing coatings where the primer surface is not as smooth, such as those containing the inorganic binders, good adhesion is obtained with any of the fluorocarbon copolymers described above. Where obtaining adhesion between the fluorocarbon polymer top coat and the zincor aluminum-containing coating is a problem under ambient temperature conditions, it is preferred to heat treat the coated article. The temperature re quired to give good adhesion and completely coalesce the fluorocarbon copolymer topcoat films varies with the nature of the fluorocarbon copolymer. However, suitable temperatures can be usually found within the range of 50 to 300 C. Application of pressure in conjunction with a heat treatment can also be useful in promoting adhesion of the topcoat.

Representative examples of the present invention follow. All parts are by weight unless specified otherwise.

The superiority of the articles of this invention to all prior art articles is shown by a variety of tests. Exposure of articles under simulated use conditions in a corrosive environment gives an accurate measure of their durability and usefulness. Accelerated tests simulating actual use conditions are also of value in determining the utility of these articles. Both types of tests were employed in the following examples. Thus, coated ferrous metal articles of this invention, together with ferrous metal articles protected by prior art methods, have been compared by exposure out of doors, side by side, under the corrosionpromoting atmosphere of a chemical plant for an extended period of time. Such articles have also been compared by being subjected for extended periods of time to the conditions of an accelerated weathering machine and salt-fog machine. Such articles have also been compared by being immersed in boiling water or in aerated sodium chloride solution for extended periods. Under each of these test conditions the fluorocarbon polymer coated articles of this invention were far superior in corrosion resistance and durable aesthetic appearance to all other corrosion-resistant coatings examined.

The weathering machine was an Atlas Weather- Ometer, Model XW (Atlas Electrical Devices Co., Chicago, Illinois) from which the Corex D glass filters had been removed. The test pieces were continuously subjected to the unfiltered light of the carbon arc and for 18 minutes out of every two hours were also subjected to a spray of distilled water. The air temperature of a black panel set in exposure position reached a high of 165 to 170 F. each cycle before being cooled by the water spray.

The salt-fog machine is an Industrial Corrosion Test Cabinet, Type 411, lABC. In this test, an X cut was made through the surface coatings of the ferrous metal articles. The articles were then placed in the cabinet so the coated surfaces were exposed. A humid atmosphere was then generated in the cabinet and the articles subjected to the salt spray (5% sodium chloride in aqueous solution at 95 F.) for a minimum of 240 hours. After the test, the articles were examined for failure of the coatings at the X cut.

EXAMPLE 1 A 400 ml. pressure vessel was flushed with nitrogen and charged with 225 ml. of acetic acid, 20 ml. of vinyl butyrate, 3 g. of itaconic acid and 0.4 ml. of t-butyl perbenzoate. The pressure vessel was closed, cooled in dry ice-acetone and evacuated. One hundred and forty grams of vinylidene fluoride and 35 g. of tetrafluoroethylene were added to the vessel. The pressure vessel and its contents were then shaken and heated to 100 C. After two hours at 100 C. the temperature was raised to 104 C. and successively in two-hour periods was raised to 106, 108, 110, 112, 115, and 120 C. At the beginning of the reaction the autogenous pressure at 100 C. was 2200 p.s.i. and this dropped to 400 p.s.i. at 120 C. at the end of the reaction period. The vessel and its contents were cooled to room temperature and, after venting any unreacted gases, the contents were discharged. The reaction mixture was diluted with an equal volume of ethanol, filtered, and the resulting filter cake washed with two liters of ethanol. The white solid product weighed 149 g. after drying at 100 C. in a vacuum oven. The dried solid polymer contained more than 30% fluorine, exhibited a melt flow rate at 195 C. of 24.9 g./ minutes and had a sticking temperature of 120 C. The dried solid polymer also had a glass transition temperature of less than 150 C.

A primer coating of a zinc-filled inorganic coating composition prepared according to US. Patent 3,056,684 was applied severally to two pieces of angle iron (a medium carbon steel). The primer coating on the angle iron measured 5 to 6 mils in thickness, The angle iron pieces were eight inches long, two inches wide on each side and onequarter inch in thickness, and were sandblasted prior to coating.

After drying, one of the primed pieces was topcoated by brush application of a coating composition prepared from 36 g. of the above fluorocarbon copolymer, 18 g. of pigment grade titanium dioxide, 150- ml. of methyl ethyl ketone and ml. of cyclohexanone. The resulting topcoat was about 1 mil in thickness after drying at room temperature.

The other primed piece of angle iron was topcoated by brush application of a commercial white pigmented polyamide-cured epoxy enamel. The air-dried epoxy resin topcoat was about 1 mil thick.

The coated angle iron pieces were then placed out of doors on a chemical laboratory building roof in a location where they were fully exposed to the elements as well as in a position vulnerable to the miscellaneous chemicals exhausted from the fume hoods of the laboratory. After 16 months of this exposure the coated pieces were examined and compared. The angle iron having the fluorocarbon copolymer topcoat exhibited no rust and the coating was unchanged in appearance. The angle iron having the epoxy resin topcoat also exhibited no signs of rust. However the aesthetic appearance of the epoxy resin topcoated angle iron was destroyed, since severe chalking, yellowing, and general failure of the epoxy resin topcoat had occurred.

It is evident from the above that the combination of the zinc-containing primer and the fluorocarbon copolymer topcoat is unchanged in appearance and exhibits no failure due to corrosion or chalking, whereas the other primer-topcoat combination shows failure in durable aesthetics.

EXAMPLE 2 Preparation of fluorocarbon copolymers The copolymers of polymerizable, terminally unsaturated fluorocarbon olefins employed in the coatings of this example were prepared by one of three methods. Typical examples of these three methods are as follows:

Method A.-Method A is illustrated by the preparation of the copolymer designated below as No. 2-K. A solution of 210 ml. of t-butanol, 100 ml. of glacial acetic acid, 30 ml. of vinyl benzoate, 10 ml. of di-n-butyl maleate and 1.5 :ml. of a solution of t-butyl peroxypivalate in mineral spirits as free radical initiator was charged to a 400 ml, stainless steel lined pressure vessel. The vessel was swept with nitrogen, cooled to C., evacuated and then charged with 30 g. of isobutylene and 75 g. of tetrafiuoroethylene. With continuous agitation, the vessel and its contents were heated to 45 C. and over a period of 14 hours the temperature was slowly increased to 65 C. After cooling to room temperature, the reaction product was discharged and slurried with 1.5 liters of methanol. The precipitated polymer was filtered and reslurried with one liter of methanol. The solid polymer isolated by filtration was dried overnight at C. in a vacuum oven to give 111 grams of a dry, colorless polymer.

Method B.-Method B is similar to Method A, but involves polymerization in a continuous manner. This procedure was employed for the preparation of the copolymer designated below as No. 2-E. The general procedure was as follows: The solid and liquid monomers being used and the initiator were dissolved in the reaction solvent and the resulting solution was pumped into an agitated pressure reaction vessel which was liquid full of the reaction mixture at the reaction temperature. At the same time, gaseous monomers such as isobutylene and tetrafluoroethylene under pressure were also forced into the same liquid full pressure vessel. The reactants were admitted into the vessel in essentially the same ratio as desired in the final product. The pressure within the vessel was maintained at or above autogenous pressure by a pressure release valve in the exit line which opened when its release pressure was reached. Thus, reactants were continuously pumped into the vessel and product was continuously discharged from the system through the pressure release valve. The copolymer product 'was isolated by addition to alcohol or other solvent to completely precipitate the copolymer which was then further washed with alcohol as in Method A above.

Method C.-The third method of preparation is also a continuous method; however, water is employed as the reaction medium. This method was employed for the preparation of the copolymer designated below as No. 2-F. The general procedure was as follows: A solution was prepared from 3500 parts of deoxygenated water, 15 parts of potassium peroxydisulfate, 15 parts of sodium biphosphite, 15 parts of sodium monohydrogen-ophosphate hepathydrate, 12. parts of isopropanol and 6 parts of an aqueous solution of a surfac- 9 tant comprising a salt of a mixture of monoand bis-polyfluoroal-kyl phosphates as described in US. Patent 3,083,224. A 1500 ml. agitated pressurized reaction vessel was filled liquid full with the solution and heated to 75 C. at a pressure of about 1600 p.s.i.g. To the heated soluble in xylene. Cyclohexanone was used as solvent for those copolymers containing units from the tetrafluoroethylene and vinylidene flouride.

The fluorocarbon polymer was dissolved in the solvent with heating whenever necessary to facilitate solution. The

pressurized reaction vessel was then added a mixture pigment mixture was placed in a pebble mill and the of vinylidene fluoride, tetrafluoroethylene and chlorotrifluorocarbon copolymer solution was added. The slurry fluoroethylene at such a rate that 120 parts by weight of was ground for seven days to achieve complete dispersion. vinylidene fluoride, 32 parts by weight of tetrafiuoroethyl- The resulting paint was separated from the pebbles and ene and 8 parts by weight of chlorotrifluoroethylene 10 was used to topcoat the steel panels as described below. passed into the liquid full reaction vessel each hour. At Zinc-containing coating preparation.A zinc-containthe same time the aqueous reaction solution was fed uning coating composition was prepared with the following der pressure into the vessel :at a rate of 2000 ml. per formulation:

- ai e hour' T pressure wlthu} the vessel was mamt. n d at Ethyl Silicate 40, a partially hydrolyzed ethyl orthoapproximately 1600 p.s.u.g. Product was continuously silicate (manufactured b Union Carbide cor discharged from the system as reactants were continuously y 425 fed into the system. The product was collected, precipi- Boric acid im a1 able owder 23 tated by addition of an equal volume of alcohol, sepa- ISO to a p p P "55 174 rated by filtration, and washed thoroughly with alcohol. P p The resulting white solid product was dried at 90 C. in These ingredients were mixed in order under dry conavacuurn oven. ditions with constant stirring and then boiled at reflux In each of the methods of preparation described above, until solution was effected (3 to 6 hours). This solution the procedure can be varied by way of monomer ratios, was stored in the absence of moisture until required for reactant concentrations, reaction temperature, and other use. reaction conditions in manners known to those skilled in 25 In 60 g. of the above solution was dispersed 135 g. of the art of polymerizing organic monomers to give the pigment grade powdered zinc. This dispersion was applied specific polymers listed below in Table I. by brush to the following pieces of steel which had been TABLE I Method Glass Melt Flow Copolymer Copolymer Monomers Parts by Wt. of Prep- Percent Transition Sticking Rate (g./10 Designation Monomers aration Fluorine Temp. Temp.,C. min. at (Tg) 0. 195 0 2-A Vinylidene flueride/tetrafluoroethylene/vinyl acetate 120/30/14 A 56.2 7 121 10.4

2-3 -do 120/30/4.5 A 60.2 -5 95 7.9

2-0 Vinylidene fluoride/tetrafluoroethylene/vinylacetate] 150/38/9.5/1.5 A 60.0 0 82 15.7

itaeonic acid.

2-D Vinylidenefluoride/tetrafluoroethylene/vinyl acetate] 150/38/9.3/1.5 A 58.4 0 82 31.7

methacrylic acid.

2-E Vinylidene fluoride/tetrafluomethylene/vinyl 80/20/3/0. 5 B 55. 0 67 12. 6

butyrate[bis(2-eh1oroethyl) vinylphosphonate.

2-F Vinylidene fluoride/tetrafiuoroethylene/chlorotri- 120/32/8 C 60. 1 0 107 31. 8

fluoroethylene.

2-G Vinyl fluoride/tetrafluoroethylene/isobutylene/ vinyl 15/75/30/20/19 A 40.0 40 101 25.5

benzoate/vinyl butyrate.

2-H '1etrafluoroethylene/isobutylene/ vinyl benzoate 75/30/30 A 41.3 35 193-109 I 177 2-I Tetrafluoroethylene/isobutylene/vinyl benzoate/ 75/30/20/19 A 39.8 34 113 vinyl butyrate.

2-.T Tetrafluoroethylene/isobutylene/vinyl benzoatc/ 75/30/30/0. 5 A 40.4 14 104 1. 7

itaconic acid.

2-K Tetrafluoroethylene/isobutylene/vinylbenzoate/ 75/30/30/9.5 A 36.8 36 167 1.7

dibutyl maleate.

2-L Vinylidene fluoride/trifiuoroethylene/bis(2- 120/30/2 A 52, 9 36 131 106. 0

chloroethyl) vinylphosphonate.

1 Melt flow rate of 2-H was determined in admixture with an equal weight of dimethyl phthalate as latent solvent.

Topcoat preparation.A series of paints were prepared from the fluorocarbon copolymers listed in Table I above using the following formulation:

Fluorocarbon copolymer g 25 Solvent ml 80 Titanium dioxide pigment g 12.5 Lampblack g 0.5 Monastral Green B pigment 1 g 2.0

1 Colour Index-N0. 10006; manufactured by E, I. du Pont de Nemours & Co. and having the formula For those copolymers containing units derived from tetrafluoroethylene and isobutylene the solvent used was xylene or 1,1,1,3 tetrachloro-2,2,3,3-tetrafluoropropane, the latter being employed only when the copolymer was insandblasted to white metal according to ASTM Class I sandblast specifications.

(1) One piece of ASTM No. 7 non-copper bearing steel angle, 12 inches long, 4 inches wide on each side and 0.25 inch thick.

(2) Two panels of 20 gauge automotive steel, 2 x 3 inches.

(3) One panel of 20 gauge automotive steel, 3 x 6 inches.

topcoat composition in the same manner. After air drying for about four hours the coating became tack-free, and a second coat of the topcoating composition was then applied over the first coat. The resulting coating, after drying, was 0.5 to 1.5 mils in thickness.

Representative fluorocarbon-free compositions such as those containing long oil alkyl, acrylic, polyamide-cured epoxy, and vinyl material were applied as topcoating materials on similar zinc-coated steels and used for comparison with the topcoating compositions containing fluorocarbon copolymers.

Testing program and results.Each topcoated piece of steel was allowed to dry at room temperature for two weeks prior to testing. A large X cut was then made on each flat surface of each piece through the coating to the bare steel with a sharp knife. A strip A; inch wide was cut from the bottom edge of each of the 3 x 6 inch panels to leave a bare steel edge. These panels together with the steel angle were mounted out of doors on an exposure rack for weathering. One of the X-cut 2 x 3 inch panels was placed in the Atlas Weather-Ometer and the second X-cut 2 x 3 inch panel was placed in the salt-fog machine.

Each of the coating formulations was given a single rating based on the over-all results of this testing program. The ratings are as follows and incorporate both corrosion resistance and appearance. Exposure times for all samples 'were comparable.

one or more of the tests.

In every case the test panel coated with the fluorocarbon copolymer coating composition alone showed extensive rusting at the edge on exposure out of doors. Also in every case, the half section of the 3 x 6 inch panel which was coated with the zinc-containing coating but uncoated with fluorocarbon copolymer coating composition developed the whitish color of white rust on exposure, whereas the other half of the panel which comprised the invention composition underwent no change in appearance. The ratings after exposure of the topc-oating materials prepared in this example are compared below in Table II with the rating for various fluorine-free, commercially available topcoating materials.

TABLE II Rating Topcoat Composition Principal Failure 0. Very slight chalking.

Do. Do. Do.

None. Extensive chalking and deterio ration Moderate chalking and deterio ration.

Extensive chalking and deterioration.

Long oil alkyd Acrylic Polyamide-cured epoxy Vinyl P EXAMPLE 3 as described in Example 2. A large X cut was made through to bare metal on one face of each panel. The panels were placed on an exposure rack out of doors for weathering.

The primers used are set forth below in Table III.

TABLE III Designation Description P-l Alkyd resin, oil-modified, red lead primer.

P-2 Zinc chromate, iron oxide, phenolic resin primer.

P-3 Alkyd resin, oil-modified, zinc chromate, iron oxide primer.

P-4 Alkyd resin, metallic zinc coating; 59.2% solids by volume.

P-5 Epoxy resin with zinc chromate and iron oxide cured with polyarnide.

P-fi A copolymer of vinyl chloride and vinyl acetate with a pigment of an equal mixture of carbon black and titanium dioxide.

P-7 Inorganic zinc coating, pigment grade zinc in a sodium silicate vehicle.

P-8 Inorganic boratemodified silicate containing zinc prepared as in Example 2.

P-9 Zincfilled inorganic silicate coating prepared according to United States Patent 3,056,684.

After extended weathering the panels were given an over-all rating incorporating both corrosion resistance and appearance using the same rating system as in Example 2. The ratings are set forth below in Table IV.

TABLE VI Topcoat Primer P-l P; Topcoatdelaminated I; Topeoat deiaminated from primer prior to exfrom primer prior to exposure. posure. P-2 do I; as above. P-3 F; Rusting at X cut F; Rusting and slight lifting of topcoat at X cut. P-4 F; Rusting and slight lifting P; 'lopcoat delaminated oi topcoat at X cut. primer prior to exposure. P-5 F; Busting and very slight F; Rusting and slight lifting lifting of topcoat at X cut. of topcoat at X cut. 1 -6-. P; Extensive rusting P; Extensive rusting and blistering. P-7 G; Very slight rusting at X F; Rusting and slight hfting cut. of topcoat at X cut. P-8 G; No rusting G; No rusting. P-9 G; \Qery slight rusting at X Do.

Similar panels coated with the same primers and topcoated with commercial alkyd and epoxy resin coatings and exposed to the same weathering test rated P for the most part with a few F ratings and no G ratings. The principal modes of failure were rusting at the X cut and chalking of the topcoat.

EXAMPLE 4 A panel of galvanized steel was coated on one side with a solution of a vinylidene fluoride/tetrafluorethylene/ t-butyl methacrylate copolymer in N,N-dimethylformamide, the solvent was allowed to evaporate in an oven at to C. and then the panel was heated at 200 C. for 2 minutes. The resulting clear, colorless, coalesced coating was 3 to 4 mils in thickness. After 18 months exposure to the weather no change in appearance of the coated face panel was found. The uncoated side of the panel was darkened and dirty with occasional whitish deposits.

The fluorocarbon copolymer was prepared by the general procedure of Method A, Example 2, using g. of vinylidene fluoride, 35 g. of tetrafluoroethylene, l g. of t-butyl methacrylate with 100 ml. of glacial acetic acid and 125 ml. of 1,1,2-trichloro-1,2,2-trifluoroethane as reaction media and 0.3 ml. of t-butyl perbenzoate as initiator. The polymerization was conducted at 85 to 115 C. over a period of 10 hours.

EXAMPLE 5 A panel of Armco No. 2 aluminized steel was coated with a dispersion prepared by ball milling 60 parts of a 12% by weight solution of a 50/5 (by weight) vinylidene fluoride/tetrafiuoroethylene copolymer in N, N-dimethylformamide with 30 parts of aluminum powder and parts of a copper phthalocyanine pigment. The coating was evaporated at 120 C. in an oven and then heated on a hot plate at 340 C. for 2 minutes. A series of cuts in a grid pattern were made through the coating to bare metal. The panel was unchanged after being immersed in boiling water for one hour. After 18 months exposure to the weather the panel was unchanged in appearance. Contrasted with this, an uncoated aluminized steel similarly exposed showed rust spots and discoloration.

EXAMPLE 6 The heads of five hundred flat-head, 2% inch long, screw-type, galvanized nails were each rinsed with acetone, soaked for one minute in 5% orthophosphoric acid aqueous solution, rinsed with water and dried. Each nailhead was then dipped into a 2% by weight solution of tetraisopropyl titanate in toluene, baked at 150 C. for 301 minutes, and dipped in a 12% by weight solution of a vinylidene fluoride/tetrafluoroethylene/tbutyl methacrylate copolymer in N,N-dimethylformamide having dispersed therein by weight of titanium dioxide pigment. The nails were placed in a box of sand so that the coated heads were exposed and heated at 120 C. until the solvent had evaporated. The application of the polymer coatings and the solvent evaporation were twice repeated. The coatings on the nailheads were then fused at 225 C. for three minutes.

A portion of the nails was subjected to accelerated weathering tests in an Atlas Weather-Ometer and the coated heads were found to be unchanged in appearance 5 to 6 times longer than conventional baked alkyd and baked acrylic coatings. Another larger portion of the nails was used to secure siding on a house and these nailheads were unchanged after two years exposure to weather.

The fluorocarbon copolymer was prepared from a mixture of 120 parts vinylidene fluoride, parts of tetrafluoroethylene and 6 parts t-butyl methacrylate by the general procedure of Method A described in Example 2.

EXAMPLE 7 A freshly sandblasted panel of automotive steel was completely coated by brush application with the zincrich silicate coating as described in Example 2. This coated panel was placed on a hot plate heated to 380 C. and a tetrafluoroethylene/isobutylene copolymer was melted onto the panel. The molten copolymer was then spread evenly over the panel surface with a spatula to give a continuous coating. After cooling to room temperature the copolymer-coated side of the panel had a glossy, attractive surface. The appearance of the copolymer-coated side of the panel was unchanged after extended immersion in boiling water and in aerated 5% sodium chloride solution.

The tetrafluoroethylene/isobutylene copolymer used contained 47.3% fluorine, had a sticking temperature of 154 C., a crystalline melting point of 160 C., a glass transition temperature of 33 C., and, when mixed with an 85% by weight dimethyl phthalate as latent solvent, a melt flow rate at 195 C. of 138 g./ 10 minutes.

It is to be understood that the preceding examples are representative and that said examples may be varied within the scope of the total specification, as understood by one skilled in the art, to produce essentially the same results.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An article of manufacture comprising a ferrous metal substrate having on at least a portion of the surface thereof (A) a galvanic action coating of from about 0.3 to

about 10.0 mils in thickness comprising at least about 10% by volume of a metal selected from the group consisting of zinc and aluminum dispersed in a binder component selected from the group consisting of fluorine-free, film-forming organic polymer compositions, alkali silicates, tetralkyl orthosilicates and partially hydrolyzed tetraalkyl orthosilicates wherein said alkyl groups are each a C to C aliphatic hydrocarbyl grouping, and (B) overlaid and adhered to said galvanic action coating a topcoat of from about 0.3 to about 5.0 mils in thickness of a normally solid copolymer of at least one terminally unsaturated fluorine-containing olefin and 0.01% of at least one polymerizable acid compound selected from the group consisting of 1) the ethylenically unsaturated monoand dicarboxylic acids having from three to eleven carbon atoms, (2) the lower alkyl monoand diesters, the salts, and the anhydrides of such carboxylic acids, (3) the ethylenically unsaturated phosphonic acids having up to eighteen carbon atoms, and (4) the lower alkyl monoand diesters, the salts, and the anhydrides of such phosphonic acids, said copolymer being characterized by a fluorine content greater than 30% by weight, a sticking temperature greater than 60 C., a glass transition temperature of less than about C., and a melt flow rate of greater than 0.5 g./l0 minutes at C.

2. The article of manufacture of claim 1 wherein the coated ferrous metal substrate is heat treated at 50 C. to 300 C.

3. An article of manufacture according to claim 1 wherein the solid copolymer topcoating (B) is a copolymer comprising vinylidene fluoride, tetrafluoroethylene and vinyl butyrate.

4. An article of manufacture according to claim 1 wherein the solid copolymer topcoating (B) is a copolymer comprising vinylidene fluoride, tetrafluoroethylene, vinyl butyrate, and bis-2-chloroethyl) vinylphosphonate.

5. An article of manufacture according to claim 1 wherein the solid copolymer topcoating (B) is a copolymer comprising tetrafluoroethylene, isobutylene, vinyl benzoate, and itaconic acid.

6. An article of manufacture according to claim 1 wherein the topcoat (B) is pigmented.

References Cited UNITED STATES PATENTS 2,419,009 4/1947 Cotfman et al. 2,43 6,420 2/ 1948 Clayton. 2,468,664 4/ 1949 Hanford et al. 260-863 X 2,599,640 6/ 1952 Joyce. 2,710,266 6/ 1955 Hochberg. 2,881,091 4/1959 Schulze. 2,952,562 9/1960 Morris et al. 3,143,241 8/ 1964 Howell. 3,194,428 7/1965 Dereich 117-97 X 3,318,850 5/1967 Stilmar.

ALFRED L. LEAVITI, Primary Examiner.

J. R. BATTEN, IR., Assistant Examiner.

v us. c1. X.-R. 117-41, 75, 132, 135.1

Patent Citations
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US2419009 *Nov 19, 1943Apr 15, 1947Du PontVinyl fluoride copolymers
US2436420 *Dec 29, 1943Feb 24, 1948Clayton Erith TMethod of coating ferrous metal articles with corrosion-resistant plastic
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3729292 *Jul 2, 1970Apr 24, 1973Duria Werk Kempf Karl KgAnti-friction bearing pad
US3859120 *Feb 28, 1973Jan 7, 1975Du PontExterior siding of an aluminum substrate coated with a durable low gloss clear coating composition containing fluorocarbon polymer particles
US4003760 *Mar 1, 1974Jan 18, 1977Mecano-Bundy GmbhMethod of applying protective coatings to metal products
Classifications
U.S. Classification428/215, 428/421, 428/450
International ClassificationB05D7/16, C09D5/10
Cooperative ClassificationC09D5/10, B05D7/16
European ClassificationB05D7/16, C09D5/10