US2773817A - Composite metal and articles thereof - Google Patents

Description

United States Patent O COMPOSITE METAL AND ARTICLES THEREOF John James Russell, Des Plaines, William A. Beck, Itasca, and Jack Kollman, Chicago, Ill., assignors to Ekco Products Company, Chicago, Ill., a corporation of Illinois No Drawing. Application December 18, 1952, Serial No. 326,765

11 Claims. (Cl. 204-37) This invention relates to a composite metallic structure which may be fabricated into shaped metallic articles having outer surfaces rendered highly absorptive to radiant energy while retaining a relative high resistance to corrosion.

An object of our invention is the PIOViSlOll of a simple, direct, and thoroughly practical process for chemically treating tin and tin alloys by anodic treatment in various electrolytes, in order that the outward surfaces of the tin and tin alloys exhibit excellent heat absorption.

Another object of our invention is to provide a fabricated article which has been anodically treated wherein the surfaces of said article shall be characterized by excellent heat absorption, high abrasion resistance, and continuity and uniformity of the treated tin or tin alloy surfaces.

Another object of our invention is the provision that the heat absorbing coating produced by the chemical process for treating the surfaces of tin or tin alloy shall be adherent and sufficiently ductile in order that articles may be fabricated by mechanical, drawing, forming and/or bending operations.

Another object of our invention is the provision that a shaped composite sheet metal fabricated article, such as a baking pan or a process tray, possess outer and inner surfaces having relatively similar heat absorbing properties.

Other objects and advantages of this invention will be made more apparent as this description proceeds.

In the art of baking, the pans heretofore used have been constructed of sheets having surfaces of tin or tin alloys. An example of such a sheet is tin plate in which the base material is steel. Of course, other tin coated sheets in which the base material is a material such as copper and brass have been used.

Hot dipped tin plate is generally considered to be steel base metal coated on its exterior surfaces with metallic tin wherein intermediate to the tin and steel interface, an iron-tin alloy composition is formed. Tin plate may be formed by either the conventional method of hot dipping or by electrolytically depositing the tin on the surface. The coating weight of the tin is usually specified in pounds of tin per basis box, or in grams of tin per square metre of tin. The conversion of weight per basis box to linearv thickness depends on an assumed density which is compensated by the fact that in the hot dipped process there is a greater proportional thickness of the alloy layer formed than in the electrodeposited process.

It is generally accepted that one pound per basis box is equivalent to 0.0000606 inch thick of tin on each face ofthe tin plate. One and one-half pounds tin plate is generally assumed to be about 0.0000909 inch thick. The proportional ratio between thickness and total weight of a tin plate can be approximated from the relative propor-' tion above mentioned for hot dipped tin plate.

In the case of the electrolytic process, tin plate thickness coatings of 8 ounces to ounces per basis box is "ice generally accepted, although some applications of tin plate may use less than 1 /2 pounds but generally not greater than 1 /2 pounds per basis box.

In the present invention, the anodic chemical treatment of tin plate is primarily directed toward tin plate having the tin content greater than about 1% pounds per basis box which would primarily be adaptable to hot dipped tin plate, although the scope of the invention is also applicable to electrolytic tin plated articles.

' The formation of oxide films of tin, as heretofore known may be produced by converting the tin into the oxide by subjecting the tin layer under oxidizing conditions, such as air, at elevated temperatures. Thisproeess of subjecting the tin to oxidizing conditions at elevated temperatures, has been conventionally used by the baking industry in converting the tin layers to oxides of tin by placing formed articles of tin plate in baking ovens at an elevated temperature of approximately 440 to 425 F. for a period in excess of about 4 to 12 hours. This has been conventionally called the burning in or burning out proc-,

ess, wherein shaped articles, such as baking pans, acquire a color ranging from the interference films of light iridescent hues ranging in-color from yellow, blue through greens, and subsequently a surface coating having a degree of coloring may be obtained depending upon the chemical and physical characteristics of the tin plate surface in conjunction with variable atmospheric conditions during the burning in cycle.

It has been found that these oxide films possess wide variations in color characteristics; and it is highly desirable to eliminate these wide variations in order to produce uniform and consistent bread crust color. In addition, the tin-iron alloy intermediate to the tin layer and the steel base-is brittle and less corrosion resistant than the tin layer. Normally, the tin-iron alloy is substantially increased with respect to the available metallic tin layer by these lengthy burning in operations; and it is highly desirous to reduce the burning in time to about 30 minutes to one hour. The baking industry finds it economically undesirable to subject the bread pan to long periods of burning in because it ties up the baking ovens, bakmg pans, as well as personnel in a non-productive operatron and also produces variable results.

In addition, the temperature controls of the oven may vary considerably. It has been found that oventemperatures generally will exceed the melting point of the tin layer on the surface; as a result the tin-iron alloy layer will be substantially increased and the baking pans will be subsequently destroyed by the evaporation and decomposition of tin surface layer. Also complete uniformity of crust color of bread is a definite sales factor,

. and a baker who can produce a uniform loaf of bread in the initial baking operation without the conventional burning in of a new set of pans, will increase his production capacity.

In addition, the adherence of oxide of tin, by the conventional burning-in method, has been found to be chemical and physical composition of the surface layers I, of the tin will produce variation in adherence of the oxide coatings.

Therefore, it is desirous to secure oxide coating formation having heat absorption which is uniform and reproducible and at the same time to have a surface ox-ide coating which will not tend to reflect heat energy that impinges upon the surface of objects made I of tin plate.

the curing of the film is simultaneous with the final step of the formation of the green oxide of tin coating. In the formation of' the green oxide of tin coating, a tin plated article is subjected, to an ,anodic electrolytic treatment,

as hereinafter described, to form a'tuniform meta s'table tin oxide coating 'on tin plate, and thereafter to the article 15 applied an organic releasing film and the resulting product is heated to an elevated temperature :to simultaneously convert the meta-stable tin oxide, which is bel1eved to be amixture of stannous oxideand stannic oxide, to the tenaciously adherent green oxide while curing the organic fi1m. v

The anodic chemical process of the present invention for treating tin; surface layers will substantiallyireduce the heretofore mentioned fobjections; and in addition, willsubstantially remove objectionable carbonaceous deposits within theporous tinplate, such as g'rea'seand oil.

In addition, the anodic chemical process will tend to seal the pores of the tin plate, thus reducing the tendency toward porosity corrosion, In the chemical anodictreatmerit of tin plate, or products of various shapesiand coi'lfigurations, the tinplate layer is electrolyticallytneated by using one or more of the plates, articles or products as the anodes in an electrolytic bath.

Y The e ectrolytic bath contains at least one "or more, or combinations thereof, of a reagent consisting of substantial amounts of 1) polybasic organic acids, such as citric acid, picric, tartaric acid, oxalic acid, malic acid, maleic acid, and succinicacidgand (2) monobasic organic acids, such as acetic acid, lactic acid, propionic acid, benzenesulphonic acid, trichloroacetic acid, and salicylic acid; and. (3) non-oxidizing inorganic acids, such asphosphoric acids, boric, molybdic, tungstic, andhydrofluoric acids;and (4) aqueous soluble salts, such as the alkali metal and/or alkaline earth salts of the above mentioned organic acids or inorganic acids and other metallic salt compositions, It has been found that combinations offthe reagentsin aqueous solutions may be employed such as: phosphoric acidcombined with citric acid; phosphoric acid combined withsodium phosphate; phosphoric acid combined with oxalic acid, acetic acid combined with sodium citrate; and sodium phosphate ,cbmbinedwith sodium citrate. The scope of this invention shall not be limited to the chemical composition of the reagents. v c t In the anodic, treatment of tin-plated articlesand prodnets in the electrolyte, it has been found advantageous to maintaincurrent densities rangingfrom about 4 amp'jere'sper square foot to about 60 amperesper square foot'of tin surfaces undergoing treatment together with a "solution temperature of at least 50 Q; and usually more, up to the maximum temperature which fallsbelow the boiling point of the solution so as not to cause ex ces'sive evaporation.- Under the chemical conditions specified together with time of immersion, it is possible to obtain a uniform meta-stable tin oxide coating on tin plate having thickness ranging from about 3 toS micr'oinches to almost complete conversion of the free tih'su'rface. Lower temperatures for the electrolyte, -ineluding room temperature, have been foundsuitable for converting at least part of the tin layer to uniform metastable "tin oxide coating, and withthese lower temperaturesthe higher current densities areutilized, y c

It is preferred to employ an electrolyte which by weight consists of at least 0.5% up to about 30% of the reagents wherein the pH of the solution'may be adjusted if necessary, with the corresponding acid or combination of other acids-so that the pH range may vary 'fro'rn 'ahout 'apH- of 2 to a pH of about 8; and the remaining parts needed to form 100% by weight being substantially of water. It has been found that the oxide of tin is more readily formed when the pH is within the range of about two and one-half (2 /2) to five (5).

One or more other tin plated articles, such as tin formed baking pans, are made the anodes of the electrolytic solution and are subject to anodic treatment while maintaining a preferred solution bath temperature of about-8O to 98 degrees C. and a current density of about 20 to 40 amperes per square foot. The cathode may consist of shaped metallic'compositions, such stainless steel, or a lead lined tank may be used as theca'thode. Under such temperature-conditions, the solution is found to remain stable to the extent that the reagent is substantially retained in the bath with respect to weight percentage. removed from the solution.

A uniformgmeta-stable oxide of tin may be imparted to the tin surface in a short interval of time. Th'e tiine of immersion togethe-rwith solution conditions arenaportant factors with regard to the amount of meta-statue tin oxide formed by the anodic treatment. It' hasheen found that interference films of about 2 to 6 ier'aiaehe" thick may be formed byanodic treatment, in the e ect'rolyte'for an interval of time corresponding to a few s'econds, In addition, it has been found that in a matter of minutes'the entire tin layer can be converted intoa ineta stable oxide of tin,

As "examples'of other exceptionally stable-conductiveand highly effective electrolyte'solut ions, [and the relalted operating conditions which are employed for rapidly obtaining a uniform continuous meta-stable oxide of an; the following treatments may be'employed:

T r eatme nt A Percent: Electrolyte Total Weight 'Of Bath Disodium'Hydi-ogen Phosphate NMHP 04 "3-15 Ortho Phosphoric Acid HaP O-i(%); -2-5 "re'r'n'ainiiig p'a'nts'needed with the-above to total 100% (percent) by weight, being substantially Water.

--re1naining--- parts needed f above --to total 100 percent by weight, beingsubstantially water.

Any rsm'ainia pam needed 'with theabove mm: 100% (percent) by weight, being substantially water.

The reagent" is not substantially chemically Any remaining parts needed with the above to total 100% (percent) by weight, being substantially water.

Bath temperature 80-100" C. Minimum current density 15 amperes per sq. foot. Time of immersion 30120 seconds.

Treatment E Percent Electrolyte Total Weight of Bath Sodium Tartrate N82C4H40e-2H20 3-30 Disodium Hydrogen Phosphate 2-10 Any remaining parts needed with the above to total 100 percent by weight, being substantially Water.

Bath temperature 90-100 C. Minimum current density 15 amperes per sq. foot. Time of. immersion 15 to 120 seconds.

Treatment F Percent Electrolyte Total Weight of Bath Disodium hydrogen phosphate 3-30 Any remaining parts needed with the above to total 100 percent by weight, being substantially Water.

Bath temperature 80-100" C. Minimum current density 20 amperes per sq. foot. Time of immersion 30 to 120 seconds.

Treatment G Percent Electrolyte Total Weight of Bath Sodium Oxalate N3zCzO4 2-15 Phosphoric Acid HsP O4 (85%) 3-10 Any remaining parts needed with the above to total 100% (percent) by weight, being substantially water.

' Any remaining parts needed with the above to total 100% (percent) by weight, being substantially water.

Bath temperature -100 C. Minimum current density 20 amperes per sq. fioot. Time of immersion 60 to seconds.

An excellent meta-stable oxide layer of tin was obtained on tin plate in the instance of using Treatment A through Treatment H, inclusive. The scope of the invention should not be bound by any such quality of chemical composition, nor by the specific proportions of acids, salts, and water given in the several illustrative examples of the treatment.

The treated tin plate articles are then removed from the electrolyte bath and rinsed with water in order to remove any occluded salts. The treated articles are then dried at slightly elevated temperature in order to remove the adherent water. The treated tin plate articles upon which the meta-stable oxide of tin is deposited or formed thereon are subjected, after the application of the organic bread releasing film, as hereinafter described, to an oxide conversion temperature condition whereby the metastable oxide of tin coating is then converted at elevated temperatures to form the stable, tenaciously adherent green oxide of tin coating while at the same time curing the organic film. For conversion of the tin oxide temperatures as low as 150 C. can be used, but since the time required for temperatures below about C. are quite long, it is preferred that the temperature range be from about 190 C. to about 230 C. Of course, where the tin coating has been entirely converted to meta-stable tin oxide in the electrolytic treatment, temperatures above 230 C., for example as high as 400 (3., can be utilized when the entire oxide of all of the oxide of tin coatings have been coated with the organic film because an inner layer of tin need not be relied upon for corrosion prevention. This heating step in the process may be obtained by direct heat application to formulate the oxide conversion.

The formation of the meta-stable oxide of tin under electrolytic treatment will vary depending upon solution compositions and conditions. Since tin exhibits amphoteric properties, it has been noted that the meta-stable oxide of tin may be formed under alkaline conditions, although the electrolytic step in the process is preferred under acid conditions (pH from 2% to 5), successful results have been obtained under alkaline conditions. In addition it has been noted that the formation of the meta-stable oxide of tin may be formed first by immersion in an alkaline medium and then subsequently into an acid medium or combinations thereof.

The meta-stable tin oxide coating exhibits the interference color on the surface of tin, and when the thickness of the meta-stable tin oxide appears to approach about seven (7) microinches, capacity of the film begins to occur. By varying the time of immersion in the electrolytic bath, the blue-black meta-stable tin oxide is formed and at about 2 to 10 minutes immersion time under the aforementioned conditions it appears that the tin layer may be converted totally into the meta-stable tin oxide. Therefore, it is desirable to reduce the time of electrolytic immersion to about fifteen to ninety (15-90) seconds in order to retain a relatively high percentage of free tin.

The time interval for electrolytic immersion will vary depending upon solution conditions. By reducing the current density and/or the temperature as well as the concentration of the reagent, it is possible to increase substantially the time interval of immersion of the tin layer in the electrolytic bath. Therefore, the scope of the invention shall not be bound by the specific time interval of immersion.

The meta-stable tin oxide exhibits various transitional interference colors approaching the blueblack. The blueblack is then considered the end point of opacity; and it has been found that the interference colors of red, purple, green, and blue-green will form, upon subjecting the then treated meta-stable tin oxide coating to conversion.

seesaw 7 conditions at"elevated'temperature; the stable tin oxide coating-exhibiting a uniform olive green color which is believed to be a mixture of stannous oxide and st-annic oxide.

The novel chemical treatment described in this process may be further accomplished by'using a fused salt, such as diso'diu mhydrogen phosphate dodeca-hydrate or magnesium phosphate, as the electrolyte, or combinations thereof. One may consider. this to be substantially an aqueous solution when the temperature of the electrolyte bath is within 80 to 100 C; We have found that satisfactory results can beobtained by holding the bath temperature between 80 and 90 C. operating at a minimum current density of about 15 amperes for a square foot for a period of time of about 20 to 90 seconds. When-the current density is held at about 30 amperes per square'foot, it-has'been found that the voltage dropped to about 2 volts.

lt shall be noted that the process as described may be applied to tin plate in sheet formwherein the anode may be a sheet of tin. plate or a shaped article. Thetin plate or 'com-p'osite sheet structure may be chemically treated by'the treatments aforementioned and then fabricated into shaped articles.

An alternative method of manufacturing these shaped articles, having heat absorbing oxide coatings formed thereon, may be accomplished by forming the tin plate and then subjecting the formed shape to the anodicchemical treatment by immersing the shaped article in the electrolyte. The cathode generally will have to be shaped into various forms in order thata uniform oxide of tin coating may be formed on the tin layer; especially wherein the surfaces of the shaped article are deeply formed.

Another step of this invention comprises the coating of the oxide of tin coatings with a stable high temperature organic bread .releasing'film. The organic bread releasing film may be applied prior to the final temperature conversion step so that the meta-stable tin oxide is coated with a stable high temperature organic bread releasing film.

Examples of this film are films of the polyorgano siloxanes, also generically known as silicones, in which silicon atoms are linked to other silicon atoms by means of oxygen atoms, and in which organic groups are attached to silicon atoms. Examples of organic groups are aliphatic radicals,-especiallyalkyl groups, and aryl radicals such as the phenol and naphthyl groups. Other examples of organic groups include the alkaryl radicals, such as tolyl and xylyl radicals, andarlkyl radicals, such as benzyl radical. In all of these organic groups there may be substitution of'other atoms or radicals, such as chlorine, hydroxyl and bromine; for example, the organic groups may be chloromethyl, chlorophenyl, brornophenyl, hydroxyethyl, and hydroxyphenyl.

These polyorgano siloxanes may be the silicone resins, such 'asthe alkyl silicones and alkyl aryl silicones in whicha considerable proportion of the siloxane units of thepolymer contain about one organic group per silicon atom, and in which another portion of the siloxane units containtwo organic groups, preferably in which one of the groups is an alkyl radical, such as methyl radical, while the'other group is an aryl radical, such as the phenyl group. 'These resins are known as alkyl aryl silicones when at least a portion of the siloxaneunits contain both an allryl group and an aryl group. In addition to the silicone'resins, viscous silicone oils. may be used.

Other examples of organic bread releasing films are the .polyorganos'ilanes, suchas disclosed in U. S. Patent 2,606,837, granted to Harold A. Clark on August 12, l95-2,'in which these polymers are merely applied to commercial b'read pans of the prior art, that is, pans which did not contain the uniform continuous tenaciouslyadhe'r'ent meta-stable tin-oxide coatings of this invention,

and thus did not contain the uniform continuous tenac iouslyadherent opaque green oxide of tin coatings that 8 are obtained in carrying-out thecomplete rocessor this invention. 7

A further example of theorganic is'fihn of'a polymer of a fluorine-containing derivative of ethylene,

such as polytetrafluoroethylene, polytrifluoromonochloroa ethylene, polydifluorodichloroethylene, and polyvinylidcne fluoride. adequately described in the published literature; for example, a process of preparing the polymer of tetrafluoroethylene is described in U. S. Patent 2,534,058, granted to M. M. Renfrew on December 12, 1950, in which an" aqueous dispersion or-suspension of the polymer isob tained. Such aqueous colloidal dispersionscan be concentrated by the method disclosed in U. S. Patent 2,478,229 granted to K. L. Berry on August 9, 1949.

The polymers of the other fluorine-containing derivatives of ethylene can be made by similar processes or by other methods, for example, the polymerization ofvinylidene fluoride is described in Industrial and Engineering Chemistry, volume 41, page 71 (January 1949), and the preparation of polymers of trifluoromonochloroethylene .is described in British Patent 465,520, granted May 3, 1937, to I. G. Farbenindustn'e A. G.

The aqueous colloidal dispersions of these polymers,

can be stabilized by the use of nonionic and anionic dispersing agents, for example, alkyl aryl polyether al- The stabilizing effect of these dispersing agents is described in Industrial and cohol and sodium lauryl sulphate.

Engineering Chemistry, volume 44, pages 1800-5 (August 1952).

A still further example of organic bread-releasing films are the films obtained using allyl polymers, piererably resinous allyl polymer. The allyl resinsare broad ly polybasic acid-alcohol esters and polymers thereof, which may be prepared by various methods such as by esterifying a polybasic acid and an allyl alcohol with p or without additional alcohols to produce the mixed ester desired. These compounds may also be prepared from the corresponding acid chlorides of the acid esters, such as allyl succinyl chloride. This acid chloride may be reacted with polyhydroxy compounds to form the desired products. Alternately, the polyhydi-ic esters of a polybasic acid such as glycol dihydrogen diphthalate or other partial esters of a polyhydric alcohol and a polybasic acid may be esterified with allyl alcohol or;

with a mixture of such alcohols as methallyl, allyl and crotyl alcohols and the like. Various catalysts are gen= erally used at elevated temperatures.

By polymerization of the compounds formed, it is possible to secure a wide range of intermediate fusible.

polymers. These fusible polymers may be prepared by polymerizing the unsaturated compounds until substantial polymerization has occurred and interrupting the polymerization before the'polymer is converted into a gel.

It is found that when polymerization of these materials is initiated, a fusible polymer is primarily formed. This fusible allyl component may be partially or totally dissolved in such organic solvents as acetone, dioxane,

benzene, toluene, chloroform, acetates and the like.

The resinous components are dispersed in the respective solvents and mixed,'-whereupon the combination is ap-' plied to tin plated bakingpans having meta-stable tin oxide coatings, dried for 30 minutesand cured, for ex-' ample, at 425 F. for one hour, which simultaneously converts the tin oxide to green oxide of tin. In making comparative tests of the releasing properties of bake goods, a standard baking dough mixture having a relatively highsugar content and a low shortening content is used 'to determine the relative releasing properties of variou coatings. By introducing this minor proportion of the incompatible resin component to the allyl resin polymer, the number of releases can be greatly increased. In addition, we have found that in many instances, cured allyl resinous coating will not'frelease. this. standard 1 dougnnixture even on the first'bake'; while in Processes for preparing .these polymers are of bake pans having a film of the resinous composition employed in the present invention, we have had as many as 250 baking releases prior to sticking.

In accordance with this invention, mixtures of organic bread releasing film materials may be used in the coating of the meta-stable oxide of tin coating with a stable, high temperature, organic bread releasing film prior to the heating treatment in which the meta-stable tin oxide is converted to the tenaciously adherent green oxide. Various modes of application of the film may be used. The film may be applied by any one of various means, including dipping, spraying or brushing with a solution or colloidal dispersion of the organic film material. In the case of the film material, such as polyorgano siloxanes and polyorgano silanes, solutions of the polymers in organic solvents may be used. Suitable organic solvents include aromatic hydrocarbons, such as toluene, xylene and coal tar naphthas; ether, such as dibutyl" ether; esters, such as amyl acetate; ketones, such as methyl isobutyl ketone; and chlorinated hydrocarbons, such as trichloroethylene. Illustrative solvents for allyl polymers are described above.

In the case where the organic film to be applied is a polymer of a fluorine-containing derivative of ethylene, aqueous dispersions are used as mentioned above.

The concentrations of the organic film materials in the organic solvents or in the aqueous dispersions can be varied widely, for example between and 70% by weight of the solution, the optimum concentration depending on the polymer and whether or not an organic solution or aqueous dispersion is used. In the case of silicones and polyorganosilanes, it is preferred that the concentration of the polymer be at least about and the maximum about 50%, whereas in the case of the polymer of fluorine-containing derivatives of ethylene it is preferred that the concentration of the polymer in the aqueous dispersion be relatively high, for example 40 to 60%. In using the allyl resin as the film material, it is preferred that the allyl resin constitute about 30 to 50%. All of these concentrations are percent by weight. It is preferred that a final organic film thickness of at least five (5) microinches be provided.

The material containing the organic polymer to provide the bread releasing film is applied to the meta-stable oxide of tin coating by any of the methods described above, and then the organic solvent or water of the dispersion, as the case may be, can be allowed to evaporate at room temperature, at least to a partial extent, followed by heating the resulting coated material to convert the meta-stable tin oxide to the green oxide of tin. This high temperature treatment is at least about 150 C., but preferably about 190 to 230 C., which will cure the organic polymers in most of the examples described above. In the case of the polymer of the fluorine-containing derivatives, treatment is completed at a considerably higher temperature in order to sinter the particles of the polymer on the surface to provide a smooth film. For example, in the case of polytetrafluoroethylene, the final temperature used is a temperature of about 350 C. Of course, in the case of films of the polymers of the fluorine-containing derivatives of ethylene, the final temperature is above the melting point of tin, so that .any tin remaining below the green tin oxide alloys with :the base metal. This does not impair the suitability of the product, because the presence of the organic film provides protection from corrosion of the base metal as well as providing a film which satisfactorily releases the bake products, such as bread, when the article of this invention is used in baking.

In an embodiment of this aspect of the invention it is thus unnecessary to insure that the original tin plated sheet is anodized so as to leave a portion of the tin un- .converted. This has the advantage that the entire tin ;-plate or coating can be completely converted by anodiz- 10 ing to the meta-stable tin oxide, which is then converted to the, tenaciously adherent coating of green tin oxide for maximum utilization of the heat absorbing prop-. erty provided by the green oxide of tin.

The articles obtained by the process of this invention provide satisfactory release of the bake goods, so that the articles can be used a great number of times before renewing the organic releasing film; at the same time, the articles are corrosion resistant during such use, and make possible a uniformity of product in the baking operation that enhances the salability of the baked product.

As many possible embodiments may be made of our invention and as many changes may be made in the embodiments hereinbefore set forth, it is to be understood that all matter described herein, is to be interpreted as illustrative and not as a limitation.

This application is a continuation-in-part of co-pending application Serial No. 156,672, filed April 18, 1950.

We claim as our invention:

1. A method of making a composite article comprising a composition of tin layer bonded to a metallic supporting base having surfaces outwardly disposed thereof, comprising the steps of subjecting the supporting base with metallic tin coating to anodic electrolytic oxidation in an electrolyte to form a tin oxide coating, removing the anodized article from the electrolyte, coating said oxide of tin coating with a stable high temperature organic releasing film, and then subjecting the coated article to an elevated temperature of about C. to 400 C. in order to convert the oxide of tin to the green oxide of tin while curing the organic film.

2. A method of making a composite article comprising a composition of tin layer bonded to a metallic supporting base having surfaces outwardly disposed thereof, comprising the steps of subjecting the supporting base with metallic tin coating to anodic electrolytic oxidation in an electrolyte to form a tin oxide coating, removing the anodized article from the electrolyte, coating said oxide of tin coating with a stable high temperature organic releasing film, and then subjecting the coated article to an elevated temperature of about 150 C. to 230 C. in order to convert the oxide of tin to the green oxide of tin while curing the organic film.

3. A method of making a baking pan article comprising a composition of tin layer bonded to a metallic supporting base having surfaces outwardly disposed thereof, comprising the steps of subjecting the supporting base with metallic tin coating to anodic electrolytic oxidation in an electrolyte to form a tin oxide coating, removing the anodized article from the electrolyte, coating a portion of said oxide of tin coating with a stable high temperature organic releasing film, and then subjecting the coated article to an elevated temperature of about C. to 230 C. in order to convert the oxide of tin to the green oxide of tin while curing the organic film.

4. The method of claim 3 in which the organic releasing film contains a polyorganosiloxane.

5. The method of claim 4 in which the polyorganosiloxane is a methyl phenyl silicone.

6. The method of claim 3 in which the organic releasing film contains polytetrafiuoroethylene.

7. The method of claim 3 in which the organic releasing film contains polytrifluoromonochloroethylene.

8. A method of making a baking pan article comprising a composition of tin layer bonded to a metallic supporting base having surfaces outwardly disposed thereof, comprising the steps of subjecting the supporting base with metallic tin coating to anodic electrolytic oxidation in an electrolyte to form a tin oxide coating, removing the anodized article from the electrolyte, fabricating said anodized article into a shaped article, coating a portion of said oxide of tin coating with a stable high temperature organic releasing film, and then subjecting the fabri cated coated article to an elevated temperature of about 190 C. to 230 C. in order to convert the oxide of tin

Claims (1)

1. A METHOD OF MAKING A COMPOSITE ARTICLE COMPRISING A COMPOSITION OF TIN LAYER BONDED TO A METALLIC SUPPORTING BASE HAVING SURFACES OUTWARDLY DISPOSED THEREOF, COMPRISING THE STEPS OF SUBJECTING THE SUPPORTING BASE WITH METALLIC TIN COATING TO ANODIC ELECTROLYTIC OXIDATION IN AN ELECTROLYTE TO FORM A TIN OXIDE COATING, REMOVING THE ANODIZED ARTICLE FROM THE ELECTROLYTE, COATING SAID OXIDE OF TIN COATING WITH A STABLE HIGH TEMPERATURE ORGANIC RELEASING FILM, AND THEN SUBJECTING THE COATED ARTICLE TO AN ELEVATED TEMPERATURE OF ABOUT 150* C. TO 400* C. IN ORDER TO CONVERT THE OXIDE OF TIN TO THE GREEN OXIDE OF TIN WHILE CURING THE ORGANIC FILM.