US3074154A

US3074154A - Tin plate and method of producing

Info

Publication number: US3074154A
Application number: US850118A
Authority: US
Inventors: Vincent P Pearson; James E Mcfarland; Henry M Roelofs
Original assignee: Inland Steel Co
Current assignee: Inland Steel Co
Priority date: 1959-11-02
Filing date: 1959-11-02
Publication date: 1963-01-22
Anticipated expiration: 1980-01-22

Description

United States Patent 3,074,154 TlN PLATE AND METHOD OF PRODUCING Vincent P. Pearson, Chesterton, Ind., and James E. Mc-

Farland and Henry M. Roelofs, Chicago, Ill., assignors to Inland Steel Company, Chicago, 111., a corporation of Delaware N0 Drawing. Filed Nov. 2, 1959, Ser. No. 850,118 17 Claims. (Cl. 29--196.4)

This invention relates generally to tin plate and more particularly to an improved tin plating process which includes the step of providing at least a portion of the surface of a metal strip with a coating which is adapted to serve as an identification marking or protective layer which retains a high degree of corrosion resistance, and to the improved tin plate thus produced.

In general, the production of tin plate by the electrolytic tinning method involves the steps of passing a cold reduced, annealed ferrous metal sheet or strip, such as black plate, continuously through a tank containing an acidic or alkaline solution of a tin salt and therein electrodepositing tip on the strip. After leaving "the tinning tank, the rough, freshly plated strip is passed through a furnace or oven at a temperature sufficiently high to fuse the tin in order to form a smooth, bright tin coating on the strip. A relatively recent development in the foregoing general electrolytic tinning process is the production of differentially coated tin plate wherein the electrolytic tinning step is so regulated that one side of the metal strip receives a relatively lower weight coating of tin. For purposes of tin can manufacturing and the like, a relatively heavy corrosion resistant coating of tin is required only on the inside of the can. Thus, the use of differentially coated tin plate avoids an unnecessarily heavy external coating of tin on the outside of the can, thereby resulting in important economies in the use of tin.

With the advent of differentially coated tin plate in the industry, it was necessary that the tin plate manufacturers have some means for marking the differentially coated tin plate which would permit the can manufacturer to identify the side having the lighter tin coating thereon, or otherwise distinguish between the different sides of the tip-plated strip. As the differentially coated tin plate is discharged from the fusion step of the electrolytic tinning line, how ever, both sides of the strip normally possess the same customary bright, highly reflective finish.

Various marking techniques have been proposed and tried heretofore but no entirely satisfactory scheme has heretofore been developed for distinguishing one side of the plated strip. For example, certain types of printed markings have been tried but these have not been acceptable because the marking or design tended to fade after a period of storage. Another method of identification which has been utilized to some extent involves the use of a roughened roll at the skin mill so that the steel strip prior to introduction to the electroplating bath has one side or a portion thereof roughened. The roughened surface after electrolytic tinning possesses a dull surface appearance or a decreased reflectance, as compared with the tin coating on the smooth side of the strip. Although this purely mechanical pretreatment of the strip to effect dulling of one side gives a permanent marking, it has been found that the dulling eifect is far from uniform. Furthermore, the corrosion resistance of the tin plate is adversely affected and this, of course, is a serious objection for most uses of tin plate. Moreover, the tin plate producer also finds the technique'inconvenient, since it necessitates frequent changes of rolls at the skin mill due to the tendency of the rough roll to become smooth after a relatively short period of rolling time.

Another marking method which'has been utilized to some extent, involves treating one side of the steel strip anodically between the eelctrolytic tinning and fusion steps. For satisfactory dulling by the latter means, however, it is also necessary that the base metal strip be roughened at least slightly in the rolling operation prior to electrolytic tinning, thereby introducing the previous objections of non-uniformity of dulling and reduced corrosion resistance of the tin plate. Moreover, the anodic treatment frequently is ineffective along the marginal edges of the strip so that the over-all dull surface appearance desired by the can manufacturers is not obtained.

Still another method of marking or dulling tin plate, which avoids certain of the objectionable features of the preceding methods, comprises applying an alkali metal salt as a continuous coating or in a distinctive pattern, to one side of a tin coated strip prior to the fusion heating thereof. However, since the latter process requires the use of a chemical salt on the exposed surface of the tin plate, it is highly preferable to provide a suitable process of marking tin plate which avoids applying a chemical to the exposed surface of tin plate.

Accordingly, it is a primary object of the present invention to provide novel and improved mean for marking or dulling tin plate.

Another object of the invention is to provide a novel and improved means for providing an identification marking on one side of differentially coated tin plate.

A further object of the invention is to provide a novel and highly satisfactory means for marking or dulling tin plate which avoids appreciable impairment of the corrosion resistance properties of the tin plate.

It is another object of the present invention to provide an improved electroplated tin coated strip having a marked or dulled tin coating.

Still another object of the invention is to provide an electroplated tin coated strip having high corrosion re sistance. Another object of the invention is to provide a novel step in an electrolytic tinning process for imparting a uniformly dull surface appearance to one side of the tin plated strip.

Other objects of the invention will be apparent to those skilled in the art from the accompanying description and claims to follow.

In the usual electrolytic tinning processes adapted to make differentially coated tin plate, a steel strip is formed by hot-rolling from slabs, continuously pickling the strip, cold-reducing to the required thickness, cleaning, annealing, temper or skin rolling, and passing the strip through electrolytic cells where the desired coating of tin is electrodeposited on each side of the strip, after which the tin coatings are fused in a fusion unit to provide a bright, lustrous-appearing surface. The present invention comprises an improvement in the foregoing electroplating processes wherein there is applied to the free metallic surface of the base steel strip, a solution or suspension of a reducible compound of a metal such as molybdenum, nickel, cobalt, titanium, tungsten, and antimony, said metals generally being in the group of adherence-promoting metals, and in addition, compounds of such metals as bismuth, tellurium, and arsenic, all the said compounds being reducible to the free metal at temperatures below about 2000 F. The selected compound preferably is applied to the metal surface just prior to its entering'the preheat zone of the continuous annealer, or just before recoiling after cleaning and drying thestrip for box annealing. The strip coated with the metal compound is then heated under conditions to cause the said metal compound to be reduced to a free metal which difiuses into the steel strip to provide a surface coating capable of withstanding skin rolling, and which gives, after electroplating and fusion, a much less reflectant tin plated surface than the normal fused tin plated surface. Also, where high corrosion resistance is desired, a compound of a metal of the above group can be selected which renders the tin plated surface more highly resistant to corrosion than previous tin plated surfaces, such as ti tanium and nickel.

The reagents which can be used for marking steel plate for use in the manufacture of electroplated tin plate in accordance with the present invention comprise aqueous solutions of water soluble compounds of the metals including molybdenum, nickel, cobalt, titanium, antimony, tungsten, bismuth, tellurium and arsenic, or aqueous sus-. pensions of compounds thereof, which on being subjected to heat in a neutral or reducing atmosphere, are reducible to a free metal and diffusible into the steel strip. The compounds of the above metals which are most useful in the present invention are the non-volatile metal oxides which are readily reducible to the free metal on heating in a non-oxidizing atmosphere. It is, of course, advisable to avoid using compounds of the said metals which on heating under neutral or reducing conditions sublime at low temperatures or leave a residue on the steel strip in addition to the free metal, particularly where the said residue is not readily removable by a washing or pickling treatment following the annealing step. More particularly, the specific compounds which can be used for marking or coating in the present invention include molybdenum oxide (Mio nickel oxide (NiO), cobalt oxide (C), titanium oxide (TiO antimony oxide ($13203), tungsten oxide (W0 or bismuth oxide 121 0,

It is also within the scope of the present invention to provide an oxide coating on the metal strip by means of a solution or suspension of a compound or salt of the said metals which can be decomposed or oxidized to yield the desired oxide in 'situ. For example, ammonium molybdate or molybdic acid, can be deposited on the metal strip and readily decomposed or oxidized by heating, to yield molybdenum trioxide. Similarly, ammonium tungstate, tungstic acid, and nickel formate, are typical examples of compounds of the above metals which can be used to form the corresponding metal oxide in situ. Among the compounds which decompose to the oxide and which are useful in the present invention as marking or coating agents, are the formates, oxalates, nitrates, tartrates, and the ammonium salts of certain of the said metals. Also, it is possible to use a combination of any twoor moreof the said salts, such as molybdenum oxide and nickel oxide in an. admixture thereof, or a complex salt of two or more of the said metals, such as the molybdenum-nickel complex salt formed by mixing a solution, of ammonium molybdate and nickel chloride, or nickel nitrate.

The foregoing marking or coating agents of they present invention are applied to the surface of the metal strip in the form of solutions, suspensions, or dispersions. One

method of providing the oxide coating on the iron or steel base is to form' a suspension or dispersion in water or. other suitable liquid medium of an oxide or oxides, in finely divided or powdered form and then apply the liquid coating material to the surface of the base by anyconvenient technique, such as spraying, brushing, wiping, roll-coating, dipping, electrostatic fogging or the like. Usually, water will be the most convenient liquid medium but other liquid vehicles such as glycerine, light oils,- or-the like, can be used. In the case of an aqueous medium, it is usually advantageous to employ therewith anaddeddispersing or suspending agent, such as starch,

and preferably including a surface active agent, in order to form a relatively stable suspension or dispersion of the finely divided oxide in the aqueous liquid. We have found that methyl cellulose, corn syrup, cornstarch, or other thickening agent is highly satisfactory for this purpose.

When the coating is applied as a suspension or dispersion containing starch as a suspending agent, it is preferred to heat or bake the coating to polymerize the starch before heating to the elevated temperature required for reduction of the oxide by interaction with the metallic iron. Thus, heating for a few minutes at a temperature between F. and 300 F. polymerizes the starch and forms a firmly adherent coating of the oxide on the base before reduction thereof to the metal state and diffusion into the base.

Although any of the above-mentioned methods of applying the marking solution or suspension may be used, spray application is generally the most satisfactory for large-scale commercial operation, since the relatively large quantities of solution or suspension required on the sheet can readily be obtained by the use of sprays. Ordinary mechanical sprays or atomizers can be utilized, but the preferred method of application is by electrostatic coating because of the ease with which over-spray is controlled, thereby avoiding contamination of the working area. Moreover, it is extremely important in the case of differentially coated tin plate that the application of the solution or suspension be confined to only one side of the strip. With electrostatic coating, it, is a relatively simple matter to avoid wrap around, i.e., contact of the marking reagent with the reverse side of the strip relative to. the spray nozzles. Electrostatic coating is Well known in the art and need not be described in any detail except to say that the treating solution is converted into a spray by air pressure or mechanical means under the influence of an electrostatic field. so that the spray particles are electrically charged and are attracted to the strip and deposited thereon. Reference is made to such prior art patents asRansburg et al. 2,334,648, Ransburg 2,658,009, and'Ransburg 2,698,814 for various details of the electristatic coating methods and devices.

In order to reduce the surface tension of the aqueous treating solution. or suspensions and to insure uniform distribution of the solution: asapplied to the surface of the strip, it is. preferred to include inthe treating solution or suspension a small amount, inthe order of from about 0.01% to about 0.5% by volume, of a suitable surface: active or wetting agent. It has been found that the non-- ionic surface active. agents, are particularly effective for" this, purpose, e.g-., the polyoxyethylene ethers and the polyethylene ethers and the polyethylene glycol alkyl ethers. Any tendency to dewetting detracts from the desired uniformv dulling or marking of the surface, and the presence of a surface active agent minimizes-this. effect to a large extent;

In order to effect uniformdulling of a tinelectroplated surface in accordance with the. present invention, it ispreferred that the metal compound: be present thereon to. the extent sufiicient to provide about 0.1 gram of the metal per square foot of treated surface. An oxide coating of the said metals, such as molybdenum oxide or nickel oxide, having a thickness of about 0.000005 inch will provide the optimum required amount of metal. In order to effect an increase in the corrosion resistance of tin plate over and above the normal resistance attributable to, the tin, it is. preferred that the metal compound be present on the surface of the steel strip in an amount suflicient to provide about 1 gram of metal per square foot of treated surface. An oxide coating of the herein disclosed metals, such as nickel oxide, having a thickness of from 0.001 and 0.00005 inch, will provide increased corrosion resistance. 'The amount of compound placed on the surface of the base plate is always correlated with the time and temperature of. treatment so that the compound is completely reduced and diffused into the base within the limited time permitted in the heating step employed. From a practical consideration, the range can vary from about 50 to about 500 mg. per square foot of surface, depending upont he particular metal salt employed and the degree of dullness desired. The concentration of the aqueous treating solution or suspension is not particularly important as long as the aforementioned minimum amounts of metal salt are deposited on the surface of the steel strip. The solutions or suspensions of the said metal compound can, for example, have a concentration from about 100 to about 360 grams per liter of solution. Also, the starch can be used in an amount between about to 30 grams per liter. It will be understood that the quantity of the metal compound applied to a given area of the steel strip must be correlated with the concentration of the metal compound therein so as to obtain the required minimum deposit of the said metal compound per square foot of treated surface. Actually, of course, the maximum concentration of the metal salt in an aqueous solution is determined only by the water solubility of the particular metal salt employed.

Following the application of the metal compound on the steel strip, the strip is heated to an elevated temperature, preferably by passing the strip through the conventional continuous annealing furnace, wherein it is maintained in the non oxidizing atmosphere therein for a suflicient time to effect decomposition of the salt to the oxide, if the oxide itself is not employed, and thereafter complete the reduction thereof to the free metal, after which the metal is diffused into the surface of the steel strip. Broadly, the temperature range at which the reduction-dilfusion heating step takes place is from about 1150 F. to about 1400 F., depending upon the particular metal compound employed and the time allowed for the heating step. For example, when molybdenum oxide is employed, a temperature of about 1400 F. is maintained and the strip is allowed to remain in the continuous annealing furnace for a period of about 2 to 10 seconds. In a box annealing process, wherein the molybdenum oxide is deposited on amild steel base (0.05 to 0.1% carbon), the heating step is conducted at a relatively lower temperature range between about 1150 F. to about 1200 F., and the period of heating is in the order of from 3 to 12 hours. It will be understood that the time and temperature of the heating step are correlative factors so that substantially equivalent results can be obtained at conditions of high temperature-short time, or low temperature-long time.

While it is possible to carry out the heating and reducing steps in a variety of treating atmospheres, the heating of the oxide coating should be carried out in an atmosphere substantially non-oxidizing to iron, and preferably in an oxygen-free atmosphere, either neutral or reducing. A wide variety of atmospheres which are either neutral or reducing to a predetermined degree are well known in connection with the various normalizing, annealing, and heat treating operations which are frequently carried out in the steelmaking art. However, generally speaking, such atmospheres comprise specially prepared mixtures of inert gases containing none or a certain predetermined amount of hydrogen which determines the reducing character of the atmosphere.

It is generally preferred to apply the marking solution of the present invention to the light-weight side of the strip which ordinarily becomes the exterior of the metal can or container. It is also advisable to pretreat the surface of the steel strip before applying the marking or coating solution so as to remove all soil and oil from the surface thereof by such means as vapor degreasing, or by means of the alkaline cleaner which is a standard operation in the continuous annealing process.

To illustrate the present invention, the following specific film oxide.

examples are set forth without, however, limiting the ditions described:

EXAMPLE 1 Clean samples of rolled steel strips measuring approximately 3" x 8", were spray coated to completely wet one surface thereof with one of the test solutions containing a compound of the present invention, and thereafter heated under conditions simulating those of a continuous annealing furnace (i.e., non-oxidizing atmosphere and a temperature of at least about 1250 F.). After allowing the steel strips to remain in the laboratory furnace under the foregoing conditions for about 10 seconds, wherein the compound of the test solution is reduced to a free metal and wherein the free metal is diffused into the steel strip, the test strips were electrolytically tinned so as to provide one-quarter pound per base box tin coating on the treated surface, and thereafter the tin coating was fused by heating to a temperature of about 450 F. to provide a smooth tin coating. The test steel strips and control samples were examined to determine the relative appearance and reflectance of the tin plate coating formed thereon.

The two test aqueous solutions employed in the fore going tests comprised:

Grams per liter aqueous solution (1) Ammonium molybdate (2) Molybdenum oxide EXAMPLE 2 Differentially coated tin plate was prepared in accordance with the present invention on production equipment, wherein the test solution was applied to the top surface of a coil of black plate immediately prior to the entry of the plate into the preheat furnace and annealing furnace. The solution was applied by contacting the upper surface of the strip with a wiping swab saturated with the test solution. Thereafter, the coil was passed through the normal annealing cycle, skin mill, and electrolytic tinning process, wherein it was differentially coated by applying one-quarter pound and one pound tin coatings per base box on the upper and lower surfaces thereof, respectively. The electroplated steel strip was then fused in the normal manner to provide a smooth t1n plate surface. The tes't'solution had the following composition:

Nickel 'formate 250 grams per liter in 1:1 mixture of corn syrup and water by volume. Nonionic wetting agent (Kyro E0) -0.1% by volume.

On heating, the nickel formate decomposes to provide a uniform coating of the nickel oxide which on continued heating in a non-oxidizing atmosphere is reduced to the free nickel metal and is difiused into the surface of the black plate.

Tests were made on the lightweight tin plate side (Lot A) and on control samples (Lot B) tov determine the coating weight, solderability, lacquer adhesion, pickle lag, stain, chromium residue, corrosion resistance and The test data obtained appear in the following Table 1:

'Nonionic Table 1 Total Pickle No. of Film Oxide, Lot Tin Sclder- Fabrication Lag, Stain Cr. hrs for M coulb. 13.3. ability Lacquer Sec. Res. 25% Corlornbs/in.

rosion A 12 11-23 OK OK OK 6 K .05 85 i 12 B-. 12 24-23 OK OK OK 8 OK .06 100 11 It will be evident from the foregoing, that identification marking of dual-coated tin plate can be accomplished by treating the surface of the steel strip prior to continuous annealing without appreciably impairing the desired properties of tin plate, such as good solderability and lacquer adherence and corrosion resistance.

EXAMPLE 3 Differentially coated tin plate was produced on fullvscale production equipment as in Example 1, wherein the treating solution consisted, of:

Ammonium molybdate 200 grams per liter in 1:1

mixture of corn syrup and water by volume.

wetting agent (Kyro E0) 0.1% by volume.

The electrolytically coated tin plate was observed to have a very uniform dull appearance in contrast with the bright appearance of the control sample of normal electrolytic tin plate which was not treated with the ammonium molybdate solution.

It is evident from the foregoing description, that while the invention is clearly applicable to a batch of semicon-tinuous tinning operation, it is particularly adapted for use in a continuous annealing line, prior to electrotinning in which case the marking or protective coating agent is conveniently applied by means of a strategically located dip-coating bath, brush applicator, or spray, positioned immediately before the annealing furnace. A marking or protective coating procedure as described herein, is useful in any application wherein a protective or dull tin-plated surface is desired, but is particularly useful in marking one side only of differentially coated tin plate with a readily distinguishable symbol or pattern, in order to enable one of the electrolytically tin plated surfaces to. be readily distinguished from the other tinplated surface, or to enable one manufacturers tin plate to be readily distinguished from another manufacturers tin plate.

We claim:

1. In the production of ditferentially coated tin plate by electrolytically depositing tin on a base steel sheet and. thereafter heating said tin to an elevated temperature for fusingthe electrolytically deposited tin, the improvement in the method of marking one side of said tin plate comprising: providing on at least certain portions of one side of said sheet having a free metallic surface a liquid film coating containing an oxygen compound of a metal selected from a group consisting of molybdenum, cobalt, nickel, titanium, tungsten, antimony, and bismuth, said compound being heat reducible to the free metal, heating said coating of said compound in a non-oxidizing atmosphere to reduce the said compound to the free metal and continuing said heating to diffuse the said metal substantially completely into the surface of the base steel sheet, electrolytically depositing tin over the said surface of the steel sheet and heating the sheet to a tin fusion temperature to form a smooth dull tin surface on said certain portions, whereby said one side of. said tin plate is distinctively marked.

, 2. A process as in claim 1, wherein the said metal sheet isheatecl. in the. first mentioned heating step at a temperature between about 1150 F. and 1400 F.

3. A process as in claim 1, wherein the said oxygen compound is selected from a group consisting of oxides and oxygen compounds decomposable to yield said oxides.

4. A process as in claim 1, wherein the said oxygen compound is molybdenum trioxide.

5. A process as in claim 1, wherein the said oxygen compound is ammonium molybdate.

6. A process as in claim 1, wherein the said oxygen compound is nickel oxide.

7. A process as in claim 1, wherein the said oxygen compound is nickel formats;

8. In the production of differentially coated tin plate by electrolytically depositing tin on a base steel sheet and thereafter heating the tin coated sheet to an elevated temperature for fusing the tin thereon, the improvement in the method of marking one side of the tin plate comprising; providing on said one side of the base steel sheet a fiuid coating of a molybdenum oxide, heating the said oxide coating in a substantially non-oxidizing atmosphere sufficiently to reduce the said oxide to the free metal and to substantially completely diffuse the metal into the surface of the said base metal sheet providing a surface substantially devoid of said oxide and said free metal, thereafter electrolytically depositing tin over said diffused metal surface of the said sheet, and fusing the electrolytically deposited tin by heating to a tin fusion temperature to provide a smooth dull tin surface on the said base sheet.

9. In the production of dilferentially coated tin plate by electrolytically depositing tin on a base steel sheet and thereafter heating the tin coated sheet to an elevated temperature for fusing the tin thereon, the improvement in the method of marking one side of the tin plate comprising; providing on said one surface of the base steel sheet a fluid coating of nickel oxide, heating the said oxide coating in .a substantially non-oxidizing atmosphere sufficiently to reduce the said oxide to the free metal and to substantially completely diffuse the metal into the surface of the said base metal sheet providing a surface substantially devoid of said oxide and free metal, thereafter electrolytically depositing tin over said diffused metal surface of the said sheet, and fusing the electrolytically deposited tin by heating to a tin fusion temperature to provide a smooth dull tin surface on the said base sheet.

10. In the continuous production of differentially coated tin plate by passing a continuous base metal strip through an annealing zone and thereafter through an electrolytic tinning zone to efiect controlled electrolytic deposition of tin so that the opposite sides of the strip have relatively light and relatively heavy tin coatings, respectively, and thereafter continuously passing the differentially coated strip through a fusion zone at elevated temperature for fusing the electrolytically deposited tin, the method of providing an identifying marking on one side of the strip which comprises: continuously passing the said strip through a treating zone and therein providing on only one of the sides of the said strip a uniform fluid coating over at least a portion of the surface thereof of an oxygen compound of a metal selected from a group consisting of molybdenum, cobalt, nickel, titanium, tungsten, antimony, and bismuth, said compound being reducible to a free metal when heated in a non-oxidizing atmosphere at a temperature between about ll50 F. and 1400 F., heating the said compound continuously in an annealing zone having a non-oxidizing atmosphere at a temperature between about 1150" F. and 1400 F. to reduce the said compound to the free metal and substantially completely diffuse the said metal into the surface of the said strip until said surface is substantially devoid of Said compound and said free metal, thereafter electrolytically depositing tin on the said one side of said strip which is substantially devoid of said compound and said free metal to provide a relatively light tin coating on the side of the strip and a relatively heavy tin coating on the other side thereof, and thereafter continuously heating the tin coatings to a fusion temperature to provide smooth tin surfaces; whereby the light tin coating side is provided with a dull surface marking having a materially reduced reflectance as compared with the bright reflectant surface of the heavy tin coating side.

11. A process as in claim 10, wherein the said compound is molybdenum oxide.

12. A process as in claim 10, wherein the said compound is ammonium molybdate.

13. A process as in claim 10, wherein the said compound is nickel oxide.

14. A process as in claim 10, wherein the said compound is nickel formate.

15. A differentially marked tin plated ferrous metal sheet having thereon electrolytically deposited tin coatings which comprises, a ferrous metal sheet having on at least certain portions of only one side of said sheet a quantity of substantially completely reduced metal selected from the group consisting of molybdenum, cobalt, nickel, titanium, tungsten, antimony, and bismuth which is completely diffused into the ferrous metal surface forming a thin diffused surface layer substantially devoid of metal oxides and unalloyed metals, and said one side of said sheet and the opposite side of said sheet both having an electrolytically deposited tin coating thereover with the tin coating formed over said thin diffused surface layer being fused and providing a dull appearance suitable for distinctively marking said one side of said tin plated metal sheet.

16. A ferrous metal sheet as in claim 15 wherein the said thin layer of reduced metal provides from about 50 to about 500 mg. metal per square foot of surface coated by said thin layer.

17. A ferrous metal sheet as in claim 15 wherein said thin layer provides about one gram of free metal per square foot of surface coated by said thin layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,266,330 Nachtman Dec. 16, 1941 2,303,035 Fink Nov. 24, 1942 2,381,778 Schoonmaker et al. Aug. 7, 1945 2,621,988 Donley Dec. 16, 1952 2,794,775 Buckingham June 4, 1957 2,839,437 Manko June 17, 1958 2,876,176 Pearson et a1. Mar. 3, 1959

Claims

1. IN THE PRODUCTION OF DIFFERENTIALLY COATED TIN PLATE BY ELECTROLYTICALLY DEPOSITING TIN ON A BASE STEEL SHEET AND THEREAFTER HEATING SAID TIN TO AN EVALUATED TEMPERATURE FOR FUSING THE ELECTROLYTICALLY DIPOSITED TIN, THE IMPROVEMENT IN THE METHOD OF MARKING OF ONE SIDE SAID TIN PLATE COMPRISING: PROVIDING ON AT LEAST CERTAIN PORTIONS OF ONE SIDE OF SAID SHEET HAVING A FREE METALLIC SURFACE A LIQUID FILM COATINH CONTAINING AN OXYGEN COMPOUND OF A METAL SELECTED FROM A GROUP CONSISTING OF MOLYBDENUM, COBALT, NICKEL, TITANIUM, TUNGSTEN, ANTIMONY, AND BISMUTH, SAID COMPOUND BEING HEAT REDUCIBLE TO THE FREE METAL, HEATING SAID COATING OF SAID COMPOUND IN A NON-OXIDIZING ATMOSPHERE TO REDUCE THE SAID COMPOUND TO THE FREE METAL AND CONTINUING SAID HEATING TO DIFFUSE THE SAID METAL SUBSTANTIALLY COMPLETELY INTO THE SURFACE OF THE BASE STEEL SHEET, ELECTROLYTICALLY DEPOSITING TIN OVER THE SAID SURFACE OF THE STEEL SHEET AND HEATING THE SHEET TO A TIN FUSION TEMPERATURE TO FORM A SMOOTH DULL TIN SURFACE ON SAID CERTAIN PORTIONS, WHEREBY SAID ONE SIDE OF SAID TIN PLATE IS DISTINCTIVELY MARKED.