US2770872A

US2770872A - Marked electrolytic tinplate and method for producing same

Info

Publication number: US2770872A
Application number: US281574A
Authority: US
Inventors: Alfred E Kadell
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1952-04-10
Filing date: 1952-04-10
Publication date: 1956-11-20
Anticipated expiration: 1973-11-20

Description

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A. E. KADELL MARKED ELECTROLYTIC TINPLATE AND Filed April 10, 1952 METHOD FOR PRODUCING SAME w 4 Niall! no Nov. 20,' 195.6

A LFRE D E ATTORNEY .Patented Nov. 20, 1956 MARKED ELECTROLYTIC TINPLAT E AND METHOD FOR PRODUCING SAME Alfred E. Kadell, Steubenville, Ohio, assignor to National Steel Corporation, a corporation of Delaware Application April 10, 1952, Serial No. 281,574

28 Claims. (Cl. 29--196.4)

The present invention relates to electrolytic tinplate marked in a novel manner and relates to a novel method for producing such marked electrolytic tinplate.

This applictaion is a continuation-in-part of my copending application Serial No. 229, 338, filed June 1, 1951, now abandoned.

Tinplate may be produced by the hot dip process or the electrolytic process. Most of the tinplate today is electrolytic tinplate and is produced by continuously and progressively passing base metal strip, such as steel black plate, through a long electroplating line at a very high rate of speed. The speed may, for example, be from a thousand to two thousand feet per minute so that an electroplating line produces a large quantity of tinplate in a short period of time. The strip as it is moved through the line is first cleaned, pickled and washed and then passed through electroplating apparatus and both surfaces are electroplated with tin while the strip is in contact with a bath of electroplating solution. The two surfaces of the strip may be progressively plated simultaneously or one surface may be plated and then the other surface plated. In one type of electroplating line which is in commercial use, the strip is moved across a first series of electroplating cells and the bottom surface is plated, and then the strip is moved back across a second series of electroplating cells and the opposite surface which is now facing downwardly, is plated. The electro-deposited tin coating has a dull matte surface having a whitish, powdery appearance. The surface is rough and the tin while firmly attached to the base metal is in an amorphous condition. The electroplated strip passing from the electroplating apparatus has thereon electroplating solution dragged out of the electroplating bath and the plated strip is washed to remove this dragged out solution. The washed strip is dried or substantially dried and the drying may be effected by passing the strip through a heated dryer, for example, or if the strip is rinsed with a hot rinsing solution the strip may be heated sufficiently hot to effect drying by evaporation. The dry rinsed strip is then passed through a flow-brightening unit in which the tin is heated to a temperature above its melting point. The strip is then quenched to solidify the tin coating. The flow-brightened tin coating has a smooth, bright mirror-like surface and in addition to an improved appearance, the flow-brightened tin coatingis alloyed, at least to a limited extent, with the base metal and has a crystalline structure. The flow-brightened coating provides better protection for the base metal than the electroplated tin in its original condition. The flow-brightened strip may then be coated with a film of oil and then coiled into large rolls or coils at the finishing end of the line. The strip before being coiled and oiled may be cathodically treated and Washed. The coils are subsequently cut into sheets from which are formed the final products, such as food containers.

Very large quantities of electrolytic tinplate are utilized in industry and millions of pounds of tin are required each year to satisfy the tinplate requirements for the food and other industries. A large portion of this electrolytic tinplate is used in containers where the tin coating on the interior surface protects and prevents contamination of the contents. The tin coating on the exterior surface enhances the appearance of the container and while having a tin coating on the exterior surface is important and highly desirable both to enhance the appearance and to protect the container, the quantity of tin on this exterior surface frequently need not be as great as the quantity of tin on the interior surface. In the present days of tin shortages a saving in tin is quite important. The commercial tinplate now produced has the same amount of tin on each surface and a large saving of tin would result if the opposite surfaces could be coated with different quantities of tin. The tin coating could be thinner on the surface which needs less protection, such as the exterior surface of containers.

If electrolytic tinplate were produced with different weights of tin on the surfaces a saving in tin could be effected but this in turn would raise a serious problem when using the tinplate. Flow-brightened tinplate has a bright, mirror-like surface and there is no appreciable visible difference between a surface having a relatively thinner coating and one having a relatively thicker coating. Thus, the manufacturer who produces the containers or other products would not be able to readily determine which surface of a sheet of tinplate should form the exterior or interior surface of a container. Marking tinplate by means of a die or other apparatus that deforms the metal is not satisfactory as it destroys a portion of the sheet that is marked. Marking ink cannot be utilized as the ink tends to spread and smear at the high speeds involved. The ink may be removed by the subsequent treatments, such as the cathodic electrolytic treatment and the washing and oiling treatments. Ink tends to transfer from the marked to the unmarked surface during coiling. In addition, ink tends to darken when the tinplate is subsequently coated with lacquer and baked and presents an unsightly appearance. Accordingly, customary marking procedures are not satisfactory or desirable for tinplate.

I have discovered a novel method of producing a novel, flow-brightened electrolytic tinplate that is marked. This marking can be utilized to differentiate one surface of a sheet from the other surface or for any other purpose of designation.

Marking is effected bypassing the electroplated strip through flow-brightening apparatus and heating and flowbrightening the tin coating on the strip while interfering with the flow-brightening of the tin coating located in the marking Zones so that these portions of the tin coating will have different, visible, light reflecting characteristics than the flow-brightened coating on the remaining area of the surface. Preferably these marking zones extend either continuously or at closely spaced intervals I along the length of the strip so that when the strip is cut into sheets, each sheet will have on one surface at least a few of these zones. The marking zones may be arranged in a repeating pattern extending along the length of the strip and may be in the shape of lines extending longitudinally along or transversely across the strip surface. In the arrangement which will hereinafter be described in detail, the marking zones are arranged in intersecting lines extending diagonally across the sheet. But other arrangements obviously can be used. Preferably these lines are relatively faint so as not to be readily noticeable under normal conditions of lighting, but readily visible when viewed under a strong light, particularly when the light source and the tinplate are arranged so that light is reflected from the marked surface to the eye at acute angles. The person or persons responsible for properly positioning the tinplate can readily distinguish the marked surface, while the marked surface will not be particularly noticeable or present an undesirable appearance to the casual observer. Relatively faint lines can be covered readily by a decorative coating. More pronounced lines can be covered but a heavier coating of greater opacity is required.

Interference with the flow-brightening of tin coating in the marking zones is effected so that the tin in the marking zones is flow-brightened in such a manner as to present a differential visual appearance. The flow-brightening may be affected by partially blocking the heat away from the marking zones or by absorbing some of the heat directed against the marking zones or by a chemical reaction between a foreign material and the tin coating so as to produce a tin coating in the marked areas having less gloss or a slightly duller appearance. On the other hand, the flow-brightening may be affected by increasing the fluidity of the tin in these zones by means of a fluxing action which may cause the tin coating to reflect less light or to diffuse the reflected light so as to have a duller or darker appearance. Interference may be effected by a combination of those methods. The marking zones will have different visible light reflecting characteristics than the remaining portions of the surface and may reflect less light or may diffuse the light in a different manner so as to appear darker to the naked eye, particularly when the marked tinplate is held at an angle to the light source.

While the marking zones on the surface of the tinplate have different light reflecting characteristics than the remaining portion of the surface area, the tin located in these zones is not in its original condition having a matte surface but is in a flow-brightened condition.

Interference with the flow-brightening may be carried out by decreasing flow-brightening of the tin in the marking zone. A decrease of flow-brightening may be effected by physically blocking some of the heat away from the zones so that less heat reaches these zones and this may be effected by applying a foreign material to the marking zones before the flow-brighting operation, such as a transparent lacquer or sizing, that will partially insulate the zones. A reduction in flow-brightening also can be effected by adding a material to the zones before the flow-brighting operation so as to reduce the amount of heat applied to the tin coating through absorption of heat by vaporization of the material. Palm oil, for example, may be used for this purpose. Interference also may be effected by applying to the marking zones a foreign material that will chemically react with the tin. An acid or acidic compound that will have an etching action on the coating during the flow brightening operation may be used for this purpose.

Interference with the flow-brightening of the tin in the marking zones can be effected by increasing the flowbrightening effect on the tin. An increase of the flowbrightening of the tin can be effected by applying a fluxing agent to the surfaces to be marked prior to the flowbrightening operation. The fluxing agent may increase the fluidity of the tin and this in turn may increase the tendency of the tin in these areas to collect in droplets so that the flow-brightened tin coating will reflect light differently than the remaining portion of the surface area depending to a limited extentupon the fluxing agent used and the temperature to which the tinplate is heated. The marking zones may be slightly brighter than the remaining area or may have a slightly roughened surface so as to diffuse the light and present a relatively dull, different visible appearance. It is to be noted that a material like palm oil has two effects. It has a limited etching action and also tends to reduce the amount of heat reaching the tin at least partially as a result of its partial vaporization. Thus, a combination of these various methods may be used when interfering with the flow-brightening in the marking zones.

The present invention will become more apparent from the following description taken with the accompanying drawings, in which:

Figure l is a diagrammatic representation of improved apparatus for carrying out the principles of the present invention;

Figure 2 is an enlarged fragmentary view taken as indicated by line 2-2 of Figure 1;

Figure 3 is an enlarged sectional view taken along line 3-3 of Figure 2; and,

Figure 4 is an enlarged view of a portion of the strip illustrating one arrangement of the marking zones.

Referring more particularly to the drawings, Figure 1 illustrates the essential portions of one type of an improved elcctroplating line for carrying out the method of the present invention. The electroplating line includes apparatus ill or electroplating the bottom surface ll of strip S with a coating of tin and other apparatus 12 for electroplating the opposite surface 13 of the strip S with a coating of tin. The apparatus for electroplating the bottom surface includes a series of similar electroplating cells 15. Between each two cells It. and at the entry and exit ends of the series of cells, there are a pair of strip engaging rolls i6 and 17. One of the rolls, usually the upper roll, is a contact roll and is connected to one side of the source of the electroplating current so as to connect the strip S to a source of electroplating current as a cathode. The other roll, roll 17 is backup roll holding the strip in contact with the upper roll 16. The rolls may or may not be driven. The cells 15 are of the type which contain a bath of electroplating solution and a plating anode (not shown) connected to the source of electroplating current as an anode. The strip S moves across the top of the cells where the bottom surface it is in contact with the electroplating solution in each cell. As the strip moves across the series of cells, a coating of tin is applied to the bottom surface 11.

At the entry and exit ends of the series of cells 15 and between each two cells there is a collecting tray 19 which collects the solution flowing out of the cells and this solution is returned through piping 26) to a collection tank, not shown, and then is pumped back into the cells through pipe 21. As the strip leaves the lower apparatus 10, it passes around a roll 23 and then up and around an upper roll 24 and then across the upper electroplating apparatus for electroplating the opposite surface 13 which is now facing downwardly. The apparatus 12 is similar to the apparatus 10 and includes a plurality of similar electroplating cells 26 across which the strip is moved in contact with the electroplating solution in each cell whereby the bottom surface 12 is plated with coating of tin. At each end of the series of cells 26 and between each two cells, there is a pair of rolls withthc upper roll 27 being a contact roll and the lower roll a backup roll 28 to connect the strip to a source of electroplating current as the cathode. From the upper series of cells 12, strip passes around roll 3i then up and around roll 31 to a washer 32. The washer 32 may be any suitable type and washes the strip to remove the residual electroplating solution that is on the strip and that has been dragged out of the electroplating cells. The strip then passes through a dryer 33 which dries the strip. The dryer 33 may be of any suitable type for applying sulTtcient heat to the strip to dry the metal. Where the wash water used in washer 32 is at an elevated temperature, there may be sufficient heat in the strip to dry the strip before the strip passes to the reflowing or flowbrightening apparatus 34, As the strip moves through the flowbrightener, the strip is heated to a temperature above the melting point of tin and heat may be applied to the strip in any suitable manner. From the bottom of the flow-brightener, the strip passes down into quench tank 35 containing a bath 36 of quench liquid such as water.

In the quench tank 35, the strip passes around a roll- 37 and from the tank up to roll 38. The strip then passes to units for subsequently treating the strips and to the usual coiler.

In the apparatus described above the strip is first plated on one surface with a protective coating of tin and is then plated on the opposite surface with a protective coating of tin, washed, dried, flow-brightened and quenched. Other types of plating apparatus may be used and both surfaces may be plated simultaneously. United States Patent No. 2,317,242 to W. S. Allen et al., for example, illustrates another type of apparatus which may be used.

Any suitable type of flow-brightener may be used and the strip and its tin coating may be electrically heated, or may be heated by radiant heaters or'may be heated in a hot, inert atmosphere. In general, liquids cannot be used as the heating medium as liquid tends to remove the foreign material. Flow-brightening units are well known to those skilled in the art.

In accordance with the present invention, one surface of the strip may be plated with a thinner coating of tin than the opposite surface. In this instance, it is the bottom surface which is plated with the thinner coating and this difference in coatings may be eifected in various ways as, for example, by utilizing a lower current density in the cells 15 than is used in cells 26, or by using fewer cells 15 or in any other suitable manner.

The weight of tin present on tinplate is usually referred to as a certain weight of tin per base box. A base box of tinplate contains 217.78 sq. ft. of tinplate. As tinplate is coatedon both surfaces with tin the amount of tin per base box is distributed over an area of 435.56 sq. ft. Thus, the expression one pound tinplate refers to tinplate having one pound of tin per base box and the tin is distributed over an area of 435.56 sq. ft. As used, hereinafter, the terms or expressions such as, one pound tinplate or one pound of tin per base box refers to tinplate which has this amount of tin distributed over i both sides of the tinplate throughout an area of 435.56 sq. ft. The expression one pound tin one side or one pound of tin per base box, one side refers to the quantity of tin distributed over one surface of a base box of tinplate or over an area equal to 217.78 sq. ft. Thus, one pound tinplate or one pound tinplate per base box is equivalent to one-half pound tinplate, one side, or onehalf pound tinplate per base box, one side.

In the present instance it is the bottom surface that is coated with the thinner coating. The difference in coating weights may be varied and will depend upon the use to which the tinplate is to be put. For example, instead of producing one pound per base box tinplate, tinplate may be produced having a half pound per base box, one side, and .25 pound tin per base box, reverse side. Thus, the one side of the tinplate will be protected with the same thickness of tin that is present on one pound tinplate. The tin coating on the other or reverse side of the tinplate will only have a thickness equal to the usual half pound tinplate. This effects a savings of 25% of tin which would normally be used to produce this tinplate. Lesser or greater savings can be effected and savings up to 50% or higher in tin can be made. Thus, where, for example, a company produces over 20,000,000 base boxes of tinplate per year, a saving of /1 pound of tin per base box would amount to over 5,000,000 pounds of tin in a year. Thus, a relatively slight savings in tin per base box is quite important and highly desirable.

In accordance wit-h the present invention, the flowbrightening of the tinplated strip in the flowbr-ightener 34 is interfered with so as to produce a tinplate having tin coating in minor zones of one surface that have different visible light reflecting characteristics than the howbrightened tin coating in the remaining area of said surface. The flow brightened tinplate in these minor or marking zones appears slightly darker to the naked eye. In the procedure shown in Figure 1, it is the bottom surface that has the thinner coating and preferably,

6 though not necessarily, it is the surface having the thinner coating that is marked. As shown more fully in Figures 2 and 3, the strip S which has been washed and which has thereon a matte surface finish is passed between a pair of

rolls

40, 41. These rolls are rotatably supported in any suitable manner. The lower roll is mounted above a tank 42 containing a bath of liquid 43. In the tank 42 there is mounted a wick 44 which extends down into the bath 43 and which contacts the surface of the roll 41. The roll 41 may be made of rubber or any other suitable material and have thereon raised portions with the raised portions being arranged in lines 45. These raised portions or lines 45 are quite narrow and extend about the periphery of the roll 41. Thus, as the strip moves between the lower roll 41 and the upper roll 49 which presses the strip against the lower roll, the lower roll 41 rotates and deposits liquid from bath 43 onto the surface of the strip in zones. These zonesare arranged as intersecting lines extending diagonally of the sheet. As the strip subsequently moves through the flowbrightener 34, the liquid or foreign material deposited on the surface by roll 41 interferes 'With the flow-brightening so as to produce a flow-brightened tin coating in the marking zones that has a different light reflecting characteristic than the remainder of the sheet. The bottom surface of the sheet will be marked with faint lines 47 as indicated in Figure 4. These marking lines or zones may reflect less than the remaining unmarked zones between the lines '47 or the tin coating in the marking zones 47 may diffuse the light differently than the remainder of the coating.

Liquid bath 43 may contain any suitable material. If, for example, the bath 43 is palm oil, the palm oil will be deposited in the minor marking zones on the bottom surface of the strip. As the strip moves through the flow-brightener 34, a portion of the palm oil will be vaporized and this heat of vaporization will reduce the amount of heat reaching the tinplate in the mark-ing zones 47 so that the tinplate in the marking zones 'will be heated to a lower temperature than the tin on the remainder of the surface. Palm oil also is believed to have some fluxing or etching action on the tin surface. Palm oil contains some higher fatty acids and it is believed that these acids may react 'with the tin surface, that is, etch the tin surface. 'Th-us, palm oil acts to both reduce the amount of heat applied to the tin coating in the marking zones 47 and acts to slightly etch the surface. The bath 43 may contain a tin reactive fluxing agent and may be for example, an aqueous solution of sal ammoniac. The water will be evaporated in the flowbrightening zone and the residual sal ammoniac will act as an etching and fluxing agent to both increase the fluidity of the tin in the marking zone and to lightly etch the surface of the tin in the marking zone. The tin in these mark-ing zones -will diffuse the light and will be visibly different from the remainder of the tin coating. This difference is particularly noticeable when the plate is held at an angle to the light so that the plate is viewed by light reflected at an acute angle. The marking zones appear darker than the remainder of the tinplate.

Other heat absorbing materials or tin reactive materials or combinations of these ingredients may be used to form the bath 43. Preferably the marking material is tin reactive acidic material that has at least a slight etching action on the tin coating as better results have been obtained with such materials as compared to non-etching materials such as cottonseed oil or glycerine, although the last mentioned materials may be used. The tin reactive, acidic material may be a mineral acid, for example, hydrochloric acid or hydrofluoric acid, or may be an acid salt of a metal such as sodium bifluoride. The strongly acid materials should be used in diluted form and may be diluted with Water or water and glycerine. For example, an aqueous solution of hydrochloric acid containing 2%, or less, of acid may be used. Where the tin reactive material is an acid salt, then only a few ounces, or less, per gallon may be needed. The preferred concentration will depend on the reactivity of the salt, the amount of film applied and other factors. The marking liquid comprising an aqueous solution of a tin reactive acid salt may contain or more, acid salt, although good results have been obtained with solu tions containing 1%, and less, of acid salt. Preferably the marking material should not have too strong an etching action as there is a tendency for such a material to shorten the shelf life of the tinplate. The term shelf life refers to the period over which tinplate can be stored without deterioration sufficient to affect its value. For this reason mineral acids and tin reactive acid salts of metals are used in diluted form with the degree of dilution depending upon the strength of the acid or acid salt. While the term etching has been used, this etching is slight and the etched surface appears to have a smooth surface so that the etched effect does not produce a rough appearing surface but does affect light reflecting characteristics of the tin coating in the marking zone.

()ther materials may be used for marking the tinplate. Alcohol and sal ammoniac may be used although a mixture of alcohol, water and sal ammoniac is better. A tin reactive material may be added to palm oil or glyccrine, for example, stearic acid may be added to palm oil and a small amount of hydrochloric acid may be added to glycerine to form the material for bath 43.

Where the bath 43 includes a liquid such as water which evaporates in the flow-brightening zone and a tin reactive agent, marking is apparently effected by a dual action. The liquid reduces the heat reaching the tinplate in the marking zone both by blanketing the surface and blocking the heat and by absorbing heat of vaporization. While all of the tin coating in the marking zone is flowbrightened this reduction in heat tends to produce a tin coating having visibly different light reflecting characteristics. In addition, the flow-brightening of the tin coating in the marking zone is interfered with by the residual tin reactive material which lightly etches the surface, particularly Where the tin reactive material is an acid salt that does not evaporate or decompose in the flow-brightening zone without reacting with the surface of the tin coating. Where the bath contains a tin reactive acid salt, it is believed that a residue of this acid salt may at times remain on the tin coating in the marking zone, probably in the form of a salt of tin. If such a salt remains on the marking zone, the salt cannot be seen by the naked eye although it may affect the light reflecting characteristics. The quenching medium may remove any such residual salt. As such an acid salt is used in a diluted form and as a very thin film is applied to the marking zone, only a minute amount of salt residue can be present on the tin coating in the marking zone. The etching is quite light and the only visible effect of such etching is to increase the difference in light reflecting characteristics. No pits or depressions can be seen. If pits or depressions were formed having a size sufficient to be distinguished by the naked eye, the protective character of the tin coating would be greatly reduced. Accordingly, the term lightly etched is intended to cover that condition where the material applied to the marking zone reacts with the surface of the tin coating sufficiently to affect the light reflecting characteristics of the surface but not sufficiently to form pits or depressions individually visible to the naked eye.

A material may be used for bath 43 which will block part of the heat directed toward these minor zones on the strip surface. For example, the bath 43 may be made up of a substantially clear sizing coating of lacquer of the type used for priming tinplate for receiving a pro tective or decorative coating of lacquer or paint. This sizing or lacquer applied to the strip S by roll 41 will block or prevent some of the heat reaching the marking zones but permits suflicient heat to reach these zones so that the tin is flow-brightened. Thus, the tin coating in the marking zones receives less heat and has less gloss than the tin coating in the remaining area of the surface.

When interference with the flow-brightening is effected by applying a foreign material to the surface of the tinplate, I prefer to employ a material that will subsequently be removed by the quench bath 36 or which may readily be removed by washing with a suitable liquid which may be different than is used in the quench bath. Many of the materials previously mentioned are water soluble and are removed in the quench bath.

As previously pointed out the bottom surface is preferably marked so that the marking area constitutes only a very small portion of the entire area. In addition, the marking zones are preferably relatively narrow and laiut. While the marking zones may be relatively wide and quite pronounced, particularly where this surface in the finished product is completely covered as by a paper label, it is preferable that the marking zones not be pronounced so that they will not be noticed by the casual observer and so that they may be readily covered and obliterated by a lacquer having a low hiding power.

The present invention has been described for marking electrolytic strip tinplate having different weights of the tin on the opposite surfaces to distinguish these surfaces. The present invention may be used for marking electrolytic tinplate of other types and for other purposes. The strip may be plated on only one surface and the marking may be used to indicate batch or lot number, coating weight or for any other purpose. The marking zones may be arranged as numerals or letters or suitable indicia of predetermined configuration and the spacing between repeating marks, either along the length or across the breadth of the strip, may be varied over a Wide range.

When producing strip tinplate having a tin coating of one weight on one surface and a tin coating of a different on the other surface, it may be desirable to interfere with the flow-brightening of an entire one of the coatings. This will result in one flow-brightened coating having different light reflecting characteristics than the other flow-brightened coating. The surface of the one coating will diffuse reflected light differently and appear slightly darker than the other coating. This may be accomplished by applying, for example, an aqueous solution of a tin reactive acid salt to the entire surface of one coating before passing the strip through the flow-brightening zone. At least at times. the strip tinplate is cut into small pieces or blanks and if the entire surface of one coating is marked there is no chance that the blank will not be marked and be improperly positioned for subsequent fabrication.

I claim:

1. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flowbrightening zone and melting and flow-brightening the tin coating, and selectively interfering with the flowbrightening of the tin coating located in a marking zone of predetermined pattern and constituting only part of the total area of the tin coating to produce a flow-brightened tin coating surface in the marking zone having visibly different light reflecting characteristics than the flow-brightened tin coating surface outside of the marking zone to mark the tin coating surface.

2. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through the flow-brightening zone and heating and melting the tin coating while the tin coating is disposed in a gaseous atmosphere and thereby flow-brightening the tin coating, and selectively reducing the amount of heat applied to the tin coating located in a marking zone of predetermined pattern and constituting only part of the total area of tin coating and thereby interfering with the flow-brightening of the tin coating in the marking zone to produce a flow-brightened tin coating surface in the marking zone having visibly different light reflecting characteristics than the flowbrightened tin coating surface outside of the marking zone to mark the tin coating surface.

3. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow-brightening zone and melting and flow-brightening the tin coating, selectively applying a liquid film to the tin coating located in a marking zone of predetermined pattern and constituting less than the total surface area of the tin coating, the liquid film being applied to the rinsed strip before the strip passes into the flow-brightening zone and thereby interfering with the flow-brightening of the tin coating in the marking zone to produce a flowbrightened tin coating surface in the marking zone having visibly different light reflecting characteristics than the flow-brightened tin coating surface outside of the marking zone to mark the tin coating surface.

4. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one stuface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow-brightening zone and melting and flow-brightening the tin coating, selectively applying a liquid film to the tin coating located in a marking Zone of predetermined pattern and constituting less than the total surface area of the tin coating, the liquid film being applied to the rinsed strip before the strip passes into the flow-brightening zone, at least part of the liquid in the film being vaporized in the flow-brightening zone, and thereby interfering with the flow-brightening of the tin coating located in the marking zone to produce a flow-brightened tin coating surface in the marking zone having visibly different light reflecting characteristics than the' flow-brightened tin coating surface outside of the marking zone to mark the tin coating surface.

' 5. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface,

passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow-brightening zone and melting and flow-brightening the tin coating, selectively applying a liquid film to the tin coating located in a marking zone of predetermined pattern and constituting less than the total surface area of the tin coating, the liquid film being applied to the rinsed strip before the strip passes into the flow-brightening zone and including Water and a tin reactive acid salt, the water being evaporated in the flow-brightening zone and the acid salt etching the surface of the tin coating to thereby interfere with the flow-brightening of the tin coating in the marking zone to produce a flow-brightened tin coating surface in the marking zone having visibly different light reflecting characteristics than the flowbrightened tin coating surface outside of the marking zone to mark the tin coating.

6. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coating, and selectively interfering with the flow brightening of the tin coating located in a marking zone of predetermined pattern and constituting only part of the total area of the tin coating by applying a tin reactive agent to the tin coating in the marking zone after the strip has been rinsed and prior to passing the strip through the flow brightened zone and thereby lightly etching the tin coating in the marking zone during flow brightening of the tin coating to produce a flow brightened tin coating surface in the marking zone having visibly different light reflecting chraacteristics than the flow brightened tin coating surface outside of the marking zone to mark the tin coating surface.

7. The method claimed in claim 6 in which the tin reactive agent is an acid salt.

8. The method claimed in claim 6 in which the tin reactive agent is a tin fluxing agent.

9. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositinga coating of tin on at least one surface of the strip while in contact with a bath of electroplating solution containing electrolyte, the tin coating in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coating, and selectively interfering with the flow brightening of the tin coating located in marking zones of predetermined pattern and constituting only part of the total area of the tin coating to produce in the marking zones a flow brightened tin coating having visibly different light reflecting characteristics than the flow brightened tin coating outside of the marking zones with the tin coating in the marking zones diffusing the light more and appearing relatively duller than the portion of the tin coating outside of the marking zones.

10. The method of continuously marking electrolytic tinplated strip as claimed in claim 9 in which the marking zones are arranged in a pattern repeating along at least one dimension of the surface of the tin coating.

11. The method of continuously marking electrolytic 11 tinplated strip as claimed in claim which includes arranging the marking zones as intersecting lines.

12. The method of continuously marking electrolytic tinplated strip as claimed in claim 11 in which the intersecting lines intersect each other on the diagonal with the intersecting lines defining therebetween diamond shaped areas of flow brightened tin coating.

13. The method of continuously marking electrolytic tinplated strip claimed in claim 9 in which a film of liquid including palm oil is applied to the marking zones prior to passing the rinsed strip through the How brightening zone.

14. The method of continuously marking electrolytic tinplated strip as claimed in claim 9 in which a trans parent film is applied to the marking zones before the rinsed strip is passed through the flow brightening zone and in which transparent film is not evaporated as the strip is passed through the flow brightening zone.

15. The method of continuously marking electrolytic tinplated strip as claimed in claim 9 which includes applying an aqueous solution of a tin reactive acid salt to the marking zones prior to passing the rinsed strip through the flow brightening zone, the water being evaporated as the strip moves through the flow brightening zone whereby the tin coating passing from the flow brightening zone has an acid salt residue on the surface in the marking zones and is lightly etched by the acid salt.

16. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on the two sides of the base metal strip, the coating of electroplated tin on one side of the strip being relatively thinner and on the other side relatively thicker, both of the tin coatings in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip ti remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coatings, and selectively interfering with the how brightening of one of the tin coatings located in marking zones of predetermined pattern and constituting only part of the total area of the one tin coating to produce a flow brightened tin coating surface in the marking zones hav ing visibly different light reflecting characteristics than the flow brightened tin coating surface outside of the marking zones to mark the one tin coating.

17. The method of continuously marking electrolytic tinplated strip as claimed in claim 16 in which the tin coating in the marking zones diffuses the light more and appears duller than the tin coating surface outside of the marking zones.

13. The method of continuously marking electrolytic tinplated strip as claimed in claim 17 in which the marking zones are on the thinner coating.

19. The method of continuously marking electrolytic tinplated strip as claimed in claim 13 which includes arranging the marking zones as lines.

20. The method of continuously marking electrolytic tinplated strip as claimed in claim 19 in which the lines are arranged as intersecting lines, intersecting each other on the diagonal.

21. in the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on the two sides of the base metal strip, the coating of electroplated tin on one side of the strip being relatively thinner and on the other side relatively thicker, both of the tin coatings in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coatings, and selectively interfering with the fiow brightening of at least a portion of one of the tin coatings located in a marking zone of predetermined pattern to produce a flow brightened tin coating portion having different light reflecting characteristics than the remaining portion of the tin coatings.

22. In the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on the two sides of the base metal strip, the coating of electroplated tin on one side of the strip being relatively thinner and on the other side relatively thicker, both of the tin coatings in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coatings, and selectively interfering with the flow brightening of the entire tin coating on one side of the strip to produce a flow brightened tin coating having different light reflecting characteristics than the flow brightened tin coating on the other side of the strip.

23. in the method of continuously marking electrolytic tinplated strip, which tinplated strip is produced by passing base metal strip across an electroplating zone and electrolytically depositing a coating of tin on the two sides of the base metal strip, the coating of electroplated tin on one side of the strip being relatively thinner and on the other side relatively thicker, both of the tin coatings in the deposited condition having a matte surface, passing the strip from the electroplating zone and rinsing the strip to remove residual electroplating solution dragged out of the electroplating zone, the steps comprising passing the rinsed strip through a flow brightening zone and melting and flow brightening the tin coatings, and selectively interfering with the fiow brightening of the entire tin coating on one side of the strip to produce a flow brightened tin coating which diffuses reflected light more and appears duller than the tin coating on the other side of the strip.

24. Electrolytic sheet tinplate having on at least one side a coating of electroplated tin in the flow brightened condition, the tin coating having a marking zone on the surface covering less than the entire surface area of the tin coating, the physical condition of the surface of the tin coating in the marking zone being different from and characterized by visibly different light-reflecting characteristics than the surface of the tin coating outside of the marking zone, the physical condition of the surface of the marking zone being the result of interference with flow brightening.

25. The electrolytic sheet tinplate claimed in claim 24 in which the tin coating surface outside of the marking zone has a bright substantially mirror-like appearance and the tin coating surface in the marking zone diffuses the light more and appears relatively duller than the tin coating outside of the marking zone.

26. The electrolytic tinplate of claim 24 which has a transparent film covering the marking zone only.

27. Electrolytic sheet tinplate having on one side a coating of electroplated tin in a flow brightened condition presenting a bright, light-reflective surface and having on the other side a coating of tin in the flow brightened condition presenting a light-reflective surface, one of the coatings being heavier than the other coating, at least a portion of the tin coating on the said other side of the sheet presenting a surface having a physical condition different from and characterized by visibly different light-reflecting characteristics than the surface of the tin coating on said one side of the sheet, the physical condition of the surface of at least the portion of the other side of the sheet being the result of interference with flow brightening whereby the two sides of the sheet tinplate are visibly distinguishable from each other.

28. The electrolytic sheet tinplate claimed in claim 24 in which the marking zone covers a minor portion of the entire surface area of the tin coating and the major portion of the entire surface area of the tin coating being outside of the marking zone and having a bright substantially mirror-like appearance.

References Cited in the file of this patent UNITED STATES PATENTS 779,887 Stewart Jan. 10, 1905 844,380 Marwick Feb. 19, 1907 1,186,217 Mark June 6, 1916 14 Bezzenberger Oct. 1, Fernv Dec. 27, Nachtman Apr. 29, Hall 1 Feb. 3, Nachtman 2 Aug. 29, Lorig Feb. 15, Munger .1 Dec. 6, Watson Apr. 4, Duby Nov. 27, Netschert Mar. 18, Peters et a1. June 3, Smith Dec. 1,

FOREIGN PATENTS Canada Apr. 23,