US3197861A

US3197861A - Production of non-porous vacuum metallized coatings on strip material

Info

Publication number: US3197861A
Application number: US33267A
Authority: US
Inventors: Robert M Brick
Original assignee: Continental Can Co Inc
Current assignee: Continental Can Co Inc
Priority date: 1960-06-01
Filing date: 1960-06-01
Publication date: 1965-08-03
Anticipated expiration: 1982-08-03

Description

g- 1965 R. M. BRICK PRODUCTION OF NON-POROUS VACUUM METALLIZED COATINGS ON STRIP MATERIAL Filed June 1, 1960 mmmnm Wm w mm g 120M; M Bria/z INV EN TOR United States Patent 3,197,861 PRODUCTION OF N 0N-POROUS VACUUM METAL LIZED CGATINGS 0N STRIP MATERIAL Robert M. Brick, Hinsdale, Ill., assignor to Continental Can Company, Inc, New York, N.Y., a corporation of New York Filed June 1, 1960, Ser. No. 33,267 16 Claims. (Cl. 29-528) This invention relates in general to new and useful improvements in stock having metal coatings thereon and the method of forming the same, and more particularly relates to the production of non-porous metallized coatings on strip material.

Metallic coatings employed for the prevention of corrosion are practically always somewhat porous when applied as thin coatings. For example, every automobile owner is familiar with rusting of the so-called chrome decorative trim which is in reality steel covered by a nickel electroplate and a superficial thin chrome plate. The electroplated chrome is always porous and is used only for a bright finish. The nickel is to prevent rusting by excluding oxygen and water vapor. However, when the nickel coating is too thin, rusting will occur by reason of pores in the electroplated nickel. The same is true of electroplated tin coatings on steel.

Tin plate normally used for the manufacture of cans is a so-called A: lb. coating, nominally 0.000015 inch thick, is very porous and the steel will rust through this coating in a few days when exposed to high humidity and warm air. After the tin plate is brightened by fusion of the tin, many of the pores are closed up, but enough of the pores remain open to show rusting after exposure to warm humid atmospheres in a few weeks.

The porosity of thin metallic coatings is not limited to those obtained by electroplating. Vacuum deposited coatings, gas plated coatings (i.e., from metal carbonyl or halide gases which decompose on hot metal to deposit a coating), sputtered coatings, etc., all exhibit porosity when the coatings are thin. For example, a vacuum metallized coating of 0.000015 inch thickness of aluminum on steel, equivalent in thickness to A lb. electroplated tin, also shows relatively rapid rusting in warm humid air and coating thicknesses of at least 0.000030 inch are required to duplicate or improve upon 4 lb. fused electro-tin plate.

It is, of course, desirable to retain the metal coating as thin as possible in order to effect a saving of both time and money. Accordingly, it is an object of the invention to close the pores of newly metal coated strips by rolling the coated strips to effect a flow of the metal of the coating and a resultant permanent closing of the pores through the welding together of the metal as it flows together.

It has been found that if the metallized coating is exposed to the atmosphere, the oxide which immediately forms will prevent the proper welding shut of the open pores even if the metal coated strips are passed through rolls which apply pressures on the metal coatings to effect the'llowing thereof. The pores are partially closed mechanically but apparently oxygen and water vapor molecules can still move through the pores to cause rusting of the steel substrate, for example. On the other hand, when metallic surfaces are free of oxides or chemisorbed oxygen and thus in a nascent state, pressure bonding or welding is very easily accomplished by bringing the atoms of two such surfaces together to normal interatomic distances for the metal concerned, i.e., about 2(l0) cm., at normal iuterat-omic metallic forces.

Accordingly, it is another object of the invention to provide a process for removing the pores in metallic coatings, the process including the rolling of the metal coated strip or other material immediately following the deposition of the coating material and prior to the exposure of the coat-ed metal to the atmosphere, whereby the closing of the pores is accomplished prior to the formation of oxides on the metal coatings while the metal is in a nascent state so that the metal of the metal coatings may flow under pressure and the pores therein be welded shut.

A further object of this invention is to provide a novel process of forming non-porous vacuum metallized coatings, the process including the normal cleaning and metal coating steps in vacuo, after which the metal coated strips or other materials are rolled while still within the vacuum and the coating metal is in a nascent state to effect a compressive deformation of the metal coating with the result that the pores thereof are welded shut and the porosity of the metal coating is eliminated.

Still another object of the invention is to provide a novel process for closing the pores in metallic coatings applied by a gas plating process where the metal coating is deposited from a carbonyl, halide or other gaseous compound, the metal coated strip or other material being rolled within the gas of the gas plating process prior to exposure to air, so that the metallic coating is rolled while in its nascent state prior to the formation of oxides thereon and the flowing of the metal coating into pressure contact during the rolling process brings about the welding shut of the pores therein.

A still further object of the invention is to provide a novel process of producing non-porous metallic coatings, the process being of a nature wherein it is adaptable to vacuum coating processes, gas plating processes and even to electroplating processes, the process essentially including the rolling of the metallic coating prior to the exposure thereof to the atmosphere to eliminate the formation of oxides thereon whereby, when the metallic coating is rolled and the pressures are sufiicient to effect the flowing of the metal of the metallic coatings with the open pores in the initially deposited metal being closed by the flowing of the metal and being welded closed through the pressure engagement of the metal while in its nascent state.

Yet another object of this invention is to provide a metal coated strip wherein the metal coated strip has been rolled prior to the exposure to the atmosphere so that the pores thereof have been entirely welded closed and the metal coating is of an impervious nature.

A further object of the invention is to provide a novel method of eliminating pores in a deposited metal coating, the method including the rolling of the metal coating while the metal is in its nascent state to effect the flowing of the metal to completely close the pores and to bring together the atoms of the opposed surfaces of the metal to the normal interatomic distance for the metal concerned, i.e., about 2(10)" cm., at normal interatomic metallic forces to cause a true joining of the metal and a permanent closing of the pores.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims, and the illustrated example in the accompanying drawing.

In the drawing:

The figure is a schematic sectional view taken through an apparatus for applying a metallic coating to strip material by a vacuum depositing process and to roll the metallic coating to close the pores therein prior to the formation of oxides on the surface thereof.

By way of illustrating an embodiment of the invention, the application of the invention is schematically illusa trated in the drawing as applied to a vacuum metallizing process.

For purposes of convenience, and because in most instances the material being coated in accordance with the process of the invention will be in the form of an elongated strip, the substrate being coated is illustrated as being in the form of a strip S. The strip S, prior to its arrival to that apparatus illustrated in the drawing, will have passed through suitable cleaning means and will have been charged with an excess amount of hydrogen. The apparatus illustrated in the drawing will include an elongated housing, generally referred to by the numeral 10, which housing has the interior thereof at subatmospheric pressures and is divided into a plurality of individual chambers. For descriptive purposes, the chambers of the housing will be identified here. The chambers include an entry chamber 11, a heating and cleaning chamber 12, a vapor coating chamber 13, a rolling chamber 14, and an exit chamber 15.

The chamber 11 is defined by an end wall 16 or" the housing 10 and a partition wall 17. A vacuum is maintained within the entry chamber 11 through a vacuum line 18 which leads to a suitable vacuum pump. Also, the entry chamber 11 is relatively sealed to the atmosphere by means of a vacuum seal 19 through which the strip S passes in entering into the housing 10.

The chamber 12 is defined by the partition wall 17 and a partition wall 20. The pressure within the chamber 12 will be less than that in the entry chamber 11. Accordingly, the partition wall 17 is provided with a vacuum seal 21 through which the strip S passes when passing from the entry chamber 11 into the chamber 12. Heaters 22 are mounted within the chamber 12 to heat the strip S, thus aiding in driving off the stored hydrogen from the strip S, which heat, together with the low pressure within the chamber 12, functions to effect a rapid removal of the hydrogen, the hydrogen carrying with it undesirable surface oxides. The hydrogen is removed from the chamber 12, and the necessary vacuum maintained therein by means of a vacuum line 23 which leads to a suitable vacuum pump.

Still another vacuum line 24 leads from the vapor coating chamber 13. The pressure within the vapor coating chamber 13 is lower still than that within the chamber 12, a very low pressure being maintained Within the chamber 13 to bring about the desired vacuum depositing of metal vapor on the strip S. Because of the differential in pressures between the chambers 10 and 155, the partition wall is provided with a vacuum seal 25. The chamber 13 is defined by the partition wall 20 and another partition wall 26.

The vapor coating chamber 13 is provided with a plurality of sources of metallic vapor, the individual sources being schematically illustrated and being referred to by the numeral 27. It is to be understood that the sources may vary and for the purpose of the present invention, the nature of the vapor sources is immaterial.

The rolling chamber 14 is defined by the partition wall 26 and a partition wall 28. A vacuum is maintained within the rolling chamber 14 by means of a vacuum line 29 which leads to a suitable vacuum pump. The pressure within the rolling chamber 14 may be greater than that Within the vapor coating chamber 13, or the chamber 14 may be sealed relative to the chamber 13 solely to exclude the coating metal vapor therefrom. Accordingly, the partition wall 26 is provided with a vacuum seal 39 on the exit face thereof.

When the strip S passes into the rolling chamber 14, it will have the desired metal coating deposited thereon. Since the rolling chamber 14 is maintained at a low pressure, it will be seen that the newly coated strip S is not exposed to the atmosphere, and therefore a non-oxidizing condition is maintained and the formation of oxides on the surface of the metal coating of the strip S is prevented, the metal coating being in a nascent state. At this time, it is proposed to roll the metal coating so as to bring about a flowing thereof with the metal flowing into the pores therein and pressure welding the pores shut. To this end, a pair of rollers 31 are mounted within the rolling chamber 14 above and below the path of the strip S. The rolls 31 are preferably of a relatively small diameter so that the rolls will deflect and thereby conform to the steel substrate or strip S. The diameters of the rolls and the material used in forming the rolls, as well as the unsupported lengths of the rolls will, of course, all have to be taken into consideration. It is, however, necessary that the rolls 31 closely follow the surface of the substrate and the metal coating since in a 36 inch wide strip, the substrate thickness may vary as much as 00005 inch and the thickness of the metal coating may be only 0.000010 inch to 0.00006 inch thick. It is also desirable to use polished rolls because a smooth attractive finish is required. The pressures exerted by the rolls 31 on the metallic coating will depend upon the particular metal utilized for the coating metal. However, the pressure must be sumcient to deform the coating metal plastically, thus requiring unit pressures above the yield point of the coating metal.

After the metal coated strip S has had the coating metal thereof rolled to close the pores, the strip S passes through a vacuum seal 32 carried by the partition wall 28 into the exit chamber 15. The exit chamber 15 is defined by the partition wall 28 and an end Wall 33 of the housing 10. A vacuum is maintained within the exit chamber 15, but the pressure within the exit chamber 15 is higher than that within the rolling chamber 14, thus necessitating the vacuum seal 32. The vacuum within the exit chamber 15 is maintained by a vacuum line 34 which is connected to a suitable vacuum pump. Since the coated strip S passes from the exit chamber 15 into the atmosphere, the end wall 33 is also provided with a vacuum seal 35 through which the strip S passes.

In the vacuum metallizing of the strip S, the most common coating metal used will be aluminum. However, the invention is not restricted to aluminum in that many other coating metals, including nickel, titanium, etc., may be utilized. In accordance with this invention, it is only necessary that the coating metal be somewhat softer than the substrate metal in order that the coating metal will deform during the rolling process as opposed to the deformation of the substrate metal, although some deformation of the substrate metal may occur.

The rolling of the coating metal while it is still in its nascent state and free of oxides or chemi-sorbed oxygen produces a pore closing result not otherwise possible. As previously mentioned, when porous metal is rolled after being subjected to oxide forming conditions, although sufficient pressures may be exerted on the metal coating to effect the flowing of the metal into the pores, the pores are not completely closed. As a result, in the case of a coated steel substrate, for example, rusting of the steel substrate will occur in a relatively short time when the coated steel substrate is subjected to a warm humid atmosphere. This is primarily due to the tendency of the metal to spring back when the rolling pressure is released with the resultant separation of metal surfaces which were in contact when the metal was under the pressure conditions imposed thereon during the rolling operation. Gn the other hand, when the atoms of two metal surfaces are in a nascent state and are brought together within the normal interatomic distance for the metal, i.e., generally 2(10) cm., at normal interatomic metallic forces, there is a true joining of the metal. Under the conditions of the present invention, the newly applied metal coating, the coating metal is maintained in a nonoxidizing condition until it has passed between the pressure applying rolls and as it passes through the pressure applying rolls, the metal is caused to flow to fill the naturally occurring pores. The surfaces of the metal coating that come into contact as the pores are closed are still in a nascent state and when sufficient pressure is applied, the surfaces move together to the normal interatomic distance for the metal, i.e., generally 2(l0)' cm., at normal interatomic forces to effect a true joining of the abutting surfaces. This joining or welding of the surfaces prevents spring back and thus results in a complete closing of the pores. Oxidation of the substrate metal cannot take place in the absence of the pores and rusting of the substrate metal is eliminated.

The application of this invention to a gas plating process has not been illustrated. It is to be understood, however, that the coated strip will pass from the gas plating chamber into a rolling chamber without being exposed to the atmosphere. Also, it is to be understood that the rolling chamber will be filled with the gas utilized in the gas plating process. Thus, the formation of oxides on the surface of the newly deposited coating metal prior to rolling will be prevented.

The present invention will also apply to electroplated coatings. However, with electroplated coatings, the coated strips must be rolled within the electrolyte and there is the problem of the electrolyte being trapped within the pores.

From the foregoing, it will be seen that novel and advantageous provision has been made for carrying out the desired end. However, attention i again directed to the fact that variations may be made in the example methods and apparatus disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A process of forming a non-porous metal coating on a substrate comprising the steps of vacuum depositing a porous metal coating on the substrate with the coating metal being somewhat softer than the substrate, and roll ing the metal coated substrate to close the pores in the metal coating while maintaining the metal coating in a non-oxidizing condition at all times between the depositing step and the rolling step.

2. A process of forming a non-porous metal coating on a strip substrate comprising the steps of vacuum depositing a porous metal coating on the substrate with the coating metal being somewhat softer than the substrate, and rolling the metal coating while continuously maintaining the metal coating within a non-oxidizing atmosphere during and between all of the steps.

3. A process of forming a non-porous metal coating on a substrate comprising the steps of vacuum depositing a porous metal coating on the substrate with the coating I metal being somewhat softer than the substrate, and rolling the metal coated substrate to close the pores in the metal coating while continuously maintaining the metal coating within a vacuum during and between all of the steps.

4. The process of claim 3 wherein the metal coating is made plastic during the rolling thereof and the metal of the metal coating flows into the pores.

5. A process of forming a non-porous metal coating on a metal substrate comprising the steps of vacuum depositing a porous metal coating on the metal substrate with the coating metal being somewhat softer than the substrate, and rolling the metal coated metal substrate to close the pores in the metal coating while continuously maintaining the metal coating within a vacuum during and between all of the steps.

6. The process of claim 5 wherein the metal of the metal substrate is steel.

7. The process of claim 5 wherein the metal of the metal coating is aluminum.

8. The process of claim 5 wherein the metal of the metal substrate is steel, and the metal of the metal coating is aluminum.

9. A process of forming a non-porous metal coating on a metal substrate comprising the steps of depositing a metal coating on the metal substrate from a metal bearing gaseous compound with the coating metal being some what softer than the substrate, and rolling the metal coated substrate to close the pores in the metal coating while continuously maintaining the metal coating in a non-oxidizing condition during and between all of the steps.

10. The process of claim 9 wherein the metal coating is maintained in the non-oxidizing condition by being passed through an atmosphere of the gaseous compound.

11. A process of forming a non-porous metal coating on a substrate comprising the steps of electro-depositing a metal coating on the substrate within an electrolyte with the coating metal being somewhat softer than the substrate, and rolling the metal coated substrate to close the pores in the metal coating while maintaining the metal coating within the electrolyte.

12. A method of completely closing the pores in a metal layer comprising the steps of providing a metal layer in a nascent state and while in said nascent state exerting a pressure on said metal to efiect the flow of the metal and the closing of the pores thereof by bringing the metal defining said pores together to normal interatornic distances for the metal at normal interatomic pressures to cause a true joining.

13. A method of completely closing the pores in a metal layer comprising the steps of depositing the metal under non-oxidizing conditions to form a metal layer so as to be in a nascent state and while in said nascent state exerting a pressure on said metal to efiect the flow of the metal and the closing of the pores thereof by bringing the metal defining said pores together to normal interatomic distances for the metal at normal interatomic pressures to cause a true joining.

14. A process of forming a non-porous metal coating on a substrate comprising the steps of depositing a porous metal coating on the substrate under non-oxidizing conditions with the coating metal being in a nascent state and somewhat softer than the substrate, and while maintaining said coating metal in said nascent state rolling the metal coated substrate to effect the flow of the metal and the closing of the pores thereof by bringing the metal defining said pores together to normal interatomic distances for the metal at normal interatornic pressures to cause a true joining.

15. A process of forming a non-porous metal coating on a substrate comprising the steps of depositing a porous metal coating on the substrate within a vacuum to maintain the nascent state of the coating metal as it is deposited with the coating metal being somewhat softer than the substrate, and rolling the metal coated substrate while retaining the metal coated substrate within a vacuum to maintain the nascent state of the coating metal and to effect the flow of the metal and the closing of the pores thereof by bringing the metal defining said pores together to normal interatomic distances for the metal at normal interatomic pressures to cause a true joining.

16. The process of claim 15 wherein the metal of the metal substrate is steel, and the metal of the metal coating is aluminum.

References Cited by the Examiner UNITED STATES PATENTS 1,823,869 9/31 Baur 29-528 2,196,002 4/40 Whitney et a1. 29-528 2,686,355 8/54 Lundin 29-528 2,708,304 5/55 Lundin 29-196.2 2,715,259 8/55 Mohler 29196.2 2,797,476 7/57 Sendzimir 29-528 2,812,270 11/57 Alexander.

2,934,478 4/60 Schickner 204--14.l X 3,066,042 ll/62 Ogden 1'l765.2

WHITMORE A. WILTZ, Primary Examiner.

HYLAND BIZOT, Examiner.

Claims

1. A PROCESS OF FORMING A NON-POROUS METAL COATING ON A SUBSTRATE COMPRISING THE STEPS OF VACUUM DEPOSITING A POROUS METAL COATING ON THE SUBSTRATE WITH THE COATING METAL BEING SOMEWHAT SOFTER THAN THE SUBSTRATE, AND ROLLING THE METAL COATED SUBSTRATE TO CLOSE THE PORES IN THE METAL COATING WHILE MAINTAINING THE METAL COATING IN A NON-OXIDIZING CONDITION AT ALL TIMES BETWEEN THE DEPOSITING STEP AND THE ROLLING STEP.