US 3619383 A
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United States Patent inventor Steve Eisner Schenectady, N.Y. Appl. No. 134,295 Filed May 4, 1970 Patented Nov. 9, 1971 Assignee Norton Company Troy, NY. Continuation-impart of application Ser. No. 718,468, Apr. 3, 1968, now abandoned.
CONTINUOUS PROCESS OF ELECTRODEPOSITION 8 Claims, 3 Drawing Figs.
US. Cl 204/35 R, 204/28, 204/36, 204/209, 204/D1G. 10 int. Cl C23] 5/50 Field 01 Search 204/216,
References Cited UNITED STATES PATENTS 9/1910 Rosenberg 204/Dl9.
Rosenberg Bugbee E'delman Chessin et al..
Kiass et a1 Porzei Andersen Davidoff..... Whitaker.... 2/1962 Bailey et a1. 4/1967 Schwartz, Jr.
FOREIGN PATENTS 12/1924 Germany....
9/1967 France OTHER REFERENCES 204/D1G. 10 204/D1G. 1O 204/D1G. 1O 204/D1G. 1O 204/D1G. 10 204/208 X 204/1 1 204/208 X 204/209 204/217 X 204/36 1ndustria1& Eng. Chem., Vol. 61, No. 10, Oct. 1969, pp. 8- l7, 204/D1G. 10
Primary E.raminer.1ohn H. Mack Assistant ExaminerR. J. Fay Anorneys-Hugh E. Smith and Herbert L. Gatewood ABSTRACT: Process and apparatus for continuously electrodepositing metal of relatively uniform thickness on a moving metal substrate at extremely high plating rates.
PATENTEDNUV 9 1971 a 7 i0 E6 3 INVENTOR STEVE E ISNER M/ffi ATI ORNEY CONTINUOUS PROCESS OF ELECTRODEPOSITION CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part, of my copending application Ser. No. 718,468 filed Apr. 3, 1968, for Electrodeposition (now abandoned), the entire disclosure of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the general field of electrodeposition. In particular, it relates to continuously forming a metal coating by means of electrodeposition on a metal substrate.
2. Description of the Prior Art The electrodeposition of metal over the past several decades has assumed a prominent position in science and industry, so that today a sizable portion of the yearly output of metals is consumed in such processing. A large variety of electrodeposition processes are known and currently in use. Electrodeposited metal coatings, as is well known, are used in providing, among other functions, hard wear-resistant surfaces on less wear-resistant metals, surfaces having desirable aesthetic properties on base metals not so pleasing in appearance, costing much less, or structurally desirable, or the like, and surfaces more resistant than the base metal to various corrosive atmospheres.
In general, electrodeposition of a metal coating on another surface is a slow process. Many efforts have been made in the past to increase the speed of these processes, but have met with only limited success. Quality is usually more important in electroplating than is rate of deposition, and, therefore, speed is almost invariably sacrificed when a good quality electrodeposit is sought. In continuous electrodeposition processes, where speed or rate of deposition is a particularly important factor, extremely long plating lines have been used to obtain an increased rate of metal substrate movement while maintaining sufficient contact with the electrolytic solution to obtain a commercially desirable electrodeposit of the required thickness on the substrate.
In commercial electroplating, the preparation of the substrate for electrodeposition has been as important to a successful process as the electrodeposition itself. This was particularly true when plated articles having a high quality finish were desired. The particular type of preparation of the substrates for electrodeposition depended on the substrate material, its condition, shape, size, composition, surface condition, and other factors. However, to provide good adhesion between the electrodeposited metal and the substrate it was generally deemed necessary to clean the substrate surface of any foreign matter, e.g. protective oils, dust deposits, salts, etc. Removal of dirt, grease and lacquers was usually accomplished by using some form of alkaline cleaner, often containing oxide solvents such as cyanides and detergents such as sodium phosphate, as well as other materials. The alkaline cleaners were used alone or in combination with electrolytic cleaning where the object to be plated is alternately made anode and cathode. At other times grease and dirt were removed by organic solvents, usually of the petroleum type. Inasmuch as the metal deposited follows the contours of the substrate on which it is deposited, generally smooth finishes were produced only on substrates having smooth surfaces. For this reason, substrate surfaces, which were rough due to scratches, or other discontinuities andimperfections were often treated by mechanical cleaning methods, such as sandblasting or the object was pickled in some suitable acid. Oftentimes, an electroplating line involving continuous electrodeposition included a number of these pretreatment steps in combination with the electroplating. These combination treatments required rather elaborate apparatus. The pretreatment processes involved elaborate schemes for handling the workpiece, thus requiring additional personnel, equipment and space, all of which added considerably to the overall manufacturing cost of the electrodeposited metal product.
In general, it has been found desirable, and in some instances necessary, to include in the electrolytic solution, in addition to the salt containing the metallic ion or radical, a socalled addition agent. These agents were used for a number of purposes, including inhibition of dendritic or columnar growth, creation of some preferred orientation of the metal crystals, and for their capability to interfere with or impede crystal growth, thus resulting in deposits having small crystals. The use of addition agents in the electrolytic solutions produces some particular advantage; however, their use can also introduce some disadvantages into the plating process. Thus, an addition agent may be found suitable in enhancing one property, e.g. brightness in a deposit, while adversely effecting other properties, e.g. hardness. Oftentimes, extreme caution had to be exercised in controlling the size and amount of addition agent used in the electrolytic solution. Moreover, with certain electrolytic solutions the rate of deposition was limited by the use of addition agents.
SUMMARY OF THE INVENTION In general, my invention provides a process by which a metal substrate can be plated continuously with a metal coating having a relatively uniform thickness and smoothness. The process precludes dendritic growth in the deposit.
Quite advantageously, my process minimizes the amount of preparation of the substrate required for electroplating. The prior art necessity of using chemical cleaning materials, mechanical preparation techniques, and electrolyte addition agents therein to inhibit dendritic growth or to obtain microleveling during operation are essentially all eliminated by my process.
In the performance of my invention the cathode surface and/or cathodic deposit is mechanically activated" simultaneously with deposition of metal ions thereon. Although the mechanism of the mechanical activation" is not totally understood, it is theorized such consists of several actions taking place essentially simultaneously. It appears to involve removal of the polarization layer with simultaneous distortion of the crystal lattice structure of the deposit. While activation" may involve removal of a minute amount of metal from the surface being activated, such removal is not absolutely necessary. The activation" process requires distortion of the metal deposit sufficiently to produce therein a scratch pattern which oftentimes is visible to the naked eye or under a magnification of 2,000 power or less, but in any event it is visible under a magnification of less than 10,000 X. This scratch pattern in many instances involves mere plowing" or rearrangement of the surface, rather than actual removal of metal from the surface. In any event, and whatever the mechanism involved, activation" is produced by contacting the metal surface with an activating means, hereinafter more fully described, which moves relative to the metal surface. The activation of the metal layer results in a markable increase in the rate of electrodeposition as is reflected in the ability of the present process to operate at current densities far in excess of prior art current densities of -150 amps per square foot.
BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood by reference to the drawings in which like numerals refer to the same parts in the various Figures.
FIG. I is a schematic representation of apparatus which may be used in the practice of my invention.
FIG. 2 is a schematic representation of a variation of the apparatus of FIG. 1.
FIG. 3 is a cross-sectional view of the activating means of FIGS. 1 and 2.
DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 of the drawings, there is shown a tank 26 containing an electrolytic solution 24. A metal strip 10 on which is to be provided an electrodeposited metal coating is passed from a source thereof, such as a coil 13, around guide roll 14, across electrical contact 115 and pressure roller 25, over guide rolls 16, 17 and 18 to wind up means (not shown in the drawing) wherein the metal strip 10 is wound into a coil 19. The metal strip H is supplied with negative current by electrical contact 15 and thereby metal strip becomes the cathode in tank 26.
In contact with metal strip 10 as it passes over electrical contact 15, pressure roller 25 and roller 16 is activating means 20 which takes the form of a continuous belt which is mounted on rollers 21 and 22. One or both of rollers 21 and 22 may be rotatively driven, thereby causing activating means 20 to move in a linear path. The direction of travel of activating means 20 is preferably opposite to that of metal strip 10; however, it can move in the same direction provided that its linear velocity is at least percent faster or slower than that of metal strip 10.
Anode 23 is located near pressure roller 25 with metal strip 10 and activating means interposed between anode 23 and roller 25. Roller is movable laterally as is shown in FIG. 1. When roller 25 is moved towards anode 23, the metal strip 10, activating means 20 and anode 23 are brought into rubbing contact. The pressure contact between activating means 20 and the strip 10 can thus be regulated by the movement of pressure roller 25. With such arrangement the pressure contact between activating means 20 and the sheet metal strip 10 can be regulated as desired, depending upon the particular metal being deposited. With the deposition of some metals the pressure will be desirably less than in the deposition of other metals to avoid removing an undesirable amount of the metal just deposited. The spacing between the anode and pressure roller can be varied as desired, depending upon the activating means used, its thickness, compressibility, relative speeds, the pressure contact desired, etc. The maximum gap distance is fixed by the IR drop considered acceptable for the particular operation.
Metal strip 10 can be any metal on which a metal coating is desired. Merely by way of example it may be copper, tin, zinc, nickel, iron, brass, steel or alloys thereof. The metal strip 10 can be of any desired width and thickness limited only by the size of the particular apparatus used in the practice of the invention. The electrolytic solution 24 can be any solution desired, taking into consideration the particular metal coating which is to be provided.
In the practice of my invention various metals can be used as the cathode. The anode may be of the consumable type, i.e., the same metal to be deposited, or of the inert type, eg an anode composed of lead or a lead composition containing from about 6-15 percent antimony. In the event a nonconsumable or inert anode is used, the concentration of the electrolytic solution 24 must be adjusted periodically as is well known in the electroplating art.
The activating means has supported at least on its surface, in closely spaced relationship to one another, a plurality of small relatively inflexible particles, as fully described in my copending application, Ser. No. 718,468, mentioned earlier. The activating means can be made from a variety of materials including open-weave fabrics or compressed nonwoven substrates. A preferred activating means has been discovered to be a compressed nonwoven abrasive member having a high degree of resiliency and porosity. Such an activating means is more fully described in my copending application, Ser. No. 718,468, mentioned earlier and in the examples hereinafter given.
A variation in the apparatus of FIG. 1 is shown in FIG. 2. In FIG. 2 there is shown a housing 33 which encloses the activating belt system composed of activating means 32 which again is in the form of a continuous belt which is mounted on rollers 31 and 34. One or both of rollers 31 and 34 may be rotatively driven, thereby causing activating means 32 to move in a linear path.
A metal strip on which is to be provided an electrodeposited metal coating is passed from a source thereof,
such as a coil 35, around electrical contact 36 to windup means (not shown in the drawing) wherein the metal strip 30 is wound into a coil 37. The metal strip 30 is supplied with negative current by electrical contact 36 and thereby acts as the cathode in the area of electrodeposition.
Anode 38 is located near electrical contact 36 with metal strip 30 and activating means 32 interposed between anode 38 and electrical contact 36. Electrical contact 36 is movable laterally as is shown in FIG. 2. When electrical contact 36 is moved towards anode 38, the metal strip 30, activating means 32, and anode 38 are brought into rubbing contact. The pressure contact between activating means 32 and strip 30 can thus be regulated by the movement of electrical contact 36 similarly to the system described for FIG. 1.
The anode 38 and the area of electrodeposition on strip 30 are not immersed in the electrolyte as in FIG. I, but rather are flooded with electrolyte by a pump 39, pipe line 40 and trough 4]. The electrolyte solution drains to the bottom of housing 33 forming a pool 42 which supplies the intake of pump 39 with electrolyte.
FIG. 3 shows a highly enlarged and idealized portion of one type of activating media suitable for use in the present invention. Reference numeral represents fibers of a nonwoven web (nonconducting fibers as polyethylene terephthalate or the like) which are anchored one to the other at their points of intersection by an adhesive binder 86. A plurality of small, hard, discrete particles 87 are positioned on the fibers 85 and in the present illustration are held to such fibers by the adhesive 86. At least some of the fibers 85 extend relatively parallel to the cathode face 89 as shown at 88 to form thin-walled cells or electrolyte sweeping members which provide fresh electrolyte constantly to the activated plating surface. (For purposes of illustration, the activating particles 87 are here shown at some distance from the cathode face 89 and associated electrodeposit 90 although in operation of the present apparatus they would be in contact therewith.)
The following specific examples will illustrate more clearly the preferred embodiments of my invention.
EXAMPLE 1 Using the apparatus as shown in FIG. 2 of the drawing steel shim stock (4 mils thick and 3 inches wide) as obtained from a steel supplier was electroplated without any prior cleaning or surface treatment with a copper deposit from a solution of copper sulfate containing 45 grams of copper sulfate per liter. This solution was held at a temperature of approximately 75 F. The activating means used in this instance, was made from a nonwoven web of polyester fibers bonded with an acrylonitrile-melamine resin adhesive and roll coated with a phenolic adhesive and abrasive grain as described in my copending application, Ser. No. 718,468, mentioned earlier. The apparatus was adapted to allow the shim stock cathode to roll past the activating means over a 1 inch diameter steel electrical contact disposed laterally opposite the anode, and laterally with respect to the activating means. The anode utilized was a lead slab 4 inches X 6 inches X one-fourth inch. The activating means, in the form of a continuous belt, operated at a linear speed of 1,050 feet per minute.
The electrical contact was adjusted so as to put the shim stock cathode in engagement with the activating means and anode at an applied load of about 29 p.s.i. The contact area made by the shim stock on the cathode was about one-fourth inch X 3 inches.
A cathode current density of 5,700 amps per square foot (a.s.f.) was maintained. The rate of travel of the shim stock over the electrical contact was 12 feet per minute.
After rinsing with tap water the copper deposit was observed to have a uniform bright appearance. The copper deposit was determined to be 0.1 mil thick uniformly over the entire strip.
When the copper deposited steel shim stock was crinkled and bent double, the copper deposit did not crack or peel off,
thus showing outstanding adhesion between the copper deposit and the steel substrate. This is indeed surprising because according to prior art teachings steel which has been plated with copper without a strike usually has shown poor adhesion.
EXAMPLE 2 In a manner similar to that disclosed in example 1, tin was plated on a brass substrate from a solution containing 36 oz./gal. of S,,SO and 36 oz./gal. of H 80 The tin deposit on subsequent examination showed excellent adhesion to the brass substrate.
EXAMPLE 3 In a similar manner to that disclosed in example 1, copper was plated on a mild steel substrate from a solution at room temperature of copper sulfate containing 45 grams of copper sulfate per liter. The steel shim stock was advanced at at rate of 3 feet per minute and the activating belt speed was 1,350 feet per minute. The current density was 725 amps per square foot and the pressure exerted on the activating belt by the cathode was 1.18 pounds per square inch.
A pressure sensitive adhesive tape adhesion test was performed in the following manner. A cross was scribed into the electrodeposit with a knife, a piece of adhesive tape was placed on the electrodeposit at an angle of 45 to the scribed lines. The tape was then pulled from the electrodeposit. The test was repeated at a direction 90 to the first tape direction. For the deposit obtained in example 3, no copper was pulled off with the tape showing good adhesion of the copper coating to the steel substrate.
Many different embodiments of the invention will readily occur to those skilled in the art of electroplating, and the specific embodiments of the invention are presented by way of illustration only and not as limiting the invention. Therefore, the scope of this invention is to be limited only by the appended claims.
1. A process for electrodepositing metal on a thin metal substrate which comprises:
a. Providing a supply of thin metal substrate in the form of long lengths of strip stock;
b. Continuously passing said strip stock into and through an electroplating zone where metal is deposited on the surface of said strip stock;
c. Providing in said electroplating zone continuous activation of the surface of said strip stock and of the entire surface of the metal being deposited thereon by contact with a plurality of small spaced activating particles secured to a supporting matrix; and
d. Continuously removing said strip stock and the metal deposited thereon from said electrodeposition zone.
2. A process, according to claim 1, wherein the continuous activation of said surfaces results in surface scratches visible under a magnification of less than 10,000 X.
3. A process, according to claim 2, wherein the sheet metal stock to be coated is steel and the electrodeposited metal is selected from the group consisting of zinc, copper, tin, nickel and alloys thereof.
4. Apparatus for the high speed electrodeposition of metal onto a thin metal substrate which comprises:
a. Means to continuously feed a thin metal substrate from one station to a second station;
b. Means to electrically connect said thin metal substrate intermediate said stations to a source of negative potential;
c. Anode means positioned adjacent said thin metal substrate intermediate said stations and electrically connected to ground;
d. Movable nonconductive activating means comprising a plurality of small, hard particles secured to a supporting matrix between and in contact with said anode and at least a portion of said thin metal substrate intermediate said stations; e. Means to move said nonconductive activating means relative to and in contact with at least said portion of said thin metal substrate; and
. Means to supply electrolyte to said portion of said thin metal substrate in contact with said activating means whereby the surface of said thin metal substrate and of the metal deposited thereon in said portion thereof is mechanically activated resulting in a rapid buildup of an electrodeposit on said thin metal substrate.
5. Apparatus as in claim 4 wherein said activating means comprises an electrolyte-permeable matrix having a plurality of small nonconductive particles adhered thereto in fixed spaced relationship one to the other.
6. Apparatus as in claim 5 wherein said matrix comprises a porous nonwoven web.
7. Apparatus as in claim 5 wherein said matrix comprises a