US 3281339 A
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United States Patent 3,281,339 PROCESS OF ELECTROFORMING USING BENZO- TRIAZOLE AS THE STRIPPING AGENT Donald E. Edgar, Westport, and Lawrence C. Kenausis, Waterbury, Conn, assignors to Anaconda American Brass Company No Drawing. Filed May 10, 1963, Ser. No. 279,634 Claims. (Cl. 204-3) This invention relates to the production of electrodedeposited metal articles, and has for its principal object the provision of means for facilitating stripping of such articles from the cathode on which they are formed. The invention is particularly directed to facilitating the stripping of electrodeposited copper sheets and other electroformed copper articles from copper cathode surfaces. The invention is based on our discovery that when a copper cathode is coated with a solution of benzot-r-iazole prior to immersion in the electrolyte from which metal ions are to be electrodeposited, and when such metal is electrodeposited on the cathode surface to which the benzotr-iazole has been applied, the electrodeposited metal may be stripped with great ease from the cathode, without injury to either the cathode or to the electroformed metal article.
The invention is particularly useful in the production of electrodeposited sheet copper and other electroformed articles of copper, but it may be employed with advantage in the manufacture of electrodeposited articles of other metals as well.
When a layer of copper or other metal is deposited upon a cathodic surface from which the deposit is subsequently to be stripped, that surface must be smooth and otherwise free from flaws. If this surface condition is not attained, the product will be damaged upon being stripped from the cathode. For example, the result of employing a flawed cathodic surface in the production of electrodeposited copper sheet is the presence of pin holes in the electrodeposited sheet or foil. A very irregular surface, or the use of an unsuitable metal cathode, can cause severe damage by virtue of large portions of the electrodeposited copper cohe-ring to the cathode. Not only is the product ruined, but the cathode surface itself must be cleaned and polished if it is to be used again.
Heretofore, lead and stainless steel have been the most commonly used metals for cathodes in the continuous production of sheet copper by electrodeposition processes. The surface of each of these metals is polished to a smooth finish, and the copper deposited thereon is quite easily removed; but the commercial practicability of these cathode materials frequently depends on variables other than the electrodeposition process environment. Thus, stainless steel is expensive. The manufacture of cathodes in the form most widely used for continuous electrodeposition operations (i.e. drum cathodes of large diameter) requires a large capital outlay. Moreover, stainless steel is hard and difficult to polish and to keep polished with an adequately smooth finish. Lead is used more widely than stainless steel, but particles of lead from cathodes of this metal commonly become included within the crystal lattice of the electrodeposited sheet. T hus, upon stripping, the copper material is slightly contaminated with lead. The degree of contamination is slight but suflicient in many cases to render the copper unsuitable for some important uses such as making printed circuits.
A copper cathode is superior to lead and stainless steel, but is subject to the disadvantage that its surface possesses a high cohesive affinity for most metals that can be electrodeposited thereon. Hence, it is hard to strip the electrodeposi-ted metal from it without irreparably damaging the electrodeposited product, unless its surface is first pre- 3,281,339 Patented Oct. 25, 1966 pared by oiling-a procedure that is not practical for drum cathodes used in the continuous production of electrodeposited sheet metal.
The present invention provides an improved elect-rodeposition process for the production of metallic articles, including copper sheet, copper foil and electrofo-rmed copper articles wherein these items may be stripped with great ease from a copper cathode surface upon which they have been formed. Our invention permits stripping of the metal from the cathode surface without danger of damage to the product or irregular coherence of the electrodeposited metal to the cathode. These desirable achievements of our invention are accomplished by coating the copper cathode surface, upon which the copper or other metal is to be electrodeposited, with a solution of benzotriazole. For example, the cathodic surface may be coated with a water solution of preferably from about 0.01% to about 1% by weight of benzotriazole. It is then immersed in the electrolyte which supplies copper or other metal cations capable of being electrodeposited on :the cathode. After the electrodeposit has been formed, the cathode is removed from the electrolyte and the de posit is stripped from it. Such treatment does not impair the suitability of the treated copper surface to serve as a cathode when immersed in an electrolyte, but metal electrodeposited on the treated surface is but weakly bonded thereto.
In the continuous production of copper sheet or copper foil, an acidified solution of a copper salt (e.g. cupric sulfate) is placed in a lead-lined tank. Anodes are arranged in the tank so as to insure optimum electrodeposition conditions. A revolving highly polished drum cathode is immersed in the electrolyte, and as an electric current flows through the electrolyte, a layer of copper is electrodeposited on it. The angular speed of the drum cathode and the electric current density determine the ultimate thickness of the deposit. As the cathode surface upon which copper has been deposited emerges from the bath, the deposit is stripped from the drum in the form of a continuous sheet. The cathode surface is repolished to the extent necessary after stripping and before it reenters the electrolyte.
The present invention permits easy stripping of the sheet from the revolving drum cathode without damaging or otherwise impairing the quality of the sheet. These ends are achieved in a simple fashion by employing copper as the material forming the drum surface and by continuously .and uniformly coating such surface with a solution of benzotriazole after the stripping and polishing steps but prior to re-immers-ion of the cathode surface in the electrolyte bath. In this way, the coated copper cathode is exposed to the standard electrolyte bath and copper (or other metal) is electrodeposited thereon. The resulting layer of deposited copper (or other metal) may be stripped off with ease.
The coating solution is preferably a water solution containing from about 0.01% to about 1% by weight, and preferably about 0.1% to 1% by weight, of benzotriazole. However, the concentration of benzotriazole in the solution is not critical, and it may be above or below the limits just stated. Enhanced results may be obtained if the solution comprises also from 5% to 20% by weight of an alcohol, such as either methyl alcohol, ethyl alcohol, n propyl alcohol or isopropyl alcohol. The alcohol behaves much as a wetting agent, insuring complete and uniform coverage of the cathode surface with the benzotriazole.
The invention is also useful when applied to another sheet metal electrodeposition process: production of starting sheets. Starting sheets are used in the electrolytic production or the electrorefin-ing of copper metal. They provide the base upon which copper is subsequently deposited in larger quantities. For the electrolytic production or refining of copper, starting sheets are hung from a busbar and are immersed in the electrolytic bath from which copper is electrodeposited. Starting sheets are commonly produced by electrodepositing a thin layer of copper on a copper starting sheet blank. It is important that the starting sheet be removed intact from the blank without tearing and without puncturing it. Heretofore, it has been common procedure to coat copper starting sheet blanks with oil to make removal of the electrodeposit possible. Improved results may be obtained by coating the copper starting sheet blanks with a solution of benzotriazole as described above, instead of with oil. Subsequent to this coating treatment, the starting sheet blanks are immersed in the bath, and copper is electrodeposited thereon until it has built up to the desired thickness, after which the electrodeposited starting sheets may be stripped from the blank with ease.
The invention herein is also applicable to electroforming operations, especially for the production of shapes which can be stripped from rigid cathode forms, or shapes which are deposited on collapsible metallic forms. In these operations, it is important that the article be stripped or removed from the specially shaped cathode on which it is produced without damaging the electroformed article. In accordance with the invention, the cathode surface upon which copper or other metal is to be electrodeposited is copper and is coated with a water solution of from 0.01% to 1% by weight of benzotriazole, or with the benzotriazole-alcohol-water solution described above. The coated copper cathode is then exposed to the electrolyte, copper or other metal is electrodeposited thereon until the desired thickness is obtained, and the article is then stripped from the cathode or the cathode is collapsed and separated from the electroformed article. In either case the separation of the electrodeposit from the copper cathode is easily elfeoted.
While the invention has been particularly described with reference to the stripping of electrodeposited copper articles from cathodes, it is equally useful in the stripping of electroformed sheets and other articles of other metals such as nickel, silver and gold which can be electrodeposited upon copper cathodes.
1. The process of making electrodeposited metal articles which comprises treating a copper cathode surface upon which said article is to be electrodeposited with a solution of benzotriazole, electrodepositing the metal of said article on said treated cathode surface, and stripping said article from said surface.
2. The process of making electrodeposited copper articles which comprises coating the surface of a copper cathode upon which said copper article is to be electrodeposited with an aqueous solution comprising benzotriazole, electrodepositing said copper article on said treated cathode surface, and stripping said copper article from said surface.
3. The process of preparing electrodeposited metal articles which comprises coating a copper cathode surface upon which said article is to be electrodeposited with a water solution containing from about 0.01% to about 1% by weight of benzotriazole, electrodepositing the metal of said article on said surface, and stripping said article from said surface.
4. The process of preparing electrodeposited copper articles which comprises coating the surface of a copper cathode upon which said copper article is to be electrodeposited with an aqueous solution containing about 5% to 20% by weight of an alcohol selected from the group consisting of methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol and about 0.01% to 1% by weight of benzotriazole, electrodepositing copper on said treated cathode surface, and stripping said copper article from said surface.
5. The process of preparing metal sheet by electrodeposition on a cathode of copper which comprises applying to the surface of said cathode an aqueous solution of benzotriazole, then immersing said cathode surface in an electrolyte containing metal ions, electrodepositing said metal ions on said treated cathode surface, thereby forming said metal sheet, and stripping said metal sheet from said cathode.
6. The process of preparing copper sheet by elect-rodeposition on a revolving drum cathode of copper which comprises applying to the surface of said cathode a water solution of from about 0.01% to about 1% by weight of benzotriazole, partially immersing said cathode in an electrolyte containing copper cations and revolving it therein, electrodepositing copper on said revolving drum cathode, thereby forming said copper sheet, and stripping said copper sheet from said cathode as the cathode revolves to above the surface of the electrolyte.
7. The process according to claim '6 wherein the benzotriazole solution is applied to the revolving cathode drum surface just prior to its immersion into the electrolyte.
8. The process of preparing a copper starting sheet by the elect-rodeposition of copper onto a copper starting sheet blank comprising coating said starting sheet blank with a water solution containing from about 0.01% to about 1% by Weight of benzotriazole, immersing said starting sheet blank in a solution of an electrolyte furnishing copper cations, electrodepositing said copper cations on said coated starting sheet blank, thereby forming said copper starting sheet, removing said starting sheet blank from said electrolyte solution, and stripping said starting sheet from said blank.
9. The process of electroforming a metallic article on a shaped cathode surface of copper which comprises applying to said cathode surface upon which said article is to be electroformed a Water solution containing from about 0.01% to about 1% by weight of benzotriazole, immersing said cathode surface in a solution containing an electrolyte which furnished cations of the metal of said article, electrodepositing said cations on said cathode surface, thereby forming said metal article, and separating said article from said cathode surface.
10. The process of electroforming a copper article on a shaped copper cathode surface which comprises coating said surface upon which said article is to be electroformed with an aqueous solution containing from about 5% to 20% by weight of an alcohol selected from the group consisting of methyl alcohol, ethyl alcohol, n-propyl alcohol and isopropyl alcohol and from about 0.01% to 1% by weight of benzotriazole, immersing the coated cathode surface in a solution which furnishes copper cations, electrodepositing said copper cations on said coated cathode surface, thereby forming said copper article, and separating said article from said surface.
No references cited.
JOHN H. MACK, Primary Examiner.
W. VAN SISE, Assistant Examiner.