US2104269A - Metal plating - Google Patents

Description

Patented Jan. 4, 1938 UNITED STATES METAL name Floyd F. Oplingcr, Niagara Falls. N. Y., assignor to E. I. du Pont de Nemours a Company, Wilmington, Del, a corporation of Delaware No Drawing.

Application April 1'], 1934, Serial No. "1.0

' Claims. (Cl. 20 4-13) This invention relates to the art of electroplating and more particularly to the production of decorative electroplated articles.

An object ofthe present invention is to pro- 5 duce certain decorative effects on metal-by electroplating, as hereinafter described. Other obiects will appear in the following description.

In my copending application Ser. No. 709,171 filed-Ian. 31, 1934 I have described and claimed a method of producing smooth, bright coatings of electroplated coatings which comprises electroplating a metal with a metal coating having a lower melting point than that of the-base metal and thereafter subjecting the plated article to a heat treatment under non-oxidizing conditions, at a temperature above the melting point of the plated metal. I

I have discovered that when an electroplated coating which has been heat treated at a temperature above its melting point is subsequently replated, preferably with a coating of the same metal or an alloy thereof, the final electroplated coating is deposited in the form of spangle-like crystals which have a decorative eflect pleasing to the eye. These spangled coatings are of a crystalline nature and resemble the ordinary galvanized iron made by coating metal sheet in a bath of molten zinc.

I have further discovered that the spangled efi'ect can be produced by plating over coatings of such metals as tin, lead or zinc or their alloys which coatings have been applied to the base metal in the molten state.

According to one method of practicing my invention, I first electroplate a metallic article to be decorated with a metal having a melting point lower than that of the base metal of which the article is constructed. For example I may plate an iron, steel, copper or brass article with such metals as tin, cadmium, zinc or suitable alloys of these metals. For the purposes of this invention, the electroplated coating may be 'made of any desired thickness. After the metal has been plated, it is washed and dried and then heated for a short time under non-oxidizing conditions at a temperature above the melting point of the' electroplated metal, so as to fuse the latter without fusing the base metal. One convenient method of carrying out this step is to dip the electroplated article in abath of molten tallow or other suitable liquid maintained at the required temperature. For example, a tin coating may be treated by dipping the plated article into a bath of molten tallow maintained at a temperature of 450-500" C. for 10 seconds to 2 minutes, depending on the size of the article. Various other means of heating under non-oxidizing conditions will be apparent. For example. the article may be heatedin an atmosphere of a non-oxidizing gas such as hydrogen or nitrogen.

After heating, the article is suitably cooled preferably at a controlled rate, since the rate of cooling affects the ultimate result as hereinafter explained. Various known methods of controlled cooling may be used, e. g. by dipping in oil or water.

After cooling, the heat treated article is again plated with the metal with which it was first plated. This second electrodeposit is produced in a bright crystalline form, having the spangled efiect above described. If desired, the spangled coating may be converted to a smooth or mirrorlike coating by heat treating as above described under non-oxidizing conditions above the melting point of the plate. If this is done,.the resulting heat treated article may again be plated with the result that the spangled coating is again reproduced.

In some cases, especially when applying my invention to the decoration of cold-rolled steel sheet and similar steel articles, it is preferable to utilize a method for preliminary treatment of the article to be decorated which is described and claimed in my copending application S. N. 709,171. In accordance with the method, I first clean the metalsurface by known means to remove oil, grease and the like. The cleaned metal article then is treated with a strong acid solution until a visible and uniformly etched surface is produced. This etching process should be continued until the etching of the metal is plainly visible to the unaided eye, so that the treated surface presents a more or less uniformly dull appearance. Various strong acids, for example sulfuric acid, hydrochloric acid, nitric acid or various mixtures of such strong acids may be used for this etching process. It is preferable to have the acid solution warm, for example to -160 F.

After the article has been suitably etched, it is rinsed with water and then it is treated in an alkaline solution for a few minutes. Various solutions of strong alkali are suitable for this treatment; it is often preferable to have substantial quantities of alkali metal cyanide present in the alkaline bath used for treating the metal. Preferably I treat the metals in the alkaline bath by using the alkaline solution as an electrolyte and making the article to be treated the anode. After the alkaline treatment, the article is plated, heat-treated and replated as described above, to produce the decorative effect.

If the above mentioned etching process has been too drastic, the surface of the plated metal may have a somewhat dull appearance after the heat treatment; when a less drastic etching is used, the article will have a smooth, mirror-like surface. However, for the purposes of the present invention it is immaterial whether the degree of etching is the minimum required to produce a smooth surface on heat treating or whether it is so drastic as to produce a dull surface by the heating step. In either case a satisfactory decorative result is obtained.

The following examples illustrate more specifically methods of carrying out my invention:

Example 1 Sheet copper was treated with a warm mixture of sulfuric and nitric acid solutions until visibly and uniformly etched The etched copper was plated with tin from an alkaline electrolyte. The plated sheet then was immersed in a bath of molten tallow maintained at a temperature of 240-260 C. until the tin plate was fused and then cooled by quenching with water. The sheet was then cooled and replated with tin. The second electrodeposit of tin had a beautiful, crystalline or spangled appearance, similar to that of galvanized iron sheet.

Example 2 Cold rolled steel sheet was cleaned to remove grease and dirt, pickled in strong sulfuric acid until visibly etched, washed with water and given an anodic treatment for about 3 minutes in an alkaline solution of sodium cyanide at a temperature of 140-160 F. The steel sheet then was plated with tin, heat treated and replated as described in Example 1, with substantially the same results.

Example 3 A coating of spangled tin was produced on cold rolled sheet steel by the method of Example 2. The spangled sheet then was electroplated with gold to a good color. The resulting gold plate accurately reproduced the underlying crystal pattern.

' Example 4 Cold-rolled steel was treated by the method described in Example 2, except that the initial plate was a tin alloy, electroplated from an alkaline tin bath to which was added a salt of the alloy constituent, i. e., cadmium or zinc. After heating the alloy-plated sheet under non-oxidizing conditions above the melting point of the plate and cooling, the sheet was replated with pure tin from an alkaline electrolyte. The alloys used for the initial plate were tin-cadmium and tin-zinc. Various decorative effects were obtained, with different crystal patterns, depending on the rate of cooling after heat treatment of the initial plate.

In utilizing my process for producing the spangled effect on cold-rolled steel, it is preferable that the base metal be visibly etched with acid and then treated with an alkali as hereinbefore described, prior to the initial plating. In any case, I prefer to visibly etch the base metal with acid and then treat with alkali prior to applying the first coating.

Various modifications of my invention will be apparent. For example. the final electroplated coating may be identical with the underlying coating, an alloy of the same or a different metal. For example, a base metal having a fused coating of tin may be replated to produce the span- Sled effect by replating the tin with tin alloy or I with another metal such as copper or gold. I prefer to replete with the same metal as is used for the under coat or an'alloy thereof. In some cases where the final coating is a different metal than the underlying coating it is advantageous to produce the spangled effect by the herein described method before the final coating is applied. For example, I may coat a metal-with a fused tin coating either by hot dipping in molten tin or by first electroplating and then heating the electroplated tin to a temperature above its using different metals or alloys for the first coat,

different decorative effects may be obtained. Also, the rate at which the first coat is cooled after having been fused often will affect the size of the crystals appearing in the final coat; in general, if the rate of cooling is rapid the crystals appearing in the final electrodeposit will be small, while slow cooling promotes the formation of large crystals. Also, preliminary treatment of the base metal prior to application of the initial coating, e. g. by etching with acid, also will influence the crystalline appearance of ,the final electrodeposit. In general, the crystalline patterns may be made more definite by a visible etching of the base metal prior to the application of the first coating.

The appearance of the final products also will depend to some extent upon the thickness of the -final coating. If the coating is. too thick, the

desired spangled effect may not appear; that is, if sufiicient metal is electrodeposited, the crystalline appearance which is at first formed may finally become obliterated. Hence, to obtain the said fused coating with a sufilciently thin layer of tin to develop a spangled coating.

2. A process for decorating metal surfaces comprising providing a metal surface with an oxidefree coating of fused tin and thereafter electroplating said fused coating with a sufilciently thin layer of tin to develop a spangled coating and finally electrodepositing on said spangled coating a thin layer of gold.

3. A process for decorating a metal surface comprising electroplating said surface with tin, heating the electroplated surface under nonoxidizing conditions to a temperature above the melting point of the electrodeposit, cooling and thereafter electroplating said surface with a sufficiently thin layer of tin to develop a spangled ing the electroplated surface under non-oxidiz- CERTIFICATE OF CORRECTION.

Patent no m -269.

ing conditions to a temperature above the melting point of the electrodeposit, cooling and thereafter electroplating said surface with a suffi- .ciently thin layer of metal to develop a spangled coating.

6. A process for decorating a cold-rolled steel surface comprising, treating said surface with an acid until the surface thereof is at least visibly etched, following with an alkaline treatment,

electroplating said etched surface with tin, heating the electroplated surface under non-oxidizing conditions to a temperature above the melting point of the electrodeposit, cooling, thereafter electroplating said surface with tin to produce a spangled coating and finally electrodepositing on said spangled coating a thin layer of gold.

FLOYD F. OPLINGER.

January 958,

FLOYD F. CPLINGER.

It is'hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page 5 second colurnn, 11116 M, claim 5, for the word "metal" read tin;.and that said Letters Batent should be read with this correction therein that the same may conform to i the record of the case,in the Patent Office.

Signed and sealed this 22nd day of February, A. D. 1958.

(Seal) Henry Van Arsdale,

Acting Commissioner 01 Patents.

oxidizing conditions to a temperature above the melting point of the electrodeposit, cooling and thereafter electroplating said surface with a sufficiently thin layer of tin to develop a spangled ing the electroplated surface under non-oxidiz- CERTIFICATE OF CORRECTION.

Patent no m -269.

ing conditions to a temperature above the melting point of the electrodeposit, cooling and thereafter electroplating said surface with a suffi- .ciently thin layer of metal to develop a spangled coating.

6. A process for decorating a cold-rolled steel surface comprising, treating said surface with an acid until the surface thereof is at least visibly etched, following with an alkaline treatment,

electroplating said etched surface with tin, heating the electroplated surface under non-oxidizing conditions to a temperature above the melting point of the electrodeposit, cooling, thereafter electroplating said surface with tin to produce a spangled coating and finally electrodepositing on said spangled coating a thin layer of gold.

FLOYD F. OPLINGER.

January 958,

FLOYD F. CPLINGER.

It is'hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows; Page 5 second colurnn, 11116 M, claim 5, for the word "metal" read tin;.and that said Letters Batent should be read with this correction therein that the same may conform to i the record of the case,in the Patent Office.

Signed and sealed this 22nd day of February, A. D. 1958.

(Seal) Henry Van Arsdale,

Acting Commissioner 01 Patents.