US2977295A

US2977295A - Electroplating process

Info

Publication number: US2977295A
Application number: US708767A
Authority: US
Inventors: Carl F Cooper
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-01-14
Filing date: 1958-01-14
Publication date: 1961-03-28
Anticipated expiration: 1978-03-28
Also published as: FR1211108A

Description

, develop a chemical graining method.

United States Patent-O 2,911,295 ELECTROPLATING PROCESS Carl F. Cooper, Grass Lake, Mich. N Drawing. Filed Jan. 14, 1958, Ser. No. 708,767

14 Claims. (Cl. 204-43) The present invention relates to an electroplating bath of particular value for the deposition of zinc on aluminum and is a continuation-in-part of my prior filed application Serial No. 402,149, filed January 4, 1954, and now abandoned.

The electroplating of zinc on steel has become a widely practicedart. However the electroplating of zinc on aluminum to form zinc plates of substantial thickness is practically unknown in the electroplating arts. In those fields where zinc plating has been used a wide variety of addition agents have been suggested for the refining of the grain structure of the zinc, the obtaining of leveling action, the improvement in adhesion, and the like. Among these suggestions which is of particular interest here is a unique, suggestion by Weanin Patent No. 2,646,397, issued July 21, 1953. In the Wean patent. it is disclosed that a small proportion of titanium, that is about .005 ounce-.02 ounce of titanium per gallon of electrolyte, has the effect of leveling the surface of a zinc plate on steel.

- As stated above the use of zinc plating on aluminum has been very limited and is limited generally to the thin plates produced by the zincating method as a preplate for copper, nickel, and chrome. Industry has practically no use for a zinc plate on aluminum where the zinc plate is to remain exposed. An outstanding exception to this statement however lies in the lithographic art. In lithography it is now quite common to use aluminum sheets which have one, two, or three layers of various metals placed thereon. In this art, however, it has been found necessary to grain the aluminum by the use of arather involved and costly .metho-d, involving. rolling marbles and a sandy slurry over the surface of the aluminum for periods in excess of one hour in order to provide a type of grain on the aluminum which can serve for the later lithographic functions. In this connection the printed art notes frequently the hope that someday someone will In passing and because it may seem pertinent I may mention that I have tried the Wean bath mentioned above in this connection as well as all other baths of the art and have secured no results favorable to the lithographing art.

It is therefore an object of this invention to treat the surface of aluminum in a manner such as to produce an electroplate thereon having a grained metal surface suitable for use in the lithographic arts.

It is a further object of this invention to electroplate zinc on aluminum in a manner such as to have control of the grain size, porosity, and the like of the deposited metal in a manner as to efiect advantages in lithography.

It is still a further object to electroplate zinc on aluminum to form a very adherent plate suitable as a preplate for the plating of a wide variety of other metals on aluminum as a basis metal;

I have now found that the foregoing and related objects can be secured in an electroplating bath comprising essentially at least about grams of dissolved zinc per liter and dissolved titanium, wherein said compositions 2,977,295 Patented Mar. 28, 1 951 "ice are further characterized by the concentration of dissolved titanium being suflicient and the acidity of the solution being suflicient such that the solution manifests at plating temperatures a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic and as opposed to the clear, grey-pink, and grey-blue colors of solutions less concentrated in titanium.

Although the concentration of dissolved zinc should be-in excess of about 10 grams perliter of solution I prefer a concentration of about 35 grams per liter. I also prefer that the zinc be added aszinc fiuoborate either in the form of the salt or by prior dissolving of the zinc metal in fiuoborate acid. Portions of the zinc fiuoborate may be replaced by zinc chloride but it ispreferred 'that the fiuoborate be used in excess over the chloride.

Larger amounts of zinc can be used but in general no additional advantage is obtained in concentrationsgreater than about grams of dissolved zinc per liter.

The concentration of dissolved titanium can be stated generally to be in excess of about 10 grams of dissolved titanium per liter. However the minimum effective concentration of titanium can be better expressed in terms of the color properties of the solution. In this latter connection the acidity of the solution can also be most accurately defined in connection with color. I have found that in very minor concentrations of titanium such as that in the Wean patent mentioned above the color of the solution varies from clear to grey-pink to grey-blue depending on the acidity of the solution. However, as the concentration of titanium is increased and as the acidity of the solution is increased over those acidities normally associated with acid zinc electroplating baths there occurs a very definite series of color changes which can be used to characterize the solution quite accurately. Actually the acidity of these solutions is so great that it is difiicult to determine them accurately on ordinary laboratory instruments. However, as one approaches these low pH ranges he notes the solution has first a brown color which, upon becoming more acidic, gradually becomes a yellow to yellow brown color and, upon going to a still lower pH, takes on a bright emerald green color. I have found that when the solution is sufficiently concentrated in titanium ions and the acidity is sufiiciently low to have attained the yellow brown color that I succeed in securing zinc plates on aluminum which have the necessary properties for their use in the lithographic arts. On the contrary if the solution is sufiiciently acidic to be emerald green or the solution is sufiiciently less acidic to be in the brown color range the plating is not successful. By successful plating in this case is meant plating where the grain of the zinc can be controlled in such a manner as to produce very satisfactory lithographic plates. These plates are, in addition, extremely adhesive and present a very beautiful blue white color in contrast to the usual grey-white zinc plate.

It is preferred that the titanium be added as titanium fiuoborate and further it -is recommended that the bath be originally prepared by dissolving titanium in fiuoboric acid. This latter step is the most economical since titanium can be secured as chips which are readily soluble in fluoboric acid. There is no upper limit on the concentration of titanium and it can be used to saturation. I have frequently plated with titanium fiuoborate precipitate in the bath with complete success,

In addition to its use in the lithographic arts the zinc plate is extremely valuable when applied generally to steel, aluminum alloys, and magnesium alloys. Its corrosion resistance is particularly noteworthy. In cornparative tests against standard galvanizing and zinc electroplating methods on steel my bath was able to produce coatings more adhesive and corrosive resistant than the standards.

In connection with my invention there has been considerable controversy among experts as to the part played by titanium in the actual plate itself. For the reason of this controversy I do not wish my invention to be limited by theory or in any way defined by a presumed action of titanium in the plated metal itself. In this connection for example, independent laboratory tests have shown, in one instance, that titanium metal had actually diffused or plated into the aluminum basis metal to form the alloy AL3TI. In other cases of spectroscopic analysis titanium was reported in the zinc plate and with the opinion that there was some sort of solid solution formed. Other experts, when titanium was found in the zinc plate, merely express the opinion that the titanium was captured as an impurity from the bath. Whatever may be the facts about the part titanium plays because its actual physical presence in the plate itself, there is no question but what it does alter the overall plating operation. Plating may be conducted in the bath of the invention by' the use of zinc anodes, inert anodes, or by the combination of zinc and titanium anodes. I have found it preferable to use mostly zinc anodes with some titanium anodes, the latter being just sufiicient to maintain the concentration of titanium in the plating solution.

The temperatures of the baths for plating purposes can be generally from 80 F. to 150 F., the bath giving -well defined continuous plates at all these temperatures.

A wide variety of current densities can be used, although 24-36 amperes per square foot at 2-3 volts is satisfactory.

. Example I A plating bath was made up as follows: 1050 grams of titanium and 850 grams of zinc were dissolved in fiuoboric acid (47%) and sufficient water added to make 6.5 gallons. The concentration of the foregoing solution is approximately about 35 grams of zinc and 40 grams oftitanium per liter. The pH of the solution was adjusted until it reached a yellow brown color at the plating temperature of 110 F. A series of steel and aluminum alloys were plated in the bath at a current density of 36 amperes per square foot and 3 volts. All plated samples were very adherent, were of a white blue color and yielded a very crystalline appearing surface. The plates were subjected to standard adhesion and salt spray tests and were found equal to or better sheets in the above composition which sheets were sub mitted for tests in the lithographing field and declared excellent by independent experts. In the latter connection the crystalline surface of the zinc acted much in the manner of the previously grained plates. A wide variety of aluminum alloys have been plated in the above bath including 248T, 52S, 25, 13H and the like.

Example II The previous example was repeated in hundreds of individual baths except that zinc in varying amounts from zero grams per liter upward to saturation, titanium ion concentrations from zero up to saturation, and pH ranges from less than zero on standard laboratory meters to approaching alkaline solutions were evaluated. In addition a wide variety of standard organic addition agents such as corn syrup, sugar, gelatin, licorice and the like were used. It was in this fashion that the limits stated within this specification were obtained. A wide variety of steel alloys, aluminum alloys, copper and magnesium alloys were plated. a

Example III Grams Titanium fiuoborate 220 Zinc fiuoborate 45 Zinc chloride Water to 1 liter.

The above solution can be adjusted with fiuoboric acid or sodium hydroxide as the case may be to secure a yellow brown color. Plating was carried out on a variety of aluminum alloys to produce a beautiful crystalline zinc plate. The plate was extremely adhesive. The solution was then adjusted gradually with amounts of corn syrup up to 10 cc. per liter and amounts of gelatin up to 2 grams per liter to produce plates of various degrees of leveling. The final solution yielded a perfectly smooth, uniform plate with no apparent crystalline'extensions beyond the plane of the plate.

I claim:

1. An aqueous composition suitable for the electroplating of zinc on a metal selected from the group consisting of aluminum, steel and magnesium, said composition comprising essentially in solution at least about 10 grams of zinc per liter and at least about 10 grams of titanium per liter, the principal negative ions of said solution being fiuoborate ions; said solution being maintained sufficiently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

2. The composition of claim 1 wherein said solution is maintained sufiiciently acidic by adjustment of its fiuoborate ion content.

3. An aqueous composition suitable for the electroplating of zinc on a metal selected from the group consisting of aluminum, steel and magnesium, said composition comprising essentially in solution at least about 10 grams of zinc per liter and at least about lO grams of titanium per liter, fiuoborate ions as the principal negative ions, and chloride ions in a concentration less than that of the fiuoborate ions; said solution being maintained sufiiciently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

4. An aqueous composition suitable for the electroplating of zinc on a metal selected from the group con: sisting of aluminum, steel and magnesium, said composition comprising essentially in solution titanium fiuoborate providing at least about 10 grams of titanium per liter and at least about 10 grams of zinc per liter derived from a member of the group consisting of zinc chloride and zinc fiuoborate; said solution being maintained sufficiently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

5. An aqueous composition suitable for the electroplating of zinc on a metal selected from the group consisting of aluminum, steel and magnesium, said composition comprising essentially in solution about 35 grams of zinc per liter and about 40 grams of titanium per liter, the principal negative, ionsof said solution being fluoborate ions; said solution being maintained sufiiciently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

6, An aqueous composition suitable for the electroplating of zinc on a metal selected from the group consisting ofaluminum, steel and magnesium, said composition consisting essentially in solution of at least about 10 grams of zinc per liter and at least about 10 grams of titanium per liter; saidv solution being maintained sufficiently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

7. An aqueous composition suitable for the electroplating of zinc on a metal selected from the group consisting of aluminum, steel and magnesium, said composition consisting essentially in solution of at least about grams of zinc per liter and at least about 10 grams of titanium per liter, the principal negative ions of said solution being fluoborate ions; said solution being maintained sufficiently acidic so that it manifests a yellow to yellow brown color as opposed to the emerald green color of solutions more acidic and the brown color of solutions less acidic.

8. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 1, the basis metal being the cathode therein.

9. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 2, the basis metal being the cathode therein.

10. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 3, the basis metal being the cathode therein.

11. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 4, the basis metal being the cathode therein.

12. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 5, the basis metal being the cathode therein.

13. The method of electroplating zinc on a basis metal selecting from the group consisting of aluminium, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 6, the basis metal being the cathode therein.

14. The method of electroplating zinc on a basis metal selected from the group consisting of aluminum, steel and magnesium; said method comprising passing an electrical current through an electroplating bath comprising the composition of claim 7, the basis metal being the cathode therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,646,397 Wean July 21, 1953

Claims

1. AN AQUEOUS COMPOSITION SUITABLE FOR THE ELECTROPLATING OF ZINC ON A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, STEEL AND MAGNESIUM, SAID COMPOSITION COMPRISING ESSENTIALLY IN SOLUTION AT LEAST ABOUT 10 GRAMS OF ZINC PER LITER AND AT LEAST ABOUT 10 GRAMS OF TITANIUM PER LITER, THE PRINCIPAL NEGATIVE IONS OF SAID SOLUTION BEING FLUOBORATE IONS; SAID SOLUTION BEING MAINTAINED SUFFICIENTLY ACIDIC SO THAT IT MANIFESTS A YELLOW TO YELLOW BROWN COLOR AS OPPOSED TO THE EMERALD GREEN COLOR OF SOLUTIONS MORE ACIDIC AND THE BROWN COLOR OF SOLUTIONS LESS ACIDIC.