US2813066A - Alkylpolyamine-modified cyanide copper plating bath - Google Patents

Description

Nov. 12, 1957 B. D. osTRow 2313,056

ALKYLPOLYAMINE MODIFIED CYANIDE COPPR PLATING BATH Filed Nov. 14, 1955 2 Sheets-Shee: l

Nov. 12, 1957 B. D. OSTROW 2,813,066

ALKYLPOLYAMINE MODIFIED .CYANIDE COPPER PLATING BATH Filed Nov. 14, 1955 2 Sheets-Sheet 2 INVENTOR( ai i/K? D. Offd United States Patents O" ALKYLPOLYAMINE-MODIFIED CYANIDE COPPER PLATING BATH ?Bamet D. Ostrow, North 'Bellmore, N. Y.

Application November 14, 1955, Serial No. 546,584

5 Clams. (c. 20442 i The present invention is directed to cyanide copper plating baths, more particularly 'to -an improvement whereby contaminations may be rendered harmless. The present application is a continuation in part of my co-pending application, Serial No. -349,935, filed April 20, 1953, entitled Electroplating Compostions for Copper, now Patent 2,'732,336; and application, Serial No. 47`9,87l, filed January 4, 1955, entitled Bath for Plating Bright Copper," now abandoned.

Cyanide copper electroplating baths are commonly used in the plating of Zinc die castings and 'of steel for the purpose of depositing a copper plate prior to plating the articles with nickel and chromium. The operation utilizes a. plating cycle wherein the same plating racks or fixtures for holding the work pass successively through the copper, nickel and chromium baths. This practice is economical in the sense that it is unnecessary to re-rack the articles between the successive plating baths, but there isthe serious disadvantage that there is a tendency to introduce a contamination by soluble salts of nickel or chromium into the copper bath. Particles'from zinc die castings often fall into the plating bath and tend to dissolve, thereby introducng soluble zinc salts as an impurity. In particular the high efficiency bright plating baths which are used extensively are particularly afiected by such soluble metallic impurities and the low efiiciency and Rochelle type baths are equally affected by chromium and zinc contaminants.

It has been proposed to remove soluble zinc mpurities by the use of sodum sulfide when the concentration of zinc reached 0.3 oz. per gallon. Such a use has an adverse eifect as it tends to lower the bright plating range of said bath by introducing the sulfide ion therein. In such a system when chromium having a valence of +6 enters the cyanide copper bath in concentrations of to parts per million, very harmful side eflects are produced, such as loss of efiiciency, decrease of covering power and in an extreme case, plating is totally interrupted. The harmful efiectof the chromium is accentuated in the presence of znc salts as impurity.

It has also been proposed to add to the cyanide copper baths sodium hydrosulfite, in order to reduce the chromium to the harmless trivalent form, which then precipitates out. While this is somewhat efiective in precipitating chromiun, it also introduced into the solution sulfide compounds, such as sodum sulfide, which adversely atfected the bright plating range. With zinc present, insoluble zinc sulfides may precipitate and cause roughness of the deposit. It also became necessary to make frequent additions of the hydrosulfite in quantities approximately equal to the concentration of the soluble c'hromium as an excess of hydrosulfite was harmful. y

The present invention s intended and adapted to overcome the difiiculties and disadvantages 'inherent in prior baths of the type described, it being among the objects 'of the present invention to provide a cyanide copper bath having small amounts of additives therein to increasethe tolerance thereof for metallic impurities and particularly in high efficiency 'bright plating baths.

2,813,066 Patented Nov. 12, 1957 It is also among the objects 'of the present invention to provide a bath composition wherein such contaminants' as zinc, chromium and nickel may be permitted to accumulate to a very substantal degree without detriment to the plating operation.

It is further among the objec-ts of the present invention to introduce into a cyanide copper bath of the usual -yPs, small amounts of additives withoutimpairng the eiciency of the bath and at the same time maintaining the bright plating range thereof. i

In practicing the present invention, it has been found that the polyamines in small amounts are very effective in increasing the tolerance of cyanide copper baths to Zinc, chromium and nickel and other metals forming soluble complexes. The polyamines have from 2 to 6 amino groups and each of the alkyl groupshas from l to 3 carbon atoms. While the polyamines as such are preferred, it is also possible -to react the polyamines to form condensation products which are also suitable for the purpose.

Baths of this character have excellent tolerance for the above mentioned soluble metallic contaminants. While they are particularly adapted to high efficiency baths, the beneficial efiects of such additives are found in practically any cyanide copper bath.

`In the accompanying `drawing constituting a part here ofand in which like symbols indicate like deposit areas,

Fgs. I-A to I-G represent diagrammatically the results obtained in a series of experiments for depositing copper' in a standard 267 ml. Hull cell utilizing a standard cyanide copper 'plating bath;

Figs. II-A to II-C are similar diagrammatical views showing the results obtained iutilizing a second standard cyanide copper bath; and

Figs. III-A to III-C are views similar to Fig. I, showing the results obtained using still a third standard cyanide copper bath.

In the drawings, the clear areas represent bright plating on copper strips, and the areas having a single central horizontal line represent semi-bright areas. The crosshatched areas indicate matte deposits and the dotubly cross-hatched areas represent burned deposits. Those areas having a series of horizontal broken'lines are areas where no deposit occurred and the areas containing a series of crcles indicate deposits which are discolored, being dull and black to grey. Those areas having a series of horizontal wavy lines indicate deposits that are uneven and swirled. i

Bath No. ,I

A standard bath such as has been nsedin the prior art was utlized in a series of comparative experiments, the bath having the followingcomposition:

Oz./gal. Copper cyanide '8.0 Potassium cyanide 12.7

Potassium hydroxide 5.6 Sodium thiocyanate 2.0 Cetyl-betaine .04

This bath was operated in a No. 267 ,Hull cell at F. with agitation at 2 amperes for five minutes. As shown in Fig. I-A,'it`.produces a -good, bright deposit at current densties from 10 to 40 amperes per square foot.

To this bath there was `addedpotassium chromate in which the chromium has a valence of +6. The amount added .was 20 parts per million or .02 grams per lter. The bath was operated as above stated, the results being shown in Fig. "I- B. There was .a total elimination .of the 'bright areas andthere was poor coverage, particularlyin the low current density .areas.

To this bathicontaining the :potassium chromate, there was added .25 `oz. per gallon *of tetraethylene pentamire and the bath was :operated ,as before. As will be seen from Fig. I-C, the original characteristics of the bath were restored so that the adverse elfect of the chromium was completely eliminated.

To the aforesaid standard Cyanide copper bath, there was added 75 parts per million ofchromium in the form of potassium chromate. In Fig. I-D, there is shown the results of operation with this bath, the deposits being striated and non-uniform in the high current density areas. There was no deposit in the low current density areas.

To this bath containing the chromium having a valence of +6, there was added .4 oz. per gallon of triethylene tetramine. The bath was operated as before, the results being shown in Fig. I-E. The initial etfectiveness of the original bath has been completely restored. V To the aforesaid standard bath, there was added .5 oz. per gallon of zine in the form of Zinc Cyanide. Upon operation of the bath, the bright areas were destroyed as shown in Fig. I-F and the deposits were brass to bronze color. To this Zinc containing bath, there was added 1.0 oz. per gallon of diethylene triamine. Upon the operation of the bath as before, the brightness of deposit has been restored, as shown in Fig. I-G.

Bath No. II

Another standard bath well-known in the art is as follows:

In Fig. II-A is shown the results of a run with this bath at a temperature of l60 F. with agitation for a period of 5 minutes. It indicates a semi-bright deposit up to 50 amperes per square foot. To this bath, there was added 100 parts per million of chromium in the form of potassium chromate. The results of operation of the bath are shown in Fig. II-B. Little or no copper tended to deposit below 20 amperes per square foot and the deposits were discolored, being black to grey. At the higher current densities, the deposits were non-uniform.

To the bath containing the chromium, there was added 1.5 oz. per gallon of triethylene tetramine. Upon the operation of the bath, the harmful efiects of the chromium as shown in Fig. II-B were completely nullified. The bath now operated approximately as it had Originally before the chromium was added.

Bath N 0. III

Still another bath commonly used in the art has the following composition:

This bath was operated in a Hull cell for five minutes ata temperature of 140 F. As shown in Fig. III-A, the deposit was smooth, had a matte surface up to 30 amperes per square foot and was burned above this range. Then there was added to the bath, 50 parts per million of chromium in the form of Sodium chromate. The results of operation of the modified bath is shown in Fig. III-B. Little or no copper was deposited below l0 amperes per square foot and this had a grey to black tone. At high current densities, the deposit 'was nonuniform.

To the bath containing the chromium there was added 1.25 oz. per gallon of triethylene tetramine vinyl acetate reaction product. As seen in Fig. III-C, the initial efi'ectiveness of the bath was restored thereby. i

Not only the amines themselves but certain reaction products thereof with unsaturated esters, such as vinyl acetate; aldehydes, such as aldol; and acylketones, such as acetonylacetone are effective. Such compounds have from 4 to 10 carbon atoms. In order to prepare such compounds, a mixture is made of a polyamine, vinyl acetate and water, the polyamine being tetraethylene pentamine and the proportions being 10 to 15 to 75 by Volume. The reaction is exothermic and the miXture is agitated and warmed in order to cause the reaction to take place. At the end of the reaction, the mixture is heated to boiling for a few minutes. Similarly the reaction products of the other polyamines with the aforesaid compounds may be caused to take place.

In another aspect of the invention, the contamination of a bath with chromium may be reduced by precipitating the chromium compound even in baths containing tartrates or similar radcals. As an example, a polyamine or its reaction product as set 'forth above is added to the bath. It is then treated with a small amount of an alkaline earth such as calcium or magnesium hydroxides or calcium oxide. This results in a precipitation of the chromium compound having a valence of +6.

In Operating this phase of the invention, the Bath No.- II, which is contaminated With parts per million of chromium having a valence of +6, is held at a temperature of to F. for about one hour in the presence of 1-2 oz. per gallon of lime. The precipitated material is allowed to settle and is filtered off. About 80% of the chromium present is thus removed. An examination of the filtered precipitate under a spectregraph shows that the chromium has been adsorbed on the alkaline earth by this treatment.

The concentration of the polyamine or its reaction product may vary from .Ol to 50 grams per liter. The lower limit used depends upon the concentration of the metallic impurities which are to be nullified. A large excess of the polyamine or its reaction product has no undesirable eflect on the piating characteristics of the bath. By this invention, impurities up to 200 to 250 parts per million may be tolerated, whereas 5 or 10 parts per million of such impurities in the standard baths made such baths practically unworkable for plating bright copper.

The polyamines and their reaction products are capabe of forming compiexes with various bath impurities other than zine, chromium and nickel, thus scquestering them. Still higher nolecular weight polyamines up to a molecular weight of about 2000 are capable of use in accordance With the invention with good results.

What is claimed is:

l. A method of treating Cyanide Copper plating baths having therein free alkali metal hydroxide and containing soluble contaminants taken from the class consisting of Zinc, chromium and nickel which comprises adding to said bath an unsubstituted alkylpolyamine in sufcient amount to sequester said contaminants, said amine having 2 to 6 amino groups and the alkyl groups each having 1 to 3 carbon atoms.

J 2. A method of treating cyanide Copper plating baths having therein free alkali metal hydroxide and containing soluble contaminants taken from the class consisting of Zinc, chromium and nickel which comprises adding to said bath an unsubstituted alkylpolyamine in suicient amount to sequester said contaminants, said amine having 2 to 6 amine groups and the alkyl groups each having 1 to 3' carbon atoms, the concentration of said polyamine being from .01 to 50 grams per liter.

3. A method of treating cyanide Copper plating baths having therein free alkali metal hydroxide and containing soluble contaminants taken from the class consistng of Zinc, chromium and nickel which comprises adding to said bath an amine selected from the group consisting of unsubstituted alkylpolyamines and alkylpolyamine compounds in sufiicient amount to sequester said contaminants, said amine having 2 to 6 amine groups and the alkyl groups each having l to 3 carbon atoms, said.

compound' being a reaction product of said a1ky1polyamne with a compound taken from the class consisting of unsaturated esters, unsaturated aldehydes and unsaturated acylketones having 4 to 10 carbon atoms.

4. A method of treating Cyanide Copper plating baths having theren free alkali metal hydroxide and containing soluble contaminants taken from the class consisting of Zinc, chromium and nickel which comprises adding to said bath an unsubsttuted alkylpolyamine having 2 to 6 amino groups in sufficient amount to sequester said contamrants, said amine having a moiecular Weight up to about 2000, and the alkyl groups thereof having 1 to 3 carbon atoms.

5. A method of treatng Cyanide copper baths having therein free alkali metal hydroxide and containing soluble contaminants capable of forming complexes with polyamines which comprises adding to said bath an unsubstituted alkylpolyarnine having 2 to 6 amino groups in suflicient amount to sequester said contaminants, said amne having a molecular weight up to about 2000, and the alkyl groups having 1 to 3 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,195,454 Greenspan Apr. 2, 1940 2,434,191 Benner et al. Jan. 6, 1948 2,582,233 Chester et al. Jan. 15, 1952 2,660,554 Ostrow Nov. 24, 1953 2,662,853 Ellis Dec. 15, 1953 FOREIGN PATENTS 694,893 Great Britain July 29, 1953 OTHER REFERENCES Versenes: Bersworth Chem. Co., Framingham, Mass., pp. 46-8, sec. II February 1952.

Gilbertson et al.: Transactions of Electrochem. Soc., vol. 79, pp. 439-442, 1941.

Claims (1)

1. A METHOD OF TREATING CYANIDE COPPER PLATING BATHS HAVING THERIN FREE ALKALI METAL HYDROXIDE AND CONTAINING SOLUBLE CONTAMINATS TAKEN FROM THE CLASS CONSISTING OF ZINC, CHROMIUN AND NICKEL WHICH COMPRISES ADDING TO SAID BATH AN UNSUBSTITUTED ALKYLPOLYAMINE IN SUFFICIENT AMOUNT TO SEQUESTER SAID CONTAMINANTS, SAID AMINE HAVING 2 TO 6 AMINO GROUPS AND THE ALKYL GROUPS EACH HAVING 1 TO 3 CARBON ATOMS.

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