US2424887A - Method and electrolyte for the electrodeposition of metals - Google Patents

Description

. Patented July 29,1947

METHOD AND ELECTROLYTE FOR THE ELECTRODEPOSITION OF METALS John A. Henricks, Ann Arbor, Mich, assignor to Houdaille-Hershey Corporation, Detroit, Mich.,

a corporation oi. Michigan No Drawing. Application October 11, 1941, Serial No. 414,610

6 Claims.

This invention relates to a method of electrodepositing metals such as copper in the form of bright and ductile coatings. More particularly, the invention pertains to methods of plating copper and other metals from baths containing novel organic brightening agents disclosed hereinbelow and described as used in connection with sulfate copper baths, although, of course, the utility of these novel brightening agents is not limited to this specific type of bath.

Various organic addition agents have heretofore been used to improve the deposits from the conventional acid copper sulfate plating bath. Some of the most frequently mentioned addition agents include glue or casein, molasses or other sugars, urea, lignin derivatives from spent sulfite pulp cooking liquors, and phenol sulfonic acids. With the exception of glue, however, none of these addition agents gives a truly bright deposit, although they all render the deposit more finely grained and, in most cases, reduce the tendency of the deposit to burn at points of high current density. While baths containing glue and casein yield bright deposits, these deposits are brittle. Other disadvantages inherent in the addition of proteins of this order are their tendency to be hydrolyzed by the low pH of the bath, as well as their tendency to produce streaked or striated deposits.

I have now discovered a new class of addition agents that produce bright and ductile copper deposits from the acid bath and that have none of the defects of the prior art addition agents referred to hereinabove. These novel addition agents are sulfurized aromatic and hydroaromatic hydrocarbons, and substitution products or derivatives thereof that have been rendered more or less water soluble or water dispersible by sulfonation. The substitution products of the hydrocarbons include specifically alkyl benzenes, phenols and aromatic amines.

The sulfurized products that may be used in accordance with my invention are not limited to those obtained by the use of sulfur chloride, sulfuryl chloride or thionyl chloride as the sulfurizing agents, but include those obtained by the use of the conventional sulfur melt, technique in which a hydrocarbon or a derivative thereof is melted with elemental sulfur, an alkali metal sulfide, or mixtures thereof.

Instead of preparing the sulfurized products specially for use in my process, I may start with commercially available thio-aromatic compounds, such as thianthrene, diphenyl sulfide, diphenyl disulfide, thiophenol, and the like.

The sulfurized product however produced is sulionated, as by means of fuming sulfuric acid, to form water soluble or water dispersible compounds that are operative, according to the present invention, as brightening agents. Sulfona tion may also precede sulfurization. However, mere sulfonation, without suliurization, is not suflicient. Phenol sulfonic acid, for instance, can be polymerized with iormaldehyde'instead of sulfur chloride to give a sulionated colloid containing aromatic rings. but such a compound when used as an addition agent gives only grain refinement without imparting a mirror luster to the metal plate.

It is therefore an important object of the present invention to provide a process for the electrodeposition of metals that employs novel and improved organic brightening agentsin the metal plating bath.

It is a further important object of this invention to provide an acid copper sulfate electroplating bath from which bright andductile copper deposits can be obtained.

A specific object of this invention is to provide an acid copper plating bath containing novel organic brightening agents, obtained by the sulfurizing and sulfonating of aromatic and hydroaromatic compounds. through the use of which electrodeposits oi copper in a bright. and ductile form can be obtained,

Other and further objects will become apparent from the following detailed description and appended claims.

Suitabie aromatic and hydroaro'matic hydrocarbons which may be utilized forthe preparation of the brightening agents employed in the metal plating baths of my invention are, for example, benzene, toluene, xylene, naphthalene, alkyl .naphthalenes, anthracene, phenanthrene, diphenyl, and hydrogenated derivatives of the same. It is possible also to use polar substitution products of these hydrocarbons, suchas amines, phenols, nitro-compounds, and sulfonic acids.

These hydrocarbons or their substitution products may be sulfurized in various ways. By sulfurization I mean to imply the reaction of arcmatic or hydroaromatic hydrocarbons, or their substitution products, with metal sulfides or polysulfides; sulfur, sulfur halides, or oxygenated sulfur halides such as sulfuryl chloride and thionyl chloride, said reaction leading to the formation of sulfurized organic compounds. Catalysts such as aluminum chloride maybe used to promote.

the sulfurization reaction. The suliurizing step 3 may, if desired, be accomplished by known sulfur melt technique, according to which the organic compound is melted with elemental sulfur, a sulfide, or a mixture of the two.

In solubilizing the sulfurized hydrocarbons the burned deposit on areas of the cathode exposed usual types of sulfonating agents such as sulfuric 1 acid, fuming sulfuric acid, and chloro-sulfonic acid may beused. The extent of sulfonation may be varied over wide limits as desired. sulfona tion may precede or follow sulfurization, or the two steps may be carried out simultaneously. An object of the sulfonation step is to render the ma.- terials soluble or colloidally dispersible in water to an extent sufficient to give the concentrations required for maximum brightening effect.

The chemical nature of the sulfurized and sulfonated brightening agents according to this invention is obscure, and varies, moreover, with the concentration and nature of the sulfurizing agent used in the preparation of the brightening agents, as well as with the conditions of reaction. The predominating reaction in the sulfurizing step appears to be a coupling of a number of aromatic rings through sulfur linkages to form a polymer of high molecular weight. When sulfur chlorides are used, oxidation and even chlorination may also take place. The reaction that is believed to be most significant for the purpose of the present invention is that leading to the production of a high molecular weight material through the coupling up of two or more aromatic rings through a sulfur linkage, or possibly an o ygen or SO linkage. The sulfonation of the high molecular weight material renders the same dispersible in the aqueous plating bath. The sulfurized and sulfonated final products to be used as brightening agents exhibit colloidal behavior. I believe that the brightening effect obtained by the novel addition agents of this invention is in some way due to their colloidal nature. 1

CuSO4.-H20 0.25 to 1.7 normal (or up to saturation) H2S04 0.01 to 5 normal Brightening agents.. 0.1 to grams per liter Temperature Room to 120 F. Current density to 300 amperes per -While it is desirable to control the acidity of the bath, nevertheless a bright deposit may be secured over the full range of acidity given above. The optimum concentration of brightening agents of this invention varies with the acid concentration, and in general as the acid concentration is increased, the quantity of brightener required will likewise be increased. A change in acidity from 0.2 normal sulfuric acid to 2.0 normal sulfuric acid may require doubling the concentration of brightener in order to maintain a given luster. The preferred acidity is 1.4 to 1.7 normal. with this acidity the bath has a higher electrical conductivity, and a lesser tendency to produce a 7 A pure compound may'not be obtained by the I sulfurizing steps referred to hereinabove, for the reactions between an aromatic or hydroaromatic to high current density than in baths of low acid concentration. Higher concentrations of acid are not in themselves objectionable but reduce the solubility of copper sulfate in the bath and therefore require the use of lower concentrations of copper sulfate than I prefer to employ.. Prefer- Y ably, a concentration of copper sulfate equivalent to about 1.5 N is used.

The optimum average cathode current density is from 30 to 150 amperes per square foot, with agitation, although this range is not critical for the obtaining of bright deposits. It will be understood that with the usual cathodes, the actual current densities on certain areas may vary considerably from the optimum average.

In the following tables, Tabl I shows the upper and lower limiting current densities for obtaining bright copper plate over a range of acid concentrations but at a, single concentration (1.5 normoi) of copper. Table II shows the upper and lower limiting current densities for obtaining bright copper plate over a range of copper concentrations but at a single concentration (1.7 normall or acid.

Table I [Copper 1.5 normal; temperature 95 F.; air and mechani cal agitation concentration of brightener, 2.5 g./l.]

Law Linit High Limit urren urrent Acidity Density, Density,

ampsJsq. it. ampsJsq. it.

Table II (Acidity, 1.7 normal; temperature F.; air and mechanical agitation; concentration of brightener, 3 g./l.]

- Lrw Limtit, High Linizit,

urren urren Copper Concentration Density, Density,

, ampalsq. it. amps/sq. it.

Temperatures elevated above 120 F. dull the luster of the deposit. A temperature range of between 90 F. and F. is preferred, but the plating bath may be operated at ordinary room temperatures.

The copper plate produced by the method of hay invention has a mirror-like luster and is ductile and adherent to the usual base metals or sub-coatings over which acid copper may be adherently plated. The scratch hardness of the bright copper plate, on the average, is of the order of 300 to 350 on a Bierbaum scratch hardnesstester. It should therefore be no more subject to scratching on handling than ordinary gray nickel, which has an average scratch hardnessof around 240. The grain size of the bright copper plate produced by my process is, in general, a micron or less, but that ofv the copper initially deposited may be considerably greater, say up to 20 microns, depending upon the nature of the surface on which deposition occurs.

The preparation and use of a number of brightening agents according to the present invention are described hereinbelow as illustrative examples of the working of this invention.

Example I The following materials were used in the preparation of the brightening agent of this example: Toluene (reagent grade) c. c 67.5 Aluminum chloride (anhydrous) g 30 Sulfur chloride (practical) c. c 3 Fuming sulfuric acid (15% C03) (C. P.) c. c 225 The anhydrous aluminum chloride was weighed into a 200 c. c. 3-neck flask and the toluene then added. The flask was fitted with a mechanical stirrer and thermometer and was cooled in a water bath. The sulfur chloride was added dropwise during about five minutes, keeping the temperature between and C. Stirring was continuous at this temperature for ten minutes after all of the sulfur chloride had been added. The amber-colored liquid was decanted from unreacted aluminum chloride and sulfonated as described in the following paragraph.

Sulfonation was carried out in a 1000 c. c. 3- neck flask fitted with a mechanical stirrer, a thermometer and a dropping funnel. The fuming sulfuric acid was heated to 105 C. by means of an oil bath, and to the heated fuming sulfuric acid was added the above reaction product, the addition being made dropwise and the mass being stirred over a period of one hour. During the addition, the temperature was held very carefully at 105 to 108 C. by controlling the rate of addition of the reaction product and also the temperature of the oil bath. The oil bath was maintained at about 95 C. during most of the reaction but somewhat higher near the end. After the addition was complete, the temperature was allowed to fall. The product obtained was a dark, thick, strongly acid liquid, which was not completely soluble in water.

Stock solutions for baths were prepared as follows: (1) technical copper sulfate crystals were dissolved in water to a concentration of 210 g./l. (2) 10 grams of the toluene- S2Cl2-H2SO4 reaction product were added with stirring to about 90 c. c. of distilled water and heated to boiling, This mixture was allowed to cool, then filtered through filter paper and the volume adjusted to 100 c. c. The solution at this point was dark orange and free from turbidity.

10 c. c. of the stock solution (2) were added to 900 c. c. of the copper sulfate solution (1) and 42 c. c. of concentrated C. P. sulfuric acid were then added, resulting in a bath approximately 1.7 N in copper sulfate, 1.5 N in sulfuric acid and containing one gram of the brightener in 950 c. c. of the solution.

Specimens for plating were prepared in a Hull cell and these specimens were plated for 15 minutes at 100 F. with a current of 5 amperes. In this type of cell, the cathode strip is at an angle to the anode, with the result that the cathode current density varies throughout the length of the cathode. In general, the copper plate de- 6 posited on the cathode was mirror-like throughout the portion of the cathode where the current density was between 40 and 130 amps/sq. ft., being particularly bright in the area where the current density was between '75 and 80 amps/sq.

ft. The cathode strip was a strip of steel that had been degreased and given a copper cyanide strike plate before being immersed in the acid copper bath,

Example II 22 cc. of commercial benzene were added dropwise to 50 cc. of 30% fuming sulfuric acid containing 0.4 cc. of sulfur monochloride, the temperature being kept below 212 F. A dark brown liquid reaction product was formed that when used as a brightening agent in the manner indicated hereinabove gave a brilliant and ductile, mirror-like copper deposit.

Example III 22 cc. of commercial benzene were sulfonated with 50 cc. of 30% fuming sulfuric acid. 6 grams of precipitated sulfur were added to themixture, which then was heated to 320-338 F. for one hour. A brown-black, water soluble liquid was produced that gave a lustrous deposit not quite equal to that of Examples I and II.

Example IV 15 grams of phenol were sulfonated in 20 cc. of 30% fuming sulfuric acid, and 0.5 cc. of sulfur monochloride were added dropwise with stirring. The pink sulfonic acid turned a dark green color during the reaction with sulfur monochloride. This product gave a lustrous deposit about equal to that of Example 111..

Example V 50 grams of naphthalene and 15 grams of precipitated sulfur were mixed with 125 cc. of 66 B. sulfuric acid and the mixture was heated for approximately one hour at 347 F. with stirring, until a homogeneous darkbrown, water soluble product was obtained. This product gave a lustrous deposit slightly inferior to that of Example IV.

Example VI 10 grams of aniline were added dropwise and with stirring to 20 cc. of 15% fuming sulfuric acid. 1 cc. of sulfur monochloride was added to the aniline-acid mixture, and the whole was stirred until the oily droplets of sulfur monochloride were taken up and a dark mauve product was obtained. This product effected a luster equivalent to that of Example V.

Example VII 5 grams of Kryogen Brown R, a sulfur vat dye made by a sulfur melt of nitro-naphthalene and an alkali metal polysulfide, were sulfonated with 15% fuming sulfuric acid at room temperature. The resultant product gave a fine-grained deposit having a relatively low luster.

Example VIII the copper plate but no luster. of reaction products may both 2.5 g./l. oi the reaction product of Example I in a copper plating bath 0.25 N in H2804 and 1.7 N in CuSO4 at a current density below 140 amps/sq. ft. and a temperature of 90 to 100 F.

Example IX l minute of time, was added 1 cc. of sulfur chlorlde (S2012) with constant stirring. The temperature remained at 25 C. while the mixture turned dark. The mixture in the beaker was then heated to 70 C. and, while stirring, 35 cc. of 20 to 30% fuming sulfuric acid were run into the beaker during a six minute period. The external heat was turned off, the addition of the 35 cc. of fuming sulfuric acid in 6 minutes keeping the temperature at '70 to 75 C. The reaction wasconsidere'd complete after the addition of the sulfuric acid.

About 1 g./l. of the resulting reaction product' were added to the standard acid copper sulfate bath and plating carried out, using both mechanical and air agitation, a temperature of 95 F. and a current density of 75 amps/sq. ft. Lustrous copper plate was obtained using the brightener of thi example.

Example X Two different types of brightener were made up as follows:

(1) 7 cc. of commercial benzene and 2% cc. of sulfur chloride (S2Cl2) were mixed in a beaker, without adding any aluminum chloride, and the mixture added dropwise and with caution to 50 cc. of 20 to 30% fuming sulfuric acid, while stirring the sulfuric acid and permitting the temperature to rise to 90 C. The resulting product was completely dispersible both in water and in an acid sulfate bath, but by itself would not give a lustrous plate, but only grain refinement of the copper plated from the bath. 1

(2) 25 cc. of dried toluene and 10 grams of aluminum chloride were mixed together. '7 cc.

of thionyl chloride were then added dropwise and with caution to the mixture of toluene and aluminum chloride. The reaction mixture was then refluxed until no further liberation of sulfur dioxide occurred.

The addition of the thionyl chloride reaction product by itself to an acid copper sulfate bath produced a bright copper plate, but the plate had a striated or nail file appearance. When, however, the sulfur chloride reaction product of (1) was added to the bath containing the thionyl chloride reaction product, auniform, mirrorbright copper plate was produced. This result indicates that there may be two different types ofreaction products: one" that is obtained by the use of thionyl chloride and that may have a sulfonium base constitution, which gives a bright but striated deposit; and secondly, a reaction product obtained by the use of sulfur chloride that gives a refinement in the grain structureof These two types be formed in the processes of Examples 1,. II, IV, VII and IX, due to the possible formation of thionyl chloride by reaction of the excess of sulfur chloride with fuming sulfuric acid in the processes of these examples. In any event, if a lustrous copper plate is not obtained by the use of a sulfur chloride reaction product, the addition of a suflicient amount of a thionyl chloride reaction product will eflect a high degree of luster in the deposit.

Conversely, if by the use of a thionyl chloride reaction product a striated, or nail file, type of deposit is obtained, the addition of a sumcient quantity of a, sulfur chloride reaction product will result in the disappearance of the nail file appearance and give a uniform, mirror-bright deposit.

The apparent superiority of the brightening agents derived from non-polar aromatic hydrocarbons, as compared to those derived from compounds containing hydroxyl, amino or nitro groups may be due to the fact that the sulfurizing and sulfonating, of non-polar hydrocarbons are less violent and more amenable to control than the reactions involving polar hydrocarbons. This invention, however, is not limited to the brightening agents derived from non-polar hydrocarbons.

Wetting agents of the alkylated naphthalene sulfonic acid and ofthe ester types may, under some conditions, be advantageously incorporated in the acid copper sulfate baths described herein.

Although only aromatic compounds have been specifically referred to in the examples, the corresponding hydroaromatic compounds may be substituted with substantially similar results.

Many other embodiments of the principles of this invention besides those disclosed hereinabove are possible, for the composition and conditions of employment of the brightening agents Of. this invention are not limited to the illustrative examples and preferred ranges indicated hereinabove. It is therefore not my intention to limit the scope of the patent granted on this invention otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. A method of electrodepositing copper, which comprises electrodepositing copper from an aqueous solution of copper sulfate and sulfuric acid, there being added to such solution as a brightening agent a colloidal sulfonated reaction product of benzene and a sulfurizing agent.

2. A method of electrodepositing bright and ductile copper, which comprises electrodepositing copper from an aqueous sulfuric acid solution of copper sulfate, there being added to such solution from 0.1 to 15 g./l. of a water dispersible brightening agent selected from the group consisting of sulfurized sulfonated hydrocarbons containing a six carbon ring and their substitution products in which the ring is nuclearly substituted with an alkyl group.

3. A method of electrodepositing bright copper, which comprises electrodepositing copper from an aqueous solution of copper sulfate and sulfuric acid, there being added to such solution a sulfurized sulfonated benzene substitution product nuclearly substituted with an alkyl group and capable of producing a bright deposit, said product being added in a suificient concentration to produce a bright deposit.

4. A copper electroplating bath consisting essentially of an aqueous solution of copper sulfate, sulfuric acid and an efiective amount of a brightening agent selected from the group consisting of sulfurized sulfonated hydrocarbons containing a six carbon ring and their substitution products in which the ring is nuclearly substituted with an alkyl group.

5. A copper electroplating bath consisting essentially of an aqueous solution of copper sui- Iate within the range of from 0.25 N up to saturation, sulfuric acid within the range of 0.01 to 5 N and from 0.1 to 15 g./l. of a water dispersible brightening agent selected from the group consisting of sulfurized sulfonated hydrocarbons containing a six carbon ring and their substitution products in which the ring is nuclearly substituted with an alkyl group.

6. A bath for use in the electrodeposition of a lustrous, ductile copper plate, consisting essentially of an aqueous acid solution of copper sulfate within the range of from 0.25 N up to saturation, sulfuric acid within the range 0.01 to 5 N and from 0.1 to-15 g./l. of a water dispersible brightening agent consisting of a sulfurized sul- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,080,520 Westbrook May 18, 1937 2,090,966 Sailer Aug. 24, 1937 Hendricks Dec. '7, 1937 OTHER REFERENCES Transactions of the American Electrochemical Society, vol. 6'7, page 338 (1935).

Modern Electroplating, Special Volume of the fonated benzene substitution product nuclearly 15 American Electrochemical Society page 12 substituted with an alkyl group.

JOHN A. I-HJNRICKS.

Principles of Electroplating, by Blum and Hogaboom, pages 205-207 (1930).