Electroplating process

United States Patent Office _P, ...

Patented Aug. 26, 1958

2,849,352

ELECTROPLATING PROCESS

Alfred Kirstahler, Dusseldorf, and Wennemar Strauss and Wolf-Dieter WiUmund, Dusseldorf-Holthausen, Germany, assignors to Dehydag, Deutsche Hydrierwerke G. m. b. H., Dusseldorf, Germany, a corporation of Germany

No Drawing. Application October 25,1956 Serial No. 618,183

Claims priority, application Germany June 15,1956

Claims. (Cl. 204—44)

This invention relates to an electroplating process, and more particularly to a method of producing bright metal electrodeposits in electroplating baths which comprise heterocyclic compounds with two or more thioalkanesulfonic acid radicals attached to the cyclic nucleus as brightening additives.

We have found that bright, highly lustrous, non-porous and firmly adhering metal electrodeposits are produced by electroplating metal objects in aqueous acid solutions of an inorganic salt of the metal to be deposited, said solutions also comprising, as a brightening additive, a compound having the general formula

R(S—Rj—SO₃H)„ (I) wherein R is a straight-chain or cyclic organic radical comprising at least two carbon atoms linked exclusively to oxygen, sulfur and/or nitrogen atoms, each of said carbon atoms being linked to a —S—Rj—SO₃H group, R_t is a bivalent lower aliphatic radical, and n is an integer equal to the number of said carbon atoms in the radical R, or water-soluble salts of such compounds.

For example, triazine derivatives having the structural formula wherein Rj has the meaning above indicated, or their water-soluble salts, such as the alkali metal or ammonium salts, are suitable as brightening additives for electroplating baths in accordance with the present invention. The bivalent radical Rj may, for instance, be a methylene, ethylene, propylene, hydroxypropylene, chloropropylene or similar radical.

Such triazine compounds may, for example, be obtained by transforming tricyanogen chloride into trimercaptocyanuric acid, and thereafter reacting an alkali metal salt of the acid With an organic halogensulfonic acid, such as 2-bromoetharie-l-sulfonic acid, 3-bromopropane-l-sulfonic acid, 3-chloro - 2 - hydroxypropane-l-sulfonic acid or their alkali metal salts, or with a sultone, such as propanesultone or butanesulfone, to form the corresponding mercapto-alkanesulfonic acid triazine derivatives or their salts.

Other suitable compounds having the above general Formula I are those wherein the radical R is a 5- or 6membered heterocyclic radical with at least two nitrogen atoms. Compounds of this type are, for example, 1,3,4thiodiazole-2,5-bis(mercaptopropane-1 -sulfonic acid) ⁸ l,3,4-thiodiazole-2,5-bis(mercapto - 2 - hydroxypropane1-sulfonic acid)

Oh s OH

HOsS—CHj—CH—CH_:-S—¢/ ^C—S—CHj— 0h—CHi-SO_aH ----------ill

1,3,4-triazole - 2,5 - bis(mercaptopropane-l-siilfonic acid)

NH

HO₃S-(CH_J)₃-S-G^/ ^C—S—(CHaJa—SOgH or 1,3,4-oxdiazole - 2,5 - bis(mercaptopropane-l-sulfonic acid)

O

Ho₃s-(cia:_J)3-s-c^/ '^s‘c-s-(CH_l)_i-so_>H

<img file="US2849352A_D0001.tif" />

and the like, or their water-soluble salts, such as alkali metal and ammonium salts.

As previously pointed out, however, the radical R in Formula I need not necessarily be a cyclic radical. Thus, similarly suitable for use as brightening agents in electro25 plating baths in accordance with the present invention are acyclic compounds, such as dithiobiuret-S,S'-dipropanesulfonic acid

HN=C— NH— C=NH

HO₃S-(CH₂)3-S 8-(ΟΗ₂)3-8Ο₃Η or dibasic S-alkanesulfonic acids having the structural formula

HN=C—NH-Bj—NH-C=NH

HO3S-R1-S S-R1-SO3H wherein Rj has the meaning defined in Formula I and R₂ is an aliphatic or aromatic radical, and their watersoluble salts. The dibasic S-alkanesulfonic acids may be obtained, for example, by reacting methylene-, ethylene-, hexamethylene- or phenyleiie-dithiourea with propanesultone, butanesultone or halogen-alkanesulfonic acids or alkali metal salts thereof.

Finally, also tribasic and higher polybasic S-alkanesulfonic acids and their water-soluble salts, such as those obtained by reacting polyurca compounds with halogenalkanesulfonic acids or sultones in accordance with the above method, are effective as brightening agents according to the present invention.

₅θ The brighteners disclosed herein may advantageously be employed in conjunction with all types of electroplating baths, and especially with electroplating solutions for the production of copper, nickel, silver, zinc, cadmium, bronze and brass electrodeposits.

_g5 While the brightening additives in accordance with the present invention will produce bright and lustrous metal electrodeposits when used as the sole additives in electroplating baths, they may also be employed in combination with known brightening additives, smoothing agents, sequestering agents, inhibitors, anionic, cationic or electroneutral surface-active agents, salts which increase the conductivity of the bath and similar additives customarily used to improve the metal electrodeposits.

For example, suitable additional brighteners are those _β5 which are disclosed in copending application Serial No.

442,199, filed July 8, 1954. Examples of sequestering agents are compounds disclosed in copending applications Serial No. 458,984, filed September 28, 1954, and

Serial No. 544,586, filed November 2, 1955, and in Gerγθ man Patent No. 934,508; in other words, the term “sequestering agents” is intended to designate those additives which prevent the mineral salts in hard water and

HOiS-tCHiJr-S-/ ^C—S-(CHi)s-SO_sH 1 IL

2,849,352 impurities in the inorganic metal salt from interfering with the brightening effect of the brightening additive.

The quantity of the S-alkanesulfonic acid compounds added to electroplating baths according to the present invention may range from 0.01 to 20 gm. per liter of bath. The effective current density range of such electroplating baths lies between 0.5 and 12 amp./dm.², and the temperature of the solution may reach as high as 60° C. during the electroplating procedure. The current density range at which the optimum brightening effect is achieved will vary from one particular brightener to the other, but in general the range is of considerable breadth for the entire group of brighteners herein disclosed. The optimum current density range may, however, be broadened by employing a mixture of two or more members of the group. .

Particularly noteworthy is the fact that the addition of the S-alkanesulfonic acid compounds described herein to electroplating baths makes it possible to produce fullbright electroplates within an exceptionally broad range of temperatures, namely between 15 and 60° C. At temperatures higher than room temperature the optimum current density range is shifted toward considerably higher values (about 15 amp./dm.²). Moreover, because of the ability of our brightening agents to produce fullbright electrodeposits at relatively high bath temperatures, it is possible to use the brighteners in copper-plating baths which because of high rates of current flow develop a considerable amount of heat and therefore operate at temperatures up to 40° C. and even 50° C.

Electroplating baths modified in accordance with our invention may be employed to deposit metal electrodeposits on any desired customary base metal, such as iron, steel, zinc and similar non-precious metals or alloys thereof. In the case of copper-plating baths, the base metal may first be provided with a thin copper coating in a separate cyanide bath in customary fashion, or the base metal may be provided directly with the final copper plate without a preliminary thin copper base coat in accordance with the process disclosed in copending application Serial No. 458,983, filed September 28, 1954.

In all cases, electroplating baths modified in accordance with the present invention produce full-bright electrodeposits of extraordinary high quality which do not require subsequent buffing or polishing.

The following examples will further illustrate the present invention and enable others skilled in the art to understand it more completely. It will be understood, however, that the invention is not limited to these particular examples.

Example I

0.3 to 1.5 gm. per liter of the trisodium salt of 1,3,5triazine-2,4-6-tri-(mercaptopropane-l-sulfonic acid) having the structural formula

N

NaOaS-(CHa)a-S-F ^C-S—(CHjJa-SOaNa 14 A

S-(CHs)a- SOjNa were dissolved in an acid aqueous copper sulfate bath composed of water, 220 gm. per liter crystalline copper sulfate and 60 gm. per liter sulfuric acid. Sheet metal objects copper-plated in this electroplating solution at room temperature and at elevated temperatures up to 60° C. with a current density from 0.5 to 8 amp./dm.²were provided with a full-bright copper electrodeposit which did not require buffing or polishing.

Example II

The same full-bright copper electrodeposits were obtained when 0.2 to 1.5 gm. per liter of the trisodium salt of l,3,5-triazine-2,4,6-tri-(mercaptopropane-2- hydroxy-1sulfonic acid) having the structural formula

OH NOH

I 4 \I

NaOaS—CHa—CH—CHa—8—C C—S—CHa—CH—CHa—SOaNa

AN ^C'⁷ OH i·!—CHa—CH—CHa—SOaNa '° or the trisodium salt of l,3,5-triazine-2,4,6-tri-(mercaptoethane-l-sulfonic acid) having the structural formula

N , _c NaO_aSN(CHa)a-S—^C—S—(CHa)j-SOaNa ¹⁵ %⁷

S-(CHa)s—SOaNa were added to the acid copper sulfate solution described in Example I instead of the trisodium salt of 1,3,5-triazine-2,4,6-tri-(mercaptopropane -1 - sulfonic acid), and brass and iron objects were copper-plated therein under the conditions of temperature and current density de25 scribed in Example I.

Example III

0.5 to 1.0 gm. per liter of the disodium salt of 1,3,4thiodiazole-2,5-bis-(mercaptopropane - 1 - sulfonic acid) 30 having the structural formula

NaOaS-(CHa)a-S—C^/ Ά—8—(CHa)a-SOaNa

A-----^!r was added to an acid copper sulfate solution composed of water, 200 gm. per liter crystalline copper sulfate and 60 gm. per liter sulfuric acid. Brass and iron objects electroplated in this solution at current densities from 2 40 to 10 amp./dm.² and at temperatures between room temperature and 45° C. were provided with a full-bright, high-quality copper plate which required no buffing or polishing subsequent to rinsing.

Example IV

0.2 to 1.0 gm. per liter of the dipotassium salt of N,N'-methylene-di-(isothiourea-S - propane - 1 - sulfonic acid) having the structural formula

NH=C—NH—CHa—ΝΉ—C=NH 50 I I

KOaS—(CHj)a—S 8—(CH₂)a-SO₈K was added to the acid copper sulfate solution of Example ΠΙ instead of the disodium salt of l,3,4-thiodiazole-2,5bis-(mercaptopropane-l-sulfonic acid). Brass and iron ⁵⁵ objects electroplated in this modified copper sulfate bath at current densities from 1 to 11 amp./dm.² and at temperatures between room temperature and about 50° C. were provided with full-bright, high-quality copper plates which required no buffing or polishing.

Example V

1.2 gm. per liter of the trisodium salt of 1,3,5-triazine2,4,6-tri-(mercaptopropane-2-hydroxy - 1 - sulfonic acid) having the structural formula shown in Example Π and 65 0.8 to 1.2 gm. per liter l,3-bis-(dibutylamino)-propanol-2, described in said copending application Serial No. 458,984, were added to an acid copper sulfate solution composed of water, 220 gm. per liter crystalline copper sulfate and 60 gm. per liter sulfuric acid. Brass and iron objects 10 electroplated in this solution at temperatures from room temperature to 60° C. and at current densities from slightly above 0 amp./dm.² up to 15 amp./dm.² were provided with full-bright copper electrodeposits of exceptionally high quality which required no additional buffing 75 or polishing.

2,849,352 . . .

Example VI

From 1 to 5 gm. per liter of the ammonium salt of l,3,5-triazine-2,4,6-tri-(mercaptopropane - 2 - hydroxy-1sulfonic acid) having the structural formula /^{N 5}

EhNOjS-tCHjh-S-C^ '''C—S—(CHj)s—SOsNHj i!r Ji θ ' io

S— (CHfo-SOsNH, were added to an acid zinc sulfate solution composed of water, 200 gm. per liter crystalline zinc sulfate, 1 gm. per liter glacial acetic acid and 1 gm. per liter citric acid. Brass and iron objects electroplated in this solution at ¹⁵a current density between 3 and 12 amp./dm.² and at a temperature from room temperature to about 35° C. were provided with full-bright, high-quality zinc electroplates which required no additional buffing or polishing.

Example VII

From 0.5 to 1.5 gm. per liter of the disodium salt of 1,3,4 - thiodiazole-2,5-di-(mercaptopropane - 1 - sulfonic acid) having the structural formula s 25

NaOsS-(CHs)s—S-C^/ ^C-S-(CHs)s-SO_sNa A were dissolved in a zinc cyanide bath composed of water, 57 gm. per liter zinc cyanide, 72 gm. per liter sodium hy- ³⁰droxide and 40 gm. per liter sodium cyanide. Sheet steel electroplated in this solution at current densities from 1 to 10 amp./dm.² and at temperatures between room temperature and about 40° C. were provided with full-bright zinc electrodeposits of extremely high quality which re- ³⁵quired no additional buffing or polishing.

Example VIII

From 1 to 2 gm. per liter of the disodium salt of N,N'methylene-di-(isothiourea - S-propane - 1 - sulfonic acid) ⁴⁰having the structural formula

HN=C—NH—CHs—NH—C=NH

NaOsS- (CH₂)₃- έ l-(CHj)»-SOsNa were dissolved in a cadmium cyanide bath composed of ⁴⁵water, 125 gm. per liter cadmium sulfate, 140 gm. per liter sodium cyanide and 72 gm. per liter sodium hydroxide. Steel and iron objects electroplated in this solution at current densities from 3 to 8 amp./dm.² and at temperatures between room temperature and about 35° C. ⁵⁰were provided with full-bright cadmium electroplates of extremely high quality which required no further buffing or polishing.

Example IX

1.0 gm. per liter of the trisodium salt of 1,3,5-triazine2,4,6-tri-(mercaptopropane - 1 - sulfonic acid) having the structural formula shown in Example II, 0.05 gm. per liter Ν,Ν-diethyl-dithiocarbamic acid-ethylester-w-sodium sulfonate and 1.2 gm. per liter l,3-bis-(diethylamino)- ₆₀propanol-2, as well as 0.5 gm. per liter of the sodium salt of an acid sulfuric acid ester mixture of ethoxylated fatty alcohols with alkyl radicals having from 12 to 18 carbon atoms, were dissolved in an acid copper sulfate bath composed of water, 220 gm. per liter crystalline copper sul- ,.fate and 60 gm. per liter sulfuric acid. Iron objects elec- '^Jtropiated in this solution at 40° C. and at a current density between 5 and 12 amp./dm.² were provided with fullbright copper electroplates of extremely high quality, even when the iron objects had not previously been provided with a preliminary copper plate in a copper cyanide ¹solution.

Example X

The disodium salt of the l,3,4-thiazole-2,5-bis-mercapto-2'-oxypropane-l'-sulfonic acid was substituted for 75 the thiadiazole derivative in Example ΠΙ. A full-bright copper plate was obtained.

Example XI

The disodium salt of the l,3,4-triazole-2,5-bis-mercaptopropane-l'-sulfonic acid was used instead of the triazin derivatives according to Example Π. An excellent copper plate was obtained.

Example XII

The disodium salt of the l,3,4-oxdiazole-2,5-bis-mercaptopropane-l'-sulfonic acid was substituted for the triazine derivatives in Example II. A bright copper plate was formed.

Example XIII

The dipotassium salt of N,N'-methylene-di-(isothiourea-S-propane-l-sulfonic acid) according to Examples IV and VIII is substituted by an equal amount of the salts of the corresponding ethylene, hexamethylene or phenylene derivatives. Full-bright copper electroplates were obtained.

Example XIV

The disodium salt of the dithiobiuret-S,S'-dipropane sulfonic acid was substituted for the N,N'-methylene-di(isothiourea-S-propane-l-sulfonic acid) in Example VIII. A good bright copper plate was formed.

While we have disclosed various specific embodiments of our invention, it will be apparent to persons skilled in the art that the present invention is not limited to these specific embodiments and that various changes and modifications may be made without departing from the spirit of the invention or the scope of the appended claims.