US 3234031 A
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*tnt dds mam Patented Feb. 8, 1966 REDUCTION NICKEL PLATING WITH BORON RE. DUCING AGENTS AND ORGANIC DIVALENT SULFUR STABILIZERS Eberhard Zirngiebl, Colognc-Flittard, and Heinz Giinter Klein, Cologne-Deutz, Germany, assignors to Farbenfnbriken Bayer Aktiengesellschaft, Leverkuscn, Germany, a corporation of Germany l lo Drawing. Filed Jan. 22, 1962, Ser. No. 167,959 Claims priority, application Germany, Feb. 4, 1961,
8 Claims. in. 1061) The present invention is directed to an improved process of chemical metal plating of metal and plastic articles employing an aqueous bath containing salts of the metals to be deposited and boron compounds as reducing agents.
Chemical plating baths for the production of metal coatings on metal or plastic surfaces are known. As coating metals there are chiefly used nickel and/ or cobalt, but iron or zinc can also be deposited together with nickel and/ or cobalt. Known reducing agnets are, besides alkali metal hypophosphites chiefly boron compounds with 1-4 hydrogen atoms directly linked with boron, for example, alkali metal borohydrides or alkylamine boranes. In order to increase the plating rate and the reduction yield, salts or other compounds of metals of Groups IIb, IIIb, 1Vb, Vb, and/or VIb of the Periodic System of Elements may be added to these baths.
However, it has been found that these baths tend to separate out metal flakes or to decompose with the formation of a black precipitate as soon as the concentration of the baths in plating metal has dropped by about 10 to in the course of plating. In some cases these baths can be further used after filtration, but in most cases the plating stops after a short time and the baths must be discarded or worked up. For example, a bath of the composition: g./liter of nickel chloride, g./liter of sodium hydroxide, g./liter of ethylenediamine, 0.6 g./liter of sodium borohydride, decomposes after 19.3% of the nickel employed have been used up from the bath by plating. Even after filtration of this bath, no further plating takes place.
It is an object of this invention to provide an improved process for chemical meta] plating of metal and plastic surfaces and an improved bath for use in the chemical metal plating of plastic and metal articles containing a salt of the metal to deposit and a boron compound with 1-4 hydrogen atoms directly linked with the boron.
It is also an object of this invention to provide an improved bath containing metal salts as additive, said metals being from the Groups IIb, IIIb, IVb, Vb, and VIb of the Periodic System of Elements.
It has been discovered that the adding of a small effective amount of an organic bivalent sulfur compound, which is soluble in the bath liquid and wherein each of the two valencies of the sulfur atom are directly linked with a carbon atom produces a particularly good stabilizing effect.
Acidic baths moreover may contain buffer substances known as such, alkaline baths may contain complex formers known as such and, if desired, buffer substances. In order to increase the reduction yield and/or plating rate, these baths may furthermore contain additives of chemically linked metals of Groups Ilb, IIIb, IVb, Vb, and VIb of the Periodic System of Elements.
The presence of organic sulfur compounds with forally bivalent sulfur in a plating bath containing as reducing agent borohydride compounds with 1 to 4 hydrogen atoms directly linked with boron and in addition thereto metal salts as additives, said metals being from the Groups IIb, Illb, IVb, Vb, and VIb of the Periodic System of Elements has been found to exert such a stabilizing effect on the bath that the process of chemical metal plating may be executed continuously. For example, a nickel bath with an optimum concentration in nickel salt (NiCl .6H O) and alkali metal borohydride (NaBH decomposes as soon as about 25 of the initial nickel content have been consumed by the plating process using a ratio of surface (in sq. 'cm.) bath volume (in cc.), S /V=0.4. When 1.6 g./liter of thio-diglycollic acid are added to a bath of the same initial concentration using the same ratio S/ V, no decomposition takes place even after a deposition of over 50% of the metal by plating.
The reduction yields, referred to the boron compound as well as to the metal salt, are likewise substantially improved by the addition of organic sulfur compounds soluble in the bath liquid. For example, with a nickel bath having an initial concentration of 30 g./liter of nickel chloride, 40 g./liter of sodium hydroxide, 50 g./liter of ethylenediainine, 0.59 g./liter of sodium borohydride, the following values are obtained for the reduction yield as a function of the quantity of nickel deposited by plating:
Deposited nickel, Reduction yield,
percent: percent 0-10.76 21.82 10.76-18.89 16.55 18.89-25.20 12.84
Decomposition of the bath.
With a bath of the same composition containing, in addition, 1.6 g./liter of thiodiglycollic acid, the following values are obtained:
Deposited nickel, Reduction yield,
percent: percent O-l5.35 31.15 15.35-30.55 30.82 30.55-43.60 26.55 43.60-52.95 18.86 52.95-64.30 23.12 64.30-75.65 23.05
No decomposition of the bath.
These values are established after 0.59 g. of sodium borohydride have been used up for plating in each test.
The addition of organic sulfur compounds with formally bivalent sulfur to chemical plating bathsleads not only to a considerable stabilization of the baths, but, in the case where mixed cobalt-nickel baths are used, also to a prefered deposition of nickel. For example, a solution of 45 g. Ni (NHQ CI 5 g. CoCl -6H O, 5 g. NH Cl and l g. NaBH, in 1 liter of 2 N ammonia solution yields at 50 C. on metal or plastic surfaces a Co-Ni-B coating containing 9.8% of nickel. From a bath of the same composition containing, in addition, 1.0 'g./liter of 3,4-diphenylthiophene-dicarboxylic acid, there is obtained at 50 C. on metal or plastic surfaces a Co-Ni-B coating in which 31.7% of nickel can be-detected.
As examples of organic sulfur compounds with formally vivalent sulfur, wherein the sulfur atom is directly linked oirzooolr Cmooorr om-oooNa CHZ COON8 SO NH The organic sulfur compounds can be added to the plating baths individually or as mixtures. It is frequently of advantage to add one or more metal salts of Groups IIb, IlIb, IVb, Vb and/or Vlb of the Periodic System of Elements to the plating bath, in addition to the organic sulfur compounds. With these new baths metal and plastie surfaces can be plated more satisfactorily and economically than has hitherto been possible. The content of the baths in salts of the plating metals such as chlorides, sulphates, acetates etc. of, for example, nickel, cobalt, nitrates and formiates corresponds to the values already known from borohydride- As reducing agents for the chemical depositing of metal there may be used for example:
- (1) Alkali metal borohydrides; drides;
(2) Water-soluble BH-compounds', e.g. trimethylamine borane. dimethylamine borane, dimethylaminoborine;
(3) BH-compounds which have been rendered watersoluble by the addition of solubilizers; e.g. diethylamine borane, isopropylamine borane etc.
Suitable solubilizers, for example, are methanol, ethanol, dioxan etc. As buffer substances for these new plating baths there may be used, for example, sodium acetate, sodium citrate, sodium tartrate etc. Suitable complex formers, for example, are ammonia and amines such as ethylene-diamine, ethanol-amine, tetramethylene diamine, diethylene triamine, triethylene tetramine, ethylenediamino tetraacetic acid, nitrilotriacetic acid.
The following Table 1 summarizes the basic concentration range of the bath components in accordance with this invention.
e.g. sodium borohy- Table 1 Concentration range in the bath liquid Compounds Although the organic sulfur compounds, when incorporated in the plating bath, may be used in concentrations as high as 5 g./l., there is no improvement to be gained from the higher concentrations, and they are preferably used in the range of concentrations from about 0.01 to 1 g./l. Metals such as nickel copper alloys, aluminum, iron as well as plastic material such as films, shectings, plates, fabrics and moulding articles from acetyl cellulose, celluloseacetobutyrate, polyvinyl-chloride, polyamidcs, polyurethanes, polystyrene, polycarbonates, polyacrylates, polyethylene and polypropylene. The surface of these plastic articles may be activated by treating said surface with acids, alkali and metal salts, prior to plating.
The following examples illustrate the applicability of using the organic sulfur compound in chemical plating baths according to the invention.
EXAMPLE 1 In each of 5 chemical plating baths (a), (b), (c), (d), and (a) each of which contains 1 liter of bath liquor or borazane-containing baths.
consisting of 30 g./liter of nickel chloride, g./liter of sodium hydroxide and g./liter of ethylene-diamine, there are suspended 2 weighed copper and 2 brass plates with a surface of 1 sq. dnr/platc. To the baths (b), (c), (:1), and (e) are added (b)=0.2 g., (c)=0.4 g., 1):0.8 g. and (e):l.6 g. of thiodiglycollic acid. The bath (0) contains no addition of thiodiglycollic acid. The baths are heated to 90 C. and to each bath is added 0.59 g. of 100% sodium borohydride previously dissolved in about 50 cc. of the bath liquor. The p13 ing of the metal plates sets in immediately after the addition of the reducing agent. After a plating time of 40 minutes, sodium borohydride can no longer be detected in any bath by iodometric analysis. Subsequently the plates are removed from the plating baths, rinsed, dried and the increase in weight is established.
In all of the plating baths there are again suspended two weighed plates each of copper and brass and 0.59
BATH (a) (WITHOUT A1)I}\IgIII()))I I OF THIODIGLYCOLLIG Deposited Ni/4 Deposited Ni, Reduction plates, g. percent. yield, percent BATH (b) (0.2 G.T11IODIGLYCOLLIC ACID) BATH (c) (0.4 G. TllIODIGLYCOLLlC ACID) BATH (d) (0.8 G.TI-IIOD1GLYCOLL1C ACID) 13AT11(0) (1.6 G. T1110 DIGLYCOLLIC ACID) 1 Bath is decomposed. 2 No decomposition.
EXAMPLE 2 To three chemical plating baths (a), (b) and (c) 01 the composition described in Example 1 and a bath volume of 1 liter there is added to bath (b)=0.08 g., tc bath (c):0.l6 g. of acetylene-dithiosalicylic acid. Bat-l (0) contains no stabilizer. The S/V ratio is 0.4. Tilt working method is the same as in Example 1. The following values are obtained for the reduction yield as a function of the quantity of nickel deposited by plating.
BATH (a) (WITHOUT ADDITION OF ACETYLENE- DITHIOSALICYLIC A'CID No decomposition.
BATH (c) 0.16 o. ACETYLENE-DITHIOSALICYLIC ACID) Deposited Ni, Reduction yield, percent: percent -8.74 17.75 8.74-27.6 37.18 27.6-42.9 32.18 42.9-56.0 26.75 56.0-72.2. 32.6 i No decomposition.
EXAMPLE 3 In 1 liter of a chemical plating bath of a composition of 30 g./li-ter of nickel chloride, 40 g./liter of sodium hydroxide, 50 g./liter of ethylenediamine, 20 mg./liter of lead chloride, 160 rug/liter of 3-hydroxy-thionaphthenecarboxylicacid-(Z), there are. suspended 4 iron plates with a surface of 1 sq. dm./plate. The plates are previously. weighed. The bath is heated to 90 C. and treated with about 50 cc. of bath liquor containing 0.6175 g. 100%- NaBHrin solution. At intervals of 30 minutes one plate is withdrawn from the bathand a new weighed plate as well as 0.6175 g. NaBH are added to the bath. The proportion .57 V=0.4 is thus not changed. The experiment is continued for a period of 2 hours. The bath volume is maintainedconstant by replacing the evaporated water. The total NaBHd, consumption amounts to 4 0.6l75 ,g.
=2.4700 g. This corresponds to a theoretically possible nickel deposit of 15.284 g. There are deposited:
G./sq. dmu After a stay of 30 minutes 0.4108 After a stay of minutes 0.6898 I After a stay of 90 minutes 0.9602 After a stay of 120 minutes 1.1719 After a stay of 90 minutes 0.8326 After a stay of 60 minutes 0.5601 After a stay of 30 minutes 0.3152
The total Ni deposit (4.9406 g.) corresponds to a reduction yield of 32.35%, calculated on the NaBH :consumption. 66.7% of the nickel present in the plating bath are deposited without decomposition of the bath.
EXAMPLE 4 a In 1 liter of a chemical plating bath of a composition of 30 g./liter of nickel chloride, 40 g./ liter of sodium hydroxide, 60 g./liter of ethylenediamine, 0.2 g./liter of thiodiglycollic acid, 0.1 g./liter of S-(Z-carboxyphenylY- thioglycollic acid, there are suspended 4 weighed iron plates with a surface of 1 sq. dm./plate; The addition of sodium borohydride is 0.5795 g. each time. The working 8' method corresponds to that of Example 1. The following values are obtained:
Deposited Ni/ Deposited Ni, Reduction 4 plates, g. percent yield, percent EXAMPLES Acetyl-cellulose foils are successively treatedin the following baths:
(a) g. of sodium hydroxide+0.3 g. of wetting agent +900 g. of water Time. of stay; 5 minutes, temperature 50-60" CL.
(b) 100 g. of stannous chloride +200 cc. of conc. hydrochloric,acid+0.2 g. of wetting agent-l-SSO ccof water.
Time of stay: 5 minutes, temperature 50-60", C.
(c). 0.5 "g./liter of palladium chloride/+10 cc./liter of cone. hydrochloric acid Time of stay: 5 minutes, temperature 20-30 C.
Four foils with a thickness of 100..- and a surface of 1 sq. ;dm./foil pre-treated in thisv way are suspended in a bath heated to 70 C- andhaving a composition of 30 g. vof nickel chloride, 5 g. of-ammoniumchloride, 10g. of sodium citrate, 20 g. of sodiumacetateylSO mg. of S-(2- carboxyphenyl)-thioglycollic acid. The-pH-value is 5.0. After the addition of 50 ml. of a solution of 3.55 g. of di,-. 7 I ethylamin'e borane in methanol, a brilliant Ni-B coating is obtained on all foils. Every 45 minutes the foils from the bath are-exchanged for 4 newfoils, another, 3.55 g. of diethylamine boranein :50 m1. ofmethanol being added every time. The consumption of amine. 'borane I per throughput is. determined by iodornetric; analysis. This 1 process is repeated five-times. The reduction yields are determined by means of the deposited amount of Ni and the consumption of amine borane per'charge. The values for a bath of the same composition conducted in the same way without an addition of organic sulfuracompound are given for, comparison. The following values are obtained:
(1) BATH WITHOUT ADDITION.
Deposited nickel, Reduction yield, percent: percent 0-18.24 20.0- 18.24-32.7 14.15 32;7.-48.4 16.33. 48.4-61.78 13.82] 61.78-74.9 14.38:
, After-the first and second charge the bath liquor has to be filtered because of metal flakes separating out.
(2) BATH WITH ADDITION'OF I 'MGJLTTER OF S-(2-CARBOXYPHENYL).-THIOGLYCOLLIC ACID Deposited nickel, Reduction yield, 5
percent: percent EXAMPLE 6 In .each of four chemical/plating baths-(a), .(b), (c) and (d). consisting of 15 got cobalt chloride, 15 g. of nickelchloride, 5 g. ofammonium chloridc, 20 g. ofsodium acetate and 950cc. of water there aresuspended twoweighed plates-each of copper and brass with a surface of 1 sq. grim/plate. To the baths (1:), (c) and (d) there are added (b)=50 mg, (c)=l00 mg. and ((1) 150 mg. of thiodiglycollic acid. The bath (:1) contains no addition of thiodiglycollic acid. The baths are heated to 70 C. and 50 [111. of a Solution of 3.55 g. of diethylamine boraue in methanol are added to each bath. The pH value of the plating baths is 5.0. Every 45 minutes the plates are exchanged for new metal plates, another 3.55 g. of diethylamine borane in 50 cc. of methanol being added each time. The consumption of diethyl amine borane is determined iodometrically. This process is repeated four times. It can be seen already from the coloration of the baths, that cobalt is preferably deposited in the baths (a) and (b), whereas nickel is preferably deposited in the baths (c) and (d). The metal coating deposited on the metal plates is removed with nitric acid and analysed as to its cobalt and nickel content. The reduction yields are established by means of the consumption of amine borane per charge and of the metal deposition on the copper and brass plates.
BATH (A) (WITHOUT ADDITION OF THIODI- GLYCOLLIC ACID) [The plating bath must be filtered after the first and second charge from the separated metal flakes] Deposited Reduction Co, Ni,
N i-C0, yield, percent percent percent percent percent;
BATH (B) (ADDITION OF 50 MG./LITER OF TIIIODIGLYCOLLIC ACID) [The bath is filtered after the second charge (few metal 11:11:05)]
Deposited Reduction Co, Ni, 13,
Ni-Co, yield, percent percent percent percent percent BATH (C) (ADDITION OF 100 MGJLITER OF THIODIGLYCOLLIC ACID) 7 ['Bath needs not to be filtered] Deposited Reduction (10, Ni, ll,
N i-Co, yield, percent. percent percent percent percent 0-l9.6 30.0 41.7 55.6 2.7 19. 6-45. 4 21. 45 i 45. 457. 7 17. 9 4b 7 51. 3 2. 0 57. 7-71. 8 16. 2
BATH (D) (ADDITION OF 150 l\IG./LI'1ER OF v THIODIGLYCOLLIC ACID) [Bath needs not to be filtered] Deposited Reduction Co, Ni, 13,
Ni-Co, yield, percent percent percent percent percent 10 EXAMPLE 7 To four chemical plating baths (a), (b), (c) and (d),
each of which contains 45 g./l. of nickel chloride, 2.5 g./l.
of sodium tetraborate, ml./l. of aqueous 25 percent solution of ammonia and 1 g./l. of sodium borohydride in a bath volume of 1 liter there is added to the bath (a) 1.0 g., to bath (b) 0.5 g. and to bath (c) 0.2 g. of 3,4 diphenyl-thiopheneQj-dicarboxylic acid. The bath temperature is 45 C. In each of the baths there are suepended the weighted plates consisting of brass, copper and iron with a surface of 1 sq. dm./plate. The proportion S/V of the bath is 0.3. After a plating time of 45 minutes, the plates have been removed from the plating baths and the increase in weight (deposited nickel) is established.
Bath Sulfur com- Deposited Stability pound, g./l. nickel, g.
1. 2828 No decomposition. 1. 1738 Do. 1. 054 Do. 0. 2735 Decomposition after 15 minutes.
EXAMPLE 8 To four chemical plating baths (a), (b), (c), and (d) of the composition described in Example 7, there are added the following amounts of the sulfur compound represented by the formula:
bath (a) 0.1 g., bath ([1) 0.06 g., bath (0) 0.02 g. and bath (d) 0 g.
The procedure is according to Example 7.
Bath Sulfur Deposited Stability compound, nickel, g.
1. 274 No decomposition. 1382 Do. 1.2l8 Do. 0. 249 Decomposition after 12 minutes.
EXAMPLE 9 In each of three chemical plating baths (a), (b), (c), of the composition of 31 g./l. of nickel chloride, 45 g./1. of sodium hydroxide, 65 g./1. of etbylene-diamine and 0.6 g./l. of sodium borohydride are suspended four weighted copper plates with a surface of 1 sq. din/plate. To the baths (a) and (c) are added 0.01 g. and 0.016 g. of 4,4- dinitro-diphenylsullide-6,6-disulfonic acid, bath (a) contains no organic sulfur compound. The procedure is according to Example 1. Bath (a) is decomposed, when 14.5 percent of the nickel has been deposited. The baths (b) and (c) do not show any decomposition, when 50 percent of the nickel has been deposited.
Example 10 The chemical plating baths according to Example 7 show a decomposition after 20 minutes of working time. A measure for the stabilization effect of the organic sulfur compounds mentioned in the Table 2 is the stability of these chemical plating baths containing said organic sulfur compounds in a bath composition according to Example 7.
Example 11 In a chemical plating bath, which has a temperatureof 90 C. and contains per, liter bath liquid 30 g. of nickel chloride (NiCl- --6H O)-,. 62 g. of ethylene diamine, 4'2 g. of sodium hydrazide, 1.0 g. of thio-diglycollic acid, 0.01 g. of lead chloride and 0.6 g. of sodium borohydride are suspended four metal plates. The proportion surface/volume of bath is 0.4.
Each half an hour one plate is withdrawn and a new plate is suspended, so that the time of stay ofthe first plate in the plating bath is amountedto half an hour, the second plate one hour, the third plate two hours and each of the following plates two hours.
Continuously there are added 100 cms" per hour of a sodium borohydride solution consisting of 12 g. sodium: borohydride and 1 liter of a 2 naqueous solution of sodium hydroxide and 100 cm. per hour of a metal salt solution consisting of 118 g./l. of .nickel, chloride (NiCl 6ll O), 60 g./l. of ethylene-diamine, 1 g./l. .of thiodiglycollic acid and 0.1 g./l. of lead chloride.- Continuously 100 cm? of the bath liquid has been withdrawn per hour.
After. 10 hours working time one liter of sodium borohydride solution and one liter of the solution of metal salts are added .to the platingv bath and accordingly one.
liter is withdrawn; 24.1836 'g., .of nickel has been deposited and the consumption of sodium borohydride. amounts to 12.0 g.,' corresponding to. a reductionyield. 1 of 32 perceut,:calculated on nickel Ewithout decomposition of the. bath :liquid. The. resulting plates show a silver luster.-
What we claim is:v 1. An aqueous metal ;and :plastic plating .bath for plating by chemical reduction consisting essentially of aniaqueous solution of i (1) a plating metal selected from the group consisting of nickel, cobalt; and mixtures thereof in an amount of between 0.02' and 0.5 'mol per liter; (2) a boron compound selected fromithe group consisting of alkali metal borohydrides, trimethylamine borane, dimethyl amine xbon'ne',-. dimethyl amine. borane, diethyl. amine borane, and isopropyl amineborane in anamount of between 0.1 and 10 g. per.
literas reducing agent for said solution, (3) a complex forming agent selected from the group consisting of: ammonia, ethylene 'diamine, ethanol amine, tetramethylene 'diamine,v diethylene triamine, triethylene tetra-amine, ethylene diamino-tetra-acetic acid, and nitrilo-triacetic acid in an amount of between 0.2 and 5 mols per litely-and.
(4) at least one organic divalent sulfur compound selected from the group consisting of thio-diglycolic acid, fl-thio-dipropionic 'acid, -1,l'-thio-bis-(2,2,2- trichloro-ethanol); v(methylene-dithi'o)-diacetic acid,
l-ethyl-thioethanoLj 2,2-thio-.diethanol, a-amino-'y- (methyl-thio)-butyric acid, bis-(N-y-oxypropynthio-xlipropylene glycol-dicarboxylic acid amide, S
(2-Carboxyphenyl)rthio-glycolic acid, ,S(8-chloro-.1- naphthyl)-thioglycolic acid, (p-cltlorophenyl-thio} acetic acid, (Z-methyl 3-chlophenyl-thio)-acetictacid, (pentachlorophenyl thio.) acetic acid, (2-nitr'0-4- acetamidophenyl-thi'o)-acetic r acid,
thio-Z-anthraquinone carboXylic acid (di-Na-salt),
acetylene-dithio-salicylic ,acid, 4,4-dinitro-diphenylsulfide-6,6'-disulfonic acid, 2,2f-thio-di(5-,aminobenzene sulfonic acid), Z-thio'phene carboxylic acid, 3,4-diphenyl-thiophene-2,5-dicarboxylic' acid, 3-hydroXy-thionaphthene-Z-carboxylic acid, Z-hydroxy: thionaphthene, 2 hydroxy 3 dibenzothiophenecarboxylic acid,- 2,3-thionaphthcnedion, '2-(p-aminophenyl)'-5-sulfo-6-bcnzothiazole :carboxylic acid, 2-1
amino- 5 (6'-methyl-2'-benzothio-azolyl)-1,3-benzene disulfonic acid,'2-(m aminophenyl)-7-hydroxynaphtho-(2,3-d)thijoazole-S-sulfoinic acid in an amount of:between 0.001 and 5 g. per liter.
2. Anaqueousmetal and plastic plating bath according toclaim'I additionally'containing. a member selected 5 from the group consisting'of methanol, ethanol, and? dioxane as solu'bilizer,.:.
3.1.An aqueous metal and plastic plating bath accord-, ing to claim] additionally containinga member selected 2 from-the group consisting ,of sodium acetate, sodium nitrate, and sodium tartrate in anamount of between 5 I and 200 g. per liter,- as bufferingagent.
4. An aqueous metal andplasticplating bath according to-claim 1 additionally containing-in solution a lead salt in an amount of between 0.001 and 1 g. per liter..
(1) a plating metal selected from the group consistingof nickel,%cobalt, and mixtures thereof in an amount of-between 0.02 and 0.5 ;mol per liter,
(2) a boron compound selected from the group consisting of alkali metal borohydrides, trimethyl amine;
2-(ix-hydroxyethyl-thio)-4-ethylbenzoic acid, S-carboxymethyl '13 borane, dimethyl amine borine, dimethyl amine borane, diethyl amine borane and isopropyl amine borane in an amount of between 0.1 and 10 g. liter as reducing agent for said solution,
(3) a complex forming agent selected from the group consisting of ammonia, ethylene diamine, ethanol amine, tetra-methylene diamine, diethylene triamine, triethylene tetra-amine, ethylene diamino-tetra-acetic acid, and nitrilo triacetic acid in an amount of between 0.2 and mols per liter, and
(4) at least one organic divalent sulfur compound selected from the group consisting of thio-diglycolic acid, p-thio-dipropionic acid, 1,l-thio-bis-(2,2,2,- trichloro-ethanol), (methylene-dithio)-diacetic acid, l-ethyl-thioethanol, 2,2'-thio-diethanol, wamino-v- (methyl-thio)-butyric acid, bis(N-'y-oxypropyl)-thiodipropylene glycol-dicarboxylic acid amide, S-(2- carboxyphenyl)-thio-glycolic acid, S-(8-chloro-lnaphthyl)-thioglycolic acid, (p-chloropheny1-thio)- acetic acid, (2-methyl-3-chlorophenyl-thio)-acetic acid, (penthachloropheyl-thio)-acetic acid, (Z-nitro- 4-acetamidophenyl-thio) acetic acid, 2-(a-hydroxyethyl-thio)-4-etl1ylbenzoic acid, 3-carboxymethylthio-2-anthraquinone carboxylic acid (di-Na-salt), acetylene-dithio-salicylic acid, 4,4-dinitro-dipl1enylsulfide-6,6-disulfonic acid, 2,2-tl1io-di(5-amino-benzene sulfonic acid), 2-thiophene carboxylic acid, 3,4- diphenyl-thiophene-Z,S-clicarboxylic acid, 3-hydroxythionaphthene-2-carboxylic acid, Z-hydroxy-thionaphthene, 2-hydroxy-3-dibenzothiophen-carboxylic acid, 2,3,-thionapl1thenedion, 2-(p-aminophenyl)-5- sulfo-6-benzothiazole carboxylic acid, 2-amino-5-(6'- methyl-2-benzothioazolyl)-1,3 benzene disulfonic 14 acid, 2- (m-aminophenyl -7-hydroxynaphtho- (2,3-d thioazole-S-sulfonic acid in an amount of between 0.001 and 5 g. per liter.
6. Process according to claim 5, wherein said plating bath additionally contains a member selected from the group consisting of methanol, phenol, and dioxane as solubilizer.
7. Process according to claim 5 wherein said plating bath additionally contains a member selected from the group consisting of sodium acetate, sodium nitrate, and. sodium tartrate in an amount of between 5 and 200 g. per liter of buflering agent.
8. Process according to claim 5 wherein said plating bath additionally contains in solution a lead salt in an amount of between 0.001 and 1 g. per liter.
References Cited by the Examiner UNITED STATES PATENTS 2,528,902 ll/ 1950 Moy et al. 204-49 2,844,530 7/ 1958 Wesyel et al 204-49 2,994,369 8/1961 Carlin 1061 3,062,666 11/1962 McLeod 106-1 3,096,182 7/ 1963 Berzins 1061 FOREIGN PATENTS 836,480 6/ 1960 Great Britain. 626,999 9/1961 Great Britain.
MORRIS LIEBMAN, Primary Examiner.
JOSEPH REBOLD, ALEXANDER H. BRODMERKLE,