Electrodeposition of bright cobalt plate
United States Patent 1191 Brown et al.  
 [ 1 Apr. 8, 1975 I ELECTRODEPOSITION OF BRIGHT COBALT PLATE [73] Assignee: Oxy Metal Finishing Corporation,  
 Warren, Mich.  
 [22] Filed: Aug. 1, 1973 [21] Appl. No.: 384,777  
 Related U.S. Application Data [63] Continuation-in-part of Ser. No. 266,105. June 26. 1972, abandoned. which is a continuation-in-part of Ser. No. 869,334, Oct. 24, 1969, both abandoned.  
 6/1958 Gundel et al. 204/49 2.900.707 8/1959 Brown 204/49 X 2.921.888 1/1960 Halpert 2,978,391 4/1961 DuRose 3.093.557 6/1963 Cope et a1 204/43 T FOREIGN PATENTS OR APPLICATIONS 261.025 12/1962 Australia 204/49 Primary. E.\&#39;aminer-G. L. Kaplan Attorney, Agent, or Firm-B. F. Claeboe [57] ABSTRACT A method to extend the bright plating range obtained with o-benzoyl sulfimide as the principle Class I brightener in acidic cobalt plating baths containing at least 90 percent by weight cobalt down into the very low current density areas or recesses by the use of bath-soluble organic sulfide compounds containing the groupings present in 2-amino thiazole and in isothiourea compounds. The concentrations of these organic sulfide compounds may be as low as l to 10 milligrams per liter, and in these concentrations extend the bright plating range obtained with o-benzoyl sulfimide and the Class II (unsaturated compounds) brighteners down into very low current density areas.  
 10 Claims, No Drawings ELECTRODEPOSITION OF BRIGHT COBALT PLATE CROSS REFERENCE TO RELATED CASES This application is a continuation-in-part of Application Ser. No. 266,105 filed June 26, 1972, which is in turn a continuation-in-part of Application Ser. No.  
 869,334 filed Oct. 24, 1969, and both now abandoned.  
  This invention relates to the electrode position from aqueous acidic baths of bright cobalt plate containing at least 90 percentby weight cobalt.  
  One object of this invention is to increase the bright plating range of acidic bright cobalt plating baths that employ O-benzoyl sulfimide (Class I nickel brightener) and Class II nickel brighteners (unsaturated organic compounds) by making possible bright plating in recessed areas where the current densities may be about amp/sq.ft. and lower.  
  Another object is to provide means to increase the tolerance of bright acidic cobalt plating baths containing at least 90% by weight cobalt to larger concentrations of copper, iron, chromic acid and zinc impurities which cause darkish plating in the recesses or low current density areas, and also to larger concentrations of Class II nickel brighteners which tend to cause dull or darkish plating in the low current density areas in cobalt baths much more readily then they do in predominately nickel baths.  
  These objects and others may be accomplished by the use in the bath of low concentrations of one or more of the bathsoluble organic sulfide compounds of the type given in Table I, in conjunction with o-benzoyl sulfimide, one of the most effective of all Class I brighteners (see Trans. Electrochem. Soc., Vol. 89. p.414. 1946). The compounds shown in Table I contain the grouping (A) I I2 R1- N I C S R3 where R is hydrogen or a carbon atom -of an organic radical, R is nitrogen or a carbon atom of an organic radical, and R is a carbon atom of an organic radical. R and R or R, and R may be linked together through a single organic radical.  
  More specifically, the bath soluble organic sulfide compounds used are 2-amino thiazoles and isothioureas having the formulae:  
 R1-CN (B) R--c C-NH-&#39;R and m M U R n 6-H wherein R is selected from H, lower alkyl sulfonic acid groups, aryl sulfonic acid groups, lower alkoxy aryl sulfonic acid groups andthe salts thereof;  
 R and R are selected from H, halogen, and lower alkyl or alkoxy groups;  
 R is selected from lower alkyl sulfonic acid groups, aryl sulfonic acid groups and lower alkyl carboxy acid groups, and the salts thereof; and  
 R is selected from H, halogen, and lower alkyl or alkoxy groups.  
  It is to be appreciated that in referring to halogens, it is intended to include chlorine, bromine, fluorine and iodine, although chlorine is generally preferred. Moreover, where reference is made to lower alkyl or alkoxy groups, it is intended to include groups containing from about 1 to 6 carbon atoms in a straight or branched chain, with from about 1 to 4 carbon atoms being preferred. Additionally, in referring to the sulfonic or carboxy acids and their salts, it is intended to include those sulfonic and carboxyacids which have halogen substituents on their alkyl, alkoxy or aryl groups, and wherein the salts are exemplified by the alkali metal salts, sodium, potassium, lithium, cesium and rubidium, and particularly sodium.  
  With o-benzoyl sulfimide present in the acidic cobalt baths in concentrations ranging from about 0.3 grams/- liter to saturation concentrations of about 12 grams/- liter, as little as l to 5 mg/liter of the Compounds of Table I are effective in clearing up and brightening up the recessed areas or low current density areasfThe obenzoyl sulfimide compounds used in conjunction with other well-known Class I brighteners such as benzene sulfonamide, o-sulfobenzaldehyde,.vinyl sulfonic, beta sulfo-styrene, allyl sulfonic, vinyl benzene, sulfonic acid and the like and in conjunction with well-knownClass ll compounds such as bath-soluble unsaturated alco-zhols and glycols, unsaturated ether alcohols, and glycols, pyridines and quinolines, and other Class II unsaty urated compounds while making possible bright ductile cobalt plate, nevertheless do not have as wide a bright plating range as these brighteners have in acidic nickel plating baths, and dull plate frequently results in the low current density areas. This is true even with lower bath temperatures than that customarily used for bright nickel plating, and also this is true even at the lower bath pH ranges such as 2 to 3.5, even though these conditions otherwise allow the broadest bright plate range. If benzene or toluene sulfinates (U.S. Pat. No. 2,654,703, Oct. 6, 1953) are also present in the cobalt plating baths containing at least percent by weight cobalt, this sensitivity is eliminated. However, the main fault of these sulfinates is that they are readily oxidized, especially when air agitation is used to obtain maximum brightness and high current density operation. While the oxidation products are not harmful (benzene or toluene sulfonates are formed), nevertheless, the rapid depletion rate of the sulfinates makes control of the bright plating range of the cobalt plating baths less simple. On the other hand, the compounds exemplified in Table I, while not decreasing the sensitivity of the bright plating range as much as the benzene and toluene sulfinates, especially when cathode-rod or mechanical solution agitation is used instead of air-agitation, nevertheless they are more stable under all bath conditions and therefore are easier to control, and in airagitated cobalt baths are far easier to control.  
  The very effective brightening in the low current density areas by the compounds exemplified in Table I is very important in bright plating intricately shaped articles such as brass plumbing goods, copper or brass plated zinc die castings, steel appliances and the like, where deep recesses must be plated bright in order to receive the subsequent thin chromium plate.  
  The compounds exemplified in Table l are preferably used in low concentrations of about 1 to 5 mg/liter in the baths containing o-benzoyl sulfimide, although in some instances concentrations as high as about mg/liter or higher may be used. It has been found that when concentrations higher than about 10 mg/liter are used, too much sulfide sulfer may be incorporated in the plate and this may cause poor or decreased chromium coverage in the low current density areas during the electrodeposition of the usual top thin chromium plate. In the straight acidic cobalt plating baths, however, higher concentrations to 50 mg/l) of the compounds of Table I do not cause poor chromium coverage of the cobalt plate in the low current density areas (recesses) as they do with the bright plate from acidic nickel plating baths, nor do they decrease the leveling as they do in bright nickel plating baths when the Class II nickel brighteners are present with obenzoyl sulfimide in the straight cobalt or high cobaltnickel alloy plating baths.  
  The Class I and Class II nickel brighteners (see Modern Electroplating,&#34; p. 311 to p. 313. John Wiley and Sons, 1953, or the Second Edition, I963 p. 272 and p. 273) as is well known (Trans. Electrochem. Soc., 1946, Vol. 89, p. 414) are more sensitive in acidic high chloride (above 150 g/l NiCl .6I-I O) baths than in Watts high nickel sulfate baths. For example, benzene or naphthalene monodior tri-sulfonic acids are poor Class I brighteners in the high chloride baths and Class II compounds cooperate hardly at all with these benzene or naphthalene sulfonic acids. In the acidic all cobalt plating baths and in the high cobalt-nickel alloy plating baths, the Class I brighteners used together with the Class II brighteners are even more sensitive than in the high chloride baths, and only one Class I brightener, o-benzoyl sulfimide (saccharin), is remarkably effective to give ductile bright leveling plate with Class II compounds as already pointed out (Trans. Electro chem. Soc., 1946, Vol. 89, p. 414, and in U.S. Pat. No. 2,654,703, Oct. 6, I953, col. 1). Nevertheless, even with o-benzoyl sulfimide present in the all cobalt or high cobalt alloy plating baths, as for example a percent cobalt- 10 percent nickel bath, the Class II brighteners are more sensitive (dull areas) in the acidic cobalt plating baths, and lower bath temperatures of about 1 15-1 30F and lower bath pH values of approximately 2.5 to 3.5 must, in general, be used for the broadest bright plating range, and the compounds of Table I must be added to obtain bright very low current density areas under most conditions. Also, in the acidic nickel baths, naphthalene sulfonic acids give good brilliance with Class llbrighteners in high sulfate baths, but they do not accomplish this in high cobalt sulfate baths, and dullish plates are obtained instead. In the case of the acidic cobalt baths, o-benzoyl sulfimide is the only effective Class I compound which gives high brilliance and ductlity with Class II compounds, as was already emphasized in the previous references.  
  Some of the compounds in Table I, such as examples (5) and (6), have been suggested in the U.S. Pat. No. 2,648,627 dated Aug. 11, 1953 for use in nickel plating baths, especially in the Watts type, in order to obtain full bright deposits, and the lower limit of the concentration to accomplish this was set at mg/liter and actually in the preferred examples higher concentrations were suggested. In the present invention, however, significantly lower concentrations are used, and even then these compounds in low concentrations are not helpful unless one particular Class I compound is present, namely; o-benzoyl sulfimide. In fact, if 0- benzoyl sulfimide is not present, the Class II brighteners are of little value, and also most all of the Class 1 compounds are of little value from the standpoint of producing bright ductile leveling cobalt deposits. When they are present in concentrations above about 0.3 g/l; and preferably in the range of2 to 12 g/l, then all of the Class I and especially Class II brighteners make important contributions to brightness and leveling. Nevertheless, the brighteners are more sensitive than in nickel baths, and the lower range of bath temperatures and pH values mustbe used for the broadest bright plating ranges, and even then in most cases, it is very helpful to use small concentrations of the compounds exemplifled in Table I to maintain bright very low current density areas, especially in air-agitated acidic cobalt plating baths.  
 TABLE I Concentration Range &#39;(g&#39;amsliter) NH2. s  
 a c-N&#39;- H mom-0.04  
 TABLE I --Continued Compound (1), Z-aminothiazole and compound (2), 2-aminobenzothiazole can be reacted with bromoethane sulfonate, propane sultone, benzyl chloride, dimethyl sulfate, diethyl sulfate, methyl bromide, propargyl bromide, ethylene dibromide, allyl bromide, methyl chloroacetate, sulfophenoxyethylene bromide, the latter, for example, can be reacted with compound l to give compound (3) to form compounds which give even more improved results over compounds (1) and (2). Also, substituted Z-aminothiazoles and 2- aminobenzothiazoles, such as 2-amino-5- chlorothiazole, 2-amino-4-methylthiazole and the like can be used instead of compounds l and (2). To form compounds such as (5) and (6), thiourea can be reacted with propiolactone, butyrolactone, chloroacetic acid, chloropropionic acid, propane sultone, dimethyl sulfate and the like. Also, phenyl thiourea, methyl thiourea, allyl thiourea and other similar substituted thoureas may be used in the reactions to form compounds similar to types (5) and (6). With the higher molecular weight compounds such as in examples (3) and (4), higher concentrations of these less critical compounds up to 40 mg/liter can be used for optimum results, whereas in general, only 1 to 5 mg/liter are needed for optimum results and in some cases, 1 to 10 mg/liter when the contamination of the baths with impurities such as chromic acid (over mg/liter) or zinc (over 30 mg/liter) or copper ions (over 5 mg/liter) are excessive. The compounds of Table I are by far more effective in air-agitated acidic cobalt plating baths, and  
 generallyless effective where just cathode-rod agitation is employed.  
  Of the listed representative acidic cobalt plating baths, the acidic high cobalt fluoborate as with nickel fluoborate baths does not allow nearly as good leveling with the brighteners as the sulfate and chloride baths or the mixed sulfate-chloride baths. At bath pH values below about 2.5 the leveling falls off, but not as&#39;rapidly as in nickel baths. The lower the bath temperatures, the higher the possible pH range which can be used without dulling setting in. The acidic cobalt plating baths, wherein the cobalt is at least 90 percent by weight, have higher limiting cathode current densities without burning as compared to equal metal ion concentration nickel baths, and therefore using lower bath temperatures for the cobalt baths, for example, about 48 to 55C, still allows at least as high cathode current densilties to be used as in comparable nickel baths operated at 60 to 65C.  
 O 0 0 l-O 0 l 20 RE l RESENTATlVE COBALT BATHS 1. CoSO,.7H O 100- 200 g/l CoCl .6H O 0 50 g/l a n 20 60 g/l pH 2-5 Temp. Room to 55C C.D. up to 150 21mps/sq.ft. (l5 ampslsqdm.) 25 2. CoCl .6H O 100 200 g/l H-IBOSI 20 80 g/l pH 2. Temp. Room to 55 C CD. up t() [50 amps/sq.ft. (l5 ampslsqdm.)  
  3. COSOJH O I00 200 g/l H 80 40 80 g/l NaF 0.5 15 g]! CoCl .6H ,O l0 g/l pH 25 Temp. Room to 55C C.D. up to 150 amps/sq.ftv (l5 ampslsq.dm.) 4. Co(BF I00 200 g/l C0Cl .6H-;O l0 40 g/l H BO l0 40 g/l pH 2.5-5.5 Temp. Room to 55 C 35 CD. up to 200 amps/sq.ft. (20 amps.sq.dm.)  
 5. C0(OSO NH lOO 300 g/l H BO 30 80 g/l pH 2.5-5 Temp. Room to 55C C.D. up to 200 ampslsqft. (20 amps.sq.dm.)  
 Below are two examples of bright cobalt plating baths.  
  (A) CoCl .6H O 100 g/l H3 60 al o-benzoyl sulfimide 2-6 g/l Allyl sulfonic acid 8&#34; lsothiourea-S-acetic acid (Compound 5, I Table l) 0.03 g/l 2-butynoxyl ,4 diethane sulfonic acid (HO,-,SC-=H OCH C E C CH OC H,SO -,H) 0.1-6 g/l 2-butynel ,4-disulfonic acid 4 /l pH 2.5 to 3.5 Temp. 50C Air-agitation CD. 50 amps/sq.ft.  
  (The sodium salts of the sulfonic acids may be used) (B) COSO .7H O lOO lSO g/l CoCl .6H O 0 30 g/l H 80 40 I g/l NaBF, 0.5 2 g/l o-benzo sulfimide 2 l0 g/l Allyl su fonic acid 0.5 3 g/l 2-amino thiazole (Compound I of Table 60 I) 0.002 g/l HOC H OCH C E C-CH OC H,OH 0.02 0.5 g/l In Example (B), use pH values of 2.5 to 3.8, temperature 50C, and CD. of 50 amps/sq.ft. If cathode-rod agitation is used, the higher concentrations of brighteners are usually used compared to air-agitation. In all sulfate acidic plating bath containing dissolved therein obenzoyl sulfimide in a concentraton of about 0.3 grams per liter to saturation and additionally an organic sulfide compound in a concentration of from about 1 to 40 milligrams per liter which compound contains the grouping wherein R is selected from H, halogen and lower alkyl or alkoxy groups, and R is selected from lower alkyl sulfonic acid groups, aryl sulfonic acid groups, and lower alkyl carboxy acid groups and the salts thereof, the lower alkyl carboxy acids and sulfonic acids are defined as those containing 1 to 6 carbon atoms in a straight or branched chain.  
  2. A bath for electrodepositing a bright cobalt plate upon a substrate, comprising an aqueous acidic plating bath fordepositing said cobalt plate upon said substrate said bath having dissolved therein o-benzoyl sulfimide in a concentration of about 0.3 grams per liter to saturation and additionally an organic sulfide compound in a concentration of from about 1 to 40 milligrams per liter which compound contains the grouping:  
 C-S--R wherein R is selected from H, halogen and lower alkyl or alkoxy groups, and R is selected from lower alkyl sulfonic groups, aryl sulfonic acid groups and lower alkyl carboxy acid groups and the salts thereof, the lower alkyl carboxy acids and sulfonic acids as well as lower alkyl and alkoxy groups are defined as those containing l to 6 carbon atoms in astraight or branched chain.  
  3. A bath for electrodepositing a bright cobalt plate upon a substrate, comprising an aqueous acidic plating bath for depositing said cobalt plate upon said substrate, said bath having dissolved therein o-benzyl sulfimide in a concentration of about 0.3 grams per liter to saturation and additionally an organic sulfide compound in a concentration of from about 1 to 40 milligrams per liter, in which the organic sulfide compound has the formulae:  
 R CN ll ll R C C- NH- R and  c s R R- N 7 wherein R is selected from H, lower alkyl sulfonic acid groups, aryl sulfonic acid groups, lower alkoxy aryl sulfonic acid groups and the salts thereof;  
 R and R are selected from H, halogen, and lower alkyl groups;  
 R is selected from lower alkyl sulfonic acid groups and lower alkyl carboxy acid groups and the salts thereof; and  
 R is selected from H, halogen, and lower alkyl groups.  
  4. A bath as claimed in claim 3, wherein the organic sulfide compound is Z-amino-thiazole in a concentration of about 1 to about 14 milligrams per liter.  
  5. A bath as claimed in claim 3, wherein the organic sulfide compound is isothiourea-S-propionic acidin a concentration of about 1 to 10 milligrams per liter.  
  6. A bath as claimed in claim 3, wherein the organic sulfide compound is HC- I H ill Ll c in a concentration of 1 to 40 milligrams per liter.  
 - 7. A method for depositing bright cobalt plate, comprising the step of electrodepositing said metal plate from an aqueous acidic plating bath containing dissolved therein o-benzyl sulfimide in a concentration of about 0.3 grams per liter to saturation and additionally an organic sulfide compound in a concentration of from about 1 to 40 milligrams per liter in which the organic sulfide compound has the formulae:  
 and;  
 wherein R is selected from H, lower alkyl sulfonic acid groups, aryl sulfonic acid groups, lower alkoxy aryl sulfonic acid groups and the salts thereof;  
 R and R are selected from H, halogen, and lower 10. A method as claimed in claim 7, wherein the oralkyl groups; ganic sulfide compound is R is selected from lower alkyl sulfonic acid groups and lower alkyl carboxy acid groups and the slats thereof; and R is selected from H, halogen, and 5 lower alkyl groups. I 8. A method as claimed in claim 7, wherein the or- HQ C c 14 M ganic sulfide compound is Z-amino-thiazole in a concentration of about 1 to about 10 milligrams per liter. 5  
  9. A method as claimed in claim 7, wherein the organic sulfide compound is isothiourea-S-propionic acid in a concentration of about 1 to about 10 milligrams in a concentration of l to 10 milligrams per liter. per liter.