US3556959A

US3556959A - Nickel plating

Info

Publication number: US3556959A
Application number: US717432A
Authority: US
Inventors: Frank Passal
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-03-29
Filing date: 1968-03-29
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: CH539122A; NL6904964A; FR2005046A1; DE1916118C3; DE1916118A1; AT285269B; DE1916118B2; GB1202827A

Abstract

AN ELECTROLYTE AND METHOD FOR ELECTROPHATING SEMIBRIGHT, SULFUR-FREE, NICKEL PLATE. THE ELECTROLYTE CONTAINS TWO COOPERATING ADDITIVES. ONE IS FROM THE GROUP CONSISTING OF FORMALDEHYDE, PARAFORMALDEHYDE, CHLORAL, CHLORAL HYDRATE, BROMAL AND BROMAL HYDRATE. THE SECOND IS A COMPOUND CONTAINING AN OXYOMEGASULFOYHYDROCARBON-DI-YL- COUMARIN ANION WHEREIN THE OXYOMEGASULFOHYDROCARBON-DI-YL GROUP IS SUBSTITUTED ON THE CARBOCYCLIC NUCLEUS OF THE COUMARIN GROUP.

Description

United States Patent ABSTRACT OF THE DISCLOSURE An electrolyte and method for electroplating semibright, sulfur-free, nickel plate. The electrolyte contains two cooperating additives. One is from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal and bromal hydrate. The second is a compound containing an oxyomegasulfoyhydrocar- 'bon-di-yl coumarin anion wherein the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group.

As is well known to those skilled-in-the-art, nickel may be electroplated onto various basis metals to obtain a bright nickel surface. When it is desired to produce a nickel surface possessing maxium brightness and luster and/or when the surface of the basis metal may possess numerous scratches or other minor imperfections, it is common to electroplate onto the surface of a first layer of nickel particularly characterized by its leveling ability. This deposit may be called a semi-bright deposit because it does not possess the extermely high brilliance and luster commonly attained by a bright-nickel deposit. There may commonly be deposited onto this first semibright nickel layer a second bright nickel layer. The semibright nickel layer may be polished and buffed prior to deposition of the bright nickel layer. The resulting duplex-nickel system may be characterized by high degree of brilliance and by superior resistance to corrosion, even when the bright nickel deposit is relatively thin.

The first or semi-bright layer of nickel has heretofore commonly been deposited from various nickel-plating baths, including for example Watts baths, sulfamate baths, chloride-free baths, etc., which contain an additive. Prior art semi-bright nickel plating baths have commonly used coumarin as an additive. Although it may be possible to produce a semi-bright nickel deposit by prior art methods, there are numerous defects which render these processes less than fully satisfactory. Semi-bright nickel deposits formed from plating baths of the prior art suffer from inadequate leveling, high tensile stress and non uniform grain size.

In an effort to correct these deficiencies of semi-bright nickel plating baths, various additives have been used including coumarin derivatives having various groups attached to the aromatic or to the hetehocyclic ring. These compounds have, however, been found not to be satisfactory in that they do not permit attainment of an improved semi-bright nickel plate, but rather they have suffered from defects such as very low solubility, difficulty of synthesis, and tendency to readily decompose during electrolysis to give undesirable products, typically resinous or polymeric materials which result in inferior deposits, etc.

It is an object of this invention to provide a novel process for the electroplating of semi-bright nickel particularly characterized by its high leveling ability. A further object of the invention is to increase the coverice age and luster in low current density areas, to increase tolerance to organic and metallic impurities, and to decrease the likelihood of pitting over the entire area to be plated. Other objects will be apparent to those skilledin-the-art on inspection of the following description.

In accordance with certain of its aspects, the novel process of this invention for electroplating a semi-bright, sulfur-free, nickel pate onto a basis metal may comprise passing current from an anode to basis metal cathode through an aqueous acidic nickel plating solution containing: at least one nickel compound providing nickel ions for electroplating of nickel; a cooperating additive selected from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal, bromal hydrate; and including as a semi bright additive, a compound containing an oxyomegasulfohydrocarbon-di-yl coumarin anion wherein the hydrocarbondi-yl moiety contains at least two carbon atoms and wherein the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group.

All nickel plating baths in commercial operation accumulate metallic (zinc, copper, etc.) and organic impurities (which may include decomposition products of the coumarin derivatives). The cooperating additives of the invention reduce and minimize deleterious effects of such impurities. For example, if some of the organic impurities tend to give coarsergrained, duller low current density deposits, the cooperating additives tend to counter-act these effects.

The basis metal onto which the semi-bright deposits of this bath may be applied may include basis metals which are characterized by a low degree of luster or brightness or which possess at degree of surface roughness which would fail to permit attainment of a satisfactory quality of final finish and appearance if they were directly plated with a bright nickel plate. Typically the basis metals may include ferrous metals such as steel; copper, including its alloys such as brass, bronze, etc.; zinc, particularly in the form of die castings which may bear a plate of copper; etc.

The novel baths of this invention may typically include Watts-type baths, sulfamate-type baths, ifluoboratetype baths, chloride-free sulfate baths, chloride-free sulfamate baths, etc.

A typical Watts bath which may be used in practice of this invention may include the following components in aqueous solution, all values being in grams per liter (g./l.) except for the pH.

TABLE I Minimum Maximum Preferred Component:

Nickel sulfate Nickel chlorid Boric acid-.. Semi-bright add pH eleetrometric i. 3 5

A typical sulfamate-type bath which may be used in practice of this invention may include the following components:

TABLE II A typical fluoborate-type bath which may be used in the practice of the invention may include the following components:

A typical chloride-free-sulfate-type bath which may be used in practice of this invention may include the following components:

TABLE IV Minimum Maximum Preferred Component:

Nickel sulfate 300 500 400 Boric acid 35 55 45 Semi-bright additive 0. 2 3 0. 75 pH electrometnc 3 5 4.

A typical chloride-free sulfarnate-type bath which may be used in practice of this invention may include the following components:

TABLE V Minimum Maximum Preferred Component:

N iekel sulfamate 300 400 350 Boric acid 35 55 45 Semi-bright addltive 0. 2 3 0. 75 pH electrometrie 3 5 4. 0

It will be apparent that the above baths may contain compounds in amounts falling outside the preferred minimum and maximum set forth, but most satisfactory and economical operation may normally be effected when the compounds are present in the baths in the amounts indicated. A particular advantage of the chloride-free baths of Tables IV and V, supra, is that the deposits obtained may be substantially free of tensile stress.

The cooperating additives which may be used in the practice of this invention are selected from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal, and bromal hydrate in a nickel plating solution containing at least one nickel compound providing nickel ions for electroplating nickel. Preferred cooperating additives may be formaldehyde, paraformaldehyde, and chloral hydrate.

Only an amount of cooperating additive sufiicient to provide improved plating characteristics for the nickel plating solution containing at least one nickel compound providing nickel ions for electroplating nickel is necessary. Typically amounts of cooperating additives of from about 0005-110 g./l., such as 0.05-0.5 g./l. and preferably 0.08-0.30 g./l. may be used in the invention. The cooperating additives may be used in combination with each other and in such case the amount of cooperating primary additives refers to the total amount of such additives.

The semi-bright additives which may be employed in practice of this invention according to certain of its aspects may include compounds containing the oxyomegasulfohydrocarbon-di-yl coumarin anion wherein the hydrocarbon moiety contains at least two carbon atoms. The oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic ring of the coumarin nucleus. The hydrocarbon-di-yl moiety may bear inert substituents. Typically such compounds may include those wherein the cation M (see infra may be a bath-compatible cation, i.e. a cation which is soluble in the electroplating bath and which does not interfere with attainment of the desired semi-bright plate. Typically, the cation M may include hydrogen and alkali metals including sodium, potassium, lithium, etc.; polyvalent metals such as nickel,

cobalt, magnesium, etc. The omega carbon atom of these novel compounds is the carbon atom linking the sulfo group to the remainder of the molecule. Most commonly the omega position is the carbon atom most distant from the coumarin nucleus. However, when a hydrocarbondi-yl group in the chain linking the coumarin nucleus to the sulfo group contains carbon-containing substituents, the omega position as herein defined may not be the carbon atom most distant from the cournarin nucleus.

When the cooperating additives are used in cooperation with the coumarin derivatives, besides increasing the general deposit luster and uniformity and acting as anti-pitters and low current density coverage and luster promoters, they also act as extenders, i.e. since they are good grain refiners they still perform one of the functions of the coumarin derivatives and since they are relatively inexpensive in comparison with the latter they permit lower cost operation.

The novel compounds containing the oxyomegasulfohydrocarbon-di-yl coumarin anion may typically have the following formula:

wherein a, b c and d are each integers less than two, i.e. o and l, the sum of a, b, c, and d being greater than 0 and preferably 1 and wherein M is a cation as defined supra, R is a hydrocarbon-di-yl group wherein the hydrocarbon moiety contains at least two carbon atoms, and X is an inert substituent. Typical inert substituents (i.e. substituents which do not cause unfavorable eifects to occur in electroplating baths including the novel compounds of this invention), include hydrogen, halagen, e.g. chloro, alkyl, alkaryl, aralkyl, aryl, alkoxy, aryloxy, etc. As shown, the inert substituent when present is preferably on the aromatic ring of the coumarin nucleus.

In the above formula R may be a divalent hydrocarbon group having at least two carbon atoms. Typically R may be arylene such as o-phenylene; m-phenylene; pphenylene; aralkylene such as o-benzyl; m-benzyl; or pbenzyl; alkarylene such as 1-methyl-2,3-phenylene; 1- methyl 2,4 phenylene; 1-methyl-2,S-phenylene; etc., alkylene such as ethane-1,2-di-yl; propane-1,2-di-yl; propane-1,3-di-yl; butane-1,4-di-yl; butane-1,3-di-yl; pentane- 1,5-di-yl; etc. These groups may bear inert substituents including hydrocarbon substituents. The preferred R group may contain at least three carbon atoms, and more preferably 3-5 carbon atoms in a straight chain extending from the carbon atom closest to the coumarin nucleus to the omega carbon atom, the omega position being as hereinbefore defined. Preferred R groups may contain a linked chain of methylene groups and the most preferred R may be propane-1,3-di-yl, CH CH CH In formulae containing a plurality of R groups, the R groups may preferably be the same.

With respect to Formula I supra, it will be apparent that when a is l, b is 1, c is 0, and d is 0 the formula may be:

and that when a is O, b is 1, c is 1, and d is the formula may be:

. X (III) and that when a is 0, b is l, c is 0, and d is O the formula may be:

It will be apparent that the values of a, b, c, and d may be independently varied between 0 and 1 to produce coumarin derivatives other than those specifically set forth.

It will also be apparent that when M is polyvalent, the valences thereof may be satisfied by linkage to other oxyomegasulfohydrocarbon-di-yl groups which may be on the same or on another coumarin nucleus. For example, when M is divalent, e.g. nickel, the compound may have one of the following illustrative formulae, inter alia:

The preferred compounds may include those having Formula IV wherein the oxyomegasulfohydrocarbon-di-yl group is substituted on the 7-position of the coumarin and M is an alkali metal; also preferred are those compounds wherein R is 'a hydrocarbon-di-yl group having 3-5 carbon atoms and most preferably one wherein R is a polymethylene chain preferably having 3 carbon atoms, viz:

wherein n is preferably 35, and most preferably 3.

It will be apparent to those skilled-in-the-art that the compounds noted supra will provide the baths of this invention with the desired anion viz:

or the following corresponding anions to the above-noted specific compounds, (II), (III), and (IV):

Typical preferred specific compounds Which may be used in practice of this invention may include:

TABLE VI potassium 7-oxyomegasulfopropyl coumarin potassium 6-chloro-7-oxyomegasulfopropy1 coumarin sodium 7-oxyomegasulfopropyl coumarin sodium 6-chloro-7-oxyomegasulfopropyl coumarin disodium 6,7-di(oxyomegasulfopropyl) coumarin disodium 7,8-di(oxyomegasulfopropyl) coumarin nickel 6,7-di(oxyomegasulfopropyl) coumarin cobalt 7,8-di(oxyomegasulfopropyl) coumarin nickel di(7,7'-oxyomegasulfopropyl) coumarin potassium (8-oxyornegasulfopropyl) coumarin potassium (6-oxyomegasulfopropyl) coumarin sodium 5-oxyomegasulfobutyl coumarin potassium 7-oxyomegasulfobutyl coumarin sodium 7-oxyomegasulfobenzyl coumarin (i.e. sodium 7-oXy-ortho sulfobenzyl coumarin), viz.:

The most preferred compounds may typically be the first four compounds in table VI. It will be apparent that other cations as hereinbefore noted may replace those present in the specific compounds in Table VI.

The novel oxyomegasulfohydrocarbon-di-yl coumarin compounds, wherein the hydrocarbon-di-yl moiety contains at least 2 carbon atoms and the oxyomegasulfohydrocarbon-di-yl is substituted on the carbocyclic nucleus of the coumarin group of this invention may, in accordance with certain of its aspects, be prepared by the process which comprises mixing in a solvent dispersion, a hydroxy coumarin wherein the hydroxy group is substituted on the carbocyclic nucleus of the coumarin group, a compound of the formula MOH wherein M is a cation including those hereinbefore noted, and a hydrocarbon sultone wherein the hydrocarbon moiety contains at least 2 carbon atoms thereby forming a reaction mixture, and heating said reaction mixture.

The solvents used in this preparation may preferably be those in which the reactants are dispersible, i.e. suspendable or soluble and most preferably one in which the compound MOH is soluble. Such solvents may typically include organic solvents such as alcohols, etc.

The sultones which may be employed to prepare the novel compounds of this invention may include those containing a carbon-oxygen-sulfur-carbon linkage in a ring, the hexavalent sulfur atom being further bonded to two additional oxygen atoms. The sultone which may preferably be used may contain 3-5 carbon atoms, these sultones being characterized by generation of a minimum of foaming. The most preferred sultone may be 1,3-propane sultone,

although sultones such as 1,4-butane sultone,

CH2 Cg GH CH2 S 62 and 1,3-butane sultone,

HCH

(IJHZ S 62 also may produce highly useful additives. The longer chain alkane sultones or other sultones containing more than 5 carbon atoms, such as tolyl sultone,

may also be used to produce additives within the scope of the invention.

Hydroxy-coumarins which may be used in preparing the novel compounds may include the following hydroxy coumarins which carry one hydroxyl substituent on the carbocyclic nucleus of coumarin, typically including monoand poly-hydroxy coumarins such as:

S-hydroxy coumarin 6-hydroxy coumarin 7-hydroxy coumarin 8-hydroxy coumarin 6,7-dihydroxy coumarin 7,8-dihydroxy coumarin 6-chloro-7-hydroxy coumarin Preferred coumarins may include the 7-hydroxy coumarins such as 7-hydroxy coumarin se.

These hydroxy coumarins may be readily available or may be prepared by the reaction of the corresponding resorcinol with malic acid in the presence of catalyst, e.g. concentrated sulfuric acid; e.g. to prepare 6-chloro-7- hydroxy coumarin, malic acid may be reacted with 4-chloro resorcinol. Besides concentrated sulfuric acid other catalysts may be used such as the pyrophosphates of titanium and zirconium used singly or in combination.

The preferred compounds MOH which may be used in the process of this invention include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide.

In a preferred embodiment of the invention, 2.3-3.3 parts, say 2.8 parts of MOH, preferably potassium hydroxide, may be added to 3-4 moles, say 3.1 moles of solvent, preferably methanol. 7.5-11 parts, preferably 8.1 parts of 5-, 6-, 7- or S-hydroxy coumarin, preferably 7-hydroxy coumarin, may then be added together with 4.9-7.3 parts, say 6.7 parts of hydrocarbon sultone, preferably 1,3-propane sultone. Preferably the molar ratio of MOH to hydrocarbon sultone may be about 1 to l. The reaction mixture may then preferably be heated typically to reflux temperature for 1-4 hours, say 2 hours. All parts referred to above are parts by weight.

At the conclusion of the reaction time, the reaction vessel may be cooled and the desired product may precipitate. The product may be separated, Washed with a solvent in which the product is sparingly soluble, such as methanol and dried. Typically the pure yield may be at least about 60% by weight based on the coumarin starting material, although crude yield may also be used as semi-bright additives to electroplating baths without deleterious results. Alternatively, the solvent, such as methanol, may be removed by heating under reduced pressure and the residual product dissolved in water to a convenient concentration and used as the additive stock solution to essentially obtain a quantitative yield of the active ingredient.

If it be desired to convert the alkali metal salt of the oxyomegasulfohydrocarbon-di-yl coumarin to other salts, the alkali metal salt of the oxyomegasulfohydrocarbondi-yl coumarin compound may preferably be reacted with a cationic exchange resin such as a sulfonic acid cationic exchange resin on the hydrogen cycle. The free sulfonic acid in the eluate may then be reacted with the oxide, hydroxide, carbonate, etc., of the metal desired, e.g. nickel or cobalt to neutrality to form the desired metal salt of the free sulfonic acid. Any excess of the oxide, hydroxide, carbonate, etc., may be removed by filtration.

The semi-bright oxyomegasulfohydrocarbon-di-yl coumarin moiety wherein the hydrocarbon-di-yl moiety contains at least two carbon atoms and wherein the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group may preferably be used in nickel plating baths such as those of Tables I-V, in amounts of at least 0.2 g./l. of plating bath. Lower concentrations may give appreciable grain refinement but the deposits may be less glossy. When the concentration of the oxyomegasulfohydrocarbon-diyl compound or group exceeds 3 g./l. of plating bath, the results obtained generally do not provide additional advantages over the lower ranges. The preferred concentration ranges from about 0.5-1 g./l. of additive in the plating bath.

The presence of the cooperating additives of this invention in a nickel plating solution in combination with an oxyomegasulfohydrocarbon-di-yl group in the plating baths which may be used in this invention may be found to impart improved surface active anti-pitting properties and such combinations extend and augment the grain refining eifects of the coumarin group, especially in low current density areas. The plating baths may in addition contain optional additional constituents such as anionic Wetting agents which may be used to further reduce pitting eifects. High foaming anionic wetting agents such as sodium lauryl sulfate may be used in conjunction with mechanical agitation; and low foaming anionic wetting agents such as sodium dialkyl sulfosuccinates may be used with air agitation. Although these wetting agents may commonly contain sulfur, it has unexpectedly been found that no increase in the sulfur content of the metal deposits may be observed when these wetting agents are used with the semi-bright additives and cooperating additives of the invention.

It is a particular feature of this invention according to certain of its aspects that medium or very high-speed electroplating of semi-bright nickel may be eifected by the process comprising passing current from a substantially non-polarizing anode to a basis metal cathode through an aqueous nickel plating solution including at least one nickel compound capable of providing nickel ions for electroplating nickel; a cooperating additive selected from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal, bromal hydrate in said nickel plating solution; and including as a semibright additive a compound containing oxyomegasulfohydrocarbon-di-yl coumarin anion wherein the hydrocarbon moiety contains at least two carbon atoms and the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group, maintaining the cathode current density during said plating at a level of at least amperes per square decimeter (ASD) and maintaining a high relative velocity between said nickel plating solution and said basis metal cathode thereby obtaining a glossy, leveled, semi-bright high-speed nickel plate with good low current density coverage and reduced pitting.

The substantially non-polarizing anodes which may be used in the medium or very high-speed electroplating aspect of this invention may be insoluble anodes, such as lead which have very little tendency to polarize, even at very high current density, or certain soluble anodes, such as the commercially available SD type of nickel which has less tendency to polarize than other soluble nickel anodes and may be used at current densities as high as 40 ASD. The SD type of nickel is an electrolytic nickel containing a controlled amount of sulfur.

Thus, according to this aspect of the invention a current density of over about 10 ASD, and preferably of -60 ASD, may be used, although a current even as high as or higher than 120 ASD may be applied during electroplating of nickel using baths containing the novel additives of the invention. Plating carried out in this manner may permit deposition of predetermined thicknesses of semi-bright, leveled nickel in a time which is as little as 10% or less of the time required when ordinarily used plating conditions with soluble nickel anodes are used. Typically production of a semi-bright nickel plate microns thick according to this aspect of the invention may require 3 minutes in contrast to minutes for usual plating conditions.

When medium or very high speed electroplating is desired, a high relative velocity may be maintained between the bath and the cathode-to attain a substantially homogeneous catholyte. This serves to replenish the cathode fihn with nickel ions as they are plated out therefrom. Typically the high relative velocity between the bath and the cathode is-maintained at a level equivalent to 60-320, say 150 cm./second. The agitation may be produced by vibration (including ultrasonic), rotation of the cathode relative to the solution, by pumping the electrolyte, e.g. catholyte, through the system and over the cathode relative to the solution, by pumping the electrolyte with appropriately positioned propellers or other devices, etc.

Semi-bright nickel plating in accordance with this invention may also be carried out under lower speed conditions by immersing a basis metal cathode into a nickel plating bath as hereinbefore disclosed. The anode may be either a soluble anode, typically nickel metal, or an insoluble anode, typically lead.

If nickel is used as the anode, it is preferably SD type of nickel and plating may be carried out in chloridecontaining baths for 30-60 minutes, say 30 minutes at 4060 0, say '50 C., with mechanical or air agitation.

The current density may typically be 2.5-5 ASD, preferably 5 ASD;

The novel process of this invention may permit attainment of a 12.5 to 50 microns, say 25 microns of semibright nickel plate characterized by its fine grain, high ductility, high gloss, uniform appearance, high leveling, and high covering power. The plate is also characterized by its essentially sulfur-free character.

The following illustrative examples disclose synthesis of typical additives of this invention, nickel plating baths containing the novel additives of this invention, and electroplatng processes wherein these baths are used.

EXAMPLE 1 100 ml. of methanol, 2.8 grams of potassium hydroxide and 8.1 grams of 7-hydroxy coumarin may be introduced into a 500 ml. Erlenmeyer flask, to form a solution. 6.7

10 grams of 1,3 -propane sultone may then be added and the flask then heated under reflux on a hot plate for 2 hours while the composition is magnetically stirred. The solution may be cooled to ambient temperatures, the precipitate obtained may be filtered out and then washed several times with methanol. The precipitate may then be dried for 2 hours at 60 C., leaving 9.4 grams (59% 'yield) of potassium 7-oxyomegasulfopropyl coumarin.

The melting point of 237 C.240 C. may then be determined.

EXAMPLE 2 6.5 grams of potassium hydroxide dissolved in ml. of methanol may be introduced into a suspension of 20 grams of 6-chloro-7-hydroxy coumarin in 300 ml. of methanol producing a precipitate. The suspension may then be heated to reflux and a solution of 13 grams of 1,3-propane sultone in 100 ml. of methanol added drop- 'wise over a 15-minute period. This may be followed by stirring and refluxing for 4 hours to obtain a precipitate of potassium 6-chloro-7-oxyomegasulfopropyl coumarin. The methanol may be removed by heating in a stream of air, leaving 40 grams of the crude coumarin derivative. The compound does not melt at temperatures of up to 300 C.

EXAMPLE 3 Other coumarin derivatives which may be prepared according to the general methods of the above examples include sodium 7-oxyomegasulfopropyl coumarin, prepared in a methanol solvent interaction of 7-hydroxy coumarin, 1,3-propane sultone and sodium hydroxide.

EXAMPLE 4 1 liter of the following Watts bath may be prepared:

Nickel sulfate: 300 g./l. Nickel chloride: 60 g./l. Boric acid: 45 g./l.

pH electrometric: 4.0 Water to 1 liter.

The bath may be thermostatically controlled at 60 C. and air agitated with a perforated glass-plastic air agitation coil. A single cotton cloth bagged SD nickel anode may be positioned in the bath. A highly polished brass strip of 20 cm. x 2.5 cm. x 0.08 cm., pleated in 45 angles, may then be cleaned and immersed as the cathode in the bath except for the top 2.5 cm.

In a control run, a current of 2.5 amperes may be passed through the bath at 50 C. for 30 minutes to obtain a dull, grainy, non-uniform deposit.

In practice of the invention, 0.8 gram of potassium 7- oxyomegasulfopropyl coumarin semi-bright additive and 0.1 gram of formaldehyde cooperating additive may then be mixed into the bath and the plating test repeated. This time a beautifully -fine grained, very ductile deposite of high gloss and very uniform appearance charterized by excellent low current density coverage and relative freedom from pitting may be obtained. When a similar cathode, which had been scribed with a single pass of 1.2 cm. wide zero-grit emery paper, was thereafter plated for 30 minutes using the bath containing the cooperating additives, the emery paper scratches may be found to be substantially filled in, indicating excellent leveling at low current density areas.

EXAMPLE 5 4 liters of the Watts bath of Example 4 may be prepared and 3.2 grams of potassium 7-oxyomegasulfopropyl coumarin and 0.5 gram of the low-foaming wetting agent sodium di-n-hexylsulfosuccinate added thereto. Electroplating may be carried out using a bagged SD nickel anode; and a highly polished, brass cathode strip pleated in 45 angles may then be plated at a current of 5 amperes at 50 C. for 30 minutes to obtain a beautifully fine grained, very ductile deposit of high gloss and very uniform appearance.

In practice of the invention, 0.1 gram of paraformaldehyde cooperating additive may then be mixed into the bath and the plating test repeated. This time a beautifully fine grained, very ductile deposit of high gloss and very uniform appearance further characterized by excellent low current density coverage and relative freedom from pits may be obtained, indicating a substantial improvement due to the use of the cooperating additive.

The essentially sulfur-free character of the deposits may be determined by analyzing the deposits obtained in Examples 4 and 5. It may be found in each instance that the sulfur content is about 0.003% by weight. This value is so unusually low that the deposits may be considered to be essentially sulfur-free.

The beneficial characteristics exemplified by Examples 4 and 5 may be maintained over prolonged periods of electrolysis, for example up to 500 ampere-hours or longer by periodically adjusting the bath pH to within recommended limits as with dilute sulfuric acid and by replenishing the additives.

EXAMPLE 6 1 liter of the following sulfamide bath formulation may be prepared:

Nickel sulfamate: 360 g./l. Nickel chloride: g./l. Boric acid: 45 g./l.

pH electrometric: 3.5 Water to 1 liter.

The process of Example 4 may be repeated using the same cooperating additives with essentially the same results obtained.

EXAMPLE 7 The process of Example 4 using the Watts bath thereof may be repeated using as the additive 0.8 gram of potassium 6 chloro 7 oxyomegasulfopropyl coumarin as semi-bright additive and 0.1 g./l. of chloral hydrate as cooperating additive with essentially the same results obtained.

EXAMPLE 8 EXAMPLE 9 4 liters of the following chlo'ride-free-nickel bath formulation may be prepared:

Nickel sulfate: 375 g./l. Boric acid: 45 g./l.

pH electrometric: 4.0 Water to 1 liter.

The bath may be thermostatically controlled at 70 C. and mechanically agitated by propellers during plating.

To this bath may be added 0.4 g./l. of potassium 6- chloro-7-oxyomegasulfopropyl coumarin and 0.05 g./l. of

chloral hydrate and 0.05 g./l. of formaldehyde. A single cotton cloth bag SD nickel anode is positioned in the bath. A highly polished brass strip cathode of 2.5 cm. x 20 cm. x 0.08 cm. may be scribed with a singlepass' of 1.2 cmywide zero-grit emery board. This strip may be clamped in a plastic fixture exposing only the scribed side of the strip to the anode and the plating bath discharged from a pressure pump to impinge on the exposed scribed area of the strip at an'angle'of about A- current density of 40 amperes per square decimeter may be applied at C. for 3 minutes to obtain by this high speed process a glossy beautifully fine grained, very ductile deposithaving a thickness of about 25 microns and further char acterized by virtual freedom from pits. The cathode plate attained from the chloride-free bath of this example possesses very little tensile stress. The emery paper scratches theextent of 0.005l.0 g./ 1. of the solution. a

may be found to be; substantially filled in and the-leveling is excellent. 1

EXAMPLE 10 11 ence to specific examples, numerous changes and modifications thereof. which clearly fall within the scope of the invention. will be apparent to those skilled in the art.

I claim: p 1. A process of electroplating a semi-bright, sulfurfree, nickel plate onto a basis metal which comprises passing current from an anode to a basis metal cathode through an aqueous acidic nickel plating solution containing at least one nickel compound providing nickel ions for electroplating nickel; and, in an amount sufficient to provide improved plating characteristics, a cooperating additive selected from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal, bromal hydrate and a compound containing an omegasulfohydrocarbon-di-yl coumarin anion wherein the hydrocarbon-di-yl moiety contains at least two carbon atoms and wherein the oxyomegasulfohydrocarbon-di-yl groups is substituted on the carbocyclic nucleus of the coumarin group.

2. The process of claim 1 wherein the cooperating additive is formaldehyde.

3. The process of claim 1 wherein the. cooperating ad ditive is chloral hydrate or chloral.

4. Theprocess of claim 1 wherein the cooperating additive is bromal hydrate or bromal.

5. The process of claim 1 wherein the cooperating additive is paraformaldehyde. v I

6. The process of claim 1 wherein saidisemi-brightad, ditive is g A, Xi-iiM-OSb2.li.-O]a wherein X'is an inert substituent, M is a cation, R is a hydrocarbon-di-yl group containing at least two carbon atoms, and a, b, c, and d are each integers less than 2,

the sum of a, b, c, and dbeing atleast 1.

7. The. process of claim 1 wherein said semi-bright additive is wherein M is a cation and-X is an inert substituent.

8. The process of claim 1 wherein said semi-bright additive is present to the extent of at least about 0.2 g./l. of the solution and the cooperating additive is present to A process of electroplating a semi-bright nickel deposit which comprises passing current from asubsta'n' tially non-polarizing anode to a basis metal cathode through an aqueous acidicnickel plating solution includ- 1 ing at least one-metal compound capable of providing" drate, bromal, bromal hydrate and 'a compoundc'oirtain ing oxyomegasulfohydrocarbon-di-yl coumarin wherein the hydrocarbon moiety contains at least two carbon atoms and the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group; maintaining the cathode current density during said plating at a level of at least ten amperes per square decimeter, and maintaining a high relative velocity between said chloride-free nickel plating solution and said basis metal cathode thereby obtaining a glossy leveled, semi-bright high speed nickel plate characterized by good low current density coverage and substantial freedom from pits.

10. A nickel plating solution comprising an acidic aqueous nickel plating solution including: at least one nickel compound capable of providing nickel ions for electrodeposition of nickel on a basis metal cathode; and in an amount sufficient to provide improved plating characteristics, a cooperating additive selected from the group consisting of formaldehyde, paraformaldehyde, chloral, chloral hydrate, bromal, and bromal hydrate; and a compound containing an oxyomegasulfohydrocarbon-di-yl coumarin ion wherein the hydrocarbon moiety contains at least two carbon atoms and the oxyomegasulfohydrocarbon-di-yl group is substituted on the carbocyclic nucleus of the coumarin group.

11. The nickel plating solution of claim wherein the cooperating additive is formaldehyde.

12. The nickel plating solution of claim 10 wherein the cooperating additive is chloral hydrate or chloral.

13. The nickel plating solution of claim 10 wherein the cooperating additive is bromal hydrate or bromal.

14. The nickel plating solution of claim 10 wherein the cooperating additive is paraformaldehyde.

15. The nickel plating solution of claim 10 wherein the semi-bright additive is wherein X is an inert substituent, M is a cation, R is a hydrocarbon-di-yl group containing at least two carbon atoms, and a, b, c, and a are each integers less than 2, the sum of a, b, c, and d being at least 1.

16. The nickel plating solution of claim 10 wherein said semi-bright additive is wherein M is a cation and X is an inert substituent.

17. The nickel plating solution of claim 10 wherein said semi-bright additive is MO-SOz(CH2)3O =0 wherein M is a cation.

18. The nickel plating solution of claim 10 wherein said semi-bright additive is wherein M is a cation.

19. The nickel plating solution of claim 10 wherein said aqueous acidic nickel plating solution is chloride-free.

20. The nickel plating solution of claim 10 wherein said semi-bright additive is present to the extent at least about 0.2 g./l. of the solution and wherein said cooperating additive is present in an amount of 0005-10 g./l. of the solution.

References Cited G. L. KAPLAN, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3 ,556 ,959 Dated January 19 1971 Inventor(s) Frank 211 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, after line 4, insert assignor to MGT Chemicals Inc., New York, N. Y. a corporation of Delaware Signed and sealed this 15th day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E SCHUYLER, JR

Attesting Officer Commissioner of Patents