ZINC-NICKEL ALLOY ELECTROPLATING SYSTEM

FIELD OF THE INVENTION

The present invention is directed to electroplating compositions, and more particularly to compositions useful for electroplating zinc-nickel alloys. The invention is specifically directed to an electroplating composition comprising an electrolyte composition and an organic composition, wherein the electroplating composition is particularly beneficial for depositing zinc-nickel alloys with a consistent nickel concentration across a broad range of current densities.

BACKGROUND Electrodeposition of zinc and nickel metal onto a substrate, particularly a metal substrate, and very particularly a ferrous substrate, is a common practice for imparting protective and decorative properties to the substrate. For example, ferrous articles are often zinc or nickel electroplated to provide corrosion resistance to the substrate. As the need for improved corrosion protection has increased over time, interest in zinc-nickel alloys has also increased, particularly as electroplated zinc- nickel alloy coatings have been shown to provide increased corrosion protection in comparison to electroplated coatings composed of zinc alone.

Electroplating baths used in zinc-nickel alloy electroplating generally can be divided into two separate categories: alkaline electrolyte baths and acidic electrolyte baths. Both types of baths, heretofore, have been known to suffer from multiple disadvantages.

When using an alkaline zinc-nickel alloy electroplating bath, a common problem encountered is maintaining a functional level of metal ions in the bath. To overcome this problem, alkaline zinc-nickel alloy electroplating baths generally require the use of strong chelating agents to solubilize the metal ions and keep them in solution. A chelator is generally recognized in the art as a compound, often an organic compound, capable of forming two or more coordination bonds with a central metal ion. Chelators can be capable of coordinating metals in general, or may be more specific for metal of certain valences (e.g., divalent cation chelators). Examples of common chelating agents include: hydroxycarboxylic acid salts, such as citrates, tartrates, gluconates, and glycollates; amino alcohols, such as monoethanolamine, diethanolamine, and triethanolamine; polyamines, such as ethylenediamine; amino

carboxylic acid salts, such as ethylenediamine tetraacetates and nitrilotriacetates; polyhydroxyalcohols, such as sorbitol; and thioureas.

The use of chelators presents a disadvantage in that plating efficiency and plating rate can both be reduced as a result of the metal ion complexation caused by the chelator. Furthermore, the presence of the metal ion complexes with the chelators makes the plating process environmentally unfavorable as the removal of the complexed metal ions from wastewater streams is difficult and costly. Accordingly, avoidance of chelators in general is preferred.

Acidic zinc-nickel alloy electroplating baths also present wastewater treatment problems. The high concentration of ammonium ions commonly found in acidic zinc- nickel alloy electroplating compositions tends to make metal ion removal more difficult, and accordingly more costly. Further, environmental discharge limits may be applicable to solutions including ammonium ions.

Apart from the waste treatment issues, the inherent physical properties of coatings applied by acidic zinc-nickel alloy electroplating have also been shown to be troublesome for various reasons. The zinc-nickel alloy deposits can lack ductility, can be brittle, and can be highly stressed. Each of these can cause the electroplated zinc- nickel alloy layer to flake and peel from the substrate, especially in regions of high current density. Another limitation seen with previous zinc-nickel alloy electroplating systems is a lack of alloy composition uniformity in deposition layers applied with such systems. The concentration of nickel in the zinc-nickel alloy tends to increase, often significantly, as the current density of the plated article is decreased. This can lead to disadvantages related to coating performance, as well as coating aesthetics. The disadvantages described above can be overcome according certain embodiments of the present invention, which provides an aqueous acidic zinc-nickel alloy electroplating composition, as well as a method of preparing zinc-nickel alloy coatings.

SUMMARY OF THE INVENTION

The present invention provides an aqueous zinc-nickel alloy electroplating composition. The composition is particularly useful for depositing a layer of a zinc- nickel alloy on a substrate, wherein the zinc-nickel alloy layer has an average nickel concentration that is within a desired range when the zinc-nickel layer is applied using

a broad range of current densities. In addition to a consistent average nickel concentration, the zinc-nickel alloy layer deposited according to certain embodiments of the invention is bright, lustrous, and ductile. Further, these properties, as well as other properties generally desirable in an electroplated coating, are achieved when the deposition is carried out using a broad range of current densities.

In one aspect, the invention is directed to an acidic, aqueous zinc-nickel alloy electroplating composition comprising an electrolyte composition and an organic composition. In one particular embodiment of the invention, the electrolyte composition comprises a zinc ion source, a nickel ion source, a pH buffering agent, and at least one additional inorganic salt. The organic composition, according to this embodiment of the invention, comprises a nickel brightener (preferentially a Class I nickel brightener and a Class II nickel brightener), an aromatic carboxylic acid, an aldehyde or ketone compound (preferably an aromatic aldehyde or ketone compound), and a surfactant (preferentially selected from non-ionic surfactants and anionic surfactants). In one preferred embodiment, the zinc-nickel alloy electroplating composition is free from chelating agents and is further free from agents producing free ammonium ions in solution.

In one particular embodiment, the electrolyte composition portion of the electroplating composition comprises zinc chloride, nickel chloride hexahydrate, potassium chloride, boric acid, and sodium acetate. The electroplating composition is particularly useful in that the electrolyte composition can be standardized to specific requirements, and the organic composition can be varied to provide desired properties.

According to another aspect, the invention provides a method for depositing a zinc-nickel alloy on a substrate. In one embodiment, the method comprises immersing the substrate in an aqueous electroplating composition and applying an electrical current to the immersed substrate for a time sufficient to deposit a layer of a zinc-nickel alloy on the substrate. In one preferred embodiment, the aqueous electroplating composition comprises an electrolyte composition comprising a zinc ion source, a nickel ion source, a pH buffering agent, and at least one additional inorganic salt, and the organic composition comprises a Class I nickel brightener, a Class II nickel brightener, an aromatic carboxylic acid, an aldehyde or ketone compound, and a non-ionic or anionic surfactant.

The method of the invention is particularly beneficial in that it provides the ability to deposit a zinc-nickel alloy layer with an average nickel concentration that is consistent when the zinc-nickel layer is deposited using current densities varying over a broad range. In one specific embodiment, the average nickel concentration of the zinc-nickel alloy layer is in the range of about 6% to about 15%, based on the overall weight of the zinc-nickel layer. Preferentially, the average nickel concentration is within this range when the deposition layer is applied using a current density that is between about 0.5 Amperes/ft ² (ASF) and about 120 ASF.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter with reference to specific embodiments of the invention. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

The present invention provides an electroplating composition useful in an electroplating method for depositing a zinc-nickel alloy layer on a substrate. The electroplating composition of the present invention is particularly useful in that it is highly versatile. For example, the electroplating composition can be varied to provide preferred physical and chemical characteristics, including corrosion protection for the underlying substrate and pleasing aesthetics. The electroplating composition is further versatile in that excellent deposition layers with favorable properties can be achieved with a single composition while using a broad range of electroplating current densities during deposition of the layer. In particular, it is possible to deposit a zinc- nickel alloy layer having a preferred average nickel concentration, even when the layer is deposited using a broad range of current densities. It is further possible, according to certain embodiments of the invention, to deposit a zinc-nickel alloy layer that is bright, lustrous, and exhibits high ductility.

Various embodiments of the invention are described in terms of being "substantially free" of certain compounds, elements, ions, or other like components. Accordingly, as used in describing the invention, "substantially free" is intended to mean that the compound, element, ion, or other like component is present, at most, in

only trace amounts (i.e., a concentration so minute that the presence of the compound, element, ion, or other like component will have no adverse affect on the desired properties of the coating). Preferably, "substantially free" indicates the specified compound, element, ion, or other like component is completely absent or is not present in any amount measurable by techniques generally used in the art.

The electroplating composition of the invention is particularly distinguished from other acidic, aqueous systems in that the composition is substantially free from chelators and is likewise substantially free from agents producing free ammonium ions in aqueous solution. As noted above, previously known electroplating systems in the industry are plagued by the use of chelators, which keep complexed metal ions in solution. Many such systems further include ammonia or ammonium ion producing compounds, which are also undesirable. The presence of such agents leads to serious and costly treatment requirements. According to the unique composition described herein, it is possible to provide an effective electroplating composition that is substantially free of chelators and ammonium ions, as well as the problems associated therewith. The electroplating composition of the invention is substantially free of chelators and agents capable of producing free ammonium ions in aqueous solution. Accordingly, the composition contains, at most, only trace amounts of chelators or ammonium ions in such a minute concentration that the presence of the chelators or ammonium ions will have no affect on the electroplating and will have no adverse health or environmental impact. Most preferably, the electroplating composition contains no chelators or ammonium ions.

The electroplating composition of the invention comprises an electrolyte composition and an organic composition. Accordingly, it is possible to prepare a number of electroplating compositions useful for depositing a zinc-nickel alloy layer with specifically defined properties. Such can be accomplished by varying one or both of the electrolyte composition and the organic composition. For example, according to one embodiment of the invention, a basic (or standard) electrolyte composition is prepared, and the overall electroplating composition is varied by selectively changing only the components of the organic composition.

The various components of the electrolyte composition and the organic composition are described more completely below both in terms of types, classes, and specific examples of the components of the composition and also amounts and concentrations of the components. Concentrations provided for the individual

components of the electrolyte composition and the organic composition are provided on a basis of the overall volume of the electroplating composition of the invention. Accordingly, while concentrations are provided for each component individually, the concentrations ranges provided should not be viewed as limited to the electrolyte composition specifically or the organic composition specifically. Rather, concentrations provided relate to the overall electroplating composition, including the electrolyte composition components and the organic composition components.

The concentrations provided herein refer to the concentrations of the overall composition at the time of use. As further described herein, the electrolyte composition or the organic composition may be provided in a form wherein the concentration of one or more components is outside the ranges provided herein for the individual components of the electroplating composition. The ability to provide the various components of the inventive composition in concentrations different than disclosed herein should not be viewed, however, as differentiating from the claimed invention. Rather, the concentrations provided herein describe the concentrations of the various components at the time of use of the electroplating composition, and any composition prepared or provided such that the concentrations of the various components would be within the ranges provided herein at the time of use of the electroplating composition would be encompassed by the present invention. The electrolyte composition comprises a zinc ion source and a nickel ion source. As used herein, the term zinc ion source means any material capable of providing free zinc cations when in an aqueous solution. Similarly, the term nickel ion source means any material capable of providing free nickel cations when in solution. The zinc ion source and the nickel ion source preferably include salts of the metals; however, the zinc ion source and the nickel ion source are not limited to such salts. Rather, the sources can be any material providing at least some free zinc ions and nickel ions, such as elemental zinc and elemental nickel. The zinc and nickel sources can further include other metal alloys, zinc- or nickel-containing compounds, and the like. In one preferred embodiment, the zinc ions and the nickel ions are supplied in the form of soluble zinc and nickel salts. Particularly, the zinc ion source and the nickel ion source can be inorganic salts of the metals. Such inorganic salts include, for example, halides, and also include carbon, nitrogen, or sulfur containing salts, such as carbonates, nitrates, and sulfates, as well as hydrates thereof. In one particular

embodiment, the zinc ion source is selected from the group consisting of zinc chloride, zinc sulfate, zinc acetate, zinc carbonate, and zinc sulfamate. In another particular embodiment, the nickel ion source is selected from the group consisting of nickel chloride, nickel sulfate, nickel acetate, nickel carbonate, and nickel sulfamate. In one particularly preferred embodiment, the zinc ion source and the nickel ion source are selected from the chloride and sulfate salts of zinc and nickel.

The zinc ion source and the nickel ion source should each be present in an amount useful for achieving and maintaining a functional concentration of zinc ions and nickel ions (i.e., a concentration sufficient for deposition of a zinc-nickel alloy layer on a substrate during electroplating). Preferably, the electrolyte composition includes zinc ions in an amount of about 15 g/L to about 120 g/L, based upon the overall volume of the electroplating composition of the invention. In further embodiments, the zinc ions are present in an amount of about 25 g/L to about 100 g/L, about 30 g/L to about 80 g/L, or about 40 g/L to about 60 g/L. To achieve and maintain a functional concentration of nickel ions in the electrolyte composition, it is preferable that the nickel ions be present in an amount of about 10 g/L to about 100 g/L, based on the overall volume of the electroplating composition. In further embodiments, the nickel ion source is present in an amount of about 15 g/L to about 80 g/L, about 20 g/L to about 60 g/L, or about 30 g/L to about 40 g/L.

The electrolyte composition according to the invention further comprises a pH buffering agent. Any pH buffering agent commonly recognized as useful in electroplating compositions, particularly zinc and nickel electroplating compositions, can be used according to the invention. For example, carboxylic acids and borates are particularly useful. The pH buffering agent used in the invention is limited only in that it should not be capable of also acting as a complexing agent (i.e., a chelator), and it should not be capable of providing free ammonium ions in aqueous solution. In one preferred embodiment, the pH buffering agent includes boric acid. In another preferred embodiment, the pH buffering agent includes sodium acetate. Further, non- limiting examples of non-complexing buffers useful according to the present invention include phosphoric acid, sodium or potassium dihydrogen phosphate, benzoates, and hydroxybenzoates.

In one embodiment of the invention, multiple buffer agents are provided. Including multiple buffer agents can be particularly useful, particularly in a complex

system, for maintaining a specified pH. Preferentially, the electrolyte composition of the invention has a pH indicating a composition that is at least slightly acidic. The electrolyte composition preferably has a pH that is less than about 7. In certain embodiments, the electrolyte composition has a pH of about 2 to about 7, about 4 to about 6.5, or about 5 to about 6.

In order to maintain a desired pH, it is preferable that the buffering agent used in the electrolyte composition is particularly suited to resisting shifts in pH outside the preferred ranges described above. Accordingly, it is preferable that the buffering agent used in the electrolyte composition has a pKa value of about 4 to about 6.5. In further embodiments, the buffering agent has a pKa of about 4.5 to about 6 or a pKa of about 5 to about 6.

The amount of buffering agent included in the electrolyte composition can vary depending upon the desired pH of the composition, the known pKa value of the buffering agent, and other electroplating process parameters as would be recognized by one of skill in the art. In one particular embodiment of the invention, boric acid and sodium acetate are included in the electrolyte composition as pH buffering agents. According to one embodiment, boric acid is provided in a concentration of about 20 g/L to about 50 g/L, about 25 g/L to about 45 g/L, or about 30 g/L to about 40 g/L, based on the overall volume of the electroplating composition. Further according to one embodiment, sodium acetate is provided in a concentration of about 20 g/L to about 60 g/L, about 25 g/L to about 55 g/L, or about 30 g/L to about 50 g/L.

According to another particular embodiment of the invention, the electrolyte composition further comprises at least one additional inorganic salt. As noted above, the zinc ion source and the nickel ion source can include inorganic salts. Preferably, at least one additional inorganic salt is included in addition to any inorganic salts included as a zinc ion source or a nickel ion source. Such language referring to at least one additional inorganic salt is meant only to distinguish the additional inorganic salt from the zinc salt or nickel salt possibly used as the zinc or nickel ion source, and is not intended to limit the zinc and nickel ion sources to inorganic salts. The additional inorganic salts are particularly included in the electrolyte composition for the function of increasing the conductivity of the overall electroplating composition. Any inorganic salt commonly recognized as useful for increasing conductivity in an electroplating solution can be used according to the invention. Preferentially, the additional inorganic salts are compatible with other salt

components of the electrolyte composition. For example, in one embodiment of the invention, the zinc ion source is zinc chloride and the nickel ion source is nickel chloride hexahydrate. In this embodiment of the invention, it is useful for the additional inorganic salt provided for increasing conductivity of the composition to include a chloride salt, such as sodium chloride or potassium chloride. Further inorganic salts particularly useful include sodium sulfate, potassium sulfate, sodium acetate, methansulfonic acid, and sulfamic acid.

The amount of additional inorganic salts added to the electrolyte composition to increase the conductivity of the composition can vary depending upon the zinc ion source and the nickel ion source used in the composition and can also be affected by further electroplating process parameters. In one embodiment, the additional inorganic salt is provided at a concentration of about 50 g/L to about 500 g/L, based on the overall volume of the electroplating composition. In further embodiments, the additional inorganic salt is provided at a concentration of about 75 g/L to about 450 g/L, about 100 g/L to about 400 g/L, about 125 g/L to about 375 g/L, or about 150 g/L to about 350 g/L.

The electroplating composition of the invention also comprises an organic composition. The inventive composition is particularly useful in that it can be widely varied to provide specific beneficial properties to the coating deposited on the substrate using the composition. Particularly, a single electrolyte composition can be prepared, for example as a stock solution, and the organic composition added to the electrolyte composition can have a variable makeup.

Multiple different types of organic compounds can be used in the organic composition. For example, the organic composition can include compounds commonly used in zinc electroplating systems, such as aromatic carboxylic acids, anionic surfactants, non-ionic surfactants, hydrotropes, and carbonyl compounds, such as ketones and aldehydes. The organic composition can also include compounds commonly used in nickel electroplating systems, particularly compounds generally known as brighteners. Generally, the organic composition of the invention can include compounds commonly classified in the field of electroplating according to a specific function provided by the compounds. For example, the organic composition can include compounds classified as Class I nickel brighteners, Class II nickel brighteners, top brighteners, auxiliary brighteners, carriers, ductilizers, leveling agents, grain refiners,

anti-corrosives, hardeners, and other classes of additives recognizable as useful to one of skill in the art. Such additives are described and exemplified in various texts. See, for example, F.A. Lowenheim, Modern Electroplating (1974), 3 ^rd ed., New York: John Wiley & Sons, Inc., and J.K. Dennis & T.E. Such, Nickel and Chromium Plating (1972), London: Butterworths & Co., both of which are incorporated herein by reference.

According to one particular embodiment of the invention, the organic composition comprises a Class I nickel brightener, a Class II nickel brightener, an aromatic carboxylic acid, an aldehyde or ketone compound, and a surfactant selected from non-ionic and anionic surfactants.

Class I nickel brighteners are typically understood to be aromatic or unsaturated organic compounds that include sulfur, such as sulfmic acids, sulfonic acids, sulfonamides, sulfonimides, sulfimides, and salts thereof. Any compounds generally understood to be Class I nickel brighteners can be used in the organic composition of the invention. In particular, such brighteners can include alkyl naphthalenes, benzene sulfonic acids, benzene disulfonic acids, benzene trisulfonic acids, naphthalene disulfonic acids, naphthalene trisulfonic acids, benzene sulfonamides, naphthalene sulfonamides, benzene sulfonimides, naphthalene sulfonimides, vinyl sulfonamides, allyl sulfonamides, salts thereof, and combinations thereof.

Class I nickel brighteners, as used according to the invention, can be incorporated into the organic composition singly or in suitable combinations. Generally, compounds identified as Class I nickel brighteners are useful for providing the following functions: - provide semi-lustrous deposits or produce grain refinement;

- act as ductilizing agents, particularly when used in combination with other types of organic compounds, such as Class II brighteners;

- control internal stress of deposits, generally by making the stress desirably compressive; - introduce controlled sulfur content into the electroplated layer to desirably affect chemical reactivity, thereby providing increased anti-corrosive action; and

- minimize pitting.

Specific, non-limiting examples of Class I nickel brighteners useful in the organic composition of the invention include: saccharin (and salts thereof, such as sodium saccharin); bis-benzenesulfonylimide; carboxyethyl isothiuronium betaine; 2- thiohydantoin; trisodium 1,3,6-naphthalene trisulfonic acid; trisodium 1,3,7- naphthalene trisulfonic acid; benzene sulfmic acid; sodium styrene sulfonate; p- toluene sulfmic acid; /7-toluene sulfonic acid; ditolylsulfimide; sodium salt of di-o- tolyl disulfimide; sodium salt of dibenzene disulfimide; pyridine-3 -sulfonic add;p- vinylbenzene sulfonic acid; sodium allyl sulfonate; sodium vinyl sulfonate; sodium propargyl sulfonate; sodium benzene monosulfonate; dibenzene sulfonimide; sodium benzene monosulfinate; sodium-3-chloro-2-butene-l -sulfonate; sodium ^-styrene sulfonate; monoallyl sulfamide; diallyl sulfamide; sodium propyne sulfonate; sodium allyl sulfonate; and allyl sulfonamide.

The concentration of the Class I nickel brightener included in the electroplating composition can vary depending upon the particular compound used, as well as the specific desired properties to be provided the zinc-nickel alloy for deposition. According to one embodiment of the invention, the Class I nickel brightener is present at a concentration of about 0.1 g/L to about 5 g/L. In further embodiments, the Class I nickel brightener is present at a concentration of about 0.2 g/L to about 4 g/L, about 0.3 g/L to about 3.5 g/L, or about 0.4 g/L to about 3 g/L. Class II nickel brighteners are generally understood to be unsaturated, organic materials which produce leveling and increase the luster of an electroplated deposit when used in conjunction with a Class I nickel brightener. Typically, Class II nickel brighteners can be used singly or in combination and include derivatives of acetylenic or ethylenic alcohols or amines (and reaction products thereof with epoxides), N- heterocyclics (such as pyridine-based compounds), ethoxylated and propoxylated acetylenic alcohols, coumarins, and compounds containing a carbonitrile (C≡N) group.

Specific, non-limiting examples of Class II nickel brighteners useful in the organic composition of the invention include: dipropoxylated 2-butyne-l,4-diol; 1,4- di-(/?-hydroxyethoxy)-2-butyne; l,4-di-(0-hydroxy-y-chloropropoxy)-2-butyne; 1,4- di-(/?-y-epoxypropoxy)-2-butyne; l,4-di-(2'-hydroxy-4'-oxa-6'-heptenoxy)-2-butyne; N-l,2-dichloropropenyl pyridinium chloride; 2,4,6-trimethyl N-propargyl pyridinium bromide; N-allyl quinaldinium bromide; N-allyl quinolinium bromide; 2-butyne-l,4- diol; propargyl alcohol; N,N-diethyl-2-propyne-amine; dimethyldiallylammonium

chloride; pyridinium-propyl-sulfobetaine; 2-methyl-3-butyn-2-ol; thiodiproprionitrile; hydroxyethyl propynyl ether; ^-hydroxypropyl propynyl ether; bis-(β-hydroxypropyl ether)-2-butyn-l,4-diol; y-propynoxy propyl sulfonic acid; γ-pτopynoxy-β- hydroxypropyl sulfonic acid; l-(j-sulfopropoxy)-2-butyn-4~ol; and 1 ,4-di~(/?~hydroxy- y-sulfonic propoxy)-2-butyne. Particularly useful Class II nickel brighteners in the organic composition of the invention include propargyl alcohol, 2-butyne-l,4-diol, N,N-diethyl-2-propyne-amine, dimethyldiallylammonium chloride, pyridinium- propyl-sulfobetaine, and derivatives thereof.

The concentration of the Class II nickel brightener included in the electroplating composition can vary depending upon the particular compound used, as well as the specific desired properties to be provided the zinc-nickel alloy for deposition. According to one embodiment of the invention, the Class II nickel brightener is present at a concentration of about 0.05 g/L to about 3 g/L. In further embodiments, the Class II nickel brightener may be present at a concentration of about 0.1 g/L to about 2.5 g/L, about 0.15 g/L to about 2 g/L, or about 0.2 g/L to about 1.8 g/L, based on the overall volume of the electroplating composition .

Aromatic carboxylic acids are commonly used in zinc electroplating baths as basic brighteners. Accordingly, any aromatic carboxylic acid (or combination thereof) generally recognized by one of skill in the art as useful in a zinc electroplating bath can be used in the aromatic composition of the present invention.

As used herein, the term aromatic carboxylic acid is also intended to refer to salts and derivatives of aromatic carboxylic acids. Non-limiting examples of aromatic carboxylic acids useful in the organic composition of the invention include benzoic acid, sodium benzoate, salicylic acid, sodium salicylate, niacin, niacinamide, cinnamic acid, phenyl propiolic acid, benzoyl acetic acid, o-coumaric acid, and benzoyl acetic acid ethyl ester. Particularly preferred organic carboxylic acids useful in the organic composition of the invention include sodium benzoate, salicylic acid, niacin, and niacinamide.

The concentration of the aromatic carboxylic acid included in the electroplating composition can vary depending upon the particular compound used, as well as the specific desired properties to be provided the zinc-nickel alloy for deposition. According to one embodiment of the invention, the aromatic carboxylic acid is present at a concentration of about 0.01 g/L to about 3 g/L. According to further embodiments, the aromatic carboxylic acid is present at a concentration of

about 0.02 g/L to about 2.5 g/L, about 0.05 g/L to about 2 g/L, or about 0.1 g/L to about 1.5 g/L, based on the overall volume of the electroplating composition. The organic composition of the invention further includes a carbonyl compound. As used herein, a carbonyl compound is intended to refer to compounds wherein the primary functional group is a carbonyl group. In particular, the carbonyl compounds of the invention are aldehydes and ketones, with particular preference being given to aromatic aldehyde compounds and aromatic ketone compounds. Such aldehyde compounds and ketone compounds are typically used as top brighteners in zinc electroplating systems to improve the specular gloss of the zinc layer deposited on a substrate.

The aldehyde or ketone compound of the organic composition can comprise a single aldehyde component or a single ketone component, or two or more of such compounds. Accordingly, the organic composition can include an aldehyde compound and one or more ketone compounds, or the composition can include a ketone compound and one or more aldehyde compounds. Preferably, the organic composition of the invention includes at least two compounds selected from the group of aldehyde compounds and ketone compounds.

The organic composition of the invention can include any aromatic aldehyde or ketone typically recognized as useful as a zinc brightener, such as aryl aldehydes, aryl ketones, ring-halogenated aryl aldehydes and ketones, heterocyclic aldehydes and ketones, aryl olefinic aldehydes and ketones, aryl olefinic lactone, and carbocyclic olefinic aldehydes and ketones. Non-limiting examples of aldehyde compounds and ketone compounds useful in the organic composition of the invention include: o- anisic aldehyde; jσ-anisic aldehyde; o-chlorobenzaldehyde; />-chlorobenzaldehyde; cinnaldehyde; piperonal, benzylidene acetone; 2,4-dichlorobenzaldehyde; 2,6- dichlorobenzaldehyde; 2-hydroxy-l-naphthaldehyde; furfuryl acetone; thiophene aldehyde; benzal acetone; and^-ionone. In particular, the aldehyde and ketone compounds useful in the organic composition include benzylidene acetone, /7-anisic aldehyde, o-chlorobenzaldehyde, dichlorobenzaldehyde, cinnaldehyde, and piperonal. The concentration of the aldehyde compound or ketone compound included in the electroplating composition can vary depending upon the particular compound used, as well as the specific desired properties to be provided the zinc-nickel alloy for deposition. According to one embodiment of the invention, the total concentration of aldehyde compounds, ketone compound, or combinations thereof, present in the

composition is about 1 mg/L to about 100 mg/L. In further embodiments, the total concentration is about 2 mg/L to about 75 mg/L, about 2.5 mg/L to about 50 mg/L, or about 3 mg/L to about 40 mg/L, based on the overall volume of the electroplating composition. The organic composition of the invention further comprises one or more surfactant selected from the group of non-ionic surfactants and anionic surfactants. Such surfactants are generally useful as brighteners or grain refining agents in zinc electroplating systems. The non-ionic or anionic surfactant used in the organic composition can be present singly or as a combination of surfactants. For example, the composition can include multiple non-ionic surfactants, multiple anionic surfactants, or one or more non-ionic surfactants in combination with one or more anionic surfactants. In one preferred embodiment of the invention, the organic composition includes at least one non-ionic surfactant and at least one anionic surfactant. Examples of non-ionic and anionic surfactants useful according to various embodiments of the invention are described in Lange, Robert K., Surfactants: A

Practical Handbook, Hanser Gardner Publications (1999), which is incorporated herein by reference in its entirety.

Types of non-ionic surfactants useful in the organic composition of the invention include the following: homopolymers of ethylene oxide (such as polyethylene glycols); homopolymers of propylene oxide (such as polypropylene glycols); propylene oxide-ethylene oxide block copolymers (such as ethylene glycol- propylene glycol block copolymers); ethylene oxide condensation products of naphthol and long chain fatty alcohols, long chain fatty amines, long chain fatty acids, and long chain alkyl phenol (wherein the long chain fatty group has 6-30 carbon atoms); alkoxylated alkyl phenols; alkyl naphthols; aliphatic monohydric alcohols; and aliphatic polyhydric alcohols; oxo alcohol ethoxylates; alkylphenol ethoxylates; fatty alcohol ethoxylates; and ^-naphthol ethoxylates.

Specific, non-limiting examples of non-ionic surfactants useful in the organic composition of the invention include the following: nonylphenol (such as the nonylphenol ethoxylate IGEPAL CO-730 ^® available from Stepan Company, and the sodium nonylphenol ethoxylate sulfate WITCOLATE™ D51-53 available from Akzo Nobel) and various polyethylene glycol (PEG) surfactants, such as Carbowax 3350, which is a PEG polymer having an average molecular weight of about 3,350. Additional non-limiting examples of non-ionic surfactants useful in the invention

include ethylene oxide/propylene oxide copolymers with molecular weights between about 2,000 and about 8,000, such as GENAPOL ^® PF20 and GENAPOL ^® PF40 (available from Clariant Corporation).

Various types of anionic surfactants useful in the organic composition of the invention include the following: sodium di-alkylsulfosuccinates, sulfonated or sulfated alkylalkoxylates, alkylphenol sulfonates or sulfates, and naphthalenesulfonic acids or condensation products. Specific, non-limiting, examples of anionic surfactants useful in the organic composition of the invention include sodium diisobutyl sulfosuccinate and sodium dihexyl sulfosuccinate (such as GEMTEX ^® 445 and GEMTEX ^® 680, available from Finetex, Inc.), and the sulfated polyalkoxy naphthyl ether salt Nape 14-90, which is available from Raschig Corporation.

The concentration of the surfactants included in the electroplating composition can vary depending upon the particular compound used, as well as the specific desired properties to be imparted to the zinc-nickel alloy for deposition. According to one embodiment of the invention, the surfactants selected from the group of non-ionic and anionic surfactants are present at a total concentration of about 0.05 g/L to about 10 g/L. In further embodiments, the surfactants are present at a total concentration of about 0.1 g/L to about 8 g/L, about 0.15 g/L to about 6 g/L, or about 0.2 g/L to about 5 g/L, based on the overall volume of the electroplating composition. In certain embodiments, the organic composition of the invention may further comprise one or more compounds recognized as hydrotropes. A hydrotrope is generally understood to be a chemical capable of increasing the aqueous solubility of various slightly soluble organic chemicals. Hydrotropes are particularly useful for increasing the solubility of surfactants, especially non-ionic surfactants. Hydrotropes may be classified as non-surfactant molecules, such as cumene sulfonates, xylene sulfonates, glycol ether sulfates, and ureas, or as surfactant molecules, such as C ₈ -Ci ₀ fatty alcohol sulfates, 2-ethylhexylsulfate, and 2-ethylhexyl-iminodipropionate. While conventional hydrotropes act mainly as solubilizers, surfactant-type hydrotropes are able to form micelles and have good wetting power. Both non- surfactant and surfactant-type hydrotropes may be used according to the invention. In one specific embodiment, the organic composition includes sodium cumene sulfate. Further salts of hydrotrope compounds may also be used in the invention.

The concentration of the hydrotrope compounds included in the electroplating composition can vary depending upon the particular compound used, as well as the

specific desired properties to be imparted to the zinc-nickel alloy for deposition. According to one embodiment of the invention, the one or more hydrotrope compounds are present at a total concentration of about 0.1 g/L to about 1 g/L. In further embodiments, the surfactants are present at a total concentration of about 0.1 g/L to about 0.8 g/L, about 0.2 g/L to about 0.7 g/L, or about 0.3 g/L to about 0.5 g/L, based on the overall volume of the electroplating composition.

As previously noted, the electroplating composition of the invention is particularly beneficial in that it is easily modifiable for particular uses. The electrolyte composition and the organic composition, particularly the organic composition, can be specifically modified to suit particular needs and plating parameters for use in an electroplating method.

The electroplating composition can be prepared batchwise, wherein all components of the electrolyte composition and all components of the organic composition are added at once, thereby forming the electroplating composition. Alternately, the electrolyte composition and the organic composition can be prepared separately and appropriates volumes of the two compositions combined to form the electroplating composition. In one particular embodiment, the electrolyte composition is prepared separately as a stock solution or standard solution. As desired to form an electroplating composition, an appropriate volume of the stock electrolyte composition can be taken for use in preparing the electroplating composition. Such preparation can encompass adding an appropriate volume of a ready prepared organic composition or separately adding the desired components of the organic composition to the separate volume of the electrolyte composition.

In one embodiment, the electrolyte composition comprises nickel chloride, zinc chloride, potassium chloride, hydroboric acid, and sodium acetate. Such an embodiment is particularly useful as a stock composition, as described herein, wherein defined amounts of the stock composition can be combined with a predetermined organic composition to prepare the electroplating composition of the invention. Of course, it is understood that other electrolyte compositions could be similarly prepared and combined with components of the organic composition to prepare an electroplating composition according to the invention.

Various different organic compositions could be prepared according to the invention. In one embodiment, an organic composition comprises sodium saccharin,

bis-benzenesulfonylimide, sodium benzoate, Nape 14-90, Carbowax 3350, dimethyldiallyl-ammonium chloride, and benzylidene acetone. Such a composition could particularly be combined with a predetermined amount of an electrolyte composition according to the invention. In another embodiment, an organic composition according to the invention comprises sodium saccharine, bis-benzenesufonylimide, sodium benzoate, Nape 14- 90, Carbowax 3350, dimethyldiallyl-ammonium chloride, and benzylidene acetone. Such a composition could likewise be combined with a predetermined amount of an electrolyte composition according to the invention. In still another embodiment, an organic composition according to the invention comprises sodium saccharin, bis-benzenesulfonylimide, sodium benzoate, Nape 14-90, Carbowax 3350, dimethyldiallyl-ammonium chloride, benzylidene acetone, chlorobenzaldehyde, and sodium cumene sulfonate. Such a composition could likewise be combined with a predetermined amount of an electrolyte composition according to the invention.

In yet another embodiment, an organic composition according to the invention comprises sodium saccharin, bis-benzenesulfonylimide, sodium benzoate, Nape 14- 90, Carbowax 3350, dimethyldiallyl-ammonium chloride, 2-thiohydantoin, benzylidene acetone, o-chlorobenzaldehyde, and sodium cumene sulfonate. Again, such a composition could be combined with a predetermined amount of an electrolyte composition according to the invention.

Moreover, in another embodiment, an organic composition according to the invention comprises sodium saccharin, bis-benzenesulfonylimide, sodium benzoate, Nape 14-90, Carbowax 3350, dimethyldiallyl-ammonium chloride, Carboxyethyl isothiuronium betaine, benzylidene acetone, o-chlorobenzaldehyde, and sodium cumene sulfonate. As before, such a composition could be combined with a predetermined amount of an electrolyte composition according to the invention.

The present invention further encompasses a method for depositing a zinc- nickel alloy on a substrate by incorporating the electroplating composition as described herein in an electroplating process. In one embodiment, the method comprises immersing the substrate in an electroplating composition according to the above description and applying an electrical current to the immersed substrate for a time sufficient to deposit a layer of zinc-nickel alloy on the substrate.

The method of the invention is particularly useful in that it provides a zinc- nickel alloy layer deposition with a desirable nickel concentration, as well as pleasing aesthetic performance, over a broad range of current densities. Uniform alloy composition independent of current density is highly desirable in the field of zinc- nickel alloy electroplating. In previously known zinc-nickel deposition methods, the nickel content in the deposited alloy increases significantly as the current density applied to the substrate decreases. This is problematic in multiple aspects. A zinc- nickel alloy layer deposited on a substrate can exhibit multiple unfavorable characteristics when the weight percentage of nickel present in the zinc-nickel alloy layer, based on the overall weight of the zinc-nickel alloy layer, is greater than about

16%. In particular, deposited zinc-nickel alloy layers having an average nickel concentration greater than about 16% can exhibit unfavorable properties, such as brittleness and difficulty in accepting subsequent coatings, such as chrome conversion coatings. Furthermore, when the average nickel concentration in the overall deposited zinc-nickel alloy exceeds about 20%, the deposited alloy becomes black in appearance, which is generally undesirable (particularly when a bright, shiny finish is required).

Preferably, the zinc-nickel alloy deposited on the substrate according to the method of the present invention has a weight percent of nickel that is in the range of about 5% to about 15%, based on the overall weight of the deposited zinc-nickel alloy. According to further embodiments, the nickel content of the deposited zinc- nickel alloy is about 6% to about 14%, about 7% to about 13%, or about 8% to about 12%. A deposited zinc-nickel alloy layer applied according to certain embodiments of the invention having a nickel content within these ranges can generally be expected to be bright, lustrous, and ductile, all of which are highly desired properties in zinc- nickel alloy electroplated substrates.

The electroplating method of the invention is particularly useful in that the method can employ current densities across a broad range without adversely affecting the physical or aesthetic properties of the zinc-nickel alloy layer deposited on the substrate. It is therefore possible to deposit a zinc-nickel alloy layer on a substrate such that the average nickel concentration of the overall layer is within a desired range even when the alloy layer is deposited using a variety of current densities. In particular embodiments, the desired average nickel concentration can be achieved

across a current density range of about 0.5 ASF to about 120 ASF, about 2 ASF to about 50 ASF, or about 5 ASF to about 40 ASF.

It is understood that a zinc-nickel alloy layer deposited on a substrate surface will generally have a specific nickel concentration (in terms of the weight of nickel based on the overall weight of the deposited alloy layer), as well as a specific zinc- concentration, that varies somewhat from one discrete point to another discrete point across the overall deposition layer. Average nickel concentration could be experimentally determined by taking specific measurements of nickel concentration at a number of points (preferably a statistically significant number of points) across the overall deposition layer and taking an average of the specific measured nickel concentrations. Generally, it is expected that the average nickel concentration for the overall zinc-nickel alloy layer deposited on the substrate would not differ significantly from the specific nickel concentration at any discrete point across the deposition layer. Accordingly, as used herein, "average nickel concentration" refers to the average nickel concentration across the overall zinc-nickel deposition layer.

The nickel concentration can be measured using various known methods. For example, alloy composition can be evaluated using an X-ray fluorescence spectrophotometer, such as the Fischerscope XDAL spectrophotometer available from Fischer Scientific. X-ray fluorescence spectrophotometers use a spectroscopic technique that is commonly used with solids, in which X-rays are used to excite a sample and generate secondary X-rays as fluorescence, which are sample dependant and element specific. Accordingly, specific components of a coating, such as nickel in a zinc-nickel coating layer, and can be easily quantified and analyzed upon calibration with sample standards and use of applicable computer software. X-ray fluorescence is commonly used in many different types of analytical laboratories and some industrial inspection systems, and X-ray fluorescence spectrometers provide a number of distinct advantages including easy sample preparation and nondestructive rapid multi-element analysis.

As noted above, currently known zinc-nickel alloy deposition methods undesirably allow for changes in the percentage of nickel in the overall deposition layer as a function of the current density. For example, at one current density, a known deposition method may form a zinc-nickel alloy layer having a specific average nickel concentration, but at a lower current density the same deposition method may form a zinc-nickel alloy layer having a much greater average nickel

concentration. Preferred embodiments of the present invention do not suffer from such a limitation. Accordingly, the consistent nickel concentration achieved according to the present invention can be characterized in terms of a maximum deviation between the highest average nickel concentration achieved at a given current density within a range of densities and the lowest average nickel concentration achieved at a given current density within the same range of densities.

The present invention is particularly useful in that, according to certain embodiments, a zinc-nickel layer can be deposited with an average nickel concentration that is substantially unchanged by differences in current density. In other words, if all other deposition conditions remain unchanged, the average nickel concentration of a zinc-nickel layer applied at one specific current density would not be substantially changed if the zinc-nickel layer was applied at a higher or lower current density. Therefore, according to the present invention, it is possible to apply a zinc-nickel layer to a substrate surface such that the average nickel concentration of the applied layer is substantially unchanged even when the current density is varied across a range of densities.

The effect of current density on the average nickel concentration of a deposited zinc-nickel layer can be easily tested. In one testing method, a defined number of identical substrates (for example, a steel plate of defined dimensions) can successively have a zinc-nickel deposition layer applied thereto wherein all deposition conditions are constantly maintained and only current density is changed for each successive substrate. The effect of current density can be determined by measuring the average nickel concentration in the deposition layer for each substrate and calculating the difference between the highest average nickel concentration and the lowest average nickel concentration for the various substrates. The effect of current density on the average nickel concentration in a zinc-nickel deposition layer is further illustrated in the Examples provided below.

As used in relation to the present invention, the average nickel concentration in a deposited zinc-nickel layer is "substantially unchanged" when the difference between the highest average nickel concentration and the lowest average nickel concentration, as determined according to the above method, is less than about 3 percentage points. In other words, the average nickel concentration is "substantially unchanged" when the highest average nickel concentration achieved at one current density within a defined range of densities and the lowest average nickel

concentration achieved at a different current density within the same range of densities (all other deposition conditions remaining constant) differs by less than about 3 percentage points. In further embodiments, "substantially unchanged" can refer to differences between a highest average nickel concentration and a lowest average nickel concentration that is even smaller. For example, the average nickel concentration can be "substantially unchanged" when the difference is less than about 2.5 percentage points, less than about 2 percentage points, or less than about 1.5 percentage points.

In light of the above, it is possible to characterize the present invention in terms of an average nickel concentration range across a current density range. Such a characterization provides a maximum variation in the average nickel concentration of a zinc-nickel deposition layer if the layer was deposited using two or more different current densities while keeping all other deposition conditions constant.

In one embodiment, the invention provides a method for depositing a zinc- nickel layer on a substrate such that the average nickel concentration in the deposited layer varies by less than about 3 percentage points when the current density during the deposition is in the range of about 2 ASF to about 50 ASF. According to further embodiments, the average nickel concentration in the deposited varies by less than about 2.5 percentage points, less than about 2 percentage points, or less than about 1.5 percentage points. According to another embodiment, the invention provides a method for depositing a zinc-nickel layer such that the average nickel concentration in the deposited layer varies by less than about 2.5 percentage points, preferably less than about 2 percentage points and more preferably less than about 1.5 percentage points, when the current density during the deposition is in the range of about 5 ASF to about 40 ASF

In yet further embodiments, the invention provides deposition methods wherein the average nickel concentration remains substantially unchanged across a broader current density range. For example, in one embodiment, invention provides a method for depositing a zinc-nickel layer on a substrate such that the average nickel concentration in the deposited layer varies by less than about 3 percentage points, preferably less than about 2.5 percentage points and more preferably less than about 2 percentage points, when the current density during the deposition is in the range of about 0.5 ASF to about 120 ASF.

The method of the invention is further beneficial in that the concentration of zinc ions and nickel ions in the electroplating composition during the electroplating method can be maintained by using zinc and nickel metal anodes (or zinc-nickel alloy anodes) that oxidize during the electroplating method. The metal anodes oxidize and partially dissolve during the electroplating process, thereby supplying additional zinc ions and nickel ions to the electroplating composition. Further, if necessary, the concentration of zinc ions and nickel ions in the electroplating composition can be adjusted during the electroplating method by addition of further amounts of the zinc ion source and the nickel ion source, as described above. The pH of the electroplating composition, as noted previously, is controlled through incorporation of appropriate pH buffering agents in the electrolyte composition. Such buffering agents are preferably suitable for maintaining the preferred pH throughout the electroplating method. The temperature of the electroplating composition is preferably controlled throughout the electroplating method to be within a range of about 85 ⁰ F (29.4 ⁰ C) to about 120 ⁰ F (48.9 ⁰ C), more preferably in the range of about 90 ⁰ F (32.2 ⁰ C) to about 110 ⁰ F (49.3 ⁰ C), most preferably about 95 ⁰ F (35 ⁰ C) to about 105 ⁰ F (40.6 ⁰ C).

EXAMPLES Various zinc-nickel alloy electroplating compositions were evaluated to determine the effect of various organic compositions in combination with a standard electrolyte composition according to the invention to deposit a zinc-nickel alloy layer on a substrate. The various compositions were evaluated in terms of the physical appearance of the zinc-nickel alloy layer deposited on the substrate and the average concentration of nickel in the deposited layer when the deposition is performed at various specific current densities.

Electroplating was conducted in a standard thermostat-controlled 267 ml Hull cell with zinc and nickel anodes. The zinc anodes were pretreated in a solution for 24 hours prior to use, the solution containing 55 g/L nickel chloride and 255 g/L ammonium chloride. The pretreatment step is useful in that the zinc anodes will spontaneously form a nickel coating in the plating bath. Pre-forming the coating prior to use of the anode in the electroplating bath is beneficial in that it provides an improved appearance of the deposition layer applied to the substrate. Steel panels e

used as the cathodes for the cell. The steel panels were treated in 50% hydrochloric acid prior to electroplating evaluations.

During electroplating, cell current was applied at a range of 1-2 Amperes for a time of 5 minutes, and cell temperature was 100 ⁰ F, +/- 5 ⁰ F (37.8 ⁰ C, +/- 2.8 ⁰ C). Cell pH was adjusted to a range of 5.5 to 5.7 using an acid or base, such as hydrochloric acid or sodium or potassium hydroxide.

The various electroplating compositions used in the evaluation are provided in Table 2 below. For each electroplating composition, the zinc-nickel alloy layer applied to the substrate was evaluated for appearance and was also evaluated for alloy composition using a Fischerscope XDAL X-ray fluorescence spectrophotometer at 5, 10, 20, and 40 Amperes/ft ² (ASF).

The electrolyte composition used in each electroplating composition evaluated was constant and is provided below in Table 1. Concentration is provided in relation to the total volume of the overall composition.

Table 1

Electrolyte Component Concentration (g/L)

NiCl ₂ ^• 6H ₂ O 140

ZnCl ₂ 115

KCl 245

H ₃ BO ₃ 40

CH ₃ CO ₂ Na 40

Only the electrolyte composition was present in the electroplating composition evaluated in Example 1. In Examples 2-18, however, varying organic compositions were also included in the electroplating composition for evaluation. The evaluations of the coatings applied using the various electroplating compositions are provided below.

Table 2

* New Era Wetter is a surface tension reducing agent available commercially from Pavco, Inc.

As can be seen from Table 2 above, preferred embodiments according to the invention are particularly useful for deposition of a zinc-nickel alloy with a consistent percentage nickel in a preferred range, even across a broad current density. Preferred embodiments are shown in Examples 16-20. As can be seen in these examples, the concentration of nickel in the deposited zinc-nickel alloy varies across the four current densities tested by less than 2 percentage points (e.g., in Example 17, the highest nickel concentration was 11.1%, while the lowest nickel percentage was 9.8% - a difference of only 1.3 percentage points). A particularly preferred composition according to the invention is provided in Example 18. Examples 1-15 are provided as comparative formulations that are less effective at providing high quality deposition coatings, such as seen with the compositions according to the invention. Example 1 ,

particularly, is provided as a baseline comparative of results achieved using an electrolyte composition alone.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.