BR112015001113B1 - method of forming a black autocatalytic nickel coating of a substrate - Google Patents

Abstract

AQUEOUS AUTOCATALYTIC NICKEL GALVANIZING BATH FOR THE FORMATION OF AUTOCATALYTIC NICKEL COATINGS, METHOD OF FORMATION OF A BLACK AUTOCATALYTIC NICKEL COATING ON A SUBSTRATE. An aqueous autocatalytic nickel plating bath for forming autocatalytic nickel coatings includes nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, a chelating agent, or a pH buffer , and is free of a sulfur compound.

Description

RELATED ORDER

[0001] This application claims priority benefit to Provisional Patent Application No. US 61/672,584, filed July 17, 2012, whose inventive subject matter is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] This application concerns autocatalytic nickel coatings, methods for forming the autocatalytic nickel coating, and autocatalytic nickel baths for forming the autocatalytic nickel coatings.

FUNDAMENTALS OF THE INVENTION

[0003] Autocatalytic nickel plating is a widely used plating process, which provides a continuous deposit of a nickel metal or nickel/alloy coating on metallic or non-metallic substrates without the need for an external electrical galvanizing current. Autocatalytic galvanizing has been described as a controlled autocatalytic chemical reduction process to deposit metals. The process involves a continuous build-up of a nickel coating on a substrate by immersing the substrate in a nickel plating bath under suitable autocatalytic plating conditions. Galvanizing baths generally comprise an autocatalytic nickel salt and a reducing agent. Some autocatalytic nickel baths use hypophosphite ions as a reducing agent, and during the process, the hypophosphite ions are oxidized to orthophosphite ions, and the nickel cations in the plating bath are reduced to form a phosphorous nickel alloy as a deposit on the surface of the desired substrate. As the reaction proceeds, the level of orthophosphite ions in the bath increases, and orthophosphite ions are often precipitated from the plating solutions as insoluble metal orthophosphites. Typically, the source of nickel ions in the autocatalytic plating baths described in the prior art included nickel chloride, nickel sulfate, nickel bromide, nickel fluoroborate, nickel sulfonate, nickel sulfamate, and nickel alkylsulfonates.

[0004] In order to have a continuous and consistent autocatalytic plating process, the reagents must be replenished. The frequency with which additions of reagents are made to the bath depends on how much the concentrations of the reagent species are allowed to vary from their ideal concentrations without negatively affecting the plating process, or simultaneously the deposit. The autocatalytic plating reaction not only yields a nickel alloy deposit, it also generates by-products which build up in solution. As the concentration of by-products increases, their influence on the plating reaction also increases.

[0005] Autocatalytic nickel-phosphorus coatings can be chemically treated, eg corroded, to produce black coatings (Ni-P black). These black autocatalytic nickel coatings can act as efficient absorbers and can be used as very low reflectance coatings on optical instruments and sensors. Chemical corrosion of autocatalytic nickel-phosphorus coatings typically involves acid corrosion of low phosphorus (1-3% phosphorus) or medium-low phosphorus (3-6% phosphorus) nickel-phosphorus alloys. Higher phosphorus content alloys are not suitable because they are too resistant to corrosion to blacken as a result of acid corrosion. ABSTRACT

[0006] An embodiment described in this document concerns an aqueous autocatalytic nickel plating bath for the formation of autocatalytic nickel coatings. The aqueous autocatalytic nickel plating bath can include nickel, a hypophosphorous reducing agent, zinc, at least one of a complexing agent, a chelating agent, and/or pH buffer, and a bismuth stabilizer in which the bath is free. of a sulfur compound.

[0007] In some embodiments, the hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and combinations thereof.

[0008] In other embodiments, the at least one pH buffer, complexing agent or chelating agent may be selected from the group consisting of acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylenediaminetetraacetic acid (EDTA), and combinations thereof. In some embodiments, mixtures of two or more of the above pH buffers, complexing agents and/or chelating agents can be used in the autocatalytic nickel plating bath described herein.

[0009] In still other embodiments, nickel can be provided in the bath in the form of a water-soluble nickel salt. The nickel salt can be selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, a nickel hypophosphite and combinations thereof.

[00010] In other embodiments, the pH of the autocatalytic nickel plating bath can be maintained at about 4.5 to about 5.0, and the bath temperature can be maintained at about 175°F (approximately 79.4°C) at about 200°F (approximately 93.3°C) during galvanizing.

[00011] In still other embodiments, the autocatalytic nickel plating bath may include about 2 g/l to about 10 g/l of nickel, about 20 g/l to about 35 g/l of a hypophosphorous reducing agent , about 1 g/l to about 75 g/l each of the complexing agent, chelating agent, and/or pH buffer, about 40 ppm to about 120 ppm zinc, and about 5 ppm to about 30 ppm of a bismuth stabilizer.

[00012] In still other embodiments, the autocatalytic nickel plating bath can include lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc and ethylenediaminetetraacetic acid (EDTA).

[00013] Autocatalytic nickel plating bath can be used to form a deposit or coating of autocatalytic nickel on the surface of a substrate by contacting or immersing a substrate surface in the bath. The pH of the autocatalytic nickel plating bath can be maintained at about 4.5 to about 5.0, and the bath temperature can be maintained at about 175°F (approximately 79.4°C) to about 200°F ( approximately 93.3°C) during autocatalytic nickel plating of the substrate. The deposit or coating can have a phosphorus content from about 8% to about 11%.

[00014] In some embodiments, the autocatalytic nickel coating may be a top coating that is electroplated onto a medium phosphorus (e.g., about 7% to about 9% phosphorus) autocatalytic nickel subcoat or one of high phosphorus content (about 9% to about 13% phosphorus) to form a deposit or duplex or multilayer coating.

[00015] In some embodiments, the deposit or duplex or multilayer coating may then be etched with a corrosive agent to provide the coated substrate with a black surface. The corrosive agent can include an iron blackening agent and an acid. In some embodiments, the corrosive agent can include ferric sulfate and hydrochloric acid.

[00016] In other embodiments, the deposit or duplex or multilayer coating may be contacted with an autocatalytic copper plating bath to provide an autocatalytic copper coating over the duplex or multilayer coating.

[00017] Other modalities described in this document relate to a method to prepare a multilayer black autocatalytic nickel coating on a substrate. The method includes contacting the substrate with a first autocatalytic nickel plating bath to form a first autocatalytic nickel coating on the substrate. The substrate is then contacted with a second autocatalytic nickel plating bath to form a second autocatalytic nickel coating on top of the first autocatalytic coating. The second autocatalytic nickel plating bath may be different from the first autocatalytic nickel plating bath and may include nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, chelating agent, or pH buffer. The second autocatalytic nickel plating bath is free of a sulfur compound. The second autocatalytic nickel coating is then etched with an etching agent to provide the coated substrate with a black surface.

[00018] In some embodiments, the first autocatalytic nickel coating may have a phosphorus content from about 7% to about 13% by weight. In other embodiments, the second autocatalytic nickel coating can have a phosphorus content of from about 8% to about 11%.

[00019] In some embodiments, the first autocatalytic nickel plating bath may include nickel, a hypophosphorous reducing agent, at least one of a complexing agent, chelating agent, or pH buffer.

[00020] In other embodiments, the at least one pH buffer, complexing agent or chelating agent of the second autocatalytic nickel plating bath can be selected from the group consisting of an acetic acid, formic acid, succinic acid, malonic acid , an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylenediaminetetraacetic acid (EDTA), and combinations thereof. In some embodiments, mixtures of two or more of the above pH buffers, complexing agents and/or chelating agents can be used in the second autocatalytic nickel plating bath described herein.

[00021] In still other embodiments, nickel can be provided in the second autocatalytic galvanizing bath in the form of a water-soluble nickel salt. The nickel salt can be selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, a nickel hypophosphite and combinations thereof.

[00022] In other embodiments, the pH of the second autocatalytic nickel plating bath can be maintained at about 4.5 to about 5.0, and the bath temperature can be maintained at about 175°F (approximately 79.4°C ) at about 200°F (approximately 93.3°C) during autocatalytic nickel plating with the second autocatalytic plating bath.

BRIEF DESCRIPTION OF THE FIGURES

[00023] Fig. 1 illustrates a flow diagram showing a black autocatalytic nickel plating process in accordance with a modality.

[00024] Fig. 2 illustrates a flow diagram showing an autocatalytic copper-nickel plating process in accordance with another modality

[00025] Fig. 3 illustrates a graph comparing metal turnover (MTO) deposition rates of autocatalytic nickel coatings formed using an autocatalytic nickel plating bath in accordance with an order modality and using an autocatalytic nickel plating bath commercially available.

[00026] Fig. 4 illustrates a graph showing the percent phosphorus content by metal turnover (MTO) of autocatalytic nickel deposits formed using an autocatalytic nickel plating bath in accordance with an order modality.

[00027] Fig. 5 illustrates a photograph comparing black autocatalytic nickel coatings subjected to neutral salt spray formed using an autocatalytic nickel plating bath in accordance with an application modality and using a commercially available autocatalytic nickel plating bath.

[00028] Fig. 6 illustrates a photograph showing an autocatalytic copper-nickel multilayer coating prepared in accordance with a modality.

[00029] Fig. 7 illustrates a photograph comparing several autocatalytic nickel deposits coated with an autocatalytic copper coating.

DETAILED DESCRIPTION

[00030] In the specification and claims, which follow, reference will be made to a number of terms, which must be defined to have the following meanings.

[00031] The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

[00032] “Optional” or “optionally” means that the event or circumstance described (a) subsequently may or may not occur, and that the description includes cases where the event occurs and cases where it does not.

[00033] As used herein, the term "solvent" may refer to a single solvent or a mixture of solvents.

[00034] It is also understood that terms such as "superior", "inferior", "exterior", "interior", and the like, are words of convenience and should not be construed as limiting terms. Furthermore, whenever a particular feature of the invention is said to comprise or consist of at least one of a number of elements of a group and their combinations, it is understood that the feature may comprise or consist of any of the elements of the group, either individually or in combination with any of the other elements of said group.

[00035] Approximation language, as used herein throughout the specification and claims, can be applied to modify any quantitative representation that may permissibly vary without resulting in a change in the basic function to which it is related. Therefore, a value modified by one or more terms, such as “about” is not to be limited to the precise value specified. In some cases, the language of approximation can match the accuracy of an instrument to measure value.

[00036] Modalities described in this document relate to autocatalytic nickel plating baths used to form autocatalytic nickel coatings on a substrate, methods of forming multilayer autocatalytic nickel coatings on a substrate, and methods of forming black autocatalytic nickel coatings .

[00037] The autocatalytic nickel plating bath used to form autocatalytic nickel coatings, multilayer autocatalytic nickel coatings, and/or black autocatalytic nickel coatings described in this document is free of sulfur compounds, such as organic sulfur compounds, and can form a sulfur-free autocatalytic nickel coating, which can be uniformly corroded or blackened to provide a black autocatalytic nickel coating. The autocatalytic nickel plating bath replaces sulfur compounds, which have typically been employed in solutions to form black autocatalytic nickel coatings, with metal-containing compounds such as zinc and bismuth. Replacing sulfur compounds with the metal-containing compound allows for improvements in operability, stability and uniformity over current methods of black autocatalytic nickel plating.

[00038] Sulfur-containing autocatalytic nickel plating baths used to form black autocatalytic nickel coatings require the addition of spent components (eg nickel) at precise times (eg additions made at least 5-10 minutes of plating to ensure sulfur codeposition) in order to obtain a repeatable coloring effect. If time is not accurate, the resulting effect will change the black tint to the point of possibly not producing the desired color. In order to obtain a repeatable coloring effect. If time is not accurate, the resulting effect will change the black tint to the point of possibly not producing the desired color. The proposed compositions, baths and methods do not require such addition, other than the usual addition to replenish used components, in accordance with the normal operation of an autocatalytic nickel plating bath.

[00039] Autocatalytic nickel plating baths having a sulfur-based chemistry also rely on the codeposition of sulfur directly into the autocatalytic nickel deposit. The result is often an uneven distribution of sulfur across the substrate surface, resulting in a non-uniform interspersed coloration. The autocatalytic nickel plating baths described in this document do not rely on the presence of sulfur for codeposition and instead rely on the available bismuth concentration to allow the autocatalytic nickel plating deposit to blacken when exposed to a corrosion solution. The presence of organic sulfur compounds can cause the sulfur compound to decompose on cathode surfaces forming very small nickel sulfide particles, which in turn negatively affect the ductility, internal stress, electrical conductivity and corrosion resistance of the deposit. The breakdown of organic compounds into sulfur can result in by-products that accumulate within the autocatalytic nickel plating bath, which interferes with sulfur deposition. This limits the bath's potential age to 2 metal turnovers (MTOs) before problems start to arise. Sulfur-free or non-sulphur-containing autocatalytic nickel plating baths have no such limitation, and can be galvanized for at least 4 MTOs. During this time, there is no loss of uniformity or depth of color of the autocatalytic nickel deposit composition formed on an autocatalytic nickel plating bath substrate.

[00040] Advantageously the inclusion of zinc in the autocatalytic nickel plating bath causes the autocatalytic nickel deposit to be formed with an increased phosphorus content. Autocatalytic nickel plating baths that include zinc may galvanize at a slower rate. Galvanizing at a slower rate causes a black autocatalytic nickel deposit to be formed with an increased overall phosphorus content (eg at least a 5% increase) compared to autocatalytic nickel deposits formed using black autocatalytic nickel chemistry. typical sulfur base, which contains on average 1-5% phosphorus. Black autocatalytic nickel deposits with an increased phosphorus content prepared using the sulfur-free autocatalytic nickel plating baths described in this document are more resistant to corrosion than autocatalytic nickel deposits from other available sulfur-based chemistry.

[00041] In some embodiments, the autocatalytic nickel plating bath used to form the autocatalytic nickel coating, multilayer coating, or black coating is free of a sulfur compound and may include an aqueous solution of nickel, a hypophosphorous reducing agent , zinc, at least one of a complexing agent, a chelating agent, and/or pH buffer, and a bismuth stabilizer.

[00042] Nickel can be provided in the bath in the form of a water-soluble nickel salt. Water-soluble nickel salts can include those which are soluble in the plating bath and which can yield an aqueous solution of a predetermined concentration. The nickel salt can be selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate, a nickel hypophosphite and combinations thereof. Water-soluble nickel salts can be used alone or as a mixture.

[00043] In some embodiments, the nickel concentration in the autocatalytic nickel plating bath can be from about 1 g/L to 70 g/L. In other embodiments, the nickel concentration in the autocatalytic nickel plating bath can be from about 4 g/l to about 6 g/l. Autocatalytic nickel coatings formed from sulfur-free autocatalytic nickel baths that include about 4 g/l showed decreased blackness; while autocatalytic nickel coatings formed from 8 g/l sulfur free autocatalytic nickel baths showed no increase in the resulting black deposit.

[00044] The hypophosphorus reducing agent used in the bath can include any of a variety of hypophosphorus reducing agents used in known types of autocatalytic nickel plating baths. In some embodiments, the hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite, and combinations thereof.

[00045] The concentration of the hypophosphorous reducing agent in the autocatalytic nickel plating may differ with different types of hypophosphorous reducing agent and can be adjusted to vary the phosphorus concentration in the autocatalytic nickel coating that is formed using the bath. In some embodiments, the concentration of hypophosphorous reducing agent in the autocatalytic nickel plating bath can be from about 15 g/l to about 40 g/l. In other embodiments, the concentration of hypophosphorous reducing agent in the autocatalytic nickel plating bath can be from about 20 to about 35 g/L. A decrease in the concentration of hypophosphorous reducing agent from about 30 g/l to about 25 g/l can result in a decrease in phosphorus in the thus formed autocatalytic nickel coating by 2%. This decrease in phosphorus content can result in a deeper black being produced over the blackening of the coating.

[00046] Zinc or zinc ions can be incorporated into the autocatalytic nickel plating bath by introducing a zinc compound into the bath. Examples of the zinc compound are zinc carbonate, zinc oxide, zinc chloride, zinc benzoate, zinc nitrate, zinc phosphate, zinc stearate, and zinc salicylate.

[00047] In some embodiments, the zinc concentration in the autocatalytic nickel plating bath can be from about 40 ppm to about 120 ppm. A zinc concentration in the autocatalytic nickel plating bath below 40 ppm can result in a loss of color from the autocatalytic nickel coating formed from the bath. A zinc concentration in the autocatalytic nickel plating bath above 100 ppm did not negatively affect the color of the autocatalytic nickel coating formed from the bath, but the plating rate decreased substantially.

[00048] The bismuth stabilizer can be incorporated into the autocatalytic nickel plating bath by introducing a bismuth salt to the bath, such as bismuth trichloride or bismuth nitrate. The concentration of bismuth stabilizer in the autocatalytic nickel plating bath can be from about 5 ppm to about 30 ppm. The higher the concentration of bismuth stabilizer provided in the autocatalytic nickel plating bath, the deeper the black color that can be produced from an autocatalytic nickel coating formed from the bath. At bismuth stabilizer concentration above about 30 ppm, the bath can become over-stabilized and further plating is inhibited.

[00049] In some embodiments, a complexing agent or a mixture of complexing agents may/may be included(s) in the autocatalytic nickel plating bath. Complexing agents as used in this document may also include chelating agents. Complexing agents and/or chelating agents generally retard the precipitation of nickel ions from the plating solution in the form of insoluble salts, such as phosphites, by forming a more stable nickel complex with nickel ions and providing a moderate rate of nickel precipitation reaction.

[00050] Complexing agents and/or chelating agents can be included in the plating bath in amounts sufficient to complex the nickel ions present in the bath and to further solubilize the hypophosphite degradation products formed during the plating process. Generally complexing agents and/or chelating agents are employed in amounts of up to about 200 g/l with amounts from about 1 to about 75 g/l being more typical. In other embodiments, complexing agents and/or chelating agents are provided in the autocatalytic nickel plating bath in amounts of from about 20 to about 40 g/l.

[00051] A variety of complexing agents, used in autocatalytic nickel plating solutions, can be used. Specific examples of complexing agents may include monocarboxylic acids such as glycolic acid, lactic acid, gluconic acid or propionic acid, dicarboxylic acids such as malic acid, malonic acid, succinic acid, tartaric acid, oxalic acid or adipic acid, aminocarboxylic acids, such as glycine or alanine, ethylenediamine derivatives such as ethylenediamine tetraacetate, versenol (N,N',N'-triacetic acid N,N',N'-hydroxyethyl) or quadrol (N,N,N',N'-tetrahydroxyethyl acid ethylene diamine), phosphonic acids, such as 1-hydroxyethane-1,1-diphosphonic acid, ethylenediamine tetramethylene phosphonic acid and their water-soluble salts. Complexing agents can be used either alone or in combination.

[00052] Some complexing agents, such as acetic or succinic acid, for example, can also act as a pH buffering agent, and the appropriate concentration of such additive components can be optimized for any plating bath after consideration of its dual functionality.

[00053] In some embodiments, at least one pH buffer, complexing agent, or chelating agent may be selected from the group consisting of an acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid , malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylenediaminetetraacetic acid (EDTA), and combinations thereof. In some embodiments, mixtures of two or more of the above pH buffers, complexing agents and/or chelating agents can be used in the autocatalytic nickel plating bath described herein, with each pH buffer, complexing agent and/or chelating agent being provided at a concentration of from about 1 to about 75 g/l.

[00054] The galvanizing bath can also contain, in addition to the above components, additives with various types of purposes, provided that the properties of the galvanizing bath are not deteriorated.

[00055] Aqueous autocatalytic nickel plating baths can be operated or maintained at a pH of about 4.5 to about 5.0 during autocatalytic nickel plating of the substrate. With this pH range, the reduction reaction by the hypophosphorous reducing agent is allowed to occur efficiently to prevent decomposition of the hypophosphorous reducing agent as well as to prevent the precipitation performance for plating from being deteriorated and to prevent the plating bath from being decomposed. Furthermore, with this pH range, it is possible to prevent the plating bath from being reduced with respect to stability as a result of the excessively high reduction potential of the reducing agent.

[00056] At least one pH adjusting agent can be used to adjust the pH to the above range. When the pH of the bath is too high, it can be adjusted by adding, for example, an acid. When the pH of the bath is too low, it can be adjusted by adding, for example, ammonium hydroxide.

[00057] The stability of the operating pH of the galvanizing bath can be controlled by adding various buffer compounds, such as acetic acid, propionic acid, boric acid, or the like, in amounts up to about 30 g/l with amounts of a from about 2 to about 30 g/l being typical. As noted above, some of the buffer compounds such as acetic acid and succinic acid can also function as complexing agents.

[00058] In accordance with the methods described in this document, a substrate can be electroplated with the autocatalytic nickel plating bath to provide a deposit or coating of autocatalytic nickel on the substrate. The substrate can be any substrate capable of supporting the autocatalytic nickel coating, but is typically a material for which the autocatalytic nickel coating exhibits sufficient affinity to form a stable coating thereon. The substrates can be inorganic materials such as metals or organic materials such as plastics or composite materials, for example organic polymers comprising inorganic filler material. In one embodiment, the substrate is a metal substrate. Non-limiting examples of metallic substrates include iron, chromium, nickel, cobalt, copper, aluminum, titanium, and the like. In another embodiment, the substrate comprises steel. In one embodiment, the substrate comprises low alloy steel, for example low alloy carbon steel.

[00059] The substrate can be galvanized by contacting the substrate with or immersing the substrate in the plating bath for an effective duration time to form an autocatalytic nickel coating or deposit on a desirable surface of the substrate. In some embodiments, the substrate can be cleaned or pre-processed prior to plating. During galvanizing, the bath can be maintained at a bath temperature of from about 175°F (approximately 79.4°C) to about 200°F (approximately 93.3°C). The duration of contact of the autocatalytic nickel plating bath with the substrate being plated will determine the thickness of the autocatalytic nickel coating. Typically, contact time can range from as little as about a minute to several hours or even several days.

[00060] During deposition of the deposit or coating of autocatalytic nickel, moderate agitation may be employed. Moderate agitation can be, for example, moderate air agitation, mechanical agitation, bath circulation by pumping, rotation of a barrel for barrel galvanizing, etc. The autocatalytic nickel plating bath can also undergo periodic or continuous filtration treatment to reduce the level of contaminants inside. Replacement of bath constituents can also be carried out, in some embodiments, on a periodic or continuous basis to maintain the concentration of constituents, and in particular the concentration of nickel ions and hypophosphite ions, as well as the pH level within limits. desired.

[00061] The autocatalytic nickel coated substrate thus formed can be removed from the autocatalytic nickel plating bath and rinsed, for example, with deionized water.

[00062] The autocatalytic nickel coating formed on a substrate surface using the autocatalytic nickel plating bath can have a relatively uniform thickness. In one embodiment, the autocatalytic nickel coating can have an average thickness in a range from about 1 micron to about 250 microns. In another embodiment, the autocatalytic nickel coating can have an average thickness in a range from about 1 micron to about 100 microns. In yet another embodiment, the autocatalytic nickel coating can have an average thickness in a range from about 1 micron to about 10 microns. The autocatalytic nickel coating can also have a phosphorus content of from about 8% to about 11%.

[00063] In some embodiments, the autocatalytic nickel coating may be a top coating that is electroplated onto a medium phosphorus (e.g., about 7% to about 9% phosphorus) autocatalytic nickel subcoat or one of high phosphorus content (about 9% to about 13% phosphorus) to form a duplex or multilayer autocatalytic nickel deposit or coating. The duplex or multilayer autocatalytic nickel coating may advantageously be blackened to form a black autocatalytic nickel coating.

[00064] Fig. 1 illustrates a flow diagram showing a method 10 of preparing a black autocatalytic nickel coating on a substrate. In method 10, in step 12 a substrate may be contacted with a first autocatalytic nickel plating bath, for example, by dipping the substrate into the first autocatalytic nickel plating bath to form a first autocatalytic nickel coating on the substrate . The first autocatalytic nickel plating bath can include nickel, a hypophosphorous reducing agent, at least one of a complexing agent, chelating agent, or pH buffer, and optionally a sulfur compound such as thiosulfates, thionic acid , or thiourea to provide a medium phosphorus or a high phosphorus subcoat

[00065] An example of an autocatalytic nickel plating bath that can be used to produce a high phosphorus autocatalytic nickel coating may include about 6 g/l nickel, about 36 g/l sodium hypophosphite, about 20 g/l malic acid, about 15 g/l lactic acid, about 5 g/l succinic acid, and about 0.4 ppm lead.

[00066] An example of an autocatalytic nickel plating bath that can be used to produce an autocatalytic nickel coating of medium phosphorus content may include about 6 g/l nickel, about 30 g/l sodium hypophosphite, about 12 g/l malic acid, about 18 g/l lactic acid, about 14 g/l acetic acid, 1.0 ppm thiourea, and about 1.0 ppm lead.

[00067] The autocatalytic nickel coating formed on a substrate surface using the first autocatalytic nickel plating bath can have a relatively uniform thickness. In one embodiment, the autocatalytic nickel subcoat can have an average thickness in a range from about 5 microns to about 250 microns, or about 5 microns to about 100 microns. In some embodiments, the thickness of the autocatalytic nickel undercoat may be at least twice, three times, four times, or five times greater than the thickness of the top coat. In yet another embodiment, the autocatalytic nickel subcoat can have an average thickness in a range from about 5 microns to about 15 microns. The autocatalytic nickel coating can also have a phosphorus content from about 7% to about 13%.

[00068] After the formation of the first autocatalytic nickel subcoat on the substrate surface, in step 14, the coated substrate can be removed from the first autocatalytic nickel plating bath, optionally rinsed, and then brought into contact with the second bath of autocatalytic nickel plating to form a second autocatalytic nickel coating on top of the first autocatalytic coating. The coated substrate can be contacted with the second autocatalytic nickel plating bath, for example, by dipping the coated substrate into the second autocatalytic nickel plating bath for an effective duration time to form the second autocatalytic nickel coating or top coating.

[00069] The second autocatalytic nickel plating bath may be different from the first autocatalytic nickel plating bath and be formulated in such a way that it is free of a sulfur compound as described above. In some embodiments, the second autocatalytic nickel plating bath includes nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, chelating agent, or pH buffer, and is free of a sulfur compound. In other embodiments, the autocatalytic nickel plating bath can include lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc, and ethylenediaminetetraacetic acid. In still other embodiments, the autocatalytic nickel plating bath can include about 2 g/l to about 10 g/l nickel, about 20 g/l to about 35 g/l of a hypophosphorous reducing agent, about 1 g/l to about 75 g/l each of complexing agent, chelating agent, and/or pH buffer, about 40 ppm to about 120 ppm zinc, and about 5 ppm to about 30 ppm of a stabilizer of bismuth.

[00070] The second autocatalytic nickel coating formed on the first autocatalytic nickel coating using the second autocatalytic nickel plating bath can be of relatively uniform thickness and of an average thickness in a range from about 1 micron to about 100 microns. In some embodiments, the average thickness may be less than the thickness of the first autocatalytic nickel coating and range from about 1 micron to about 10 microns. The second autocatalytic nickel coating can also have a phosphorus content of from about 8% to about 11%.

[00071] After the formation of the second autocatalytic nickel top coating over the first autocatalytic nickel coating, in step 16, the multilayer or duplex coated substrate can be removed from the second autocatalytic nickel plating bath, optionally rinsed, and then corroded with a corrosive agent to provide the coated substrate with a black surface. The corrosive agent can include an aqueous solution of an iron blackening agent and an acid. In some embodiments, the corrosive agent can include an aqueous solution of ferric sulfate and hydrochloric acid. In still other embodiments, the corrosive agent can include ferric sulfate, hydrochloric acid, and reaction enhancer such as potassium iodate. The temperature of the corroding agent can be from about 70°F (approximately 21°C) to 90°F (approximately 32°C) and the coated substrate can be immersed in the corroding agent for an effective duration time to blacken the coating, for example, for about 1 minute to about 3 minutes.

[00072] In removing the black autocatalytic nickel coated substrate from the corroding agent, the substrate can be rinsed and dried. The black autocatalytic coating thus formed has a consistently uniform deposit of black autocatalytic nickel with a uniform thickness and black coloration, which is not streaked.

[00073] In other embodiments, the duplex or multilayer autocatalytic nickel coating can advantageously be additionally galvanized with another material to modify the coating. Fig. 2 illustrates a flow diagram showing a method 20 of preparing an autocatalytic copper-nickel coating on a substrate. In method 20, in step 22 a substrate may be contacted with a first autocatalytic nickel plating bath, for example, by dipping the substrate into the first autocatalytic nickel plating bath to form a first autocatalytic nickel coating on the substrate . The first autocatalytic nickel plating bath can include nickel, a hypophosphorous reducing agent, at least one of a complexing agent, chelating agent, or pH buffer, and optionally a sulfur compound such as thiosulfates, thionic acid , or thiourea to provide a medium phosphorus or a high phosphorus subcoat

[00074] The autocatalytic nickel coating formed on a substrate surface using the first autocatalytic nickel plating bath can have a relatively uniform thickness. In one embodiment, the autocatalytic nickel subcoat can have an average thickness in a range from about 5 microns to about 250 microns, or about 5 microns to about 100 microns. In some embodiments, the thickness of the autocatalytic nickel undercoat may be at least twice, three times, four times, or more times greater than the thickness of the top coat. In yet another embodiment, the autocatalytic nickel subcoat can have an average thickness in a range from about 5 microns to about 15 microns. The autocatalytic nickel coating can also have a phosphorus content from about 7% to about 13%.

[00075] After the formation of the first autocatalytic nickel subcoat on the substrate surface, in step 24, the coated substrate can be removed from the first autocatalytic nickel plating bath, optionally rinsed, and then brought into contact with the second bath of autocatalytic nickel plating to form a second autocatalytic nickel coating on top of the first autocatalytic coating. The coated substrate can be contacted with the second autocatalytic nickel plating bath, for example, by dipping the coated substrate into the second autocatalytic nickel plating bath for an effective duration time to form the second autocatalytic nickel coating or top coating.

[00076] The second autocatalytic nickel plating bath can be different from the first autocatalytic nickel plating bath and be formulated in such a way that it is free of a sulfur compound as described above. In some embodiments, the second autocatalytic nickel plating bath includes nickel, a hypophosphorous reducing agent, zinc, a bismuth stabilizer, and at least one of a complexing agent, chelating agent, or pH buffer, and is free of a sulfur compound. In other embodiments, the autocatalytic nickel plating bath can include lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc, and ethylenediaminetetraacetic acid. In still other embodiments, the autocatalytic nickel plating bath can include about 2 g/l to about 10 g/l nickel, about 20 g/l to about 35 g/l hypophosphorous reducing agent, about 1 g about 75 g/l each of the complexing agent, chelating agent, and/or pH buffer, about 40 ppm to about 120 ppm zinc, and about 5 ppm to about 30 ppm bismuth stabilizer.

[00077] The second autocatalytic nickel coating formed on the first autocatalytic nickel coating using the second autocatalytic nickel plating bath can be of relatively uniform thickness and of an average thickness in a range from about 1 micron to about 100 microns. In some embodiments, the average thickness may be less than the thickness of the first autocatalytic nickel coating and be in a range of from about 1 micron to about 10 microns. The second autocatalytic nickel coating can also have a phosphorus content of from about 8% to about 11%.

[00078] After the formation of the second autocatalytic nickel top coating on the first autocatalytic nickel coating, in step 26, the multilayer or duplex coated substrate can be removed from the second autocatalytic nickel plating bath, optionally rinsed, and then immersed in an acidic solution, such as a hydrochloric acid solution, to reactivate the coating surface. Surface reactivation using an acid solution has been found to advantageously improve copper deposition in the subsequent copper plating step.

[00079] After reactivation of the duplex coating, in step 28, the multilayer or duplex coated substrate can be removed from the acidic solution, optionally rinsed, and then brought into contact with an autocatalytic copper plating bath, for example, by immersing the Duplex coated substrate in autocatalytic copper plating bath. The autocatalytic copper plating bath can include an aqueous solution of copper sulfate pentahydrate and sulfuric acid. The coated substrate can be immersed in the autocatalytic copper plating bath for an effective duration to form a copper coating, for example, for about 1 minute to about 3 minutes.

[00080] In removing the autocatalytic copper-nickel coated substrate from the autocatalytic copper plating bath, the substrate can be rinsed and dried. The autocatalytic copper-nickel coating thus formed had a consistently uniform deposit with a uniform thickness and copper coloration.

[00081] The following examples illustrate the autocatalytic nickel plating solutions of the invention. Unless otherwise indicated in the following examples, specification, and written claims, all parts and percentages are by weight, temperatures are in degrees Centigrade, and pressure is at or near atmospheric pressure. Example 1

[00082] A black autocatalytic coating was prepared using a high phosphorus nickel subcoat, a sulfur free autocatalytic nickel topcoat, and an acidic iron sulfate corrosive product.

[00083] The high phosphorus autocatalytic nickel plating bath was prepared with the following formulation:

[00084] The sulfur free autocatalytic nickel plating bath was prepared with the following formulation.

[00085] The corrosion agent for blackening the sulfur free autocatalytic nickel plating bath was prepared with the following formulation.

[00086] A subcoat of high phosphorus autocatalytic nickel was electroplated onto a steel substrate for a time of about 1 hour, to provide a high phosphorus autocatalytic nickel coating having a thickness of about 0.50 mils. The steel substrate was then rinsed and placed in the sulfur-free autocatalytic nickel plating bath for 30 minutes to provide an autocatalytic nickel top coating with a thickness of about 0.15 mils. The steel substrate was then removed from the sulfur-free autocatalytic nickel bath, rinsed for 30 seconds, and then submerged in the corrosion solution for about 1 minute. The steel substrate was again removed, rinsed, and allowed to stabilize for 24 hours to achieve maximum stiffness. The chemistry of the process allows the autocatalytic nickel-coated steel substrate to be stored after subcoating is applied at a later date if the user so desires. If this is the case, the autocatalytic nickel coated steel substrate needs to be electron cleaned (electrocleaning) and reactivated in 50% acid HCL before the steel substrate can be submerged.

[00087] A summary of the black autocatalytic nickel plating process is shown below. Process: 1) Appropriate cleaning cycle for substrate being plated. 2) High Phosphorous NA Bath — 60 mins 3) Rinse - 30 secs 4) Electroclean - 2 mins* 5) Activation - 10 secs* 6) Proposed Sulfur Free NA Bath - 30 mins 7) Rinse - 30 secs 8) Ferric Sulfate Solution - 1 min 9) Rinse - 30 secs 10) Blow dry the parts * These steps only need to be done if the part is left to set for 1 hour or more before the top coat is applied. Example 2

[00088] Each component of the autocatalytic solution was modified in an attempt to increase the black produced. Lactic acid

[00089] 20% increase showed no benefit, while 20% decrease seemed to result in a slight increase in black. Further removal of lactic acid, 40% and 60% decrease, resulted in no increase in black depth, but the bath began to exhibit stability issues. Acetic Acid

[00090] 20% decrease had no effect on the final product. 20% increase caused slight increase in black. Further increase in acetic acid showed no benefit in overall depot quality. malic acid

[00091] Any increase in malic acid resulted in a decrease in black coloration. When complete removal was tested, the result was the best black color produced, but stability issues were observed when levels dropped below 3 g/l. Glycine

[00092] Showed no effect on black when levels were increased or decreased. For this reason, Glycine has been completely removed from the formula to reduce the potential cost. Sodium Hypophosphite

[00093] Solution reduction test was done in an attempt to reduce the %P in the deposit. From the initial value, the concentration was reduced to 25 g/l from 30 g/l, which resulted in a 2% drop in percentage phosphorus in the final product. This drop resulted in the production of a deeper black. Ammonium hydroxide

[00094] The concentration was adjusted in order to compensate for the increased acetic acid in solution. Attempts to assess the effect that ammonia had on the solution resulted in an attempt to produce an ammonia-free chemistry, but the resulting solution did not blacken. Nickel

[00095] Tests at 4 g/l showed decreased blackening, whereas an 8 g/l solution showed no increase in the resulting black deposit. succinic acid

[00096] Succinic acid has been added to help control the phosphorus content and deepen the final color. Tested concentrations, which rose to 12 g/l. The result was an overall darker deposit of up to 8 g/l, which gradually decreases as concentrations exceed this value. EDTA

[00097] Increasing or decreasing the amount in solution showed no final effect on the black color. Values were left at baseline to ensure proper chelation of filler metals. Zinc

[00098] When tests dropped below this value of less than 40 ppm, the result was a loss of color. In tests where the amount was increased above 100 ppm there was no effect on the black produced, but the plating rate dropped dramatically. bismuth trichloride

[00099] Tests have shown that the higher the concentration that can be maintained, the deeper the black that is produced. Although if you exceed 30 ppm, the bath would become super-stabilized and further galvanizing would be impossible. 15 ppm would allow 1 hour of plating without any refueling before a black color effect could be observed. Example 3

[000100] Initial bath life test showed that the bath is capable of aging at least 4 per metal turnovers (MTOs), without loss of color or uniformity compared to conventional autocatalytic nickel baths, such as a nickel bath. electroplating of autocatalytic nickel of medium phosphorus content containing a sulfur compound. The metal turnover deposition (MTO) rate of autocatalytic nickel coatings formed using the sulfur-free autocatalytic nickel plating bath was compared to the metal turnover deposition (MTO) using a commercially available autocatalytic nickel plating bath. (Fig. 3) The test was repeated in triplicate to validate this information. Solutions were also tested for phosphorus percentage at 0 and 4 MTOs. The result showed that their respective phosphorus concentrations were 10.8% and 8.5%, respectively. (Fig. 4) Intrinsic stress was also measured at the 0 and 4 MTOs to determine the effect that higher levels of bismuth would have on the bath. Values were measured to be 1500 PSI of compression in both cases. Additional tests were also performed to determine adequate adhesion. In this case, the tanks at 0 and 4 MTOs were subjected to the Quench Test (free translation, Cooling test) (rapid heating, then cooling of the tank), tilt test (the tank was tilted to 90° and examined to look for poor adhesion for deposit to the substrate), and Scribe Test (in free translation, the Scribe Test) (in which the surface of the deposit is marked and then examined for cracks due to stress). The proposed chemistry passed all tests. When the deposit is left 24 hours to stabilize, the color passes the Eraser Test (in the original, Eraser Test) (> 10 strokes of a rubber across the entire surface and examined for abrasion). Furthermore, compared to black autocatalytic nickel coatings prepared using commercially available black autocatalytic nickel plating processes, a black autocatalytic nickel coating prepared by the process described in this document when subjected to 116 hours of exposure to neutral salt spray maintains a higher level. high in black (Fig. 5). Example 4

[000101] The duplex coated substrate with the sulfur free autocatalytic nickel top coating prepared by the process described above (ebENi process) was further studied by submitting the duplex coating to a copper dip process for bare steel surfaces. The duplex coated steel substrate described above was immersed in an autocatalytic copper bath having the following formulation.

[000102] A summary of autocatalytic copper plating process is shown below: 1) Panel was galvanized to a thickness of 0.4 mils in High Phosphorous NA Bath 2) Rinse: 1 min 3) Panel was Galvanized in NA Bath Sulfur Free Proposed at a thickness of 0.2 mils 4) Rinse: 30 secs 5) 50% HCl: 20 secs 6) Rinse: 30 secs 7) Autocatalytic CuSO4 solution: 2 mins 8) Rinse: 30 secs 9) Dry

[000103] An example of the deposit thus formed is illustrated in Fig. 6. Testing showed that an intermediate step to that required to reactivate the surface before exposure to the autocatalytic copper plating bath.

[000104] In order to fully assess the deposit, the immersion properties needed to be compared with traditional EN (Autocatalytic Nickel, original EN) processes.

[000105] Four NA Baths were galvanized and then exposed to a cycle in an attempt to facilitate copper immersion over the NA deposit: NA Chemistry: 1. Traditional 60 mL/L low phosphorus autocatalytic nickel plating bath 6% LNS 150 mL/L Enova EF-163B Temperature: 190°F pH: 4.9 2. Traditional 60 mL/L medium phosphorus autocatalytic nickel plating bath 6% LNS 150 mL/L Enova MS-9 Temperature: 190 °F pH: 4.9 3. Traditional high phosphorus autocatalytic nickel plating bath 60 mL/L 6% LNS 150 mL/L Enova EF-949B. Temperature: 190°F pH: 4.8 4. Proposed ebENi process: 60 mL/L Enova 949 150 mL/L Proposed Sulfur Free NA Bath Temperature: 190°F pH: 4.9 Galvanization Cycle Cycle for Low Phosphorus System, Medium and High: 1. Panel was galvanized to a thickness of 0.4 mils 2. Rinse: 30 secs 3. 50% HCL: 20 secs 4. Rinse: 30 secs 5. CuSO4 solution: 2 mins 6. Rinse: 30 secs 7 Dry Cycle for ebENi System: 1. Panel was galvanized to a thickness of 0.4 mils in Enova 949 2. Rinse: 1 min 3. Panel was galvanized in ebENi to a thickness of 0.2 mils 4. Rinse: 30 secs 5. 50% HCL 20 secs 6. Rinse: 30 secs 7. CuSO4 solution: 2 mins 8. Rinse: 30 secs 9. Dry

[000106] As illustrated in Fig. 6, all three traditional processes show that copper has not completely covered the panel. The ebENi system shows complete and uniform copper coverage over the top of the NA deposit.

[000107] From the description above, those skilled in the technique will notice improvements, changes and modifications. Such improvements, changes and modifications within the scope of the prior art are intended to be covered by the appended claims. All references, patents and publications cited in the present application are hereby incorporated by reference in their entirety.

Claims (11)

1. Method of forming an autocatalytic nickel coating on a substrate, the method characterized in that it comprises: i. contacting the substrate with a first autocatalytic nickel plating bath to form a first autocatalytic nickel coating on the substrate, the first autocatalytic nickel coating having a phosphorus content of 7% to 13% by weight; ii. contacting the substrate coated with the first autocatalytic coating with a second aqueous autocatalytic nickel plating bath to form a second autocatalytic nickel coating on the first autocatalytic coating, the second autocatalytic coating having a phosphorus content of 8% to 11% by weight, the second bath including nickel, a hypophosphorous reducing agent, from 40 to 100 ppm zinc, at least one of a complexing agent, a chelating agent, and/or pH buffer, and from 5 ppm to 30 ppm of bismuth stabilizer, wherein the bath is free of an organic sulfur compound; erode the autocatalytic nickel coating with an etching agent to provide the coated substrate with a black surface. 2. Method according to claim 1, characterized in that the hypophosphorous reducing agent is selected from the group consisting of sodium hypophosphite, potassium hypophosphite, ammonium hypophosphite and combinations thereof. 3. Method according to claim 1, characterized in that the second autocatalytic nickel plating bath includes at least one pH buffer, complexing agent or chelating agent that is selected from the group consisting of acetic acid, formic acid, succinic acid, malonic acid, an ammonium salt, lactic acid, malic acid, citric acid, glycine, alanine, glycolic acid, lysine, aspartic acid, ethylenediaminetetraacetic acid (EDTA) and combinations thereof. 4. Method according to claim 3, characterized in that it comprises at least two of a pH buffer, complexing agent and/or chelating agent. 5. Method according to claim 1, characterized in that the nickel is provided in the second autocatalytic nickel plating bath in the form of a water-soluble nickel salt. 6. Method according to claim 5, characterized in that the nickel salt is selected from the group consisting of nickel chloride, nickel bromide, nickel iodide, nickel acetate, nickel malate and hypophosphite of nickel. 7. Method according to claim 1, characterized in that the pH of the second autocatalytic nickel plating bath is maintained at 4.5 to 5.0 and the temperature at 79 °C to about 93 °C. 8. Method according to claim 1, characterized in that the second autocatalytic nickel plating bath comprises 2 g/l to 10 g/l of nickel, 20 g/l to 35 g/l of the hypophosphorous reducing agent, about 1 g/l to about 75 g/l of each of the complexing agent, chelating agent, and/or pH buffer. 9. Method according to claim 1, characterized in that the bath comprises lactic acid, acetic acid, malic acid, succinic acid, sodium hypophosphite, ammonium hydroxide, nickel, zinc and ethylenediaminetetraacetic acid. 10. Method according to claim 1, characterized in that the corrosion agent comprises an iron blackening agent and an acid. 11. Method according to claim 1, characterized in that the corrosion agent comprises ferric sulfate and hydrochloric acid.

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