TWI636161B - Production method of dark colored chromium based electrodeposits and trivalent chromium electrolyte - Google Patents

Abstract

An aqueous trivalent chromium electrolyte containing trivalent chromium ions and amino acids, which allows a dark color to be produced in a trivalent chromium coating plated on a substrate. The amino acids described herein include a cationic side chain and are at least substantially free of sulfur. The cationic side chain of the amino acid further contains nitrogen. When used in trivalent chromium electrolytes, these amino acids allow the production of significantly darker trivalent chromium deposits. The trivalent chromium electrolyte is used in a method for producing a trivalent chromium coating having a desired dark color using electrodeposition on a substrate.

Description

Manufacturing method of dark chromium-based electrodeposition and trivalent chromium electrolyte

The present invention generally relates to a composition and method for manufacturing a dark chromium coating by electrodeposition.

Chromium has been used as a decorative coating for many years and has many applications. For decorative purposes, chromium is usually applied on nickel coatings as a thin coating, typically less than 1 micron thick. Chromium provides a hard, abrasion-resistant layer, and because the chromium layer is related to the underlying nickel deposit system cathode, it also obtains excellent corrosion performance. Therefore, the lower layer of nickel that becomes the anode in a corroded battery is preferentially corroded, leaving the chromium layer uncorroded.

Typically, these thin decorative chromium layers are applied by electrodeposition from a hexavalent chromium-based electrolyte that typically contains chromic acid. The chromium deposits obtained from these electrolytes are essentially pure chromium and have a uniform and constant color. The formation of a thin oxide layer on top of this coating provides a very well-known blue / white appearance. In addition to the motivation to use alternative electrolytes due to the serious health and environmental hazards associated with chromic acid, there is also a need in the market for coatings with darker shades.

By performing electrodeposition of a chromium coating from an electrolyte mainly composed of trivalent chromium, an initial solution can be obtained that provides a darker-colored deposit from the chromium electrolyte. Due to the nature of the deposition mechanism of these electrolytes, The resulting chromium coating is less pure than that produced from a hexavalent electrolyte. This is due to the co-deposition of other elements within the coating. These co-deposited elements are most commonly iron, sulfur, and carbon or a combination thereof. By adjusting the electrolyte formulation based on the trivalent chromium method to maximize the darkness of the deposits resulting from the incorporation of these co-deposition elements, a fairly dark coating can be obtained.

Although the coating provided by the trivalent chromium electrolyte typically produces darker-colored deposits than the hexavalent chromium electrolyte deposits, the coatings produced from the previously described techniques are still not sufficiently dark to meet market demand and produce deeper manufacturing There is a need for colored chromium-based coatings. It is an object of the present invention to provide a method for manufacturing these coatings.

An object of the present invention is to provide a trivalent chromium electroplating electrolyte capable of providing a dark chromium deposit on a substrate.

One of the objectives of the present invention is to provide an amino acid in the trivalent chromium electrolyte, which can produce a dark color in the trivalent chromium deposits produced.

Another object of the present invention is to provide an amino acid having a nitrogen-containing side chain in the trivalent chromium electrolyte.

Another object of the present invention is to provide a sulfur-free amino acid in the trivalent chromium electrolyte to provide a darker-colored chromium deposit on the substrate.

Yet another object of the present invention is to provide a deposit having a darker color on the substrate than the trivalent chromium electroplating electrolyte of the aforementioned technique, which can be achieved using a trivalent chromium electrolyte containing a selected amino acid.

Yet another object of the present invention is to provide a method for electroplating a trivalent chromium deposit having a dark color on a nickel deposit.

In a specific example, a composition for a trivalent chromium electrolyte is provided, comprising: i) trivalent chromium ions; ii) one or more complexing agents capable of maintaining the trivalent chromium ions in a solution; and iii ) One or more amino acids, wherein the amino acid comprises a nitrogen-containing cationic side chain and wherein the cationic side chain system is at least substantially free of sulfur; and wherein the electrolyte system is substantially free of hexavalent chromium salts. In another specific example, a method for manufacturing a dark chromium deposit on a substrate is provided, the steps of which include: i) providing a trivalent chromium-based electrolyte comprising: a) trivalent chromium ions; b ) One or more complexing agents capable of maintaining the trivalent chromium ion in solution; and c) one or more amino acids, wherein the amino acid includes a nitrogen-containing cationic side chain and the cationic side chain system thereof is at least Substantially free of sulfur; and wherein the electrolyte is substantially free of hexavalent chromium salts; and ii) using the trivalent chromium-based electrolyte to electrodeposit a dark chromium deposit on the substrate.

Figure 1 depicts various amino acid species.

The inventors of this case have surprisingly discovered that the incorporation of an amino acid selected to include nitrogen-containing side chains into a trivalent chromium electrolyte results in a coating that is substantially darker than those obtained from the same electrolyte lacking these compounds . Additionally, the amino acids useful in the present invention are at least substantially free of sulfur. Substantially sulfur-free means that there is no sulfur at any concentration other than the trace amount that can occur in this compound as a contaminant. The darkest coating can be obtained when a selected amino acid is added to an electrolyte that has been optimized to incorporate a darker coating by incorporating other elements such as sulfur, iron, carbon, or a combination thereof.

The use of amino acids as complexing agents in trivalent chromium plating baths has been described by Ward et al. In U.S. Patent No. 4,107,004 and by Barnes et al. In U.S. Patent No. 4,157,945, which describes the use of glycine as a fault mixture. U.S. Patent No. 4,161,432 to Barclay et al. Describes the use of glycine, aspartic acid, arginine, and histidine as complexing agents. Both US Patent No. 4,448,648 and US Patent No. 4,448,649 to Barclay et al. Describe the use of aspartic acid as a complexing agent. The subject matter of each of these patents is incorporated herein by reference in its entirety. These patents all focus on the production of light-colored coatings and do not provide changes in the color of the deposited deposits or those associated with different amino acids.

Amino acids are divided into several groups, as shown in FIG. 1. Methionine and cysteine (and cystine) amino acids include divalent sulfur in their side chains. The use of these sulfur compounds as trivalent chromium baths has been previously disclosed by Schulz et al in the examples of WO 2012 / 150198A1 as Darkening agents, the entire contents of which are hereby incorporated herein by reference. This is understood to be the effect of sulfur present in this compound, because sulfur is known to cause a deeper coloration in trivalent chromium deposits as compared to purer deposits made from hexavalent chromium electrolytes.

The inventors of the present invention have surprisingly discovered that thiamine-free acids including those selected from groups having nitrogen-containing cation side chains can have the desired effect of darkening the deposit in a uniform manner. Due to the presence of nitrogen-containing (amine) functional groups in the side chain, the side chain is a cation under normal pH conditions (pH 2.5-4.0) of most commercially available trivalent chromium plating baths.

Amino acids useful in the present invention include, for example, arginine, histidine, lysine, and combinations thereof. These amino acids have been found to produce significantly deeper trivalent chromium deposits. In addition, although tryptophan is not listed under the amino group containing a positive charge group in FIG. 1, it has a nitrogen-containing side chain and it has also been found to have an enhanced deepening effect. Although not intended to be bound by theory, from this result it is also believed that the side chains of tryptophan are cationic under the normal pH conditions of a trivalent chromium plating bath.

The effective concentration range of the preferred amino acid in the trivalent chromium electrolyte is preferably between about 1 g / l to about 50 g / l, and more preferably between about 2 g / l to about 20 g / l between. The amino acid concentration in the trivalent chromium electrolyte is preferably between about 5 g / l and about 10 g / l.

When electroplating is performed using the electrolyte solution described herein, an inert anode such as a carbon anode is typically used. Other inert anodes can also be used, such as platinized titanium, platinum, titanium coated with iridium oxide, or titanium coated with tantalum oxide.

The temperature of the trivalent chromium-based electrolyte ranges from 40 ° C to 60 ° C, and preferably about 50 ° C. The pH range of the electrolyte is about 2 to about 5, and most preferably about 3.5. The current range used during plating ranges from about 1 amp to about 10 amps, most preferably about 4 amps. This trivalent chromium electrolyte does not need to be agitated during substrate plating.

As used herein, the term "about" refers to a measurable value, such as a parameter, or concentration, or a similar value, and means a change that includes +/- 15% or less of a specifically recited value, Preferably +/- 10% or less change, more preferably +/- 5% or less change and most preferably +/- 0.1% or less change, as described in the invention It is suitable to carry out within the scope of this change. Furthermore, it should also be understood that the value indicated by the modifier "about" itself is specifically disclosed herein.

In a preferred embodiment, the substrate comprises nickel deposited on an underlying substrate and chromium plated on the nickel deposit.

To clarify the scope of the present invention, a Konica Minolta CM2600d spectrophotometer is used to determine the "brightness" values of various deposits by measuring the L * value according to the L * a * b * color space system. This color space system provides a magnitude (L *) that can be used to compare the degree of darkening obtained from a combination of various amino acid additives. The higher the L * value, the lighter the sediment; and the lower the L * value, the darker the sediment. L * value 0 is black and L * 100 is white. The present invention wants lower L * values.

The dark-colored coatings produced by the electrolytic deposition of trivalent chromium using the electrolyte described herein are preferably measured according to the L * a * b * color space system, and have an L * value that is less than that of a typical light-colored coating. Valence chromium deposits and those that have maximized the darkness of the resulting deposits.

The trivalent chromium-based electrolyte may include a thiocyanate ion. The concentration of the thiocyanate ion that can be developed everywhere is about 0.2 g / liter to a maximum of about 5.0 g / liter.

The trivalent chromium-based electrolytes presented herein are at least substantially free of hexavalent chromium salts, where no Cr (VI) ions are detectable in the electrolyte by ordinary measurement techniques.

The trivalent chromium electrolyte includes a source of trivalent chromium ions, one or more complexing agents (complexing agents) capable of maintaining the trivalent chromium ions in solution, and an amino acid selected as described herein. Compared to those using the same electrolyte without this amino acid, this amino acid has provided a deeper color in the electroplated deposits.

The trivalent chromium electrolyte used as the standard is an electrolyte designed to make light-colored chromium deposits. The electrolyte and plating method are based on U.S. Patent No. 4,473,448 to Deeman. This patent is hereby incorporated by reference in its entirety.

In addition, based on US Patent No. 4,161,432 of Barclay et al., A trivalent chromium electrolyte solution capable of producing dark deposits is mainly provided to provide embodiments of the invention. The amino acid used in this electrolyte composition is aspartic acid. This reference is hereby incorporated by reference in its entirety.

The following non-limiting examples illustrate the effectiveness of the invention. All examples were prepared by electroplating trivalent chromium deposits onto Hull battery panels. The Hull battery panel has previously been plated with 10 micron bright nickel deposits and then placed in a Hull battery containing the trivalent chromium electrolyte to be tested. For this trivalent chromium plating step, its condition The pieces are as shown in Table 1. Regardless of the composition to be tested, the conditions used for trivalent chromium plating remain the same.

In all cases, the brightness or L * value of the trivalent chromium deposit was measured at a position corresponding to the current density of 8 Amperes per square inch of the Hull battery panel, where the current density is a typical normal operation of chromium plating range.

Comparative Example 1

Table 2 provides L * values measured using Deeman based U.S. Patent No. 4,473,448 as the standard (1) and various amino acids added as non-effective darkening agents.

As can be seen from the results presented in Table 2, the amino acids tested did not produce any significant reduction in the L * value when compared to trivalent chromium electrolytes without the addition of amino acids. The average reduction in L * values was 1.17%.

Example 1

Table 3 provides the L * values obtained when the amino acids described herein were added to an electrolyte based on US Patent No. 4,473,448 to Deeman. The same standard (1) electrolyte as in the above comparative example was used. As mentioned previously, this electrolyte typically produces light-colored trivalent chromium deposits.

In this case, the average reduction in the L * value of the examples using the arginine and histidine of the present invention is 12.7%. This line is a significant difference that can be easily seen by the eyes. Adding arginine, histidine, or lysine provides uniform color throughout the entire deposit. The addition of tryptophan provides a dramatic effect, but results in very uneven and streaky deposits, which, although significantly deeper, are commercially unacceptable.

Example 2

Table 4 provides the L * values obtained when the amino acids of the present invention were added to an electrolyte based on US Patent No. 4,161,432 based on Barclay et al. This electrolyte was used as standard (2) and compared with the L * value after the amino acid was added. As mentioned previously, the deposits produced using this electrolyte method have previously been formulated to provide dark trivalent chromium deposits.

In this case, the average reduction in L * value was 15.02%. This series is very noteworthy for color differences. Although electrolytes based on Barclay et al. US Patent No. 4,161,432 naturally produce a dark deposit, the darkness of the deposit can be increased by adding an amino acid as described herein.

As has been shown by the examples presented herein, the inventors have surprisingly discovered that darker-colored deposits can be obtained from a trivalent chromium electrolyte containing an amino acid as described herein. When this effective amino acid does not include sulfur, but a cationic nitrogen-containing side chain is present, the result is unexpected, which allows a deeper color in the deposits obtained using the trivalent chromium electrolyte of the present invention.

It should also be understood that the following patent application scope is intended to cover all the general and specific features of the invention as described herein, and all statements of the scope of the invention that fall literally between them.

Claims (24)

A trivalent chromium electrolyte comprising: i) trivalent chromium ions; ii) more than one complexing agent capable of maintaining the trivalent chromium ions in a solution; and iii) more than one amino acid, wherein the amino acid includes A nitrogen-containing cationic side chain, and wherein the cationic side chain system is at least substantially free of sulfur; and wherein the electrolyte system is substantially free of a hexavalent chromium salt; wherein the electrolyte can produce a deposit having an L * value equal to or less than 78.47 The L * value is measured according to the L * a * b * color space system. The trivalent chromium electrolyte according to claim 1, wherein the one or more amino acids are selected from the group consisting of arginine, histidine, lysine, tryptophan, and combinations thereof. The trivalent chromium electrolyte according to claim 1, wherein the total concentration of the amino acid is between 1 g / L and 50 g / L. The trivalent chromium electrolyte according to claim 3, wherein the total concentration of the amino acid is between 2 g / L and 20 g / L. The trivalent chromium electrolyte according to claim 4, wherein the total concentration of the amino acid is between 5 g / l and 10 g / l. The trivalent chromium electrolyte of claim 1, wherein the trivalent chromium plating electrolyte includes a thiocyanate ion. The trivalent chromium electrolyte according to claim 6, wherein the thiocyanate ion is present at a concentration between 0.2 g / L and 5 g / L. The trivalent chromium electrolyte of claim 2, wherein the amino acid comprises histidine. The trivalent chromium electrolyte of claim 2, wherein the amino acid comprises arginine. The trivalent chromium electrolyte of claim 2, wherein the amino acid comprises a mixture of histidine and arginine. A method for manufacturing a dark chromium deposit on a substrate, the steps include: i) providing a trivalent chromium-based electrolyte comprising: a) trivalent chromium ions; b) more than one kind of trivalent chromium ions A complexing agent maintained in solution; and c) more than one amino acid, wherein the amino acid includes a nitrogen-containing cationic side chain, and wherein the cationic side chain system is at least substantially free of sulfur; and wherein the electrolyte system is substantially No hexavalent chromium salt; and ii) electrodepositing a dark chromium deposit on a substrate using the trivalent chromium-based electrolyte; and wherein the dark chromium deposit has an L * value equal to or less than 78.47, wherein the L * Values are measured according to the L * a * b * color space system. The method of claim 11, wherein the one or more amino acids are selected from the group consisting of arginine, histidine, lysine, tryptophan, and combinations thereof. The method of claim 11, wherein the total concentration of the amino acid is between 1 g / liter and 50 g / liter. The method of claim 13, wherein the total concentration of the amino acid is between 2 g / L and 20 g / L. The method of claim 14, wherein the total concentration of the amino acid is between 5 g / l and 10 g / l. The method of claim 11, wherein the trivalent chromium-based electrolyte further comprises a thiocyanate ion. The method of claim 16, wherein the thiocyanate ion is present at a concentration between 0.2 g / L and 5 g / L. The method of claim 12, wherein the one or more amino acids comprise histidine. The method of claim 12, wherein the one or more amino acids comprise arginine. The method of claim 12, wherein the one or more amino acids comprise a mixture of histidine and arginine. The method of claim 11, wherein the chrome coating manufactured on the substrate is measured according to the L * a * b * color space system, and having an L * value is lower than that of the same by not including the one or more amino acids. Trivalent chromium deposits made from trivalent chromium electrolytes. The method of claim 11, wherein the substrate comprises a nickel deposit on the substrate and trivalent chromium plated on the nickel deposit. The method according to claim 11, wherein the pH of the trivalent chromium electrolyte is between 2.0 and 5.0. The method of claim 23, wherein the pH of the trivalent chromium electrolyte is 3.5.